JPS61174941A - Preparation of microcapsule - Google Patents

Abstract

PURPOSE:To improve holding capacity for a core substance of an acidic system held at >=65 deg.C comprising aq. mixture, etc. contg. a modifier and a hydrophobic core substance by adding further hydrophilic melamine/foraldehyde resin or initial condensation stage. CONSTITUTION:A hydrophobic core substance is added to an aq. or hydrophilic medium contg. a modifier such as anionic, nonionic, cationic, or amphoteric polymer or an emulsifier of low degree of polymn. The system is acidified at >=65 deg.C. Initial stage hydrophilic condensate of melamine/formaldehyde is added to the system, which is coated on the hydrophobic core substance by causing polycondensation to prepare microcapsules. The amt. of the hydrophilic initial stage condensation product of melamine/formaldehyde to be added to generally 2-40pts.wt. expressed in terms of the weight of melamine basing on 100pts.wt. hydrophobic core substance. Suitable hydrophobic core substance is animal oil, vegetable oil, mineral oil, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to a method for producing extremely high performance microcapsules containing a hydrophobic core material.

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

Various methods are known for producing microcapsules, such as coacervation, interfacial polymerization, and 1n-situ polymerization, but among them, microcapsules with melamine-formaldehyde resin as a wall film are water resistant,
Because of its excellent solvent resistance, various encapsulation methods have been proposed, such as a method in which a melamine-formaldehyde resin initial condensate present in water or a hydrophilic medium is deposited around a hydrophobic core material. , Japanese Patent Publication No. 5
3-84881, JP-A-54-49984, JP-A-55-15660, JP-A-55-47139, JP-A-55-51431, JP-A-55-67329, JP-A-55- No. 92135, JP-A No. 56-51238,
JP-A-56-58536, JP-A-56-100629
No., JP-A-56-102934, JP-A-56-121
No. 628, Japanese Unexamined Patent Publication No. 5'1103891, etc. have been proposed.

However, these encapsulation methods generally require a relatively large amount of water-soluble polymer as a system modifier; This tends to inhibit the transfer of capsule inclusions during pressurization recording, resulting in poor color development.

(2) When obtaining powder capsules by filtration and drying, this water-soluble polymer acts as an adhesive and aggregates the resulting capsules into polynuclear capsules, making it difficult to obtain mononuclear capsules.

There is still room for improvement due to the following drawbacks.

"Problems to be Solved by the Invention" In view of the current situation, the present inventors have conducted extensive research on a method for producing microcapsules having a wall film of melamine-formaldehyde resin, and have found that by selecting specific capsule preparation conditions, the above-mentioned It has been discovered that the drawbacks can be avoided and microcapsules having high performance can be easily obtained, and the present invention has been achieved.

"Means for Solving the Problem" The present invention involves polycondensing a hydrophilic melamine-formaldehyde resin initial condensate contained in water or a hydrophilic medium containing a system modifier to coat a hydrophobic core material. The method for producing microcapsules is characterized in that the temperature of the system at the time of addition of the initial condensate is 65° C. or higher, and the system is under acidic conditions.

"Function" The hydrophilic melamine-formaldehyde resin initial condensate used in the present invention includes, in addition to the melamine-formaldehyde resin initial condensate, its methylated products, as well as other amines, phenols, aldehydes, etc. Examples include those partially modified with anionic, cationic, or nonionic modifiers.

Examples of amines include urea, thiourea, alkylurea, ethyleneurea, acetoguanamine, benzoguanamine, melamine, guanidine, dicyandiamide, biuret, cyanamide, etc.; examples of phenols include phenol, cresol, xylenol, resorcinol, hydroquinone, pyroquinone, etc. Catechol, pyrogallol, etc.;
Examples of aldehydes include formaldehyde, acetaldehyde, paraformaldehyde, hexamethylenetetramine, geltaraldehyde, glyoxal,
Furfural, etc.; Examples of anion modifiers include sulfamic acid, sulfanilic acid, glycolic acid, glycine, acidic sulfite, phenol sulfonate, taurine, etc.
Examples of cationic modifiers include diethylenetriamine, triethylenetetramine, tetraethylenepentamine, dimethylaminoethanol, and the like; examples of nonionic modifiers include ethylene glycol, diethylene glycol, and the like.

As the hydrophilic melamine-formaldehyde resin initial condensate, various products such as those mentioned above can be used, but among them, the melamine-formaldehyde resin initial condensate and its methylated product are most preferably used because a dense film can be obtained. .

The blending amount of the hydrophilic melamine-formaldehyde resin initial condensate is adjusted appropriately depending on the type of hydrophobic core material used, the use of the capsule, etc., but in general, the amount of the hydrophobic core material 1
00 parts by weight, 2 to 40 parts by weight in terms of melamine,
More preferably, it is blended in an amount of about 4 to 30 parts by weight.

In the present invention, the hydrophilic melamine-formaldehyde resin initial condensate can be added to the system at any stage before, during, or after emulsifying the hydrophobic core substance in water or a hydrophilic medium. However, when adding the initial condensate after emulsifying the hydrophobic core material, it is desirable to further emulsify the hydrophobic core material after adding the initial condensate.

As mentioned above, the method of the present invention has extremely important features in that the temperature of the system is maintained at 65°C or higher when adding the initial condensate, and the initial condensate is added under acidic conditions. However, if the temperature of the system is lower than 65° C., the core substance retention of the resulting microcapsules is reduced, making it impossible to obtain the desired effects of the present invention. Therefore, it is necessary to maintain the temperature of the system at the time of addition of the initial condensate at 65°C or higher, more preferably 70°C or higher, and most preferably 80°C or higher.

Note that after the initial condensate is added and a thin capsule film is formed at the initial stage of polycondensation, it is not necessary to maintain the system temperature above 65°C, and the reaction should proceed at a temperature below 65°C. is also possible. However, in order to obtain good capsules, after the initial coating is formed, it is desirable to maintain the temperature at 40°C or higher for 1 hour or more, more preferably at 60°C or higher for 1 hour or more, and most preferably at 60°C or higher for 3 hours or more.

When manufacturing microcapsules for pressure-sensitive copying paper, P
It is desirable to maintain the capsule under conditions of H5.0 or lower and 60°C or higher for 2 hours or more, and capsules with extremely high quality can be obtained if the pH is maintained at 4.0 or lower and 80°C or higher for 2 hours or longer.

Examples of the system modifier used in the present invention include anionic, nonionic, cationic, and amphoteric polymers and low-molecular emulsifiers.

The anionic polymer may be natural or synthetic, such as -coo-1-SO3, -0P023
Specific examples include natural polymers such as gum arabic, carrageenan, sodium alginate, pectic acid, gum tragacanth, almond gum, and agar;
Carboxymethylcellulose, sulfated cellulose, sulfated methylcellulose, carboxymethylated starch, phosphorylated starch, semi-synthetic polymers such as lignin sulfonic acid, maleic anhydride-based (including hydrolyzed) copolymers, acrylic acid-based, Methacrylic acid-based or crotonic acid-based polymers and copolymers, vinylbenzenesulfonic acid-based or 2-
Acrylamide-2-methyl-propanesulfonic acid polymers and copolymers, partial amides or partial esters of such polymers and copolymers, carboxy-modified polyvinyl alcohol, sulfone-acid-modified polyvinyl alcohol, phosphoric acid-modified polyvinyl Examples include synthetic polymers such as alcohol.

More specifically, maleic anhydride-based (including hydrolyzed) copolymers include methyl vinyl ether-maleic anhydride copolymer, ethylene-maleic anhydride copolymer, and vinyl acetate-maleic anhydride copolymer. Examples include a polymer, an isobutylene-maleic anhydride copolymer, a styrene-maleic anhydride copolymer, and the like.

Examples of the acrylic acid copolymer, methacrylic acid copolymer, or crotonic acid copolymer include methyl acrylate-acrylic acid copolymer (hereinafter, 'copolymer 2' is abbreviated), ethyl acrylate-acrylic Acid, methyl acrylate-methacrylic acid, methyl methacrylate-acrylic acid, methyl methacrylate-methacrylic acid, methyl acrylate-acrylamide-acrylic acid, acrylonitrile-acrylic acid, acrylonitrile-methacrylic acid, hydroxyethyl acrylate-acrylic acid, hydroxy Ethyl methacrylate-methacrylic acid, vinyl acetate-acrylic acid, vinyl acetate-methacrylic acid, acrylamide-acrylic acid,
Examples include copolymers of acrylamide-methacrylic acid, methacrylamide-acrylic acid, methacrylamide-methacrylic acid, vinyl acetate-crotonic acid, and the like.

Examples of vinylbenzenesulfonic acid copolymers or 2-acrylamido-2-methyl-propanesulfonic acid copolymers include methyl acrylate-vinylbenzenesulfonic acid (or salts thereof) copolymers, and vinyl acetate-vinylbenzenesulfonic acid copolymers. Polymer, acrylamide-vinylbenzenesulfone H copolymer ff1, acryloylmorpholine-vinylbenzenesulfonic acid copolymer, vinylpyrrolidone-vinylbenzenesulfonic acid copolymer, vinylpyrrolidone-2
-acrylamide-2-methyl-propanesulfonic acid copolymer and the like.

The nonionic polymer may be either natural or synthetic, and includes, for example, those having -0H groups.

Specific examples include hydroxyethylcellulose, methylcellulose, amorphous, easily water-soluble polymeric polysaccharides produced by microbial fermentation using pullulan powder as raw materials, soluble starch, and oxidized starch. Synthetic products include polyvinyl alcohol.

Examples of the cationic polymer include cation-modified polyvinyl alcohol, and examples of the amphoteric polymer include gelatin.

Examples of low-molecular emulsifiers include anionic, cationic, nonionic, and amphoteric ones, but anionic ones are preferable, and among them, organic sulfuric acid or organic phosphoric acid having a total carbon number of 1 to 14 is used. N a” + K”
tNL deca salt is preferred. Specifically, sodium vinylsulfonate, sodium benzenesulfonate, sodium benzenesulfinate, sodium p-)toluenesulfonate, sodium p-toluenesulfinate, sodium p-vinylbenzenesulfonate, p-1-amylbenzenesulfonic acid. Sodium, sodium naphthalene-α-sulfonate, sodium naphthalene-β-sulfonate, 2
-Sodium methylnaphthalene-6-sulfonate, sodium 2゜6-dimethylnaphthalene-8-sulfonate,
2. Sodium 6-dimethylnaphthalene-3-sulfonate, sodium 1-naphthol-4-sulfonate, sodium benzene-m,-disulfonate, funnel oil, sodium diphenylphosphate, sodium phenylphosphonate, di-n-butylphosphorus Examples include sodium acid, diamyl sodium phosphate, and the like.

In the present invention, the above-mentioned high-molecular or low-molecular emulsifiers are used alone or in combination, and preferably a high-molecular emulsifier is used. Among these, polymers or copolymers consisting of anionic monomer units, copolymers of anionic monomer units and hydrophobic monomer units are preferred, and in particular polymers of acrylic acid and acrylic esters such as acrylic acid-methyl acrylate copolymers are preferred. Copolymers of maleic anhydride and hydrophobic monomer units, such as copolymers and styrene-maleic anhydride copolymers, are more preferably used because emulsified particles can be easily stabilized.

In addition, the emulsifier as mentioned above is added to water or a hydrophilic medium at a concentration of 0.1% from the viewpoint of ease of preparation of the emulsion and stabilization of the emulsion.
or more, more preferably 0.3% or more, most preferably 0
．． It is desirable to contain about 5 to 5%. The upper limit of the amount used is determined by the viscosity of the system, the capsule preparation device, etc., but is generally kept at 20% or less.

In order to maintain the reaction system acidic in the present invention, so-called acid catalysts commonly used in the field of aminoaldehyde resin production, such as formic acid, acetic acid, citric acid, oxalic acid, valatoluenesulfonic acid, hydrochloric acid, and sulfuric acid, are used. It will be done.

The hydrophobic core substance encapsulated in the microcapsules is not particularly limited, but includes, for example, animal oils such as fish oil and lard oil, vegetable oils such as olive oil, peanut oil, linseed oil, soybean oil, and castor oil. , petroleum, mineral oils such as kerosene, xylene, toluene, etc., alkyl-substituted diphenylalkanes, alkyl-substituted naphthalenes, biphenyl ethane, methyl salicylate, diethyl adipate, di-n-propyl adipate, di-n adipate.
- Liquids that are insoluble or substantially insoluble in water, such as synthetic oils such as butyl, dimethyl phthalate, diethyl phthalate, di-n-propyl phthalate, di-n-butyl phthalate, di-n-octyl phthalate, etc. , and furthermore, solutions in which electron-donating color formers, electron-accepting color developers, ligand compounds, organic metal salts, etc. are dissolved in the synthetic oil, water-insoluble metal oxides and salts, cellulose, asbestos, etc. Fiber-like substances, water-insoluble synthetic polymeric substances, minerals, pigments, glasses, perfumes, flavors, fungicidal compositions, physiological compositions, fertilizer compositions, flame retardants, temperature-indicating materials , liquid crystal, etc.

Microcapsules prepared by the method of the present invention can be prepared by filtration,
Washing, drying, spray drying, or patent application No. 59-94825
It is also possible to form powdered capsules by adding an aldehyde-based resin-forming material after capsule preparation, polycondensing the resin-forming material, and then removing the dispersion medium, as described in No.

"Examples" Examples will be described below to more specifically explain the method of the present invention, but of course the present invention is not limited thereto. Further, unless otherwise specified, parts and % in the examples represent parts by weight and % by weight, respectively.

Example 1 An internal phase liquid was obtained by dissolving 4 parts of crystal bioleft lactone in 100 parts of alkylnaphthalene.

Separately, in a stirred mixing vessel equipped with a heating device, add acrylic acid.
An aqueous solution prepared by heating and dissolving 3 parts of methyl acrylate copolymer (molar ratio of acrylic acid and methyl acrylate 9:1) in 200 parts of water was added, and a 20% aqueous solution of caustic soda was added to the PH. was adjusted to 5.0 to prepare an aqueous medium for capsule production.

This aqueous medium was heated to 70° C., and the internal phase liquid was emulsified therein so that the average particle size was 15 μm.

A 60°C melamine-formaldehyde resin initial condensate prepared by heating a mixture of 30 parts of a 37% formaldehyde aqueous solution and 10 parts of melamine was added to the above emulsion kept at 70°C with strong stirring, and then Emulsification of the internal phase liquid was continued until the average particle size was 6°0μ. The liquid temperature after emulsification was 67°C.

Subsequently, the reaction was carried out at 65°C for 2 hours and then at 90°C for 2 hours.
After adjusting the pH to 3.8 by dropping 0.05 N-hydrochloric acid, the mixture was reacted at 95° C. for 5 hours to obtain a capsule dispersion.

50 parts of starch particles were added to this capsule dispersion and diluted to a concentration of 20% to obtain a capsule coating liquid.The resulting coating liquid was coated on a 40g/m base paper with an air knife coater to coat it with a solid content of 4g. /rd was smeared to create the upper paper.

[Creating the bottom sheet]

65 parts of aluminum hydroxide, 20 parts of zinc oxide, 3.5-
Mixture of zinc di(α-methylbenzyl)salicylate and α-methylstyrene/styrene copolymer (melt ratio 80/
20) Add 20 parts (solid content) of carboxy-modified styrene-butadiene copolymer latex to a dispersion obtained by grinding 15 parts of polyvinyl alcohol aqueous solution (solid content) and 300 parts of water in a ball mill for 24 hours. In addition, the prepared color developer coating liquid was smeared on 40 g/r+ paper using an air knife coater so that the solid content was 5 g/rd to prepare a base paper.

When the upper paper was superimposed on the lower paper and printed using a typewriter, an extremely clear colored image was obtained. Further, the upper paper and the lower paper were stacked and heat-treated at 100''c for 3 hours, but no stains were observed on the surface of the lower paper, indicating that the core substance retention of the capsules was good.

Example 2 Example except that instead of the acrylic acid-methyl acrylate copolymer in which the molar ratio of acrylic acid to methyl acrylate was 9:1, a copolymer in which the molar ratio of acrylic acid to methyl acrylate was 8:2 was used. 1
A capsule dispersion liquid was prepared in the same manner as above, and a top paper was prepared in the same manner.

As a result of evaluation in the same manner as in Example 1, it was found that both color development and core substance retention were good.

Example 3 An internal phase liquid was obtained by dissolving 4 parts of crystal violet lactone in 17,100 parts of alkyl naphtha.

Separately, in a stirring mixing vessel equipped with a heating device, a styrene-maleic anhydride copolymer (trade name Suflibcent 520.
Add an aqueous solution prepared by heating and dissolving 3 parts (manufactured by Monsando) in 140 parts of water, and add IN-acetic acid to this to prepare P.
H was adjusted to 5.0 to prepare an aqueous medium for capsule production.

This aqueous medium was heated to 75°C, and a 60°C melamine-formaldehyde resin precondensate prepared by heating a mixture of 30 parts of a 37% formaldehyde aqueous solution and 10 parts of melamine therein was mixed with the above mixture heated to 75°C. The phase liquid was simultaneously added and emulsified with strong stirring to obtain an emulsion having an average particle size of 6.0 μm.

The liquid temperature after emulsification was 72°C.

Subsequently, the reaction was carried out at 65°C for 2 hours and then at 90°C for 2 hours, and 0.05N-hydrochloric acid was added dropwise to adjust the pH to 3.8. A capsule dispersion was obtained by reacting at C for 5 hours.

Thereafter, a coating liquid was prepared in the same manner as in Example 1, and a top paper was created. As a result of evaluation in the same manner as in Example 1, it was found that both color development and core substance retention were good.

Example 4 An internal phase liquid and an aqueous medium for capsule production were prepared in the same manner as in Example 1.

This aqueous medium was heated to 85°C, and a 60°C melamine-formaldehyde resin precondensate prepared by heating a mixture of 30 parts of a 37% formaldehyde aqueous solution and 10 parts of melamine therein was mixed with the above mixture heated to 85°C. The phase liquid was simultaneously added and emulsified with strong stirring to obtain an emulsion having an average particle size of 5.8 μm.

The liquid temperature after emulsification was 82°C.

Subsequently, the mixture was reacted at 80°C for 2 hours and then at 95°C for 2 hours, and 0.05 N-hydrochloric acid was added dropwise to adjust the pH to 3.6, followed by reaction at 95°C for 5 hours to obtain a capsule dispersion. .

Thereafter, a coating liquid was prepared in the same manner as in Example 1, and a top paper was created. As a result of evaluation in the same manner as in Example 1, it was found that both color development and core substance retention were extremely good.

Comparative Example 1 An internal phase liquid and an aqueous medium for capsule production were prepared in the same manner as in Example 1.

This aqueous medium was heated to 50° C., and the internal phase liquid was emulsified therein so that the average particle size was 15 μm.

A 50°C melamine-formaldehyde resin initial condensate prepared by heating a mixture of 30 parts of a 37% formaldehyde aqueous solution and 10 parts of melamine was added to the above emulsion kept at 50°C with strong stirring, and then Emulsification of the internal phase liquid was continued until the average particle size was 6°0μ. The liquid temperature after emulsification was 50°C.

Subsequently, the reaction was carried out at 65°C for 2 hours and then at 90"C for 2 hours, and 0.05N-hydrochloric acid was added dropwise to adjust the pH to 8.
A capsule dispersion was obtained by reacting at 95° C. for 5 hours.

Thereafter, a coating liquid was prepared in the same manner as in Example 1, and a top paper was created. As a result of evaluation in the same manner as in Example 1, the color development was good, but when heat treated at 100'C for 3 hours, stains appeared on the lower paper surface and the capsule core material retention was poor. I understand.

Comparative Example 2 An internal phase liquid and an aqueous medium for capsule production were produced in the same manner as in Example 1.

This aqueous medium was heated to 50°C, and a 50″C melamine-formaldehyde resin precondensate prepared by heating a mixture of 30 parts of a 37% formaldehyde aqueous solution and 10 parts of melamine therein was added to the aqueous medium heated to 50°C. The internal phase liquid was simultaneously added and emulsified with strong stirring until the average particle size was 6.0μ.
An emulsion was obtained.

The liquid temperature after emulsification was 50°C.

Subsequently, the mixture was reacted at 65°C for 2 hours and then at 90°C for 2 hours, and 0.05 N-hydrochloric acid was added dropwise to adjust the pH to 3.8, followed by reaction at 95°C for 5 hours to obtain a capsule dispersion. .

Thereafter, a coating liquid was prepared in the same manner as in Example 1, and a top paper was created. As a result of evaluation in the same manner as in Example 1, the color development was still good, but when heat treated at 100°C for 3 hours, stains appeared on the lower paper surface and the capsule core material retention was poor. I understand the song.

"Effect" As is clear from the results of each example, the microcapsules obtained by the method of the present invention have excellent core substance retention properties compared to the conventional method, and can be used for pressure-sensitive copying paper. However, even in the case of

Claims (5)

[Claims] (1) A method for producing microcapsules in which a hydrophilic melamine-formaldehyde resin initial condensate contained in water or a hydrophilic medium containing a system modifier is polycondensed to coat a hydrophobic core material. A method for producing microcapsules, characterized in that the temperature of the system at the time of addition of the condensate is 65° C. or higher, and the system is under acidic conditions. (2) After emulsifying the hydrophobic core substance in water or a hydrophilic medium containing a system modifier, the initial condensate is added and the hydrophobic core substance is further emulsified. Production method. (3) The production method according to claim (1), wherein the initial condensate is added to water or a hydrophilic medium containing a system modifier, and then the hydrophobic core substance is emulsified. (4) Claims (1) to (3) in which the system modifier is at least one of a polymer or copolymer composed of anionic monomer units, and a copolymer of anionic monomer units and hydrophobic monomer units. Manufacturing method described in section. (5) The method according to claim (4), wherein the modifier is an acrylic acid-methyl acrylate copolymer or a styrene-maleic anhydride copolymer.