U.S. patent application number 16/629146 was filed with the patent office on 2020-04-30 for treatment method using zinc phosphate-free treatment agent that includes cationic urethane resin, and treated automobile compone.
The applicant listed for this patent is NIPPON PAINT SURF CHEMICALS CO., LTD. TOYOTA JIDOSHA KABUSHIKI KAISHA. Invention is credited to Hiroshi HOSONO, Masato KISHI, Takayuki UENO.
Application Number | 20200131642 16/629146 |
Document ID | / |
Family ID | 65002066 |
Filed Date | 2020-04-30 |
United States Patent
Application |
20200131642 |
Kind Code |
A1 |
KISHI; Masato ; et
al. |
April 30, 2020 |
TREATMENT METHOD USING ZINC PHOSPHATE-FREE TREATMENT AGENT THAT
INCLUDES CATIONIC URETHANE RESIN, AND TREATED AUTOMOBILE
COMPONENT
Abstract
Provided is a coating pre-treatment method that does not limit
the coating method, has a small impact on the environment, and can
ensure good post-coating corrosion resistance in a hot-rolled steel
sheet. A coating pre-treatment method in which a hot-rolled steel
sheet is treated with a chemical conversion treatment agent to form
a chemical conversion coating film, wherein the chemical conversion
treatment agent includes at least one type (A) of element selected
from the group consisting of zirconium, titanium, and hafnium, at
least one type (B) of substance selected from the group consisting
of amino group-including silane coupling agents, hydrolysates
thereof, and polymers thereof, fluorine (C), and a cationic
urethane resin (D), and the content of (A) is 20-600 mass ppm in
total in terms of metals, and the pH is 3.5-5.5.
Inventors: |
KISHI; Masato; (TOKYO,
JP) ; UENO; Takayuki; (TOKYO, JP) ; HOSONO;
Hiroshi; (AICHI, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
NIPPON PAINT SURF CHEMICALS CO., LTD.
TOYOTA JIDOSHA KABUSHIKI KAISHA |
TOKYO
AICHI |
|
JP
JP |
|
|
Family ID: |
65002066 |
Appl. No.: |
16/629146 |
Filed: |
July 12, 2018 |
PCT Filed: |
July 12, 2018 |
PCT NO: |
PCT/JP2018/026326 |
371 Date: |
January 7, 2020 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C23C 22/34 20130101;
B32B 15/095 20130101 |
International
Class: |
C23C 22/34 20060101
C23C022/34 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 13, 2017 |
JP |
2017-137373 |
Claims
1. A pre-coating treatment method, comprising: treating a
hot-rolled steel sheet with a chemical conversion treatment agent
to form a chemical conversion film, wherein the chemical conversion
treatment agent includes at least one (A) selected from the group
consisting of zirconium, titanium, and hafnium, at least one (B)
selected from the group consisting of an amino group-containing
silane coupling agent, hydrolysates thereof, and polymers thereof,
fluorine (C), and a cationic urethane resin (D), and wherein the
total content of (A) is 20 to 600 ppm by mass in terms of metal,
and pH is 3.5 to 5.5.
2. The pre-coating treatment method according to claim 1, wherein
the total content of (B) is 5 to 1000 ppm by mass in terms of a
solid content concentration, the content of (D) is 5 to 1000 ppm by
mass in terms of a solid content concentration, and the solid
content mass ratio ((B)/(D)) of (B) to (D) is 0.005 to 200.
3. The pre-coating treatment method according to claim 1, wherein
the chemical conversion treatment agent further includes at least
one adhesiveness and corrosion resistance-conferring agent selected
from the group consisting of magnesium ions, zinc ions, calcium
ions, aluminum ions, gallium ions, indium ions, and copper
ions.
4. A hot-rolled steel sheet treated with the pre-coating treatment
method according to claim 1.
Description
TECHNICAL FIELD
[0001] The present invention relates to a pre-coating treatment
method and a hot-rolled steel sheet.
BACKGROUND ART
[0002] Chemical conversion treatment is usually performed for the
purpose of improving properties such as corrosion resistance and
coating adhesiveness when a surface of a metal material is
subjected to cation electrodeposition coating, powder coating, or
the like. Chromate treatment is commonly used for chemical
conversion in view of its capability of further improving adhesion
and corrosion resistance of a coated film. In recent years, the
hazardous properties of chromium, however, have been noted, and
thus there have been demands for developing a chemical conversion
treatment agent which does not contain chromium. As such chemical
conversion, widely performed is zinc phosphate treatment.
[0003] However, zinc phosphate-based treatment agents contain high
concentrations of metal ions and acids, and are highly reactive.
This may result in poor waste-treatment economy and poor
workability. Further, when a metal surface is treated with a zinc
phosphate-based treatment agent, water-insoluble salts may be
generated and deposited as precipitates. These precipitates are
generally referred to sludge. The removal and disposal of such
sludge may add undesirable costs and other problems. Further,
phosphate ions may be responsible for increased environmental
burden due to eutrophication, and may require additional efforts
for waste treatment. Therefore, use of phosphate ions is preferably
avoided. Moreover, the treatment of a metal surface with a zinc
phosphate-based treatment agent requires surface conditioning.
This, disadvantageously, may result in a prolonged process.
[0004] As metal-surface treatment agent other than such a zinc
phosphate-based treatment agent or a chromate chemical conversion
treatment agent, known is a metal-surface treatment agent including
a zirconium compound. Such a metal-surface treatment agent
including a zirconium compound has a superior property as compared
with a zinc phosphate-based chemical conversion treatment agent as
described above in that the generation of sludge can be
prevented.
[0005] Unfortunately, a chemical conversion film obtained by a
metal-surface treatment agent including a zirconium compound shows
poor adhesiveness, in particular with a coated film obtained by
cation electrodeposition coating, and is less often used as a
pre-treatment step of cation electrodeposition coating. In such a
metal-surface treatment agent including a zirconium compound, a
component such as phosphate ions may be used in combination for
improving adhesiveness and corrosion resistance. However, when
phosphate ions are used in combination, the aforementioned problems
such as eutrophication may occur. Moreover, an iron-based base
material treated with such a metal-surface treatment agent may have
a problem in that neither sufficient coating adhesiveness nor
post-coating corrosion resistance can be obtained.
[0006] A non-chromate metal-surface treatment agent is also known
which includes a zirconium compound and an amino group-containing
silane coupling agent. However, surface treatment with such a
non-chromate metal-surface treatment agent as an application-type
treatment agent used in the field of so-called coil coating is not
comparable with post-treatment water-washing. Further, such a
non-chromate metal-surface treatment agent is not intended for a
target workpiece having a complicated shape.
[0007] Furthermore, for an article, such as an automobile body and
parts, composed of a metal material such as iron, zinc, and
aluminum, the entire metal surface may need to be treated in a
single treatment. Accordingly, a pre-coating treatment method is
desired to be developed, by which chemical conversion can be
performed without causing any problem even in such a case.
Meanwhile, a pre-coating treatment method is also desired to be
developed, by which chemical conversion can be performed without
causing the aforementioned problems even in coating other than
cation electrodeposition coating using a powder coating material, a
solvent coating material, a water-based paint, and the like.
[0008] In an attempt to solve the above problems, a pre-coating
treatment method is known, the method involving treating a target
workpiece with a chemical conversion treatment agent including at
least one selected from the group consisting of zirconium,
titanium, and hafnium; fluorine; and at least one selected from the
group consisting of an amino group-containing silane coupling
agent, hydrolysates thereof, polymers thereof to form a chemical
conversion film (for example, see Patent Document 1 below).
[0009] The above pre-coating treatment method is compatible with
any common coating methods, and can provide similar adhesiveness
and post-coating corrosion resistance as a case where a zinc
phosphate-based chemical conversion treatment agent is used.
Nonetheless, it has been difficult to obtain sufficient
post-coating corrosion resistance when applied to a hot-rolled
steel sheet having a surface on which an oxide film is formed. Such
a hot-rolled steel sheet is used in suspension related parts of
automobiles and the like.
[0010] Patent Document 1: Japanese Unexamined Patent Application,
Publication No. 2004-218070
DISCLOSURE OF THE INVENTION
Problems to be Solved by the Invention
[0011] The present invention is made in view of the above
circumstances. An object of the present invention is to provide a
pre-coating treatment method which may cause less environmental
burden, and can ensure good post-coating corrosion resistance for
hot-rolled steel sheets.
Means for Solving the Problems
[0012] The present invention relates to a pre-coating treatment
method, including: treating a hot-rolled steel sheet with a
chemical conversion treatment agent to form a chemical conversion
film, wherein the chemical conversion treatment agent includes at
least one (A) selected from the group consisting of zirconium,
titanium, and hafnium; at least one (B) selected from the group
consisting of an amino group-containing silane coupling agent,
hydrolysates thereof, and polymers thereof; fluorine (C); a
cationic urethane resin (D), and the total content of (A) is 20 to
600 ppm by mass in terms of metal, and pH is 3.5 to 5.5.
[0013] Further, it is preferred that a total of 5 to 1000 ppm by
mass of (B) in terms of the solid content concentration is
included, and 5 to 1000 ppm by mass of (D) in terms of the solid
content concentration is included, and the solid content mass ratio
((B)/(D)) of (B) to (D) is 0.005 to 200.
[0014] Moreover, it is preferred that the above chemical conversion
treatment agent further contains at least one adhesiveness and
corrosion resistance-conferring agent selected from the group
consisting of magnesium ions, zinc ions, calcium ions, aluminum
ions, gallium ions, indium ions, and copper ions.
[0015] The present invention also relates to a hot-rolled steel
sheet treated by the above pre-coating treatment method.
Effects of the Invention
[0016] The present invention can provide a pre-coating treatment
method which is compatible with any common coating method, and may
cause less environmental burden, and can ensure good post-coating
corrosion resistance for hot-rolled steel sheets.
PREFERRED MODE FOR CARRYING OUT THE INVENTION
[0017] Below, the embodiments of the present invention will be
described. It is noted that the present invention shall not be
limited to the following embodiments.
[0018] The pre-coating treatment method according to the present
embodiment can form a chemical conversion film on a surface of a
hot-rolled steel plate as a target workpiece (hereinafter referred
to as a "hot-rolled steel sheet") to ensure preferred post-coating
corrosion resistance. There is no particular limitation for a
hot-rolled steel sheet as a target workpiece, and a wide spectrum
of materials from common hot-rolled steel sheets to specialty steel
can be treated. These treated hot-rolled steel sheets are widely
used as suspension related parts of automobiles and the like. An
oxide film is formed on a surface of a hot-rolled steel sheet as
described below, and thus formation of a uniform chemical
conversion film on that surface may be difficult. Nonetheless, the
pre-coating treatment method according to the present embodiment
can form a uniform chemical conversion film on a surface of a
hot-rolled steel sheet. Consequently, this can ensure good
post-coating corrosion resistance of the treated hot-rolled steel
sheet.
[0019] The pre-coating treatment method according to the present
embodiment is a method of treating a hot-rolled steel sheet, the
method including forming a chemical conversion film on a surface of
the hot-rolled steel sheet with a chemical conversion treatment
agent. The chemical conversion treatment agent according to the
present embodiment includes at least one (A) selected from the
group consisting of zirconium, titanium, and hafnium; at least one
(B) selected from the group consisting of an amino group-containing
silane coupling agent, hydrolysates thereof, and polymers thereof;
fluorine (C); and a cationic urethane resin (D). The chemical
conversion treatment agent according to the present embodiment is
substantially free of phosphate ions and hazardous heavy metal
ions, but can form a chemical conversion film having sufficient
post-coating corrosion resistance even on a surface of a hot-rolled
steel sheet.
[0020] The at least one (A) selected from the group consisting of
zirconium, titanium, and hafnium corresponds to a component for
forming a chemical conversion film. Formation of a chemical
conversion film including at least one selected from the group
consisting of zirconium, titanium, and hafnium on a base material
can improve corrosion resistance and abrasion resistance of the
base material, and further can enhance adhesiveness with a coated
film.
[0021] For example, when a hot-rolled steel sheet is surface
treated with a chemical conversion treatment agent containing
zirconium, iron ions which are eluted into the chemical conversion
treatment agent due to a dissolution reaction of metal may extract
fluorine from ZrF.sub.6.sup.2-, or an interface pH may be
increased. These may result in generation of hydroxides or oxides
of zirconium. These hydroxides or oxides of zirconium are thought
to be deposited on a surface of a base material. As described
above, the chemical conversion treatment agent according to the
present embodiment, which is a reactive chemical conversion
treatment agent, can be used even for dipping treatment of a
hot-rolled steel sheet having a complicated shape. Moreover,
surface treatment performed with the above chemical conversion
treatment agent can produce a chemical conversion film adhering
firmly on a hot-rolled steel sheet by virtue of a chemical
reaction. This also can allow post-treatment water-washing to be
performed.
[0022] There is no particular limitation for a source of the above
zirconium, but examples of the source include, for example, alkali
metal fluorozirconate such as K.sub.2ZrF.sub.6; fluorozirconate
such as (NH.sub.4).sub.2ZrF.sub.6; soluble fluorozirconate such as
fluorozirconate acid such as H.sub.2ZrF.sub.6; zirconium fluoride;
zirconium oxide; and the like.
[0023] There is no particular limitation for a source of the above
titanium, but examples of the source include, for example,
fluorotitanate such as alkali metal fluorotitanate,
(NH.sub.4).sub.2TiF.sub.6; soluble fluorotitanate such as
fluorotitanate acid such as H.sub.2TiF.sub.6; titanium fluoride;
titanium oxide; and the like.
[0024] There is no particular limitation for a source of the above
hafnium, but examples of the source include, for example,
fluorohafnate acid such as H.sub.2HfF.sub.6; hafnium fluoride; and
the like. A source of the at least one selected from the group
consisting of zirconium, titanium, and hafnium is preferably a
compound having at least one selected from the group consisting of
ZrF.sub.6.sup.2-, TiF.sub.6.sup.2-, and HfF.sub.6.sup.2- in view of
high film-forming capability.
[0025] The total content of the at least one selected from the
group consisting of zirconium, titanium, and hafnium included in
the chemical conversion treatment agent according to the present
embodiment is within a range between a lower limit of 20 ppm by
mass and an upper limit of 600 ppm by mass in terms of metal. When
the amount is less than 20 ppm by mass, the resulting chemical
conversion film may have insufficient performance. On the other
hand an amount of more than 600 ppm by mass can not provide
additional effects, and is thus economically disadvantageous. The
above lower limit is more preferably 100 ppm by mass. The above
upper limit is more preferably 500 ppm by mass, and even more
preferably 300 ppm by mass.
[0026] The at least one (B) selected from the group consisting of
an amino group-containing silane coupling agent, hydrolysates
thereof, and polymers thereof is a compound having at least one
amino group in a molecule thereof and also having a siloxane bond.
The above at least one (B) selected from the group consisting of an
amino group-containing silane coupling agent, hydrolysates thereof,
and polymers thereof can interact with both a chemical conversion
film and a coated film. This can improve adhesiveness between
them.
[0027] This effect can be obtained presumably because a group which
can undergo hydrolysis to produce silanol is hydrolyzed and
adsorbed on a surface of a metal base material via hydrogen bond,
and an amino group can act to enhance adhesiveness between a
chemical conversion film and a metal base material. As described
above, the at least one (B) selected from the group consisting of
an amino group-containing silane coupling agent, hydrolysates
thereof, and polymers thereof is thought to act on both a metal
base material and a coated film to show an effect of improving
mutual adhesiveness.
[0028] There is no particular limitation for the above amino
group-containing silane coupling agent, but examples thereof can
include, for example, publicly known silane coupling agents such as
N-2(aminoethyl)3-aminopropylmethyldimethoxysilane,
N-2(aminoethyl)3-aminopropyltrimethoxysilane,
N-2(aminoethyl)3-aminopropyltriethoxysilane,
3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane,
3-triethoxysilyl-N-(1,3-dimethyl-butylidene)propylamine,
N-phenyl-3-aminopropyltrimethoxysilane,
N,N-bis[(3-(trimethoxysilyl)propyl)]ethylenediamine, and the like.
Commercially available amino group-containing silane coupling
agents KBM-602, KBM-603, KBE-603, KBM-903, KBE-9103, KBM-573
(Shin-Etsu Chemical Co., Ltd.), XS1003 (Chisso Corp.), and the like
may also be used.
[0029] Hydrolysates of the above amino group-containing silane
coupling agent can be prepared by conventionally known methods, for
example, by a method including dissolving the above amino
group-containing silane coupling agent in ion-exchanged water, and
adjusting it to be acidic with any acid, and the like. As a
hydrolysate of the above amino group-containing silane coupling
agent, a commercially available product such as KBP-90 (Shin-Etsu
Chemical Co., Ltd., Active ingredient: 32%) may also be used.
[0030] There is no particular limitation for a polymer of the above
amino group-containing silane coupling agent, but examples thereof
can include, for example, commercially available products such as
Sila-Ace S-330 (.gamma.-aminopropyltriethoxysilane; Chisso Corp.),
Sila-Ace S-320 (N-(2-aminoethyl)-3-aminopropyltrimethoxysilane;
Chisso Corp.).
[0031] The total blending amount of the at least one (B) selected
from the group consisting of an amino group-containing silane
coupling agent, hydrolysates thereof, and polymers thereof in the
chemical conversion treatment agent according to the present
embodiment is preferably within a range between a lower limit of 5
ppm by mass and an upper limit of 1000 ppm by mass in terms of the
solid content concentration. An amount of less than 5 ppm by mass
can not provide sufficient coating adhesiveness. An amount of more
than 1000 ppm by mass can not provide additional effects, and is
thus economically disadvantageous. The above lower limit is more
preferably 100 ppm by mass, and even more preferably 200 ppm by
mass. The above upper limit is more preferably 400 ppm by
masses.
[0032] Fluorine (C) can serve as an etching agent for a base
material. There is no particular limitation for a source of
fluorine (C), but examples of the source can include, for example,
fluorides such as hydrofluoric acid, ammonium fluoride, fluoroboric
acid, ammonium hydrogen fluoride, sodium fluoride, and sodium
hydrogenfluoride. Further, complex fluorides include, for example,
hexafluorosilicate, and specific examples thereof can include
hydrosilicofluoric acid, zinc hydrofluorosilicate, manganese
hydrofluorosilicate, magnesium hydrofluorosilicate, nickel
hydrofluorosilicate, iron hydrofluorosilicate, calcium
hydrofluorosilicate, and the like.
[0033] The cationic urethane resin (D) will form a uniform chemical
conversion film on a surface of a hot-rolled steel sheet as a
target workpiece. The cationic urethane resin (D) has a cationic
functional group. Cationic functional groups include, for example,
an amino group, an ammonium group, a methylamino group, an
ethylamino group, a dimethylamino group, a diethylamino group, a
trimethylamino group, a triethylamino group, and the like. Among
these, prepared is a quaternary ammonium group. Moreover, there is
no particular limitation for a polyol, isocyanate components of a
urethane resin of the cationic urethane resin (D), and a method of
polymerization, but conventionally known components and methods may
be used. As the cationic urethane resin (D), the followings may be
used: for example, commercially available products such as F2667D
(DKS Co. Ltd., Effective concentration: 25%), Superflex 620 (DKS
Co. Ltd., Effective concentration: 30%), and Superflex 650 (DKS Co.
Ltd., Effective concentration: 26%).
[0034] Inclusion of the cationic urethane resin (D) alone to a
chemical conversion treatment agent can not provide preferred
effects such as post-coating corrosion resistance. However, when it
is included in a chemical conversion treatment agent in combination
with the at least one (B) selected from the group consisting of an
amino group-containing silane coupling agent, hydrolysates thereof,
and polymers thereof, a uniform chemical conversion film can be
formed on a surface of a hot-rolled steel sheet as a target
workpiece, ensuring a preferred post-coating anticorrosion
properties of the hot-rolled steel sheet. Further, the cationic
urethane resin (D) does not undergo a competing reaction with the
at least one (B) selected from the group consisting of an amino
group-containing silane coupling agent, hydrolysates thereof, and
polymers thereof, and thus may be preferably used without
inhibiting the functionality of the amino group-containing silane
coupling agent, hydrolysates thereof, and polymers thereof (B).
[0035] The blending amount of the cationic urethane resin (D) in
the chemical conversion treatment agent according to the present
embodiment is preferably within a range between a lower limit of 5
ppm by mass and an upper limit of 1000 ppm by mass in terms of the
solid content concentration. An amount of less than 5 ppm by mass
can not provide sufficient coating adhesiveness. An amount of more
than 1000 ppm by mass can not provide additional effects, and is
thus economically disadvantageous. The above lower limit is more
preferably 100 ppm by mass, and even more preferably 200 ppm by
mass. The above upper limit is more preferably 400 ppm by mass.
[0036] In the chemical conversion treatment agent according to the
present embodiment, the mass ratio ((B)/(D)) of the at least one
(B) selected from the group consisting of an amino group-containing
silane coupling agent, hydrolysates thereof, and polymers thereof
to the cationic urethane resin (D) is preferably 0.005 to 200. A
mass ratio ((B)/(D)) falling within the above range can provide
preferred corrosion resistance of a hot-rolled steel sheet having a
chemical conversion film formed thereon. The mass ratio ((B)/(D))
is more preferably 0.05 to 20, and even more preferably 0.5 to
2.
[0037] Preferably, the chemical conversion treatment agent
according to the present embodiment is substantially free of
phosphate ions. The phrase "substantially free of phosphate ions"
means that phosphate ions may be included in an amount such that
they do not function as a component of a chemical conversion
treatment agent. The chemical conversion treatment agent used in
the present embodiment is substantially free of phosphate ions.
Therefore, essentially no phosphorus is used which is potentially
responsible for increased environmental burden. Further, generation
of sludge such as iron phosphate and zinc phosphate can be
prevented, which otherwise may be generated when a zinc
phosphate-based treatment agent is used.
[0038] The chemical conversion treatment agent according to the
present embodiment has a pH falling within a range between a lower
limit of 3.5 and an upper limit of 5.5. A pH of lower than 3.5 may
result in excessive etching, and a sufficient film can not be
formed. A pH of more than 5.5 may result in insufficient etching,
and can not provide a good film. The above lower limit is
preferably 3.8, and more preferably 4.0. The above upper limit is
preferably 4.7, and more preferably 4.5. In order to adjust a pH of
the chemical conversion treatment agent according to the present
embodiment, an acidic compound such as nitric acid and sulfuric
acid and a basic compound such as sodium hydroxide, potassium
hydroxide, and ammonia may be used.
[0039] Preferably, the chemical conversion treatment agent
according to the present embodiment further includes at least one
selected from the group consisting of magnesium ions, zinc ions,
calcium ions, aluminum ions, gallium ions, indium ions, and copper
ions as an adhesiveness and corrosion resistance-conferring agent.
Inclusion of the above adhesiveness and corrosion
resistance-conferring agent can provide a chemical conversion film
having better adhesiveness and corrosion resistance.
[0040] The content of the above at least one selected from the
group consisting of magnesium ions, zinc ions, calcium ions,
aluminum ions, gallium ions, indium ions, and copper ions is
preferably within a range between a lower limit of 1 ppm by mass
and an upper limit of 5000 ppm by mass. When the above content is
less than the above lower limit, sufficient effects can not be
obtained. This is not preferred. When the above content is more
than the above upper limit, additional effects can not be obtained.
This is economically disadvantageous, and may also decrease
post-coating adhesiveness. The above lower limit is more preferably
25 ppm by mass, and the above upper limit is more preferably 3000
ppm by mass.
[0041] The above chemical conversion treatment agent may be used in
combination with any component in addition to the above components,
if needed. Components which can be used can include silica and the
like. It is possible to increase post-coating corrosion resistance
by adding such a component.
<Pre-Coating Treatment Method>
[0042] There is no particular limitation for chemical conversion in
the pre-coating treatment method according to the present
embodiment, but it may be performed by contacting a chemical
conversion treatment agent with a surface of a hot-rolled steel
sheet under common treatment conditions. The treatment temperature
upon the above chemical conversion is preferably within a range
between a lower limit of 20.degree. C. and an upper limit of
70.degree. C. The above lower limit is more preferably 30.degree.
C., and the above upper limit is more preferably 50.degree. C. The
chemical conversion time for the above chemical conversion is
preferably within a range between a lower limit of 5 seconds and an
upper limit of 1200 seconds. The above lower limit is more
preferably 30 seconds, and the above upper limit is more preferably
120 seconds. There is no particular limitation for a method of
conversion treatment, but examples thereof can include, for
example, the dipping method, the spray method, the roll coating
method, and the like.
[0043] In the pre-coating treatment method according to the present
embodiment, it is preferred that a surface of a hot-rolled steel
sheet may be subjected to degreasing treatment, post-degreasing
water-washing treatment before performing the above chemical
conversion, and subjected to post-chemical conversion
waster-washing treatment after the above chemical conversion. The
above degreasing treatment may be performed in order to remove oils
and stains adhering on a surface of a base material, and usually
performed by dipping treatment at 30 to 55.degree. C. for about
several minutes with a degreaser such as
phosphorus-free/nitrogen-free degreasing wash liquid. Preliminary
degreasing treatment may be performed, if needed, prior to
degreasing treatment.
[0044] The above post-degreasing water-washing treatment may be
conducted by performing spray treatment using a large amount of
wash water once or more times in order to wash out a degreaser with
water after degreasing treatment. The above post-chemical
conversion water-washing treatment may be performed once or more
times in order to avoid negative effects on adhesiveness, corrosion
resistance, and the like after various subsequent coatings. In that
case, the final water-washing is properly performed with pure
water. In this post-chemical conversion water-washing treatment,
water washing may be performed by either one of spray water-washing
or dip water-washing or in combination of these. After the above
post-chemical conversion water-washing treatment, drying may be
performed in accordance with a known method, if needed, and then
various coatings may be applied.
[0045] The pre-coating treatment method according to the present
embodiment does not require surface conditioning treatment which is
required in a conventionally used practical method involving
treatment with a zinc phosphate-based chemical conversion treatment
agent. This enables chemical conversion of a hot-rolled steel sheet
to be performed in fewer steps.
<Hot-Rolled Steel Sheet>
[0046] A hot-rolled steel sheet according to the present embodiment
has at least one surface on which a chemical conversion film is
formed by the pre-coating treatment method according to the present
embodiment. There is no particular limitation for the hot-rolled
steel sheet according to the present embodiment, and a wide
spectrum of materials from common hot-rolled steel sheets to
specialty steel can be treated.
[0047] A hot-rolled steel sheet may be subjected to rolling at a
temperature region of above 800.degree. C. This enables a thick
oxide film (a scale) with several .mu.m to tens of .mu.m to be
formed on a surface of the steel sheet. Such an oxide film may be
removed by performing treatment such as acid wash before use.
However, an oxide film may be again generated by heat treatment
such as quenching and tempering after processing such as pressing.
Further an oxide film itself has anticorrosion properties. In view
of these, a chemical conversion film is preferably formed on an
oxide film by chemical conversion. Such an oxide film formed on a
hot-rolled steel sheet has a fine surface unevenness, and the oxide
film is also of a porous state in which a large number of pores are
present. For this reason, it is very difficult to form a uniform
chemical conversion film on a hot-rolled steel sheet where an oxide
film is formed. An ununiform chemical conversion film formed on a
surface may cause different potentials between a coated portion and
an uncoated portion, preventing formation of a uniform
electrodeposition coated film upon electrodeposition coating.
Consequently, a pre-coating treatment method using a conventional
chemical conversion treatment agent including zirconium and others
can not ensure post-coating corrosion resistance comparable to that
in a case where a zinc phosphate-based chemical conversion
treatment agent. In contrast, a hot-rolled steel sheet treated by
the pre-coating treatment method according to the present
embodiment has a surface on which a uniform chemical conversion
film is formed. Such a hot-rolled steel sheet on which a uniform
chemical conversion film is formed has preferred post-coating
corrosion resistance.
[0048] The mechanism by which such an effect can be obtained is not
clearly understood. Nonetheless, one possibility is that the
cationic urethane resin (D) may preferentially cover depressed
portions and pores of an oxide film through the interaction between
the cationic groups of the cationic urethane resin (D) included in
a chemical conversion treatment agent and a surface of a steel
sheet.
[0049] The film content of the chemical conversion film formed on a
surface of a hot-rolled steel sheet according to the present
embodiment is preferably within a range between a lower limit of
0.1 mg/m.sup.2 and an upper limit of 500 mg/m.sup.2 in terms of the
total amount of metal included in a chemical conversion treatment
agent. An amount of less than 0.1 mg/m.sup.2 can not provide a
uniform chemical conversion film, and is thus not preferred. An
amount of more than 500 mg/m.sup.2 can not provide additional
effects, and is thus economically disadvantageous. The above lower
limit is more preferably 5 mg/m.sup.2, and the above upper limit is
more preferably 200 mg/m.sup.2.
[0050] A hot-rolled steel sheet treated by the above pre-coating
treatment method may be subjected to laser processing, press
working, and the like to obtain a metal member formed and processed
depending on various purposes. Alternatively, a pre-formed and
processed hot-rolled steel sheet may be subjected to the above
pre-coating treatment method. There is no particular limitation for
the applications of a metal member according to the present
embodiment, but examples of thereof include metal members of
automobiles such as a door, a bonnet, a roof, a hood, a fender, a
trunk room, and the like. Further, they also include metal members
used for motorcycles, buses, bicycles, and the like. A metal member
made of a hot-rolled steel sheet treated by the above pre-coating
treatment method may preferably be used in those applications as
described above in which a high level of post-coating corrosion
resistance is required in view of safely and aesthetics.
[0051] There is no particular limitation for coating which can be
performed on a hot-rolled steel sheet treated by the pre-coating
treatment method according to the present embodiment, but coating
may be performed with a conventionally known coating material such
as a cationic electrodeposition coating material, a solvent coating
material, a water-based coating material, and a powder coating
material. For example, there is no particular limitation for the
above cationic electrodeposition coating material, but a
conventionally known cationic electrodeposition coating material
including an aminated epoxy resin, aminated acrylic resin, a
sulfonated epoxy resin, and the like may be applied. Amount these,
a cationic electrodeposition coating material including a resin
having a functional group which shows reactivity or compatibility
with an amino group is preferred in order to enhance adhesiveness
between an electrodeposition coated film and a chemical conversion
film, considering that at least one selected from the group
consisting of an amino group-containing silane coupling agent,
hydrolysates thereof, and polymers thereof is blended in a chemical
conversion treatment agent.
[0052] The present invention shall not be limited to the above
embodiments. Modifications, improvements, and the like can be made
within a scope of the present invention as long as an effect of the
present invention can be achieved.
EXAMPLES
[0053] Next, the present invention will be described in more detail
with reference to Examples, but the present invention shall not be
limited to these Examples. It is noted that the term "ppm" as used
in Examples and Comparative Examples refers to "ppm by mass."
Example 1
[0054] A commercially available hot-rolled steel plate (SPH 270,
Nippon Testpanel Co., Ltd., 70 mm.times.150 mm.times.0.8 mm) as a
base material was subjected to pre-coating treatment under the
following conditions.
(1) Pre-Coating Treatment
[0055] Degreasing treatment: Dipping treatment was performed at
40.degree. C. with 2% by mass of "Surfcleaner 53" (a degreaser from
Nippon Paint Surf Chemicals Co., Ltd.). Post-degreasing
water-washing treatment: Spray treatment was performed with tap
water for 30 seconds. Chemical conversion treatment: Zircon
hydrofluoric acid and KBM-603
(N-2(aminoethyl)3-aminopropyltrimethoxysilane, Effective
concentration: 100%, Shin-Etsu Chemical Co., Ltd.) as an amino
group-containing silane coupling agent; and F2667D (DKS Co. Ltd.,
Effective concentration: 25%) as a cationic urethane resin were
used to prepare a chemical conversion treatment agent including
zirconium (A) in a concentration of 100 ppm by mass, an amino
group-containing silane coupling agent (B) in a concentration of
100 ppm by mass in terms of the solid content, and a cationic
urethane resin (D) in a concentration of 100 ppm by mass. Sodium
hydroxide was used to adjusted pH to 4. The temperature of the
chemical conversion treatment agent was adjusted to 40.degree. C.,
and a base material was dip-treated for 60 seconds. The film amount
in the initial stage of the treatment was 13.4 mg/m.sup.2.
[0056] Post-chemical conversion water-washing treatment: Spray
treatment was performed with tap water for 30 seconds. Further,
spray treatment was performed with ion-exchanged water for 10
seconds. Then, electrodeposition coating was performed in a wet
condition. A cold-rolled steel sheet after water washing was dried
at 80.degree. C. for 5 minutes in an electric drying furnace, and
then the film amount was analyzed as the total amount of metal
contained in a chemical conversion treatment agent with a "ZSX
PrimusII" (an X-ray analyzer from Rigaku Corporation).
(2) Coating
[0057] A cold-rolled steel plate was treated with a chemical
conversion treatment agent at 1 L per m.sup.2, and then
electrodeposition-coated with "Powernics 310" (a cationic
electrodeposition coating material from Nipponpaint Industrial
Coatings Co., Ltd.) so as to obtain a dry coating thickness of 20
.mu.m, and washed with water, and then heated for baking at
170.degree. C. for 20 minutes to obtain a test plate.
Examples 2 and 3
[0058] Test plates were prepared as in Example 1 except that a
hot-rolled steel plate (SPH 440, SPH 590 from Nippon testpanel Co.,
Ltd., 70 mm.times.150 mm.times.0.8 mm) was used as a base
material.
Examples 4, 5, 8, 10, 19 and 20
[0059] Test plates were prepared as in Example 1 except that the
concentrations of the silane coupling agent (B) and the cationic
urethane resin (D) were varied as shown in Table 1.
Examples 6 and 7
[0060] Test plates were prepared as in Example 1 except that
Superflex 620 (DKS Co. Ltd., Effective concentration: 30%) or
Superflex 650 (DKS Co. Ltd., Effective concentration: 26%) was used
as the cationic urethane resin (D) as shown in Table 1.
Examples 9, 11 and 12
[0061] As shown in Table 1, test plates were prepared as in Example
1 except that the concentration of zirconium (A) was 100 ppm by
mass or 500 ppm by mass, and KBM-903
(3-aminopropyltrimethoxysilane, Effective concentration: 100%,
Shin-Etsu Chemical Co., Ltd.) or XS1003
(N,N-bis[3-(trimethoxysilyl)propyl]ethylenediamine, Effective
concentration: 50%, Nichibitrading Co., Ltd.), or KBE-903
(3-aminopropyltriethoxysilane, Effective concentration: 100%,
Shin-Etsu Chemical Co., Ltd.) was used as the silane coupling agent
(B), and the concentrations of the silane coupling agent (B) and
the cationic urethane resin (D) were varied as shown in Table
1.
Examples 13 to 18
[0062] Test plates were prepared as in Example 1 except that the
concentration of zirconium (A) was varied as shown in Table 1, and
zinc nitrate (Zn) was used as an adhesiveness and
corrosion-resistance conferring agent, and the concentrations of
the silane coupling agent (B) and the cationic urethane resin (D)
were varied as shown in Table 1.
Comparative Examples 1 to 5
[0063] Test plates were prepared as in Example 1 except that the
concentrations of the silane coupling agent (B) and the cationic
urethane resin (D) were varied as shown in Table 1.
Reference Example 1
[0064] A test plate was prepared as in Example 1 except that as
shown in Table 1, surface conditioning was performed with Surffine
GL1 (Nippon Paint Surf Chemicals Co., Ltd.) at room temperature for
30 seconds after post-degreasing water-washing treatment, and then
chemical conversion treatment was performed by dipping treatment
using Surfdine SD-5350 (a zinc phosphate-based chemical conversion
treatment agent from Nippon Paint Surf Chemicals Co., Ltd.) at
35.degree. C. for 2 minutes instead of using the above chemical
conversion treatment agents.
[0065] The following evaluation tests were performed for the test
plates obtained as described above from Examples 1 to 20,
Comparative Examples 1 to 5, and Reference Example 1.
[Secondary Adhesiveness Tests (SDT)]
[0066] The resulting test plates were each nicked deep enough to
reach an underlying material along two parallel and longitudinal
lines, and then dipped under a 5% NaCl aqueous solution at
50.degree. C. for 480 hours. Subsequently, a cut portion was
exfoliated off with a tape, and the exfoliation state of a coating
material was observed. The exfoliation state was evaluated in
accordance with the following evaluation criteria, and an
evaluation score of 2 or more was considered as acceptable. The
results were shown in Tables 1 and 2.
1: Not exfoliated 2: Somewhat exfoliated 3: Exfoliation width is 3
mm or more
[Salt-Water Spray Tests (SST)]
[0067] The resulting test plates were each cross-cut deep enough to
reach an underlying material, and continuously sprayed with a 5%
NaCl aqueous solution for 240 hours in a salt-water spry test
chamber maintained at 35.degree. C. Subsequently, the width of a
blister from a cut portion was measured. Those having a blister
width comparable to or less than that in a case where a zinc
phosphate-based surface treatment agent was used as shown in
Reference Example 1 was considered as acceptable. The results were
shown in Tables 1 and 2.
[Combined Cyclic Corrosion Tests (CCT)]
[0068] The resulting test plates were each cross-cut deep enough to
reach an underlying material, and then combined cyclic corrosion
tests were performed. Combined tests were performed for 100 cycles
by a test method in accordance with JASO M609-91. After the tests,
the width of a blister from a cut portion was measured. Those
having a blister width comparable to or less than that in a case
where a zinc phosphate-based surface treatment agent was used as
shown in Reference Example 1 was considered as acceptable. The
results were shown in Tables 1 and 2.
TABLE-US-00001 TABLE 1 Adhesiveness and Cationic
corrosion-resistance Silane coupling urethane Zirconium conferring
agent agent(B) resin(D) concen- Concen- Solid content Solid content
tration(A) tration concentration concentration (ppm) Types (ppm)
Types (ppm) Types (ppm) Examples 1 100 None 0 KBM-603 100 F2667D
100 2 100 None 0 KBM-603 100 100 3 100 None 0 KBM-603 100 100 4 100
None 0 KBM-603 5 5 5 100 None 0 KBM-603 50 50 6 100 None 0 KBM-603
100 Superflex 620 100 7 100 None 0 KBM-603 100 Superflex 650 100 8
100 None 0 KBM-603 5 F2667D 1000 9 100 None 0 KBM-903 1000 5 10 100
None 0 KBM-603 1000 1000 11 500 None 0 XS-1003 100 100 12 500 None
0 KBE-903 1000 1000 13 100 None 500 KBM-603 100 100 14 20 None 500
KBM-603 400 400 15 600 None 500 KBM-603 400 400 16 200 None 500
KBM-603 400 400 17 200 None 500 KBM-603 200 400 18 200 None 500
KBM-603 400 200 19 100 None 0 KBM-603 5 100 20 100 None 0 KBM-603
100 5 Compar- 1 100 None 0 KBM-603 0 F2667D 100 ative 2 100 None 0
KBM-603 0 100 Examples 3 100 None 0 KBM-603 0 100 4 100 None 0
KBM-603 100 0 5 100 None 0 KBM-603 0 5000 Reference 1 Zinc
phosphate treatment Example Amount of Base film SST CCT ((B)/(D))
material (mg/m.sup.2) Coating SDT (mm) (mm) Examples 1 1 SPH270
17.6 Powernics 1 1.7 5.1 2 1 SPH440 21.8 310 1 2.0 7.2 3 1 SPH590
25.3 1 1.9 9.9 4 1 SPH270 22.2 2 2.2 9.2 5 1 SPH270 16.2 1 1.6 6.5
6 1 SPH270 15.9 1 2.0 7.4 7 1 SPH270 18.4 1 2.2 7.6 8 0.005 SPH270
17.4 1 1.5 5.9 9 200 SPH270 14.6 1 1.8 5.9 10 1 SPH270 11.6 1 1.6
7.0 11 1 SPH270 40.8 1 1.6 5.0 12 1 SPH270 14.2 1 1.8 6.8 13 1
SPH270 17.2 1 1.3 4.9 14 1 SPH270 11.2 1 1.9 7.1 15 1 SPH270 19.6 1
1.9 8.2 16 1 SPH270 19.7 1 1.6 4.5 17 05 SPH270 21.2 1 0.9 5.0 18 2
SPH270 20.2 1 0.9 5.0 19 0.05 SPH270 16.3 2 1.9 8.7 20 20 SPH270
17.8 1 2.2 10.2 Compar- 1 -- SFH270 26.4 Powernics 3 2.4 11.9 ative
2 -- SPH440 30.3 310 3 2.2 15.3 Examples 3 -- SPH590 34.1 3 2.5
14.2 4 -- SPH270 21.4 1 2.0 13.5 5 -- SPH270 22.1 3 2.0 14.3
Reference 1 Zinc phosphate treatment SPH270 2500 2 2.5 11.3
Example
[0069] Comparison of Examples 1 to 20 with Comparative Examples 1
to 3 and 5 shows that the hot-rolled steel sheets treated with the
chemical conversion treatment agents from Examples 1 to 20 have
superior secondary adhesiveness (SDT) as compared with the
hot-rolled steel sheets treated with the chemical conversion
treatment agents from Comparative Examples 1 to 3 and 5. These
results demonstrate that preferred post-coating corrosion
resistance can be conferred on a hot-rolled steel sheet by
performing pre-coating treatment of the hot-rolled steel sheet with
a chemical conversion treatment agent including the at least one
(B) selected from the group consisting of an amino group-containing
silane coupling agent, hydrolysates thereof, and polymers thereof.
Further, neither the hot-rolled steel sheet treated with the
chemical conversion treatment agent from Comparative Example 1 nor
the hot-rolled steel sheet treated with the chemical conversion
treatment agent from Comparative Example 5 show preferred secondary
adhesiveness (SDT). This indicates that an increased content of the
cationic urethane resin (D) can not provide preferred results when
a chemical conversion treatment agent does not contain the at least
one (B) selected from the group consisting of an amino
group-containing silane coupling agent, hydrolysates thereof, and
polymers thereof, and also indicates that preferred post-coating
corrosion resistance can be conferred on a hot-rolled steel sheet
by pre-coating treatment of the hot-rolled steel sheet with a
chemical conversion treatment agent including the at least one (B)
selected from the group consisting of an amino group-containing
silane coupling agent, hydrolysates thereof, and polymers thereof
in combination with the cationic urethane resin (D).
[0070] Comparison of Examples 1 to 20 with Comparative Example 4
shows that the hot-rolled steel sheets treated with the chemical
conversion treatment agents from Examples 1 to 20 have superior
results from the combined cyclic corrosion tests (CCT) as compared
with the hot-rolled steel sheet treated with the chemical
conversion treatment agent from Comparative Example 4. These
results demonstrate that preferred post-coating corrosion
resistance can be conferred on a hot-rolled steel sheet by
pre-coating treatment of the hot-rolled steel sheet with a chemical
conversion treatment agent including the cationic urethane resin
(D).
[0071] Comparison of Examples 1 to 20 with Reference Example 1
shows that the hot-rolled steel sheets treated with the chemical
conversion treatment agents from Examples 1 to 20 have comparable
or superior results from the salt-water spray tests (SST), the
combined cyclic corrosion tests (CCT) as compared with the
hot-rolled steel sheet treated with the chemical conversion
treatment agent from Reference Example 1. These results indicate
that the pre-coating treatment method involving use of the chemical
conversion treatment agent according to an embodiment of the
present invention can confer comparable or superior post-coating
corrosion resistance on a hot-rolled steel sheet as compared with
the pre-coating treatment method involving use of a conventional
zinc phosphate-based treatment agent.
* * * * *