Coating processes – With post-treatment of coating or coating material – Heating or drying
Reexamination Certificate
2001-01-05
2002-05-28
Cameron, Emma (Department: 1762)
Coating processes
With post-treatment of coating or coating material
Heating or drying
Reexamination Certificate
active
06395339
ABSTRACT:
TECHNICAL FIELD
The present invention relates to dispersions of silicon compounds and to a process for making them.
BACKGROUND ART
Ordinary emulsions contain dispersed drops in the micrometer range and are unstable over time, although the shelf life may be adequate for most purposes. They are inherently turbid. However, the amount of scattered light is dependent on the difference in refractive index between the dispersed phase and the continuous phase. It is possible to obtain transparent emulsions by selecting materials whose refractive indices match. However, materials which may be useful components of liquid products containing a dispersed phase may have refractive indices which are sufficiently different from one another that a non-turbid dispersion is not obtained in a conventional emulsion.
Micro-emulsions contain a dispersed phase with a droplet size of the order of nanometers, as opposed to the micrometers of conventional emulsions. They are stable indefinitely and are not turbid even if the refractive indices of the dispersed phase and the continued phase do not match. They form spontaneously on mixing the components but it is difficult to predict the combination of water-insoluble components (oil phase) and surfactant required to prepare them.
Aqueous emulsions containing polydimethyl siloxanes (PDMS) may be used for various purposes. Thus U.S. Pat. No. 5,017,221 discloses that aqueous emulsions of polydimethyl siloxane fluids (i.e. PDMS) have been used as a protective coating on many surfaces including rubber, vinyl, plastic, leather, and sealed wood, and refers to U.S. Pat. Nos. 3,956,174 and 4,133,921 as showing such compositions.
It would be desirable to be able to prepare aqueous dispersions containing water-immiscible silicone liquids, e.g. polydimethyl silicone, with improved transparency and stability. It is particularly desirable to produce aqueous dispersions with improved transparency and stability which contain significant amounts of silicone liquids. However, dispersions prepared from polydimethyl silicone, water, and an anionic surfactant are generally turbid.
DISCLOSURE OF INVENTION
According to the present invention an aqueous dispersion comprising water, a separate liquid phase of an incompatible silicone, and an anionic surfactant is characterized in that (a) the water contains a stabilizing amount of a dissolved electrolyte, and (b) the dispersion contains an effective amount of a stabilizing anionic surfactant.
According to a further aspect of the present invention, a process for forming an aqueous dispersion comprising water, a separate liquid phase of an incompatible silicone and a surfactant is characterized by the steps of: (a) forming an aqueous phase containing a stabilizing amount of a dissolved electrolyte, (b) introducing an effective amount of a stabilizing anionic surfactant into the aqueous phase containing dissolved electrolyte, and (c) bringing liquid incompatible silicone into contact with the aqueous phase containing surfactant and electrolyte.
According to a still further aspect of the present invention a process for forming an aqueous dispersion comprising a separate continuous liquid phase of an incompatible silicone, water dispersed within the silicone, and a surfactant is characterized by the steps of: (a) forming an aqueous phase containing a stabilizing amount of a dissolved electrolyte, (b) forming a silicone oil phase containing an effective amount of a stabilizing anionic surfactant, and (c) introducing the aqueous phase into the liquid incompatible silicone with agitation.
According to yet another aspect of the present invention, a method of treating a surface by applying to the surface an aqueous dispersion containing a dispersed liquid silicone phase is characterized in that (a) the water contains a stabilizing amount of a dissolved electrolyte, and (b) the dispersion contains an effective amount of a stabilizing anionic surfactant.
We have found that in order to have a possibility of obtaining a dispersion of increased stability when using an anionic surfactant, it is necessary to use water containing sufficient dissolved electrolyte instead of pure water. Not all anionic surfactants will give improved stability even in the presence of dissolved electrolyte, and it is necessary to select specific anionic surfactants from the general class of anionic surfactants. However, the skilled person who has understood the inventive idea disclosed by the present specification, namely that it is necessary to use water containing a dissolved electrolyte and then to select a suitable anionic surfactant, will be able to identify suitable anionic surfactants by simple non-inventive tests.
When reference is made in this specification to improve stability, the improvement is determined by comparison with the corresponding composition containing pure water without dissolved electrolyte. Improved stability is most readily indicated by improved clarity of the dispersion, which may also have a blue tinge. It will be understood that the dispersion must remain as a dispersion. The separation of a turbid dispersion into two clear layers does not represent an improvement in stability.
Improved stability may also be indicated by improved storage life (often referred to as “shelf life”) before the dispersion separates into its components. However, as many conventional emulsions have relatively long storage lives, it may not be practicable to use storage life as a routine measure of stability.
It is believed that the present invention makes possible the preparation of dispersions which are true microemulsions. In such cases instrumental determination of the droplet size of the dispersed phase may be used to give a more precise indication of the improvement given by the present invention.
An “incompatible” silicone is one which does not disperse in water in the absence of a separate surfactant, as is explained in more detail below. It may be desirable to use water which is substantially free of ions as the basis of the dispersion so as to be able to control the nature of the electrolyte more closely, and to avoid the formation of insoluble salts. In particular the presence of significant amounts of divalent ions is undesirable.
Where the dispersions according to the invention are oil-in-water dispersions (i.e. water is the continuous phase), then the proportion of water in the composition may be for example greater than 85% by weight of total composition, e.g. 85% to 98%, preferably 85% to 90%.
The electrolyte is preferably selected so as to give a substantially neutral aqueous phase e.g. pH 6-8. It will be apparent that the electrolyte must not adversely affect the anionic surfactant, e.g. by causing it to form an insoluble salt or to hydrolyze. As indicated above, the presence of divalent ions, e.g. ions of Ca or Mg, will be undesirable. An example of a suitable electrolyte is NaCl.
The concentration of the electrolyte may be for example in the range 0.01 to 0.1M, if the object is to produce oil-in-water dispersions. Higher concentrations of electrolyte may be used with larger amounts of silicone oil to produce water-in-oil dispersions.
The use of a relatively low concentration of electrolyte favours the production of oil-in-water dispersions, while higher concentrations favour the production of water-in-oil dispersions. The optimum concentration of electrolyte will depend on the specific electrolyte used, but can be determined by simple tests.
The dispersion of the present invention comprises a separate liquid phase of an incompatible silicone. The term “silicone” indicates an organic compound of silicon containing Si—O repeating units with the silicon atom carrying two organic groups; preferably the organic groups are methyl groups. Some liquid silicone compounds, e.g. certain copolymers containing alkylene oxide groups, act as surfactants so that they will disperse in water without the need to use a separate surfactant. Such self-dispersing silicones are not incompatible silicones as required by the present invention. The silicone compound i
Binks Bernard P.
Dong Jinfeng
Cameron Emma
S. C. Johnson & Son Inc.
LandOfFree
Dispersions and process for making them does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Dispersions and process for making them, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Dispersions and process for making them will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2893194