GB1573361A - Metho of making microcapsules - Google Patents

Description

(54) A METHOD OF MAKING MICROCAPSULES (71) We, CARBON PAPER CO., LTD., of 10 Shodaitajika 3-chome, Hirakata City, Osaka, Japan, a Japanese Company, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to a process for making microcapsules for use on no-carbon copying paper, especially a method for encapsulating hydrophobic substance in an oil-inwater emulsion with a protective colloid.

The complex coacervation method is conventionally known as one of the methods for encapsulating a hydrophobic substance i.e. oil into microcapsules. This method comprises mixing aqueous dispersions of a polycationic protective colloid and a polyanionic protective colloid with each other, coacervating the mixture into a thick colloid phase and a thin colloid phase by dilution or pH adjustment, accumulating complex colloid material around microscopic oil droplets as nuclei, and then hardening the complex colloid material.

The complex coacervation method permits a hydrophobic substance to be encapsulated into microcapsules with higher efficiency and in larger amount than other methods for encapsulating in microcapsules. This method, however, has the following serious disadvantages.

(1) Throughout the coacervation step in which the protective colloid composition is separated and accumulated on the surface of the hydrophobic substance and the hardening step in which the accumulated substance is hardened, a very long time is required for adding and mixing various kinds of agents, as well as very strict control of the variable condition in each step. Therefore, various kinds of necessary operations are complicated and require skilled arts, so that a high production efficiency cannot be held as demanded in the art today.

For example, with an insufficient maturation time in each step, the accumulated protective colloid (encapsulating film) becomes of a low density, and when such microcapsules are applied on a sheet of no-carbon copying paper, they, under a slight unintentional pressure, stain the paper. Further, even a slight error in the control of the conditions of forming the encapsulating film brings a wide range of difference in quality between batches of products. It is also difficult to ascertain which operation was the cause of the problem.

(2) In the hardening step, fine particles of the hydrophobic substance to be formed into microcapsules aggregate and form capsules each comprising a plurality of aggregated oil droplets, or the whole of the encapsulating solution is often gelatinized. The cause thereof is not known, and as the solids content of the solution rises, more aggregation and gelatinization occurs, and therefore the upper limit of the solids content is about 9%. Consequently, as long a time as 7 hours is taken from the emulsifying step to the completion of the encapsulation.

Thus, the limit on the solids content is another main cause of low production efficiency.

(3) In spite of complicated operations and a long maturation time, the density and the tightness of the construction of the encapsulating film has a certain limit, so that improvement thereof beyond the limit cannot be expected according to this method.

This is because this method is based on the coacervation from the mixture of the polycationic protective colloid and the polyanionic protective colloid by successively changing the specified conditions of the whole system and therefore it is necessary to limit the coacervation process to an extremely moderate one in order to prevent the aggregation and gelatinization of the whole mixture. This is, however, impossible in practice, and certain errors inevitably occur in the operation, which are often amplified to result in a low density of encapsulating film due to the abovementioned basis of the coacervation method. Further, a double- or more-layered and stable encapsulating film cannot be produced except under the special condition.

The present invention provides a method of making microcapsules comprising forming an emulsion of a hydrophobic substance in an aqueous colloidal solution of a cationic protective colloid, mixing an aqueous solution of carboxymethyl cellulose with said emulsion to form a first encapsulating film of protective colloid on the dispersed droplets of the hydrophobic substance, mixing the resultant mixture with an aqueous solution of a water-soluble polymer (A) having carboxylic acid, carboxylic acid anhydride or sulfonic acid groups and/or a water-soluble product (B) of a water-insoluble polymer (i) having carboxylic acid, carboxylic acid anhydride, carboxylic acid ester or phenolic hydroxyl groups, and an oxide of a saccharide (ii) having carboxylic add or lactone groups to form a secdnd encapsulating film of protective colloid on said first encapsulating film, the emulsification step and each filmforming step being carried oui at a temperature above the gelatinization point of the protective colloid, cooling the resultant mixture to a temperature below the gelatinization point of the protective colloid, and then adding a hardening agent to harden said first and second encapsulating films of protective colloid.

In accordance with this method a high content of microcapsules can be obtained. The method permits a very high production efficiency and the microcapsules formed are of high quality and very stable.

Each step of the method of the invention will now be described in more detail: a) An emulsification step in which a hydrophobic substance is uniformly emulsified and dispersed in an aqueous colloidal solution of a slightly acidic or cationic protective colloid having an excellent protective colloid property: this step is carried out at a temperature above the gelatinization point of the protective colloid and in it a uniform distribution of the protective colloid particles is obtained on the surfaces of the dispersed droplets of the hydrophobic substance. b) A first film-forming step in which a first encapsulating film of protective colloid is formed by adding the aqueous solution of carboxymethyl cellulose: in this step an aqueous solution of carboxymethyl cellulose is mixed with the emulsion from step a) while keeping the temperature of the mixture above the gelatinization point of the protective colloid so that a neutralization reaction takes place between the carboxymethyl cellulose and the cationic protective colloid not instantaneously but relatively slowly, and a first encapsulating film of the protective colloid accumulates uniformly on the surface of the dispersed droplets as a neutralization product.

If the hydrophobic substance were to be emulsified and dispersed in the aqueos solution of carboxymethyl cellulose and then the protective colloid were to be added thereto, not a thick but a thin film of the protective colloid would be formed on the surface of the dispersed droplets in the emulsion. c) A second film-forming step in which a second encapsulating film is formed on the first encapsulating film by adding the aqueous solution of the water-soluble polymer (A) or the water-soluble product (B): in this step the addition of the aqueous solution of polymer (A) and/or product (B) causes a rapid neutralization reaction between polymer (A) and/or product (B) and unchanged protective colloid remaining after step b) and/or protective colloid in neutralization products from step b) and/or protective colloid in neutralization products from step b) not deposited as first encapsulating film, and a second encapsulating film of protective colloid forms on the first encapsulating film to form a two-layered encapsulating film. In this step, due to the reduction in the pH of the mixture, the protective colloid is substantially completely deposited by neutralization, and the viscosity of the mixture is remarkably reduced. d) A step of hardening the encapsulating films: in this step a conventional hardening process is applied depending upon the kind of the protective colloid used. For example, when gelatine is used as the protective colloid, the mixture from step c) is cooled to a temperature below the gelatinization point of the gelatine to gelatinize the encapsulating films, and then a base and an aqueous solution of formaldehyde are added to harden the first and second encapsulating films.

Each substance used in the method of present invention will now be described.

As the hydrophobic substance, an oil containing a colorless (leuco) dye can be used as in the conventional method of making microcapsules.

As the protective colloid which is able to become cationic and has an excellent protective colloid property suitable for use in the method according to the present invention, there may be mentioned gelatine, albumin, casein, alginate, oxyhemoglobin, pectin, fibrinogen, cationic starch, polyvinylacetal diethyl aminoacetate, polyvinylpyridine, polyacrylamide, poly-Nmethylol acrylamide, quaternary aminopolymer, diethylamino ethylmethacrylate, polyethylene-imine and polymethacryl glycineamide.

Of these protective colloids, the preferred one because of its protective colloid capacity is an acid-treated or cationic gelatine, an aqueous colloidal solution of which is acidic.

Carboxymethyl cellulose for use in the method of the present invention preferably has a pH of 6.5 to 8.0 in pure water and etherification degree of 0.5 to 1.0 and a 1 Soby weight aqueous solution thereof has a viscosity (at 25"C) of 150 to 3000 centipoise. If the etherification degree is above 1.0, the deposit of the first encapsulating film by neutralization of the protective colloid is delayed, while if it is below 0.5, the rate of formation of free fibrous material increases and causes the protective colloid to be non-uniformly separated. When the viscosity is above 3,000 centipoise, the carboxymethyl cellulose is hard to treat while when it is below 150 centipoise, the rate of neutralization increases considerably, causing undesirable non-uniform encapsulating film formation.

The water-soluble polymer (A) and/or product (B) are used as anionic reagents to neutralize residual cationic protective colloid and so form the second encapsulating film.

As the water-soluble polymer (A), there can be used polyacrylic acid, polymethacrylic acid, polyacrylic acid-methacrylic acid, polyethylene-acrylic acid, polyethylene-methacrylic acid, polyvinyl methyl ether-maleic anhydride, polystyrene sulphonic acid, polyphenol sulphonic acid or phenol novolak sulphonic acid. These polymers are water-soluble without neutralization.

The water-soluble product (B) preferably is a product formed between a water-insoluble polymer (i) selected from polystyrene-maleic anhydride, polyvinylacetate-maleic anhydride, polyisobutene-maleic anhydride, polymers obtained by replacing the maleic anhydride moiety in the foregoing polymers by maleic acid, phthalic acid, malonic acid or crotonic acid, polyhydroxypropyl cellulose phthalate, polycellulose phthalate, polyvinyl phenol, vinylphenol copolymer, polyphenol novolak and polymer of polyphenol maleate, and an oxide of a saccharide (ii) selected from gluconic acid, gluconolactone, ribonic acid, ribonolactone, arabonic acid, arabonolactone, erythronic acid, heptonic acid, heptonolactone and higharabonic acid.

The polymer (A) or product (B) preferably is one a 2 % by weight aqueous solution of which has a pH of 2.0 to 4.0.

By the way, if an inorganic or organic metal salt e.g. a sulfate, phosphate, acetate or formate of an alkaline metal or alkaline earth metal were to be used as a neutralizing separating agent for the second encapsulating film, the microcapsules would flocculate and a large number of capsules would aggregate, so that they would be unsuitable for use in making single oil droplet microcapsules. Similarly, when as the abovementioned neutralizingseparating agent, an aqueous solution of an acid, e.g. acetic acid, hydrochloric acid or gallic acid was used, oil droplets began to aggregate at pH 4.8 of the solution. By applying on no-carbon copying paper the microcapsules produced using the abovementioned metal salt or acid, unusual coloration and spotted stain took place on the paper to prove the agents unsuitable for use in the method according to the present invention.

The method according to the present invention has the following advantages in comparison with the conventional complex coacervation method.

The method according to the present invention does not utilise coacervation and therefore requires neither water dilution nor pH adjustment, but comprises directly accumulating a polycationic protective colloid as a neutralization product, thereby forming capsule films in a simple process.

According to the method of the present invention, substantially perfect single oil droplet micro-capsules can be produced and the obtained microcapsules are very stable.

According to the method of the present invention, the solids content in the encapsulating medium can be as high as 20%.

According to the method of the present invention, the time required from the emulsifying step to the microcapsule formation can be reduced to less than half the time required for the corresponding process in the conventional coacervation method.

According to the method of the present invention, no strict control of various conditions with the lapse of time is required, thereby substantially eliminating difference in quality between batches of products.

According to the method of the present invention, the obtained microcapsules have practically a double film and undesirable coloration hardly takes place even when they are applied directly on an acidic China clay coated lower sheet of paper.

According to the method of the present invention, the gelatinization of the whole solution as well as the aggregation of the hydrophobic substance or the produced microcapsules hardly occurs.

The present invention will now be described with reference to the following Examples in comparison with Reference Examples.

Example solution 1 To a colloidal solution of 6.5g acid treated gelatine (acidic cationic protective colloid) in 45g pure water, was added a dye-containing oil (hydrophobic substance) obtained by dissolving 0.7g crystal violet lactone and 0.3g benzoylleucomethylene blue in 25g isopropyl naph- thalene. The mixture was high speed emulsified and dispersed by means of a homogenizer (emulsifying step). The resultant mixture had pH 4.5. To this mixture was added 152g of 1.315% by weight aqueous solution of carboxymethyl cellulose over about 10 min., the carboxymethyl cellulose having an etherification degree of 0.6, and a 1 % by weight aqueous solution of the carboxymethyl cellulose at 250C having a viscosity of 2000 centipoise and pH 7.0. Then, the resulting mixture was matured with stirring for about 10 min., to deposit on the surface of the dye-containing oil the separated composition resulting from a neutralization reaction between the cationic acid treated gelatine and the anionic carboxymethyl cellulose, thereby producing a first encapsulating film. The mixture then was pH 4.7. After that, 10.4g of 5.4% aqueous solution of polyvinyl-methylether-maleic anhydride (pH 2.0) was added to the mixture over about 5 min. At this stage, a second neutralization reaction occurred rapidly between gelatine dissolved in the solution and/or gelatine ingredient in the undeposited first neutralization product and polyvinylmethylether-maleic anhydride and the obtained second neutralization product was deposited so as to be layered on the first encapsulating film on the dye containing oil surface thereby producing the second encapsulating film. Then the viscosity of the mixture was confirmed to have been remarkably lowered to 80 - 45 centipoise at 60"C (the solution was pH 4.3). In the foregoing steps, the temperature of the mixture was not allowed to drop below 55"C.

Then, the mixture was cooled from outside the container to 9"C which is below the gelatinization point of the gelatine. As a hardening agent, a mixture of 7g of 37% formaldehyde with 3g of 20% aqueous solution of sodium hydroxide (aqueous solution of a base) was added to raise the pH of the mixture to 10 and to harden the gelatine (hardening step).

And after 1 hour maturation (maturation step), a dispersion of microcapsules for use in no-carbon paper copying having 20.0% by weight solids content was obtained after 2.5 hours from the beginning of the emulsifying step.

The obtained dispersion had a viscosity as low as 200 centipoise at 27"C and it was confirmed with a microscope that each microcapsule comprised a single oil droplet.

A mixture consisting of 30g of acidic China clay, 12g of 50% by weight styrene-butadiene latex and 75g of water was adjusted with 30%by weight sodium hydroxide to be pH 9.5. The mixture was applied and dried on the surface of a sheet on pure paper so that the dry solids content was 10g/m2 and calendered to form a lower sheet for no-carbon copying paper.

The dispersion of microcapsules was applied over the acidic China clay layer so that the solids content was 5g/m2, sufficiently dried with 500C hot air and allowed to stand at room temperature for 2 hours. Then reflected ray on the colored portion was measured by a Macbeth densitometer RD-100R, a differential one. The result was that when a red color filter #25 (a gelatine filter by Kodak Co., Ltd.) which cuts any ray below 580 Nans meter was used, the absorbance was of as small a value as 0.41.

Example 2 The same method as Example 1 was carried out except that as the neutralizing-separating agent for the first encapsulating film, carboxymethyl cellulose having etherification degree of 0.7 was used, a 1 %by weight aqueous solution of the carboxymethyl cellulose at 25"C having a viscosity of 1,000 centipoise and pH 7.2, and that as the neutralizing-separating agent for the second encapsulating film, polyacrylic acid (pH 2.0) was used.

In the obtained dispersion of microcapsules, each microcapsule comprised a single oil droplet. The dispersion had as low a viscosity as 205 centipoise at 270C and when applied directly on the acidic China clay coated sheet, it had an absorbance of as small a value as 0.42.

Example 3 The same method as Example 1 was carried out except that as the neutralizing-separating agent for the first encapsulating film, carboxymethyl cellulose having etherification degree of 0.58 was used, a 1% by weight aqueous solution of said carboxymethyl cellulose at 250C having a viscosity of 800 centipoise and pH 6.8, and that, as the neutralizing-separating agent for the second encapsulating film, was used 11.8g of an aqueous solution of a reaction product formed by adding 3g of 50% by weight aqueous solution of heptonic acid to 8.8g of 5% by weight aqueous solution of polyvinylacetate-crotonic acid (adjusted with sodium hydroxide to pH 9.0) and then adjusting pH of the mixture to 2.8. In the obtained dispersion of microcapsules, each microcapsule comprised a single oil droplet. The dispersion had as low a viscosity as 210 centipoise at 27"C and when applied directly on the acidic China clay coated sheet, it had an absorbance of as small a value as 0.41.

Example 4 The same method as Example 1 was carried out except that as the neutralizing-separating agent for the first encapsulating film, carboxymethyl cellulose having etherification degree of 0.8 was used, a 1% by weight aqueous solution of said carboxymethyl cellulose at 250C having a viscosity of 1200 centipoise and pH 8.0, and that, as the neutralizing-separating agent for the second encapsulating film, was used 12g of an aqueous solution of a reaction product obtained by adding 4g of 50% by weight aqueous solution of high arabonic acid to 8g of 5% by weight of aqueous solution of polyvinyl phenol oligomer (adjusted with sodium hydroxide to pH 9.0). In the obtained dispersion of microcapsules, each microcapsule comprised a single oil droplet. The dispersion had as low a viscosity as 198 centipoise and when applied on the acidic China clay coated lower sheet, it had an absorbance of as small a value as 0.40.

Example 5 25 parts of rose oil was emulsified and dispersed in a colloidal solution (pH 4.3) of 6.5g acid-treated gelatine in 45g water.

The emulsion was mixed with 152 parts of 1.315% by weight aqueous solution of carboxymethyl cellulose having etherification degree of 0.9 over about 10 min., a 1% by weight aqueous solution of said carboxymethyl cellulose at 250C having a viscosity of 250 centipoise and pH 6.5. After maturation in about 10 min., the mixture was mixed over about 5 min., with 10.3g polyisobutene-maleic anhydride gluconic acid reaction product formed by adding 1.5g gluconolactone to 8.8g aqueous solution of polyisobutene-maleic anhydride (adjusted with sodium hydroxide to pH 9.0) and adjusting pH to 2.5, and then the mixture was cooled from outside the container to 70C and hardened by the addition of 7g of 37% by weight formaldehyde and 4g of 20% by weight sodium hydroxide. After the maturation, a dispersion of microcapsules containing rose oil was obtained. The dispersion was then applied and dried on a sheet of pure paper but a rose scent could not be detected. Strong scent was detected only when the microcapsules were broken. The dispersion had a viscosity of 233 centipoise at 27"C, and each microcapsule comprised a single oil droplet.

Example 6 In the method of Example 1, dye containing oil was emulsified and dispersed in an aqueous solution of the protective colloid. The emulsion was mixed with an aqueous solution of the neutralizing-separating agent for the first encapsulating film and further mixed with an aqueous solution of the neutralizing-separating agent for the second encapsulating film.

Then, the mixture was further mixed with 5g of 25% by weight of aqueous solution of the neutralizing-separating agent for the second encapsulating film as described in Example 4, and then subjected to the hardening and maturation step similar to those of Example 1. In the obtained dispersion of microcapsules, each microcapsule comprised a single oil droplet. The dispersion had a viscosity as low as 208 centipoise at 27"C. When the dispersion was applied over an acidic China clay coated lower sheet of paper, the colored portion had an absorbace as low as 0.40.

Example 7 The same method as Example 1 was carried out except that as the neutralizing-separating agent for the second encapsulating film, was used 10.4g of a 5.4% by weight aqueous solution (pH 2.3) of polystyrene sulfonic acid obtained by sulfonating polystyrene oligomer with sulfuric anhydride. Each microcapsule in the obtained dispersion comprised a single oil droplet. The dispersion had a viscosity as low as 209 centipoise at 27"C. When the dispersion was applied on an acidic China clay coated lower sheet of paper, the colored portion had an absorbance as low as 0.39.

Reference Example I The same method as Example 1 was carried out except that the aqueous solution of the neutralizing-separating agent for the second encapsulating film was substituted by 150g of 8% by weight aqueous solution of sodium sulfate. In the finally obtained dispersion of microcapsules, oil droplets had entirely aggregated. When the dispersion was applied and dried on an acidic China clay coated lower sheet of paper, the colored portion had an absorbance as high as 0.72. Further, the microcapsule dispersion was applied and dried on a nonacidic China clay coated surface of an acidic China clay coated lower sheet of copying paper described in Example 1 at the density of 7g dry solid substance per 1 m2 to form an intermediate sheet of copying paper. When eight thicknesses of the intermediate sheets were wound around a platen of a typewriter, the sheets were stained with spots over all their surfaces.

Reference Example 2 The same method was carried out as Example 1 except that the dye containing oil was emulsified and dispersed in an aqueous solution of the neutralizing-separating agent for the first encapsulating film and then the emulsion was mixed with an aqueous colloidal solution of the protective colloid. The finally obtained microcapsule dispersion had a viscosity as high as 1200 centipoise at 27"C. Further, in the dispersion, oil droplets had aggregated. When the dispersion was applied on an acidic China clay coated lower sheet of copying paper, the colored portion had an absorbance as high as 0.60.

Reference Example 3 In the method of Example 1, as the solution for the second encapsulating film, about 100g of 0.1% by weight aqueous solution of acetic acid with the pH lowered to 4.8 was used, and as the result, original oil droplets having the mean diameter of 3,u entirely aggregated to become 200eel of long diameter and 80cry of short one in a microcapsule. Further, the dispersion had a comparatively high viscosity of 320 centipoise at 27"C. When the dispersion was applied on an acidic China clay coated sheet, the colored portion had an absorbance as high as 0.58.

Further, intermediate sheets of copying paper were formed using this microcapsule dispersion similarly to Reference Example 1, and wound around a typewriter platen, and as the result, they were stained with spots. Further, when these intermediate sheets of copying paper were stored for 12 months, the whole surfaces were colored due to spontaneous coloration.

As the result of the tests on the change with respect to long time storage of the products of the above-mentioned examples the sheets of the Reference Examples were unusually colored in 1 or 2 years to become unusable while no change was observed on the sheets of Examples 1 to 7 even after 7 years.

The results of the summarization of the abovementioned Examples and Reference Examples and the evaluation thereof were shown in the following Table.

Table State of capsule Absorbance of colored Storage property General portion on acidic evaluation China clay coated lower sheet Example 1 An oil droplet 0.41 Unchanged Very good in a capsule after 7 years Example 2 " 0.42 " " Example 3 " 0.41 " " Example 4 " 0.40 " " Example 5 " - " " Example 6 " 0.40 " " Example 7 " 0.39 " " Reference Aggregated drop- 0.72 Unusable Bad Example 1 lets in a capsule 0.72 after 1 year Example 2 " 0.60 Unusable " after 1.5 year Example 3 " 0.58 Unusable " after 1.5 year (Note): Macbeth densitometer RD 100R type & Kodak gelatine filter Red #25 were used.

Claims (9)

WHAT WE CLAIM IS:

1. A method of making microcapsules comprising forming an emulsion of a hydrophobic substance in an aqueous solution of a cationic protective colloid, mixing an aqueous solution of carboxymethyl cellulose with said emulsion to form a first encapsulating film of protective colloid on the dispersed droplets of the hydrophobic substance, mixing the resultant mixture with an aqueous solution of a water-soluble polymer (A) having carboxylic acid, carboxylic acid anhydride or sulfonic acid groups and/or a water-soluble product (B) of a waterinsoluble polymer (i) having carboxylic acid, carboxylic acid anhydride, carboxylic acid ester or phenolic hydroxyl groups, and an oxide of a saccharide (ii) having carboxylic acid or lactone groups to form a second encapsulating film of protective colloid on said first encapsulating film, the emulsification step and each film-forming step being carried out at a temperature above the gelatinization point of the protective colloid, cooling the resultant mixture to a temperature below the gelatinization point of the protective colloid, and then adding a hardening agent to harden said first and second encapsulating films of protective colloid.

2. A method according to claim 1, wherein the cationic protective colloid is gelatine, albumin, casein, alginate, oxyhemoglobin, pectin, fibrinogen, cationic starch, polyvinylacetaldiethyl-aminoacetate, polyvinylpyridine, polyacrylamide, poly-N-methylol acrylamide, a quaternary aminopolymer, diethylaminoethylmethacrylate, polyethyleneimine or polymethacryl glycineamide.

3. A method according to claim 1 or 2, wherein the carboxymethyl cellulose has an etherification degree of 0.5 - 1.0 and a 1% % by weight aqueous solution thereof has a viscosity at 25"C of 150 to 3000 centipoise and a pH of 6.5 to 8.0.

4. A method according to claim 1, 2 or 3, wherein the water-soluble polymer (A) is polyacrylic acid, polymethacrylic acid, polyacrylic acid-methacrylic acid, polyethyleneacrylic acid, polyethylene-methacrylic acid, polyvinylmethylether-maleic anhydride, polystyrene sulphonic acid, polyphenol sulphonic acid or polyphenol novolak sulphonic acid.

5. A method according to claim 1, 2 or 3, wherein the water-soluble product (B) is a product formed between a water-insoluble polymer (i) selected from polystyrene-maleic anhydride, polyvinylacetate-maleic anhydride, polyisobutene-maleic anhydride, polymers obtained by replacing the maleic anhydride moiety in the foregoing polymers by maleic acid, phthalic acid, malonic acid or crotonic acid, polyhydroxypropyl cellulose phthalate, polycellulose phthalate, polyvinylphenol, vinylphenol copolymer, polyphenol novolak, and polymer of polyphenol maleate, and an oxide of a saccharide (ii) selected from gluconic acid, gluconolactone, ribonic acid, ribonolactone, arabonic acid, arabonolactone, erythronic acid, heptonic acid, heptonolactone and higharabonic acid.

6. A method according to any one of the preceding claims, wherein a 2% by weight aqueous solution of the water-soluble polyment (A) or water-soluble product (B) has a pH of 2.0 to 4.0.

7. A method according to claim 1 substantially as described in any one of the Examples.

8. Microcapsules obtained by a method as claimed in any one of the preceding claims.

9. A no-carbon copying paper comprising a coating of microcapsules as claimed in claim 8.