JPH0214739A - Preparation of liquid dispersion of microcapsule - Google Patents

Abstract

PURPOSE:To execute efficient removal of formaldehyde in the title process by adding an alkaline earth hydroxide, etc., at 11-13.5pH to a liquid dispersion of microcapsules having shell film consisting of an aldehyde polycondensation resin, and heating the mixture at >=80 deg.C. CONSTITUTION:A liquid dispersion of microcapsules having shell film comprising an aldehyde polycondensation resin formed by an acid catalyst and contg. formaldehyde as a component in the liquid dispersion is prepd. The pH of the liquid dispersion of the microcapsules is adjusted to 11-13.5, and an alkaline earth hydroxide and/or a compd. having a hydroxyoxo structure at a terminal of the carbon chain is(are) added to the liquid dispersion. Then, the liquid dispersion is held at >=80 deg.C by heating to remove thus residual formaldehyde in the dispersion. Thus, a liquid dispersion of microcapsules is prepd. The liquid dispersion is pref. heated at >=90 deg.C for <=1hr.

Description

Detailed Description of the Invention "Industrial Application Field" The present invention relates to a method for producing a microcapsule dispersion, and particularly to microcapsules using formaldehyde as one component and having an aldehyde polycondensation resin wall formed by an acid catalyst. The present invention relates to a method for efficiently removing formaldehyde remaining in a dispersion without impairing the performance of capsules, and also for efficiently removing caramel odor generated during formaldehyde removal.

"Prior Art" In recent years, microcapsule technology has made remarkable progress and the fields of use of these microcapsules are now extremely wide and diverse, including pressure-sensitive copying paper.

Various methods are known for producing microcapsules, such as coacervation, interfacial polymerization, and 1n-situ polymerization. Among them, aldehyde polymerization, which uses an aldehyde substance as one component and is formed by an acid catalyst, is known. Microcapsules with condensed resin walls are particularly sought after due to their excellent quality characteristics.

For example, Japanese Patent Publication No. 37-12380, Japanese Patent Publication No. 38
-12518, JP-A-51-9079, JP-A-53
-84881, JP-A-55-92135, JP-A-5
6-51238, JP-A-56-58536, JP-A-56-102934, JP-A-57-56293, JP-A-58-8689, JP-A-60-68045, JP-A-60- No. 216838, JP 60-2-3814
No. 0, JP-A-61-11138, JP-A-61-256
No. 35, JP-A-62-19238, JP-A-62-12
No. 5851, JP-A-62-269742, JP-A-63
Various manufacturing methods have been proposed in publications such as No.-65944.

In all of these methods, formaldehyde is used as a component constituting the capsule wall membrane, but formaldehyde not only emits a unique pungent odor, but also its toxicity is seen as a problem in terms of hygiene management, for example, according to the Ministry of Health and Welfare Ordinance. Strict regulations have been added under No. 34 and other regulations.

Therefore, it is necessary to prepare the capsule dispersion so that no formaldehyde remains at least in the resulting capsule dispersion.

However, in the capsule manufacturing method described above, it is necessary to use an excessive amount of formaldehyde in order to form a desirable capsule wall film, and it is inevitable that formaldehyde remains in the capsule dispersion. However, despite its excellent properties, its field of use is currently severely restricted.

Various methods for removing formaldehyde remaining in the capsule dispersion have been proposed up to now; for example, a method using hydroxylamine salt is disclosed in JP-A-51-756.
No. 76, JP-A-54-5874, JP-A-55-145
524, JP-A No. 61-438, a method using hydroxyalkylamine is described in JP-A-55-35967,
A method using the Knoeve-nage 1 reaction is described in JP-A-57-32729, a method using aliphatic aldehyde is described in JP-A-57-71634, and a method using formamide is described in JP-A-56-15835. There is. In addition, a method using urea and sulfite (hydrogen) salt was developed in 1973.
-27254, JP-A-55-67328, a method using urea and resorcinol is JP-A-56-15837, and a method using ethylene urea derivatives is JP-A-61-2.
In No. 04035, ethylene urea derivatives and sulfite (hydrogen)
A method using salt is described in JP-A-55-119437. Furthermore, methods using distillation or inert gas are published in JP-A-55-47138 and JP-A-55-99337, and methods using membrane permeation treatment are published in JP-A-56-21639.
A method using an absorbent is described in JP-A-56-40430.

Among these various methods, there are various methods ranging from good to poor formaldehyde removal efficiency, but there is still room for practical improvement because new drawbacks accompany the removal operation.

In other words, the chemicals used are expensive, the odor and toxicity of the chemicals themselves are problematic, and expensive equipment is required.
This method is accompanied by new drawbacks such as complicated operating procedures and increased viscosity or agglomeration of the capsule dispersion after treatment.

``Problems to be Solved by the Invention'' Therefore, as a method that does not involve these drawbacks, a hydroxide of an alkaline earth metal and/or a compound having a hydroxyoxo structure at the carbon chain end is added and a heating reaction is carried out under alkaline conditions. Methods for doing this have been proposed in Japanese Patent Application Laid-open Nos. 55-18218, 56-33030, 57-50541, 57-147430, and 61-438. However, since the removal of formaldehyde is accompanied by a new drawback of a strong caramel odor, there is still room for improvement.

In view of the current situation, the present inventors used an aldehyde substance as one component to efficiently extract formaldehyde from a microcapsule dispersion having an aldehyde polycondensation resin wall formed by an acid catalyst, without the above-mentioned drawbacks. As a result of intensive research into a method that can remove 80.
The present inventors have discovered that formaldehyde can be removed extremely efficiently when the capsule dispersion is kept under high-temperature conditions of ℃ or higher for a short period of time without any loss in capsule quality and without caramel odor, leading to the completion of the present invention. .

"Means for Solving the Problems" The present invention uses formaldehyde as one component, and injects an alkali into a microcapsule dispersion having an aldehyde polycondensation resin wall formed by an acid catalyst under conditions of pi (11 to 13.5). The formaldehyde remaining in the dispersion is removed by adding an earth metal hydroxide and/or a compound having a hydroxyoxo structure at the end of the carbon chain, and heating and maintaining the capsule dispersion at a temperature of 80°C or higher. This is a characteristic method for producing a microcapsule dispersion.

"Operation" In the method of the present invention, as long as the dispersion of microcapsules having an aldehyde polycondensation resin wall contains formaldehyde as one component and is formed using an acid catalyst,
The preparation method is not particularly limited, and various capsule dispersions prepared by the various methods described above can be used as appropriate.

In addition, examples of acid catalysts include formic acid, acetic acid, citric acid,
Oxalic acid, paratoluenesulfonic acid, hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, pectic acid, carboxymethyl cellulose,
Various water-soluble acids such as polyacrylic acid and hydrolyzates of maleic acid copolymers can be mentioned. In addition, various known materials are used for forming the aldehyde polycondensation resin wall film together with formaldehyde, including urea, 1,000 urea, alkyl urea, ethylene urea, acetoguanamine, benzoguanamine, melamine, Amines such as guanidine, dicyandiamide, biuret cyanamide, and melamine are preferred because they form an aminoaldehyde polycondensation resin wall film having excellent capsule performance, and urea and melamine are particularly preferred.

The capsule dispersion prepared in this way generally has a low pH value of 6.0 or less, but in such a pH range, even if chemical modification is performed, the desired effect cannot be obtained. In the method of the invention, the capsule dispersion is alkaline, particularly adjusted to a pHN range of 11 to 13.5, and denatured.

Examples of pH adjusters include metal oxides, hydroxides,
Sulfates, carbonates and bicarbonates, metal salts of organic acids, minerals such as kaolinite, alumina, zeolite, calcite, -
Examples include secondary, secondary, and tertiary amines, amino alcohols, aniline, methylmorpholine, methylpiperidine, tetraethylammonium hydroxide, morpholine, acetamide, benzamide, pyridine, collidine, picoline, and the like.

Examples of the alkaline earth metal hydroxide used in the method of the present invention include calcium hydroxide, magnesium hydroxide, barium hydroxide, and the like. In addition, compounds with a hydroxyoxo structure at the end of the carbon chain are R-Co-C
It is a water-soluble compound with a terminal structure of 1hOH or R-CI(OH)-(:HO (R represents a substituted or unsubstituted aliphatic or aromatic residue), and is mainly a saccharide, but specifically Examples include triose such as glyceraldehyde and dioxyacetone, tetrose such as erythrose, threose, and erythreose, ribose, arabinose,
Pentoses such as xylose, refsauce, xylulose, ribulose, fucose, aldrose, glucose,
Mannose, Gulose, Idose, Galactose,
Talose, fructose, sorbose, boucicose,
Monosaccharides such as hexoses such as tagatose, maltose, isomaltose, cellobiose, gentiobiose, melibiose, lactose, turanose, sophorose, laminaribiose, allolactose, lactulose, primeverose, vicyanose, rutinose, erythreose, trehalose, isotrehalose, neotrehalose , oligosaccharides such as saccharose, isosaccharose, amino alcohol, cellotriose, robiniose, raffinose, gentianose, raffinose, meletitose, branchiose, cellotriose, stathiose, ethers such as methylglucose, dimethylglucose, trimethylglucose, rhamnose, fucose, etc. 11! Amino sugars such as deoxy sugar, D-glucosamine, D-chondrosamine, and D-fructosamine! Derivatives and glycolaldehyde, lactic aldehyde, oxybutyraldehyde, oxyisobutyraldehyde, oxyacetone,
Dihydroxyacetone, propionyl carbinol, oxymethylallyl ketone, 2-hydroxyacetophenone, hydroxylmethyl-2-naphthylketone, 5-(
Examples include 2-hydroxyacetyl)acenaphthene, among which fructose, glucose, and maltose are particularly preferably used because they have an excellent effect of reducing formaldehyde.

The proportion of alkaline earth metal hydroxides and compounds having a hydroxyoxo structure at the end of the carbon chain added to the capsule dispersion liquid is adjusted as appropriate depending on the substance to be added and the type of capsule dispersion liquid, but in general. 0.0% per mole of formaldehyde remaining in the capsule dispersion. About 1 to 10 moles of O is added.

Furthermore, it is possible to expect an effect even when adding a small amount of less than 0.01 mol, and there is no need to add a large amount of formaldehyde absorbent as in conventional methods, resulting in improved capsule quality that accompanies the addition of a large amount of absorbent. This effectively eliminates drawbacks such as a decrease in the viscosity of the capsule dispersion and an increase in the viscosity of the capsule dispersion.

Therefore, in the method of the present invention, a capsule dispersion to which an alkaline earth metal hydroxide and/or a compound having a hydroxyoxo structure at the carbon chain end is added is heated and held in a specific pH range as described above. , which removes the formaldehyde remaining in the dispersion liquid, but if the reaction temperature is low, it takes a long time to remove the residual formaldehyde, and an even longer heating period is required to remove the caramel odor. Therefore, residual formaldehyde can be removed extremely efficiently by heating to a temperature of 80° C. or higher, more preferably 90° C. or higher, and a short treatment time of about 1 hour or less. Furthermore, caramel odor is effectively removed without deterioration of capsule quality.

In this way, the microcapsule dispersion obtained by the method of the present invention is extremely safe because the residual formaldehyde contained in the dispersion is efficiently removed, and the caramel odor generated at this time is also efficiently removed. can be,
The excellent properties unique to aldehyde polycondensation resin wall capsules can be used in a wide range of fields such as fragrances, dyes, agricultural chemicals, adhesives, liquid crystals, solvents, rust preventives, and toners.

"Example" In order to more specifically explain the method of the present invention, examples will be described below using pressure-sensitive copying paper as an example, but it is of course not limited to these. ” and “%” indicate “part by weight” and “% by weight”, respectively.

Reference Example 1 100 parts of a 5% aqueous solution of styrene maleic anhydride copolymer was added to a stirring mixing container equipped with a heating device, and the pH of the system was adjusted.
was adjusted to 4.5 to prepare an aqueous medium for capsule production. Separately, a solution obtained by dissolving 5 parts of crystal violet lactone in 100 parts of alkylnaphthalene (trade name, KMC Oil, manufactured by Kureha Chemical Co., Ltd.) was used as a capsule core material.
It was emulsified and dispersed in the above aqueous medium for capsule production so that the average particle size was 4.0 μm.

50 parts of a 30% aqueous solution of a commercially available melamine/formaldehyde initial condensate was added to this emulsified dispersion, and the mixture was reacted at 70°C for 2 hours with continuous stirring, and then the temperature was lowered to room temperature to form a melamine/formaldehyde resin wall. A microcapsule dispersion was obtained.

100% of the core substance in the capsule is added to the obtained capsule dispersion.
A capsule coating solution prepared by adding 100 parts of wheat starch and 30 parts (solid content) of carboxy-modified styrene-butadiene copolymer latex to 40 g/rtr base paper was applied to a dry weight of 3.0 g/m'. A top sheet for pressure-sensitive copying paper was prepared by coating and drying to give the following.

For the obtained upper paper, formaldehyde was quantified by an elution method (acetylacetone coloration) according to Ministry of Health and Welfare Ordinance No. 34. That is, 2.5 g of finely cut paper was heated to 40° C. with 100 cc of distilled water to elute for 1 hour, and then heated at 4000 r.p.

The supernatant obtained by centrifuging for 10 minutes under the conditions of 5. Occ acetylacetone solution 5,
Qcc was added, mixed, heated at 40° C. for 30 minutes, and the absorbance was measured at 415 μm for the sample obtained by standing for 30 minutes. As a result, from this top paper, 1100
pp of formaldehyde was detected.

Example 1 After adjusting the pH of the capsule dispersion obtained in Reference Example 1 to 12.8 with a 20% aqueous sodium hydroxide solution, 0.5 part of calcium hydroxide was added, and the mixture was heated and maintained at 90°C with stirring. After reacting for a certain period of time, the mixture was cooled to room temperature to obtain a capsule dispersion. The amount of formaldehyde in the resulting capsule dispersion was determined in the same manner as in Reference Example 1, and the results are shown in Table I along with the degree of caramel odor.

Table ■ Example 2 A capsule dispersion was treated in the same manner as in Example 1 except that the reaction temperature was 80°C, and the results are shown in Table H.

Table ■ Comparative Example 1 A capsule dispersion was treated in the same manner as in Example 1 except that the reaction temperature was 60°C, and the results are shown in Table ■.

Table ■ Comparative Example 2 A capsule dispersion was treated in the same manner as in Example 1 except that the reaction time was changed to 40°C, and the results are shown in Table ■.

Table ■ Example 3 A capsule dispersion was treated in the same manner as in Example 1 except that glucose was used instead of calcium hydroxide, and the results are shown in Table ■.

Table ■ Example 4 A capsule dispersion was treated in the same manner as in Example 3 except that the reaction temperature was 80°C, and the results are shown in Table ■.

Table ■ Comparative Example 3 A capsule dispersion was treated in the same manner as in Example 3 except that the reaction temperature was 60° C., and the results are shown in Table ■.

Table ■ Comparative Example 4 A capsule dispersion was treated in the same manner as in Example 3 except that the reaction temperature was 40°C, and the results are shown in Table ■.

Table ■ "Effect" As is clear from the results in each table, residual formaldehyde is efficiently removed from the macrocapsule dispersions obtained by the method of the present invention, there is no caramel odor, and they are extremely safe. It could be used in a wide variety of fields.

Claims (2)

[Claims] (1) Using formaldehyde as one component, alkaline earth metal hydroxide and/or carbon are added to a microcapsule dispersion having an aldehyde polycondensation resin wall formed by an acid catalyst under conditions of pH 11 to 13.5. A method for producing a microcapsule dispersion, which comprises adding a compound having a hydroxyoxo structure at the chain end, heating and maintaining the capsule dispersion at a temperature of 80° C. or higher to remove formaldehyde remaining in the dispersion. (2) The method for producing a microcapsule dispersion according to claim (1), wherein the capsule dispersion is heated and held at 90° C. or higher for less than one hour.