KR920009491B1 - Manufacturing method of micro-capsule for recording paper - Google Patents

Abstract

Microcopsules are produced by (1) precondensating melamine-urea- formaldehyde in an alkali solution, (2) emulsifying a core material of a hydrophobic dye solution using an emulsifier solution composed of (a) alkali metal salt- and ammonium salt-substituted styrene-maleic acid anhydride copolymer and (b) NOPCO 1470-K, (3) forming a microcapsule walls by reacting the precondensates with the emulsified solution in pH 5.5-6.5 at 60-70 deg.C and (4) stabilizing the encapsuled liquid using aqueous ammonium and sodium hydroxide solution. The microcapsules are used for a pressure sensitive recording paper.

Description

Preparation method of microcapsules for pressure-sensitive recording paper

The present invention relates to a method of manufacturing microcapsules for pressure-sensitive recording paper.

In the problems of the prior art, generally the pressure recording paper is composed of the upper (CB: Coated Back) and the lower (CF: Coated Front) bar, the back of the upper limb is a plurality of pressure rupture containing an electron-donating colorless basic dye solution It is coated with microcapsules and the surface of the lower extremity is covered with an electron-receiving substance that can develop a colored image on the lower extremity when it comes into contact with a colorless basic dye. The image is configured to be developed. Although the pressure-sensitive recording paper was commercialized in the 1950's, efforts have been made to increase its performance, and recently, many studies on reinforcing capsules excellent in heat resistance, moisture resistance, light resistance, chemical resistance, and impact resistance have been conducted.

The microcapsules for decompression recording paper are largely divided into three types: coacervation method, interfacial polymerization method, and in-situ method.

The coacervation method is a method that uses a reaction between a natural positive electrolyte such as gelatin and gum arabic and an anionic polymer, which is relatively expensive, and the wall membrane is easily affected by microorganisms and has a disadvantage of not having a compact structure. It's being replaced in a different way.

The interfacial polymerization method is a method of using synthetic polymers as a membrane material, and various capsule wall membranes can be obtained depending on the type of monomers used. In general, polymers widely used as a film material of microcapsules for pressure-sensitive recording papers include pulley urea and polyurethane. The capsule produced by this interfacial polymerization method has a disadvantage in that the thickness of the formed wall film is thin, making it difficult to obtain a capsule wall film of an appropriate strength, and the price is rather high. (U.S Patent, 4,105,823)

On the other hand, in-situ microcapsules generally have high quality because they are less influenced by microorganisms and have good strength, but the wall membrane is not completely impermeable and has difficulty in obtaining satisfactory emulsified state of hydrophobic dye solution during capsule manufacture. have. Therefore, in order to overcome these disadvantages in emulsification, ethylene-maleic anhydride copolymer, ethylene-maleic anhydride copolymer, methylvinylether-maleic anhydride copolymer, acrylic acid polymer, and other dispersing agents are used as emulsifiers to improve the emulsion stability of the emulsion. An emulsion having a high and uniform particle size distribution is obtained. (GB Patent 2,115,372)

Capsules made of melamine-formaldehyde resin or melamine-urea-formaldehyde resin, which are one of the in-situ methods, have excellent properties such as heat resistance, moisture resistance, light resistance, chemical resistance, and impact resistance than other membrane materials. Emulsification stability and uniform particle size distribution are difficult to obtain, and the above-mentioned styrene-maleic anhydride copolymer and ethylene-maleic anhydride copolymer are used as emulsifiers to improve the manufacturing method. (US 4,105,823, GB 2,115,372, GB 2,006,709 52-66,878, 55-15,660, 55-47,139, 59-177,128, 60-216,839

However, it is difficult to obtain satisfactory emulsification stability even when emulsifying using such an emulsifier. In particular, the styrene-maleic anhydride copolymer, which is generally used, has no problem in laboratory small scale production, but the viscosity of the emulsifier aqueous solution in large scale production Because of the high mixing, the mixing is not complete, and there is a case where there is a partial emulsification part.

This poor emulsification site is present in some portion of the capsule even in the encapsulation process is a direct cause of blue spot contamination after the pressure-sensitive paper production. In addition, when the viscosity of the emulsion is high, the viscosity of the capsule is also increased. This high viscosity capsule solution is difficult to obtain a uniform surface of the pressure-sensitive recording paper due to the difficulty in setting the application conditions during the production of the pressure-sensitive recording paper. In addition, if the stability is not good, it is necessary to have a larger emulsification equipment than necessary, so there is a problem such as a large initial investment in the capsule production, and as a result may be a cause of raising the production cost.

In order to solve the above problems, in the present invention, a microcapsule for pressure-sensitive recording paper is prepared using a polymer based on melamine-formaldehyde resin and copolymerized with urea-formaldehyde resin at 0.01 to 95% molar ratio. In this case, an emulsion having excellent emulsion stability and good fluidity when emulsifying the hydrophobic dye solution is prepared to improve work efficiency in manufacturing a pressure-sensitive recording paper and to produce an excellent pressure-sensitive recording paper.

In embodying the present invention, the microcapsules are prepared in the following steps.

1) preparing a melamine-urea-formaldehyde prepolymer having a titration composition in an alkaline aqueous solution.

2) The emulsifying step of emulsifying the hydrophobic dye solution using an styrene-maleic anhydride copolymer substituted with an alkali metal salt and an ammonium salt as an emulsifier.

3) A polymerization step of forming a capsule wall membrane by adding the emulsion solution prepared in step 2) to the precondensate prepared in step 1) at pH5.5 to 6.5 and a temperature of 60 to 90 ° C.

4) After encapsulation polymerization in step 3), the temperature is naturally cooled to room temperature and reacted for 12 hours or more, and residual formalin is first removed with ammonia water, the capsule is stabilized, and the capsule is second stabilized with an aqueous solution of caustic soda. Stabilization step.

In step 1), the prepolymer is reacted with melamine, urea and formaldehyde in a molar ratio of 1: 3 to 1: 4.5, a reaction temperature of 55 to 65 ° C, and a pH of 9 to 10 minutes to obtain a prepolymer.

In step 2), the emulsifier is modified to have both ammonium and alkali metal salts in the styrene-maleic anhydride co-polymer, so that the emulsifier contains both hydrophilic and lipophilic groups and has a branching point.

The manufacturing method is to gradually disperse 50g of styrene-maleic anhydride copolymer (molecular weight 50,000) powder in 500g aqueous solution of 10-80g of aqueous ammonia (28%) and increase the temperature and at the same time 1-9g of caustic soda (95%). 450 g of dissolved caustic soda solution is added, the temperature is maintained at 90-95 ° C., and the reaction is performed for about 1 hour while stirring. At this time, ammonium phosphate or ammonium sulfate can be used in place of caustic soda instead of caustic soda in the same molar ratio. The emulsifier aqueous solution prepared in this way and the hydrophobic dye solution were made into the ratio of 100-200 weight part of emulsifier aqueous solution per 100 weight part of dye solutions, and NOPCO 1407-K made by SAN NOPCO, Japan was 0.0001-0.5 (0.01-50 weight%) per 100 weight of dye solutions. Emulsion was added to the mixture to prepare an emulsion having a particle size distribution of 3 to 8 micrometers. NOPCO 1407-K used at this time is a fatty acid ester emulsifier with 18 to 24 carbon atoms containing both hydrophilic and hydrophobic groups, which facilitates emulsification of aqueous emulsifier solution and hydrophobic dye solution during emulsification, and improves emulsification stability. It serves to form an excellent emulsion that does not occur.

In step 3), the prepolymer and the emulsion are reacted at a weight ratio of 1: 1 to 1: 2 at a pH of 5.5 to 6.0 at a temperature of 60 to 65 ° C. for 30 minutes to 1 hour to form a wall film, and then the temperature is gradually increased to 80 ° C. Reaction is strengthened for at least 15 minutes at the above temperature, mainly at 90 ° C or more.

In step 4), the capsules prepared in step 3) are reacted for at least 12 hours while naturally cooling the temperature to room temperature, and then first stabilized to pH8.5 with ammonia water, and then secondary to pH9.0 to 9.5 using an aqueous solution of caustic soda. Stabilize.

The present invention will be described in detail with reference to Examples.

Example 1

70 g of melamine and 30 g of urea were sufficiently dispersed in 450 g of distilled water, and then 280 g of 35% formalin was added thereto, and the pH was adjusted to 8.8 to 9.5 using an aqueous solution of caustic soda for about 30 minutes at 60 ° C. to obtain a prepolymer.

On the other hand, the emulsion of the hydrophobic dye solution was first dispersed in 50 g of styrene-maleic anhydride copolymer (molecular weight 50,000) in a 500 g aqueous solution containing 20 g of ammonia water (28%) while increasing the temperature and dissolving 5 g of caustic soda (95%). 450 g of caustic soda solution was added to maintain the temperature at 90-95 ° C. and reacted for about 1 hour with stirring. 1760 g of the emulsifier thus obtained was charged with 760 g of a 5% hydrophobic dye solution in which Japan Hodogaya dye crystal violet lactan was dissolved in SAS-296 oil of Nippon Petrochemical, and 2 g of NOPCO 1407-K made by SAN NOPCO, Japan, and then emulsified. Obtain an emulsion of 6.5 micrometers. 1720 g of the emulsion thus obtained was gradually added to the prepolymer prepared with stirring, and then polymerized for 1 hour at a temperature of 60 to 65 ° C. to form a wall film. The temperature was raised to 90 ° C. over 90 minutes at 90 to 92 ° C. The reaction is continued for at least 30 minutes to reinforce the wall, and the stirring is continued for more than 12 hours while cooling slowly. The capsules thus prepared were adjusted to pH 8.5 with ammonia water to remove the odor of unreacted residual formalin, and the capsules were first stabilized and the pH was adjusted to 9.0 to 9.5 using an aqueous solution of caustic soda. Stabilize.

Comparative Example 1

Except that 50g of styrene-maleic anhydride was added to 8.5g of caustic soda (95%) and 941.5g of distilled water for 1 hour at 90-95 ° C to prepare an emulsifier aqueous solution of pH5.1. Same as Example 1).

Comparative Example 2

The emulsifier in emulsifying the hydrophobic dye solution was the same as in Example 1) except that the emulsifier prepared in the method of Comparative Example 1) was used and the emulsifier was emulsified without adding NOPCO 1407-K.

※ effect of the present invention.

Performance measurement results of the emulsion and microcapsules prepared by the above examples are shown in Table 1 below.

TABLE 1

○: excellent, △: normal, ×: poor

As a result of performance evaluation, when the emulsion is prepared using the emulsifier according to the method of the present invention, the viscosity of the emulsifier is very low, and even after 1 day of emulsification, the fluidity of the emulsion is maintained in an excellent state and there is no entanglement. In addition, there was no sufficient shape between the partial hydrophobic dye solution and the emulsifier solution, so that the emulsion stability was excellent.

Claims (8)

In preparing microcapsules for pressure-sensitive recording paper, an aqueous solution of an emulsifier of styrene-maleic anhydride copolymer and an aqueous solution of styrene-maleic anhydride copolymer substituted with an alkali metal salt and an ammonium salt in a hydrophobic dye solution, which is a melamine-urea-formaldehyde resin, is used as a membrane material. -K is added to obtain an emulsion, the method of producing a microcapsule for pressure-sensitive recording paper, characterized in that by mixing the membrane material and the emulsion. The method of claim 1, wherein the ammonium salt is ammonia water or ammonium sulfate or ammonium phosphate, and the alkali metal salt is caustic soda or cacalumum. The method of claim 1, wherein the molar ratio of the alkali metal salt to the ammonium salt is 1: 0.5 to 1: 3. The method of claim 1, wherein NOPCO 1407-K is added at 0.01 to 50% by weight per 100 parts by weight of the hydrophobic dye solution. The method of claim 1, wherein the molar ratio of melamine-urea formaldehyde is 1: 3 to 1: 4.5. The method of claim 1, wherein 100 to 200 parts by weight of an aqueous solution of an emulsifier is added per 100 parts by weight of a hydrophobic dye solution. The method of manufacturing a microcapsule for pressure-sensitive recording paper according to claim 1, wherein the emulsion is 3 to 8 m. The method for producing a microcapsule according to claim 1, wherein the melamine-urea-formaldehyde resin film material and the emulsion are reacted in a weight ratio of 1: 1 to 1: 2.