Method for continuous emulsifying organopolysiloxane gums

A method of continuous emulsification that can emulsify high-viscosity organopolysiloxane gums and is capable of continuous mass production. A compounding extruder is used whose barrel 1 contains at least 2 mixing element-equipped shafts 3 installed in parallel. On each shaft elevations and depressions are formed along the axial direction and the elevations and depressions on respective shafts intermesh. Organopolysiloxane gum, emulsifying agent, and water are continuously supplied as starting materials to this compounding extruder, and an organopolysiloxane-in-water emulsion is produced by mixing and homogenizing the starting materials by subjecting them through rotation of the mixing element-equipped shafts to a shearing action at a shear rate of at least 10/second (i.e. 10 reciprocal seconds).

BACKGROUND OF THE INVENTION 
This invention relates to a method for continuously emulsifying 
organopolysiloxane gums. More particularly, this invention relates to a 
method that is capable of the continuous emulsification of 
organopolysiloxane gums that have been difficult to emulsify due to their 
very high degrees of polymerization. 
Emulsions of organopolysiloxanes are widely used in industry as lubricants, 
release agents including mold-release agents, fiber-treatment agents, 
glass fiber-treatment agents, cosmetic bases, lustrants, and paint 
additives. These organopolysiloxane emulsions are prepared by mixing an 
emulsifying agent and water into a starting fluid organopolysiloxane gum. 
However, conversion into an emulsion can be a problem as the viscosity of 
the organopolysiloxane rises, resulting in a corresponding increasing 
difficulty of emulsification. 
Japanese Patent Publication Number Sho 59-51565 51,565/1984! proposes a 
method for emulsification of such high-viscosity organopolysiloxanes. This 
method uses a cylindrical container, and installed therein, a mixing 
element comprising at least 3 disks placed at fixed intervals on a 
rotating shaft. Shearing and stirring are conducted by rotation of the 
mixing element. However, the use of at least 3 disks in this method 
installed on the rotating shaft coaxially and with a narrow interposed 
gap, limits the viscosity of organopolysiloxanes that can be mixed across 
these closely spaced disks, to at most about 70,000 centistokes. It is not 
practical to emulsify organopolysiloxanes with higher viscosities using 
this method. 
BRIEF SUMMARY OF THE INVENTION 
The object of our invention in contrast is to provide a highly productive 
method for continuous emulsification of organopolysiloxane gums that is 
capable of continuous mass production, and that can emulsify even 
high-viscosity organopolysiloxane gums heretofore difficult to emulsify. 
These and other objects will become apparent from a consideration of the 
detailed description.

DETAILED DESCRIPTION 
Our invention is characterized by continuously feeding an 
organopolysiloxane gum, an emulsifying agent, and water, as starting 
materials into the supply port of a compounding extruder whose barrel 
contains at least 2 mixing element-equipped shafts installed in parallel. 
On each shaft, elevations and depressions are formed along the axial 
direction in alternating sequence, and the elevations and depressions on 
one shaft intermesh with the elevations and depressions on the second 
shaft. An organopolysiloxane-in-water emulsion is produced by mixing and 
homogenizing the starting materials by subjecting them through rotation of 
the mixing element-equipped shafts to a shearing action at a shear rate of 
at least 10/second; and discharging the emulsion from the discharge port 
of the compounding extruder. 
Mixed and homogenized emulsions of high-viscosity organopolysiloxane gums 
can be easily prepared due to application to the starting materials of a 
shearing action at a shear rate of at least 10/second, and due to the 
above-described arrangement in which at least 2 mixing element-equipped 
shafts having elevations and depressions along the axial direction, are 
installed in parallel within the barrel, and the elevations and 
depressions on one shaft intermesh with the corresponding elevations and 
depressions on the second shaft. 
The "shear rate" according to our invention is defined by the formula: 
EQU shear rate Vs (1/sec.)=V/t 
wherein V is the peripheral velocity at the outer surface of the mixing 
element-equipped shaft in cm/sec., and t is the minimum clearance in cm 
between the outer surface of the mixing element-equipped shaft and the 
interior wall of the barrel. 
Our method can be explained more fully by reference to the compounding 
extruder as depicted in the drawings. Thus, FIGS. 1 and 2 depict a 
compounding extruder for carrying out the method of our invention for 
continuously emulsifying organopolysiloxane gums. In FIGS. 1 and 2, 1 is a 
barrel whose axis is fixed on the horizontal, and whose interior space has 
an 8-shaped transverse cross-section (i.e., transverse cross-section 
normal to the axial direction). A starting material supply port 4 is fixed 
to the top of one end of the barrel 1, and a discharge port 5 is fixed at 
the bottom of the other end of the barrel 1, for discharge of the emulsion 
made by the mixing operation. 
Two mixing element-equipped shafts 3 are inserted in parallel, on the left 
and right respectively, in the interior space of the barrel 1 with 
8-shaped transverse cross-section. These shafts are set up to be driven in 
the same direction as indicated by the arrows with motors not shown in the 
drawings. 
In the arrangement of these mixing element-equipped shafts 3 moving from 
upstream at the supply port 4 to downstream at the discharge port 5, a 
plural number of lens-shaped paddles 3a are first stacked on the rotating 
shaft 2 moving along the axial direction followed by installation of a 
screw 3s. The plural number of paddles 3a makes up the major portion of 
the mixing mechanism. Both ends of the lens-shape lie in close proximity 
to the interior surface of the barrel 1 and are separated therefrom by a 
small clearance t. A small clearance t similarly exists for the periphery 
of the screw 3s. 
The paddles 3a are attached on the rotating shaft 2 as groups, consisting 
in each case of 2-4 paddles with the same angle, and the attachment angle 
can be changed in 45.degree. increments between the groups. The axial and 
alternating sequence of elevations and depressions on the mixing 
element-equipped shaft 3 is formed by changing the phase between the 
attachment angles of the multi-element groups. In addition, the elevations 
and depressions formed along the axial direction in alternating sequence 
on a mixing element-equipped shaft 3, intermesh with the elevations and 
depressions on a neighboring parallel mixing element-equipped shaft 3. 
At least 2 mixing element-equipped shafts 3 must be present, and the 
elevations and depressions on neighboring shafts must intermesh. Three or 
more mixing element-equipped shafts may be installed, but the intermeshing 
relationship must be preserved. The attachment angles of the multi-paddle 
3a groups are not necessarily staggered in 45.degree. increments on the 
rotating shaft 2, and other increments can be used such as 15.degree. or 
30.degree.. 
In addition to the organopolysiloxane gum, water and the emulsifying agent 
are also mixed as starting materials in the continuous emulsification of 
the organopolysiloxane gum using the compounding extruder described above. 
These three starting materials may be introduced separately into the 
supply port 4, or they may be preliminarily mixed, and the resulting 
mixture may be introduced into the supply port 4. 
Due to the different attachment angles for the multi-paddle 3a groups on 
the 2 mixing element-equipped shafts 3, and the elevation/depression 
intermeshing of reciprocal paddles 3a between the two shafts, the starting 
materials are subjected to a mixing action and a shearing action within 
the compounding extruder as the intermesh configuration of the paddles 3a 
changes as shown in FIGS. 3A-3C. In addition, because both tips of the 
lens-shaped paddles 3a generate a shearing action by virtue of the small 
clearance t with the inner wall of the barrel 1, the three starting 
materials are subjected to additional strong mixing and homogenizing 
activities that serve to generate a microparticulate emulsion. The mixture 
thereby emulsified by the paddles 3a is finally discharged through the 
discharge port 5 while being subjected to additional mixing by the 
downstream screw 3s. 
In applying the mixing action described above, the shear rate in the 
shearing action (i.e., between paddles and between the paddle tips and 
barrel interior wall) must be at least 10/sec., and is preferably at least 
100/sec. A homogeneous microparticulate emulsion cannot be obtained when 
the shear rate applied to the mixture is less than 10/sec. 
In addition, the compounding extruder is preferably arranged in such a 
manner that the ratio L/D is at least 5, and more preferably at least 10, 
wherein L is the axial length of the mixing element-equipped shaft within 
the barrel 1, and D is the diameter of rotation of the peripheral surface 
of the paddles 3a. The clearance t between the paddles 3a or screw 3s and 
the interior wall of the barrel 1 preferably is no greater than 5 mm. 
High-viscosity organopolysiloxane gums with viscosities at 25.degree. C. in 
excess of 500,000 centipoise can be used as the starting 
organopolysiloxane gum (i.e., Component A) for emulsification in our 
continuous emulsification method. Even when the viscosity of the 
organopolysiloxane is higher, it can still be easily emulsified by 
dissolving it in a solvent. 
Any organopolysiloxane which is a gum at ambient temperature can be used. 
The plasticity of the organopolysiloxane gum is measured at 25.degree. C. 
by the method described in Japanese Industrial Standard JIS C2123, and is 
at least 0.75 mm, preferably 1.0-2.5 mm. 
Organopolysiloxane gums suitable for our invention can be illustrated by 
the formula: 
EQU R.sub.a SiO.sub.(4-a)/2 
wherein R is a substituted or unsubstituted monovalent hydrocarbon group. R 
can be an alkyl group such as methyl, ethyl, and propyl; an aryl group 
such as phenyl and tolyl; and such groups in which all or part of the 
hydrogen has been replaced by halogen, such as chloromethyl and 
3,3,3-trifluoropropyl. a has a value from 1.9-2.1. 
Such organopolysiloxane gums are exemplified by trimethylsiloxy-endblocked 
dimethylpolysiloxane gums, silanol-endblocked dimethylpolysiloxane gums, 
trimethylsiloxy-endblocked dimethylsiloxane-phenylmethylsiloxane copolymer 
gums, silanol-endblocked dimethylsiloxane-phenylmethylsiloxane copolymer 
gums, trimethylsiloxy-endblocked dimethylsiloxane-diphenylsiloxane 
copolymer gums, silanol-endblocked dimethylsiloxane-diphenylsiloxane 
copolymer gums, trimethylsiloxy-endblocked dimethylsiloxane-methyl 
(3,3,3-trifluoropropyl)siloxane copolymer gums, and silanol-endblocked 
dimethylsiloxane-methyl (3,3,3-trifluoropropyl)siloxane copolymer gums. 
The molecular structure of the organopolysiloxane gum can be linear, 
partially branched and linear, or a network. A linear organopolysiloxane 
gum is preferred. 
Additives such as silica micropowder can be present in the 
organopolysiloxane gum so long as the object of the invention is not 
compromised. 
Water (Component B) can be tap water or ion-exchanged water. Component B is 
admixed at the rate of 1-400 weight parts per 100 weight parts of 
organopolysiloxane gum Component A. 
Emulsifying agent (Component C) can be a nonionic, anionic, or cationic 
surfactant. Nonionic surfactants are exemplified by polyoxyalkylene alkyl 
ethers, polyoxyalkylene alkylphenol ethers, polyoxyalkylene alkyl esters, 
polyoxyalkylene sorbitan alkyl esters, polypropylene glycol, and 
diethylene glycol. Anionic surfactants are exemplified by fatty acid salts 
such as sodium laurate, sodium stearate, sodium oleate, and sodium 
linolenate; alkylbenzenesulfonic acids such as hexylbenzenesulfonic acid, 
octylbenzenesulfonic acid, and dodecylbenzenesulfonic acid; salts of the 
preceding; alkylsulfonates; and sodium polyoxyethylene alkylphenyl ether 
sulfate. Cationic surfactants are exemplified by octyltrimethylammonium 
hydroxide, dodecyltrimethylammonium hydroxide, alkyltrimethylammonium 
chlorides, and benzylammonium salts. Two or more of these surfactants may 
be used in combination. 
Component C is added in sufficient quantity to thoroughly emulsify 
organopolysiloxane gum Component A in the water Component B. In specific 
terms, Component C is preferably blended at from 0.1-100 weight parts per 
100 weight parts of organopolysiloxane gum Component A. 
Organopolysiloxane gum emulsions prepared by our continuous emulsification 
method are generally obtained in the form of emulsions in which the 
organopolysiloxane gum is emulsified and dispersed in water. These 
emulsions generally have an average particle size in the range from 0.1-50 
micrometers. 
An organopolysiloxane gum emulsion adapted to a particular application or 
end use can be obtained either by the direct use of the organopolysiloxane 
gum emulsion as prepared, or by diluting the product with water. These 
emulsions can be used as fiber-treatment agents, lubricants, release 
agents including mold-release agents, glass fiber-treatment agents, 
cosmetic oil bases, lustrants, defoamers, and paint additives. 
EXAMPLE 
The following ingredients were continuously supplied to the compounding 
extruder depicted in FIGS. 1 and 2: 100 weight parts of a 
trimethylsiloxy-endblocked dimethylpolysiloxane gum with a viscosity at 
25.degree. C. of 10 million centipoise; 10.0 weight parts polyoxyethylene 
lauryl ether (i.e., a 6 mol ethylene oxide adduct); and 5.0 weight parts 
ion-exchanged water. These ingredients were sheared and mixed in the 
compounding extruder, and yielded an emulsion of the dimethylpolysiloxane 
gum. 
The L/D ratio for the compounding extruder employed was 10 wherein L was 
the length L of the barrel interior (i.e., the mixing element-equipped 
shaft) and D was the diameter of rotation of the paddles. The minimum 
clearance t for this compounding extruder was 0.1 cm. The mixing 
element-equipped shaft was rotated at 340 rpm, which provided a shear rate 
of 890/sec. 
The dimethylpolysiloxane emulsion was a translucent paste-like emulsion in 
which the dimethylpolysiloxane gum was uniformly dispersed and emulsified 
in water. The emulsion contained an average particle size of 9.9 
micrometers of dimethylpolysiloxane gum as measured after dilution with 
water using a laser light scattering instrument for measuring particle 
size distribution. 
As can be seen from the above description, our continuous emulsification 
method can emulsify high-viscosity organopolysiloxane gums previously 
difficult to emulsify, and it can accomplish this continuously and 
efficiently at high levels of production. 
Other variations may be made in compounds, compositions, apparatus, and 
methods described without departing from the essential features of the 
invention. The forms of invention are exemplary and not limitations on its 
scope as defined in the claims.