KR100381370B1 - Process for preparing microcapsule - Google Patents

Abstract

The present invention is to provide a method for producing a microcapsule surrounded by a polymeric wall obtained by reaction of a water-soluble melamine resin with an ammonium salt.

Description

Manufacturing method of microcapsules {PROCESS FOR PREPARING MICROCAPSULE}

The present invention relates to a method for producing a microcapsule. More specifically, the present invention relates to a method for producing a microcapsule surrounded by a polymeric wall obtained by the reaction of a water-soluble melamine resin with an ammonium salt.

The microcapsules of the present invention are useful in various fields, and in particular, have excellent heat resistance and have sustained sustained release for at least one year.

Microcapsules have been studied to be applied to various fields such as pressure-sensitive recording materials and recording materials such as thermal recording materials, pharmaceuticals, pesticides, adhesives, foods, rust inhibitors, liquid crystals, and display materials according to temperature. The test is reaching.

In particular, a number of techniques have already been proposed for microcapsules of hydrophobic substances, among them, a coacervation method using gelatin, an interfacial polymerization method, an in situ polymerization method and the like are known. In the early capsules, many coacervation capsules made by gelatin have been used, but only low-density capsules can be obtained. Because of the preservation restrictions in using natural gelatin as a raw material, it is now being converted into a synthetic resin capsule.

Among synthetic resin capsules, in situ polymerization capsules are used as microcapsules for pressure-sensitive recording papers in terms of performance, raw materials, manufacturing cost, and the like. However, there are drawbacks such as formalin generated during the reaction, formalin remaining in the capsule liquid, and the like, and difficulty in controlling the particle size.

The most commonly used methods to make microcapsules to date are coacervation methods from aqueous hydrophilic colloidal solutions such as gelatin, gum arabic, polyvinylmethylether / maleic anhydride copolymers and carboxymethylcellulose. However, coacervation technology has many drawbacks.

Firstly, encapsulation is possible only by using a low solids aqueous solution. This is because coacervation occurs only at low colloidal concentrations, and at high solids content, the viscosity of the system tends to be unmanageably high. Thus encapsulation by coacervation technique was done at a solids content of typical 18-23%.

Secondly, hydrophilic colloids tend to be expensive, in particular gelatin, the most commonly used substance, tends to be strong, and the characteristics and purity of the colloids used are limited and must be strictly conditioned.

Third, since most of the hydrophilic colloids used are natural products or derivatives thereof, problems arise in the storage of substances against microorganisms, which limits the time that the colloids can be preserved as raw materials and final microcapsules before coacervation. .

Fourth, the colloidal walls of capsules produced by coacervation do not become completely impermeable, which in some cases results in leaching the capsule contents. This sometimes becomes important as a conduction that interferes with the encapsulation of some material.

Fifth, the price of natural materials such as gelatin and gum arabic is also uncertain.

In contrast, aminoplast wall materials, such as melamine resins, are inexpensive compared to hydrophilic colloids, are not limited to stringent conditions such as hydrophilic colloids used in coacervation techniques, and are less concerned about microorganisms, It can be obtained in the condition of almost constant standard product. Therefore, capsules made from such synthetic resins are very advantageous to maintain a certain level of quality than microcapsules manufactured using natural materials such as gelatin.

Early proposals for in situ polymerization techniques are shown in Example 4 of US Pat. No. 3,016,308. The shim material is dispersed in an aqueous solution of a water-soluble urea-formaldehyde initial condensate and further condensed by the addition of hydrochloric acid to give a precipitate of urea-formaldehyde. Small amounts of carboxymethylcellulose are present as emulsifiers.

Other techniques using urea and formaldehyde (or urea-formaldehyde prepolymers) are also described in US Pat. Nos. 3,516,846 and 3,516,941. These techniques emphasize the careful adjustment of the acidification stage. These patents also claim that wetting agents such as carboxymethylcellulose are not compatible with the formation of useful capsules.

The above three US patents emphasize the importance of rapidly stirring the dispersion through a condensation reaction. Of course, without stirring, the dispersion becomes unstable, for example, droplets aggregate. This tendency to produce flocculation is very difficult to control the size of the droplets (the size of the microcapsules) and prevents the production of small capsules. Reproducible adjustment of the droplet size is very important. The necessity of maintaining the dispersion state by rapid agitation requires a large amount of energy and increases manufacturing costs.

All of these suggest the use of reactive surfactants or 'tensides', as described in British Patent Nos. 1,156,725, 1,301,052 and 1,355,124 as suggestions for overcoming dispersion stability. These are polymeric materials, for example amino plaster materials, which are chemically modified like surfactants. In this way they give the possibility that the droplets to be encapsulated form a more stable dispersion.

However, chemically modified materials have an increased cost compared to unmodified materials. Capsules made with the reactive surfactants described in British Patents 1,156,725, 1,301,052 and 1,355,124 are not used on commercial scale.

A method for producing microcapsules with walls of formaldehyde condensation products such as melamine resins is to use aqueous thermosetting resin aqueous solutions having the property of separating a solution to form a phase in the form of a polymer under alkaline water addition. In such dilution steps, the microcapsules must be prepared to limit the solids content obtained. It is because it is not clear to what extent resin hardens in order to form a microcapsule wall since it does not contain a hardening | curing agent and a pH adjuster in this process.

It is an object of the present invention to solve the drawbacks of the microcapsules produced by the coacervation and other techniques described above, and to produce microcapsules with excellent orientation.

Another object of the present invention is to provide a method for producing a microcapsule having excellent heat resistance and sustained release, and in particular, a microcapsules using melamine having excellent manufacturing performance of the microcapsule and having a bad production environment due to the generation of an irritating odor. It is to provide a method for simplifying and automating the manufacturing method of the capsule.

1 is a photograph taken at 1000 times magnification of the microcapsule dispersion.

The present invention provides a polymer wall by preparing a dispersion of a specific substance in an aqueous solution containing a natural polymer, blending a water-soluble polymer such as a melamine resin in this dispersion, condensing with an ammonium salt, and crosslinking the polymer around the specific substance. And encapsulating a finely divided specific material, wherein the specific material is surrounded by a polymeric wall.

The crosslinking action of the initial condensate is considered to be mainly due to the presence of methylol groups, but there is no difference even if other groups are included.

The present invention includes microcapsules made by the methods defined in other literature and sheet materials carrying such microcapsules. Such sheet material is obtained from paper and the microcapsules are present as a coating or in the gaps between the paper fibers. Certain finely divided materials should be obtained as a solid and have dispersion stability.

Examples of natural polymers are cellulose derivatives such as carboxymethyl cellulose (CMC) and gelatin, gum arabic, starch and the like. Synthetic water-soluble polymers include urea resins, polyvinyl methyl ether / maleic anhydride copolymers, and polyacrylamides in addition to melamine resins. Or acrylamide / acrylic acid copolymers. Particularly advantageous polymers of these are melamine resins and acrylamide / acrylic acid copolymers.

A polymer having dispersion stability means a polymer that is dispersion stable in itself in solution or a polymer that is dispersion stable in the presence of at least one initial condensate. Such polymers include sulfated melamine resins and acrylamide / acrylic acid copolymers. Acrylamide / acrylic acid copolymers, by themselves, do not have dispersion stability but are mixed with the urea-formaldehyde initial condensate to stabilize the dispersion. In order for a polymer to have dispersion stability, it is preferable that the said polymer is charged, and anionic property is good for dispersion stability.

The chemical properties of the initial condensate are not particularly limited, but first the initial condensate must be soluble in water and secondly the droplets must be stable in the presence of a good dispersion stability polymer.

It is preferred that the urea-formaldehyde initial condensate is cationic and the melamine-formaldehyde initial condensate is a methylated melamine-formaldehyde initial condensate. Obtained using a mixture of two or more of these materials instead of a single melamine-formaldehyde precondensate. It is also possible to use two or more mixtures of urea-formaldehyde precondensates in the same form. Of course, using only polymer and urea-formaldehyde initial condensate, in other words it is possible to form capsules without the presence of melamine-formaldehyde, but these capsules tend to be very weak, and the drying operation (tenter) Temperature) is impossible. In addition, even if it is possible to withstand such an operation, aging and embrittlement are found.

The method of the present invention can be carried out in various ways. For example, urea-formaldehyde initial condensates, melamine-formaldehyde initial condensates and natural polymers can be completely present in the aqueous medium before the addition of the oily liquid to be encapsulated, and acids to bring about condensation of these initial condensates It can also be added.

Previously, the acid was used before or after the addition of the melamine-formaldehyde initial condensate, by the method of adding little by little after the addition of the encapsulated material.However, the method of the present invention using ammonium salt is initially performed by temperature manipulation after addition of ammonium salt. The condensation of the condensate can be controlled.

If the initial condensate causes excessive condensation before the formation of the oily droplets or if the melamine-formaldehyde initial condensate is added after the acid addition, excessive condensation is likely to occur, so temperature control and the amount of ammonium salt have a great influence on the capsule formation. Therefore, conditions to avoid excessive condensation should be determined through preliminary experiments.

The appropriate pH for the condensation and crosslinking reaction depends on the amount of melamine-formaldehyde precondensate and natural polymer used to a certain extent. For the mainly used melamine-formaldehyde initial condensate, it is possible to form capsules in the range of 3.5 to 5, and for the purpose of sustained release, the pH range should be 4.0 or more.

The acid used for pH adjustment is not limited, For example, acetic acid, hydrochloric acid, or citric acid are mainly used, but in the present invention, the pH can be arbitrarily adjusted to the set temperature using an acid and an ammonium salt rather than the use of these acids.

In the previous method, the order in which the capsule wall material is added often affected the manufacture of the capsule. In the process of the present invention, however, melamine-formaldehyde precondensates tend to destabilize the dispersion of the encapsulated material, which aggregates smaller droplets to produce larger droplets.

Therefore, the addition of natural polymer is an essential method to prevent the aggregation of melamine-formaldehyde initial condensate. In addition, the size of the capsule can be controlled to some extent by this method. For example, in a small patch, as the addition amount increases, the aggregate size becomes larger, and aggregation can be prevented to some extent by adding natural polymer in advance.

In order to minimize the aggregation, the dispersion requires the addition of natural polymers before the addition of the melamine-formaldehyde initial condensate, and it is advantageous to gradually increase the temperature at low temperatures at the time of capsule formation to bring the condensation into account. It is effective to use acid addition methods.

Acidification of the aqueous solution to which the natural polymer and the melamine resin are added is obtained by decomposition of the ammonium salt under a warm state, for example, at a temperature of 40 ° C. or higher, and a capsule can be obtained by maintaining the mixture for a certain time. If the melamine-formaldehyde precondensate is added without a cooling step after the addition of the encapsulating oily substance, the pH of the dispersion prior to the addition of the melamine-formaldehyde precondensate is adjusted to alkaline and the melamine-formaldehyde precondensate is subsequently After addition, the dispersion needs to be kept at 40 ° C. for 20 minutes or more.

It is advantageous that the pH of the dispersion causing condensation and crosslinking of the wall material is alkaline to stop the wall material from further reaction. In the method of adding acid, a large amount of alkali is required, but in the case of using an ammonium salt, there is an advantage in that the amount of alkali can be further reduced because the acidity decreases when the temperature is lowered.

The degree to which the core dispersion is agitated affects the capsule size produced. In general, increasing the stirring speed results in a smaller single capsule size and a higher production rate.

Changing the relative proportions of the initial condensate and the polymer allows the preparation of the capsule, but is strongly influenced by the mechanical properties and production yield of the capsule. Examples using the relative ratios of the initial condensate to the polymer are described below.

In the method of the present invention, when the best natural polymer and initial condensate are used, it can be seen that a capsule is produced even at a solid content of 20%.

Selecting, in other words, the parameters of the wall material and method used, it can be seen that it contains many variations in the experimental conditions and sequence in which the various process steps are performed. Thus, experimentation is required to find the optimal way of practicing the present invention to obtain capsules with good properties for certain combinations of wall materials.

Melamine-formaldehyde initial condensate aqueous solution is initially prepared and pulverized with the addition of core material until the desired droplet size, for example 1 to 3 μm, is obtained. The dispersion is alkalized to pH about 8.0 and heated to about 40 ° C. for 20 minutes or more. The temperature of this dispersion was then raised to 70 ° C., and capsules were prepared by maintaining the ionicity for 2 hours after forming the capsules.

The obtained capsules were gradually cooled, and the resulting capsule dispersion was stirred with NaOH solution to raise the pH to about 8.5 and maintained for at least 3 hours.

Although the release of formaldehyde from the capsule dispersion is a concern because of the formaldehyde present in the initial condensate, it is a feature of the present invention to clean it by adding ammonium salts.

The present invention allows continuous stirring at a slow speed to prevent agglomeration of a stable dispersion of core liquid, so that the droplet size can be easily adjusted accurately, and a small size of the encapsulation can be produced. In the present invention, a relatively cheap raw material can be used, and this method itself can be performed in a short time as compared with many conventional methods. The fact that the wall material is a synthetic material means that it is difficult to be attacked by microorganisms, and the chemical properties and purity of the material can overcome limitations as used in coacervation systems, for example.

Another advantage of the present invention is that this capsule is stronger and much smaller than the capsule obtained in the coacervation system.

This means that encapsulation of highly porous materials is generally difficult and impossible to encapsulate sufficiently in coacervation systems. Examples of such highly porous materials are esters such as ceramics and phthalates.

Another advantage of this invention is that by controlling the amount of ammonium salt, the permeability of the microcapsules can be arbitrarily controlled and the capsule can be formed at any temperature.

The core material may be dispersed in an aqueous medium in addition to the aromatic material, and may also be used for encapsulating a material for use in a reduced pressure radiation system by directly using a medium or a solid which is substantially insoluble in the medium. The materials used in the decompression radiation system generally consist of a color-forming solution of one or more leuco dye derivatives in an oily solvent.

Examples of such solvents are paraffin chloride, biphenyl derivatives, alkyl naphthalenes, diarylmethane derivatives, and dibenzylbenzene derivatives. Good leuco dyes include crystal violet lactones (CVL), fluorene derivatives, diphenylamine derivatives, spiropyran derivatives and phthalimidine derivatives. Such solvents and color formers are well known in the art of pressure-sensitive copy paper.

Hereinafter, the present invention will be described in more detail with reference to Examples. The photographs taken by enlarging 1000 times the microcapsule dispersion obtained in Examples are shown in FIG. 1.

Example 1

50 g of mugwort oil was added to 400 g of 2% gelatin aqueous solution and stirred at 6000 rpm to form oil droplets having a diameter of 1 to 2 μm. Subsequently, 50 g of melamine resin (80% solids) was added to the solution, 5 g of an aqueous ammonium sulfate solution (20%) was added thereto, and the mixture was reacted at 80 ° C for 2 hours to prepare a microcapsule dispersion having a melamine-formaldehyde resin wall. The average diameter of the prepared microcapsules was 1.62 μm, and the obtained microcapsule dispersion was 173 g.

Example 2

It carried out on the conditions similar to Example 1 except having made the melamine resin amount 100g. The obtained microcapsule dispersion was 289 g and the average diameter was 1.88 mu m.

Example 3

100 g of strawberry oil was added to 400 g of an aqueous 5% gelatin solution and stirred at 6000 rpm to form oil droplets having a diameter of 1-2 m. After the formation of oil residue, 20 g of aqueous ammonium sulfate solution (20%) was added and emulsified at 40 ° C. for 5 minutes. Then, 100 g of melamine resin (in terms of solid content) was added, and the temperature was raised. A capsule dispersion was obtained. The average diameter of the obtained microcapsules was 1.12 µm, and 346 g was obtained.

Example 4

The same procedure as in Example 3 was carried out except that 0.05% NP-5 (polyoxyethylene nonylphenyl ether n ≒ 5) was added to a 5% gelatin aqueous solution. The average diameter of the obtained microcapsules was 1.08 mu m, and the yield was 325 g.

Example 5

<Scale Up>

50 g of NP-5 was added to 10 L of 5% gelatin aqueous solution, and 2 kg of jasmine oil was added thereto, stirred at 5000 rpm for 10 minutes, and 400 g of ammonium sulfate (20% aqueous solution) was added thereto, followed by stirring for 5 minutes. 2 kg of melamine resin (solid content) was added while maintaining 40 ° C., the temperature was raised to 60 ° C., and the stirring speed was adjusted to 700-1000 rpm. After reacting for 2 hours while maintaining the temperature and stirring speed, a microcapsule dispersion was obtained. The average diameter of the obtained microcapsules was 1.53 µm, and a 13.4 kg microcapsule dispersion was obtained.

Example 6

The same procedure as in Example 3 was carried out except that 2% spiroxazine (blue) dissolved in cooking oil was added instead of 100 g of strawberry oil. The average diameter of the obtained microcapsules was 0.89 m, and the capsule dispersion was 240 g. The obtained microcapsules were colored blue by sunlight and had the characteristic of no color in the cow.

Example 7

<Method of manufacturing anti-micro capsule

To 20 g of 2% gelatin aqueous solution, a mixture of 10 g of toluene diisocyanate, 1 g of cypermethrin, and 20 g of cyclohexane was added and stirred at 1000 rpm for 5 minutes to prepare an emulsion, and 5 g of ethylenediamine was added slowly and stirred at 50 ° C. for 3 hours. 48 g of microcapsule dispersion were obtained.

Comparative Example 1

The same procedure as in Example 1 was carried out in addition to using water from which gelatin was removed. The prepared microcapsules were obtained in the same shape and yield as in Example 1, but after 3 days, the capsules were associated with each other, and thus the microcapsules could not be used.

Comparative Example 2

It carried out on the conditions similar to Example 1 except having adjusted pH to 4.2 using acetic acid instead of ammonium sulfate salt. The unique flavor of strawberry oil was slightly changed by acetic acid and was almost the same as in Example 1 except that the prepared microcapsule dispersion was acidic. However, the work environment was poor due to exposure to formalin gas during pH adjustment.

According to the method of the present invention, the preparation of the microcapsules is simple, the yield is high, and the obtained microcapsules not only have the functions of sustained release and disintegrating function but also have excellent heat resistance.

Claims (6)

The fat-soluble core material is dispersed in an aqueous gelatin solution, which is a natural surfactant, and a water-soluble melamine resin is added to the dispersion to form a capsule wall. At this time, an ammonium sulfate catalyst is added 2.5 to 4 weight percent of the melamine resin content without supplying an organic acid. Method for producing a microcapsule, characterized in that the dispersion is adjusted to an acidic pH of 3.5 to 5, and heated to 50 to 80 ℃ by adding in%. delete The method of claim 1, wherein in the dispersing of the initial fat-soluble core material, a non-ionic surfactant is further added in addition to the natural surfactant. delete The method of claim 1, wherein the ammonium sulfate salt is added to the dispersion after melamine resin is added. The method of claim 1, further comprising neutralizing the dispersion to pH 8 after the microcapsules are formed.