AU642010B2

AU642010B2 - Microcapsules

Info

Publication number: AU642010B2
Application number: AU76204/91A
Authority: AU
Inventors: Ulrich Freundschuh; Ekkehard Jahns
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 1990-05-16
Filing date: 1991-04-29
Publication date: 1993-10-07
Anticipated expiration: 2011-04-29
Also published as: CA2041792A1; JPH04227845A; ATE102504T1; BR9101956A; JP3241396B2; FI104794B; FI912364A0; DK0457154T3; EP0457154B1; FI912364L; DE4015753A1; DE59101133D1; AU7620491A; EP0457154A1; CA2041792C; ES2062608T3

Abstract

Microcapsules are obtainable by polymerisation of A) 30 to 100% by weight of one or more C1-C24-alkyl acrylates and/or methacrylates (monomers I), B) 0 to 80% by weight of a bifunctional or polyfunctional monomer (monomers II) which is soluble in solvents which are insoluble or sparingly soluble in water, and C) 0 to 40% by weight of other monomers (monomers III), the solvent, if any, being in the form of a stable oil-in-water emulsion together with the monomers and a free-radical initiator as the disperse phase, and the polymerisation being initiated and controlled by the thermal decomposition of the free-radical initiator. The products preferably serve for the manufacture of pressure-sensitive recording materials.

Description

Form COMMONWEALTH OF AUSTRALIA PATENTS ACT 1952-69 COMPLETE SPECIFICATiON (ORIGINAL) Class Int. Class Application Number: Lodged: SComplete Specification Lodged: Accepted: Published: SPriority Related Art rame of Applicant: BASF AKTIENGESELLSCHAFT Addressof Applicant: D-6700 Ludwigshafen, Federal Republic of Germany SAttual Inventor: Address for Service EKKEHARD JAHNS and ULRICH FREUNDSCHUH WATERMARK PATENT TRADEMARK ATTORNEYS.

LOCKED BAG NO. 5, HAWTHORN, VICTORIA 3122, AUSTRALIA Complete Specification for the invention entitled:

MICROCAPSULES

The following statement is a full description of this invention, including the best method of performing it known to Microcapsules The present invention relates to microcapsules comprising a polymeric shell and a water-insoluble or only sparingly water-soluble solvent core optionally containing another substance to be encapsulated which is dissolved in said solvent, said microcapsules being obtained by polymerizing A) 30 100 by weight of one or more Ci-C 24 -alkyl esters of acrylic or methacrylic acid (monomers 1), B) 0 80 by weight of a bi- or polyfunctional ethylenically unsaturated monomer (monomer 1I) which is soluble in the solvent which is insoluble or only sparingly soluble in water, and C) 0 40 by weight of other ethylenically unsaturated monomers (monomers III), said monomers being in solution, together with a free radical initiator and optionally the substance to be encapsulated, with the water-insoluble or sparingly water-soluble solvent which forms the disperse phase of a stable oil-in-water emulsion, the polymerization of the monomers being initiated and controlled by the thermal decomposition of the free radical initiator such that, at the beginning of the polymerization, a low number of radicals formed by decomposition of the initiator is present and that the number of radicals is later increased by raising the polymerization temperature.

The present invention also relates to a process for preparing microcapsules, to the use of color former microcapsules for producing pressure-sensitive recording materials and to these recording materials.

EP-A-026 914, EP-A-133 295 and EP-A-218 887 disclose microcapsules S which are based on melamine-formaldehyde resins and are recommended for pressure- S 25 sensitive recording materials.

*r\bc Cz A further method for preparing microcapsules is that of in situ polymerization. The microcapsules are produced, for example by the method described in SEP-A-198 089, by first preparing a solution of monomers such as acrylic esters, a waterinsoluble solvent, a free radical initiator, a polymer and the substance to be encapsulated and then converting this solution into a stable oil-in-water emulsion. Then the polymerization of the monomers is initiated by raising the temperature, and the resulting polymers form the walls of capsules which tightly enclose the remaining organic solution of the substance which is to be encapsulated.

The substances mentioned for microencapsulation in this context are dyes, detergents, printing inks, perfumes, adhesives, medicines, agrochemicals, fertilizers, fats, oils, nutrients, enzymes, liquid crystals, paints, rustproofing agents, recording materials, 2 O.Z. 0050/41614 catalysts, chemical reactants and magnetic substances.

The microcapsules of the present invention are prepared from 30 to 100 by weight, preferably 30-95 by weight, of one or more Ci-C 24 -alkyl esters of acrylic and/or methacrylic acid as monomers I.

In addition, the microcapsules of the present invention may also be formed from up to 80 by weight, preferably 5-40 by weight, of a bi- or polyfunctional monomer which is soluble in a water-insoluble or only sparingly water-soluble solvent as monomer II and from up to 40 by weight, preferably up to 30 by weight, of other monomers III.

Suitable monomers I are C 1

-C

24 -alkyl esters of acrylic and/or methacrylic acid. Particularly preferred 15 monomers I are methyl, ethyl, n-propyl, n-butyl and 2-ethylhexyl acrylates and methacrylates. Preference is given to isopropyl, Isobutyl, sec-butyl and tert-butyl acrylates and methacrylates. But it is also possible to use n-pentyl, n-hexyl, n-heptyl, n-octyl and lauryl 20 acrylates and methacrylates.

Suitable additional monomers II are bi- or polyfunctional monomers which are soluble in waterinsoluble or only sparingly water-soluble solvents, chiefly divinyl and polyvinyl monomers which bring about 25 a crosslinking of the capsule walls during the polymerization.

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Preferred divinyl monomers are ethanediol diacrylate, divinylbenzene, ethylene glycol dimethacrylate, 1,3-butylene glycol dimethacrylate, methallylmethacryl- 30 amide and allyl methacrylate. Particular preference is given to propanediol, butanediol, pentanediol and hexanediol diacrylates or methacrylates.

Preferred polyvinyl monomers are trimethylolpropane triacrylate and methacrylate, pentaerythritol triallyl ether and pentaerythritol tetraacrylate.

The crosslinking may also be effected via groups capable of addition or condensation, with or without further at least bifunctional such groups, in which case the crosslinking reaction is carried out after the 3 O.Z. 0050/41614 polymerization.

Monomers having such groups are, for example glycidyl acrylate and methacrylate and in particular vinyl compounds which contain amino, acetylacetone, epoxy or methylol groups.

The functional groups of these monomers may be crosslinked for example via bi- or polyfunctional epoxies, amines and alcohols, preferably via urea- and melamine-formaldehyde precondensates.

Particularly good results with subsequent crosslinking are obtained on using acetoacetoxy ethyl methacrylate as functional monomer and formaldehyde or glutaraldehyde as crosslinking component.

Suitable monomers III are any other monomers, 15 preferably styrene, a-methylstyrene, p-methylstyrene, butadiena, isoprene, vinyl acetate, v nyl propionate and 0*O vinylpyridine.

S" Particularly preferred monomers III are acrylonitrile, methacrylamide, acrylic acid, methacrylic acid, ,*20 itaconic acid, maleic acid, maleic anhydride, N-vinylpyrrolidone, 2-hydroxyethyl methacrylate and acrylamido- 2-methylpropanesulfonic acid.

It is also possible to use N-methylolacrylamide, N-methylolmethacrylamide, dimethylaminoethyl methacrylate 25 and diethylaminoethyl methacrylate.

The microcapsules of the present invention are 6;04 prepared by polymerization of monomers I, II and III, said polymerization being initiated and controlled by raising the temperature to a level where the thermal o' 30 decomposition of the free radical initiator takes place.

Suitable free radical initiators for the polymerization reaction are the customary peroxo and azo compounds, advantageously in amounts of from 0.2 to 5 by weight, based on the weight of the monomers.

Preferred free radical initiators are tert-butyl peroxyneodecanoate, tert-amyl peroxypivalate, dilauryl peroxide, tert-amyl peroxy-2-ethylhexanoate, 2,2'-azobis- (2,4-dimethyl)valeronitrile, 2,2'-azobis(2-methylbutyronitrile), dibenzoyl peroxide, tert-butyl per-2-ethyl- 4 O.Z. 0050/41614 0*0e

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hexanoate, di-tert-butyl peroxide, tert-butyl hydroperoxide, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane and cumene hydroperoxide.

Particularly preferred free radical initiators are di(3,5,5-trimethylhexanoyl) peroxide,4,4'-azobisisobutyronitrile, tert-butyl perpivalate and dimethyl 2,2-azobisisobutyrate. These have a half-life of 10 hours within the temperature range from 30 to 100"C.

The monomers and the free radical initiator can be dissolved in a water-insoluble or only sparingly water-soluble solvent which forms the disperse phase of a stable oil-in-water emulsion. It is however also possible first to disperse the solvent and add the monomers and the free radical initiator to the dispersion. A further possibility is to place the solvent and monomers in dispersion and to add just the free radical initiator subsequently. The solvent may of course contain other substances, such as color formers.

Suitable water-insoluble or only sparingly water- 20 soluble solvents are natural oils, synthetic oils and solvents having boiling points within the range from to 350"C, preferably from 150 to 350"C. The oil content of the oil-in-water emulsion is preferably 20-60 by weight.

25 Preferred water-insoluble or only sparingly water-soluble solvents are gasolines, mineral oils, paraffins, chloroparaffins, fluorocarbons, groundnut oil, soybean oil, chlorinated biphenyls, tributyl phosphate, dibutyl maleate, o-dichlorobenzene, benzyl alcohol, 30 diisopropylenenaphthalene and l-phenyl-l-xylylethane.

Particularly high solubilities of the substances such as color formers contained in the water-insoluble or only sparingly water-soluble solvents are obtained in those solvents whose boiling points are within the range from 150 to 350 0 C, for example in dibutyl phthalate, diisoheptyl phthalate, dioctyl phthalate, alkylnaphthalenes and partially hydrogenated terphenyls and in particular in diisopropylnaphthalene, dodecylbenzene and mixtures thereof.

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0 5 a The substances contained in the capsules are in particular those mentioned on page 2, with color formers being preferred.

Suitable color formers for encapsulation are for example colorless or only slightly colored compounds which are converted into dyes in the presence of acids, as is true for example of numerous phthalides, which as the lactone ring opens form colored open-chain acids.

Preferred color formers are 3,3-bis(p-dimethylaminophenyl)phthalide, 3-(p-dimethylaminophenyl)-3-(1,2-dimethylindol-3yl)phthalide, 3-(p-dimethylaminophenyl)-3-(2-phenylindol-3-yl)phthalide, Rhodamine-B-anilino-lactam, 3-dimethylamino-7-methoxyfluoran, pnitrobenzoyl-leuco methylene blue, 3-methylspirodinaphthopyran and 3propylspirodibenzopyran.

Particular preference is given to 3,3-bis(p-dimethyiaminophenyl)-6dimethylaminophthalide and N-benzoyl-leuco methylene blue and mixtures thereof.

In general, the color formers are used in amounts of from 1 to 10 by weight, preferably from 2 to 8 by weight, based on the oil phase of the emulsion.

Suitable acidic color developers are acid clay, attapulgite, 20 aluminum silicate, benzoic acid, chloro-benzoic acid, toluylic acid, salicylic acid and 4-tert-butylsalicyclic acid and also in particular kaolin and alkyl-substituted Sphenols.

The microcapsules according to the invention are differentiated in their method of production from the method described in EP-A-198 089 in that 25 the present invention proposes a two stage polymerisation, with polymerisation being accomplished by polymerising at a first temperature and then raising the temperature to a second temperature and continuing the polymerisation at this second temperature.

As a general procedure, a mixture of water, protective colloids, 30 ionic emulsifiers, water-insoluble or only sparingly water-soluble solvents, other substances contained therein in dissolved form, free radical initiators and monomers, added simultaneously or successively, is dispersed with a high-

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4 shear mixer to yield a stable oil-in-water emulsion having the desired oil drop Size. Then the emulsion is transferred to a different container with a propeller- or 6 anchor-type stirring blade to prevent damage to the capsule shells built up by polymerization by means of the high-shear mixer. The mixture is now heated with stirring to start polymerization by decomposition of the free radical initiators.

To obtain suitable microcapsules for carbonless copy paper the polymerization conditions must be different from those of EP-A-198 089. In Example 1 of EP-A-198 089 a constant polymerization temperature of 700C is chosen for 15 hours. The free radical initiator used is 3,5,5-trimethylhexanoyl peroxide. This initiator has a half-life of 2.3 hours at 700C (taken from "Interox" product information, Peroxid-Chemie, D-8023 H1llriegelskreuth). That means that half of the initiator has decomposed after 2.3 hours at 70°C to radicals that may start a polymerization if monomers are present.

The rate of thermal decomposition of the free radical initiators mentioned in this application is exponentially dependent on the temperature.

For example the 3,5,5-trimethylhexanoyl peroxide has a half-life of 31 hours at 500C, 8.8 hours at 60°C, 2.3 hours at 700C and 0.8 hours at 800C. A person skilled in the art is able to calculate the half-life times over a wide temperature range from the data published by the producers of initiators or from scientific iiterature.

For use in carbonless copy paper microcapsules are needed 20 whose walls are as impermeable as possible for the core material. Otherwise the capsules dry out very quickly and no copy of a written text is obtained. It was found in this invention that it is necessary to use the initiators at different half-life times, and therefore polymerise at different temperatures in contrast to the single temperature polymerisation proposed in EP-A-198 089 for obtaining 25 microcapsules useful in carbonless copy paper. Good capsules are obtained in accordance with the invention if the total polymerization time is divided into at least two periods. The first polymerization period is characterized by a slow decomposition of the free radical initiators, In the second and possibly further polymerization periods the temperature of the reaction mixture is increased to S 30 accelerate the decomposition of the free radical initiators. The temperature may be increased in one or more steps or continuously, and linearly or nonlinearly. It is not yet fully understood why these special polymerization conditions give 6a much better microcapsules for carbonless copy paper than the normal method of polymerizing at one temperature only. It may be due to the complicated process of crosslinking and phase separation inside the capsules during polymerization.

In the first polymerization period the half-life of the initiators is set at long times, preferably between 3 and 30 hours, to obtain a slow rate of polymerization. In the second and possible further polymerization periods the decomposition of the initiators is increased by raising the temperature and therefore decreasing their half-life times by at least about a factor of two.

Suitable total polymerization times are in the range of 0.5 to 10 hours.

It is obvious to a person skilled in the art that the half-life time of the initiators at a certain temperature is not the only reason for a definite rate of polymerization or polymerization speed. The amount of initiators with reference o: 15 to the total monomer content of the polymerization mixture is of importance, too.

Therefore the figures in the last paragraph refer to an amount of initiators of 1 to 3% by weight of the total monomer weight. Using more initiator may require a shorter half-life, just as less initiator may require a longer half-life to adjust the polymerization conditions to their optimal values.

Advantageously, the polymerization is carried out under atmospheric pressure, but it may also be carried out under a reduced or slightly

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superatmospheric pressure, say within the range of 0.5 to 5 bar.

*s 7 O.Z. 0050/41614 and methacrylate, of sulfopropyl acrylate and methacrylate, of N-(sulfoethyl)maleimide, of 2-acrylamido-2alkanesulfonic acids, of styrenesulfonic acid or of vinylsulfonic acid.

Preferred ionic emulsifiers are naphthalenesulfonic acid and naphthalenesulfonic acid/formaldehyde condensates and in particular polyacrylic acids and phenolsulfonic acid/formaldehyde condensates.

The ionic emulsifiers are in general used in amounts of from 0.1 to 10 by weight, based on the water phase of the emulsion.

Preferably, the polymerization conditions are selected in a conventional manner which serves to ensure that the microcapsules have diameters of from 1 to 35 pm, 15 in particular from 3 to 15 pm.

The viscosities of the capsule dispersions are measured in seconds as efflux times of 100 ml of the dispersion from the 4 mm Ford cup in accordance with German Standard Specification DIN 53 211.

20 The dispersions of the microcapsules of the present invention have solids contents of preferably 20-60 by weight.

The color former microcapsules of the present invention are used for producing pressure-sensitive 25 recording materials.

These materials are primarily copy papers which are impregnated with the color developer and coated with a dispersion of microcapsules. The pressure of the writing implement causes the microcapsules to burst open, 30 so that the color formers, or dye-forming components, form a dye on development.

The microcapsule dispersions obtainable according to the present invention can be used directly for paper coating or they can be dried, for example spray dried, and redispersed before use.

EXAMPLES

Preparation of color former microcapsules EXAMPLE 1 A mixture of 8 O.Z. 0050/41614 1280 g of water g of polyvinylpyrrolidone of K g of phenolsulfonic acid/formaldehyde condensate 522 g of diisopropylnaphthalene 522 g of dodecylbenzene 48 g of a mixture of 36 g of 3,3-bis(p-dimethylaminophenyl)-6-dimethylaminophthalide and 12 g of N-benzoylleuco methylene blue 168 g of methyl methacrylate 19 g of butanediol diacrylate 1.4 g of azobisisobutyronitrile 2 g of dimethyl 2,2-azobisisobutyrate was dispersed at room temperature for 20 minutes. It was then heated, with continuing dispersing, to 60*C and maintained at that temperature for 1 1/2 hours. This is followed by heating at 65 0 C, further polymerization for 4 hours and cooling.

The solids content of the dispersion obtained was 49.1 by weight, and efflux time from the Ford cup was 101 seconds.

The average particle size of the microcapsules is 5.6 pm with a practical variation in size from 3 to 7 pm.

EXAMPLE 2 This dispersion was prepared in the manner of 25 Example 1 from the following components: 1287 g of water 20 g of polyvinylpyrrolidone of K 18 g of phenolsulfonic acid/formaldehyde condensate 732 g of diisopropylnaphthalene 30 314 g of a high-boiling aliphatic hydrocarbon mixture (boiling range 230-265°C) 48 g of a mixture of 36 g of 3,3-bis(p-dimethylaminophenyl)-6-dimethylaminophthalide and 12 g of N-benzoylleuco methylene blue 131 g of methyl methacrylate 56 g of butanediol diacrylate 1.4 g of azobisisobutyronitrile 2 g of dimethyl 2,2-azobisisobutyrate.

The solids content of the dispersion obtained was 9 O.Z. 0050/41614 48.5 by weight, and efflux time from the Ford cup was 135 seconds.

The average particle size of the microcapsules is 5.4 pm with a practical variation in size from 3 to 7 pm.

EXAMPLE 3 This dispersion was prepared in the manner of Example 1 from the following components: 1280 g of water g of polyvinylpyrrolidone of K 15 g of phenolsulfonic acid/formaldehyde condensate 732 g of diisopropylnaphthalene 314 g of a high-boiling aliphatic hydrocarbon mixture (boiling range 230-265"C) 48 g of a mixture of 36 g of 3,3-bis(p-dimethyl- 15 aminophenyl)-6-dimethylaiainophthalide and 12 g of N-benzoylleuco methylene blue 93.5 g of methyl methacrylate 37.4 g of butanediol diacrylate 1.4 g of azobisisobutyronitrile S. 20 2 g of dimethyl 2,2-azobisisobutyrate.

The solids content of the dispersion obtained was 48.6 by weight, and efflux time from the Ford cup was 103 seconds.

The average particle size of the microcapsules is 25 5.8 pm with a practical variation in size from 3 to 8 pm.

EXAMPLE 4 This dispersion was prepared in the manner of Example 1 from the following components: 1270 g of water 30 15 g of polyvinylpyrrolidone of K 15 g of phenolsulfonic acid/formaldehyde condensate 636 g of diisopropylnaphthalene 273 g of a high-boiling aliphatic hydrocarbon mixture (boiling range 230-265"C) 48 g of a mixture of 36 g of 3,3-bis(p-dimethylaminophenyl)-6-dimethylaminophthalide and 12 g of N-benzoylleuco methylene blue 287 g of methyl methacrylate 33 g of acetoacetoxyethyl methacrylate 10 O.Z. 0050/41614 g of azobisisobutyronitrile 2 g of dimethyl 2,2-azobisisobutyrate.

However, after 1 1/2 hours' polymerization at SOoC a solution of 4.7 g of formaldehyde and 28 g of water was added over 1 hour, and the temperature was raised tD 65 0 C and left at that level for 1 1/2 hours.

The solids content of the dispersion obtained was 48.2 by weight, and efflux time from the Ford cup was 74 seconds.

The average particle size of the microcapsules is pm with a practical variation in size from 3 to 8 pm.

EXAMPLE This dispersion was prepared in the manner of Example 1 from the following components: 1280 g of water 20 g of polyvinylpyrrolidone of K 15 g of phenolsulfonic acid/formaldehyde condensate 522 g of diisopropylnaphthalene 522 g of dodecylbenzene *20 48 g of a mixture of 36 g of 3,3-bis(p-dimethylaminophenyl)-6-dimethylaminophthalide and 12 g of N-benzoylleuco methylene blue 19 g of ethyl acrylate 9 g of ethyl methacrylate 25 19 g of 2-ethylhexylacrylate 112 g of methyl methacrylate 28 g divinylbenzene 1.4 g azobisisobutyronitrile 2 g of dimethyl 2,2-azobisisobutyrate.

30 The solids content of the dispersion obtained was 43.5 by weight, and efflux time from the Ford cup was 106 seconds.

The average particle size of the microcapsules is 5.8 pm with a practical variation in size from 3 to 12 pm.

EXAMPLE 6 This dispersion was prepared in the manner of Example 1 from the following components: 1464 g of water g of polyvinylpyrrolidone of K 11 O.Z. 0050/41614 15 ease

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3 *0 0 20 25 *ee, 30 g of polyacrylic acid of K 645 g of diisopropylnaphthalene 285 g of a high-boiling aliphatic hydrocarbon mixture (boiling range 230-265 0

C)

50 g of a mixture of 35.5 g of 3,3-bis(p-dimethylaminophenyl)-6-dimethylaminophthalide and 12.5 g of N-benzoylleuco methylene blue 120 g of methyl methacrylate 2 g of azobisisobutyronitrile 30 g of a 20 strength nonaqueous dispersion of a methacrylate copolymer in cyclohexane (methacrylic acid content 4.8 However, after heating at 65"C the polymerization was initially carried out at that temperature for 2 1/2 hours and then at 70°C for 2 1/4 hours.

The solids content of the dispersion obtained was 41.6 by weight, and efflux time from the Ford cup was seconds.

The average particle size of the microcapsules is 5.2 pm with a practical variation in size from 2 to 6 pm.

EXAMPLE 7 This dispersion was prepared in the manner of Example 6 from the following components: 1334 g of water 45 g of polyvinylpyrrolidone of K 11 g of polyacrylic acid of K 732 g of diisopropylnaphthalene 313 g of a high-boiling aliphatic hydrocarbon mixture (boiling range 230-265 0

C)

55 g of a mixture of 41 g of 3,3-bis(p-dimethylaminophenyl)-6-dimethylaminophthalide and 14 g of N-benzoylleuco methylene blue 187 g of methyl methacrylate 3.1 g of azobisi£-butyronitrile 45 g of a 20 strength nonaqueous dispersion of a methacrylate copolymer in cyclohexane (methacrylic acid content 4.8 The solids content of the dispersion obtained was 47 by weight, and efflux time from the Ford cup was 12 O.Z. 0050/41614 106 seconds.

The average particle size of the microcapsules is 5.4 pm with a practical variation in size from 3 to 6 pm.

Application properties The microcapsules of the present invention were examined in respect of permeability, color intensity and rub sensitivity.

To this end, the microcapsule dispersions were diluted to a solids content of 16.5 by weight and then applied at a rate of 5 g of microcapsules per m 2 to a) standard typewriting paper and p) typewriting paper which had been pretreated with attapulgite as color developer, after which these papers were dried.

'*15 A) Determination of the permeability The permeability is a measure of the amount of nonencapsulated color former.

To determine the permeability, paper A) was slightly moistened with dodecylbenzene, causing the 0O 20 nonencapsulated color former to become detached to form a dye with the developer. The degree of coloring of the papers thus treated was measured as the difference in reflectance between an unsprayed sheet of paper p) and a *sprayed sheet in a reflectance photometer and expressed 25 in relative units, with the reflectance of the unsprayed sheet of paper p) being set equal to 100.

B) Determination of the color intensity The color intensity in question here is the intensity of a certain copy.

30 To determine the color intensity, a sheet of paper a) was placed with the coated face on a sheet of paper which had been coated with a color developer and a further 3 layers of paper of 38 g/m 2 were placed on top.

This pile was then clamped into an electric typewriter and imprinted with a letter over an area of 4.2 x 3.4 cm with maximum impression. The intensity of the fourth copy was measured in a reflectance photometer as the difference in the reflectances of the typed and untyped paper and reported in relative units with the 13 O.Z. 0050/41614 reflectance of the untyped sheet being set equal to 100.

C) Determination of the rub sensitivity The rub value is a measure of the coloring produced by rubbing only.

To determine the rub value, a sheet of paper a) was placed on top of a sheet of paper coated with a color developer and the sheet of paper a) was pulled slowly and uniformly over the developer-coated paper underneath with a circular, flat weight of 2.1 N/cm 2 placed on top.

Then the developer-coated paper was stored in the dark for 1 hour, and afterwards its degree of coloring was measured in a reflectance photometer as the difference in the reflectances of the rubbed and unrubbed 15 sheets and reported in relative units with a reflectance of the unrubbed sheet being set equal to 100.

The table shows the results of test A, B and C.

TABLE

Application properties of microcapsules of Examples 1 20 to 5 PCo Example Permeability Color intensity Rub value

&*OWN:

4 1.

P 25 4 2 29.8 38.8 42.0 23.3 28.5 EXAMPLE 8 23.7 15.5 19.8 15.3 38.5 12 A mixture of: 87 g of water g of polyrinylpyrrolidone of K 18 g of a phenolsulfonic acid-formaldehyde condensate 70 g of diisopropylnaphthalene 30 g of a high-boiling aliphatic hydrocarbon mixture (boiling range 230-265°C) 48 g of a mixture of 36 g of 3,3-bis(p-dimethylaminophenyl)-6-dimethylaminophthalide and 12 g 7 3 14 0. Z. 0050/41614 of N-benzoylleuco methylene blue 131 g of methyl methacrylate 56 g of butarxediol diacrylate 3.4 g of t-butyl perpivalate was treated as described in Example 1. It was polymerized at 51 0 C for 2 hours and then at increasing temperature up to 72*C for 4 hours.

EXAM4PLE 9 000015 000 *Off 00 a 4dO 0 0 900 V. 20 060000 A& 0 400 0 a 04 A mixture of: 1293 g of water g of polyvinylpyrrolidone of K 27 g of a phenolsulfonic acid-formaldehyde condensate 770 g of diisopropylnaphthalene 330 g of a high-boiling aliphatic hydrocarbon mixture (boiling range 230-265 0

C)

48 g of a mixtu:Le of 36 g of 3,3-bis(p-dimethylaminopheii yl)-6-dimethylaminophthalide and 12 g of N-benzoylleuco methylene blue 131 g of methyl methacrylate 56 g of butanediol diacrylate 1.4 g of azobisisobutyronitrile 1 g of dimethyl 2,2-azobisisobutyrate was treated as desc~ibed in Example 1. It was polymerized at 65*C for 2 hours and then at increasing temperature up to 71*C for 4 hours.

EXAMPLE A mixture of: 1287 g of water 20 g of polyvinylpyrrolidone of K 18 g of a phenolsulfonic acid- formaldehyde condensate 770 g diisopropylnaphthalene 330 g of a high-boiling aliphatic hydrocarbon mixture (boiling range 230-265 0

C)

48 g of a mixture of 36 g of 3,3-bis(p-dimethylaminophenyl)-6-dimethirlaminophthalide and 12 g of N-benzoylleuco methylene bluo 131 g of methyl methacrylate 15 O.Z. 0050/41614 56 g of butanediol diacrylate 1.4 g of azobisisobutyronitrile 2 g of dimethyl 2,2-azobisisobutyrate was treated as described in Example 1. It was polymerized at 60°C for 2 hours and then at increasing temperature up to 75 0 C for 4 hours.

EXAMPLE 11 A mixture of: 1287 g of water 20 g of polyvinylpyrrolidone of K 18 g of a phenolsulfonic acid-formaldehyde condensate 1 g of carboxymethylcellulose 770 g of diisopropylnaphthalene 15 330 g of a high-boiling aliphatic hydrocarbon mixture (boiling range 230-265 0

C)

48 g of a mixture of 36 g of 3,3-bis(p-dimethylaminophenyl)-6-dimethylaminophthalide and 12 g of N-benzoylleuco methylene blue 20 131 g of methyl methacrylate 56 g of butanediol diacrylate 1.4 g of azobisisobutyronitrile 2 g of dimethyl 2,2-azobisisobutyrate was treated as described in Example 1.

25 EXAMPLE 12 A mixture of: 1287 g of water g of polyvinylpyrrolidone of K 18 g of a phenolsulfonic acid-formaldehyde conden- 30 sate 1.3 g of polyacrylic acid 770 g of diisopropylnaphthalene 330 g of a high-boiling aliphatic hydrocarbon mixture (boiling range 230-265 0

C)

48 g of a mixture of 36 g of 3,3-bis(p-dimethylaminophenyl)-6-dimethylaminophthalide and 12 g of N-benzoylleuco methylene blue 131 g of methyl methacrylate 56 g of butanediol diacrylate -16 O.Z. 0050/41614 1.4 g of azobisisobutyronitrile 2 g of dimethyl 2,2-azobisisobutyrate was treated as described in Example 1. It was polymerized at 60 0 C for 2 hours and then at 65 0 C for 4 hours.

EXAMPLE 13 A mixture of: 1287 g of water g of polyvinylpyrrolidone of K 18 g of a phenolsulfonic acid-formaldehyde condensate 770 g of diisopropylnaphthalene 330 g of a high-boiling aliphatic hydrocarbon mixture (boiling range 230-265*C) 48 g of a mixture of 36 g of 3,3-bis(p-dimethyl- 000015aminophenyl)-6-dimethylamiinophthalide and 12 g of N-benzoylleuco methylene blue so..*131 g of methyl methacrylate so.:56 g of 1,3-propanediol diacrylate .1.4 g of azobisisobutyronitrile 2 g of dimethyl 2,2-azobisisobutyrate was treated as described in Example 1. It was polymerized at 60 0 C for 2 hours and then at 65*C for 4 hours.

EXAMPLE 14 A mixture of: *5 1287 g of water g of polyvinylpyrrolidone of K 18 g of a phenolsulfonic acid-formaldehyde condensate 770 g of diisopropylnaphthalene 330 g of a high-boiling aliphatic hydrocarbon mixture (boiling range 230-265 0

C)

c48 g of a mixture of 36 g of 3,3-bis(p-dimethylaminophenyl)-6-dimethyiaminophthalide and 12 g of N-benzoylleuco methylene, blue 131 g of methyl methacrylate 56 g of hexanediol diacrylate 1.4 g of azobisisobuty.-nitrile 2 g of dimethyl 2,2-aezobisisobutyrate was treated as described in Example 1. It was polymerized 17 O.Z. 0050/41614 at 60*C for 2 hours and then at 65°C for 4 hours.

EXAMPLE A mixture of: 1287 g of water 20 g of polyvinylpyrrolidone of K 18 g of a phenolsulfonic acid-formaldehyde condensate 770 g of diisopropylnaphthalene 330 g of a high-boiling aliphatic hydrocarbon mixture (boiling range 230-265 0

C)

48 g of a mixture of 36 g of 3,3-bis(p-dimethylaminophenyl)-6-dimethylaminophthalide and 12 g of N-benzoylleuco methylene blue 131 g of methyl methacrylate 15 56 g of butanediol diacrylate 000. 5.4 g of bis(3,5,5-trimethylhexanoyl) peroxide was treated as described in Example 1. It was polymerized at 52 0 C for 2 hours and then at 59°C for 4 hours.

EXAMPLE 16 S 20 A mixture of: eg.

1287 g of water g of polyvinylpyrrolidone of K 18 g of a phenolsulfonic acid-formaldehyde condensate 25 1 g of carboxymethylcellulose S770 g of diisopropylnaphthalene 330 g of a high-boiling aliphatic hydrocarbon mixture (boiling range 230-265 0

C)

48 g of a mixture of 36 g of 3,3-bis(p-dimethyl- 30 aminophenyl)-6-dimethylaminophthalide and 12 g of N-benzoylleuco methylene blue S" 131 g of methyl methacrylate 56 g of butanediol diacrylate 1.4 g of azobisisobutyronitrile 2 g of dimethyl 2,2-azobisisobutyrate All ingredients except the monomers and the initiators were dispersed at room temperature for minutes. The remaining substances were then added and dispersing was continued for a further 15 minutes. The 18 O.Z. 0050/41614 mixture was polymerized at 60*C for 2 hours and then at 0 C for 4 hours.

EXAMPLE 17 goes

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20 A mixture of: 128 g of water 2 g of polyvinylpyrrolidone of K 1.8 g of a phenolsulfonic acid-formaldehyde condensate 13.1 g of methyl methacrylate 5.6 g of butanediol diacrylate 88 g of di(2-ethylhexyl) phthalate 22 g of a scent 0.14 g of azobisisobutyronitrile 0.2 g of dimethyl 2,2-azobisisobutyrate All the ingredients were dispersed at room temperature for 3 minutes. The mixture was polymerized at 60"C for 2 hours and then at 65"C for 4 hours. The scentcontaining microcapsules have a diameter within the range from 2 to 5 pm.

EXAMPLE 18 A mixture of: 128 g of water 2 g of polyvinylpyrrolidone of K 1.8 g of a phenolsulfonic acid-formaldehyde conden- 25 sate 13.1 g of methyl methacrylate 5.6 g of butanediol diacrylate 110 g of metolachlor 0.14 g of azobisisobutyronitrile 30 0.2 g of dimethyl 2,2-azobisisobutyrate All the ingredients were dispersed at room temperature for 3 minutes. The mixture was polymerized at for 2 hours and then at 65*C for 4 hours. The microcapsules containing the crop protection agent have a diameter within the range from 3 to 8 pm.

EXAMPLE 19 128 2 mixture of: of water of polyvinylpyrrolidone of K 19 O.Z. 0050/41614 1.8 g of a phenolsulfonic acid-formaldehyde condensate 18.6 g of methyl methacrylate 88 g of lead(II).2-ethylhexanoate 22 g of white oil 0.1 g of azobisisobutyronitrile 0.2 g of dimethyl 2,2-azobsisobutyrate All the ingredients were dispersed at room temperature for 5 minutes. The mixture was polymerized at 60*C for 2 hours and then at 65"C for 4 hours. The microcapsules containing the lead salt have a diameter within the range from 2 to 6 Am.

Examples 8 to 19 likewise produce microcapsules having properties similar to those of Examples 1 to 7.

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Claims

1. Microcapsules comprising a polymeric shell and a water-insoluble or only sparingly water-soluble solvent core optionally containing another substance to be encapsulated which is dissolved in said solvent, said microcapsules being obtained by polymerizing A) 30 100 by weight of one or more C 1 -C 24 -alkyl esters of acrylic or methacryiic acid (monomers I), B) 0 80 by weight of a bi- or polyfunctional ethylenically unsaturated monomer (monomer II) which is soluble in the solvent which is insoluble or only sparingly soluble in water, and C) 0 40 by weight of other ethylenically unsaturated monomers (monomers Ill), said monomers being in solution, together with a free radical initiator and optionally the substance to be encapsulated, with the water-insoluble or sparingly water-soluble solvent which forms the disperse phase of a stable oil-in- water emulsion, the polymerization of the monomers being initiated and controlled by the thermal decomposition of the free radical initiator such that, at the beginning of the polymerization, a low number of radicals formed by decomposition of the initiator is present and that the number of radicals is later increased by raising the polymerization temperature.

2. Microcapsules as claimed in claim 1, obtained by polymerizing A) 30-95 by weight of monomers I, B) 5-40 by weight of monomer II, and C) 0-30 by weight of other monomers IIl.

3. Microcapsules as claimed in claim 1, in which the water-insoluble or only sparingly water-soluble solvent has a boiling point within the range from 150 to 3500C.

4. Microcapsules as claimed in claim 1, in which the water-insoluble or only sparingly water-soluble solvent is diisopropylnaphthalene or dodecylbenzene.

A process for preparing microcapsules composed of a polymeric shell and a water-insoluble or only sparingly water-soluble solvent core optionally containing another substance to be encapsulated which is dissolved in said solvent, which comprises converting the water-soluble or only sparingly water-soluble solvent, A) 30 100 by weight of one or more Ci-C 24 -alkyl esters of acrylic or methacrylic acid (monomers I), B) 0 80 by weight of a bi- or polyfunctional ethylenically unsaturated monomer (monomer II) which is soluble in the solvent, and C) 0 40 by weight of other ethylenically unsaturated monomers (monomers III), a free radical initiator, and optionally another substance to be encapsulated in water into a stable oil-in-water emulsion in a conventional manner, then, by thermal decomposition of the free radical initiator, initiating and controlling the polymerization of the monomers such that at the beginning of the polymerization a low number of radicals formed by decomposition of the initiator is present and that the number of radicals is later increased by raising the polymerization temperature, to form the capsules.

6. Microcapsules as claimed in claim 1, containing a color former.

7. A pressure-sensitive recording material containing microcapsules as claimed in claim 6 and a further component for developing the dye. DATED this 27th day of July, 1993 BASF AKTIENGESELLSCHAFT WATERMARK PATENT TRADEMARK ATTORNEYS THE ATRIUM 290 BURWOOD ROAD HAWTHORN VICTORIA 3122 AUSTRALIA O* lo* *Ol O.Z. 0050/41614 Abstract of the Disclosure: Microcapsules useful for producing pressure-sensitive recording materials are obtainable by polymerizing A) 30-100 by weight of one or more Cl-C 2 4 -alkyI esters of acrylic or methacrylic acid (monomers I), B) 0-80 by weight of a bi- or polyfunctional monomer (monomer II) which is soluble in a solvent which is insoluble or only sparingly soluble in water, and C) 0-40 by weight of other monomers (monomers III), the solvent being present alone or together with the monomers and a free radical initiator as the disperse phase of a stable oil-in-water emulsion and the poly- merization being initiated and controlled by the thermal decomposition of the free radical initiator. 6 •i a a ob 9* 0 0* *6 *O6 0