As a countermeasure to corrosion of ferrous metal materials, much use has been made of zinc-rich paints made using a zinc powder containing unavoidable impurities as a pigment and organic materials and/or inorganic materials as a vehicle (liquid binder ingredient).
Zinc-rich paints are mainly used as primers for heavy duty corrosion protection paint. The corrosion protection mechanism features the sacrificial corrosion protection of the zinc powder contained in a coat.
Further, the corrosion protection of a coat of a zinc-rich paint is strongly dependent on the extent of the sacrificial corrosion protection of the zinc powder, so depending on the usage environment, the rate of consumption of the zinc sometimes becomes larger and the corrosion protection on the ferrous metal material will not last long.
Therefore, in the past, the practice has been to increase the content of the zinc powder in the coat or increase the coat thickness, but as a result a drop in the adhesion with the surface of the steel material, cracking or sagging of the coat, etc. easily occur.
In the end, it is difficult to realize both the corrosion protection performance of the coat and the physical properties or coating ability. Measures increasing the content of the zinc powder in the coat are not perfect.
In view of this situation, development of a high performance zinc-rich paint able to maintain the advantages of conventional zinc-rich paints and furthermore exhibit a sacrificial corrosion protection over a long period of time has been hoped for. Up until now, various proposals have been made.
For example, Japanese Patent Publication (A) No. 59-52645 and Japanese Patent Publication (A) No. 59-167249 propose an organic-based zinc-rich paint containing not only a zinc powder, but also a Zn—Mg alloy powder, while Japanese Patent Publication (A) No. 59-198142 proposes an organic-based zinc-rich paint containing not only a zinc powder, but also a Zn—Mg alloy powder and Mn powder.
Furthermore, Japanese Patent Publication (A) No. 1-311178 discloses the long lasting corrosion protection performance of a Zn-(5 to 15%)Mg alloy powder in an organic paint, while Japanese Patent Publication (A) No. 2-73932 discloses the long lasting corrosion protection performance of an organic coat containing an Zn—Mg alloy powder with a metal structure comprised of Zn and MgZn2.
Further, Japanese Patent Publication (A) No. 11-343422 proposes a rust protection pigment for an organic-based corrosion resistant paint containing flake-shaped particles of Zn alloy containing Al, Mg, etc.
In addition to the above, Japanese Patent Publication (A) No. 2001-164194 proposes an organic-based zinc-rich paint obtained by crushing an ingot of Zn—Al—Mg-based alloy powder where over 50% of the alloy powder is an Al/Zn/Zn2Mg eutectic structure, while Japanese Patent Publication (A) No. 2005-314501 proposes an organic-based paint for improving the corrosion resistance of cut parts of a high corrosion resistance galvannealed steel material containing a powder of a Zn—Al alloy containing Mg or Si, having a spherical or oval shape, and having a value of the ratio of maximum size and minimum size (maximum size/minimum size) of 1 to 1.5.
The above proposals try to improve the corrosion protection performance of an organic-based paint and the corrosion resistance by the combination of a new alloy powder.
However, a general organic-based paint has the secondary problems of deteriorating in a composite environment of UV rays, moisture, oxygen, etc. and requiring maintenance in relatively short cycles.
In such a situation, several proposals have been made up to now for the purpose of improving the corrosion protection performance of inorganic-based paints not having such defects of organic-based paints.
For example, while different in object from the present invention, Japanese Patent Publication (A) No. 61-213270 proposes a paint composition containing a mixture of a zinc powder and Mg or Mg alloy for the purpose of inhibiting paint deterioration at the time of welding and cutting.
On the other hand, Japanese Patent Publication (A) No. 2000-80309 proposes a corrosion resistant paint having three types of phases, a Zn phase, Zn—Mg alloy phase, and Zn and Mg solid solution phase, as main ingredients and having these mixed in inorganic-based paint as powder particles and a corrosion resistant ferrous metal material coated with this paint.
The proposal of Japanese Patent Publication (A) No. 2000-80309 is noteworthy as being a fundamental means for improving corrosion resistance, but according to studies of the inventors, there are actually both cases where the corrosion resistance is improved and cases where the improvement in the corrosion resistance is not clear. There are questions as to the stability of the effect of improvement of the corrosion resistance.
Further, Japanese Patent Publication (A) No. 2002-285102 and Japanese Patent Publication (A) No. 2005-336431 propose an inorganic-based corrosion resistant paint containing flake-shaped particles of a Zn alloy containing Mg etc. and a corrosion resistant ferrous metal material coated with that paint.
However, including the proposal of Japanese Patent Publication (A) No. 11-343422, in the above proposals, the particles have flake shapes, so the new problem is caused that spray coating is difficult.