CA1227768A - Composite article of polymer with nickel-based and tin-based metal layers - Google Patents
Composite article of polymer with nickel-based and tin-based metal layersInfo
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- CA1227768A CA1227768A CA000441975A CA441975A CA1227768A CA 1227768 A CA1227768 A CA 1227768A CA 000441975 A CA000441975 A CA 000441975A CA 441975 A CA441975 A CA 441975A CA 1227768 A CA1227768 A CA 1227768A
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Abstract
Abstract of the Disclosure Metal-polymer composite articles, e.g., knobs, nuts, trimmings or ornaments, automotive components including grilles, headlamp bezels and surrounds, wheel covers, trim, hubs and like parts, having silvery hued metal surfaces comprise a surface plating composed essentially of an alloy of tin and Group VIII metal that is durably joined to a supportive solid body containing a directly electroplate able polymeric material, e.g., a composition wherein carbon black and sulfur are combined with a polymer. Polyvinyls, polyolefins, polystyrene, elastomers, polyamides and polyesters are among the suitable polymers.
A durably adherent layer of nickel-based metal is disposed between the body and the surface plating. Durability of the surface plating includes resistance to thermal cycling and to salt spray corrosion. Disclosure includes process whereby an article is prepared by electrode positing nickel-based and tin-based metal strata to provide desirable composite articles expeditiously at low cost for high quality production.
A durably adherent layer of nickel-based metal is disposed between the body and the surface plating. Durability of the surface plating includes resistance to thermal cycling and to salt spray corrosion. Disclosure includes process whereby an article is prepared by electrode positing nickel-based and tin-based metal strata to provide desirable composite articles expeditiously at low cost for high quality production.
Description
sty The present invention relates to composite articles and more particularly to providing metal-surfaced polymeric articles.
Many articles, e.g., knobs, nuts, ornaments and urns, automotive components including grilles, headlamp besets and surrounds, wheel covers, trim, hubs and like parts, are made of polymers (sometimes called plastics or resins). Frequently it is desired that polymeric articles have adhering metal surfaces for benefits such as appearance and cleanliness. Also in at least some instances metal surfacing it desirable for protection, smoothness and possib~ for imparting rigidity to the part, Very often silvery hued or colored surf such as those like freshly cleaned steel or brightly polished silver are desired Durability of desired characteristics is an important concede-earache The surface metal should be stable to maintain the desired color and continuity; and, accordingly, should resist corrosion, tarnish or other discoloration and avoid blistering cracking or other undue deterioration. Moreover, the metal-polymer structure should have endurance to certain environmental variations e.g., elevated temperatures, sub-zero temperature, salt water splashes and alkaline detergents.
Economy of production must also be considered and in this respect shorter production times, fewer steps, simplicity and avoiding waste disposal difficulties are desirable advantages.
Heretofore various metal coating methods, ego, vapor deposition, metal lamination, chemical plating, and electroplating haze been used on some polymers. Still, for providing metal-surfaced polymeric articles there are unfilled needs for achieving desired production economy sod product quality, particularly the inclusion of adherent durability of plating with desired color. Attempts at obtaining improved results have often involved adding speoiQlized layers of metal or other material and thus whatever the intended benefits introduced undesirable complexity, production costs and ox en unintended detrimental effects from the specialized material.
A promising approach to the production of metal-surfaced polymeric bodies was disclosed by luck in US. Patents 3,865~699 and 4~099,093.
In tress disclosures luck taught the use of polymeric composition, containing carbon black sulfur and polymer matrix as substrates that could be directly electroplated without pretreatment.
Because of its resistance to abrasion and tarnish relative ease of application and reasonable cost electroplated chromium ha achieved I
almost universal acceptance as an exterior electrode posit to provide a silvery-hued color where long-term durability is required.
Thus prior endeavors hare tried electroplated chromium to provide silvery-hued exteriors on bodies of directly electroplate able polymer which contain carbon black and surlier in a polymeric matrix. For example, nickel/chromium electrode posits on polymeric substrates in-clung directly electroplate able substrates, were suggested by luck (US. No. 3~865~699 and US. No. 4~009,093) and Hurler (US. 3~868~229).
Efforts at commercial development of directly electroplate able pullers after the initial disclosures by Lucia revealed that the bond joining an electrode posit to a directly electroplate able polymeric substrate containing sulfur and carbon black can deteriorate with age. This possible bond deterioration was recognized when electron plated samples were examined after long periods (about two years or more) of storage and exposure. Many possible causes have been ad-lanced for the bond instability phenomenon of directly electroplate-able polymers. No explanation appear complete and therefore the cause remains mainly speculative defying a priori solutions. Indeed all of the solutions to this problem remain to this date largely empirical and unpredictable.
lZ~Z776a Recondition of the bond instability phenomenon along with absence of predictable solutions, led to definition of an accelerated test, termed the "heat soak thermal stability HUTS test, to predict the tendency and extent of bond instability with changes in composite structure end processing. The test consists of placing an electroplated "directly placeable" part sty B5C for 16 hours, normalizing to root temperature and either evaluating residual adhesion or placing at _30& to test for blistering tendencies. This HUTS test has been found far more severe for directly electroplate able resins than the three or four combined thermal cycle/CASS cycles used for electroplated AS. Nevertheless, the HUTS test has been adopted as an acceptance test for electroplated "directly electroplate able" plastics where long-term (e.g. two years or more) durability against thermal shock and thermal cycling is required. The test is described in US.
Patents No. ~,195,117 (luck) and ~,191,617 (Hurler, luck and nipple), It is now known that neither the "all nickel chromium" deposits proposed by Hurler for AYE substrates (US. 3,868,229) nor the all nickel chromium" deposit of Lucius Example V (column 9, lines ; 20 3~-41 of US. ~,0~9,093), when applied to a directly electroplate able substrate, would acceptably pass the HUTS test and therefore would be unsatisfactory for use where long term durability against thermal shock and thermal cycling is required. This fact Ted to the ~nsertiQn of a copper inter layer, after initial plating of B directly electron placeable polymer with nickel and before finishing with nickel plus chromium. Copper inter layers have long been recognized for their beneficial effects on performance of electroplated plastics under thermal cycling conditions and copper inter layers were found to give improved performance for directly electroplate able plastics in the HUTS test. It was found however that acceptable performance in the ~,~,. . .
HUTS test could not be consistently achieved on all parts having various complex geometries even when relatively thick copper layers were employed.
Inconsistent performance of the composite structure (directly electroplate able plastic/nickel/copper/nickel/chromium) in HUTS stimulated development of nickel alloy strike coatings as disclosed in US. Patents No. 4,191~617 and No. 4,195,117.
Part of simple design capable of surviving the 16 heroic (HUTS) test (and therefore suitable for use where long term durability against thermal shock and thermal cycling is required were prepared under closely controlled plating conditions in a laboratory by first plating a directly electroplate able substrate with nickel/cobalt (or nickel/iron) and subsequently applying an all-nickel ; plus cur d us electrode posit. However the good HUTS results achieved with laboratory plating on simple parts could not be obtained with more variable production plating. Furthermore the nickel alloy strike followed by all-nickel plus cur d us electron deposit Has unsatisfactory on parts of complex design. Specifically deeply recessed areas experiencing low current densities during electrode position or those areas having a tortuous potential path to the anode were particularly unacceptable in the HUTS test when plated with 8 nickel alloy strike followed by all-nickel plus cur d us.
Many parts including automotive part such as grilles, lamp frame and other trim have such areas and these parts failed the HUTS when plated with nickel alloy strike + all-nickel+chro~ium.
Thus the nickel alloy strike coatings did not permit applying "all-nickel plus chromium" electrode posits on many production parts for use where long term durability against thermal shock and thermal cycling is required. In order to achieve consistently acceptable performance in the HUTS test in production and on complicated parts, it was necessary to reimpose a copper inter layer after the initial nickel alloy strike.
1;2Z77fi8 Thus for those applications where long-term durability against thermal shock and thermal cycling is required, current art offers the following composite structure: directly electroplate able substrate/
nickel alloy strike/ copper/nickel/chromium. This composite system suffers from a number of inherent deficiencies as follows. (1) The copper inter layer bleeds objectionable green corrosion products when corrosive media penetrates to it. Thus when used in corrosive environments such as exterior automotive a relatively thick multi-layered nickel deposit it necessary to protect the copper. Extended electroplating times may be required for such protection in deeply recessed areas. (2) Use of a copper inter layer significantly comply-gates the overall electroplating process. Multiple rinsing acid dips and reverse current leaning baths are generally recommended to prevent adhesion difficulties between copper and nickel. I Acid copper baths have the tendency to undercut the very thin nickel alloy strike deposits especially in recessed low current density areas. Thus, extended strike times are often required on comply-acted parts to ensure a strike layer thickness adequate to prevent undercutting by acid copper. These difficulties add up to signify scantly reduce the economic savings achievable via use of directly electroplate able plastic substrates.
There have now been discovered new metal-polymer composite articles and a process for production thereof that involve progress in overcoming difficulties in the metal-polymer composite art, and specifically those difficulties which have impeded selection of directly electroplate able polymers for metal-polymer composites for use in applications where long-term durability against thermal shock thermal cycling and corrosion is required.
An object of the present invention is to provide a new metal-polymer composite article.
~2~7768 Another object of the present invention is to provide a process for accomplishing a new combining of metal and polymer.
Objects and benefits of the invention will also become apparent from the following description and accompanying drawing, wherein the single view depicts a partial cross-section of an embodiment of the composite article of the invention.
The present invention contemplates a composite article having a body component at least part of whose surface is a directly electroplate able polymeric surface; an exterior stratum made of a silvery hued alloy comprising tin and metal chosen from Group VIII
of the Periodic Table of Chemical Elements (Group VIII metal), ad van-tageously a silvery hued tin-based tin/cobalt alloy; and an interior stratum located between and durably joined to both the directly elect troplateable polymeric surface of the body component and the exterior stratum to maintain the exterior stratum in a desired position in relation to the body. The interior stratum includes a nickel-based layer adherent to the directly electroplate able polymeric surface and can also include more layers durably joined among them-selves.
Herein "nickel-based" refers to metals including alloys) containing, by weight, 50% to 100~ nickel, and similarly, tin-based refers to metals containing 50% or more tin. Also, "alloy" refers to a substance having metallic properties and being composed of two or more chemical elements of which at least one is an elemental metal.
Also, the invention contemplates a process including providing a body component a portion of whose surface is a directly electroplate able polymeric surface; electrode positing a nickel-based metal in a layer with one face of the layer durably adherent to the directly electroplateable~rtioh ill the surface of the body; possibly depositing additional layers in a fashion to adherently bond these layers song themselves and to the initial nickel-~ased 1227~768 layer, and depositing an alloy containing tin and cobalt or possibly another Group VIII metal such as nickel onto the underlying layers in locations and proportions to form a stratum durably joined to the underlying layers and having an exterior Rilver-colored metallic character.
The directly electroplate able polymeric composition which forms at least a portion of the surface of the body component of the invention it characterized by:
a) having a polymeric matrix;
b) presence of carbon black in amounts sufficient for the overall composition to have an electrical volume resistivity of less than about 1000 ohm-cm., ego 100 ohm-cm.~ 10 ohm-cm.~ 1 ohm-cm.;
c) presence of sulfur (including any sulfur provided by sulfur donors) in amounts greater than about 0.1%
by weight of the overall polymer-carbon-sulfur composition; and d) presence en the polymer, carbon and sulfur in said directly electroplate able composition of matter in cooperative amounts required to achieve direct uniform, d and adherent coverage Or said composition of matter with an electrode posited nickel-based metal thus character-icing the surface as a directly electroplate able polymeric surface .
The minimum workable level of carbon black required to achieve electrical resistivities less than about 1000 ohm-cm appears to be about ô weight percent based on the weight of the polymer plus carbon black plus sulfur.
Polymers such as polyvinyls, polyolefins, polystyrene, elastomers, polyamides and polyesters are suitable for the matrix resin. Selection is made according to the physical properties no-``` ~227768 squired of the article. For instance whey the body component it jade entirely of a directly electroplate able polymeric eompo~itio~, handling and dimensional requirements generally dictate that the composition be rigid. In such cases one Gould choose a nutria polymer high when combined with appropriate amounts of carbon black and sulfur, would result in a directly olectroplateable polymeric composition having a modulus of olastieit~ other it flyer or id tenon Or greater than 7000 Guam (99,3~5 pi) at 23C and 50~
relative humidity. Various polymeric rosins and compositions for directly electroplate able polymers are referred to inter alias in my US. Patent No. 3~ô65,699 and in my SUE Technical Paper 790218 untitled "Directly Eleetro-Plato able Resins".
Good results have boon obtained with the directly olectroplateabl~
expositions supplied by MUD Technology Corp. under the trademark C~PREZ DIP
The tin-eontaining exterior metal stratum can be a binary alloy comprising tin and another element from Group VIII of the Periodic Taboo of Elements. Specifically twinkle alloys and tin/cobalt alloys ore reported to have good tarnish and abrasion resistance. Both of these alloys hays been suggested as possible substitutes for electrode posited ehromiu~. It it contemplated that other Group VIII metals, e.g., Pod, Pi, Gould show uproar corrosion resistance in similar tin-based alloys.
The earn re~istanee of both twinkle or tin/cobalt may be further onhaneed by brief contact (1 to 300 seconds) with aqueous, acidic 901-unions of ehromic acid ehrom3te or doormat ions, eom~only known as-ehromating. Alternatively, or in combination, earn resistance of the exterior tin-based metal stratum may be further enhanced if necessary by coating with elsewhere or pigmented film forming ~ubstanees.
However, widespread substitution of tin/cobalt or tin/nickel for chromium has not occurred because of chromiuml.s relatively low C08t, ease of plating and generally satisfactory performance. Applications for twinkle and tunability exterior electrodepo~its are generally in specs ialized eases such as barrel plating of Molly metal parts, which cannot be readily accomplished with electroplated chromium.
I
Twinkle electrode posits from acidic baths are reported to consist of 50 atomic percent tin / 50 atomic percent nickel, (66.9 weight percent tin / 33.1 weight percent nickel) with the deposit composition varying only about 3 weight percent either way over a wide range of operating conditions Details of composition and operating parameters for tin/nickel baths are given on page 338 of Metal Finishing Guidebook, Edited by Nathaniel Hall 1978. Details of composition and operating parameters for acidic tin/cobalt baths are less well-known than for tin/nickel. It is proposed that an operable acidic tin/cobalt bath would be obtained by substituting cobalt for nickel in the published compositions for tin/nickel baths. Tin/cobalt electrode posits from acidic baths, by analogy, would consist primarily of Snuck, an alloy of 50 atomic percent tin / 50 atomic percent cobalt (66.8 weight percent tin / 33.2 weight percent cobalt).
Thy color and hue of tin/cobalt electrode posits from alkaline baths is sensitive to operating conditions, indicating that the alloy composition is varied by changing conditions in the alkaline bath.
The tunability alloy electrode posits from alkaline baths ens thought to contain up to about 67 atomic percent cobalt with the balance tin.
Desirable proportions of tin and cobalt in the alloy are considered to be about 70 atomic percent tin and 30 atomic percent cobalt. The deposit color attains greater whiteness at increasing percentages of tin, e.g., 80~ Tony% cobalt or even 90% tin/10% cobalt. The deposit color be-comes increasingly darker and bluer as the percentage of cobalt is increased, ego 60% Tony cobalt or 50% Tony cobalt (atomic). An alkaline tin/cobalt bath is proposed in Example IV of this disclosure.
; Deposits of tin/cobalt are sometimes preferred from the stand-point that their blue-white coloration resembles that of chromium thereby improving color-matching in assemblies with parts made in different ways. Tin/nickel deposits have a slight pinkish cast which has certain aesthetic appeal but hinders good color matching to chromium plated parts.
The initial nickel-based layer in contact with and adherent to the directly electroplate able polymeric surface can be electrode posited I
from known nickel-based metal plating baths. Advantageously, the initial layer and subsequent layers in the interior stratum have nickel contents of about 70~ or higher e.g., 80%, 90%, nickel.
Watts nickel baths, all-chloride nickel baths sulfate-chloride nickel baths, all-sulfate nickel baths, and nickel sulfa mate contain-in baths can be used to electrode posit an initial nickel layer.
Good results have been obtained using a Watts bath, which may contain brighteners and other functional additives. Details of operation for these and other nickel baths can be obtained from textbooks on electroplating, ego Metal Finishing Guidebook, Edited by Nathaniel Hail Metals and Plastics Publications, Inc. 1978.
Nickel-based alloys with other Group VIII metals ego Nikko, Nephew can be deposited in contact with and adherent to the directly electron placeable polymeric surface from well-known electroplating baths employed for such alloy deposition. Suitable compositions and operational parameters can be obtained from US. Patents ~195,117 (Nephew) and ~,191,617 (Nikko).
It has been noted that addition of brighteners to the nickel-based plating bath used to deposit the initial nickel-based layer results in improved HIS performance for the composite of the invention, an effect particularly evident on complex parts in deeply recessed areas.
- Additional layers joining the initial electrode posited nickel-based layer and the exterior tin-based stratum can be advantageously employed to achieve functional, appearance or cost benefits, such as to impart brightness and provide durability to thermal and corrosive environments. For example, additional layers of soft "Watts" nickel followed by bright nickel followed by Doreen nickel are contemplated to be advantageous in manufacture of complex parts for automotive or other use where both harsh corrosive media and environmental extremes can be encountered. In applications requiring ; minimum cost, additional layers may include a zinc electrode posit or may be omitted entirely.
~227768 Neither the interior stratum nor the exterior Stratum nest contain copper either as an alloy or pure layer. Both strata can be essentially free of copper. Heretofore electrode posited copper layers have been found practically necessary in order to ensure long-term thermal cycling durability of electroplated polymers. The ability to achieve excellent results without having copper on the composite structure avoids detrimental effects of green copper staining in corrosive environments and the inherent complications of processing and pollution control involved in depositing copper.
lo The new composite structure disclosed here also does not no-quite the use of complicated and difficult to control multi-metal alloy strike deposits immediately adjacent to the directly electron placeable polymeric surface. Simple dull or bright nickel-based layers including pure nickel suffice thereby significantly reducing electroplating process complexity, pollution control requirements and overall costs. Specifically avoidance of n~ckel-iron strike deposits for articles of exterior automotive application improves the composite corrosion performance by avoiding the potential for red rust staining / Turning now to the accompanying drawing, which is taken in conjunction with the present specification, numeral 10 refers to a tin/cobalt plus nickel plus directly electroplate able polymer embodiment of the composite article of the invention. Article 10 has an exterior metal surface if which is of a silvery hue. Surface 11 is an exterior surface of tin/cobalt alloy exterior stratum 12 which is adherent to the upper face of interior stratum 13~ The interior stratum 13 is a double layer stratum comprising DurNi*~nickel layer aye adhering to bright nickel layer 13b. The downward face of stratum 13 adheres to the directly electroplate able polymer 14.
Article lo has durable adherence at alloy-nickel junction 15 and nickel-polymer junction 16. Thus stratum 12 (with surface 11) is Joined to directly electroplate able polymer 14.
* Registered Trademark and product ox Ox Metal Industries Corporation Z~768 For carrying the process of the invention into practice it is desirable that the directly electroplate able surface be of material selected in light of tune previous discussions of directly placeable polymers.
The layer adjoining the directly electroplate able polymeric surface ( the initial electrode posited nickel-based layer) can be applied by those procedures presently known for achieving initial coverage and growth of electrode posits on directly electroplate able polymers. In general the temperature of the electroplating bath used to achieve initial deposition of the nickel-based layer onto the directly electroplate able resin surface should not exceed about 65C.
For purposes of providing those skilled in the art with a further understanding of the invention, the following examples are set forth.
EXAMPLE I
A directly placeable polymeric composition known as KIPPERS DIP
Hi-Flow was injection molded to the configuration of l-inch hexagonal nuts The nuts had surfaces satisfactory for electron plating directly without additional surface preparation. A
quantity of the molded nuts were mounted as cathodes on an electron plating rack in a bright nickel plating bath and electroplated with nickel to provide a owe cm. (nominal) thick stratum of bright nickel adjoining the outer surfaces of the nuts. Particulars of the electroplating were:
Bath -- Udylite 66 Current -- 538 amperes per square meter Time -- 30 minutes Temperature -- 57&
The bright nickel plated nuts were rinsed in water. Next for the * Registered Trademark of POD Technology Corp.
** Registered Trademark of Ox Metal Industries Corporation lZZ7768 exterior metal stratum, the bright nicks plated nuts still racked a cathodes, were electroplated with tin/cobalt alloy onto the nickel to deposit a 0.00003 cm. thick layer of a silver-colored tin/cobalt alloy adhering as an exterior stratum over the nickel. The results satisfactorily provided the hex nuts with attractive silvery surfaces resembling freshly cleaned and polished steel. Analysis of the electrode posited tin/cobalt exterior stratum revealed a composition of approximately 70 atomic percent tin/30 atomic percent cobalt.
Particulars of this second plating of Example I are:
Bath -- * Udylite Achrolyte (slightly alkaline, pi about 800 to 8.6) Current -- 100 amperes per square meter Time -- 2 minutes Temperature -- 43&
Other configurations of metal-polymer composites satisfactorily made according to Example I included water tap strainers and bottle closures.
Satisfactory durability characteristics of Example I articles ; were confirmed with chemically and thermally accelerated evaluations of long-term corrosion resistance and thermal stability. In CUSS
(topper accelerated salt spray) exposures of 22 hours duration, all 3 of the specimens (hex nuts) that were exposed passed satisfactorily without suffering green or red rust staining, tarnishing or electron deposit blistering.
In HUTS (heat soak thermal stability) evaluations with programs of 16 hours in 85& air plus 1 hour in room temperature air plus 2 hours in minus 30C air, 2 specimens of Example I were evaluated and both endured successfully without deterioration.
The HUTS program it used as an accelerated evaluation of long term durability of bonding of electrode posits to directly electroplate able polymers.
In TO (Thermal Cycle) evaluations with cycle programs of * Registered Trademark of XY Metal Industries Corporation -- ~Z27768
Many articles, e.g., knobs, nuts, ornaments and urns, automotive components including grilles, headlamp besets and surrounds, wheel covers, trim, hubs and like parts, are made of polymers (sometimes called plastics or resins). Frequently it is desired that polymeric articles have adhering metal surfaces for benefits such as appearance and cleanliness. Also in at least some instances metal surfacing it desirable for protection, smoothness and possib~ for imparting rigidity to the part, Very often silvery hued or colored surf such as those like freshly cleaned steel or brightly polished silver are desired Durability of desired characteristics is an important concede-earache The surface metal should be stable to maintain the desired color and continuity; and, accordingly, should resist corrosion, tarnish or other discoloration and avoid blistering cracking or other undue deterioration. Moreover, the metal-polymer structure should have endurance to certain environmental variations e.g., elevated temperatures, sub-zero temperature, salt water splashes and alkaline detergents.
Economy of production must also be considered and in this respect shorter production times, fewer steps, simplicity and avoiding waste disposal difficulties are desirable advantages.
Heretofore various metal coating methods, ego, vapor deposition, metal lamination, chemical plating, and electroplating haze been used on some polymers. Still, for providing metal-surfaced polymeric articles there are unfilled needs for achieving desired production economy sod product quality, particularly the inclusion of adherent durability of plating with desired color. Attempts at obtaining improved results have often involved adding speoiQlized layers of metal or other material and thus whatever the intended benefits introduced undesirable complexity, production costs and ox en unintended detrimental effects from the specialized material.
A promising approach to the production of metal-surfaced polymeric bodies was disclosed by luck in US. Patents 3,865~699 and 4~099,093.
In tress disclosures luck taught the use of polymeric composition, containing carbon black sulfur and polymer matrix as substrates that could be directly electroplated without pretreatment.
Because of its resistance to abrasion and tarnish relative ease of application and reasonable cost electroplated chromium ha achieved I
almost universal acceptance as an exterior electrode posit to provide a silvery-hued color where long-term durability is required.
Thus prior endeavors hare tried electroplated chromium to provide silvery-hued exteriors on bodies of directly electroplate able polymer which contain carbon black and surlier in a polymeric matrix. For example, nickel/chromium electrode posits on polymeric substrates in-clung directly electroplate able substrates, were suggested by luck (US. No. 3~865~699 and US. No. 4~009,093) and Hurler (US. 3~868~229).
Efforts at commercial development of directly electroplate able pullers after the initial disclosures by Lucia revealed that the bond joining an electrode posit to a directly electroplate able polymeric substrate containing sulfur and carbon black can deteriorate with age. This possible bond deterioration was recognized when electron plated samples were examined after long periods (about two years or more) of storage and exposure. Many possible causes have been ad-lanced for the bond instability phenomenon of directly electroplate-able polymers. No explanation appear complete and therefore the cause remains mainly speculative defying a priori solutions. Indeed all of the solutions to this problem remain to this date largely empirical and unpredictable.
lZ~Z776a Recondition of the bond instability phenomenon along with absence of predictable solutions, led to definition of an accelerated test, termed the "heat soak thermal stability HUTS test, to predict the tendency and extent of bond instability with changes in composite structure end processing. The test consists of placing an electroplated "directly placeable" part sty B5C for 16 hours, normalizing to root temperature and either evaluating residual adhesion or placing at _30& to test for blistering tendencies. This HUTS test has been found far more severe for directly electroplate able resins than the three or four combined thermal cycle/CASS cycles used for electroplated AS. Nevertheless, the HUTS test has been adopted as an acceptance test for electroplated "directly electroplate able" plastics where long-term (e.g. two years or more) durability against thermal shock and thermal cycling is required. The test is described in US.
Patents No. ~,195,117 (luck) and ~,191,617 (Hurler, luck and nipple), It is now known that neither the "all nickel chromium" deposits proposed by Hurler for AYE substrates (US. 3,868,229) nor the all nickel chromium" deposit of Lucius Example V (column 9, lines ; 20 3~-41 of US. ~,0~9,093), when applied to a directly electroplate able substrate, would acceptably pass the HUTS test and therefore would be unsatisfactory for use where long term durability against thermal shock and thermal cycling is required. This fact Ted to the ~nsertiQn of a copper inter layer, after initial plating of B directly electron placeable polymer with nickel and before finishing with nickel plus chromium. Copper inter layers have long been recognized for their beneficial effects on performance of electroplated plastics under thermal cycling conditions and copper inter layers were found to give improved performance for directly electroplate able plastics in the HUTS test. It was found however that acceptable performance in the ~,~,. . .
HUTS test could not be consistently achieved on all parts having various complex geometries even when relatively thick copper layers were employed.
Inconsistent performance of the composite structure (directly electroplate able plastic/nickel/copper/nickel/chromium) in HUTS stimulated development of nickel alloy strike coatings as disclosed in US. Patents No. 4,191~617 and No. 4,195,117.
Part of simple design capable of surviving the 16 heroic (HUTS) test (and therefore suitable for use where long term durability against thermal shock and thermal cycling is required were prepared under closely controlled plating conditions in a laboratory by first plating a directly electroplate able substrate with nickel/cobalt (or nickel/iron) and subsequently applying an all-nickel ; plus cur d us electrode posit. However the good HUTS results achieved with laboratory plating on simple parts could not be obtained with more variable production plating. Furthermore the nickel alloy strike followed by all-nickel plus cur d us electron deposit Has unsatisfactory on parts of complex design. Specifically deeply recessed areas experiencing low current densities during electrode position or those areas having a tortuous potential path to the anode were particularly unacceptable in the HUTS test when plated with 8 nickel alloy strike followed by all-nickel plus cur d us.
Many parts including automotive part such as grilles, lamp frame and other trim have such areas and these parts failed the HUTS when plated with nickel alloy strike + all-nickel+chro~ium.
Thus the nickel alloy strike coatings did not permit applying "all-nickel plus chromium" electrode posits on many production parts for use where long term durability against thermal shock and thermal cycling is required. In order to achieve consistently acceptable performance in the HUTS test in production and on complicated parts, it was necessary to reimpose a copper inter layer after the initial nickel alloy strike.
1;2Z77fi8 Thus for those applications where long-term durability against thermal shock and thermal cycling is required, current art offers the following composite structure: directly electroplate able substrate/
nickel alloy strike/ copper/nickel/chromium. This composite system suffers from a number of inherent deficiencies as follows. (1) The copper inter layer bleeds objectionable green corrosion products when corrosive media penetrates to it. Thus when used in corrosive environments such as exterior automotive a relatively thick multi-layered nickel deposit it necessary to protect the copper. Extended electroplating times may be required for such protection in deeply recessed areas. (2) Use of a copper inter layer significantly comply-gates the overall electroplating process. Multiple rinsing acid dips and reverse current leaning baths are generally recommended to prevent adhesion difficulties between copper and nickel. I Acid copper baths have the tendency to undercut the very thin nickel alloy strike deposits especially in recessed low current density areas. Thus, extended strike times are often required on comply-acted parts to ensure a strike layer thickness adequate to prevent undercutting by acid copper. These difficulties add up to signify scantly reduce the economic savings achievable via use of directly electroplate able plastic substrates.
There have now been discovered new metal-polymer composite articles and a process for production thereof that involve progress in overcoming difficulties in the metal-polymer composite art, and specifically those difficulties which have impeded selection of directly electroplate able polymers for metal-polymer composites for use in applications where long-term durability against thermal shock thermal cycling and corrosion is required.
An object of the present invention is to provide a new metal-polymer composite article.
~2~7768 Another object of the present invention is to provide a process for accomplishing a new combining of metal and polymer.
Objects and benefits of the invention will also become apparent from the following description and accompanying drawing, wherein the single view depicts a partial cross-section of an embodiment of the composite article of the invention.
The present invention contemplates a composite article having a body component at least part of whose surface is a directly electroplate able polymeric surface; an exterior stratum made of a silvery hued alloy comprising tin and metal chosen from Group VIII
of the Periodic Table of Chemical Elements (Group VIII metal), ad van-tageously a silvery hued tin-based tin/cobalt alloy; and an interior stratum located between and durably joined to both the directly elect troplateable polymeric surface of the body component and the exterior stratum to maintain the exterior stratum in a desired position in relation to the body. The interior stratum includes a nickel-based layer adherent to the directly electroplate able polymeric surface and can also include more layers durably joined among them-selves.
Herein "nickel-based" refers to metals including alloys) containing, by weight, 50% to 100~ nickel, and similarly, tin-based refers to metals containing 50% or more tin. Also, "alloy" refers to a substance having metallic properties and being composed of two or more chemical elements of which at least one is an elemental metal.
Also, the invention contemplates a process including providing a body component a portion of whose surface is a directly electroplate able polymeric surface; electrode positing a nickel-based metal in a layer with one face of the layer durably adherent to the directly electroplateable~rtioh ill the surface of the body; possibly depositing additional layers in a fashion to adherently bond these layers song themselves and to the initial nickel-~ased 1227~768 layer, and depositing an alloy containing tin and cobalt or possibly another Group VIII metal such as nickel onto the underlying layers in locations and proportions to form a stratum durably joined to the underlying layers and having an exterior Rilver-colored metallic character.
The directly electroplate able polymeric composition which forms at least a portion of the surface of the body component of the invention it characterized by:
a) having a polymeric matrix;
b) presence of carbon black in amounts sufficient for the overall composition to have an electrical volume resistivity of less than about 1000 ohm-cm., ego 100 ohm-cm.~ 10 ohm-cm.~ 1 ohm-cm.;
c) presence of sulfur (including any sulfur provided by sulfur donors) in amounts greater than about 0.1%
by weight of the overall polymer-carbon-sulfur composition; and d) presence en the polymer, carbon and sulfur in said directly electroplate able composition of matter in cooperative amounts required to achieve direct uniform, d and adherent coverage Or said composition of matter with an electrode posited nickel-based metal thus character-icing the surface as a directly electroplate able polymeric surface .
The minimum workable level of carbon black required to achieve electrical resistivities less than about 1000 ohm-cm appears to be about ô weight percent based on the weight of the polymer plus carbon black plus sulfur.
Polymers such as polyvinyls, polyolefins, polystyrene, elastomers, polyamides and polyesters are suitable for the matrix resin. Selection is made according to the physical properties no-``` ~227768 squired of the article. For instance whey the body component it jade entirely of a directly electroplate able polymeric eompo~itio~, handling and dimensional requirements generally dictate that the composition be rigid. In such cases one Gould choose a nutria polymer high when combined with appropriate amounts of carbon black and sulfur, would result in a directly olectroplateable polymeric composition having a modulus of olastieit~ other it flyer or id tenon Or greater than 7000 Guam (99,3~5 pi) at 23C and 50~
relative humidity. Various polymeric rosins and compositions for directly electroplate able polymers are referred to inter alias in my US. Patent No. 3~ô65,699 and in my SUE Technical Paper 790218 untitled "Directly Eleetro-Plato able Resins".
Good results have boon obtained with the directly olectroplateabl~
expositions supplied by MUD Technology Corp. under the trademark C~PREZ DIP
The tin-eontaining exterior metal stratum can be a binary alloy comprising tin and another element from Group VIII of the Periodic Taboo of Elements. Specifically twinkle alloys and tin/cobalt alloys ore reported to have good tarnish and abrasion resistance. Both of these alloys hays been suggested as possible substitutes for electrode posited ehromiu~. It it contemplated that other Group VIII metals, e.g., Pod, Pi, Gould show uproar corrosion resistance in similar tin-based alloys.
The earn re~istanee of both twinkle or tin/cobalt may be further onhaneed by brief contact (1 to 300 seconds) with aqueous, acidic 901-unions of ehromic acid ehrom3te or doormat ions, eom~only known as-ehromating. Alternatively, or in combination, earn resistance of the exterior tin-based metal stratum may be further enhanced if necessary by coating with elsewhere or pigmented film forming ~ubstanees.
However, widespread substitution of tin/cobalt or tin/nickel for chromium has not occurred because of chromiuml.s relatively low C08t, ease of plating and generally satisfactory performance. Applications for twinkle and tunability exterior electrodepo~its are generally in specs ialized eases such as barrel plating of Molly metal parts, which cannot be readily accomplished with electroplated chromium.
I
Twinkle electrode posits from acidic baths are reported to consist of 50 atomic percent tin / 50 atomic percent nickel, (66.9 weight percent tin / 33.1 weight percent nickel) with the deposit composition varying only about 3 weight percent either way over a wide range of operating conditions Details of composition and operating parameters for tin/nickel baths are given on page 338 of Metal Finishing Guidebook, Edited by Nathaniel Hall 1978. Details of composition and operating parameters for acidic tin/cobalt baths are less well-known than for tin/nickel. It is proposed that an operable acidic tin/cobalt bath would be obtained by substituting cobalt for nickel in the published compositions for tin/nickel baths. Tin/cobalt electrode posits from acidic baths, by analogy, would consist primarily of Snuck, an alloy of 50 atomic percent tin / 50 atomic percent cobalt (66.8 weight percent tin / 33.2 weight percent cobalt).
Thy color and hue of tin/cobalt electrode posits from alkaline baths is sensitive to operating conditions, indicating that the alloy composition is varied by changing conditions in the alkaline bath.
The tunability alloy electrode posits from alkaline baths ens thought to contain up to about 67 atomic percent cobalt with the balance tin.
Desirable proportions of tin and cobalt in the alloy are considered to be about 70 atomic percent tin and 30 atomic percent cobalt. The deposit color attains greater whiteness at increasing percentages of tin, e.g., 80~ Tony% cobalt or even 90% tin/10% cobalt. The deposit color be-comes increasingly darker and bluer as the percentage of cobalt is increased, ego 60% Tony cobalt or 50% Tony cobalt (atomic). An alkaline tin/cobalt bath is proposed in Example IV of this disclosure.
; Deposits of tin/cobalt are sometimes preferred from the stand-point that their blue-white coloration resembles that of chromium thereby improving color-matching in assemblies with parts made in different ways. Tin/nickel deposits have a slight pinkish cast which has certain aesthetic appeal but hinders good color matching to chromium plated parts.
The initial nickel-based layer in contact with and adherent to the directly electroplate able polymeric surface can be electrode posited I
from known nickel-based metal plating baths. Advantageously, the initial layer and subsequent layers in the interior stratum have nickel contents of about 70~ or higher e.g., 80%, 90%, nickel.
Watts nickel baths, all-chloride nickel baths sulfate-chloride nickel baths, all-sulfate nickel baths, and nickel sulfa mate contain-in baths can be used to electrode posit an initial nickel layer.
Good results have been obtained using a Watts bath, which may contain brighteners and other functional additives. Details of operation for these and other nickel baths can be obtained from textbooks on electroplating, ego Metal Finishing Guidebook, Edited by Nathaniel Hail Metals and Plastics Publications, Inc. 1978.
Nickel-based alloys with other Group VIII metals ego Nikko, Nephew can be deposited in contact with and adherent to the directly electron placeable polymeric surface from well-known electroplating baths employed for such alloy deposition. Suitable compositions and operational parameters can be obtained from US. Patents ~195,117 (Nephew) and ~,191,617 (Nikko).
It has been noted that addition of brighteners to the nickel-based plating bath used to deposit the initial nickel-based layer results in improved HIS performance for the composite of the invention, an effect particularly evident on complex parts in deeply recessed areas.
- Additional layers joining the initial electrode posited nickel-based layer and the exterior tin-based stratum can be advantageously employed to achieve functional, appearance or cost benefits, such as to impart brightness and provide durability to thermal and corrosive environments. For example, additional layers of soft "Watts" nickel followed by bright nickel followed by Doreen nickel are contemplated to be advantageous in manufacture of complex parts for automotive or other use where both harsh corrosive media and environmental extremes can be encountered. In applications requiring ; minimum cost, additional layers may include a zinc electrode posit or may be omitted entirely.
~227768 Neither the interior stratum nor the exterior Stratum nest contain copper either as an alloy or pure layer. Both strata can be essentially free of copper. Heretofore electrode posited copper layers have been found practically necessary in order to ensure long-term thermal cycling durability of electroplated polymers. The ability to achieve excellent results without having copper on the composite structure avoids detrimental effects of green copper staining in corrosive environments and the inherent complications of processing and pollution control involved in depositing copper.
lo The new composite structure disclosed here also does not no-quite the use of complicated and difficult to control multi-metal alloy strike deposits immediately adjacent to the directly electron placeable polymeric surface. Simple dull or bright nickel-based layers including pure nickel suffice thereby significantly reducing electroplating process complexity, pollution control requirements and overall costs. Specifically avoidance of n~ckel-iron strike deposits for articles of exterior automotive application improves the composite corrosion performance by avoiding the potential for red rust staining / Turning now to the accompanying drawing, which is taken in conjunction with the present specification, numeral 10 refers to a tin/cobalt plus nickel plus directly electroplate able polymer embodiment of the composite article of the invention. Article 10 has an exterior metal surface if which is of a silvery hue. Surface 11 is an exterior surface of tin/cobalt alloy exterior stratum 12 which is adherent to the upper face of interior stratum 13~ The interior stratum 13 is a double layer stratum comprising DurNi*~nickel layer aye adhering to bright nickel layer 13b. The downward face of stratum 13 adheres to the directly electroplate able polymer 14.
Article lo has durable adherence at alloy-nickel junction 15 and nickel-polymer junction 16. Thus stratum 12 (with surface 11) is Joined to directly electroplate able polymer 14.
* Registered Trademark and product ox Ox Metal Industries Corporation Z~768 For carrying the process of the invention into practice it is desirable that the directly electroplate able surface be of material selected in light of tune previous discussions of directly placeable polymers.
The layer adjoining the directly electroplate able polymeric surface ( the initial electrode posited nickel-based layer) can be applied by those procedures presently known for achieving initial coverage and growth of electrode posits on directly electroplate able polymers. In general the temperature of the electroplating bath used to achieve initial deposition of the nickel-based layer onto the directly electroplate able resin surface should not exceed about 65C.
For purposes of providing those skilled in the art with a further understanding of the invention, the following examples are set forth.
EXAMPLE I
A directly placeable polymeric composition known as KIPPERS DIP
Hi-Flow was injection molded to the configuration of l-inch hexagonal nuts The nuts had surfaces satisfactory for electron plating directly without additional surface preparation. A
quantity of the molded nuts were mounted as cathodes on an electron plating rack in a bright nickel plating bath and electroplated with nickel to provide a owe cm. (nominal) thick stratum of bright nickel adjoining the outer surfaces of the nuts. Particulars of the electroplating were:
Bath -- Udylite 66 Current -- 538 amperes per square meter Time -- 30 minutes Temperature -- 57&
The bright nickel plated nuts were rinsed in water. Next for the * Registered Trademark of POD Technology Corp.
** Registered Trademark of Ox Metal Industries Corporation lZZ7768 exterior metal stratum, the bright nicks plated nuts still racked a cathodes, were electroplated with tin/cobalt alloy onto the nickel to deposit a 0.00003 cm. thick layer of a silver-colored tin/cobalt alloy adhering as an exterior stratum over the nickel. The results satisfactorily provided the hex nuts with attractive silvery surfaces resembling freshly cleaned and polished steel. Analysis of the electrode posited tin/cobalt exterior stratum revealed a composition of approximately 70 atomic percent tin/30 atomic percent cobalt.
Particulars of this second plating of Example I are:
Bath -- * Udylite Achrolyte (slightly alkaline, pi about 800 to 8.6) Current -- 100 amperes per square meter Time -- 2 minutes Temperature -- 43&
Other configurations of metal-polymer composites satisfactorily made according to Example I included water tap strainers and bottle closures.
Satisfactory durability characteristics of Example I articles ; were confirmed with chemically and thermally accelerated evaluations of long-term corrosion resistance and thermal stability. In CUSS
(topper accelerated salt spray) exposures of 22 hours duration, all 3 of the specimens (hex nuts) that were exposed passed satisfactorily without suffering green or red rust staining, tarnishing or electron deposit blistering.
In HUTS (heat soak thermal stability) evaluations with programs of 16 hours in 85& air plus 1 hour in room temperature air plus 2 hours in minus 30C air, 2 specimens of Example I were evaluated and both endured successfully without deterioration.
The HUTS program it used as an accelerated evaluation of long term durability of bonding of electrode posits to directly electroplate able polymers.
In TO (Thermal Cycle) evaluations with cycle programs of * Registered Trademark of XY Metal Industries Corporation -- ~Z27768
2 hours in 85 C air plus 1 hour in room temperature air plus 2 hours in minus 30C air, repeated for 3 cycles, both Example I specimens exposed survived without deterioration.
EXAMPLE II
Injection molded l-inch hex nuts of CAPRF.Z DIP Hi-Flow were provided with a multiple layer electrode posit which had a 000023 cm. trick layer of bright nickel electroplated directly onto the nuts and a 0.0003 cm. layer of dispersed particle nickel elect troplated onto tune bright nickel layer. The bright nickel plating way done as in Example I except the plating time was reduced to 28 minutes. Particulars of plating the dispersed particle nickel were:
Bath -- Udylite Doreen Current -- 538 amperes per square meter Time -- 3 minutes Temperature -- 57C
the electroplated nuts were then rinsed in water and a 0000003 I
exterior stratum of tin/cobalt alloy was electroplated onto the Doreen layer using the bath and plating techniques for depositing the tin/cobalt alloy as in example I. This resulted in a microdis-continuous stratum of tin/cobalt alloy. Example II successfully pro-voided hex nuts with attractive silvery surfaces resembling freshly cleaned steel.
Satisfactory durability characteristics of articles made in Example II were confirmed with accelerated evaluations of long term corrosion resistance and thermal stability. In 22 hour CUSS
exposures, both of the two Example II specimens (hex nuts) exposed passed satisfactorily without suffering green or rust staining tarnish or electrode posit blistering. Further, specimens of Example II were subjected to 88 hours of CUSS exposure and still did not suffer staining. Moreover, the specimens of Example II success-fully resisted pitting corrosion during the 88 hour CUSS test In HUTS evaluation (programmed as in Example I) of Example II specimens, all 3 of 3 specimens evaluated survived satisfactorily without deterioration.
In a TO evaluation (triple cycle program of Example I) the one specimen evaluated survived tune 3 cycles successfully.
In considering result achieved by Examples I and IT
it is noted that, relative to each other, Example I has special advantages of reduced cost and process complexity and Example II
(with a micro discontinuous stratum of tin/cobalt) has advantages of increased resistance to pitting corrosive attack.
EXAMPLE III
.
bodies in forms of wheel hub covers, about 9 cm. diameter and about 6 cm. high were injection molded of KIPPERS DIP Hi-Flow .
After individual mounting on a plating rack, an initial electrodepos-tied layer of about 0.0012 cm. thickness was deposited from a Watts nickel bath onto the surface of the hub covers. This was followed by electrode positing a second layer about 0.0012 cm. thick of bright nickel from a Udylite 66 bright nickel bath. A 0.00003 cm.
exterior stratum of æilver-colored tin/cobalt alloy was then deposited onto the bright nickel with the hub covers till connected as cathodes on a plating rack. Electroplating the exterior tin/cobalt stratum was done in a Udylite Achrolyte bath. Satisfactory results of silvery metallic surfaces on the hub covers were obtained.
Evaluation by the HUTS thermal program of Example I conformed satisfactory thermal stability.
EgAl~PLE IV
As an illustrative example of the invention, molded bodies of KIPPERS DIP Hi-Flow directly electroplate able polymer are electron plated with a owe cm. stratum of bright nickel adhering to the polymer and then a 0.00003 cm. exterior stratum of silver-colored tin/cobalt alloy it electroplated onto the bright nickel (the interior stratum --,.5--l~:Z776~3 Particulars of the plating are:
t Nickel Bath In dint Grams/liter Volume Percentage Nickel Sulfate 225-375 __ Nickel Chloride 30-90 --Boric Acid 30-~0 Jo Brighteners --- 400 Current -- 538 amperes per square meter Time -- 24 minutes Temperature -- 57C
pi -- owe Tin/Cobalt Bath Ingredient Grams/liter Cobalt Sulfate 5 Stuns Sulfate 7 Current -- 100 amperes per square meter Time -- 105 minutes Temperature -- 43C
pi -- 8.3 It is understood that a suitable chelating agent is included in the bath to maintain volubility of the tin and cobalt at the pi of 8.3. Common chelating agents are identified on page 39 of Electroplating Point Source Category Development Document, United States Environmental Protection Agency February 1978.
Results are satisfactory composite bodies having silver-colored metallic exteriors and good durability characteristics.
EXAMPLE V
In another actual example of the invention, the 9 cm. diameter wheel hub covers, as in Example III, were mounted on a plating rack.
A nickel layer of about owe coo thick (nominal) was electroplated from a bright bath (Udylite 66 ) directly onto the surfaces of the i227768 hub covers. Electroplating bath parameters for the bright nickel plating were as described in Example I. After water rinsing, a 0.00003 cm. exterior stratum of silver-colored tin cobalt alloy was then deposited onto the bright nickel with the hub cover still connected as cathodes on a plating rack. Electroplate my the exterior tin/cobalt stratum was done in a Udylite Achrolyte bath as in Example I. After evaluation in the HUTS thermal program the parts showed no blistering or deterioration of bond strength.
To further illustrate advantages of the invention, the following descriptions of results obtained with other composite articles different from the invention are presented.
Chromium Composite A
l-inch hexagonal nuts were electroplated with bright nickel as in Example I. After rinsing in water, the bright nickel plated nuts still racked as cathode were electroplated with chromium onto the nickel to deposit a 0.00003 cm. thick layer of silver-colored chromium adhering as an exterior stratum over the nickel. Chromium was deposited from a standard chromium plating bath, such as described on page 194 of the Metal Finishing Guidebook, Nathaniel Hall Editor, 1978. Particulars of the chromium plating were:
Current -- 1900 amperes per square meter Time -- 1.5 minutes Temperature -- 45&
The nickel-chromium plated nuts were exposed to the HUTS program at the same time as those from Example I. After the HUTS test, the nickel-chrcmium plated nuts, Composite A, showed extensive electron deposit blistering and peeling of the electrode posit showed severe deterioration of adhesion.
Chromium Composite B
9 cm. diameter wheel hub covers were first electroplated with a owe cm. thick bright nickel deposit as in Example V. After water rinsing a 0.00003 cm. exterior stratum of chromium was depose tied onto the bright nickel with the hub covers still connected as cathodes on a plating rack. Chromium electroplating was done as in Chromium Composite A. After evaluation in the HUTS program, massive blistering of the electrode posit was observed and residual bond strength was nil.
The foregoing compositions, resins, metals and baths are illustrative of materials that are marketed in varieties and ranges usable in the invention. For instance, thy KIPPERS DIP
resin in the Examples is illustrative of a broader range of compositions containing polymers, carbon blank and sulfur. Also, the Udylite 66 and Achrolyte~ baths are illustrative of various other bright nickel and tin/cobalt baths used for electrode position or chemical depose it ion of nickel-based metal and tin/cobalt alloys.
The present invention is particularly applicable to providing manufactured composite articles expected to have longer (two years) durability against thermal extremes and possibly corrosive conditions.
It it clear from the foregoing that the use of tin/cobalt or tin/nickel alloys when used in conjunction with a directly elect troplateable plastic substrate is more than a simple substitution for the widely used chromium and results in unexpected improvement in long-term durability of the directly electroplate able plastic/electrodeposit composite. While the results presented here were obtained with strike layers composed of essentially pure nickel adjacent and adherent to the directly electroplate able substrate, it is contemplated that the bone-filial effects of tin/cobalt, and possibly tin/nickel, will be forth-coming independently of the nature of the strike layers. In other words, tin/cobalt and tin/nickel exterior deposits are asserted to be uniquely suitable and advantageous when used in a composite structure with a directly electroplate able plastic substrate containing carbon black, sulfur and polymer matrix, especially under production plating conditions and on highly complex parts where efforts using "all-nickel plus chromium" electrode posits have failed.
`-` 12X7768 It has been noted that the prior art offers no satisfactory system for elimination of troublesome copper inter layers in product lion of complex, chromium plated directly electroplate able parts requiring long term durability. It is proposed that the unique, and independent, beneficial results achieved by replacing chromium with tin/cobalt will exist over and above any prior improvements achieved in other ways (-i.e., through manipulation of the directly electroplate able polymer substrate composition, under-lying electrode posit system, or strike layer) and such replacement will expand permissible operating parameters and part geometries to allow the desired elimination of copper in production and on complex parts.
The present invention is particularly applicable to providing manufactured articles for use as handles, emblems and other decorative trim, knobs, fasteners, automotive wheel covers and hubs, grilles, headlamp surrounds and mirror housings, plumbing components such as faucet housings, strainers and non-pressure piping, escutcheons, containers and closures, tape cases and other hardware components, machine and tool housings, and packaging to provide shielding for electronic devices.
Although the present invention has been described in conjunction with preferred embodiments, it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention, as those skilled in the art will readily understand, Such modifications and variations are considered to be within the purview and scope of the invention and appended claims.
EXAMPLE II
Injection molded l-inch hex nuts of CAPRF.Z DIP Hi-Flow were provided with a multiple layer electrode posit which had a 000023 cm. trick layer of bright nickel electroplated directly onto the nuts and a 0.0003 cm. layer of dispersed particle nickel elect troplated onto tune bright nickel layer. The bright nickel plating way done as in Example I except the plating time was reduced to 28 minutes. Particulars of plating the dispersed particle nickel were:
Bath -- Udylite Doreen Current -- 538 amperes per square meter Time -- 3 minutes Temperature -- 57C
the electroplated nuts were then rinsed in water and a 0000003 I
exterior stratum of tin/cobalt alloy was electroplated onto the Doreen layer using the bath and plating techniques for depositing the tin/cobalt alloy as in example I. This resulted in a microdis-continuous stratum of tin/cobalt alloy. Example II successfully pro-voided hex nuts with attractive silvery surfaces resembling freshly cleaned steel.
Satisfactory durability characteristics of articles made in Example II were confirmed with accelerated evaluations of long term corrosion resistance and thermal stability. In 22 hour CUSS
exposures, both of the two Example II specimens (hex nuts) exposed passed satisfactorily without suffering green or rust staining tarnish or electrode posit blistering. Further, specimens of Example II were subjected to 88 hours of CUSS exposure and still did not suffer staining. Moreover, the specimens of Example II success-fully resisted pitting corrosion during the 88 hour CUSS test In HUTS evaluation (programmed as in Example I) of Example II specimens, all 3 of 3 specimens evaluated survived satisfactorily without deterioration.
In a TO evaluation (triple cycle program of Example I) the one specimen evaluated survived tune 3 cycles successfully.
In considering result achieved by Examples I and IT
it is noted that, relative to each other, Example I has special advantages of reduced cost and process complexity and Example II
(with a micro discontinuous stratum of tin/cobalt) has advantages of increased resistance to pitting corrosive attack.
EXAMPLE III
.
bodies in forms of wheel hub covers, about 9 cm. diameter and about 6 cm. high were injection molded of KIPPERS DIP Hi-Flow .
After individual mounting on a plating rack, an initial electrodepos-tied layer of about 0.0012 cm. thickness was deposited from a Watts nickel bath onto the surface of the hub covers. This was followed by electrode positing a second layer about 0.0012 cm. thick of bright nickel from a Udylite 66 bright nickel bath. A 0.00003 cm.
exterior stratum of æilver-colored tin/cobalt alloy was then deposited onto the bright nickel with the hub covers till connected as cathodes on a plating rack. Electroplating the exterior tin/cobalt stratum was done in a Udylite Achrolyte bath. Satisfactory results of silvery metallic surfaces on the hub covers were obtained.
Evaluation by the HUTS thermal program of Example I conformed satisfactory thermal stability.
EgAl~PLE IV
As an illustrative example of the invention, molded bodies of KIPPERS DIP Hi-Flow directly electroplate able polymer are electron plated with a owe cm. stratum of bright nickel adhering to the polymer and then a 0.00003 cm. exterior stratum of silver-colored tin/cobalt alloy it electroplated onto the bright nickel (the interior stratum --,.5--l~:Z776~3 Particulars of the plating are:
t Nickel Bath In dint Grams/liter Volume Percentage Nickel Sulfate 225-375 __ Nickel Chloride 30-90 --Boric Acid 30-~0 Jo Brighteners --- 400 Current -- 538 amperes per square meter Time -- 24 minutes Temperature -- 57C
pi -- owe Tin/Cobalt Bath Ingredient Grams/liter Cobalt Sulfate 5 Stuns Sulfate 7 Current -- 100 amperes per square meter Time -- 105 minutes Temperature -- 43C
pi -- 8.3 It is understood that a suitable chelating agent is included in the bath to maintain volubility of the tin and cobalt at the pi of 8.3. Common chelating agents are identified on page 39 of Electroplating Point Source Category Development Document, United States Environmental Protection Agency February 1978.
Results are satisfactory composite bodies having silver-colored metallic exteriors and good durability characteristics.
EXAMPLE V
In another actual example of the invention, the 9 cm. diameter wheel hub covers, as in Example III, were mounted on a plating rack.
A nickel layer of about owe coo thick (nominal) was electroplated from a bright bath (Udylite 66 ) directly onto the surfaces of the i227768 hub covers. Electroplating bath parameters for the bright nickel plating were as described in Example I. After water rinsing, a 0.00003 cm. exterior stratum of silver-colored tin cobalt alloy was then deposited onto the bright nickel with the hub cover still connected as cathodes on a plating rack. Electroplate my the exterior tin/cobalt stratum was done in a Udylite Achrolyte bath as in Example I. After evaluation in the HUTS thermal program the parts showed no blistering or deterioration of bond strength.
To further illustrate advantages of the invention, the following descriptions of results obtained with other composite articles different from the invention are presented.
Chromium Composite A
l-inch hexagonal nuts were electroplated with bright nickel as in Example I. After rinsing in water, the bright nickel plated nuts still racked as cathode were electroplated with chromium onto the nickel to deposit a 0.00003 cm. thick layer of silver-colored chromium adhering as an exterior stratum over the nickel. Chromium was deposited from a standard chromium plating bath, such as described on page 194 of the Metal Finishing Guidebook, Nathaniel Hall Editor, 1978. Particulars of the chromium plating were:
Current -- 1900 amperes per square meter Time -- 1.5 minutes Temperature -- 45&
The nickel-chromium plated nuts were exposed to the HUTS program at the same time as those from Example I. After the HUTS test, the nickel-chrcmium plated nuts, Composite A, showed extensive electron deposit blistering and peeling of the electrode posit showed severe deterioration of adhesion.
Chromium Composite B
9 cm. diameter wheel hub covers were first electroplated with a owe cm. thick bright nickel deposit as in Example V. After water rinsing a 0.00003 cm. exterior stratum of chromium was depose tied onto the bright nickel with the hub covers still connected as cathodes on a plating rack. Chromium electroplating was done as in Chromium Composite A. After evaluation in the HUTS program, massive blistering of the electrode posit was observed and residual bond strength was nil.
The foregoing compositions, resins, metals and baths are illustrative of materials that are marketed in varieties and ranges usable in the invention. For instance, thy KIPPERS DIP
resin in the Examples is illustrative of a broader range of compositions containing polymers, carbon blank and sulfur. Also, the Udylite 66 and Achrolyte~ baths are illustrative of various other bright nickel and tin/cobalt baths used for electrode position or chemical depose it ion of nickel-based metal and tin/cobalt alloys.
The present invention is particularly applicable to providing manufactured composite articles expected to have longer (two years) durability against thermal extremes and possibly corrosive conditions.
It it clear from the foregoing that the use of tin/cobalt or tin/nickel alloys when used in conjunction with a directly elect troplateable plastic substrate is more than a simple substitution for the widely used chromium and results in unexpected improvement in long-term durability of the directly electroplate able plastic/electrodeposit composite. While the results presented here were obtained with strike layers composed of essentially pure nickel adjacent and adherent to the directly electroplate able substrate, it is contemplated that the bone-filial effects of tin/cobalt, and possibly tin/nickel, will be forth-coming independently of the nature of the strike layers. In other words, tin/cobalt and tin/nickel exterior deposits are asserted to be uniquely suitable and advantageous when used in a composite structure with a directly electroplate able plastic substrate containing carbon black, sulfur and polymer matrix, especially under production plating conditions and on highly complex parts where efforts using "all-nickel plus chromium" electrode posits have failed.
`-` 12X7768 It has been noted that the prior art offers no satisfactory system for elimination of troublesome copper inter layers in product lion of complex, chromium plated directly electroplate able parts requiring long term durability. It is proposed that the unique, and independent, beneficial results achieved by replacing chromium with tin/cobalt will exist over and above any prior improvements achieved in other ways (-i.e., through manipulation of the directly electroplate able polymer substrate composition, under-lying electrode posit system, or strike layer) and such replacement will expand permissible operating parameters and part geometries to allow the desired elimination of copper in production and on complex parts.
The present invention is particularly applicable to providing manufactured articles for use as handles, emblems and other decorative trim, knobs, fasteners, automotive wheel covers and hubs, grilles, headlamp surrounds and mirror housings, plumbing components such as faucet housings, strainers and non-pressure piping, escutcheons, containers and closures, tape cases and other hardware components, machine and tool housings, and packaging to provide shielding for electronic devices.
Although the present invention has been described in conjunction with preferred embodiments, it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention, as those skilled in the art will readily understand, Such modifications and variations are considered to be within the purview and scope of the invention and appended claims.
Claims (10)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A metal-polymer composite article comprising: a body component comprising a directly electroplateable polymeric material at least on the surface thereof; an exterior metal stratum of a tin-based alloy composed essentially of tin metal from the group nickel, cobalt and mixtures thereof; and an interior metal stratum disposed between, and durably joined to, the body and the exterior stratum, said having included in the interior stratum including a nickel-based electrodeposit consisting essentially of metal from the group nickel, cobalt and iron and mixtures thereof adhering to said directly electroplateable poly-meric material in the body, said article being charac-terized by having the aforesaid body and strata joined together with durable adherency sufficient for satis-factorily surviving the HSTS and TC thermally accelerated evaluation programs.
2. A composite article as set forth in claim 1 wherein the interior stratum consists essentially of nickel.
3. A composite article as set forth in claim 1 wherein the directly electroplateable polymeric material com-prises a polymeric resin matrix and has carbon black and sulfur in weight proportions of at least 8% carbon black and 0.1% sulfur based on the weight total of matrix resin-plus-carbon black-plus sulfur.
4. A composite article as set forth in claim 1 wherein the exterior metal stratum includes a microdiscontinuous structure.
5. A composite article as set forth in claim 1 wherein the interior stratum consists of a single electrodeposited layer.
6. A composite article as set forth in claim 1, at least part of whose exterior tin-based metal stratum has been subjected to a chromating treatment.
7. In a process of preparing a silvery hued article for use where long term durability against thermal shock and thermal cycling is required, the improvement comprising providing a body of solid material having a directly electroplateable polymer at an exterior surface, electrodepositing nickel-based metal adherent onto the plateable polymer, and subsequently electrodepositing tin-based alloy composed essentially of tin and metal from the group nickel,cobalt and mixtures thereof joined to the electrodeposited nickel-based metal adhering to the directly electroplateable polymer at the body with durability characterized by capability for satisfactorily surviving the HSTS and TC thermally accelerated evaluation programs.
8. A process as set forth in claim 7 wherein the body of solid material is mounted on an electroplating fixture during electroplating of the nickel-based layer onto the plateable polymer.
9. A process as set forth in claim 7 wherein the nickel-based metal adherent to the polymer is electrodeposited from a Watts nickel bath formulation containing nickel chloride, nickel sulfate and boric acid.
10. A process as set forth in claim 7 wherein the electroplating bath used to deposit the nickel-based layer adherent onto the plateable polymer contains brighteners.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000441975A CA1227768A (en) | 1983-11-25 | 1983-11-25 | Composite article of polymer with nickel-based and tin-based metal layers |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000441975A CA1227768A (en) | 1983-11-25 | 1983-11-25 | Composite article of polymer with nickel-based and tin-based metal layers |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1227768A true CA1227768A (en) | 1987-10-06 |
Family
ID=4126605
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000441975A Expired CA1227768A (en) | 1983-11-25 | 1983-11-25 | Composite article of polymer with nickel-based and tin-based metal layers |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1227768A (en) |
-
1983
- 1983-11-25 CA CA000441975A patent/CA1227768A/en not_active Expired
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