JPH0367735B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to thermally expandable microcapsules having solvent resistance, particularly polar organic solvent resistance.

Thermoexpandable microspheres, which microencapsulate volatile liquids in thermoplastic polymer shells, are already known. For example, Japanese Patent Publication No. 42-26524 describes a thermally expandable microcapsule in which a monomer having a polymerizable unsaturated bond is polymerized in the presence of a volatile liquid, and the volatile liquid is encapsulated inside the polymer at the same time as the polymerization. has been done.

However, these thermally expandable microcapsules are thermally expandable in the presence of highly polar solvents such as methanol, ethanol, acetic acid ethyl ester, methyl ethyl ketone, etc. because the polymer shell swells and the liquid inside the capsule evaporates. It was considered impossible to use it because it could not function as a microcapsule.

In order to overcome these drawbacks, a method was attempted in which at least 80% by weight of acrylonitrile was used as a monomer having polymer unsaturated bonds constituting the shell, but a slight improvement in solvent resistance was observed with this method. The coefficient of thermal expansion decreases, and the temperature required for expansion decreases.
It has many drawbacks, such as requiring a lot of energy because the temperature is as high as 150 to 160°C, and the desired thermally expandable microcapsules with sufficient solvent resistance could not be obtained.

The present invention eliminates the drawbacks of these conventional thermally expandable microcapsules and provides thermally expandable microcapsules that have sufficient solvent resistance and sufficient thermal expandability.

That is, the present invention has a volatile liquid in the center, a thermoplastic polymer layer that softens at a temperature higher than the vaporization temperature of the volatile liquid on the outside (a microcapsule having the above structure is hereinafter referred to as a core capsule), and a The present invention relates to a solvent-resistant thermally expandable microcapsule having an outer coating layer mainly composed of gelatin.

Solvent-resistant thermally expandable microcapsules (hereinafter abbreviated as double capsules) in which the core capsule of the present invention is surface-coated with gelatin have a lower coefficient of thermal expansion than the core capsule due to the influence of gelatin. Looking only at the coefficient of thermal expansion, it is possible to reduce the amount of gelatin covering the core capsule, but if it is too small, sufficient solvent resistance cannot be obtained. Furthermore, in terms of solvent resistance alone, it is sufficient to increase the amount of gelatin that coats the core capsule, but if it is too large, a sufficient coefficient of thermal expansion cannot be obtained. The amount of gelatin used to coat the surface of the core capsule is preferably 1 to 30%, more preferably 5 to 20%, based on the total dry weight of the double capsule obtained. If the amount of gelatin is less than 1%, sufficient solvent resistance cannot be obtained, and if it exceeds 30%, although the solvent resistance is good, the coefficient of thermal expansion is significantly reduced.

The core capsule preferably has a high coefficient of thermal expansion that can compensate for a decrease in the coefficient of thermal expansion after double encapsulation.

In the present invention, the core capsule is
It is obtained by coating a volatile liquid with a thermoplastic polymer that softens at a temperature higher than the vaporization temperature of the volatile liquid described in Japanese Patent No. 26524, and the volatile liquid includes propane, propylene, butane, isobutane, pentane, isopentane , hexane, heptane, etc., low-boiling point organic halogen compounds such as fluorotrichloromethane, difluorochlorobromomethane, tetrafluorodibromoethane, etc., and low-boiling point hydrocarbons and low-boiling point organic halogen compounds. Although they can be used in combination, isobutane, butane, and hexane are particularly preferred because they can increase the coefficient of thermal expansion of the core capsule and are easy to produce.
The content of volatile liquid in the core capsule is preferably 3 to 50%, and in order to obtain a high coefficient of thermal expansion,
~30% is particularly preferred.

As the thermoplastic resin used for coating the volatile liquid, any resin obtained by a polymerization reaction by selecting a monomer having a polymer unsaturated bond as exemplified in the above-mentioned Japanese Patent Publication No. 42-26524 can be used, but it is expensive. To obtain the thermal expansion coefficient, vinylidene chloride-acrylonitrile, vinylidene chloride-acrylonitrile-methyl acrylate, vinylidene chloride-acrylonitrile, ethyl acrylate, vinylidene chloride-acrylonitrile-methyl methacrylate, vinylidene chloride-acrylonitrile-vinyl acetate, vinylidene chloride- Methyl methacrylate, acrylonitrile
Methyl methacrylate-acrylonitrile-vinyl acetate copolymer resin is particularly preferred.

The particle size of the core capsule can be arbitrarily adjusted from 0.1 to 200 .mu.m in the step of dispersing the oil phase into the water phase before the polymerization reaction, but it is particularly preferably from 1 to 50 .mu.m in order to obtain a high coefficient of thermal expansion. In addition, it has been experimentally confirmed that if the particle size is 50 μm or more, the gelatin coating layer after double encapsulation tends to be uneven and has poor solvent resistance. preferable.

The core capsules obtained as described above easily form an outer shell with gelatin, which acts synergistically to suppress the dissipation of volatile liquid over time, and also has a negative effect on the thermal expansion temperature of the microcapsules. No impact.

In the present invention, the core capsule is coated with a coating material containing gelatin as a main ingredient.

The method of coating with gelatin is not particularly limited, but may be carried out by a method often used for microencapsulation, in which a phase rich in polymers is separated from a polymer solution, ie, a coacervation method.

The coacervation method using gelatin is a simple coacervation method in which sodium sulfate or ethanol is added to an aqueous gelatin solution in which core capsules are dispersed, and a coacervation method in which gum arabic or carboxymethyl cellulose (hereinafter abbreviated as CMC) is added to an aqueous gelatin solution in which core capsules are dispersed. There is a composite coacervation method that is carried out by adding an aqueous solution of polymer anions such as The core capsule was then coated with gelatin.

The method involves dispersing core capsules with a high coefficient of thermal expansion in an aqueous gelatin solution, adding an aqueous polymer anion solution while maintaining the temperature at 40 to 50°C, and mixing uniformly. In addition to the above-mentioned gum arabic and CMC, many polymeric anions can be used, such as sodium alginate, carrageenan, styrene maleic anhydride copolymer, and polyvinylbenzenesulfonic acid. In the present invention, CMC was used because it is available in terms of quality, is easy to coacervate, and is relatively easy to convert into mononucleated double capsules. then 40-50
While maintaining the temperature at °C, a 10% acetic acid aqueous solution was added dropwise to control the pH and form a coacervation. PH
Control is the most important point in coacervation, and must be carried out carefully because mononucleus is desired for the intended use of the resulting double capsule. the
The PH value was 4.5 when gelatin:CMC=1:0.5 (weight ratio), and 5.0 when gelatin:CMC=1:0.25. Next, the entire reaction system is cooled to 5°C to fix the gelatin-CMC around the core capsule, and the gelatin film is hardened with formalin and sodium hydroxide.The temperature is gradually raised to 50°C to complete the hardening of the gelatin film. CMC is dissolved in water to create double capsules. When the temperature is raised from 5℃ to 50℃, the CMC that has settled around the core capsule is eluted into the water, but if the temperature is raised suddenly, the CMC elution temperature becomes faster and the gelatin film becomes uneven. It is necessary to carry out the process gradually since it will worsen the solvent resistance of the double capsule. Furthermore, it is desirable to reduce the amount of CMC used relative to gelatin due to the phenomenon of elution. The preferred gelatin:CMC ratio in the present invention was 1:0.5 to 1:0.1. The resulting double capsules were washed with a spray dryer or with isoperopyl alcohol, overdried, and taken out as a powder.

As shown in Figure 1, the double capsule has a protruding shape at both ends, which is typical of gelatin capsules.
10% and the average particle diameter of the core capsule was 15 μm, the thickness of the protruding portion was 2 μm and the thickness of the non-protruding portion was 0.2 μm. Also, the specific gravity of the double capsule is that the amount of gelatin is 2.
It is 10% of the total dry weight of heavy capsules, the average particle size of the core capsules is 15μm, and the specific gravity of the core capsules is
In the case of 1.13, it was 1.14, and the specific gravity was higher due to the gelatin coating.

A schematic cross-sectional view of the solvent-resistant thermally expandable microcapsules of the present invention is shown in FIG. In the figure, 1 is a volatile liquid, 2 is a thermoplastic polymer, and 3 is a gelatin layer.

The microcapsules of the present invention do not swell in polar organic solvents such as methanol, ethanol, acetic acid ethyl ester, acetone, methyl ethyl ketone, and methyl isobutyl ketone, which dissolve or swell conventional foamable microcapsules without gelatin coating. In addition, highly polar acid anhydrides such as methyltetrahydrophthalic anhydride, endomethylenetetrahydrophthalic anhydride, chloredic anhydride, trimellitic anhydride, pyrolimethic anhydride, and methylendomethylenetetrahydrophthalic anhydride are used as curing agents for epoxy resins. It also does not swell.
Since it easily foams when heated, it can be easily incorporated into solvent-based inks, solvent-based paints, organic sealants, resins, or monomers, which was previously impossible, and can be used for a variety of purposes.

The present invention will be explained below with reference to Examples.

Unless otherwise specified, parts and percentages are by weight.

Example 1 70 parts of acrylonitrile, 120 parts of vinylidene chloride,
10 parts of methyl acrylate, 0.5 parts of divinylbenzene,
2 parts diisopropyl peroxydicarbonate,
An oil phase consisting of 35 parts of isobutane was prepared.

Next, 400 parts of deionized water, 90 parts of a 20% solids colloidal silica dispersion, and 2.5 parts of potassium dichromate.
An aqueous phase was prepared by adjusting the pH of 2 parts of an aqueous solution and 1.5 parts of a 50% aqueous solution of a condensate of diethanolamine and adipic acid to 3.5 with hydrochloric acid.

Subsequently, the above-mentioned oil phase and water phase were mixed at 6000 rpm for 90 seconds and charged into a 1.5 pressure polymerization reactor purged with nitrogen, and reacted at 3.5 to 4.5 Kg/cm ² at 50°C for 20 hours.

The product thus obtained has a viscosity at room temperature of
The product was a light yellow liquid with a volume of 210 cps, and was repeatedly passed through a centrifuge and washed with water to obtain thermally expandable microcapsules with an average particle diameter of 15 μm and a moisture content of 25%.

Next, cake-shaped heat-expandable microcapsules with 25% moisture were added to an aqueous solution of 20 parts of gelatin and 450 parts of deionized water.
10 parts of carboxymethylcellulose (CMC), while uniformly dispersing 160 parts and keeping it at 50℃ under stirring.
After adding an aqueous solution consisting of 200 parts of deionized water and thoroughly mixing, a 10% acetic acid aqueous solution was added dropwise to adjust the pH to 4.5, and gelatin-CMC complex coacervation was performed. Subsequently, the entire reaction system was cooled to 5°C, gelatin-CMC was fixed around the heat-expandable microcapsules, and 6 parts of 37% formalin was added, followed by 10% formalin.
The pH was adjusted to 10 with sodium hydroxide, and the temperature was gradually raised to 50°C to harden the gelatin film and dissolve CMC in water, creating thermally expandable gelatin double microcapsules. The thermally expandable gelatin double microcapsules produced had an average particle size of 15 μm and were all mononuclear. This material was repeatedly washed with a spray dryer or with isopropyl alcohol, overdried, and taken out as a powder.

Heat-expandable gelatin double capsule of the produced powder
Mix 10 parts of acrylic resin with 40 parts of acrylic resin containing 50% ethyl acetate, put it in a sealed container and leave it at 40℃ for 48 hours, then print this mixture on paper and let the ethyl acetate scatter at room temperature to form a film. 120℃×1
When heat-treated for 30 minutes, it expanded to about 8 times the original thickness, creating a printed product with a three-dimensional effect.

In addition, for the purpose of preventing distortion due to hardening of the epoxy resin, 1.5 parts of thermally expandable gelatin double microcapsules in powder form, a mixture of a specified amount of epoxy resin base and methyltetrahydrophthalic anhydride as a hardening agent.
When 100 parts were mixed well and cured at 100°C, a good molded epoxy resin product was obtained that was free from distortion due to curing.

Example 2 80 parts of acrylonitrile, 110 parts of vinylidene chloride,
An oil phase consisting of 10 parts of ethyl acrylate, 0.5 parts of trimethylolpropane trimethacrylate, 2 parts of diisopropyl peroxydicarbonate, and 35 parts of isobutane was mixed with an aqueous phase having the same contents as in Example 1 at 6000 rpm.
The mixture was mixed for 90 seconds and charged into a 1.5 pressure polymerization reactor purged with nitrogen at a pressure of 4 to 5 kg/cm ² and reacted at 55°C for 24 hours, followed by washing with water in the same manner as in Example 1, with an average particle size of 15 μm and a moisture content of 25. % cake-like thermally expandable microcapsules were obtained.

Next, 240 parts of cake-like heat-expandable microcapsules with a water content of 25% were uniformly dispersed in an aqueous solution of 20 parts of gelatin and 450 parts of deionized water, and heated at 50°C with stirring.
An aqueous solution consisting of 5 parts of CMC and 100 parts of deionized water was added thereto while maintaining the same temperature, and after thorough mixing, a 10% acetic acid aqueous solution was added dropwise to adjust the pH to 5.0, and gelatin-CMC complex coacervation was performed.

Subsequently, the entire reaction system was cooled to 5°C and gelatin-
CMC was fixed around the heat-expandable microcapsules, 6 parts of 37% formalin was added, the pH was adjusted to 10 with 10% sodium hydroxide, and the temperature was gradually raised to 50°C to harden the gelatin film and dissolve the CMC in the water. Elution was carried out to prepare thermally expandable gelatin double microcapsules.

The thermally expandable gelatin double microcapsules produced had an average particle size of 15 μm and were all mononuclear. This material was washed repeatedly with a spray dryer or isopropyl alcohol, dried, and taken out as a powder.

Mix 5 parts of the thermally expandable gelatin double microcapsules of the powder produced and 70 parts of urethane resin containing 70% methyl ethyl ketone and place in a sealed container at 40°C.
After leaving it for 48 hours, apply it to the entire surface of cotton broadcloth and let the methyl ethyl ketone scatter at room temperature to form a film.
When heat treated at ℃ for 1 minute, the film expanded to three times the original thickness, resulting in a sheet with a soft feel and leather touch.

In addition, in order to reduce the weight of the epoxy resin, 10 parts of thermally expandable gelatin double microcapsules in powder form and 100 parts of a mixture of a specified amount of epoxy resin base material and methyltetrahydrophthalic anhydride as a curing agent were thoroughly mixed and cured at 100°C. As a result, a molded epoxy resin was created that foamed as it cured and had a light specific gravity of 0.25.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view of the solvent-resistant thermally expandable microcapsules of the present invention. In the figure, 1 indicates a volatile liquid, 2 a thermoplastic resin layer, and 3 a gelatin-based layer.

Claims (1)

[Scope of Claims] 1. A durable material having a volatile liquid in the center, an outer layer of a thermoplastic polymer that softens at a temperature higher than the vaporization temperature of the volatile liquid, and a coating layer mainly composed of gelatin as the outermost layer. Solvent-based thermally expandable microcapsules. 2. The heat-expandable microcapsule according to item 1, wherein the gelatin-based coating agent accounts for 1 to 30% by weight of the total solid content of the solvent-resistant heat-expandable microcapsule.