Microcapsule toner and processes for preparation of microcapsule and microcapsule toner

The present invention provides a process for the preparation of a microcapsule excellent in core substance retention and mechanical strength as well as in environmental protection, safety and sanitation which can be used in the form of powder in a short capsulization time at a low cost. The present invention also provides an electrophotographic microcapsule toner having an excellent environmental stability of chargeability and a process for the preparation thereof. A novel process for the preparation of a microcapsule is provided which comprises emulsifying an oily composition containing a low boiling solvent in the presence of a cellulose dispersion stabilizer, and then subjecting the emulsion to interfacial polymerization so that it is capsulized, characterized in that said capsulization is effected at a temperature of not lower than the gelation temperature of said cellulose dispersion stabilizer while said low boiling solvent being removed from the oily droplets. In the case where a microcapsule toner is produced, as the oily composition there may be used one containing at least a coloring material, a fixing material and a shell-forming substance besides the low boiling solvent.

FIELD OF THE INVENTION 
The present invention relates to a process for the preparation of a 
microcapsule. More particularly, the present invention relates to a 
microcapsule toner for use in the development of an electrostatic latent 
image in electrophotography and electrostatic printing and a process for 
the preparation thereof. 
BACKGROUND OF THE INVENTION 
Various proposals have heretofore been made on microcapsules consisting of 
a core material and a shell covering the core material. Among these 
proposals, microcapsules whose capsule shell have been formed by 
interfacial polymerization are excellent in the completeness of covering 
of the core material and the inner retention and some of them have been 
put into practical use, e.g., non-carbon paper and pressure measuring 
paper. In these uses, the microcapsule is applied to a support such as 
paper with a proper binder resin. Thus, microcapsules particles are used 
in the form of suspension in the binder resin. However, if microcapsule 
particles are used in the form of independent powder, it is difficult to 
keep a volatile liquid in the core substance over a prolonged period of 
time because the capsule obtained by interfacial polymerization has a low 
mechanical strength and normally has a shell thickness of not more than 
0.5 .mu.m. In the production of interfacial polymerization type 
microcapsule, a method is normally employed which comprises using a low 
boiling solvent along with the core substance (see JP-A-56-119137 (The 
term "JP-A" as used herein means an "unexamined published Japanese patent 
application"), JP-A-58-145964, JP-A-63-163373, JP-A-64-40949, "New 
Microcapsulization Technology and Examples of Development of Its 
Application", Microcapsule Kenkyukai, pp. 50-52, Keiei Kaihatsu Center, 
September 1978, Tamotsu Kondo, Masumi Koishi, "Microcapsule", pp. 30-32, 
Sankyo Shuppan, November 1987). In some detail, an oily composition 
comprising a core substance, a capsule shell-forming monomer, a low 
boiling solvent, and optionally other additives is emulsified in an 
aqueous medium. The emulsion is then capsulized while the low boiling 
solvent being removed from the oily droplets. The low boiling solvent 
present in the oily droplets serves not only to lower the viscosity of the 
oily composition to facilitate emulsification but also to cause the 
capsule shell-forming monomer to migrate to the interface with the 
droplets to accelerate capsulization reaction. In accordance with this 
method, microcapsules can be normally obtained having a better mechanical 
strength and core substance retention than those obtained free of low 
boiling solvent. 
However, this method is disadvantageous in that the low boiling solvent 
cannot be recovered. In this method, the reaction is allowed to proceed by 
evaporating the low boiling solvent from the reaction system to the 
atmosphere. If the low boiling solvent is recovered by distillation under 
reduced pressure, the reaction solution suffers from violent foaming, 
making it extremely difficult to recover the solvent. Further, the 
evaporation of the low boiling solvent to the atmosphere not only adds to 
production cost but also worsens the environmental protection, safety and 
sanitation. Moreover, in the case where capsulization is effected while 
the low boiling solvent being evaporated to the atmosphere, the reaction 
must be effected over a prolonged period of time to fully remove the low 
boiling solvent. If the low boiling solvent remains in the core, it causes 
a great problem when the microcapsule is used as a toner. In some detail, 
the solvent remaining in the core exudes out to the surface of the capsule 
and thus deteriorates the fluidity of the toner, resulting in the 
deterioration of chargeability and hence developability of the toner. The 
exudation of the solvent also causes the modification of the 
photoreceptor. Solvents having a relatively higher boiling point and a 
lower water solubility can remain in the core more remarkably. 
In the case where the microcapsule is used as a toner, it is more difficult 
to assure both mechanical strength and core substance retention. Various 
proposals have heretofore been made on microcapsule toners comprising a 
capsule shell covering a core substance. For example, JP-A-54-66844, 
JP-A-55-18630, JP-A-57-41647, and JP-A-57-202547 disclose the use of a 
wax compound as a core substance. JP-A-52-108134, JP-A-58-9153, 
JP-A-59-159174, and JP-A-59-159177 disclose the use of a soft polymer as a 
core substance. Further, JP-A-56-119137, JP-A-58-145964, and 
JP-A-63-163373 disclose an interfacial polymerization type microcapsule 
toner comprising a polymer solution as a fixing component for core 
substance. Among these proposals, the interfacial polymerization type 
microcapsule toner comprising a polymer solution as a core component has 
an extremely excellent fixability but can hardly maintain a high boiling 
solvent in the polymer solution in the core substance. Further, the 
foregoing microcapsule toner can hardly maintain a sufficient mechanical 
strength without impairing the fixability thereof. 
Since it has been believed that in a process for producing a microcapsule 
using cellulose dispersion stabilizer as a dispersant, the dispersion 
stabilizer undergoes gelation at an elevated temperature higher than 
gelation temperature to cause lowering of capsule strength. Therefore, the 
elevated temperature has not been used in the process. Further, in the 
prior arts, the stabilizer is not set in a form of gelation, but in a form 
of solution. Accordingly, when a low boiling solvent contained in a 
capsule is excluded from the system at a polymerizing step, foams are 
generated in the solution of the dispersant, i.e., paste-like solution, to 
be a foam-solution. Thereby, it has been difficult to recover the solvent 
contained in the foam-solution. 
While, it has been found by the inventors that since the stabilizer is 
effective at only the initial stage of dispersion of the oily droplets 
into water, an interface polymerization takes place immediately at the 
interface of oily phase and hydrophilic phase to form polymer film (outer 
shell), after the dispersion once has been completed. Accordingly, it has 
been also found that the stabilizer is allowed to act in a minimized 
degree after formation of polymer film. As a result, it has been also 
found that the environmental temperature for polymerization higher than 
the temperature of gelation leads to providing rice grain-like gel of the 
dispersant in water, and thereby the low boiling solvent which is released 
from the water at the polymerization step is liable to be recovered under 
cooling. 
SUMMARY OF THE INVENTION 
It is therefore an object of the present invention to provide a process for 
the preparation of a microcapsule excellent in core substance retention 
and mechanical strength as well as in environmental protection, safety and 
sanitation which can be used in the form of powder in a short 
capsulization time at a low cost. 
It is another object of the present invention to provide a process for the 
preparation of a microcapsule at a low cost by reducing the capsulization 
reaction time in the prior art. 
It is a further object of the present invention to provide an 
electrophotographic microcapsule toner having an excellent environmental 
stability of chargeability. 
It is a still further object of the present invention to provide a process 
for the preparation of an electrophotographic microcapsule toner which 
exhibits an excellent mechanical strength, requires neither special 
reaction apparatus nor complicated operation and can be used as a capsule 
toner having a liquid core without impairing the fixability that the core 
substance should possess. 
These and other objects of the present invention will become more apparent 
from the following detailed description and examples. 
As a result of extensive studies, the inventors found that the foaming 
involved in the distillation of the low boiling solvent in the reaction 
solution is mainly attributed to the dispersion stabilizer. It was also 
found that the foaming involved in the distillation of the low boiling 
solvent can be inhibited by using as a dispersion stabilizer a cellulose 
dispersion stabilizer whose thermal behavior can be made the best use of. 
A cellulose dispersion stabilizer has been known to undergo gelation at an 
elevated temperature. However, it has been found that when capsulization 
reaction is effected with a cellulose dispersion stabilizer as an 
emulsification stabilizer at a reaction solution temperature of not lower 
than the gelation temperature of the cellulose dispersion stabilizer, the 
low boiling solvent can be easily recovered. Thus, the present invention 
has been worked out. 
The first aspect of the present invention concerns a process for the 
preparation of a microcapsule which comprises emulsifying an oily 
composition containing a low boiling solvent in the presence of a 
cellulose dispersion stabilizer, and then subjecting the emulsion to 
interfacial polymerization so that it is capsulized, characterized in that 
said capsulization is effected at a temperature of not lower than the 
gelation temperature of said cellulose dispersion stabilizer while said 
low boiling solvent being removed from the oily droplets. 
The second aspect of the present invention concerns a microcapsule toner, 
prepared by a process which comprises emulsifying an oily composition 
containing at least a coloring material, a fixing material and a 
shell-forming substance with a low boiling solvent in the presence of a 
cellulose dispersion stabilizer to produce oily droplets, and then 
capsulizing said oily droplets at a temperature of not lower than the 
gelation temperature of said cellulose dispersion stabilizer while said 
low boiling solvent being removed from the oily droplets. 
The third aspect of the present invention concerns a process for the 
preparation of a microcapsule toner which comprises the steps of 
emulsifying an oily composition containing at least a coloring material, a 
fixing material and a shell-forming substance with a low boiling solvent 
in the presence of a cellulose dispersion stabilizer to produce oily 
droplets, and then subjecting said oily droplets to interfacial 
polymerization so that said oily droplets are capsulized, characterized in 
that said interfacial polymerization in said capsulization step is 
effected at a temperature of not lower than the gelation temperature of 
said cellulose dispersion stabilizer while said low boiling solvent being 
removed from the oily droplets. 
DETAILED DESCRIPTION OF THE INVENTION 
The microcapsule and microcapsule toner to be used in the present invention 
are prepared by a so-called interfacial polymerization process. The 
interfacial polymerization process for the preparation of a microcapsule 
is disclosed in JP-B-38-19574 (The term "JP-B" as used herein means an 
"examined Japanese patent publication"), JP-B-42-446, JP-B-2-31381, 
JP-A-58-66948, JP-A-59-148066, and JP-A-59-162562. 
In the process for the preparation of a microcapsule according to the 
present invention, an oily composition containing a low boiling solvent is 
first emulsified in the presence of a cellulose dispersion stabilizer to 
produce oily droplets. 
The oily composition contains a low boiling solvent and a core substance. 
The oily composition further needs to contain a shell-forming substance 
for forming a capsule shell by interfacial polymerization. In general, as 
described in the above cited patents, a first capsule shell-forming 
monomer is incorporated in an oily composition which forms oily droplets 
while a second capsule shell-forming monomer is incorporated in an aqueous 
solvent. However, both the first capsule shell-forming monomer and second 
capsule shell-forming monomer may be incorporated in the oily composition. 
Examples of the first capsule shell-forming monomer include isocyanate 
compound, acid halide compound, and epoxy compound. 
Specific examples of the isocyanate compound include diisocyanates such as 
methaphenylene diisocyanate, tolylene diisocyanate, diphenylmethane 
diisocyanate, 3,3'-dimethyl-diphenyl-4,4'-diisocyanate, 
3,3'-dimethyl-diphenylmethane-4,4'-diisocyanate, xylylene diisocyanate, 
naphthalene diisocyanate and hexamethylene diisocyanate, and 
polyisocyanates such as so-called buret type, adduct type and isocyanurate 
type. For example, polyisocyanates such as Sumidur Series available from 
Sumitomo Vier Urethane Co., Ltd., Takenate Series available from Takeda 
Chemical Industries, Ltd., and Millionate Series available from Nihon 
Polyurethane Co., Ltd. are preferred. Examples of the acid halide include 
dibasic halides such as adipoyl dichloride, phthaloyl dichloride, 
terephthaloyl dichloride and 1,4-cyclohexanedicarbonyl chloride. Examples 
of the epoxy compound include epoxy compounds known as bisphenol A type, 
resorcinol type, bisphenol F type, tetraphenylmethane type, novolak type, 
polyalcohol type, polyglycol type and glycerintriether type. 
Preferred among these capsule shell-forming monomers for use in the 
preparation of a microcapsule toner are isocyanate compounds from the 
standpoint of electrical resistance. Particularly preferred among these 
isocyanate compounds are polyisocyanates. In an even preferred embodiment, 
polyisocyanates which are soluble in a low boiling solvent but are not 
fully soluble in a mixture of a core substance and a low boiling solvent 
to provide suspensions are employed. This is because that this embodiment 
allows the smooth migration of the first shell-forming monomer to the 
interface with droplet, resulting in the efficient progress of 
capsulization or shell formation. 
The term "second capsule shell-forming monomer" as used herein is meant to 
indicate a monomer which reacts with the foregoing first capsule 
shell-forming monomer to produce a polymer. Specific examples of the 
second capsule shell-forming monomer include water; polyols such as 
ethylene glycol, 1,4-butanediol, catechol, resorcinol, hydroquinone, 
o-dihydroxymethylbenzene, 4,4'-dihydroxydiphenylmethane and 
2,2-bis(4-hydroxyphenyl)-propane; polyamines such as ethylenediamine, 
tetramethylenediamine, hexamethylenediamine, phenylenediamine, 
diethylenetriamine, triethylenetetramine, diethylaminopropylamine and 
tetraethylenepentamine, and piperazine compounds such as piperazine, 
2-methylpiperazine and 2,5-dimethylpiperazine. These compounds may be used 
in admixture. In a particularly preferred embodiment, the oily composition 
comprises an isocyanate compound as the first capsule shell-forming 
monomer while water and a polyamine are used as second capsule 
shell-forming monomers. 
Such a second capsule shell-forming monomer is incorporated in an aqueous 
medium having an oily composition emulsified therein. For example, a part 
of the polyamine to be added may be previously incorporated in the aqueous 
medium prior to emulsion. If a polyol is used, it may be incorporated in 
the oily droplets with the first capsule shell-forming monomer. 
The low boiling solvent to be incorporated in the oily composition in the 
present invention will be further described hereinafter. The low boiling 
solvent to be used in the present invention is a solvent having a boiling 
point of not higher than 120.degree. C., preferably not higher than 
100.degree. C., at 760 mmHg. It is incorporated in the oily composition as 
a component of the capsule with the core substance and first shell-forming 
substance and removed from the system during the emulsification and 
capsulization reaction. The low boiling solvent not only serves as a 
diluent for lowering the viscosity of the core substance to facilitate 
emulsification but also serves to allow the efficient migration of the 
first shell-forming substance to the interface of droplets to accelerate 
the reaction with the second shell-forming substance. 
Examples of the low boiling solvent employable in the present invention 
include ester solvents such as ethyl acetate and butyl acetate; ketone 
solvents such as methylethyl ketone, methyl isopropyl ketone and methyl 
isobutyl ketone; aromatic solvents such as toluene and xylene; and 
halogenated hydrocarbon solvents such as dichloromethane and chloroform. 
Particularly preferred among these solvents are ethyl acetate and methyl 
isopropyl ketone, which form an azeotrope with water and thus can be 
easily distilled. 
The core substance to be incorporated in the oily composition is not 
specifically limited so far as it is oil-soluble. If the microcapsule 
serves as a microcapsule toner (hereinafter referred to as "capsule 
toner"), it is necessary that at least a coloring material and a fixing 
material be incorporated therein as core substances. 
Examples of the coloring material include inorganic pigments such as carbon 
black, red oxide, Prussian blue and titanium oxide; azo pigments such as 
fast yellow, disazo yellow, pyrazolone red, chelate red, brilliant carmine 
and parabrown; phthalocyanine pigments such as copper phthalocyanine blue 
and metal-free phthalocyanine; and condensed polycyclic pigments such as 
flavanthrone yellow, dibromoanthrone orange, perylene red, quinacridone 
red and dioxazine violet. Further, disperse dyes and oil-soluble dyes may 
be used. If necessary, a magnetic powder may be used instead of such a 
coloring material. For example, if the capsule toner is used as a magnetic 
unitary toner, a black coloring material may be partially or entirely 
replaced by a magnetic powder. As such a magnetic powder there may be used 
a particulate magnetite or ferrite or a metal such as cobalt, iron and 
nickel or alloy thereof in particulate form. 
The coloring material or magnetic powder incorporated as a component of the 
core substance may be present on the core-shell interface or in the shell 
after the formation of capsules. 
Referring to the fixing material, if it is adapted for pressure fixing, a 
fixing material mainly composed of a pressure-fixable component is used. 
If it is adapted for heat fixing, a fixing material mainly composed of a 
heat-fixable component is used. In particular, if it is adapted for 
pressure fixing, a fixing material mainly composed of a binder resin and a 
high boiling solvent for dissolving it therein or mainly composed of a 
soft solid substance is preferred. For the purpose of improving the 
fixability of the fixing material, an additive such as silicone oil may be 
added thereto. Further, a high boiling solvent which doesn't dissolve the 
binder resin therein may be added to the high boiling solvent for 
dissolving the binder therein. The kind or composition ratio of 
constituents preferably varies depending on fixing system of pressure 
fixing or heat fixing. 
As the binder resin there may be used a known fixing resin. Specific 
examples of such a known fixing resin employable in the present invention 
include acrylate polymers such as polymethylacrylate, polyethylacrylate, 
polybutylacrylate, poly-2-ethylhexylacrylate and polylaurylacrylate; 
methylacrylate polymers such as polymethylmethacrylate, 
polybutylmethacrylate, polyhexylmethacrylate, 
poly-2-ethylhexylmethacrylate and polylaurylmethacrylate; ethylenic 
polymers and copolymers thereof such as copolymer of styrene monomer with 
acrylate or methacrylate, polyvinylacetate, polyvinylpropionate, 
polyvinylbutyrate, polyethylene and polypropylene; styrene copolymers such 
as styrene-butadine copolymer, styrene-isoprene copolymer and 
styrene-maleic acid copolymer, polyvinylethers, polyvinylketones, 
polyesters, polyamides, polyurethanes, rubbers, epoxy resins, 
polyvinylbutyral, rosins, modified rosins, terpene resins, and phenolic 
resins. These binder resins may be used singly or in admixture. 
Alternatively, these binder resins may be incorporated in the form of 
monomer so that they can be polymerized into a binder resin after 
capsulization. 
As the high boiling solvent for dissolving the binder resin therein there 
may be used an oily solvent having a boiling point of not lower than 
140.degree. C., preferably not lower than 160.degree. C. Such an oily 
solvent can be selected from those described in, e.g., clause 
"Plasticizers" in "Modern Plastics Encyclopedia", 1975-1976. Further, the 
oily solvent can be selected from high boiling solvents disclosed as core 
substances for pressure-fixable capsule toner in, e.g., JP-A-58-145964 and 
JP-A-63-163373. 
Specific examples of the high boiling solvent include phthalic esters 
(e.g., diethyl phthalate, dibutyl phthalate), aliphatic dicarboxylic 
esters (e.g., diethyl malonate, dimethyl oxalate), phosphoric esters 
(e.g., tricresyl phosphate, trixylyl phosphate), citric esters (e.g., 
o-acetyltriethyl citrate), aromatic esters (e.g., butyl benzoate, hexyl 
benzoate), aliphatic esters (e.g., hexadecyl myristate, dioctyl adipate), 
alkylnaphthalenes (e.g., methyl naphthalene, dimethylnaphthalene, 
monoisopropyl naphthalene, diisopropyl naphthalene), alkyldiphenyl ethers 
(e.g., o-, m-, p-methylphenyl ether), higher aliphatic or aromatic 
sulfonic amide compounds (e.g., N,N-dimethyllauroylamide, 
N-butylbenzenesulfonamide), trimellitic esters (e.g., trioctyl 
trimellitate), diarylalkanes (e.g., diarylmethane such as 
dimethyldiphenylmethane, diarylethane such as 
1-phenyl-1methylphenylethane, 1-dimethylphenyl-1-phenylethane and 
1-ethylphenyl-1-phenylethane), and chlorinated paraffins. If a polymer 
having a long-chain alkyl group such as lauryl methacrylate homopolymer or 
copolymer is used as a binder resin, an organic solvent mainly composed of 
aliphatic saturated hydrocarbon or aliphatic saturated hydrocarbon (e.g., 
Isopar-G, Isopar-H, Isopar-M, available from Exxon Inc.) may be used. 
As the soft solid substance there may be any kind of a material which is 
normally flexible and fixable at a room temperature. A polymer having Tg 
of -60.degree. C. to 5.degree. C. or a mixture thereof with other polymers 
is preferred. 
As the method for incorporating the soft solid substance in capsules as a 
component of the core substance there may be used a method which comprises 
charging the soft solid substance in the form of polymer with other core 
substance components, the low boiling solvent and the shell-forming 
components, and then expelling the low boiling solvent from the system at 
the same time with or after the formation of the shell by the interfacial 
polymerization process to produce a core substance. Alternatively, a 
method may be used which comprises charging the soft solid substance in 
the form of monomer, subjecting the system to interfacial polymerization 
to form a shell, and then polymerizing the monomer to produce a core 
substance. 
The composition ratio of the various components in the oily composition of 
the present invention can be determined to a proper range as necessary. In 
the case of capsule toner, the percentage of low boiling solvent, coloring 
material, fixing agent and core-shell substance are preferably in the 
range of 10 to 60% by weight, 1 to 60% by weight, 20 to 80% by weight, and 
5 to 30% by weight, respectively, based on the total weight of the raw 
materials. 
If the foregoing oily composition is emulsified in an aqueous medium, a 
cellulose dispersion stabilizer may be used for the purpose of stabilizing 
the emulsification of the oily composition. The term "cellulose dispersion 
stabilizer" as used herein means a cellulose which has been rendered 
water-soluble by chemical treatment and becomes turbid to gel when heated 
in the form of aqueous solution. In particular, a water-soluble cellulose 
ether obtained by treating a cellulose with caustic soda, and then 
reacting the treated cellulose with an etherifying agent such as methyl 
chloride, propylene oxide and ethylene oxide is preferred. This is because 
that such a water-soluble cellulose ether can provide a high viscosity 
even at a low concentration to give an excellent dispersion stability. 
Specific examples of such a water-soluble cellulose ether include 
hydroxymethyl cellulose, hydroxyethyl cellulose, hydroxyethylmethyl 
cellulose, hydroxypropyl cellulose, and hydroxypropylmethyl cellulose. 
These water-soluble cellulose ethers are commercially available. Examples 
of such commercially available water-soluble cellulose ethers include 
Metrose Series produced by Shin-Etsu Chemical Co., Ltd. Preferred among 
these products are Metrose 65SH50, 65SH4000, 90SH400, 90SH4000, SEB04T, 
etc. Water-soluble cellulose ethers having a higher gelation temperature 
can foam more difficultly and thus can be used more preferably. More 
preferably, the gelation temperature of the water-soluble cellulose ethers 
is not lower than 60.degree. C. These cellulose dispersion stabilizers may 
be used in an amount of from 0.1 to 10 g based on 100 g of aqueous medium 
used. 
"Gelation temperature" generally has two meanings, i.e., a temperature 
(T.sub.1) at which viscosity decrease is started and a temperature 
(T.sub.2) at which viscosity increase is started. In the present 
invention, the gelation temperature means the former, i.e., a temperature 
(T.sub.1) at which viscosity decrease is started. 
For example, Metrose 65SH50 and Metrose 65SH4000 each have 60.degree. C. of 
gelation temperature (T.sub.1), Metrose 90SH400 and Metrose 90SH4000 each 
have 70.degree. C. of gelation temperature (T.sub.1) and SEB04T has 
70.degree. C. of gelation temperature (T.sub.1). 
The temperature (T.sub.2) at which viscosity increase is started is 
generally higher than the temperature (T.sub.1) at which viscosity 
decrease is started. For instance, Metrose 65SH50 and Metrose 65SH4000 
each have 75.degree. C. of gelation temperature (T.sub.2), Metrose 90SH400 
and Matrose 90SH4000 each have 80.degree. C. of gelation temperature 
(T.sub.2) and SEB04T has 85.degree. C. of gelation temperature (T.sub.2). 
The size of the oily droplets thus formed may be properly determined. In 
the case of capsule toner, it is preferably in the range of 3 to 20 .mu.m. 
The emulsion thus formed is then heated so that the oily droplets undergo 
interfacial polymerization and capsulization. During this process, heating 
needs to be effected to a temperature of not lower than the gelation 
temperature of cellulose dispersion stabilizer. More particularly, the 
heating temperature is preferably about 10.degree. to 50.degree. C. higher 
than the gelation temperature of the cellulose dispersion stabilizer. 
During this process, capsulization needs to be effected while the low 
boiling solvent is removed from the oily droplets by distillation. After 
the completion of capsulization, the low boiling solvent present in the 
aqueous medium and in capsules may be distilled off. However, it takes 
much time to complete the distillation of the low boiling solvent. 
Further, this process can disadvantageously give different capsule shapes. 
The distillation of the low boiling solvent may be effected under either 
reduced or normal pressure. During this process, the low boiling solvent 
is preferably drawn out from the reaction system by taking advantage of 
azeotropy with water, and then recovered through a condenser. In 
particular, the distillation of the low boiling solvent is preferably 
effected under normal pressure because it foams less to provide an easier 
operation. Further, the distillation of the low boiling solvent may be 
effected in the presence of an anti-foaming agent. 
When capsulization is effected in the foregoing manner, the first 
shell-forming substance and the second shell-forming substance undergo 
polymerization reaction on the interface of the oily droplets and the 
aqueous medium to form a capsule shell. The microcapsules thus obtained 
may be separated from the system by an ordinary method, and then dried. 
In the case of capsule toner, a chargeability-controlling polymer is 
preferably attached to the surface of the shell of the microcapsules thus 
formed to provide the capsule particles with chargeability. Examples of 
the method for attaching the chargeability-controlling polymer to the 
surface of the capsule shell include (1) a method which comprises applying 
a chargeability-controlling polymer to a toner by spray drying, heating or 
pressure, (2) a method which comprises chemically bonding a bridging 
molecule such as ethylene glycol dimethacrylate to the surface of a toner 
by graft polymerization, and then causing a polymerizable monomer having a 
chargeability-controlling group to be polymerized, and (3) a method which 
comprises allowing capsule particles to be suspended in water, and then 
allowing a monomer to be polymerized in the suspension so that the polymer 
is attached to the surface of capsules. Preferred among these methods are 
the methods (2) and (3), which enable submerged treatment and thus require 
no special apparatus. 
Examples of the polymerizable monomer include (meth)acrylic acid; 
(meth)acrylic esters such as methyl (meth)acrylate, ethyl (meth)acrylate, 
propyl (meth)acrylate, butyl (meth)acrylate, pentyl (meth)acrylate, hexyl 
(meth)acrylate, lauryl (meth)acrylate, cyclohexyl (meth)acrylate, 
2-ethylhexyl (meth)acrylate, benzyl (meth)acrylate, hydroxyethyl 
(meth)acrylate, hydroxypropyl (meth)acrylate, 2-ethoxyethyl 
(meth)acrylate, glycidyl (meth)acrylate, phenyl (meth)acrylate, 
trifluoroethyl (meth)acrylate, acrylonitrile, dimethylaminoethyl 
(meth)acrylate and diethylaminoethyl (meth)acrylate; aliphatic vinyl 
esters such as vinyl formate, vinyl acetate, vinyl propionate, vinyl 
butyrate, vinyl trimethylacetate, vinyl caproate, vinyl caprylate and 
vinyl stearate; vinyl ethers such as ethyl vinyl ether, propyl vinyl 
ether, butyl vinyl ether, hexyl vinyl ether, 2-ethylhexyl vinyl ether and 
phenyl vinyl ether; vinyl ketones such as methyl vinyl ketone and phenyl 
vinyl ketone, vinyl aromatic compounds such as styrene, chlorostyrene, 
hydroxystyrene and .alpha.-methylstyrene, (meth)acrylic ester ammonium 
salt monomers such as acryloyloxyethyl trimethylammonium chloride, 
acryloyloxyethyl triethylammonium chloride, methacryloyloxyethyl 
trimethylammonium chloride, methacryloyloxyethyl triethylammonium chloride 
and methacryloyloxyethyl tribenzylammonium chloride; (meth)acrylamide 
ammonium salt monomers such as acrylamido-trimethylpropyl ammonium 
chloride, acrylamido-triethylpropyl ammonium chloride, methacrylamido 
trimethylpropylammonium chloride and methacrylamido-benzylpropylammonium 
chloride; vinylbenzyl ammonium salt monomers such as vinylbenzyl 
triethylammonium chloride and vinylbenzyl trimethylammonium chloride; 
vinylpyridium salt monomers such as N-butylvinylpyridium bromide and 
N-cetylvinylpyridium chloride; vinyl monomers having quaternary nitrogen 
such as vinylimidazolium salt monomer (e.g., N-vinyl-2-methylimidazolium 
chloride and N-vinyl-2,3-dimethylimidazolium chloride), and vinyl monomers 
obtained by replacing halogen ions in these vinyl monomers by different 
organic anions. These monomers may be used singly or in admixture. 
Particularly preferred among these monomers are (meth)acrylic esters, 
(meth)acrylic ester ammonium salt monomers, and (meth)acrylamidoammonium 
salt monomers.

The present invention will be further described in the following examples, 
but the present invention should not be construed as being limited 
thereto. 
EXAMPLE 1 
(Preparation of capsule particles) 
To a mixture of 60 g of an aliphatic saturated hydrocarbon (Isoper-M, 
available from Exxon Corp.) and 60 g of methyl isopropyl ketone was added 
70 g of a styrene-lauryl methacrylate (50 wt. %:50 wt. %) 
(Mw=8.times.10.sup.4) to make a solution. To the resulting solution was 
then added 120 g of a magnetic powder (EPT-1000, available from Toda Kogyo 
Corp.). The mixture was then subjected to dispersion by means of a sand 
mill for 3 hours. To 200 g of the resulting dispersion were then added 40 
g of an isocyanate compound (Takenate D110N, available from Takeda 
Chemical Industries, Ltd.) and 20 g of methyl isopropyl ketone. The 
mixture was then thoroughly mixed to obtain Solution A. 
Separately, 10 g of hydroxypropyl methyl cellulose (Metrose 90SH4000; 
gelation temperature: 70.degree. C.; available from Shin-Etsu Chemical 
Co., Ltd.) were dissolved in 200 g of ion-exchanged water. The solution 
was then cooled to a temperature of 5.degree. C. to obtain Solution B. 
Solution B was then stirred by means of an emulsifier (autohomomixer, 
available from Shuki Kakosha K.K.). Into the solution was then slowly 
charged Solution A to effect emulsification. In this manner, an O/W type 
emulsion comprising oily droplets having an average particle diameter of 
about 12 .mu.m was obtained. 
The O/W type emulsion thus obtained was stirred in a separable flask 
equipped with a propeller agitating blade and a Liebig condenser at 400 
r.p.m. During this process, 200 g of a 5% aqueous solution of diethylene 
triamine was added dropwise to the emulsion. After the completion of 
dropwise addition, the emulsion was heated to a temperature of 90.degree. 
C. After 15 minutes, methyl isopropyl ketone was distilled off in 
azeotropy with water. After 1 hour, the reaction was completed. The 
percent recovery of methyl isopropyl ketone was 90%. The resulting capsule 
slurry was then poured into 2 l of ion-exchanged water. The mixture was 
thoroughly stirred, and then allowed to stand. After the sedimentation of 
capsule particles, the supernatant liquid was removed. This procedure was 
repeated seven times to wash the capsule particles. The resulting capsule 
suspension was emptied into a stainless steel tray, and then dried at a 
temperature of 80.degree. C. in a dryer (available from Yamato Kagaku 
K.K.) for 24 hours. In this manner, the desired microcapsule was obtained. 
The microcapsule thus obtained was partially withdrawn and heated to a 
temperature of 100.degree. C. for 24 hours to determine the evaporation 
loss of Isoper-M from the capsules. As a result, it was confirmed that 
about 98% of Isoper-M originally present in the capsules had remained 
therein. These capsule particles were compressed to determine the percent 
breakage thereof. As a result, the percent breakage of the capsule 
particles was 8% at 4.9 MPa (50 kgf/cm.sup.2). From these results, the 
microcapsule thus obtained was confirmed to have an excellent core 
substance retention and mechanical strength. 
EXAMPLE 2 
(Preparation of toner) 
Capsule particles which had been prepared in the same manner as in Example 
1 were subjected to centrifugal separation to obtain a cake having a solid 
concentration of 75%. 67 g of the cake (corresponding to 50 g of capsule 
particles) was then charged into a 500-ml separable flask. To the cake was 
then added 200 g of ion-exchanged water having 3 g of methyl methacrylate 
dissolved therein. The cake was then stirred at 200 r.p.m. by means of an 
agitator equipped with a propeller agitating blade (Three One Motor, 
available from Shinto Kagaku K.K.). The atmosphere of the separable flask 
was then replaced by nitrogen. To the cake were then added 0.3 g of 
methacryloyloxyethyl trimethylammonium chloride and 0.2 g of a 
polymerization initiator (VA-044, available from Wako Junyaku K.K.). The 
reaction system was then allowed to undergo reaction at a temperature of 
45.degree. C. for 5 hours. After the completion of reaction, the reaction 
solution was poured into 2 l of ion-exchanged water. The solution was then 
filtered under reduced pressure. The capsule particles were then washed 
with 1 l of ion-exchanged water. 
To these capsule particles was then added 100 g of a 0.01% aqueous solution 
of caustic soda. The mixture was then stirred at room temperature for 30 
minutes. The solution was then poured into 1 l of ion-exchanged water. The 
solution was then filtered under reduced pressure. The capsule particles 
were again washed with 1 l of ion-exchanged water. To the capsule 
particles was then added 2 g of a 5% aqueous solution of sodium 
4-naphtholsulfonate. The mixture was then stirred at room temperature to 
effect ion exchange reaction. After the completion of reaction, the 
mixture was filtered under reduced pressure, and then washed with 1 l of 
ion-exchanged water. In this manner, a capsule toner comprising 
chargeability-controlling polymer attached to the surface of capsule 
particles was obtained. The resulting toner cake was emptied into a 
stainless steel tray, and then dried at a temperature of 60.degree. C. in 
a dryer (available from Yamato Kagaku K.K.) for 10 hours. To 100 parts of 
the capsule toner thus obtained were then added 0.1 parts of a basic 
carbon black (pH value: 8.5) (REGAL330R: available from Cabot Corp.). The 
mixture was then thoroughly mixed. 
The capsule toner thus obtained had no smell of methyl isopropyl ketone. 
The capsule toner was smashed, and then measured for the content of methyl 
isopropyl ketone by gas chromatography. As a result, no methyl isopropyl 
ketone was detected. 
The capsule toner was then evaluated for image quality under an atmosphere 
of 20.degree. C. and 50% RH. The copying machine used for the evaluation 
of image quality was a Fuji Xerox's Type 2700 which had been remodelled 
for capsule toner. As a result, a stable duplication could be made free of 
image defects up to 5,000th sheet. The toner feed roll and the 
photoreceptor were observed. As a result, no attachment of smashed toner 
was found. 
COMATIVE EXAMPLE 1 
A comparative microcapsule was prepared in the same manner as in Example 1 
except that the reaction was effected with the flask being made airtight 
to cause no distillation of methyl isopropyl ketone. 
The microcapsule thus obtained was partially withdrawn, and then heated to 
a temperature of 100.degree. C. for 24 hours to determine the evaporation 
loss of Isoper-M therefrom. As a result, it was found that about 50% of 
Isoper-M originally present in the capsule had disappeared. The capsule 
particles were then compressed to determine the percent break thereof. As 
a result, it was found to be 50% at 4.9 MPa (50 kgf/cm.sup.2). From these 
results, this microcapsule was found to have a poor core substance 
retention and mechanical strength. 
COMATIVE EXAMPLE 2 
The distillation of methyl isopropyl ketone under reduced pressure was 
attempted in the same manner as in Example 1 except that the capsulization 
reaction was effected at a temperature of 60.degree. C., which is lower 
than the gelation temperature. However, violent foaming occurred, making 
it impossible to recover methyl isopropyl ketone. 
COMATIVE EXAMPLE 3 
The microcapsule prepared in Comparative Example 1 was processed to produce 
a toner in the same manner as in Example 2. The capsule toner thus 
obtained smelled of methyl isopropyl ketone. The capsule toner was 
smashed, and then measured for the content of methyl isopropyl ketone by 
gas chromatography. As a result, it was found that methyl isopropyl ketone 
had remained in a proportion of 5% based on the total weight of the 
capsule. 
The capsule toner thus obtained was then evaluated for image quality under 
an atmosphere of 20.degree. C. and 50% RH in the same manner as in Example 
2. As a result, smashed toner was attached to the surface of the toner 
feed roll even when the 1st sheet of copying paper was supplied into the 
copying machine. Numerous white lines were formed on the 100th sheet and 
after. Thus, a remarkably poor image quality was shown. The surface of the 
photoreceptor was observed. As a result, it was confirmed that smashed 
toner had been attached to the surface of the photoreceptor. 
As mentioned above, in accordance with the process for the preparation of a 
microcapsule of the present invention, capsulization is effected at a 
temperature of not lower than the gelation temperature of the cellulose 
dispersion stabilizer while the low boiling solvent being removed from the 
oily droplets, making it possible to produce a microcapsule excellent in 
core substance retention and mechanical strength as well as in 
environmental protection, safety and sanitation which can be used in the 
form of powder in a short capsulization time at a low cost. The 
microcapsule toner produced according to the present invention has an 
excellent environmental stability of chargeability and thus can be used as 
an electrophotographic developer. 
While the invention has been described in detail and with reference to 
specific embodiments thereof, it will be apparent to one skilled in the 
art that various changes and modifications can be made therein without 
departing from the spirit and scope thereof.