JP2007000756A - Alkali-soluble microcapsule - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an alkali-soluble microcapsule which is dissolved quickly according to the optionally predetermined temperature or pH condition in a specific alkaline region while keeping heat resistance, strength and transparency to release an involved material and toxicity of which is made low. <P>SOLUTION: The microcapsule is characterized in that the outer skin of the microcapsule is formed by hardening hydrophilic colloid having a carboxyl group by using a compound having an oxazoline group. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a soluble microcapsule. More specifically, the present invention relates to a microcapsule in which a film is formed by a specific hydrophilic colloid and a compound having an oxazoline group (hereinafter sometimes referred to as an oxazoline compound). The present invention relates to alkali-soluble microcapsules that can be solubilized at any given temperature in the region and release inclusions.

Conventionally, microcapsules have been applied to various uses, and many proposals have been made regarding their production methods. For example, a complex coacervation method, which is one of the microencapsulation methods applied industrially, produces microcapsules by the following treatment example.
(1) A core substance (oil-based substance) is dispersed in an aqueous solution containing a film substance (polycation) to obtain an O / W emulsion in which oil droplets are dispersed in the aqueous solution.
(2) A polyanion is added to the emulsion and mixed, and an acid is added to adjust the pH to about 3-5. As a result, coacervation occurs and a coacervate film is formed.
(3) The film of coacervate droplets is gelled at a low temperature, and a curing agent is further added to cure (crosslink and / or modify) the film.

  In such a method, aldehydes such as formaldehyde and glutaraldehyde are generally used as a curing agent for the microcapsule film. However, although aldehydes are effective curing agents, they have high reactivity, and it has not been possible to arbitrarily solubilize microcapsules that have been cured once and release the inclusions. In addition, it is highly toxic and cannot be used for oral use. In other uses and production processes, it is not preferable to use it from the viewpoint of toxicity and consideration for the environment. Both formaldehyde and glutaraldehyde have been designated as PRTR Class 1 Designated Chemical Substances. In particular, formaldehyde has been suspected as a causative substance of sick house syndrome in recent years, and volatile organic compounds (hereinafter referred to as VOCs). It is positioned as a substance subject to emission control. For this reason, various studies have been made to form solubilized microcapsules with a curing agent other than aldehydes.

There are various proposals for the study of solubilized microcapsules.
For example, Patent Document 1 and the like propose a capsule having a wall material made of a polymer soluble in an alkaline aqueous solution as a heat-developable copying material. Examples of the alkali-soluble polymer include styrene-acrylic polymers and the like, but a relatively special polymer is used because the application is a heat-developable copying material. Therefore, the capsule formation is somewhat lacking in versatility in the production method, as exemplified by using the heated phase separation method. Further, the polymer was not suitable for edible or oral use.

  In addition, Patent Document 2 proposes an edible microcapsule containing oil as a solubilized microcapsule utilizing the protective colloid property of gelatin. However, there is no specific description regarding the release of inclusions, and there is no description regarding the present invention regarding the method for hardening gelatin.

On the other hand, a compound (polymer) having an oxazoline group has been proposed as a curable resin composition as a laminated film, an inkjet recording paper, a silver halide photographic light-sensitive material, etc. (Patent Documents 3 to 5). The oxazoline group can react with a carboxyl group, and some examples of the carboxyl group-containing substance include gelatin. Accordingly, the reaction itself between the carboxyl group and the oxazoline group and the hardening of gelatin and the oxazoline compound are known per se.
However, these uses are primarily related to coatings and react at relatively high temperatures. In some cases, when a compound having an oxazoline group is used, it is disclosed that it can be cured at a relatively low temperature (for example, 60 to 120 ° C.) (Patent Document 3). It was not intended to obtain a microcapsule holding a desired inclusion.
Japanese Patent Laid-Open No. 11-109549 Japanese Patent Laid-Open No. 60-37934 JP-A-5-25361 Japanese Patent Laid-Open No. 11-231447 JP 2002-296723 A

  The present invention is an alkali-soluble microcapsule that has heat resistance, strength, and transparency, can be quickly solubilized at any predetermined temperature and pH conditions in a specific alkaline region, and release inclusions. Furthermore, the present invention intends to provide a low-toxic alkali-soluble microcapsule.

In order to solve the above-mentioned problems, the present invention provides an alkali-soluble microcapsule according to the present invention by forming a hydrophilic colloid having a carboxyl group with a compound having an oxazoline group in forming a microcapsule film. Etc. were completed.
That is, the present invention
“1. An alkali-soluble microcapsule having a film obtained by curing a hydrophilic colloid having a carboxyl group with a compound having an oxazoline group.
2. 2. The microcapsule according to item 1, wherein the compound having an oxazoline group is a polymer compound.
3. Item 3. The microcapsule according to Item 1 or 2, wherein the hydrophilic colloid is gelatin. ".

According to the present invention, an alkali that has heat resistance, strength, and transparency, has low toxicity, can be quickly solubilized at any given temperature and pH conditions in a specific alkali region, and can release inclusions. Soluble microcapsules can be obtained.
In addition, there is no need to adjust the pH to the alkaline region when the microcapsule film is cured, and the phenomenon such as thickening of the microcapsule dispersion, aggregation of the microcapsules, and swelling of the microcapsule film can be avoided. Obtainable.

Method for Producing Microcapsule The alkali-soluble microcapsule of the present invention is characterized by forming a microcapsule by curing a hydrophilic colloid having a carboxyl group with a compound having an oxazoline group.
Here, the hydrophilic colloid indicates a molecular colloid or the like that exists in a solvent and can be coordinated around a core substance to form an emulsion.
For example, hydrophilic colloids having a carboxyl group (hereinafter sometimes referred to as basic film substances) include water-soluble proteins such as gelatin and albumin, natural polymer substances such as starch, agar, and gum arabic, carboxymethylcellulose, and carboxymethyl. Synthetic cellulose ethers such as hydroxyethyl cellulose, synthetic polymer compounds such as polyvinyl methyl ether / maleic anhydride copolymer, carboxyl group-modified polyvinyl alcohol, and the like are used. Can do. Among them, a water-soluble protein having gelling property is preferable for use as a basic film substance. Further, gelatins such as alkali-treated gelatin and acid-treated gelatin are preferable, and among them, alkali-treated gelatin is most suitable. Gelatin has no toxicity and is suitable for edible and oral use.
Gelatin is roughly classified into acid-treated gelatin and alkali-treated gelatin according to the difference in the treatment method when extracting from collagen. Alkali-treated gelatin undergoes deamidation of amino acid side chains in the calcination treatment step, and has a higher amount of modification to carboxyl groups than acid-treated gelatin. Since the oxazoline group has high activity with respect to the reaction with the carboxyl group, alkali-treated gelatin having many carboxyl groups is suitable as a cross-linking material by the oxazoline compound.

As an example using the complex coacervation method, the microcapsules of the present invention are described according to the order of the manufacturing process as follows. However, it goes without saying that other methods can be used as a method for producing microcapsules.
First, a core material (oil-based substance) is dispersed in an aqueous solution containing a carboxyl group-containing hydrophilic colloid, that is, a basic film material, thereby forming an O / W emulsion in which oil droplets are dispersed in the aqueous solution.

  The core substance to be used is arbitrarily selected according to the target microcapsule. Examples include pressure-sensitive adhesives, adhesives, coloring materials, foods, pharmaceuticals, quasi drugs, agricultural chemicals, insect repellents, fertilizers, fragrances, detergents, and the like, and those that are immiscible with water can be used as the core substance.

  As the hydrophilic colloid (basic film substance) having a carboxyl group, a gelable hydrophilic colloid having an isoionic point as a polycation is used, and a water-soluble protein is generally used. More specifically, gelatin, agar, casein, soybean protein, collagen, albumin and the like can be mentioned. Of these, gelatin such as acid-treated gelatin and alkali-treated gelatin is preferred, and alkali-treated gelatin is most preferred.

  In order to disperse the core substance in the aqueous solution containing the basic film substance, a method such as stirring and ultrasonic irradiation can be used by adding the core substance to the aqueous solution. The concentrations of the core substance and the film substance are arbitrarily selected depending on the properties and shapes required for the target microcapsules. Further, the size of the core material droplet obtained by the dispersion is related to the size of the microcapsule finally obtained. The size of the microcapsules is selected according to the purpose, and the size of the droplets of the emulsion is substantially reflected as the particle size of the microcapsules. The final size of the microcapsules is specifically, oil droplets corresponding to a sphere equivalent diameter of generally 0.1 to 3000 μm, preferably 0.1 to 2000 μm, more preferably 0.1 to 1000 μm. Disperse as follows.

  Subsequently, a polyanion is mixed into the obtained O / W emulsion to make it uniform, and then the pH is acidified to form a coacervate film.

  The polyanion to be used is selected as necessary, and specific examples thereof include gum arabic, sodium carboxymethylcellulose, sodium alginate, sodium polyvinylbenzenesulfonate, polyvinylmethyl ether / maleic anhydride copolymer, and the like. Of these, gum arabic and sodium carboxymethyl cellulose are preferably used.

  After mixing the polyanions, the pH of the emulsion is adjusted to acidic, for example, pH = 3-5, preferably 4-5. The acid used at this time is preferably selected from those that do not impair the properties of the core material and the coating material, and those that do not inhibit the curing reaction. In general, organic acids such as acetic acid, citric acid, succinic acid, oxalic acid, lactic acid and salicylic acid, and inorganic acids such as hydrochloric acid, sulfuric acid and phosphoric acid are used.

  The emulsion on which the coacervate film is formed is subsequently cooled in order to gel the film. Usually, the emulsion is cooled to 5 to 25 ° C., preferably 5 to 10 ° C. to gel the film.

（式中、Ｒ1、Ｒ2、Ｒ3、Ｒ4、はそれぞれ独立に水素、ハロゲン、アルキル、アラルキル、フェニルまたは置換フェニルを表し、Ｒ5 は付加重合性不飽和結合を持つ非環状有機基を表す。） In order to cure the gelled film, a curing agent is subsequently mixed into the emulsion. Although it can be cured with aldehydes such as formaldehyde and glutaraldehyde which are conventionally known, they cannot be alkali-soluble and cannot be used from the viewpoint of toxicity and environmental considerations.
Therefore, in the present invention, a compound having an oxazoline group is used as a curing agent. Such a so-called oxazoline compound is a compound having an oxazoline group as shown in (Chemical Formula 1). For example, 2,2′-bis- (2-oxazoline), 2,2′-methylene-bis- ( 2-oxazoline), 2,2′-ethylene-bis- (2-oxazoline), 2,2′-trimethylene-bis- (2-oxazoline), 2,2′-tetramethylene-bis- (2-oxazoline) 2,2′-hexamethylene-bis- (2-oxazoline), 2,2′-octamethylene-bis- (2-oxazoline), 2,2′-ethylene-bis- (4,4′-dimethyl-) 2-oxazoline), 2,2'-p-phenylene-bis- (2-oxazoline), 2,2'-m-phenylene-bis- (2-oxazoline), 2,2'-m-phenylene-bis- (4,4'-dimethyl- 2-oxazoline), bis- (2-oxazolinylcyclohexane) sulfide, bis- (2-oxazolinyl norbornane) sulfide, and the like. Further, as addition polymerizable oxazoline compounds, 2-vinyl-2-oxazoline, 2-vinyl-4-methyl-2-oxazoline, 2-vinyl-5-methyl-2-oxazoline, 2-isopropenyl-2-oxazoline, 2 -Isopropenyl-4-methyl-2-oxazoline, 2-isopropenyl-5-ethyl-2-oxazoline and the like. Those obtained by polymerizing or copolymerizing one or more of these compounds can be used.
Further, the compound and (meth) acrylic acid esters such as methyl (meth) acrylate, butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate; unsaturated nitriles such as (meth) acrylonitrile; Unsaturated amides such as meth) acrylamide and N-methylol (meth) acrylamide; vinyl esters such as vinyl acetate and vinyl propionate; vinyl ethers such as methyl vinyl ether and ethyl vinyl ether; α-olefins such as ethylene and propylene; Halogenated α, β-unsaturated monomers such as vinyl chloride, vinylidene chloride and vinyl fluoride; copolymers of α, β-unsaturated aromatic monomers such as styrene and α-methylstyrene Can also be used.
As an example of such a compound, the oxazoline compounds described in Patent Document 3, Patent Document 4 and the like can be exemplified.
Specific examples of commercially available products include Epocross WS-500, Epocross WS-700, Epocross K-1010E, Epocross K-1020E, Epocross K-1030E, Epocross K-2010E, Epocross K-2020E, Epocross K-2030E. , Epocross RPS-1005, Epocross RAS-1005 (all manufactured by Nippon Shokubai Co., Ltd.), NK Linker FX (Shin Nakamura Chemical Co., Ltd.) and the like.

(In the formula, R1, R2, R3, and R4 each independently represent hydrogen, halogen, alkyl, aralkyl, phenyl, or substituted phenyl, and R5 represents an acyclic organic group having an addition polymerizable unsaturated bond.)

The compound having an oxazoline group is preferably a polymer compound. Here, the polymer compound means a compound having a number average molecular weight of 10,000 or more.
Further, when the polymer compound has film-forming properties, effects such as further improvement of the strength of the microcapsule film and improvement of the holding ability of the inclusions can be obtained. This is presumed to be because the curing agent itself has film-forming properties, so that the coating substance is cured, and at the same time, a double coating is formed by the curing agent itself, thereby strengthening the microcapsule film.
Here, the film forming property means having a film-like film forming property when a solution of a polymer compound having an oxazoline group alone is applied and evaporated to dryness.
In addition to further improving the strength of the capsule film, it is possible to obtain favorable effects such as improvement in sealing performance, flexibility and flexibility.
However, when alkali solubilization is concerned, there are concerns about the lack of quick response, and caution is required. When it is desired to obtain a so-called sustained-release microcapsule that does not immediately solubilize but dissolves gradually, it can be used as an effective method.

  After the coating is cured in this way, the desired microcapsules can be obtained by operations such as filtration, decantation, dehydration, liquid separation, and drying as necessary.

  In addition to the above components, the composition of the microcapsule contains a third component in a range that does not adversely affect the performance of the microcapsule, such as not inhibiting the curing by the oxazoline group compound, or to give a special effect. You can also For example, when an onium salt such as diammonium hydrogen phosphate is blended, it may act as a curing catalyst.

  When an uncured gel film is subjected to a curing reaction in an aqueous solution, it is problematic to set the treatment temperature to be equal to or higher than the gel point of the basic film material. This is because a gel film that does not have heat resistance before curing readily dissolves in water at a temperature above its gel point. In addition, there is a problem that the microcapsules tend to aggregate at a temperature near the gel point. In particular, it is very difficult to dispose the basic film material at an arbitrary position and shape with respect to the periphery of the core material (encapsulated material) like a microcapsule and to desire curing while maintaining the state. For example, the general gel point of an aqueous gelatin solution, which is a kind of basic film material, is around 25 ° C.

There are no examples of microcapsules obtained by curing a basic film material such as gelatin with an oxazoline compound.
Examples of appropriate reaction conditions when using an oxazoline compound as a curing agent in the present invention are shown below. According to this condition, the film can be cured in water, and a suitable microcapsule can be cured.

Curing with the oxazoline compound in the complex coacervation method needs to be performed after separating the uncured basic film substance (gelatin) microcapsule from the adjustment liquid and washing the microcapsule several times with water. If such an operation is not performed, sufficient curing cannot be achieved. This is because when microcapsules are prepared by the complex coacervation method, polyanions necessary for coacervation and undeposited (dissolved) basic coating substance (gelatin) molecules are present in the aqueous solution in which the microcapsules are dispersed. Is considered to exist. As the polyanion, a compound having a carboxyl group (such as gum arabic or carboxymethyl cellulose) is generally used. In addition, the basic film substance (gelatin) molecule naturally has a carboxyl group.
That is, in the microcapsule dispersion in this state, as a carboxyl group-containing component that can react with the oxazoline group,
a) Basic film substance molecules in dissolved state (gelatin, etc.)
b) Dissolved polyanion molecules (gum arabic, carboxymethyl cellulose, etc.)
c) Dispersed basic film material gel (gelatin gel, etc.)
Can be said to exist. This is because it is presumed that it is necessary to remove dissolved a) and b) in order to efficiently react the dispersed basic film substance (gelatin gel) with the oxazoline compound.

The oxazoline compound reacts with all the hydrophilic colloids having a carboxyl group to give microcapsules having a cured film. As the hydrophilic colloid having a carboxyl group, a water-soluble protein is preferable, and gelatin is particularly preferable. In particular, those having a pI (isoionic point) of 4.9 to 8.1 are desirable, and alkali-treated gelatin is more preferred. This is because gelatin in this range and type is likely to be a mononuclear microcapsule and contributes to the quick response to alkali solubilization.
In the present invention, the measured value of pI is a value obtained by treating an aqueous gelatin solution with an ion exchange resin and then measuring the pH of the aqueous gelatin solution at 35 ° C., but other commonly used pI (isoionic point: Isoionic point) measurements and equivalents can also be used.
The oxazoline compound forms a hardened film on gelatin in general, and a suitable microcapsule can be obtained. However, a microcapsule using gelatin whose pI exceeds 8.1 (for example, acid-treated gelatin) is allowed to stand after hardening. When stored over time in the (rt) state, the microcapsules tend to aggregate together, making redispersion difficult.
pI represents an isoionic point of gelatin or the like, which can be said to indicate the amount of carboxyl groups and amino groups of the basic film substance (gelatin) molecules.
Gelatin with a low pI indicates that the acid amide bond of the amino acid side chain is decreased by deamidation and the carboxyl group is increased. Since the oxazoline group reacts with the carboxyl group, it is considered that as the amount of the carboxyl group increases, the number of crosslinking points by the basic film substance (gelatin) and the oxazoline compound increases. That is, sufficient crosslinking can be secured, and it is presumed that stable microcapsules can be easily obtained over time.
As described above, when the pI value is 4.9 to 8.1, it is easy to form a mononuclear microcapsule without aggregation.

  The reaction between the oxazoline compound and the basic film material is r. t. Progress even under conditions. However, as in general organic reactions, it is desirable to advance the reaction by heating as much as possible. For this reason, it is possible to secure the reaction temperature and to perform a desired treatment in a shorter time by using a basic film substance having a gel point as high as possible.

  In addition, although this example demonstrated by the complex coacervation method, it is as above-mentioned that a similar effect can be acquired also by other microcapsule manufacturing methods, such as a simple coacervation method and an orifice method.

Microcapsule The microcapsule according to the present invention is a film formed by curing a basic film substance, which is a hydrophilic colloid having a carboxyl group, with a compound having an oxazoline group, and is obtained by the above-described manufacturing process of the microcapsule. .
As a result, microcapsules that can be solubilized with alkali at a specific pH and temperature can be obtained.

The microcapsules according to the present invention can be used for various applications by selecting a core material and a coating material. Specific examples include adhesives, adhesives, coloring materials, foods, pharmaceuticals, quasi drugs, agricultural chemicals, insect repellents, fertilizers, fragrances, and cleaning agents. That is, it can be used for applications in which it is desired to release the inclusions at a specific pH (alkaline region) temperature while maintaining the inclusions and maintaining the heat resistance and strength under normal conditions.
In these applications, since it is necessary to consider toxicity, it is preferable not to use toxic aldehydes such as formaldehyde and glutaraldehyde as the material of the microcapsules. Also, toy, stationery and the like are not preferable because volatilization of formaldehyde, which is a VOC, accidents due to incorrect usage, and the like are assumed. That is, it is preferable that the film does not substantially contain aldehydes having high toxicity that can cause VOC and sick house syndrome, which are substances subject to emission control.

  The alkali-soluble microcapsules of the present invention become soluble at a predetermined temperature of 20 to 80 ° C. in the alkaline region of pH = 11 to 14. The pH range and the predetermined temperature are determined by selection of a hydrophilic colloid (basic film substance) having a carboxyl group to be used.

  Hereinafter, the present invention will be described using various examples.

Example 1
Maintaining the temperature of the system at 40 ° C., 10 mass% alkali-treated gelatin aqueous solution (Nippi Corporation AD pI: 5.06) While stirring 60 mass parts, 80 mass parts of 40 ° C. warm water (ion exchange water), isoparaffin (Isopar M manufactured by Esso Chemical Co., Ltd.) 80 parts by mass were sequentially added and emulsified and dispersed to form an O / W emulsion. Furthermore, 60 mass parts of 1.25 mass% carboxymethylcellulose aqueous solution (Daiichi Kogyo Seiyaku Co., Ltd. cellogen F-7A) was mixed as a polyanion, and it was made uniform. 10% by mass hydrochloric acid (a reagent manufactured by Wako Pure Chemical Industries, Ltd.) was added to adjust the pH to 4.2, thereby forming a coacervate film. The emulsion was gradually cooled to 5 ° C. while stirring to gel the film, and kept at 30 min / 5 ° C. for stabilization. The cooled microcapsule dispersion was transferred to a separatory funnel and allowed to stand to separate into a microcapsule layer and a dispersion layer. Ion exchange water cooled to 5 ° C. was added to the separated microcapsule layer, and after stirring and washing, the microcapsule layer and the dispersion layer were separated again. After repeating this operation several times, the washed microcapsule dispersion was transferred to a beaker and stirred. The temperature of the system was raised to 25 ° C., and 48.9 parts by mass of an oxazoline polymer compound (Nippon Shokubai Epocros WS-700) was adjusted to pH 4.0 with 10% by mass hydrochloric acid (a reagent manufactured by Wako Pure Chemical Industries, Ltd.). The adjusted one was added. 10% by mass hydrochloric acid (reagent manufactured by Wako Pure Chemical Industries, Ltd.) was added to adjust the pH to 4.0, and stirring was continued for 67 h while the system temperature was kept at 25 ° C. to disperse the microcapsules with the cured film. A liquid was obtained. The obtained microcapsules were mononuclear microcapsules having no heat swell and heat resistance.

Examples 2-6
Microcapsules were produced in the same manner as in Example 1 except that the gelatin type was changed to that shown in Table 1. In Examples 4 to 6, the pH during the formation of the coacervate film when using acid-treated gelatin was adjusted to 4.6.
The pH was measured with a glass electrode type hydrogen ion concentration meter (HM-30S manufactured by Toa DKK Corporation).

Table 2 shows the results of evaluating the pH dependence of the solubility of the microcapsules of Example 1.
Whether or not the microcapsules could be dissolved was collected every time the pH of the aqueous solution was adjusted, and immediately transferred to a screw tube and observed. In adjusting the pH, 10% by mass hydrochloric acid and 10% by mass sodium hydroxide aqueous solution were appropriately used.

これらの表からグラフを書くと図１に示したように一定の温度とｐＨによる可溶化領域が判る。
図中のＡの領域がマイクロカプセルの可溶化領域である。本実施例にて基本皮膜物質として用いたゼラチンにおける可溶化境界線を越えるとマイクロカプセルはすみやかに溶解する。
その境界線は、ｆ(x)＝−１９Ｘ＋２９０ で表すことができ、
ｆ(x)＋１９Ｘ≧２９０ のとき、マイクロカプセルが溶解し、
ｆ(x)＋１９Ｘ＜２９０ のとき、マイクロカプセルの形状を保持する。
すなわち、ｐＨ＝１１のときは、約８０℃以上で可溶化する。
ｐＨ＝１４のときは、約２０℃以上で可溶化する。
ｐＨ＝１１未満では、水溶液の温度を上げても可溶化しないことが判る。
この可溶化境界線については、用いる基本皮膜物質等に固有の性質であり、その選定に応じてある程度、任意の可溶化条件を得ることができる。 Next, the soluble point at other temperatures was evaluated. The results are shown in Table 3.
The acid-treated gelatin used in Example 6 was used.

When the graphs are drawn from these tables, the solubilized region at a certain temperature and pH can be seen as shown in FIG.
The area A in the figure is the solubilized area of the microcapsules. When the solubilization boundary line in the gelatin used as the basic film material in the present example is exceeded, the microcapsules dissolve immediately.
The boundary line can be expressed as f (x) = − 19X + 290,
When f (x) + 19X ≧ 290, the microcapsule is dissolved,
When f (x) + 19X <290, the shape of the microcapsule is maintained.
That is, when pH = 11, it is solubilized at about 80 ° C. or higher.
When pH = 14, it is solubilized at about 20 ° C. or higher.
It can be seen that when the pH is less than 11, it is not solubilized even if the temperature of the aqueous solution is increased.
About this solubilization boundary line, it is a property intrinsic | native to the basic film substance etc. to be used, and arbitrary solubilization conditions can be obtained to some extent according to the selection.

Comparative Example 1
Maintaining the temperature of the system at 40 ° C., 10 mass% alkali-treated gelatin aqueous solution (Nippi Corporation AD pI: 5.06) While stirring 60 mass parts, 80 mass parts of 40 ° C. warm water (ion exchange water), isoparaffin (Isopar M manufactured by Esso Chemical Co., Ltd.) 80 parts by mass were sequentially added and emulsified and dispersed to form an O / W emulsion. Furthermore, 60 mass parts of 1.25 mass% carboxymethylcellulose aqueous solution (Daiichi Kogyo Seiyaku Co., Ltd. cellogen F-7A) was mixed as a polyanion, and it was made uniform. 10% by mass acetic acid (a reagent manufactured by Wako Pure Chemical Industries, Ltd.) was added to adjust pH to 4.2 to form a coacervate film. The emulsion was gradually cooled to 5 ° C. while stirring to gel the film, and kept at 30 min / 5 ° C. for stabilization. While maintaining the temperature of the system at 5 ° C., 3 parts by weight of an aqueous formaldehyde solution (formaldehyde solution (36-38%) manufactured by Wako Pure Chemical Industries, Ltd.) was added and stirred for 30 minutes, and then an aqueous 10% by weight sodium hydroxide solution was added. The pH was adjusted to 10.0. The temperature of the system was gradually raised to 50 ° C., held for 30 minutes, and then cooled to 20 ° C. with stirring to obtain a microcapsule dispersion in which the film was cured. The obtained microcapsules were mononuclear microcapsules having heat resistance.

Table 4 shows whether the microcapsules of Comparative Example 1 can be dissolved under strong alkali or high temperature.
From this table, it can be seen that those cured with formaldehyde are not solubilized microcapsules because they are dissolved only when pH = 14 and the temperature exceeds 40 ° C.

  In the above-mentioned Examples and Comparative Examples, the inclusion was experimentally made into a single isoparaffin system, but the inclusion can be placed for each desired purpose (Example omitted).

  INDUSTRIAL APPLICABILITY The present invention can be used for various applications as an alkali-soluble microcapsule, and can be solubilized at a predetermined temperature in an arbitrary alkali region and release inclusions depending on the core material used, for example, an adhesive. It can be used for adhesives, coloring materials, foods, pharmaceuticals, quasi drugs, agriculture, insect repellents, fertilizers, fragrances, cleaning agents, and the like.

It is a graph showing the solubilization area | region of the microcapsule of this invention.

Claims (3)

  An alkali-soluble microcapsule comprising a film obtained by curing a hydrophilic colloid having a carboxyl group with a compound having an oxazoline group.   The microcapsule according to claim 1, wherein the compound having an oxazoline group is a polymer compound. The microcapsule according to claim 1 or 2, wherein the hydrophilic colloid is gelatin.

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