JPS5855813B2 - Microcapsules and their manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention can provide such a breaking strength if it is desired to break with relatively low pressure;
On the other hand, if it is desired to prevent the microcapsules from being destroyed even if the pressure is applied even stronger than this, the present invention relates to a microcapsule that can be easily adjusted in such a manner, and a method for manufacturing the same.

In general, the suitable breaking strength of microcapsules is that, for example, in the case of pressure-sensitive copying paper, microcapsules can only be broken by relatively strong writing pressure from a ballpoint pen, etc., and depending on the application, they can be easily broken even by weak external pressure. There are many different options, such as which one is more convenient.

It is impossible to satisfy such a wide range of breaking strength with a single film-forming material using conventionally known film-forming materials. Therefore, the film-forming materials and the microencapsulation methods had to be different.

The inventors of the present invention have conducted various studies to solve this inconvenience, but recently they have focused on degradable polymers that are decomposed by light, and have found that they cannot be used as film-forming materials for microcapsules. I considered it.

As a result, in most decomposable polymers, the polymer chains are cut by light irradiation, the molecular weight decreases, and the polymer becomes crumbly, whereas high-molecular-weight crystalline thermoplastic resins with a syndiotactic structure1・Only 2-polybutadiene has the property that the molecular weight does not decrease, but the double bonds attached to the side chains become brittle when exposed to light. Therefore, if this is used as a film-forming material for microcapsules, It was found that only the morosa can be appropriately changed by light irradiation by changing the strength without impairing the sealing performance and airtightness of the film, and the present invention has finally been completed.

Therefore, it is an object of the present invention to provide microcapsules and a method for producing the same, in which the breaking strength can be appropriately changed to be strong or weak, the range of change is extremely wide, and the strength of the microcapsules can be easily designed.

The present invention consists of two inventions. The first invention is that the double bonds attached to the side chains of crystalline 1,2 polybutadiene having a syndiotactic structure (stereoregular structure) and a molecular weight of at least 10,000 are bridged. It is a microcapsule characterized by enclosing an aqueous liquid filling with a shaded outer skin.

In order to facilitate understanding of the present invention, Japanese Unexamined Patent Publication No. 52-4
Let's compare this with the invention disclosed in Publication No. 3779.

The above-mentioned publication describes the use of a photosensitive resin that can be cross-linked into a three-dimensional network structure by irradiation with light having a dominant wavelength of 230 to 600 nm as a film-forming material. means a relatively low molecular weight compound (polyfunctional monomer or oligomer) having two or more photosensitive groups that undergoes a polymerization reaction with light energy, alone or in combination with a monomer (monomer) having one photosensitive group as described above. (functional monomers), initiators, photosensitizers,
It refers to normally liquid, solvent-free compositions with the addition of additives such as stabilizers, which modify the properties of the coating after photocuring, in other words, depending on the desired breaking strength of the microcapsules. In order to achieve this, it was necessary to change the combination of monofunctional monomers and polyfunctional monomers or oligomers, that is, to change the composition.

On the other hand, the present invention has the above-mentioned structure, so that the degree of curing-type deterioration can be changed simply by changing the irradiation time with light of 370 nm or less (ultraviolet light), and in this way, the breaking strength of the film can be freely adjusted. It is extremely superior in that it can be controlled.

For example, if the irradiation time with ultraviolet rays is about 5 minutes, it will not be easy to crush with fingertips, but if it is irradiated with ultraviolet light for about 1 hour, it will be easily broken with a little guidance with fingertips.

As mentioned above, the fact that the microcapsules of the present invention are photodegraded by light of 370nrn or less but not by light of wavelengths of 370nm or more means that even if the microcapsules of the present invention are left indoors, there is no change in capsule strength and they are stable. In this respect, it is extremely convenient in practice.

Furthermore, since the capsule wall has excellent transparency, it is convenient in that the color of the contained cardiac substance can be seen through from the outside.

Next, the manufacturing method, which is the second aspect of the present invention, will be described.

2. Various techniques can be applied to envelop the aqueous liquid filling with the 2-polybutadiene shell.

"Powder bed method Jl (see U, S, P. 3328256 specification) prepares a powder bed by pulverizing the polymer material that will become the wall membrane, and then making small droplets of the heart substance solution and dropping them onto the powder bed. This method dissolves the polymer powder adhering to the droplet surface and forms the capsule wall by selecting a solvent for the core material that is also a good solvent for the polymer. It is possible.

Apart from this, encapsulation is also possible from a resin solution in which 2-2-polybutadiene is dissolved in an organic solvent.

For example, in Japanese Patent Publication No. 41-2612, an aqueous liquid filling is frozen at low temperature and finely pulverized to form a powder.
While this powder is placed in a tower that blows hot air from the bottom of the tower and suspended in a fluidized bed, the resin liquid is sprayed from the top of the tower to cover the surface of the aqueous liquid powder with the resin liquid, and the resin liquid in the resin liquid is The solvent is volatilized with hot air as described above, and coating is performed in this manner, but such an air suspension coating method may also be used.

Furthermore, Japanese Patent Publication No. 42-13703 discloses that a Wlo-type primary dispersion liquid is prepared by emulsifying and dispersing an aqueous liquid to be the contents of microcapsules in a solution of a simulating substance dissolved in an organic solvent that is immiscible with water. A method is disclosed in which the aqueous liquid is encapsulated in microcapsules by further emulsifying and dispersing the liquid into a dilute aqueous solution of a surfactant to form a (Wlo)/W type secondary dispersion, and then removing the solvent by evaporation. However, it is also possible by such an in-liquid drying method.

As described above, there are various methods for enclosing an aqueous liquid filling with a high molecular weight crystalline 1,2-polybutadiene shell having a syndiotactic structure, but none of them are suitable. Next, the second layer is combined with the step of bridging the double bonds attached to the side chains of 1,2-polybutadiene by irradiating ultraviolet rays of 370 nm or less for a time corresponding to the target value of capsule strength. It has the characteristics of an invention.

As a suitable light source, an arc lamp, a mercury lamp, a xenon lamp, etc. can be used, and the irradiation time is from several minutes to several hours depending on the intensity of the light source and the target value of the capsule strength.

As mentioned above, if the irradiation time is long, the capsule will be brittle and easy to break, whereas if the irradiation time is short, the capsule will be elastic and hard to break.

What is needed is to accelerate photocurable deterioration by adding an appropriate amount of photosensitizer to the 1,2-polybutadiene solution.

The photosensitizers include benzophenone and its derivatives,
Examples include benzoin, dibendiyl, benzoin ether, aldol-α-naphthylamine, dimethyldithiocarbamate complex salt, 2.2-penzanthraquinone, 5-nitroacenaphthene, N-phenylthioacridone, and the like.

The amount of these photosensitizers added varies depending on the strength of the intended capsule, but is usually about 0.001 to 5% by weight relative to 1,2-polybutadiene.

If the molecular weight of the high-molecular-weight crystalline 1,2-polybutadiene resin with a syndiotactic structure used as the film-forming material of the present invention is less than 10,000, it will lose its film-forming ability. be.

In general, this resin has the property that rubber-like properties increase as the degree of crystallinity decreases, and on the contrary, plastic-like properties increase as the degree of crystallinity increases, but the degree of crystallinity is 5 to 60%.
Particularly preferred is 10 to 30% from the viewpoint of solubility in solvents.

Examples of the solvent include benzene, toluene, cyclohexane, ethylcyclohexane, chlorobenzene, chloroform, and carbon tetrachloride.

The aqueous liquid to be the contents of the microcapsules is not particularly limited as long as it is substantially incompatible with the 1,2-polybutadiene solution, such as water, alkali, acid, water-based ink, alcoholic ink, and alcohol. Applicable examples include glycerin, acetic acid, amines, esters, ketones, ethers, formamides, dimethyl sulfoxide, hexamethylphosphoramide, lactic acid esters, dioxane, tetrahydrofuran, ethylene glycol, cellosolve, calpitol, and the like.

Among these, formacide and cellosolve have not been easily microencapsulated in the past.

The effects of the method of the present invention are outstanding not only in that the strength of the microcapsules can be adjusted in any way by simply changing the irradiation time of ultraviolet rays, but also in that the solvent can be easily removed.

That is, as the irradiation time is increased in order to obtain capsules that are brittle and easily breakable, (1).2-polybutadiene becomes insolubilized and the solvent is separated, so that it can be easily removed by centrifugation or the like.

In addition, if the irradiation time is short to obtain a strong capsule,
Select and use methods as appropriate, such as raising the temperature above the boiling point of the solvent, using reduced pressure, or adding a liquid that is miscible with the solvent but does not swell the 1,2-polybutadiene after curing. However, since 2-polybutadiene is already partially crosslinked and three-dimensional, there is no need to remove the solvent carefully and for a long time as in the conventional submerged drying method. It has the advantage that it can be carried out under very strong conditions.

Examples are given below.

Example 1 Ethylene glycol 41', a viscous liquid, was mixed with ultrafine anhydrous silica particles [Nippon Aerosil Co., Ltd. Aerosil-200]
)16. i? After gelation, particles are created by freezing and crushing at low temperatures, and the particles are placed in a tower that blows up air at 85°C from the bottom of the tower, causing the particles to move up and down in a fluidized bed. From the top of the tower, crystallinity is 15% and molecular weight is 12.
1,2-polybutadiene 4M' and microhexane 3
A resin solution in which 00 was dissolved was sprayed and souffled for about 15 minutes.

After spraying, the mixture was irradiated with a low-pressure mercury lamp for 40 minutes while blowing hot air from the bottom of the tower.

When the coated particles were recovered after the irradiation, the particle size was in the range of 50 to 200 μm, and the capsules were strong enough to be crushed if pressed strongly with a fingertip.

Example 2 Formamide 50P was mixed with benzene 80F, -i room temperature curable silicone resin (KE-4 manufactured by Shin-Etsu Silicone Co., Ltd.)
55) It was added to a solution consisting of 5y benzo, y/70.6 F, and 0.2 P of a nonionic surfactant, and stirred vigorously with a homogenizer to form a dispersion.

This dispersion was made into fine droplets using an atomizer and dropped onto a mixed powder bed of 1,2-polybutadiene and calcium carbonate (3:1.200 mesh or less) with a crystallinity of 15% and a molecular weight of 50,000. .

Only the capsules were sieved and collected, and then irradiated with a low-pressure mercury lamp for 30 minutes on a fluidized bed, and then dried with warm air at 80°C to obtain 30 to 100 mesh capsules.

This capsule could be crushed if pressed strongly with a fingertip.

Example 3 In a solution of 1,2-polybutadiene IOS' having a crystallinity of 15% and a molecular weight of 120,000 dissolved in cyclohexane 80P, 0.21 g of benzoin ethyl ether as a photosensitizer was dissolved.

Add methyl lactate 20P and ultrafine anhydrous silica to this solution.
A solution consisting of Aerosil-200) l' manufactured by Nippon Aerosil Co., Ltd. was added and emulsified with a homogenizer to prepare a primary emulsion of W10 type CW; methyl lactate 10; cyclohexane] having a particle size of 5 to 10 μm.

Next, this first emulsion was quickly emulsified and dispersed in 600 ml of a 1% gelatin aqueous solution containing 0.1% of a nonionic surfactant to obtain a second emulsion.

Two types of irradiation were performed using a low-pressure mercury lamp, one for 5 minutes and one for 1 hour, while keeping the temperature of the secondary emulsion below 20'C.

After irradiation, the temperature of the system was raised to 50℃, the cyclohexane was removed by placing it under reduced pressure, and then the particle size was 15.
Colorless and transparent microcapsules of ~25μ were obtained.

The capsules that were irradiated for 5 minutes were highly elastic and did not break when pressed with a fingertip, but only broke when rubbed strongly against a hard surface, whereas the capsules that were irradiated for 1 hour were easily broken when pressed with a fingertip. It was strong enough to easily break if pushed.

Example 4 0.2i of benzophenone as a photosensitizer was dissolved in a solution of 1,2-polybutadiene IOP having a crystallinity of 25% and a molecular weight of 110,000 dissolved in 9M' of toluene.

Add 25 g of ethylene glycol to this solution, emulsify it with a homogenizer, and make WlO type [W; ethylene glycol 1
0 ; ) luene] was prepared.

Next, this primary emulsion was quickly emulsified and dispersed in 600 rfLl of a 1% aqueous gelatin solution containing 0.1% of a nonionic surfactant to obtain a secondary emulsion.

The secondary emulsion was irradiated with a low-pressure mercury lamp for 20 minutes while keeping the temperature below 20° C., and then dried with a spray dryer to obtain colorless and transparent microcapsules with a particle size of 15 to 25 μm.

This capsule could be crushed by pressing strongly with a fingertip.

Claims (1)

[Scope of Claims] 1. An aqueous liquid filling is covered with an outer shell in which double bonds attached to the side chains of crystalline 1,2-polybutadiene having a syndiotactic structure and a molecular weight of at least 10,000 are bridged. Microcapsules are characterized by: 2. A first step of enveloping the aqueous liquid filling with a shell of crystalline 1,2-polybutadiene having a syndiotactic structure and a molecular weight of at least 10,000, and 3.
A second step of bridging the double bonds attached to the side chains of 1,2-polybutadiene by irradiating a light beam with a wavelength of 70n77L or less for a time corresponding to the target value of capsule strength. A method for producing microcapsules.