[Technical Field]
[0001]
The present invention relates to a Zn-based plated steel sheet.
Priority is claimed on Japanese Patent Application No. 2020-176149, filed on
October 20, 2020, the content of which is incorporated herein by reference.
[Background Art]
[0002]
There are Zn-based plated steel sheets as plated steel sheets that are much used
and have favorable corrosion resistance. Zn-based plated steel sheets are used in
various manufacturing industries such as automobiles, home appliances, and building
materials. Among these, the use of Al-added plating has been increasing in recent years
15 because of its high corrosion resistance.
[0003]
As an example of a Zn-based plated steel sheet developed for the purpose of
improving corrosion resistance, Patent Document 1 discloses a hot-dip Zn-Al-Mg-Siplated
steel sheet. Since this plated steel sheet has a pear skin-like appearance, it has
20 excellent external beautifulness.
[0004]
Incidentally, conventionally, chromate treatment using hexavalent chromate or
the like is widely performed after plating in order to impart a further advanced anti-rust
function to Zn-based plated steel sheets. Furthermore, in order to impart high-value-
25 added functions such as designability, stain resistance, and lubricity, coating with an
1
organic resin has been carried out as necessary. However, due to the background of
increasing environmental problems, there is a movement to refrain from using chromate
treatment. Therefore, there is a surface-treated plated steel sheet disclosed in Patent
Document 2 below for the purpose of easily imparting an advanced anti-rust function
5 with only a single-layer treatment with a resin-based film without performing chromate
treatment.
[0005]
By using the film disclosed in Patent Document 2, it is possible to further
improve the corrosion resistance. However, Zn-based plated steel sheets containing Al
10 have a problem that, when stored for a long period of time, the plated surface partially or
wholly turns black due to oxidation of Al contained in the plated layer.
[Citation List]
[Patent Documents]
[0006]
15 [Patent Document 1]
Japanese Patent No. 3179446
[Patent Document 2]
Japanese Unexamined Patent Application, First Publication No. 2006-52462
[Summary of the Invention]
20 [Problems to be Solved by the Invention]
[0007]
The present invention has been made from the viewpoint of the above-described
circumstances, and an object of the present invention is to provide a Zn-based plated steel
sheet which contains Al and has improved corrosion resistance and weather resistance
2
5
10
and in which, even if a plated surface partially or wholly turns black, the blackening is
inconspicuous and the metallic appearance can be maintained.
[Means for Solving the Problem]
[0008]
In order to solve the above-described problem, the present inventors have
conducted extensive studies and found that by incorporating a pigment into a chemical
conversion treatment layer, the black discoloration on the surface of the plated layer is
made less noticeable and the metallic appearance of the surface of the plated layer is not
impaired. The present invention employs the following configuration.
[0009]
[1] A Zn-based plated steel sheet including: a steel sheet; a Zn-based plated layer
which contains Zn and 0.05 to 60 mass% of Aland is placed on at least one surface of the
steel sheet; and a chromate-free chemical conversion treatment layer which has a
deposition amount of 0.1 to 15 g/m2 per surface and is placed on the Zn-based plated
15 layer, in which the chemical conversion treatment layer contains 20 mass% or more of a
resin, 1 to 20 mass% of silica particles having an average particle diameter of 5 to 200
nm, a pigment containing one or more of Cu, Co, or Fe, b * of an appearance of the Znbased
plated steel sheet evaluated in a CIE 1976 (L*, a*, b*) color space is -30 to -2, a 60-
degree mirror surface glossiness Gs (60°) specified in JIS Z 8741:1997 is 50 to 200, and
20 the Zn-based plated steel sheet exhibits a metallic appearance.
[2] The Zn-based plated steel sheet according to [1], in which the pigment is any
one or more of copper(II) phthalocyanine, cobalt(II) phthalocyanine, copper sulfate,
cobalt sulfate, iron sulfate, and iron oxide.
[3] The Zn-based plated steel sheet according to [1] or [2], in which
25 [Si]/([Cu]+[Co]+[Fe]) is within a range of 1 to 200 as a mixing ratio between the silica
3
5
particles and the pigment in the chemical conversion treatment layer in a case where an
equivalent amount of Si in the silica particles is represented by [Si] and equivalent
amounts of Cu, Co, and Fe in the pigment are respectively represented by [Cu], [Co], and
[Fe].
[ 4] The Zn-based plated steel sheet according to any one of [1] to [3], in which
an arithmetic average roughness Ra of the Zn-based plated layer is 0.5 to 2.0 J.lm and an
arithmetic average height Sa of the chemical conversion treatment layer is 5 nm to 100
nm.
[5] The Zn-based plated steel sheet according to any one of [1] to [ 4], in which
10 the chemical conversion treatment layer further contains either one or both of an Nb
compound and a phosphoric acid compound.
[6] The Zn-based plated steel sheet according to any one of [1] to [5], in which
the resin in the chemical conversion treatment layer includes any one or more of a
polyolefin resin, a fluororesin, an acrylic resin, a urethane resin, a polyester resin, an
15 epoxy resin, and a phenol resin.
[7] The Zn-based plated steel sheet according to any one of [1] to [6], in which
the Zn-based plated layer contains 4 mass% to 22 mass% of Al, 1 mass% to 10 mass% of
Mg, and the balance being Zn and impurities in an average composition.
[8] The Zn-based plated steel sheet according to any one of [1] to [7], in which
20 the Zn-based plated layer further contains 0.0001 to 2 mass% of Si in an average
composition.
[9] The Zn-based plated steel sheet according to any one of [1] to [8], in which
the Zn-based plated layer further contains one or more of Ni, Sb, and Pb in a total of
0.0001 to 2 mass% in an average composition.
4
[10] The Zn-based plated steel sheet according to any one of [1] to [9], in which
a non-pattern portion and a pattern portion placed to have a predetermined shape are
formed on the Zn-based plated layer, the pattern portion and the non-pattern portion each
contain one or two of a first region and a second region determined by any of
5 determination methods 1 to 5 below, and an absolute value of a difference between an
area proportion of the first region in the pattern portion and an area proportion of the first
region in the non-pattern portion is 30% or more.
(Determination method 1)
Virtual grid lines are drawn on a surface of the Zn-based plated layer at intervals
10 of 0.5 mm, a circle with a diameter of 0.5 mm centered at a centroid point of each region
partitioned by the virtual grid lines is defined as a measurement region A, and an L *value
in each measurement region A is measured. When arbitrary 50 points are selected
from the obtained L *-values and an average of the obtained L *-values at the 50 points is
defined as a standard L* -value, a region in which the L* -value is equal to or more than
15 the standard L *-value is defined as a first region and a region in which the L *-value is less
than the standard L* -value is defined as a second region.
(Determination method 2)
Virtual grid lines are drawn on a surface of the Zn-based plated layer at intervals
of 0.5 mm, a circle with a diameter of 0.5 mm centered at a centroid point of each region
20 partitioned by the virtual grid lines is defined as a measurement region A, an L* -value in
each measurement region A is measured, a region in which the L* -value is 45 or more is
defined as a first region, and a region in which the L* -value is less than 45 is defined as a
second region.
(Determination method 3)
5
Virtual grid lines are drawn on a surface of the Zn-based plated layer at intervals
of 0.5 mm, and an arithmetic average height Sa2 is measured in each of a plurality of
regions partitioned by the virtual grid lines. A region in which the obtained arithmetic
average height Sa2 is 1 J.lm or more is defined as a first region, and a region in which the
5 obtained arithmetic average height Sa2 is less than 1 J.lm is defined as a second region.
(Determination method 4)
Virtual grid lines are drawn on a surface of the Zn-based plated layer at intervals
of 1 mm or 10 mm, a diffraction peak intensity Ioo02 of a plane (0002) of a Zn phase and a
diffraction peak intensity I10-11 of a plane (1 0-11) of the Zn phase are measured for each
10 region through an X-ray diffraction method in which X-rays are respectively made to be
incident on the plurality of regions partitioned by the virtual grid lines, and a proportion
of these intensities (Ioo02II10-11) is defined as an orientation rate. A region in which the
orientation rate is 3.5 or more is defined as a first region, and a region in which the
orientation rate is less than 3.5 is defined as a second region.