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...
Reexamination Certificate
2001-02-13
2003-09-30
Hartley, Michael G. (Department: 1616)
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...
C528S010000, C528S012000, C528S034000, C524S588000, C424S407000, C424S070100, C424S078020
Reexamination Certificate
active
06627698
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
Not applicable.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not applicable.
REFERENCE TO A MICROFICHE APPENDIX
Not applicable.
FIELD OF THE INVENTION
This invention is directed to a method of removing residual volatile siloxane oligomers from emulsions containing siloxane polymers prepared by emulsion polymerization of the volatile siloxane oligomers. In particular, volatile siloxane oligomers are removed from emulsions containing siloxane polymers by a batch steam distillation process. In one embodiment, emulsions stripped of volatile siloxane oligomers are re-catalyzed to initiate condensation polymerization. In another embodiment, clear emulsions stripped of volatile siloxane oligomers are provided even though an antifoam is used in the stripping process.
BACKGROUND OF THE INVENTION
U.S. Pat. No. 2,834,754 (May 13, 1958) describes a batch process for removing volatile organopolysiloxanes from high molecular weight organopolysiloxanes with a stripping gas such as steam, neon, nitrogen or argon, while kneading. According to that process, a Banbury mixer with sigma-type blades is used to remove octamethylcyclotetrasiloxane from a highly viscous masse or gummy elastic silicone solid. Stripping emulsions is not disclosed, however.
A continuous process employing a stripping unit containing heated parallel plates is used in U.S. Pat. No. 4,096,160 (Jun. 20, 1978) to remove a steam heated mixture of hexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane, decamethylcyclopentasiloxane, and dodecamethylcyclohexasiloxane, from silanol terminated dimethylpolysiloxane fluids having a viscosity of 1,000-1,000,000 centistoke (mm
2
/s). Stripping emulsions is not disclosed, however.
Both U.S. Pat. Nos. 2,834,754 and 4,096,160 require specialized equipment for handling viscous polymers. Also, the rate of heat transfer is substantially reduced when processing such viscous polymers.
One known method for obviating processing difficulties associated with viscous polymers is to prepare and handle such polymers in the form of an aqueous emulsion. A batch process carried out in a heated flask is described in U.S. Pat. No. 4,600,436 (Jul. 15, 1986) for stripping emulsion polymerized polysiloxane emulsions of the cyclic siloxanes or other low molecular weight siloxanes used to prepare the emulsions. According to the '436 patent, emulsions stripped by such a batch process possess improved film properties.
In another batch process described in U.S. Pat. No. 5,922,108 (Jul. 13, 1999), volatile organopolysiloxanes such as octamethylcyclotetrasiloxane are removed from a fluid stream such as air containing volatile organopolysiloxanes and a hydrocarbon such as methane or pentane, by passing the fluid stream through a column packed with dry soil. Stripping emulsions is not disclosed, however.
Unexpectedly, however, it was discovered that emulsion polymerized polysiloxane emulsions stripped of cyclic siloxanes or other low molecular weight siloxanes from which they were prepared, by the batch steam distillation process according to this invention, rather than by processes described in such patents, possess improved properties not realized by any of those patentees. The terms stripping and distillation are used herein interchangeably to describe processes according to this invention.
For example, in steam stripping emulsions to remove cyclic siloxanes, conditions were unexpectedly identified enabling preparation of clear emulsions. The ability to prepare a clear emulsion in this manner in the presence of an antifoam during the stripping process was unexpected because the clarity of such materials can be reduced significantly by a relatively low concentration of large particles, the formation of which would be expected when an antifoam is used and when operating under the harsh conditions of a steam stripping process.
It was also found that emulsions stripped of volatile siloxane oligomers could be re-catalyzed to initiate condensation polymerization, and that the viscosity or molecular weight of the polymer in stripped emulsions could be further increased without appreciably increasing the content of volatile siloxane oligomers in stripped emulsions. This enables one to prepare emulsions containing polymers of yet higher molecular weight, while at the same time producing emulsions containing lower levels of volatile cyclic oligomers, than would otherwise be present under typical emulsion polymerization conditions.
BRIEF SUMMARY OF THE INVENTION
The invention relates to a batch steam distillation process for removing volatile siloxane oligomers from an emulsion containing siloxane polymers and volatile siloxane oligomers prepared by emulsion polymerization of volatile siloxane oligomers.
According to the process, the emulsion is fed batchwise to a steam distillation device for vaporizing liquids in which the emulsion is subjected to vaporization in the steam distillation device. An overhead fraction containing volatile siloxane oligomers is removed from the steam distillation device, while an unvaporized bottom fraction remains in the steam distillation device. The unvaporized bottoms fraction can be removed at the completion of the stripping process. The unvaporized bottom fraction consists of an emulsion containing siloxane polymers which is substantially free of any residual volatile siloxane oligomers used to prepare the emulsion.
The steam extracts the volatile siloxane oligomer from the emulsion, and the extracted volatile siloxane oligomer can be recovered from the overhead fraction by known condensing and decanting processes. The operating temperature used in the steam distillation device is generally in the range of 70-110° C., preferably 80-105° C.
According to one embodiment of the invention, the method of preparing an aqueous emulsion containing a siloxane polymer involves:
(I) heating and emulsion polymerizing a mixture containing a volatile siloxane oligomer or mixture of volatile siloxane oligomers, at least one anionic surfactant or cationic surfactant, optionally a nonionic surfactant, water, and an emulsion polymerization catalyst or mixture of emulsion polymerization catalysts;
(II) neutralizing the emulsion polymerization catalyst;
(III) stripping the emulsion prepared in (I) using steam until the emulsion contains less than 0.18 parts by weight of volatile siloxane oligomer per unit weight of the siloxane polymer in the emulsion;
(IV) cooling the stripped emulsion to a temperature less than the temperature in (I);
(V) adding another catalyst to the cooled stripped emulsion of (IV) and allowing the contents of the cooled stripped emulsion to further polymerize; and
(VI) neutralizing the catalyst added in (V) to provide an emulsion containing a siloxane polymer with a higher molecular weight than the molecular weight of the siloxane polymer prepared in (I) and further containing less than 0.18 parts by weight of volatile siloxane oligomer per unit weight of the siloxane polymer in the emulsion;
In this embodiment, the mixture in (I) for emulsion polymerizing is heated to a temperature in the range of 50-95° C.; the stripping temperature in (III) is in the range of 70-110° C.; the temperature in (IV) is in the range of 0-50° C. The steam in (III) can be generated in situ or fed into the emulsion from an external source. The catalyst used in (V) can be the same catalyst used in (I) or it can be a different catalyst.
According to the other embodiment of the invention, the method of preparing an aqueous emulsion containing particles of siloxane polymer of an average size less than 0.1 micron/100 nanometer involves:
(I) heating and emulsion polymerizing a mixture containing a volatile siloxane oligomer or mixture of volatile siloxane oligomers, at least one anionic surfactant or cationic surfactant, optionally a nonionic surfactant, water, and an emulsion polymerization catalyst or mixture of emulsion polymerization catalysts;
(II) neutralizing the emulsion polymerization catalyst;
(III) adding an antifoam composition to the neut
Wrolson Burt Michael
Zimmerman Brett Lee
DeCesare Jim L.
Dow Corning Corporation
Gollamudi Sharmila
Hartley Michael G.
LandOfFree
Method of making silicone emulsions having low residual... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method of making silicone emulsions having low residual..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method of making silicone emulsions having low residual... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3020957