JPH01130727A - Production of microcapsule - Google Patents

Abstract

PURPOSE:To efficiently form capsule having an excellent property of preserving a core substance, by polycondensing aminoaldehyde resin precondensate in the presence of copolymer consisting of specified monomers to coat the surface of a hydrophobic core substance. CONSTITUTION:The aminoaldehyde resin precondensate is polycondensed in the presence of the copolymer consisting of acrylic acid, intaconic acid and hydrophobic monomer to coat the surface of the hydrophobic core substance and produce microcapsule. As the aminoaldehyde resin precondensate, melamine.formaldehyde resin precondensate and melamine.urea.formaldehyde resin condensate are suitable. The contents of the monomers composing the copolymer above-mentioned are suitably 60-95wt.% acrylic acid, 2-20wt.% itaconic acid and 2-25wt.% hydrophobic monomer.

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 coacervation, interfacial polymerization, and 1n-situ polymerization, but among them, capsules having a wall film made of aminoaldehyde polycondensation resin are water resistant and resistant. Because of its excellent solvent properties, for example, the encapsulation method in which a urea/formaldehyde polycondensation resin wall film is formed in the presence of carboxymethylcellulose [US Pat. No. 3,016,308] is used in a suspension containing substantially no dispersant. Various methods have been proposed, including an encapsulation method [Japanese Patent Publication No. 47-28165] in which a urea/formaldehyde polycondensation resin wall film 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 interactions have been proposed (Japanese Patent Publication No. 3B-12380, Japanese Patent Publication No. 48-4717, Japanese Patent Publication No. 49-18456), etc. However, in these improved 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-60-238140, JP-A-61-1) 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 provides (al acrylic acid, (bl itaconic acid, (C1
This method of producing microcapsules is characterized by polycondensing an aminoaldehyde resin initial condensate in the presence of a copolymer composed of a hydrophobic monomer to cover the surface of a hydrophobic core material.

"Function" In the copolymer composed of the above-mentioned specific monomer used in the present invention, (c) hydrophobic monomer means an unsaturated compound containing a hydrophobic group, specifically, for example, ethylene, methyl Examples include vinyl ether, propylene, isobutylene, butadiene, styrene, vinyltoluene, α-methylstyrene, isopropenyltoluene, vinyl acetate, acrylonitrile, methacrylonitrile, acrylic ester, methacrylic ester, itaconic ester, and the like.

Among these, vinyl acetate, alkyl esters of acrylic acid, and alkyl esters of methacrylic acid are particularly preferably used. In addition, examples of alkyl esters of acrylic acid include methyl acrylate, ethyl acrylate,
Propyl acrylate, butyl acrylate, amyl acrylate, hexyl acrylate, cyclohexyl acrylate, 2-ethylhexyl acrylate, etc., and examples of alkyl esters of methacrylate include methyl methacrylate, ethyl methacrylate, propyl methacrylate. ,
Examples include butyl methacrylate, amyl methacrylate, hexyl methacrylate, cyclohexyl methacrylate, etc. Among them, esters having 3 to 4 carbon atoms in the alcohol residue are particularly preferably used.

The specific copolymer used in the present invention is synthesized by copolymerizing (a) acrylic acid and (b) itaconic acid with one or more of the above-mentioned C1 hydrophobic monomers. It is desirable to adjust the content of each monomer constituting the combination within the following range.

(a) Content of acrylic acid: 60-95% by weight, preferably 70-90% by weight (50% by weight)
If the amount is less than % by weight, sufficient water solubility will not be obtained and the ability to form a capsule wall will be weakened. Moreover, if it exceeds 97% by weight, the emulsion stability of the copolymer decreases. ] (b) Content of itaconic acid: 2 to 20% by weight, preferably 3 to 10% by weight [1% by weight
If it is less than 30% by weight, the desired effect will not be obtained, and if it is more than 30% by weight, the water solubility will be insufficient. ] (C) Content of hydrophobic monomer: 2 to 25% by weight, preferably 4 to 15% by weight [1% by weight
If it is less than 30% by weight, emulsifying ability and emulsion stability will be insufficient, and if it is more than 30% by weight, water solubility will be insufficient. ] The specific copolymer thus obtained is used as an aqueous solution by neutralizing the carboxyl groups with an alkali such as sodium hydroxide or potassium hydroxide, but the pH of the aqueous solution is adjusted in the range of 3 to 6. It is desirable that the viscosity of the 20% aqueous solution is 30 to 5000c.
ps (25℃.

p1)2.0), preferably 100-2500cps
It is desirable to adjust it so that

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. ~6.0
It is desirable to adjust within a range of about %. The upper limit of the amount to be blended is determined by the viscosity of the system, capsule preparation equipment, 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 because of the fine 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 their use
must be kept within a range that does not inhibit the desired effects of the present invention.

Further, in order to enhance the emulsion stability of the core material and prevent the formation of giant capsules, a 6'Ht polyvalent isocyanate may be added to the hydrophobic liquid.

Examples of polyvalent isocyanates include naphthalene diisocyanate, triphenylmethane triisocyanate,
Examples include polymethylene polyphenylisocyanate, lysine diisocyanate, modified isocyanate such as an adduct obtained by reacting a monomer isocyanate with a polyhydric alcohol, and a urethane prepolymer. These may be used alone or in combination, but it is more preferable to use a combination of aromatic and aliphatic isocyanates. The amount of the isocyanate compound added to the hydrophobic liquid is desirably kept at 10 parts by weight or less based on 100 parts by weight of the wall film-forming substance in the capsule production system.

Examples of hydrophobic liquids include cottonseed oil, hydrogenated terphenyl, hydrogenated terphenyl derivatives, alkylnaphthalenes,
Examples include dibasic acid esters such as alkylnaphthalenes, diarylalkanes, kerosene, paraffins, naphthenic oils, and phthalic acid esters, and two or more of these 4 may be used in combination.

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

Furthermore, a capsule dispersion is prepared in which the formation of large capsules and aggregates is small, and the presence of unencapsulated core material is extremely small.

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, "part" and "1%" in the examples indicate "part by weight" and "wt%", respectively, unless otherwise specified.

Example 1 Copolymer consisting of 80% acrylic acid, 10% itaconic acid, and 10% butyl acrylate (viscosity 450 cps at 25°C, pH 1, 7, 2% concentration) 37.5 parts water 1) 2
．． 5 parts were added thereto and the pH was adjusted to 4.8 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 μm, the temperature of the liquid The temperature was raised to 70°C.

Next, 20 parts of methylated methylolmelamine initial condensate (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 Copolymer consisting of 85% acrylic acid, 5% itaconic acid, 5% butyl acrylate, 5% 1so-propyl methacrylate (viscosity 1 at 25°C, pl+ 1.8.20 parts concentration)
A capsule dispersion was obtained in the same manner as in Example 1 except that 200 cps) was used.

Example 3 Copolymer (25%) consisting of 90% acrylic acid, 5% itaconic acid, 2.5% butyl acrylate, and 2.5% vinyl acetate.
℃, pH 1, 7, viscosity at 20 parts concentration 215 cps)
To 37.5 parts, 162.5 parts of water was added, and the pH was adjusted to 4.6 with a 20% NaOH aqueous solution, which was used as an aqueous medium for capsule production.

105 parts of diisopropylnaphthalene (trade name: Ni-1), manufactured by Kureha Chemical Co., Ltd., with 5 parts of crystal violet lactone dissolved therein, and 0.0 parts of polymethylene polyphenylisocyanate (trade name: Millionate MR400, manufactured by Nippon Polyurethane Industries, Ltd.). A hydrophobic core material prepared by adding 5 parts was added and emulsified and dispersed so that the average particle size was 5 μm.

Next, 25 parts of a melamine/urea/formaldehyde-based initial condensate (trade name: Vesokamine MA-3, 70% 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.

Comparative Example 1 Copolymer consisting of 70% acrylic acid and 30% itaconic acid (viscosity 100 cp at 25°C, pH 2.2, 20 parts concentration)
A capsule dispersion liquid was obtained in the same manner as in Example 1 except that s) was used.

Comparative Example 2 Copolymer consisting of 92.5% acrylic acid, 5% butyl acrylate, and 2.5% butyl methacrylate (25°C).

A capsule dispersion liquid was obtained in the same manner as in Example 1, except that a viscosity of 350 cps at pH 1, 7, and 20% concentration was used.

Comparative Example 3 Copolymer consisting of 90% acrylic acid and 10% butyl acrylate (viscosity 1 at 25°C, pH 1, 8, 20% concentration)
) A capsule dispersion was obtained in the same manner as in Example 1 except that 00 cps) was used.

Comparative Example 4 Copolymer consisting of 90% acrylic acid, 5% tert-butylacrylamide sulfonic acid, and 5% butyl acrylate (viscosity 190 at 25°C, pH 1, 8, 20% concentration)
A capsule dispersion liquid was obtained in the same manner as in Example 1 except that 0 cps) was used.

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 Industries), and dried. . 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 material that is not encapsulated, it will appear as a spot-like stain, so the size of 15 cm x 25 cm
The number of spot-like dirt existing on the m area was measured.

[Giant capsules, aggregates]

The capsule dispersion was processed through a 200 mesh screen and evaluated based on the amount of residue. The evaluation criteria are as follows.

○: Hardly any.

△: A little bit.

×: There are many.

Table 1 "Effects" The specific copolymer used in the method of the present invention has a good balance between hydrophobicity and hydrophilicity, and has excellent emulsifying ability and capsule wall forming ability. As is clear from the results, the occurrence of unencapsulated core material, giant capsules, and agglomerated capsules was extremely low, and capsules with excellent core material retention were efficiently formed.

Patent applicant: Kanzaki Paper Co., Ltd.

Claims (5)

[Claims] (1) In the presence of a copolymer consisting of (a) acrylic acid, (b) itaconic acid, and (c) a hydrophobic monomer, an aminoaldehyde resin initial condensate is polycondensed to cover the surface of the hydrophobic core material. A method for producing microcapsules, characterized by: (2) The aminoaldehyde resin initial condensate is a melamine formaldehyde resin initial condensate (
The manufacturing method described in section 1). (3) The production method according to claim (1), wherein the aminoaldehyde resin initial condensate is a melamine/urea/formaldehyde resin initial condensate. (4) Claims (1) to (3) in which the hydrophobic monomer is an acrylic ester and/or a methacrylic ester
The manufacturing method described in ). (5) The production method according to claims (1) to (3), wherein the hydrophobic monomer is an acrylic ester and vinyl acetate.