JPH0217938A - Preparation of microcapsule - Google Patents

Abstract

PURPOSE:To eliminate the generation of a large capsule of an air bubble by dispersing a hydrophobic substance having a leuco dye dissolved therein in a specific aqueous dispersant solution in an emulsified state and adding a melamine/formaldehyde precondensate thereto to heat the solution. CONSTITUTION:Dimethylpolysiloxane, a nonionic surfactant and synthetic silica are together used along with a copolymer of styrenes, which contain a compound represented by formula I(wherein R1 and R2 are a hydrogen atom or a 1-4C alkyl group and not simultaneously a hydrogen atom), and maleic anhydride to prepare an aqueous dispersant solution. After a hydrophobic substance having a colorless or light-colored leuco dye dissolved therein is emulsified and dispersed in the aforementioned aqueous dispersant solution, a melamine/ formaldehyde precondensate or a urea/formaldehyde precondensate is added to the obtained dispersion. Next, the formed composition is heated and reacted under acidic condition to prepare a microcapsule having the hydrophobic substance as a core substance.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Utilization Public Funds> The present invention relates to a method for producing microcapsules for pressure-sensitive recording paper containing a hydrophobic substance in which a leuco dye is dissolved.

<Prior Art> Conventionally, as a dispersant for dispersing a hydrophobic core substance used in manufacturing microcapsules, styrene-keleic anhydride copolymer (Japanese Patent Publication No. 58-88116.
Maleic anhydride copolymers such as JP-A-59-177128) and styrene sulfonic acid-based copolymers (JP-A-59-177128)
8-14912) etc. are commonly known.

However, using these conventionally known dispersants, a hydrophobic substance in which a leuco dye is dissolved is dispersed, a melamine-formaldehyde initial condensate or a urea-formaldehyde initial condensate is added, and the mixture is heated and reacted under acidic conditions. When microcapsules are manufactured, their dispersibility is insufficient;
As a result, the amount of unencapsulated particles increases and the microencapsulation rate decreases. In addition, the dispersant and leuco dye partially reacted, causing color development in the liquid, making it impossible to obtain satisfactory microcapsules.

When producing microcapsules, the present inventors investigated dispersants that minimize uncapsules and do not cause liquid color development, and used styrenes containing nuclear alkyl-substituted α-alkylstyrene as an essential component and maleanhydride as dispersants. Method using copolymer with acid (JP-A-62-125851)
, and a method using a copolymer of styrenes and maleic anhydride containing α-methylstyrene as an essential component as a dispersant (Special Patent No. '91 Sho 62-269742).

<Problems to be Solved by the Invention> However, when emulsifying and dispersing using these dispersants, although the dispersibility is excellent, there is a lot of foaming, the liquid content during emulsifying and dispersing increases, and giant capsules of air bubbles are formed. was still insufficient. In order to suppress foaming, it is possible to add an antifoaming agent, but the commonly used silicone antifoaming agents cause problems such as repellency during coating.

<Means for Solving the Problems> The present inventors have studied a method for efficiently dispersing a hydrophobic substance in which a leuco dye is dissolved, suppressing foaming, and eliminating the generation of giant capsules of air bubbles. By using a dispersant and a specific silicone antifoaming agent in combination, a microcapsule dispersion can be obtained that suppresses uncapsule formation and eliminates the troubles caused by foaming, and also reduces the problem during coating that occurs with ordinary silicone antifoaming agents. They found that there were no problems such as repellency and completed the present invention.

That is, in the present invention, after emulsifying and dispersing a hydrophobic substance in which a colorless or light-colored leuco dye is dissolved in an aqueous dispersant solution,
In a method for producing microcapsules with a hydrophobic substance as a core material by adding a melamine-formaldehyde initial condensate or a urea-formaldehyde initial condensate and carrying out a heating reaction under acidic conditions, the dispersant is a compound of the general formula (1).
) using a copolymer of styrenes and maleic anhydride that contains the compound represented by () as an essential component, and also uses a silicone antifoaming agent that contains dimethylpolysiloxane, a nonionic surfactant, and synthetic silica as essential components. The present invention provides a method for producing microcapsules characterized by:

[In the formula, R1-R1 represents a hydrogen atom or a C1-4 alkyl group, and Rte and R1 are not hydrogen atoms at the same time. ] Examples of the compound represented by the general formula α) include α-methylstyrene, nuclear methyl-substituted α-methylstyrene, nuclear ethyl-substituted α-methylstyrene, nuclear isopropyl-substituted α-methylstyrene, and vinyltoluene. General formula (
Other styrenes can be used simultaneously with the compound represented by 1), and styrene is a typical example of the other styrenes.

The usage of the compound represented by the general formula (1) is lθ mol% or more, preferably 80 mol% or more based on the total amount of styrenes.

The copolymerization reaction of these styrenes and maleic anhydride is carried out by a known method, for example, in a solvent that also dissolves the copolymer such as acetone, methyl ethyl ketone, methyl isobutyl ketone, benzene, toluene, There is a method in which the copolymer is precipitated in a solvent such as xylene. When the copolymer thus obtained is a solid or powder, it is water-solubilized with an aqueous solution of ammonia, an aqueous solution of an alkali metal such as sodium hydroxide, or an aqueous solution of an organic amine such as monomethylamine or dimethylamine. When dissolved in a solvent or containing a solvent, it is made water-solubilized by adding an aqueous solution of ammonia, an alkali metal, or an organic amine to replace the solvent with water.

The thus obtained aqueous solution of a copolymer of styrene and maleic anhydride containing the compound of general formula (1) as an essential component is used as a dispersant for a hydrophobic substance in which a leuco dye is dissolved, but the concentration of the dispersant is It is used in an amount of 0.6 to 10 weight percent.

The specific silicone antifoaming agent used in the present invention contains dimethylpolysiloxane, a nonionic surfactant, and synthetic silica as essential components. The blending ratio is 20 parts/6 parts to 60 parts/20 parts, and water is added as necessary.

The preferred nonionic surfactant is polyethylene glycol alkyl ether. The amount of this specific silicone antifoaming agent added is 100 to 800% to the emulsified dispersion system.
0 ppm, preferably 200 to 2000 ppm.

Examples of the leuco dyes used in the present invention include triphenylmethane leuco dyes, fluoran leuco dyes, and spiropyran leuco dyes. The method of manufacturing microcapsules itself is known;
For example, after dispersing or emulsifying a hydrophobic substance using the dispersant aqueous solution of the present invention under acidic conditions, a melamine-formaldehyde initial condensate or a urea-formaldehyde initial condensate is added, and the microorganisms are reacted under acidic conditions and heating. Manufacture capsules.

<Effects of the invention> When microcapsules are produced by the production method of the present invention,
Foaming during emulsification and dispersion is suppressed, there is no increase in liquid volume, high quality microcapsules are obtained without the formation of giant capsules of air bubbles, and no repellency occurs when coated on paper.

<Example> This will be explained below using examples.

Reference Example 1 144 equipped with a thermometer, stirrer, reflux condenser, and dropping spout
Acetone 1 O9 t1 Maleic anhydride 6 in a Tulo flask
6 F, styrene 7? , α-methylstyrene 71F was charged, and the temperature was raised to 70° C. while stirring. Next, a solution prepared by dissolving 8.6 F of azobisisobutyronitrile in 81.5 F of acetone was added dropwise from the dropping spout over 1 hour, and the mixture was kept warm for 7 hours under refluxing acetone. Next, 711f of an 8.896 aqueous sodium hydroxide solution was added dropwise from the dropping spout over 1 hour under stirring at a temperature of 66°C, and then the acetone was distilled off. The obtained copolymer aqueous solution was adjusted to a concentration of 20%, p
856 tons of a slightly warm viscous liquid having a viscosity of 20 poise and H6,0 was obtained. Let's call it resin liquid A.

9 Reference Examples 2 to 4 The amounts of maleic anhydride, α-methylstyrene, nuclear methyl-substituted α-methylstyrene, styrene, and caustic soda were changed so that the monomer composition and neutralization rate shown in Table-1 were obtained, and An aqueous copolymer solution was obtained in the same manner as in Reference Example 1, except that the conditions for copolymerization and concentration adjustment were changed to obtain the concentration shown in Example 1. They are referred to as resin liquids B to D, respectively.

Example 1 Crystal violet lactone as hydrophobic substance 8.
6 parts by weight of KMC-118 (oil manufactured by Kureha Chemical Co., Ltd.) 96
．． A solution of 5 parts by weight is used.

Resin liquid A 40f and 160 t of water were added to a II four-eye flask equipped with a stirrer, a thermometer, and a reflux condenser, and the mixture was heated to 60° C. and stirred. The pH was adjusted to 6.0 with acetic acid, and 0.19 F of 86 parts of polyethylene glycol monobutyl ether and 10 parts of synthetic silica dispersed in 146 parts of water to 100 parts of dimethylpolysiloxane was added as an antifoaming agent. The above hydrophobic substance 180F was added and emulsified and dispersed.

Add to this emulsified dispersion liquid [Laze Resin 618 (Sumitomo Chemical Co., Ltd. melamine-formaldehyde initial bond product 80% product)]
An aqueous solution of 80 t and 60 g of water was added and stirred at 60° C. for 1 hour to obtain microcapsules.

When the particle size distribution of the obtained microcapsules was measured using a Coulter counter, no giant capsules of zeta bubbles were observed.

In addition, a coating liquid was prepared using the following formulation, and a commercially available high-quality paper (tsubo [55 tsubo]
F/♂) at a dry weight of 4 W/l,
It was dried at 120° C. for 1 minute to obtain microcapsule coated paper.

No repellency was observed on this coated paper.

Examples 2 to 4 The same procedure as Example 1 was carried out except that resin liquids B to D were used instead of resin liquid A and the amount of antifoaming agent was changed.
Microcapsules were created and evaluated. The results are shown in Table 2 together with Example 1.

Comparative Examples-1 to 2 Example-1 except that no antifoaming agent was used or a commercially available silicone antifoaming agent with a nonionic surfactant ratio of 7% to dimethylpolysiloxane was used. I did the same thing. The results are also shown in Table-2.

Claims (1)

[Claims] After emulsifying and dispersing a hydrophobic substance in which a colorless or light-colored leuco dye is dissolved in an aqueous dispersant solution, a melamine-formaldehyde initial condensate or a urea-formaldehyde initial condensate is added, and the mixture is treated under acidic conditions. A copolymer of styrenes and maleic anhydride containing a compound represented by the general formula (I) as an essential component as a dispersant in a method for producing microcapsules with a hydrophobic substance as a core material by heating reaction with 1. A method for producing microcapsules, characterized by using a silicone antifoaming agent containing dimethylpolysiloxane, a nonionic surfactant, and synthetic silica as essential components. ▲There are mathematical formulas, chemical formulas, tables, etc.▼(I) [In the formula, R_1 and R_■ are hydrogen atoms or C_1_ to_4
represents an alkyl group, and R_1 and R_■ are not hydrogen atoms at the same time. ]