JPS621777B2 - - 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 the production of 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. The products also include pharmaceuticals, agricultural chemicals, fragrances, dyes, adhesives, etc. The most well-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 particular, the fundamental drawback of not being able to produce colloids at high concentrations is due to the fact that coacervation occurs only at low colloid concentrations, so it will be difficult to improve in the future. 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. ) will vary. It has disadvantages such as 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. It was only put into practical use for some purposes. 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. 116249/1983). The main improvement was to stably obtain a microcapsule dispersion with a higher solid content concentration and lower viscosity. This was achieved by adding a maleic acid copolymer. That is, in the present invention, in water, 1:0.5~
In the coexistence of styrene maleic anhydride copolymer and vinyl acetate 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. A microcapsule is produced by depositing a melamine-formalin polymer film around the molecule. 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 vinyl acetate maleic anhydride copolymer to styrene maleic anhydride copolymer, a microcapsule dispersion with a higher solid content concentration and lower viscosity could be created. It was found that it could be manufactured more stably, and the present invention was achieved. Stability here means that the arrangement of the emulsified particles is stable and that it is also stable against factors such as encapsulation conditions (temperature, pH, etc.). In other words, when it comes to emulsified particles, by appropriately mixing two copolymers with highly hydrophobic styrene and relatively highly hydrophilic vinyl acetate, the emulsification of hydrophobic substances can be controlled quite freely. Emulsified particles with uniform particle sizes can be made. On the other hand, for example, when vinyl acetate maleic anhydride copolymer is used alone, emulsified particles are irregular, stability is poor, and good capsules cannot be obtained. Regarding the reaction temperature, 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 the combination system of the present invention, good capsules can be obtained even at temperatures above 40°C and 95°C. Regarding the solid content concentration of the capsule dispersion,
Various membranes can be produced depending on the thickness of the membrane and the amount and type of core material, but where the styrene-maleic anhydride copolymer alone can produce a solids concentration of, for example, 50%, the combined system of the present invention can produce a solids concentration of 65% with the same formulation. It can be manufactured with a solid content concentration. In other words, the throughput is improved by 30%. This not only increases facility capacity but also brings various industrial benefits such as reduced movement and transportation costs and improved drying efficiency. 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, it is thought that different types of carboxylic acids (the same maleic acid has different adjacent groups) have conditions suitable for concentration, and when used together, melamine formalin can be used to form capsule membranes over a wide range. It is thought that the resin 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 melamine resins are also commercially available, and phenols,
Modification with benzoguanamine, urea, etc. has also been carried out, but as long as it is water-soluble, it can often be used in the same way as the melamine-formalin initial condensate. 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. 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 most important objective is to stably obtain more stable capsules with high concentration and low viscosity. The object of the present invention was achieved by adding vinyl acetate maleic anhydride copolymer to the styrene maleic anhydride copolymer to form a melamine-formalin resin. The styrene maleic anhydride copolymer and the vinyl acetate maleic anhydride copolymer may be dissolved in water at the same time, or after being dispersed and emulsified,
The other may be added, and the combination amount and mixing method of the two types can be arbitrarily selected depending on the hydrophobic substance. 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. 2.5 g of Scribset 520 (manufactured by Monsanto, styrene maleic anhydride copolymer) and Tamanoli CN
(Manufactured by Arakawa Forestry Co., Ltd., vinyl acetate maleic anhydride copolymer)
6% mixed and dissolved with 2.5g (solid) at PH5.5
An aqueous solution was prepared and the above hydrophobic substance was emulsified therein. 5.5g of melamine and 12g of 37% formalin, PH9
An aqueous solution of the melamine-formalin initial condensate dissolved in was added to the emulsion, the solid content was adjusted to 50%, and the mixture was heated at 50°C for 1 hour to complete encapsulation. Comparative Example 1 Capsules of a styrene maleic anhydride sole modifier were prepared under the same conditions as in Example 1, using the same amount of Scriptset 520 in place of Tamanoli CN in Example 1. Comparative Example 2 Contrary to Comparative Example 1, capsules of a vinyl acetate maleic anhydride sole modifier were produced under the same conditions as in Example 1, using Tamanori CN instead of Script Set 520. . Example 2 Encapsulation was carried out using the same amount of chemicals as in Example 1 and reaction conditions at 80° C. for 1 hour. Comparative Example 3 Encapsulation was carried out in the same manner as in Comparative Example 1, except that the reaction conditions were changed to 80° C. for 1 hour. Comparative Example 4 Encapsulation was carried out in the same manner as in Comparative Example 2 except that the reaction conditions were changed to 80° C. for 1 hour. Example 3 The six types of capsules mentioned above 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. The viscosity of the capsule liquid was measured using a B-type viscometer. The whiteness data is a value determined by a Nippon Denshi colorimeter.

[Table] As shown in Table 1, it can be seen that according to the present invention, good capsules are produced in a wide temperature range, and since the liquid has a low viscosity, it is possible to achieve high concentration. For carbonless paper applications, the paper is usually coated with several additive adhesives. Capsules of other hydrophobic substances can be produced in a similar manner, and the thickness of the membrane material can be freely adjusted depending on the application. Example 4 Encapsulation was carried out in the same manner as in Example 2, except that the amount of water was adjusted so that the solid content of the finished product was 63%. The viscosity of the resulting capsules was 6300 CPS. The capsule had excellent properties and was useful for carbonless copying paper. Comparative Example 5 In Comparative Example 3, encapsulation was carried out in the same manner as in Comparative Example 3 except that the amount of water was adjusted so that the finished solid content was 63%, but the entire capsule liquid turned into a gel and was stirred. It became impossible.

Claims (1)

[Claims] 1. After dispersing or emulsifying a hydrophobic substance into discontinuous fine particles in an acidic aqueous solution of a styrene maleic anhydride copolymer, a melamine-formalin initial condensate is added, and the mixture is acidified and heated. In a method for manufacturing microcapsules containing a hydrophobic substance as a core material by reacting to form a wall film, vinyl acetate maleic anhydride copolymer is further added to an acidic aqueous solution of styrene maleic anhydride copolymer. - An improved method for manufacturing microcapsules characterized by dissolution. 2. Improved microcapsule production according to claim 1, wherein the amount of the vinyl acetate maleic anhydride copolymer added is in the range of 0.5 to 2 parts by weight per 1 part by weight of the styrene maleic anhydride copolymer. Law.