Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Patent
1998-02-17
2000-08-01
Krass, Frederick
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
523335, 523336, 523337, 523403, 523404, 523414, 523415, 523426, 210291, 21050027, 210511, 210635, 210639, 210696, 210768, 210787, 210789, 210790, 210806, C08K 320, C08L 6300
Patent
active
060968060
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to the use of aqueous liquid compositions (either dispersions or true solutions) with which active metal surfaces can be coated, by mere contact with the liquid composition, with an adherent polymer film that increases in thickness the longer the time of contact, even though the liquid composition is stable for a long time against spontaneous precipitation or flocculation of any solid phase, in the absence of contact with active metal. (For the purposes of this specification, the term "active metal" is to be understood in its broadest sense as including all metals and alloys more active than hydrogen in the electromotive series, or, in other words, a metal which is thermodynamically capable of dissolving to produce dissolved cations derived from the metal, with accompanying evolution of hydrogen gas, when contacted with an aqueous solution of a non-oxidizing acid in which the activity of hydrogen ions is 1 equivalent per liter.) Such liquid compositions are denoted in this specification, and commonly in the art, as "autodeposition" or "autodepositing" compositions, dispersions, emulsions, suspensions, baths, solutions, or a like term. Autodeposition is often contrasted with electrodeposition, which can produce very similar adherent films but requires that the surface to be coated be connected to a source of direct current electricity for coating to occur.
In particular, this invention is concerned with autodeposition of high quality, corrosion inhibiting coatings that include epoxy resins and/or products of reaction of molecules of epoxy resins with one another and/or with other materials.
2. Statement of Related Art
It is generally believed in the art that autodeposition works because cations dissolving from the metal surface to be coated, which cations when initially dissolved are, of course, confined to the volume of contacting liquid in the immediate vicinity of the metal surface from which they are dissolving, interact with the liquid autodepositing composition in at least one of the following ways: (i) The dissolved cations precipitate previously dissolved polymers by displacing previously associated cations or cation-forming moieties, in association with which the polymers are soluble, by the newly dissolved cations in association with which the polymers are much less soluble; and/or (ii) the dissolved cations destabilize numerous individual dispersed phase units in a dispersion of a polymer with inherently low water solubility, which nevertheless can remain in stable suspension for a long time in the absence of dissolved polyvalent cations, because the outer surfaces of the dispersed phase units carry a net negative electrical charge, derived from anionic components of the dispersed polymer itself and/or from an anionic dispersing agent used to prepare the autodepositing composition in question.
The net negative charge on the units of the dispersed phase in an autodepositing liquid composition is believed to be electrically counterbalanced by a diffuse excess of cations, usually monovalent cations, in the surrounding continuous phase of the dispersion, this excess of cations together with the negative charges on the dispersed phase units constituting an example of the well known "electrical double layer" or "Helmholz double layer" that is characteristic of most interfaces between liquid phases containing charged solute particles and solids in contact with such liquid phases. As long as this double layer remains intact, the net negative charge on the exterior of each unit of dispersed phase causes it to repel other units of the disperse phase that also carry a net negative charge, and thereby prevents spontaneous coalescence of the dispersed phase units.
When the double layer is sufficiently disturbed, or in the case of a soluble polymer, when the solubility is reduced, by introduction of new cations, the polymeric parts of numerous dispersed phase units and/or solute polymer molecules can aggregate to form a continuous co
REFERENCES:
patent: 4123403 (1978-10-01), Warner et al.
patent: 5352726 (1994-10-01), Hall
Mueller Brian L.
Siebert Elizabeth J.
Henkel Corporation
Jaeschke Wayne C.
Krass Frederick
Szoke Ernest G.
Wisdom Norvell E.
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