US 3804724 A
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April 16, 1974 J LGER' ETAL 3,804,724 PRODUCTION OF B KS ED IN THE ELE, ODEPOSITION METAL OF S PPABLE CO I Filed D60. ll, 19
United States Patent 3,804,724 PRODUCTION OF BLANKS USED IN THE ELEC- TRODEPOSITION 0F STRIPPABLE METAL COATINGS Justin C. Bolger, Dover, and Henry E. Molvar, Jr., Billerica, Mass., assignors to Canadian Copper Refiners Limited, Province of Quebec, Canada Filed Dec. 11, 1972, Ser. No. 313,839
Inc. Cl. C23b 7/08; B01k 1/00; C09j /02 US. Cl. 204-12 23 Claims ABSTRACT on THE DISCLOSURE Considerably improved metal blanks are produced when edge strips made of non-conductive synthetic plastic material are bonded to the edges of such blanks using an adhesive composition based on liquid bis-phenol A type epoxy resin and dicyandiamide curing agent. Such blanks aroused in the electrodeposition of strippable metal coatings such as copper cathode starting sheets.
This invention relates broadly to the electrodeposition of metals. More particularly, the invention relates to electrodeposition of strippable metal coatings, such as copper cathode starting sheets, on suitable metal blanks. The invention also covers the production of considerably improved metal blanks, for the purposes mentioned above, which blanks comprise edge strips of non-conductive synthetic plastic material; bonded onto at least the side edges thereof by means of an appropriate adhesive composition. i 1
It is well known in the art of electrorefining to produce starting sheets by electrodepositing onto a blank a thin, smooth and coherent metal coating or sheet which is then stripped from the. blank and used as the cathode starting sheet in the electrore'fining process.
With the advent of automatic stripping machines, it hasbecome very important to achieve a relatively easy removalof the starting sheets from the blank and several parting agents have recently been developed to facilitate thisoperation. One such parting agent is described in US. Pat. No. 3,523,873 of Aug. 11, 1970, by E. M. Elkin and consists of an aqueous emulsion comprising 220% by weight, of a polar, saturated, substantially water-insoluble, aliphatic organic compound selected from the group consisting of fatty acids, fatty alcohols and ester and glyceride derivatives thereof and a minor amount in the range of 0.05l% by weight of a sulfurv containing material.
Although such parting agents may produce the desired result of facilitating the stripping of the electrodeposited metal sheets, they do not solve the probem of metal seprather difficult. To partially obviate this difliculty, slotted edge strips of non-conductive plastic material have been mounted onto the side edges of the blank and held thereon by friction. This, however, is not a very satisfactory solution, because the frictional hold is usually insuificient- 1y tight and the electrolyte tends to penetrate between the plastic strip and the metal blank with resulting growth of metal on the edges and deformation or destruction of the plastic edge strip.
Suggestions have also been made to glue or bond the plastic edge strips to the metal blanks by means of a suitable adhesive, however, the extremely unfavorable and corrosive conditions of the hot acidic electrolytic bath lead to rapid degradation of most adhesives and the bond or :weld produced by such adhesives usually fails within a few days or at the most within a few weeks. Such adhesives, therefore, do not solve the problem because it is impractical and uneconomic to replace the plastic edge strips on the metal blanks every few weeks or so, as this involves a time consuming, usually manual and therefore expensive procedure during which the blank edges and the plastic strips must be thoroughly cleaned and in some instances the plastic strips must be etched, then the adhesive must be properly applied on the blank edges as well as on the plastic strips, then the strips must be properly applied onto the edges, then the excess adhesive must be removed, then the starting sheets with the plastic strips thereon must be cured, and finally they must be inspected to make sure that everything is satisfactory.
It is obvious that in a refinery where some 5,000 to 8,000 such blanks may be continuously used to produce starting sheets, if such procedure is repeated too often, it will not be economical. Also, procedure involving additional steps or materials would again be disadvantageous and impractical.
The applicants have therefore undertaken a thorough research program to find anadhesive composition which can be applied without any special difficulty, which will satisfactorily bond or weld the plastic'edge strips to the metal blanks and which will withstand the extremely unfavorable conditions of the hot acidic electrolytic bath as well as repeated strippings of the metal coatings deposited on the blank for a period-of at least one year and preferably longer, before the plastic edges need to be replaced.
It is generally known that in hot and humid conditions, it is particularly difficult to achieve a good bond between plastic materials and strongly alkaline metals, such as copper and zinc, and the applicants research program was therefore carried out with particular emphasis on these metals, although other metals such as steel, aluminum and the like which are generally easier to bond, were also included therein.
A good number of adhesives which were reasonably expected to succeed have been tested. Among these were:
(1) An amine cured liquid epoxy adhesive having approximately the following composition:
(2) Solvent based vinyl phenolic adhesive known under the trademark Bloomingdale FM-47:
Cure time/temp. 1 hr. 350 F. (3) Vinyl phenolic film adhesive known under the trademark Bloomingdale FM-238:
Cure time/temp. hr./350 F. 1
(4) Polyamide cured epoxy adhesive having approximately the following composition:
Epon 828 parts 100 Versamid 125 do 80 Silica filler do 100 Cure time/temp hr./210 F.-- 1 /2 (5) Liquid epoxy adhesive of approximately the following composition:
Epon 828 parts 100 EMI do 4 Cure time/temp. hr./300 F. 1
(6) Phenolic cured epoxy adhesive of approximately In the above the various terms have the following meanmgs:
Bloomingdale 'FM-47 and Bloomingdale FM-238: These are trademarks of the Bloomingdale Division of the American Cyanamid Company. Chemically they are composed of a mixture of a high molecular weight vinyl acetal resin, dissolved in organic solvent, mixed with a resol phenolic curing agent.
Epon 828: Liquid epoxy resin, made from bisphenol A and epichlorohydrin, molecular weight about 380. Epon is a trademark of Shell Chemical.
Epon 1007: Solid bisphenol A-epichlorohydrin epoxy resin. Molecular weight about 2000. Epon is a trademark of Shell Chemical.
DEAPA: Diethyl amino propylamine.
EMI: 2-ethyl, 4-methyl imidazole.
Versamid 125: Epoxy curing agent made by condensing dimer acid with an aliphatic polyamine. A trademark of General Mills Corporation.
Methylon 75108: Alkylated resol phenolic curing agent. A
trademark of General Electric Corporation.
All the above adhesives have, however, been found unsatisfactory and have failed within two or three days immersion in the hot acidic electrolyte.
It is therefore extremely surprising and unexpected that an adhesive which contains as essential constitutents a liquid bis-phenol A type epoxy resin, such as Epon 828, and dicyandiamide curing agent, provides a good long term resistance and bond retention of plastic to metal under the extremely unfavorable conditions of the electrolytic bath, as this has been found in accordance with the present invention.
The liquid bis-phenol A type epoxy resin is obtained in a generally known manner, namely by reacting bisphenol A with an epihalohydrin, such as epichlorohydrin. The reaction preferably takes place in the presence of an alkaline material such as sodium hydroxide or potassium hydroxide, sufficient to combine with the halogen released by the epihalohydrin during the course of the reaction. The amount of epihalohydrin used is generally in excess of the stoichiometric quantity.
The dicyandiamide curing agent is a dimer of cyanamide and is prepared by dimerization of cyanamide in a known manner:
NH ZNEC-CH: NEG-N-C cyanamide dicyandiamide M.P. 150 C.
In addition to the two above-mentioned essential components, the adhesive which is suitable for the purposes of 1 this invention may comprise a fiexibilizing agent to improve the peel strength and to provide a better adhesion to the plastic material. This may consists, for example, of carboxyl terminated nitrile rubbers such as CTBN or CTBNX which are trademarks of B. F. Goodrich. Or it can be achieved by replacing part of the bis-phenol A type epoxy resin with an ester-type epoxy resin made by reacting a di-basic acid with epichlorohydrin. An example of such a resin would be Epon 871 made by reacting dimer acid with epichlorohydrin or Epon 872 made by reacting dimer acid with a molar excess of Epon 828.
In addition, the adhesive will usually include a thickening agent or filler to give it some thixotropy to prevent it from running out of the joints when the parts are cured. Thickening agents such as colloidal silica, e.g. Cab-O-Sil which is a trademark of Cabot Corporation, or finely divided fillers such as silica, alumina or other oxides or silicates (such as kaolin, talc, asbestos, or pyrophyllite) are well known in the art and can be added to provide the necessary body and also to reduce shrinkage.
Furthermore, dicyandiamide curing agent reacts too slowly with the epoxy resin and requires too high a cure temperature for bonding most plastics. It is therefore a practice well known in the art to include accelerators or promoters to speed the reaction of dicyandiamide with the epoxy resins. Examples of such promoters or accelerators include tertiary amines, ureas, guanidines, imidazoles or other nitrogenous compounds or acid salts there of. Specific examples of such promoters are, for instance, 2-ethyl-4-methyl imidazole and benzyl dimethyl amine.
The proportions of the various components are not critical and are generally known in the art. The amount of the dicyandiamide must, of course, be effective to achieve proper curing of the epoxy resin employed; this amount is usually between 5 and 15% by weight with respect to the weight of the epoxy resin.
The amount of the flexibilizing agent must be effective to achieve the flexibilizing efiect and to improve peeling strength and adhesion to the plastic material. Generally, it can be anywhere between 5 and 60% by weight with respect to the weight of the epoxy resin, depending on the type of the fiexibilizing agent employed and on the desired final properties of the adhesive.
The amount of the thickening agent is again not critical; it depends on the type of thickening agent used and the consistency of thixotropy desired. Usually from 1 to 50% by weight relative to the weight of the epoxy resin can be used.
Finally, the amount of the accelerator or promoter employed depends again on its type and on the desired curing conditions. It can vary anywhere between 0.1% and about 20% by weight relative to the weight of the epoxy resin. Several patents are known describing the use of such promoters, such as U.S. Pat. No. 3,386,956 of June 4, 1969 issued to A. C. Nawakowski et al.: U.S. Pat. No. 3,391,113 of July 12, 1968 issued to Romeo Lopez et al.; U.S. Pat. No. 3,397,157 of Aug. 13, 1968 issued to G. W. Holmes and U.S. Pat. No. 3,562,215 of Feb. 9, 1971 issued to N. E. Moore. This illustrates that several adhesive compositions on the basis of epoxy resins and dicyandiamide curing agent are known in the art and they are ued with suitable accelerators or promoters.
A preferred but not limitative embodiment of the invention will now be described in greater detail with reference to the appended drawings in which:
FIG. 1 is a front view of a copper blank showing one plastic strip bonded to the edge thereof while the other plastic strip is in a position ready for bonding;
FIG. 2 is an enlarged section view of the plastic edge strip along line A--A; and
FIG. 3 is an enlarged section view of the bottom part of the copper blank along line B-B.
To test the effectiveness of the bond between metal blanks and plastic edge strips in accordance with this invention, regular refinery copper blanks were used. The upper portion of such blanks is provided with projections 11, 12 and 13 which are riveted byrivets 14 to a suspension bar 15 which supports the blank 10 when it is immersed in the electrolyte solution where starting sheets of about ,4 of pure copper are electrodeposited thereon.
In accordance with the present invention, the blanks 10 are provided with plastic edge strips 16 which are bonded to the edges 17 of these blanks 10 with an adhesive consisting essentially of a liquid bis-phenol A type epoxy resin combined with an effective amount of dicyandiamide curing agent. As already mentioned above, the adhesive may also compriseother constituents such as an accelerator or promoter, a fiexibilizing agent and a thickener or a filler.
Two preferred but not limitative compositions of such adhesive are as follows: I
Such adhesives can be prepared in ready to use form, e.g. in the form of a paste which is stored in suitable sealed cartridges or the like. They can also be prepared in the form of premixed powder by substituting a solid bis-phenol A-type epoxy resin for the above liquid resin, to which an organic solvent such as methyl ethyl ketone may be added to achieve desired consistency. One such particularly suitable paste adhesive is known under the trademark Uniset A-161 of Amicon Corporation.
For copper blanks and PVC edge strips the following bonding procedure can be employed:
(1) The PVC edge strips are soaked in hot water at about 150 F. for one hour in order to pre-relax the same.
(2) The PVC edge strips are washed with a soap-water solution.
(3) The edges of the blanks are washed with soapwater solution using a bristle brush or a steel rougher, then rinsed with water, distilled water and acetone.
(4) A layer of Uniset A-l61 adhesive is applied onto the edges of the blanks 10 and within grooves 18 of PVC edge strips 16 and allowed to set for 10-15 minutes.
(5) The edge strips are hammered onto the edges using a wooden hammer.
(6) The excess adhesive is removed from the edges.
(7) The blanks with the edge strips thereon are allowed to cure for 24 hours at room temperature or for 4 hours at 220 F.
(8) The blanks with the PVC strips bonded thereto are inspected before using them for electrodeposition of copper starting sheets.
Obviously, there may be many variations in the above procedure, however, one must ensure that the edges of the blanks and the inside grooved surfaces of the plastic strip are thoroughly cleaned and dried before applying the adhesive thereonto.
Also, although in the above procedure, edge strips made of rubberized PVC have been used, other non conducting synthetic resin materials can be employed provided they are sufficiently strong and flexible to be appliedonto the edges and to withstand the conditions of electrolytic process and of successive stripping operations without cracking or degradation. For example, polyethylene edge strips have been tried and found satisfactory. However, in the case of polyethylene strips, they must be acid etched prior to bonding. An example of such acid etching procedure is as follows:
(1) The edge strips are completely immersed in a fresh solution consisting of five parts sodium dichromate, eight parts tap water and one hundred parts of -98% sulfuric acid. The temperature of the etching bath is maintained at 6070 C. The time of immersion is about 5 minutes.
(2) The plastic strips are then removed from the etching bath and thoroughly rinsed with tap water.
(3) The strips are then dried with acetone.
There are many other etching procedures known for polyethylene and they can be adopted instead of the one described above. The man of the art should have no difficulty'in finding and using a procedure that fits him best.
It is interesting to note that the bond formed between the copper blank and the polyethylene strip was so strong as to tear the polyethylene when the joint was pulled apart. Also, polyethylene edge strips do not need to be soaked'in hot water to pre-relax the same as this is the case with PVC.
In addition to the above, polypropylene edge strips have been tried and again found satisfactory.
The shape of the edge strips 16 used by the applicants is illustrated in FIG. 2. The groove 18 provided in these strips is generally adapted to fit closely the edge 17 of the metal blank and the outside surface of the strip is preferably rounded. However, these again are not essential features of the invention and any suitable shape or form of the strips can be employed.
The edge strips 16 may be secured only to the side edges 17 of the blank 10 or they may be secured to the side edges 17 and the bottom edge 19 thereof. When they are secured only to the side edges, the bottom edge 19 is usually provided with an inverted V groove 20 on the bottom surface thereof as shown in FIG. 3. This V-grooved shape of the bottom edge prevents a strong bridging of electrodeposited metal at the bottom of the blank and in most cases during stripping the copper wedge formed at the bottom is weak enough to enable easy separation of the two starting sheets from one another. However, if stripping is carried out by way of automatic stripping machines using, for example, suction cups to efiect the stripping operation, then it may be preferable to have a plastic edge strip also at the bottom edge of the blank to achieve an easier and sharper separation.
Furthermore, when the edge strips are secured only to the side edges of the blank, it has been found preferable to extend them beyond the bottom corners of the blank andto seal the remaining gap, where groove 18 is empty, by filling it with a suitable thermoplastic material such as PVC. This provides an excellent seal at the corners of the blank. Moreover, if for some reason the edge strips 16 crack after being bonded to the edges 17 of blank 10, they can readily be repaired by simply sealing them with a suitable thermoplastic material. 7
When the metal blanks have been prepared as described above with the plastic edge strips securedly bonded thereto, they may be immersed in the conventional electrolytic bath solution for electrodeposition of metallic coatings thereon. In the case of copper blanks, these are suspended in the hot copper sulfate solution containing about 20% sulphuric acid and having a temperature of about F. When the required copper layer of about A has been deposited on each face of the blank, the blanks are removed, cooled in air to about 80 F. and the layers are stripped and sent for preparation as cathode starting sheets. The blanks remain in the electrolytic bath about 24 hours and are then removed and replaced by fresh blanks. The same blanks are therefore undergoing approximately a 48 hour immersion cycle.
Before immersion, the blanks are preferably treated with a parting agent, for example, by dipping them into an aqueous emulsion comprising 220% by weight of a polar, saturated, substantially water insoluble, aliphatic organic compound selected from the group consisting of fatty acids, fatty alcohols and ester and glyceride derivatives thereof and a minor amount in the range of 0.05 to 1% by weight of a sulfur containing material, as already mentioned at the beginning of this specification.
The first two copper blanks produced in accordance with the present invention have been tested on a regular industrial scale in the refinery of Canadian Copper Refiners Limited, Montreal-East, Canada, since Feb. 12, 1971 and they are still in service with any adverse effects being evident. In addition, a Whole cell using 47 blanks prepared in accordance with this invention has been tested on industrial scale in the same refinery since Aug. 14, 1971 and all these blanks are still in service without showing any adverse effects or degradation of the adhesive bond. It will be readily realized that this indeed is a surprising and unobvious result and a clear advance in the art of metal deposition. It should also be noted that the starting sheets are easily stripped from such blanks and have good sharp edges at the places where separation from the plastic edge strips is effected.
Although the specific embodiment described above refers to copper banks, this invention is by no means limited thereto. Zinc blanks, for example, can be prepared in the same manner and the plastic edge strips secured to such zinc blanks will also be entirely adequate. Metals such as steel and aluminum, which are not strongly alkaline in nature, will adhere to the plastic edge strips with even greater case than to copper and zinc and therefore will again produce entirely satisfactory results. The invention is therefore not limited to the specifically described embodiments and many modifications obvious to those familiar with the art can be made without departing from the spirit of the invention and the scope of the following claims.
1. Method of producing improved metal blanks used for eelctrodeposition of strippable metal sheets onto the opposite faces thereof, which comprises bonding onto at least the side edges of said blanks, edge strips made of non-conductive synthetic plastic material, said bonding being effected with an adhesive composition based on liquid bis-phenol A type epoxy resin and dicyandiamide curing agent.
2. Method according to claim 1, wherein said adhesive composition further comprises an effective amount of a fiexibilizing agent and a thickening agent for achieving a predetermined consistency and thixotropy.
3. Method according to claim 2, wherein said fiexibilizing agent is a carboxyl terminated nitrile rubber.
4. Method according to claim 2, wherein said flexibilizing agent is an ester type epoxy resin and it replaces part of the bis-phenol A type epoxy resin in the composition.
5. Method according to claim 2, wherein said thick ening agent consists of colloidal silica.
6. Method according to claim 2, wherein said thickening agent is selected from the group of silica and silicate fillers.
7. Method according to claim 2, wherein the flexibilizing agent is used in a proportion between about 5 and 60% by weight relative to the weight of the bis-phenol A type epoxy resin and the thickening agent is used in the proportion between about 1 and 50% by weight relative to the weight of the epoxy resin.
8. Method according to claim 1, wherein said adhesive composition further includes an accelerator to speed the reaction between the bis-phenol A type epoxy resin and the dicyanadiarnide curing agent.
9. Method according to claim 8, wherein said accelerator is selected from the group consisting of nitrogenous compounds and acid salts thereof.
10. Method according to claim 9, wherein said nitrogenous compounds are selected from the group consisting of tertiary amines, ureas, guanidines and imidazoles.
11. Method according to claim 8, wherein said accelerator is used in a proportion of 0.l20% by weight with respect to the weight of the bis-phenol A type epoxy resin.
12. Method according to claim 1, wherein said blanks are copper blanks.
13. Method according to claim 1, wherein said plastic strips are made of PVC.
14. Method according to claim 1, wherein said plastic strips are made of polyethylene or polypropylene.
15. Method according to claim 1, wherein said plastic stirps are bonded to the side edges and to the bottom edge of the metal blank.
16. Method according to claim 1, wherein said plastic strips are bonded only to the side edges of the metal blank and the bottom edge surface of said blank is provided with a groove in the form of an inverted V over its entire length.
17. Method according to claim 1, wherein said plastic strips are of rounded configuration and have a groove in the middle thereof adapted to be tightly fitted over the edges of the metal blank.
18. Method of producing improved copper blanks used for electrodeposition in a hot acidic electrolyte of copper starting sheets on the opposite faces thereof, which comprises bonding onto at least the side edges of said blanks, edge strips made of non conductive synthetic plastic material capable of withstanding the hot acidic electrolyte and the abuse of repeated starting sheet stripping operations, said plastic edge strips being bonded using the following procedure:
(a) the edges of the blanks and the plastic strips are thoroughly cleaned and dried;
(b) a layer of adhesive composition based on liquid bis-phenol A type epoxy resin and dicyandiamide curing agent is applied onto the edges of the blank and onto the surfaces of the plastic strips to be bonded thereto.
(c) the adhesive is allowed to set;
(d) the plastic edge strips are secured to the edges of the blank and any excess adhesive is removed; and
(e) the adhesive is allowed to cure.
19. Method according to claim 18, wherein the plastic edge strips are of PVC and are pre-relaxed by soaking them in hot water prior to cleaning them and applying the adhesive thereonto.
20. Method according to claim 18, wherein the plastic edge strips are of polyethylene and are acid etched prior to cleaning them and applying the adhesive thereto.
21. A method of making copper cathode starting sheets which comprises forming a copper blank comprising edge strips made of non conductive synthetic plastic material bonded onto at least the side edges thereof by means of an adhesive composition based on liquid bis-phenol A type epoxy resin and dicyandiamide curing agent, applying onto said blank a coating of a parting agent, electrodepositing substantially pure copper on the opposite faces of said blank, stripping the resulting electrodeposited copper sheets from said surfaces of the blank in the form of smooth, coherent copper sheets with sharp edges, and reusing the same blanks for successive operations on a 48 hour cycle for at least one year, before replacement of the plastic edge strips may be needed.
22. Method according to claim 21, wherein said parting agent is an aqueous emulsion comprising 220% by weight of a polar, saturated, substantially water-insoluble, aliphatic, organic compound selected from the group consisting of fatty acids, fatty alcohols and ester and glyceride derivatives thereof and a minor amount in 9 the range of 0.05-1% by weight of a sulfur-containing material.
23. Method according to claim 1, wherein said electrodeposited copper sheets are stripped 01f the blanks by an automatic stripping machine.
References Cited UNITED STATES PATENTS 1,994,144 3/1935 Merrill 204-281 Nawakowski 26047 Lopez 26047 Billett 204-12 Zolg 156-330 Moore 26047 THOMAS M. TUFARIELLO, Primary Examiner US. Cl. X.R.
2 1944 Tetrault 20 297 10 155-307, 204-281 P nt no -a.son .72n
Justin C. Bolger and Henry E. Molvar, Jr.
Inventor-( s) It is certified that error appears in the above -iden tified patent and that said Letters Patent are hereby correeted as shewn below:
- Column], line 16, 'with" should cbrrectly read. without has been misspelled 1 ins M (Claim 1)," "eleeiirodeposition" Signed 'end sesled this 3rd day of December 1974.
(SEAL-)- Attest: I McCOY M. GIBSON 3R.- Y I c. MARSHALL-HAHN Attesting Officer Commissioner of: Parents UNITED STATES PATENT 05mm CER'HFIQATE @F CQWEMWN Patent No. 3.80%.?24- I Damd Apx il 16,, 197
Inventor) Just 1n 0., Balgm' am Hmrey E9 NONI, Jr
ppears in the above-idntified patent It is certified that error a hereby corrected. as shown below:
and that said Letters Patent are Claim 23 moulfl mafia Method according to claim 2:1 wmwin I said electronee'bs ara fibfi'Q'Qfid @ff the deposited copper s Wtgtic mriwmg mafihin M blanks-by Cggumfi line 55, "1969" sheuld corrw'tly read 19 Signed and sealed this 1st day of October 1974.
McCOY M. GIBSON JR, C.a MARSHALL DANN Attesting Officer Commissioner of Patents USCOMM-DC GONG-P69 v.5. oovtmmum "mime omcl 1 nu o-nu-lu 1 FQORM PO-1050HO-69)