JP7094260B2 - A pH-responsive microcapsule and a method for producing the same, and a resin composition for a wall material of the pH-responsive microcapsule. - Google Patents

Description

The present invention relates to microcapsules in which the wall material dissolves and releases inclusions in a specific pH range.

Conventionally, as microcapsules that release inclusion substances in a specific pH range, a hybrid gel composed of anionic or cationic polysaccharides or a copolymer of poly (N-isopropylacrylamide) (PNIPAM) and polyacrylic acid (PAA) is used. Microcapsules using pH-responsive polymers such as coalesced or yoke-shell structures, polystyrene and polyamine or copolymers of polystyrene and polyvinylpyridine are known.
For example, Non-Patent Document 1 uses a method of microencapsulating using polystyrene, Non-Patent Document 2 uses a method of microencapsulating using a copolymer of PNIPAM and PAA, and Non-Patent Document 3 contains PNIPAM. The method of microencapsulating the shell and PAA as a yoke, the method of microencapsulating using a polystyrene and polyamine copolymer in Patent Document 1, and the method of using a polystyrene and polyvinyl pyridine copolymer in Patent Document 2 are used. Each method of microencapsulation is disclosed.

Further, as a microcapsule containing a rust preventive additive for metal, an organic silicone resin-encapsulating microcapsule by a phase separation method of polyvinyl alcohol (PVA) has been proposed. Regarding such microcapsules, for example, Non-Patent Documents 4 and 5 disclose a rust preventive treatment using a composite film of copper and microcapsules.
Further, as a microcapsule containing a rust preventive additive for metal and imparting pH responsiveness, one using an amine derivative has been proposed. Regarding such microcapsules, for example, Non-Patent Document 6 discloses microcapsules containing triethanolamine.

Japanese Unexamined Patent Publication No. 2006-255536 Japanese Unexamined Patent Publication No. 2006-83544

Ghazi Ben Messaoud and four others, “Alginate / sodium caseinate aqueous-core capsules: A pH-responsive matrix”, Journal of Colloid and Interface Science, USA, Elsevier, 15 February 2015, Volume 440, p.1-8 Guofeng Zhou and five others, “A new drug-loading technique with high efficaciency and sustained-releasing ability via the Pickering emulsion interfacial assembly of temperature / pH-sensitive nanogels”, Reactive & Functional Polymers, Netherlands, Elsevier, November 2013, Volume 73 , Issue 11, p.1537-1543 Lei Liu and four others, “Independent temperature and pH dual-stimuli responsive yolk / shell polymer microspheres for controlled release: Structural effect”, European Polymer Journal, UK, Elsevier, August 2015, Volume 69, p.540-551 XU Xiu-qing and three others, “Microstructure and deposition mechanism of electrodeposited Cu / liquid microcapsule composite”, Transactions of Nonferrous Metals Society of China, China, Elsevier, October 2011, Volume 21, Issue 10, p.2210-2215 ZHU LIQUN and two others, “Electrodeposition of composite copper / liquid-containing microcapsule coatings”, Journal of Material Science, Netherlands, Kluwer Academic Publishers, January 2004, Volume 39, Issue 2, p.495-499 Hana Choi and two others, “Encapsulation of pertaining amines into nanoparticles for self-healing corrosion protection of steel sheets”, Progress in Organic Coatings, Netherlands, Elsevier, October 2013, Volume 76, Issue 10, p.1316-1324

However, since the microcapsules described in Non-Patent Document 1 and Patent Documents 1 and 2 release the encapsulated substance from the acidic to the neutral region, the encapsulated substance cannot be retained when dispersed in an aqueous solution having the pH. .. In addition, industrial production is difficult because the synthesis method is complicated.
The microcapsules described in Non-Patent Documents 2 and 3 are composed of PNIPAM and PAA, but in the acidic region because they utilize the acid-base equilibrium reaction between the sulfaziazine group or carboxyl group in PAA and the inclusion substance doxorubicin. Since the contained substance is released even in the neutral region having a large pH and a pH of 7.4, the contained substance cannot be retained when dispersed in an aqueous solution having the pH.

Further, although the microcapsules described in Non-Patent Documents 4 and 5 contain a rust preventive additive for metals, they do not have pH responsiveness, so that a physical force is required to release the rust preventive additive. The capsule wall needs to collapse due to the fact that the rust preventive additive cannot be released in response to chemical environmental changes such as metal corrosion reactions.
Further, Non-Patent Document 6 pays attention to the fact that the pH changes due to the corrosion reaction of the metal, and uses microcapsules having pH responsiveness as a corrosion inhibitor by utilizing the acid dissociation reaction of the amine derivative. , Capsule wall is synthesized by seed polymerization from core latex, which is not industrially suitable from the viewpoint of manufacturing cost. Further, since the inclusion substance is released even in the neutral region having a pH of 6.5, the inclusion substance cannot be retained when dispersed in an aqueous solution having the pH.

Therefore, an object of the present invention is to solve the above-mentioned problems of the prior art, to obtain microcapsules having high pH responsiveness to release contained substances in a specific pH range, and to be able to easily and inexpensively produce microcapsules. To provide. Another object of the present invention is to provide a production method capable of stably producing such microcapsules easily and at low cost.

As a result of diligent research to solve the above problems, the present inventors have selected one or more of N-substituted (meth) acrylamide and N-substituted (meth) acrylamide derivatives for the wall material (meth). By using one or more random copolymers selected from acrylic acid and (meth) acrylic acid derivatives, microcapsules with high pH responsiveness that release inclusion substances in a specific pH range can be obtained. In particular, since this microcapsule can have a pH responsiveness to release an inclusion substance in a region where the pH becomes 8 or more due to a metal corrosion reaction, it is suitable for a microcapsule containing a metal rust preventive additive as an inclusion substance. I found that it was a thing. Further, it was found that the microcapsules can be manufactured easily and at low cost by a manufacturing method in which the in-liquid drying method and the core selvation method are performed in parallel.

The present invention has been made based on the above findings, and has the following gist.
[1] In microcapsules in which the wall material dissolves and releases the inclusion substance in a specific pH range.
One or more random copolymers selected from N-substituted (meth) acrylamide and N-substituted (meth) acrylamide derivatives and one or more random copolymers selected from (meth) acrylic acid and (meth) acrylic acid derivatives. Equipped with a wall material whose main component is
The random copolymer is selected from one or more selected from N-substituted (meth) acrylamide and N-substituted (meth) acrylamide derivatives and one selected from (meth) acrylic acid and (meth) acrylic acid derivatives 1. A pH-responsive microcapsule having a copolymerization ratio (molar ratio) of 1.0: 0.5 to 1.0: 2.0 for each species or more.

[2] In the microcapsules of the above [1], a pH-responsive microcapsule characterized in that the pH range in which the wall material is dissolved is pH 8 or higher.
[3] In the microcapsules of the above [1] or [2], a pH-responsive microcapsule characterized in that the contained substance is a rust preventive additive for metals.
[4] In the microcapsule of the above [3], the pH-responsive microcapsule is characterized in that the rust preventive additive for metal is one or more selected from nitrates, sulfates and acetates.

[5] In the method for producing microcapsules in which the wall material dissolves in a specific pH range and releases the inclusion substance.
As the wall material substance (a) used as the wall material of the microcapsules, one or more selected from N-substituted (meth) acrylamide and N-substituted (meth) acrylamide derivatives, and (meth) acrylic acid and (meth) acrylic. A step (A) of obtaining a solution (x) in which a wall material (a) and a surfactant (c) are dissolved in a polar organic solvent (d) using one or more random copolymers selected from acid derivatives. )When,
In the step (B) of obtaining a solution (y) in which the solution (x) obtained in the step (A) is mixed with the core material (b) to be the inclusion substance of the microcapsules.
By maintaining the solution (y) obtained in the step (B) at a temperature at which the polar organic solvent (d) evaporates, the polar organic solvent (d) is evaporated, and the solution (y) is stirred while being a poor solvent. Has a step (C) of adding
The random copolymer used in the step (A) includes one or more selected from N-substituted (meth) acrylamide and N-substituted (meth) acrylamide derivatives, and (meth) acrylic acid and (meth) acrylic acid derivatives. The copolymerization ratio (molar ratio) of one or more selected from the above is 1.0: 0.5 to 1.0: 2.0.
In step (C), a method for producing pH-responsive microcapsules, wherein the rate of addition of the poor solvent to the solution (y) is 0.25 to 3.5 mL / min.

[6] In the production method of the above [5], in the step (C), the wall material substance (a) is precipitated in the solution (y), and the precipitated wall material substance (a) is a surfactant ( A method for producing a pH-responsive microcapsule, characterized in that microcapsules are formed by coating the core material (b) via c).
[7] A method for producing pH-responsive microcapsules, which comprises maintaining the solution (y) at a temperature of 30 to 60 ° C. in the step (C) in the production method of the above [5] or [6].
[8] In any of the above-mentioned production methods [5] to [7], a method for producing pH-responsive microcapsules, wherein the core material (b) is a rust preventive additive for metals.

[9] A method for producing a pH-responsive microcapsule, wherein the rust preventive additive for a metal is one or more selected from nitrates, sulfates, and acetates in the production method of the above [8].
[10] In a resin composition for a wall material of microcapsules, which dissolves the wall material in a specific pH range and releases an inclusion substance.
One or more random copolymers selected from N-substituted (meth) acrylamide and N-substituted (meth) acrylamide derivatives and one or more selected from (meth) acrylic acid and (meth) acrylic acid derivatives. A resin composition for a wall material of pH-responsive microcapsules, which comprises.

The microcapsules of the present invention are selected from one or more selected from N-substituted (meth) acrylamide and N-substituted (meth) acrylamide derivatives and one selected from (meth) acrylic acid and (meth) acrylic acid derivatives 1. By providing a wall material containing a random copolymer of more than one species as a main component, it has a high pH responsiveness to release inclusion substances in a specific pH range. In particular, the microcapsules of the present invention can have a pH responsiveness that releases an inclusion substance in a region (alkaline region) where the pH becomes 8 or more due to a metal corrosion reaction. Therefore, for example, an inclusion of a rust preventive additive for metal is included. It can be used as a substance and as a self-healing microcapsule triggered by a metal corrosion reaction. Further, the microcapsules of the present invention include one or more selected from N-substituted (meth) acrylamide and N-substituted (meth) acrylamide derivatives constituting the wall material, and (meth) acrylic acid and (meth) acrylic acid. By adjusting the copolymerization ratio of one or more random copolymers selected from the derivatives, there is an advantage that the pH level at which the inclusion substance is released can be changed according to the usage environment and application of the microcapsules. be.
Further, according to the production method of the present invention, the above-mentioned microcapsules can be stably produced easily and at low cost by a production method in which the in-liquid drying method and the core selvation method are performed in parallel. can.

Explanatory drawing schematically showing a series of steps in one Embodiment of the manufacturing method of this invention.

The microcapsules of the present invention are pH-responsive microcapsules in which the wall material dissolves in a specific pH range to release inclusion substances, and are among N-substituted (meth) acrylamide and N-substituted (meth) acrylamide derivatives. One or more selected (hereinafter, referred to as "N-substituted (meth) acrylamide or a derivative thereof" for convenience of explanation) and one or more selected from (meth) acrylic acid and (meth) acrylic acid derivative (hereinafter,). For convenience of explanation, it is characterized by comprising a wall material (capsule wall) containing a random copolymer of (referred to as "(meth) acrylamide or a derivative thereof") as a main component.

Conventionally, as microcapsules that respond to pH, those using polysaccharides are known, and they are used especially in the medical field, but since they are intended for drug delivery in vivo, they respond to pH in an alkaline region. The sex was poor. On the other hand, the microcapsules of the present invention are provided with a wall material containing N-substituted (meth) acrylamide or a derivative thereof and a random copolymer of (meth) acrylic acid or a derivative thereof as a main component as described above. It has a high pH responsiveness in which the wall material dissolves and releases the inclusion substance only in a specific pH region (for example, an alkaline region having a pH of 8 or more).

The encapsulating substance of the microcapsules of the present invention is not particularly limited as long as it does not impair the stability of the core / shell structure when producing (synthesizing) the microcapsules. It may be selected, but the rust preventive additive for metals is particularly suitable. That is, since the microcapsules of the present invention can have a pH responsiveness to release the contained substance in a region (alkaline region) where the pH becomes 8 or more due to the corrosion reaction of the metal, the rust preventive additive for metal is used as the contained substance. , Can be a self-healing microcapsule triggered by a metal corrosion reaction.

There are no particular restrictions on the metal rust preventive additive used as an inclusion substance, but nitrates, acetates, sulfates, etc. are particularly suitable because they do not impair the stability of the core / shell structure, and one or more of them is used. be able to. As the nitrate, general rust preventive additives such as cerium nitrate, aluminum nitrate and magnesium nitrate can be used. Further, as the acetate, a general rust preventive additive such as calcium acetate or magnesium acetate can be used. Further, as the sulfate salt, a general rust preventive additive such as aluminum sulfate or cobalt sulfate can be used.
When the microcapsules of the present invention are produced by a production method as described later, the contained substance must be soluble in water and insoluble or sparingly soluble in an organic solvent, and even if it is added to an organic solvent, it must be added. Since part or all of it does not dissolve in the organic solvent, a dispersion treatment for dispersing it in the organic solvent is required. The above-mentioned nitrates, acetates, sulfates and the like (rust preventive additives for metals) are also such substances.

In the microcapsules of the present invention, N-substituted (meth) acrylamide or a derivative thereof, which is the main component of the wall material, and N-substituted (meth) acrylamide or a derivative thereof constituting a random copolymer of (meth) acrylic acid or a derivative thereof. Examples of the derivative include N-methylacrylamide, N-methylmethacrylamide, N-methylolacrylamide, N-methylolmethacrylamide, N-methoxymethylacrylamide, N-methoxymethylmethacrylamide, N-ethoxymethylacrylamide, and N-ethoxy. Methylmethacrylamide, N-propoxymethylacrylamide, N-propoxymethylmethacrylamide, N-butoxymethylacrylamide, N-butoxymethylmethacrylamide, N-phenoxymethylacrylamide, N-phenoxymethylmethacrylamide, N-ethylacrylamide, N- Examples thereof include ethyl methacrylamide, Nn-propylacrylamide, Nn-propylmethacrylamide, N-isopropylacrylamide, N-isopropylmethacrylamide, N-cyclopropylacrylamide, N-cyclopropylmethacrylamide, and the like. Seeds or two or more species can be used.

Further, in the microcapsules of the present invention, (meth) acrylic acid or a (meth) acrylic acid constituting a random copolymer of N-substituted (meth) acrylamide or a derivative thereof, which is the main component of the wall material, and (meth) acrylic acid or a derivative thereof. The derivative is not particularly limited as long as it has a carboxyl group and can be copolymerized with N-substituted (meth) acrylamide or a derivative thereof, and one or more of those (meth) acrylic acids or derivatives thereof is used. be able to. As the acrylic acid derivative, for example, ethoxytriethylene glycol acrylate and the like can be used, and as the methacrylic acid derivative, for example, 2-diethylaminoethyl methacrylate, ethylene glycol dimethacrylate, glycidyl methacrylate and the like can be used.

Here, the random copolymer of N-substituted (meth) acrylamide or a derivative thereof and (meth) acrylic acid or a derivative thereof can obtain a desired pH responsiveness by dissolving each polymer chain, but has a block copolymer weight. In the case of coalescence, since the molecular weight of each polymer chain is high, for example, poly (N-isopropylacrylamide) cannot be dissolved even at a pH at which polyacrylic acid is dissolved, and therefore a sufficient pH response is obtained. I can't get sex. Therefore, in the present invention, a random copolymer of N-substituted (meth) acrylamide or a derivative thereof and (meth) acrylic acid or a derivative thereof is used as a wall material.

A random copolymer of N-substituted (meth) acrylamide or a derivative thereof and (meth) acrylic acid or a derivative thereof is a copolymerization ratio of N-substituted (meth) acrylamide or a derivative thereof and (meth) acrylic acid or a derivative thereof. The molar ratio) is 1.0: 0.5 to 1.0: 2.0. When the ratio of (meth) acrylic acid or its derivative to 1.0 mol of N-substituted (meth) acrylamide or its derivative is less than 0.5 mol, the wall material does not dissolve even in the high pH region, and pH responsiveness is obtained. do not have. On the other hand, when the ratio of (meth) acrylic acid or its derivative to 1.0 mol of N-substituted (meth) acrylamide or its derivative is more than 2.0 mol, the wall material starts to dissolve even in the region below pH 8, so that it is neutral. Partially dissolves even in the aqueous solution of.

As described above, the microcapsules of the present invention can have a pH responsiveness in which the wall material dissolves when the pH rises due to the corrosion reaction of the metal and becomes an alkaline region of pH 8 or higher. For example, N-. Adjusting the pH range in which the wall material dissolves by adjusting the ratio of (meth) acrylic acid or its derivative to 1.0 mol of substituted (meth) acrylamide or its derivative in the range of 0.5 mol to 2.0 mol. (For example, shift to the high pH side or the low pH side in the region of pH 8 or higher). That is, the lower the ratio of (meth) acrylic acid or its derivative to N-substituted (meth) acrylamide or its derivative, the higher the pH range in which the wall material dissolves, so it depends on the usage environment and application of the microcapsules. The pH level at which the inclusion substance is released can be selected.
The wall material of the microcapsules of the present invention contains N-substituted (meth) acrylamide or a derivative thereof and a random copolymer of (meth) acrylic acid or a derivative thereof as a main component, and is used as other components in the production of microcapsules. It contains a surfactant component (a surfactant component adsorbed on the outside of the core material during the manufacture of microcapsules) and the like.

A random copolymer of N-substituted (meth) acrylamide or a derivative thereof and (meth) acrylic acid or a derivative thereof used as a wall material for microcapsules can be synthesized, for example, as follows.
N-substituted (meth) acrylamide or its derivative and (meth) acrylic acid or its derivative are added to a solvent such as methanol, ethanol and acetone and stirred to completely dissolve N-substituted (meth) acrylamide or its derivative. Here, the compounding ratio of N-substituted (meth) acrylamide or a derivative thereof and (meth) acrylic acid or a derivative thereof is as described above, as described above, N-substituted (meth) acrylamide or a derivative thereof and (meth) acrylic acid or a derivative thereof. The copolymerization ratio (molar ratio) of the above is adjusted to be 1.0: 0.5 to 1.0: 2.0. The reason for this is as mentioned earlier.

Next, an appropriate amount of a polymerization initiator (for example, azobisisobutyronitrile) was added to the above solution, and when the solution was completely dissolved by stirring, the solution was heated to about 68 to 74 ° C. and in this heated state. By continuing stirring for about 3 to 7 hours, N-substituted (meth) acrylamide or a derivative thereof is copolymerized with (meth) acrylic acid or a derivative thereof. Here, when the temperature of the solution is less than 68 ° C, the polymerization rate is low, while when it exceeds 74 ° C, it is economically inefficient.
After completion of the reaction, the temperature of the solution is lowered to collect the reaction product by filtration, and the reaction product is dried to obtain a powdery "N-substituted (meth) acrylamide or a derivative thereof" used as a wall material for microcapsules. And a random copolymer of (meth) acrylic acid or a derivative thereof.

Next, the method for producing the microcapsules of the present invention will be described.
In this production method, as the wall material material a used as the wall material of the microcapsules, the above-mentioned N-substituted (meth) acrylamide or a derivative thereof and a random copolymer of (meth) acrylic acid or a derivative thereof are used as the wall material material. The step (A) of obtaining a solution x in which a and the surfactant c are dissolved in the polar organic solvent d and the core material b to be the encapsulating substance of the microcapsules are mixed with the solution x obtained in this step (A). The solution y is stirred while evaporating the polar organic solvent d by maintaining the solution y obtained in the step (B) and the solution y obtained in this step (B) at a temperature at which the polar organic solvent d evaporates. However, it has a step (C) of adding a poor solvent. In this step (C), the wall material substance a is precipitated in the solution y, and the precipitated wall material a coats the core material b via the surfactant c to form microcapsules. To. That is, in the solution y, the wall material substance a is precipitated and the hydrophilic group of the surfactant c is adsorbed on the core material b, so that the hydrophilic group of the core material b and the interface active agent c is used as a core. A core / shell structure having the hydrophobic group of the interface active agent c as a shell is formed, and the precipitated wall material material a is concentrated in the shell of the core / shell structure, so that the wall material (capsule) is outside the core material b. A wall) is formed, and a microcapsule containing the core material b as an encapsulating substance is obtained.

Hereinafter, embodiments of this manufacturing method will be described in detail.
FIG. 1 schematically shows a series of steps (A) to (C) in one embodiment of the manufacturing method of the present invention.
In the present invention, the random copolymer of N-substituted (meth) acrylamide or a derivative thereof and (meth) acrylic acid or a derivative thereof used as the wall material material a is insoluble in water, but is a polar organic solvent such as methanol. It is soluble in d. In the step (A) of the present invention, for example, the wall material substance a and the surfactant c are dissolved in the polar organic solvent d by adding the wall material substance a together with the surfactant c to the polar organic solvent d. Get x.

Examples of the polar organic solvent d include methanol, ethanol, propanol and the like, and one or more of these can be used.
There are no particular restrictions on the type of surfactant c, and examples thereof include Span80 (sorbitan monooleart), Span20 (sorbitan monolaurate), Tween20 (polyoxyethylene sorbitan monolaurate), and diethylene glycol monolaurate. One or more of these can be used. Of these, Span80 and Tween20, which are oil-soluble and have a relatively large HLB value, are particularly preferable.

In the subsequent step (B), a solution y is obtained by mixing the solution x obtained in the step (A) with the core material b which is the inclusion substance of the microcapsules, but the core material b is soluble in water. Since it is insoluble or sparingly soluble in an organic solvent (that is, part or all of it does not dissolve in an organic solvent), it is subjected to a dispersion treatment in which it is dispersed in a solution x (organic solvent). As a specific example, a core material b, which is a substance contained in microcapsules, is added to a solution x (hereinafter, a case where the polar organic solvent d is methanol will be described), and the core is irradiated with ultrasonic waves, for example. The material b is dispersed in the solution x to obtain a solution y in a continuous phase (medium in which emulsified particles are dispersed).
The core material b is not particularly limited as long as it does not impair the stability of the core / shell structure in the manufacturing process, as described earlier as the substance contained in the microcapsules, and is suitable for the use of microcapsules and the like. It may be selected according to the situation, but among them, the rust preventive additive for metal is preferable. The rust preventive additive for metals is as described above. The core material b dispersed in the solution y may be either a solid or a liquid.

In the subsequent step (C), the solution y (continuous phase) is heated as necessary to maintain the temperature at which methanol evaporates, and the poor solvent is added while stirring the solution y while evaporating the methanol. The type of the poor solvent is not particularly limited, but since water is generally used, the case where water is used will be described below as an example. The temperature of the solution y is preferably a relatively low temperature at which methanol can evaporate. Here, if the temperature of the solution y is too low, the reaction time becomes long and the productivity decreases, and depending on the type of the core material, the core material may be separated and the content rate may decrease, while the solution. If the temperature of y is too high, ethanol may evaporate rapidly, destabilizing the system and reducing the yield of microcapsules. Therefore, the temperature of the solution y is usually about 30 to 60 ° C.

In this step, it is preferable to add water at a constant rate while stirring the solution y. The stirring time of the solution y is appropriately about 1 to 3 hours. If the rate of addition of water to the solution y (drop rate) is too small, the microcapsules may become coarse and the content may decrease depending on the type of core material, and the reaction time may become longer, resulting in higher productivity. On the other hand, if the addition rate is too high, problems such as widening of the particle size distribution of the microcapsules are likely to occur, so 0.25 to 3.5 mL / min is appropriate.

In this step (C), the evaporation of methanol progresses, and with the evaporation of methanol and the addition of water, the wall material a that is insoluble in water is deposited, and the hydrophilic group of the surfactant c is added to the core material b. By adsorbing and forming an adsorption layer with a surfactant, a stabilized core substance (core) is generated, and the precipitated wall material substance a is absorbed and solubilized by the hydrophobic group of the surfactant adsorption layer. By thickening, a microcapsule e containing the core material b as an encapsulating substance can be obtained. That is, in this step (C), the element of the in-liquid drying method that promotes the formation of the shell by evaporating the polar organic solvent d (methanol) in the solution y, and the precipitation of the wall material substance a by the addition of water. By promoting, the wall material a forms a dense shell on the outside of the core material b by the mechanism of the core selvation method, which forms a dense shell on the outside of the core material b. A wall material (capsule wall) is formed, and microcapsules consisting of an inclusion substance and a wall material are formed in the solution y. Moreover, since capsules are rapidly produced by the above mechanism, microcapsules can be obtained in a short time.
After returning the solution y to room temperature, the precipitate (microcapsules) are collected, washed, and then dried to remove water to obtain powdered microcapsules.

[Example of synthesis of wall material]
To 150 g of 1,4-dioxane, 10.4 g of N-isopropylacrylamide (manufactured by Wako Pure Chemical Industries, Ltd.) and (meth) acrylic acid (manufactured by Wako Pure Chemical Industries, Ltd.) are added and stirred to completely dissolve N-isopropylacrylamide. did. The amount of (meth) acrylic acid added was adjusted so as to have a molar ratio (N-isopropylacrylamide: (meth) acrylic acid = 1.0: 0.3 to 1.0: 2.5) shown in Table 1. .. When 1.35 g of azobisisobutyronitrile (manufactured by Wako Pure Chemical Industries, Ltd.), which is a polymerization initiator, was added to this solution and completely dissolved, the temperature of the solution was heated to 70 ° C. with stirring to 200 rpm. The mixture was heated at a stirring rate of 6 hours to polymerize N-isopropylacrylamide and (meth) acrylic acid. The temperature of the solution was lowered to around 40 ° C., filtration was performed, and the solution was dried at 38 to 45 ° C. for 5 hours to obtain a random copolymer of powdered N-isopropylacrylamide and (meth) acrylic acid.

[Manufacturing example of microcapsules]
-Example 1
A microcapsule containing aluminum nitrate as an inclusion substance was manufactured.
0.55 g of the wall material (random copolymer of N-isopropylacrylamide and (meth) acrylic acid) synthesized as described above was added to 5.0 g of methanol, and further, sorbitan monooleate (sorbitan monooleate) as a surfactant ( Span80, manufactured by Wako Pure Chemical Industries, Ltd.) 11.4 mg and polyoxyethylene sorbitan monolaurate (Tween20, manufactured by Wako Pure Chemical Industries, Ltd.) 6.1 mg were added to obtain a solution in which the wall material was completely dissolved (manufactured by Wako Pure Chemical Industries, Ltd.). Step A).

Next, 0.25 g of aluminum nitrate nine hydrate (manufactured by Kanto Chemical Co., Inc.) was added to this solution as a core material, and the solution was irradiated with ultrasonic waves for 3 minutes to disperse it in the solution to obtain a continuous phase (step B).
Next, the temperature of this solution was kept at 30 to 60 ° C., 40 mL of distilled water was added at an addition rate of 0.25 to 3.5 mL / min while stirring at 700 rpm, and then the mixture was further stirred at 200 rpm for 1 hour (step). C).
After returning the solution to room temperature, centrifugation was performed at 10,000 rpm for 15 minutes, the precipitate was collected, washed, and then dried at 38 to 45 ° C. for 5 hours to completely remove water. ..

In Invention Examples 1 to 14 shown in Table 1, it was confirmed that spherical capsules were obtained by SEM analysis of the obtained powder, and Al was detected by EDX analysis, so that aluminum nitrate was included. It was confirmed that. The same was true for Comparative Example 3. On the other hand, in Comparative Examples 1 and 2, the powder was in the form of a lump, and microcapsules could not be obtained.
The pH responsiveness of the produced microcapsules was evaluated as follows.
0.05 g of microcapsules were added to 50 mL of distilled water in a transparent container, and ultrasonic waves were applied for 30 seconds to confirm the white turbidity of the solution (pH = 5.6) due to the emulsification and dispersion of the microcapsules. Then, a 10% sodium hydroxide solution was added to adjust the pH to 7.0, 8.0, 9.0, 10.0, 12.0, and after further irradiating with ultrasonic waves for 30 seconds, the state of the solution. When the solution became transparent, it was judged that the microcapsules had dissolved. The results are shown in Table 1 together with the conditions for synthesizing the wall material and the conditions for producing microcapsules.
According to Table 1, it can be seen that the microcapsules of Invention Examples 1 to 14 have a pH responsiveness that dissolves only at pH 8 or higher. On the other hand, it can be seen that the microcapsules of Comparative Example 3 are dissolved in the region of pH less than 8.

-Example 2
Microcapsules containing cerium nitrate as an inclusion substance were manufactured.
Wall material synthesized as described above (random copolymer of N-isopropylacrylamide and methacrylic acid, copolymerization ratio (molar ratio) of N-isopropylacrylamide and methacrylic acid = 1.0: 1.08) 0. In addition to 5.0 g of methanol, 55 g was added as a surfactant, and 11.4 mg of sorbitan monooleate (span80, manufactured by Wako Pure Chemical Industries, Ltd.) and polyoxyethylene sorbitan monolaurate (Tween20, manufactured by Wako Pure Chemical Industries, Ltd.) 6 .1 mg was added to obtain a solution in which the wall material was completely dissolved (step A).

Next, 0.25 g of cerium nitrate hexahydrate (manufactured by Kanto Chemical Co., Inc.) was added to this solution as a core material, and the solution was irradiated with ultrasonic waves for 3 minutes to disperse it in the solution to obtain a continuous phase (step B).
Next, the temperature of this solution was kept at 40 ° C., 40 mL of distilled water was added at an addition rate of 1.4 mL / min while stirring at 700 rpm, and then the mixture was further stirred at 200 rpm for 1 hour (step C).
After returning the solution to room temperature, centrifugation was performed at 10,000 rpm for 15 minutes, the precipitate was collected, washed, and then dried at 38 to 45 ° C. for 5 hours to completely remove water. ..
It was confirmed that spherical capsules were obtained by SEM analysis of the obtained powder, and Ce was detected by EDX analysis, so that it was confirmed that cerium nitrate was contained.

-Example 3
Microcapsules containing magnesium nitrate as an inclusion substance were manufactured.
Wall material synthesized as described above (random copolymer of N-isopropylacrylamide and methacrylic acid, copolymerization ratio (molar ratio) of N-isopropylacrylamide and methacrylic acid = 1.0: 1.08) 0. In addition to 5.0 g of methanol, 55 g of sorbitan monooleate (span80, manufactured by Wako Pure Chemical Industries, Ltd.) and 11.4 mg of polyoxyethylene sorbitan monolaurate (Tween20, manufactured by Wako Pure Chemical Industries, Ltd.) 6 .1 mg was added to obtain a solution in which the wall material was completely dissolved (step A).
Next, 0.25 g of magnesium nitrate hexahydrate (manufactured by Kanto Chemical Co., Inc.) was added to this solution as a core material, and the solution was irradiated with ultrasonic waves for 3 minutes to disperse it in the solution to obtain a continuous phase (step B).

Next, the temperature of this solution was kept at 40 ° C., 40 mL of distilled water was added at an addition rate of 1.4 mL / min while stirring at 700 rpm, and then the mixture was further stirred at 200 rpm for 1 hour (step C).
After returning the solution to room temperature, centrifugation was performed at 10,000 rpm for 15 minutes, the precipitate was collected, washed, and then dried at 38 to 45 ° C. for 5 hours to completely remove water. ..
SEM analysis of the obtained powder confirmed that spherical capsules were obtained, and EDX analysis detected Mg, confirming that magnesium nitrate was contained.

a Wall material
b Core material
c Surfactant
x solution
y solution

Claims (8)

In microcapsules where the wall material dissolves and releases inclusions in a specific pH range
A wall material containing a random copolymer of N-isopropylacrylamide and (meth) acrylic acid as a main component is provided.
The random copolymer has a copolymerization ratio (molar ratio) of N-isopropylacrylamide and (meth) acrylic acid of 1.0: 0.5 to 1.0: 2.0 .
A pH-responsive microcapsule characterized by having a pH range in which the wall material dissolves is pH 8 or higher . The pH-responsive microcapsule according to claim 1 , wherein the inclusion substance is a rust preventive additive for metals. The pH-responsive microcapsule according to claim 2 , wherein the rust preventive additive for metal is one or more selected from nitrates, sulfates, and acetates. In a method for producing microcapsules in which a wall material is dissolved to release an inclusion substance in a specific pH range.
A random copolymer of N-isopropylacrylamide and (meth) acrylic acid is used as the wall material (a) to be the wall material of the microcapsules, and the wall material (a) and the surfactant (c) are polar organic solvents. The step (A) of obtaining the solution (x) dissolved in (d), and
In the step (B) of obtaining a solution (y) in which the solution (x) obtained in the step (A) is mixed with the core material (b) to be the inclusion substance of the microcapsules.
By maintaining the solution (y) obtained in the step (B) at a temperature at which the polar organic solvent (d) evaporates, the polar organic solvent (d) is evaporated, and the solution (y) is stirred while being a poor solvent. Has a step (C) of adding
The surfactant (c) is sorbitan monooleate and polyoxyethylene sorbitan monolaurate, and the polar organic solvent (d) is methanol.
The random copolymer used in the step (A) has a copolymerization ratio (molar ratio) of N-isopropylacrylamide and (meth) acrylic acid of 1.0: 0.5 to 1.0: 2.0.
In step (C), a method for producing pH-responsive microcapsules, wherein the rate of addition of the poor solvent to the solution (y) is 0.25 to 3.5 mL / min. In the step (C), the wall material (a) is precipitated in the solution (y), and the precipitated wall material (a) is used as the core material (b) via the surfactant (c). The method for producing a pH-responsive microcapsule according to claim 4 , wherein microcapsules are formed by coating. The method for producing pH-responsive microcapsules according to claim 4 or 5 , wherein in step (C), the solution (y) is maintained at a temperature of 30 to 60 ° C. The method for producing pH-responsive microcapsules according to any one of claims 4 to 6 , wherein the core material (b) is a rust preventive additive for metals. The method for producing a pH-responsive microcapsule according to claim 7 , wherein the rust preventive additive for metal is one or more selected from nitrates, sulfates, and acetates.

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