JP2007222786A - Microcapsule, its manufacturing method and display medium equipped with microcapsule - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a microcapsule reduced in the change of its film even if pH is changed within a wide range, having sufficient strength and heat resistance and low in toxicity or free from toxicity, its manufacturing method and a display medium using the microcapsule. <P>SOLUTION: The microcapsule is equipped with a protein film and this protein film is obtained by curing a water soluble protein film by both of an amino acid crosslinked type curing agent and a carboxyl group crosslinked type curing agent. The microcapsule is manufactured, for example, by first curing a film comprising water soluble protein by the amino acid crosslinked type curing agent and subsequently curing the cured film by the carboxyl group crosslinked type curing agent. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

The present invention relates to a microcapsule and a method for producing the microcapsule. More specifically, the present invention relates to a microcapsule in which a protein film is cured by both an amino group crosslinking type curing agent and a carboxyl group crosslinking type curing agent, and a method for producing the same.
The present invention further relates to a display medium such as a magnetic display medium comprising such a microcapsule.

  Conventionally, microcapsules have been applied to various uses, and many proposals have been made regarding their production methods. Among them, the complex coacervation method is one of the microencapsulation methods applied industrially.

A general complex coacervation method is to produce microcapsules by the following process.
(1) A core substance (oil-based substance) is dispersed in an aqueous solution containing a coating 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 coacervate droplet coating is gelled at a low temperature, and a curing agent is further added to cure (crosslink and / or modify) the coating.

  Conventionally, aldehyde group-containing curing agents such as formaldehyde and glutaraldehyde are generally used as a curing agent for the microcapsule film by such a method (Cited documents 1-2). However, the aldehyde group-containing curing agent is an effective curing agent having a relatively fast film curing reaction rate, but its use is severely restricted 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.

  Therefore, various methods for producing microcapsules using a curing agent in place of an aldehyde group-containing curing agent have been studied. A typical example is a method using transglutaminase (Patent Documents 3 to 5). However, according to the study of the present inventor, when transglutaminase is simply used as a curing agent, the microcapsule after curing does not swell in a relatively high pH range such as neutrality or alkalinity. Tend to occur. Such swelling of the film is not preferable because it leads to deformation of the microcapsules. For this reason, there is room for improvement in the microcapsules using transglutaminase as a curing agent, which has been conventionally known.

  Further, as a curing agent to replace the aldehyde group-containing curing agent, a curing agent other than transglutaminase has been studied. For example, a method of curing a film applied to a substrate with an oxazoline group-containing compound, a carbodiimide group-containing compound or the like is known (Patent Documents 6 and 7), but when these are applied to the film curing of a microcapsule, There was a concern that the reaction takes time due to the reactivity.

On the other hand, magnetic display media and heat-sensitive recording materials using microcapsules have been studied (Patent Document 8). However, these materials use microcapsules manufactured by a conventional method, and microcapsules containing a relatively large amount of harmful aldehydes are generally used.
JP-A-56-15837 JP 50-142477 A Japanese Patent Laid-Open No. 10-249184 JP-A-2-86741 JP-A-5-292899 JP-A-5-25361 Japanese Patent Laid-Open No. 10-316930 JP 2001-75510 A

  The present invention is intended to provide a low-toxicity or non-toxic microcapsule with sufficient strength and heat resistance, and a method for producing the same, even if the pH changes over a wide range.

  The microcapsule according to the present invention is a microcapsule comprising a protein film, wherein the protein film is obtained by curing a water-soluble protein film with both an amino group cross-linking curing agent and a carboxyl group cross-linking curing agent. It is characterized by being.

  In the method for producing a microcapsule according to the present invention, when producing a microcapsule having a protein film, the film made of a water-soluble protein is cured by both an amino group crosslinking type curing agent and a carboxyl group crosslinking type curing agent. It is characterized by this.

  Another microcapsule according to the present invention is manufactured by the method described above.

  Furthermore, a display medium according to the present invention comprises any one of the above microcapsules.

  According to the present invention, there is provided a low-toxicity or non-toxic microcapsule having a small change in film even when pH changes in a wide range and having sufficient strength and heat resistance, or a method for producing the same. In particular, according to the method for producing a microcapsule according to the present invention, sufficient strength and heat resistance of the coating film can be achieved by crosslinking the amino group and the carboxyl group of the water-soluble protein coating film, respectively. By using the microcapsules obtained from this method, a display medium or a recording material that does not contain harmful substances and has excellent resolution can be formed.

Method for Producing Microcapsules The method for producing microcapsules according to the present invention comprises curing a water-soluble protein film using both an amino group cross-linking type curing agent and a carboxyl group cross-linking type curing agent. Any other method can be combined as long as the conditions for curing such a film are satisfied. An example of the method according to the present invention according to the complex coacervation method will be described according to the order of the manufacturing steps as follows.

  First, a core material (oil-based material) is dispersed in an aqueous solution containing a coating material to form 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. For example, a pressure-sensitive adhesive, an adhesive, a color material, and the like can be given. In addition, an element of a display medium, for example, an oily substance containing fine magnetic particles of a magnetic display medium as a dispersion, an electrophoretic particle used in electronic paper, an inverted particle such as a twist ball, an oily substance containing liquid crystal, or the like by heating A heat-sensitive recording material that changes color can also be used. In addition, foods, pharmaceuticals, quasi drugs, fragrances, detergents and the like that are immiscible with water can be used as the core substance.

  Examples of the water-soluble protein that can be used in the present invention include gelatin, agar, casein, soybean protein, collagen, and albumin. Among these water-soluble proteins, gelatin is preferably used in the method according to the present invention. These water-soluble proteins generally have an acidic group and a basic group, but the pH when the number of protons dissociated from the acidic group and the number of protons bonded to the basic group coincide with each other is adjusted to the pH of the water-soluble protein. It is called an isoionic point (hereinafter sometimes referred to as pI). If only an amino group crosslinking curing agent such as transglutaminase is used for this water-soluble protein having a low pI, a relatively large amount of carboxyl groups remain after the crosslinking reaction. As a result, the microcapsules after curing are considered to swell due to repulsion between carboxyl groups under the condition of high pH. In the present invention, even when a water-soluble protein having a low pI, that is, having a large amount of carboxyl groups is used, sufficient crosslinking is performed, and even if the pH changes over a wide range, the change in the film is small and sufficient. Microcapsules having heat resistance and strength can be achieved. Particularly for gelatin, its pI varies depending on the raw material and the processing method during production. Gelatin can be roughly classified into acid-treated gelatin and alkali-treated gelatin depending on the method of treatment at the time of production, and acid-treated gelatin tends to have high pI and alkali-treated gelatin has low pI. For this reason, acid-treated gelatin can be used in the present invention, but alkali-treated gelatin can also be used since it can be sufficiently crosslinked even if it contains many carboxyl groups. It is preferable to use alkali-treated gelatin because higher strength and heat resistance can be realized compared to when transglutaminase is used alone. Moreover, even if it is acid-processed gelatin, if a pI is low, the effect equivalent to alkali-processed gelatin can also be acquired. A mixture of a plurality of water-soluble proteins or gelatins having different pIs can also be used in the method of the present invention.

  In order to disperse the core substance in the aqueous solution containing the coating substance, it is usually possible to add a core substance to the aqueous solution and use a method such as stirring or ultrasonic irradiation. The concentrations of the core substance and the coating 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 microcapsule size, specifically the diameter in terms of sphere, is generally 0.1 to 3000 μm, preferably 0.1 to 2000 μm, more preferably 0.1 to 1000 μm. To disperse.

  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. Among them, gum arabic has a tendency to be slightly inferior in the ability to form a coacervate film with respect to an emulsion having a relatively large particle size of 100 μm or more. Is particularly preferable because a sufficient coacervate film can be easily formed.

  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 so as not to impair the properties of the core substance and the coating material. 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 with the coacervate coating is subsequently cooled to effect gelation of the coating. Usually, the emulsion is cooled to 5 to 25 ° C., preferably 5 to 10 ° C., and the film is gelled.

  In order to cure the gelled film, a curing agent is subsequently mixed into the emulsion. Here, in the method according to the present invention, an amino group cross-linking curing agent and a carboxyl group cross-linking curing agent are used.

  The amino group crosslinking type curing agent is a curing agent having an action of crosslinking and curing the amino group of the water-soluble protein. There are no particular limitations on the reaction mode when the amino group is cross-linked, and any type can be used as long as it can cross-link a plurality of amino groups and harden the water-soluble protein. Examples of such amino group crosslinking type curing agents include protein sclerosing enzymes, particularly transglutaminase. A conventionally known crosslinking agent containing an aldehyde group, such as formaldehyde, has a function of curing the protein film by crosslinking the amino group of the protein, and can also be used in the present invention. However, as described above, from the viewpoint of harmfulness, it is preferable not to use it when safety considerations are important.

  On the other hand, the carboxyl group-crosslinking type curing agent is a curing agent having an action of crosslinking and curing the carboxyl group of the water-soluble protein. There is no particular limitation on the reaction mode when the carboxyl group is crosslinked, and any one can be used as long as it can cure a water-soluble protein by crosslinking a plurality of carboxyl groups. As such a carboxyl group-crosslinking type curing agent, an oxazoline group-containing compound, a carbodiimide group-containing compound, and an epoxy group-containing compound are preferable, but among other conventionally known curing agents, those that crosslink carboxyl groups. Any arbitrary one can be used.

  Among these, the oxazoline group-containing compound has an action of curing the protein film by crosslinking the carboxyl group by the action of the oxazoline group. Examples of such oxazoline group-containing compounds include 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-oxazo Sulfonyl cyclohexane) sulfide, bis - (2-oxazolinyl sulfonyl norbornane) oxazoline compounds such as sulfides. 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.

（式中、Ｒ^１、Ｒ^２、Ｒ^３、Ｒ^４、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、Ｒ^５は付加重合性不飽和結合を持つ非環状有機基を表す。）
により表すことができる。そのような化合物の一例としては、上記の特許文献６等にも記載されている。 Two or more of these compounds can be used in combination. Moreover, what superposed | polymerized or copolymerized 1 type, or 2 or more types of these compounds can also 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. Such polymers are of formula (I):

(Wherein R ¹ , R ² , R ³ and R ⁴ each independently represents hydrogen, halogen, alkyl, aralkyl, phenyl or substituted phenyl, and R ⁵ is an acyclic organic group having an addition-polymerizable unsaturated bond. Represents.)
Can be represented by An example of such a compound is also described in Patent Document 6 and the like described above.

  Such oxazoline group-containing compounds 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. It is commercially available as RPS-1005, Epocross RAS-1005 (all trade names, manufactured by Nippon Shokubai Co., Ltd.), NK linker FX (trade names, manufactured by Shin-Nakamura Chemical Co., Ltd.), and the like.

The carbodiimide group-containing compound is particularly capable of reacting with a carboxyl group by the action of the carbodiimide group, and has a function of curing them by cross-linking them. The carbodiimide group can react with an active hydrogen such as an amino group and a hydroxyl group other than the carboxyl group, but the reaction with the carboxyl group is dominant, and in the present invention, it is classified as a carboxyl group cross-linking type curing agent. Such a carbodiimide group-containing compound has the formula (II):
-N = C = N- (II)
It is a compound having a carbodiimide group, and can be obtained by combining one or more isocyanate compounds.

Examples of such carbodiimide group-containing compounds include hexamethylene diisocyanate (HDI), hydrogenated xylylene diisocyanate (H ₂ XDI), xylylene diisocyanate (XDI), 2,2,4-trimethylhexamethylene diisocyanate (TMHDI). 1,12-diisocyanate dodecane (DDI), norbornane diisocyanate (NBDI), 2,4-bis- (8-isocyanate octyl) -1,3-dioctylcyclobutane (OCDI), 4,4′-dicyclohexylmethane diisocyanate (HMDI) , Tetramethylxylylene diisocyanate (TMXDI), isophorone diisocyanate (IPDI), and the like, which are obtained by subjecting one or more of these compounds to a deoxygenation condensation reaction. Door can be.

In addition, carbodiimide group-containing compounds described in Patent Document 7 and the like can also be used.
Such carbodiimide group-containing compounds include carbodilite V-02, carbodilite V-02-L2, carbodilite V-04, carbodilite V-06, carbodilite E-02, carbodilite E-02, carbodilite V-01, carbodilite V-03. , Carbodilite V-05, Carbodilite V-07, Carbodilite V-09 (all trade names, manufactured by Nisshinbo Industries, Inc.) and the like.

  The oxazoline group-containing compound or the carbodiimide group-containing compound is preferably a polymer compound, and more preferably a polymer compound having film-forming properties. Here, the polymer compound means a compound having a number average molecular weight of 10,000 or more.

  When a film-forming polymer compound is used as these compounds, 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 coating. Here, the film-forming property means having a film-form film-forming property when a single solution such as an oxazoline group-containing polymer compound is applied and evaporated to dryness. Further, when such a film-forming polymer compound is used, not only the strength of the capsule film can be further improved, but also advantageous effects such as improved sealing, flexibility and flexibility can be obtained.

  The epoxy group-containing compound has an action of curing a protein film by crosslinking a carboxyl group, an amino group, an imino group, or a hydroxyl group by the action of the epoxy group. In the present invention, the carboxyl group-crosslinking type curing agent is used. Classified as Examples of such epoxy group-containing compounds include sorbitol polyglycidyl ether, polyglycerol polyglycidyl ether, diglycerol polyglycidyl ether, glycerol polyglycidyl ether, trimethylolpropane polyglycidyl ether, ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether. Examples thereof include glycidyl ether, propylene glycol diglycidyl ether, and polypropylene glycol diglycidyl ether, and two or more of these compounds can be used in combination. Such epoxy group-containing compounds include Denacol EX-611, Denacol EX-612, Denacol EX-614, Denacol EX-614B, Denacol EX-512, Denacol EX-521, Denacol EX-421, Denacol EX-313, Denacol EX-314, Denacol EX-321, Denacol EX-810, Denacol EX-811, Denacol EX-850, Denacol EX-851, Denacol EX-821, Denacol EX-830, Denacol EX-832, Denacol EX-841, Denacol EX-861, Denacol EX-911, Denacol EX-941, Denacol EX-920, Denacol EX-145, Denacol EX-171 (all trade names, manufactured by Nagase ChemteX Corporation), SR-P G, SR-2EG, SR-8EG, SR-8EGS, SR-GLG, SR-DGE, SR-4GL, SR-4GLS, SR-SEP (all are trade names, manufactured by Sakamoto Pharmaceutical Co., Ltd.) ing.

  In addition, conventionally known alum, gallic acid, tannic acid, and the like can be used as the carboxyl group-crosslinking type curing agent.

  In the method of the present invention, the protein film is cured by both the amino group crosslinking curing agent and the carboxyl group crosslinking curing agent. For example, the protein film is first cured using an amino group cross-linking curing agent, and after the reaction has progressed to some extent, the curing of the protein film is terminated using a carboxyl group cross-linking curing agent.

  Here, the addition amount of the amino group cross-linking type curing agent varies depending on the curing agent used, but is generally 0.001 to 0.7%, preferably 0.01 to 0.5, based on the mass of the water-soluble protein. %. In particular, when transglutaminase is used, the content is 0.001 to 0.3%, preferably 0.01 to 0.2% based on the mass of the water-soluble protein. The amount is preferably such that the amino group of the coating can be crosslinked and cured sufficiently, but in addition to the curing reaction with a carboxyl group-crosslinking curing agent described later, an amount capable of imparting sufficient strength and heat resistance to the microcapsule. If it is.

  The conditions for reacting the amino group cross-linking curing agent vary depending on the curing agent to be used, but are generally pH 5 to 14, preferably 9 to 12. Particularly when transglutaminase is used, the pH is 5-9, preferably 6-8, temperature 10-40 ° C, preferably 15-30 ° C. The reaction is carried out under these conditions for 3 to 30 hours, preferably 10 to 20 hours.

  Next, after washing as necessary, the resin is cured with a carboxyl group crosslinking curing agent. The addition amount of the carboxyl group-crosslinking type curing agent varies depending on the curing agent used, but is generally 0.5 to 2.0 equivalent, preferably 0.8 to 1.5 equivalent based on the carboxyl group of the water-soluble protein. is there. This addition amount is selected so that sufficient strength and heat resistance of the coating can be achieved by the curing by the amino group crosslinking reaction and the curing by the carboxyl group crosslinking reaction.

  The conditions for reacting the carboxyl group crosslinking curing agent are generally pH 3-5, preferably 4-5, temperature 20-80 ° C, preferably 40-60 ° C. The reaction is carried out under these conditions for 1 to 30 hours, preferably 2 to 24 hours. In this case, since the heat resistance temperature of the protein film is raised by partially curing the film with the amino group cross-linking type curing agent, the reaction temperature is higher than when the carboxyl group cross-linking type curing agent is used alone. As a result, the reaction time can be shortened.

  Thus, after hardening a film, the target microcapsule can be obtained by operation, such as filtration, a decantation, and drying, as needed.

  The above description is based on the method of first curing with an amino group crosslinking type curing agent and then curing with a carboxyl group crosslinking type curing agent. In addition, a method of first curing with a carboxyl group crosslinking type curing agent and then curing with an amino group crosslinking type curing agent can be employed. However, it is preferable to use the amino group cross-linking curing agent first as described above, rather than adopting such an order, because the overall reaction time tends to be shortened. Furthermore, these curing agents can be mixed and used simultaneously. However, the curing reaction conditions may differ depending on the curing agent, or the mixed curing agents may react with each other. As described above, the curing reaction time at the second stage can be shortened by the first curing reaction. Since there exists an advantage, it is preferable to perform hardening reaction in two steps, and it is especially preferable to use an amino group cross-linking type curing agent in the first step.

  In the method for producing microcapsules according to the present invention, if necessary, a water-soluble polymer compound different from the polyanion essential for the complex coacervation method can coexist. When such a water-soluble polymer compound is allowed to coexist in the method according to the present invention, the method is optional, but it is general to add a water-soluble polymer compound or an aqueous solution thereof to the system. The addition timing of the water-soluble polymer compound is not necessarily limited. That is, it can be added in advance to an aqueous solution containing a water-soluble protein before dispersing the core substance, or can be added at any time before and after the addition of the polyanion. Furthermore, even if it is added in the washing step after the first-stage curing reaction is completed, the water-soluble polymer compound is added to the microcapsule dispersion having the swollen film after the second-stage curing agent is added. May be. By adding such a water-soluble polymer compound, an effect of contracting the film can be obtained, and an effect of preventing aggregation in the washing process and suppressing the swelling of the film during the curing reaction can also be obtained. However, from the viewpoint of increasing the viscosity of an aqueous solution by adding a water-soluble polymer compound, increasing the viscosity of a dispersion due to film swelling, changing coacervate conditions, etc., the water-soluble polymer compound is immediately before the first stage curing reaction, Or it is preferable to add at the time after it. In particular, in the method according to the present invention, when transglutaminase is used as an amino group cross-linking type curing agent, the pH is often adjusted relatively high after the coacervate coating is gelled. Is preferably added in advance. This is because if the increase in viscosity due to the swelling of the coating exceeds the desired range, it is necessary to apply a larger shearing force in order to maintain the stirring conditions, and if the shearing force is too strong, the capsule coating is broken, which is not preferable.

  In addition, the coacervate film has a strong tendency to swell with an increase in pH, but the water-soluble polymer compound in the present invention suppresses or reduces the swelling of the film, so in this respect as well, before raising the pH to adjust the curing conditions. It is particularly preferable to add a water-soluble polymer compound to. Therefore, the most preferable is after the polyanion is added, after the formation and gelation of the coacervate film in the system, and before the pH adjusting agent and / or the curing agent is added to cure the film. By adding the water-soluble polymer compound at such a time, the water-soluble polymer compound does not affect the formation of the coacervate coating, and the surface of the coacervate coating is effectively treated with the polymer compound.

  Examples of the water-soluble polymer compound used include polyvinyl alcohol, polyvinyl pyrrolidone, polyethylene oxide, and mixtures thereof. These water-soluble polymer compounds preferably have an electric conductivity of 0.005 to 1.2 S / m, more preferably 0.005 to 0.3 S / m, when a 10% by mass aqueous solution is used. These all suppress or reduce swelling of the coating as described above, not as a function of polyanion in complex coacervation. In the present invention, the terms polyvinyl alcohol, polyvinyl pyrrolidone and polyethylene oxide are used. Includes derivatives thereof.

  The water-soluble polymer compound may be a compound in which part or all of the water-soluble polymer compound is modified. In particular, when it is appropriately modified by a chemical species containing an ionic group, the water-soluble polymer compound itself can be configured to have an appropriate ionicity, resulting in an interaction with the protein film and more effective. This is preferable.

  Examples of such an ionic group include a sulfone group, a carboxyl group, and a phosphoric acid group. In the method for producing microcapsules according to the present invention, one or more selected from sulfonic acid and / or carboxylic acid-modified polyvinyl alcohol is particularly preferable as the water-soluble polymer compound.

  Further, a copolymer containing the water-soluble polymer compound as a polymerization unit, such as a copolymer having polyvinyl pyrrolidone as a polymerization unit, can also be used. Polyvinyl pyrrolidone and derivatives thereof may act more favorably than other water-soluble polymers when using alkali-processed gelatin as a protein, and are more preferred in combination.

  Although the molecular weight of these water-soluble polymer compounds is not particularly limited, those having a mass average molecular weight of 2000 to 200000, preferably 2000 to 20000 are generally used. In general, a water-soluble polymer compound having a large molecular weight has a large viscosity when it is used as an aqueous solution, and therefore, care must be taken because a load is applied to the stirring power during stirring and excessive shearing occurs on the microcapsules. Polyvinyl alcohol is not particularly limited to a completely saponified type or a partially saponified type, but a partially saponified type is preferred from the viewpoint of solubility in water. Generally, the addition amount of the water-soluble polymer compound is 0.1 to 5.0 parts by mass, preferably 0.3 to 2.0 parts by mass based on the mass of the water-soluble protein.

Microcapsule The microcapsule according to the present invention is a microcapsule comprising a protein coating, wherein the protein coating cures a water-soluble protein coating with both an amino group cross-linking curing agent and a carboxyl group cross-linking curing agent. It has been made. Such microcapsules can be manufactured by any method, and can be manufactured by, for example, the above-described manufacturing method of microcapsules.

  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 uses for pressure-sensitive adhesives, adhesives, coloring materials, foods, pharmaceuticals, quasi drugs, fragrances, cleaning agents, and the like. In these applications, since it is necessary to consider toxicity, it is preferable to minimize the amount of aldehydes having toxicity, such as formaldehyde and glutaraldehyde, as the microcapsule material. Also, display media, toys, 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 coating does not substantially contain aldehydes having high toxicity that can cause VOC and sick house syndrome, which are substances subject to emission control. Furthermore, a display medium or a recording material can be formed using the microcapsules according to the present invention. For example, by using an oily substance containing fine magnetic particles as a dispersion as a core substance, it can be used as an element of a magnetic display medium. Further, if a heat-sensitive color-changing substance that changes color by heating is used as the core substance, an element of a heat-sensitive recording material can be obtained. In particular, a reversible thermosensitive recording material is formed by using, as a heat-sensitive discoloring substance, a substance that can be colored, decolored and decolored by heat, for example, a combination of an electron-accepting compound and an electron-donating color-forming compound. It can also be made.

  Display media and thermosensitive recording materials using microcapsules are already known (for example, Patent Document 8). However, in the method for producing microcapsules used therefor, in many cases, only an aldehyde group-containing compound is used for curing the protein film. The use of such an aldehyde group-containing compound is not preferred from the viewpoint of toxicity and the environment. However, if only the above-mentioned transglutaminase is used as a curing agent in place of the aldehyde group-containing compound, for example, the curing reaction is relatively slow and the productivity is low. It was disadvantageous from the viewpoint. In addition, since transglutaminase is an amino group cross-linking type hardener, there are many unreacted carboxyl groups on gelatin even after the hardening, and even if it is a microcapsule after hardening, it is neutral or alkaline. In such a relatively high pH range, the coating tends to swell. Such swelling of the film is not preferable because it leads to deformation of the microcapsule or a decrease in resolution when used as a display medium. On the other hand, according to the method of the present invention, since the hardening reaction can be efficiently performed on the amino group and carboxyl group of gelatin, the swelling in the pH change as described above can be suppressed. Therefore, even if the pH changes over a wide range, the coating changes little, and a microcapsule having sufficient strength and heat resistance can be produced efficiently and without substantially using harmful aldehydes. . Furthermore, since the microcapsule according to the present invention uses a small amount of the aldehyde group-containing compound used even if it is used, the content of the aldehyde group-containing compound after production is also small. Therefore, unlike a microcapsule using only a conventionally known aldehyde group-containing compound as a curing agent, a substantially harmless display medium or heat-sensitive recording material can be provided.

  The microcapsule of the present invention is an oily substance including an element of a display medium, for example, an oily substance containing fine magnetic particles of a magnetic display medium as a dispersion, an electrophoretic particle used in electronic paper, an inverted particle such as a twist ball, and a liquid crystal Although it can be used as a material or a heat-sensitive recording material that changes color by heating, it is particularly useful as a magnetic display medium containing fine magnetic particles.

  The microcapsules according to the present invention that can be used for such applications can be produced, for example, by the method for producing microcapsules described above. The microcapsule has an appropriate size selected according to its use, but generally has a sphere equivalent diameter of 0.1 to 3000 μm, preferably 0.1 to 2000 μm. Among them, the magnetic display medium is preferably 50 to 1000 μm, and the thermosensitive recording material is preferably 0.1 to 10 μm. An appropriate thickness of the coating is selected depending on the application.

  The present invention will be described below with reference to various examples.

Example 1
While maintaining the temperature of the system at 40 ° C. and stirring 90 parts by mass of 10% by weight alkali-treated gelatin aqueous solution (ST1: trade name, manufactured by Nippi Co., Ltd.), 120 parts by mass of ion-exchanged water at 40 ° C., isoparaffin (Isopar M) (Trade name, manufactured by Esso Chemical Co., Ltd.) 120 parts by mass were added in order and emulsified and dispersed to form an O / W emulsion. Furthermore, 90 mass parts of 1.25 mass% sodium carboxymethylcellulose aqueous solution (Serogen F-7A: brand name, Dai-ichi Kogyo Seiyaku Co., Ltd. product) was mixed and made uniform as a polyanion. Acetic acid was added to adjust the pH to 4.2, and a coacervate film was formed. The emulsion was gradually cooled to 5 ° C. while stirring to gel the coating, and maintained at 5 ° C. for 30 minutes for stabilization.

  The temperature of the system was raised again to 20 ° C., and 120 parts by mass of a 10% by mass aqueous solution of sulfonic acid-modified polyvinyl alcohol (Goselan L-3266: trade name, manufactured by Nippon Synthetic Chemical Industry Co., Ltd.) was added. A 30% by mass aqueous sodium hydroxide solution was added to adjust the pH to 7.2, and a 1% by mass transglutaminase preparation (Activa TG-S: trade name, manufactured by Ajinomoto Co., Inc.) as an amino group cross-linking curing agent was reduced to 0.0. 9 parts by mass were added. Stirring was continued for 16 hours while maintaining the temperature of the system at 20 ° C. to obtain a microcapsule dispersion in which the film was cured.

  After adjusting the pH to 4.0 by adding 10% by mass sulfuric acid, the microcapsule dispersion was transferred to a separating funnel and allowed to stand to separate into a microcapsule phase and a dispersion liquid phase. Ion exchange water was added to the separated microcapsule phase, and after stirring and washing, the microcapsule phase and the dispersion liquid phase were separated again. After repeating this operation several times, the washed microcapsule dispersion was transferred to a beaker and stirred. As the carboxyl group-crosslinking type curing agent, an oxazoline group-containing compound (Epocross WS-700: trade name, manufactured by Nippon Shokubai Co., Ltd.) 73.4 parts by mass was adjusted to pH 4.0 with 10% by mass sulfuric acid. The temperature of the system was raised to 60 ° C., 10 mass% sulfuric acid was added to adjust the pH to 4.0, and the stirring was continued for 24 hours while maintaining the temperature at 60 ° C. Obtained. The obtained microcapsule was a mononuclear microcapsule having no swelling of the film and having heat resistance and strength.

Examples 2-3
Microcapsules were formed in the same manner as in Example 1 except that the oxazoline group-containing compound was replaced with the following carboxyl group-crosslinking type curing agent and the reaction time was adjusted as shown in Table 1.
Epoxy group-containing compound: 33.6 parts by mass (Denacol EX-614B: trade name, manufactured by Nagase ChemteX Corporation)
Carbodiimide group-containing compound: 32.1 parts by mass (carbodilite V-02-L2: trade name, manufactured by Nisshinbo Industries, Ltd.)

Comparative Example 1
While maintaining the temperature of the system at 40 ° C. and stirring 90 parts by mass of 10% by weight alkali-treated gelatin aqueous solution (ST1: trade name, manufactured by Nippi Co., Ltd.), 120 parts by mass of ion-exchanged water at 40 ° C., isoparaffin (Isopar M) (Trade name, manufactured by Esso Chemical Co., Ltd.) 120 parts by mass were added in order and emulsified and dispersed to form an O / W emulsion. Furthermore, 90 mass parts of 1.25 mass% sodium carboxymethylcellulose aqueous solution (Serogen F-7A: brand name, Dai-ichi Kogyo Seiyaku Co., Ltd. product) was mixed and made uniform as a polyanion. Acetic acid was added to adjust the pH to 4.2, and a coacervate film was formed. The emulsion was gradually cooled to 5 ° C. while stirring to gel the coating, and maintained at 5 ° C. for 30 minutes for stabilization.

  The temperature of the system was raised again to 20 ° C., and 120 parts by mass of a 10% by mass aqueous solution of sulfonic acid-modified polyvinyl alcohol (Goselan L-3266: trade name, manufactured by Nippon Synthetic Chemical Industry Co., Ltd.) was added. A 30% by mass aqueous sodium hydroxide solution was added to adjust the pH to 7.2, and 0.9% by mass of a 1% by mass transglutaminase preparation (Activa TG-S: trade name, manufactured by Ajinomoto Co., Inc.) was added. Stirring was continued for 16 hours while maintaining the temperature of the system at 20 ° C. to obtain a microcapsule dispersion in which the film was cured.

Comparative Example 2
While maintaining the temperature of the system at 40 ° C., stirring 90 parts by mass of 10% by mass alkali-treated gelatin aqueous solution (ST1: trade name, manufactured by Nippi Co., Ltd.), 120 parts by mass of warm water (ion-exchanged water) at 40 ° C., isoparaffin (Isopar M manufactured by Esso Chemical Co.) 120 parts by mass were added in order, and emulsified and dispersed to form an O / W emulsion. Furthermore, 90 mass parts of 1.25 mass% carboxymethylcellulose sodium aqueous solution (Serogen F-7A: a brand name, Daiichi Kogyo Seiyaku Co., Ltd.) is added as a polyanion, pH is adjusted to 4.2, and a coacervate film is formed. It was. The emulsion was gradually cooled to 5 ° C. while stirring to gel the coating, and maintained at 5 ° C. for 30 minutes for stabilization.

  Next, the cooled microcapsule dispersion was transferred to a separating funnel and allowed to stand to separate into a microcapsule phase and a dispersion liquid phase. Ion exchange water cooled to 5 ° C. was added to the separated microcapsule phase, and after stirring and washing, the mixture was allowed to stand again to separate into a microcapsule phase and a dispersion liquid phase. After repeating this operation several times, the washed microcapsule phase was transferred to a beaker and stirred. The temperature of the reaction solution was kept at 25 ° C., and 73.4 parts by mass of an oxazoline group-containing compound (Epocross WS-700: trade name, manufactured by Nippon Shokubai Co., Ltd.) was adjusted to pH 4.0 with 10% by mass hydrochloric acid. Was added. Further, 10% by mass hydrochloric acid was added to adjust the pH of the reaction solution to 4.0, and stirring was continued for 64 hours while maintaining the system temperature at 25 ° C. to obtain a microcapsule dispersion liquid in which the film was cured. The obtained microcapsules were mononuclear microcapsules having heat resistance. In addition, although reaction temperature was 25 degreeC, the film melt | dissolved at 60 degreeC similar to Example 1, and the hardening reaction of the film could not be performed.

評価基準
膨潤評価（２５℃）
○：被膜収縮状態が維持されているもの。
×：膨潤が進み、被膜が広がるもの。
耐熱性評価（６０℃）
○：被膜が維持されているもの。
×：被膜が溶解するもの。 Regarding the microcapsules obtained in Examples 1 to 3 and Comparative Examples 1 to 2, the swelling evaluation, heat resistance, and comprehensive evaluation in pH 4.01, 6.86, and 9.18 buffer solutions are summarized as follows. It was street.
pH 4.01 buffer solution: phthalate pH standard solution pH 6.86 buffer solution: neutral phosphate pH standard solution pH 9.18 buffer solution: borate pH standard solution (both reagents, manufactured by Wako Pure Chemical Industries, Ltd.)

Evaluation criteria swelling evaluation (25 ° C)
○: The film contracted state is maintained.
X: Swelling proceeds and the coating spreads.
Heat resistance evaluation (60 ° C)
○: The film is maintained.
X: The film dissolves.

  For all of Examples 1 to 3, even if pH changes in a wide range, there is little change in coating, and low-toxic or non-toxic microcapsules with sufficient strength and heat resistance can be obtained in a relatively short time. did it.

  For Comparative Examples 1 and 2, the microcapsules having approximately sufficient heat resistance and strength were cured because either one of the amino group crosslinking type curing agent and the carboxyl group crosslinking type curing agent was cured as in the prior art. Although it could be obtained, the film swelled in a specific pH range, the reaction temperature could not be raised, the reaction time was long, and microcapsules could not be obtained in a short time .

Application Example 1
While maintaining the temperature of the system at 40 ° C., 132 parts by mass of a plastic dispersion obtained by mixing an oily plastic liquid mainly composed of a fine particle magnetic material and isoparaffin (Isopar M: trade name, manufactured by Esso Chemical Co., Ltd.) as a core substance is used. A 90% by mass aqueous solution of alkali-treated gelatin (ST1: trade name, manufactured by Nippi Co., Ltd.) and 120 parts by mass of warm water (ion-exchanged water) at 40 ° C. are uniformly emulsified and dispersed in an aqueous solution. A W emulsion was formed. Furthermore, 90 mass parts of 1.25 mass% sodium carboxymethylcellulose aqueous solution (Serogen F-7A: brand name, Dai-ichi Kogyo Seiyaku Co., Ltd. product) was mixed and made uniform as a polyanion. Acetic acid was added to adjust the pH to 4.2, and a coacervate film was formed. The emulsion was gradually cooled to 5 ° C. while stirring to gel the coating, and maintained at 5 ° C. for 30 minutes for stabilization.

  The temperature of the system was raised again to 20 ° C., and 120 parts by mass of a 10% by mass aqueous solution of sulfonic acid-modified polyvinyl alcohol (Goselan L-3266: trade name, manufactured by Nippon Synthetic Chemical Industry Co., Ltd.) was added. 30% by mass aqueous sodium hydroxide solution was added to adjust the pH to 7.2, and 0.9 part by mass of transglutaminase (Activa TG-S: trade name, manufactured by Ajinomoto Co., Inc.) was added as an amino group cross-linking curing agent. did. Stirring was continued for 16 hours while maintaining the temperature of the system at 20 ° C. to obtain a microcapsule dispersion in which the film was cured.

  After adjusting the pH to 4.0 by adding 10% by mass sulfuric acid, the microcapsule dispersion was transferred to a separating funnel and allowed to stand to separate into a microcapsule phase and a dispersion liquid phase. Ion exchange water was added to the separated microcapsule phase, and after stirring and washing, the microcapsule phase and the dispersion liquid phase were separated again. After repeating this operation several times, the washed microcapsule dispersion was transferred to a beaker and stirred. As the carboxyl group-crosslinking type curing agent, an oxazoline group-containing compound (Epocross WS-700: trade name, manufactured by Nippon Shokubai Co., Ltd.) 73.4 parts by mass was adjusted to pH 4.0 with 10% by mass sulfuric acid. The temperature of the system was raised to 60 ° C., 10 mass% sulfuric acid was added to adjust the pH to 4.0, and the stirring was continued for 24 hours while maintaining the temperature at 60 ° C. Obtained. The obtained microcapsule was a mononuclear microcapsule having no swelling of the film and having heat resistance and strength.

  The obtained microcapsule dispersion was applied to a PET film having a thickness of 125 μm as a support to form a magnetic display medium. The obtained magnetic display medium had sufficient resolution.

Claims (9)

  A microcapsule comprising a protein coating, wherein the protein coating is obtained by curing a water-soluble protein coating with both an amino group cross-linking curing agent and a carboxyl group cross-linking curing agent. Microcapsules to do.   When producing microcapsules with a protein coating by the complex coacervation method, the coating consisting of water-soluble protein is cured by both an amino group crosslinking curing agent and a carboxyl group crosslinking curing agent. A method for producing microcapsules.   3. The microcapsule according to claim 2, wherein the film made of the water-soluble protein is first cured with one of an amino group crosslinking curing agent and a carboxyl group crosslinking curing agent, and then further cured with the other curing agent. Manufacturing method.   The manufacturing method of the microcapsule of any one of Claims 2-3 whose said amino group bridge | crosslinking type hardening | curing agent is transglutaminase.   The manufacturing method of the microcapsule of any one of Claims 2-4 from which the said carboxyl group bridge | crosslinking type hardening | curing agent is chosen from the group which consists of an oxazoline group containing compound, a carbodiimide group containing compound, and an epoxy group containing compound.   The method for producing a microcapsule according to any one of claims 2 to 5, wherein the water-soluble protein is gelatin.   A water-soluble polymer having an electric conductivity of 0.005 to 1.2 S / m when a 10% by mass aqueous solution is formed after the formation of a coacervate film in the complex coacervation method in producing a microcapsule having a protein film The method for producing microcapsules according to any one of claims 2 to 6, wherein a compound is allowed to coexist.   A microcapsule produced by the method according to claim 2.   A display medium comprising the microcapsule according to claim 1.