JPS5987036A - Preparation of microcapsule - Google Patents

Abstract

PURPOSE:To make it possible to prepare a microcapsule having a desired particle size and narrow particle size distribution, by passing all solutions through an emulsifying space capable of obtaining uniform shearing force under a pressure controllable condition to form an oil in water type emulsion. CONSTITUTION:In preparing a resin capsule of urea-formaldehyde or melamine- formaldehyde, an oily liquid and a solution containing a water soluble monomer or polymer are mixed and the obtained liquid mixture 10 is forced into an emulsifying member having an almost spindle-shaped space from an inflow small orifice opened in the tangential direction of the central part of the almost spindle-shaped member and allowed to reach outflow small orifices opened to both ends of the almost spindle-shaped space while rotated in a whriled state in said space to form an oil in water type emulsion to which wall film forming treatment is applied to prepare a microcapsule. As the result, the microcapsule having a desired particle size and narrow particle size distribution is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing microcapsules containing oil droplets, and is particularly characterized by a step of forming an oil-in-water emulsion, and a method for producing microcapsules with uniform particle size. It is related to.

As is well known, microcapsules are suitable for stably holding chemically reactive substances, unstable substances susceptible to air oxidation, liquid or gaseous substances, and the like. Currently, there are a wide range of application technologies for these microcapsules, and they have been put into practical use in pharmaceuticals, agricultural chemicals, dyes, adhesives, liquid fuels, fragrances, liquid crystals, etc. Among these, application to pressure-sensitive copying paper has a long industrial track record.

Methods for producing microcapsules include coacervation method, interfacial polymerization method, in-situ method, etc.
Although various methods are known, the urea-formalin or melamine-formalin resin capsules targeted by the present invention belong to the in-situ method;
In general, a capsule in which a monomer, a low polymer, or an initial condensate forming a wall film is supplied together with a polymerization catalyst from either the inside or outside of a core material dispersed in a dispersion medium, and a polymerization or condensation reaction is carried out on the surface of the core material. It is a legal method.

The particle form of the microcapsules obtained by this method for producing microcapsules is a mononuclear capsule in which each particle exists separately. It is a general rule that these particle forms are expressed by particle size and particle size distribution. Since the particle size and particle size distribution of microcapsules are important factors in determining capsule quality, when manufacturing microcapsules,
It is desired to stably obtain capsules having a desired particle size and a narrow particle size distribution.

To explain this about colorless dye-containing capsules for pressure-sensitive copying paper, there is generally a tendency for recording color development during multi-copying to be at odds with stain resistance against color development caused by static pressure and friction during storage and handling. Therefore, if the recording color development during multi-sheet copying is improved, stain resistance becomes insufficient, and if stain resistance is emphasized, the purpose of multi-sheet copying cannot be completely achieved. If we look at this problem from the particle size distribution of capsules, we can generally consider the various properties of the base paper, the concentration of colorless dye in the oil-based liquid, the slip resistance between the wall material and the oil-based liquid, and the ratio of each material in the capsule coating liquid as conditions. In this case, the more uniform the particle size, that is, the narrower the particle size distribution, the more excellent the pressure-sensitive copying paper tends to be in both recording color development and stain resistance. The reason for this is that the main cause of colored stains is the presence of large particle size capsules that are easily destroyed, while capsules that are extremely smaller than the average particle size are not destroyed even at G1 and do not contribute to recording color development. It is. Therefore, in producing a good pressure-sensitive copying paper, it is an important technical issue to produce capsules with a desired particle size and a narrow particle size distribution.

Here, if we outline the manufacturing process of microcapsules, it can be said that it generally consists of the following three steps.

(1) Preparation of materials such as preparation of an oily liquid (which may contain a polymer or monomer) and dissolution of a water-soluble monomer or polymer to be included in the capsule.

(2) A step of mixing and emulsifying the oily liquid and a water-soluble monomer or poly solution to form an oil-in-water emulsion.

(3) A wall film forming process in which phase separation, hardening and reinforcement of the wall film are performed while controlling the temperature, pH, solid content, etc. of the system.

Among these, the two-phase emulsion formation (2) is an extremely important step in controlling the particle size and particle size distribution of the capsules in the production of microcapsules. In fact, if an emulsion with a uniform particle size is prepared in the emulsification process, capsules with a uniform particle size can be obtained.

However, there are many aspects of emulsification that have not been sufficiently elucidated from an engineering perspective. The reasons why it is difficult to understand stirring or emulsification include the distinction between Newtonian liquids and non-Newtonian liquids, differences in physical properties such as viscosity and interfacial tension depending on the type of mixed two liquids, the shape and rotation speed of emulsifying blades, and the presence or absence of baffles. This is said to be due to the diversity of machines and the complicated and wide-ranging factors involved in stirring or emulsification. By the way, the emulsification process in the production of microcapsules refers to the formation of an oil-in-water emulsion with a size of several microns to several hundred microns.
, refers to the process of encapsulating oily microdroplets in a solution containing a water-soluble monomer or polymer. In this case, emulsification can be thought of as a case where stirring is extremely strong, and the emulsification effect is greatly influenced by the fluid flow state of the liquid. In other words, it includes circulation flow and turbulent flow (convection state throughout the building), and microscopic flow, that is, localized shear flow around the emulsifying blade where liquid viscosity and interfacial tension act strongly. We can consider them separately.

Therefore, an emulsifying machine conventionally used for manufacturing microcapsules will be considered. Commonly used machines include stirrers, homomixers, homogenizers, colloid mills, flowant mixers, and in-line mills, but all of these emulsifying machines use emulsifying blades that are driven by external power. The emulsification effect is obtained by a combination of macroscopic flow and microscopic flow due to rotational motion. In this case, a pump or stirring device is often incorporated into the system to accelerate or supplement the macroscopic flow. The principle of emulsification will be explained using a typical conventional emulsifying machine shown in the first factor.

In FIG. 1, a liquid 5 is held in an emulsifying tank 1, and a motor 2 installed at the top of the emulsifying tank 1 is connected to an emulsifying blade 4 in the emulsifying tank by a shirt 3. Therefore, when the motor 2 starts, its rotational force is transmitted to the emulsifying blade 4 via the shaft 3, so that the liquid 5 held in the emulsifier m1 can be stirred and emulsified. This emulsifying wing is thought to perform two main functions. That is, the liquid is circulated as a macroscopic flow and sheared as a microscopic flow. When the emulsifying blade rotates at high speed, shearing force increases in the immediate vicinity of the emulsifying blade, causing violent collisions between the liquids both discharged and inflowed, resulting in emulsification. On the other hand, the liquid removed from the periphery of the emulsifying blade circulates up and down the tank, mixes with the accompanying flow, and returns to the emulsifying area. This circulating flow is extremely irregular and varies depending on the structure, dimensions, liquid viscosity, flow velocity distribution, etc. of the emulsifying tank, but from the perspective of particle size distribution, it is important to consider how many times the circulating flow passes through the emulsifying zone ( The average number of cycles) is important. In other words, in conventional emulsifiers that produce an emulsifying effect through the rotational movement of the emulsifying blade, the emulsifying effect is determined by the liquid shear that occurs in the immediate vicinity of the emulsifying blade and the average number of circulations based on the circulating flow in the tank. It can be said that it is done.

Accordingly, the disadvantages of conventional emulsifiers are (1) the emulsifying area is limited to the area around the emulsifying blade, and the average number of circulations to the emulsifying area is not uniform throughout the liquid; (2) shear Due to the fact that the force is non-uniform near and far from the center of rotation of emulsion 1,
The problem is that the particle size distribution becomes wider. For this reason, in the actual emulsifying machines used for microcapsule production, improvements have been made to some extent by adjusting the internal structure of the tank, the shape and rotation speed of the emulsifying blades, the emulsifying time, etc., but there are limits to this. be. In particular, when mass-producing the capsules using a large emulsifying machine, the particle size distribution of the capsules becomes even wider.

The present invention provides a novel method for manufacturing microcapsules that is fundamentally different from conventional methods for manufacturing microcapsules in which the emulsification process is performed using rotation of emulsifying blades by external power such as steaming. . That is, in the production of urea-formalin or melamine-formalin resin capsules, the present invention
Mixing an oil-based liquid and a solution containing a water-soluble monomer or polymer, and pressurizing the mixed liquid into an emulsifying member having a substantially spindle-shaped space through an inlet pore opened in a tangential direction at the center of the substantially spindle-shaped part, He formed an oil-in-water emulsion by rotating the microcapsules in a vortex in a space through outflow pores opened at both ends of a substantially spindle shape, and provided a method for producing microcapsules characterized by a wall film formation process. It is something to do.

The basic feature of the invention is that, as opposed to the conventional method of emulsifying the liquid in a tank with rotating blades, the liquid is pumped into an emulsification zone where it is safe for the formation of a nimulsion.

In other words, an emulsification space where a stable shear force can be obtained is formed, and by passing the combined liquid through this emulsification space under pressure-controllable conditions, an oil-in-water chamber emulsion is formed, and the desired particle size is obtained. The objective is to obtain microcapsules with a narrow particle size distribution.

In the present invention, the space for emulsification in ζ is approximately spindle-shaped, and includes inflow pores that open in the tangential direction at the center of the approximately spindle shape, and outflow pores that open at both ends of the approximately spindle shape. It is sufficient that the shape of the space is approximately spindle-shaped, so for example,
Shapes such as a cone or truncated cone connected to the top and bottom of a cylinder, etc.
It may be similar to a spindle shape, but in this case as well, the inflow pores must open in the tangential direction of the cylinder, and the outflow pores must open at the apex of the cone or at the center of the upper base of the truncated cone.

The basic idea of emulsification in the present invention will be explained with respect to the above-mentioned emulsifying member having a space in which a truncated cone is connected to a cylinder. The liquid flowing into the cylindrical space is gradually directed from the tangential direction toward the axial center; The idea is to rotate it in a spiral while reducing the radius of rotation. In other words, the pre-stirred two liquids enter the cylindrical space from a tangential direction and form a fluid layer that gradually swirls inward toward the axial center. This fluid layer flows in a layered manner toward the center, so as it moves inward, the radius of the flow becomes smaller and, conversely, the velocity increases.

Since the flows in adjacent layers have different velocities, emulsification occurs as a result of receiving strong shearing force.

Although this phenomenon is not completely understood, vortex vibrations (Woltenox core) or shear shear are formed between adjacent layers, and each particle receives high energy like high-frequency vibration and becomes smaller. considered to be a thing. In addition to this, it is thought that the process in which the flow flows into the emulsification space and finally flows out from the outflow pores is also subjected to impact or shear due to the movement of the passing flow itself. Although the strength of the vortex greatly influences the conditions for forming emulsified particles, the strength of the vortex can be controlled by adjusting the pressure of the liquid flowing into the emulsifying member. If the pressure of the inflow liquid is increased, the emulsifying power becomes stronger, and if the pressure is lowered, the emulsifying power becomes weaker.

The outline of the method for manufacturing microcapsules according to the present invention will be generally explained according to the configuration example shown in FIG.

In Figure 2, a stainless steel holding tank 6 and a constant volume pump 7 are shown.
and the emulsifying member 8 are sequentially
ie, forming a circulation system. The pipe llc branches into two branches, one connected to the holding tank 6 and the other connected to the wall film forming treatment tank 9, respectively.

12c. Outlet port Ic of holding tank 6
A Haparub 12a is provided.

Therefore, with only the pulp 12c closed, if the two liquids 10 to be emulsified are placed in the holding tank 6 and the constant volume pump 7 is started, the two liquids sent out from the holding tank 6 will be press-fitted into the emulsifying member 8. It is emulsified and returns to the holding tank 6 again.

After carrying out the emulsification treatment as described above for a certain period of time considering the average number of circulation, the pulp 12b is closed, the pulp 12c is opened and the liquid is transferred to the next wall film forming treatment tank 9, where the wall film forming treatment is carried out. to obtain microcapsules.

The process of forming an oil-in-water type emulsion in the non-explosion process is realized by using an emulsifying member having a unique emulsifying space and a constant volume pump. The emulsifying member used here does not perform liquid shearing motion using external power like conventional rotary blades, but rather produces a shearing effect as a result of vortices and impact when the liquid itself passes through the emulsifying member. be.

In this emulsifying section, when the inflow pressure P is increased, the particle size becomes smaller. The average number of circulations N, which indicates the probability that the liquid has passed through the emulsifying member, is the total amount of the mixed liquid to be emulsified as V (ynl
), constant volume pump discharge amount f: A (=&/second), T If the emulsification processing time is T (second), it can be determined by N=-1. Since the quality of liquid shearing efficiency affects the average number of circulations, it is necessary to select an efficient liquid shearing means in order to shorten processing time and increase emulsification efficiency.

Desirable conditions for forming an oil-in-water emulsion are that the inflow pressure P (Ky/at ) is 3≦P≦10, and the average number of circulations N (times) is 1≦N≦20.

If the inflow pressure exceeds the above upper limit, the particle size of the capsules will become extremely small and will be impractical, while if it is below the lower limit, the processing time will be long. On the other hand, by increasing the average number of circulations, the particle size distribution can be narrowed, but once a certain limit is reached, the processing time is simply elapsed and the effectiveness is not improved.

The present invention: The emulsification method used is an encapsulation method using an interfacial polymerization method for forming a so-called polyurethane film, in which an oily liquid containing a polyvalent incyanate solution is emulsified with a water-soluble hexamer or polymer. When applied to the process, by performing emulsification for a long time, the reactive substances come into contact with each other and the reaction begins, and the reaction products are deposited in the outflow pores, resulting in the quality of the emulsified particles being the same as at the beginning of emulsification. The drawback is that they are significantly different. In addition, when applied to the encapsulation process using the so-called coacervation method in which oily liquid and gelatin solution are emulsified, emulsified particles of perfect quality are obtained, but in actual production, it is difficult to form gelatin particles at room temperature. The emulsifying member must be equipped with incidental equipment such as a heating device and a cleaning device to prevent the jelly-forming phenomenon, which poses problems in cost and workability.

In the production of urea-formalin or melamine-formalin resin capsules, there are no problems such as steaming, and the oil-in-water emulsion formed can be cured while controlling the temperature and pH of the dormitory. The film forming process is also relatively easy.

The water-soluble monomers or polymers used in the present invention are not different from those used in conventional methods for producing urea-formalin or melamine-formalin resin capsules. Examples include i-unacrylic styrene sulfonic acid copolymerized rice, polypinyl methyl ether maleic anhydride copolymer, ethylene form, and isocyanic acid-modified gelatin.

The effects achieved by the present invention are as follows.

(1) The average particle diameter of the capsules can be easily controlled by adjusting the inflow pressure to the emulsifying member.

(2) Capsules with a narrow particle size distribution and stable quality can be obtained.

(3) Enables continuous capsule manufacturing as an alternative to traditional batch processing.

(4) Since no motor is used to rotate the emulsifying blade, noise at the capsule manufacturing site is significantly reduced.

(5) Manufacturing equipment is simplified and efficient capsule manufacturing is realized.

(6) Mass production efficiency can be easily increased by installing a plurality of emulsifying members in parallel.

14-1 A method for manufacturing Micro Cub=l- using the system shown in FIG. 2 will be described below with reference to Examples. hill,
In the following, parts and parts refer to parts and parts by weight.

Example 10% aqueous solution of acrylic styrene sulfonic acid copolymer 1
00 parts, 10 parts of urea, 1 part of resorcinol, and 20 parts of water.
0 parts were added and mixed. Thereafter, the pH of the system was adjusted to 3.4 using a 20% aqueous sodium hydroxide solution to prepare a water-soluble polymer solution. Separately, 4 parts of crystal violet lactone, which is a dye for pressure-sensitive copying paper, and 2 parts of benzoyl leucomethylene blue were dissolved in 194 parts of diallyl ethano oil (trade name: Hysol SAS, manufactured by Nippon Petrochemicals) to prepare 200 parts of an oily liquid.

Total amount of water-soluble polymer solution and oily liquid prepared as above 2
000 parts were placed in the holding tank 6 and lightly stirred.

Thereafter, the constant volume pump 7 was started to perform emulsification.

The emulsifying member 8 used was a Hydroshear emulsifying machine H8-2 type (manufactured by Gorlin, Inc., USA), and the inflow pressure was 5°/Ca.

Emulsification was stopped after an average circulation of 10 times, and the obtained emulsion dispersion was transferred to wall film forming treatment tank 9, 102 parts of a 37% formaldehyde aqueous solution was added, and the temperature was heated to 55°C. After being held at 55°C for 2 hours, the heat source was turned off and the mixture was left to cool to room temperature, yielding a dispersion of mononuclear microcapsules for pressure-sensitive copying paper whose capsule walls were made of urea-foI-maldehyde polymer. .

When the particle size distribution of the capsules was measured using a Coulter counter, as shown in Figure 3, the proportion of particles contained in three channels centered around the maximum peak was 75.2%, and the average particle diameter was 4.8 microns. A pressure-sensitive copying paper obtained by laminating an upper sheet coated with the capsule and a lower sheet coated with a color developer had excellent stain resistance and good recording color development.

[Example 2] In order to increase the solid content concentration of the turnip cells, mononuclear cells were treated in the same manner as in Example 1, except that the amount of water added was changed to 100 parts when preparing the water-soluble polymer solution. A dispersion of microcapsules was obtained. As shown in Fig. 4, this microcapsule has an average ratio of particles contained in three channels centered on the maximum peak of 77.8%. ' was 4.6μ in diameter.

The pressure-sensitive copying paper using the above capsule was excellent in both stain resistance and recording color development.

[Example 3] Ethylene maleic anhydride copolymer (trade name EMA-31
, to 100 parts of a 10 aqueous solution manufactured by Monsanto Chemical,
10 parts of urea, 1 part of resorcinol, and 200 parts of water were added and mixed. Thereafter, a water-soluble polymer solution was prepared by adjusting the PR of the system to 3.5 using an insoluble solution of 20% hydrogen hydroxide. On the other hand, 200 parts of the same oily liquid as in Example 1 was prepared. A total of 2,000 parts of the water-soluble polymer solution and oily liquid prepared above were placed in a holding tank 6 in the same manner as in 1 to obtain a dispersion of microcapsules.

When the particle size distribution of the capsules was measured using a Coulter counter, as shown in Figure 5, the proportion of particles contained in three channels centered around the maximum peak was 732%, and the average particle diameter was 4.6 microns. Pressure-sensitive copying paper using the above capsules had excellent stain resistance and good recording color development.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of a typical conventional emulsifying machine, and FIG. 2 is a station-to-station diagram of the apparatus used in an embodiment of the present invention. Section 3.4.
5. The figures are respectively Example 1.2.3#-? FIG. 3 is a partial diagram of a chart showing the measurement results of Coulter's tester in . 1... Emulsification tank, 2... Motor, 4... Emulsifier, 6
. . . Holding tank, 7. Constant volume pump, 8. Emulsifying member, 9. Wall film forming treatment tank. Shi Knee-1': 1 8-3 Figure I + Yu Figure 4 +, 6 Nocha 5 Figure Doo 6JJ

Claims (2)

[Claims] (1) In the production of urea-formalin or melamine-formalin resin capsules? A tropic liquid and a solution containing a water-soluble monomer or polymer are mixed, and the mixed liquid is forced into a milk member having an approximately spindle-shaped space through an inlet pore opened in a tangential direction at the center of the approximately spindle-shaped space. death,
A method of manufacturing microcapsules by forming an oil-in-water emulsion by rotating it in a vortex in a space until it reaches outflow pores that are open at both ends of a substantially spindle shape, and then subjecting it to a wall film formation treatment. (2) A method for producing microcapsules according to claim 1, characterized in that an oil-in-water emulsion is formed under the following conditions.