DK180529B1

DK180529B1 - A method for electroplating antimicrobial coatings consisting of copper-silver alloys for highly and frequently bacterial contaminated surfaces in healthcare settings and food industry.

Info

Publication number: DK180529B1
Application number: DKPA201900223A
Authority: DK
Inventors: Rasmussen Jan; Ciacotich Nicole; Møller Per; Gram Lone
Original assignee: Univ Danmarks Tekniske; Elplatek As Af 1995
Priority date: 2019-02-20
Filing date: 2019-02-20
Publication date: 2021-06-10
Also published as: DK201900223A1

Abstract

A method for electroplating antimicrobial coatings consisting of copper-silver alloys for highly and frequently bacterial contaminated surfaces in e.g. healthcare settings and food industry. The present invention describes a method for electroplating antimicrobial consisting of copper-silver alloys comprising between 50 and 65 wt% copper and correspondingly 50 to 35 wt% silver in the final deposit of a thickness up to 10 ± 0.5 μm. A highly antibacterial electroplated copper-silver (60-40) alloy coating can only be manufactured according to the method here described. Surface structure, composition and combination of solely copper and silver as metallic mixture in the final deposit are together responsible for the excellent antibacterial properties of the electroplated copper-silver alloy coating. According to the method described in the present invention, various-shaped metallic, plastic, ceramic or composite substrates can be electroplated with an antimicrobial copper-silver alloy coating.

Description

DK 180529 B1 1

TECHNICAL FIELD OF INVENTION The present invention relates to a method for electroplating antimicrobial coatings consisting of copper-silver alloys comprising 50-65 wt.% copper and 50-35 wt.% silver in the final deposit. Antimicrobial coatings are receiving increasing interest as material solution against microbial contamination and transmission in several applications. Among the manufacturing methods, electroplating appears particularly advantageous being a consolidated technique in the coating manufacturing industry.

BACKGROUND — Here, the purpose of the present invention is to provide a method for electroplating a copper-silver alloys having a copper content from 50 to 65 wt.% (and correspondingly a silver content of 50 to 35 wt.%) in the final deposited layer.

The Ag-Cu system is characterized by a limited solid solubility, i.e. a metal cast alloy consisting of a solid solution of silver in copper can contain maximum 8 wt.%.

However, the simultaneous electroplating of copper and silver described in the present invention allows to obtain an electroplated alloy consisting of solid solution of silver in copper in the composition range of 50-35 wt.% Ag and 50-65 wt.% Cu. By following the steps described in the present invention, a 10 = 0.5 um thick final deposited layer within this composition range can be achieved.

The present invention relates to the method for manufacturing an antimicrobial electroplated copper-silver (60-40) alloy coating of proven high antibacterial efficacy. A related prior art to this invention is Ciacotich et al., An electroplated copper—silver alloy as antibacterial coating on stainless steel, Surface & Coating Technology Elsevier 2018 published by the inventors here.

In Ciacotich et al., the antimicrobial electroplated copper-silver (60-40) alloy coating is characterized and its high antibacterial activity demonstrated. This prior art document does not disclose the description of the manufacturing method (referred as “commercially modified copper-silver bath”), which is a non-conventional electroplating process. The method described in the present invention comprises four steps and a method for obtaining the highly antimicrobial copper-silver alloy coating

DK 180529 B1 2 presented in Ciacotich et al. The antimicrobial copper-silver alloy coating owes it antibacterial properties to the combination of the two metals in an alloy of the mentioned composition and the surface structure typical of an electroplated deposit. In Ciacotich at al., the antibacterial properties of the electroplated copper-silver (60-40) alloy coating have been demonstrated against S. aureus and E. coli.

Another related prior art is Korean Patent KR 20130128511 (A) (KR101403456 (B1) — 2014-06-03) titled “The fabrication method of Cu-Ag alloy coating and interconnection using electrodeposition”.

KR 20130128511 (A) relates to a method of electroplating a copper-silver alloy for use in wiring of electronic devices. According to the claims of KR 20130128511 (A), a substrate may be immersed into a copper and silver alloy electrolytic plating solution and a copper-silver alloy thin film may form by applying a potential (claim 1). In claim 5 of KR 20130128511 (A), it is described that the concentration of the copper ion compound in the electroplating solution may be 0.025 M to 1.0 M, preferably 0.05 to

0.3 M, and the concentration of the silver ion compound may be 0.1 mM to 100 mM, preferably 1 to 100 mM. In claim 1 of the present invention, the concentration of the copper and silver ion compounds (CuCN and AgCN) falls within the range of claim 5 according to KR 20130128511 (A), however not within the preferred range for the copper ion compound.

KR 20130128511 (A) also mentions that the applied current may be 0.5 to 100 mA/cm2 such as preferred 1 to 20 mA/cm2. According to claim 3 of the present invention, a current of 4-8 A/dm2 is used (i.e. a current of 40-80 mA/cm?), which falls within the overall, but not preferred range mentioned in KR 20130128511 (A).

KR 20130128511 (A) also mentions in [0036] that the temperature of the electrolytic plating solution during is suitably from 10°C to 70°C, preferably between 15°C and 35°C. Claim 2 of the present invention describes a temperature range of 50-70°C.

These elements described in claim 1-3 of the present invention are already disclosed in KR 20130128511 (A), although they are not found in combination. However, KR 20130128511 (A) 1 mentions that the silver content in the alloy can be adjusted from 1 at. % to 12 at.%. Assuming that the alloy mainly comprises of silver and copper, this would result in a wt.% of silver between 1.7 and 18.8 wt.%. Accordingly, KR 20130128511 (A) does not appear to describe a product having a copper-silver alloy

DK 180529 B1 3 with a composition as described in claim 1 of the present invention (50-65 wt.% copper and 50-35 wt.% silver). Neither does KR 20130128511 (A) appear to describe the use of a copper-silver alloy for antimicrobial purposes.

SUMMARY OF THE INVENTION A method for electroplating antimicrobial coatings consisting of copper-silver alloys for highly and frequently bacterial contaminated surfaces in e.g. healthcare settings and food industry. The present invention describes a method for electroplating antimicrobial consisting of copper-silver alloys comprising between 50 and 65 wt% copper and correspondingly 50 to 35 wt% silver in the final deposit of a thickness up to 10 + 0.5 um. A highly antibacterial electroplated copper-silver (60-40) alloy coating can only be manufactured according to the method here described. The surface structure, the composition and the combination of solely copper and silver as metallic mixture in the — final deposit are together responsible for the excellent antibacterial properties of the electroplated copper-silver alloy coating. According to the method described in the present invention, various-shaped metallic, plastic, ceramic or composite substrates can be electroplated with an antimicrobial copper-silver alloy coating.

DETAILED DESCRIPTION OF THE INVENTION In the present invention, the method for producing antimicrobial electroplated copper- silver alloy coatings comprising 50-65 wt.% copper and 50-35 wt.% silver according to claims 1 to 4 and with a final deposited layer up to 10 + 0.5 um is provided. The method may comprise of four steps, where steps c) is required. a) Surface preparation (e.g. electrocleaning) b) Surface activation (e.g. Wood’s nickel strike, autocatalytic deposition) c) Simultaneous copper-silver alloy electroplating d) Automated brush (e.g. brass) grinding

DK 180529 B1 4 a) The substrate material may be submitted to cathodic or anodic electrocleaning after the removal of organic soil and scale transferred during manufacturing processes, or a milder surface cleaning through e.g. alkaline cleaners depending on the base material.

b) Before the electrolytic plating, an activation step may be necessary to remove residues from the electrocleaning process and surface oxide layers in order to ensure adequate adhesion in the successive step. Wood’s nickel process may be used if the substrate is a chromium-alloyed steel, pickling in sulfuric acid or nitric acid bright- dipping process if copper and alloys. In the case of non-conductive base materials, etching, activation with a colloidal metal, autocatalytic deposition of copper or nickel may be performed prior to electrolytic plating. c) Simultaneous copper-silver alloy electroplating is performed in the electrolytic plating solution comprising a copper ion and silver ion containing compounds, a complexing agent, a conductivity-improving additive and deionized water. The copper ion containing compound CuCN is selected in the composition range 0.54-

0.70 M, and correspondingly the silver ion containing compound AgCN in the composition range 13-9 mM is added to achieve 50-65 wt.% metallic copper and 50-35 wt.% metallic silver in the final deposit. Complexing agent KCN is correspondingly added in the composition range 1.78-2.31 M, as complexant for the metal ions and as surplus (free cyanide) to increase the conductivity and the diffusion overpotential of silver. In aqueous solution copper cyanide CuCN dissolves and forms cyanocuprate ions Cu(CN),”, Cu(CN); 7, Cu(CN), > in excess of cyanide. Depending on the pH of the solution some species may predominate and (1), (2), (3), (4) and (5) describe the equilibrium reactions. CuCN =Cu + CN" (1) CuCN + CN" = Cu(CN)- (2) Cu” + 2CN™ = Cu(CN),~ (3) Cu(CN),” + CN™ = Cu(CN); 7 (4)

DK 180529 B1 Cu CN); 7 + CN" = CUCN) (5) Similarly, the formation of silver cyanide species (6), (7) is considered.

Ag++2CN = Ag(CN),~ (6) Ag(CN),” + CN" =Ag(CN);~ (7) 5 The ratio between CuCN, AgCN and KCN is calculated according to the cyanocuprate ions and silver cyanide complexes that are formed at pH 14 in the here described electrolytic plating solution. KCN is preferred over NaCN due to its superior conductivity. KOH is the only introduced additive in order to increase the bath conductivity, no other plating additive (e.g. levelling agents or brighteners) are required.

According to claims 2 and 3, the simultaneous copper-silver electroplating is conducted with a current density of 4-8 A/dm” at 50-70 °C. The simultaneous copper-silver electroplating may be performed for 2 minutes. According to claim 1, it is essential that no electrolyte agitation is performed during plating in order to get the desired composition in the deposit, due to the different mechanisms of deposition of the two metals (current- and diffusion-controlled).

According to claim 4, silver or stainless-steel anodes may be used. The composition of the electrolytic plating solution may be monitored and periodically filtered to remove possible presence of impurities.

As an example, the antimicrobial electroplated copper-silver (60-40) alloy coating is obtained with an electrolytic plating solution consisting of 0.65 M CuCN, 0.01 M AgCN, 2.15 M KCN, 0.69 M KOH in deionized water. Simultaneous electroplating is conducted using silver anodes with a current density of 6 A/dm” for 2 minutes at 60 °C.

d) After the electrolytic plating, the item may be submitted to automatic brush grinding using e.g. brass or nylon brushes in order to confer it superior finishing and allow subsequent plating without any other step than regular rising in water. Approx. one cycle may be sufficient to get the desired finishing, and the item may be directly

DK 180529 B1 6 recoated in the copper-silver electrolytic bath. This process may be repeated four times in order to get a thick final electroplated deposit. A scheme of the automated electroplating production line for the process described in this invention is reported in fig. 1.

In fig 1. the plating tanks for surface preparation, activation, simultaneous copper-silver electroplating as described above are alternated with water tanks for rinsing. At the end of the automated electroplating production line for the process described in this invention, grinding brushes are mounted inside the assigned tank. Rack plating is assumed in the presented setup, but the process and setup can be also tailored to coil stock continuous plating.

A final electroplated deposit of a thickness ranging from 2 to 10 + 0.5 um depending on the number of repeated steps c) and d) according to the process described in claims I to 4 can be obtained.

— After step d) of the present method the electroplated deposit has a thickness of 2 + 0.5 um. If steps c) and d) are repeated four times the thickness of the final electroplated deposit is 10 + 0.5 um.

The present invention described in claims 1-4 relates to a method for manufacturing antimicrobial surfaces on a various-shaped metallic, plastic, ceramic or composite substrates to be applied on highly and frequently bacterial contaminated surfaces such as furniture items, instruments or part of, equipment or part of in e.g. healthcare settings and food industry.

Various-shaped metallic, plastic, ceramic or composite base materials can be the substrates for the electroplated antimicrobial copper-silver alloys coatings consisting of 50-65 wt.% copper and 50-35 wt.% silver. In the case of non-conductive base materials, surface preparation and autocatalytic deposition of copper or nickel may be performed prior to electrolytic plating.

The electroplated antimicrobial copper-silver alloys coatings obtained according to the method described in claims 1 to 4 contain only metallic copper and silver, and there is no presence of nickel in the deposit, well-known responsible for allergic contact

DK 180529 B1 7 dermatitis. This is a high-priority requirement e.g. in the case of antimicrobial applications that foresee contact with skin. The electroplated antimicrobial copper-silver alloys coatings obtained according to the method described in the present invention are characterized by a pleasant warm ruddy silver color, therefore meeting also potential high demand on aesthetic requirements as well as visual appearance.

The electroplated antimicrobial copper-silver alloys coatings are thus suitable to be applied on furniture items, instruments or parts thereof, equipment or parts thereof in e.g. healthcare settings and food industry where microbial contamination must be prevented or minimized.

According to claim 1, the antimicrobial copper-silver alloy coatings obtained according to the method described in the present invention consist of 50-65 wt.% copper and respectively 50-35 wt.% silver. Such coatings are homogeneous metallic mixtures with a characteristic surface morphology and finishing. Composition and surface characteristics are jointly responsible for the high antibacterial activity of the antimicrobial copper-silver (60-40) alloy coating as demonstrated previously in Ciacotich et al.

The antimicrobial copper-silver alloy coatings obtained according to the method described in the present invention can be subjected to routine cleaning procedures and sterilization, although not strictly necessary.

— The lifetime of the antimicrobial copper-silver alloy coatings obtained according to the method described in the present invention may be adjusted depending on the desired thickness and the intended application.

The same item may be recoated and re-installed in the light of a regenerative design approach. Alternatively, exhausted copper-silver alloy coatings may be stripped by using persulfate-based chemistry, and copper and silver oxide particles may be recovered and reclaimed by filtering or electrolytic methods.

The antimicrobial copper-silver alloy coatings obtained according to the method described in claims 1 to 4 in the present invention may be applied on instruments and equipment including but not limited to parts thereof in e.g. food industry that are difficult (if not impossible) to clean efficiently due to design demands.

DK 180529 B1 8 The antimicrobial copper-silver alloy coatings obtained according to the method described in claims 1 to 4 in the present invention may be applied to e.g. basic hospital equipment and furniture, including but not limited to life support equipment, filters, bed rails, tables, doorknobs and handles, and medical devices and accessories such as stethoscopes, IV drip tubes, syringes, etc.

Claims

DK 180529 B1 Patent claim

A process for electrolytic precipitation of an antimicrobial copper-silver alloy containing 50-65 wt% copper and 50-35 wt% silver on cathodic substrates, containing: contact with substrates through aqueous electrolyte containing: 0,54-0,70 M copper (I) cyanide, 13-9 mM silver cyanide, 1.78-2.31 M potassium cyanide and potassium hydroxide; wherein electrodeposition is performed without agitation of electrolytes.

The process of claim 1, wherein the temperature of the bath is adjusted to 50-70 ° C.

The process of claim 1 or 2, wherein the current density of 4-8 A / dm ”is applied.

The process of any one of claims 1 to 3, wherein silver or stainless steel anodes are used.