JPH078334B2 - Microcapsule manufacturing method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a microcapsule containing a hydrophobic core substance, and particularly a method capable of extremely easily producing a capsule excellent in retention of the core substance. It is about.

"Conventional Technology" In recent years, the microencapsulation technology has made remarkable progress, and the fields of use of encapsulated materials are extremely wide-ranging and various fields including pressure-sensitive copying paper.

As a method for producing microcapsules, various methods such as coacervation method, interfacial polymerization method and in-situ polymerization method are known. Among them, capsules having an aminoaldehyde polycondensation resin as a wall film are water-resistant and resistant. Because of its excellent solvent properties, for example, an encapsulation method for forming a urea / formaldehyde polycondensation resin wall film in the presence of carboxymethyl cellulose [US Patent No. 3016308] in a suspension containing substantially no dispersant Encapsulation method to form urea / formaldehyde polycondensation resin wall film with a glass [JP-B-47-28165]
Etc., various methods have been proposed. However, in such an encapsulation method, the polycondensation resin is not efficiently deposited on the surface of the capsule core material, and therefore extremely careful control of the preparation conditions such as addition of dilution water is necessary.

In order to efficiently deposit the polycondensation resin on the surface of the capsule core material, for example, a method in which a substance having an active group capable of chemical or physicochemical bonding is used as a dispersant [JP-B-37-12380] electrostatic A method utilizing phase separation by various interactions [Japanese Patent Publication No. 38-12380, Japanese Patent Publication No. 48-4717, Japanese Patent Publication No. 49-18456] and the like have been proposed. However, these improved methods not only require the same complicated steps as the conventional encapsulation method using complex coacervation but also contain a water-soluble component having a heterogeneous charge in the capsule wall membrane. Therefore, defects that cause cracking of the capsule wall film during drying accompany.

Further, a method of polycondensing melamine and formaldehyde in the presence of ethylene / maleic anhydride copolymer, methyl vinyl ether / maleic anhydride copolymer or the like to obtain a capsule having an aminoaldehyde resin wall membrane [JP-A-53- 848
No. 81] has been proposed, and a similar encapsulation method by an in-situ polymerization method is disclosed in, for example, JP-A-55-92135, JP-A-56-51238, JP-A-56-58536, and JP-A-56-58536. 56-102934
JP, 57-56293, 58-8689, 60-68
045, JP60-216838, JP60-238140, JP61-11138, JP61-25635, JP62-1451,
Various proposals have been made in JP-A-62-19238.

[Problems to be Solved by the Invention] However, even though many encapsulation methods have been developed and proposed in this way, there is still room for improvement because these methods are accompanied by the following disadvantages. It is left.

When a colorless basic dye used in pressure-sensitive copying paper is used as a capsule core substance, the colorless dye may be colored.

The aminoaldehyde resin may not be sufficiently deposited on the surface of the capsule core material, resulting in a capsule having poor heat resistance, moisture resistance, solvent resistance and the like.

When the emulsifying ability and emulsion stability of the anionic water-soluble polymer substance are insufficient, giant capsules of several hundreds of μm may be produced, or unencapsulated core substance may remain in the system.

When producing an anionic water-soluble polymer, a high-concentration aqueous solution cannot be prepared depending on the monomer composition, which may result in an increase in transportation cost and energy cost required for dissolution.

The object of the present invention is to improve the above-mentioned problems in the in-situ polymerization method of emulsifying and encapsulating a hydrophobic liquid in a hydrophilic liquid in which an anionic water-soluble polymer substance is dissolved, which is excellent. An object of the present invention is to provide a method for efficiently producing microcapsules having characteristics.

"Means for Solving the Problem" The present invention is a method of polycondensing an aminoaldehyde resin initial condensate in the presence of an anionic polymer copolymer containing vinyl sulfonic acid and an aromatic vinyl compound as constituent monomers to make it hydrophobic. A method for producing a microcapsule, which comprises covering the surface of a core substance.

"Function" The aromatic vinyl compound which is a constituent monomer of the anionic polymer copolymer used in the present invention is a compound in which a vinyl group is introduced into an aromatic ring, and specifically, styrene and vinyltoluene. , Α-methylstyrene, nuclear alkyl-substituted α-alkylstyrenes such as isopropenyltoluene, β-bromostyrene, vinylnaphthalene, and the like.

Among these, styrene or vinyltoluene is particularly preferably used.

The anionic polymer copolymer of the present invention contains vinyl sulfonic acid and an aromatic vinyl compound as essential constituent monomers, but in order to facilitate the progress of polymerization in the production of the copolymer, depending on the capsule quality, etc. It is preferable to contain various hydrophobic monomers and hydrophilic monomers, specifically, ethylene, propylene, alkyl (meth) acrylate, hydroxyalkyl (meth) acrylate, acrylonitrile, vinyl acetate, acrylamide, tertiary butyl acrylamide. Sulfonic acid, sulfoethyl methacrylate, allyl sulfonic acid, methallyl sulfonic acid, vinylbenzene sulfonic acid, acrylic acid, methacrylic acid,
Crotonic acid, maleic anhydride, itaconic acid and the like are exemplified.

Above all, when acrylic acid and / or alkyl (meth) acrylate is contained, a capsule excellent in core substance retention can be obtained [the alkyl group of the alkyl (meth) acrylate preferably has 1 to 8 carbon atoms], Acrylic acid and (meth)
Excellent capsules are obtained when both of the alkyl acrylates are included.

In the specific copolymer used in the present invention, the effect of suppressing the viscosity increase of the capsule dispersion cannot be sufficiently obtained when the content of vinyl sulfonic acid is small, and when it is large, the emulsion stability is impaired. Mol%, preferably 10 to 80 mol%, more preferably about 10 to 40 mol%. Further, when the content of the aromatic vinyl compound is small, the effect of imparting sufficient emulsion stability cannot be obtained, and when it is large, the water solubility of the copolymer is deteriorated, and sufficient capsule strength cannot be obtained. 20 mol%, preferably 0.1-10 mol%,
More preferably, it is contained in an amount of about 1 to 8 mol%. Further, it is desirable that the constituent monomers other than the above are contained in the range of 0 to 95 mol%, preferably 5 to 90 mol%, and more preferably 50 to 85 mol%.

The specific copolymer thus obtained is used as an aqueous solution or an aqueous dispersion in the range of pH 3 to 6 with an alkali such as sodium hydroxide, potassium hydroxide or sodium carbonate or an acid such as acetic acid, oxalic acid or hydrochloric acid. However, the viscosity of a 20% by weight aqueous solution is 20 to 5000 cps (25 ° C, pH 2.0), preferably 40 to 1500 cps
It is desirable to adjust so that In addition, the blending amount in the hydrophilic liquid injection is in the range of 0.5% or more, more preferably 1.0% or more, and most preferably about 2.0 to 6.0% in consideration of the ease of preparation of the emulsion and the stability of the emulsion. It is desirable to adjust with. The upper limit of the compounding amount is determined by the viscosity of the system, the capsule preparation device, etc., but is generally limited to 20% or less.

The aminoaldehyde resin used for covering the surface of the hydrophobic core substance in the present invention is obtained by polycondensing one or more amines such as urea and melamine with aldehydes such as formaldehyde, glutaraldehyde and furfural. However, it may be modified with glycine, sulfamic acid, or methanolic acid. These are preferably used in the form of precondensate due to the denseness of the capsule wall membrane, but they may be monomers.

Among them, the melamine / formaldehyde type resin whose main starting materials are melamine and formaldehyde or the melamine / urea / formaldehyde type resin whose main starting materials are melamine, urea and formaldehyde are excellent in the uniformity and physical strength of the capsule wall film. Therefore, it is particularly preferably used in the present invention because a capsule having good core substance retention is obtained.

The capsule production system is adjusted to an acidic region, preferably pH 3 to 6, to proceed the polycondensation reaction. However, since heating the system accelerates the reaction, it is desirable to heat to a temperature of about 60 to 95 ° C. If necessary, a natural or synthetic polymer having a carboxyl group or a sulfone group or a low molecular weight surfactant such as dodecylbenzenesulfonic acid may be used in combination in the capsule manufacturing system, but the amount used is It is necessary to keep it within a range that does not impair the desired effect of the present invention.

In the present invention, the hydrophobic core substance contained in the microcapsules is not particularly limited, but the following substances are exemplified.

Animal oils such as fish oil and lard oil, vegetable oils such as olive oil, peanut oil, linseed oil, soybean oil and castor oil, mineral oils such as petroleum, kerosene, xylene and toluene, alkyl-substituted diphenylalkanes, alkyl-substituted Naphthalene, biphenyl ethane, methyl salicylate, diethyl adipate, -n-propyl adipate,
Like synthetic oils such as di-n-butyl adipate, di-methyl phthalate, diethyl phthalate, di-n-propyl phthalate, di-n-butyl phthalate, di-n-octyl phthalate, etc. A solution in which a water-insoluble or substantially water-insoluble liquid or the above-mentioned synthetic oil is dissolved with an electron-donating color former, an electron-accepting developer, a ligand compound, an organic metal salt, etc.
Water-insoluble metal oxides and salts, cellulose-like or fibrous substances such as asbestos, water-insoluble synthetic polymer substances, minerals, pigments, glasses, perfumes, flavors, bactericidal compositions , Physiological compositions, fertilizer compositions,
Liquid crystals, temperature indicating materials, flame retardants, etc. You may use together 2 or more types of these.

Thus, according to the method of the present invention, without requiring careful control of capsule preparation conditions such as addition of dilution water,
The polycondensation resin is efficiently deposited on the surface of the capsule core material simply by mixing the capsule-forming material and applying simple polycondensation conditions, and a capsule having excellent heat resistance, moisture resistance and solvent resistance is formed. Moreover, the obtained capsule dispersion liquid has a low viscosity, little formation of huge capsules or aggregates, and extremely small amount of unencapsulated core substance is prepared.

Microcapsules prepared by the method of the present invention,
Various medicines, fragrances, paints, agricultural chemicals, adhesives, liquid crystals, foods,
It is suitable for encapsulating rust preventive agents, toners, etc., and is particularly useful for applications such as printing ink and pressure-sensitive copying paper.

[Examples] In order to more specifically describe the present invention, examples of preparing microcapsules for pressure-sensitive copying paper will be described below, but of course, the present invention is not limited thereto. Absent. In addition, "parts" and "%" in the examples mean "parts by weight" and "% by weight", respectively, unless otherwise specified.

Example 1 A 20% aqueous solution of a copolymer consisting of 15 mol% of vinyl sulfonic acid, 5 mol% of styrene, 70 mol% of acrylic acid and 10 mol% of ethyl acrylate (25 ° C, pH 2.0, viscosity of 20%, 50 cp).
s) 112.5 parts of water was added to 37.5 parts, and the pH was adjusted to 4 with a 20% NaOH aqueous solution.
The product adjusted to 6 was used as an aqueous medium for capsule production.

To this was added 105 parts of diisopropylnaphthalene (trade name: K-113, manufactured by Kureha Chemical Co., Ltd.) in which 5 parts of crystal violet lactone was dissolved, and the mixture was emulsified and dispersed so that the average particle size was 5 μm. The temperature was raised to 70 ° C.

Next, 20 parts of methylated methylol melamine initial condensate (trade name: Beckamine APM, 80% concentration, Dainippon Ink and Chemicals, Inc.) was added to the system, and the system temperature was maintained at 70 ° C for 1 hour while continuing stirring. After that, the mixture was cooled to obtain a milky white capsule dispersion liquid.

Example 2 Vinyl sulfonic acid 15 mol%, vinyltoluene 5 mol%,
112.5 parts of water was added to 37.5 parts of a 20% aqueous solution (a viscosity of 130 cps at 25 ° C, pH 1.8, 20% concentration) of a copolymer consisting of 75% by mole of acrylic acid and 5% by mole of butyl acrylate to prepare a 20% aqueous solution of NaOH. The aqueous medium for capsule production was prepared by adjusting the pH to 4.6.

To this was added 105 parts of diisopropylnaphthalene (trade name: K-113, manufactured by Kureha Chemical Co., Ltd.) in which 5 parts of crystal violet lactone was dissolved, and the mixture was emulsified and dispersed so that the average particle size was 5 μm.

Next, 20 parts of melamine / urea / formaldehyde type initial condensate (trade name: Beckamine MA-S, 70% concentration, manufactured by Dainippon Ink and Chemicals, Inc.) was added to the system, and the system temperature was maintained at 80 ° C while continuing stirring. It was held for 2 hours and then cooled to obtain a milky white capsule dispersion.

Example 3 As Example 1 except that a copolymer consisting of 25 mol% vinyl sulfonic acid, 5 mol% styrene and 70 mol% acrylic acid (viscosity 300 cps at 25 ° C., pH 2.1, 20% concentration) was used. A capsule dispersion was obtained in the same manner.

Example 4 Capsule dispersion liquid was prepared in the same manner as in Example 1 except that a copolymer consisting of 98 mol% of vinyl sulfonic acid and 2 mol% of styrene (viscosity 110 cps at 25 ° C., pH 2.6, 20% concentration) was used. Got

Example 5 Vinyl sulfonic acid 10 mol%, α-methylstyrene 5 mol%, acrylic acid 75 mol%, iso-propyl methacrylate 1
A capsule dispersion liquid was obtained in the same manner as in Example 1 except that a 0 mol% copolymer (25 ° C., pH 2.1, viscosity at 20% concentration: 90 cps) was used.

Comparative Example 1 Copolymer (94 mol% acrylic acid, 3 mol% butyl acrylate, 3 mol% iso-propyl methacrylate)
A capsule dispersion liquid was obtained in the same manner as in Example 1, except that the temperature was 1.8 ° C., the viscosity was 200 cps at 20% concentration.

Comparative Example 2 Capsule dispersion was performed in the same manner as in Example 1 except that a copolymer consisting of 80 mol% of acrylic acid and 20 mol% of vinyl sulfonic acid (25 ° C., pH 2.2, viscosity of 60 cps at 20% concentration) was used. A liquid was obtained.

The capsule dispersion thus obtained was diluted to a concentration of 35%, and applied to the CF surface of the lower paper for pressure-sensitive copying paper (trade name: KS Copy Bright, manufactured by Kanzaki Paper Co., Ltd.) with a wire bar No. 18 and dried. did. The following performance comparison test was conducted using this paper and each capsule dispersion, and the results are shown in Table 1.

[Core substance retention]

The test paper was treated at 120 ° C. for 5 hours, and the degree of color development on the coated surface was measured with a Macbeth densitometer (filter: visual). The better the retention of the core substance, the lower the color density of the coated surface (the smaller the value).

[Un-chamicelled core substance]

When the capsule dispersion is applied to the CF surface of the lower paper and dried, the presence of non-encapsulated hydrophobic core substance will appear as spot-like stains, so the number of spot-like stains existing on an area of 15 cm × 25 cm should be adjusted. It was measured.

[Giant capsules, aggregates]

The weight of the residue obtained by treating the capsule dispersion with a 200-mesh screen was shown as a percentage of the total weight of the capsule.

[Capsule dispersion viscosity]

 The sample was measured at 25 ° C. with a B-type viscometer at 60 rpm.

"Effect" The specific anionic polymer copolymer used in the method of the present invention has a good balance between hydrophobicity and hydrophilicity, and is also excellent in emulsifying ability, emulsion stability, and capsule wall membrane forming ability. Therefore, as is clear from the results of Table 1, the generation of unencapsulated core substance, huge capsules, and aggregates is extremely small,
Capsules excellent in core substance retention were efficiently formed.
Further, the copolymer used in the present invention is excellent in emulsifying ability, emulsion stability and capsule wall film forming ability even at a relatively low viscosity, and the obtained capsule dispersion has a low viscosity, so that high speed smearing in pressure-sensitive copying paper production is possible. Excellent suitability.

Claims (5)

[Claims] 1. A hydrophobic core substance surface is covered by polycondensing an aminoaldehyde resin initial condensate in the presence of an anionic polymer copolymer containing vinyl sulfonic acid and an aromatic vinyl compound as constituent monomers. A method for producing a microcapsule, which is characterized in that 2. The production method according to claim 1, wherein the aminoaldehyde resin initial condensate is a melamine-formaldehyde resin initial condensate. 3. The production method according to claim 1, wherein the aminoaldehyde resin precondensate is a melamine / urea / formaldehyde resin precondensate. 4. The production method according to claim 1, wherein the aromatic vinyl compound is at least one selected from styrene and vinyltoluene. 5. The anionic polymer copolymer further contains at least one of acrylic acid and alkyl (meth) acrylate as a constituent monomer.
The manufacturing method according to the item.