JPH0453584B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing microcapsules. More specifically, the present invention relates to an improved method for producing microcapsules having a melamine-formaldehyde resin film obtained by an in-situ polymerization method. Microcapsules are used in recording materials such as pressure-sensitive recording paper, pharmaceuticals, fragrances, pesticides, adhesives, dyes, solvents,
It has been studied in a wide variety of fields such as rust preventives, liquid crystals, and health foods, and various products have reached the practical or practical testing stage. In particular, many techniques have already been proposed for microencapsulation of hydrophobic substances (oils and solids), and among them, the coacervation method (phase separation method) using gelatin is mainly used to Produced on a commercial scale for pressure copy paper. However, regarding complex coacervation microcapsules using gelatin and anionic polymer electrolyte, (1) it is difficult in principle to obtain a microcapsule liquid with a high solid content concentration of 20% or more; (2) When used in pressure-sensitive copying paper, a large amount of water must be evaporated, so there is considerable room for improvement in terms of work speed and energy costs, and transportation costs are high. Since it is a commercially available product, it has problems such as large fluctuations in quality and price, and (3) it cannot withstand long-term storage because it has a tendency to rot and agglomerate. Improvements in these problems have been strongly desired from the viewpoint of quality of pressure-sensitive copying paper. In-
A high-concentration microencapsulation method using urea-formaldehyde resin or melamine-formaldehyde resin as a film material by the in-situ polymerization method was proposed (Japanese Patent Application Laid-Open No. 1989-51).
(No. 9079, also No. 53-84881) Various improved techniques have been proposed since then. For example, a method using melamine-formaldehyde resin as the membrane material,
As anionic polymer electrolyte, ethylene maleic anhydride copolymer, methyl vinyl ether maleic anhydride copolymer, polyacrylic acid propylene maleic anhydride copolymer, butadiene maleic anhydride copolymer, vinyl acetate maleic anhydride copolymer Coalescence has been proposed (Japanese Patent Application Laid-Open No. 53-84881), but such polymers require high temperatures and a long time to dissolve, and the resulting microcapsule slurry has a high viscosity. It has the disadvantage that it is difficult to obtain a minute capsule slurry. In addition, a method of microencapsulation using a system using a styrene-maleic acid copolymer or a copolymer of a styrene-maleic acid copolymer and another maleic acid copolymer has been proposed (Japanese Patent Application Laid-Open No. 1989-1999-
No. 49984, also No. 55-47139). However, styrene-maleic acid copolymer has poor solubility in water, so it requires a long period of time at high temperature while adding an alkali to dissolve it, and at a low pH of 4 or less, the polymer precipitates, resulting in thickening of the system and dispersion destruction. For this reason, formaldehyde removal cannot be performed on the acidic side. In addition, a relatively high viscosity microcapsule slurry is obtained, which is not preferable. In addition, sulfonic acid groups containing no phenyl group and/or sulfophenyl group such as sulfoethyl (meth)acrylate, sulfopropyl (meth)acrylate, maleimido-N-ethanesulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, etc. A homopolymer of a compound having
_C1 ~ _C3 alkyl acrylate, hydroxy _C2 ~
After emulsifying and dispersing the core material to be encapsulated in a copolymer solution of _C4 alkyl acrylate and N-vinylpyrrolidone, the melamine formaldehyde precondensate is added continuously or in small amounts depending on the condensation rate. A method of adding it has been proposed (Japanese Patent Application Laid-open No. 58536/1983). However, in such a method, when the core material is oily, the dispersion system after adding the melamine-formaldehyde precondensate until the capsule wall is formed is unstable, and strong shearing such as intense stirring is required. In the absence of stress, oil droplets tend to coalesce and the particle size grows, making it difficult to set the emulsion particle size to a desired size. In addition, unless the melamine formaldehyde precondensate is charged slowly and carefully, the entire system may gel or aggregate particles may be formed, which is not preferable from the viewpoint of workability. Moreover, according to this method, 50wt
It is not possible to obtain a microcapsule slurry with a high solids content exceeding %. Furthermore, although the polymer itself does not have dispersion stability with respect to the core material on the acidic side, it forms a substance that imparts dispersion stability to the liquid material that becomes the core material through interaction with the melamine formaldehyde initial condensate. An aqueous medium containing the melamine formaldehyde precondensate is prepared, and after the corresponding dispersion stable substance is formed, a core material is added to prepare a stable dispersion, and then the melamine formaldehyde precondensate is mixed with an acid catalyst. A method has been proposed in which a capsule wall membrane is formed by condensing the following (Japanese Patent Application Laid-open No. 155636/1983). however,
In this method, in order to form a dispersion-stable substance for the core material between the melamine formaldehyde initial condensate and the polymer, it is necessary to carry out partial condensation at low temperature for a long time before the presence of the core material. ,
After that, the core material is emulsified and dispersed and condensed at elevated temperature.If the conditions for partial condensation of the melamine formaldehyde initial condensate in the presence of the polymer are not strictly controlled, emulsion stability will be poor and capsules with irregular particle sizes will be formed. was obtained, and the microcapsule slurry showed a remarkable tendency to increase in viscosity. Additionally, problems remained in terms of work process management. Furthermore, with this method, it is not possible to obtain microcapsules having a solid content of 55 wt% or more. In view of the above-mentioned problems, the present inventors have developed a method for producing microcapsules using an in-situ polymerization method that has a high solid content, low viscosity, and a dense microcapsule wall, and has excellent overall quality. As a result of our investigation, we found that in a method for producing microcapsules whose walls are substantially made of melamine formaldehyde polycondensate in an aqueous medium containing an anionic water-soluble polymer substance under acidic conditions, as the anionic water-soluble polymer substance, , (A) acrylic acid, (B) acrylonitrile, and (C) anionic compound obtained by copolymerizing at least three or more monomers selected from acrylamide alkyl sulfonic acid and sulfoalkyl ester of acrylic acid in an aqueous system. The inventors have discovered that by using a water-soluble polymer, microcapsules with excellent wall density can be obtained as a slurry with an extremely high solids content of 50 wt% or more and a low viscosity, and the present invention has been achieved. That is, the method for producing microcapsules of the present invention includes (A) acrylic acid, (B) acrylonitrile, and
(C) Hydrophobic core in an aqueous solution containing an anionic water-soluble polymer that is a copolymer of at least three or more acrylic monomers selected from acrylamide alkyl sulfonic acid and sulfoalkyl ester of acrylic acid. After emulsifying or dispersing the substances, melamine and formalin or a melamine formaldehyde initial condensate are added, and a polycondensation reaction of melamine formaldehyde is carried out in an acidic pH range, forming a dense melamine formaldehyde polycondensate around the core substance. This is a method of forming a film. In the method of the present invention, microcapsules whose walls are made of a melamine-formaldehyde polycondensate, which has superior membrane density and flexibility compared to urea-formaldehyde polycondensates, have a wide solid content concentration range exceeding 65 wt%. It can be obtained with a slurry of low viscosity over the years, and moreover, it has extremely good workability compared to various methods proposed so far. The anionic water-soluble polymer used in the method of the present invention is a copolymer obtained by copolymerizing at least three of the above three types of acrylic monomers. Various known methods can be used for the copolymerization, but preferably an aqueous radical polymerization method is used. A copolymer radically polymerized in an aqueous system is generally obtained as an aqueous solution with a nonvolatile content of 5 to 30 wt%, and unlike the aforementioned maleic acid copolymer, a dissolution operation is not required, and the process of microencapsulation is easy. This will lead to significant simplification. The anionic water-soluble polymer used in the method of the present invention is one or more selected from acrylic acid 20-70 mol%, acrylonitrile 20-60 mol%, acrylamide alkyl sulfonic acid, and sulfoalkyl ester of acrylic acid as a raw material monomer. 2-
30 mol% of the copolymer, which optionally contains hydroxyalkyl esters of acrylic acid or methacrylic acid, methacrylic acid, methacrylonitrile, lower alkyl esters of acrylic acid or methacrylic acid, acrylamide as the fourth component and subsequent components. , N-alkyl substituted acrylamide, etc. may be copolymerized. The copolymer of the present invention may be in an acid form, or may be partially or entirely in a salt form. When used in a salt form, an alkali metal salt such as sodium, potassium, lithium, rubidium or an ammonium salt, Lower amine salts are preferred. When copolymerizing acidic monomers such as acrylamide alkyl sulfonic acid and sulfoalkyl ester of acrylic acid, a free acid may be used, or part or all of the monomer may be copolymerized as the above-mentioned salt. Examples of the acrylamide alkyl sulfonic acid used in the method of the present invention include acrylamide ethylpropanesulfonic acid, acrylamide propane sulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, and acrylamide butanesulfonic acid. Specific examples of the sulfoalkyl ester of acrylic acid used in the method of the present invention include sulfo-lower alkyl esters of acrylic acid such as sulfomethyl ester, sulfoethyl ester, sulfopropyl ester, and sulfobutyl ester. Preferred anionic water-soluble polymers used in the method of the present invention include 20 to 70 mol% of acrylic acid, 20 to 60 mol% of acrylonitrile, 2-acrylamide- 2-methylpropanesulfonic acid 2-30
It has a monomer composition of mol% and is obtained by aqueous radical copolymerization. In addition, the anionic water-soluble polymer has a molecular weight of 1 to 1, measured by gel permeation chromatography.
10 million (calibrated using dextran as standard molecular weight), typically 20 wt%, PH
4.0, as measured by a B-type viscometer in an aqueous solution at 25°C.
10~10000cps is suitable, more preferably 50
~3000cps is used. At 5 cps, the emulsifying power and emulsion stability are somewhat insufficient, resulting in capsules with a wide particle size distribution, and at 10,000 cps or more, the viscosity of the resulting capsule slurry increases, making it difficult to manufacture and handle highly solid microcapsules. Accompanied by sadness. The aqueous solution of the anionic water-soluble polymer used in the method of the present invention does not precipitate and become cloudy in the pH range of 3 to 14, and unlike the case where an aqueous solution of maleic acid copolymer is used, the viscosity does not depend on the pH. It is easy to handle because the viscosity of the aqueous solution and the resulting microcapsule slurry does not significantly increase when the pH is increased. In addition, in pressure-sensitive copying paper, which is a suitable application for the microcapsules of the present invention, the support is generally coated with an alkali side.
The fact that there is little tendency for viscosity to increase due to an increase in pH is extremely favorable from the viewpoint of coating work. As the starting material for the melamine-formaldehyde polycondensate which becomes the wall membrane of the microcapsules in the method of the present invention, melamine and formaldehyde or a melamine-formaldehyde initial condensate is used.
As a melamine formaldehyde initial condensate,
A transparent solution mainly composed of methylolmelamine obtained by heating reaction with melamine and formaldehyde, methylolmelamine having 1.5 to 6.0 moles of methylolmelamine groups per mole of melamine, or lower condensates thereof (these have a non-volatile content of 50 −
commercially available as a 100 wt% solution), ketylated methylolmelamine, butylated methylolmelamine or their lower condensates (which are commercially available as a 50-100 wt% non-volatile content solution). ), phenols, benzoguanamine, sulfamic acid,
Examples include melamine formaldehyde initial condensates modified with urea or the like. Among these, water-soluble methylated tyromelamine or an aqueous solution thereof is preferred in terms of stability before use and ease of handling. In the method of the present invention, the amount of anionic water-soluble polymer used is 0.5-10wt% of the microcapsule production system, and the amount of the water-soluble polymer used, the capsule membrane forming starting material used, and the core material to be encapsulated are It varies depending on the type, capsule manufacturing conditions, etc.
Generally 1-5wt% of microcapsule manufacturing system
It is common to use degrees. If necessary, in addition to the water-soluble polymer of the present invention, other anionic water-soluble polymers such as ethylene maleic anhydride copolymer, methyl vinyl ether maleic anhydride copolymer, polyacrylic acid-vinyl acetate copolymer, etc. It is also possible to use a maleic anhydride copolymer, a styrene sulfonic acid polymer or copolymer, an anion-modified poval, gum arabic, a cellulose derivative, etc. in combination as appropriate. The ratio of melamine and aldehyde or melamine aldehyde initial condensate and core material used in the method of the present invention is generally 1:3 to 1:20 (wt/
wt), but varies depending on the core material or use. The microcapsule core material used in the method of the invention is a water-immiscible liquid or solid;
It is a substance that is substantially inert to water. Preferred core materials include hydrophobic liquids, and specific examples include partially hydrogenated terphenyls, chlorinated paraffins, diallylalkane, alkylnaphthalenes, dibenzylbenzene derivatives, alkylbenzenes, paraffins, cycloparaffins, and various Esters such as phthalic acid, adipic acid, citric acid, myristic acid, trimellitic acid, sebacic acid, stearic acid, benzoic acid, phosphoric acid, etc. Nitrogen-containing compounds such as nitrobenzene, dimethylaniline, dimethyl-P-toluidine Examples include. Furthermore, a hydrophobic liquid in which a water-insoluble solid substance is dissolved can also be used as the core material. Preferred applications for pressure-sensitive copying paper for the microcapsule slurry produced by the method of the present invention include phthalide derivatives, fluorane derivatives, acylleucophenothiazine derivatives, leucotriarylmethane derivatives, leucoindolylmethane A dye precursor substance such as a derivative, a spiropyran derivative, or a phthalimidine derivative is dissolved in a hydrophobic high-boiling solvent such as an alkylnaphthalene, a diallylalkane, or a partially hydrogenated terphenyl. The outline of the method of the present invention is as follows. (1) Preparation of anionic water-soluble polymer aqueous solution, (2) Emulsification or dispersion of the core substance in the anionic water-soluble polymer aqueous solution, (3) Addition of melamine formaldehyde wall film forming substance, (4) If necessary (5) encapsulation step by forming a melamine-formaldehyde resin film, and (6) treatment of residual formalin as necessary. The anionic water-soluble polymer aqueous solution used in the method of the present invention provides a stable emulsified dispersion for the core substance over a wide PH range and temperature range, and even if a melamine formaldehyde film-forming substance is added, Since there is no tendency to increase the viscosity or to grow giant particles due to coalescence or aggregation of core material particles, it has extremely good workability. Emulsification and dispersion of the core substance is carried out using a homomixer, homogenizer, flow jet mixer, in-line mill, or the like. The preferred particle size of the emulsified dispersion varies depending on the use of the microcapsules, but when used for pressure-sensitive copying paper, the average particle size is 2.
-5μ or so, and the presence of many coarse particles exceeding 10μ is not preferable because it causes background smearing due to weak pressure. Capsule wall film formation reaction is generally carried out at temperatures between 40°C and 90°C.
℃, preferably 50-60℃, PH range of 3.3-6.5,
Preferably, the pH is within the range of 4.0 to 5.5. Melamine formaldehyde resin wall formation reaction is low
PH value, promoted by high temperature, but low below 3.5
If the pH value is used, the acidic coloring of the dye precursor will cause significant coloring of the capsule slurry, which is inconvenient for pressure-sensitive copying paper, and if the pH value is higher than 6.5, the wall film formation reaction will be too slow, making it difficult to encapsulate. This is inconvenient because it involves high temperatures and long periods of time. Generally 50~60℃,
The film forming reaction is completed in about 1 to 10 hours under reaction conditions of pH 4.0 to 5.0. Furthermore, there is no problem in using a reaction accelerator such as an ammonium salt of an acid (for example, ammonium chloride). After forming the microcapsule wall, if it is necessary for sanitary reasons to remove and reduce the remaining free formaldehyde, use urea, ethylene urea, sulfites, sugars, ammonia, amines, formaldehyde, hydroxyamine salts (hydrochloride,
By adding sulfates, phosphates), melamine, compounds with active methylene groups, hydroxyalkylamines, acrylamide, acrylamide-based polymers, etc., and under appropriate reaction conditions, formaldehyde can be converted into a harmless form. Formalin can be removed. As mentioned above, the microcapsule slurry produced by the method of the present invention has no agglomeration tendency and exhibits a low and stable viscosity value over a wide PH range, so it can be easily applied to a wide range of formaldehyde processing conditions and is generally used as a binder and other additives. Since the viscosity does not change even under weakly alkaline conditions when mixed with other materials and applied to a support such as paper, the coating workability is also extremely good. Hereinafter, the present invention will be explained in detail with reference to Examples and Comparative Examples. Example 1 2-acrylamido-2-methylpropanesulfonic acid (manufactured by Nippon Lubrizol Co., Ltd.: “AMPS-R”)
107 parts (parts by weight; the same applies below) ion-exchanged water
After dissolving in 1413 parts, PH with 10% caustic soda aqueous solution.
was neutralized to 7.0. 229 parts of 98% acrylic acid and 83 parts of acrylonitrile were added and mixed and stirred to obtain a homogeneous aqueous solution. (The molar composition of the raw material is 2-acrylamide-2
- 40 mol% of methylpropanesulfonic acid, 60 mol% of acrylic acid, 30 mol% of acrylonitrile)
After heating to °C, 112.5 parts of a 10% aqueous solution of ammonium persulfate was added with gentle stirring, and after 5 minutes, 12.5 parts of a 10% aqueous solution of sodium bisulfite was added to initiate the polymerization reaction under adiabatic conditions. The heat of polymerization raised the temperature of the system to 80°C in 30 minutes. Furthermore, 22 parts of a 10% aqueous solution of sodium bisulfite was added, and after reacting for 1 hour, it was cooled and the pH was adjusted with a 20% aqueous solution of caustic soda.
4.0 to obtain a 20% aqueous solution (A) of anionic water-soluble polymer. The aqueous solution (A) had a viscosity value of 1700 cps.
Using this aqueous solution (A), microencapsulation was carried out in a constant temperature water bath at 55°C as follows. 32.5 parts of the aqueous solution (A) was diluted with water to make 105.6 parts. Phenyl was prepared by dissolving 2.8% by weight of crystal violet lactone as a core substance and 0.8% by weight of benzoylleucomethylene blue in the aqueous solution (PH4.0). Add 130 parts of xylylethane (Nippon Petrochemical "Hysol SAS-296") and emulsify and mix at 9000 rpm using a homomixer (manufactured by Tokushu Kika).After 10 minutes, an O/W type with an average particle size of 4.0μ is stabilized. An emulsion was obtained. While stirring, 24.4 parts of methylated methylolmelamine aqueous solution (non-volatile content 80wt%, Mitsui Toatsu Chemical Co., Ltd. "Eulamine P-6300") was added and condensed at 55°C for 2 hours. The pH of the condensation system was 4.62, and the condensation system was After completion, the mixture was cooled to complete microencapsulation. The microcapsule slurry in this example is 60.0wt%
Despite having a high solids concentration of
It exhibited a low viscosity value of 510 cps and no tendency to agglomerate was observed. Take 100 parts of the microcapsule slurry thus obtained, add urea in an amount of 1/10 of the methylated methylolmelamine used, adjust the pH to 3.0 with acetic acid, and stir and mix at 70°C for 1 hour. The remaining formalin was removed using a 20% aqueous solution of caustic soda, and the pH was adjusted to 9.0 to obtain a microcapsule liquid with no formalin odor. Even in the formalin removal process, there was no tendency for thickening or aggregation, and the final microcapsules had a viscosity of 540 cps. Example 2 The same amount of alkylnaphthalene (Kureha Chemical "KMC-113") in which 4% by weight of 3-diethylamino-6-methyl-7-anilinofluorane was dissolved was used as the core material, and the moisture content was increased to form a solid product. Minute concentration
Light-colored microcapsules with an average particle diameter of 4.5 μm were obtained in the same manner as in Example 1, except that the content was 50 wt%. The microcapsule slurry of this example showed an extremely low viscosity value of 25 cps, and no tendency to aggregate was observed. Even after removing formalin with 28% ammonia water, the microcapsule slurry remained stable with an extremely low viscosity of 27 cps. Example 3 After dissolving 187.2 parts of 2-acrylamido-2-methylpropanesulfonic acid in 2304.6 parts of water, 20
% caustic soda aqueous solution to adjust the pH to 7.0. 98%
331 parts of acrylic acid and 191 parts of acrylonitrile were stirred and mixed to form a homogeneous aqueous solution (monomer composition was 10 mol% of 2-acrylamido-2-methylpropanesulfonic acid, 40 mol% of acrylonitrile, and 50 mol% of acrylic acid). When 240 parts of a 10% aqueous solution of potassium persulfate and 200 parts of a 10% aqueous solution of sodium bisulfite were added at room temperature (25°C) under gentle stirring, polymerization started and the temperature of the system rose to 65°C in 40 minutes due to the heat of polymerization. did. Furthermore, 40 parts of a 10% aqueous sodium bisulfite solution was added and reacted at 80°C for one hour, then cooled and the pH was adjusted to 4.0 with a 20% aqueous sodium hydroxide solution to form a 20% aqueous solution of anionic water-soluble polymer (B). I got it. The aqueous solution (B)
had a viscosity of 970 cps. Using this aqueous solution, microencapsulation was carried out in a constant temperature water bath at 60°C as follows. Partially hydrogenated terphenyl containing 3.0wt% of krytal violet lactone as a core material is made by stirring and mixing 50 parts of a 20% aqueous solution (B) of anionic water-soluble polymer with 120.4 parts of water and adjusting the pH to 3.9. (Monsanto "HB-40") was added and emulsified for 20 minutes using a homomixer to obtain a stable O/W emulsion with an average particle size of about 5 μm (microscopic observation). An aqueous solution of methylated methylolmelamine (non-volatile content 80 wt%...Euramine P-
6300) was added all at once, and the mixture was reacted for 1 hour with stirring. (The PH of the reaction system was 4.81), and after adjusting the PH to 4.3 with acetic acid, the reaction was continued for 1 hour.
Thereafter, it was cooled to complete microencapsulation. Although the microcapsule slurry in this example has a very high solid content concentration of 65wt%,
It exhibited a low viscosity of 1200 cps. Example 4 20 of the anionic water-soluble polymer obtained in Example-3
Stir and mix 36.1 parts of % aqueous solution (B) with 110 parts of water and adjust the pH to 4.2.
The same core material as in Example-3 was added to the
130 parts were mixed and emulsified using a homomixer to obtain a stable O/W type emulsion. Separately, melamine
A melamine-formaldehyde initial condensate containing methylolmelamine as a main component was obtained by mixing and heating and dissolving 10 parts of 37% formalin and 21.4 parts of 37% formalin. The mixture was added to the emulsion with stirring, and condensation was carried out at 50°C for 3 hours. The pH during condensation was 5.02. After 3 hours, the mixture was cooled to complete microencapsulation. The microcapsule slurry in this example is 50wt%
It has a solid content concentration of , and the average particle size is 2.9μ.
It showed a viscosity value of 150 cps. Example 5 36.1 parts of a 20% aqueous solution (B) of anionic water-soluble polymer was mixed and stirred into 110.9 parts of water, and the pH was adjusted to 5.0.
To this was added 130 parts of the same core material as in Example 3 and emulsified with a homomixer to obtain a stable O/W type emulsion. To this, 9.1 g of melamine and 19.5 parts of 37% formalin were gradually added, reacted at 60° C. for 7 hours, and then cooled to complete microencapsulation. The microcapsule slurry in this example is 50wt.
% solids concentration and an average particle size of 3.4 μ
It had a viscosity of 75 cps. Example 6 Sulfopropyl ester of acrylic acid was prepared according to the method for producing anionic water-soluble polymer in Example-1.
A 20% aqueous solution (C) of a copolymer anionic water-soluble polymer having a monomer composition of 15 mol %, acrylic acid 40 mol %, and acrylonitrile 45 mol % was obtained. The aqueous solution (C) exhibited a viscosity of 4300 cps. This aqueous solution was used in a constant temperature bath at 55°C. 15 parts of a 20% aqueous solution (C) of an anionic water-soluble polymer was stirred and mixed with 107 parts of water, and the pH was adjusted to 4.0. 130 parts of the same core material as in Example 3 was added to this and emulsified with a homomixer to obtain a stable O/W emulsion. To this, 13 parts of methylated methylolmelamine ("Cymel 350" manufactured by Mitsui Cyanamid) (non-volatile content 98 wt% or more) was added and condensed for 2 hours.
The pH during condensation was 4.75. This product had a solids content of 55 wt% and a viscosity of 150 cps. Furthermore, to remove formaldehyde, use a 10% caustic soda aqueous solution.
After adjusting the pH to 8.5, 2 g of urea was added, and the mixture was stirred and kept at 70°C for 1 hour, and the formalin odor disappeared.
The treated capsule liquid also had a low viscosity of 170 cps. Comparative Example 1 50 parts of ethylene maleic anhydride copolymer and 450 parts of water
10% aqueous solution (D) was obtained. The aqueous solution
100 parts of (D) and 200 parts of water were mixed, and the pH was raised to 4.0 with a 10% caustic soda aqueous solution. In this, 200 parts of the same core material as in Example 3 was emulsified with a homomixer,
A stable O/W type emulsion was obtained. Melamine prepared by heating and stirring a separately prepared mixture of 26.5 parts of 37% formaldehyde and 20 parts of melamine.
Add formaldehyde initial condensate and heat at 55°C for 2 hours.
Microencapsulation is completed by stirring while keeping warm. Although the microcapsule liquid of this example has a solid content concentration of 43.9wt%, the viscosity of the system increases significantly as a wall film is formed due to the condensation of the melamine formaldehyde initial condensate. Capsule slurry has no agglomeration tendency but 6000cps
It exhibited a high viscosity and almost lost its fluidity. Comparative Example 2 The solid content of the finished microcapsule liquid was 35wt.
Comparative example-1 except that the moisture content was adjusted to %.
Microencapsulation was completed in the same manner as above. The microcapsule slurry in this example had a pH of
It showed a viscosity of 250 cps at 4.8. Adjust the pH by adding 28% ammonia water to remove residual formalin.
When adjusted to 8.5, the formaldehyde odor completely disappeared, but the capsule liquid increased in viscosity and showed a viscosity of 670 cps, and it was observed that the viscosity/PH dependence was large, so careful attention should be paid to PH control during coating work. It was hot. Comparative Example 3 Using 2.5 parts of styrene maleic anhydride copolymer (Monsanto "Scripset-520") and 2.5 parts of vinyl acetate maleic anhydride copolymer (Nippon Nyukazai "DisrolH-12" unneutralized product) diluted caustic soda aqueous solution pH 5.0
The mixture was heated and dissolved to give 100 parts of an aqueous solution.
It took 4 hours at 90°C to completely dissolve.
Microencapsulation was performed in a constant temperature water bath at 55°C. After emulsifying and dispersing 100 parts of the same core material used in Example-1 in a mixture of 100 parts of an aqueous solution of the styrene-maleic acid copolymer and bimaleic acid acetate and 17.5 parts of water using a homomixer, methylated methylolmelamine was added. 80% aqueous solution (Euramine P-
6300) was added, condensed for 2 hours, and then cooled to complete the capsule membrane formation. The microcapsule slurry of this example has a solid content of 50wt%,
It had a viscosity of 420 cps. To remove residual formalin, warm to 60℃ again, add 3 parts of 40wt% urea aqueous solution, and PH with acetic acid.
When the pH was adjusted to 4.0, the entire mixture thickened and stirring became impossible, making it impossible to remove residual formaldehyde on the acidic side, such as by adding urea. Comparative Example 4 (Based on JP-A-56-58536, Example-1) 40 parts of 2-acrylamide-2-methylpropanesulfonic acid was stirred and dissolved in 160 parts of water, and then 20%
Adjust the pH to 5.0 with aqueous caustic soda solution, add 3.7 parts of a 10% aqueous solution of ammonium persulfate and 0.8 parts of a 10% aqueous solution of sodium hydrogen sulfite, and polymerize under adiabatic conditions to obtain a polyamide with a viscosity of 430 cps at 25°C.
A 20 wt % aqueous solution (D) of the sodium salt of (2-acrylamido-2-methyl-propanesulfonic acid) was obtained. (4-1) Using this aqueous solution (D), microencapsulation was carried out in a constant temperature water bath at 60°C. Stir and mix 25 parts of aqueous solution (D) and 85 parts of water, and PH with acetic acid.
Adjusted to 4.0. 100 parts of the same core material as in Example-1 was added to the system and emulsified and dispersed for 20 minutes using a homomixer. The O/W type emulsion of this example has poor emulsion stability, and as soon as stirring is stopped, the oil droplets coalesce, so it is necessary to constantly apply strong shearing force to maintain the oil droplets in minute size. Moreover, it was very difficult to control the size of emulsified droplets. Under strong stirring, add a 50% aqueous solution of methylated methylol melamine (manufactured by Mitsui Toatsu Chemical Co., Ltd., “Euramin P-
When 30 parts of 6100'') were added, the system rapidly thickened and the entire system coagulated into a gel after 5 minutes. (4-2) On the other hand, methylated methylolmelamine (Eulamine P-6100), which has the same composition as above, was carefully added dropwise under strong stirring over a period of 2 hours to prevent gelation of the system. ,
The reaction was further carried out for 2 hours to complete the encapsulation. Due to poor emulsion stability against oil, many coarse particles and aggregated particles were found in the resulting microcapsules, which was inconvenient for use in pressure-sensitive copying paper unless they were passed through a sieve. The average particle diameter is 7.4μ,
It had a solid content concentration of 50 wt% and a viscosity of 350 cps. Comparative Example 5 8.4 parts of styrene sulfonic acid sodium salt (Toyo Soda "Spinomer SS") (purity 85%) was dissolved in 161.3 parts of water, and then 29.9 parts of 98% acrylic acid and 6.5 parts of hydroxyethyl methacrylate (HEMA) were added. The mixture was stirred to form a homogeneous aqueous solution and kept at 40°C. When radical polymerization was started by adding 12.9 parts of a 10% aqueous solution of ammonium persulfate and 4.0 parts of a 10% aqueous solution of sodium bisulfite, the internal temperature rose within 30 minutes.
The temperature was raised to 65℃. The polymerization is further kept at 70℃ for 30 minutes, and the solid content is
A 20wt% anionic water-soluble polymer aqueous solution (E) was obtained. The viscosity of this product was 4800 cps at 25°C. (5-1) Using this aqueous solution (E), microencapsulation with melamine-formaldehyde resin was carried out in a constant temperature water bath at 60°C. 32.5 parts of polymer aqueous solution (E) was stirred and mixed with 125.1 parts of water, and the pH was raised from 2.4 to 4.0 with a 10% aqueous sodium hydroxide solution. Add 130 parts of the same core material used in Example-1 and mix 20 parts with a homomixer.
Emulsification was carried out for minutes to obtain an O/W type emulsion. The emulsion stability is somewhat insufficient, and if left as is, the droplet size tends to increase due to coalescence of oil droplets. Methylated methylolmelamine 80% aqueous solution (Euramine P-6300) under stirring
When condensation was carried out by adding 16.25 parts, 10
After a few minutes, the entire system gelled and no microcapsules were obtained. (5-2) Also, using aqueous solution (E), urea,
Microencapsulation with formaldehyde resin was carried out in a constant temperature water bath at 60°C. Stir and mix 19.88 parts of polymer aqueous solution (E) with 138.23 parts of water, add and dissolve 6.63 parts of urea and 0.93 parts of resorcin, and adjust the pH to 2.75 with 10% aqueous caustic soda solution.
It was raised from 3.40 to 3.40. 117 parts of the same core substance used in Example-2 was added to this and emulsified in a homomixer for 20 minutes.
An O/W emulsion with an average particle size of 4μ was obtained, but due to its strong acidity, the emulsion was colored deep reddish-purple.
After adding 17.2 parts of % formalin and reacting for 3 hours, microencapsulation was completed and the mixture was cooled.
The microcapsule liquid had a solid content of 45 wt% and a viscosity of 250 cps. However, the liquid was extremely colored reddish-purple, and the coloring did not disappear even when made alkaline with caustic soda or the like, and the surface of the pressure-sensitive paper coated with the capsules was also too colored to be practical. Examples 7 to 9 and Comparative Examples 6 to 8 Examples of melamine formaldehyde resin film microencapsulation having a solid content concentration of 55% using different anionic water-soluble polymers shown in Table 1 are summarized below. Microencapsulation was performed by the following method. 69 parts of a 20% aqueous solution of anionic water-soluble polymer and 199 parts of ion-exchanged water were mixed, and the pH was adjusted to 4.0 by adding a 10% aqueous solution of caustic soda. Crystal violet lactone here
270 parts of phenylxylylethane dissolved at 3.0 wt% was added and emulsified at high speed for 20 minutes using a homomixer to obtain an O/W emulsion with an average particle size of about 3 μm. To this, 67.5 parts of an 80% aqueous solution of methylated methylolmelamine (Eulamine P-6300) was added and condensed for 2 hours, and then acetic acid was added to adjust the pH to 4.2.
Condensation was continued for a period of time to complete the formation of the microcapsule membrane. The above operations were performed at 60°C. Thereafter, it was cooled and returned to room temperature to complete microencapsulation.

[Table] Comparative Example 9 20 parts of acid-treated gelatin was heated and dissolved in 200 parts of water,
Mix 100 parts of phenylxylylethane in which 3 wt% of the original crystal violet lactone dissolved in 10.0 pH with 10% caustic soda aqueous solution is emulsified with high-speed stirring using a homomixer at 55°C, and while continuing to stir, carboxyl methyl cellulose ( 10% aqueous solution with average degree of polymerization 160 and degree of etherification 0.70) 50
1030 parts of warm water are added to dilute the mixture, and the pH is adjusted to 4.3 with acetic acid to cause coacervation. Next, while stirring, increase the liquid temperature to 80℃.
The coacervate film is gelled by cooling to ℃. Furthermore, after adding 1.75 parts to formalin, the pH was raised to 10.5 while gradually adding a 10% aqueous solution of caustic soda to harden the coacervate film to obtain a gelatin carboxymethyl cellulose complex coacervation microcapsule slurry. Comparative Example 10 60 parts of phenylxylylethane in which 4.5wt% of crystal violet lactone was dissolved and 9.78 parts of terephthaloyl chloride dissolved in 30 parts of phenylxylylethane were mixed, and polyvinyl alcohol (Kuraray... 2wt% of Poval-205”)
Add to 300 parts of aqueous solution and emulsify with a homomixer.
An O/W type emulsion with an average particle size of 4-5 μm was obtained. Then, while cooling and stirring, 5.5 parts of diethylene triamine and 2.88 parts of sodium carbonate dissolved in 60 parts of water were added dropwise, followed by stirring at room temperature for 24 hours to form a polyamide film formed by interfacial polycondensation of diethylene triamine and terephthaloyl chloride. Microcapsules were obtained. Example 10 Anionic water-soluble polymer obtained in Example-3
40 parts of a 20% aqueous solution and 2.1 parts of a 40% aqueous solution of sodium diethylenetriaminepentaacetate (Kylest Chemical "Kylest-P") were mixed with 98 parts of water with stirring, and acetic acid was added to adjust the pH to 4.1. Add to this 4,4′,4″-tris-
Add 130 parts of dioctyl phthalate in which 2.5 wt% of dimethylamino-triphenylmethane and 0.7 wt% of 4,4'-bis-dimethylamino-3'-methyl-4''-ethoxy-triphenylmethane were dissolved and emulsify with a homomixer. A stable O/W type emulsion with an average particle size of about 4μ was obtained.
Melamine formaldehyde initial condensate with solid content (Sumitomo Chemical "Sumiretsuta Resin #613")
32.5 parts were added and heat condensation was carried out at 55°C for 4 hours. Add the microcapsule liquid to 28% ammonia water at pH 8.0.
After removing the formalin, 6 parts of triethanolamine was further added to complete the microencapsulation. The microcapsule slurry of this example had a solids concentration of 55 wt% and a viscosity of 180 cps. Using this microcapsule slurry, redox coloring pressure-sensitive copying paper was prepared. Reference Example The properties of pressure-sensitive recording paper prepared using the microcapsule liquids obtained in the above Examples and Comparative Examples were measured by the following method, and the results shown in Table 2 were obtained. (A) Pressure staining property: For each 100 parts of solid microcapsules, 38 parts of wheat flour starch granules and 25 parts of a 20% boiled oxidized starch aqueous solution (Oji Cornstarch "Ace B") were mixed and the whole was diluted with water. A water-based paint with a solid content of 25 wt% was prepared, and then coated with a wire bar on a base paper of 40 g/m ² to a dry coating weight of 4.5 g/m ² and dried to obtain top paper for pressure-sensitive copying paper. This top paper and a commercially available bottom paper (Resin CCP W-50BR manufactured by Jujo Paper Co., Ltd.) using P-phenylphenol formaldehyde condensate as a color developer were superimposed.
Pressure was applied for 30 seconds at a pressure of 10 kg/cm ² using a Müllen burst tester, and the degree of coloring on the lower paper surface before and after the test was measured using a Hunter whiteness meter (amber filter) before and after the test.
It was calculated from the difference in reflectance. The smaller this difference is, the more flexible the capsule membrane is. (B) Denseness of the membrane The upper paper prepared in (A) was placed in an oven at 105℃ for 20 minutes.
Leave it for a while, overlap it with the bottom paper (Jujo Paper W-50BR), and use an electric typewriter (Hermes model 808).
After one hour, the color was measured using a Hunter colorimeter (amber filter). The difference between this reflectance and the reflectance of a top sheet of paper that had not been left in the oven that was similarly colored with a typewriter was determined. The smaller this difference is, the more compact the capsule membrane is and the better the storage stability is. (C) Water resistance 10 parts of the microcapsule liquid was mixed with a 40% dispersion of P-phenylphenol resin (PBE manufactured by Mitsui Toatsu Chemical Co., Ltd.).
-40...Practical color developer for pressure-sensitive copying paper) was mixed with 50 parts of diluted with twice the amount of water.
The degree of coloring of the liquid was determined visually. In the case of microcapsules with poor water resistance, they come into contact with a color developer in water and develop color in the liquid.

【table】

[Table] ○: Slight tendency for coloring
×: Significantly colored.

Claims (1)

[Scope of Claims] 1. In an acidic aqueous medium containing an anionic water-soluble polymer substance, a method for producing microcapsules having a wall material substantially composed of a melamine formaldehyde polycondensate; As a molecular substance, at least three or more acrylic monomers selected from (A) acrylic acid, (B) acrylonitrile, and (C) acrylamide alkyl sulfonic acid and sulfoalkyl ester of acrylic acid are copolymerized. A method for producing microcapsules, characterized by using a polymer or a salt thereof. 2. Claim 1, wherein the anionic water-soluble polymeric substance is a terpolymer of (A) acrylic acid, (B) acrylonitrile, and (C) 2-acrylamido-2-methylpropanesulfonic acid or a salt thereof. 2. Method for producing microcapsules as described in Section 1. 3 The anionic water-soluble polymer substance is acrylic acid20
-70 mol%, acrylonitrile 20-60 mol%, 2
-acrylamide-2-methylpropanesulfonic acid with a monomer composition of 2-30 mol%, 20wt
% aqueous solution has a viscosity of 50 to 10,000 cps.