Metal treatment – Process of modifying or maintaining internal physical... – Processes of coating utilizing a reactive composition which...
Patent
1996-11-08
1998-08-18
Simmons, David A.
Metal treatment
Process of modifying or maintaining internal physical...
Processes of coating utilizing a reactive composition which...
148255, C23C 2207
Patent
active
057954070
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
1. Field of the Invention
This invention concerns a method of pre-treating aluminum materials prior to painting which imparts superior paint film adhesion and corrosion resistance to aluminum and aluminum alloys that contain at least 45 % by weight of alumin- um, these alloys and pure aluminum being referred to hereinafter collectively as "aluminum material", for example, in the form of sheets and die-castings.
2. Statement of Related Art
At the present time, zinc phosphate based conversion coatings and chro- mate treatments are generally being used as means of improving the paint film performance on aluminum materials after painting. From among these treat- ments, the zinc phosphate based conversion coatings are superior, with respect to less need for effluent treatment to avoid adverse environmental impacts, to the chromate treatments, which involve harmful hexavalent chromium. There is a further advantage for phosphate over chromate treatments in that aluminum materials can be treated together at the same time as other metals, such as cold rolled steel and zinc based coated steel sheets for example, so that these con- version coatings have been widely used as pre-treatments prior to painting auto- mobile bodies and domestic electrical appliances.
In the past it has been more difficult to form a uniform zinc phosphate based conversion coating continuously with aluminum materials than with other metal substrates, such as iron and steel sheets and zinc plated steel sheets for example. However, at the present time, methods in which aluminum ions are re- moved from the system as a precipitate by adding specified additives to the treatment liquid (cf. Japanese patent Kokai H2-277781) and methods in which uniform etching is carried out and the uniformity of the phosphate film is ensured by controlling the fluoride concentration in the treatment liquid (cf. Japanese patent Kokai 63-157879), for example, have been developed, and it has become possible to form a uniform zinc phosphate based conversion coating continu- ously.
However, while providing good corrosion resistance with uniform film formation, zinc phosphate based conversion coatings sometimes do not achieve a satisfactory performance with respect to adhesion of the paint film, especially the secondary adhesion, where it is assumed that moisture will have been absorbed (referred to hereinafter as the "water resisting secondary adhesion"), when exposed to the natural environment for a prolonged period. Thus, the development of a method of pre-treating aluminum materials prior to painting which satisfies the requirements of corrosion resistance after painting and water resisting secondary adhesion at the same time is required.
PROBLEMS TO BE SOLVED BY THE INVENTION
This present invention is for solving problems such as those noted above in connection with the prior art, and, in practical terms, it is intended to provide a method of pre-treating aluminum materials prior to painting which can impart superior corrosion resistance and water resisting secondary adhesion to aluminum materials after painting.
SUMMARY OF THE INVENTION
The inventors have discovered that: (1) a conversion coating which has been formed by a dipping treatment exhibits better painting performance than one obtained using a spray treatment; (2) the corrosion resistance after painting increases as the film weight is increased; (3) it is necessary to increase the fluorine component concentration in the treatment liquid to a specified concentration in order to obtain a satisfactory film weight; (4) in those cases where an aluminum material is treated with a zinc phosphate conversion coating composition which contains a fluorine component, a compound that contains fluorine, along with the zinc phosphate which is the main component of the conversion coating, is precipitated, this compound being referred to below as a fluoride based coprecipitate, and the water resisting secondary adhesion of the paint film is worsened; and (5) the amount of fluoride based co-precipitate wh
REFERENCES:
patent: 4292096 (1981-09-01), Murakami
patent: 4849031 (1989-07-01), Hauffe et al.
patent: 5200000 (1993-04-01), Yamamoto et al.
patent: 5308413 (1994-05-01), Sobata
Ishii Hiroshi
Kamio Hiroshi
Henkel Corporation
Jaeschke Wayne C.
Koehler Robert R.
Robbins Frank E.
Simmons David A.
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