GB2072613A - Process for preparing microcapsules - Google Patents

Abstract

According to the present invention a process for preparing microcapsules with the use of a polyisocyanate as a film forming material and a derivative of Michler's hydrol as a chromogenic material by polymerizing the polyisocyanate at the interface between an oily liquid and an aqueous liquid to form a microcapsule film, the derivative of Michler's hydrol being represented by the formula <IMAGE> wherein R1, R2, R3 and R4 are the same or different and are each alkyl; alkyl substituted with halogen, alkoxy or cyano; aralkyl, or aralkyl substituted with halogen, alkyl, alkoxy, cyano, substituted amino or nitro; X and Y are each halogen; alkyl; alkoxy; substituted amino or nitro; m and n are each 0 or an integer of 1 or 2; and Z is OH; N3; SO2-R5; NH-R5 or <IMAGE> wherein R5 and R6 are the same or different and are each alkyl; aralkyl, aryl or aryl substituted with halogen, alkyl, alkoxy, cyano, substituted amino or nitro, and R5 and R6, when taken together, form a heterocyclic ring, the microcapsules being formed in the presence of a tertiary amine.

Description

SPECIFICATION Process for preparing microcapsules Technical field This invention reiates to a process for preparing microcapsules, and more particularly to a process for preparing microcapsules by the interface polymerization of a polyisocyanate, the microcapsules having enclosed therein a specific derivative of Michler's hydrol as a chromogenic material.

Background art In recent years various recording methods have been proposed which utilize the color forming reaction between an electron donating basic colorless chromogenic material and an electron accepting acidic reactant material. Especially microcapsules enclosing droplets of hydrophobic oily solutions of colorless chromogenic materials are widely used for pressure sensitive manifold paper, etc.

Such organic chromogenic materials to be enclosed in microcapsules must fuifil the following two requirements. First, when hydrophobic oily droplets having the organic chromogenic material dissolved therein are emulsified in an aqueous solution for capsulation, the chromogenic material must remain stable during the capsulation process and must be encapsulated efficiently. Second, the chromogenic material must have good chromogenic properties for recording and produce color records of high stability.

Derivativies of Michler's hydrol have heretofore been used as a type of organic chromogenic materials.

These derivatives are represented by the formula

wherein R1, R2, R3 and R4 are the same or different and are each alkyl; alkyl substituted with halogen, alkoxy or cyano; aralkyl, or aralkyl substituted with halogen, alkyl, alkoxy, cyano, substituted amino or nitro; X and Y are each halogen; alkyl; alkoxy; substituted amino or nitro; m and n are each 0 or an integer of 1 or 2; and Z is OH; N3; SO2-R5;

wherein R5 and R6 are the same or different and are each alkyl, aralkyl, aryl, or aryl substituted with halogen, alkyl, alkoxy, cyano, substituted amino or nitro, and R5 and Re, when taken together, may form a heterocyclic ring.

Although the hydrol derivatives have good chromogenic properties for recording and afford records of high stability, the derivatives have the drawback that when capsulated especially by the interface polymerization of a polyisocyanate, the reaction step following emulsification entails coloring. The coloring of the reaction product further leads to the following serious drawbacks. The pressure sensitive manifold paper prepared with use of the colored microcapsules bears a colored coating which greatly reduces the commercial value of the paper. The colored hydrol derivative itself has seriously impaired properties, for example, reduced heat resistance, such that when heated, the derivative readily decomposes and becomes unable to produce any color.

The main object of this invention is to overcome the foregoing drawbacks of the process for preparing microcapsules having enclosed therein a derivative of Michler's hydrol of the formula (I) as a chromogenic material.

The above and other objects of the present invention will become apparent from the following description The present invention provides a process for preparing microcapsules with use of a polyisocyanate as a film forming material and a derivative of Michler's hydrol as a chromogenic material by polymerizing the polyisocyanate at the interface between and oily liquid and an aqueous liquid to form a microcapsule film, the derivative of Michler's hydrol being represented by the formula

wherein R1, R2, R3 and R4 are the same or different and are each alkyl; alkyl substituted with halogen, alkoxy or cyano; aralkyl, or aralkyl substituted with halogen, alkyl, alkoxy, cyano, substituted amino or nitro;X and Y are each halogen; alkyl; alkoxy; substituted amino or nitro; m and n are each 0 or an integer of 1 or 2; and Z is OH; SO2-R5;

wherein R5 and R6 are the same or different and are each alkyl, aralkyl, aryl, or aryl substituted with halogen, alkyl, alkoxy, cyano, substituted amino or nitro, and Rg and R6, when taken together, may form a heterocyclic ring, the process being characterized in that the microcapsules are formed in the presence of a tertiary amine.

Our research has revealed the following. When microcapsules are prepared by the interface polymerization of polyisocyanate compounds using derivatives of Micheler's hydrol represented by the formula (I), the pH of the capsule forming system lowers with the reaction of the polyisocyanate. The reduction of the pH is greatly responsible for the above drawbacks. Accordingly we made attempts to adjust the pH by adding caustic soda to the capsule forming system before the reaction of the polyisocyanate to render the system alkaline, by adding an alkali to the system in small portions, by using a pH buffer, etc. However, we found that these methods, which need an excess of alkali or a pH buffer, involve the drawback of frequently promoting the decomposition of the chromogenic material.Through the research subsequently conducted, we have eventually found that the contemplated object can be achieved by the use of specific amines, namely, tertiary amines. This finding has matured to the present invention.

According to the invention, useful derivatives of Micheler's hydrol are those represented by the formula (I)

wherein R1, R2, R3, R4, X, Y, Z, m and n are as defined above. Of the derivatives of the formula (I), those in which R1 to R4 are alkyl groups having 1 to 4 carbon atoms are outstanding in chromogenic properties and in the stability of color records obtained, hence preferable. Similarly preferable are those in which m and n are 0, or those having SO2-R5,

wherein R5 and R6 are each phenyl, phenyl substituted with halogen, alkyl having 1 to 4 carbon atoms, alkoxy having 1 or 2 carbon atoms or nitro or naphthyl.

Examples of such useful derivatives of Micheler's hydrol are: 4,4'-bis-dimethylamino-benzhydrolyl-p-toluenesulfinate, 4,4'-bis-diethylamino-benzhydrolyl-p-toluenesulfinate, 4,4'-bis-dimethylamino-benzhydrolyl-benzenesulfinate, 4,4'-bis-dimethylamino-benzhydrolyl-4-chlorobenzene-sulfinate, 4,4'-bis-dimethylamino-benzhydrolyl-3-chloro-4-methyl-benzenesulfinate, 4,4'-bis-dimethylamino-benzhydrolyl-xylenesulfinate, 4,4'-bis-dimethylamino-benzhydrolyl-2,5-dichlorobenzene-su Ifinate, 4,4'-bis-(N-ethyl-N-benzyl)amino-benzhydrolyl-3-nitro-4-methyl benzenesulfinate, 4A'-bis-diethylamino-2,2'-dichlornbenzhydrnlyl-p-dodecylbenzenesulfinate, 4,4'-bis-dimethylamino-benzhydrolyl-ethylsulfinate, 4,4'-bis-dimethylamino-benzhydrolyl-butylsulfinate, and like sulfinate derivatives of Michler's hydrol; N-p-ethoxyphenyl leuco auramine, N-2,5-dichlorophenyl leuco auramine, N-phenyl leuco auramine, N-o (or m or p)-methylphenyl leuco auramine, N-o (or m or p)-chlorophenyl leuco auramine, N-o (or m or p)-nitrophenyl leuco auramine, N-P-naphthyl leuco auramine, N-p-phenylenebis leuco auramine, N-phthalimido leuco auramine, and like N-substituted leuco auramine derivatives; 4,4'-bisdimethylaminobenzhydrol, 2,2'-dimethylaminobenzhydrol, 3,3'-dimethylaminobenzhydrol, and 3,3'-dimethyl-4,4'-diethylaminobenzhydrol; and Micheler's hydrolazide.

These derivatives (I) are used in an amount of about 0.1 to about 12.0 parts by weight, preferably about 0.5 to about 6.0 parts by weight, per 100 parts by weight of the oily liquid.

The amines to be used in this invention are tertiary amines represented by the formula (II)

wherein R7, R8, and Rg are the same or different and are each alkyl, cyclohexyl, phenyl or benzyl and may have hydroxyl, ether bond or tertiary amine, and R7, R8 and Rg, when taken together, may form a heterocyciic ring. It is critical that the amine be a tertiary amine. The use of primary or secondary amines, for example, fails to achieve the object of the invention, that is, to avoid the coloring of the derivative. Among tertiary amines, those having exceedingly high solubility in water are not desirable since they are likely to abruptly and markedly increase the pH of the capsule forming system.

According to this invention, preferred tertiary amines are those highly soluble in oily liquids but not highly soluble in aqueous liquids, such as those in which R7, R8and Rg each have up to about 15 carbon atoms when they are alkyl, cyclohexyl, phenyl, benzyl or phenol groups.Examples of such preferred tertiary amines are N,N-dimethyllaurylamine, N-methyldilaurylamine and liketrialkylamines, N,Ndimethylcyclohexylamine,N-methyldicyclohexylamine and like cyclohexylamines, N,Ndimethylbenzylamine, dimethylaminomethylphenol, bis(dimethylaminomethyl)phenol, 2,4,6-tris(dimethylaminomethyl)phenol, 1 ,8-diaza-bicyclo(5,4,0)-unde cene-7, triethylenediamine, N-methylmorpholine and like morpholine derivatives, N,N'-dimethylpiperazine and like piperazine derivatives, tetramethylpropylenediamine, pentamethyldiethylenetriamine and like tertiary polyamines, etc.Of these tertiary amines, especially preferable are N,N-dimethyllaurylamine, N,N-dimethylcyclohexylamine, Nmethyldicyclohexylamine, N,N-dimethylbenzylamine, dimethylaminomethylphenol and 2,4,6 tris(dimethylamino-methyl)phenol. At least one of these tertiary amines is used. Such amines are used usually in an amount of about 0.1 to about 5 parts by weight, preferably about 0.5 to about 2 parts by weight, per 100 parts by weight of the oily liquid.

According to the present invention, microcapsules are prepared by emulsifying an oily liquid containing a derivative of Michler's hydrol, tertiary amine and polyisocyanate in an aqueous liquid, and reacting the polyisocyanate at the interface between the two liquids.

Useful polyisocyanates are those heretofore used for preparing microcapsules of the type described.

Examples are diisocyanates such as m-phenylene diisocyanate, p-phenylene diisocyanate, 2,6-tolylene diisocyanate, 2,4-tolylene diisocyanate, napththalene-1 ,4-diisocyanate, diphenylmethane-4,4'-diisocyanate, 3,3'-dimethoxy-4,4'-biphenyl diisocyanate, 3,3'-dimethyl-diphenylmethane-4-4'-diisocyanate, xylylene-1,3diisocyanate, xylylene-1,4-diisocyanate, 4,4'-diphenyl-propane diisocyanate, trimethylene diisocyanate, hexamethylene diisocyanate, propylene-1 2-dilsocyanate, butylene-1 ,2-diisocyanate, ethylidynediisocyanate, cyclohexylene-1 ,2-diisocyanate and cyclohexhylene-1 ,4-diisocyanate, triisocyanates such as 4,4',4"triphenyl-methane triisocyanate and toluene-2,4,6-triisocyanate, polyisocyanate monomers such as 4,4' dimethyldiphenyl-methane-2,2', 5,5'-tetraisocyanate, and adducts of such polyisocyanates with polyamines, polycarboxylic acids, polythiols, polyhydroxy compounds, epoxy compounds or like compounds having hydrophilic groups.

Examples of useful polyamines to which polyisocyanates are adducted are o-phenylenediamine, p-phenylenediamine, 1,5-diaminonaphthalene and like aromatic polyamines, and 1,3-propylenediamine, 1,4-butylenediamine, hexamethylenediamine and like aliphatic polyamines. Examples of useful polycarboxylic acids are pimelic acid, suberic acid, azelaic acid, sebasic acid, phthalic acid, terephthalic acid, 4,4'-biphenyl-dicarboxylic acid, 4,4'-sulfonyldibenzoic acid and the like. Examples of useful polythiols are a condensation product of thioglycol and reaction products of polyhydric alcohols with suitable thioetherglycol. Examples of polyhydroxy compounds are aliphatic or aromatic polyhydric alcohols, hydroxypolyesters, hydroxypolypropylene ether, etc.Examples of useful epoxy compounds are diglycidyl ether and like aliphatic glycidyl ethers, aliphatic glycidyl esters, aromatic glycidyl ethers, etc.

Useful oily liquids are also those heretofore used for preparing microcapsules. They are divided generally into vegetable oils, animal oils, mineral oils and synthetic oils. Examples of suitable vegetable oils are castor oil, soybean oil, linseed oil, peanut oil, corn oil, etc. Examples of useful animal oils are fish oil, lard, etc.

Examples of useful mineral oils are kerosene, naphtha, paraffin oil, etc. Examples of synthetic oils are alkylated naphthalene, alkylated biphenyl, hydrogenated terphenyl, alkylated diphenylmethane, diarylethane, triaryldimethane, phthalate, etc.

According to this invention, auxiliary solvents are usable for dissolving polyisocyanates in oily liquids.

Useful solvents are those heretofore used as such. Useful examples are acetone, tetrahydrofuran, dimethylformamide, ethyl acetate, butyl acetate, etc. These auxiliary solvents are used usually in an amount 5 10 15 20 25 30 35 40 45 50 55 60 65 of about 1 to about 30 parts by weight, preferably about 3 to about 20 parts by weight, per 100 parts by weight of the oily liquid.

To incorporate the desired derivative of Micheler's hydrol, polyisocyanate, tertiary amine and auxiliary solvent into the oily liquid, these compounds are added thereto separately or at the same time, followed by mixing. The order in which such compounds are added is not particularly important.

The oily liquid having incorporated therein the desired compounds in specified proportions is then emulsified in an aqueous liquid. The method of emulsification is not particularly limited; any known method is usable. For emulsification, it is preferable to use a protective colloid and/or surfactant. Examples of useful protective colloids are polyvinyl alcohol, gelatin, gum arabic, casein, carboxymethyl cellulose, starch, methyl vinyl ether-maleic anhydride copolymer and like hydrophilic high-molecular-weight substances. According to this invention, it is especially preferable to use a polyvinyl alcohol or a copolymer of methyl vinyl ether and maleic anhydride.Examples of useful surfactants are anionic surfactants such as alkylbenzenesulfonate, alkylnaphthalenesulfonate, polyoxyethylene-sulfate, Turkey red oil, etc., and nonionic surfactants such as polyoxyethylene alkyl ether, polyoxyethylene alkyl phenol ether, sorbitan fatty acid ester, etc. Such protective colloids or surfactants are used usually in an amount of about 0.1 to about 10 parts by weight, preferably about 2 to about 6 parts by weight, per 100 parts by weight of the oily liquid itself (not containing the other materials).

When desired, the aqueous liquid may further contain ethylene glycol, glycerin, butyl alcohol, octyl alcohol or the like.

The oily liquid having the specified substances incorporated therein is added to the aqueous liquid for emuisification usually in an amount of about 40 to about 120 parts by weight, preferably about 70 to about 90 parts by weight, per 100 parts by weight of the aqueous liquid.

The polyisocyanate contained in the resulting emulsion is then polymerized at the oil-water interface to form a capsule film for capsulation. The polymerization is effected, for example, under the following conditions.

When forming a capsule film by reacting a polyisocyanate with water, the emulsion is heated at 500C to 90"C, preferably 65"C to 85"C for 1 to 5 hours to complete the capsulation.

Alternatively, another type of film-forming material may be added to the aqueous liquid before the polymerization is carried out after the emulsification. This type of film-forming materials which can be used include known compounds such as polyvalent amines, polyvalent alcohols, polyvalent carboxylic acids and epoxy compounds. When such film-forming material is used, the reaction can be effected at a lower temperature than when employing the first-mentioned type of film-forming material. For example, the mixture is stirred at 20"C to 70"C, preferably 30"C to 60"C for 1 to 5 hours to complete the reaction.

The polymerization gives a polyurea film which is insoluble in both the liquids, thus forming microcapsules.

According to this invention, the tertiary amine incorporated in the oily liquid acts to maintain the capsule forming system in a very stable pH range during the reaction of the polyisocyanate, with the result that microcapsules can be obtained very efficiently without permitting coloring of the derivative of Michler's hydrol of the formula (I) and, in particular, without impairing the properties of the derivative in any way. Thus the present process is well-suited to the preparation of microcapsules for pressure sensitive manifold papers.

The features of this invention will be described in greater detail with reference to the following examples and comparison examples, in which the parts and percentages are all by weight unless otherwise indicated.

Example 1 An addition product (25 parts, trade mark "Coronate-L," product of Nippcn Polyurethane Kogyo Co., Ltd., Japan) of tolylene diisocyanate and trimethylolpropane, and 2 parts of N,N-dimethylcyclohexylamine were dissolved in 100 parts of dibutyl phthalate having dissolved therein 2.5 parts of Michler's hydrol-ptoluenesulfinate. The resulting solution was emulsified in 150 parts of 3% aqueous solution of a polyvinyl alcohol (trade mark "PVA-117," product of Kuraray Co., Ltd., Japan) with use of a homomixer. The oily droplets in the emulsion were 6.7 Lt in mean particle size.

The emulsion was heated to 80 C while being stirred in a propeller mixer, further agitated for 3 hours to permit the isocyanate to react with the other components, and cooled to room temperature to obtain a microcapsule dispersion.

After the completion of the reaction, the microcapsule dispersion was found to have a pH of 7.6 and not to have been colored by the hydrol derivative.

Example 2 The same procedure of Example 1 was repeated except that N,N'-dimethyllaurylamine was used in place of the N,N-dimethylcyclohexylamine as the tertiary amine. After the completion of the reaction, the microcapsule dispersion was found to have a pH of 7.5 and not to have been colored by the hydrol derivative.

Example 3 A microcapsule dispersion was prepared in the same manner as in Example 1 with the exception of using 25 parts of an addition product (trade mark "Coronate-HL, product of Nippon Polyurethane Kogyo Co., Ltd.) of hexamethylene diisocyanate and trimethylolpropane in place of that of tolylene diisocyanate and trimethylolpropane, and also employing 0.5 parts of 2,4,6-tris-(dimethylaminoethyl)phenol in lieu of the N,N-dimethyl-cyclohexylamine. After the completion of the reaction, the microcapsule dispersion was found to have a pH of 8.8 and not to have been colored by the hydrol derivative.

Example 4 A microcapsule dispersion was prepared in the same manner as in Example 1 except that Michler's hydrol (4,4'-bisdimethylaminobenzhydrol) was used as the chromogenic material. The microcapsule dispersion was found to have a pH of 8.3 without being colored by the chromogenic material.

Example 5 A microcapsule dispersion was produced in the same manner as in Example 1 except that N-phthalimido leuco auramine was used as the chromogenic material. The microcapsule dispersion was prepared with a pH of 8.1 without being colored.

Comparison Examples 1-5 Five kinds of microcapsule dispersions were prepared in the same manner as in Examples 1-5 except that no tertiary amine was employed. The microcapsule dispersions thus produced had the pH values as listed in Table 1 and were all colored blue by the chromogenic materials.

Pulp powder was added, in a ratio of 30 parts of per 100 parts of oily core materials, to one of the 10 kinds of capsule dispersions prepared in Examples 1-5 and comparison Examples 1-5 to obtain a coating composition, which was then applied, in an amount of 4 g/cm2 when dried, to one side of a paper substrate weighing 40g/cm2 to prepare a capsule-coated sheet of pressure sensitive manifold paper. In the same manner as above, 9 kinds of capsule-coated sheets of pressure sensitive manifold paper were prepared with use of the other capsule dispersions.

An 8 part portion of 3,5-di-(a-methylbenzyl)-salicylic zinc salt and 2 parts of styrene-a-methyl-styrene copolymer were heated and melted to prepare a uniform mixture, which was finely divided. Subsequently a coating composition was prepared which comprised 12 parts of the foregoing finely divided particles, 53 parts of aluminium hydroxide, 20 parts of activated clay, 15 parts of zinc oxide, 30 parts of styrenebutadiene copolymer latex (50% solds), 6 parts of 10% aqueous solution of modified polyvinyl alcohol and 300 parts of water. The coating composition was applied, in an amount of 6 g/cm2 when dried, to one side of a paper substrate weighing 40 g/cm2 to obtain an acceptor material-coated sheet of pressure sensitive manifold paper.

The 10 kinds of capsule-coated sheets were superposed on the 10 kinds of acceptor material-coated sheets with the coatings facing each other, and each pair of sheets was subjected to pressure of 500 kg/cm2 for 30 seconds to form a color mark on the acceptor material-coated sheet. The color density of the mark was measured with use of a Macbeth densitometer (with a yellow filter). Table 1 shows the results.

TABLE 1 pH of Coloring on Light Heat Moisture No. capsule capsule resistance resistance resistance dispersion dispersion Ex.

1 7.6 0.08 B B A 2 7.5 0.07 B B A 3 8.8 0.09 B B A 4 8.3 0.07 B A B 5 8.1 0.07 B B A Comp. Ex.

1 5.0 0.08 D E B 2 5.8 0.09 D E B 3 5.1 0.07 D E B 4 5.2 0.07 D D B 5 5.4 0.08 D E B Note: The letters A, B, C, D and E used in Table 1 indicate the following states or changes of the marks formed on the sheets: A, not faded; B, slightly faded but usable; C, faded with a small portion colored; D, extremely faded with only a very small portion colored; and E, not colored at all.

The properties shown in Table 1 were obtained by the following methods.

1. Light resistance The capsule-coated sheets were subjected to sunlight for 1 hour.

2. Heat resistance The capsule-coated sheets were allowed to stand at 12O0Cfor 5 hours.

3. Moisture resistance The capsule-coated sheets were left to stand at 50"C and 90O RH for 5 hours.

Example 6 An addition product (15 parts, trade mark "Coronate-L") of tolylene diisocyanate and trimethylol-propane, 12 parts of addition product of hexamethylene diisocyanate and trimethylolpropane (trade mark, "Coronate-HL") and 2.5 parts of N,N-dimethylpiperazine were dissolved in 100 parts of diisopropylnaphthalene having dissolved therein 2.7 parts of Michler's hydrol-p-toluenesulfinate. Thereto added was 15 parts of acetone to dissolve the polyisocyanate. The solution was emulsified in 180 parts of an aqueous solution comprising 2% of polyvinyl alcohol and 2% of carboxymethyl cellulose with use of a homomixerto prepare an oil-in-water emulsion. The oily droplets in the emulsion were 7.0 1* in mean particle size.Then the emulsion was stirred at room temperature for 1 hour and heated to 70"C followed by 3 hours of stirring to complete the reaction. The microcapsule dispersion thus prepared had a pH of 6.5 and was not colored at all. Example 7 Polymethylene polyphenyl isocyanate (20 parts) as the polyisocyanate, and 2.0 parts of N,N-diethylbenzylamine as the tertiary amine were dissolved in 100 parts of diethyl diphenyl having dissolved therein 3.0 parts of Michler's hydrol-p-toluenesulfinate. The solution was added to 160 parts of an aqueous solution comprising 2% of gum arabic and 1.5% of ethylene-maleic anhydride copolymer. Then the mixture was emulsified in a homomixerto give an emulsion containing oily droplets 8.5 y in mean particle size.The microcapsule dispersion thus prepared was diluted with 30 parts of water, heated to 65"C and allowed to stand at this temperature for 3 hours to complete the reaction. The microcapsule dispersion obtained above had a pH of 6.8 and was not colored at all.

Example 8 An addition product (15 parts) of hexamethylene diisocyanate and trimethylolpropane, 5 parts of an epoxy compound (i.e. a condensation product of bisphenol A and epichlorohydrin) as the film forming material and 1.0 part of triethylenediamine as the tertiary amine were dissolved in a hydrophobic solution of 100 parts of 1,1-ditolylethane having dissolved therein 2.7 parts of N-p-ethoxyphenyl-leucoauramine. The solution was then added to 140 parts of 2% aqueous solution of polyvinyl alcohol containing 0.5 part of alkylbenzenesulfonate, and the mixture was emulsified by a homomixerto obtain an emulsion containing oily droplets 6.0 p in mean particle size. The emulsion was diluted with 30 parts of water and 5 parts of diethylene triamine was added to the dilute.The resultant admixture was stirred at room temperature for 1 hour and was heated to 60"C to complete the reaction. The microcapsule dispersion had a pH of 6.8 and was not colored at all.

Example 9 A 2.7 parts portion of N-p-ethoxyphenyl-leucoauraminewas dissolved in 90 parts of 1,2-ditolylpropane at 90"C. The solution was cooled to ambient temperature and thereto added were 10 parts of kerosene and 1.5 parts of 1 ,8-diazabicyclo(5,4,0)undecene-7 as the tertiary amine. In the mixture was dissolved a solution of 8 parts of diphenymethane-4,4-diisocyanate and 3 parts of polyesterpolyol in 15 parts of acetone.

To 150 parts of 1% aqueous solution of polyvinyl alcohol containing 1 part of Turkey red oil was added the hydrophobic solution. And the mixture was emulsified to obtain an emulsion containing oily droplets 5 to 12 IL in mean particle size. The microcapsule dispersion thus produced was diluted with 50 parts of water, and to the dilute was dropwise added 6 parts of 3,9-bisaminopropyl-2,4,8,10-tetraoxaspiro-[5,5]undecane

And the mixture was stirred at room temperature for 1 hour and heated to 50"C for reaction for 1 hour. The microcapsule dispersion thus obtained was 7.1 in pH and was not colored at all.

Example 10 N-phthalimidoleucoauramine (2.8 parts) was dissolved in 100 parts of isopropylbiphenyl at 90"C. The solution was then allowed to stand until it was cooled to the room temperature. Then 2.0 parts of N-methylimidazole was dissolved therein to form a solution with which a trimer of hexamethylene diisocyanate (22 parts) as the polyisocyanate was admixed. The hydrophobic solution was mixed with 150 parts of an aqueous solution which contained 1 part of Turkey red oil and which comprised 1% of gelatin and 1% polyvinyl alcohol, and the mixture was emulsified to give an emulsion containing oily droplets 3-2011 in mean particle size. The emulsion was then diluted with 30 parts of water.The dilute was stirred for 3 hours at morn temperature and heated to 80"C to complete the reaction. The microcapsule dispersion had a pH of 7.0 and was not colored.

Example 11 A microcapsule dispersion was prepared in the same manner as in Example 10 except that 2-ethylpyridine was used as the tertiary amine. The microcapsule dispersion thus prepared had a pH of 7.4 and was not colored.

Comparison Examples 6-11 Six kinds of microcapsule dispersions were prepared in the same manner as in Examples 6 to 11 respectively with the exception of using no tertiary amine.

Puip powder was added, in a ratio of 30 parts per 100 parts of oily core materials, to one of the 12 kinds of capsule dispersions prepared in Examples 6-11 and Comparison Examples 6-11 to obtain a coating composition, which was then applied, in an amount of 4 g/cm2 when dried, to one side of a paper substrate weighing 40 g/cm2 to prepare a capsule-coated sheet of pressure sensitive manifold paper.

In the same manner as above, 11 kinds of capsule-coated sheets of pressure sensitive manifold paper were prepared with use of the other capsule dispersions.

A coating composition was prepared which comprised 30 parts of aluminium hydroxide, 100 parts of activated clay, 15 parts of zinc oxide, 30 parts of styrenebutadiene copolymer latex (50% solds), 6 parts of 10% aqueous solution of modified polyvinyl alcohol and 450 parts of water. The coating composition was applied, in an amount of 6 g/cm2 when dried, to one side of a paper substrate weighing 40 g/m2 to obtain an acceptor material-coated sheet of pressure sensitive manifold paper.

The 12 kinds of capsule-coated sheets were superposed on the 12 kinds of acceptor material-coated sheets with the coatings facing each other, and each pair of sheets was subjected to pressure of 500 kg/cm2 for 30 seconds to form a color mark on the acceptor material-coated sheet. The color density of the mark was measured with use of a Macbeth densitometer (with a yellow filter). Table 2 shows the results. In Table 2, the higher the value, the higher the level of color density. The sheets were checked for other properties with the results indicated in Table 2.

TABLE 2 pH of Coloring on Coloring Light Heat Moisture No. capsule capsule- before resistance resistance resistance dispersion coated surface treatment Ex.

6 6.5 0.08 0.72 0.36 0.60 0.66 7 6.8 0.09 0.74 0.36 0.59 0.67 8 6.8 0.07 0.71 0.35 0.59 0.65 9 7.1 0.07 0.72 0.36 0.50 0.63 10 7.0 0.08 0.73 0.36 0.50 0.66 11 7.4 0.08 0.72 0.36 0.51 0.65 Comp. Ex.

6 5.9 0.12 0.72 0.25 0.08 0.60 7 5.0 0.15 0.75 0.31 0.07 0.63 8 6.2 0.11 0.70 0.33 0.08 0.63 9 5.5 0.12 0.71 0.23 0.08 0.60 10 5.2 0.13 0.72 0.30 0.09 0.60 11 5.3 0.13 0.73 0.30 0.09 0.58 The values of the properties shown in Table 2 were obtained by the following methods.

1. Light resistance The capsule-coated sheets were subjected to sunlight for 1 hour.

2. Heat resistance The capsule-coated sheets were allowed to stand at 1200C for 5 hours.

3. Moisture resistance The capsule-coated sheets were left to stand at 50"C and 90% RH for 5 hours.

As evident from Tables 1 and 2, the microcapsule dispersions of the present invention were prepared in the Examples without being colored at ail. Further the sheets of pressure sensitive manifold paper produced with use of the above microcapsule dispersions exhibited outstanding properties in light resistance, heat resistance and moisture resistance. On the other hand, the microcapsule dispersions were prepared in the Comparison Examples with deep blue colors given by the chromogenic materials. Moreover, the sheets of pressure sensitive manifold paper obtained by use of such microcapsule dispersions were extremely poor in light resistance and heat resistance. The colors measured by the Macbeth densitometer as being high than 0.1 are all seen as blue with unaided eyes.

Claims (7)

1. A process for preparing microcapsules with use of a polyisocyanate as a film forming material and a derivative of Michler's hydrol as a chromogenic material by polymerizing the polyisocyanate at the interface between an oily liquid and an aqueous liquid to form a microcapsule film, the derivative of Michler's hydrol being represented by the formula

wherein R1, R2, R3 and R4 are the same or different and are each alkyl; alkyl substituted with halogen, alkoxy or cyano; aralkyl, or aralkyl substituted with halogen, alkyl, alkoxy, cyano, substituted amino or nitro; X and Y are each halogen; alkyl; alkoxy; substituted amino or nitro; m and n are each 0 or an integer of 1 or 2; and Z is OH; N3;S02-R5;

wherein R5 and Re are the same or different and are each alkyl, aralkyl, aryl, or aryl substituted with halogen, alkyl, alkoxy, cyano, substituted amino or nitro, and Rg and Re, when taken together, form a heterocyclic ring, the process being characterized in that the microcapsules are formed in the presence of a tertiary amine.

2. A process as defined in Claim 1 wherein the tertiary amine is an amine represented by the formula

wherein R7, R8, Rs are the same or different and are each alkyl, cyclohexyl, phenyl or benzyl and may have hydroxyl, ether bond or tertiary amine, and R7, R8 and Rg, when taken together, may form a heterocyclic ring.

3. A process as defined in Claim 1 wherein the tertiary amine is an amine selected from the group consiting of N,N-dimethyllaurylamine, N,N-dimethylcyclohexylamine, N-methyldicyclohexylamine, N,Ndimethylbenzylamine, dimethylaminomethylphenol and 2,4,6-tris-(dimethylaminomethyl )phenol.

4. A process as defined in Claim 1 wherein the tertiary amine is used in an amount of about 0.1 to about 5 parts by eight per 100 parts by weight of the oily liquid.

5. A process as defined in Claim 1 or Claim 4 wherein the amount of the tertiary amine is about 0.5 to about 2 parts by weight per 100 parts by weight of the oily liquid.

6. A process for preparing microcapsules substantially as hereinbefore described with reference to any of Examples 1 to 11.

7. Microcapsules prepared by a process claimed in claims 1 to 6.