Record receiver having plural interactive leaves or a colorless – Having a colorless color-former – developer therefor – or... – Identified reactant isolating material or capsule wall...
Reexamination Certificate
2002-02-12
2004-04-27
Hess, B. Hamilton (Department: 1774)
Record receiver having plural interactive leaves or a colorless
Having a colorless color-former, developer therefor, or...
Identified reactant isolating material or capsule wall...
C424S423000, C424S450000, C424S489000, C428S402200, C428S402210, C428S402220, C503S213000
Reexamination Certificate
active
06727203
ABSTRACT:
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 for use in a heat-sensitive recording material. The present invention also relates to the heat-sensitive recording material.
2. Description of the Related Art
Various methods for producing microcapsules are known, and among these methods, there is a method in which a material to be micro-encapsulated and a material used for a microcapsule wall are dissolved in an organic solvent, then added to water in which a water-soluble high polymer has been dissolved, and then mixed. This mixture is emulsified into finer particles by using emulsification means such as a high-speed stirrer (dissolver), a homogenizer, or an inline mixer thus obtaining a stable emulsion. Afterwards, a microcapsule wall is formed from the material for the microcapsule wall. As the microcapsule wall, polyurethane and/or polyurea in which polyol and/or polyamine and polyisocyanate are mixed are well known.
A heat-sensitive recording material is known as a recording material using such microcapsules. For example, Japanese Patent Application Laid-Open (JP-A) No. 6-297856 discloses such a heat-sensitive recording material. In this disclosure, in order to emulsify a coupler and a basic substance, these compounds are dissolved in an organic solvent. An aqueous solution of the water-soluble high polymer is added to this mixture while being stirred by a homogenizer.
In the emulsification means such as the high-speed stirrer (dissolver), the homogenizer, or the inline mixer which are described above and which are used in the step of producing microcapsules, a region to which shearing force required for emulsification is applied is limited to the immediate vicinities of emulsification wings. For this reason, there has been caused a problem that the shearing force is not applied uniformly to portions that are apart from or close to the emulsification wings, thus causing the particle diameter distribution of dispersed droplets to be large.
In the heat-sensitive recording material, the particle diameter distribution of microcapsules is desired to be limited so as to form a balanced relationship between heat-sensitivity characteristics and a so-called textile fogging. Since the particle diameter distribution of the microcapsules depends on that of droplets contained in the emulsion during the step of producing the microcapsules, an emulsification method must be used in which the particle diameter distribution of droplets is limited.
With respect to this, as an emulsification method for solving the problem of the particle diameter distribution through the use of the above-described emulsification means, JP-A No. 2630501 discloses an emulsification method in which a so-called “cylindrical mill” is used. In this emulsification method, the inner cylinder is rotated inside the fixed outer cylinder to pass the mixture of a dispersion solvent and a dispersion through a space between the inner cylinder and the outer cylinder to thereby obtain an emulsion. The mixture is supplied from a tangent direction side surface end portion of the outer cylinder along the circumference thereof. While the mixture is rotated to move into the space between the inner cylinder and the outer cylinder, uniform shearing force is applied to the inner cylinder in the lengthwise direction thereof so that the mixture can be emulsified sufficiently. By this emulsification method, an emulsion whose particle diameter distribution is extremely limited can be obtained. However, since the size of particle diameters of the droplets thus obtained depends on the size of the space between the inner cylinder and the outer cylinder, it is not easy to obtain emulsified particles having no more than a limited particle diameter. Therefore, the particle diameter of the droplets thus obtained is generally limited to about 10 &mgr;m, thus making it impossible to obtain droplets whose particle diameters are no more than a few &mgr;m.
From a viewpoint of heat color formation characteristics, especially of controlling preferable color formation gradation, microcapsules used for the heat-sensitive recording material needed to have limited particle diameter distribution as described above and to have particles whose particle diameters are generally a few &mgr;m or less, and more preferably 1 &mgr;m or less. Therefore, it is difficult to adopt an emulsification method using the cylindrical mill. On the contrary, it is desirable to adopt an emulsification method by using microcapsules whose particle diameters are 1 &mgr;m or less and whose particle diameter distribution is limited.
A device i.e., a so-called microreactor has been used in a fine chemical field or a biochemical field, and in recent years, has made much progress (see W. Ehrfeld, V. Hessel, and H. Lowe, “Microreactor”, 1Ed. (2000), WILEY-VCH). The microreactor generally refers to a reactor having microscaled channels. For example, while two types of solutions pass through different channels, these solutions come into contact with each other in a form of an extremely thin membrane, in which substances transfer via the interface between layers, and then react with each other. Further, the microreactor is utilized not only for chemical reactions but also for mixing or separating two or more different solutions. Specifically, the microreactor used for mixing is called a “micromixer”. The micromixer mixes these different solutions by the steps of forming liquid films of these different solutions which are to be mixed such that the films are superposed, and passing the liquid films through narrow passages. For example, by using the oil phase and the aqueous phase as liquids, an emulsion can be prepared.
WO00/62913 proposes a dispersion device (micromixer) for conducting dispersion by using such a microreactor. This dispersion device is used by a method in which fluids which are formed of liquid A and liquid B are passed through respective microscaled channels and then divided into spatially separate liquid layers (liquid films). Then, the separate fluids are combined with each other, passed through narrow passages, and the liquid A and the liquid B are dispersed into fine droplets, during which a mechanical oscillator is used to promote the formation of droplets.
However, in the emulsification step for producing microcapsules, especially that used for the heat-sensitive recording material, a technique for conducting emulsification by means of a microreactor, and for producing microcapsules having a target particle diameter and a target particle diameter distribution is not known. This is because of the below described reason. Namely, in the production of microcapsules, during the emulsification step, a water-soluble high polymer compound is usually added to an aqueous phase to be added to an oil phase for stabilizing the dispersion of droplets. However, the aqueous solution to which the water-soluble high polymer compound was added has a high viscosity, thus making it impossible to increase the processing amount from a viewpoint that pressure loss is likely to occur inside the micromixer. Further, emulsification cannot usually be carried out without adding the water-soluble high polymer compound to the aqueous phase.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a method for producing microcapsules whose particle diameters are small and whose particle diameter distribution is limited, with industrially realizable production efficiency, specifically microcapsules used for a heat-sensitive recording material, and the heat-sensitive recording material containing microcapsules produced through the use of this method.
The object can be achieved by providing a method for producing microcapsules and a heat-sensitive recording material described below.
A first aspect of the present invention is a method for producing microcapsules comprising the steps of: (1) preparing an emulsion from an oil phase that contains at leas
Fuji Photo Film Co. , Ltd.
Hess B. Hamilton
Sughrue & Mion, PLLC
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