JPS6043766B2 - Method for decoloring colored capsule dispersions - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for decoloring a colored dispersion of microcapsules containing a hydrophobic substance in which an electron-donating organic coloring agent is dissolved.

In recent years, there have been remarkable advances and improvements in microencapsulation technology as it has been applied to pressure-sensitive copying paper.

Various methods are known for producing microcapsules, such as coacervation, interfacial polymerization, and in-situ polymerization, and their applications are wide-ranging, including pressure-sensitive copying paper.

When applying microcapsules to pressure-sensitive copying paper, the microcapsules usually contain a hydrophobic substance in which an electron-donating organic coloring agent that undergoes a coloring reaction with an electron-accepting coloring agent is dissolved. ing. This specific manufacturing method for microcapsules has been most commonly used since the development of microcapsules by NCR. For example, a practical microcapsule wall is created by hardening gelatin coacervate with formaldehyde, glutaraldehyde, etc. Method for obtaining membranes (USP-2800457, USP-2
800458), a method for producing microcapsules using a coacervation method, such as a method for obtaining microcapsules by reacting a coacervate consisting of polyvinyl alcohol and a polyhydroxyphenol substance with an aldehyde substance (Japanese Patent Publication No. 51714/1983). Furthermore, there is a method using an in-situ polymerization method by polycondensation of amine and aldehyde (USP-3516941), and a method of forming a urea/formaldehyde polycondensation resin wall capsule using a system modifier (JP-A-51-1999). 907), a method for efficiently carrying out aldehyde polycondensation reaction at the oil-water interface using chemical or physicochemical bonds (Japanese Patent Publication No. 37-12
38 o'clock, Special Publication No. 38-12518, Special Publication No. 48-47
No. 17), a method for forming a composite capsule wall with a suspension polymeric substance and a hydrophilic polymeric substance by reacting a polyhydroxyphenolic substance with an aldehyde (British Patent No. 1)
190721), a method for forming a capsule membrane using a polymerization product resulting from an aggregation reaction between an aldehyde substance and a polyhydroxyphenol substance complexed with polyvinyl alcohol (Japanese Unexamined Patent Application Publication No. 1987-5789), and a method for forming a capsule membrane using an interfacial polycondensation method. Various methods have been proposed for producing microcapsules using various synthetic polymer production reactions, such as a method of subjecting substances to a polycondensation reaction (Japanese Unexamined Patent Publication No. 47-200).

Most of the microcapsules for pressure-sensitive copying paper containing a hydrophobic substance in which an electron-donating organic coloring agent is dissolved are generally manufactured under acidic conditions, and the electron-donating organic coloring agent is inherently acid-sensitive. For this reason, depending on the method for manufacturing microcapsules, the dispersion liquid often ends up being colored.

This tendency is particularly noticeable in the manufacturing process of microcapsules whose walls are composed of synthetic polymers. This is because an acid-catalyzed polycondensation reaction is generally used, and since the reaction is heated to increase reaction efficiency, an electron-donating organic coloring agent that is sensitive to acid, heat, and light causes a coloring reaction. Although it varies depending on the type of electron-donating organic coloring agent used, it often becomes a dark color. Although the desired strength of the microcapsules itself can be obtained, the capsule dispersion is colored, so if such a colored dispersion is applied directly to the base paper, the coated surface will be colored as is. Therefore, the appearance of the blank paper deteriorates and the commercial value decreases or is lost. Therefore, the present inventors have conducted intensive research on a method for decoloring the capsule dispersion liquid that is colored during the manufacturing process of microcapsules with a synthetic polymer wall film containing a hydrophobic substance in which an electron-donating organic coloring agent is dissolved. Conclusion.

As a result, the present invention has been achieved. In the present invention, after forming microcapsules with a synthetic polymer wall film containing a hydrophobic substance in which an electron-donating organic coloring agent is dissolved, a colored dispersion of the microcapsules is heated at 35°C or higher in the presence of a basic substance. Clothes that are characterized by heating. This is a method for decoloring a colored capsule dispersion. In the present invention, "in the presence of a basic substance" means that a basic substance such as an alkali metal or alkaline earth metal hydroxide, carbonate, or water-soluble amine is added to the colored dispersion of the microcapsules. It means adding and making the acidic substance present in an amount equal to or more than the amount equivalent to that present in the dispersion/liquid, and generally refers to a state in which the pH of the system is adjusted to 7 or more.

The optimum pH range for decoloring is determined individually depending on the capsule wall material and electron-donating organic coloring agent used, and the relationship with the heating temperature, and cannot be determined uniformly. However, it will be determined as appropriate within the range of approximately 7 to 12. Incidentally, when a basic substance exceeding the optimum PH range is added, a phenomenon of deterioration of the capsule wall film and the electron-donating organic coloring agent appears, which also causes a deterioration in quality even if it is formed into pressure-sensitive copying paper. Specific basic substances include caustic soda, caustic calcium octahydroxide, barium hydroxide, soda carbonate, ammonia, methylamine, ethanolamine, and the like.

Although the selection is arbitrary, ammonia is particularly preferred from the viewpoint of ease of handling and processing. There is no problem in using these substances in combination. In the present invention, heating means heating the system to 35° C. or higher in a state in which the above-mentioned basic substance is added to the colored capsule dispersion.

The purpose of this heating is to promote the decoloring effect of the colored capsule dispersion by the basic substance, and what is the optimum heating range for the microcapsule wall material and the electron-donating organic coloring agent? It is determined individually depending on the relationship with pH and reaction time, and cannot be set uniformly, but it is generally set appropriately within the range of 35°C to 80°C, but usually 40°C to In many cases, 70°C is suitable, but as the heating temperature increases, it is effective to increase the efficiency of promoting decolorization of the colored capsule dispersion by the basic substance. , a deterioration phenomenon of the microcapsule wall film and the electron-donating organic coloring agent appeared,
Even if pressure-sensitive copying paper is used, the quality will deteriorate, so it is preferable to avoid this.

Note that, below 35°C, the effect of promoting the decolorization of the colored capsule dispersion by the basic substance is not sufficient. Therefore, in the present invention, addition of a basic substance and heating are essential requirements, and these steps are carried out after the dispersion of microcapsules for pressure-sensitive copying paper has been prepared.

Therefore, it can be said that the present invention has meaning as a post-treatment method for the capsule dispersion. In the present invention, the electron-donating organic coloring agent included in the microcapsules includes lactone compounds, lactam compounds, sultone compounds, spiropyran compounds, leucotriphenylmethane compounds, leucodiphenylmethane compounds, acylleucophenothiazine compounds, etc. As the hydrophobic solvent, animal oil, vegetable oil, mineral oil, synthetic oil, etc. are appropriately selected and used. According to the present invention, the capsule dispersion colored during the manufacturing stage of microcapsules for pressure-sensitive copying paper can be decolored, which would otherwise result in colored pressure-sensitive copying paper, which would result in quality deterioration. However, excellent effects such as the ability to restore commercial value can be obtained, and in particular, microcapsules can be produced using an aldehyde polycondensation resin. The present invention expands the field of microcapsule manufacturing methods that can be used for pressure-sensitive copying paper, so that it can be put to practical use, although it was not actually adopted because the dispersion liquid was colored. , and it is of great significance that it enables the use of microcapsules of higher quality.

Furthermore, unexpectedly, the implementation of the present invention greatly improves the physical properties of the capsule dispersion, especially its low foaming and fluidity properties, which not only improves the work efficiency when coating and drying base paper. It also has the advantage that a uniform coated surface without repelling can be obtained, and pressure-sensitive copying paper of stable quality can be obtained. Examples of the present invention are described below.

However, it goes without saying that the present invention is not limited only to these examples. Example 1 Ethylene-maleic anhydride copolymer (EMA-31, 1 manufactured by Monsanto) was placed in a stirring mixing vessel equipped with a heating device.
Add 15 parts of an aqueous hydrolyzate solution (5%) and add 5 parts of urea.
After uniformly dissolving parts by weight and 0.5 parts by weight of resorcin, the pH was adjusted to 3.5 to prepare an aqueous medium for capsule production.

Separately, diallylethane (SAS oil; manufactured by Nippon Petrochemical)
A hydrophobic solvent solution was prepared by dissolving 3 parts by weight of crystal violet lactone and 1 part by weight of benzoylleucomethylene blue in 10 parts by weight, and this was emulsified in the aqueous medium prepared above so that the average particle size was 4 μm. Dispersed.
Next, 1 part of a 37% formaldehyde aqueous solution was added to this dispersion.
2.5 parts by weight was added, the temperature of the system was raised to 55°C with gentle heating, held for 2 hours, and then allowed to cool to determine the pH.
A capsule dispersion colored deep blue of 3.5 was obtained.

Next, ammonia was added to the obtained colored capsule dispersion to adjust the pH to 9, and the mixture was stirred at 50° C. for 3 hours to decolorize the colored capsule dispersion.

Next, auxiliary agents and other substances were added to this dispersion, which was then coated on base paper to produce pressure-sensitive copying paper. The coated surface did not become colored over time, and no abnormalities were observed in the copying function. In addition, in the above example, when the colored capsule dispersion was added with auxiliary agents and others without decoloring, and then coated on base paper to finish pressure-sensitive copying paper, the coated surface was colored. It became pressure-sensitive copying paper with low commercial value.

Example 2 Into a stirring mixing container equipped with a heating device, 15 parts of a 5% aqueous solution of partially saponified polyvinyl alcohol (PvA-217: Kurare J) was placed, and 1 part of sodium p-toluenesulfinate was added. It was dissolved to provide an aqueous medium for capsule production.

Separately, 1 part by weight of 4.4''-bis-dimethylaminobenzhydro-methyl ether was dissolved in a mixed solution of 3 parts by weight of alkylnaphthalene (KMC Oil; 0 J manufactured by Kureha Chemical Co., Ltd.) and 1 part by weight of dibutyl phthalate. Hydrophobic solvent solution and polyvalent isocyanate (1 part dibutyl phthalate)
A solution was prepared in which 7.5 parts by weight of Coronate L (1 manufactured by Nippon Polyurethane Industries) was dissolved, and after mixing these, this was emulsified and dispersed in the aqueous medium prepared above so that the average particle size was 9p. did. During the emulsification process, the pH of the system is adjusted to 4-5.
When 10% hydrochloric acid was added dropwise to maintain the p-toluenesulfinic acid in the aqueous medium, the 4.4-
It reacted with bis-dimethylamino-benzhydrol-methyl ether 7 to obtain oil droplets containing the desired p-toluenesulfinic acid-4.4''-bis-dimethylamino-benzhydrol.Then, the system was heated to 70°C. After heating for 3 hours, the mixture was allowed to cool to obtain a deep blue-purple colored capsule dispersion.

Next, caustic soda was added to the obtained colored dispersion to adjust the pH to 7.
The color of the colored dispersion was decolored by further adding aqueous ammonia to adjust the pH to PHIO and heating at 65° C. for 1 hour.

Next, when this dispersion was added with auxiliary agents and others and coated on base paper to produce pressure-sensitive copying paper, the coated surface did not become colored over time and no abnormality was observed in the copying function.

In addition, in the above example, when the colored capsule dispersion was added with auxiliary agents and others without decoloring, and then coated on base paper to make pressure-sensitive copying paper, the coated surface was colored. It became a pressure-sensitive copying paper with low commercial value.

Claims (1)

[Claims] 1. After forming microcapsules with a synthetic polymer wall film containing a hydrophobic substance in which an electron-donating organic coloring agent is dissolved, a colored dispersion of the microcapsules is treated in the presence of a basic substance, 3
A method for decoloring a colored capsule dispersion, the method comprising heating to 5°C or higher. 2. The method according to claim 1, wherein the basic substance is an alkali metal or alkaline earth metal hydroxide, carbonate, or water-soluble amine. 3. The method according to claims 1 and 2, wherein the basic substance is caustic soda, caustic potash, calcium hydroxide, soda carbonate, ammonia, or ethanolamine.