JPH0248039A - Production of microcapsule - Google Patents

Abstract

PURPOSE:To efficiently form microcapsules without forming macrocapsules and flocks by adding a polyisocyanate to a hydrophobic oily liq. CONSTITUTION:An alpha-methylstyrene-maleic anhydride copolymer is added to a hydrophilic medium by about 2.0-6.0% and a precondensate of aminoaldehyde such as melamine formaldehyde is polymerized in the medium to form microcapsules covering the surface of a hydrophobic oily liq. A polyisocyanate such as naphthalene diisocyanate is added to the hydrophobic oily liq. by 0.05-1.5 pts.wt. per 100 pts.wt. liq. By adding the polyisocyanate, microcapsules having superior light resistance can be efficiently obtd. without leaving the uncapsuled core substance or forming macrocapsules and flocks.

Description

Detailed Description of the Invention "Field of Industrial Application" The present invention relates to a method for producing microcapsules encapsulating a hydrophobic oily liquid, and in particular, a method for producing microcapsules that contain less unencapsulated oily liquid and large capsules and has excellent light resistance. The present invention relates to a method for extremely easily producing microcapsules from which pressure-sensitive copying paper can be obtained.

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

Various methods are known for manufacturing microcapsules, such as coacervation, interfacial polymerization, and 1n-situ polymerization, but among them, capsules having a wall film made of aminoaldehyde polycondensation resin are water resistant and resistant. Because of its excellent solvent properties, it can be used, for example, in the encapsulation method of forming a urea/formaldehyde polycondensation resin wall film in the presence of carboxymethyl cellulose [US Pat. Among them, various methods have been proposed, such as an encapsulation method [Japanese Patent Publication No. 4718165] in which a urea/formaldehyde polycondensation resin wall film is formed. However, in such an encapsulation method, since the polycondensation resin is not efficiently deposited on the surface of the capsule core material, extremely careful control of the preparation conditions such as the addition of dilution water is required.

In order to improve the efficiency of depositing the polycondensation resin on the surface of the capsule core material, for example, a method of using a substance having an active group capable of chemically or physicochemically bonding as a dispersant [Japanese Patent Publication No. 37-12380], electrostatic Methods that utilize phase separation due to natural interactions [Japanese Patent Publication No. 3B-12380, Japanese Patent Publication No. 48-4717, Japanese Patent Publication No. 4918456] have been proposed. However, with these improvement methods,
Not only does it require a complicated process like the conventional encapsulation method using complex coacervation, but it also contains a water-soluble component with a foreign charge in the capsule wall, which causes the capsule wall to dry during drying. accompanied by defects that cause cracks.

Furthermore, a method for obtaining capsules having an aminoaldehyde resin wall by polycondensing melamine and formaldehyde in the presence of an ethylene/maleic anhydride copolymer, a methyl vinyl ether/maleic anhydride copolymer, etc.
No. 84881] has been proposed, and a similar in 5i
Regarding the encapsulation method using the tu polymerization method, for example, JP-A-55-92135, JP-A-56-51238, JP-A-56-58536, JP-A-56100629,
JP-A-56-102934, JP-A-56-10293
No. 5, JP-A-57-56293, JP-A-58-868
September, JP-A-60-68045, JP-A-60-216
No. 838, JP-A-60-238140, JP-A-61-
No. 11138, JP-A-61-25635, JP-A-62
-1451, Japanese Patent Publication No. 62-19238, Japanese Patent Publication No. 62-1923
Various proposals have also been made in No. 2-269742 and the like.

[Problem to be solved by the invention] However, although many encapsulation methods have been developed and proposed, there is still room for improvement as these methods have the following disadvantages. has been done.

■ When a colorless basic dye used in pressure-sensitive copying paper is used as a capsule core material, the colorless dye may become colored.

(2) The aminoaldehyde resin may not be sufficiently deposited on the surface of the capsule core material, resulting in capsules with poor light resistance, heat resistance, moisture resistance, solvent resistance, etc.

(2) When the emulsifying ability and emulsifying stability of anionic water-soluble polymeric substances are insufficient, giant capsules of several hundred μm may be formed or unencapsulated core substances may remain in the system.

(2) When producing anionic water-soluble polymer substances, it may not be possible to prepare a highly concentrated aqueous solution depending on the monomer composition, resulting in increased transportation costs and energy costs required for dissolution.

Furthermore, in the production of microcapsules having an aminoaldehyde resin wall, when a styrene-maleic anhydride copolymer or polystyrene sulfonic acid is added as an emulsifier to a hydrophilic medium, the emulsifying ability and emulsion stability are insufficient. However, there were disadvantages in that giant capsules of several hundred μm were formed and unencapsulated core material remained. The present inventors have found that the above-mentioned drawbacks can be improved by using α-methylstyrene-maleic anhydride copolymer as an emulsifier, but the effect is not necessarily sufficient, and the inner paper for pressure-sensitive copying When finished, there is a problem in that spot-like colored stains occur on the surface coated with the color developer layer.

The present invention improves the above-mentioned problems in the microencapsulation method in which a hydrophobic liquid is emulsified and dispersed in a hydrophilic liquid in which an anionic water-soluble polymer substance is dissolved, and an aminoaldehyde resin wall film is formed. The purpose is to efficiently produce microcapsules with excellent properties.

1. Means for Solving the Problems The present invention involves polymerizing an amino-aldehyde initial condensate in a hydrophilic medium containing an α-methylstyrene-maleic anhydride copolymer to form a hydrophobic oily liquid surface. In this method, the hydrophobic oily liquid contains a polyvalent isocyanate compound.

"Operation" The α-methylstyrene maleic anhydride copolymer to be added to the hydrophilic medium is produced by a known method. For example, it is carried out in a solvent that dissolves the copolymer such as acetone, methyl ethyl ketone, methyl isobutyl ketone, benzene,
A copolymerization reaction is carried out in a solvent that precipitates a copolymer, such as l.luene or xylene. The copolymer thus obtained is hydrolyzed with ammonia, an alkali metal hydroxide, an organic amine, etc. to make it water-soluble.

The hydrolysis rate is adjusted as appropriate. The monomer ratio constituting the copolymer of α-methylstyrene and maleic anhydride is approximately 50
A composition of about mol % to 50 mol % is preferable.

The amount of α-methylstyrene-maleic anhydride copolymer to be blended in the hydrophilic liquid is 0.5% or more, more preferably 1.0% or more, taking into account ease of emulsion preparation and stability of the emulsion.
It is desirable to adjust the content to 0% or more, most preferably within a range of about 2.0 to 6.0%. The upper limit of the blending amount is determined by the viscosity of the system, the capsule preparation device, etc., but is generally kept at 20% or less.

The aminoaldehyde resin used to cover the surface of the hydrophobic core substance in the present invention is obtained by polycondensing one or more types of amines such as urea and melamine with one or more aldehydes such as formaldehyde, geltaraldehyde, and furfural. However, it may also be modified with glycine, sulfamic acid, methanol, etc. These are preferably used in the form of an initial condensate in view of the density of the capsule wall, but monomers may also be used.

Among them, a melamine-formaldehyde initial condensate containing melamine and formaldehyde as the main starting materials, or a melamine-glutaraldehyde-formaldehyde initial condensate containing melamine, geltaraldehyde, and formaldehyde as the main starting materials has a significant effect on the uniformity of the capsule wall membrane. It is particularly preferably used in the present invention because it provides capsules with excellent physical strength and good core material retention.

The present invention is characterized in that a trace amount of a polyvalent isocyanate compound is added to the hydrophobic oily liquid, which has the effect of increasing the emulsion stability of the core substance and preventing the formation of giant capsules.

Examples of such polyvalent isocyanate compounds include naphthalene diisocyanate, triphenylmethane triisocyanate, polymethylene polyphenyl polyisocyanate, lysine diisocyanate, and adducts obtained by reacting monomeric isocyanates with polyhydric alcohols. Examples include modified isocyanates and urethane prepolymers.

These may be used alone or in combination, but it is more preferable to use a combination of aromatic and aliphatic isocyanates. Note that it is desirable to limit the amount of the additive to 5 to 1.5 parts by weight in the hydrophobic liquid.

If the amount of the polyvalent isocyanate compound added is large, the time required for emulsification will become longer and the original advantages of the aminoaldehyde resin wall film will be impaired.

Furthermore, unexpectedly, it has been found that the use of a polyvalent isocyanate compound, particularly polymethylene polyphenyl polyisocyanate exemplified by the following formula, improves the light resistance of the capsule.

[n represents an integer of 0 or more, and usually n=0 to 9 or a mixture thereof is preferably used. ] Here, light resistance refers to a decrease in coloring ability caused by exposing a microcapsule-containing layer containing a basic colorless dye to sunlight, an ultraviolet lamp, etc. Examples of the liquid include cottonseed oil, hydrogenated terphenyl, hydrogenated terphenyl derivatives, alkyl biphenyl, alkylnaphthalene, diarylalkane, kerosene, paraffin, naphthenic oil, and dibasic acid esters such as phthalate esters. Two or more types of these may be used in combination.

The capsule manufacturing system is adjusted to an acidic range, preferably p113 to 6, to proceed with the polycondensation reaction, but since heating the system accelerates the reaction, it is desirable to heat the system to a temperature of about 60 to 95°C. In addition, if necessary, natural or synthetic polymers having carboxyl groups or sulfonic groups or low-molecular surfactants such as dodecylbenzenesulfonic acid can be used in the hydrophilic medium, but their use is not recommended. The amount must be kept within a range that does not inhibit the desired effects of the present invention.

Thus, the method of the present invention does not require careful control of capsule preparation conditions such as addition of dilution water;
By simply mixing capsule-forming materials and applying simple polycondensation conditions, the polycondensed resin is efficiently deposited on the surface of the capsule core material, forming capsules with excellent light resistance, heat resistance, moisture resistance, and solvent resistance. Ru. Moreover, a capsule dispersion is prepared without the formation of giant capsules or aggregates, and without the presence of unencapsulated core material.

The microcapsules prepared by the method of the present invention are
Various pharmaceuticals, fragrances, paints, M medicines, adhesives, liquid crystals, foods,
It is suitable for encapsulating rust preventive agents, toners, etc., and is particularly useful for applications such as printing ink and pressure-sensitive copying paper.

"Example" In order to explain the present invention more specifically, examples for preparing microcapsules for pressure-sensitive copying paper will be described below, but the present invention is of course not limited to these. do not have. In addition, "part J and 1%" in the examples indicate "part by weight" and "weight %", respectively, unless otherwise specified.

Example 35% aqueous solution of α-methylstyrene-maleic anhydride copolymer (molar ratio 50%-50%) hydrolyzate (25°C
, pH 11.9, viscosity 400 cps) 30 parts water 17
0 parts was added and the pH was adjusted to 4.5 with acetic acid, which was used as a hydrophilic medium for capsule production.

To 105 parts of diisopropyl naphthalene (trade name: Ni-113, manufactured by Kureha Kagaku Co., Ltd.) in which 75 parts of Crystal High Olene Tract was dissolved, 1 part of polymethylene polyphenyl polyisocyanate (trade name: 2 Millionate MR400, manufactured by Nippon Polyurethane Industries, Ltd.) was added. In addition, the prepared hydrophobic core material was added and emulsified and dispersed so that the average particle size was 5 μm.

Next, methylated methylolmelamine initial condensate (product name:
Add 20 parts of Beckamine APM, 85% concentration, manufactured by Dainippon Ink Chemical Co., Ltd.) and raise the temperature of the system to 90% while stirring continuously.
After being kept at °C for 1 hour, it was cooled to obtain a milky white capsule dispersion.

Example 2 Hexamethylene diisocyanate adduct (trade name: Duraney) 24A- was added to 105 parts of diisopropylnaphthalene in which 5 parts of crystal violet lactone was dissolved.
A hydrophobic core material prepared by adding 0.1 part of 10 (manufactured by Asahi Kasei Kogyo Co., Ltd.) was added to the same hydrophilic medium as in Example 1,
It was emulsified and dispersed so that the average particle size was 5 μm.

Next, 30 parts of melamine/glutaraldehyde/formaldehyde initial aggregation material (60% concentration) was added, and the temperature of the system was maintained at 90'C for 1 hour while stirring, and then cooled to form a milky white capsule dispersion. Obtained.

Example 3 Add 30 parts of a melamine/glutaraldehyde/formaldehyde initial condensate (70% concentration) to the same emulsified dispersion as in Example 1, and raise the temperature of the system to 80°C while continuing to stir.
After being kept at ℃ for 2 hours, it was cooled to obtain a milky white capsule dispersion.

Example 4 A capsule dispersion was obtained in the same manner as in Example 1, except that the amount of polymethylene polyphenyl polyisocyanate added was 0.1 part.

Comparative Example 1 The same procedure as Example 1 was carried out except that the methylated methylolmelamine initial condensate was not added.

Comparative Example 2 A capsule dispersion was obtained in the same manner as in Example 1 except that polymethylene polyphenyl polyisocyanate was not added.

Comparative Example 3 Sodium polystyrene sulfonate (trade name: VE) was used instead of α-methylstyrene/maleic anhydride copolymer.
A capsule dispersion was obtained in the same manner as in Example 1 except that R5A Tl2O3 (manufactured by National Starch) was used.

Comparative Example 4 A capsule dispersion was obtained in the same manner as in Comparative Example 3 except that polymethylene polyphenyl polyisocyanate was not added.

Comparative Example 5 Capsules were prepared in the same manner as in Example 1, except that a styrene/maleic anhydride copolymer (trade name: Suflipset 520, manufactured by Monsanto) was used instead of the α-methylstyrene/maleic anhydride copolymer. A dispersion was obtained.

Comparative Example 6 A capsule dispersion was obtained in the same manner as in Comparative Example 5 except that polymethylene polyphenyl polyisocyanate was not added.

The capsule dispersion thus obtained was diluted to a concentration of 30%, applied to the CF field using a wire bar No. 20 (product name: KS Copy Bright, manufactured by Kanzaki Paper Co., Ltd.), and dried. and obtained a test paper. Using this paper and each capsule dispersion, we conducted the following performance comparison test.
The results are listed in Table 1.

[Core material retention]

The test paper was treated at 120°C for 5 hours, and the degree of color development on the coated surface was measured using a Macbeth densitometer (filter: visual). Culm with excellent core material retention, low coloring density on coated surface (small value) [Unencapsulated core material] The number of spot-like stains present on an area of 15 cm x 25 cm was measured.

When coating the capsule dispersion liquid on the CF side of the bottom paper and drying it,
The presence of unencapsulated hydrophobic core material appears as spots.

[Giant capsules, aggregates] The capsule dispersion was processed through a 200-mesh screen, and the weight of the residue was expressed as a percentage (%) of the total weight of the capsules.

In addition, 70 parts of wheat starch and 20 parts of dissolved oxidized starch (solid content) were added to each separately obtained capsule dispersion liquid for 100 parts of the core material in the capsule, and 40 g/m2 was added.
A top paper for pressure-sensitive copying paper was prepared by coating and drying the mixture on base paper to a dry weight of 4 g/m2.

[Lightfastness test]

The upper paper and the lower paper were overlapped, a color image was formed by applying a load of 100 kg/cm2, and the color density was measured using a visual filter using a MacHess densitometer (Model RD-914, manufactured by MacBec). The color density at the time was set as Do.

After irradiating the surface of the upper paper coated with the microcapsule dispersion liquid with ultraviolet rays from a distance of 20 cm for 5 hours (National Inc.'s Rank Light Filter, IOW, FLIOBLB), it was placed facing the lower paper in the same manner as above, and was heated at 100 kg/cm2. A color image was formed by applying a load of 1, and the color density was measured using a Macbeth densitometer, and the color density at this time was defined as .

Light resistance was defined as follows from the above color density. [The closer the number is to 100, the better the light resistance] L Light resistance - x 100 Table 1 "Effects" As is clear from the results in Table 1, the microcapsules of the present invention have a large Capsules with excellent core material retention properties were efficiently formed without the generation of capsules or aggregates.

The present invention also provides a method for producing microcapsules for pressure-sensitive copying paper that have excellent light resistance.

Claims (5)

[Claims] (1) A method for producing microcapsules in which an aminoaldehyde initial condensate is polymerized in a hydrophilic medium containing an α-methylstyrene-maleic anhydride copolymer to cover the surface of a hydrophobic oily liquid. A method for producing microcapsules, characterized in that the oily liquid contains a polyvalent isocyanate compound. (2) The method for producing microcapsules according to claim (1), wherein the aminoaldehyde initial condensate is a melamine formaldehyde initial condensate. (3) The method for producing microcapsules according to claim 1, wherein the aminoaldehyde initial condensate is a melamine/glutaraldehyde/formaldehyde initial condensate. (4) The method for producing microcapsules according to claim (1), wherein the polyvalent isocyanate compound is polymethylene polyphenyl polyisocyanate. (5) The method for producing microcapsules according to claim 1, wherein the amount of the polyvalent isocyanate compound added is 0.05 to 1.5 parts by weight per 100 parts by weight of the hydrophobic oily liquid.