CA1203198A - Coating process - Google Patents
Coating processInfo
- Publication number
- CA1203198A CA1203198A CA000424731A CA424731A CA1203198A CA 1203198 A CA1203198 A CA 1203198A CA 000424731 A CA000424731 A CA 000424731A CA 424731 A CA424731 A CA 424731A CA 1203198 A CA1203198 A CA 1203198A
- Authority
- CA
- Canada
- Prior art keywords
- coating
- substrate
- slip
- process according
- metal
- 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
Links
Landscapes
- Paints Or Removers (AREA)
- Laminated Bodies (AREA)
Abstract
ABSTRACT
A process of coating a conductive substrate in which the substrate is first coated by electro-deposition and the initial coating is subsequently treated in a separate step with an aqueous dispersion of a slip-promoting additive.
A process of coating a conductive substrate in which the substrate is first coated by electro-deposition and the initial coating is subsequently treated in a separate step with an aqueous dispersion of a slip-promoting additive.
Description
~2~3~9~3 COATING PROCESS
This invention relates to a process for apply-ing a coating to a conductive substrate by electro-deposition.
The application of a coatinq to a conductive substrate by an electrodeposition process is advantageous, as compared with application by a co~ventional dip process using a more viscous and concentrated coating composition, since electrodeposition ensures that the final coating is of uniform thickness; there is good penetration into recesses; articles o~ complex shape can be coated; and there is little wastage due to drainage and rinsing of the more dilute coating composition.
In the electrodeposition process an adherent ; coating film, together with an outer layer of the coating composition, is present on the substrate immediately after the passage of electric current and removal of the substrate from a coating bath. The substrat~ may be, and is most usually, subjected to a subsequent rinsing treat-ment before the electrodeposited coating film is dried and/or stoved. In the conventional dip process, however, only a layer of coating composition is present on the substrate and this must be freed from water or other solvent by evaporation or it must be otherwise treated before an adherent coatinq film is produced.
It is known to add to coating compositions used in a dip coating process certain additives which modify the surface properties of the final coating, for example ;; additives which make the surface of the final coating more slippery so that it has improved resistance tp~
~203~98 scratching or abrasion. It has been believed to be necessary for success that the additive is already present in the composition before application to a sub-strate and the improved properties of the final coating are believed to be due to a high concentration of the additive at the surface of the coating film. In the case of an electrodeposition process it would seem reasonable to assume that when the initial adherent coating film is subjected to rinsing, the additive would be sub-stantially removed from the film surface and that the potential for improvement of surface properties would be lost. ~owever, we have found surprisingly that the sur~ace properties of the final coating film resulting from an electrodeposition process are improved, even when no slip-promoting additive has been added to the coating composition used, if the initial electro-deposited film is treated in a separate step with an aqueous dispersion of a slip-promoting additive.
Therefore according to this invention we provide a process for applying to a conductive substrate by elect-rodeposition a coating ha~ing improved surface properties, wherein an electric current is passed between the sub-strate as one electrode and a counter-electrode when immersed in a coating composition comprising a dispersion of film-forming polymer in an aqueous medium, the coated substrate being subsequently treated in a separate step with an a~ueous dispersion of a slip-promoting additive.
We also provide an aqueous dispersion of a slip-promoting additive for use in the present process.
We further provide a coated conductive substrate and a coated article which have been coated by the present process.
By a slip-promoting additive we mean any .--~
-~-` 12~13~98 additive which when present in a chemically similar aqueous coating composition used in a conventional dip or spray coating process makes a significant improvement in the resistance to scratching or abrasion, i.e. the mar-resistance, of the final coating. Suitable chemical categories of slip-promoting additive include the water-dispersible silicone resins, and hydrocarbons such as polyethylene wax. Particularly suitable additives are the water-dispersible silicones commercially available from Byk-Mallinckrodt under the trademark Byk, for example Byk 303 and 341, and from Dow Corning as Paint Additives 114 and 57; and polyethylene wax commercially available as Lubaprint 405/lOX. (Re~. TM) By an aqueous dispersion of the additive we mean that it is stably dispersed in particulate form or is dissolved in an agueous medium such as rinse water during its use. Similarly the film-forming polymer used in the coating composition may be present as a solution or as a stable dispersion of particles.
Preferably the initial coating film electro-deposited on the substrate is allowed to remain wet until it i5 treated with the aqueous dispersion of slip-promot-ing additive. Preferably the treated coating film is subjected to a heat treatment, for example stoving,as an imme~;ately following step. Preferably the slip-promoting additive is present in an aqueous rinse liquid and pref-erably the initial coating film is subjected to at least one rinse treatment before it i9 subjected to treatment with a rinse liquid containing the slip-promoting additive.
The general method of applying the electro-deposited coating film in the present process is conven-tional and the conductive substrate may be made an anode or a cathode. The process is particularly appropriate for the continuous coating of metal articles for example articles ~2~3~9~3 which comprise iron, steel, copper, aluminium, zinc, brass and other metals or alloys.
In one important embodiment of this invention a substantially transparent coating is first applied to a metal substrate having a surface appearance which it is desired to see and yet to protect from deterioration. A
process of this type is described in our Spanish Patent No. 493712 wherein an article which has been previously plated with a decorative metal or which comprises a polished or bright metal surface is made a cathode and is coated by electrodeposition with a transparent coating of film-forming material from an aqueous medium. By a decor-ative metal we mean a metal which imparts, optionally together with the cathodic coating, a decorative effect to the article for example high reflectivity, or a pleasing colour such as that of silver or gold. Such a metal may comprise for example a precious metal, for example gold, silver or platinum, or a non-precious metal such as copper, nickel ox tin, or a mixture or separate layers of precious or non-precious metals for example brass, or separate successive layers of nickel and silver.
The invention is particularly appropriate to the high cost metals such as silver. In many cases the metal will possess both decorative and preservative properties.
Polished or bright metal surfaces, as distinct from plated metal surfaces, may be produced, for example, by chemical, electrochemical or mechanical polishing of metal such as brass, copper or a precious metal.
The initial, electrodeposited, transparent film is then subjected to at least one aqueous rinse treatment before it is subjected to treatment with an aqueous rinse liquid containing the slip-promoting additive according to this invention.
lZ()3~1l98 The transparent coating described above may be tinted, for example by the presence of a dyestuff, but in a further embodiment of the invention,when it is not desired to see the surface of the substrate but to obliterate it,the coating may be opaque due to the presence of pigment, extender and the like.
In both of the embodiments just described there is obtained a final coating which has improved surface properties, for example improved mar resistance.
Suitable film-forming polymers for use in this invention include addition polymers such as those prepared from acrylic monomers; epoxy resins, for example the epoxy-amine adducts; polybutadiene resins; and alkyd resins.
The aqueous dispersion of slip-promoting agent may also contain other materials for example organic solv-ents and surface active agents.
Following the treatment with the aqueous disper-sions of slip-promoting additive the substrate is prefer-ably heated to an elevated temperature, for example in the range 120 - 220C.
In a typical process according to the invention in which it was desired to obtain a mar-resistant trans-parent coating on a steel article electxoplated with a thin coating of silver, the electroplated article was first coated by electrodeposition with an initial film of an epoxy-amine resin as described in our Spanish Patent mentioned above. The article was then rinsed with de-ionised water and was then rinsed again with de-ionised water in which was dispexsed the Dow Corning silicone slip-promoting additive PA57 reduced with water to an actual concentration of 0.5% silicone by weight in the rinse water. After stoving at 150C the final coating on the article had improved mar resistance as compared 319~
c~rlcl~ lay~r. ,n an~ particular case, the op~im~n ql~n~ of additional n~tal to ke used can be ~Pt~nrin~l ~y sir~le tr.ial following the ~P~rhin~ of this srPcification.
Any adlitiunal met~l m~$t, of course, be a met~ suitable for sputtPr;ng; it should have a melting point above 50C, ~e sta~le in air and electrically ~n~u~Ling. The preferred metals are generally transition metals and met~ls of Groups 3a to 5a of ~he Periodic Table (as se~ out on page B-3 of the ~n~h~k of Chemistry and Physi~s, 50th edition, pllhli~he~ by The Ch~m;r~
Rubber Co., Cleveland, Ohio), although other metals which are stable in air, melt above 50C and are electrically ~r~u~Ling may be used if desired.
~pP~iAlly good results have been obtained using, as the additional metal, metals which are thpm~plves n~ efl to fonm metal c~ides, preferably colourless met~l oxides (i.eO metal oxides that do not absorb light in the visible part of the ~e~-L~ ), during reactive sputtering of the overlying anti-reflection metal oxide layer, e.g.
aluminium, titanium and zirconium. When uslng metals ~hich become ~Yi~ised to colourl~ss metal oxides, increasing the amount of the metal used has less effect on the light trAn~mi~sion of the pr~u~L
than when using coloured netalsj e.g. copper and gold, which are not so readily nYi~i~e~ m e ~n~ncy of a metal to fonm an o~ide dL~en~s on the free energy of forma ion of the metal oxide. Apart from the surprisingly gocd results obtained with c~pFer, which is not readily nx;~;s~, the best results have been obtained using metals whose oxides `
'~7._ 1 . ", ,
This invention relates to a process for apply-ing a coating to a conductive substrate by electro-deposition.
The application of a coatinq to a conductive substrate by an electrodeposition process is advantageous, as compared with application by a co~ventional dip process using a more viscous and concentrated coating composition, since electrodeposition ensures that the final coating is of uniform thickness; there is good penetration into recesses; articles o~ complex shape can be coated; and there is little wastage due to drainage and rinsing of the more dilute coating composition.
In the electrodeposition process an adherent ; coating film, together with an outer layer of the coating composition, is present on the substrate immediately after the passage of electric current and removal of the substrate from a coating bath. The substrat~ may be, and is most usually, subjected to a subsequent rinsing treat-ment before the electrodeposited coating film is dried and/or stoved. In the conventional dip process, however, only a layer of coating composition is present on the substrate and this must be freed from water or other solvent by evaporation or it must be otherwise treated before an adherent coatinq film is produced.
It is known to add to coating compositions used in a dip coating process certain additives which modify the surface properties of the final coating, for example ;; additives which make the surface of the final coating more slippery so that it has improved resistance tp~
~203~98 scratching or abrasion. It has been believed to be necessary for success that the additive is already present in the composition before application to a sub-strate and the improved properties of the final coating are believed to be due to a high concentration of the additive at the surface of the coating film. In the case of an electrodeposition process it would seem reasonable to assume that when the initial adherent coating film is subjected to rinsing, the additive would be sub-stantially removed from the film surface and that the potential for improvement of surface properties would be lost. ~owever, we have found surprisingly that the sur~ace properties of the final coating film resulting from an electrodeposition process are improved, even when no slip-promoting additive has been added to the coating composition used, if the initial electro-deposited film is treated in a separate step with an aqueous dispersion of a slip-promoting additive.
Therefore according to this invention we provide a process for applying to a conductive substrate by elect-rodeposition a coating ha~ing improved surface properties, wherein an electric current is passed between the sub-strate as one electrode and a counter-electrode when immersed in a coating composition comprising a dispersion of film-forming polymer in an aqueous medium, the coated substrate being subsequently treated in a separate step with an a~ueous dispersion of a slip-promoting additive.
We also provide an aqueous dispersion of a slip-promoting additive for use in the present process.
We further provide a coated conductive substrate and a coated article which have been coated by the present process.
By a slip-promoting additive we mean any .--~
-~-` 12~13~98 additive which when present in a chemically similar aqueous coating composition used in a conventional dip or spray coating process makes a significant improvement in the resistance to scratching or abrasion, i.e. the mar-resistance, of the final coating. Suitable chemical categories of slip-promoting additive include the water-dispersible silicone resins, and hydrocarbons such as polyethylene wax. Particularly suitable additives are the water-dispersible silicones commercially available from Byk-Mallinckrodt under the trademark Byk, for example Byk 303 and 341, and from Dow Corning as Paint Additives 114 and 57; and polyethylene wax commercially available as Lubaprint 405/lOX. (Re~. TM) By an aqueous dispersion of the additive we mean that it is stably dispersed in particulate form or is dissolved in an agueous medium such as rinse water during its use. Similarly the film-forming polymer used in the coating composition may be present as a solution or as a stable dispersion of particles.
Preferably the initial coating film electro-deposited on the substrate is allowed to remain wet until it i5 treated with the aqueous dispersion of slip-promot-ing additive. Preferably the treated coating film is subjected to a heat treatment, for example stoving,as an imme~;ately following step. Preferably the slip-promoting additive is present in an aqueous rinse liquid and pref-erably the initial coating film is subjected to at least one rinse treatment before it i9 subjected to treatment with a rinse liquid containing the slip-promoting additive.
The general method of applying the electro-deposited coating film in the present process is conven-tional and the conductive substrate may be made an anode or a cathode. The process is particularly appropriate for the continuous coating of metal articles for example articles ~2~3~9~3 which comprise iron, steel, copper, aluminium, zinc, brass and other metals or alloys.
In one important embodiment of this invention a substantially transparent coating is first applied to a metal substrate having a surface appearance which it is desired to see and yet to protect from deterioration. A
process of this type is described in our Spanish Patent No. 493712 wherein an article which has been previously plated with a decorative metal or which comprises a polished or bright metal surface is made a cathode and is coated by electrodeposition with a transparent coating of film-forming material from an aqueous medium. By a decor-ative metal we mean a metal which imparts, optionally together with the cathodic coating, a decorative effect to the article for example high reflectivity, or a pleasing colour such as that of silver or gold. Such a metal may comprise for example a precious metal, for example gold, silver or platinum, or a non-precious metal such as copper, nickel ox tin, or a mixture or separate layers of precious or non-precious metals for example brass, or separate successive layers of nickel and silver.
The invention is particularly appropriate to the high cost metals such as silver. In many cases the metal will possess both decorative and preservative properties.
Polished or bright metal surfaces, as distinct from plated metal surfaces, may be produced, for example, by chemical, electrochemical or mechanical polishing of metal such as brass, copper or a precious metal.
The initial, electrodeposited, transparent film is then subjected to at least one aqueous rinse treatment before it is subjected to treatment with an aqueous rinse liquid containing the slip-promoting additive according to this invention.
lZ()3~1l98 The transparent coating described above may be tinted, for example by the presence of a dyestuff, but in a further embodiment of the invention,when it is not desired to see the surface of the substrate but to obliterate it,the coating may be opaque due to the presence of pigment, extender and the like.
In both of the embodiments just described there is obtained a final coating which has improved surface properties, for example improved mar resistance.
Suitable film-forming polymers for use in this invention include addition polymers such as those prepared from acrylic monomers; epoxy resins, for example the epoxy-amine adducts; polybutadiene resins; and alkyd resins.
The aqueous dispersion of slip-promoting agent may also contain other materials for example organic solv-ents and surface active agents.
Following the treatment with the aqueous disper-sions of slip-promoting additive the substrate is prefer-ably heated to an elevated temperature, for example in the range 120 - 220C.
In a typical process according to the invention in which it was desired to obtain a mar-resistant trans-parent coating on a steel article electxoplated with a thin coating of silver, the electroplated article was first coated by electrodeposition with an initial film of an epoxy-amine resin as described in our Spanish Patent mentioned above. The article was then rinsed with de-ionised water and was then rinsed again with de-ionised water in which was dispexsed the Dow Corning silicone slip-promoting additive PA57 reduced with water to an actual concentration of 0.5% silicone by weight in the rinse water. After stoving at 150C the final coating on the article had improved mar resistance as compared 319~
c~rlcl~ lay~r. ,n an~ particular case, the op~im~n ql~n~ of additional n~tal to ke used can be ~Pt~nrin~l ~y sir~le tr.ial following the ~P~rhin~ of this srPcification.
Any adlitiunal met~l m~$t, of course, be a met~ suitable for sputtPr;ng; it should have a melting point above 50C, ~e sta~le in air and electrically ~n~u~Ling. The preferred metals are generally transition metals and met~ls of Groups 3a to 5a of ~he Periodic Table (as se~ out on page B-3 of the ~n~h~k of Chemistry and Physi~s, 50th edition, pllhli~he~ by The Ch~m;r~
Rubber Co., Cleveland, Ohio), although other metals which are stable in air, melt above 50C and are electrically ~r~u~Ling may be used if desired.
~pP~iAlly good results have been obtained using, as the additional metal, metals which are thpm~plves n~ efl to fonm metal c~ides, preferably colourless met~l oxides (i.eO metal oxides that do not absorb light in the visible part of the ~e~-L~ ), during reactive sputtering of the overlying anti-reflection metal oxide layer, e.g.
aluminium, titanium and zirconium. When uslng metals ~hich become ~Yi~ised to colourl~ss metal oxides, increasing the amount of the metal used has less effect on the light trAn~mi~sion of the pr~u~L
than when using coloured netalsj e.g. copper and gold, which are not so readily nYi~i~e~ m e ~n~ncy of a metal to fonm an o~ide dL~en~s on the free energy of forma ion of the metal oxide. Apart from the surprisingly gocd results obtained with c~pFer, which is not readily nx;~;s~, the best results have been obtained using metals whose oxides `
'~7._ 1 . ", ,
Claims (6)
1. A process for applying a coating to a conductive substrate by electrodeposition wherein an electric current is passed between the substrate as one electrode and a counter-electrode when immersed in a composition comprising a dispersion of film forming polymer in an aqueous medium wherein the wet substrate having an intermediate coating is treated in a separate step with an aqueous dispersion of a slip-promoting additive and is then subjected to a heat treatment to produce a final coating.
2. A process according to Claim 1, wherein the coated substrate is subjected to at least one aqueous rinse before it is treated with the aqueous dispersion of slip-promoting additive.
3. A process according to Claim 1, wherein the substrate to be coated has been previously plated with a decorative metal which imparts a decorative effect to the article or comprises a polished or bright metal surface.
4. A process according to Claim 3, wherein the decorative metal is silver.
5. A process according to Claim 1, wherein the slip-promoting additive is selected from water-dispersible silicone resins and polyethylene waxes.
6. An article which has been coated by a process according to Claim 1.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8209244 | 1982-03-30 | ||
| GB8209244 | 1982-03-30 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1203198A true CA1203198A (en) | 1986-04-15 |
Family
ID=10529381
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000424731A Expired CA1203198A (en) | 1982-03-30 | 1983-03-29 | Coating process |
Country Status (3)
| Country | Link |
|---|---|
| CA (1) | CA1203198A (en) |
| ES (1) | ES521103A0 (en) |
| IT (1) | IT1201962B (en) |
-
1983
- 1983-03-22 IT IT20205/83A patent/IT1201962B/en active
- 1983-03-29 CA CA000424731A patent/CA1203198A/en not_active Expired
- 1983-03-29 ES ES521103A patent/ES521103A0/en active Granted
Also Published As
| Publication number | Publication date |
|---|---|
| IT1201962B (en) | 1989-02-02 |
| IT8320205A0 (en) | 1983-03-22 |
| ES8405451A1 (en) | 1984-06-01 |
| ES521103A0 (en) | 1984-06-01 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |