JPS6112484B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a novel method for producing microcapsules containing hydrophobic oily liquids. In particular, it relates to a method for extremely easily manufacturing capsules that have excellent retention of capsule core materials. Various methods are known for producing microcapsules, such as coacervation method, interfacial polymerization method, and in-situ polymerization method.Among them, microcapsules having an aminoaldehyde polycondensation resin as a wall film are known to produce microcapsules. It has attracted attention since its early stages of development and many attempts have been made. For example, microencapsulation method (USP-3016308) in which a urea-formaldehyde polycondensation resin wall film is formed in the presence of carboxymethyl cellulose, and urea-formaldehyde polycondensation in a suspension containing substantially no dispersant. Microencapsulation method to form a resin wall film (Special Publication No. 47-23165), method using phase separation due to electrostatic interaction (Special Publication No. 38-12518, Japanese Patent Publication No. 1987-12518)
48-4717, Japanese Patent Publication No. 49-13456), a method for forming a melamine-formaldehyde resin wall film in the presence of a system modifying substance (Japanese Patent Application Laid-open No. 53-84881), resorcinol when forming a urea-formaldehyde polycondensation resin wall film. A method of adding polyhydric phenols such as
Various methods have been proposed, such as No. 9079). However, the capsule wall membrane formed by these encapsulation methods has an unsatisfactory ability to retain the capsule core substance, which is thought to be due to the brittleness due to the characteristics of the aminoaldehyde resin. In view of the current situation, the present inventors have conducted intensive research on a method to improve the above-mentioned drawbacks without reducing the properties of aminoaldehyde polycondensation resin wall microcapsules. The present invention was completed based on the discovery that the intended purpose could be achieved simply by incorporating the compound into a certain hydrophobic oily liquid. The present invention provides a method for dispersing a hydrophobic oily liquid and enveloping the hydrophobic oily liquid by polycondensing an aminoaldehyde resin in a hydrophilic medium containing an anionic colloid substance. This is a method for producing microcapsules characterized by containing a polyfunctional epoxy compound in the liquid. The hydrophobic oily liquid used in the present invention is not particularly limited, but the following substances may be exemplified. Animal oils such as fish oil, lard oil, etc., vegetable oils such as olive oil, peanut oil, linseed oil, soybean oil, string oil, castor oil, etc., mineral oils such as petroleum spirits, kerosene, xylene, toluene, etc., alkyl-substituted diphenyl alkanes. , alkyl-substituted naphthalenes, alkyl-substituted diphenyls, hydrogenated terphenyls, methyl salicylate, dibutyl phthalate, dibutyl adipate, butylbenzyl adipate, trioctyl phosphate, etc., which are insoluble or substantially soluble in water. Insoluble liquid. The anionic colloid substances used in the present invention are not particularly limited, but include:
For example, natural polymers such as gum arabic, carrageenan, sodium alginate, pectic acid, gum tragacanth, almond gum, agar, semi-synthetic polymers such as carboxymethyl cellulose, carboxymethylated starch, phosphorylated starch, acrylic acid, methacrylic acid, maleic acid. , various polymers having anionic monomer units such as crotonic acid, and partial amides or partial esters of such polymers,
Examples include synthetic polymers such as carboxy-modified polyvinyl alcohol and sulfonic acid-modified polyvinyl alcohol. One or more types of such anionic colloidal substances are appropriately selected and used depending on the core substance to be encapsulated, but especially synthetic anionic colloidal substances containing hydrophobic monomer units such as ethylene, propylene, isobutylene, methyl vinyl ether, and vinyl acetate are used. Colloids are preferably used because they provide excellent stabilization during the emulsification process. Furthermore, anion-modified polyvinyl alcohol is particularly preferably used because the effects of the present invention are more remarkable. The anionic colloid substance is preferably contained in the hydrophilic medium in an amount of 0.5% by weight or more, and more preferably 1.5% by weight or more in terms of ease of capsule preparation and quality of the capsules obtained. The upper limit of the amount to be used is determined by the viscosity of the system, the capsule preparation equipment, etc., but it is generally desirable to keep it to 20% by weight or less. The aminoaldehyde resin used for enveloping the hydrophobic core material in the present invention includes, for example, urea, thiourea, alkyl urea, ethylene urea, acetoguanamine, benzoguanamine, melamine,
Amines such as guanidine, dicyandiamide, biuret, cyanamide, and formaldehyde, paraformaldehyde, hexamethylenetetramine, acetaldehyde, butyraldehyde,
Crotonaldehyde, benzaldehyde, furfural, glyoxal, glutaraldehyde,
It refers to a resin obtained by polycondensation or copolycondensation of aldehydes such as acrolein and aldol, and among them, when melamine is used as at least one component, the effects of the present invention are remarkable, and it is particularly preferably used. In addition, in the present invention, it is of course possible to contain a part of copolycondensation components other than amines and aldehydes for the purpose of modifying the aminoaldehyde resin, etc., but the amount contained is It should be kept within a range that does not impair the desired effects of the invention. The polyfunctional epoxy compound used in the present invention is a compound having at least one epoxy group in one molecule and must be polyfunctional, such as epihalohydrin such as epichlorohydrin and epibromohydrin. class, hydroxyl group,
Reaction products of compounds having two or more active hydrogen groups such as amino groups and carboxyl groups with the above epihalohydrins, and reaction products of compounds having two or more double bonds epoxidized with peracetic acid etc. Illustrated. Among them, reaction products of compounds having two or more hydroxyl groups and epihalohydrins are preferably used because they provide high-quality capsule wall membranes. In particular, the epoxy equivalent (the number of grams of resin containing 1 gram equivalent of epoxy groups) is 150
-1000 is more preferably selected because particularly stable capsule quality can be obtained. These polyfunctional epoxy compounds need to be soluble in the hydrophobic oily liquid as the capsule core material, and for this purpose, the hydrophobic oily liquid and the polyfunctional epoxy compound are appropriately selected and used. Also,
It is also possible to use a water-soluble solvent such as ethyl acetate or acetone in combination as a solubilizing agent for the polyfunctional epoxy compound in the hydrophobic oily liquid. In the present invention,
Although the amount of such polyfunctional epoxy compound to be used is not particularly limited, it is generally preferable to contain it in an amount of 1 to 30% by weight based on the hydrophobic oily liquid, since particularly stable capsule quality can be obtained. It is more desirable to contain up to 20% by weight. In the present invention, the aminoaldehyde resin is added in the form of a monomer or prepolymer to a hydrophilic medium, and together with a finely dispersed hydrophobic oily liquid containing a polyfunctional epoxy compound and an anionic colloid substance, the aminoaldehyde resin is added to a capsule manufacturing system. is configured. The capsule manufacturing system is maintained acidic if necessary, and the polycondensation reaction of the aminoaldehyde resin proceeds. At that time, in order to maintain the capsule production system acidic, for example, formic acid, acetic acid, citric acid, etc.
So-called acid catalysts commonly used in the field of aminoaldehyde resin production such as oxalic acid, para-toluenesulfonic acid, hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, ammonium chloride, ammonium sulfate, etc. are used, but in the present invention, anion coexisting in the system is used. Acid groups of sex colloid substances can also be used. Note that the polycondensation reaction of aminoaldehyde resin is accelerated by heating the system, so
Preferably, the system is heated to a temperature of .degree. Especially 45
A temperature in the range of ~75°C is more preferable because capsules with stable quality are formed in a relatively short time. Thus, according to the method of the present invention, by simply mixing the capsule-forming materials and providing simple polycondensation conditions, the polycondensation resin can be efficiently deposited on the surface of the capsule core material, and the capsule quality such as core material retention is excellent. microcapsules are obtained. In order to specifically explain the method of the present invention, examples will be described below regarding the case where the method is applied to the field of pressure-sensitive copying paper, but the present invention is of course not limited to these. Further, unless otherwise specified, parts and % in the examples represent parts by weight and % by weight, respectively. Example 1 150 parts of a 5% aqueous solution of carboxy-modified polyvinyl alcohol (trade name Gosenal T-350, manufactured by Nippon Gosei Co., Ltd.) was added to a stirring mixing vessel equipped with a heating device to prepare an aqueous medium for capsule production. Separately, a capsule core material obtained by dissolving 5 parts of epichlorohydrin, 2.8 parts of crystal violet lactone, and 0.7 parts of benzoylleucomethylene blue in 95 parts of alkylnaphthalene (trade name: KMC Oil, manufactured by Kureha Chemical Co., Ltd.) was prepared with an average particle size of 3.8 μm. The mixture was emulsified and dispersed in the above aqueous medium for capsule production.
Next, 300 parts of water was added to this system and heated to 70°C. Separately, 30 parts of a 37% formaldehyde aqueous solution was added to 10 parts of melamine, heated for 20 minutes at 60°C, and then 10 parts of a 10% glycine aqueous solution was added. A melamine-formaldehyde resin prepolymer obtained by heating for a minute was added, and the mixture was maintained at 70° C. for 3 hours with gentle stirring to obtain a microcapsule dispersion. Example 2 Instead of the capsule core material used in Example 1, 5 parts of the reaction product of bisphenol A and epichlorohydrin (epoxy equivalent: 180) was added to a mixed oil of 25 parts of alkylnaphthalene and 70 parts of dibutyl phthalate.
A microcapsule dispersion was obtained in exactly the same manner as in Example 1, except that a solution containing 2.8 parts of crystal violet lactone, and 0.7 parts of benzoyl leucometalene blue was used. Example 3 A microcapsule dispersion was obtained in exactly the same manner as in Example 2 except that an epoxy equivalent of 300 was used. Example 4 A microcapsule dispersion was obtained in exactly the same manner as in Example 2 except that epoxy equivalent of 600 was used. Example 5 In Example 4, 10 parts of melamine and 37 parts of melamine were used instead of the melamine-formaldehyde resin prepolymer.
% formaldehyde aqueous solution 30 parts and glycine 1
A microcapsule dispersion was obtained in exactly the same manner except that each part was separately added to the capsule manufacturing medium. Comparative Example 1 A microcapsule dispersion was obtained in exactly the same manner as in Example 1, except that epichlorohydrin was not added. After allowing the six types of capsule dispersions thus obtained to cool, 30 parts of cellulose powder and 100 parts of a 20% oxidized starch aqueous solution were added to prepare a capsule coating solution. The capsule coating solution was coated on a base paper of 40 g/m ² to a dry coating amount of 4 g/m ² and dried to prepare a top sheet for pressure-sensitive copying paper. Separately, 65 parts aluminum hydroxide, 20 parts zinc oxide
15 parts of a mixed melt of 3,5-di(α-methylbenzyl)zinc salicylate and α-methylstyrene/styrene copolymer (melt ratio 80/20), 5 parts of an aqueous polypynyl alcohol solution (solid content) ) and 300 parts of water in a ball mill for 24 hours.
40 parts of coloring agent coating liquid prepared by adding 20 parts (solid content)
g/m ² base paper to a dry weight of 5 g/m ² and dried to prepare a lower sheet for pressure-sensitive copying paper. Further, on the opposite side of the coloring agent-coated side of the bottom paper, the six kinds of capsule coating liquids described above were applied in the same manner as for the top paper and dried to prepare middle paper for pressure-sensitive copying paper. Using the top paper, middle paper, and bottom paper thus obtained, a performance comparison test was conducted in the manner described below, and the results are listed in Table 1. () Heat resistance Layer the top paper and bottom paper so that the coated surfaces are facing each other and apply a load of 5 kg/cm ² .
It was treated in a heat treatment machine at 100°C for 3 hours, and the degree of color staining on the surface coated with the coloring agent was determined. () Solvent resistance The medium paper was left in a saturated atmosphere of trichlorethylene at room temperature for 1 hour, and the degree of colored staining on the surface coated with the coloring agent was determined. () Moisture resistance After leaving the top paper in an atmosphere of 50℃ and 90% RH for 8 hours, the bottom paper and the bottom paper were stacked so that the coated sides were facing each other, and the bottom paper was colored under pressure at 150 kg/cm ^2. The color density on the paper was compared with the color density when the color was similarly developed under pressure using untreated top paper. Color density when using treated top paper / Color density when using untreated top paper x 100

[Table] As is clear from the results in Table 1, all pressure-sensitive copying papers using microcapsules obtained by the method of the present invention had sufficient practicality.

Claims (1)

[Scope of Claims] 1 In enveloping the hydrophobic oily liquid by polycondensing an aminoaldehyde resin in a hydrophilic medium containing a hydrophobic oily liquid and containing an anionic colloid substance, the hydrophobic oily liquid is dispersed. A method for producing microcapsules, which comprises containing a polyfunctional epoxy compound in an oily liquid. 2. The manufacturing method according to claim 1, wherein the aminoaldehyde resin is a melamine-formaldehyde resin. 3. The manufacturing method according to claim 1, wherein the polyfunctional epoxy compound is a reaction product of a compound having two or more hydroxyl groups and an epihalohydrin.