Patent Application
20100193367
Polymers are often also referred to as plastics or resins. For the present invention, it is understood that polymers include any of the group of synthetic or natural organic materials that may be shaped or applied when soft and then solidified or hardened. Polymers include thermoplastics and three-dimensional curing materials such as epoxies and thermosets. In addition, certain silicon based materials such as silicones can be considered as polymers or resins. Polymers also include any coating, ink, or paint fabricated using a polymer binder or film forming material.
There a numerous applications where it is desired to impart a metallic property to a polymer. One such property is electrical conductivity. Electrical conductivity may allow for the material to function in many processes requiring conductivity such as electroplating, electrostatic coating, current transport, etc. Techniques have been developed to impart electrical conductivity to a polymer. One way is to add a conductive filler to the polymer matrix. An example of such a filler is particulate silver. A second technique is to apply a metal coating to the surface of the polymer.
One way to apply a metal coating to the surface of a polymer is through simple lamination of a metal foil to a polymeric substrate, a process which is well known in the art. A well-established application of this approach is the starting laminate structure for manufacture of many printed circuit boards. This approach can be design limited to essentially two-dimensional surfaces. Furthermore, if it is desired to have selective placement of metal on the final article, the metal foil must be selectively etched.
Another way to apply a metal coating to the surface of a polymer is by physically depositing metal onto a plastic substrate. Physical deposition can be achieved by arc spraying or vacuum deposition processes such as sputtering. These processes are well known in the art.
Yet another way to apply a metal coating to the surface of a polymer is through chemical deposition (for example, electroless plating). Chemical deposition is conventionally achieved by a multi-step process which is well known in the art. The plastic substrate is normally first chemically etched to microscopically roughen the surface. This etching promotes adhesion between the plastic substrate and the subsequently deposited metal. Further steps catalyze the plastic surface in preparation for metal deposition by chemical reduction of metal from solution. Nickel and copper are typical metals employed for “electroless plating”.
The “electroless plating” process employed with conventional plating on plastics comprises many steps involving expensive and harsh chemicals. This increases costs dramatically and involves environmental difficulties. The process is also sensitive to processing variables used to fabricate the plastic substrate, limiting the applications to carefully fabricated parts and designs.
The conventional technology for electroless plating has been extensively documented and discussed in the public and commercial literature. See, for example, Saubestre, Transactions of the Institute of Metal Finishing, 1969, Vol. 47., or Arcilesi et al., Products Finishing, March 1984.
There are a number of limitations associated with conventional vacuum deposition and chemical deposition. One is the relatively thin metallic thickness typically achieved with these techniques. Deposition speed, equipment utilization, deposit integrity and chemical cost often restrict deposits to these relatively small thicknesses. Typical thicknesses for vacuum deposition and chemical deposition are of the order 1 micrometer. Another limitation is the restricted types of metals that can be applied with these processes.
In many cases it is desired to have increased thickness or variety of the metal deposit. In these cases, a particularly advantageous way to apply metal to a surface is electroplating. Electroplating builds metallic thickness relatively quickly and a wide variety of metals can be electroplated in conventional manner. Regarding plastics however, one will recognize that the surface of the plastic substrate must be conductive in order to permit electroplating.
In many instances the electroplating process is applied to individual articles arrayed on a positioning rack. The rack is rendered cathodic and all of the articles positioned on the rack are electroplated simultaneously. While the rack may be transported in a sequential fashion through multiple steps it can be considered as a discrete array of parts all processed together as a batch. Since parts are normally individually positioned onto the rack manual labor and added cost must be addressed.
It is a common practice to electroplate metal articles in an essentially continuous fashion. Such processing is often accomplished by unrolling the metal substrate from a spool or roll, passing it through the electroplating sequence, then winding the electroplated material onto a takeup roll. This type of process is often referred to as roll-to-roll or reel-to-reel. Articles such as a metal wire or a metal strip are suitable for such continuous electroplating. With such continuous electroplating handling requirements for the metal articles are reduced and thus the processing cost can be reduced. Furthermore, the continuous electroplating allows for careful control of the manufacturing process (metal thickness etc.) which again results in reduced costs as well as consistent output. To achieve similar benefits it would be desirable to electroplate certain plastic forms in a continuous manner. Continuous electroplating could be particularly suitable for articles produced by certain plastic fabrication processes characterized by a continuous or semi-continuous output. These may include extrusion, thermoforming, printing of inks comprising plastic binders, indexed injection molding etc.
There are a number of concerns regarding the electroplating of plastics in a continuous fashion. One of the primary reasons is the complexity and cost associated with conventional electroplating of plastic. The “electroless plating” process employed with conventional plating on plastics comprises many steps involving expensive and harsh chemicals. This increases costs dramatically and involves environmental difficulties. The process is also very sensitive to processing variables used to fabricate the plastic substrate, limiting the applications to carefully fabricated parts and designs. Furthermore, the multiple process steps required are often not conducive to a continuous processing environment. For example, transporting a web or film through multiple baths increases problems associated with cross contamination etc. Yet another problem is that the electroless process tends to be relatively slow in nature. From a practical standpoint, a metal film deposited “electrolessly” has limited thickness and current carrying capacity. Thus, managing high electroplating currents associated with a subsequent continuous electroplating step can be troublesome, as further explained below.
Another approach that has been proposed to achieve continuous electroplating of polymeric film forms is to first form a very thin layer of metal deposited by vacuum processing such as sputtering. This “metallized” film is then subjected to electroplating to build metal thickness. The result is a structure similar to a metal foil/polymer film lamination but with a possibly different (often thinner) metal layer. As with “electroless” plating, the thin initial metal coating complicates current management during subsequent electroplating. The capital equipment required for the electroplating can be very expensive and complicated. In addition, unless expensive masking is employed, metal would normally cover the entire film surface and further metal removal processing is required to give the often desired selective metal placement.
In a discussion of the electroplating of thin conductive films the current carrying capacity of the initial film is often a major concern. The film's current carrying capacity determines the ability of the thin film to manage relatively high electroplating currents associated with the electrodeposition process, especially during the initial stage of the electrodeposition step. The current carrying capacity of a thin film is often reported as a surface resistance in ohms per square. This measurement is made by determining the resistance over a unit length of film having a width of the same unit distance. Ohms per square is not an intrinsic material characteristic because it depends on the thickness of the material. However, it does represent a convenient measurement of relative current carrying capacity for thin films.
A common characteristic of sputtered, vacuum metallized or chemically deposited metallic films is that they possess relatively low current carrying ability. This is a result of the typically relatively thin nature of the metallic film. Sputtering, vacuum metallizing, and chemical deposition are characterized by relatively slow rates of metallic thickness buildup. It is often impractical or uneconomic, or physically difficult to increase the thickness of the metallic film in a significant way. Thus, the metallic films, prior to electroplating, may often be characterized as having low current carrying ability. This intrinsically leads to problems regarding current transport or conveyance and electrical contacting especially during the initial stages of the electrodeposition process.
For example, it is the current inventor's understanding that a typical thickness for a sputtered copper film intended to be electroplated is approximately 0.25 microns. This would result in a surface resistance of approximately 0.1 ohms per square. It is also the current inventor's understanding that typical metal thicknesses for electroless copper layers prior to electroplating are approximately 0.75 microns. This would result in a surface resistance of approximately 0.03 ohms per square.
It is known that electroplating onto sputtered, or chemically deposited metallic films of these typical thicknesses can be difficult for a number of reasons. One primary reason is that the low current carrying capacity of these deposits makes management of initial electroplating currents conveyance sensitive and difficult to control. Burning and breach of cathodic contacts is frequently a problem due to convergence of electroplating current and heating in the area of the contact. This requires special techniques which often increase the capital cost and complexity of the electroplating equipment. For example, during initial stages of electroplating on such films, careful control of current densities, agitation etc. are required. It is one of the objects of the current invention to teach processing and structure which reduces the cost and complexity of electroplating onto films characterized as having a low current carrying capacity including those produced by sputtering, vacuum metallizing, and chemical deposition. For purposes of this specification and claims, a structure having a surface resistance greater than 0.01 ohms per square will be considered as a structure having a low current carrying ability.
A number of attempts have been made to simplify the electroplating of plastics. If successful such efforts could result in significant cost reductions for electroplated plastics and could allow facile continuous electroplating of plastics to be practically employed. Some simplification attempts involve special chemical techniques, other than conventional electroless metal deposition, to produce an electrically conductive film on the surface. Typical examples of the approach are taught by U.S. Pat. No. 3,523,875 to Minklei, U.S. Pat. No. 3,682,786 to Brown et al., and U.S. Pat. No. 3,619,382 to Lupinski. The electrically conductive surface film produced was intended to be electroplated. Multiple performance problems thwarted these attempts.
Other approaches contemplate making the plastic surface itself conductive enough to allow it to be electroplated directly thereby avoiding the “electroless plating” or lamination processes. Efforts have been made to advance systems contemplating metal electrodeposition directly onto the surface of polymers made conductive through incorporating conductive fillers. When considering polymers rendered electrically conductive by loading with electrically conductive fillers, it may be important to distinguish between “microscopic resistivity” and “bulk” or macroscopic resistivity”. “Microscopic resistivity” refers to a characteristic of a polymer/filler mix considered at a relatively small linear dimension of for example 1 micrometer or less. “Bulk” or “macroscopic resistivity” refers to a characteristic determined over larger linear dimensions. To illustrate the difference between “microscopic” and “bulk, macroscopic” resistivities, one can consider a polymer loaded with conductive fibers at a fiber loading of 10 weight percent. Such a material might show a low “bulk, macroscopic” resistivity when the measurement is made over a relatively large distance. However, because of fiber separation (holes) such a composite might not exhibit consistent “microscopic” resistivity. When producing an electrically conductive polymer intended to be electroplated, one should consider “microscopic resistivity” in order to achieve uniform, “hole-free” deposit coverage. Thus, it may be advantageous to consider conductive fillers comprising those that are relatively small, but with loadings sufficient to supply the required conductive contacting. Such fillers include metal powders and flake, metal coated mica or spheres, conductive carbon black and the like.
Efforts to produce electrically conductive polymers suitable for direct electroplating have encountered a number of obstacles. The first is the combination of fabrication difficulty and material property deterioration brought about by the heavy filler loadings often required. A second is the high cost of many conductive fillers employed such as silver flake.
Another obstacle involved in the electroplating of electrically conductive polymers is a consideration of adhesion between the electrodeposited metal and polymeric substrate (metal/polymer adhesion). In some cases such as electroforming, where the electrodeposited metal is eventually removed from the substrate, metal/polymer adhesion may actually be detrimental. However, in most cases sufficient adhesion is required to prevent metal/polymer separation during extended environmental and use cycles.
A number of methods to enhance adhesion have been employed. For example, etching of the surface prior to plating can be considered. Etching can often be achieved by immersion in vigorous solutions such as chromic/sulfuric acid. Alternatively, or in addition, an etchable species can be incorporated into the conductive polymeric compound. The etchable species at exposed surfaces is removed by immersion in an etchant prior to electroplating. Oxidizing surface treatments can also be considered to improve metal/plastic adhesion. These include processes such as flame or plasma treatments or immersion in oxidizing acids.
In the case of conductive polymers containing finely divided metal, one can propose achieving direct metal-to-metal adhesion between electrodeposit and filler. However, here the metal particles are generally encapsulated by the resin binder, often resulting in a resin rich “skin”. To overcome this effect, one could propose methods to remove the “skin”, exposing active metal filler to bond to subsequently electrodeposited metal.
Another approach to impart adhesion between conductive resin substrates and electrodeposits is incorporation of an “adhesion promoter” at the surface of the electrically conductive resin substrate. This approach was taught by Chien et al. in U.S. Pat. No. 4,278,510 where maleic anhydride modified propylene polymers were taught as an adhesion promoter. Luch, in U.S. Pat. No. 3,865,699 taught that certain sulfur bearing chemicals could function to improve adhesion of initially electrodeposited Group VIII metals.
An additional major obstacle confronting development of electrically conductive polymeric resin compositions capable of being directly electroplated is the initial “bridge” of electrodeposit on the surface of the electrically conductive resin. In electrodeposition, the substrate to be plated is often made cathodic through a pressure contact to a metal contact, itself under cathodic potential. However, if the contact resistance is excessive or the substrate is insufficiently conductive, the electrodeposit current favors the metal contact and the electrodeposit may have difficulty bridging to the substrate. The “bridging” problem extends to substrates having low surface current carrying capacity such as vacuum metallized or electrolessly plated films. In some cases, “burning” or actual “deplating” of very thin metal deposits can be experienced during the initial moments of “bridge” formation.
Moreover, a further problem is encountered even if specialized racking successfully achieves electrodeposit bridging to the substrate. Many of the electrically conductive polymeric resins have resistivities far higher than those of typical metal substrates. Also in many cases, such as the electroplating of conductive ink patterns or thin metal films, the conductive material may be relatively thin. The initial conductive substrate can be relatively limited in the amount of electrodeposition current which it alone can convey. In these cases the initial conductive substrate may not cover almost instantly with electrodeposit as is typical with thicker metallic substrates. Rather the electrodeposit coverage may result from a continuous lateral growth of electrodeposited metal over the surface emanating from the cathodic contact. In this case a significant portion of the electrodeposition current, including that associated with the lateral electrodeposit growth, may be conveyed back to the cathodic contact through the previously electrodeposited metal. This restricts the size and “growth length” of the substrate conductive pattern, increases plating costs, and can also result in large non-uniformities in electrodeposit integrity and thickness over the pattern.
Rates of this lateral growth likely depend on the ability of the substrate to convey current. Thus, the thickness and resistivity of the initial conductive substrate can be defining factors in the ability to achieve satisfactory electrodeposit coverage rates. When dealing with continuously electroplated patterns, long narrow metal traces are often desired, deposited on relatively thin initial conductive substrates such as printed inks. These factors of course work against achieving the desired result.
This coverage rate problem likely can be characterized by a continuum, being dependent on many factors such as the nature of the initially electrodeposited metal, applied voltage, electroplating bath chemistry, the nature of the polymeric binder and the resistivity of the electrically conductive polymeric substrate. As a “rule of thumb”, the instant inventor estimates that coverage rate problems would demand attention if the resistivity of the conductive polymeric substrate rose above about 0.001 ohm-cm. Alternatively, electrical current carrying capacity of thin films is often reported as a surface resistivity in “ohms per square”. Using this measure, the inventor estimates that coverage rate issues may demand attention should the surface resistivity rise above about 0.01 ohms per square.
Beset with the problems of achieving adhesion and satisfactory electrodeposit coverage rates, investigators have attempted to produce directly electroplateable polymers by heavily loading polymers with relatively small conductive filler particles. Fillers include finely divided metal powders and flake, conductive metal oxides and intrinsically conductive polymers. Heavy loadings may be sufficient to reduce both microscopic and macroscopic resistivity to levels where the coverage rate phenomenon may be manageable. However, attempts to make an acceptable directly electroplateable resin using the relatively small fillers alone encounter a number of barriers. First, the fine conductive fillers can be relatively expensive. The loadings required to achieve the particle-to-particle proximity to achieve acceptable conductivity increases the cost of the polymer/filler blend dramatically. The fine fillers may bring further problems. They tend to cause deterioration of the mechanical properties and processing characteristics of many resins. This significantly limits options in resin selection. All polymer processing is best achieved by formulating resins with processing characteristics specifically tailored to the specific process (injection molding, extrusion, blow molding, printing, etc.). A required heavy loading of filler severely restricts ability to manipulate processing properties in this way. A further problem is that metal fillers can be abrasive to processing machinery and may require specialized screws, barrels, and the like. Finally, despite being electrically conductive, a polymer filled with conductive particles still offers no mechanism to produce adhesion of an electrodeposit since the particles may be essentially encapsulated by the resin binder, often resulting in a non-conductive or non-binding resin-rich “skin”.
For the above reasons, fine conductive particle containing plastics have not been widely used as bulk substrates for directly electroplateable articles. Rather, they have found applications in production of conductive adhesives, pastes, and inks. Recent activity has been reported wherein polymer inks heavily loaded with silver particles have been proposed as a “seed layer” upon which subsequent electrodeposition of metal is achieved. However, high material costs, application complexity, electrodeposit growth rate and adhesion issues remain with these approaches. In addition, it has been reported that these films are typically deposited at a thickness of approximately 3 microns resulting in a surface resistance of approximately 150 milliohms per square. Significantly, such low current carrying capacity films likely would experience the electroplating problems being addressed by the processes and structure of the instant invention.
The least expensive (and least conductive) of the readily available conductive fillers for plastics are carbon blacks. Typically the resistivity of a conductive polymer is not reduced below approximately 1 ohm-cm using carbon black alone. Thus in a thin film form at a thickness of 5 microns a surface resistivity would typically be approximately 2,000 ohms per square. Attempts have been made to produce electrically conductive polymers based on carbon black loading intended to be subsequently electroplated. Examples of this approach are the teachings of U.S. Pat. Nos. 4,038,042, 3,865,699, and 4,278,510 to Adelman, Luch, and Chien et al. respectively.
Adelman taught incorporation of conductive carbon black into a polymeric matrix to achieve electrical conductivity required for electroplating. The substrate was pre-etched in chromic/sulfuric acid to achieve adhesion of the subsequently electroplated metal. However, the rates of electrodeposit coverage reported by Adelman may be insufficient for many applications.
Luch in U.S. Pat. No. 3,865,699 and Chien et al. in U.S. Pat. No. 4,278,510 also chose carbon black as a filler to provide an electrically conductive surface for the polymeric compounds to be electroplated. The Luch U.S. Pat. No. 3,865,699 and the Chien U.S. Pat. No. 4,278,510 are hereby incorporated in their entirety by this reference. However, these inventors further taught inclusion of an electrodeposit coverage or growth rate accelerator to overcome the galvanic bridging and lateral electrodeposit growth rate problems described above. An electrodeposit coverage rate accelerator is an additive functioning to increase the electrodeposition coverage rate over and above any affect it may have on the conductivity of an electrically conductive polymer. In the embodiments, examples and teachings of U.S. Pat. Nos. 3,865,699 and 4,278,510, it was shown that certain sulfur bearing materials, including elemental sulfur, can function as electrodeposit coverage or growth rate accelerators to overcome those problems associated with electrically conductive polymeric substrates having relatively high resistivity.
In addition to elemental sulfur, sulfur in the form of sulfur donors such as sulfur chloride, 2-mercapto-benzothiazole, N-cyclohexyle-2-benzothiaozole sulfonomide, dibutyl xanthogen disulfide, and tetramethyl thiuram disulfide or combinations of these and sulfur were identified. Those skilled in the art will recognize that these sulfur donors are the materials which have been used or have been proposed for use as vulcanizing agents or accelerators. Since the polymer-based compositions taught by Luch and Chien et al. could be electroplated directly they could be accurately defined as directly electroplateable resins (DER). These DER materials can be generally described as electrically conductive polymers characterized by having an electrically conductive surface with the inclusion of an electrodeposit coverage rate accelerator. In the following, the acronym “DER” will be used to designate a directly electroplateable resin as defined in this specification.
Specifically for the present invention, directly electroplateable resins, (DER), are characterized by the following features.
In his patents, Luch specifically identified elastomers such as natural rubber, polychloroprene, butyl rubber, chlorinated butyl rubber, polybutadiene rubber, acrylonitrile-butadiene rubber, styrene-butadiene rubber etc. as suitable for the matrix polymer of a directly electroplateable resin. Other polymers identified by Luch as useful included polyvinyls, polyolefins, polystyrenes, polyamides, polyesters and polyurethanes.
In his patents, Luch identified carbon black as a means to render a polymer and its surface electrically conductive. As is known in the art, other conductive fillers can be used to impart conductivity to a polymer. These include metallic flakes or powders such as those comprising nickel or silver. Other fillers such as metal coated minerals and certain metal oxides may also suffice. Furthermore, one might expect that compositions comprising intrinsically conductive polymers may be suitable.
Regarding electrodeposit coverage rate accelerators, both Luch and Chien et al. in the above discussed U.S. patents demonstrated that sulfur and other sulfur bearing materials such as sulfur donors and accelerators served this purpose when using an initial Group VIII “strike” layer. One might expect that other elements of Group 6A nonmetals, such as oxygen, selenium and tellurium, could function in a way similar to sulfur. In addition, other combinations of electrodeposited metals and nonmetal coverage rate accelerators may be identified. Finally, the electrodeposit coverage rate accelerator may not necessarily be a discrete material entity. For example, the coverage rate accelerator may consist of a functional species appended to the polymeric binder chain or a species adsorbed onto the surface of the conductive filler. It is important to recognize that such an electrodeposit coverage rate accelerator can be extremely important in order to achieve direct electrodeposition in a practical way onto polymeric substrates having low conductivity or very thin electrically conductive polymeric substrates having restricted current carrying ability.
Despite the multiple attempts identified above to dramatically simplify the plastics plating process, the current inventor is not aware of any such attempt having achieved recognizable commercial success.
In order to eliminate ambiguity in terminology, for the present invention the following definitions are supplied:
While not precisely definable, for the purposes of this specification, electrically insulating materials may generally be characterized as having electrical resistivities greater than 10,000 ohm-cm. Also, electrically conductive materials may generally be characterized as having electrical resistivities less than 10,000 ohm-cm. A subset of conductive materials, electrically resistive or semi-conductive materials may generally be characterized as having electrical resistivities in the range of 0.001 ohm-cm to 10,000 ohm-cm. The term “electrically conductive polymer or resin” as used in the art and in this specification and claims extends to materials of a very wide range of resitivities from about 0.00001 ohm-cm. to about 10,000 ohm-cm and higher.
“Metal-based” refers to a material or structure having at least one metallic property and comprising one or more components at least one of which is a metal or metal-containing alloy.
“Alloy” refers to a substance composed of two or more intimately mixed materials.
“Group VIII metal-based” refers to a substance containing by weight 50% to 100% metal from Group VIII of the Periodic Table of Elements.
“Electroplateable material” refers to a material forming a surface that can be exposed to an electroplating process to cause the surface to cover with electrodeposited material, either directly or following a preplating process.
A “metallizable material” is a material suitable to be coated with a metal deposited by any one or more of the available metallizing process, including chemical deposition, vacuum metallizing, sputtering, metal spraying, sintering and electrodeposition.
A “metal-based foil” refers to a thin structure of metal or metal-based material that may maintain its integrity absent a supporting structure. Generally, metal of thickness greater than about 2 micrometers may have this characteristic (i.e. 2 micrometers, 10 micrometers, 25 micrometers, 100 micrometers, 250 micrometers).
A “film” refers to a thin material form that may or may not be self supporting.
In this specification and claims, the terms “monolithic” or “monolithic structure” are used as is common in industry to describe structure that is made or formed from a single or uniform material. An example would be a “boat having a monolithic plastic hull”.
A “continuous” form of material is one that has a length dimension far greater or than its width or thickness such that the material can be supplied in its length dimension without substantial interruption.
A “continuous” process is one wherein a continuous form of a material component is supplied to the process. The material feed can be a continuous motion or repetitively intermittent, and the output is timed to remove product either by continuous motion or repetitively intermittent according to the rate of input.
A “roll-to-roll” process is one wherein a material component is fed to the process from a roll of material and the output of the process is accumulated in a roll form.
The “machine direction” is that direction in which material is transported through a process step.
The term “multiple” is used herein to mean “two or more”.
A “web” is a thin, flexible sheetlike material form often characterized as continuous in a length direction.
“Sheetlike” characterized a structure having surface dimensions far greater than the thickness dimension.
“Substantially planar” characterizes a surface structure which may comprise minor variations in surface topography but from an overall and functional perspective can be considered flat.
The terms “upper” and “top” surfaces of structure refer to those surfaces of structure depicted in the drawing embodiments as facing upward.
The terms “lower” or “bottom” surface refer to surfaces facing away from the upward facing surface of the structure.
An object of the invention is to provide novel methods of facile continuous manufacture of electrochemically or electrophysically treated items.
A further object of the invention is to expand permissible options for the continuous production of electroplated items.
A further object of the invention is to expand options for the electrochemical or electrophysical treatment of objects in a continuous fashion.
A further object of the invention is to teach novel and facile methods for achieving electrical connections via electrodeposition.
A further object of the invention is to teach processing and structure which reduces the cost and complexity of electroplating onto material films characterized as having a low current carrying capacity.
A further object of the invention is to provide methods to achieve acceptable coverage of films having low current carrying capacity with an initial coverage of electrodeposited metal.
The current invention involves production of electrochemically or electrophysically treated objects.
In an embodiment of the invention the production can be characterized as continuous.
In embodiments the electrochemical treatments comprise electrodeposition.
In embodiments the electrodeposition involves electroplating onto substrates whose initial current carrying capacity is relatively limited, including vacuum and chemically deposited metal films.
In embodiments the production involves the electroplating of electrically conductive polymers. In embodiments the electrically conductive polymer comprises a directly electroplateable resin.
The various factors and details of the structures and manufacturing methods of the present invention are hereinafter more fully set forth with reference to the accompanying drawings wherein:
Many applications of the current invention will employ a generally planar or sheet-like structure having thickness much smaller than its length or width. This sheet-like structure may also have a length far greater than its width, in which case it is commonly referred to as a “web”. Because of its extensive length, a web can be conveyed through one or more processing steps in a way that can be described as “continuous”. “Continuous” web processing is well known in the paper and packaging industries. It is often accomplished by supplying web material from a feed roll to the process steps and retrieving the web onto a takeup roll following processing (roll-to-roll or reel-to-reel processing).
Web processing of metal forms is known in the electrochemical art. For example, “continuous” anodizing or electroplating of metal sheet or strip is practiced. In these cases the metal dimensions are as described above characterizing a “web”. Use of web processing for electrochemical processing polymeric materials is more difficult, at least in part because of the insulating characteristics of most polymers. Nevertheless, the instant inventor has recognized that web processing can be practiced with many advantages in the electrochemical or electrophysical processing of polymers.
A first advantage is that an insulating web can serve as a permanent or temporary positioning or support structure for articles intended for electrochemical processing. Electrochemical processes are normally immersion processes. Electrochemical baths are often heavily agitated. Many forms would not be self-supporting in such an environment. Forms of thin metal foil or conductive polymer ink patterns are examples. Conductive inks or paints such as particulate metal filled inks or paints can be considered for electrochemical treatment when supported on a web. Another advantage is many electrochemical and electrophysical processes may require certain positioning or placement among the items to be treated. Size or structural constraints might prevent certain items from being adequately positioned using a classic batch electrical processing rack. Positioning of such items onto a conveyance web could facilitate such processing and reduce labor burden in racking.
Another advantage of web processing using polymeric based webs is that the web can remain as a permanent support for the treated items or can be removed, in which latter case it would serve as a temporary or surrogate support during processing. As a permanent support, the web may serve as a base for packaging material options such as pressure sensitive or hot melt adhesive layers, overlaminates, printing, etc.
Another advantage of web processing is that often it can be accomplished in an essentially continuous operation thereby achieving the advantages of continuous processing.
Another advantage of web processing is that the web can comprise many different materials, surface characteristics and forms. For example, the web can constitute a nonporous film or may be a fabric. Relatively inexpensive substrates such as coated paper can be employed when such laminate materials can tolerate exposure to the electrochemical process. Combinations of such differences over the expansive surface of the web can be achieved. Indeed, as will be shown, the web itself can comprise materials such as conductive polymers or even metal fibers which will allow the web itself to undergo electrochemical processing.
Because the surface area of web being processed at any one time in an individual electrochemical operation can be relatively expansive and moving, it may be inconvenient to bring an electrical characteristic such as current or voltage to a myriad of different points simultaneously using discrete individual contacts. Thus another characteristic of web processing is that it allows the desired electrical characteristic (current, voltage, etc.) to be conveyed to a large number of points over an expansive surface using simplified buss structures, as will become clear in the discussion of embodiments to follow. Because the items being electrochemically treated may have complex structure, it may be difficult to specify a direction of electrical flow at any one point on the surface of an item being treated. However, often web processing will be characterized as having a conductive path, or buss, intended to convey the electrical characteristic (current, voltage etc.) between a source of electrical characteristic contacting the conductive path and a remote structure intended to be exposed to the electrical process. For example, a buss used for electroplating is a conductive path extending from a source of electrical potential to a point proximal or contacting a surface intended to be electroplated. The buss often extends in a direction parallel to the length direction of the web (sometimes referred to as “machine direction”). However, this is not necessarily the case. A buss is intended to convey the appropriate electrical characteristic and may extend in a direction angular to the “machine direction”. A buss can constitute a portion of the final electrotreated article or can be separate, in which case it may be removed following electrotreatment. A buss may comprise structure in the form of extending arms or fingers to electrically connect remote points to a main buss artery. In typical practice a buss may supply electrical communication between one or more items or structures and the source of the electrical characteristic. Thus in many cases the buss may electrically connect multiple structures undergoing treatment. However, this is not necessarily the case. As will be seen, buss structural concepts can be used to effectively promote treatment of the entire web itself or to form a convenient surface to facilitate a sliding contact.
In many cases it is desirable to have a buss exhibiting relatively high current carrying capacity. This allows the buss to transport necessary current without experiencing significant variations in voltage. This consideration leads one in the direction of using very conductive materials such as copper of a form having adequate cross section perpendicular to current flow. However, maintaining positioning and contact of such forms with structure to be electroplated can be complicated and expensive.
As will be taught herein, in many cases it would be advantageous to form portions of a buss structure from electrically conductive resins positioned on the web prior to electrochemical processing. This takes advantage of the ease of application, adhesive characteristics, and flexibility of conductive resins. In these cases a subsequent electrodeposition of metal over the surface of the initial buss structure may augment the current carrying ability of the buss structure. However, in many situations the buss would be severed and discarded following the electroplating and therefore the cost of the electrically conductive polymer used to define the buss structure can be a significant factor. The electrically conductive polymeric materials chosen to define the buss structure may need to be inexpensive and thin, factors which may lead to reductions in initial current carrying capacity of the buss structure.
The following specification discussion, taken along with the descriptive figures, will reveal and teach structural, process, and material improvements related to the continuous electroplating of material forms having limited current carrying ability prior to electroplating. In many cases the eminently suitable characteristics of electrically conductive polymers in the production of continuously electroplated articles will become clear. In many embodiments, an electrically conductive polymer formulated as a directly electroplateable resin (DER) is particularly suitable.
As pointed out above in this specification, attempts to dramatically simplify the process of electroplating on plastics have met with commercial difficulties. Nevertheless, the current inventor has persisted in personal efforts to overcome certain performance deficiencies associated with electroplating onto material structures having low current carrying ability, conductive plastics and DER's. Along with these efforts has come a recognition of unique and eminently suitable applications for electrically conductive polymers and often more specifically the DER technology for continuous electroplating. Some examples of these unique applications for continuously electroplated items include electrical circuits, electrical traces, circuit boards, antennas, capacitors, induction heaters, connectors, switches, resistors, inductors, batteries, fuel cells, coils, signal lines, power lines, radiation reflectors, coolers, diodes, transistors, piezoelectric elements, photovoltaic cells, emi shields, biosensors and sensors.
Regarding the DER technology, a first recognition is that the “microscopic” material resistivity generally is not reduced below about 1 ohm-cm. by using conductive carbon black alone. This is several orders of magnitude larger than typical metal resistivities. Other well known finely divided conductive fillers (such as metal flake or powder, metal coated minerals, graphite, or other forms of conductive carbon) can be considered in DER applications requiring lower “microscopic” resistivity. In these cases the more highly conductive fillers can be considered to augment or even replace the conductive carbon black.
Moreover, the “bulk, macroscopic” resistivity of conductive carbon black filled polymers can be further reduced by augmenting the carbon black filler with additional highly conductive, high aspect ratio fillers such as metal containing fibers. This can be an important consideration in the success of certain applications such as achieving higher current carrying capacity for a buss. Furthermore, one should realize that incorporation of non-conductive fillers may increase the “bulk, macroscopic” resistivity of conductive polymers loaded with finely divided conductive fillers without significantly altering the “microscopic resistivity” of the conductive polymer. This is an important recognition regarding DER's in that electrodeposit coverage speed depends on the presence of an electrodeposit coverage rate accelerator and on the “microscopic resistivity” and less so on the “macroscopic resistivity” of the DER formulation. Thus, large additional loadings of functional non-conductive fillers can be tolerated in DER formulations without undue sacrifice in electrodeposit coverage rates or adhesion. These additional non-conductive loadings do not greatly affect the “microscopic resistivity” associated with the polymer/conductive filler/electrodeposit coverage rate accelerator “matrix” since the non-conductive filler is essentially encapsulated by “matrix” material. Conventional “electroless” plating technology does not permit this compositional flexibility.
Yet another recognition regarding the DER technology is its ability to employ polymer resins and formulations generally chosen in recognition of the fabrication process envisioned and the intended end use requirements. Thus DER's can be produced in material forms that are often suitable for continuous electroplating. In order to provide clarity, examples of some such fabrication processes are presented immediately below in subparagraphs 1 through 6.
All polymer fabrication processes require specific resin processing characteristics for success. The ability to “custom formulate” DER's to comply with these changing processing and end use requirements while still allowing facile, quality electroplating is a significant factor in the continuous electroplating teachings of the current invention. Conventional plastic electroplating technology does not permit great flexibility to “custom formulate”.
Another important recognition regarding the suitability of DER's for continuous electroplating is the simplicity of the electroplating process. Unlike many conventional electroplated plastics, DER's do not require a significant number of process steps during the manufacturing process. This allows for simplified manufacturing and improved process control. It also reduces the risk of cross contamination such as solution dragout from one process bath being transported to another process bath. The simplified manufacturing process will also result in reduced manufacturing costs.
Yet another recognition of the benefit of DER's for continuous electroplating is the ability they offer to selectively electroplate an article or structure. As will be shown in later embodiments, it is often desired to continuously electroplate a polymer or polymer-based structure in a selective manner. DER's are eminently suitable for such continuous yet selective electroplating.
Yet another recognition of the benefit of DER's for continuous electroplating is their ability to withstand the pre-treatments often required to prepare other materials for plating. For example, were a DER to be combined with a metal, the DER material would be resistant to many of the pre-treatments such as cleaning which may be necessary to electroplate the metal.
Yet another recognition of the benefit of DER's for continuous electroplating is that the desired plated structure often requires the plating of long and/or broad surface areas. As discussed previously, the coverage rate accelerators included in DER formulations allow for such extended surfaces to be covered in a relatively rapid manner thus allowing one to consider the use of continuous electroplating of conductive polymers.
These and other attributes of DER's in the production of continuously and sequentially electroplated articles will become clear through the following remaining specification, accompanying figures and claims.
Reference will now be made in detail to the preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. In some of the drawings, like reference numerals designate identical or corresponding parts throughout several embodiments and an additional letter designation is characteristic of a particular embodiment.
Referring to
Article 10 has a surface 11 at least a portion of which is to be exposed to an electrochemical process such as electroplating. It may be desirable for example, to coat the entire Article 10 surface 11 with an electrodeposit. Alternatively, Article 10 could constitute a supporting substrate for a surface pattern intended to be electroplated. For the teachings of this invention, an article may be described as having structural characteristics such as planar, film, web-like, sheet-like, etc.
For purposes of this instant specification and claims, continuous or sequential electroplating will be construed as a process wherein at least a first portion of an article is exposed to an electroplating process while at least a second portion of the article remains unexposed to that electroplating process. In order to provide clarity, examples of processing which can be considered within the scope of the definition of continuous or sequential electroplating are presented immediately below in subparagraphs 1 through 3.
Referring now to
Referring now to
The embodiment of
In
In some cases, it may be desirable to electrodeposit material in a way to achieve thru web conductivity of the final article. Such was described in application Ser. No. 11/035,799 herein incorporated in its entirety by reference.
Another specific embodiment of a film or web structure according to the invention is identified generally by the article designated by numeral 22 of
As one of normal skill in the art will understand, in order for the patterns 26 to be electroplated, there has to be electrical communication between structural patterns 26 and a source of cathodic potential or contact. In the
A significant object of the current invention is to provide methods to achieve acceptable coverage of structure having low current carrying capacity with an initial deposit of electrodeposited metal. Once covered, the electrodeposited metal contributes significantly to current management during subsequent electrodeposition.
In
Thus in the
Considering now the processing of article 22a through electroplating process 36a of
Thus, when electroplating a continuous “buss” defined by material or structure of low current carrying capacity (such as many DER formulations, conductive polymeric inks, vacuum or chemically deposited metals) cathodic contact is often best achieved by contacting to previously electrodeposited metal surface. In this way the conductive electrodeposited metal increases in thickness and robustness during the travel time between the initial electrodeposit growth front and the initial cathodic contact, promoting reliable ohmic contact between the cathodic contact and metal electrodeposit.
The ability for the conductive electrodeposit to effectively convey the required cathodic electroplating current depends on its cross sectional area as well as the conductivity of the electrodeposited metal employed. The conductive electrodeposit thickness at any particular point in the
Many electrically conductive resins, including many DER formulations, can be characterized as materials of low current carrying ability wherein conductive electrodeposit coverage is achieved by lateral electrodeposit growth over the surface with the conductive electrodeposit carrying a large portion of the electroplating current to/from the cathodic contact. This situation would also exist even for relatively higher conductivity materials, such as a particulate metal filled polymer or very thin vacuum metallized or electrolessly deposited metal. It is currently believed that the speed of this lateral electrodeposit growth is at least partially dependent on the driving potential difference between the solution and the initial conductive surface at the advancing electrodeposit”s lateral growth front. Typically the higher the driving potential difference, the more rapid the rate of lateral growth. It will be appreciated that in a process such as depicted in
The lateral electrodeposit growth situation is illustrated in greater detail in the embodiments of
As shown in
An important parameter determining the lateral growth of electrodeposit over the surface of a buss 27b is the voltage at the electrodeposit growth front. This parameter is not only dependent on the overall applied voltage to the cell, but also on the voltage drop between the cathodic contact and the growth front. When electroplating a continuous buss artery 28b extending in a continuous web direction, the voltage drop from the cathodic contact to the growth front can be an important consideration. In practice, one prefers to have some measurable “lead length” between the contact and growth front to ensure that electrodeposited metal is present at contact 58b despite minor process disruptions which may occur. Such a “lead length” is illustrated in
A first way to maintain an acceptably high rate of the electrodeposit lateral growth is to simply increase the overall rectified potential applied to the bath. This will tend to raise the growth front potential, but is counteracted to some extent by the increased IR drop from the growth front to the initial cathodic contact due to the inevitable increased current densities on surfaces already plated between the growth front and cathodic contact. This method may also be restricted in that current densities in those portions where the voltage drop is less of a factor (for example downstream from the initial contact) may be caused to exceed desirable values leading to undesired electrodeposit thickness for the overall process or burning at contact 58b.
Another way to achieve an acceptably high rate of electrodeposit lateral growth is compositional modification to increase coverage rates. This can take the form of additives to increase current carrying capacity and/or in the case of DER's variation in the amounts and nature of the growth rate accelerators. For example, it has been observed that DER inks comprising a weight percentage of 4% sulfur will typically cover more rapidly than a DER ink comprising a weight percentage of 2% sulfur. In this regard one will recognize that the material defining the buss structure 27b need not be the same as the material defining the selective patterns 26b.
Yet another way to achieve an acceptably high rate of electrodeposit lateral growth is to the increase the thickness of the electroplateable material. For example, multiple printing operations can be employed to increase the buss thickness. Also, the buss structure may be formed through a process operation different than that used to form the structural patterns intended for electroplating. For example, while the structural patterns may be formed with flexographic printing techniques, the buss or portions of the buss may be formed with a roller, extrusion etc. One will thus recognize that it may be advantageous to process a web whereby the composition and/or thickness of the buss material is chosen to have higher current carrying capacity than that of the selective patterns.
Another way to achieve an acceptably high rate of electrodeposit lateral growth is to reduce the distance between the initial cathodic contact and the growth front. This decreases the distance over which current must be conveyed thereby reducing potential loss. One can institute feedback control wherein the “lead length” is closely integrated with the web speed so that the “lead length” is always maintained within a certain (normally shortened) distance. In this way the IR drop associated with electroplating on previously electrodeposited surfaces can be closely maintained and minimized. A potential problem with this approach is that cathodic contact will be occurring to a very thin electrodeposit and special precautions may be required to avoid burning and scraping and possible bipolar effects leading to actual deplating of the thin electrodeposit. In order to maintain acceptable manufacturing tolerances regarding the linear growth front speed and to achieve an acceptable thickness of electrodeposit at contact point 58b the linear distance between the growth front and contact 58b may be typically of the magnitude of greater than 2 inches.
Yet another method to achieve acceptably high driving potential at the growth front is demonstrated in
One will recognize that while the embodiments above of article 22a, 22b, and 22c involve the plating of a buss and selective patterns, the teachings and principles could also be applied to plating other structures in a continuous manner such as an entire web or film.
Yet another way to accelerate electrodeposit coverage of a material structure having low initial current carrying capacity is to position a conductive trace proximal or in contact with the structure. The conductive trace possesses a higher current carrying capacity than that of the material structure. In this way a conductive “parallel path” is supplied to transport electroplating current from those areas between the cathodic contact and the growth front on the material structure which consequently minimizes associated voltage drop along this length.
One such approach is embodied in
Augmenting the current carrying ability of the buss artery 28d by extending a highly conductive material contacting the buss can be accomplished using numerous process design techniques. One such process is embodied in
In describing some of the processes in the present specification, the web embodiment similar to that presented in
Upon exiting the bath, the structure originally defining buss portion 27e may be capable of adequately conveying associated electroplating currents since it is now coated with conductive electrodeposit. The composite web indicated as 110 in
Another web embodiment made possible using the electroplating process concept of
After exiting the electroplating process 36g, wire 90g may be separated from contact with the web and fingers 30g as shown in the embodiment of
Yet another structural web article 22h suitable for processing via a process embodiment similar to that depicted in
Yet another option to achieve rapid processing rates through increasing web speed would be to avoid the situation wherein the electroplating current is required to be transported primarily in the length direction of the web. Such a situation can be achieved by causing the web to be supported vertically in the electroplating bath (i.e. the width dimension is caused to have a vertical component). Cathodic contacting is made through a series of “clips” positioned proximal the upper edge of the web. Each of these “clips” would be responsible for current associated with a limited surface area of the web, approximately the distance between “clips” times the web width. Such a process has been utilized commercially to electroplate complete web surfaces having an initial thin coating of sputtered or chemically deposited metal. When electroplating patterned structures however, it is often difficult, expensive or inconvenient to generate the initial electroplateable patterns on the expansive web using chemical or physical metal deposition techniques. In addition, since the patterned structures can be relatively small in comparison to the web width, it is often desired to position multiple patterned structures across the width dimension. Electrical connecting of these multiple structures requires a buss structure extending in the web width direction. One will realize that the use of a conductive wire as shown in
Another option which increases the current carrying capacity of an initially low current carrying capacity buss, is to apply a distinct trace of highly conductive ink along the length and in contact with the initial buss structure. This approach was taught in application Ser. No. 11/035,799 herein incorporated in entirety by reference. This approach has an advantage in that the highly conductive ink augments the current carrying capacity of the buss structure not only during initial electrodeposit coverage but throughout possible subsequent electrochemical processing which may be desired.
The following solid ingredients were weighed out:
1. 33 grams of Kraton (Kraton 1450 Kraton Polymers)
2. 16.5 grams of carbon black (Vulcan XC-72 Cabot Corporation)
3. 0.5 grams of elemental sulfur
These solid ingredients were mixed and dissolved in approximately 10 ounces of a xylene solvent. This produced a fluid ink/coating formulation which, after drying, consisted of:
1. Kraton=66%
2. Carbon Black=33%
3. Sulfur=1%
A length of PET film was coated with this ink/coating solution in the form of a 1 inch wide buss stripe pattern. The stripe pattern was allowed to dry and then was immersed as a cathode in a standard Watts nickel plating bath similar to that depicted in
A piece of PET sheet 4 mil thick was cut into a sheet of linear dimensions 13 inch by 8.5 inch. This sheet was then wrapped around a polyethylene pipe having a 4 inch diameter. A DER strip, 1 inch wide was applied as a simulated buss on the exterior of the PET sheet extending circumferentially around the pipe. A length of copper wire, 0.019 inch in diameter was then wrapped around the pipe overlaying and in contact with the DER buss. The pipe/PET/DER buss/copper wire assembly was immersed in a standard Watts nickel electroplating bath and the copper wire was made cathodic at 3 volts overall potential relative to the anode. It was observed that the buss completely covered with nickel electrodeposit in 15 seconds. This shows that very rapid coverage of extended lengths of buss can be achieved with this approach. The approach therefore allows linear web process speeds to be greatly increased.
One intent of the electroplating processes and embodiments of
Additional electrodeposit thickening or variations in electrodeposited material on the patterned structures may be achieved in subsequent electroplating processes similar to that originally presented in the
An alternative arrangement to accomplishing electrodeposit thickening while allowing increased web processing speed is presented in
One of the major advantages to a multiple cell arrangement such as that depicted in
In
One realizes that using the arrangement of
It is to be noted that the process of using multiple individual cells to accomplish electrodeposition has significant advantages for web processing. In the
The benefits of using multiple individual electroplating cells to electrochemically process a web in a substantially horizontal fashion extend to web articles which may be characterized as having current carrying capacities greater than the low current carrying materials and structures as defined earlier in this specification. For example, this process arrangement can have significant advantages when processing a wide range of web articles including those wherein the electrodeposit extends over a major or complete portion of the web.
Turning now to
One problem that can be encountered with the electrical connections as illustrated in
The high bending stress level at the region indicated by arrow 174 in
A number of techniques can be used to alleviate the stress concentration problem depicted in
Yet another option to counteract the stress concentration problem is to use a thin, flexible material for substrate 156, such as a PET film. Such a conformable substrate would resist the stress concentration depicted in
Yet another option to counteract the stress concentration effect depicted in
In
For example,
Although the present invention has been described in conjunction with preferred embodiments, it is to be understood that modifications, alternatives and equivalents may be included without departing from the spirit and scope of the invention, as those skilled in the art will readily understand. Such modifications, alternatives and equivalents are considered to be within the purview and scope of the invention and following claims.
This application is a Continuation in-Part of U.S. patent application Ser. No. 11/198,520 filed Aug. 5, 2005 entitled Methods and Structures for the Production of Electrically Treated Items and Electrical Connections, which is a Continuation-in-Part of U.S. patent application Ser. No. 11/035,799 filed Jan. 14, 2005 entitled Methods and Structures for the Production of Electrically Treated Items and Electrical Connections, which is a Continuation-in-Part of U.S. patent application Ser. No. 10/776,359 filed Feb. 11, 2004 entitled Methods and Structures for the Production of Electrically Treated Items and Electrical Connections. The entire contents of the above identified applications are incorporated herein by this reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 11198520 | Aug 2005 | US |
| Child | 12655718 | US | |
| Parent | 11035799 | Jan 2005 | US |
| Child | 11198520 | US | |
| Parent | 10776359 | Feb 2004 | US |
| Child | 11035799 | US |
