JPS621776B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing microcapsules containing a hydrophobic substance as a core material, and more particularly to an improvement in a method for producing microcapsules using melamine-formalin resin as a membrane material. Microcapsules are used to contain and stabilize unstable substances such as highly reactive, volatile, and liquid substances, making them convenient for subsequent use and handling. , pharmaceuticals, agricultural chemicals, fragrances, dyes, adhesives, etc. The best known use is carbonless copying paper, which has been used for over 30 years. A currently known method for producing microcapsules is a coacervation method using gelatin. This method is widely used because it produces a relatively dense capsule membrane, but because it uses natural products, there are inevitably variations in quality, it does not have water resistance, and it is susceptible to microorganisms (i.e., it is easily putrefied). ), they have drawbacks such as not being able to be made at high concentrations, requiring complicated manufacturing steps, and requiring a long time to complete encapsulation. In addition to this, interfacial polymerization is an effective method for obtaining a dense capsule membrane (Tokuko Sho 38-19574,
42-446, Special Publication No. 42-2882, Special Publication No. 42-8693). This method allows encapsulation with membrane materials with various characteristics, but since highly reactive chemicals are used as raw materials for membrane materials, it is industrially difficult to control the reaction. ), it cannot be used because it will cause a chemical reaction with contents containing active hydrogen (-OH-NH, etc.), and the raw chemicals are highly toxic, so care must be taken during the process or unreacted substances. Because of its drawbacks, it was put into practical use only for a limited number of applications. Microcapsules made of aminoplast (amino resin) membranes have also been put to practical use (for example,
12380, Special Publication 12381, Special Publication 12381, Special Publication 1977-3495, Special Publication 14379, Special Publication 14379, Special Publication 30282, Special Publication 1977-
10780, Special Publication Showa 47-23165). This method uses a synthetic and inexpensive urea-formalin resin as the membrane material, and can produce capsules with excellent water resistance and microbial resistance, but it is difficult to make the wall around the hydrophobic substance sufficiently dense. Another drawback was that it was difficult to sufficiently disperse and emulsify hydrophobic substances. As an improvement to this method, as described in JP-A-51-9079, ethylene maleic anhydride copolymer, methyl vinyl ether maleic anhydride copolymer, and polyacrylic acid are used as modifiers for the capsule membrane. A method was proposed, and subsequently, the use of melamine-formalin resin as a modifier for urea-formalin resin was announced (Japanese Patent Application Laid-Open No. 52-66878).
issue). One of the inventors of this application previously proposed melamine-formalin resin microcapsules using styrene-maleic anhydride copolymer as the optimal capsule wall modifier as a new technology (Japanese Patent Application No. 116249/1989, title of the invention "Microcapsules"). Capsule”, filing date September 28, 1978). The purpose was to provide microcapsules with dense and durable capsule walls. The purpose of the present invention is to improve the above-mentioned earlier application (Japanese Patent Application No. 116249/1986). The main improvement is that more stable microcapsules can be obtained at higher concentrations by adding ethylene maleic anhydride copolymer on top of the styrene maleic anhydride copolymer as a modifier. It was achieved. That is, in the present invention, in water, 1:0.5~
In the coexistence of styrene-maleic anhydride copolymer and ethylene-maleic anhydride copolymer dissolved at a ratio of 1:2 (weight ratio), the melamine-formalin initial condensate is reacted under acidic heating to form a hydrophobic substance. Microcapsules are produced by depositing a melamine-formalin polymer film around them. As mentioned in the previous application (Japanese Patent Application No. 116249/1986), melamine-formalin resin itself has a faster curing speed, stronger tensile strength and compressive strength, and higher heat resistance than urea-formalin resin. It has characteristics such as high deformation temperature, low water absorption, and resistance to weak acids and weak alkalis, and these properties are exhibited even when used as a membrane material for capsules. Traditionally, for example, the aforementioned Tokko Sho 37-12380, Tokko Sho No.
No. 38-12518 and the like also describe encapsulation with melamine-formalin, but the specific method is not described in detail, and good capsules cannot be obtained even if the combination is encapsulated. The present invention is characterized by the modifier used. As mentioned above, the present inventors have previously discovered that the most suitable modifier is a styrene maleic anhydride copolymer (Japanese Patent Application No.
116249). As a result of further various studies, the present inventors found that by adding ethylene maleic anhydride copolymer to styrene maleic anhydride copolymer,
It has been found that more stable encapsulation is possible, leading to the present invention. Stability here means that the arrangement of the emulsified particles is stable, that it is stable against factors such as encapsulation conditions (temperature, pH, etc.), and that it is more stable than other modifiers. of
Since the pH can be raised, it can be used in a variety of ways, including stably encapsulating contents that are sensitive to acids, and is in fact an excellent capsule in all respects. In other words, when it comes to emulsified particles, by appropriately mixing a styrene maleic anhydride copolymer with large hydrophobic groups and ethylene maleic anhydride with small groups, the emulsification of hydrophobic substances can be controlled quite freely, and the particle size can be made uniform. It is possible to make ivy emulsified particles. On the other hand, for example, when ethylene maleic anhydride copolymer is used alone, emulsified particles are irregular and stability is poor. Regarding the reaction temperature, for ethylene maleic anhydride copolymer,
A temperature of around 50℃ is optimal; if it exceeds 70℃, the capsules will not form properly. On the other hand, if the styrene maleic anhydride copolymer is used alone, a desirable capsule can be formed at a temperature of 60°C or higher, but it is difficult to obtain a good capsule at a temperature of about 40°C. On the other hand, in a combination system like the present invention,
Good capsules can be obtained even at temperatures above 40°C and 95°C. Even in the preferred pH range, when using ethylene maleic anhydride copolymer alone, the pH is about 4.5 to 5.0, and when using styrene maleic anhydride copolymer alone, it is about 5.3 to 5.8. In the case of a pH of 5.0 to 6.0, good capsules can be produced in a wide range of pH. The effect of modifiers on encapsulation is not fully understood, but when melamine-formalin is precipitated as a resin under acidic heating, the carboxylic acid is sucked and concentrated to efficiently precipitate around the hydrophobic liquid. It seems that there is.
Therefore, different types of carboxylic acids (the same maleic acid has different adjacent groups) are thought to have a suitable pH range, and when used together, melamine-formalin resin can be used as a capsule membrane over a wide range. It is thought that it is concentrated. The melamine-formalin initial condensate used in the present invention is one in which 1.2 mol or more, preferably 1.5 to 3.5 mol, of formalin is added to 1 mol of melamine under alkaline conditions, and is generally prepared by adding hexamethylol from monomethylolmelamine. It is said to be a mixture of methylolmelamine and formalin, and there are many commercially available products. In addition, modified melamine resins such as methylated and butylated are also commercially available, and modified with phenols, benzoguanamine, urea, etc., but as long as they are water-soluble, they are similar to the melamine-formalin initial condensate. There are many things that can be used for. The ratio of melamine-formalin resin to the above modifier is 0.5 to 1.5 to 1 part melamine (single substance) by weight.
is the preferred range. Encapsulation involves dispersing and emulsifying a hydrophobic substance in an aqueous solution containing a pH-adjusted denaturing agent.
Add melamine-formalin initial condensate and maintain at the above temperature for a short time (within 1 hour)
, encapsulation is complete. The solid content concentration of the capsule dispersion can be made in various ways depending mainly on the hydrophobic substance and the thickness of the membrane.
% to 50% are common concentrations in this invention. In summary, the aim of the invention is to obtain microcapsules with a dense membrane. Another objective is to obtain capsules with strong water resistance and excellent microbial resistance. The main goal is to obtain more stable capsules at higher concentrations. The object of the present invention was achieved by adding an ethylene maleic anhydride copolymer to the styrene maleic anhydride copolymer to form a melamine-formalin resin. The styrene maleic anhydride copolymer and the ethylene maleic anhydride copolymer may be dissolved in water at the same time, or one may be dispersed and emulsified before the other is added. The amount of combination of seeds and the mixing method can be arbitrarily selected. If both of them coexist, a remarkable improvement effect will be exhibited compared to when they are used alone. For the sake of clarity, a specific example will be described below regarding microcapsules for carbonless copying paper, but other hydrophobic substances can be encapsulated in the same way. Example 1 2g of crystal violet lactone was added to KMC
-113 (trade name, oil manufactured by Kureha Chemical Co., Ltd.) by heating and dissolving it in 100 g was used as a hydrophobic substance. A hydrophobic substance was emulsified in a solution of 6.5 g of SCRIPSET 520 (manufactured by Monsanto, styrene maleic anhydride copolymer) and 0.1 g of caustic soda in 100 g of water. Furthermore, 5 g of EMA-31 (manufactured by Monsanto, ethylene maleic anhydride copolymer), 0.1 g of caustic soda, and 100 g of water were added to the emulsion. A melamine-formalin initial condensate aqueous solution containing 15 g of melamine and 30 g of 37% formalin dissolved at pH 9 was added to the above emulsion, heated at 55° C. for 1 hour, and encapsulation was completed. During encapsulation
The pH was 5. Comparative Example 1 Instead of script set 520 of Example 1,
Melamine-formalin resin microcapsules were made using the same amount of EMA31 and ethylene-maleic anhydride copolymer alone as the modifier under conditions of heating at pH 5 and temperature of 55° C. for 1 hour. Comparative example 2 Script set instead of EMA31 of Example 1
Melamine-formalin resin microcapsules were prepared using the same amount of 520 and styrene-maleic anhydride copolymer alone as the modifier under conditions of pH 5 and heating at 55° C. for 1 hour. Example 2 Among the conditions of Example 1, the reaction conditions were PH5.7 and temperature.
Capsules were produced by changing the temperature to 70°C. Comparative Example 3 The reaction conditions of Comparative Example 2 were PH5.7 and temperature 70°C.
This was the capsule of Comparative Example 3. Comparative Example 4 102 g of the above hydrophobic substance was emulsified in 200 g of 5% EMA, 22 g of urea, 2 g of resorcin, and 50 g of formalin.
g was added thereto, and encapsulation was carried out under conditions of pH 3.5 and 55°C. 1 hour was not enough, so 3
After a time reaction, capsules made of urea-formalin resin were created. Comparative Example 5 Encapsulation was carried out under the same conditions as in Example 2, using the same amount of gum arabic instead of Script Set 520 in Example 2. Example 3 The above seven types of capsules were printed on commercially available Mitsubishi NCR paper “Bottom”
(paraphenylphenol resin that develops crystal violet lactone color) was smeared with a wire bar at a concentration of 2 g/m ² (dry basis), dried, and the degree of completion of the capsule was examined. Incidentally, the average particle diameter of all capsules was 3 to 5 μm.

[Table] It can be seen that according to the present invention, good capsules can be produced over a wide range. That is, in Examples 1 and 2 according to the present invention, excellent microcapsules could be stably produced even when the pH was changed from 5 to 5.7 and the temperature was changed from 55°C to 70°C. On the other hand, in Comparative Examples 2 and 3 based on the earlier application (Japanese Patent Application No. 116249/1982), fairly good microcapsules were certainly obtained at PH5.7 and temperature 70°C; 55
℃, the encapsulation is incomplete and therefore extremely sensitive to fluctuations in conditions, and the present invention was found to be superior and more lenient as an industrial microencapsulation method. Moreover, the microcapsule liquid of Comparative Example 3 had a high viscosity. In this respect as well, the present invention is superior in that it has a lower viscosity and can be put to practical use with a high solid content concentration. Example 4 Paraphenylphenol resin (mP83℃) 50
g to KMC-113, 25g and SASN-296 (product name,
A hydrophobic substance was obtained by heating and dissolving the mixture with 25 g of oil (manufactured by Nisseki Chemical Co., Ltd.). 200 g of 5% aqueous solution of 1:1 (weight ratio) of EMA31 and Script Set 520 (PH
4.8) Disperse the above hydrophobic substance inside. Emulsified. A melamine-formalin initial condensate aqueous solution obtained by heating 20 g of melamine, 45 g of formalin, and 55 g of water at a pH of 9 was added to the emulsion and allowed to react at 65° C. for 1 hour, and after cooling, the pH was adjusted to 9.0 with an aqueous ammonia solution. Microcapsules containing the phenolic resin solution as the core material were obtained. Example 5 The capsules of Example 2 and Example 4 were mixed in a 1:1 ratio to yield 41 g/m ² to give 5 g/m ² (dry basis).
When smeared on high-quality paper, a bright white self-coloring sheet with a whiteness of 83.0 was obtained. In order to check the density of the film, one drop each of toluene and ethanol was dropped on the smeared surface and dried, but there was no effect. When printed using a ribbonless typewriter, dark blue colored characters were obtained on a pure white background. These are tests to investigate the characteristics of capsules, and in reality, good carbonless paper can be obtained by smearing them with pigments, adhesives, and other additives, and the microcapsules of the present invention It could be used for practically excellent carbonless paper.

Claims (1)

[Claims] 1. After dispersing or emulsifying a hydrophobic substance into discontinuous fine particles in an acidic aqueous solution of styrene maleic anhydride copolymer, a melamine-formalin initial condensate is added, and the mixture is reacted under acidic conditions and heat to form a wall. In a method for producing microcapsules containing a hydrophobic substance as a core material by forming a membrane, 0.5 to 2 parts by weight of ethylene maleic anhydride copolymer is further added to an acidic aqueous solution of 1 part by weight of styrene maleic anhydride copolymer. An improved microcapsule production method characterized by adding and dissolving microcapsules at a ratio of