The invention teaches improved materials and processes for production of structures to shield against ingress or egress of electromagnetic radiation. The structures and processes taught are based on the recognition and use of directly electroplateable resins. The directly electroplateable resins are combined with electrodeposited metal-based coatings to result in uniquely suitable structures to achieve radiation shielding. Fabrication and compositional flexibility of directly electroplateable resins and low cost material possibilities contribute to the unique suitability of directly electroplateable resins in the production of improved electromagnetic radiation shields.

The proliferation of electronic devices over the past several years has created problems of radiation containment from these devices. When a digital device changes voltage, it emits electrical and magnetic energy that is comparable to frictional heat loss in any mechanical machine. When not controlled, this radiation can interfere with the normal operating use of other electrical devices. In addition, many devices need to be shielded against incoming radiation to prevent damage to the product itself. As is known in the art, the prevention of egress or ingress of electromagnetic radiation is referred to as electromagnetic interference (EMI) shielding.
The typical methods to shield electronic devices consist of surrounding the electronic components with a conductive barrier which reflects and/or absorbs the radiation. However, the problems associated with electromagnetic interference continue to challenge manufacturers due to the proliferation of devices, increasing clock speeds, and the increased density of electronic packaging resulting from continual size reductions in portable devices. The problems have been further compounded by the increased use of plastic housings. Plastics tend to cost and weigh less than alternative metal structures, are resistant to corrosion and provide much greater design flexibility. However, plastics are natural insulators and as such are generally transparent to electromagnetic radiation in the applicable frequency range. Electronic equipment manufacturers have therefore been forced to find ways to shield the plastic enclosures to protect the components inside and comply with applicable regulations.
When evaluated according to standard testing protocol, the shielding imparted by a particular structure is reported in decibels. The shielding effect is measured by the following equation:Shielding effect (dB)=20 log (E.sub.1/E.sub.2)
Where:                E.sub.1 is the receiving level when no shielding material is placed between the transmitting and receiving antennas, and        E.sub.2 is the receiving level when a shielding material is placed between transmitting and receiving antennas.
20 dB is generally considered a minimum range for meaningful shielding. 30–60 dB can be sufficient to solve moderate problems. 60–90 dB represents excellent shielding solving moderate to severe problems.
Many different electromagnetic shielding methods exist. The simplest in concept is to select a metal housing or cabinet for the shield. The use of metal shields includes stamped shells or cabinets, zinc die castings, and sheet metal liners. Stamped shells can be a cost effective way to shield sensitive components inside a device. However, such shells do not necessarily protect the rest of the device from external sources of radiation and design flexibility is limited. Zinc die castings provide effective shielding, especially in high temperature environments. However, zinc die castings are costly, heavy, and design flexibility is limited. Sheet metal liners can be combined with the appeal of a plastic exterior, but sheet metal liners tend to be expensive and have to be attached to the plastic housing which complicates and lengthens the assembly process.
A number of methods have been developed to provide shielding to plastic components. Perhaps the simplest is to make the bulk plastic itself sufficiently conductive to impart required shielding performance. This technology generally involves mixing of the conductive filler into the polymer resin prior to fabrication of the material into its final shape. The conductive fillers typically consist of very high aspect ratio particles such as metal fibers to minimize the adverse processing and physical property affects and high cost associated with required loadings when using fillers of lower aspect ratios (for example metal powders).
The most effective and widely employed fibers are stainless steel fibers and nickel coated graphite fibers. Properly molded conductive fiber loaded plastics offer good shielding performance but suffer from a number of major downfalls. The first is the need to maintain integrity and even distribution of the conductive fibers in the plastic matrix during compounding and fabrication. High shear processing can result in the breakage of the fibers and reduction in the material conductivity. It also may be difficult to maintain uniformity of fiber concentration in a final molded part. A further problem is the need to maintain good surface conductivity. Conductive fiber filled plastics can exhibit poor surface conductivity even though bulk conductivity is acceptable. This "skin" effect can result in slot antennas at mating surfaces and prevent additional processing, if desired or necessary, requiring such surface conductivity. The fiber loadings required can negatively impact the aesthetic quality of the surface finish. Finally, the cost of the fibrous filler is very high, often negating the savings achieved through the elimination of secondary processing.
Efforts have been made to overcome the reduced surface conductivity often associated with conductive fiber filled plastics. For example, U.S. Pat. No. 4,596,670 to Liu teaches compositions containing polymer binder, metal flake, conductive fibrous fillers and conductive carbon black. However, these heavily loaded compositions can be difficult to process and other material properties are negatively impacted. Further, these compositions do not eliminate the other problems associated with using fibers mentioned above.
Another widely used material form in the art of electromagnetic (EMI) shielding consists of electrically conductive meshes or webs. These structures generally comprise conductive fibers, normally metal containing, fabricated into a mesh or screen by knitting, braiding or non-woven fabric technology. Alternatively, metal foils with a myriad of punched holes can be considered.
Metal containing fiber mesh structures have been used for many years to provide EMI shielding for openings in enclosures to allow an air flow for cooling and ventilation.
Another direction of development to provide EMI shielding to plastic components is incorporation of the conductive fabrics, webs, or meshes into a final composite article. The general concept is to confine the expensive conductive filler to an essentially sheetlike structure and thereby eliminate the need to have conductivity throughout the bulk volume of the article. Thus, introduction of such a conductive web during fabrication of the article conceptually eliminates secondary operations while eliminating the difficulties and expense associated with imparting bulk conductivity throughout the entire volume of the article. One form of this technology involves production of a metal mesh or web by weaving or hole punching a thin foil. This technique is taught in U.S. Pat. No. 5,473,111 to Hattori et al. and U.S. Pat. No. 6,054,647 to Ridener. Hattori taught a shield member of planar plate-shaped wire netting made of copper wires (or the like) 30 to 60 micrometers in diameter or a copper foil having a plurality of small holes. A precut shield member was placed inside a mold cavity such that a portion of the member extends from the outer peripheries of the cavity upon closure of the mold. Unfortunately, injection of plastic resin into a mold cavity typically involves high pressures and shear which can cause destruction to fragile netting or foils. Hattori proposed to solve this by injecting a portion of the resin prior to mold closing and carefully monitoring the rate of mold closure to achieve a partial "compression molding" process. Clearly, this would be impractical except for the very simplest of geometries.
Ridener taught weaving a grid from nickel coated steel fibers and then annealing and calendering to bond the fibers together at the cross-over points of the grid. The bonding was taught to provide increased integrity and conductivity to the grid, allowing it to be used as an insert in an injection molding operation. Unfortunately, the combined operations of nickel plating, drawing, weaving, annealing and sintering involved in the grids taught considerably adds to manufacturing cost. In addition, the insert molding involves preforming of the insert and considerable restriction of the design aspects of the part.
Another form of the conductive web technology envisions formation of a non-woven fabric by combining electrically conductive fibers bound together with resinous fibers. For example, U.S. Pat. No. 4,939,027 to Daimon et al. teaches manufacture of an electroconductive thermoplastic resin sheet comprising a non-woven fabric composed mainly of electroconductive fibers and heat-meltable fibers laminated between first and second thermoplastic films. Stainless steel fibers were taught as one example of the conductive fibers used to produce the non-woven fabric. The Daimon patent reports EMI shielding as high as 60 dB (at 300 MHz) for the conductive sheets taught. U.S. Pat. No. 4,943,477 to Kanamura et al. taught production of a conductive sheet by combining chemically metal plated fibers with heat fusible fibers to form a non-woven fabric which was subsequently hot-press molded to effect a monolithic fused sheet. Kanamura reported electric shielding effectiveness as high as 70 dB (at 1000 MHz) for the sheets taught in the patent.
The conductive fibers taught by Daimon and Kanamura are expensive and the processing to produce the precursor conductive non-woven sheets is complicated. In addition, the reasonably high shielding values reported by Daimon and Kanamura were obtained on essentially flat sheets of the composites taught. However, a significant problem arises when one attempts to form more useful three dimensional articles from such sheets, either through stamping or thermoforming. The resin flow and expansion involved in these operations tends to separate and fracture the fibers, resulting in loss of fiber to fiber contact and conductivity necessary to achieve shielding. Thus, the shielding of the Daimon and Kanamura composites would be expected to be drastically reduced should those composites be formed into three dimensional articles. This problem was addressed by U.S. Pat. Nos. 5,028,490, 5,124,198, and 5,226,210 to Koskenmaki et al. and U.S. Pat. Nos. 5,869,412, 6,013,376 and 6,090,728 to Yenni, Jr. et al. One of the major goals of this group of patents is production of metal/polymer composite sheets which are thermoformable without significant deterioration of shielding quality. The metal is present in the form of fine, randomly oriented metal fibers forming a mat supported by a polymeric substrate or carrier sheet. The metal fibers are made of metals and alloys having melting points less than the temperatures required to soften the polymeric components sufficiently to carry out the thermoforming operation. In this case, fibers are molten and rupture is minimized during the dimensional expansion of the sheet during the thermoforming operation. The patents reported shielding effectiveness of a thermoformed article (metal fiber loading of 242 grams per square meter) ranging from 48–58 dB over the range 30–1000 MHz. A problem is that the low melting point metal fibers employed are relatively expensive and manufacture of the precursor sheets is complicated, thereby significantly increasing the cost of the final shaped article. In addition, significant amounts of trim waste of the expensive sheets can be associated with the thermoforming operation, further increasing cost.
Further general problems with the use of conductive mats or sheets as shields exist in that they normally end up embedded in the final article, resulting in a non-conductive surface. This can result in loss of electrical communication along the edges of mating parts and production of a "slot antenna". Further, special operations are required if electrical communication must be achieved to other components of the device (for example the ground plane of a circuit board). Special connectors can be used, but at added cost. The Hattori U.S. Pat. No. 5,473,111 discussed above proposed to address this problem by extending the shield member outside the periphery of the resin portion of the part, but this is clearly impractical in most cases. Yenni et al. U.S. Pat. No. 6,090,728 taught exterior electrical connection by confining the insulating resinous layer covering the metal fiber mat to a thickness less than 0.15 mm. Using a specially designed and precisely controlled heat staking die, electrical connection to exterior conductive components was achieved. The unique design of the part and die along with the precise heat control required limits the application of this technique. In addition, the heat staking technique does not address the additional "slot antenna" problem.
There is thus a need to improve the "conductive mat" technology to avoid the use of very expensive metal fibers currently employed and simplify the elaborate processing currently necessary for production of the precursor materials.
Further teachings regarding EMI shielding comprising conductive webs or meshes involves the design and manufacture of high performance shielding gaskets. The outer covers of electronic equipment are usually formed by combining more than one housing component. To provide the entire cover with EMI shielding properties, electrical continuity must be achieved among the multiple components. In addition, should the mating surfaces of housing components not contact adequately, a gap is formed in the joint between housing components. Leakage of electromagnetic radiation can occur through this gap.
Electrical continuity among multiple housing components can be achieved in a number of ways. As pointed out in U.S. Pat. No. 5,170,009 to Kadokura, methods such as lead wires, application of silver paste, spray coating of conductive paints and use of damping screws have been employed. All of these techniques have characteristic disadvantages. Kadokura in U.S. Pat. No. 5,170,009 taught simultaneously electrodepositing a conductive coating comprising fine conductive particles and an electroplateable resin base. The coating was sufficiently conductive and conformable to act as a "conductive gasket" between mating surfaces. The many steps, expensive materials and the fact that the entire component has to be coated with the specialized electrodeposited coating severely limit applications of the technique.
Shielding gaskets are known which comprise resilient materials such as elastomers filled with a conductive filler. For example, U.S. Pat. No. 4,662,967 to Bogan et al. describes a shielding gasket comprising conductive filler mixed with an elastomer and bonding agent. The gasket is bonded to a surface by curing the gasket material in contact with the surface.
As electronic equipment has evolved, higher frequencies are encountered, and the electrical conductivity imparted by conductive fillers becomes only marginally effective for adequate attenuation of the high frequency spectrum of the radiation. Thus, where such higher frequencies are encountered, it becomes necessary to utilize conductive mesh materials supported on a resilient core material such as an elastomer or foam to provide adequate shielding levels. Shielding structures comprising metal mesh supported by an internal resilient core are taught in U.S. Pat. RE33,256, U.S. Pat. Nos. 5,028,739, 5,386,345, and 5,142,101. A common feature of these higher performance gaskets is the requirement of providing some form of metal fiber mesh. These meshes utilize fibers made of relatively expensive materials such as stainless steel, Monel, tin-coated copper, or metal plated polymeric fibers. In addition, processing of the individual fibers into the mesh adds considerably to the overall cost of the gasket.
It is clear that the shielding techniques using metal-containing meshes, whether aimed at shielding ventilation openings, incorporation into final plastic components or for use in gasketing, could be greatly advanced by improved processing techniques for production of the mesh structures and the use of a minimum of expensive materials.
Another method for imparting EMI shielding capability to plastic articles is the use of conductive paints. These paints usually comprise copper or nickel powder or flake in a polymeric binder. Conductive paints can be applied with simple, conventional spray painting equipment. For parts with simple designs, painting is a low cost shielding option due to low capital costs. The paints can usually be applied to most plastics although some require an adhesion promoting treatment. One major disadvantage of conductive painting is that it is a line of sight process making it difficult to successfully shield recessed or ribbed areas. Thin coatings also will not provide good shielding effectiveness so multiple coats may be required. This may be a particular problem at sharp corners where the well-known "pull-away" characteristic of paints may lead to slot antenna effects. Finally, the multiple coats which may be required result in significant material overspray waste, environmental difficulties, and increased costs. It is also difficult to achieve consistent paint thickness over the surface of an article which can result in variations in shielding performance. Finally, conductive paints often suffer from problems with durability over time. Due to these drawbacks the use of conductive paint coatings has grown very slowly over the past several years.
Yet another method for imparting EMI shielding capability to plastic articles is vacuum metallizing. In the vacuum metallizing process, parts are masked if necessary and then placed on rotating fixtures inside a vacuum chamber. Inside the chamber a metal, usually aluminum, is heated and vaporized. The metal will then condense on the surface of the plastic. Vacuum metallizing is generally a batch process that is best suited for small to moderate sized parts with limited geometrical complexity. For example, U.S. Pat. No. 5,811,050 to Gabower teaches the use of vacuum metallizing to shield thermoformed plastic parts. Thermoforming is a process limited to parts of relatively simple geometry. Gabower reported shielding effectiveness values of up to 60 dB for vacuum metallized, thermoformed parts. Thus, for these types of parts, vacuum metallizing provides reasonable shielding effectiveness at a relatively moderate cost. A major disadvantage of vacuum metallizing is the need for special equipment which requires a significant capital investment as well as a high operator skill level. In addition, vacuum deposition of the relatively thick films required for EMI shielding can be complex and process sensitive, as discussed in the Gabower U.S. Pat. No. 5,811,050. Like spray painting, vacuum metallizing is generally a line of sight process which makes it difficult to successfully shield recessed or ribbed areas. Finally, a base coat or ionization treatment is often required between the plastic and aluminum to minimize surface defects, and a protective coating may be required to protect the vacuum deposited metal.
An alternative method for imparting EMI shielding to plastics is electroless plating. Electroless plating involves chemically coating a nonconductive surface such as a plastic with a continuous metallic film. Unlike conventional electroplating, electroless plating does not require the use of electricity to deposit the metal. Instead, a series of chemical steps involving etchants and catalysts prepare the non-conductive plastic substrate to accept a metal layer deposited by chemical reduction of metal from solution. The process usually involves depositing a thin layer of highly conductive copper followed by a nickel topcoat which protects the copper sublayer from oxidation and corrosion. The thickness of the nickel topcoat can be adjusted depending on the abrasion and corrosion requirements of the final product. Because electroless plating is an immersion process, uniform coatings can be applied to almost any configuration regardless of size or complexity without a high reliance on operator skill. Electroless plating also provides a highly conductive pure metal surface which results in relatively good shielding effectiveness. In addition, electrolessly plated parts can be subsequently electroplated, although electroplating is generally not used unless a part also has certain decorative or functional requirements. On average, the cost of electroless plating will be higher than vacuum metallizing and conductive paints. The many steps employing harsh and expensive chemicals make the process intrinsically costly and environmentally difficult. The process comprises many steps and is very sensitive to processing variables used to fabricate the plastic substrate, limiting applications to carefully molded parts and designs. It may be difficult to properly mold conventional plateable plastics using the rapid injection rates often required for the thin walls of electronic components. The rapid injection rates can cause poor surface distribution of etchable species, resulting in poor surface roughening and subsequent inferior bonding of the chemically deposited metal. The rates at which metals can be chemically deposited are relatively slow, leading to increased process times to deposit the thicknesses required for adequate shielding and abrasion resistance. Finally, selective metallizing can be difficult, especially on complex parts, since the electroless plating may tend to coat any exposed surface unless the overall process is carefully controlled. The conventional technology for metal plating on plastic (etching, chemical reduction, optional electroplating) 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.
Many attempts have been made to simplify the process of plating on plastic substrates. Some involve special chemical techniques to produce an electrically conductive film on the surface followed by electroplating. 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 then electroplated.
Another approach proposed to simplify electroplating of plastic substrates is incorporation of electrically conductive fillers into the resin to produce an electrically conductive plastic that is then electroplated. When considering producing an electrically conductive polymer intended to be electroplated, one should consider "microscopic" resistivity in order to achieve uniform, "hole-free" deposit coverage. Thus, the fillers chosen will likely comprise 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 advance systems contemplating metal electrodeposition directly onto the surface of an electrically conductive polymer 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 major 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 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 rack tip, itself under cathodic potential. However, if the contact resistance is excessive or the substrate is insufficiently conductive, the electrodeposit current favors the rack tip to the point where the electrodeposit will not bridge to the substrate.
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. The polymeric substrate can be relatively limited in the amount of electrodeposition current which it alone can convey. Thus, the conductive polymeric substrate does not cover almost instantly with electrodeposit as is typical with metallic substrates. Except for the most heavily loaded and highly conductive polymer substrates, a large portion of the electrodeposition current must pass back through the previously electrodeposited metal growing laterally over the surface of the conductive plastic substrate. In a fashion similar to the bridging problem discussed above, the electrodeposition current favors the electrodeposited metal and the lateral growth can be extremely slow and erratic. 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.
This lateral growth is dependent on the ability of the substrate to convey current. Thus, the thickness and resistivity of the conductive polymeric substrate can be defining factors in the ability to achieve satisfactory electrodeposit coverage rates.
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, 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.
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 metal containing fillers. Such heavy loadings are sufficient to reduce both microscopic and macroscopic resistivity to a level where the coverage rate phenomenon may be manageable. However, attempts to make an acceptable directly electroplateable resin using the relatively small metal containing fillers alone encounter a number of barriers. First, the fine metal containing fillers are 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 metal containing fillers are accompanied by further problems. They tend to cause deterioration of the mechanical properties and processing characteristics of many resins. This significantly limits options in resin and fabriation selection. All polymer processing is best achieved by formulating resins with processing characteristics specifically tailored to the specific process (injection molding, extrusion, blow molding etc.). A required heavy loading of metal 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 simple metal-filled polymer still offers no mechanism to produce adhesion of an electrodeposit since the metal particles are generally encapsulated by the resin binder, often resulting in a non-conductive resin-rich "skin". For the above reasons, fine metal particle containing plastics have not been widely used as substrates for directly electroplateable articles. Rather, they have found applications in production of conductive adhesives, pastes, and paints.
The least expensive (and least conductive) of the readily available conductive fillers for plastics are carbon blacks. 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. A fundamental problem remaining unresolved by the Adelman teaching is the relatively high resistivity of carbon loaded polymers. The lowest "microscopic resistivity" generally achievable with carbon black loaded polymers is about 1 ohm-cm. This is about five orders of magnitude higher than typical electrodeposited metals such as copper or nickel. Thus, the electrodeposit bridging and coverage rate problems described above remained unresolved by the Adelman teachings.
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 an electrically conductive filler for polymeric compounds to be electroplated. However, these inventors further taught incorporation of an electrodeposit coverage or deposition rate accelerator to overcome the galvanic bridging and lateral electrodeposit growth rate problems described above. 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 resins can be generally described as electrically conductive polymers with the inclusion of a growth rate accelerator.
Specifically for the present invention, directly electroplateable resins, (DER), are characterized by the following features.                (a) having a polymer or resin matrix or binder;        (b) presence of conductive fillers in the polymer matrix in amounts sufficient to provide an electrical volume resistivity of the polymer/conductive filler mix which is sufficiently low to allow direct electrodeposition. Typically, a resistivity less than 1000 ohm-cm., e.g., 100 ohm-cm., 10 ohm-cm., 1 ohm-cm. 0.1 ohm-cm., 0.01 ohm-cm., 0.001 ohm-cm., suffices;        (c) presence of an electrodeposit coverage rate accelerator;        (d) presence of the polymer, conductive filler and electrodeposit coverage rate accelerator in the directly electroplateable composition in cooperative amounts required to achieve direct coverage of the composition with an electrodeposited metal or metal-based alloy. It has been found that Group VIII metals or Group VIII metal-based alloys are particularly suitable as the initial electrodeposit on the DER surface.
It is understood the electrical conductivity required to allow for direct electrodeposition can also be achieved thru the use of an inherently conductive polymer. In this instance it may not be necessary to add conductive fillers to the polymer.
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.
When used alone, the minimum workable level of carbon black required to achieve "microscopic" electrical resistivities of less than 1000 ohm-cm. for a polymer/carbon black mix appears to be about 8 weight percent based on the combined weight of polymer plus carbon black. 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 highly conductive fillers (such as metal flake) can be considered in DER applications requiring lower "microscopic" resistivity. In these cases the more highly conductive fillers can be used to augment or even replace the conductive carbon black.
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. 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.
It is important to recognize a number of important characteristics of directly electroplateable resins (DERs) which facilitate the current invention. First, 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. It is important to recognize that such an electrodeposit coverage rate accelerator is extremely important in order to achieve direct electrodeposition in a practical way onto polymeric substrates having relatively high resistivity compared to metals (i.e. 0.001 ohm-cm. or above) or very thin electrically conductive polymeric substrates having restricted current carrying ability.
A second important characteristic of directly electroplateable resins is that electrodeposit coverage speed depends not only on the presence of an electrodeposit coverage rate accelerator but also 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 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 broad compositional flexibility.
A third important characteristic of DER technology is its ability to employ polymer resins generally chosen in recognition of the fabrication process envisioned and the intended end use requirements. For example, should an extrusion blow molding fabrication be desired, resins having the required high melt strength can be employed. Should the part be injection molded and have thin wall cross-sections, a typical situation encountered in EMI shielding, a high flow resin can be chosen. Should a coating, ink, paint, or paste be envisioned, a soluble resin such as an elastomer can be considered. 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 selective electroplating teachings of the current invention. Conventional "electroless" plating technology does not permit great flexibility to "custom formulate".
Due to multiple performance problems associated with their intended end use, none of the attempts identified above to produce a directly electroplateable plastic has ever achieved any recognizable commercial success. Nevertheless, the current inventor has persisted in personal efforts to overcome certain performance deficiencies associated with the initial DER technology. Along with these efforts has come a recognition of unique and eminently suitable applications employing the DER technology especially for those applications requiring electromagnetic shielding.
In order to eliminate ambiguity in terminology, for the present invention the following definitions are supplied:
"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.

Electromagnetic interference shields and methods of manufacture


Fuel additive compositions that include synergistic mixtures of one or more neutral lubricity additives and one or more monoacidic lubricity additives to provide wear and/or friction reduction in fuels.

Fuel compositions for vehicles are continually being improved to enhance various performance properties of the fuels in order to accommodate their use in newer, more advanced engines. Often, improvements in fuel compositions center around improved additives and other components used in the fuel. For example, friction modifiers may be added to fuel to reduce friction and wear in the fuel delivery systems of an engine. Other additives may be included to reduce the corrosion potential of the fuel or to improve the conductivity properties. Still other additives may be blended with the fuel to improve fuel economy. Engine and fuel delivery system deposits represent another concern with modern combustion engines, and therefore other additives often include various deposit control components to regulate and/or mitigate engine deposit problems. Thus, fuel compositions typically include a complex mixture of additives.


A safety port needle assembly used to connect an IV line to an implanted port needle receiving port. The assembly includes an L-shaped port needle with an integrally attached horizontal leg member, a vertical leg member, an elongated, fixed main body and a pivotally attached needle arm. The horizontal leg member is longitudinally aligned and attached to the needle arm. The vertical leg member extends downward perpendicular to the longitudinal axis of the needle arm. A channel is formed in the main body that enables the needle arm to rest longitudinally against the main body. A bore is also formed in the main body so that the vertical leg member may extend downward through the main body. Formed near the distal end of the main body is a pair of laterally extended wings.

1. Field of the Invention
The present invention relates generally to the field of body entering conduits, and, more particularly, to conduits having protective levers to prevent accidental punctures.
2. Description of the Related Art
Medications are commonly administered by injection or continuous infusion into an implanted port, known as a vascular access port (VAP). VAPs are typically used in patients who need intermittent long-term I.V. therapy but can""t use an external central venous catheter.
In order to administer medication through the port, access through the port must be obtained by carefully inserting a non-coring bent needle known as a Huber needle into the silicone injection septum located in the port. During the procedure, known as xe2x80x9caccessing the portxe2x80x9d, the nurse or I.V. therapist is required to palpate and stabilize the port under the skin between his or her thumb and forefinger. While holding the Huber needle like a dart, at a 90-degree angle over the septum, the needle is pushed through the skin until it hits the needle stop located at the back of the septum.
Complications such as blockage, burning sensation, or when the central venous access is no longer required may occur that require the Huber needle to be removed, or xe2x80x9cdeaccessedxe2x80x9d from the port. When xe2x80x9cde-accessingxe2x80x9d the port, the nurse or I.V. therapist must grab the end of the Huber needle with one hand and palpate the port under the skin between his or her finger with the other hand. The needle is then pulled upward with considerable force, removing it from the septum. After the needle is removed, the nurse or I.V. therapist must quickly deposit the needle in a safe location so that his or her hands may be used to stop any bleeding or provide additional treatment.
Because the nurse or I.V. therapist must stabilize the port between his or her fingers while the Huber needle is pushed or pulled from the port, accidental puncture sometimes occurs. Also, because the old needle may be quickly deposited, placing the old needle into the opening of a Sharps container can lead to accidental skin punctures.
What is needed is a safety port needle assembly that prevents accidental punctures when accessing and de-accessing a VAP and that completely covers the sharp end of the contaminated needle after it has been de-accessed from the port assembly.
It is an object of the present invention to provide a safety port needle assembly that reduces the risk of needle stick injury when accessing and de-accessing a VAP. It is a further object of this invention to provide a safety port needle assembly that is easy to use.
It is a further object of the present invention to provide a safety port needle assembly that fully contains the sharp end of the contaminated needle after de-accessing from the VAP.
These and other objects of the present invention are met by a safety port needle assembly used to connect an IV line to an implanted port needle receiving port. The assembly includes an L-shaped port needle with an integrally attached horizontal leg member and a vertical leg member. The horizontal leg member is disposed inside an elongated needle arm that is pivotally attached at one end to an elongated main body. The vertical leg member is perpendicularly aligned and extends downward from the distal end of the needle arm. A channel is formed in the main body that enables the needle arm to nest longitudinally inside the main body. A bore is also formed in the main body that enables the vertical leg member to extend downward through the main body when the needle arm is longitudinally aligned with the main body. Located in front of the bore is a pocket space which receives the tip of the port needle when extended above the bore. Also, formed near the distal end of the main body is a pair of laterally extended wings that enable a healthcare worker to securely hold the main body over the implant port using his or her fingers.
Disposed between the needle arm and the main body is an upward rotation limiting means that prevents the needle arm from being rotated upward excessively so that the tip of the needle is exposed. In the preferred embodiment, the upward rotating limiting means is a beveled surface formed on the needle arm that presses against the main body and prevents the needle arm from pivoting upward beyond a desired angle. Also provided is an optional downward rotation limiting means that provides the needle arm from being accidentally rotated downward after being rotated upward to prevent punctures. Also attached to the distal end of the needle arm is an optional pair of laterally extended wings that enables the needle arm to be easily rotated by the healthcare worker.
During use, an IV tube is connected to the proximal end of the horizontal leg member that extends rearward from the proximal end of the needle arm. The tip of the vertical leg member is then inserted into the implant port so that the second pair of wings is positioned directly against the patient""s skin surround the implant port. The needle assembly can then be used to deliver fluids to the implant port. When de-accessing the implant port, the healthcare worker places the fingers of one hand over the first pair of wings to stabilize the main body over the implant port. The healthcare worker then grasps the second pair of wings with the fingers of the opposite hand, and lifts upward. As the second pair of wings is lifted, the needle arm pivots upward over the main body. When the needle arm pivots a sufficient distance, as determined by the length of the vertical leg of the port needle and the relative angle of the beveled surface, the tip of the vertical leg member extends above the bore on the main body. As the needle arm is pivoted rearward, a rearward directed force is applied to the vertical leg member. When the distal end of the vertical leg member extends past the bore, the vertical leg member snaps forward so that it is perpendicularly aligned with the horizontal member. When the vertical leg member snaps forward, it is received by the pocket space formed on the main body to further protect against accidental punctures.
There as thus been outlined, rather broadly, the more important features of the invention in order that the detailed description thereof that follows may be better understood, and in order that the present contribution to the art may be better appreciated. There are additional features of the invention that will be described hereinafter and which will form the subject matter of the claims appended hereto.


Disclose is a low-pressure atomizing spray gun. The spray gun comprises an air spray gun body, a paint nozzle attached to the spray gun body, an air cap attached to the air spray gun body to cover the paint nozzle, and air groove on a tip portion of the paint nozzle. An annular slit is defined between a central opening of the air cap and the paint nozzle. The air grooves extend from at or upstream of an inlet end of the annular slit towards a discharge end of the nozzle. Also, a discharge end of the paint nozzle projects from 0.3 mm to 0.8 mm from a front end of the central opening in the air caps.

The present invention relates to a spray gun for atomization of paint under a spraying air pressure of 0.07 MPa or less, and more particularly to a low-pressure air spray gun having an improved atomization mechanism used in a non-premixing type air spray gun in which compressed air and paint are mixed outside a spray head, and which is capable of providing a spray pattern which assures an improved atomization of the paint.
Non-mixing type air spray guns are widely used in the field of general industrial paint coating. They are defined as xe2x80x9cspray gunxe2x80x9d in the Japanese Industrial Standard (JIS) as well. According to the definition in JIS, the non-premixing type air spray gun is one adapted to jet compressed air from an annular slit defined between a paint nozzle and air cap and around the paint nozzle at a velocity greater than the speed of sound under a specified spraying air pressure of 0.24 to 0.34 MPa, and thus atomize and spray the paint to an object surface, thereby forming a paint coating on the object surface. This paint coating method has great applicability not depending upon any shape of an object surface to be coated and type of a paint used. However, the coating method is not advantageous in that much atomized paint is easily airborne or scattered and overspray causes a large loss of the paint. Because of the possible environment and air pollution by the airborne atomized paint with the conventional air spray guns, there has been a growing trend over the world to impose limitations on conditions of using the air spray gun.
To accommodate such a trend, various measures have been proposed heretofore. Accordingly, much attention has been focused on a low-pressure spray gun using spraying air pressure limited to less than 0.07 MPa for minimizing the airborne atomized paint and enabling an improved efficiency of paint coating to an object surface.
The low-pressure spray guns include some types based on different principles. One of the principles is to limit the spraying air pressure to less than the standard atmosphere to prevent paint particles from getting airborne or being scattered. With this spray gun, however, the limited spraying air pressure will lead to a reduced air speed, with the result that the paint atomization based on the difference in speed between gas and liquid flows, will be extremely poor. To compensate for the insufficiency of paint atomization, a low-pressure spray gun has been proposed in which the width of an air jet slit formed between a paint nozzle and air cap is increased to atomize the paint with a correspondingly increased amount of air. The mechanism of this low-pressure spray gun is basically the same as that of the conventional high-pressure spray guns. Namely, the air jet slit formed around the paint nozzle is designed wider to provide a larger amount of air jet even under a low pressure.
The poor atomization of the paint due to the reduced spraying air pressure involves some problems which cannot be solved just by increasing the air amount. Namely, it has been pointed out, as such problems, that when the amount of paint flow is increased, the central portion of the paint flow will not sufficiently mix the flow of air, resulting in an incomplete mixing, so that the paint flow in the center of the spray pattern cannot sufficiently be atomized, which is likely to take place with a paint having a slightly higher viscosity, and thus coarse paint particles will fly around the spray pattern when the width of an elliptical spray pattern is adjusted. That is, the;reduction of the spraying air pressure will lead to a non-uniform atomization of the paint.
To solve the above problems, the Applicant of the present invention has proposed to form a plurality of v-shaped air grooves in the tip of the paint nozzle as disclosed in his Japanese Patent Application No. 7-25907 (Japanese unexamined Patent Publication No. 8-196950). However, this method was found practically not satisfactory and involves some problems to be solved.
According to the invention disclosed in the above Japanese Patent Application, compressed air will flow into a flow of paint still in the paint nozzle, thereby improving the efficiency of paint atomization. However, since paint and air flows will prematurely be mixed in the paint nozzle or just before the tip of the paint nozzle, the paint spray will be limited, resulting in a lower efficiency of the paint coating.
That is, when a paint flow from the delivery portion of a paint nozzle is supplied under pressure, the amount of paint spray will depend upon the pressure applied to the paint flow, independently of the pressure and amount of the compressed air jet supplied from the aforementioned annular slit. However, in a gravity or suction type spray gun in which the paint spraying depends upon the attraction by the compressed air jet supplied from the annular slit, the condition of jetting the compressed air to the paint delivery port will not only seriously influence the atomization but also the amount of paint spray; that is, the efficiency of coating and optimization of the spray gun itself.
To atomize a paint under a low pressure and prevent occurrence of coarse particles in parts of a paint spray and non-uniform paint atomization, the present invention has an object to overcome the above-mentioned drawbacks of the prior art by providing a practically high efficiency spray gun.
More particularly, the present invention has a primary object to overcome the drawbacks, of the low-pressure atomization mechanism used in the conventional non-premixing type air spray gun, that atomization of paint is partially insufficient due to a low pressure of air flow, by providing a low-pressure atomizing spray gun including an atomization mechanism for a non-premixing type air spray gun, adapted to effectively mix low-pressure air jets supplied from an annular slit defined between the tip of a paint nozzle and a central opening in an air cap when the latter is fixed on the paint nozzle, with a paint flow from the paint nozzle and uniformly atomize the central portion of the paint flow. Accordingly, provided is a uniform spray pattern without reduction in the amount of the paint spray due to the attraction by the air jet supplied.
The present invention has another object to overcome the drawbacks of the prior art, that the sprayed paint particles easily adhere to the surface of the air cap depending upon a position where the mixed flow is diffused, the air cap surface has to be cleaned periodically, and it is necessary to prevent a paint coating once formed from being spoiled by the paint particles re-flying from the air cap surface.
According to a first aspect of the present invention, there is provided a low-pressure atomizing spray gun including an air spray gun body, a paint nozzle screwed to the spray gun body, and an air cap installed with a cover thereof to the spray gun body to cover the paint nozzle. The paint nozzle and air cap corporate with each other to mix, in the atmosphere, compressed air and a paint flow just delivered from the paint nozzle and to atomize the paint. The spray gun includes a plurality of air grooves formed in the tip of the paint nozzle convergently towards the center of the delivery port of the paint nozzle. And, each of the air grooves begins at or upstream of the inlet end of a central opening in the air cap.
In the above spray gun, the inner end is the starting point at which the air flow through a central annular slit will substantially form an axial flow. The air grooves are formed such that the cross section of each groove increases towards the paint nozzle delivery port end, and the plurality of air grooves extends toward the center of the delivery port end while converging at an angle of 45 to 90 degrees to the inside diameter from the outside diameter. Thus, owing to the air jets supplied from the plurality of air grooves, the compressed air is mixed with the paint flow deep to the center of the latter, thereby permitting the paint to be completely and uniformly atomized.
Also, according to a second aspect of the present invention, there is provided a low-pressure atomizing spray gun of a suction or gravity type including an air spray gun body, a paint nozzle screwed to the spray gun body, an air cap installed with a cover thereof to the spray gun body to cover the paint nozzle. The paint nozzle and air cap work cooperatively with each other to mix, in the atmosphere, compressed air and a paint just delivered from the nozzle to atomize the paint, wherein an annular-slit is defined between the tip portion of the paint nozzle and the wall of a central hole formed in the air cap. A plurality of air grooves is formed on the tip portion of the paint nozzle convergently at an angle of 45 to 90 degrees from the circumference of the nozzle tip towards the wall of a delivery hole in the nozzle to the inside diameter of the nozzle. The intersection of the bottom of a v-shaped air groove with the inside diameter of the paint nozzle approximately coincides with the front end of the central opening in the air cap, and the front end of the paint nozzle tip projects 0.3 to 0.8 mm from the front end of the central opening in the air cap.
With the above construction, the atomized paint flow is controlled against any further flying, the amount of paint spray is prevented from being reduced-under the action of the air inflow from the air grooves to limit the air jets, and the paint is prevented from adhering to the air cap, thereby assuring a stable spraying of the paint. The relatively thick air flow jet from the annular slit defined around the paint nozzle assures uniform atomization of the paint. Thus, the low-pressure atomizing spray gun according to the present invention can effectively atomize the paint as with a high pressure air spray gun.
The addition of the atomization mechanism of the present invention to the paint atomization mechanism of the conventional low-pressure air spray gun, which is based only on the increase of the central air flow, defines a positional relationship between the paint nozzle and air cap, which assures atomization of the paint with a highly improved efficiency and a reduced amount of air.
These and other objects, features and advantages of the present invention will become more apparent from the ensuing detailed description of the preferred embodiments of the present invention when taken in conjunction with the accompanying drawings.


A method for catalytic conversion of carbon monoxide with water to carbon dioxide and water in a hydrogen-containing gas mixture (carbon monoxide conversion) by passing the gas mixture over a shift catalyst that is at an operating temperature for the carbon monoxide conversion. The method is carried out with a shift catalyst based on noble metals that is applied to an inert support element in the form of a coating.

The present invention relates to a method for catalytic conversion of carbon monoxide with water to carbon dioxide and hydrogen in a gas mixture that contains hydrogen and other oxidizable components.
The conversion of carbon monoxide with water to carbon dioxide and hydrogen in the presence of catalysts is a known method for producing hydrogen-rich gas mixtures, which is based on the following exothermic reaction:
CO+H2O⇄H2+CO2xcex94H greater than 0xe2x80x83xe2x80x83(1)
Here the following side reactions can occur:
CO methanation: CO+3H2⇄CH4+H2O xcex94H greater than 0xe2x80x83xe2x80x83(2)
and
CO2 methanation: CO2+4H2⇄CH4+H2O xcex94H greater than 0xe2x80x83xe2x80x83(3)
The reaction in accordance with reaction equation (1) is called carbon monoxide conversion or CO conversion herein. The term xe2x80x9cwater gas shift reactionxe2x80x9d is commonly used for this in the USA.
The production of hydrogen-rich gas mixtures from hydrocarbons, or alcohols, by steam reforming, partial oxidation or autothermic reforming is a known process. These gas mixtures (reformates) contain 1 to 40 vol % carbon monoxide, depending on the method that is used.
To use the reformate as fuel in fuel cells, it is necessary to reduce the carbon monoxide contained in them as far as possible, in order to avoid poisoning of the platinum-containing anode catalyst of the fuel cell in the oxidation of the hydrogen. In addition, the conversion of carbon monoxide in accordance with reaction equation (1) leads to an increase of the hydrogen content of the reformate and thus to an improvement of the efficiency of the overall process.
For reasons of size and weight catalysts for conversion of carbon monoxide with very high activity and selectivity are required for use in motor vehicles. The high space-time yields that can be achieved by this allow the volume of the reactors that are required to be kept small.
The known catalysts for the conversion of carbon monoxide have chiefly been developed for stationary industrial applications. The emphasis lay in the production of pure hydrogen, ammonia and other large scale products that are based on the use of synthesis gas mixtures (CO/H2). Catalysts for the conversion of carbon monoxide in accordance with reaction equation (1) are also called shift catalysts herein.
These known catalysts are complete catalysts that contain non-noble metals. They are used in two-stage processes. In the first process stage a so-called high temperature CO conversion (high temperature water-gas shift, HTS) is carried out on Fe/Cr catalysts at temperatures between 360 and 450xc2x0 C. In the subsequent second stage a low-temperature CO conversion (low temperature water-gas shift, LTS) is undertaken on Cu/ZnO catalysts at temperatures between 200 and 270xc2x0 C. After the low temperature process stage carbon monoxide concentrations of less than 1 vol % in correspondence with the thermal equilibrium are obtained.
The conventional catalysts for the conversion of carbon monoxide have crucial disadvantages:
The described two stage conduct of the process is necessary because of the properties of these catalysts. While Cu/ZnO-containing catalysts become deactivated above 270xc2x0 C. because of recrystallization, or sintering, of the copper, the Fe/Cr-containing catalysts that are used in the high temperature range cannot be used at low temperatures because of insufficient activity. If the indicated temperature range of the high temperature catalysts is exceeded, methanation reactions (reaction equations (2) and (3)) can occur, which reduce the selectivity of the high temperature catalyst and because of this lower the overall efficiency of the hydrogen generation system.
Both the known high-temperature and the low-temperature catalysts are bulk catalysts, in which the catalyst material is pressed to form pellets or other molded bodies. Accordingly, they consist entirely of catalytically active mass and are also called complete catalysts. As a rule, they have a very high bulk weight.
The known industrial methods for conversion of carbon monoxide on catalysts according to reaction equation (1) operate at space velocities of the gas mixture between 300 and 3000 hxe2x88x921. These low velocities are not sufficient for use in motor vehicles.
High bulk weights and low space velocities lead to low specific conversion rates RCO for the carbon monoxide, which is understood within the scope of this invention to mean the amount of carbon monoxide NCO converted per weight of the catalyst mcat and reaction time xcex94t. The weight of the catalyst here is given in grams, the reaction time in seconds and the amount of carbon monoxide in mol:                               R          CO                =                                            n              co                                                      m                Cat                                          Δ                                            xe2x80x83                                          t                                                      xe2x80x83                    [                      mo1                          g              ·              s                                ]                                    (        4        )
The known Cu/ZnO and Fe/Cr catalysts have to be activated by reduction before they are used. The activated catalysts are sensitive to oxygen. Upon contact with atmospheric oxygen they are reoxidized and deactivated in an exothermic reaction.
In comparison with the just described industrial high temperature and low temperature catalysts based on Fe/Cr or Cu/ZnO, noble metal catalysts for these uses are also known, mainly from the scientific literature.
D. C. Grenoble et al. describe in xe2x80x9cThe Chemistry and Catalysis of the Water Gas Shift Reaction. 1. The Kinetics over Supported Metal Catalysts,xe2x80x9d J. Catal. 67 (1980) 90-102, powdered catalysts that contain Cu, Re, Co, Ru, Ni, Pt, Os, Au, Fe, Pd, Rh or Ir as active components and that are deposited on aluminum oxide (Al2O3) as a support material. The kinetic tests gave a reaction order of about 0.2 for carbon monoxide and about 0.5 for the water that was used.
In xe2x80x9cMethanization and Water Gas Shift Reactions over Pt/CeO2,xe2x80x9d J. Catal. 96 (1985), 285-287, Steinberg et al. observed poor selectivities in view of the carbon monoxide conversion according to reaction equation (1). Accordingly, the product gas mixture contains high proportions of methane.
In xe2x80x9cWater gas shift conversion using a feed with a low steam to carbon monoxide ratio and containing sulfur,xe2x80x9d Catal. Today 30 (1996) 107-118, J. Ross et al. investigate a Pt/ZrO2 catalyst, in addition to Fe/Cr, Cu/ZnO and Co/Cr catalysts. This catalyst shows a carbon monoxide conversion of 50% at 320xc2x0 C. The Pt/ZrO2 catalyst shows the highest tolerance for sulfur-containing compounds among the tested compounds. It shows a conversion of 25% at 300xc2x0 C. and a conversion of 70% at 350xc2x0 C. This corresponds to a specific carbon monoxide conversion rate RCO (300xc2x0 C.)=7.00xc3x9710xe2x88x926 mol/(gcatxc2x7sec), or RCO (350xc2x0 C.)=1.95xc3x9710xe2x88x925 mol/(gcatxc2x7sec).
FR 2567866 A describes a copper- and/or palladium-containing catalyst on a support of ZnAl2O4 spinel, which is obtained by impregnating the spinel formed into particles with diameters between 0.4 and 0.6 mm with solutions of copper and/or palladium and calcining it. A conversion of 86% is achieved with this catalyst at pressures of 40 bar and a temperature of 250xc2x0 C. at a very high excess of water (H2O/CO=10).
The powdered catalyst systems that have been investigated in the scientific literature are not suitable for industrial use.
The known complete catalysts in the form of tablets, pellets or irregularly shaped particles are used as so called bulk catalysts. Only unsatisfactory space-time yields are obtained with such catalysts. In addition, the achievable specific conversion rates with these catalysts are low.
Accordingly, an object of the present invention is to provide a method for conversion of carbon monoxide in a hydrogen-containing gas mixture that, under the conditions of mobile use in motor vehicles with their rapidly changing power requirements, a high specific conversion rate for carbon monoxide with good selectivity, has high temperature stability and is insensitive to oxygen in the educt gas mixture.
This above and other objects of the invention can be achieved by a method for catalytic conversion of carbon monoxide to carbon dioxide and hydrogen (carbon monoxide conversion) in a hydrogen-containing gas mixture. For conversion of the carbon monoxide, the gas mixture is passed over a shift catalyst, which is at the operating temperature for carbon monoxide conversion. The method features a shift catalyst based on noble metals that is applied to an inert carrier in the form of a coating.
The method of the present invention is specifically directed to mobile use in motor vehicles powered by fuel cells in order to effectively removed carbon monoxide from the hydrogen-rich gas mixture that is obtained by steam reforming, partial oxidation or autothermic reforming (hereinafter also called reformate gas) under all conditions of operation of the motor vehicle. The gas mixture can contain up to 40 vol % carbon monoxide, depending on its production.
The mobile use of the method imposes high requirements on its efficiency and dynamics. During the operation of the motor vehicle, the catalysts are loaded with very different space velocities. They vary between a low space velocity at idling and 100,000 hxe2x88x921 at full load.
The method of the invention enables a high efficiency, i.e., a high space-time yield through the application of the catalyst in the form of a coating onto an inert carrier. Such a catalyst is also called a coating catalyst herein. The monolithic honeycomb elements of ceramic or metal with cell densities (number of flow channels per area of cross section) of more than 10 cmxe2x88x922 that are known from auto exhaust treatment are suitable as carrier. However, metal sheet, heat exchanger plates, open-cell ceramic or metal foam elements and irregularly shaped elements formed in each case according to requirements can also be used as carriers. The thickness of the coating can vary between 10 and 100 xcexcm according to application.
A carrier within the scope of this invention is characterized as inert if the material of the carrier does not participate or participates only negligibly in the catalytic conversion. As a rule, these are bodies with low specific surface and low porosity.
A catalyst that contains the elements of the platinum group of metals, thus platinum, palladium, rhodium, iridium, ruthenium and osmium, or gold as the catalytic active components on an oxide support made from the group consisting of aluminum oxide, silicon dioxide, titanium oxide, rare earth oxides or mixed oxides of these or zeolites is suitable for the proposed method. In order to enable distribution of the catalytically active components on the support material that is as fine as possible, the support material should have at least a specific surface (BET surface, measured in accordance with DIN 66132) of more than 10 m2/g.
This noble metal catalyst exhibits a shift activity, i.e., it is capable, if the appropriate reaction conditions exist (temperature, gas composition), of converting carbon monoxide with water in accordance with reaction equation (1) to carbon dioxide and hydrogen. For this reason it is also called a noble metal shift catalyst herein. Its shift activity and selectivity can be improved by the addition of other catalytically active components, or promoters. Among these are elements of the rare earth metals, in particular cerium and lanthanum, as well as the non-noble metals of the subgroups of the periodic system of elements, especially iron or copper.
The shift activity and selectivity can, moreover, also be increased by doping the support material with redox-active oxides of the metals cerium, zirconium, titanium, vanadium, manganese and iron in an amount of 1 to 50 wt % with respect to the total weight of the support material.
A preferred shift catalyst for the method in accordance with the invention contains platinum and/or palladium together with iron or copper as well as cerium oxide on a finely divided aluminum oxide.
The use of the shift catalyst based on noble metals for the method also has the advantage that this catalyst does not become deactivated by contact with oxygen. For this reason no costly measures to protect the catalyst from contact with air are necessary in a motor vehicle.
The present invention will now be described in further detail.
In accordance with the invention, the described catalyst material is not processed to complete catalysts, but rather is applied in the form of a coating to inert supports. In this way the disadvantages of complete catalysts that consist of the catalytically active centers in the interior of the complete catalyst being poorly accessible to the reactants are avoided in this method. Poor accessibility reduces the specific conversion rate for carbon monoxide and thus the achievable space-time yield. This has the corresponding negative effects on the volume of the required reactor. The vibrations caused by operation of the motor vehicle additionally lead to undesired abrasion of complete catalysts, which blocks the flow paths in the catalyst bed and thus continuously increases the pressure difference in the reactor.
The process operates at gas mixture space velocities from idling space velocity up to a value of 100,000 hxe2x88x921 and at a pressure between atmospheric pressure and 10 bar, where the space velocity is given in reference to the volume of carrier coated with the catalyst. The method can be used both for low-temperature CO conversion as well as for high-temperature CO conversion.
A noble metal shift catalyst with an operating temperature between 180 and 300xc2x0 C. is used for the low-temperature CO conversion. The low operating temperature is achieved through a relatively high charge of catalytically active noble metals on the catalyst. In low-temperature CO conversion the reformate gas usually contains 2 to 15 vol % carbon monoxide and has an input temperature between 100 and 250xc2x0 C., which results from the reforming process.
A noble metal shift catalyst with an operating temperature between 280 and 550xc2x0 C. is used for the high temperature CO conversion. In the high temperature CO conversion the reformate gas usually contains 2 to 40 vol % carbon monoxide and has an input temperature between 300 and 600xc2x0 C., which results from the reforming process.
The method also allows a high temperature conversion stage and a low temperature conversion stage to be connected in succession. The gas mixture in this case leaves the high temperature stage at a temperature that corresponds to the operating temperature of the catalyst of the high temperature stage and for this reason has to be cooled to the operating temperature of the catalyst of the low-temperature stage before contact with it.
There are various possibilities for production of a coating catalyst suitable for the method, a few of which are discussed here.
To produce a shift catalyst on a carrier element in accordance with the invention, the support material for the catalytically active components can be suspended in an aqueous solution of soluble compounds of a noble metal selected from the group consisting of platinum, palladium, rhodium, ruthenium, iridium, osmium, gold and mixtures thereof and other soluble compounds of non-noble metals of the subgroups. Then the acid suspension is neutralized at elevated temperature with a base, for example, a sodium carbonate, and then reduced at the same temperature with an aqueous reducing agent (formaldehyde, hydrazine), filtered, washed, dried, calcined in an oxidizing atmosphere at temperatures between 300 and 550xc2x0 C., and then reduced at temperatures between 300 and 600xc2x0 C. The catalyst material is again suspended in water to produce a coating suspension. The carrier element is coated with this suspension. For this, the methods for coating carrier elements that are known from auto exhaust catalysis can be used. To finish the production of the coating catalyst the coating is dried, calcined at temperatures between 300 and 600xc2x0 C. and reduced in a hydrogen-containing gas at temperatures between 300 and 600xc2x0 C.
As an alternative to the described method, the carrier element is first coated only with the support material, where the support material can contain rare earth oxides and oxides of non-noble metals of the subgroups. The coating on the carrier element is then impregnated with a solution of at least one soluble noble metal compound, soluble compounds of the rare earths and the non-noble metals of the subgroups. To finish the production of the coating catalyst, the coated carrier element is dried, calcined at temperatures between 300 and 600xc2x0 C. and reduced in a hydrogen-containing gas at temperatures between 300 and 600xc2x0 C.
Another variation for making a coating catalyst in accordance with the invention resides in first producing a suspension of the support material, the soluble compounds of the noble metals and optionally the soluble compounds of the non-noble metals of the subgroups and the rare earths. The dissolved components of the suspension are then precipitated onto the suspended support material through the addition of a basic precipitation agent such as sodium hydroxide. The suspension prepared in this way is used directly for coating the carrier element. To finish the production of the coating catalyst, the coated carrier element is dried, calcined at temperatures between 300 and 600xc2x0 C. and reduced in a hydrogen-containing gas at temperatures between 300 and 600xc2x0 C.

Method for catalytic conversion of carbon monoxide in a hydrogen-containing gas mixture


The invention discloses an apparatus for treating fabrics which comprises a first chamber for forming a reserve of infeed fabric, a second chamber for forming a reserve of outfeed fabric, first means for slowly infeeding the fabric into the first chamber, second means for slowly removing the fabric from the second chamber, a duct allowing for the passage therethrough of the fabric between the first chamber and the second chamber, fabric transport means capable of forward and backward operation which generates a forward and backward movement of the fabric between both chambers, and control means, operation of which causes inversion of the forward and backward movement, and collision members adapted to be impacted by the fabric, which move between a collision position and a free passage position in synchronism with the forward and backward movement of the fabric.

The invention relates to an apparatus for treating fabrics, of the type comprising a first chamber for forming a reserve of infeed fabric, a second chamber for forming a reserve of outfeed fabric, first means for slowly infeeding the fabric into the first chamber, second means for slowly removing the fabric from the second chamber, a duct allowing for the passage therethrough of the fabric between the first chamber and the second chamber, fabric transport means capable of forward and backward operation including nozzles and which is adapted to generate a forward and backward movement of the fabric between the first chamber and the second chamber, and control means, operation of which causes inversion of the forward and backward movement.
Such apparatus are already known. For example, EP-0 653 508 discloses an apparatus for the wet treatment of fabrics having two chambers, slow fabric infeed and delivery means and transport means which move the fabric accumulated in the chambers forward and backward from one of the chambers to the other, thereby allowing the fabric to be more rapidly and effectively treated, and without deterioration thereof due to friction. Such treatments may form a very wide range and there may even be diverse groups of modules each formed by a pair of chambers, such that various treatments may be carried out in series. Similar apparatus are also known for the dry treatment of fabrics.
It is frequently of interest that the fabric be subjected to blows during the treatment, so that it may acquire enhanced softness and handle qualities. Apparatus of the type first mentioned above are known which include a striking device. Thus, for example, EP-0 787 963 discloses an apparatus for the dry treatment of fabrics in which there is to be observed, apart from the two chambers, the fabric infeed and delivery means and the fabric transport means, a striking device comprising a rotor with which the fabric collides during the forward and backward movement thereof.
Nevertheless, these apparatus have drawbacks when it is necessary to work at high speeds, i.e., with very high transport fluid flows and/or fabrics of low specific weight. In these cases, the striking device is less effective, and may even in certain cases cause the fabric to wind around the striking device. It is likewise desirable to intensify the striking effect to increase the performance of the apparatus and allow the treatment times to be shortened.
It is an object of the invention to overcome these drawbacks. This objective is achieved by a fabric treatment apparatus of the type first mentioned above, characterized in that it is provided with at least one collision member adapted to be impacted upon by the fabric, the collision members defining collision surfaces, in that the collision members are adapted to move between a collision position and a free passage position, and in that the movement between the collision position and the free passage position takes place synchronized with the forward and backward movement of the fabric.
In fact, the collision members allow the fabric to undergo a plurality of collisions in each of the directions of forward and backward movement. Furthermore, since the collision members may move between the collision position and the free passage position, the apparatus may be designed in such a way that said collision members are in the collision position when the fabric is moving in one of the directions of the forward and backward movement, while the collision members move to the free passage position when the fabric changes direction, whereby they do not hinder or interfere in the passage of the fabric. This allows the geometry and the position of the collision members to be designed with greater liberty, such that the effect of the blows is optimized.
The apparatus is preferably provided with at least two collision member groups, in such a way that in each direction of the forward and backward movement, at least one of the collision member groups is in the collision position. In this way, the fabric is subjected to the effect of blows in each direction of forward and backward movement, whereby the speed of treatment is doubled relative to the case wherein there are only provided collision members which move into the collision position in one direction of the forward and backward movement.
It is particularly advantageous that the collision members be permeable, or at least partly permeable, to the transport fluid, since, otherwise, the transport fluid is excessively diverted from its original path, causing additional turbulence which makes the transport capacity of the transport fluid less effective and entrains the fabric with it, whereby the effectiveness of the collision of the fabric on the collision members is lowered.
The collision members are preferably formed by substantially rectangular flaps, having at one side a shaft about which they may pivot, so as to pass from the collision position to the free passage position and vice versa. The flap thus forms a wall which is interposed in the path that the fabric would follow in the absence of the collision members, whereby the fabric will collide against the surface of the wall facing the direction of movement of the fabric and which forms the collision surface. There are various ways in which these walls may be formed. They may, for example, be formed by a number of preferably co-planar rods and/or tubes having one end attached to the shaft and the opposite end free. The free ends may optionally be joined together with another rod. Said wall may also be formed by a, for example, metal sheet which may optionally be provided with orifices, allowing for an enhancement of the passage of the transport fluid. The collision surface is generally flat. Nevertheless, it is preferable that in certain cases, said collision surface should not be flat, but should be concave or convex in the direction of incidence of the fabric. An apparatus for the treatment of fabrics according to the invention may have all the collision members identical, or may mount a plurality of mutually different collision members. Furthermore, it is also advantageous for the collision position of the collision members to be adjustable, and it is particularly advantageous that such adjustment may be carried out individually. This adjustment may be desirable both at the start of a treatment, depending on the treatment to be performed and the fabric to be treated, and during the treatment itself.
These collision members are preferably arranged along a duct connecting both chambers. It has been found that it is advantageous to have two additional, also adjustable, collision members, one at each end of the duct connecting both chambers. These additional collision members, apart from the collision function, also have the function of enhancing the piling of the fabric in the corresponding chamber. It is not necessary for these additional collision members to be subjected to movement between the collision position and the free passage position undergone by the remaining collision members, since they are practically outside the path of the fabric, when the latter travels in the opposite direction to the collision direction against the additional collision member, whereby the fabric does not touch the additional collision member and, therefore, it is not necessary for the additional collision member to move to a free passage position, as the remaining collision members do.
The transport means are usually housed at an intermediate point, usually in the mid-point, of the duct connecting both chambers. In certain cases, for example when the duct has an inverted U shape, the transport means are divided into two transport units, each responsible for one direction of movement and between both transport groups, there is a portion of the duct curved in 180 degrees. The fabric, in its forward or backward movement from one chamber to the other, defines a direction of feed or direction of movement, which is also forward or backward. The collision means is preferably arranged on both sides of the transport means, and preferably only those collision members which are downstream of the transport means in the direction of feed of the fabric are in the collision position.
These apparatus are adapted for both dry and wet treatment of fabrics. Likewise, although they are preferably adapted for the treatment of open width fabrics, it is also possible to use apparatus according to the invention for the treatment of fabrics in rope form.
The second means is usually situated in the upper part of the apparatus, approximately above the second chamber. The second means thus removes the fabric from the top of the apparatus, thereby causing the formation of a web of fabric from the bottom of the chamber, where the fabric is alternately accumulated, due to the forward and backward movement, to the top of the apparatus, where it exits the apparatus through the second removal means. In certain cases, the weight of the fabric web may affect the fabric, stretching it for example in the longitudinal direction of the web and contracting it in the transverse direction perpendicular to the web. To avoid these drawbacks, it is preferable to provide the apparatus with removal means having sloping conveyor belts which run from a low point, situated close to the bottom of the second chamber, to a high point and entrain the web of fabric which is resting on the conveyor belt. In this way, the fabric is moved to the top, without being subjected to tensile stress.
The collision members may be driven in different ways. They may, for example, be driven by hydraulic rams. All the collision members may preferably be operated by a single hydraulic ram and a number of levers which transmit the movement to all the collision members. Other drive systems are also possible, such as for example gear trains which may be directly meshed together or which may be associated together with transmission chains. A preferred solution contemplates the possibility of the collision members having individualized drive mechanisms.