Note: Descriptions are shown in the official language in which they were submitted.
WO 95/21277 ~ 1 ~ 2 3 ~ P~l/ . "
Descrir~tion
SURFACE TREATMENT AGENT FOR ZINCIFEROUS-PLATED STEEL
Technical Field
The invention relates to an optimized surface treatment agent that imparts
both an excellent corrosion resistance and an excellent paint ddl ,e, ~ ce to the
surface of steel, espedally steel sheet, plated with zinc or zinc-cul Itd;l lil l9 alloy
5 (ht~ il I " dbLJI L.;; ' ' as zinciferous-plated steel). The invention will be de-
suibed below primarily with respect to use on steel sheet, but it is to be under-
stood that any other shape of steel substrate may also be treated according to
the invention.
Bad~Qround Art
Zinciferous-plated steel sheet utilizes the prindple of sauificial zinc corro-
sion, which is a general method for preventing the corrosion of iron and steel.
Zinciferous-plated steel sheet is used in a broad range of:,, ' ' Ia, extending
over the automotive, building material, and household electrical appliance sect-ors. However, the corrosion product generated when zinc corrodes in the atmos-
s phere produces so-called white nust on the steel sheet, which leads to a deterior-
ationin d,~J,UedldlILt. Moreov~r,thiswhiterustalsoimpairspaint dL~ i 'ceto
the plated steel sheet.
These problems are generally solved by subjecting the surface of zincifer-
ous-plated steel sheet to a chromate treatment with a treatment bath whose main
20 CUI I I,UUI It~l Ita are chromic acid, dichromic acid, or a salt thereof. This treatment
produces a highly corrosion-resistant and strongly paint-adherent chromate film.Unfortunately, the 11 . . ' ,I chromium present in the chromate treatment
baths used on zinciferous-plated steel sheet has a direct negative effect on thehuman body. This, and the recent increased demand for envi, u"" ,t:, ILdl protec-
25 tion, has created a desire to avoid the use of chromate 1, ~d~ e~ ,t~. In addition,the use of chromate l,t:dl",~"~a requires the illlyl~lllt:llldliOI~ of special waste
water treatment as stipulated in the Water Pollution Prevention Law, which drives
up costs as a whole. Finally, when discarded or dUdl Idul ~ed, chromate-treated
zinciferous-plated steel sheet is classified as a chromium-containing waste and
W095121277 2 ~3g~ ~,"~ 5 ,"
therefore cannot be recycled.
- One well-known non-chromate surface treatment method uses surface
treatment agents based on tannic acid (tannic acid contains r 1~ ' 113r,- ~' carbox-
ylic acid). Vvhen zinciferous-plated steel sheet is treated with an aqueous solu-
5 tion of tannic acid, the zinc tannate produced by the reaction between tannic acidand zinc fomms a protective coating. It is thought that the corrosion resistance of
the zincfferous-plated steel sheet is improved through the action of this protective
coating as a barrier to the infiltration of corrosive substances.
Japanese Patent Publication Number Sho 54-22781 [22,78111979] teach-
0 es a tannic acid-based surface treatment method Wlll~ ilIy the treatment of
zinciferous-plated steel sheet with an aqueous solution that contains at least tan-
nic acid and silica sol. This method forms an ultrathin surface film that has a
nust-inhibiting activity. The problem with this method is that this film still cannot
deliver a sd~i~rd~,luly corrosion resistance.
s Otherwise, Japanese Patent Publication Number Sho 61-33910 [33,910/
1986] teaches a method in which zinc-containing metal articles are first treatedwith a strongly alkaline ~pH 2 12.5) aqueous solution and are thereafter treatedwith an acidic aqueous solution whose main cv,, ,~,or,c~ is tannic acid. While the
coating produced by this method has a relatively good corrosion resistance, this20 method requires a strongly alkaline treatment and a water rinse prior to the tannic
acid treatment. This results in a poor productivity and poor ~wl ,u" ,ics.
Another surface treatment method is disclosed in Japanese Patent Publi-
cation Number Sho 58-15541 [15,54111983]. In this method, the surface of zinc-
if erous-plated steel sheet is treated with an aqueous solution containing organo-
25 silane coupling agent and one or both of water glass and sodium silicate. Thesurface film yielded by this method exhibits a good primary ~ "ce, but a
poor secondary adl ,~ ce and a poor corrosion resistance.
Thus, no chromium-free surface treatment agent introduced to date is able
to impart both an excellent corrosion resistance and an excellent paint adherence
30 tozinciferous-plated steel sheet.
WO95/21277 2~ P~l/, "
Disclosure of the Invention
Problems to Be Solved by the Invention
The present invention takes as its object the introduction of a chromium-
free surface treatment agent that solves the problems described above for the
s prior art by simultaneously providing the excellent corrosion resistance and ex-
cellent paint adl ~ required for zinciferous-plated steel sheet.
Summary of the Invention
A coating having both a high conrosion resistance and a strong paint ad-
herence can be produced by treating the su~face of zinciferous-plated steel sheet
with a surface treatment agent that contains a particular type of silane coupling
agent and at least one selection from polyhydroxyaryl carboxylic acids and dep-
sides of polyhydroxyaryl carboxylic acids. The invention was achieved based on
this finding.
In specific temms, the surface treatment agent according to the inYention
for zinciferous-plated steel sheet ~,1 Idl a~ l ialiwll y comprises, preferably consists
essentially of, or more preferably consists of, water and the following essential
c~" ,~u"~"ts.
(A) a cc " ,,vu"-;"l selected from the group consisting of polyhydroxyaryl car- boAylicacidsanddepsidesofpol~,"dlvA~a,ylcarboxylicacids;and
20 . (B) a cc", ,~,u, ,~"t selected from the group consisting of silane coupling agents
with the following general formula (1):
(YR)mR~SiX(~m~)
in which R denotes an alkyl group, which may be the same or different
from one of the m YR and the n R moieties to another; X denotes a meth-
2s OXy or ethoxy moiety; Y denotes a moiety selected from the group consist-
ing of vinyl, amino, mercapto, glycidoxy, and methacryloxy moieties,
which may be the same or different from one of the m YR moieties to an-
other; m is an integer with a value from 1 to 3; and n is an integer with a
value of û to (3-m); and optionally, one or more of:
30 (C) watermiSCiblelllullual~ol~ol~
(D) metal cations with a valence of two or more; and
(E) acc el~, ' anions
wo 95nl277 218 2 3 9 ~ P~
It is preferred, furthemmore, that the total content of essential cu,,,,uul ,~"~(A) and (B) in the surface treatment agent according to the invention should be
1 to 5û weight %.
Detailed Description of the Invention
6 Zinciferous-plated steel which can be treated with the surface treatment
agent of the invention ~, IWIIIIJdS:~eS steel coated with zinc or a zinc alloy, for ex-
ample, ZnlFe alloy, Zn/Ni alloy, ZnlAI alloy, and the like.
Polyhydroxyaryl carboxylic acids usable by the present invention must
have st least two hydroxyl substituents and at least one cdrboxyl substituent on~ a single aromatic nucleus. Such acids are cz~:, ", ~ by gallic acid, protocate-
chuic acid, ~, " IJO;CJ I;- acid, and the like. Suitable as the depsides of polyhy-
droxyaryl csrboxylic acids are, for example, meta-digallic acid, trigallic acid, diplo-
schistesic acid, tannin, tannic acid, and so forth. The tannin used in the present
invention is a general term for substances ~LItn,~dL~l~ by hot water from the
~s seeds, fruits, shells, leaves, roots, wood, and bark of plants and able to convert
raw animal hides into leather. Tannic acid is the tannin obtained from Chinese
or Turkish nutgall, etc. The type and quantity of addition of these substances is
not critical.
Any silane coupling agent that has a chemical stnucture with general form-
ula (1) may be used in the present invention. For example, compounds from the
following groups (a) - (c) can be used and are generally preferred
(a) glycidoxy-functional silane couDling agents
e.g., 3-glycidoxypropyl trimethoxy silane
3-glycidoxypropyl methyl dimethoxy silane
2b 2-(3,4-epoxycyclohexyl)ethyl trimethoxy silane
(b) amino-functional silane couplin~ a~ents
e.g, N-(2-aminoethyl)-3-~",i"o~,u~yl methyl dimethoxy silane
N-(2-aminoethyl)-3-d, llil lù~l u~yl trimethoxy silane
3-dlllillUplU~Jyl triethoxy silane
30 (C) mercspto-functional silane coupling agents
e.g., 3-lll_l-,d,UlUUlUI yl trimethoxy silane.
WO9~/21277 ~8~ p ~ "
No specific ~a~ri,,ti~" "~ apply to the content of these silane coupling
agents in the surface treatment agent.
The surFace treatment agent of the invention may in general be prepared
by dissolving or dispersing the drVI ~11It:l I~iUI ,ed essential cc " ,,uu"~ a in water.
s Vvhile the total w"w, I~ dliUI, of the essential cul, ,,uul~, lla is not ~,v~,iri~.~y re-
stricted, the sum of the ,~"w"t~ iu, la of the essential Cv"~pO~ l ,ta, i.e., silane
coupling agent + polyhydroxyaryl carboxylic acid(s) and/or depside(s) of polyhy-droxyaryl carboxylic acid(s) is preferably 1 to 5û weight %. When the total
amount of these essential wn ,,vul~ a falls below 1 weight %, the treated zincif-
0 erous-plated steel sheet wili not always exhibit the good corrosion resistance that
is the goal of the present invention. On the other hand, a total amount of essen-
tial ~" ,,uu"t" lla in excess of 5û weight % is ~ co"u" liCdl because no furtherimprovement in corrosion resistanr,e is obtained for the treated zinciferous-plated
steel sheet at such values. The weisht ratio between subject essential compon-
ents is preferably {polyhydroxyaryl carboxylic acid(s) and/or depside(s) thereof~:
{silane coupling agent} = 10: 1 to 1: 2, or preferably 10: 1 to 1: 1.
The surface treatment agent according to the invention may contain addi-
tives in addition to the essential cu,,,,vu"~"~s already discussed ab~ve. Metal
ions may be added in order to improve the insolubility of the treated zinciferous-
20 plated steel sheet. Metal ions usable for this purpose are ~ d by iron,
nickel""d"~,d,~ese, cobalt, zinc, aluminum, calcium, and magnesium ions, with
zinc and magnesium ions being particularly preferred. In addition, a reaction ac-
celerator may be added in order to accelerate the reaction with the surface of the
zinciferous-plated steel sheet. Preferred for use as this reaction d~elt:l are,
2s for example, phosphate ions, nitrate ions, fluoride ions, and organic acids other
than those that are part of cu~,uul)elll (A). Fluoride ions are particularly
preferred as the reaction dccel~ v, . Finally, no particular, c:a~ ,liv, 15 apply to
the sources of the ions and quantities of addition for the described additives.
An additive that is generally preferred is optional av",po"e"~ (C) as de-
30 saibed above, of which methanol is the most preferred ~" ,uovi" ,t:"I. Independ-
ently, a w"w, It~ " , of optional w",,uu"el~ (C) in the range from 1 to 30, more
WO 95/21277 2 1 8 2 3 g ~ "
preferably 5 to 15, or still more preferably 9 to 11, weight % is preferred in the
treatment cc " ,,uu~itiu, ,~ according to the invention.
No particular restriction obtains on the method for treating 2inciferous-plat-
ed steel sheet using the surface treatment agent of the invention, and, for ex-
6 ample, immersion, spray, and roll coating methods are ~ ' ' Nor is thetreatment temperature or treatment time crucial, but in general the treatment
temperature is preferably 1 û C to 4û C and the treatment time is preferably 0.1
to 1 û seconds.
anciferous-plated steel sheet treated with the surface treatment agent of
o the invention exhibits both an excellent corrosion resistance and an excellent
paint adherence. In regard to the improved corrosion resistance, the polyhydrox-yaryl carboxylic acid or depside thereof in the treatment agent is believed to react
wffl the 2inc to form a protective coating on the surface of the zinciferous-plated
steel sheet. This protective coating then would prevent the infiltration of corros-
s ive substanr~es, thus yielding the improved corrosion resistance. The improvedpaint adherence is believed to occur as the result of a~au, ,u~;~,,, of the functional
groups in the silane coupling agent to the surface of the zinciferous-plated steel
sheet.
The invention is explained in greater detail below through working examp-
20 les, which, however, should not be construed as placing particular limits on thescope of the invention.
~mQles
The following materials and procedure for cleaning the steel sheet were
used in the examples.
25 1 Test materials
The following were used as the zinciferous-plated steel sheet substrates:
cu"""t:,uial steel sheet (sheet thickness = û.6 mm) hot-dip galvanized on both
sides (denoted below as "HDG" material, coating weight = 40 g/m2) or electrogal-vanized on both sides ~denoted below as "EG" material, coating weight = 20
30 9/m2)
W09512~277 ~ t ~ 2 3~5 F~~ ."
~, Cleanin~ rJrocedure
A " ,ud~, ut~y alkaline degreaser (FINECLEANER~A 4336, cor"" ,~, ~;;. '!y
available from Nihon Parkerizing Company, Limited, Tokyo) was used a concen-
tration of 20 g/L. The dirt and oil adhering on the surface were removed by
s spraying the zinciferous-plated steel sheet with the aqueous degreaser solution
9 using a treatment temperature of 60 C and a treatment time of 20 seconds. The
alkali remaining on the surface of the treated steel sheet was then washed off
using tap water to yield the clean zinciferous-plated steel sheet surface.
FYArnvle 1
o The EG material, cleaned as described above, was immersed at room
temperature for 20 seconds in a surface treatment bath prepared by dissolving
0.5 weight % of gallic acid, 0.5 weight % of 3-glycidoxypropyl trimethoxy silane,
and 10 weight % of methanol in deionized water. This was followed by draining
and drying to a sheet temperature of 100 C.
~s FYArnple 2
The treatment procedure of Example 1 was executed on the HDG material
instead of the EG material used in Example 1.
FYArnple 3
The surface of the EG material, cleaned as described above, was roll
coated with a surface treatment bath prepared by dissolving 5.0 weight % of Chi-nese nutgall tannin, 3.4 weight % of 3-glycidoxypropyl methyl dimethoxy silane,
and 10 weight % methanol in deionized water. This was followed by drying to a
sheet temperature of 100 C.
EYA~nDle 4
The treatment procedure of Example 3 was executed on the HDG material
instead of the EG material used in Example 3.
FYA~le S
The surface of the EG material, cleaned as described above, was roll
coated with a surface treatment bath prepared by dissolving 10 weight % of pro-
tocatechuic acid, 2.5 weight % of 3-~",i, ,u~,, u,uyl triethoxy silane, and 10 weight
% of methanol in deionized water. This was followed by drying to a sheet tem-
perature of 100 C.
W095/21277 ~1~2~5 P~ll-J.,. '~:,// ~
FYAmple 6
The treatment procedure of Example 5 was executed on the HDG material
instead of the EG material used in Example 5.
FxA~ple 7
s The EG material, cleaned as described above, was immersed at room
temperature for 20 seconds in a surface treatment bath prepared by dissolving
18.0 weight % of quebracho tannin, 32.0 weight % of 3~ l w~iu,ul u~u~l trime-
thoxy silane, and 10 weight % of methanol in deionized water. This was followed
by draining with a wringer roll and drying to a sheet temperature of 100 C.
Example 8
The treatment prooedure of Example 7 was executed on the HDG material
instead of the EG materiai used in Example 7.
Com~arative FyA~Dle 1
The EG material, cleaned as described above, was immersed at room
15 temperature for 2û seconds in a Cc/lll,Udl~;~C treatment bath prepared by dissolv-
ing 5.0 weight % of Chinese nutgall tannin in deionized water. This was followedby draining using a wringer roll and drying to a sheet It l l I~JC:l ~re of 100 C.
Cu" IVdl dt~ ~c ExamDle 2
The treatment proosdure of Col l l~udl ~ Exdmple 1 was executed on the
zc HDG material instead of the EG material used in Comparative Example 1.
Cc" I IUdl dli C EYA~ple 3
The EG material, cleaned as described above, was sprayed for 10 seG
onds at room temperature with a CUIII,Udl "~'~. treatment bath prepared by dis-
solving 5.0 weight % of 3-glycidoxypropy"u il l l~ u,~ysilane, 10 weight % of meth-
anol, and 25 weight % of 20 % silicic acid sol in deionized water. This was fol-lowed by draining using a wringer roll and drying to a sheet temperature of 1005C.
CII dli ~rc Example 4
The treatment procedure of Cu" l~dl ..~;~'C Example 3 was executed on the
30 HDG material instead of the EG material used in CUlllUdl ~;./C Example 3.
~ wo95m27~ 39~- P~
Evaluation Testin~
The products from Examples 1 to 8 and Comparative Examples 1 to 4
were tested by the following methods.
(1 ! Corrosion resistance
s The resistance to white nusting was tested by the salt spray test of
JIS Z-2371. The following scale was employed to report the results.
+ + +: no di~
+ + : area of white rust d~v~'viJ, "t:"L less than 5 %
+ : areaofwhiterustd~v~lv,.,"lt:"Lis5to 10%
x : area of white nust d~v~'v,~ l ,l is 11 to 50 %
x x : area of white rust development is 51 % or greater
S,2~ Paint a-ll ,e, t ,lce
After treatment with a surface treatment agent as described above, the
zinciferous-piated steel sheet was coated with paint (Delicon #700 from Dainip-
.s pon Toryo Kabushiki Kaisha) and baked at 140D C for 20 minutes to yield a 25
,l ull l~t~_. -thick paint fllm.
(i~ Primary rJaint a~l ,~,~,'ce
Crosscut test: a c, u~ ~l Id~i I pattern of 1 mm x 1 mm squares was cut in the paint
film on the product's surface using an NT cutter, and the number of squares re-
maining after peeling with adhesive tape was counted.
Crossc~UCri~ en test: the specimen was extruded 5 mm after the crosscut
evaluation, and the number of squares remaining after peeling with adhesive
tape was counted.
(ii) Secondary r~aint a~ ".,e
2s The painted sheet was immersed in boiling pure water for 2 hours and
was then evaluated by the crosscut test and crosscuilErichsen test as described
above for primary paint a~ ,e.
The results of these tests are shown in Table 1 below. The results in Tab-
le 1 conhmm that excellent values for both corrosion resistance and paint adher-ence (both primary and secondary) were obtained for Examples 1 to 8 of the in-
vention. In Cu" I,Udl ,_t; ~'~ Examples 1 to 4, on the other hand, no treatment gave
good results in all the tests conducted, and the results from the secondary paint
wo95/21277 218~9~i r~l,u~ s .Il i~
Table 1: RESULTS OF THE EVALUATION TESTS
Example Corrosion Primnry Puint Second~ry P~int
("E") or r Adherence /~ '' .i .
Compari- 24 Elr. Salt
son E~- SprAy
umple Crosscut CrosscuV Crosscut Crosscut/
("CE") Only Erichsen onb Erichsen
Number
E l ++ 100/100 100/100 100/100 100/100
E 2 + + 100/100 100/100 100/100 100/100
E 3 + + + 100/100 100/100 100/100 '100/100
E4+++ 100/100 100/100 100/100 '100/100
E5+++ 100/100 100/100 100/100 99/100
E 6 + + + 100/100 100/100 100/100 98/100
E 7 + + + 100/100 100/100 100/100 97/100
E 8 + + + 100/100 100/100 100/100 96/100
CE I + 100/100 100/100 88/100 '47/100
CE2 + 100/100 100/100 82/100 51/100
CE 3 X X 100/100 100/100 88/100 29/100
CE 4 X X 100/100 100/100 80/100 33/100
Notes for Table I
The results reported for the crosscut and ~IUD~ E1;~ tests are the number of
squares remairling unpeeled after tape peeling before the virgule ("/") out ûf the number
of total squares after the virgule. I
adherence tests v~ere particularly inferior to the results given by the invention ex-
amples.
Benefits of the Invention
Zinciferous-plated steel treated v~ith the surface treatment agent according
5 to the invention exhibits an excellent ~ ru~ d~ e in both critical areas of corro-
sion resistance and paint adherence. The surface treatment agent of the inven-
tion is also very safe and highly advantageous in terms of ~" ,1;. u"" ,t~ dl protec-
W0 95121277 ~ 1 8 2 ~ g ~ P~ u., 5 ~
tion and ,~cy, ' ~ "'y. in particular, since it is clearthat future~~ iu~,a on sol-
vents will ~ a change from solvent-based cleaning to water-based
cleaning, the treatment agent of the invention will be particularly effective in those
sectors in which er;~ ;. u, " "t~ dl problems might occur due to chromium elution
5 from the surface of cl " u,, Ic.lc:d zinciferous-plated steel sheet.
