CA1081407A - Treating zinc with aqueous tannin and silica or alumina - Google Patents
Treating zinc with aqueous tannin and silica or aluminaInfo
- Publication number
- CA1081407A CA1081407A CA268,064A CA268064A CA1081407A CA 1081407 A CA1081407 A CA 1081407A CA 268064 A CA268064 A CA 268064A CA 1081407 A CA1081407 A CA 1081407A
- Authority
- CA
- Canada
- Prior art keywords
- silica
- acid
- tannin
- tannic acid
- coating
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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Classifications
-
- C—CHEMISTRY; METALLURGY
- C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
- C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
- C09D5/00—Coating compositions, e.g. paints, varnishes or lacquers, characterised by their physical nature or the effects produced; Filling pastes
- C09D5/08—Anti-corrosive paints
- C09D5/082—Anti-corrosive paints characterised by the anti-corrosive pigment
-
- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
- C23C22/05—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions
- C23C22/06—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6
- C23C22/48—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6 not containing phosphates, hexavalent chromium compounds, fluorides or complex fluorides, molybdates, tungstates, vanadates or oxalates
- C23C22/53—Treatment of zinc or alloys based thereon
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- Chemical & Material Sciences (AREA)
- Materials Engineering (AREA)
- Organic Chemistry (AREA)
- Engineering & Computer Science (AREA)
- Metallurgy (AREA)
- Mechanical Engineering (AREA)
- Chemical Kinetics & Catalysis (AREA)
- General Chemical & Material Sciences (AREA)
- Life Sciences & Earth Sciences (AREA)
- Wood Science & Technology (AREA)
- Paints Or Removers (AREA)
- Application Of Or Painting With Fluid Materials (AREA)
- Chemical Treatment Of Metals (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
Disclosed are a process and composition useful for forming a corrosion resistant, abrasion resistant paint receptive coating on a zinc or zinc alloy surface. The compo-sition contains a tannin or tannic acid and a refractory oxide.
Disclosed are a process and composition useful for forming a corrosion resistant, abrasion resistant paint receptive coating on a zinc or zinc alloy surface. The compo-sition contains a tannin or tannic acid and a refractory oxide.
Description
:3~08~7 The present invention relates to an aqueous composition, process for forming a protective coating on zinc or an alloy thereof employing such a composition, and a coated article produced thereby.
Zinc has conventionally been employed mainly for imparting corrosion resistance to steel by means of the hot galvanized or electrolytic plating method. However, under a high humidity atmosphere, zinc metal develops white stains on the surface which are detrimental to the appearance and corrosion resistance thereof and which reduce markedly the adhesion of paints applied thereon.
Chromating processes employing mainly chromic acid, bichromic acid or a salt thereof have been employed to prevent the development of such white stains. The chromating processes are inexpensive and exhibit good corrosion resistance, however, the toxic effects of chromates and their destructive effect on the natural environment have come closely into question. Thus standards for controlling the use of chromic acids and chromates have become more and more severe. At the same time, there have arisen various problems such as the process control for chro-mating, waste water treatment of chromating operation, secondary contamination by the chromated articles and the like.
It has been well known to treat metal surfaces with tannic acid as disclosed, for example, in Japanese Patent Kokai Nos. 47224/74 and 8317/73.
However, the corrosion resistance imparted to sur-faces by such conventional processes is not sufficient. In addition, when used as a base for paints, the resistance against scratches is insufficient and blistering of paint film tends to occur under a high-humidity atmosphere.
The surface treatment of the metal emplo~ing mainly silica or silicates has been also disclosed in Japanese Patent '.
~ .
-.. . ~-:. ' , - 101~1~07 Publication Nos. 19686/69 and 5130/70. However, the coating free from chromates and obtained by such processes provides insufficient corrosion resistance and has been used as an electrically insulating rather than corrosion resistant coating in many cases as disclosed in Japanes~ Patent Publication Nos.
7~49/68 and 13562/69.
It has now been found that by combining tannin or tannic acid and an aqueous suspension containing one or more refracting oxides such as silica, silica sol and alumina sol, a protective coating can be formed on the surface of zinc or an alloy thereof which improves the corrosion resistance markedly as compared with those achieved by either component alone and which can prevent humidity blistering of paint film applied thereto. Thus this invention has been completed.
According to the invention there is provided an aqueous composition comprising a tannin or tannic acid and a refractory oxide in a weight ratio of 100:1 to 1:100, wherein the concentration of tannin or tannic acid is 0.01 to 20 wt.%
and the concentration of refractory oxide is 0.1 to 20 wt.%.
According to another aspect of the invention there is provided a coated article comprising a substrate having a zinc or zinc alloy surface and a protective coating on said surface comprising a tannin or tannic acid and a refractory oxide in a weight ratio of 100:1 to 1:100.
According to yet another aspect of the invention there is provided a process for forming a protective coating on a zinc or zinc alloy surface comprising contacting the surface with an aqueous compo~ition of the invention and thereafter drying the ~urface. In a particular embodiment the surface is contacted with the composition for at least 0.1 seconds at a temperature of at least 20C.
-2_ ... ... . .
~81~0'7 In the process of the invention for forming the pro- :
tective coating on zinc or an alloy thereof, the coating may suitably be formed by treating the latter with an aqueous solution or suspension containing at least one refractory oxide, for example, silica, silica sol and alumina sol in a content ranging from 0.1 to 2~/o by weight and tannin or tannic acid in a content ranging from O.Ql to 2~o by weight. ~.
Tannin or tannic acid useful in this invention may be any hydrolyzable tannin or condensed tannin or partial decomposition products thereof and includes, for example, :
depside tannin, Gallotannin, Chinese tannic acid, Turkey tannic acid, hamamelitannic acid, tannic acid from Acer Ginnala, cheblinic acid, sumac tannin, Chinese gallotannin ellagitannin, catechine, catechine-tannic acid, quebracho-tannin and the like in a concentration ranging from 0.01 to 2 ~/o by weight, At a concentration of less than 0.01% by weight, ~ -2a-. .
: . ... , . ~ . :
the effect of tannin becomes insignificant and a concentration of higher than 20~ by weight is disadvantageous from the workability and econom~, Any particulate silica may be used in this invention S including, for e~ample, Aerosil (a trademark for silica available from Nihon Aerosil Co., Ltd~) and Siloid (a trademark for silica available from Fuji Devison Co., Ltd~). As silica gel, there may be used in this invention a solution obtained by removing sodium ion from an aqueous solution of sodium silicate through an ion exchange column or commercially available silica sol containing SiO2 in an amount ranging from 20 to 30% such as Snowtex (a trademark product available from Nissan Chemicals Co., Ltd,), There may also be used silica sol wherein silica gel is dispersed evenly in an alkali solution, such as that obtained by neutralizing sodium silicate with an appropriate acid and isolating the resulting sol so as to be free from Na ion, or that obtained by dispersing solid SiO2 such as Aerosil or the like in an aqueous medium. In every silica sol, the SiO2 should be dispersed homogeneously in the ,20 colloidal state in the aqueous medium. There may also be usable an aqueous solution or dispersion of silica or silica sol containing lithium oxide as disclosed in Japanese Patent Publication Nos. 19686/69 and 5130/70 to improve the corrosion Xesistance~ Com~ercially available products include Lithium `25 $i1icate (a trademark product available from Nissan Chemicals Co " ~td~)~
Any alum~na sol is usable in this invention~
Commercially available alumina sol dispersed in water ~avail-able from Nissan Chemicals Co., ~td,) is convenient for the handling, This product contains A12O3 in an amount of higher than 10~ and is stabilized at a pH value from 2,5 to 6 with an !
.. ,., . . p, , P-10679 ~0 81 407 inorganic acid or OrgalliC acid~
The precise composition of the aqueous solution or suspension depends on the proce~s to be employed ~orming the protectiVe coating, such as immersion, roll coating, flooding, spr~ying, electrostatic coating, brushin~ or the like but is generally an aqueous solution or suspension containing 0~01 to 20~ by weight of tannin or tannic acid and 0,1 to 20%
~frdcto 7,~
~-' by weight of at least one re-a6~4~ oxide, Preferably the xefractor~ is selected from the group consisting of silica, silica sol and alumina sol, the effective ratio of tannin or tannic acid to silica and/or silica sol and/or alumina sol ranging from 100:1 to 1:100 as the treating agent, If tannin or tannic acid is present in a higher content than the specified upper limit, blistering will tend to occur in painted specimens by the corrosion test~ If silica and/or silica sol and/o~
alumina sol are present in a higher content than the specified upper limit, the ~oxmed coating will tend to become too brittle~
~; Since the stable pH ranges depend on the kinds of tannin, tannic acid, silica, silica sol, or alumina sol, an .
. . ~ . .
.20 inorganic acid such as phosphoric acid, nitric acid, sulfuric acid, hydrofluoric acid, hydrochloric acid and salts thereof ~ or an organic acid such as oxalic acid, citric acid, malic :
.. acid, maleic acid, phthalic acid, acetic acid, lactic acid, taxtaric acid, chloroacetic acid, acrylic acid and salts there-o~ ma~ ~e used to adjust the pH value of the aqueous solutions .
; and suspensions~
An alkaline compound such as sodium hydroxide, potassium h~dxoxide, lithium hydroxide, ammonium h~vdroxide or the like, ~ OX an amine such as ethyl amine, diethyl amine, triethyl ;`30 amine, ethanol amine or the like may be used for pH adjustment.
Since, however, the residual content of such water-soluble salts in the coating facilitates the adsorption of ~4~
. ', , ,,, , . . . - - - - ' F'--- '-- ' ., ~ , . .
~081407 . P-106-/g moisture in the air and at the same time has a possibility to enhance the corxosion, such ~Jater-soluble salts should be limited to an am~unt as small as possible and preferably excess soluble sal.ts are removed, if possible, by rinsing with water.
The aqueous solution or suspension of this invention may be added with a water-soluble, emulsifiable or dispersible organic polymer resin to improve the adhesion of the coating comprising mainly tannin, tannic acid, and silica, silica sol or alumina sol onto the metal surface, to provide flexibility to the coating and also to improve the corrosion resistance of the coating.
By embodying the process of this invention, it is possible to form a protective coating having an excellent corXosion resistance and to provide a paint base having excellent adhe~ion.
The invention will be illustrated by way of the follow.ing examples.
; EXAMPL~ 1 :. . .
A hot galvanized steel plate which had been temporarily treated with chromic acid and had a size of 100 x 300 x 0.3 mm .. was polished thrice by the wet Scotch prvcess to remove the chxomic acid adhered on the surface thereof. A treating ; suspension was-prepared by dispersing and dissolving 30 g of Chi~nese gallatannin (available from Fuji Chemical Industries , ~, Ltd~ as Tannic Acid AL) and 30 g of powdery silica (avail-: able ~rom Nihon Aexosil Co, Ltd, under the trademark ~erosil . 380~ into about 500 ml o~ deionized water and b~ making up to ; lOOO.g with pure water~ The pH value o~ the prepared suspension 3~ was about 3~5, The cleaned galvanized steel plate was coated with the suspension by the bar coating process with a No. 6 ~5~
.. ...... . -- F---.
108~407 P-10679 :~
bar and dxied in a hot air circulating oven at 120C for one minute to form the protective coating. The treated plate was then subjected to the salt spray test according to JIS-Z-2371.
It took about 200 to 240 hours prior to the development of white stains, thus the coating showed excellent corrosion resistance as compared with those obtained for the comparative test plates prepared according to Comparative Examples 1, 2, 3 and 4, Comparative Example 1 .
A hot galvanized steel plate identical to that of Example 1 was polished thrice by the wet Scotch process and the cleaned galvanized steel plate free from chromic acid was employed as the test plate.
i. . .. .
Comparative Example 2 15 A cleaned galvanized steel plate identical to that o~ Example 1 was txeated to as in Comparative Example 1 and wa~ coatèd with an aqueous solution of 1% by weight chromic ~ ''' acid in a manner similar to Example l and dried.
Camparative Example 3 ,20 A cleaned galvanized-steel plate identical.to that o~ Example 1 was treated as in Comparative Example 1 and was coated with an aqueous solution prepared by dissolving 30 g , of Chinese gallotannin in about 500 ml of deionized water and ~ade up to 1000 g by adding with deionized water in a manner ,.-si~m~lar to Example 1 and d~ied~
~omparati~e Example 4 cleaned galvanized steel plate identical to that . o~ Example 1 was treated as in Comparative Example 1 and was coated with an aqueous suspension prepared by dispersing 30 g ,30 of powdery silica (Aerosil 380) in about 500 ml of deionized water by means o~ a high speed agitator in a manner similar to Example 1 and dried~ -. . . ' :
~' . .. . .
~08140'7 P-10~79 The test plates prepared according to Example 1 and Comparative Examples 1, 2, 3 and 4 were coa~ed with a thermo~
settlng alkyd paint (,a paint for coating the back surface of S colored galvanized steel plates) by the bar coating process with a No~ 12 bar and dried and baked in a hot air circulating ,,,' oven at 280C for 50 seconds to form coatings having a thickness of 6 microns. The coated plates were scribed through the painted layer to the base metal by means of a razor blade edge and then subjected to salt spray test according to JIS-Z-2371 for 240 hours, Transparent tape was then applied to the ' coated surfaces and then peeled rapidly, On the test plate prepared in Example 1, the extent of corrosion developed from the scribe was a width of less than 3 mm on both of the sides ' 15 and no blistering was observed on the smooth surface of the p~int film.
When the film surface was scratched with a copper coin, it was difficult to penetrate to the galvanized layer.
' ~ When the test plates prep-ared in Comparative ~xamples ~20 1, 2, 3 and 4 were coated with the paint and subjected to , the corrosion test in the manner of Example 2, the results - were inferior to those in Example 2, These results are shown , in Table 1.
' .
, .
' ~7~
I
' , ~ - ~
P-10679 ~0 8 1 407 - TAble 1 Corrosion re- Corrosion Resis~ Scratch sistance of tance of painted resistance Unpainted test pl.ate 1) by coin test plate test 2) by salt spray test Width Blister .. . . . . . . . . . . . ..
Examples 1 and 2 200 - 240 hr 3 mm No blisters Good Comparative 2 hr, More Blisters Inferior Example 1 than ovex all 10 mm surface :.--10Comparative 120 -240 hr 3 mm Slightly Example 2 blistered Infexior - Comparative . Example 3 48 - 72 hx More Blisters Inferior than over all .:
10 mm - surface Comparative Example 4 24 hr More Blisters than over all Good 10 mm surface .... .... ... .~.~.. ~..... .. ..... .
.. _ . . . . :. . . . ~ . ___ I Note 1): Test for 240 hours according to the salt spray , test according to JIS-Z-2371, Note 2): Scratch resistance by copper coin.
.
A hot galvanized steeI plate cleaned as in Example 1 : . . ,. - - : . : -w~s coated.as in Example 1 with a suspension which was prepared by dissolving 30 g of Chinese gallotannin in about 500 ml of . deionized water, dispersing 100 g of alumina sol (available from Nissan Chemicals Co. Ltd, under the trade,mark Alumina Sol 100) and making up to 1000 g by adding deionized water,j When a.aorxosion test was carried out a~ in Example l, it.took 200 ` to 2~0 hours prior to the development o~ white stains.
, .
. -8~ ~.
.
. .... .
' '
Zinc has conventionally been employed mainly for imparting corrosion resistance to steel by means of the hot galvanized or electrolytic plating method. However, under a high humidity atmosphere, zinc metal develops white stains on the surface which are detrimental to the appearance and corrosion resistance thereof and which reduce markedly the adhesion of paints applied thereon.
Chromating processes employing mainly chromic acid, bichromic acid or a salt thereof have been employed to prevent the development of such white stains. The chromating processes are inexpensive and exhibit good corrosion resistance, however, the toxic effects of chromates and their destructive effect on the natural environment have come closely into question. Thus standards for controlling the use of chromic acids and chromates have become more and more severe. At the same time, there have arisen various problems such as the process control for chro-mating, waste water treatment of chromating operation, secondary contamination by the chromated articles and the like.
It has been well known to treat metal surfaces with tannic acid as disclosed, for example, in Japanese Patent Kokai Nos. 47224/74 and 8317/73.
However, the corrosion resistance imparted to sur-faces by such conventional processes is not sufficient. In addition, when used as a base for paints, the resistance against scratches is insufficient and blistering of paint film tends to occur under a high-humidity atmosphere.
The surface treatment of the metal emplo~ing mainly silica or silicates has been also disclosed in Japanese Patent '.
~ .
-.. . ~-:. ' , - 101~1~07 Publication Nos. 19686/69 and 5130/70. However, the coating free from chromates and obtained by such processes provides insufficient corrosion resistance and has been used as an electrically insulating rather than corrosion resistant coating in many cases as disclosed in Japanes~ Patent Publication Nos.
7~49/68 and 13562/69.
It has now been found that by combining tannin or tannic acid and an aqueous suspension containing one or more refracting oxides such as silica, silica sol and alumina sol, a protective coating can be formed on the surface of zinc or an alloy thereof which improves the corrosion resistance markedly as compared with those achieved by either component alone and which can prevent humidity blistering of paint film applied thereto. Thus this invention has been completed.
According to the invention there is provided an aqueous composition comprising a tannin or tannic acid and a refractory oxide in a weight ratio of 100:1 to 1:100, wherein the concentration of tannin or tannic acid is 0.01 to 20 wt.%
and the concentration of refractory oxide is 0.1 to 20 wt.%.
According to another aspect of the invention there is provided a coated article comprising a substrate having a zinc or zinc alloy surface and a protective coating on said surface comprising a tannin or tannic acid and a refractory oxide in a weight ratio of 100:1 to 1:100.
According to yet another aspect of the invention there is provided a process for forming a protective coating on a zinc or zinc alloy surface comprising contacting the surface with an aqueous compo~ition of the invention and thereafter drying the ~urface. In a particular embodiment the surface is contacted with the composition for at least 0.1 seconds at a temperature of at least 20C.
-2_ ... ... . .
~81~0'7 In the process of the invention for forming the pro- :
tective coating on zinc or an alloy thereof, the coating may suitably be formed by treating the latter with an aqueous solution or suspension containing at least one refractory oxide, for example, silica, silica sol and alumina sol in a content ranging from 0.1 to 2~/o by weight and tannin or tannic acid in a content ranging from O.Ql to 2~o by weight. ~.
Tannin or tannic acid useful in this invention may be any hydrolyzable tannin or condensed tannin or partial decomposition products thereof and includes, for example, :
depside tannin, Gallotannin, Chinese tannic acid, Turkey tannic acid, hamamelitannic acid, tannic acid from Acer Ginnala, cheblinic acid, sumac tannin, Chinese gallotannin ellagitannin, catechine, catechine-tannic acid, quebracho-tannin and the like in a concentration ranging from 0.01 to 2 ~/o by weight, At a concentration of less than 0.01% by weight, ~ -2a-. .
: . ... , . ~ . :
the effect of tannin becomes insignificant and a concentration of higher than 20~ by weight is disadvantageous from the workability and econom~, Any particulate silica may be used in this invention S including, for e~ample, Aerosil (a trademark for silica available from Nihon Aerosil Co., Ltd~) and Siloid (a trademark for silica available from Fuji Devison Co., Ltd~). As silica gel, there may be used in this invention a solution obtained by removing sodium ion from an aqueous solution of sodium silicate through an ion exchange column or commercially available silica sol containing SiO2 in an amount ranging from 20 to 30% such as Snowtex (a trademark product available from Nissan Chemicals Co., Ltd,), There may also be used silica sol wherein silica gel is dispersed evenly in an alkali solution, such as that obtained by neutralizing sodium silicate with an appropriate acid and isolating the resulting sol so as to be free from Na ion, or that obtained by dispersing solid SiO2 such as Aerosil or the like in an aqueous medium. In every silica sol, the SiO2 should be dispersed homogeneously in the ,20 colloidal state in the aqueous medium. There may also be usable an aqueous solution or dispersion of silica or silica sol containing lithium oxide as disclosed in Japanese Patent Publication Nos. 19686/69 and 5130/70 to improve the corrosion Xesistance~ Com~ercially available products include Lithium `25 $i1icate (a trademark product available from Nissan Chemicals Co " ~td~)~
Any alum~na sol is usable in this invention~
Commercially available alumina sol dispersed in water ~avail-able from Nissan Chemicals Co., ~td,) is convenient for the handling, This product contains A12O3 in an amount of higher than 10~ and is stabilized at a pH value from 2,5 to 6 with an !
.. ,., . . p, , P-10679 ~0 81 407 inorganic acid or OrgalliC acid~
The precise composition of the aqueous solution or suspension depends on the proce~s to be employed ~orming the protectiVe coating, such as immersion, roll coating, flooding, spr~ying, electrostatic coating, brushin~ or the like but is generally an aqueous solution or suspension containing 0~01 to 20~ by weight of tannin or tannic acid and 0,1 to 20%
~frdcto 7,~
~-' by weight of at least one re-a6~4~ oxide, Preferably the xefractor~ is selected from the group consisting of silica, silica sol and alumina sol, the effective ratio of tannin or tannic acid to silica and/or silica sol and/or alumina sol ranging from 100:1 to 1:100 as the treating agent, If tannin or tannic acid is present in a higher content than the specified upper limit, blistering will tend to occur in painted specimens by the corrosion test~ If silica and/or silica sol and/o~
alumina sol are present in a higher content than the specified upper limit, the ~oxmed coating will tend to become too brittle~
~; Since the stable pH ranges depend on the kinds of tannin, tannic acid, silica, silica sol, or alumina sol, an .
. . ~ . .
.20 inorganic acid such as phosphoric acid, nitric acid, sulfuric acid, hydrofluoric acid, hydrochloric acid and salts thereof ~ or an organic acid such as oxalic acid, citric acid, malic :
.. acid, maleic acid, phthalic acid, acetic acid, lactic acid, taxtaric acid, chloroacetic acid, acrylic acid and salts there-o~ ma~ ~e used to adjust the pH value of the aqueous solutions .
; and suspensions~
An alkaline compound such as sodium hydroxide, potassium h~dxoxide, lithium hydroxide, ammonium h~vdroxide or the like, ~ OX an amine such as ethyl amine, diethyl amine, triethyl ;`30 amine, ethanol amine or the like may be used for pH adjustment.
Since, however, the residual content of such water-soluble salts in the coating facilitates the adsorption of ~4~
. ', , ,,, , . . . - - - - ' F'--- '-- ' ., ~ , . .
~081407 . P-106-/g moisture in the air and at the same time has a possibility to enhance the corxosion, such ~Jater-soluble salts should be limited to an am~unt as small as possible and preferably excess soluble sal.ts are removed, if possible, by rinsing with water.
The aqueous solution or suspension of this invention may be added with a water-soluble, emulsifiable or dispersible organic polymer resin to improve the adhesion of the coating comprising mainly tannin, tannic acid, and silica, silica sol or alumina sol onto the metal surface, to provide flexibility to the coating and also to improve the corrosion resistance of the coating.
By embodying the process of this invention, it is possible to form a protective coating having an excellent corXosion resistance and to provide a paint base having excellent adhe~ion.
The invention will be illustrated by way of the follow.ing examples.
; EXAMPL~ 1 :. . .
A hot galvanized steel plate which had been temporarily treated with chromic acid and had a size of 100 x 300 x 0.3 mm .. was polished thrice by the wet Scotch prvcess to remove the chxomic acid adhered on the surface thereof. A treating ; suspension was-prepared by dispersing and dissolving 30 g of Chi~nese gallatannin (available from Fuji Chemical Industries , ~, Ltd~ as Tannic Acid AL) and 30 g of powdery silica (avail-: able ~rom Nihon Aexosil Co, Ltd, under the trademark ~erosil . 380~ into about 500 ml o~ deionized water and b~ making up to ; lOOO.g with pure water~ The pH value o~ the prepared suspension 3~ was about 3~5, The cleaned galvanized steel plate was coated with the suspension by the bar coating process with a No. 6 ~5~
.. ...... . -- F---.
108~407 P-10679 :~
bar and dxied in a hot air circulating oven at 120C for one minute to form the protective coating. The treated plate was then subjected to the salt spray test according to JIS-Z-2371.
It took about 200 to 240 hours prior to the development of white stains, thus the coating showed excellent corrosion resistance as compared with those obtained for the comparative test plates prepared according to Comparative Examples 1, 2, 3 and 4, Comparative Example 1 .
A hot galvanized steel plate identical to that of Example 1 was polished thrice by the wet Scotch process and the cleaned galvanized steel plate free from chromic acid was employed as the test plate.
i. . .. .
Comparative Example 2 15 A cleaned galvanized steel plate identical to that o~ Example 1 was txeated to as in Comparative Example 1 and wa~ coatèd with an aqueous solution of 1% by weight chromic ~ ''' acid in a manner similar to Example l and dried.
Camparative Example 3 ,20 A cleaned galvanized-steel plate identical.to that o~ Example 1 was treated as in Comparative Example 1 and was coated with an aqueous solution prepared by dissolving 30 g , of Chinese gallotannin in about 500 ml of deionized water and ~ade up to 1000 g by adding with deionized water in a manner ,.-si~m~lar to Example 1 and d~ied~
~omparati~e Example 4 cleaned galvanized steel plate identical to that . o~ Example 1 was treated as in Comparative Example 1 and was coated with an aqueous suspension prepared by dispersing 30 g ,30 of powdery silica (Aerosil 380) in about 500 ml of deionized water by means o~ a high speed agitator in a manner similar to Example 1 and dried~ -. . . ' :
~' . .. . .
~08140'7 P-10~79 The test plates prepared according to Example 1 and Comparative Examples 1, 2, 3 and 4 were coa~ed with a thermo~
settlng alkyd paint (,a paint for coating the back surface of S colored galvanized steel plates) by the bar coating process with a No~ 12 bar and dried and baked in a hot air circulating ,,,' oven at 280C for 50 seconds to form coatings having a thickness of 6 microns. The coated plates were scribed through the painted layer to the base metal by means of a razor blade edge and then subjected to salt spray test according to JIS-Z-2371 for 240 hours, Transparent tape was then applied to the ' coated surfaces and then peeled rapidly, On the test plate prepared in Example 1, the extent of corrosion developed from the scribe was a width of less than 3 mm on both of the sides ' 15 and no blistering was observed on the smooth surface of the p~int film.
When the film surface was scratched with a copper coin, it was difficult to penetrate to the galvanized layer.
' ~ When the test plates prep-ared in Comparative ~xamples ~20 1, 2, 3 and 4 were coated with the paint and subjected to , the corrosion test in the manner of Example 2, the results - were inferior to those in Example 2, These results are shown , in Table 1.
' .
, .
' ~7~
I
' , ~ - ~
P-10679 ~0 8 1 407 - TAble 1 Corrosion re- Corrosion Resis~ Scratch sistance of tance of painted resistance Unpainted test pl.ate 1) by coin test plate test 2) by salt spray test Width Blister .. . . . . . . . . . . . ..
Examples 1 and 2 200 - 240 hr 3 mm No blisters Good Comparative 2 hr, More Blisters Inferior Example 1 than ovex all 10 mm surface :.--10Comparative 120 -240 hr 3 mm Slightly Example 2 blistered Infexior - Comparative . Example 3 48 - 72 hx More Blisters Inferior than over all .:
10 mm - surface Comparative Example 4 24 hr More Blisters than over all Good 10 mm surface .... .... ... .~.~.. ~..... .. ..... .
.. _ . . . . :. . . . ~ . ___ I Note 1): Test for 240 hours according to the salt spray , test according to JIS-Z-2371, Note 2): Scratch resistance by copper coin.
.
A hot galvanized steeI plate cleaned as in Example 1 : . . ,. - - : . : -w~s coated.as in Example 1 with a suspension which was prepared by dissolving 30 g of Chinese gallotannin in about 500 ml of . deionized water, dispersing 100 g of alumina sol (available from Nissan Chemicals Co. Ltd, under the trade,mark Alumina Sol 100) and making up to 1000 g by adding deionized water,j When a.aorxosion test was carried out a~ in Example l, it.took 200 ` to 2~0 hours prior to the development o~ white stains.
, .
. -8~ ~.
.
. .... .
' '
Claims (2)
1. An aqueous composition comprising a tannin or tannic acid and a refractory oxide in a weight ratio of 100:1 to 1:100, wherein the concentration of tannin or tannic acid is 0.01 to 20 wt.% and the concentration of refractory oxide is 0.1 to 20 wt.%.
2. The composition of claim 1, wherein the refractory oxide is selected from the group consisting of silica, silica sol and alumina sol.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP50149557A JPS5273137A (en) | 1975-12-17 | 1975-12-17 | Process for forming protective coating on zinc or its alloy |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1081407A true CA1081407A (en) | 1980-07-15 |
Family
ID=15477762
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA268,064A Expired CA1081407A (en) | 1975-12-17 | 1976-12-16 | Treating zinc with aqueous tannin and silica or alumina |
Country Status (12)
| Country | Link |
|---|---|
| JP (1) | JPS5273137A (en) |
| AT (1) | AT346146B (en) |
| AU (1) | AU511796B2 (en) |
| BE (1) | BE849448A (en) |
| CA (1) | CA1081407A (en) |
| DE (1) | DE2654580A1 (en) |
| FR (1) | FR2335575A1 (en) |
| GB (1) | GB1558779A (en) |
| IT (1) | IT1065967B (en) |
| NL (1) | NL7613966A (en) |
| SE (1) | SE7614251L (en) |
| ZA (1) | ZA767497B (en) |
Families Citing this family (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4247344A (en) | 1975-10-15 | 1981-01-27 | Nippon Steel Corporation | Rust preventing treatment of metal-plated steel materials |
| JPS5337150A (en) * | 1976-09-02 | 1978-04-06 | Nippon Packaging Kk | Surface treatment of zinc or zinc alloy |
| DE3365679D1 (en) * | 1982-10-21 | 1986-10-02 | Ici Plc | Method of thickening aqueous latex compositions |
| DE19814605A1 (en) * | 1998-04-01 | 1999-10-07 | Kunz Gmbh | Means for sealing metallic substrates, in particular of zinc or zinc alloys |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS4827936A (en) * | 1971-08-14 | 1973-04-13 | ||
| JPS5028444A (en) * | 1973-07-07 | 1975-03-24 | ||
| JPS5171233A (en) * | 1974-12-18 | 1976-06-19 | Nippon Steel Corp | Aenmetsukikozaino boseishitajishoriho |
-
1975
- 1975-12-17 JP JP50149557A patent/JPS5273137A/en active Granted
-
1976
- 1976-12-02 DE DE19762654580 patent/DE2654580A1/en active Pending
- 1976-12-13 AU AU20499/76A patent/AU511796B2/en not_active Expired
- 1976-12-13 AT AT921876A patent/AT346146B/en not_active IP Right Cessation
- 1976-12-14 GB GB52051/76A patent/GB1558779A/en not_active Expired
- 1976-12-15 BE BE173298A patent/BE849448A/en unknown
- 1976-12-15 FR FR7637736A patent/FR2335575A1/en active Granted
- 1976-12-15 IT IT30429/76A patent/IT1065967B/en active
- 1976-12-16 NL NL7613966A patent/NL7613966A/en not_active Application Discontinuation
- 1976-12-16 CA CA268,064A patent/CA1081407A/en not_active Expired
- 1976-12-17 ZA ZA767497A patent/ZA767497B/en unknown
- 1976-12-17 SE SE7614251A patent/SE7614251L/en unknown
Also Published As
| Publication number | Publication date |
|---|---|
| AT346146B (en) | 1978-10-25 |
| BE849448A (en) | 1977-04-01 |
| IT1065967B (en) | 1985-03-04 |
| AU511796B2 (en) | 1980-09-04 |
| NL7613966A (en) | 1977-06-21 |
| JPS5433778B2 (en) | 1979-10-23 |
| SE7614251L (en) | 1977-06-18 |
| GB1558779A (en) | 1980-01-09 |
| DE2654580A1 (en) | 1977-06-30 |
| JPS5273137A (en) | 1977-06-18 |
| FR2335575B1 (en) | 1980-03-07 |
| ZA767497B (en) | 1977-11-30 |
| ATA921876A (en) | 1978-02-15 |
| FR2335575A1 (en) | 1977-07-15 |
| AU2049976A (en) | 1978-06-22 |
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