JP2002282678A - Method for producing microcapsule and thermal recording material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a microcapsule, which has a small particle diameter with a narrow particle size distribution and is especially useful for a thermal recording material, at a production efficiency satisfactory for industrial production and to provide a thermal recording material containing the microcapsule to be produced by the method. SOLUTION: The microcapsule production method comprises the steps of producing an emulsion using an oil-phase liquid containing at least a material to be microcapsulated and a microcapsule wall material and a water-phase liquid and carrying out microcapsulation using the emulsion. In the production method, the step of producing the emulsion is carried out by employing a micro- reactor having a plurality of flow channels with the equivalent diameter of 1 mm or narrower. The thermal recording material contains the microcapsule obtained by the method.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing microcapsules, and more particularly, to a method for producing microcapsules used for a heat-sensitive recording material and a heat-sensitive recording material.

[0002]

2. Description of the Related Art There are various known methods for producing microcapsules. One of the methods is to dissolve a material to be microencapsulated and a microcapsule wall material in an organic solvent and dissolve a water-soluble polymer in the organic solvent. The mixture is added to and mixed with water, and the mixture is further emulsified into fine particles by an emulsifying means such as a high-speed stirrer (dissolver), a homogenizer, or an in-line mixer to prepare a stable emulsified dispersion. There is known a method for forming a microcapsule wall. As the microcapsule wall material, polyurethane and / or polyurea in which a polyol and / or a polyamine and a polyisocyanate are combined are well known.

A heat-sensitive recording material is known as a recording material utilizing such microcapsules. For example, Japanese Patent Application Laid-Open No. 6-297856 describes such a heat-sensitive recording material, and includes a coupler and a base substance. In order to emulsify the compound, these compounds are dissolved in an organic solvent, and an aqueous solution of a water-soluble polymer is added thereto with stirring using a homogenizer or the like.

In the process of producing microcapsules, emulsifying means such as a high-speed stirrer (dissolver), a homogenizer, and an in-line mixer as described above require a region where a shear force required for emulsification acts to be very close to an emulsifying blade. The shear force becomes uneven at the distance from the emulsifying wing,
There is a problem that the particle size distribution of the dispersed droplets is widened. Thermosensitive recording materials have a narrow particle size distribution of microcapsules,
It is desired for the purpose of achieving both heat sensitivity characteristics and so-called background fog, but the particle size distribution of the microcapsules depends on the particle size distribution of the droplets in the emulsified dispersion in the microcapsule manufacturing process. It is necessary to use an emulsification method with a narrow particle size distribution.

In this regard, Japanese Patent No. 2,630,501 discloses an emulsification method using a so-called cylindrical mill as an emulsification method for solving the problem of the particle size distribution caused by using the above emulsification means. I have. This emulsification method is an emulsification method in which an inner cylinder is rotated in a fixed outer cylinder to obtain an emulsion through a mixture of a dispersion medium and a dispersion in a gap between the inner cylinder and the outer cylinder. The liquid is supplied tangentially along the circumference from the side of one end of the outer cylinder so that the mixed liquid exerts a uniform shearing force over the length of the inner cylinder while moving while rotating in the gap between the inner and outer cylinders. And emulsify it sufficiently. According to this emulsification method, an emulsion having an extremely narrow particle size distribution can be obtained, but the size of the droplet diameter obtained by this method depends on the size of the gap between the inner cylinder and the outer cylinder, so that It is difficult to obtain emulsified particles having a particle size below a certain limit, and the particle size of the droplet obtained by the above method is usually 10 μm.
To the extent possible, it is not possible to obtain droplets having a particle size of several μm or less.

[0006] The microcapsules used for the heat-sensitive recording material not only have a narrow particle size distribution as described above, but also generally have a particle size of several μm or less, more preferably 1 μm or less. However, since it is necessary in terms of controlling thermal color development characteristics, particularly preferred color development gradation, the emulsification method using the cylindrical mill is difficult to employ, and is a microcapsule having a particle size of 1 μm or less, and It is desirable to use an emulsification method with a narrow distribution.

[0007] By the way, devices called so-called microreactors have been used in the fields of fine chemicals, biochemicals and the like, and have recently made great progress (W. Ehrfeld, V. Hessel, H. Lowe, "Microreacto").
r ", 1Ed. (2000), WILEY-VCH.) A microreactor consists of multiple microscale channels.
Is a general term for a reaction device having, for example, two kinds of liquids that come into contact with each other as an extremely thin liquid film while passing through different flow paths, during which mass transfer is performed through the interface of the layers, Occurs. Microreactors are used not only for chemical reactions but also for mixing or separating two or more liquids. In particular, a microreactor used for mixing is called a micromixer, in which liquid films of different liquids to be mixed are formed in a laminated structure and mixed with each other by passing them through a narrow passage. An emulsified dispersion can be prepared by using an oil phase liquid and an aqueous phase liquid as the above. WO 00/62913 proposes a dispersing machine (micromixer) for performing dispersion using such a microreactor. In this disperser, the liquid streams of the liquid A and the liquid B are separately passed through micro-scale flow channels (channels), thereby dividing into spatially divided liquid layers (liquid films), and then dividing. By combining the liquid flows and passing them through a narrow passage, the liquid A
Alternatively, the liquid B is dispersed into fine droplets, and in this case, a mechanical oscillator is used to promote the formation of droplets.

[0008] However, in the emulsification step of producing microcapsules, particularly microcapsules used for heat-sensitive recording materials, there is known a technique for producing microcapsules having a desired particle size and particle size distribution by emulsification using a microreactor. Not. The reason is considered as follows. That is, during the microcapsule production process, the water phase liquid added to the oil phase liquid in the emulsification dispersion step is usually added with a water-soluble polymer compound in order to increase the dispersion stability of the droplets. The reason is that the aqueous solution to which the water-soluble polymer is added has a high viscosity, and it is impossible to increase the processing flow rate from the viewpoint of the pressure loss in the micromixer. Further, it is not usually conceivable to emulsify and disperse the aqueous phase liquid without adding the water-soluble polymer compound as described above.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to produce microcapsules having a small particle size and a narrow particle size distribution, particularly microcapsules used for thermosensitive recording materials, with a production efficiency that can be industrially implemented. And a thermosensitive recording material including the microcapsules produced by the method.

[0010]

The above objects can be attained by providing the following method for producing microcapsules and a heat-sensitive recording material. (1) A microcapsule including a step of preparing an emulsified dispersion from an oil phase liquid and an aqueous phase liquid containing at least a material to be microencapsulated and a microcapsule wall material, and a step of microencapsulating using the emulsified dispersion. Wherein the step of preparing the emulsified dispersion is performed using a microreactor having a plurality of flow channels having an equivalent diameter of 1 mm or less. (2) The method for producing microcapsules according to (1), wherein the aqueous phase liquid is water. (3) The aqueous phase liquid is an aqueous solution containing a low molecular surfactant. The method for producing microcapsules according to the above (1) or (2). (4) In the microencapsulation step, microencapsulation is performed by using an emulsified dispersion further added with an aqueous solution containing a water-soluble polymer compound having at least surfactant. The method for producing a microcapsule according to any one of 1) to (3).

(5) The oil phase liquid according to any one of (1) to (4), wherein the oil phase liquid contains a diazonium salt compound or an electron-donating dye precursor and a microcapsule wall material. Manufacturing method of microcapsules. (6) The method for producing microcapsules according to any one of (1) to (5), wherein the microcapsule wall material contains a polyvalent isocyanate compound. (7) In a heat-sensitive recording material having a heat-sensitive recording layer provided on a support, the heat-sensitive recording layer comprises a microcapsule obtained by the method for producing microcapsules according to (5) or (6) and a developer. A heat-sensitive recording material comprising:

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The microreactor used in the present invention is a reactor having a plurality of microscale flow channels (specifically, W. Ehrfel).
d, V.Hessel, H.Lowe, "Microreactor", 1Ed. (2000), W
ILEY-VCH). Since the flow path of the microreactor is microscale, both the size and the flow rate are small, and the Reynolds number is 200 or less. Therefore, a reactor having a micro-scale flow path is not a turbulent one, but a laminar one. In a world dominated by laminar flow, two liquid streams can only be mixed by diffusion through the interface, even if they are in contact. Since the specific area is large in the micro-scale space, it is advantageous for diffusion mixing at the interface where the laminar flow contacts. The time required for mixing depends on the cross-sectional area of the interface between the two liquids and the thickness of the liquid layer.
According to diffusion theory, the time required for mixing (mass transfer) (t)
Is represented by t = d _eq ² / D (D; mass diffusivity), so that the smaller the channel width, the faster the mixing time. That is, if the equivalent diameter becomes 1/10, the mixing time becomes 1
/ 100. In a micro-scale space, molecular transport, reaction, and separation can be quickly performed only by spontaneous behavior of molecules without using mechanical stirring or the like.

For such reasons, it is generally said that the reaction speed in a laminar flow of a microreactor is faster than that in a turbulent flow using a conventional macro-reactor. In the case of a macro apparatus, it is not always advantageous to control the reaction if the reaction rate is too fast.However, in the case of a micro reactor, the reaction time is basically controlled because the reaction is performed in a flow. In addition to the fact that the temperature control is easy as described below, the selectivity of the reaction is likely to be significantly improved. Furthermore, since phase separation and the like are simplified, it is expected that a two-phase reaction and the separation and purification of products can be achieved by making use of the features.

A feature of the microreactor is that the reaction field is a very small space in addition to the above-mentioned points, and therefore, if a material such as metal or ceramics is used, a high-temperature and high-pressure reaction can be performed safely. For example, it is described that hydrogen peroxide can be generated from oxygen and hydrogen, and an oxidation reaction and the like can be performed, which is dangerous and cannot be performed at all with a general reaction apparatus.

In a microreactor, the equivalent diameter of a flow channel (channel) affects reactivity and the like. The equivalent diameter (also called equivalent diameter) is a term used in the field of mechanical engineering, also called equivalent (straight) diameter. When assuming a circular pipe equivalent to a pipe having an arbitrary cross-sectional shape (a flow path in the present invention), the diameter of the equivalent circular pipe is called an equivalent diameter, A: cross-sectional area of the pipe, p: wet length of the pipe. (Perimeter), d _eq = 4A
/ P. When applied to a pipe, this equivalent diameter corresponds to the pipe diameter. The equivalent diameter is used to estimate the flow or heat transfer characteristics of the pipe based on the data of the equivalent circular pipe, and represents the spatial scale (representative length) of the phenomenon. The equivalent diameter is d _eq = 4a ^{2 for a} square tube with one side a.
/ 4a = a, d _eq = a / for an equilateral triangular tube with one side a, and d _eq = 2h for a flow between parallel flat plates with a road height h (see:
Encyclopedia of Mechanical Engineering, edited by The Japan Society of Mechanical Engineers, 1997, Maruzen Co., Ltd.

Since the surface area per unit volume (specific surface area) increases as the equivalent diameter of the flow path decreases, the specific surface area increases remarkably when the flow path becomes a micro-scale as in the present invention. The heat transfer efficiency through the vessel wall is very high. Since the heat transfer time (t) in the fluid flowing through the flow path is represented by t = d _eq ² / α (α: thermal diffusivity of the liquid), the heat transfer time becomes shorter as the equivalent diameter becomes smaller. That is, if the equivalent diameter becomes 1/10, the heat transfer time becomes 1/100. When the equivalent diameter is on the microscale, the heat transfer rate is very fast.

According to the present invention, in the method for producing microcapsules, the emulsifying and dispersing step, which is one of the steps for producing microcapsules, is carried out using a microreactor having a plurality of flow paths having an equivalent diameter of 1 mm or less as described above. It is characterized by: In the method for producing microcapsules of the present invention, the microreactor as described above is used in the emulsification and dispersion step, so that microcapsules having a small particle size and a narrow particle size distribution can be produced. Further, since the aqueous phase liquid used in the emulsification dispersion step is water or an aqueous solution of a low-molecular surfactant and has a low viscosity, the flow rate in the microreactor can be increased, and the preparation of the emulsification dispersion liquid can be made more efficient. be able to.

The equivalent diameter of the plurality of flow paths as described above is 1 m.
The liquid phase of the oil phase liquid and the aqueous phase liquid is formed by passing the oil phase liquid and the aqueous phase liquid through the flow path of the microreactor having a diameter of not more than m. The liquid and the aqueous phase liquid are mixed to form an emulsified dispersion. For example, the liquid film is formed such that the liquid film of the oil phase liquid and the liquid film of the aqueous phase liquid are alternately laminated, for example, as described in WO 00/62913.
As shown in FIG. 1 or FIG. 3 of the publication, an oil phase liquid flow path and an aqueous phase flow path are alternately formed, and the oil phase liquid and the aqueous phase liquid are separately passed through this flow path. The oil phase liquid can be dispersed as fine droplets in the aqueous phase liquid by dividing the liquid streams into spatially divided liquid films and then combining the divided liquid streams and passing through the narrow passages. Examples of such microreactors are WO97 / 12665, WO97 / 17130,
WO97 / 17133, WO97 / 28894, WO9
8/33582.

In the emulsification and dispersion of the present invention, by setting the equivalent diameter of the flow channel of the microreactor to 1 mm or less, good emulsification and dispersion can be performed, and the emulsification of droplets having a small particle size and a narrow particle size distribution can be achieved. A dispersion is obtained. The equivalent diameter of the channel is preferably from 10 to 500 μm, particularly preferably from 20 to 300 μm. The length of the channel is not particularly limited, but is preferably 1 mm to 1000 mm, and particularly preferably 10 mm to 500 mm. (Note that in this specification, “to” indicates a range including numerical values described before and after it as a minimum value and a maximum value, respectively.)

The plurality of flow paths used in the present invention are:
In addition, parallelize as many as necessary (Numbering-u
p), the processing amount can be increased. In addition, the time for staying in the channel is generally 1 hour or less, preferably 10 minutes or less, and particularly preferably 1 second to 5 minutes.

The channel of the present invention is formed on a solid substrate by a fine processing technique. To give examples of the materials used,
Metal, silicon, Teflon (registered trademark), glass, ceramics, plastic, or the like. When heat resistance, pressure resistance and solvent resistance are required, preferred materials are metal, silicon, Teflon, glass or ceramics,
Particularly preferred are metals. Examples of metals include nickel, aluminum, silver, gold, platinum, tantalum, stainless steel,
Hastelloy (Ni-Fe alloy) or titanium, preferably stainless steel, hastelloy or titanium having high corrosion resistance.

In a conventional batch type reaction apparatus, an apparatus in which a metal (such as stainless steel) is glass-lined is used when handling an acidic substance or the like, but a microreactor or a metal coating may be performed on the metal surface. The present invention is not limited to glass, and may be coated on a metal with another metal or another material, or on a material other than metal (for example, ceramic) with metal or glass. The channel of the device (microreactor) may be subjected to surface treatment according to the purpose. In particular, when an aqueous solution is operated, surface treatment is important because adsorption of a sample to glass or silicon may be a problem. For fluid control in micro-sized channels, it is desirable to achieve this without incorporating moving parts that require complex fabrication processes. For example, it becomes possible to create a hydrophilic region and a hydrophobic region in a flow path by surface treatment, and to operate a fluid by utilizing a surface tension difference acting on the boundary.

A typical example of a fine processing technique for producing a flow path is L using X-ray lithography.
IGA technology, high aspect ratio photolithography using EPON SU-8, micro electric discharge machining (μ-EDM),
Hot processing of high aspect ratio silicon by Deep RIE
Emboss processing, stereolithography, laser processing, ion beam processing, and mechanical micro cutting using a micro tool made of a hard material such as diamond. These techniques may be used alone or in combination. Preferred micromachining techniques are the LIGA technique using X-ray lithography, the high aspect ratio photolithography method using EPON SU-8, the micro electric discharge machining method (μ-EDM), and the mechanical micro cutting method.

When assembling the apparatus (microreactor) of the present invention, a joining technique is often used. Conventional joining techniques can be broadly divided into solid-phase joining and liquid-phase joining. Commonly used joining methods are pressure welding and diffusion joining as solid-phase joining, welding, eutectic joining, soldering as liquid-phase joining. Adhesion and the like are typical joining methods. Furthermore, when assembling, it is desirable to use a high-precision bonding method that maintains dimensional accuracy without destruction of microstructures such as flow paths due to material deterioration or large deformation due to high-temperature heating. There are anodic bonding, surface activated bonding, direct bonding using hydrogen bonding, bonding using HF aqueous solution, Au-Si eutectic bonding, void-free bonding, and the like.

In order to emulsify and disperse the oil phase liquid droplets into the aqueous phase liquid through the plurality of flow paths of the microreactor, the oil phase liquid and the aqueous phase liquid are introduced. Control function is required. In particular, since the behavior of the fluid in the minute region has a property different from that of the macro scale, a control method suitable for the micro scale must be considered.
The fluid control method is classified into a continuous flow method and a liquid drop (liquid plug) method when classified into forms, and is classified into an electric driving method and a pressure driving method when classified into driving forces.

These systems will be described in detail below. The most widely used form of handling fluid is the continuous flow method. In the continuous flow type fluid control, it is general that the entire flow path of the microreactor is filled with fluid, and the entire fluid is driven by a pressure source such as a syringe pump provided outside. In this case, one advantage is that the control system can be realized with a relatively simple setup.However, operation involving liquid exchange is difficult, the degree of freedom in system configuration is small, and the drive medium is the solution itself. Therefore, the disadvantage is that the dead volume is large. As a method different from the continuous flow method, there is a droplet (liquid plug) method. In this method, droplets separated by air are moved inside the reactor or in a flow path leading to the reactor, and each droplet is driven by air pressure. At this time, a vent structure that allows air between the droplets and the flow path wall or between the droplets to escape to the outside as necessary,
In addition, it is necessary to provide a valve structure for keeping the pressure in the branched flow path independent of other parts inside the reactor system. Further, in order to control the pressure difference and operate the droplet, it is necessary to construct a pressure control system including a pressure source and a switching valve outside. As described above, in the droplet method, the configuration of the apparatus and the structure of the reactor are slightly complicated, but the degree of freedom of the system configuration is increased.

As a driving method for performing fluid control, an electric driving method in which a high voltage is applied to both ends of a flow channel (channel) to generate an electroosmotic flow, and thereby the fluid is moved, and a pressure source is provided outside. In general, a pressure driving method of applying pressure to a fluid to move the fluid is widely used. The difference between the two is, for example, that the flow velocity profile in the cross section of the flow path is flat when the electric drive method is used, whereas the flow path profile is hyperbolic in the pressure drive method and the flow path center is It is known that the distribution is fast and the wall portion has a slow distribution. The electric drive method is more suitable for the purpose of moving the sample plug or the like while maintaining the shape. When the electric drive method is used, the flow path needs to be filled with a fluid, so it is inevitable to take the form of a continuous flow method.However, it is possible to operate the fluid by electric control. For this reason, for example, a relatively complicated process such as creating a temporal concentration gradient by continuously changing the mixing ratio of two types of solutions has also been realized. In the case of the pressure drive system, there is almost no influence on the substrate because it can be controlled regardless of the electrical properties of the fluid and there is no need to consider secondary effects such as heat generation and electrolysis. , Its applicability is wide. On the other hand, it is necessary to automate complicated processes such as the need to prepare an external pressure source and the change in response characteristics of the operation depending on the size of the dead volume of the pressure system.

The method used as the fluid control method is appropriately selected depending on the purpose, but is preferably a continuous flow type pressure drive system.

The temperature of the microreactor may be controlled by putting the entire apparatus in a temperature-controlled container, or by forming a heater structure such as a metal resistance wire or polysilicon in the apparatus and controlling the heating. May be used, and the thermal cycle may be performed by natural cooling. For temperature sensing, another resistance wire identical to the heater is formed in the metal resistance wire, and the temperature is detected based on a change in the resistance value, and the polysilicon is detected using a thermocouple. Heating and cooling may be performed from the outside by bringing the Peltier element into contact with the reactor. Which method is used is selected according to the use and the material of the reactor body.

In order to increase the processing flow rate, it is also possible to use an array type (mixer array) in which a plurality of microreactors as described above are incorporated in parallel.

[Manufacture of Microcapsules] Next, a method of manufacturing the microcapsules of the present invention will be described. In the method for producing microcapsules of the present invention, the emulsified dispersion is prepared from the oil phase liquid and the aqueous phase liquid as described above, and the microcapsule wall material is reacted to form the microcapsule walls. When an isocyanate compound is used as a wall material at the time of microcapsule wall formation, a polymerization reaction catalyst for the isocyanate compound may be added after emulsification, or the temperature of the emulsion may be increased to promote the capsule wall formation reaction. As the aqueous phase liquid, an aqueous solution of a low molecular surfactant can be used in addition to water. As the low-molecular surfactant, those having a molecular weight of about 1000 or less can be used without particular limitation. In addition, the following surfactants of a formalin condensate of an aromatic sulfonate or an aromatic carboxylate and an alkylglucoside surfactant can also be used.

[0032]

Embedded image

[0033] In the formula, R represents an alkyl group having 1 to 4 carbon atoms, X is SO3 ^- or COO ^-, M is an integer of sodium or potassium, q is 1-20. The surfactant has a structure in which an aromatic sulfonic acid or an aromatic carboxylic acid, for example, benzenesulfonic acid, benzoic acid, naphthalenesulfonic acid, naphthalenecarboxylic acid, and a derivative thereof are condensed with formalin. The average degree of polymerization is preferably 2 to 10. The aromatic ring has 1 to 1 carbon atoms
Those to which an alkyl group or substituted alkyl group of No. 4 is added are more preferable. These surfactants may be used as a mixture of two or more.

[0034]

Embedded image

In the above formula, n represents an integer of 0 to 2, and R represents an alkyl group having 4 to 18 carbon atoms which may be linear or branched. Specifically, the alkyl group represented by R is n-butyl, i-butyl, n-hexyl, n-heptyl, n-butyl.
Octyl, 2-ethylhexyl, n-decyl, n-dodecyl, n-hexadecyl, n-octadecyl, branched octadecyl and the like can be mentioned. In the industrial production method, n has a composition in which the monosaccharide glucoside of 0 is the main component and the components of 1 and 2 are mixed, but these composition ratios do not affect the effect of the present invention. The use of two or more different alkyl groups does not impair the effect.

The content of the surfactant in the aqueous phase liquid is as follows:
It is 0.001 to 10% by mass, preferably 0.01 to 6% by mass.

In the microencapsulation step, an aqueous solution containing at least a water-soluble polymer compound having surface activity is added to the emulsified dispersion, and then the microcapsule wall material is reacted to form microcapsule walls. Is preferred. By adding this aqueous solution,
Aggregation of microcapsule particles that rarely occurs during the reaction process can be prevented. The aqueous solution to be added is suitably added such that the solid content concentration of the microcapsule dispersion liquid after the reaction becomes 5 to 50% by mass, preferably 10 to 40% by mass. In the following, the aqueous phase liquid added to the oil phase liquid during emulsification and dispersion is referred to as “first aqueous phase liquid”, and the aqueous phase liquid added to the emulsified dispersion liquid during microencapsulation is referred to as “second aqueous phase liquid”. There is.

Examples of the water-soluble high molecular compound having at least surface activity to be added to the second aqueous phase liquid include polyvinyl alcohol and its modified products, polyacrylamide and its derivatives, ethylene-vinyl acetate copolymer, styrene- Maleic anhydride copolymer, ethylene-maleic anhydride copolymer, isobutylene-maleic anhydride copolymer,
Examples include polyvinylpyrrolidone, ethylene-acrylic acid copolymer, vinyl acetate-acrylic acid copolymer, carboxymethylcellulose, methylcellulose, casein, gelatin, starch derivatives, gum arabic, sodium alginate and the like. It is preferable that these water-soluble polymers have no or low reactivity with the isocyanate compound.For example, those having a reactive amino group in the molecular chain, such as gelatin, should be previously deactivated. is necessary. The content of the water-soluble polymer compound in the second aqueous phase liquid is 1 to 20% by mass, preferably 2 to 10% by mass.
It is.

[Preparation of Thermosensitive Recording Material] Next, a method of preparing a thermosensitive recording material by using the above-described method of manufacturing a microcapsule will be described. The heat-sensitive recording layer of the heat-sensitive recording material contains microcapsules containing a diazonium salt compound or an electron-donating dye precursor as a color-forming component. Further, the heat-sensitive recording layer contains the above-mentioned microcapsules and a coupler or an electron-accepting compound as a color developer depending on the color-forming component contained in the microcapsules. The developer is emulsified or dispersed to form fine particles. The heat-sensitive recording layer is formed by applying a mixture of a microcapsule solution prepared as described later and a developer dispersion to a support. The heat-sensitive recording material of the present invention, in the emulsification dispersion step of microcapsule production,
Since a microreactor is used, the coloring density is high and the background fog during long-term storage is small.

In the production of microcapsules containing a diazonium salt compound or an electron donating dye precursor, first, an oil phase liquid containing a diazonium salt compound or an electron donating dye precursor and a microcapsule wall material and an aqueous phase liquid are prepared. Then, these are emulsified and dispersed using a microreactor having a plurality of flow paths having an equivalent diameter of 1 mm or less. Next, microcapsulation is performed using the obtained emulsified dispersion to obtain microcapsules. At this time, as described above,
It is preferable to add an aqueous solution containing a water-soluble polymer compound having surfactant to the emulsified dispersion, and then to perform microcapsulation.

The oil phase solution is prepared by adding a diazonium salt compound or an electron-donating dye precursor, a microcapsule wall material, and, if necessary, various additives.
It is carried out by dissolving in a water-insoluble or insoluble organic solvent. As the aqueous phase liquid, water alone or one obtained by dissolving various low molecular surfactants in water is used.

Examples of the organic solvent include low-boiling auxiliary solvents such as acetate, methylene chloride and cyclohexanone, and / or phosphates, phthalates, acrylic esters, methacrylic esters, other carboxylic esters, fatty acid amides, and the like. Alkylated biphenyl, alkylated terphenyl, alkylated naphthalene,
Diarylethane, chlorinated paraffin, alcoholic,
Phenol type, ether type, monoolefin type, epoxy type and the like can be mentioned. Specific examples include tricresyl phosphate, trioctyl phosphate, octyl diphenyl phosphate, tricyclohexyl phosphate, dibutyl phthalate, dioctyl phthalate, dilaurate phthalate, dicyclohexyl phthalate, butyl olefin, diethylene glycol benzoate, dioctyl sebacate, Dibutyl sebacate, dioctyl adipate, trioctyl trimellitate, acetyl triethyl citrate, octyl maleate, dibutyl maleate, isoamyl biphenyl, chlorinated paraffin, diisopropyl naphthalene,
1,1'-ditolylethane, 2,4-ditertiaryamylphenol, N, N-dibutyl-2-butoxy-5
Tert-octylaniline, hydroxybenzoic acid 2-
Ethylhexyl ester, high-boiling oils such as polyethylene glycol, and among them, alcohols, phosphates, carboxylic esters,
Preferred are alkylated biphenyls, alkylated terphenyls, alkylated naphthalenes, and diarylethanes. Further, an anti-carbonizing agent such as hindered phenol and hindered amine may be added to the high boiling point oil. Further, as the oil, those having an unsaturated fatty acid are particularly desirable,
α-methylstyrene dimer and the like.
Examples of the α-methylstyrene dimer include “MSD100” manufactured by Mitsui Toatsu Chemicals, Inc.

The diazonium salt compound is a compound represented by the following formula, which is a compound which undergoes a coupling reaction with a coupler upon heating to form a color and is decomposed by light. These can control the maximum absorption wavelength depending on the position and type of the substituent in the Ar portion. Ar-N ₂ ⁺ X ^- (wherein, Ar represents an aromatic moiety, X ^- represents an acid anion.)

Specific examples of the salt-forming diazonium include 4- (p-tolylthio) -2,5-dibutoxybenzenediazonium and 4- (4-chlorophenylthio)-
2,5-dibutoxybenzenediazonium, 4- (N,
N-dimethylamino) benzenediazonium, 4-
(N, N-diethylamino) benzenediazonium, 4
-(N, N-dipropylamino) benzenediazonium, 4- (N-methyl-N-benzylamino) benzenediazonium, 4- (N, N-dibenzylamino) benzenediazonium, 4- (N-ethyl-N -Hydroxyethylamino) benzenediazonium, 4- (N, N-
Diethylamino) -3-methoxybenzenediazonium, 4- (N, N-dimethylamino) -2-methoxybenzenediazonium, 4- (N-benzoylamino)-
2,5-diethoxybenzenediazonium, 4-morpholino-2,5-dibutoxybenzenediazonium, 4-
Anilinobenzenediazonium, 4- [N- (4-methoxybenzoyl) amino] -2.5-diethoxybenzenediazonium, 4-pyrrolidino-3-ethylbenzenediazonium, 4- [N- (1-methyl-2- ( 4-methoxyphenoxy) ethyl) -N-hexylamino]-
2-hexyloxybenzenediazonium, 4- [N-
(2- (4-methoxyphenoxy) ethyl) -N-hexylamino] -2-hexyloxybenzenediazonium, 2- (1-ethylpropyloxy) -4- [di-
(Di-n-butylaminocarbonylmethyl) amino] benzenediazonium, 2-benzylsulfonyl-4-
[N-methyl-N- (2-octanoyloxyethyl)] aminobenzenediazonium and the like.

In the present invention, any coupler capable of forming a dye by coupling with a diazo compound in a basic atmosphere and / or a neutral atmosphere can be used as a coupler for forming a dye by coupling with a diazo compound. It is possible. All so-called 4-equivalent couplers for silver halide photographic light-sensitive materials can be used as couplers. These can be selected according to the desired hue.

Specific examples include resorcin, phloroglucin, 2,3-dihydroxynaphthalene, sodium 2,3-dihydroxynaphthalene-6-sulfonate, 1
-Hydroxy-2-naphthoic acid morpholinopropylamide, 2-hydroxy-3-naphthalenesulfonic acid sodium salt, 2-hydroxy-3-naphthalenesulfonic acid anilide, 2-hydroxy-3-naphthalenesulfonic acid morpholinopropylamide, 2-hydroxy- 3-naphthalenesulfonic acid-2-ethylhexyloxypropylamide, 2-hydroxy-3-naphthalenesulfonic acid-2-
Ethylhexylamide, 5-acetamido-1-naphthol, 1-hydroxy-8-acetamidonaphthalene-
Sodium 3,6-disulfonate, 1-hydroxy-8
-Acetamidonaphthalene-3,6-disulfonic acid dianilide, 1,5-dihydroxynaphthalene, 2-hydroxy-3-naphthoic acid morpholinopropylamide, 2-
Hydroxy-3-naphthoic acid octylamide, 2-hydroxy-3-naphthoic acid anilide, 5,5-dimethyl-
1,3-cyclohexanedione, 1,3-cyclopentanedione, 5- (2-n-tetradecyloxyphenyl) -1,3-cyclohexanedione, 5-phenyl-
4-methoxycarbonyl-1,3-cyclohexanedione, 5- (2,5-di-n-octyloxyphenyl)
-1,3-cyclohexanedione, N, N'-dicyclohexylbarbituric acid, N, N'-di-n-dodecylbarbituric acid, Nn-octyl-N'-n-octadecyl barbituric acid, N- Phenyl-N '-(2,5
-Di-n-octyloxyphenyl) barbituric acid,
N, N'-bis (octadecyloxycarbonylmethyl) barbituric acid, 1-phenyl-3-methyl-5-
Pyrazolone, 1- (2,4,6-trichlorophenyl)
-3-anilino-5-pyrazolone, 1- (2,4,6-
Trichlorophenyl) -3-benzamido-5-pyrazolone, 6-hydroxy-4-methyl-3-cyano-1-
(2-ethylhexyl) -2-pyridone, 2,4-bis- (benzoylacetamido) toluene, 1,3-bis- (pivaloylacetoamidomethyl) benzene, benzoylacetonitrile, thenoylacetonitrile, acetoacetanilide, benzoylacetanilide, Pivaloylacetoanilide, 2-chloro-5- (Nn-butylsulfamoyl) -1-pivaloylacetamidobenzene, 1- (2-ethylhexyloxypropyl) -3-
Cyano-4-methyl-6-hydroxy-1,2-dihydropyridin-2-one, 1- (dodecyloxypropyl) -3-acetyl-4-methyl-6-hydroxy-
1,2-dihydropyridin-2-one, 1- (4-n-
Octyloxyphenyl) -3-tert-butyl-5
-Aminopyrazole and the like. For details of the coupler, see JP-A-4-201483 and JP-A-7-2233.
No. 67, JP-A-7-223368, JP-A-7-323
No. 660, Japanese Patent Application No. 5-278608, Japanese Patent Application No. 5-29
7024, Japanese Patent Application No. 6-18669, Japanese Patent Application No. 6-18
No. 670, Japanese Patent Application No. 7-316280, Japanese Patent Application No. 8-02
No. 7095, Japanese Patent Application No. 8-027096, Japanese Patent Application No. 8-0
No. 30799, Japanese Patent Application No. 8-12610, Japanese Patent Application No. 8-1
No. 32394, Japanese Patent Application No. 8-358755, Japanese Patent Application No. 8-
358756 and Japanese Patent Application No. 9-069990.

The electron-donating dye precursor encapsulated in the microcapsules of the present invention includes triarylmethane compounds, diphenylmethane compounds, thiazine compounds, xanthene compounds, spiropyran compounds, and the like. Triarylmethane compounds and xanthene compounds are useful because of their high color density. Examples of some of these are 3,3-bis (p-dimethylaminophenyl) -6-dimethylaminophthalide (that is, crystal violet lactone), 3,3-bis (p-dimethylamino) phthalide, (P-dimethylaminophenyl) -3- (1,3-dimethylindol-3-yl) phthalide, 3- (p-dimethylaminophenyl)-
3- (2-methylindol-3-yl) phthalide, 3
-(O-methyl-p-diethylaminophenyl) -3-
(2-methylindol-3-yl) phthalide, 4,
4'-bis (dimethylamino) benzhydrin benzyl ether, N-halophenylleuco auramine, N-
2,4,5-trichlorophenylleuco auramine, rhodamine-B-anilinolactam, rhodamine (p-nitroanilino) lactam, rhodamine-B- (p-chloroanilino) lactam, 2-benzylamino-6-diethylaminofluoran, 2-anilino-6-diethylaminofluoran, 2-anilino-3-methyl-6-diethylaminofluoran, 2-anilino-3-methyl-6
-Cyclohexylmethylaminofluoran, 2-anilino-3-methyl-6-isoamylethylaminofluoran, 2- (o-chloroanilino) -6-diethylaminofluoran, 2-octylamino-6-diethylaminofluoran, 2- Ethoxyethylamino-3-chloro-
2-diethylaminofluoran, 2-anilino-3-chloro-6-diethylaminofluoran, benzoylleucomethylene blue, p-nitrobenzylleucomethylene blue, 3-methyl-spiro-dinaphthopyran, 3-ethyl-spiro-dinaphthopyran, 3,3 '-Dichloro-
Spiro-dinaphthopyran, 3-benzylspirodinaphthopyran, 3-propyl-spiro-dibenzopyran and the like can be mentioned.

Examples of the electron-accepting compound include phenol derivatives, salicylic acid derivatives, and hydroxybenzoic acid esters. Particularly, bisphenols and hydroxybenzoates are preferred. Some examples of these include 2,2-bis (p-hydroxyphenyl) propane (ie, bisphenol A), 4,4 ′-(p-phenylenediisopropylidene) diphenol (ie, bisphenol P), 2,2-bis (p-hydroxyphenyl) pentane, 2,2-bis (p-hydroxyphenyl) ethane, 2,2-bis (p-hydroxyphenyl)
Butane, 2,2-bis (4'-hydroxy-3 ', 5'
-Dichlorophenyl) propane, 1,1- (p-hydroxyphenyl) cyclohexane, 1,1- (p-hydroxyphenyl) propane, 1,1- (p-hydroxyphenyl) pentane, 1,1- (p-hydroxyphenyl) ) -2-Ethylhexane, 3,5-di (α-methylbenzyl) salicylic acid and its polyvalent metal salts, 3,5-di (tert-butyl) salicylic acid and its polyvalent metal salts, 3-α, α- Dimethylbenzyl salicylic acid and its polyvalent metal salts, butyl p-hydroxybenzoate, benzyl p-hydroxybenzoate, p-hydroxybenzoic acid
2-ethylhexyl, p-phenylphenol, p-cumylphenol and the like can be mentioned.

As the sensitizer, a low-melting organic compound having an appropriate aromatic group and polar group in the molecule is preferable, and benzyl p-benzyloxybenzoate, α-naphthyl benzyl ether, β- Naphthyl benzyl ether,
β-naphthoic acid phenyl ester, α-hydroxy-β
-Naphthoic acid phenyl ester, β-naphthol- (p
-Chlorobenzyl) ether, 1,4-butanediol phenyl ether, 1,4-butanediol-p-methylphenyl ether, 1,4-butanediol-p-ethylphenyl ether, 1,4-butanediol-m-
Methyl phenyl ether, 1-phenoxy-2- (p-
Tolyloxy) ethane, 1-phenoxy-2- (p-ethylphenoxy) ethane, 1-phenoxy-2- (p-
Chlorophenoxy) ethane, p-benzylbiphenyl and the like.

The wall material of the microcapsules is preferably a polymer material. Specific examples thereof include polyurethane resin, polyurea resin, polyamide resin, polyester resin, polycarbonate resin, aminoaldehyde resin, melamine resin, polystyrene resin, and styrene-acrylate. Copolymer resins, styrene-methacrylate copolymer resins, gelatin, polyvinyl alcohol and the like can be mentioned.
Of these, particularly preferred wall materials include polyurethane and
Polyurea resin. Microcapsules having a wall film made of polyurethane / polyurea resin, a microcapsule wall precursor such as polyvalent isocyanate is mixed in a core material to be encapsulated, and emulsified and dispersed in an aqueous solution of a water-soluble polymer such as polyvinyl alcohol. It is produced by raising the liquid temperature and causing a polymer forming reaction at the oil droplet interface.

Here, some specific examples of the polyvalent isocyanate compound are shown below. For example, m-phenylene diisocyanate, p-phenylene diisocyanate, 2,6-
Tolylene diisocyanate, 2,4-tolylene diisocyanate, naphthalene-1,4-diisocyanate, diphenylmethane-4,4′-diisocyanate, 3,
3'-diphenylmethane-4,4'-diisocyanate, xylene-1,4-diisocyanate, 4,4'-
Diphenylpropane diisocyanate, trimethylene diisocyanate, hexamethylene diisocyanate, propylene-1,2-diisocyanate, butylene-1,
Diisocyanates such as 2-diisocyanate, cyclohexylene-1,2-diisocyanate, and cyclohexylene-1,4-diisocyanate; 4,4 ′, 4 ″-
Triphenylmethane triisocyanate, toluene
Triisocyanates such as 2,4,6-triisocyanate, 4,4′-dimethylphenylmethane-2,2 ′,
Tetraisocyanates such as 5,5′-tetraisocyanate, adducts of hexamethylene diisocyanate with trimethylolpropane, adducts of 2,4-tolylenediisocyanate with trimethylolpropane, and xylylenediisocyanate with trimethylolpropane Isocyanate prepolymers such as adducts and adducts of tolylene diisocyanate and hexanetriol, and the like. If necessary, two or more kinds can be used in combination. Of these, particularly preferred are those having three or more isocyanate groups in the molecule.

The coupler or the electron-accepting compound contained in the heat-sensitive recording layer of the heat-sensitive recording material is emulsified or solid-dispersed into fine particles, but is preferably solid-dispersed. The thermosensitive recording material of the present invention is produced by mixing the microcapsule dispersion prepared as described above and a dispersion of a coupler or an electron-accepting compound, and applying the mixture to a support to form a thermosensitive recording layer. can do.

[0053]

The present invention will be described in more detail with reference to the following Examples, but it should not be construed that the present invention is limited to these Examples. In the following, unless otherwise specified, parts mean parts by mass and% means mass%. Example 1 < Preparation of diazonium salt compound microcapsule> Preparation of oil phase solution As a diazonium salt compound, 4.4 parts of a compound represented by the following structural formula having a maximum absorption wavelength of decomposition at 420 nm was dissolved in 16.4 parts of ethyl acetate, and further dissolved. 9.8 parts of isopropyl biphenyl as a boiling point solvent was added, and the mixture was heated and uniformly mixed.
As a capsule wall material, 18 parts of a 50% by mass ethyl acetate solution (trade name: Takenate D119N, manufactured by Takeda Pharmaceutical Co., Ltd.) of a mixture of xylylene diisocyanate / trimethylolpropane adduct and xylylene diisocyanate / bisphenol A adduct was added. The solution was further added and stirred uniformly.

[0054]

Embedded image

Preparation of First Aqueous Solution 50 parts of pure water was used as a first aqueous solution. Emulsified dispersion microreactor (trade name: single mixer, IM
The above oil phase liquid and the first aqueous phase liquid are sent to the inlet of a single mixer at room temperature at a constant flow rate (1 L / hr) using a syringe pump at an equivalent diameter of 80 μm manufactured by Company M. As a result, a desired emulsified dispersion could be obtained. Microcapsules The resulting emulsified dispersion is added to 40 parts of pure water (second aqueous phase liquid) maintained at 40 ° C. while mixing and stirring, and microcapsules can be obtained by reacting with isocyanate. did it.

Example 2 Instead of the first aqueous phase liquid in Example 1, 50 parts of pure water was used.
Except for using a first aqueous phase solution to which 1.5 parts by weight of a 50% by mass aqueous solution of an alkylglucoside surfactant (trade name: Scraph AG-8, manufactured by Nippon Seika Co., Ltd.) was used, the same procedure as in Example 1 was used. Obtain microcapsules.

Example 3 Instead of the first aqueous phase liquid in Example 1, 50 parts of pure water was used.
10% by weight aqueous solution of sodium dodecylbenzenesulfonate
Microcapsules are obtained in the same manner as in Example 1 except that 7.5 parts of the first aqueous phase liquid is used.

Example 4 The same procedure as in Example 1 was repeated except that 40 parts of an aqueous phthalated gelatin solution having a concentration of 8% by mass was used as the second aqueous phase liquid in place of the second aqueous phase liquid in Example 1. Get a capsule.

Example 5 Instead of the second aqueous phase liquid in Example 1, 40 parts of an aqueous solution of polyvinyl alcohol (trade name: PVA217, manufactured by Kuraray Co., Ltd.) having a concentration of 2% by mass is used as the second aqueous phase liquid. Others are the same as in Example 1 to obtain microcapsules.

Example 6 A mixer array (manufactured by IMM, equivalent diameter: 80 μm) was used instead of the single mixer in Example 1.
Microcapsules are obtained in the same manner as in Example 1.

[0061]

According to the method for producing microcapsules of the present invention, microcapsules having a small particle size and a narrow particle size distribution can be produced since the microreactor is used in the emulsifying and dispersing step. Further, since the aqueous phase liquid used in the emulsification dispersion step is water or an aqueous solution of a low-molecular surfactant and has a low viscosity, the flow rate in the microreactor can be increased, and the preparation of the emulsification dispersion liquid can be made more efficient. be able to. Further, the thermosensitive recording material of the present invention, in the emulsification dispersion step of microcapsule production,
Since a microreactor is used, the coloring density is high and the background fog during long-term storage is small.

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Claims (7)

[Claims] 1. A step of preparing an emulsified dispersion from at least an oil phase liquid and an aqueous phase liquid containing a material to be microencapsulated and a microcapsule wall material, and a step of microencapsulation using the emulsified dispersion. In the method for producing microcapsules, the step of preparing the emulsified dispersion liquid is performed using a microreactor having a plurality of flow paths having an equivalent diameter of 1 mm or less. 2. The method for producing microcapsules according to claim 1, wherein the aqueous phase liquid is water. 3. The method according to claim 1, wherein the aqueous phase liquid is an aqueous solution containing a low molecular surfactant.
3. The method for producing a microcapsule according to 1. 4. The method of microencapsulation, wherein the microencapsulation step is performed by using an emulsified dispersion further added with an aqueous solution containing a water-soluble polymer compound having at least surfactant. Claim 1
A method for producing the microcapsules according to claim 3. 5. The microparticle according to claim 1, wherein the oil phase liquid contains a diazonium salt compound or an electron-donating dye precursor, and a microcapsule wall material. Manufacturing method of capsule. 6. The method for producing microcapsules according to claim 1, wherein the microcapsule wall material contains a polyvalent isocyanate compound. 7. A heat-sensitive recording material having a heat-sensitive recording layer provided on a support, wherein the heat-sensitive recording layer comprises a microcapsule obtained by the method for producing a microcapsule according to claim 5 and a developer. A heat-sensitive recording material comprising: