CA1089155A - Treating autodeposited coatings with cr composition - Google Patents
Treating autodeposited coatings with cr compositionInfo
- Publication number
- CA1089155A CA1089155A CA258,668A CA258668A CA1089155A CA 1089155 A CA1089155 A CA 1089155A CA 258668 A CA258668 A CA 258668A CA 1089155 A CA1089155 A CA 1089155A
- Authority
- CA
- Canada
- Prior art keywords
- coating
- composition
- resinous coating
- aqueous
- coatings
- 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
- C09D5/088—Autophoretic paints
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
- B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
- B05D7/00—Processes, other than flocking, specially adapted for applying liquids or other fluent materials to particular surfaces or for applying particular liquids or other fluent materials
- B05D7/14—Processes, other than flocking, specially adapted for applying liquids or other fluent materials to particular surfaces or for applying particular liquids or other fluent materials to metal, e.g. car bodies
- B05D7/142—Auto-deposited coatings, i.e. autophoretic coatings
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
- B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
- B05D7/00—Processes, other than flocking, specially adapted for applying liquids or other fluent materials to particular surfaces or for applying particular liquids or other fluent materials
- B05D7/14—Processes, other than flocking, specially adapted for applying liquids or other fluent materials to particular surfaces or for applying particular liquids or other fluent materials to metal, e.g. car bodies
- B05D7/142—Auto-deposited coatings, i.e. autophoretic coatings
- B05D7/144—After-treatment of auto-deposited coatings
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- Life Sciences & Earth Sciences (AREA)
- Engineering & Computer Science (AREA)
- Wood Science & Technology (AREA)
- Chemical & Material Sciences (AREA)
- Materials Engineering (AREA)
- Organic Chemistry (AREA)
- Application Of Or Painting With Fluid Materials (AREA)
- Chemical Treatment Of Metals (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
In a process wherein a resinous coating is formed on a metallic surface by immersing the surface in an acidic aqueous coating composition containing dispersed particles of resin, wherein said composition forms on said surface a resinous coating which increases in thickness the longer the surface is immersed in the composition and wherein the resinous coating is contacted with an aqueous solution containing Cr to improve properties of the resinous coating, the improvement com-prising contacting said resinous coating with an aqueous solution prepared by combining a hexavalent Cr-containing compound and hexavalent chromium/reduced chromium.
In a process wherein a resinous coating is formed on a metallic surface by immersing the surface in an acidic aqueous coating composition containing dispersed particles of resin, wherein said composition forms on said surface a resinous coating which increases in thickness the longer the surface is immersed in the composition and wherein the resinous coating is contacted with an aqueous solution containing Cr to improve properties of the resinous coating, the improvement com-prising contacting said resinous coating with an aqueous solution prepared by combining a hexavalent Cr-containing compound and hexavalent chromium/reduced chromium.
Description
10891SS ~-,' TREATING AUTODEPOSITED COATINGS WITH Cr COMPOSITION
Field of the Invention i . . ,, ~
This invention relates to the formation of .~ -organic coatings on metallic surfaces. More specifical~
- 5 ly, this inverltion relates to the deposition on metallic ;
,~ surfaces of organic coatings by contacting the metallic surfaces with an acidic aqueous coating solution contain~
ing dispersed particles of an organic coating-~orming ` ~ :
. ~
~ material such as resin particles. . ~ .
;~ 10 A relatively recent development in the coating field is the provision of water-based coating : .~
:~ compositions which are effective, without the aid of ~ -!~ electricity, in forming on metallic surfaces immersed .~ therein organic coatings that increase in thickness or -weight the longer the time the surfaces are immersed in the compositions. (For convenience, a coating _ ~ . ., .~ ': ' . , :
,' ' 1 ' ,~ , ''' , 1~85~55 formed from such a composition is hereafter referred to as "an organic coating which grows with time" or as an "autodeposited coating".) Speaking generally, compositions which are so effective comprise acidic aqueous coating solutions having dispersed therein particles of an organic material such as resin particles. Autodeposited coatings are formed from such compositions as a result of their ability to attack and dissolve from the metallic surface metal ions in amounts which cause the particles to deposit on the surface in a manner such that there 10 is a continuous buildup of organic coating on the surface.
Coatings formed from such compositions are distinctly different from coatings formed by immersing the metallic sur- '~
faces in conventional latices, that is, compositions compris-ing solid r?sin paxticles dispersed in water. The weight or 15 thickness of a coating formed by immersing a metallic surface ; in a conventional latex is not influenced by the time the surface is immersed in the latex. It is in the main influenced by the amount of resin solids dispersed in the aqueous medium.
. :.
, Coatings formed.from the aforementioned recently 20 developed coating composi~ions are also distinctly'different from coatings formed from earlier known acidic aqueous coat-ing solutions containing disper~ed solid resin particles and relatively high amounts of water soluble corrosion inhibitors, such as compounds containing hexavalent chromium. The use of ~,~ 25 relatively high amounts of corrosion inhibitors in such sol,u-tions deters-attack of the metallic surface to an extent such ~ that resinous coatings which grow with time are not obtaine~.
'~ Thus, resinous coatings formed by immersing metallic surfaces in such compositions are like those formed from immersing the ,30 metallic surfaces in conventional latices in that they do not grow with time.
,-2-. . , The use of the recently developed coating composi-tions which produce coatings which grow with time offer a number of advantages. For example, other factors held constant, they can be used to apply thicker organic coatinys to the 5 metallic surface in a shorter period of time and in a one-step ~ ~
operation. Also, the coating thickness can be controlled by ~ -varying the immersion time of the metallic surface in the coating composition. In general, coatings which have improved corrosion resistant properties and aesthetic appearance are 10 obtainable. These are but a few of the advantages which flow . from the use of said compositions.
The aforementioned type of composition is capable of forming organic coatings of excellent quality. However, for ~ertain applications it is desired that the corrosion re~
,-.- , 15 ~istant properties of the coating be better than those possessed ` ~ -by the coating formed from said composition and/or that the coating have a different appearance than that of the coating formed from said composition. -The present invention relates to improving the -corrosion resistant properties of autodeposited coatings and providing coatings which have a matted, dulled or lusterless appearance rather than a glossy appearance. -~
: . ~ .
, ' ' '' ' Reported Developments ~, .. ~;
It is ];~own ~:o improve the corrosion resistant properties of autodeposited coatings by contacting the wet or unfused coating '~ .
_3 - - . - - -- ~08~155 with: (a) an aqueous solution of hexavalent chromium, the source of which may be a water or acid soluble chromate or dichromate or CrO3; ~b) an aqueous solution of hexavalent chromium and formaldehyde-reduced forms of hexavalent chromium;
or an aqueous solution of phosphorous acid. For example, see U.S. Patent Nos.: 3,585,084; 3,592,699; 3,647,567; and 3,795,546.
The use of an aqueous solution of hexavalent chromium or of a hexavalent chromium/reduced chromium (formaldehyde-reduced)solution to dull the glossy surface of an autodeposited 10 coating is disclosed also in U.S. Patent No. 3,795,546.
The present invention relates to a chromium-containing aqueous solution which is particularly effective in improving the corrosion resistant properties of an autodeposited coating and dulling the glossy appearances thereof.
Summary of the Invention In accordance with this invention a wet or uncured autodeposited coating is contacted with an aqueous Cr solution comprlsing~
. . :. , `~ (a) at least about 0.3 g/l of Cr+6 in the form of a hexavalent chromium-containing compound;-and -.
(b) a Cr+6/reduced Cr mix in an amount such that the ;
total Cr from the mix in the composition is at least about 0.3 g/1, with about 30 to about 60 wt. % of the -, Cr in reduced form. ~
25 The use of the above aqueous Cr solution is effective in imparting ~ ;
a matted appearance to autodeposited coatings which otherwise would ~-... .
have a glossy appearance and is effective also in improving the corrosion resistant properties of the autodeposited coatings.
Detailed Description of the Invention ` 3G Coating compositions which are effective in forming organic coatings which grow with time are known. Examples of -; such coating compositions are described in U.S. Patent Nos.
~ .
1089155 D-11,759-C
3,585,084, 3,592,699, 3,709,743 and 3,776,848, in British Patent No. 1,241,991, in Canadian Patent No.
1,032,678 and in Belgian Patent of Addition No. 811,841.
Speaking generally, the acidic aqueous coating compositions of the aforementioned type function to attack and dissolve from a metallic surface contacted therewith metal ions in an amount sufficient to directly or indirectly cause organic particles in the region of the metallic surface to deposit thereon in a continuous fashion, that is, in a manner such that there is a buildup in the amount of organic material deposited on the surface the longer the time the surface is in contact with the composition. This deposition of the organic material on the metallic surface is achieved through chemical action of the coating composition on the metallic surface. The use of electricity which is necessary for the operation of some coating methods, such as the electrocoating method, is not required.
¦~ It is believed that the present invention will ¦ 20 be used most widely in connection with coatings formed 1 from compositions that contain solid particles of resin -~
dispersed in the aqueous phase of the compos-ltion~. The preferred composition has a pH of about 1.6 to about 4 and -is prepared from water, a ferric-containing compound, most preferably ferric fluoride, in an amount such that it contains the equivalent of about 0.5 to about 3.5 g/l of ferric iron, about 0.2 to about 5 g/l of HF, a pigment ~ -such as carbon black, and about 50 to about ;~ _ 5 _ . I
lO0 ~/1 of resin particles which are all of substantially the same size and substantially chemically homocJeneous, that is, each particle is comprised of thq same monomeric constituents present in substantially the same proportions or resin particles which are prepared by copolymerizing the following monomer~:
1) ahout 25 to about 70, and preferably about 40 to about 65 wt. ~ of a conjugated diene having, for example, 4 to about 9 carbon atoms, such as butadiene or isoprene;
Field of the Invention i . . ,, ~
This invention relates to the formation of .~ -organic coatings on metallic surfaces. More specifical~
- 5 ly, this inverltion relates to the deposition on metallic ;
,~ surfaces of organic coatings by contacting the metallic surfaces with an acidic aqueous coating solution contain~
ing dispersed particles of an organic coating-~orming ` ~ :
. ~
~ material such as resin particles. . ~ .
;~ 10 A relatively recent development in the coating field is the provision of water-based coating : .~
:~ compositions which are effective, without the aid of ~ -!~ electricity, in forming on metallic surfaces immersed .~ therein organic coatings that increase in thickness or -weight the longer the time the surfaces are immersed in the compositions. (For convenience, a coating _ ~ . ., .~ ': ' . , :
,' ' 1 ' ,~ , ''' , 1~85~55 formed from such a composition is hereafter referred to as "an organic coating which grows with time" or as an "autodeposited coating".) Speaking generally, compositions which are so effective comprise acidic aqueous coating solutions having dispersed therein particles of an organic material such as resin particles. Autodeposited coatings are formed from such compositions as a result of their ability to attack and dissolve from the metallic surface metal ions in amounts which cause the particles to deposit on the surface in a manner such that there 10 is a continuous buildup of organic coating on the surface.
Coatings formed from such compositions are distinctly different from coatings formed by immersing the metallic sur- '~
faces in conventional latices, that is, compositions compris-ing solid r?sin paxticles dispersed in water. The weight or 15 thickness of a coating formed by immersing a metallic surface ; in a conventional latex is not influenced by the time the surface is immersed in the latex. It is in the main influenced by the amount of resin solids dispersed in the aqueous medium.
. :.
, Coatings formed.from the aforementioned recently 20 developed coating composi~ions are also distinctly'different from coatings formed from earlier known acidic aqueous coat-ing solutions containing disper~ed solid resin particles and relatively high amounts of water soluble corrosion inhibitors, such as compounds containing hexavalent chromium. The use of ~,~ 25 relatively high amounts of corrosion inhibitors in such sol,u-tions deters-attack of the metallic surface to an extent such ~ that resinous coatings which grow with time are not obtaine~.
'~ Thus, resinous coatings formed by immersing metallic surfaces in such compositions are like those formed from immersing the ,30 metallic surfaces in conventional latices in that they do not grow with time.
,-2-. . , The use of the recently developed coating composi-tions which produce coatings which grow with time offer a number of advantages. For example, other factors held constant, they can be used to apply thicker organic coatinys to the 5 metallic surface in a shorter period of time and in a one-step ~ ~
operation. Also, the coating thickness can be controlled by ~ -varying the immersion time of the metallic surface in the coating composition. In general, coatings which have improved corrosion resistant properties and aesthetic appearance are 10 obtainable. These are but a few of the advantages which flow . from the use of said compositions.
The aforementioned type of composition is capable of forming organic coatings of excellent quality. However, for ~ertain applications it is desired that the corrosion re~
,-.- , 15 ~istant properties of the coating be better than those possessed ` ~ -by the coating formed from said composition and/or that the coating have a different appearance than that of the coating formed from said composition. -The present invention relates to improving the -corrosion resistant properties of autodeposited coatings and providing coatings which have a matted, dulled or lusterless appearance rather than a glossy appearance. -~
: . ~ .
, ' ' '' ' Reported Developments ~, .. ~;
It is ];~own ~:o improve the corrosion resistant properties of autodeposited coatings by contacting the wet or unfused coating '~ .
_3 - - . - - -- ~08~155 with: (a) an aqueous solution of hexavalent chromium, the source of which may be a water or acid soluble chromate or dichromate or CrO3; ~b) an aqueous solution of hexavalent chromium and formaldehyde-reduced forms of hexavalent chromium;
or an aqueous solution of phosphorous acid. For example, see U.S. Patent Nos.: 3,585,084; 3,592,699; 3,647,567; and 3,795,546.
The use of an aqueous solution of hexavalent chromium or of a hexavalent chromium/reduced chromium (formaldehyde-reduced)solution to dull the glossy surface of an autodeposited 10 coating is disclosed also in U.S. Patent No. 3,795,546.
The present invention relates to a chromium-containing aqueous solution which is particularly effective in improving the corrosion resistant properties of an autodeposited coating and dulling the glossy appearances thereof.
Summary of the Invention In accordance with this invention a wet or uncured autodeposited coating is contacted with an aqueous Cr solution comprlsing~
. . :. , `~ (a) at least about 0.3 g/l of Cr+6 in the form of a hexavalent chromium-containing compound;-and -.
(b) a Cr+6/reduced Cr mix in an amount such that the ;
total Cr from the mix in the composition is at least about 0.3 g/1, with about 30 to about 60 wt. % of the -, Cr in reduced form. ~
25 The use of the above aqueous Cr solution is effective in imparting ~ ;
a matted appearance to autodeposited coatings which otherwise would ~-... .
have a glossy appearance and is effective also in improving the corrosion resistant properties of the autodeposited coatings.
Detailed Description of the Invention ` 3G Coating compositions which are effective in forming organic coatings which grow with time are known. Examples of -; such coating compositions are described in U.S. Patent Nos.
~ .
1089155 D-11,759-C
3,585,084, 3,592,699, 3,709,743 and 3,776,848, in British Patent No. 1,241,991, in Canadian Patent No.
1,032,678 and in Belgian Patent of Addition No. 811,841.
Speaking generally, the acidic aqueous coating compositions of the aforementioned type function to attack and dissolve from a metallic surface contacted therewith metal ions in an amount sufficient to directly or indirectly cause organic particles in the region of the metallic surface to deposit thereon in a continuous fashion, that is, in a manner such that there is a buildup in the amount of organic material deposited on the surface the longer the time the surface is in contact with the composition. This deposition of the organic material on the metallic surface is achieved through chemical action of the coating composition on the metallic surface. The use of electricity which is necessary for the operation of some coating methods, such as the electrocoating method, is not required.
¦~ It is believed that the present invention will ¦ 20 be used most widely in connection with coatings formed 1 from compositions that contain solid particles of resin -~
dispersed in the aqueous phase of the compos-ltion~. The preferred composition has a pH of about 1.6 to about 4 and -is prepared from water, a ferric-containing compound, most preferably ferric fluoride, in an amount such that it contains the equivalent of about 0.5 to about 3.5 g/l of ferric iron, about 0.2 to about 5 g/l of HF, a pigment ~ -such as carbon black, and about 50 to about ;~ _ 5 _ . I
lO0 ~/1 of resin particles which are all of substantially the same size and substantially chemically homocJeneous, that is, each particle is comprised of thq same monomeric constituents present in substantially the same proportions or resin particles which are prepared by copolymerizing the following monomer~:
1) ahout 25 to about 70, and preferably about 40 to about 65 wt. ~ of a conjugated diene having, for example, 4 to about 9 carbon atoms, such as butadiene or isoprene;
2) about 5 to about 70, and preferably about 30 to about 65 wt. % of CH2=CHR, where;n ~-~
R is an aryl or a cyano group, for example, styrene or acrylonitrile;
R is an aryl or a cyano group, for example, styrene or acrylonitrile;
3) about 1 to about 50, and preferably 'a~out 3 to about 15 ~It. ~ of a vinyl halide such as vinyl chloride or vinylidene chloride; and
4) abou~ 0.5 to about 15, and preferably about - ~
1 to about 4 wt. % of a monoethylenically unsaturated ~onomer having a functional group selected from the class consisting of amide and carboxylic groups, such as acrylamide, methacrylamide, octyl acid maleate and mono~
ethylenically unsaturated monocarboxylic and dicarboxylic acids having about 3 to about 12 carbon atoms, and preferably about 3 to a~out 5 carbon atoms, such as, for example:
acrylic acid; cinnamic acid; methacrylic acid;
- crotonic acid; itaconic acid; maleic acid;
and fumaric acid.
~ . . ..... .
` -6~
. . - . ... . .: .. : -101~155 The resin is used most conveniently in the form of a latex which can be prepared a~cording to availabl~ techniques.
A particularly preferred latex contains particles of resin prepared from the aforementioned monomers, which particles are chemically and physically homogeneous. The resin particles of the-preferred latex are prepared from sty-rene, butadiene, vinylidene chloride and methacrylic acid.
In addition, the emulsifier content of the preferred latex ;
is about 1 to about 4% based on the resin solids and comprises ;
10 at least 90 wt. %, most preferably 100 wt. ~ of an anionic emulsifier such as a sulfonate, for example, sodium dodecyl-; benzene sulfonate, or ~ sulfosuccinate, for example, sodium `-oleoyl isopropanolamide sulfosuccinate, or a mixture thereof. -~
Although the coating compGsition can be contacted 15 with the metallic surface in a variety of ways, it is believed ~`
that the most widely-used method-of contact will comprise im~
mersing the metallic surface in the coating composition at room temperature. As mentioned above, the longer the metallic sur- ;~
; face is immersed in the coating composition, the greater the build~
20 up in coating thickness. It is believed that for most appli~
, ~ .
cations, desired coating thicknesses can be obtained by immers~
~-~ ing the metallic surface in the composition for a period of time within the range of about 30 seconds to about 3 minutes. .
However, it should be understood that longer or shorter periods 25 of time can be used.
Agitating the composition aids in maintaining it uniform. Also, agitation of the composition is effective in improving the uniformity of the coatings formed.
,' $~
101~5~15S
Water rinsing the coated surface after it has been withdrawn from the composition, and before significant drying takes place is effective in removing therefrom residuals such as acid and other ingredients of the bath that adhere to the coated surface. If such residuals are allowed to remain on the coated surface, they may change or adversely affect the quality of the coating. For a specific application, a deter~
mination can be made as to whether the residuals cause adverse effects which are not tolerable. If they do, they should be removed, for example, by water rinsing with tap or deionized water. If they do not, this step of removing them can be avoided.
Follo~ing any water rinse step that might be employed or after the coated surface is withdrawn from the compositio~
it is subjected to the aqueous chromium composition of this ~ ~
15 invention (described in detail below) and then dried. Fusion ~ ~ -of the resinous coating renders it continuous, thereby improv-ing its resistance to corrosion and adherence to the underlying metallic surface. ~`
The conditions under which the drying and/or fusion operation is carried out depend somewhat upon the type of resin employed. In general, heat will be required to fuse the resin.
The corrosion resistant properties of coatings fused at elevated temperature have been observed to be better than coatings which have been air dried. However, there are applications where air dried coatings can be used satisfactorily. The fusion of the coating should be carried out below temperatures which ~...:, - .
cause the resinous coating to degrade. Exemplary conditions used in fusing coatings produced according to the present in-vention are temperatures within the range of about 100 to about 200C for periods of time within the range of about 10 . ,. . "
IolB5~l5s to about 30 minutes, dependincJ on the mass of the coated part.
Baking the co~ting for a period of time until the metallic sur- :
face has reached the temperature of the heated environment has been used effectively.
For applications in which it is desired that the coated surface have particularly good corrosion resistant properties and ....... a matted appearance, as opposed to a glossy appearance, the co~ted surface is subjected to the aqueous chromium composition of the present invention prior to the curing or fusing of the coating. .
The Cr composi.tion of the present invention is prepared by mix-ing in water a soluble hexa~iale.~lt chrolmium compound t~i.th he~-avalent chromium/reduced chromium (Cr+6/reduced Cr) compounds. ~.
Examples of the soluble hexavalent chromium compound ;
that can be used are ammonium dichromate and alkali metal di-.15 chromates, for example, lithium dichromate, sodium dichromate and potasslum dichromate.
With respect to the Cr+6/reduced ~r constituent, it is i . ~
obtained by reacting a hexavalent chromium compound or mixture ~::
of such.compounds with a material that is effective in reducing .~ 20 some of the hexavalent chromium to a reduced form. Although var~
:: ious materials can be used to accomplish this, as is known in : . the art, it is preferred to use formaldehyde as the reducing .
. agent as disclosed in U.S. Patent No. 3,063,~77. For example, an :
aqueous concentrate of the composition is prepared by treating an : 25 aqueous solution of a hexavalent chromium compound, for example, an aqueous solution of chromic acid, with formaldehyde to reduce ~; a portion of the hexavalent chromium.
For the purposes of this invention, about 30 t:o abc,ut 60 wt~ % o the hexavalen~ chromi.uln should be :reduced. Suitable amounts of reducing ag~nt can ~e used to reduce the desired amount of 1(389~5S
hexavalent chromium. In preparing the aqueous concentra-te of -~ , Cr+6/reduced chromium, it may be found that the concentrate tends to gel on standing. The tendency toward gel formation may be substantially eliminated by the addition of small amounts of phosphoric acid either before or after the con-centrate is diluted. As little as about 0.05 ml of 75~ ~
H3PO4 solution (about 0.06 g of H3PO4) per gram of the total ''' chromium (both Cr+6 and reduced Cr) is usually sufficient to prevent such gelling. Higher amounts of H3PO4 can be used. ,~
The aqueous chromium solution for treating the coated `~
surface should comprise at least about 0.3 g/1 of Cr+6 added '~
,as a soluble Cr+6 compound and a Cr+6~reduced Cr mixture in '`
an amount such that the total, chrom~Dm in the composition from the mixture is at least abovt 0.3 g/l with about 30 to about 60 wt. ~ of the Cr in reduced form and preferably about 50 wt.
% of,the Cr in reduced form. Although the aforementioned in-: .
gredients can be used in amounts up to their solubility limits, ',~ ' ., , . , ~
satisfactory results can generally,be attained by using no ~ ~' more than about 3 g/1 of Cr+6 in the form of the soluble Cr+6 compound and a Cr+6/reduced Cr mix in an amount such that the ~' total Cr concentration from the mix in the composition is no , ;~
more than about 3 g~1. ' "~' l'he pH of the chromium solution is preferably within ,~ '', the range of about 2.5 to about 6.
' -10- ~ '~
108~1SS
The dilute aqueous Cr composition can be pre-pared by diluting with an appropriate amount of water an aqueous concentrate containing about 25 to about 400 g/l of Cr~6, added as the soluble Cr+6 compound, and a Cr+6/
reduced Cr mix in an amount such that the total Cr concentra-tion from the mix in the composition is about 25 to about 400 g/l with about 30 to about 60 wt. % of the Cr in re-duced form. ~;
After treating the coated substrate with the 1~ Cr composition of the present invention, the coating of thesurface can be fused as de~cribed above or it may be rinsed with water prior to the fusion of the coating.
Various types of metallic surfaces can be coated and treated in accordance with the present invention. Ferrifer~
1~ ous surface such as, for example, hot rolled and cold rolled ;~
; steel, and other metallic surfaces, for example, aluminum and zinc, can be used.
i, , ÆY~PL~S ~ -~
.- : ' . . ' ' ; :
~xamples below are illustrative of the practice of 20~the present invention.
The basic coating compositions used in all of the examples were prepared by combining Ingredients Amounts latex containing about 54% solids 180 g . -25 fer.~ic fluoride 3 g `~ `
hydro~luoric acid . . 2.3 g .-black pigment dispersion ~ S g - w~ter to make 1 liter.
~ ~ .
~10895155 .
` The resin of the latex used in the above composi-tion compl-ised ~bou~ 62~ styrene, about 30~ bu~adiene, about
1 to about 4 wt. % of a monoethylenically unsaturated ~onomer having a functional group selected from the class consisting of amide and carboxylic groups, such as acrylamide, methacrylamide, octyl acid maleate and mono~
ethylenically unsaturated monocarboxylic and dicarboxylic acids having about 3 to about 12 carbon atoms, and preferably about 3 to a~out 5 carbon atoms, such as, for example:
acrylic acid; cinnamic acid; methacrylic acid;
- crotonic acid; itaconic acid; maleic acid;
and fumaric acid.
~ . . ..... .
` -6~
. . - . ... . .: .. : -101~155 The resin is used most conveniently in the form of a latex which can be prepared a~cording to availabl~ techniques.
A particularly preferred latex contains particles of resin prepared from the aforementioned monomers, which particles are chemically and physically homogeneous. The resin particles of the-preferred latex are prepared from sty-rene, butadiene, vinylidene chloride and methacrylic acid.
In addition, the emulsifier content of the preferred latex ;
is about 1 to about 4% based on the resin solids and comprises ;
10 at least 90 wt. %, most preferably 100 wt. ~ of an anionic emulsifier such as a sulfonate, for example, sodium dodecyl-; benzene sulfonate, or ~ sulfosuccinate, for example, sodium `-oleoyl isopropanolamide sulfosuccinate, or a mixture thereof. -~
Although the coating compGsition can be contacted 15 with the metallic surface in a variety of ways, it is believed ~`
that the most widely-used method-of contact will comprise im~
mersing the metallic surface in the coating composition at room temperature. As mentioned above, the longer the metallic sur- ;~
; face is immersed in the coating composition, the greater the build~
20 up in coating thickness. It is believed that for most appli~
, ~ .
cations, desired coating thicknesses can be obtained by immers~
~-~ ing the metallic surface in the composition for a period of time within the range of about 30 seconds to about 3 minutes. .
However, it should be understood that longer or shorter periods 25 of time can be used.
Agitating the composition aids in maintaining it uniform. Also, agitation of the composition is effective in improving the uniformity of the coatings formed.
,' $~
101~5~15S
Water rinsing the coated surface after it has been withdrawn from the composition, and before significant drying takes place is effective in removing therefrom residuals such as acid and other ingredients of the bath that adhere to the coated surface. If such residuals are allowed to remain on the coated surface, they may change or adversely affect the quality of the coating. For a specific application, a deter~
mination can be made as to whether the residuals cause adverse effects which are not tolerable. If they do, they should be removed, for example, by water rinsing with tap or deionized water. If they do not, this step of removing them can be avoided.
Follo~ing any water rinse step that might be employed or after the coated surface is withdrawn from the compositio~
it is subjected to the aqueous chromium composition of this ~ ~
15 invention (described in detail below) and then dried. Fusion ~ ~ -of the resinous coating renders it continuous, thereby improv-ing its resistance to corrosion and adherence to the underlying metallic surface. ~`
The conditions under which the drying and/or fusion operation is carried out depend somewhat upon the type of resin employed. In general, heat will be required to fuse the resin.
The corrosion resistant properties of coatings fused at elevated temperature have been observed to be better than coatings which have been air dried. However, there are applications where air dried coatings can be used satisfactorily. The fusion of the coating should be carried out below temperatures which ~...:, - .
cause the resinous coating to degrade. Exemplary conditions used in fusing coatings produced according to the present in-vention are temperatures within the range of about 100 to about 200C for periods of time within the range of about 10 . ,. . "
IolB5~l5s to about 30 minutes, dependincJ on the mass of the coated part.
Baking the co~ting for a period of time until the metallic sur- :
face has reached the temperature of the heated environment has been used effectively.
For applications in which it is desired that the coated surface have particularly good corrosion resistant properties and ....... a matted appearance, as opposed to a glossy appearance, the co~ted surface is subjected to the aqueous chromium composition of the present invention prior to the curing or fusing of the coating. .
The Cr composi.tion of the present invention is prepared by mix-ing in water a soluble hexa~iale.~lt chrolmium compound t~i.th he~-avalent chromium/reduced chromium (Cr+6/reduced Cr) compounds. ~.
Examples of the soluble hexavalent chromium compound ;
that can be used are ammonium dichromate and alkali metal di-.15 chromates, for example, lithium dichromate, sodium dichromate and potasslum dichromate.
With respect to the Cr+6/reduced ~r constituent, it is i . ~
obtained by reacting a hexavalent chromium compound or mixture ~::
of such.compounds with a material that is effective in reducing .~ 20 some of the hexavalent chromium to a reduced form. Although var~
:: ious materials can be used to accomplish this, as is known in : . the art, it is preferred to use formaldehyde as the reducing .
. agent as disclosed in U.S. Patent No. 3,063,~77. For example, an :
aqueous concentrate of the composition is prepared by treating an : 25 aqueous solution of a hexavalent chromium compound, for example, an aqueous solution of chromic acid, with formaldehyde to reduce ~; a portion of the hexavalent chromium.
For the purposes of this invention, about 30 t:o abc,ut 60 wt~ % o the hexavalen~ chromi.uln should be :reduced. Suitable amounts of reducing ag~nt can ~e used to reduce the desired amount of 1(389~5S
hexavalent chromium. In preparing the aqueous concentra-te of -~ , Cr+6/reduced chromium, it may be found that the concentrate tends to gel on standing. The tendency toward gel formation may be substantially eliminated by the addition of small amounts of phosphoric acid either before or after the con-centrate is diluted. As little as about 0.05 ml of 75~ ~
H3PO4 solution (about 0.06 g of H3PO4) per gram of the total ''' chromium (both Cr+6 and reduced Cr) is usually sufficient to prevent such gelling. Higher amounts of H3PO4 can be used. ,~
The aqueous chromium solution for treating the coated `~
surface should comprise at least about 0.3 g/1 of Cr+6 added '~
,as a soluble Cr+6 compound and a Cr+6~reduced Cr mixture in '`
an amount such that the total, chrom~Dm in the composition from the mixture is at least abovt 0.3 g/l with about 30 to about 60 wt. ~ of the Cr in reduced form and preferably about 50 wt.
% of,the Cr in reduced form. Although the aforementioned in-: .
gredients can be used in amounts up to their solubility limits, ',~ ' ., , . , ~
satisfactory results can generally,be attained by using no ~ ~' more than about 3 g/1 of Cr+6 in the form of the soluble Cr+6 compound and a Cr+6/reduced Cr mix in an amount such that the ~' total Cr concentration from the mix in the composition is no , ;~
more than about 3 g~1. ' "~' l'he pH of the chromium solution is preferably within ,~ '', the range of about 2.5 to about 6.
' -10- ~ '~
108~1SS
The dilute aqueous Cr composition can be pre-pared by diluting with an appropriate amount of water an aqueous concentrate containing about 25 to about 400 g/l of Cr~6, added as the soluble Cr+6 compound, and a Cr+6/
reduced Cr mix in an amount such that the total Cr concentra-tion from the mix in the composition is about 25 to about 400 g/l with about 30 to about 60 wt. % of the Cr in re-duced form. ~;
After treating the coated substrate with the 1~ Cr composition of the present invention, the coating of thesurface can be fused as de~cribed above or it may be rinsed with water prior to the fusion of the coating.
Various types of metallic surfaces can be coated and treated in accordance with the present invention. Ferrifer~
1~ ous surface such as, for example, hot rolled and cold rolled ;~
; steel, and other metallic surfaces, for example, aluminum and zinc, can be used.
i, , ÆY~PL~S ~ -~
.- : ' . . ' ' ; :
~xamples below are illustrative of the practice of 20~the present invention.
The basic coating compositions used in all of the examples were prepared by combining Ingredients Amounts latex containing about 54% solids 180 g . -25 fer.~ic fluoride 3 g `~ `
hydro~luoric acid . . 2.3 g .-black pigment dispersion ~ S g - w~ter to make 1 liter.
~ ~ .
~10895155 .
` The resin of the latex used in the above composi-tion compl-ised ~bou~ 62~ styrene, about 30~ bu~adiene, about
5~ vinylidcne chlo~ide and about 3~ methacrylic acid. A
. film formed from the resin is soluble in refluxing chloro-benzene to the extent of about 13~. That the resin is cross-linked is indicated by its insolubility in Soxhlet extraction with chlorobenzene. The water soluble content of the latex is about 2~ based on the weight of dried resin, with the water soluble content comprising about lOg sodium phosphate, about 13% sodium oleoyl isopropanolamide sulfosuccinate and about 75% sodium dodecylbenzene sulfonate, the first mentioned ingredient being a buferlng agent used ln preparing tne latex, and the last ~ mentioned ingredients being emulsifierS.
The pH of the latex was about 7.8 and the surface tension thereof about 45-50 dynes/cm. The average par,ticle size of the resin was about 2,000 A.
The~ black pigment dispersion used in the above com-position is an aqueous dispersion having a total solids conte of about 36%. Carbon black comprises about 30~ of the dis-persion. It has a pH of about 10-11.5 and a specific gravity of about 1.17. The di$persion contains a nonionic dispersing agent for the solids, and is sold under the trademark Aquablak ; 115.
Unless stated otherwise, the metallic surfaces coated ~ ~
25 in the examples below are unpolished cold rolled steel panels -(Q-panels) 3" x 4". All metallic surfaces were cleaned with ` -~ -a conventional alkali cleaner and rinsed with water prior to ` ~--being coated.
-12- ;
- ,: ' ':
.
1~}89155 The salt spray test used in the examples was ASTM D-117, with the coating being scribed. At the co~pletion of the salt spray tests, the panels were rated on a numerical scale ranging from 10 to 0, the number '!10" representing no failure, that is, the appearance of the coated panel before ~-and af.er the salt spray test was basically the same, and the number "0" representing a coating failure of 1" or more from the scribe.
Example No. 1 One liter of aqueous Cr solution was prepared by ; -~
combining 3.6 g of ammonium dichromate with a formaldehyde~
reduced aqueous CrO3 solution in an amount such that the total -`~
Cr concentration from this solution was about 1.5 g, one-half o whicn was in ~e~uced form, and about 0.3 g Gf ~3PO~
A steel panel was immersed in the above described coating composition fox 2 minutes. The coated panel was then partially dried in air for 1 minute, immersed in the afore-i~ mentioned aqueous Cr solution for 30 seconds and thereafter y~
baked for 10 minutes at 170C. The baked coating had a matted appearance. After 168 hours of salt spray testing, the rating of the coating was 9 and after 336 hours and 480 -hours of testing the rating was 7. -~ `~
Example Nos. 2 to 5 The aqueous chromium solutions set forth in Table 1 :.
~ 25 below were prepared. ~ ~
....
~` , . .~ .
;, ' '~
~O~91~S
-Formaldehyde-Reduced Cr Solution Ex. g/l of Cr+6 from No. Cr+6 g/lreduced Cr, g/l (NH4)2 Cr27 2 0.13 0.13 0.28 3 0.26 0.26 0.56 4 0.51 0.51 1.12 0.77 0.77 1.67 The compositions of the above examples contained also 0.125, 0.25, 0.5 and 0.75 g/l respectively of 75% H3PO4. Steel head-light mounting rings were immersed in the above described coat- ~;~
ing compos;tion for 75 seconds. The coated rings were then partially dried in air for 1 minute, immersed in water for 30 seconds, immersed in the aqueous chromium solutions of Example ~ ~
.....
Nos. 2 to 5 above and then baked for 10 minutes at 220F and for 10 minutes at 315F. The baked coatings had a matted ~ -~
.-- . ~ ~:
appearance. The coated parts were then subjected to salt spray testing for 168 hours. The salt spray ratings are set ` ; ~
forth below. ~ ;
Cr Solution Rating Ex. No. 2 5 (coating blistered) ~ 3 7 7 ~ ~
" "
. :
A mounting ring treated in the same way, but without the Cr . ~ . ~ . .
treatment, had a glossy coating and a rating of 0.
~, -.-, ~- . : : : - . . - - - . . .. ` .
1089:~55 Example No. 6 An aqueous chromium concentrate containing 150 g/l of Na2O7.2H2O and a mixture of Cr+6/formaldehyde-reduced Cr in an amount such that the total Cr concentration from the mix-ture in said concentrate was S0 g/l with about 50 wt. % of theCr in reduced form, and 25 g/l of 75 wt. % H3PO4 was prepared.
The concentrate was diluted with water to provide a Cr treat-ment solution comprising about 3 wt. % of the concentrate.
A hot rolled steel car frame was immersed in the coating composition described above for 90 seconds. The coated frame was dried partially in air for 60 seconds, immersed in -~
water for 30 seconds, immersed in the above described Cr solu-tion for 30 seconds and then baked for 15 minutes at 315F.
The black coating on the frame had a matted appearance and the ;
salt spray rating after 504 hours of testing was 9. A frame ubiected to the same process steps, except for the Cr treat-ment step, has thereon a glossy coating and a ra~ting of 0 after 504 hours of salt spray testing.
, ' -.
'~
. ~. ~ ' "
~ ' ' `' " ~
~ .
:
. film formed from the resin is soluble in refluxing chloro-benzene to the extent of about 13~. That the resin is cross-linked is indicated by its insolubility in Soxhlet extraction with chlorobenzene. The water soluble content of the latex is about 2~ based on the weight of dried resin, with the water soluble content comprising about lOg sodium phosphate, about 13% sodium oleoyl isopropanolamide sulfosuccinate and about 75% sodium dodecylbenzene sulfonate, the first mentioned ingredient being a buferlng agent used ln preparing tne latex, and the last ~ mentioned ingredients being emulsifierS.
The pH of the latex was about 7.8 and the surface tension thereof about 45-50 dynes/cm. The average par,ticle size of the resin was about 2,000 A.
The~ black pigment dispersion used in the above com-position is an aqueous dispersion having a total solids conte of about 36%. Carbon black comprises about 30~ of the dis-persion. It has a pH of about 10-11.5 and a specific gravity of about 1.17. The di$persion contains a nonionic dispersing agent for the solids, and is sold under the trademark Aquablak ; 115.
Unless stated otherwise, the metallic surfaces coated ~ ~
25 in the examples below are unpolished cold rolled steel panels -(Q-panels) 3" x 4". All metallic surfaces were cleaned with ` -~ -a conventional alkali cleaner and rinsed with water prior to ` ~--being coated.
-12- ;
- ,: ' ':
.
1~}89155 The salt spray test used in the examples was ASTM D-117, with the coating being scribed. At the co~pletion of the salt spray tests, the panels were rated on a numerical scale ranging from 10 to 0, the number '!10" representing no failure, that is, the appearance of the coated panel before ~-and af.er the salt spray test was basically the same, and the number "0" representing a coating failure of 1" or more from the scribe.
Example No. 1 One liter of aqueous Cr solution was prepared by ; -~
combining 3.6 g of ammonium dichromate with a formaldehyde~
reduced aqueous CrO3 solution in an amount such that the total -`~
Cr concentration from this solution was about 1.5 g, one-half o whicn was in ~e~uced form, and about 0.3 g Gf ~3PO~
A steel panel was immersed in the above described coating composition fox 2 minutes. The coated panel was then partially dried in air for 1 minute, immersed in the afore-i~ mentioned aqueous Cr solution for 30 seconds and thereafter y~
baked for 10 minutes at 170C. The baked coating had a matted appearance. After 168 hours of salt spray testing, the rating of the coating was 9 and after 336 hours and 480 -hours of testing the rating was 7. -~ `~
Example Nos. 2 to 5 The aqueous chromium solutions set forth in Table 1 :.
~ 25 below were prepared. ~ ~
....
~` , . .~ .
;, ' '~
~O~91~S
-Formaldehyde-Reduced Cr Solution Ex. g/l of Cr+6 from No. Cr+6 g/lreduced Cr, g/l (NH4)2 Cr27 2 0.13 0.13 0.28 3 0.26 0.26 0.56 4 0.51 0.51 1.12 0.77 0.77 1.67 The compositions of the above examples contained also 0.125, 0.25, 0.5 and 0.75 g/l respectively of 75% H3PO4. Steel head-light mounting rings were immersed in the above described coat- ~;~
ing compos;tion for 75 seconds. The coated rings were then partially dried in air for 1 minute, immersed in water for 30 seconds, immersed in the aqueous chromium solutions of Example ~ ~
.....
Nos. 2 to 5 above and then baked for 10 minutes at 220F and for 10 minutes at 315F. The baked coatings had a matted ~ -~
.-- . ~ ~:
appearance. The coated parts were then subjected to salt spray testing for 168 hours. The salt spray ratings are set ` ; ~
forth below. ~ ;
Cr Solution Rating Ex. No. 2 5 (coating blistered) ~ 3 7 7 ~ ~
" "
. :
A mounting ring treated in the same way, but without the Cr . ~ . ~ . .
treatment, had a glossy coating and a rating of 0.
~, -.-, ~- . : : : - . . - - - . . .. ` .
1089:~55 Example No. 6 An aqueous chromium concentrate containing 150 g/l of Na2O7.2H2O and a mixture of Cr+6/formaldehyde-reduced Cr in an amount such that the total Cr concentration from the mix-ture in said concentrate was S0 g/l with about 50 wt. % of theCr in reduced form, and 25 g/l of 75 wt. % H3PO4 was prepared.
The concentrate was diluted with water to provide a Cr treat-ment solution comprising about 3 wt. % of the concentrate.
A hot rolled steel car frame was immersed in the coating composition described above for 90 seconds. The coated frame was dried partially in air for 60 seconds, immersed in -~
water for 30 seconds, immersed in the above described Cr solu-tion for 30 seconds and then baked for 15 minutes at 315F.
The black coating on the frame had a matted appearance and the ;
salt spray rating after 504 hours of testing was 9. A frame ubiected to the same process steps, except for the Cr treat-ment step, has thereon a glossy coating and a ra~ting of 0 after 504 hours of salt spray testing.
, ' -.
'~
. ~. ~ ' "
~ ' ' `' " ~
~ .
:
Claims
WHAT IS CLAIMED IS:
1. In a process wherein a resinous coating is formed on a metallic surface by immersing the surface in an acidic aqueous coating composition containing dispersed particles of resin, wherein said composition forms on said surface a resinous coating which increases in thickness the longer the surface is immersed in the composition and wherein the resinous coating is contacted with an aqueous solution containing Cr to improve properties of the resinous coating, the improvement comprising contacting said resinous coating with an aqueous solution containing a soluble hexavalent Cr-containing compound and hexavalent chromium/formaldehyde-reduced chromium, said aqueous solution comprising:
(a) at least about 0.3 g/l of Cr+6 in the form of a hexavalent chromium-containing compound and;
(b) a Cr+6/reduced Cr mix in an amount such that the total Cr from the mix in the composition is at least about 0.3 g/l, with about 30 to about 60 wt. % of the Cr in reduced form.
(a) at least about 0.3 g/l of Cr+6 in the form of a hexavalent chromium-containing compound and;
(b) a Cr+6/reduced Cr mix in an amount such that the total Cr from the mix in the composition is at least about 0.3 g/l, with about 30 to about 60 wt. % of the Cr in reduced form.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US60901775A | 1975-08-29 | 1975-08-29 | |
| US609,017 | 1975-08-29 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1089155A true CA1089155A (en) | 1980-11-11 |
Family
ID=24439022
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA258,668A Expired CA1089155A (en) | 1975-08-29 | 1976-08-09 | Treating autodeposited coatings with cr composition |
Country Status (5)
| Country | Link |
|---|---|
| JP (1) | JPS5228534A (en) |
| CA (1) | CA1089155A (en) |
| DE (1) | DE2638714C3 (en) |
| FR (1) | FR2321954A1 (en) |
| GB (1) | GB1559118A (en) |
Families Citing this family (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4098620A (en) * | 1977-06-20 | 1978-07-04 | Diamond Shamrock Corporation | Composite coating of enhanced resistance to attack |
| US6224947B1 (en) | 1983-07-25 | 2001-05-01 | Henkel Corporation | Process for forming a resinous coating from an autodepositing composition which includes internally stabilized vinylidene chloride copolymer |
| US5912297A (en) * | 1983-07-25 | 1999-06-15 | Henkel Corporation | Internally stabilized vinylidene chloride resin in autodeposition |
| US4647316A (en) * | 1984-03-23 | 1987-03-03 | Parker Chemical Company | Metal base coating composition comprising chromium, silica and phosphate and process for coating metal therewith |
| CA1256003A (en) * | 1984-03-23 | 1989-06-20 | Parker Chemical Company | Metal base coating composition comprising chromium, silica and phosphate and process for coating metal therewith |
| DE3442985A1 (en) * | 1984-11-26 | 1986-05-28 | Henkel KGaA, 4000 Düsseldorf | METHOD FOR IMPROVING THE CORROSION PROTECTION OF AUTOPHORETICALLY SEPARATED RESIN COATINGS ON METAL SURFACES |
| DE3500443A1 (en) * | 1985-01-09 | 1986-09-11 | Gerhard Collardin GmbH, 5000 Köln | METHOD FOR IMPROVING THE CORROSION PROTECTION OF AUTOPHORETICALLY DEPOSIT RESIN LAYERS ON METAL SURFACES |
| GB2215740B (en) * | 1988-02-08 | 1992-06-03 | Brent Chemicals Int | Composition and process for treating metal surfaces |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS5235692B1 (en) * | 1971-03-10 | 1977-09-10 |
-
1976
- 1976-08-09 CA CA258,668A patent/CA1089155A/en not_active Expired
- 1976-08-16 JP JP9811476A patent/JPS5228534A/en active Pending
- 1976-08-27 DE DE19762638714 patent/DE2638714C3/en not_active Expired
- 1976-08-30 FR FR7626135A patent/FR2321954A1/en active Granted
- 1976-08-31 GB GB3603076A patent/GB1559118A/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| JPS5228534A (en) | 1977-03-03 |
| FR2321954B1 (en) | 1980-06-13 |
| GB1559118A (en) | 1980-01-16 |
| DE2638714B2 (en) | 1980-11-20 |
| DE2638714C3 (en) | 1982-02-04 |
| FR2321954A1 (en) | 1977-03-25 |
| DE2638714A1 (en) | 1977-03-03 |
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