JPH0226636A - Capsule and its preparation method - Google Patents

Abstract

PURPOSE:To provide a capsule capable of releasing the enclosed substance by heating with a high degree of stability by forming said capsule of a urea or melamine resin containing a predetermined amount of a thermoplastic resin used as a wall membrane and enclosing a hydrophobic substance therein. CONSTITUTION:The subject capsule is formed with the wall membrane of a urea of melamine resin containing not less than 40wt.% of a thermoplastic resin such as the emulsion of vinylidene chloride resin. The hydrophobic substance such as alkyl naphthalene and pigment is dispersed in the aqueous solution of prepolymer of urea or melamine resin, whereby the formation of the urea or melamine resin wall membrane is commenced around such hydrophobic substance and a thermoplastic resin dispersion medium is then added thereto. The resulting wall membrane of the capsule has resistances to thermoplasticity, heat, water and oil and releases the enclosed substance by heating.

Description

Detailed Description of the Invention (a) Purpose of the Invention [Field of Industrial Application] The present invention is characterized in that not only the core material is released by being destroyed by pressure, but also the core material is released by partially destroying the wall membrane by heating. The present invention relates to a capsule body capable of gradually releasing a substance and a method for producing the same. Core materials include peroxides, amine compounds, polyisocyanates, etc., and the capsule body according to the present invention can be applied to adhesives, molding materials, etc. can.

[Conventional technology]

Prepolymer of urea resin or melamine resin (hereinafter simply referred to as “
called "prepolymer". ) is a well-known method for encapsulating hydrophobic substances, and the resulting capsule bodies have been widely used in applications where the capsule is destroyed by pressure, such as in pressure-sensitive recording paper.

[Problem to be solved by the invention] However, the wall membrane formed by this method is made of resin with an extremely high degree of crosslinking, and therefore it is difficult to destroy the capsule by heating, which limits the use of the capsule body. .

On the other hand, methods of encapsulation using a thermoplastic wall such as gelatin, ethyl cellulose, or polystyrene have been considered, but these methods are less productive than the aforementioned capsules whose walls are made of urea resin or melamine resin. , which was disadvantageous in terms of cost.

Furthermore, the gelatin wall membrane has poor water resistance and oil resistance, and therefore the produced capsule bodies have the disadvantage of lacking stability.

(B) Structure of the Invention [Means for Solving the Problems] The present invention solves the above problems, and provides a capsule body that releases the core substance even when heated and is highly stable, and a method for manufacturing the same. The first invention provides thermoplastic polymers with four
The capsule body has a wall made of a urea resin or a melamine resin containing 0% by weight or more and a hydrophobic substance as a core substance. After dispersing the hydrophobic substance and starting the formation of a urea resin wall film or a melamine resin wall film around the hydrophobic substance, a thermoplastic polymer aqueous dispersion is added to the aqueous solution. It is the law.

The wall membrane of the capsule body of the present invention has thermoplasticity and maintains the heat resistance, water resistance, oil resistance, etc. originally possessed by urea resin and the like.

The first invention is a capsule body that has particularly excellent sustained release properties of a core substance by heating, and the second invention is a capsule body that has a wall made of urea resin or melamine resin containing a thermoplastic polymer and a hydrophobic substance. This makes it possible to commercially advantageously produce a capsule body as a core material by a simple method.

The capsule body of the present invention not only ruptures under pressure and releases the core substance, but also partially ruptures the wall membrane by heating and gradually releases the core substance, so it is more versatile than conventional capsule bodies. can be greatly expanded, and specifically used in adhesives, molding materials, heat-sensitive recording paper, etc.

In the case of adhesives, especially highly reactive thermosetting adhesives such as epoxy adhesives and polyurethane adhesives, curing agents such as peroxides or curing components such as amine compounds and isocyanate compounds are used in the method of the present invention. By encapsulating the adhesive, it is possible to obtain a one-component or two-component adhesive with slow-acting properties and a long pot life.

The capsule body of the present invention can also be applied to molding materials such as polyester resin for FRP and epoxy resin for mold formation.

For example, in the past, FRP was produced by applying a mixture of styrene monomer, unsaturated polyester, and peroxide to a glass fiber base material and polymerizing it. There is a problem in that the decomposition is rapidly accelerated, which further accelerates the reaction, resulting in coloring of the resulting FRP molded product. In such a case, if the peroxide-containing capsule according to the present invention is used as a part of the peroxide, the peroxide in the capsule can be removed only after the thermoplastic component in the capsule wall is destroyed by the heat of reaction. Since decomposition is initiated, the reaction as a whole can have a delayed effect.

In addition, since the thermoplastic polymer is swollen by styrene, even if all the peroxide is encapsulated and blended, it can provide a delayed effect on the reaction.

The first invention is a capsule body that exhibits particularly excellent sustained release of the core material upon heating, which is achieved by setting the content of thermoplastic polymer in the wall film to 40% by weight or more.

A preferable upper limit of the thermoplastic polymer content is 95% by weight.

The second invention is not only optimal as a method for manufacturing the capsule body of the first invention, but also improves the physical properties of the wall film by introducing a smaller amount of thermoplastic polymer into the wall film than in the 40 overlapping parts. It is also useful as a method for producing a capsule body.

The dispersion of the hydrophobic substance into the prepolymer in the second invention will be explained as follows.

When the hydrophobic substance is in powder or liquid form, it can be directly added to the aqueous solution and dispersed.

On the other hand, if the hydrophobic substance is in the form of coarse particles, there is a method of adding it as a solution using a hydrophobic solvent.

For coarse peroxide particles, either add a hydrophilic organic solvent to the aqueous prepolymer solution and leave it there, or directly add the hydrophilic organic solvent to the peroxide to form a suspension and then mix together. When added to an aqueous prepolymer solution and dispersed, it can be easily made into a fine powder.

The hydrophilic organic solvent used is one that dissolves in the prepolymer aqueous solution, and specific examples include methanol, ethanol,
Examples include alcohols such as isopropanol; esters such as methyl acetate and ethyl acetate; ketones such as acetone, methyl ethyl ketone, and diethyl ketone; acetonitrile and dimethyl formamide; It is preferable that a capsule body having a diameter can be obtained.

The amount of these hydrophilic organic solvents used is preferably 20 to 300 parts by weight based on 100 parts by weight of the prepolymer in terms of solid content present in the reaction medium (aqueous solution). If the amount is less than 20 parts by weight, no sufficient effect will be obtained, and if it exceeds 300 parts by weight, the methylenation reaction rate and the encapsulation reaction rate will decrease, both of which are unfavorable.

Note that the presence of an organic solvent that does not dissolve in the reaction medium must be avoided since the capsules will become extremely coarse particles.

Furthermore, in order to facilitate the dispersion at this stage, a nonionic or anionic surfactant or suspending agent may be added to the reaction system.

The ratio of the hydrophobic substance to the prepolymer is preferably 10 to 200 parts by weight per 100 parts by weight of the prepolymer in terms of solid content. If it exceeds 200 parts by weight, the strength of the capsule wall will be low, and if it is less than 10 parts by weight, the wall will be too thick and productivity will be poor, both of which are not preferred.

Furthermore, a portion of the prepolymer in the aqueous solution is condensed to produce a small amount of urea resin or melamine resin having methylene groups (hereinafter referred to as "methylene resin"), and then a hydrophobic substance is added. Dispersing is preferable than dispersing before the start of production of methylene resin because it is easier to form a dense film.

Specifically, the prepolymer aqueous solution was stirred with a homogenizer at a rotation speed of 3000 to 8000 rpm, and the pH
, adjust to 5-4. For this pH adjustment, hydrochloric acid or sulfuric acid at about IN level, citric acid at 10 to 30% aqueous solution, or the like can be used.

While the prepolymer is water-soluble, the methylene resin is insoluble, and when the resin begins to form, the system becomes cloudy.
Its formation can be confirmed as it gradually becomes colloidal.

Furthermore, by filtering this, the amount produced can be confirmed.

When the production of methylene resin is confirmed by clouding of the reaction system, a fine powder or liquid hydrophobic substance is charged and dispersed by stirring for about 30 minutes to 1 hour.

Hydrophobic substances that can be used as core substances in the present invention include the following.

Those that are liquid at room temperature include alkylnaphthalene, chlorinated paraffin, soybean oil, or fragrance oil rings; esters such as acrylic esters, methacrylic esters, adipic esters, or phosphoric esters; aliphatic or aromatic amines. Compounds, polyisocyanates, etc. may be mentioned.

On the other hand, examples of substances that are solid at room temperature include organic peroxides, lead peroxide, amines, epoxy resins, magnetic powders, pigments, and finely powdered pharmaceuticals.

The amount of methylene resin present before the hydrophobic substance is charged may be extremely small, but when the amount of the hydrophobic substance charged is 100 parts by weight, it is preferably 0.1 to 20 parts by weight. If a hydrophobic substance is added to the system in the absence of methylene resin or in an amount less than 0.1 part by weight, agglomeration will occur between the hydrophobic substances, and they will either float on the liquid surface with air entrained or aggregate into lumps. However, a uniform encapsulation reaction may become impossible. Furthermore, it is preferable that the methylene resin is present in the aqueous medium before adding the hydrophobic substance.

On the other hand, if a hydrophobic substance is added in the presence of a large amount of methylene resin exceeding 20 parts by weight, 1. This is undesirable because it tends to produce capsules that do not contain the core material and also increases costs.

The prepolymer aqueous solution used in the present invention can be prepared by a conventional method, and an example thereof is as follows.

For urea resins, the formaldehyde to urea molar ratio is between 1.0 and 2.5, while for melamine resins, the formaldehyde to melamine ratio is between 2.5 and 7.
Make an aqueous solution of both, place it in a container equipped with a rotating machine, and incubate at pH 7.5-9.60-80°C for 1-3.
By reacting for a period of time, a prepolymer in the form of a transparent aqueous solution can be obtained.

In this case, it is possible to replace a part of urea or melamine with each other, and furthermore, by replacing about 30% by weight or less with other compounds that perform condensation reactions, such as guanamidine or p-toluenesulfonamide, the wall membrane can be improved. water resistance can be improved.

In order to raise the pH of the reaction system, an aqueous solution of caustic soda, aqueous ammonia, triethanolamine, etc. can be used, but triethanolamine is preferably used because side reactions can be easily controlled.

Next, the encapsulation reaction of a hydrophobic substance will be explained.

After the above steps, when the temperature of the reaction system is adjusted to 30-60°C and stirring is continued, a film of urea resin or melamine resin is formed around the hydrophobic substance.

If the stirring is continued for 3 to 30 hours thereafter, the wall film content in the capsule body increases, but the final wall film content in the capsule body is preferably 30 to 95% by weight.

If it is less than 30% by weight, the stability of the capsule during storage will decrease, and if it exceeds 95% by weight, the capsule will be difficult to break even at low pressure or temperature during use, and the efficiency in manufacturing the capsule will be poor. Neither is preferable.

The wall film content can be determined by adding a solvent in which the core substance is highly soluble to the capsule body, extracting the core substance for a long time using a Soxhlet, and measuring the remaining insoluble matter.

The feature of the production method of the second invention is that after starting the formation of a urea resin or melamine resin wall film around the hydrophobic substance, an aqueous thermoplastic polymer dispersion is added to an aqueous prepolymer solution, This solves the problem of aggregation of hydrophobic substances that often occurs when an aqueous dispersion of a thermoplastic polymer is added before the formation of a wall film, making it extremely easy to form a wall film containing a thermoplastic polymer. can be done.

At this time, the timing and amount of the thermoplastic polymer aqueous dispersion to be added should be determined as appropriate, depending on the intended use of the resulting capsule, taking into consideration the balance between the thermosetting properties of the urea resin or melamine resin and the newly imparted thermoplasticity. However, at the point when 10 to 60% of the urea resin or melamine resin contained in the finally formed wall film partially constitutes the mounting part, the thermoplastic polymer It is preferable to add an aqueous dispersion, and the amount added is 10% in terms of solid content based on the amount of urea resin or melamine resin that partially constitutes the wall membrane.
It is preferable to set it to 1000% by weight.

According to the manufacturing method of the present invention, as described above, the finally formed wall film can contain 40% by weight or more of the thermoplastic polymer.

Of course, with the production method of the second invention, it is also possible to produce a wall film with a content of less than 40% by weight, and in this case as well, aggregation of the phobic substances is unlikely to occur, and the content can be adjusted as appropriate. It is.

Specific examples of thermoplastic polymers used in the present invention include acrylic ester resins and methacrylic ester resins with a low degree of crosslinking, vinylidene chloride resins, urethane resins, chloroprene polymers, butadiene-acrylonitrile copolymers, and butadiene-styrene. Examples include emulsions of copolymers, polyolefins, carboxyl group-modified polyolefins, olefin-vinyl acetate copolymers, vinyl chloride-vinyl acetate copolymers, and the like.

Among these, it is preferable to use emulsions of thermoplastic polymers that coagulate in acidic aqueous media, are difficult to coagulate, and are not subject to modification such as hydrolysis. Examples include emulsions of modified polyolefins.

The capsule body produced as described above may be collected and dried as follows.

The resulting slurry is neutralized with an aqueous IN caustic soda solution, thoroughly washed with pure water, dehydrated using a centrifuge, and further passed through a fluidized fluid dryer or tray dryer to obtain fine powder capsules. be able to.

Since the wall of this capsule body partially has thermoplasticity, a strong and dense wall can be preferably formed by increasing the drying temperature to near the melting point of the thermoplastic polymer.

[Effect]

In the present invention, it is necessary to add the thermoplastic polymer water dispersion to the prepolymer aqueous solution after the urea resin wall film or melamine resin wall film has been formed on the hydrophobic substance to some extent.

This is because if added to the prepolymer aqueous solution from the beginning, particles of the hydrophobic substance tend to aggregate with each other, making encapsulation difficult.

Furthermore, this makes it easy to adjust the content of the thermoplastic polymer as appropriate.

[Examples and comparative examples]

The present invention will be explained in more detail by giving examples and comparative examples below.

In addition, the test method of JIS K 4810 is applied mutatis mutandis for the sensitivity test, and the measurement of Vicat softening point is according to ASTM D.
1525-To.

Example 1 700 g of a 37% by weight formalin aqueous solution, 262 g of urea and 3.4 g of triethanolamine were placed in 12 flasks equipped with a reflux condenser, and the mixture was stirred at 300 rpm and 70°C for 2 hours to react. An aqueous prepolymer solution of urea-formaldehyde resin (prepolymer concentration 54.3% by weight) was obtained.

Next, 368 g of the prepolymer aqueous solution and 368 g of pure water were charged into a 21 beaker at room temperature. While stirring at 4000 rpm in a homogenizer, 7 cc of an aqueous sulfuric acid solution of IN was added to adjust the pI to 3.0 and the reaction temperature was set to 37°C, resulting in white turbidity. After 1 minute, dicumyl peroxide Fine powder (average particle size 100μm)
After adding 12.8 g and continuing stirring for 1 hour, the temperature was increased to 40°C.
The reaction was maintained for 4 hours under stirring at 5000 rpm.

Add 300g of pure water to this, remove the homogenizer, switch to a seed type stirrer, lower the rpm to 300rpm, and add low density polyolefin emulsion M-200 (
Solid content: 40% by weight, film forming temperature: 105°C, Vicat softening point: 76°C (manufactured by Mitsui Petrochemicals Ltd.) (212g) was charged and the reaction continued for an additional 15 hours to obtain a slurry.

Note that the wall film content when low-density polyolefin is added is 2.
It was 4% by weight.

This slurry was neutralized with IN aqueous sodium hydroxide solution, washed with pure water and methanol, centrifuged, and dried for 10 minutes in a fluidized fluid dryer with a hot air temperature of 110°C at the inlet and a hot air temperature of 80 to 90°C inside. 80 g of capsule fine particles having a narrow average particle size of about 150 μm were obtained.

The wall film content of this capsule was 84% by weight and 1% by weight, and the polyolefin content in the wall was 88% by weight. In addition, this capsule body can withstand 5kg from a height of 1m in a calm sensitivity test.
I dropped the weight and could not see the sensitivity.

When the melt-flowing state of this capsule was observed using a microscope, it was found that the capsule wall membrane was destroyed at around 110°C. Note that the microscopy method is a method in which a heater is set under the sample and the sample is heated for a certain temperature increase time, and the melt flow of the sample is observed under a microscope and its temperature is measured.

These results are shown in Tables 1 and 2.

Examples 2 to 4, Comparative Examples 1 to 2 The type and amount of thermoplastic polymer aqueous dispersion used instead of the low density polyolefin emulsion in Example 1, the type of core material, or the inlet hot air temperature and drying time of fluidized drying. Table 2 shows the evaluation results of capsules obtained when the capsules were produced in exactly the same manner as in Example 1 except for the changes shown in Table 1.

Example 5 700 g of a 37% by weight formalin aqueous solution, 132 g of melamine, and 3.4 g of triethanolamine were placed in a 1β flask equipped with a reflux condenser, and heated at 300 rpm at 70'C.
The mixture was stirred and reacted for 2 hours to obtain an aqueous prepolymer solution of melamine-formaldehyde resin (prepolymer solid content concentration: 47.2% by weight) having a pH of 8.5.

Next, 426 g of the prepolymer aqueous solution and 309 g of pure water were charged into 22 beakers at room temperature. While stirring at 500 rpm with a homogenizer, the pH was adjusted to 4.0 by adding 3 cc of an IN aqueous solution of hydrochloric acid, and the reaction temperature was raised to 40° C., resulting in white turbidity. After 1 minute,
After charging 29.8 g of triethyltetramine and continuing stirring for 1 hour, the temperature was raised to 60°C and the reaction was maintained for 1 hour while stirring at 5000 rpm.

Add 300g of pure water to this, remove the homogenizer, switch to a seed stirrer, lower the rpm to 300rpm, and add styrene-butadiene copolymer emulsion N1.
po ILX416 (solid content 48% by weight, film formation temperature 50°C, glass transition temperature 39°C, manufactured by Zeon ■) 178
The reaction was continued for an additional 2 hours to obtain a slurry.

Note that the wall film content when the styrene-butadiene copolymer emulsion was added was 5.0% by weight.

This slurry was neutralized with IN aqueous sodium hydroxide solution, washed with pure water and methanol, centrifuged, and dried for 30 minutes in a fluidized fluid dryer with an internal hot air temperature of 60°C and an internal hot air temperature of 40 to 50°C. , 130 g of capsule fine particles having an average particle size of about 30 μm were obtained.

This capsule body had a wall film content of 77% by weight, and a styrene-butadiene copolymer content in the wall film of 80% by weight.

50 g of this capsule body and 50 g of bisphenol type epoxy resin Epicoat 82B (manufactured by Shell Chemical ■) were mixed and left at 30° C. for 2 months, but no hardening of the epoxy resin was observed.

In addition, when observing the melt flow state using a microscope, it was found that the melt flow state was 70°.
It was observed that the capsule wall membrane was destroyed near C. These results are shown in Tables 1 and 2.

Examples 6 to 7 The type and amount of thermoplastic polymer aqueous dispersion used instead of the styrene-butadiene copolymer emulsion in Example 5, the type of core material, and the inlet hot air temperature and drying time of fluidized drying were as shown in Table 1. Table 2 shows the evaluation results of the capsule obtained when the capsule was manufactured in exactly the same manner as in Example 5 except for the following changes.
It is written in

(C) Effects of the Invention The wall membrane of the capsule body of the present invention has thermoplasticity and maintains the heat resistance, water resistance, oil resistance, etc. originally possessed by urea resins and the like.

Furthermore, the present invention makes it possible to commercially advantageously produce a capsule body with a wall made of urea resin or melamine resin containing a thermoplastic polymer and a hydrophobic substance as the core material by a simple method. be.

The capsule body of the present invention not only ruptures under pressure to release the core material, but also partially ruptures the wall membrane by heating to gradually release the core material. It can be used in highly reactive thermosetting adhesives such as adhesives and polyurethane adhesives to produce one-component or two-component adhesives with slow-acting properties and a long pot life.

Furthermore, it can be used in polyester resins for FRP and epoxy resins for mold molding to obtain molding materials without coloring.

Claims (1)

[Scope of Claims] 1. A capsule whose wall is made of a urea resin or melamine resin containing 40% by weight or more of a thermoplastic polymer and whose core material is a hydrophobic substance. 2. After dispersing a hydrophobic substance in an aqueous solution of a urea resin or melamine resin prepolymer and starting to form a urea resin wall film or a melamine resin wall film around the hydrophobic substance,
A method for producing a capsule body, which comprises adding an aqueous thermoplastic polymer dispersion to the aqueous solution.