Metal treatment – Process of modifying or maintaining internal physical... – Processes of coating utilizing a reactive composition which...
Patent
1998-06-01
2000-11-21
Sheehan, John
Metal treatment
Process of modifying or maintaining internal physical...
Processes of coating utilizing a reactive composition which...
148251, 106 1444, C23C 2224
Patent
active
061497355
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to chromate treatment bath compositions and treatment methods for application to metals. More particularly, the present invention relates to a chromate treatment bath composition that, when dried into place on the surface being treated, can provide metal surfaces with a sparingly soluble chromate film that exhibits an excellent coatability with waterborne paints and at the same time has an excellent corrosion resistance, paint adherence, alkali resistance, and water resistance. The invention also relates to a treatment method using said chromate treatment bath composition.
DESCRIPTION OF RELATED ART
Unlike reactive chromate treatment technology and electrolytic chromate treatment technology, dry-in-place chromate treatment technology is able to form a chromate film on metals simply by coating the metals and then drying. As a result, a distinguishing feature of dry-in-place chromate treatment is that it is not limited to particular metal substrates. As a result, dry-in-place chromate treatment is frequently used to impart corrosion resistance to metal surfaces, to improve their adherence to resins, and most importantly to improve paint adherence and post-painting corrosion resistance when painting is carried out. At the present time the main metals used in flat sheet structures are zinciferous-plated steel sheet and aluminum and aluminum alloy flat sheet. These are widely used in such economic sectors as automotive applications, household electrical appliances, building materials, and so forth. These materials are almost inevitably subjected to a chromate treatment due to contemporary demands for high added value.
As stated above, a distinguishing feature of dry-in-place chromate treatment technology is that it is not limited to particular metal substrates. However, this technology has other advantages. Because a desirable film is obtained through just a simple application step, there is no specific requirement for long reaction times, and simple equipment can be used, so that the line length can be reduced. Moreover, the effluent treatment load is light because a post-treatment water rinse is not required. Also, because dry-in-place films usually contain a higher proportion of corrosion-inhibiting hexavalent chromium than do reactive chromate and electrolytic chromate films, dry-in-place chromate films can provide a higher corrosion resistance than the other two types at the same add-on weight.
However, the corrosion-inhibiting hexavalent chromium is soluble in the water in wet corrosive ambients, and as a result one drawback to dry-in-place chromate films is that they are generally more soluble in water than reactive or electrolytic chromate films. The main component exhibiting water solubility in dry-in-place chromate films is the hexavalent chromium ions, and films exhibiting a high water solubility of this type are denoted below as "low-fixed-chromium" films. As is well known, the hexavalent chromium ions is a pollutant, and this fact has generally created demand for a sparingly water soluble dry-in-place chromate film having a high proportion of fixed or immobilized chromium.
In addition to the problem of environmental pollution, the low proportion of fixed chromium in dry-in-place chromate films creates other problems for industrial application. One such problem is that the hexavalent chromium is eluted by alkaline degreasing processes. A degreasing step is generally required during the conversion of dry-in-place chromated metal stock into finished product in downstream channels in order to remove contaminants, such as oil, dust, iron powder, and the like, that have been picked up during various stages and of course during press forming. Since traditional solvent degreasing is in the course of being discontinued due to global environmental issues, waterborne degreasing, such as alkaline degreasing, normally must be employed for this purpose. The elution of a portion of the dry-in-place chromate film by alkaline degreasing requires the installation of
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Mizuno Kensuke
Oue Takashi
Harper Stephen D.
Henkel Corporation
Jaeschke Wayne C.
Oltmans Aldrew L.
Sheehan John
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