KR20050074951A - Improved silver plating method and articles made therefrom - Google Patents

Abstract

An improved method for plating an organic substrate with silver is disclosed. Improved plating is achieved in part through the use of Na4EDTA, which facilitates improved grain formation and recovery of silver from waste material. Articles prepared using the method of the invention are also disclosed.

Description

Improved silver plating method and articles made therefrom

The present invention relates to an improved electroless silver plating method, and more particularly to a silver plating method suitable for the production of articles having antibacterial and anti-static properties.

Metallization of organic substrates (eg polymeric foams) with silver and other inert metals is well known. One such technique is described in US Pat. No. 3,877,965. The patent describes the metallization of nylon substrates with silver, which patents are incorporated herein by reference. Silver metallized materials are widely used because of the inherent antibacterial and antistatic properties of silver. For example, silver-plated nylon fibers are generally made of textile materials, and are subject to electrostatic interference (EMI) of consumer goods (e.g. socks, trauma bandages) and electrical appliances (e.g. mobile phones, computers). Used as a prevention member.

However, current processes for metallizing substrates with silver have certain disadvantages. For example, the process described in patent number 3,877,965 is known to exhibit several disadvantages. First, in most metallization processes, tin salts (e.g. stannous chloride or stannous chloride) are added by the addition of water-soluble alcohols (e.g. C1-C4 alcohols) in the pre-metalization process. It is necessary to dissolve. The use of alcohol leads to serious evaporation problems.

A more serious problem is the use of surfactants (eg sodium lauryl sulfate) during the metallization process. For example, surfactants can result in gelation of the plating bath if the temperature of the bath is too low. As such, the surfactant may generate severe bubbles in the plating bath. And it is difficult to remove after the metallization is over. Generally, bubbles made during the metallization process will appear on the surface of the fibers. Once on the fiber surface, the bubbles are not easy to wash off. This potentially leads to the inhibition of silver ion release and, when exposed to high temperatures, also presents adhesion problems due to surface cracks. Cracks occur when contaminants (eg entrained air) are released under pressure from just below the surface of the silver layer.

Moreover, the use of surfactants results in a very dark grey / silver color of the deposited silver. Consumers generally expect metallized silver to have a bright metallic color, so this different color of deposited silver reduces the aesthetic value of the product.

However, one of the most serious problems associated with the use of surfactants is the impact on the environment, and the associated costs of removing surfactants from the effluents emitted. Local sewage authorities, namely the Environmental Protection Agency (EPA) and other similar agencies, now require very low "methylene blue active substances" (ie MBAS) discharge levels. Surfactants, such as sodium lauryl sulfate, fall within the scope of MBAS. Great efforts and costs are required for waste disposal to reduce MBAS to within standard limits (typically 5 ppm or lower). This increases production costs and time. In general, the removal of MBAS requires the use of activated charcoal reactions in conjunction with highly adsorptive (activated char) filters, which must be replaced frequently because the filter is clogged with particles. The amount of silver recovered from the waste is problematic because the silver recovered in this way is at a low rate relative to the amount of sludge (eg, about 1% by weight).

Because of the problems associated with surfactants, other metallization processes have been developed that use non-surfactant baths. Generally this process uses disodicone ethylenediaminetetraacetic acid (EDTA) as ligand in place of surfactant. Representative patents relating to the use of disodium EDTA in silver plating are US Pat. Nos. 5,318,621 and 5,322,553, owned by Applied Electroless Concepts. Another example is US Pat. No. 5,158,604, owned by Monsanto Company. However, this technique is not without problems because it must be used to melt a large amount of caustic soda to adjust the pH of the plating bath.

Summary of the Invention

The present invention provides an improved method of plating an organic substrate with silver that overcomes many of the disadvantages associated with conventional silver plating methods. The method of the present invention comprises the following steps: (1) scouring; (2) pre-metalization step; And (3) at least three steps followed by a plating step. The organic substrate to be plated may be fibers, textiles woven from fibers, or polymeric foams (eg open cell foams). According to the invention the organic substrate is first refined to prepare the surface for premetalization. Preferably an aqueous washing solution is used.

Once the organic substrate is sufficiently washed, the purified organic substrate is contacted with an aqueous premetallization solution comprising tin salts and inorganic salts. In an embodiment, the premetalization solution omits a water soluble or water miscible solvent. In another embodiment, the premetalization solution omits the surfactant. Tin salts used include stannous chloride, stannous chloride and mixtures thereof. Inorganic salts used include hydrochloric acid, sulfuric acid and mixtures thereof.

The premetalized organic substrate is then plated with silver. This process comprises the steps of: 1) contacting the premetalized organic substrate with a water soluble Na ₄ EDTA solution; 2) then contacting the premetalized organic substrate with an additional aqueous silver salt solution, further comprising a complexing agent, to form a silver oxide deposition onto the organic substrate; And 3) contacting the organic substrate having silver oxide deposited thereon with a reducing agent to form metal silver on the organic substrate. Particularly preferred silver salts and complexing agents are silver nitrate and water soluble ammonia, respectively. Preferred types of reducing agents are reducing agents comprising aldehyde functional groups. Representative examples of reducing agents are formaldehyde, rochelle salt (sodium potassium tartrate), hydrazine, dextrose, triethanol amine, glyoxal, Inverted sugar, glucose, sodium borohydride, dimethyl aminoborane, hydrazine borane and mixtures thereof. In another embodiment all solutions in the plating process preferably omit the surfactant.

The present invention also provides a molded article produced according to the method of the present invention. In an embodiment the organic substrate comprises at least one non-noble metal deposition layer, and is preferably deposited on the plated metallic silver layer. Particularly preferred non-noble metals are copper. According to the present invention, the metallic silver layer is included in the molded article at least 5% by weight, preferably at least 10% by weight.

Advantageously, the process of the present invention allows omitting the use of surfactants while increasing the recovery of silver in the waste material. Therefore, compared to the preceding process, environmental problems can be alleviated through the use of the present invention.

1 is a 960 times magnified electron micrograph of a nylon fiber plated with silver using the method of the present invention.

FIG. 2 is a 5000 times magnified electron micrograph of a nylon fiber plated with silver using a conventional method.

The present invention provides an improved method of applying an organic substrate with metallic silver that overcomes many of the problems of the prior art. The present invention first involves refining an organic substrate to prepare a substrate for premetalization. When the organic material is sufficiently refined, the organic substrate is brought into contact with a water-soluble, premetallized solution containing tin salt and inorganic acid. Thereafter, the pre-metalized organic substrate is contacted with a water-soluble Na ₄ EDTA solution, which in turn is applied by contacting the pre-metalized organic substrate with a water-soluble silver salt solution that effectively deposits silver oxide on the organic substrate. The silver salt solution further includes a known complexing agent. The deposited silver oxide is converted (ie, reduced) to metallic silver by contacting the organic substrate with a reducing agent to promote the formation of metallic silver.

According to the present invention, the organic substrate metallized with silver includes all organic materials capable of containing the deposited metal layer. The organic material is preferably a synthetic (eg, by polymerization) material, but may be synthetic or natural. What can be used as synthetic polymeric materials includes, but is not limited to, nylon, polyester, acrylic, rayon and polyurethane. What may be included as a natural substance includes, but is not limited to, cellulose and silk. The organic material may include any material capable of containing a deposited metallic layer. For example, the organic material may be filaments, nonwovens, staples, chopped fibers, micronized fibers, foams, particulates, and fillers. materials). Preferably, the organic material may be in the form of fibers or filaments or a textile matrix made from them. If the organic material is in foam form, it is preferred to use open-cell foam (ie, having a network of three-dimensionally interconnected pores) during metallization.

The organic substrate is first prepared for preliminary metallization by a process of separating debris and / or separating the coating or film from materials that may interfere during metallization. The refining process is a technique known in the art that no further discussion is needed. In general, the organic material is washed with an aqueous cleaning solution with or without a surfactant (eg, a nonionic surfactant). In the present invention, "water-soluble" means that a plurality of mediums are water and the remainder are water-soluble or water miscible organic solvents. The organic material can be polished using a scouring brush or equivalent device. In a preferred embodiment, the refining process is carried out by a high-speed water spray that facilitates in-line processing and does not require a refining brush.

When the organic substrate is sufficiently refined, the material is subjected to premetallization with an aqueous solution of tin salt and inorganic acid. As will be apparent to those skilled in the art, such solutions are often referred to as "sensitizing" solutions. However, unlike known "sensitizing" solutions, the premetalization solution may preferably contain no water soluble or water miscible organic solvents such as surfactants and / or C ₁ -C ₄ alcohols. Preferably the tin salt is a tin halide such as stannous chloride, stannic chloride and mixtures thereof. Inorganic acids may include, but are not limited to, hydrochloric acid, sulfuric acid, and mixtures thereof. In the most preferred embodiment the tin salt is stannous chloride and the inorganic acid is hydrochloric acid. The content range of the two compounds is shown in Table 1 below.

Tin salt (grams / liter) Inorganic acid (volume /%) Desirable range 1-30 1-20 More desirable range 2-25 3-18 Optimal range 4-20 6-15

When the organic substrate has been premetalized, the organic substrate is preferably washed to remove excess salts and acids from the organic material which may interfere with the continuous metallization. For example, the organic substrate can be washed with a counter flow rinse with controlled water flow. This removes excess salts and acids from the substrate and leaves the optimum amount at the active site on the surface of the substrate. The preferred range of water streams capable of cleaning the substrate is from about 25 to about 55 gallons per minute (gpm), more preferably from 30 to 50 gpm, even more preferably from 35 to 35 gpm.

In the present invention, the metallization process is carried out in three steps. Water soluble tetrasodicetene ethylenediaminetetraacetic acid (Na ₄ EDTA) can be prepared by immersing the premetalized organic substrate in an aqueous solution and preferably contacting it. The aqueous solution is preferably prepared using deionized water (DI water) to prevent possible contamination. The DI number has a resistance value of about 0.4 to 20 megaohms, preferably 0.8 to 10 megohms, more preferably 3 to 7 megohms. The concentration of the water soluble Na ₄ EDTA solution should be about 5 to 30% by weight (wt.%), Preferably 10 to 25% by weight, more preferably 10 to 20% by weight. It is preferable that the Na ₄ EDTA solution omit the surfactant generally used in the conventional silver plating process. In addition, the Na ₄ EDTA solution is preferably omitted the caustic soda (caustic soda) generally used in Na ₄ EDTA solution. The use of Na ₄ EDTA has the advantage of facilitating the deposition of metallic silver with a tighter grain structure, and a relatively softer surface, as evidenced by the electron microscopy of silver-plated nylon fibers. There is an advantage to that. Na ₄ EDTA can also alleviate environmental problems, depending on the level of surfactant in the effluent, by eliminating the use of surfactants.

A water soluble silver salt solution is also prepared in sufficient contact with the organic substrate. Preferably the organic substrate is contacted with the silver salt solution by adding the silver salt solution directly to a bath comprising the organic substrate and the water soluble Na ₄ EDTA solution. Therefore, the organic substrate is immersed in both solutions simultaneously and the solution is called a “metallization bath.” Alternatively, the organic substrate can be transferred from a Na ₄ EDTA solution and then immersed in a silver salt solution. Particularly preferred silver The salt is silver nitrate, ie AgNO _{3 The} silver salt solution further comprises a known complexing agent, which complexes in situ with the dissolved silver salt. The agent is a water soluble ammonia or aqueous ammonia (ie NH ₄ OH) commonly used as a complexing agent for silver nitrate When combined with Na ₄ EDTA, the silver salt solution preferably omits the surfactant.

The silver salt solution is preferably prepared by first dissolving the silver salt in water. Once the silver salt is dissolved, the complexing agent is added to the solution. A precipitate of silver oxide can form, which is dissolved again by adding excess complexing agent. It is believed that the addition of excess complexing agent will form a complex of silver salt and complexing agent. For example, if silver nitrate and ammonia water are used, a precipitate of silver oxide, which melts again by addition of excess ammonia water, forms in situ to provide a metallization bath having a bright amber color. The preferred initial weight / volume ratio of the silver salt (ie AgX) to water (H 2 O) and the volume percent ratio of the complexing agent are listed in Table 2. Preferred molar ratios of silver salts to the complexing agent in the final metallization bath (ie, for redissolution of silver precipitates) are listed in Table 3.

AgX: H2O (Weight: Volume) Complexing agent (volume percent) Desirable value 0.25: 2 to 1.75: 2 17 to 38 More desirable value 0.5: 2 to 1.5: 2 20 to 35 Optimal value 0.75: 2 to 1.25: 2 25 to 31

Complexing agent: molar ratio of AgX Desirable value 2.5: 1 to 5.5: 1 More desirable value 3: 1 to 5: 1 Optimal value 3.5: 1 to 4.5: 1

According to the present invention, immersion of the organic substrate in the metallization vessel deposits silver oxide on the substrate surface. As will be apparent to those skilled in the art, deposition can be confirmed by visual diagnosis of the substrate undergoing a change in color due to the deposited silver oxide. For example, in the case of AgNO ₃ : NH ₃ , it can be observed that the surface generally corresponding to the silver oxide layer is colored brown. Preferably, the reducing agent is added for about 30 seconds more preferably 20 seconds before the organic substrate is immersed in the metallization vessel. The temperature of the metallization vessel is not critical but may range from about 15 to 45 ° C., more preferably 20 to 30 ° C. Such variables can be readily determined by one skilled in the art.

An organic substrate on which silver oxide is deposited is contacted with a reducing agent to convert silver oxide to metal silver. Preferably the contacting is carried out by adding a reducing agent directly to the metallization vessel. Optionally, the organic substrate is removed from the metallization vessel and brought into contact with the reducing agent aqueous solution independently (eg immersion). Reducing agents used in the present invention may be those known in the art. Examples of reducing agents include, but are not limited to, formaldehyde, rochelle salts (sodium titanate), hydrazine, dextrose, triethanol amine, glyoxal, invert sugar, glucose, sodium borohydride, dimethyl amineborane, hydrazine Boran is included. More preferably, the reducing agent comprises an aldehyde functional group, such as formaldehyde. When AgNO ₃ : NH ₃ is used, the addition of a reducing agent (e.g. formaldehyde) converts the silver oxide to metal silver so that the color of the silver oxide layer on the surface of the substrate changes to bright gold or grayish gold. Preferably, the amount of reducing agent is about 5-40%, more preferably 6-25%, most preferably 8-22% of the substrate weight.

When the metal is sufficiently converted to, the organic substrate is taken out of the metallization vessel and washed. Preferably, the silver plated substrate is immersed in hot water. The silvered substrate is then immersed, preferably in a weak sodium hydroxide solution, so that the plated silver becomes light gold or light gray gold. This represents a pure layer of silver deposited on the surface. Multiple cleaning cycles may be performed on the molded article for cleanliness of the product.

As will be apparent to those skilled in the art, the amount of metal silver deposited on the organic substrate is related to the immersion time. According to the invention, the time for complete deposition of the metal silver layer can be up to 4 hours. On the other hand, the immersion time of the substrate in the various solutions can be easily changed according to the amount of the target silver deposition. The amount of silver deposited on the organic substrate depends on the specific properties of the desired end product, but may be 0.1% to 15% by weight. Preferably, the deposited silver layer is at least 5%, more preferably at least 10% by weight. The actual amount of silver deposited on the substrate is easily calculated by simple titration methods such as the Vollard process.

Unlike prior art US Pat. No. 3,877,965, the metallization vessel is treated as a case. The pH of the metallization vessel rises to about 13 as a result of the conversion of dissolved silver into colloidal form. The pH is then generally reduced by about 2 due to the inorganic acid (eg sulfuric acid). Colloidal silver settles or sinks to the bottom of the container after several hours. The purity of precipitated silver is at least 50% by weight.

As will be apparent to those skilled in the art, the adhesion of plated silver is readily ascertained. One simple method for testing the adhesion of silver to a substrate involves leaving the sample in an oven at 200 ° C. for 5 minutes and then boiling in water for 1 hour. The resistance of the sample is compared before and after heating and boiling. A change in durability of about 20% or less means excellent adhesion. In a more preferred embodiment, the change in durability was less than 10%.

In another embodiment of the present invention, the silvered substrate may be further plated with a non-noble metal, such as copper, as disclosed in US Pat. No. 3,877,965. Copper is auto-catalyzed over the silver layer and can easily be reduced by itself to form the copper layer. Using this procedure, at least 30% by weight of copper is deposited on the silver plated substrate. Commercial plating solutions can be purchased from Atotech USA, Enthone OMI and MacDermid Corporation.

The following non-limiting examples illustrate the use of the method of the present invention to plate an organic substrate with a metal silver layer.

Example 1

25 g of nylon 30/10 knit sample was refined to remove contaminants. The knit sample was wound to a scale and then refined in counter flow deionized water. The sample was premetalized for about 2 minutes with a solution containing 1% by volume of HCL and 10 g of anhydrous tin chloride (SnCl ₂ ). A silver salt solution was prepared by dissolving 0.04 g of silver nitrate (0.1 wt% silver) in deionized water. The silver salt was mixed with 0.045 mL of 27% by volume aqueous ammonia. A tetrasodium EDTA solution was prepared by dissolving 0.002 g of Na ₄ EDTA in 1 L of deionized water. The scine was rotated in a reactor containing Na ₄ EDTA solution. A silver salt solution (ie a mixture of silver nitrate and ammonia) was slowly added to the reactor until all contents were empty. Then 0.016 mL formaldehyde was added. After 3 hours the sample was taken and washed with hot water. A 0.1 volume% NaOH solution at 70 ° C. was prepared. Metallized strain was immersed in the solution and washed thoroughly. Dow Corning Experiment 0909 was performed on the sample. Microorganisms- Staphylococcus aureus ATCC 7538; Sample size-0.75 g; Results-Colony Reduction Percentage> 99.9%.

Example 2

As in Example 1, 25 g of nylon 30/10 knit sample was refined to remove contaminants. The knit sample was wound to a scale and then refined in countercurrent deionized water. The sample was premetalized for 2 minutes with a solution containing 1% by volume of HCL and anhydrous tin chloride (SnCl ₂ ). Silver salt solution was prepared by dissolving 1.95 g of silver nitrate (5 wt% silver) in deionized water. The silver salt was mixed with 2.25 ml of 27% by volume aqueous ammonia. Tetrasodium EDTA solution was prepared by dissolving 0.1 g of Na ₄ EDTA in 1 L of deionized water. Skene was placed in a reactor containing Na ₄ EDTA solution and rotated. The silver salt solution (ie, a mixture of silver nitrate and ammonia) was added and treated with 0.8 mL of formaldehyde. After 3 hours a sample was taken and washed with hot water. The metallized strain was washed with NaOH solution as in Example 1. Dow Corning Experimental Method 0923 was then performed on the sample: microorganism-Staphylococcus aureus ATCC 7538; Sample size-0.75 g; Result-Colony Reduction Percentage> 99.9%

Example 3

25 grams of samples of ripstop fabric were processed by the methods of Examples 1 and 2. The silver-plated sample was then applied to Dow Corning Corporate Test Method 0923: Organism-Staphylocococcus aureaus ATCC 7538 ; Sample size-0.75 grams; Results-percent reduction in colony> 99.9%.

Example 4

25 grams of a sample of filter material comprising nano powders (eg powders made from nylon and polyethylene) were processed by the methods of Examples 1 and 2. The silver plated sample was then subjected to Dough Corning Corporative Test Method 0923: organismism-Staphylocococcus aureaus ATCC 7538; Sample size-0.75 grams; Results-percent reduction in colony> 99.9%.

Example 5

Contaminants were removed by refining a 30/10 knit sample of 118 grams of nylon. The knit sample was wound into a skein and then refined in counter flow deionized water. The sample was premetalized for 2 minutes with a solution containing 10% by volume HCL and 100 grams of anhydrous tin chloride (SnCl ₂ ). The silver salt solution was prepared by dissolving 45 grams of silver nitrate (about 22 weight percent silver target) in deionized water. The silver salt was then mixed with 52 mL of 27% by volume aqueous ammonia solution. Tetrasodium EDTA was prepared by dissolving 2.2 grams of Na ₄ EDTA in 6 liters of deionized water. The scine was placed in a reactor containing the Na ₄ EDTA solution to dissolve. Silver salt solutions (eg mixed silver nitrate and ammonia) were slowly added to the reactor until all contents were empty. Then 18 mL of formaldehyde was added. After 3 hours the samples were removed and washed with warm water. 0.1 volume% NaOH solution (5 liters) was prepared at a temperature of 70 ° C. Metallized strain was dipped into the solution and then thoroughly washed. The color turned bright and almost golden silver. After the sample was dried, an adhesion test was performed. The results are as follows: as is-484 Ohms (50 cm distance) using Keithley 580 micro-ohmmeter; After heating-345 Ohms; After boiling-365 Ohms.

Example 6

In Example 5 a sample obtained from silver-lated materials was cut to make a 1.5 gram sleeve. The sleeve was placed in a beaker with 5% by volume sodium chloride solution for 24 hours. After 24 hours the solution was subjected to silver ion testing with Perkin Elmer Analyst 300. Sample tests were repeated for at least 7 days. Ion release was consistent at 0.5 ppm every day, which accounts for the consistent release of silver produced according to the present invention.

Example 7

Samples obtained from the silver plated materials of Example 5 were cut to a weight of 0.75 grams and subjected to Dough Corning Corporate Test Method 0923. The microorganism used was Staphylococcus aureus ATCC 6538. The sample reduced the growth of microorganisms by at least 99.9%.

Example 8

210/34 knitted nylon samples weighing 118 grams were washed. The sample was wound to a scale and then refined with countercurrent of deionized water. The scane was premetalized for 2 minutes in a solution of 10 vol% HCL and 100 grams of anhydrous tin chloride (SnCl ₂ ). The silver salt solution was prepared by dissolving 45 grams of silver nitrate in deionized water. The silver salt was then mixed in 52 mL of a 27% aqueous ammonia solution. Tetrasodium EDTA solution was prepared by dissolving 2.2 grams of Na ₄ EDTA in 6 liters of deionized water. The scine was placed in a reactor containing the Na ₄ EDTA solution to dissolve. Silver salt complexes were added to the reactor followed by 18 mL of formaldehyde. After 3 hours the samples were removed and washed with warm water. As in the previous example, 0.1 volume% NaOH solution was prepared and the metallized scale was dipped into the solution. The color changed from gray to bright, almost golden silver.

The silver plated sample was then metallized with copper chemistry, which is commercially available from Atotech USA. The metallization process was performed according to the instructions given by the supplier. Completion of copper deposition can be determined visually when the color of the bath changes from dark blue to colorless, indicating complete reduction of the metal.

A 10.6 gram sample of silver-copper material was then cut and placed in a beaker filled with 2.1 grams of Rochelle salt (eg, sodium potassium tartrate) dissolved in deionized water. A silver salt complex made of 3.6 grams of silver nitrate and 4.3 mL of an aqueous ammonia solution were poured into the sample under constant stirring. At this time, the silver-salt pink turned light brown. A few more drops of diluted aqueous ammonia solution were added to the bath using an ink dropper under constant stirring. The color of the sample began to turn pale white and eventually turned bright white. This step took about 35 minutes to complete. At this time the sample was removed from the bath and washed thoroughly with deionized water for 15 minutes. Silver was calculated to give 15% of the gain. In addition, the resistance of the material after the deposition of each metal layer was recorded; Silver resistance-80 Ohms / 50 cm using Keithley 580 micro-ohmmeter; Silver-copper resistance-25 Ohms / 50 cm; And silver-copper-silver resistance—18 Ohms / 50 cm.

Example 9

Samples of the silver-copper-silver material obtained in Example 8 were cut into 1.5 gram sleeves. The sleeve was then placed in a beaker with 5% by volume sodium chloride solution for 24 hours. After 24 hours the solution was tested for silver and copper ions with Perkin Elmer Analyst 300. Sample tests were repeated for at least 7 days. Ion release coincided daily at 2 ppm for silver and 3 ppm for copper.

Example 10

The sample of silver-copper-silver material obtained in Example 8 was cut to a weight of 0.75 grams and subjected to Dough Corning Corporate Test Method 0923. The microorganism used was Staphylococcus aureus ATCC 6538. The material caused a reduction in microbial growth of at least 99.9%.

Example 11

11.8 g of quench foam samples were washed with a nonionic surfactant Triton X-100 and thoroughly washed. 83% by weight of sulfuric acid solution was prepared, and the foam was immersed in this solution for 25 to 45 seconds to give an appropriate etching on the surface. Immediately afterwards the samples were washed with excess deionized water. The foam was premetalized for 2 minutes with a solution containing 12% by volume of HCl and 120g of anhydrous tin chloride (SnCl ₂ ). The foam samples were then washed with counter flow deionized water. 0.22 g of Na ₄ EDTA was dissolved in 2 liters of deionized water to prepare a tetrasodium EDTA solution. The premetalized foam is prepared to be placed and circulated in the reactor containing the Na ₄ EDTA solution. A silver salt solution was prepared by dissolving 4.5 g of silver nitrate in deionized water. The silver salt solution was then mixed with 5.2 mL of 27 volume% ammonia water. The mixed silver salt was added to the reactor, and 18 mL of formaldehyde was added to the reactor. After 3 hours the samples were removed and washed with warm water. The metallized foam was immersed in the NaOH solution prepared in the above example. The color turned to pale white silver. After drying the sample, the resistance was measured. Silver-plated foams exhibited 0.5 Ohm / 50 cm resistivity using a Keithley 580 microohm meter.

Example 12

Silver plated fiber samples prepared according to the present invention were compared to silver plated fiber prepared by the method according to US Pat. No. 3,877,965. Two fibrin samples were examined by scanning electron microscopy. A micrograph of the fiber of the invention is shown in FIG. 1, while a micrograph of the comparative fiber is shown in FIG. 2. As can be clearly seen in the micrographs, the fiber plated by the method of the present invention exhibits a smoother surface compared to the fiber produced by the method of the prior art. This result is believed to be due to the denser grain structure of the temperature gold provided by the method of the present invention.

Claims (19)

(a) refining the organic substrate to prepare a surface for premetalization; (b) contacting the refined organic substrate with a water soluble premetallization solution comprising tin salt and inorganic acid; And (c) (i) contacting the premetalized organic substrate with a water soluble Na ₄ EDTA solution; (ii) then contacting the premetalized organic substrate with an additional aqueous silver salt solution, further comprising a complexing agent, to form a silver oxide deposition onto the organic substrate; And (iii) plating the premetalized organic substrate with silver comprising contacting the organic substrate having silver oxide deposited thereon with a reducing agent to form metal silver on the organic substrate. Improved plating method of an organic substrate, including. The method of claim 1 wherein the organic substrate is in the form of a fiber. 3. The method of claim 2 wherein the fiber is woven into a textile. The method of claim 1 wherein the organic substrate is in the form of a polymeric foam. 5. The method of claim 4 wherein said polymeric foam is a continuous pore foam. The method of claim 1, wherein the refining step comprises the step of washing the organic substrate with an aqueous cleaning solution. The method of claim 1, wherein the tin salt is tin halide selected from the group consisting of stannous chloride, stannic chloride, and mixtures thereof. The method of claim 1 wherein the inorganic acid is selected from the group consisting of hydrochloric acid, sulfuric acid and mixtures thereof. The method according to claim 1, wherein the silver salt is silver nitrate and the complexing agent is water-soluble ammonia. The method of claim 1 wherein the reducing agent comprises an aldehyde functional group. 2. The reducing agent according to claim 1, wherein the reducing agent is formaldehyde, rochelle salt (sodium titanate), hydrazine, dextrose, triethanol amine, glyoxal, invert sugar, glucose, sodium borohydride, dimethyl amineborane, hydrazine borane (hydrazine borane) and mixtures thereof. The method of claim 1 wherein the premetalization solution does not comprise a water soluble or water miscible solvent. The method of claim 1, wherein the premetallization solution, Na ₄ EDTA solution, and silver salt solution do not contain a surfactant. (a) refining the organic substrate to prepare a surface for premetalization; (b) contacting the refined organic substrate with a water soluble premetallization solution comprising tin salt and inorganic acid; And (c) (i) contacting the premetalized organic substrate with a water soluble Na ₄ EDTA solution; (ii) then contacting the premetalized organic substrate with an additional aqueous silver salt solution, further comprising a complexing agent, to form a silver oxide deposition onto the organic substrate; And (iii) a molded article having a metal salt layer prepared by a method comprising plating a pre-metalized organic substrate with silver, the method comprising contacting the organic substrate having silver oxide deposited thereon with a reducing agent to form metal silver on the organic substrate. . 15. The molded article of claim 14, wherein said organic substrate further comprises at least one non-noble metal deposition layer. The molded article of claim 15, wherein the non-noble metal is copper. 15. The molded article of claim 14, wherein the non-noble metal is deposited on a metal silver layer. 15. The molded article of claim 14, wherein said metal silver layer comprises at least 5% by weight. 15. The molded article of claim 14, wherein said metal silver layer comprises at least 10 weight percent.