JP3301082B2 - Microcapsule and method for producing the same - Google Patents

Description

The present invention relates to a microcapsule and a method for producing the same. More particularly, the present invention relates to a method for producing microcapsules, which comprises using a resin having a carboxyl group having a self-dispersing ability in water as a component of an essential organic phase, and relates to a so-called hydrophilic such as an emulsifier or a protective colloid. The present invention provides a completely novel method of producing microcapsules free of the use of auxiliary substances which are sexual substances.

And the particle size obtained by the production method of the present invention is 1 μm
The so-called ultra-fine particle capsules of the order of submicrons described below are extremely useful as capsules containing paints, inks, recording materials such as electrostatic toners, coloring materials such as cosmetics and fiber coloring agents, that is, pigment-containing capsules.

[Conventional technology]

Conventional microencapsulation methods are roughly classified into two methods: a physical / mechanical method and a chemical method.

Among the latter chemical methods, there are a physicochemical method (core-selvation method), an interfacial polymerization method, and an in-situ method, respectively.

By the way, the control of the particle size of the capsule is, in the former mechanical method, of course, various conditions in the mechanical device, while in the latter chemical method, the hydrophilicity such as an emulsifier and a protective colloid is used. It is necessary to appropriately control the kind and amount of the substance and various conditions such as stirring speed, reaction rate, pH and temperature.

For example, JP-A-51-129485 discloses a pigment using an unsaturated polyester resin modified with a polyethylene oxide having hydrophilicity as a part of a wall forming material, and using an emulsifier and / or a water-soluble resin in combination. There is an example of a capsule containing the same, but the average particle size is as large as 5 μm. Japanese Patent Publication No. 58-501631 discloses an example of a liquid crystal capsule using a water-soluble resin such as polyvinyl alcohol and / or gelatin, but has a large particle diameter of 2 to 25 μm. Further, Japanese Patent Application Laid-Open No. 62-254833 discloses an example containing a pigment very similar to the method of the present invention, but as far as the examples are concerned, emulsifiers and resins for water-soluble protective colloids are essential components. Are used in combination, and also include particles of 5 μm.

Furthermore, Japanese Patent Application Laid-Open No. 57-190647 also discloses a production method in which a water-insoluble resin is used as a part of a wall forming material, and the next step of a surfactant or the like is continued to obtain microcapsules. Although disclosed, the micronization is performed exclusively in an aqueous solution of a water-soluble protective colloid resin such as gelatin or gum arabic as a micronization stabilizer, and the resulting particles are as large as 5 to 20 μm. is there.

The particle size of the microcapsules thus obtained is usually at a level of several μm or more, regardless of which method is used. Become.

In the chemical method obtained with a relatively small particle size,
By increasing the amount of the hydrophilic substance used for dispersing the core material and the wall material, in principle, it is possible to further reduce the particle size, but it is not possible to reach a level of 1 μm or less. It's a very difficult technique,
Even if this could be done, it is by no means desirable to increase the amount of auxiliary materials, such as hydrophilic substances, in order to put the capsule into practical use. At present, it is said that obtaining fine capsules still has a feeling of being away from the road.

As described above, even when an auxiliary material such as an emulsifier or a water-soluble protective colloid is used as a micronization aid, there is no example of a method for preparing capsule particles controlled to a particle size of 1 μm or less. Needless to say, there is no preparation example using no.

[Problems to be solved by the invention]

Even if, for example, microcapsules with a pigment as a core material are used for paints and inks,
There is also a strong demand for the development of gloss, and in order to meet this demand, it is absolutely necessary to use a so-called ultrafine capsule having a particle diameter of 1 μm or less (submicron). Requires that the use of hydrophilic substances be avoided.

Accordingly, the present inventors have each sought a novel method for producing microcapsules, which can achieve encapsulation of ultrafine particles without using an auxiliary material such as an emulsifier.
Research has begun.

Therefore, the problem to be solved by the present invention is, at least, first, a particle size of 1 μm or less (submicron),
To provide so-called ultrafine capsules,
Next, it is an object of the present invention to provide a method of encapsulation which enables extremely simple preparation of ultrafine particle capsules.

Therefore, the problems to be solved by the present invention are: 1) that it can be achieved without using any auxiliary material such as an emulsifier; 2) that ultrafine particle capsules of 1 μm or less can be realized; 3) The control conditions for obtaining such ultrafine particle capsules are simple.

[Means for solving the problem]

The present inventors have conducted intensive studies, aiming at the problems to be solved by the invention as described above, and as a result, as a wall material of the microcapsules, a resin having a carboxyl group neutralized by a basic compound as a wall material. The key technology is to use resins that have self-dispersing ability in water, so that the desired ultrafine microcapsules can be used without using auxiliary materials such as emulsifiers, The present invention has been completed by finding a novel method that can be easily obtained without impairing the physical properties at all.

That is, in order to solve the above problems, the present invention, in producing a microcapsule containing a pigment in a resin, a resin having a carboxyl group, a pigment, and a mixture of an organic solvent as an organic phase, a base The organic phase is poured into an aqueous medium in which a basic compound is dissolved, or a basic compound is mixed with the organic phase, and then water is supplied to neutralize the carboxyl groups, and then self-dispersed. A microcapsule using a pigment as a core material and a resin having a carboxyl group as a wall material, and simultaneously performing micronization and capsule wall formation in an aqueous medium. And a method for producing the same.

The resin having a carboxyl group used in the present invention is obtained by neutralizing the resin solution dissolved in methyl ethyl ketone or the like with a basic compound, and then removing the water in a stirring system that is not significantly high-speed stirring. Phase-inverted emulsification without using auxiliary materials (emulsifying aids) such as emulsifiers and water-soluble protective colloid resins, and the particle size is easily 0.1μ.
m, which has a self-water dispersing ability at a level obtained in a state of not more than m. When the resin is used in the encapsulation step, the dispersing ability is adjusted to a level suitable for obtaining the desired capsule particle size before use. Specifically, it can be adjusted depending on the amount of neutralization of the resin having a carboxyl group.

Resins having such properties are not new at all, and are called dispersion-type resins.
For example, various types of dispersion resins, such as urethane-based, acrylic-based, or epoxy-based dispersion resins, may be used as long as they have been produced and used for applications such as inks, paints, textile materials, and adhesives.

The resin having a carboxyl group is already a resin having a sufficient level of molecular weight as a capsule membrane, usually from 3,000 to 100,000, preferably from 5,000 to 30,000. Used in dissolved and diluted form.

The organic solvent is not particularly limited, and any organic solvent can be used as long as it can dissolve resins.

When considering the subsequent solvent removal step, among various organic solvents such as ketones such as acetone and methyl ethyl ketone; esters such as ethyl acetate; or aromatic hydrocarbons such as benzene, among others, Of course, low boiling solvents should be used.

That is, particularly recommended organic solvents include acetone, methyl ethyl ketone, ethyl acetate and / or benzene.

The pigment used in the present invention is a solid substance that is hardly soluble or insoluble in water, and serves as a core material of the microcapsules obtained when the production method of the present invention is carried out.

 Hereinafter, the production method of the present invention will be specifically described.

First, a pigment as a core material is dispersed in an organic solvent solution of a resin having a carboxyl group (hereinafter, this is also referred to as a first step), and then a self-dispersible resin in which the core material is dispersed. The phase is dispersed in an aqueous medium in which a basic compound is dissolved (hereinafter, this step is also referred to as a second step), and thereafter, the organic solvent used for diluting the self-dispersing resin is distilled off. (Hereinafter, this step is also referred to as a third step.) Then, when a powder capsule is required, moisture is removed by a spray-drying device or the like to obtain a desired powder capsule (dry capsule). A series of processes (hereinafter, such a powdering step is also referred to as a fourth step) is an outline of microencapsulation in the present invention.

The first step is a step of dispersing a pigment as a capsule core material in an organic solvent solution of a resin having a carboxyl group serving as a capsule wall material.

When the pigment serving as the core material has a large particle diameter, it may be finely dispersed (finely dispersed) by a known means such as a roll mill or a sand mill.

Further, when the hydrophobic substance as the core material is, for example, a pigment, most of such pigments are first obtained in the form of a wet cake, and then dried to obtain a commercial product in the form of a powder. Particle size is usually several μm
m or more, and therefore, when used as a coloring material, fine dispersion treatment as described above is required, but in the wet cake stage, strong aggregation of the pigment particles has not occurred, and If it is put to practical use in this state straight from a place at a near level, no forced fine dispersion process using a special device is required at all,
That is advantageous.

That is, when such a wet cake is used, only by performing a normal stirring operation, a desired level of a finely dispersed product can be obtained. But,
Especially recommended.

Needless to say, it is necessary to pay attention to the amount of water in the wet cake to be used.

As long as the method of the present invention is followed, self-dispersion can be achieved by neutralizing the carboxyl groups in the resin with a basic compound such as triethylamine, so that the resin before the carboxyl groups are neutralized is used, and excess water is removed. While discharging, the core material can be dispersed in the organic solvent solution of the resin. This is the so-called flash method,
Since such a method can be adopted, the method of the present invention can advantageously cope with a case where a wet cake having a high water content is used.

After the discharged water is separated and removed, the neutralization treatment may be completed to make the water self-dispersed.

Further, the viscosity of the mixture of the pigment and the organic solvent solution of the resin having a carboxyl group prepared in the first step, that is, the viscosity of the finely dispersed mixture (dispersion liquid) is determined by the dispersion in the next second step. In order to further facilitate (microencapsulation) and further facilitate the subsequent removal of the organic solvent in the third step, the amount of solvent used should be as small as possible, About 20 poise is preferred, and about 2-10 poise is most desirable.

The second step is a step in which the organic continuous phase (O phase), which is the finely dispersed mixture thus obtained in the first step, is self-dispersed in water (W phase) to form a discontinuous phase.

One of the points here is that the above-mentioned O phase is used.

That is, if the organic phase containing the self-dispersible resin is dispersed in the place where the pigment, which is the capsule core material, is dispersed in the W phase, the diameter of the capsule becomes large, and furthermore, the core which is not included is not included. This is because the amount of wood increases.

The second point in the second step is that adequate stirring should be sufficiently performed.

That is, by slowly adding one of the O-phase or the W-phase to a place where one of the O-phase and the W-phase is moderately stirred, the desired ultrafine particle capsule (submicron) is instantly obtained. A capsule) is formed.

By the way, the higher the speed of stirring, the smaller the particle size of the capsule tends to be. However, when the production method of the present invention is carried out, no significant difference is observed.

When the above-mentioned neutralized self-dispersible resins are used, a basic compound for neutralization or a crosslinking agent for gelling the capsule wall to be formed is water-soluble such as polyamines. If they are, these compounds may be dissolved in a necessary amount in the W phase in advance.

The third and fourth steps are steps of removing an organic solvent, water, etc., respectively, but in the third step,
On the other hand, in the fourth step, a known and commonly used method such as a spray drying method can be used in the fourth step.

In the fourth step, in order to obtain a powdery dry capsule, as the resin having a carboxyl group as a wall material, a resin having a high glass transition point, which is designed so that the capsules do not fuse with each other, should be used. Needless to say,

As such a resin, it is desirable to use a vinyl resin having a glass transition point of 50 ° C. or higher, and particularly, an acrylic resin.

As described above, according to the production method of the present invention, in a simple manner, without using any auxiliary material such as an emulsifier, and surprisingly, ultrafine particles of 1 μm or less. This means that even microcapsules (submicron capsules) having a diameter can be formed instantaneously, which is one of the features of the present invention that is unprecedented.

Of course, according to the method of the present invention, the degree of hydrophilicity of the self-dispersing resin, the amount used, the stirring speed in the atomization step, the viscosity of the organic phase,
Needless to say, a capsule having a particle size of 1 μm or more can be obtained as appropriate by selecting conditions such as the type of the organic phase solvent and the temperature.

In addition, since the resin having a carboxyl group used in the production method of the present invention has a molecular weight sufficient to exhibit the necessary film properties as a capsule wall material, the resin is dispersed in water in the second step. At the same time, the capsule wall has been completed, and basically, no further wall forming operation is required, but the properties such as solvent resistance and durability of the capsule wall are further improved. In order to make the reaction, a so-called reactive active group such as a glycidyl group, an isocyanate group, a hydroxyl group or an α, β-ethylenically unsaturated double bond (unsaturated group) is previously added to the resin having a carboxyl group to be used. In the form of a pendant, during or after the formation of the capsule, the reactive active group (functional group) or the like is used to, for example, separate the resin for the capsule wall material itself. Needless to say, the amount of particles can be further increased, or the resin for the wall material itself can be crosslinked and gelled.

Alternatively, the aqueous dispersion of the obtained microcapsules is used as a seed to further form a monofunctional or polyfunctional α, β-
Polymerize ethylenically unsaturated monomers and the like, thereby
A microcapsule with a reinforced capsule wall can also be used.

By the way, in the conventional encapsulation method process, whether it is a mechanical method or a chemical method, in any method, first, formation of coarse capsule unit particles (element for wall material) Raw material may be contained), followed by formation of the capsule wall and two steps, and each step is performed as an independent and separate step.

On the other hand, the method of the present invention is characterized in that the two steps described above are performed at the same time, without distinction and distinction, and only at the point that they proceed instantaneously.
One of the features of the present invention is that it is a completely new technique that is completely different from the prior art, and whether it is a new and useful technique. This is as described above.

The production method of the present invention is closer to a mechanical method in terms of instantaneous formation of capsule walls, whereas it is closer to a physicochemical method in terms of emulsification dispersion or phase change, and therefore It can be considered that the two methods are a fusion.

In addition, according to the production method of the present invention, the capsule formed in the above-mentioned second step (microencapsulation step) and then obtained in the third step (desolvation step) is in a state of being dispersed in water. However, the particle size of the capsule in such a state can be as small as 1 μm or less, that is, a submicron class particle. Therefore, it can be obtained by the production method of the present invention from the place where the particle size is in the emulsion region. Ultrafine particle capsules (submicron capsules) are characterized by good dispersion stability.

Therefore, capsules obtained by the production method of the present invention, for example, by using a pigment as a core material,
In this state, that is, in a state of being dispersed in water, as a colorant component when preparing a water-based ink or a water-based paint, only by adding and blending, it can be practically used. This has an enormous merit that the conventional pigment dispersing step itself can be omitted.

In addition, this means that, even when practically used in the form of mixed colors, troubles such as "color separation" do not occur and the characteristics as a stable color material are exhibited.

However, the dispersion stability of pigments in water-based coloring materials has been a major unsolved problem so far, and in particular, the maintenance of the dispersion stability of such organic pigments in emulsion-based coloring materials has involved many problems. Difficulties are present, and dispersion has been attempted by using auxiliary materials such as surfactants, which should be avoided, and practical use has been done while leaving problems. Is the actual situation.

The present invention can solve all the unsolved problems of the related arts in another system at a glance.

Above, the microcapsule of the present invention and the method for preparing the same have been specifically described. As the resin having a carboxyl group used in the production method of the present invention, the carboxyl group is neutralized with a basic compound. By doing, it has the property of self-dispersibility, and,
It has a molecular weight capable of forming a film, and
In the case where a powdered capsule is required, if the capsule does not cause fusion, basically,
Any of them can be used, and there is no limitation on the type or grade.

However, as the ratio of the core pigment to the resin having a carboxyl group, that is, the resin for the wall material, increases, the self-dispersibility (self-dispersion stability) of the resin increases.
Need to be of a higher level.

The level of the self-dispersion performance basically changes depending on the type and amount of the hydrophilic group bonded to the resin and the bonding site (bonding position) of the hydrophilic group in the resin structure. Needless to say, each should be selected appropriately.

If only typical representative examples of the hydrophilic group are given, hydroxyl group, oxazoline group, cyclocarbonate group, ether bond, phosphate group, carboxyl group (carboxylic acid group), sulfonic acid group or amino group, or And neutral bases.

And if only particularly typical resins are exemplified as these resins having a hydrophilic group, various resins such as vinyl-based, ester-based, urethane-based, epoxy-based, amide-based or cellulose-based resins can be used. .

The ultrafine particle capsules of the present invention thus obtained can be used and applied as recording materials such as paints, inks, electrostatic toners, coloring materials such as cosmetics and fiber coloring agents, that is, pigment-containing capsules. Can be.

〔Example〕

Next, the present invention will be described more specifically with reference examples, examples and comparative examples. In the following, all parts and percentages are by weight unless otherwise specified.

Reference Example 1 (Preparation example of resin having carboxyl group) "Unisafe PT-200" [Polytetramethylene glycol manufactured by NOF Corporation; number average molecular weight = about 2,000]
293 parts and 77 parts of isophorone diisocyanate were charged into a flask, heated to 120 ° C. while stirring under a nitrogen seal, and kept at the same temperature for 30 minutes, and then 0.05 part of tin octenoate was added. After 1 hour, the temperature was lowered to 80 ° C, 210 parts of methyl ethyl ketone and 20 parts of dimethylolpropionic acid were added, and the mixture was kept at 75 ° C for 5 hours to continue the reaction. No decrease in the group content was observed, where the acid number and isocyanate group content of the solution were 13 and 0.9, respectively.
% Of a polyurethane resin having an isocyanate group at a molecular terminal.

The nonvolatile content of this resin solution was 65%, and the Gardner-Holtz viscosity at 25 ° C. (the same applies hereinafter) was W.

 Hereinafter, this is abbreviated as resin (A-1).

Reference Example 2 (same as above) 200 parts of styrene, 176 parts of methyl methacrylate and 24 parts of methacrylic acid, and 8 parts of "perbutyl O" (tert-butyl peroxyoctoate manufactured by NOF Corporation) A liquid was prepared.

Then, 60 parts of this mixture and 40 parts of methyl ethyl ketone
0 parts into a flask, and while stirring under a nitrogen blanket, the temperature was raised to 75 ° C. and maintained for 30 minutes.
After dropwise addition over a period of time, and after completion of the dropwise addition, the reaction was continued for 12 hours at the same temperature to continue the reaction. As a result, a vinyl resin solution having an acid value of 20 was obtained.

The nonvolatile content of this resin solution was 50%, and the viscosity was W.

 Hereinafter, this is abbreviated as resin (A-2).

Example 1 100 g of resin (A-1), "Fastogen Blue TGR-Wet" (Cyanine Blue Cake manufactured by Dainippon Ink and Chemicals, Incorporated; nonvolatile content = 60%)
Was mixed well with a stirring bar to prepare an organic phase in which the cyanine blue pigment was uniformly dispersed.

Separately, an organic solution in which 2.3 g of triethylamine was dissolved in 200 g of distilled water was gradually added to a place where the solution was stirred by a stirrer equipped with stirring blades.

Then, while heating to 70 ° C., methyl ethyl ketone was removed by vacuum distillation using an aspirator.

Thus, the desired microcapsules stably dispersed in water were obtained.

As a result of observation with an optical microscope (magnification: 600) (the same applies hereinafter), it was confirmed that the product was spherical, and "Model N-4" manufactured by COULTER, USA
The average particle diameter measured by using (the same applies hereinafter) is 0.9 μm
Met.

Example 2 The same procedure as in Example 1 was repeated except that 0.64 g of ethylenediamine was added to the triethylamine aqueous solution to obtain a target substance in which spherical microcapsules having an average particle diameter of 0.7 μm were stably dispersed in water. Obtained.

In this example, the isocyanate-terminated urethane resin used as the capsule wall material is subjected to a chain extension reaction with ethylenediamine to further increase the molecular weight.

Example 3 Spherical capsules dispersed in water were obtained in the same manner as in Example 1, except that 0.44 g of ethylenediamine and 0.21 g of diethylenetriamine were used in addition to the aqueous triethylamine solution.

 This had an average particle size of 0.8 μm.

In this example, the isocyanate-terminated urethane resin used as the capsule wall material was subjected to a chain extension reaction with ethylenediamine, respectively, while being crosslinked and gelled with diethylenetriamine, thereby further increasing the molecular weight and improving the properties. It was intended to be.

Example 4 Spherical capsules dispersed in water were obtained in the same manner as in Example 3, except that 48.5 g of "Fast Gen Blue TGR-Wet" and 50 g of methyl ethyl ketone were used.

 This had an average particle size of 0.9 μm.

Example 5 To 100 g of the resin (A-2), 7.5 g of "MA-100" (carbon black manufactured by Mitsubishi Carbon Co., Ltd.), 3.5 g of triethylamine and 30 g of methyl ethyl ketone were added. Was added, and the mixture was dispersed with a paint conditioner. First, an organic phase was prepared.

Next, 200 g of distilled water was gradually added while the organic phase was continuously stirred by a stirrer.

Thereafter, as in Example 1, methyl ethyl ketone was distilled off to obtain spherical capsules dispersed in water.

 This had an average particle size of 0.7 μm.

Example 6 Instead of using "MA-100", 50 g of "Taipek R" was used.
-820 "[rutile-type titanium oxide manufactured by Ishihara Sangyo Co., Ltd.] and the amount of methyl ethyl ketone used is 50
A spherical capsule dispersed in water was obtained in the same manner as in Example 5 except that g was used.

 This had an average particle size of 0.8 μm.

Example 7 Instead of "Taipek R-820", the same amount of "130
A spherical capsule dispersed in water was obtained in the same manner as in Example 6, except that D "(a red handle made by Toda Kogyo Co., Ltd.) was used.

 This had an average particle size of 0.6 μm.

N Next, the water-dispersed capsules were applied to a spray-drying apparatus, and made into powder by a conventional method.

It was confirmed that the powder thus obtained was redispersible in water and had the same particle diameter as before powdering.

Table 1 summarizes the results of the evaluation study on the development of gloss when each capsule obtained in each example was used as a coloring material.

However, the evaluation of the gloss development was performed in the following manner.

That is, using the microcapsules dispersed in water as they are, separately applied to a glass plate, and at room temperature,
Alternatively, after drying at a temperature of 60 ° C., the glossiness of each dried coating film was visually determined.

Separately, the presence or absence of the solubility of the above-mentioned dried coating film (capsule film) in methyl ethyl ketone was confirmed. However, it is shown in the following table for the purpose of merely providing a reference.

Therefore, it is not intended to directly show the effects of the present invention.

As is evident from the results in Table 1, the microcapsules obtained by the method of the present invention are ultrafine capsules of 1 μm or less, that is, submicron capsules, and therefore have the property of exhibiting gloss. I know.

〔The invention's effect〕

As described above, the ultrafine particle capsule (submicron capsule) obtained by the production method of the present invention can be easily produced in a short time without using an auxiliary material such as a surfactant, Moreover, it has a particle size of 1 μm or less.

In other words, the production method of the present invention is a very simple method, and is a completely novel method that is unprecedented.

The ultrafine particle capsules of the present invention thus obtained can be used and applied as recording materials such as paints, inks, electrostatic toners, coloring materials such as cosmetics and fiber coloring agents, that is, pigment-containing capsules. Can be.

That is, the pigment-containing microcapsules having a fine particle diameter obtained by the production method of the present invention are used for paints, for inks, as electrostatic printing toners, and further, for cosmetics, as compositions for fiber colorants. It is very useful for a wide range of applications.

In addition, the pigment-containing microcapsules obtained by the production method of the present invention can solve the unsolved problem of the dispersion stability of the pigment in the water-based coloring material, particularly, the emulsion-based coloring material at once. In this respect, the effect of the present invention is enormous.

Continuation of the front page (56) References JP-A-57-100144 (JP, A) JP-A-55-89855 (JP, A) JP-A-62-254833 (JP, A) JP-A-2-229545 (JP) , A) JP-B-42-446 (JP, B1) (58) Fields investigated (Int. Cl. ⁷ , DB name) B01J 13/04 C09D 7 / 12,11 / 00 A61K 7/00

Claims (4)

(57) [Claims] In producing a microcapsule containing a pigment in a resin, a resin having a carboxyl group is provided;
A mixture of a pigment and an organic solvent is used as an organic phase, and the organic phase is poured into an aqueous medium in which a basic compound is dissolved, or water is added after mixing the basic compound with the organic phase. Thus, by neutralizing the carboxyl groups and self-dispersing, the microcapsules having the pigment as the core material and the resin having the carboxyl group as the wall material are formed, and the fine particles are dispersed in the aqueous medium. A method for producing a microcapsule, comprising simultaneously forming a capsule and forming a capsule wall. 2. The method according to claim 1, wherein the resin having a carboxyl group is a urethane resin having a carboxyl group. 3. The method according to claim 1, wherein the resin having a carboxyl group is a vinyl resin having a carboxyl group. 4. An ultrafine particle capsule having a particle diameter of 1 μm or less, obtained by the method according to claim 1, 2 or 3.