JPH01164433A - Production of microcapsule - Google Patents

Abstract

PURPOSE:To efficiently form microcapsules having superior core substance retentivity by polycondensing a precondensate of aminoaldehyde resin in the presence of an anionic copolymer contg. vinylsulfonic acid and an arom. vinyl compd. CONSTITUTION:An aq. soln. of a copolymer consisting of vinylsulfonic acid, an arom. vinyl compd. such as styrene and acrylic acid, etc., added to facilitate the progress of polymn. is adjusted to the acidic region of 3-6pH. A precondensate of melamine-formaldehyde resin such as a precondensate of methylated methylol melamine is added to the aq. soln. and they are stirred at a constant temp. and cooled to obtain an opal white dispersion liq. contg. microcapsules. The microcapsules have superior heat, moisture and solvent resistances and useful for printing ink, pressure sensitive copying paper, etc.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a method for manufacturing microcapsules containing a hydrophobic core substance, and in particular a method for extremely easily manufacturing capsules that have excellent core substance retention properties. It is related to.

"Prior Art" In recent years, microencapsulation technology has made remarkable progress, and the fields of use of encapsulated products are extremely wide and diverse, including pressure-sensitive copying paper.

Various methods are known for manufacturing microcapsules, such as coacelhesion, interfacial polymerization, and 1n-situ polymerization, but among them, capsules having a wall film made of aminoaldehyde polycondensation resin are water resistant. , excellent solvent resistance, etc., for example, an encapsulation method in which a urea/formaldehyde polycondensation resin wall film is formed in the presence of carboxymethylcellulose [US Pat. No. 3,016,308], a suspension containing substantially no dispersant. Among them, various methods have been proposed, such as an encapsulation method [Japanese Patent Publication No. 47-28165] in which a wall film of a urea/formaldehyde polycondensation resin is formed. However, in such an encapsulation method, since the polycondensation resin is not efficiently deposited on the surface of the capsule core material, extremely careful control of the preparation conditions such as the addition of dilution water is required.

In order to improve the efficiency of depositing the polycondensation resin on the surface of the capsule core material, for example, a method of using a substance having an active group capable of chemically or physicochemically bonding as a dispersant [Japanese Patent Publication No. 37-12380] Electrostatic Methods that utilize phase separation due to such interactions [Japanese Patent Publication No. 38-12380, Japanese Patent Publication No. 48-4717, Japanese Patent Publication No. 49-18456] have been proposed. However, with these improvement methods,
Not only does it require a complicated process like the conventional encapsulation method using complex coacervation, but it also contains water-soluble components with different charges in the capsule wall, which causes the capsule wall to dry during drying. It is accompanied by defects that cause cracks.

Furthermore, a method for obtaining capsules having an aminoaldehyde resin wall by polycondensing melamine and formaldehyde in the presence of an ethylene/maleic anhydride copolymer, a methyl vinyl ether/maleic anhydride copolymer, etc.
No. 84881] has been proposed, and a similar 1n-sit
Regarding the encapsulation method using the u-polymerization method, for example, JP-A-55-92135, JP-A-56-51238, JP-A-56-58536, JP-A-56-102934,
JP-A-57-56293, JP-A-58-8689,
JP 60-68045, JP 60-216838
No., JP-A-60-231 (No. 140, JP-A-61) 1)
No. 38, JP-A-61-25635, JP-A-62-14
Various proposals have also been made in No. 51, JP-A No. 62-19238, etc.

"Problems to be Solved by the Invention" However, although many encapsulation methods have been developed and proposed, these methods still have the following disadvantages, so there is still room for improvement. left behind.

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

(2) The aminoaldehyde resin may not be sufficiently deposited on the surface of the capsule core material, resulting in capsules with poor heat resistance, moisture resistance, solvent resistance, etc.

(2) When the emulsifying ability and emulsifying stability of anionic water-soluble polymeric substances are insufficient, giant capsules of several hundred μm may be formed or unencapsulated core substances may remain in the system.

(2) When producing anionic water-soluble polymer substances, it may not be possible to prepare a highly concentrated aqueous solution depending on the monomer composition, resulting in increased transportation costs and energy costs required for dissolution.

The purpose of the present invention is to improve the above-mentioned problems in the 1n-situ polymerization method in which a hydrophobic liquid is emulsified and dispersed in a hydrophilic liquid containing an anionic water-soluble polymer substance and encapsulated. An object of the present invention is to provide a method for efficiently producing microcapsules having specific properties.

"Means for Solving the Problem" The present invention involves polycondensing an initial condensate of aminoaldehyde resin in the presence of an anionic polymer copolymer containing vinyl sulfonic acid and an aromatic vinyl compound as constituent monomers to form a hydrophobic material. This is a method for producing microcapsules characterized by enveloping the surface of a core substance.

"Function" The aromatic vinyl compound, which is a component 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, Nuclear alkyl-substituted α-alkylstyrenes such as vinyltoluene, α-methylstyrene and isopropenyltoluene, β-bromostyrene, and vinylnaphthalene are exemplified.

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. It is preferable to contain various hydrophobic monomers and wood-philic monomers, specifically ethylene, propylene, alkyl (meth)acrylates, hydroxyalkyl (meth)acrylates, acrylonitrile, vinyl acetate, acrylamide, and tertiary butyl. Acrylamide sulfonic acid, sulfoethyl methacrylate, allyl sulfonic acid, methallyl sulfonic acid, vinylbenzenesulfonic acid, acrylic acid, methacrylic acid,
Examples include crotonic acid, maleic anhydride, and itaconic acid.

Among them, when acrylic acid and/or alkyl (meth)acrylate is contained, capsules with excellent core material retention properties can be obtained [the alkyl group of the alkyl (meth)acrylate preferably has 1 to 8 carbon atoms], and especially Acrylic acid and (meth)
Excellent capsules are obtained when both alkyl acrylates are included.

In the specific copolymer used in the present invention, if the content of vinyl sulfonic acid is small, the effect of suppressing the increase in viscosity of the capsule dispersion liquid cannot be sufficiently obtained, and if the content is too large, the emulsion stability will be impaired. Mol%, preferably 10-80
The content is preferably about 10 to 40 mol%. Furthermore, if the content of the aromatic vinyl compound is too low, the effect of imparting sufficient emulsion stability cannot be obtained, and if the content is too high, the water solubility of the copolymer becomes poor, and sufficient capsule strength cannot be obtained. 05-20 mol%, preferably 0.05 to 20 mol%.
It is contained in an amount of about 1 to 10 mol%, more preferably about 1 to 8 mol%. Furthermore, the constituent monomers other than the above are 0 to 95
mol%, preferably 5 to 90 mol%, more preferably 5
It is desirable to contain it in a range of about 0 to 85 mol%.

The specific copolymer thus obtained is used as an aqueous solution or dispersion in the pH range of 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 weight aqueous solution is 20 to 5000 cps (at 25°C).

It is desirable to adjust the pH to 2.0), preferably 40 to 1500 cps. In addition, the amount to be added to the hydrophilic liquid is 0.5% or more, more preferably 1.0% or more, and most preferably 2.0% or more, considering ease of emulsion preparation and emulsion stability. It is desirable to adjust it within a range of about 6.0%. The upper limit of the blending amount is determined by the viscosity of the system, the capsule preparation device, etc., but is limited to 20% or less for boat fishing.

The aminoaldehyde resin used to cover the surface of the hydrophobic core substance in the present invention is obtained by polycondensing one or more types of amines such as urea and melamine with one or more aldehydes such as formaldehyde, geltaraldehyde, and furfural. However, it may also be modified with glycine, sulfamic acid, methanol, etc. These are preferably used in the form of an initial condensate in view of the density of the capsule wall, but monomers may also be used.

Among them, melamine-formaldehyde resins whose main starting materials are melamine and formaldehyde, and melamine-urea-formaldehyde resins whose main starting materials are melamine, urea, and formaldehyde are excellent in the uniformity and physical strength of the capsule wall membrane. It is particularly preferably used in the present invention because capsules having good core substance retention properties can be obtained.

The capsule manufacturing system is adjusted to an acidic range, preferably pH 3 to 6, to allow the polycondensation reaction to proceed, but since heating the system accelerates the reaction, it is desirable to heat the system to a temperature of about 60 to 95°C. In addition, if necessary, natural or synthetic polymers having carboxyl groups or sulfonic groups or low-molecular surfactants such as dodecylbenzenesulfonic acid can be used in the capsule manufacturing system, but the amount used is limited. It is necessary to keep the amount within a range that does not inhibit the desired effects of the present invention.

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

Animal oils such as fish oil, lard oil, etc., vegetable oils such as olive oil, peanut oil, linseed oil, soybean oil, castor oil, etc., mineral oils such as petroleum, kerosene, xylene, toluene, etc., alkyl-substituted diphenylalkanes, alkyl-substituted naphthalene, biphenylethane, methyl salicylate, diethyl adipate, di-n-propyl adipate,
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 an electron-donating color former, an electron-accepting color developer, a ligand compound, an organic metal salt, etc. are dissolved in a water-insoluble or substantially water-insoluble liquid or the above-mentioned synthetic oil;
Water-insoluble metal oxides and salts, fibrous materials such as cellulose or asbestos, water-insoluble synthetic polymeric materials, minerals, pigments, glasses, fragrances, flavors, fungicidal compositions, Physiological compositions, fertilizer compositions,
Liquid crystals, temperature indicating materials, flame retardants, etc. Two or more types of these may be used in combination.

Thus, the method of the present invention does not require careful control of capsule preparation conditions, such as the addition of dilution water.
By simply mixing the capsule-forming materials and providing simple polycondensation conditions, the polycondensation resin is efficiently deposited on the surface of the capsule core material, forming capsules with excellent heat resistance, moisture resistance, and solvent resistance.

In addition, the obtained capsule dispersion has a low viscosity, has little formation of giant capsules or aggregates, and has an extremely small amount of unencapsulated core material.

The microcapsules prepared by the method of the present invention are
Various pharmaceuticals, fragrances, paints, pesticides, 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.

"Example" In order to explain the present invention more specifically, examples for preparing microcapsules for pressure-sensitive copying paper will be described below, but the present invention is of course not limited to these. do not have. In addition, "parts" and "%" in the examples indicate "parts by weight" and "% by weight", respectively, unless otherwise specified.

Example 1 A 20% aqueous solution of a copolymer consisting of 15 mol% vinyl sulfonic acid, 5 mol% styrene, 70 mol% acrylic acid, and 10 mol% ethyl acrylate (25°C, pH 2°0, viscosity at 20% concentration) 50cps) 37.5 parts water 1) 2
．． 5 parts were added and the pi was adjusted to 4.6 with a 20% NaOH aqueous solution, which was used as an aqueous medium for capsule production.

To this was added 105 parts of diisopropylnaphthalene (trade name: Ni-1) 3, manufactured by Kureha Chemical Co., Ltd., in which 5 parts of crystal violet lactone had been dissolved, and after emulsifying and dispersing it so that the average particle size was 5 μ-, the emulsion was The temperature was raised to 70°C.

Next, 20 parts of methylated methylolmelamine precondensate (trade name: Beckamine APM, 80% concentration, manufactured by Dainippon Ink Chemical Co., Ltd.) was added to the system, and the temperature of the system was maintained at 70°C for 1 hour while stirring was continued. After cooling, a milky white capsule dispersion was obtained.

Example 2 Vinyl sulfonic acid 15 mol%, vinyltoluene 5 mol%
, a 20% aqueous solution of a copolymer consisting of 75 mol% acrylic acid and 5 mol% butyl acrylate (25°C, pH 1.8,
Viscosity at a concentration of 20 parts: 130 cps) 2.5 parts of water was added to 37.5 parts of water, and the pH was adjusted to 4.6 with a 20% NaOH aqueous solution to prepare an aqueous medium for capsule production.

To this was added 105 parts of diisopropylnaphthalene (trade name: Ni-1) 3, 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 a melamine/urea/formaldehyde-based initial condensate (trade name: Beckamine MA-3, 70 parts concentration, manufactured by Dainippon Ink Chemical Co., Ltd.) was added to the system, and the temperature of the system was raised to 80°C while stirring was continued. After being held for 2 hours, the mixture was cooled to obtain a milky white capsule dispersion.

Example 3 A copolymer consisting of 25 mol% vinyl sulfonic acid, 5 mol% styrene, and 70 mol% acrylic acid (25°C, pH 2,
A capsule dispersion liquid was obtained in the same manner as in Example 1, except that a solution having a viscosity of 300 cps at a concentration of 1.20 parts was used.

Example 4 Same as Example 1 except that a copolymer consisting of 98 mol% vinyl sulfonic acid and 2 mol% styrene (25°C, I) H2, 6, viscosity at 20% concentration 1) 0 cps) was used. A capsule dispersion was obtained.

Example 5 A copolymer (25°C, pH
A capsule dispersion liquid was obtained in the same manner as in Example 1, except that a viscosity of 90 cps at a concentration of 1,20% was used.

Comparative Example 1 Copolymer consisting of 94 mol% acrylic acid, 3 mol% butyl acrylate, and 3 mol% 1so-propyl methacrylate (viscosity at 25°C, pH 1, 8, 20% concentration: 200 cp)
A capsule dispersion liquid was obtained in the same manner as in Example 1 except that s) was used.

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

The capsule dispersion thus obtained was diluted to a concentration of 35%, applied to the CF field using a wire bar No. 18 (product name: KS Copy Bright, manufactured by Kanzaki Paper Co., Ltd.), and dried. did. The following performance comparison tests were conducted using this paper and each capsule dispersion, and the results are listed in Table 1.

[Core material retention]

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

[Unencapsulated core material]

When applying the capsule dispersion liquid to the CF surface of the lower paper and drying it, if there is a hydrophobic core substance that is not encapsulated, it will appear as a spot-like stain.
The number of spot-like stains present on the area was measured.

[Giant capsules, aggregates]

The capsule dispersion was processed through a 200 mesh screen and the weight of the residue was expressed as a percentage (%) of the total weight of the capsules.

[Capsule dispersion viscosity]

The sample was heated to 25° C. and measured using a B-type viscometer at 60 rpm.

Table 1 "Effects" The specific anionic polymer copolymer used in the method of the present invention has a good balance between hydrophobicity and hydrophilicity, and has good emulsifying ability, emulsion stability, and capsule wall forming ability. As is clear from the results in Table 1, the generation of unencapsulated core material, giant capsules, and aggregates was extremely small, and capsules with excellent core material retention were efficiently formed. Furthermore, the copolymer used in the present invention has excellent emulsifying ability, emulsion stability, and capsule wall forming ability even at a relatively low viscosity, and the capsule dispersion obtained also has a low viscosity, so it can be used for high-speed coating in the production of pressure-sensitive copying paper. Excellent aptitude.

Patent applicant: Kanzaki Paper Co., Ltd.

Claims (5)

[Claims] (1) In the presence of an anionic polymer copolymer containing vinyl sulfonic acid and an aromatic vinyl compound as constituent monomers, the initial condensate of aminoaldehyde resin is polycondensed to cover the surface of the hydrophobic core material. Characteristic method for producing microcapsules. (2) The manufacturing method according to claim (1), wherein the aminoaldehyde resin initial condensate is a melamine formaldehyde resin initial condensate. (3) The manufacturing method according to claim (1), wherein the aminoaldehyde resin initial condensate is a melamine/urea/formaldehyde resin initial condensate. (4) The manufacturing method according to claim (1), wherein the aromatic vinyl compound is at least one type selected from styrene and vinyltoluene. (5) The production method according to claim (1), wherein the anionic polymer copolymer further contains at least one of acrylic acid and alkyl (meth)acrylate as a constituent monomer.