Continuous emulsification tank and process

The continuous emulsification tank of the invention is provided with a feed port of an oil phase solution and the continuous emulsification method uses the tank. By constituting the tank as above, continuous emulsification is possible for a long time without clogging by the deposition of solid material on the inside wall of pipes and apparatuses.

BACKGROUND OF THE INVENTION 
This invention relates to a continuous emulsification tank for the 
production of an oil-in-water type emulsion from an oil phase solution 
containing at least a polyvalent isocyanate and a water phase solution. 
Preparation of oil-in-water type emulsion by adding an oil phase solution 
containing a solute which becomes core material and a polyvalent 
isocyanate to a water phase solution followed by agitating is widely 
utilized in the production of pressure-sensitive papers, photographic 
photosensitive materials, cosmetics, paints, etc. In most of the 
preparations, an oil phase solution containing a core material is 
prepared, and a polyvalent isocyanate is added thereto. The oil phase 
solution is then emulsified in a water phase solution resulting in the 
occurence of reaction of the polyvalent isocyanate with amine, polyol or 
the like to form microcapsules with urethane or polyurea membrane. 
In every conventional emulsification, a polyvalent isocyanate is added to 
an oil phase solution containing a core material, further mixed with a 
water phase solution, and emulsified continuously in an emulsification 
tank, a pipe line homomixer or the like (U.S. Pat. No. 5,192,130, U.S. 
Pat. No. 5,401,443 and Japanese Patent KOKAI 3-258332). 
A conventional apparatus is illustrated in FIG. 4. In the apparatus, an oil 
phase solution 1 wherein a solute has previously been dissolved, a 
polyvalent isocyanate 4 and a water phase solution 7 are stored in tanks 
2, 5, 8, respectively. The polyvalent isocyanate 4 is fed quantitatively 
by a volumetric pump 6, and added continuously in a pipe to the oil phase 
solution which is fed similarly by a volumetric pump 3, and mixed by a 
continuous mixer 10. Subsequently, the water phase solution 7 fed by a 
volumetric pump 9 is added continuously in a pipe, and fed to an 
emulsification tank 11. The feeding position of the above mixture is the 
upper side (Japanese Patent KOKAI 3-258332) or bottom (U.S. Pat. No. 
5,401,443) of the emulsification tank. 
Incidentally, when an oil phase solution contains polyvalent isocyanate, 
feeding manner of the oil phase solution and water phase solution to a 
continuous emulsification tank is important in view of stabilization of 
manufacturing process. In the prior art, the oil phase solution joins with 
a water phase solution in a pipe on the upstream of a continuous emulsion 
tank, and deposition at the joining point is a problem, because of 
clogging in a short period operation. As a result, overhaul of the 
pipeline with stopping the production was necessary frequently degrade 
production efficiency. 
SUMMARY OF THE INVENTION 
An object of the invention is to provide an emulsification tank which can 
be operated for a long period without clogging troubles by a reaction 
product upon preparation of oil-in-water type emulsion from an oil phase 
solution containing a polyvalent isocyanate and a water phase solution. 
Another object of the invention is to provide a continuous emulsification 
method which can also be operated for a long period without clogging 
troubles by a reaction product upon preparation of oil-in-water type 
emulsion from an oil phase solution containing a polyvalent isocyanate and 
a water phase solution. 
The inventors investigated eagerly in order to resolve the above problem, 
and found that, polyurea resin produced by the reaction of the polyvalent 
isocyanate in the oil phase solution with water in the water phase 
solution was adhered to inner wall of pipe at a position where an 
interface between the oil phase solution and the water phase solution 
contacts, and the deposits grows finally to clog the pipe at the joining 
point. 
The present invention provides an emulsification tank, which has achieved 
the above object, which is provided a continuous emulsification tank 
provided with a feed port of an oil phase solution containing a polyvalent 
isocyanate at bottom of the tank, a water phase solution feed port on 
lower side on the tank, and an emulsion discharge port on upper part of 
the tank, and include a mixing blade. 
The present invention also provides an emulsification process, which has 
achieved the above object, which utilizes the continuous emulsification 
tank wherein said mixing blade is propeller blade, edged turbine or the 
like.

DETAILED DESCRIPTION OF THE INVENTION 
FIGS. 1 and 2 are schematic illustrations of an emulsification tank 
according to the invention, and FIG. 3 illustrates a flow diagram of an 
emulsification apparatus into which the emulsification tank is 
incorporated. In FIG. 3, various attachment devices, such as valves, 
flowmeters and the like are not illustrated. 
An oil phase solution 1 wherein a solute has been dissolved previously, a 
polyvalent isocyanate 4 and a water phase solution 7 are stored in tanks 
2, 5, 8, respectively. 
Although not illustrated, each of the tanks 2, 5, 8 may be provided with a 
stirrer, a temperature controller, an automatic liquid supplier for 
regulating liquid level constant or the like. 
Polyvalent isocyanate 4 and a water phase solution 7 are stored in tanks 2, 
5, 8, respectively. The polyvalent isocyanate 4 is fed quantitatively by a 
volumetric pump 6, and added continuously in a pipe to the oil phase 
solution which is fed similarly by a volumetric pump 3. Then, the oil 
phase solution is fed into the emulsification tank 11 from the lowermost 
position. The volumetric pumps have metering ability, and illustrative of 
them are gear pump, plunger pump, motor pump, diaphragm pump, and the 
like. In order to improve homogeneity of the oil phase solution containing 
polyvalent isocyanate, a continuous mixer 10 may be incorporated. 
Illustrative of the mixers 10 are in-line mixers, such as static mixer and 
high shearing mixer, pipeline homomixer, homomix line flow, and the like. 
On the other hand, the water phase solution 7 is delivered quantitatively 
by a volumetric pump 9, and fed into the emulsification tank 11 from the 
lower side in the tangential direction which conforms with the flow 
direction generated by the rotation of a stirrer provided in the 
emulsification tank 11. In order to achieve the emulsification operation 
it is better to select the feed point of the water phase solution at lower 
side of the mixing blade. 
The emulsification tank 11 may be provided with baffle members. The 
stirring blade may be in a form of propeller blade, turbine blade, or the 
like, and the stirring blade may be doubled or more. 
The oil phase solution contains a solute which is in accordance with the 
object of use of emulsion. Illustrative of the solutes are various basic 
colorless dyes used for capsules in pressure-sensitive copying papers, and 
various materials in accordance with the use of capsules, such as various 
other recording materials, medicines, perfumes, agricultural chemicals, 
chemical conversions, adhesives, liquid crystals, paints, foods, 
detergents, solvents, catalysts, enzymes, antirust agents, etc. Exemplary 
of the basic colorless dyes are triarylmethane-based compounds such as 
Crystal Violet lactone, 8,8-bis (p-dimethylaminophenyl) phthalide and 
3-(p-dimethylaminophenyl)-3-(1,2-dimethylindole-3-yl) phthalide, 
dephenylmethane-based compounds, such as 4,4'-bis-dimethylaminobenzhydryl 
benzyl ether, N-halophenyl-leucoauramine and 
N-2,4,5-trichlorophenylleucoauramine, xanthene-based compounds, such as 
Rhodamine B-anilinolactum, 3-diethylamino-7-chlorofluoran, 
3-diethylamino-6,8-dimethylfluoran, 8,7-diethylaminofluoran and 
3-diethylamino-7-chloroethylmethyla minofluoran, thiazine-based compounds, 
such as Benzoylleucomethylene Blue and p-Nitrobenzylleucomethylene Blue, 
spiro compounds, such as 3-methyl-spiro-dinaphthopyran, 
3-ethyl-spiro-dinaphthopyran and 3-propyl-spiro-dibenzopyran, and the 
like, and combinations thereof. 
Suitable oil substances composition the oil phase solution are various 
animal oils, such as fish oils and lard, vegetable oils, such as castor 
oil and soybean oil, mineral oils, such as Kerosene and naphtha, synthetic 
oils, such as alkylated naphthalenes, alkylated biphenyls, hydrogenated 
terphenyls, alkylated diphenylmethanes and alkylated benzenes, and the 
like, and combinations thereof. 
The polyvalent isocyanate applicable to the invention includes various 
diisocyanates, such as m-phenylene diisocyanate, p-phenylene diisocyanate, 
2,6-tolylene diisocyanate, 2,4-tolylene diisocyanate, 
naphthalene-1,4-diisocyanate, diphenylmethane-4,4'-diisocyanate, 3,3'- 
dimethyldiphenylmethane-4,4'-diisocyanate, xylylene-1,4-diisocyanate, 
xylylene-1,3-diisocyanate, 4,4'-diphenylpropane diisocyanate, trimethylene 
diisocyanate, hexamethylene diisocyanate, propylene-1,2-diisocyanate, 
butylene-1,2-diisocyanate, ethylidyne diisocyanate, cyclohexylene-1,2- 
diisocyanate and cyclohexylene-1,4-diisocyanate, triisocyanates, such as 
4,4',4"-triphenylmethane triisocyanate and toluene-2,4,6-triisocyanate, 
tetraisocyanates, such as 
4,4'-dimethyldiphenylmethane-2,2',5,5'-tetraisocyanate, and the like. In 
the case that the polyvalent isocyanate is solid, the isocyanate is 
dissolved in a solvent, such as acetone, tetrahydrofuran, 
dimethylformamide, ethyl acetate, butyl acetate, dimethyl phthalate, 
dibutyl phthalate or dioctyl phthalate or a mixture of two or more of 
them, prior to use. Optionally, the polyvalent isocyanate has been 
dissolved in the aforementioned oil substance. 
It is preferable to add an emulsifier to the water phase solution. Suitable 
emulsifiers include natural or synthetic hydrophilic polymer protective 
colloids, such as gelatin, gum arabic, casein, carboxymethyl cellulose, 
starch and polyvinyl alcohol, anionic surfactants, such as alkylbenzene 
sulfonate, alkylnaphthalene sulfonate, polyoxyethylene sulfate and Turkey 
red oil, nonionic surfactants, such as polyoxyethylene alkyl ether, 
polyoxyethylene alkylphenol ether and sorbitan fatty acid ester, and the 
like. 
The mixing ratio of the oil phase solution to the water phase solution is 
adjusted according to materials to be used, object of capsules, or the 
like within the range of not phase inversion, i.e. of forming oil-in-water 
type emulsion. In general, the ratio is 45 to 95% by weight, particularly 
45 to 55% by weight of water phase solution, i. e. 55 to 5% by weight, 
particularly 55 to 45% by weight of oil phase solution. 
When the emulsion is made microcapsules, a polyvalent amine, a polyvalent 
carboxylic acid, a polyvalent thiol, a polyvalent hydroxyl compound, an 
epoxy compound or the like is added. Illustrative of the polyvalent amines 
are polyvalent aromatic amines, such as o-phenylenediamines, 
p-phenylenediamine and 1,5-diaminonaphthalene, polyvalent aliphatic 
amines, such as 1,3-propylenediamine, 1,4-butylenediamine and 
hexamethylenediamine, etc. Illustrative of the polyvalent carboxylic acids 
are pimelic acid, suberic acid, azelaic acid, sebacic acid, phthalic acid, 
terephthalic acid, 4,4'-biphenyl-dicarboxylic acid and 
4,4'-sulfonyldibenzoic acid, etc. Illustrative of the polyvalent thiols 
are condensates of thioglycol and reaction products of polyvalent alcohol 
with a suitable thioether glycol, etc. Illustrative of the polyvalent 
hydroxyl compounds are polyvalent aliphatic alcohols, polyvalent aromatic 
alcohols, hydroxypolyesters and hydroxypolypropylene ethers, etc. 
Illustrative of the epoxy compounds are aliphatic glycidyl ethers, such as 
diglycidyl ether, aliphatic glycidyl esters, etc. 
EXAMPLES 
Example 1 
The apparatus shown in FIGS. 1-3 was used. 
The oil phase solution was prepared by dissolving 10 parts by weight of 
Crystal Violet lactone, 1 part by weight of Benzoylleucomethylene Blue and 
4 parts by weight of 
3-4-(diethylamino)-2-ethoxyphenyl!-3-(2-methyl-1-ethyl-3-indolyl)-4-azaph 
thalide as coloring agents into 200 parts by weight of 
diisopropylnaphthalene, and stored in a storage tank 2 at 65.degree. C. 
As the polyvalent isocyanate, buret form of hexamethylene diisocyanate 
("Sumijule N 3200", Sumitomo Bayer Urethane Co., Ltd.) was stored in a 
storage tank 5 at room temperature. 
The water phase solution was prepared by dissolving 15 parts by weight of 
polyvinyl alcohol ("PVA 205", Kuraray Co., Ltd.) as protective colloid in 
emulsification into 135 parts by weight of water, and stored in a storage 
tank 8 at 65.degree. C. 
Although not illustrated, respective storage tanks 2, 5, 8 were provided 
with an automatic liquid supply system for maintaining liquid level 
constant. 
Hereupon, using a volumetric pump 3, 6, the oil phase solution was fed at a 
speed of 45 parts by weight/minute, and the polyuvalent isocyanate was fed 
at a speed of 5 parts by weight/minute. They were mixed continuously by a 
continuous mixer 10, and supplied into a continuous emulsification tank 11 
from the bottom. 
The water phase solution was fed at a speed of 50 parts by weight/minute 
from the lower side in the tangential direction which conformed with the 
flow direction generated by the stirren in the tank. 
As a result, clogging did not occur in pipes and apparatuses at all through 
continuous operation of 500 hours. Moreover, foreign matter was not 
adhered to the inside of the continuous emulsification tank 11 throughout 
the operation. 
Comparative Example 1 
The apparatus shown in FIG. 4 was used. The same oil phase solution, 
polyvalent isocyanate and water phase solution as Example 1 were used, and 
fed at the same speed as Example 1. 
As a result, the joining point of the oil phase solution with the water 
phase solution was almost clogged after about 40 hours from the start. 
Example 2 
The apparatus shown in FIGS. 1-3 was used, and the same oil phase solution, 
polyvalent isocyanate and water phase solution were fed in the same manner 
as Example 1, except that their feeding speed was changed, i.e. the oil 
phase solution was fed at a speed of 47 parts by weight/minute, the 
polyvalent isocyanate was fed at a speed of 3 parts by weight/minute, and 
the water phase solution was fed at a speed of 50 parts by weight/minute. 
As a result, clogging and its symptom did not occur in pipes and 
apparatuses through continuous operation of 500 hours. 
As described in the example, the present invention provides method and 
apparatus capable of operation for a long period without clogging troubles 
by a reaction product upon preparation of oil-in-water type emulsion from 
an oil phase solution containing a polyvalent isocyanate and water phase 
solution. 
It should also be understood that the foregoing relates to only a preferred 
embodiment of the invention, and that it is intended to cover all changes 
and modifications of the examples of the invention herein chosen for the 
purposes of the disclosure, which do not constitute departures from the 
spirit and scope of the invention.