Emulsion polymerization process

Details Emulsion polymerization process Emulsion polymerization process

1999-07-26

2001-05-15

Dawson, Robert (Department: 1712)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

At least one aryl ring which is part of a fused or bridged...

C524S588000, C528S033000, C556S459000, C556S469000, C424S401000

Reexamination Certificate

active

06232396

ABSTRACT:

TECHNICAL FIELD
The present invention is directed to an emulsion polymerization process, more particularly, to an emulsion polymerization process that allows for control of the level of cyclic siloxanes and the particle size.
BACKGROUND
Current emulsion polymerization processes have cyclic siloxane levels greater than one percent in the final emulsion. With a lower cyclic siloxane level, final product formulations can be better controlled.
Cyclic siloxane contaminants are undesirable from the perspective of health and safety, and there are regulations on the allowed levels in products. Additionally, cyclic siloxanes have a tendency to lower the viscosity of shampoos.
Emulsion polymerization processes have been previously reported, but prior art processes utilized either cyclic siloxanes or mixtures of cyclic and linear siloxanes, and these processes cannot produce emulsions with low cyclic siloxane levels. See, for example, U.S. Pat. No. 5,504,149, which utilizes cyclic siloxanes, surfactant and an initiator that is a silanolate or an organosilanolate; U.S. Pat. No. 4,066,594, which uses cyclic siloxanes and benzene sulfonic acid and optionally a platinum catalyst; EPA 874017, which uses a metal containing catalyst for a chain extension reaction; and JP 9278626, which uses a catalyst and heat for the emulsion polymerization. When cyclic siloxanes are used, the emulsion must be heated to allow polymerization and then cooled for condensation, and the final polymer viscosity is a function of the condensation temperature.
A process is needed in which the particle size of the emulsion can be controlled, as well as the viscosity and the level of cyclic siloxanes in the emulsion. It has been discovered that by using a neutral surfactant system instead of an acid catalyst surfactant during homogenization, particle size, viscosity and cyclic siloxanes can be controlled. A benefit is that with the lower cyclic siloxane level, a safer product can be produced.
SUMMARY OF THE INVENTION
In a first aspect, the present invention is directed to a process for making a silicone emulsion comprising:
a) preparing a neutral aqueous surfactant by adding to water an anionic surfactant and a base, and mixing to form a uniform neutral aqueous surfactant having a pH of about 7;
b) forming a mixture of approximately equal portions of the surfactant and a polysiloxane;
c) homogenizing the mixture to form an emulsion, wherein the emulsion is homogenized until a desired particle size is achieved;
d) cooling the homogenized emulsion;
e) adding an acid to the cooled emulsion and condensing the emulsion to form a polymer, wherein the polymer is condensed until the viscosity reaches the desired level; and
f) neutralizing the condensed emulsion with an effective amount of a neutralizing agent
wherein the level of cyclic siloxanes in the emulsion is less than one percent by weight.
In a second aspect, the present invention is directed to an emulsion that is used in personal care applications comprising the silicone produced by the process of the present invention.
The process of the present invention is effective in controlling the particle size and the viscosity of the emulsion as well as controlling the level of cyclic siloxanes at a level of less than one percent. Another advantage of the present invention is that the emulsion does not need to be heated for polymerization to take place.
DETAILED DESCRIPTION OF THE INVENTION
In a preferred embodiment, from about 0.3 to 5.0, more preferably from about 0.8 to about 3.0, even more preferably from about 0.9 to about 1.8 parts by weight (“pbw”), of an anionic surfactant and from about 0.06 to about 1.1, more preferably from about 0.2 to about 0.7, even more preferably from about 0.2 to about 0.35 pbw of a base are added to a vessel containing from about 30 to about 90, more preferably from about 35 to about 70, even more preferably from about 40 to about 55 pbw deionized water to form a mixture. In a preferred embodiment, this mixture is then metered with approximately from 8 to about 65, more preferably from about 25 to about 65, even more preferably from about 45 to about 55 pbw of a polysiloxane. In a preferred embodiment, the mixture is then blended by passing the mixture through a paste disperser, such as for example, Premier, and then by milling the mixture, by for example, a colloid mill such as IKA or Gaulin. After blending, the mixture is then fed to a homogenizer, such as a Gaulin, Bran & Lubbe, or a microfluidizer by Microfluidics, to form an emulsion. In a preferred embodiment, the mixture is homogenized, preferably without the addition of heat, at a pressure of from about 4,000 to 12,000 psig, more preferably at a pressure of from about 5,000 to about 8,000, even more preferably at a pressure of about 6000 psig, and a recycle loop is utilized to set the desired particle size and to ensure stability of the emulsion. In a preferred embodiment, the particle size ranges from about 0.1 to about 2.0, more preferably from about 0.2 to about 1.0, even more preferably from about 0.3 to about 0.6 microns, as measured by a Malvern Mastercizer or a Nicomp 170. Once homogenized, the emulsion is fed to a condensation vessel where it is cooled to about 15 to 50° C., more preferably, from about 20 to 35° C., even more preferably to about 20 to 25° C., and from about 0.09 to about 1.5, more preferably from about 0.25 to about 0.9, even more preferably from about 0.29 to about 0.45 pbw of a strong acid is added to bring the pH of the emulsion to about 2, more preferably less than 2. Once the emulsion is acidified, a controlled condensation begins. Once the condensation is complete and the desired polymer viscosity has been achieved, preferably between 100,000 centipoise (cps) and 6,000,000 cps, more preferably between 500,000 and 3,000,000 cps, even more preferably between 1,000,000 and 2,000,000 cps, the emulsion is neutralized to prevent further condensation. In a preferred embodiment, the pH is from about 6 to about 8.5, more preferably from about 6.5 to about 8, even more preferably from about 7 to about 7.5 with a neutralizing agent.
Anionic surfactants suitable for use in the present invention are those that emulsify and provide good condensation. Examples of suitable surfactants include alkylbenzenesulfonic acids and salts such as hexylbenzenesulfonic acid, octylbenzenesulfonic acid, decylbenzenesulfonic acid, dodecylbenzenesulfonic acid, cetylbenzenesulfonic acid and myristylbenzenesulfonic acid, more preferably dodecylbenzenesulfonic acid. Additionally, co-surfactants, such as sodium lauryl sulfate, may also be used.
In a preferred embodiment, the base of the present invention is one that will neutralize the anionic surfactant. Examples of bases suitable for use in the present include, but are not limited to, sodium carbonate, sodium hydroxide, potassium hydroxide, calcium carbonate. Preferably, the base is sodium carbonate.
Compounds suitable as the polysiloxane intermediate of the present invention are those that are hydrolyzates. Examples of polysiloxane intermediates that may be used in the present invention include, but are not limited to, linear silanol-stopped polyorganosiloxanes. Preferably, the polysiloxane intermediate of the present invention is a low viscosity silanol-stopped polymer of the formula:
HO—(R
2
SiO)
x —
H
wherein each R is independently a monovalent hydrocarbon radical;
and x is an integer, wherein x is chosen such that the viscosity is from about 15 to about 1000 centistokes, more preferably from about 50 to about 500 centistokes, and even more preferably from about 70 to about 150 centistokes.
Suitable monovalent hydrocarbon groups include acyclic hydrocarbon radicals, monovalent alicyclic hydrocarbon radicals, monovalent and aromatic hydrocarbon radicals. Preferred monovalent hydrocarbon radicals are monovalent (C
1
-C
6
)alkyl radicals, monovalent aryl radicals and monovalent aralkyl radicals.
As used herein, the term “(C
1
-C
6
)alkyl” means a linear or branched alkyl group containing from 1 to 6 carbons per group, such as, for ex

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