JPS5813213B2 - Capsule no Koukahouhou - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improved method for curing capsules containing hydrophobic oil droplets consisting of a coacervate wall membrane of hydrophilic colloids.

More specifically, when microcapsules are manufactured by a complex coacervation method using gelatin as at least one hydrophilic colloid and ketoaldehydes as a curing reagent, after the pre-curing process, especially during the curing process. The present invention relates to a curing method for preventing a rapid increase in viscosity and yellowing of capsule liquid due to the reaction between gelatin and the aldehyde.

In this specification, pre-hardening treatment refers to an operation to convert the pH of the system to alkaline in order to accelerate the reaction between gelatin and aldehydes, and hardening treatment refers to an operation that further accelerates the reaction between gelatin and aldehydes to improve heat resistance. The temperature of the system is gradually increased to obtain a wall film with .

For example, the following method is known as a method for microencapsulating a hydrophobic oily liquid using complex coacervation.

That is, (1) an oil immiscible with water is emulsified in an aqueous solution (first sol) of at least one kind of hydrophilic colloid that is ionized in water, and then an oil that is ionized in water and is in the first sol is emulsified. Either an aqueous solution (second sol) of a hydrophilic colloid having an opposite charge to that of the colloid is mixed into the emulsion, or at least two types of hydrophilic colloids (second sol) capable of ionizing water-immiscible oil in water are used. (2) A process of causing coacervation by adding water or adjusting the pH and fixing the complex colloid around individual oil droplets (emulsification process) (Coacervation step) (3) Step of cooling and gelling the coacervate (gelling step) (4) Adjusting the pH to the alkaline side in the presence of a curing reagent, or after adjusting the pH to the alkaline side, It consists of four steps: adding a curing reagent or adding a curing reagent and an alkali simultaneously.

Since the microcapsules obtained by the above method are extremely unstable, they have a fatal flaw in the manufacturing process, which requires that they be allowed to stand naturally for a long time under mild conditions below room temperature and gradually harden. However, it was later improved.

That is, after the step (4) mentioned above, the temperature is gradually heated to 40 to 60 ml.
This method includes a hardening treatment step in which the temperature is raised to 0°C to quickly and completely harden the oil-containing capsule.

Although ketoaldehydes have a fast curing speed and the resulting wall film has excellent thermal properties, the viscosity of the system gradually increases if left at low temperatures for a relatively long time after the pre-curing process. The fatal drawback is that the capsules produced gradually aggregate and the capsule liquid itself becomes yellow in color.

These drawbacks become even more noticeable if the system is not stirred.
Microcapsule. This was an important issue to be solved in that the slurry had to have good stability over time.

In addition, in the conventional method, in order to harden the oil-containing capsules quickly and completely, the temperature of the system is gradually raised and the curing process is performed, which causes the viscosity to rise rapidly and the capsules to coagulate into a huge block shape, resulting in the capsule liquid. had the disadvantage that it turned bright yellow.

Furthermore, when oil-impregnated capsules produced by conventional methods are used in pressure-sensitive recording paper, the large capsule particles have the disadvantage of deteriorating the resolution of colored characters when a large number of copies are made.

Furthermore, when the capsules produced by these methods are applied to base paper using an air knife coater, the viscosity of the coating liquid is high, so it is necessary to increase the air pressure of the coating machine, which is an obstacle to increasing the coating speed.

The purpose of the present invention is to solve the above-mentioned drawbacks, and firstly, even when ketoaldehydes are used as a curing reagent, the viscosity does not increase over time, and there is no aggregation; An object of the present invention is to provide a method for producing microcapsules that does not cause yellowing.

Secondly, even when ketoaldehydes are used as a curing reagent, the viscosity does not increase rapidly during the heat curing process, the microcapsules do not aggregate into huge flocs, and furthermore, the microcapsules do not become yellow colored. An object of the present invention is to provide a method for manufacturing capsules.

Third, even if ketoaldehydes are used as curing reagents,
It is an object of the present invention to provide a method for producing microcapsules that can increase the coating speed and shorten the drying process.

Other objects of the invention will become apparent from the description.

It has been found that the above and other objects can be achieved by using formaldehyde in combination with ketoaldehydes of the following general formula as curing reagents.

General formula (where R represents a lower alkyl group, such as methyl, ethyl, etc.)

) It is completely surprising that the above-mentioned object of the present invention can be successfully achieved by using both of these in combination, breaking the conventional wisdom.

In the present invention, microcapsule coating with a hydrophobic oily liquid is carried out by complex coacervation induced by water dilution or pH adjustment.

That is, the production of a complex coacervate based on liquid-liquid phase separation involves the separation of at least two types of hydrophilic colloidal sols into one colloid-rich phase and the other colloid-poor phase.

At this time, it is necessary that the coacervated colloid contains at least two types of hydrophilic colloids having opposite charges, and that at least one of the colloids is capable of gelatinization.

In the process to which this invention is compatible, the first step is an emulsification step.

In this step, the water-immiscible oil is treated with an aqueous solution of at least one hydrophilic colloid (first
sol) and then an aqueous solution of a hydrophilic colloid with an opposite charge to the first sol (second sol) is mixed with the previous emulsion.

Alternatively, a water-immiscible oil is emulsified in an aqueous solution of at least two hydrophilic colloids, at least one of which has an opposite charge, that can be ionized in water.

The temperature of emulsification and oil droplet formation is not critical, but must be kept below gelatinization temperature (preferably around 40° C.).

The size of the oil droplets formed in this process is critical (crit
not cal).

The weight of the hydrophilic colloid can also be chosen freely since the solution is then diluted with water, which is added in the coacervation step described below.

The timing of mixing the first sol and the second sol can also be changed freely.

The ratio of hydrophilic colloids used can be varied to suit. Preferably, the weight ratio (on a solid basis) of one hydrophilic colloid to a second hydrophilic colloid of opposite charge is about 1.

In the next step, water is added or the pH is adjusted to cause coacervation.

The amount of water to be added may be sufficient as long as it causes coacervation, and a person skilled in the art can appropriately determine the amount of water by a conventional test (
For example, see US Pat. No. 2,800,457).

Next, the temperature of the system is not particularly limited, but it should be kept below the gelation point of gelatin.

It is also preferred that the temperature of the system be kept substantially constant until coacervation is achieved.

If pH adjustment is utilized, the initial pH of the system and the pH
Although the variation is not particularly limited, the initial pH of the system must be below the isoelectric point of gelatin (pH between 7 and 2, preferably about 4).

Suitable pH adjusting agents include organic acids such as succinic acid,
(acetic acid, etc.) and mineral acids (eg, hydrochloric acid, etc.).

In the third step, the coacervate is cooled to cause gelation.

The temperature at the beginning of the cooling step is substantially the same as that used in the coacervation step.

The temperature at which the cooling step is completed should not exceed the gelling point of the gelatin and should not fall below the freezing point of water (e.g. to about 5°C, usually about 10°C).
.

The cooling rate is not particularly important and depends on the volume being cooled.

Rapid cooling may be performed. Once the coacervate has gelled, the pH of the system is adjusted to be alkaline.

The preferred pH after adjustment is a pH of about 7.5-12.

Usually the final pH value is about 10.

The temperature through pH adjustment towards the alkaline side is critical (cr
(itcal) but should not exceed the gelation point of the gelatin.

The pH can be made alkaline using an alkali such as caustic soda or caustic potash.

After the above steps, the temperature of the coacervate can optionally be raised to more effectively cure the coacervate.

The steps described above are generally well known.

Examples of hydrophilic colloids include natural or synthetic ones, such as amino acid-containing compounds (e.g., gelatin, casein, etc.), saccharides (e.g., gum arabic, carrageenan, etc.), and copolymers (e.g., styrene-maleic anhydride). copolymers, methyl vinyl ether-maleic anhydride copolymers, etc.), cellulose compounds (for example, carboxymethyl cellulose, sulfated cellulose, etc.), starches (for example, sulfated starch, etc.), and the like.

Examples of hydrophobic substances that form the core of individual capsules include natural mineral oils, animal oils, vegetable oils, and synthetic oils.

Examples of mineral oils are petroleum oils and their fractions such as kerosene, catholine, naphtha and paraffin oils.

Examples of animal oils include fish oil and lard oil. Examples of vegetable oils include peanut oil, linseed oil, soybean oil, castor oil and corn oil.

Examples of synthetic oils include alkylated biphenyls (such as methyl, ethyl, or isopropyl-substituted biphenyl).
Examples include biphenyl derivatives such as phosphoric acid esters, naphthalene derivatives, phthalic acid derivatives, and salicylic acid derivatives.

Anionic, cationic, or nonionic surfactants can be used to emulsify and disperse the hydrophobic oily liquid that serves as the core substance in water to prevent reversal (i.e. water-in-oil emulsion).
The addition of these substances is preferred because it prevents the formation of emulsions).

The formation of oil-in-water emulsions is caused by at least one type of (
It can be obtained by emulsifying a hydrophobic oily liquid, which will become a core material, in an aqueous solution of a hydrophilic colloid (which will become a wall material).

The emulsion is diluted with water and pH adjusted to deposit coacervate around the emulsified oil droplets.

The coacervate deposited on the surface of the oil droplet after the coacervation operation is solidified by cooling from the outside of the container to gel the wall film.

Then, in order to harden the wall film, a ketoaldehyde is added to adjust the pH of the system to alkaline, or the pH of the system is adjusted to alkaline and then a ketoaldehyde is added.

The timing of adding formaldehyde is not particularly limited, as the combined effect is the same whether it is during or after this curing operation.

In order to make the capsule wall membrane heat resistant,
For example, leave it at a low temperature (for example, room temperature) for one day, or heat it to about 40 to 60°C if you want to do it in a short time.

The amount of formaldehyde to be added together with the ketoaldehyde used as a curing reagent is the amount necessary to improve the stability over time after the pre-curing treatment step, and varies depending on the amount of the ketoaldehyde.

In other words, as the amount of ketoaldehydes used increases, the minimum required amount of formaldehyde to be added in combination decreases, and from a certain amount of ketoaldehydes onwards, the minimum required amount of formaldehyde becomes constant.

For example, if 0.6 parts of methylglyoxal is used per 100 parts of gelatin, the minimum required amount of formaldehyde to be added is 10 parts.

Next, if 1.3 parts of methylglyoxal is used, the minimum required amount of formaldehyde to be added becomes 0.6 parts.

If 2.5 parts of methylglyoxal is used, the minimum required amount of formaldehyde to be added is 0.25 parts.

If the amount of methylglyoxal used is further increased to 5 parts, the minimum required amount of formaldehyde to be added is 0.07.
It decreases to the department.

Even if the amount of methylglyoxal used is increased, the minimum amount of formaldehyde required will remain 0.
．． It is part 07.

The effects of the combined addition of formaldehyde in the present invention are shown below.

Using 100 parts of gelatin and 75 parts of gum arabic, add 50 parts of water.
After cooling and adding 12.5 parts of a 40% aqueous methylglyoxazole solution, the pH was adjusted to 10 by dropping an alkali solution.

The viscosity of the liquid at this point is 74 cp, but if it is stirred overnight at a low temperature, the viscosity of the liquid will increase to 181 cp, and the liquid will turn yellow and coagulate.

Without stirring, the viscosity of the liquid increases even more rapidly (672c)
becomes p.

In addition, in order to harden the capsule wall film in a short time, instead of stirring at a low temperature all day and night, raising the temperature of the liquid to 50°C will result in 2.
The viscosity increased to 27 cp and the liquid also turned yellow.

According to the invention 40% methylglyoxal aqueous solution 12
．． When 0.3 part of a 37% formaldehyde aqueous solution is added to 5 parts, the viscosity becomes 65 cp when the pH reaches 10 after dropping the alkali.

After stirring all day and night at a low temperature, the viscosity of the liquid decreased to 36 cp, and the phenomenon of yellowing and aggregation of the liquid did not occur.

Further, even if the temperature of the liquid is raised to 50° C. and a thermosetting treatment is performed, the viscosity of the liquid decreases significantly to 12 cp.

As mentioned above, the combined addition of formaldehyde and ketoaldehydes in the present invention provides microcapsules with excellent stability over time after the curing pretreatment step.

The encapsulation method using complex coacervation has the disadvantage of requiring a long time for the pre-curing process, but British Patent No. 1,253,11 improves this disadvantage.
It is useful to combine invention No. 3 with the present invention.

That is, by adding an "anti-shock agent" in the presence of an aldehyde, which is a gelatin hardening reagent, in the pre-hardening treatment step, it is possible to convert the gelatin to alkalinity all at once.

"Shock" is a phenomenon that is described in the above-mentioned British Specification, and that when pre-curing a coacervation solution containing seratin, the viscosity suddenly increases when the pH of the system is near the isoelectric point of gelatin. The term "anti-shock agent" refers to a solution that prevents such shock.

The anti-shock agent that can be used in this invention is a polymer electrolyte having an anionic functional group.

Examples of such polymer electrolytes include anionic modified celluloses, anionic starches, acidic polysaccharides, condensates of napucrenesulfonic acid and formalin, hydroxyethylcelluloses, copolymers of vinylbenzenesulfonic acid, Examples include copolymers of acrylic acid and copolymers of maleic anhydride.

Examples of modified cellulose include glucose β-1,4
-Polysaccharides having glucosidic bonds and anionic functional groups can be mentioned.

Some or all of the hydroxy groups in cellulose may be etherified or esterified.

Examples of cellulose ethers include carboxymethyl cellulose, carboxyethyl cellulose, and metal salts thereof.

Examples of cellulose esters include cellulose sulfate, cellulose phosphate, and metal salts thereof.

Anionic starch derivatives are, for example, α-1,4-linked D
- amylose, a linear polysaccharide made from glucose, mainly α-1,4 linked and partly α-1,6
It consists of the side chain polysaccharide amylopectin created by the side chain D-glucose by bonding.

Examples of the above starch derivatives include carboxymethyl starch,
Examples include carboxyethyl starch, sulfate starch, phosphate starch and xanthate starch.

These can be obtained by etherification or esterification of corn starch, wheat starch, rice starch, potato starch, sweet potato starch or tapioca starch (the above natural starches are extracted in high yields from the seeds and roots of plants). be able to).

As an example of acidic polysaccharide, D-galacturonic acid is α-1
, polygalacturonic acid polycondensed into a linear chain with 4 bonds, or a salt thereof.

More specifically, pectin, pectic acid, pectinic acid, etc. can be mentioned.

These compounds are the basic substances of the pectin structure present in all higher plants, and are generally defined as follows.

Pectic acid - a colloidal polygalacturonic acid containing a negligible proportion of methyl ester groups.

Pectin - A water-soluble pectic acid with variable content of methyl ester groups and degree of neutralization.

Pectic acid monocolloidal polycalacturonic acid, practically free of methyl ester groups.

Separation of these compounds is usually carried out by extraction with acids.

The condensate of naphthalene sulfonic acid and formalin can be represented by the following general formula.

Here, X represents a hydrogen atom, an alkali metal, or an ammonium group, and n is a positive integer.

The anti-shock ability of the above condensate is influenced by the degree of polymerization, and it is preferred that n is from 5 to 9.

Generally, the larger the value of n, the greater the water solubility and viscosity.

These compounds are [Industrial Chemistry Journal 166 (1), 55-
69 (1963).

Examples of hydroxyethyl cellulose derivatives include carboxymethyl ether of hydroxyethyl cellulose,
Examples include sulfate ester of hydroxyethyl cellulose and phosphate ester of hydroxyethyl cellulose.

Examples of copolymers of vinylbenzenesulfonic acid (salt) include copolymers of vinylbenzenesulfonic acid (salt) and acryloylmorpholine; copolymers of vinylbenzenesulfonic acid (salt) and morpholinomethylacrylamide; vinylbenzene Examples include copolymers of sulfonic acid (salt) and acrylamide; copolymers of vinylbenzenesulfonic acid (salt) and vinylpyrrolidone; and copolymers of vinylbenzenesulfonic acid (salt) and methoxyacrylamide.

These copolymers have the following groups in their molecules.

Here, M represents an alkali metal and n is a positive integer.

The amount of vinylbenzenesulfonate in the copolymer is preferably 45 to 95 mol%, more preferably 60 to 85 mol%.

Furthermore, for the purposes of this invention, molecular weights of 10,000 to 3
000000, more preferably 100000 to 1000
000 is preferably used.

Examples of acrylic acid copolymers include copolymers of acrylic acid and acryloylmorpholine; copolymers of acrylic acid and morpholinomethylacrylamide; copolymers of acrylic acid and acrylamide; copolymers of acrylic acid and vinylpyrrolidone. Examples include a copolymer of acrylic acid and methoxymethylacrylamide.

These copolymers have the following groups in their molecules.

Here, X represents a hydrogen atom or an alkali metal, and n
is a positive integer.

The amount of acrylic acid in the copolymer is preferably from 40 to
It is 95 mol%, more preferably 50 to 85 mol%.

Furthermore, for the purposes of this invention, molecular weights between 6000 and 2
000000, more preferably 50000 to 10000
Preferably, a copolymer of 0.00 is used.

Examples of copolymers of maleic anhydride include maleic anhydride and unsaturated compounds with active double bonds. copolymers of substances (e.g. styrene, ethylene, methyl vinyl ether, vinyl acetate), salts thereof (e.g. alkali metal salts such as potassium and sodium, ammonium salts, etc.), or half esters of the above copolymers (e.g. methyl esters, Alkyl esters such as ethyl ether, suel, etc.) can be mentioned.

In addition, OLS2133052, OLS2138842, or U.S. S. Serial, No.
It is useful to combine inventions such as No. 354050/'73 with the present invention.

Other inventions include adding a "coacervate inducer" in the process before gelation is completed (for example, OLS212
0922, 213568, 2210367, etc.) may be combined with the present invention.

This creates a thick capsule wall membrane with low permeability.

The microcapsules obtained by this method are
Particularly suitable for pressure-sensitive paper capsules.

As described above, the production method of the present invention is a very useful invention for producing microcapsules.

The present invention will be specifically explained below using Examples.

The invention is not limited to the examples.

In the present invention, the heat resistance of the capsules is determined by dissolving 2% crystal violet lactone in oil in oil droplets, applying the resulting capsules to base paper, and then conducting a heat resistance test in a hot air drying box. Judgment was made by whether or not the clay paper surface developed color when superimposed on the clay paper.

The clay paper was made in the following way.

100 parts of sulfuric acid treated acid clay to 40% caustic soda aqueous solution 6
After dispersing with a homogenizer, 40 parts of Dow Latex 636 (trade name: styrene-butadiene latex manufactured by Dow Chemical Company) was added.
The material was coated onto 0 g/rrl base paper using a coating rond so that the solid content was 12 g/m.

In addition, in the following examples, "parts" indicate "parts by weight."

Example 1 6 parts of acid-treated gelatin having an isoelectric point of 7.8 and 6 parts of gum arabic were dissolved in 30 parts of water at 40°C.

To this was added 0.5 part of funnel oil as an emulsifier.

30 parts of diisopropyl biphenyl in which 2% crystal violet lactone (CVL) was dissolved was added to the colloid solution with vigorous stirring to form an o/w emulsion, and stirred when the oil droplet size became 6-10μ. stopped.

To this was added 250 parts of 45°C hot water.

Then, while stirring, 50% acetic acid was added dropwise to adjust the pH to 4.5.

After maintaining this temperature for 15 minutes with stirring, the container was cooled from the outside to gel and fix the deposited colloid wall.

While stirring, when the liquid temperature was 15° C., 10 parts of a 40% aqueous methylglyoxal solution and 0.2 part of a 3.7% formaldehyde aqueous solution were simultaneously added.

When the liquid temperature was 10° C., a 10% aqueous solution of caustic soda was started to be added dropwise, and the pH was finally adjusted to 10.

After standing for 30 minutes, the temperature of the liquid was raised to 50° C. in 20 minutes to obtain CVL-dissolved diisopropyl biphenyl-containing capsules with no yellow coloration and high heat resistance.

When the viscosity of this capsule liquid was measured, it was 65 cp when the pH was 10. It was 14 cp after the temperature was raised to 50°C.

If formaldehyde was not added together, the pH would be 1.
78 cp when the temperature is 0, and 20 cp after raising the temperature to 50°C.
6 cp, yellow coloration, and formation of huge floc-like capsules, a very serious problem.

Example 2 40 parts of diisopropylbiphenyl and degree of chlorination 20% by weight
, CV to 10 parts of chlorinated normal paraffin having 14 carbon atoms
1 part of L and 0.7 part of benzoylleucomethylene blue were dissolved.

This oily liquid was added to an aqueous solution consisting of 7 parts of gum arabic and 60 parts of hot water at 40 DEG C. to prepare an oil-in-water emulsion with oil droplets of 6 to 10 microns.

Next, add 10 parts of acid-treated gelatin having an isoelectric point of 8.1 to 40
An aqueous solution dissolved in 80 parts of warm water at °C was added, and with constant stirring, 50% acetic acid was added to adjust the pH to 4.3.

Then, 7JO of 250 parts of 40°C warm water was added to induce coacervation.

While stirring was continued, the container was cooled from the outside to solidify the colloid deposited around the oil droplets.

When the liquid temperature reached 10°C, 0.7 parts of a 40% methylglyoxal aqueous solution was added, and a 10% carboxymethyl cellulose sodium salt aqueous solution (hereinafter referred to as CMC solution) (degree of etherification 0.75, 2% aqueous solution 25 parts) was added. Add 40 parts (viscosity 16 cp at
was set to 10.

Then, 1.0 part of a 37% formaldehyde aqueous solution was added, and the temperature of the solution was raised to 50°C.

At this time, the viscosity of the liquid was 15 cp.

The capsule shape was normal, and no yellow discoloration of the capsule fluid was observed.

After coating this capsule liquid on base paper, it was subjected to a heat resistance test for 3 hours in a drying box at 150°C.

When this capsule paper was superimposed on the clay paper surface and copied with a ballpoint pen, a clear colored mark was obtained on the clay paper surface.

In this example, when formaldehyde was not added after adjusting the pH to 10, the viscosity after raising the temperature to 50°C was 3.
The concentration increased sharply to 62 cp, resulting in an unfavorable yellowing of the capsule liquid.

Example 3 A hydrophobic oily liquid prepared by dissolving 1 part of CVL in 40 parts of phenylcyclohexane was added to an aqueous solution consisting of 10 parts of gum arabic and 60 parts of hot water to prepare an oil-in-water emulsion with oil droplets of 8 to 11 microns.

Next, add 10 parts of acid-treated gelatin having an isoelectric point of 8.0 to 40 parts.
An aqueous solution dissolved in 80 parts of warm water at .degree. C. was added, and with constant stirring, 50% acetic acid was added to adjust the pH to 4.5.

Coacervation was then caused by adding 250 parts of hot water at 40°C.

While stirring was continued, the container was cooled from the outside to solidify the colloid deposited around the oil droplets.

When the liquid temperature reached 10°C, add 10% CMC solution 40
10% aqueous sodium hydroxide solution was added to bring the pH to 11.

Thereafter, a mixed solution consisting of 0.15 part of a 40% aqueous methylglyoxal solution and 0.4 part of a 37% aqueous formaldehyde solution was added dropwise.

The viscosity after the completion of dropping was 43 cp.

In order to completely harden the capsule wall membrane and obtain capsules with excellent heat resistance, stirring was continued for 2 days to allow the liquid temperature to rise naturally.
It was set to ℃.

There is no problem with the shape and color of the capsule, and the viscosity is 18 cp.
Met.

In this example, when methylglyoxal was added dropwise in the same amount as before without adding formaldehyde in combination, the viscosity of the capsule liquid after dropping was 107 cp, and after further stirring for 2 days, the viscosity increased significantly to 572 cp, resulting in a large increase in capsule size. were irregularly shaped and the largest ones were 2 mm to 3 mm.

The capsule liquid was also colored yellow.

Example 4 A hydrophobic oily liquid prepared by dissolving 1 part of CVL in 30 parts of diisopropylnaphthalene was emulsified into a colloidal sol consisting of 0.5 parts of methylcellulose, 4 parts of gum arabic, and 25 parts of warm water.
An o/w emulsion was made.

Stirring was stopped when the oil droplets reached a maximum size of 10 μm.

This was mixed with 6 parts of acid-treated gelatin having an isoelectric point of 7.9, 45
It was added to an aqueous gelatin solution consisting of 170 parts of °C warm water.

While stirring, add 5.0% succinic acid aqueous solution to adjust the pH to 4.
．． Adjusted to 2.

The coacervate wall film was gelled and fixed by cooling the container from the surrounding area while continuing to stir slowly.

40% methylglyoxal aqueous solution 3.0 at 10℃
1 part and 0.3 parts of a 3.7% formaldehyde aqueous solution were simultaneously added, and then 30 parts of a 5% CMC aqueous solution was added.

Add 10% caustic soda aqueous solution to adjust the pH of the solution to 10.5.
Adjusted to.

The viscosity at this time was 67 cp. Capsule liquid at 50℃
The capsules were heated to a temperature of 100° C. to obtain cured capsules with no yellow coloration.

The viscosity at this time was 15 cp.

During this experiment, when formaldehyde was not added together, it was 78 cp at pH 10.5, and 29 cp after raising the temperature to 50°C.
When the concentration reached 2 cp, the capsule liquid turned bright yellow and a huge floc-like capsule was formed.

Example 5 6 parts of acid-treated gelatin having an isoelectric point of 7.8 and 6 parts of gum arabic were dissolved in 35 parts of hot water at 40°C.

To this was added 0.3 parts of sodium alkylbenzenesulfonate as an emulsifier, and 35 parts of xylyl phenylethane in which 2% CVL was dissolved was emulsified to produce an o/w emulsion.

The oil droplet size was 8-12μ.

Aqueous solution 2 at 45°C containing 0.08% sodium sulfate
The above emulsion was poured into 0.00 parts, and while stirring, a 50% acetic acid aqueous solution was added dropwise to adjust the pH to 4.3.

Next, 0.2 parts of 40% methylglyoxal aqueous solution and 3 parts
．． After simultaneously adding 1.5 parts of a 7% formaldehyde aqueous solution, the container was cooled from the outside to bring the liquid temperature to 8°C.

Then, 25 parts of a 7% CMC aqueous solution was added, and a 10% caustic soda aqueous solution was added dropwise to adjust the pH to 9.5.

The viscosity at this time was 42 cp.

The solution was heated to a temperature of 50°C. The viscosity at this time is 13c
At p, the capsule liquid did not turn yellow at all, and no abnormality was observed in the shape of the capsule.

In this example, when formaldehyde was not added together, at pH 9.5, it was 88 cp, and after raising the temperature to 50°C, it was 1
The viscosity increased significantly to 184 cp, the capsule liquid was colored bright yellow, and huge floc-like capsules were formed.

Claims (1)

[Scope of Claims] 1. In the pre-hardening treatment step of the microencapsulation step of hydrophobic oil droplets by complex coacervation of hydrophilic colloids, ketoaldehydes represented by the following general formula and formaldehyde are combined into formaldehyde and formaldehyde. 1. A method for curing microcapsules, which is characterized in that the microcapsules are used in combination, such as at the same time as or added later. General formula (where R represents a lower alkyl group)