Method for providing a conductive surface on a non-conductive polymer surface

Abstract

A rapid, low-temperature, sustainable polymer plating process for producing adherent metal coatings is provided. The present disclosure relates to a method for providing a conductive surface on a non-conductive surface, particularly a polymeric surface, and in particular to the attachment of silver ions to a polymeric surface to facilitate adhesion of a metal layer to the polymeric surface.

Description

[Technical Field]

[0001] The present disclosure relates to a method for providing a conductive surface on a non-conductive surface, particularly a polymeric surface, and in particular to the binding of silver ions to a polymeric surface to facilitate adhesion of a metal layer to the polymeric surface. [Background technology]

[0002] In recent years, engineering polymers have been applied in various industries around the world, and electroplating is a common approach to finishing polymer components to improve chemical and abrasion protection, surface hardness, electrical conductivity, EMI shielding, or decorative appearance. However, polymer substrates are non-conductive and cannot be directly electroplated, so pretreatment is required before electroplating.

[0003] The conventional approach to metallizing non-conductive polymer substrates involves four major steps: etching, catalysis, electroless plating, and finishing with the electroplating metal of choice.

[0004] Etching typically produces a rough, hydrophilic surface containing micro- and nanopores. This step not only prepares the polymer substrate for subsequent wet processing, but is also essential for the formation of pores, which promote film adhesion through mechanical interlocking. Widely used etchants include chromium trioxide (a form of hexavalent chromium) and sulfuric acid. However, hexavalent chromium poses numerous health and environmental concerns and requires complex disposal procedures. Therefore, non-chromium etchants are preferred, and numerous patents exist protecting formulations and processes related to non-chromium etchants. Permanganate is a strong oxidizing agent and is non-toxic, making it an ideal alternative to chromic acid etchants. However, permanganate is easily decomposed by the oxidizing power of the solution and the acidic environment required to ensure etching performance. This instability of permanganate reduces its performance and prevents its widespread application. U.S. Patent No. 9,657,226 discloses acidic permanganate etching, along with approaches to stabilizing the etch. Despite many improvements, all non-chromic acid etches in the art still rely heavily on the creation of a dense porous polymer surface to create a mechanical interlock between the metal surface and the polymer substrate.

[0005] After etching, the polymer substrate is subjected to a catalysis treatment for subsequent electroless plating. Again, the art contains numerous catalysis processes and methods, typically employing palladium as the catalyst. Palladium is expensive, and traditional processes often employ three substeps: sensitization, catalysis, and activation. While the catalysis process has been improved to a two-step process by using colloidal palladium, rinsing between steps is still required, and the unstable catalysis bath requires careful maintenance, making the process unsustainable. Silver (Ag) is one of the well-known and cheaper alternatives to palladium (Pd), but existing technologies routinely require a Sn sensitization step before Ag activation. The art mentions the addition of a silver ion catalyst to the etching step, as proposed in EP 09013498, but this process still requires a chemical step after catalyst activation.

[0006] WO 2018208177 proposes a method for reducing silver ions to silver metal in the absence of an external reducing agent by directly incorporating silver nanoparticles into a polymer using polymer chemical energy. This method is primarily concerned with polymer precursors and does not provide a method for reactivating polymerized materials.

[0007] More recently, a new generation of polymer plating has been developed (disclosed in U.S. Patent Application Publication No. 20210238748). This process modifies the surface chemistry of the polymer by chemically bonding additional long polymer chains to the surface. This chemical bonding, along with the high density of vertically aligned long chains, promotes film adhesion through mechanical interlocking without etching the polymer surface. The disclosed process still requires catalysis to support electroless metal deposition. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] European Patent No. 09013498 [Patent Document 2] International Publication No. 2018208177 [Patent Document 3] US Patent Application Publication No. 20210238748 Summary of the Invention [Problem to be solved by the invention]

[0009] Currently, conventional techniques for plating onto polymer substrates are toxic, expensive, energy intensive, time consuming, and typically specialized for a narrow range of polymer substrates. Thus, there is a need in the art for a fast, low-temperature, sustainable polymer plating process for producing adherent metallic coatings.

[0010] Where prior art publications are referred to herein, it will be expressly understood that this reference does not constitute an acknowledgement that the publications form part of the common general knowledge in the art in New Zealand or any other country. [Means for solving the problem]

[0011] In a first aspect, the present disclosure provides a conductive surface on a non-conductive substrate, comprising: a. providing a non-conductive substrate; b. conditioning the non-conductive substrate with a hydrophilizing agent to render the substrate hydrophilic; c. contacting the non-conductive substrate with an aqueous solution containing metal ions; d. covalently bonding metal ions to the conditioned non-conductive substrate by application of energy to form an activated substrate surface containing metal ion seeds; and e. contacting the activated substrate surface with an electroless plating solution comprising a plating metal salt and a reducing agent to form a conductive surface on the non-conductive substrate, wherein the reducing agent is suitable for reducing both the plating metal salt and the metal ion seeds on the activated substrate surface. to provide a conductive surface comprising:

[0012] In one example, the non-conductive substrate is a polymer substrate.

[0013] In one example, the conditioned chemical bonds on the surface of the non-conductive substrate comprise carbon-carbon double bonds in a proportion of about 10 to about 50% of the carbon backbone of the substrate.

[0014] In one example, the hydrophilizing agent is a solution containing one type of permanganate, one type of acid, and one type of complexing agent provided from a phosphorus-containing species having about 0.01 to about 1 mol / L of a phosphorus-containing anionic group.

[0015] In one example, the conditioning step with the hydrophilizing agent is carried out for about 5 to about 20 minutes.

[0016] In one example, the metal ion-containing aqueous solution further comprises a complexing agent and, optionally, a surfactant.

[0017] In one example, the complexing agent may be ammonium ions.

[0018] In one example, if a surfactant is present, the surfactant may be polyvinylpyrrolidone (PVP).

[0019] In one example, the metal ion-containing aqueous solution is maintained at a temperature of about 10 to about 40°C.

[0020] In one example, the non-conductive substrate is contacted with an aqueous solution containing metal ions.

[0021] In one example, the contact time between the substrate and the aqueous solution is about 1 to about 10 minutes.

[0022] In one example, an aqueous solution containing metal ions is sprayed onto a non-conductive substrate.

[0023] In one example, the metal ion-containing aqueous solution includes one or more of AgNO3, CuSO4, NiSO4, or CuCl2 at a concentration of about 0.005 to about 0.1 mol / L.

[0024] In one example, the energy source is heat, and the temperature is about 60 to about 90°C.

[0025] In one example, the energy source is applied as a hot air current or environment.

[0026] In one example, the energy source is applied for a contact time of about 2 to about 10 minutes.

[0027] In one example, the metal is Ag and the electroless plating solution includes electroless nickel boron and an amine borane as a reducing agent.

[0028] In one example, the metal is Ag, the electroless plating solution includes copper, and the reducing agent is selected from formaldehyde or an amine borane.

[0029] In another aspect, the present disclosure provides a conductive metal surface comprising a hydrophilically conditioned non-conductive substrate, an activated metal seed, an electrolessly metal-deposited metal surface, and an electroplated metal surface.

[0030] In one example, the density of activated metal seeds on the non-conductive substrate is sufficient to produce a bond strength of 10 N / cm or greater when tested according to ASTM B533.

[0031] The conductive metal surfaces include hydrophilically conditioned non-conductive substrates, activated metal seeds, electrolessly metal-deposited metal surfaces, and electroplated metal surfaces produced according to any one of the aspects and examples disclosed herein.

[0032] According to aspects presented herein, a method for metallizing a chemically conditioned substrate is provided. In one step of the process, the substrate is hydrophilized with metal-absorbent functional groups. The substrate can be selected from one or more long-chain polymers containing double-bonded carbon atoms.

[0033] In one step, the conditioning step can further include or consist of stress-releasing the polymer substrate. The stress-releasing process can include a heat treatment step. Alternatively, the stress-releasing step can include immersion in an organic solvent, such as, but not limited to, acetic acid or acetone.

[0034] The conditioning step can consist of or include hydrophilizing the relaxed substrate with a solution, the composition of which is selected based on the properties of the substrate. In one example, the hydrophilizing agent can include a stable potassium permanganate salt, an acid, and a phosphorus source, including phosphate or pyrophosphate. The conditioning step can be performed at a temperature of about 25 to about 45°C.

[0035] In one example, the conditioning step can include a manganese dioxide removal step using, for example, an oxalic acid and / or sulfuric acid solution.

[0036] In one example, the polymer substrate is contacted with the metal ions by immersion or spraying in a metal-containing solution containing monovalent or divalent ions for about 1 to about 10 minutes. In one example, the catalytic ions may require an activation step.

[0037] In a preferred example, the metal ion source is an aqueous silver nitrate solution. Functional groups introduced during the conditioning step allow for the absorption of metal ions. Without wishing to be bound by any particular theory, hydrogen atoms on the conditioned polymer surface are likely exchanged with metal ions during this step. In a subsequent step, the metal ions are activated by the influence of external energy, strengthening the bond between the polymer surface and the metal ions. After a period of time, preferably about 1 to about 10 minutes, the polymer chains reorient the hydroxyl groups, binding the metal seeds to the polymer surface.

[0038] The catalyst bath may also contain a surfactant, which allows for uniform seeding of metal ions onto the polymer surface.

[0039] To promote the reorientation of the metal-seeded hydroxyl groups on the polymer surface, a one-step or two-step activation process can be used. In a preferred example, a slow hot air stream is employed. Another activation step involves a two-step process involving slow air drying followed by heat treatment in an oven.

[0040] Commercially available electroless and electrolytic plating baths produce one or more layers of conductive metal coatings that are compatible with metal seeds on conditioned polymer surfaces. In one example, metallized polymers are post-treated to enhance covalent adhesion between the metal coating and the polymer substrate. The post-treatment step involves either a heat treatment for a duration of about 1 to about 5 hours or aging at ambient conditions for about 5 to about 10 days.

[0041] It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention as claimed. In this specification and claims, the word "comprising" and its derivatives, including "comprises" and "comprise," include each stated integer but do not exclude the inclusion of one or more additional integers.

[0042] It will be understood that references herein to "preferably" or "preferably" are for illustrative purposes only. The claims as filed and appended hereto are hereby incorporated by reference into the body of this specification.

[0043] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate several embodiments of the invention and, together with the description, serve to explain the principles of the invention. [Brief explanation of the drawings]

[0044] [Figure 1] FIG. 1 is a flow diagram of a method for metallizing a non-conductive surface. [Figure 2] FIG. 1 shows the results of ASTM D3359 crosshatch testing on various substrates. [Figure 3] FIG. 1 shows the results of peel tests performed according to ASTM B533 on metal surfaces deposited according to an embodiment of the present invention. [Figure 4] FIG. 1 shows ASTM D3359 crosshatch test on ABS treated with various activation-enhancing treatments. [Figure 5] FIG. 1 shows an XPS analysis of an activated ABS surface showing information on the chemical bonding between the polymer and the metal seeds. [Figure 6] FIG. 1 shows an SEM of a conditioned ABS polymer (left) and a SEM of a conditioned PPS polymer (right) according to an embodiment of the present invention. [Figure 7]1 is an SEM image of a traditionally etched polymer substrate. [Figure 8] FIG. 1 shows an XPS analysis of an activated PPS surface. [Figure 9] 1 is a surface and cross-sectional image of a PPS-CF substrate showing the adhesion of metal formed by the disclosed process.

[0045] Reference will now be made in detail to the preferred embodiments of the present disclosure, examples of which are illustrated in the accompanying drawings.

[0046] definition In each instance herein, in the description and examples of the present invention, the terms "comprising," "including," and the like, should be interpreted broadly and without limitation. Thus, unless the context clearly requires otherwise, throughout the description of the present invention and the claims, the words "comprise," "comprising," and the like, should be interpreted in an inclusive rather than exclusive sense, i.e., in the sense of "including but not limited to."

[0047] The term "about" or "approximately" typically means within 20%, more preferably within 10%, and most preferably even within 5% of a given value or range. Alternatively, the word "about" means within 10-fold (i.e., an order of magnitude), and preferably within 2-fold of a given numerical value. DETAILED DESCRIPTION OF THE INVENTION

[0048] FIG. 1 illustrates an exemplary method for forming a metal coating on a non-conductive polymer substrate.

[0049] At block 102, the method begins.

[0050] In block 104, the method conditions the polymer substrate. The conditioning step, for example and without limitation, conditions the polymer substrate surface for the purpose of binding metal ions. The conditioning step creates a hydrophilic surface on the polymer substrate and introduces functional groups that readily absorb metal ions. The polymer substrate may be a single polymer or a copolymer, and may be reinforced with glass fiber, carbon fiber, or other reinforcing materials known in the art. Preferred polymer chains contain easily oxidizable functional groups, such as vinyl groups or double-bonded carbons found in hydrocarbons containing benzyl rings and sulfides. A preferred structure is shown below. Polyesters and polymers containing only C-C single bonds are less preferred. However, blends with other preferred polymers can be selected. The polymer substrate may be selected from acrylonitrile butadiene styrene (ABS), polyamide (PA), polyphenylene sulfide (PPS), phenolic resins, or mixtures of these polymers. [ka]

[0051] The polymer substrate can be manufactured by injection molding, 3D printing, or other methods that result in the desired finished product shape. The polymer substrate can be solid or can contain blind holes, through-holes or channels, or other structures appropriate for the end use. In one example, the conditioning step can consist of or include stress relief of the substrate. The stress relief process is selected based on the shape of the polymer substrate, its composition, and processing conditions. The stress relief process can include heat treatment, preferably at 60-75°C for 0-2 hours. The heat treatment can be performed in an oven or in hot water. In one example, the stress relief process can include immersion in an organic solvent at 15-30°C for 0.5-30 minutes. One example of such an organic solvent is acetic acid. In another example, the organic solvent can be 25% acetone.

[0052] In one example, the conditioning step can include hydrophilizing the polymer substrate after stress release. The hydrophilizing agent bath composition is selected based on the polymer substrate chemistry, as the hydrophilizing agent selectively breaks the polymer chains and attaches active functional groups to the polymer chains. These active functional groups increase the hydrophilicity of the polymer substrate. The hydrophilic groups have an affinity for metal ions, so the metal ions are absorbed and attached to the polymer chains. The hydrophilic functional groups can be selected from polar groups, such as hydroxyl groups, sulfonic groups, and carbonyl groups, among others, known in the art.

[0053] In one example, the polymer substrate is ABS, the conditioning step includes a hydrophilization step, and the hydrophilizing agent solution includes at least one permanganate, one acid, and one source of a phosphorus-containing species selected from phosphate and pyrophosphate. The permanganate can be selected from those known in the art that dissolve in aqueous solution, preferably potassium permanganate or sodium permanganate. The permanganate concentration is 10 g / L to 200 g / L, or the maximum solubility of the particular permanganate. The acid can be an inorganic or organic acid. The inorganic acid can be sulfuric acid, nitric acid, or phosphoric acid. The organic acid can be acetic acid. The acid concentration is 3.8 to 10 mol / L for monobasic acids. The phosphorus-containing species can be phosphate, hydrogen phosphate, dihydrogen phosphate, or pyrophosphate. The phosphorus-containing species concentration is 0.05 to 1 mol / L. The conditioning hydrophilizing agent can act at 25 to 45°C for 5 to 20 minutes.

[0054] Permanganate is a strong oxidizing agent, and its oxidizing power is further enhanced in acidic environments or increases as the solution pH decreases. Compared to traditional chromium-based etching, permanganate retains sufficient oxidizing power while being environmentally friendly and posing no health concerns. However, permanganate readily decomposes, especially in acidic solutions, to form divalent manganese ions and manganese dioxide. The divalent manganese ions further catalyze and thus accelerate the decomposition of permanganate. Complexing the divalent manganese ions with a stabilizer reduces their effect on the permanganate anion, inhibiting permanganate decomposition. Inorganic species are preferred over organic species because permanganate can destroy organic species in oxidizing environments. In this case, phosphates and pyrophosphates are preferred complexing agents. The presence of a complexing agent can extend the life of permanganate hydrophilizing agents.

[0055] In one example, the conditioning step involves removing residual manganese dioxide produced in the preceding step. In one example, the substrate is immersed in a solution containing 5 to 20 g / L of oxalic acid and 5 to 15% by volume of sulfuric acid. The manganese dioxide removal step can be performed by soaking or ultrasonic treatment. In one example, the manganese dioxide removal solution is applied at 30 to 80°C, preferably 50 to 60°C, for 0.5 to 10 minutes, preferably 2 to 5 minutes. In one example, the removal step is performed with ultrasonic treatment for 1 to 5 minutes, preferably 3 minutes.

[0056] At block 106, the method includes contacting the conditioned polymer surface with a metal ion-containing solution. In one example, the substrate is immersed in a bath to contact the solution, and in an alternative example, the solution is sprayed onto the substrate. In principle, the metal ions can be any monovalent or divalent metal ions suitable for catalyzing the electroless reduction of the coating metal, including, among others, Ag. + , Ni + , Ni 2+ , Cu + , Cu 2+ , Co + , Co 2+Monovalent ions are preferred over divalent ions because the hydrophilic hydroxyl groups introduced onto the polymer surface can reduce monovalent ions. Divalent ions may require an additional step of adding a reducing chemical to complete the reduction. The reducing chemical depends on the ion selected. A preferred monovalent ion is silver.

[0057] The solution containing the metal ion source is an aqueous solution, and the Ag ion source can be selected from water-soluble Ag salts. In a preferred example, the Ag ion source is silver nitrate, and its concentration in the bath is 0.005 to 0.1 mol / L, preferably 0.01 to 0.05 mol / L. The preferred concentration of the silver ion source is determined by the plating rate of the subsequent electroless deposition step. In an alternative example, the silver ions are complexed, and the complexing agent is ammonium ions. The complexation of the silver ion source helps extend the life of the metal ion-containing solution. In another example, the silver ions are stabilized with polyvinylpyrrolidone (PVP), which minimizes aggregation of silver nanoparticles during activation.

[0058] Without wishing to be bound by theory, the inventors believe that polar functional groups, such as hydroxyl or carboxyl, are introduced into the polymer chain during the conditioning step. Upon contact with a solution containing monovalent metal ions, the metal ions are absorbed onto the hydrophilic polymer surface. In a later step, under the influence of an external energy source, hydrogen anions from the functional groups replace the reduced monovalent metal ions. Elsewhere on the polymer surface, the monovalent metal ions are reduced but do not bond to the surface and do not contribute to film adhesion. At the same time, water molecules bound to the polymer chains or trapped in the polymer matrix are eliminated, improving the bond strength between the metal atoms and the polymer. Over time, reorientation of the outer hydroxyl groups by the polymer chains minimizes the surface energy that tightly couples the attached metal particles to the polymer surface.

[0059] In a preferred example, the metal ion bath is at room temperature, or the catalyst ion bath may be at any temperature between 10°C and 40°C. The temperature is selected to maximize the life of the metal ion solution and optimize the reaction of the metal ions with the hydrophilic groups on the substrate. The time sufficient for the metal ions to be absorbed by the hydrophilic groups is 1 to 10 minutes, preferably 5 minutes. Excessive contact time between the substrate and the metal ion solution can result in excessive absorption of metal ions on the surface, which can lead to excessive reaction rates in the subsequent electroless deposition step.

[0060] In one example, the substrate is ABS, the metal ion bath contains 2 g / L silver nitrate, and the contact process is run for 10 minutes at room temperature.

[0061] In an alternative example, the metal ion bath contains 8 g / L silver nitrate and a liquid polymer / surfactant, such as 40 g / L polyvinylpyrrolidone, allowing for more uniform seeding of the metal ions onto the polymer surface.

[0062] In an alternative example, the metal ion bath contains 0.3 mol / L cuprous chloride with 5.2 mol / L hydrochloric acid to increase the solubility of the cuprous chloride.

[0063] In an alternative example, the catalytic metal bath contains 0.1-0.2 mol / L of cupric ion, which can be provided by copper sulfate, copper acetate, or any water-soluble cupric salt known in the art.

[0064] In block 108, the method enhances the metal ions on the substrate. The enhancement step reduces the metal ions and fixes them to the polymer substrate. While metal ion reduction can occur naturally over time, the process can be accelerated by an external energy source, such as heat treatment. The enhancement process can include either one or two steps. In a preferred example, the enhancement step employs a low-velocity hot air stream at a temperature of 60-90°C for 2-10 minutes, preferably a flow rate of 15 m / s at a temperature of 80°C for 3 minutes. In an alternative example, a two-step activation involves drying in a low-velocity compressed air stream at room temperature, followed by oven heat treatment at 60-90°C for 5-10 minutes. In one example, the activated substrate is stored for 1 hour before the next step is performed to further incorporate the reduced nanoparticles into the polymer substrate.

[0065] In block 110, the method deposits a conductive surface on the polymer substrate from an electroless plating bath compatible with the metal-catalyzed seeds. The electroless plating bath can be selected from commercially available nickel or copper plating baths to produce a nickel or copper conductive layer. In one example, the electroless plating bath contains 50 g / L nickel sulfate hexahydrate, 100 g / L sodium pyrophosphate, and 3 g / L dimethylamine borane, operates at 25-40°C, and completely coats the polymer substrate with a conductive layer in 30 minutes.

[0066] At block 112, the method electroplates the substrate with one or more surface metal layers selected according to the required component functionality. The metal layers can include a single metal or metal alloy layer or multiple metal or metal alloy layers. The metal coatings can be selected from nickel, copper, tin, cobalt, and nickel-zinc alloys, among others, with various matte to full bright finishes.

[0067] In block 114, the method post-treats the metallized polymer surface to improve adhesion between the metal coating and the substrate. The post-treatment can include a heat treatment at about 40 to about 70° C. for about 1 to about 3 hours, aging under ambient conditions for about 1 week, or a combination of these two steps. The post-treatment further improves coating adhesion by eliminating moisture trapped in the polymer substrate.

[0068] Adhesion between a polymer substrate and a metal surface occurs through covalent bonding of the metal atoms to the polymer surface. This covalent bond is initially formed through hydroxyl or carboxyl groups introduced to the polymer surface by the conditioning step. The conditioning step introduces new functional groups by breaking bonds on one or more surface polymers and attaching the functional groups to the bonding sites. The metal ions are reduced by the new functional groups, as shown in the following equation:

[0069] In a subsequent step, the initial bonding of the catalyst atoms to the substrate can be improved by rearrangement of the polymer chains, allowing for better incorporation of the metal nanoparticles. This process is illustrated in the following equation: This process can occur naturally over time or can be accelerated by the application of heat. In one example, the metal-coated substrate is heat-treated at about 40°C to about 100°C, preferably about 60°C, for about 10 minutes to about 2 hours, preferably about 30 minutes. In an alternative example, the metallized polymer substrate is allowed to naturally age at room temperature for about 12 hours to about 72 hours, preferably about 24 hours. [Example]

[0070] The following examples are provided to illustrate the practice of the present disclosure under specific operating conditions. However, these examples should not be construed as limiting the scope of the present disclosure. These examples were selected to specifically illustrate aspects of polymer surface activation and bonding to form adherent metal coatings on metal seeds.

[0071] Example 1: Conditioning Process Conditioning is dependent on the polymer substrate, and the examples provided herein discuss conditioning according to aspects of the present invention for a variety of commercially important substrates.

[0072] Conditioning breaks polymer chains on the substrate surface and introduces hydrophilic functional groups to the substrate surface. Conditioning may also result in etching of the surface, but creating a very rough surface is not necessary for film adhesion. The conditioning step includes an optional stress-relief step and a hydrophilization step. If the hydrophilizing agent solution is permanganate-based, a MnO2 removal step may be required. The effectiveness of the conditioning process can be measured by a wettability test. A polymer surface is considered sufficiently conditioned if the contact angle between the polymer surface and water is less than 10°. Table 1 summarizes the condition parameters for various polymer substrates.

[0073] [Table 1]

[0074] Example 2: Metal Seed Implantation and First Metallization The metal ion selection and activation process depends on the functional groups created on the polymer by the conditioning step and the electroless coating bath selected for the subsequent first metallization step. The examples provided herein discuss metal seed implantation according to aspects of the present invention.

[0075] In one example, conditioned ABS coupons were activated with Ag and plated in an electroless Ni bath. The ABS coupons were first conditioned in a solution containing 20 g / L KMnO4 and 20% by volume H2SO4. This conditioning step was performed at approximately 35°C for approximately 10 minutes. Residual MnO2 from the conditioning step was then removed in a solution containing 10 g / L oxalic acid and 10% sulfuric acid, which was run at approximately 50°C for approximately 2 minutes. The ABS coupons were then rinsed with deionized water and immersed in a solution containing 10 g / L silver nitrate at room temperature for 10 minutes. After immersion, the ABS coupons were treated in a stream of hot air at approximately 70°C until the surface was dry, which typically takes approximately 2 minutes. Finally, the ABS coupons were immersed in an electroless Ni-B bath containing 50 g / L nickel sulfate hexahydrate, 100 g / L sodium pyrophosphate, and 3 g / L dimethylamine borane. The electroless Ni-B was run at approximately 30°C for approximately 30 minutes. The ABS coupons were completely plated with a conductive Ni layer, preparing them for subsequent electroplating with the metal of choice.

[0076] In another example, conditioned ABS was activated with Cu and plated in an electroless Cu bath. The ABS coupon was conditioned using the process detailed above. The ABS coupon was then immersed in a solution containing cuprous chloride and chloric acid for approximately 10 minutes. The ABS coupon was then intensified in a hot air stream and plated with electroless Ni as detailed above.

[0077] In another example, PPS coupons were activated with Cu and plated in an electroless Ni bath. The PPS coupons were first conditioned in a solution containing 20 g / L KMnO4 and 40% H2SO4. Conditioning was performed at approximately 27°C for approximately 30 minutes. Residual MnO2 from the conditioning step was then removed in a solution containing 10 g / L oxalic acid and 10% sulfuric acid, which was then run at approximately 50°C for approximately 2 minutes with sonication. After rinsing with deionized water, the PPS coupons were then immersed in a solution containing cuprous ions. The cuprous solution was prepared by mixing an ascorbic acid solution with a copper sulfate solution, and contained 0.125 mol / L Cu and 0.002 mol / L ascorbic acid. The PPS coupons were then rinsed with deionized water and plated with electroless Cu containing 50 mmol / L EDTA, 50 mmol / L copper chloride, 0.1 mol / L boric acid, and 0.1 mol / L DMAB. Table 2 summarizes the activation parameters using various metal ion sources.

[0078] [Table 2]

[0079] Example 3: Coating process performance The objective of the disclosed method was to produce an adherent metallic coating on a polymer surface. Two commonly employed measurements of coating adhesion are the quantitative peel test and the qualitative crosshatch test. Peel tests were performed according to ASTM B533, with results recorded continuously in Newtons / cm during peel and presented as the peak, mean, and standard deviation of the test. Crosshatch tests were performed according to ASTM D3359, with qualitative results recorded as 0B to 5B, where 5B was the best adhesion with 0% coating removal.

[0080] The following examples describe processes for producing adherent metallic coatings on a number of commercially important polymer surfaces in accordance with certain aspects of the present invention.

[0081] In one example, ABS coupons were plated with electroless Ni and then electroplated with bright Ni according to the process detailed in Example 2. The bright Ni bath contained 270 g / L nickel sulfate, 60 g / L nickel chloride, 40 g / L boric acid, and commercial additives. Bright nickel plating was performed at approximately 4 A / dm 2 The coating was applied for approximately 20 minutes at 1000 W ...

[0082] In one example, ABS coupons were plated with electroless Ni and then electroplated with bright Cu according to the process detailed in Example 2. The bright Cu bath contained 195 g / L copper sulfate, 75 g / L sulfuric acid, and a commercially available additive. Bright Cu plating was performed at approximately 4 A / dm 2 The copper-plated ABS coupons were conditioned at about 70°C for about 1 hour, after which they were subjected to peel strength testing (Figure 301) according to ASTM B533. The average peel strength of 19.2 N / cm demonstrated excellent coating adhesion (Figure 302).

[0083] In another embodiment, PPS coupons reinforced with glass fiber (PPS-GF) were first conditioned in a solution containing 20 g / L KMnO4 and 40% by volume H2SO4. Conditioning was performed at approximately 27°C for approximately 30 minutes. Residual MnO2 from the conditioning step was then removed in a solution containing 10 g / L oxalic acid and 10% sulfuric acid, which was then run at approximately 50°C for approximately 2 minutes with sonication. After rinsing with deionized water, the PPS-GF coupons were rinsed with deionized water and immersed in a solution containing 2 g / L silver nitrate at room temperature for approximately 10 minutes. After immersion, the PPS-GF coupons were treated in a hot air stream at approximately 70°C until the surface was dry. Finally, the PPS-GF coupons were plated with electroless and electrolytic Ni to a thickness of approximately 10 μm. The Ni coating path crosshatch test according to ASTM D3359 classified the PPS-GF coupons as 5B (Figure 202).

[0084] In another embodiment, PETG coupons were first conditioned in a solution containing 20 g / L KMnO4 and 40% by volume H2SO4. Conditioning was performed at approximately 27°C for approximately 1 hour. Residual MnO2 from the conditioning step was then removed in a solution containing 10 g / L oxalic acid and 10% sulfuric acid, which was then run at approximately 50°C for approximately 2 minutes. The PETG coupons were then rinsed with deionized water and immersed in a solution containing 2 g / L silver nitrate at room temperature for approximately 10 minutes. After immersion, the PETG coupons were treated in a hot air stream at approximately 70°C until the surface was dry. Finally, the PPS coupons were electroless plated with Ni. The Ni coating path crosshatch test according to ASTM D3359 resulted in a classification of 5B (Figure 203).

[0085] In another example, a PA6 coupon was first conditioned in a solution containing 20% ​​sulfuric acid at about 20°C for about 20 seconds. After rinsing with deionized water, the conditioned PA6 coupon was immersed in a solution containing 2 g / L silver nitrate at room temperature for about 10 minutes. The PA6 coupon was then activated in a hot air stream at about 70°C until the surface was dry. Finally, the PA6 coupon was electrolessly and electrolytically plated with Ni to a thickness of about 10 μm. The Ni coating adhesion was rated 5B according to ASTM D3359.

[0086] In another example, paper-reinforced phenolic resin coupons were first conditioned in a solution containing 20 g / L potassium permanganate and 20% sulfuric acid at about 35°C for about 15 minutes. Residual MnO2 was removed in a solution containing 10 g / L oxalic acid and 10% sulfuric acid at about 50°C for about 2 minutes. After rinsing with deionized water, the conditioned paper-reinforced phenolic resin was immersed in a solution containing 2 g / L silver nitrate at room temperature for about 5 minutes. The paper-reinforced phenolic resin was then treated in a hot air stream at about 70°C for about 2 minutes. The activated paper-reinforced phenolic resin was finally plated with electroless and electrolytic Ni to a thickness of about 10 μm. The Ni coating adhesion was measured according to ASTM D3359 and was rated at 5B. Table 3 summarizes the coating adhesion results for various polymer substrates.

[0087] [Table 3]

[0088] Example 4: Activation Performance A method for activating polymer surfaces for electroless plating by an external heat source is described herein. The following examples demonstrate how heat treatment affects film adhesion.

[0089] The ABS coupons in this example were conditioned as detailed in Table 3 and immersed in a solution containing 10 g / L silver nitrate at room temperature for approximately 10 minutes.

[0090] In one example, the ABS coupon was then left at ambient conditions to dry and then plated with electroless and electrolytic Ni. Crosshatch testing according to ASTM determined that the coating adhesion was classified as 1B (Figure 401).

[0091] In one example, an ABS coupon was activated in a hot air stream at approximately 70°C for approximately 1 hour, and then electroless and electrolytic Ni plating was performed. The coating had excellent adhesion and was classified as 5B (Figure 402).

[0092] In one example, excess Ag solution was blown off an ABS coupon using cold air, and the coupon was heat treated in an oven at about 60°C for about 5 minutes before electroless and electrolytic Ni plating. The coating had excellent adhesion and was classified as 5B (Figure 403).

[0093] In one example, excess Ag solution was blown off an ABS coupon using cold air, and the coupon was heat treated in an oven at about 40°C for about 5 minutes before electroless and electrolytic Ni plating. The coating showed good adhesion and was classified as 4B (Figure 404).

[0094] The above examples demonstrate that various forms of heat treatment significantly improve the adhesion of metal coatings to ABS substrates. XPS analysis detected only COO-Ag bonds (504, 505, and 506 in Figure 5) on the ABS surface activated by heat treatment. The ABS surface conditioned according to embodiments of the present disclosure exhibited only widely dispersed, relatively deep pores (603), as shown in the SEM image (Figure 601). In contrast, the polymer surface etched according to conventional techniques exhibited a dense, deep porous structure (701 in Figure 7), which is necessary for the creation of mechanical interlocks (J.S. Seo, et al., Surfaces and Interfaces, Volume 26, 2021). Therefore, it can be inferred that the chemical bonds generated during the heat treatment step govern the coating adhesion mechanism.

[0095] Example 5: Metal Binding to Sulfone Functional Groups on PPS Substrates PPS has traditionally been a very difficult substrate on which to produce adherent metal coatings, with mechanical etching often providing the only viable approach. In the examples, it was demonstrated that hydrophilization in a permanganate, sulfuric acid-based solution effectively produced sulfone functional groups to which silver was covalently bound after thermal activation.

[0096] Figure 8, 801, shows the aromatic polymer signature corresponding to the benzyl ring (803) of the hydrophilized substrate. Figure 8, 802, shows the metal seeds attached to the PPS polymer surface by covalent bonding of Ag to the (-C6H4S-) functional group (804).

[0097] 805 in Figure 8 provides concentration data of metal seeds on the polymer surface and at a depth of 15 nm from the surface. The increase in concentration of metal seeds below the surface demonstrates the enhancement process described in this invention, i.e., reorientation of polar groups and the concomitant migration of metal seeds below the polymer surface.

[0098] The foregoing descriptions are merely exemplary and may vary greatly without departing from the scope of the present disclosure. For example, a wide variety of hydrophilization baths and processes produce identical polar groups on polymer surfaces, many monovalent and divalent metal ion species effectively bind to the activated polar groups, and various external energy sources assist in activating the bonds between the polar groups and metal ion species.

[0099] Example 6: Adhesion test to PPS-CF substrate As noted in Example 5, PPS-CF (carbon fiber) substrates are inherently difficult surfaces for the formation of adherent metal coatings. The previous example demonstrated that hydrophilization in a permanganate, sulfuric acid-based solution effectively produced sulfone functional groups to which silver was covalently attached after thermal activation. Here, we demonstrate adherent plating on such activated surfaces.

[0100] The activated PPS-CF coupon was then immersed in an electroless Ni plating bath. The resulting coating (Figure 9) was approximately 9 mm thick (901) and showed excellent adhesion (902). Image 901 shows that the Ni coating adhered not only to the PPS matrix but also to the carbon fiber filler in the composite.

[0101] Crosshatch testing was performed according to ASTM D3359 and qualitative results were recorded as 0B to 5B, where 5B was the best adhesion with 0% film removal.

[0102] Features described with respect to one example may be applied to, combined with, or substituted for features of other examples, as appropriate, without departing from the technical scope of the present disclosure.

[0103] The present disclosure in one preferred form offers the advantages of higher adhesion and greater energy efficiency in shorter processing times, while providing an inherently safer process due to lower processing temperatures than those often associated with prior art methods and the elimination of toxic chemicals.

[0104] Other examples of the present disclosure will be apparent to those skilled in the art from consideration of the specification and practice of the embodiments disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the present disclosure being indicated by the following claims.

Claims

1. A method for providing a conductive surface on a non-conductive substrate, a. Step of providing a non-conductive substrate; b. A step of conditioning the non-conductive substrate with a hydrophilic agent to impart hydrophilicity to the substrate; c. The step of bringing the non-conductive substrate into contact with an aqueous solution containing metal ions; d. A step of forming an activated substrate surface containing metal seeds by covalently bonding the metal ions to the conditioned nonconductive substrate by applying energy; and e. A step of bringing the surface of the activated substrate into contact with an electroless plating solution containing a plating metal salt and a reducing agent to form a conductive surface on the non-conductive substrate, wherein the reducing agent is suitable for reducing both the plating metal salt and the metal ion seeds on the surface of the activated substrate. Methods that include...

2. The method according to claim 1, wherein the nonconductive substrate is a polymer substrate.

3. The method according to claim 1 or 2, wherein the conditioned chemical bonds on the surface of the nonconductive substrate include carbon-carbon double bonds in a percentage / ratio of about 10 to about 50% of the carbon skeleton of the substrate.

4. The method according to claim 1 or 2, wherein the hydrophilizing agent is a solution comprising one type of permanganate, one type of acid, and one type of complexing agent supplied from a phosphorus-containing species having about 0.01 to about 1 mol / L of phosphorus-containing anionic groups.

5. The method according to claim 1, wherein the conditioning step with the hydrophilic agent is carried out for about 5 to about 20 minutes.

6. The method according to claim 1 or 5, wherein the conditioning step with the hydrophilic agent is carried out at approximately 25 to approximately 45°C.

7. The method according to claim 1 or 2, wherein the metal ion-containing aqueous solution further comprises a complexing agent and optionally a surfactant.

8. The method according to claim 7, wherein the complexing agent may be an ammonium ion.

9. The method according to claim 7, wherein, if the surfactant is present, the surfactant may be polyvinylpyrrolidone (PVP).

10. The method according to claim 7, wherein the metal ion-containing aqueous solution is maintained at a temperature of about 10 to about 40°C.

11. The method according to claim 1 or 2, wherein the non-conductive substrate is brought into contact with the metal ion-containing aqueous solution.

12. The method according to claim 11, wherein the contact time between the substrate and the aqueous solution is about 1 to about 10 minutes.

13. The method according to claim 1, wherein the metal ion-containing aqueous solution is sprayed onto the non-conductive substrate.

14. The aforementioned metal ion-containing aqueous solution is AgNO ３ , CdSO ４ NiSO ４ , or CuCl ２ The method according to claim 1 or 2, comprising one or more of the above in a concentration of about 0.005 to about 0.1 mol / L.

15. The method according to claim 1 or 2, wherein the energy source is heat, and the temperature is about 60 to about 90°C.

16. The method according to claim 15, wherein the energy source is applied as a hot air flow or a hot air environment.

17. The method according to claim 15, wherein the energy source is applied over a contact time of approximately 2 to approximately 10 minutes.

18. The method according to claim 1 or 2, wherein the metal is Ag, and the electroless plating solution comprises electroless nickel-boron and the reducing agent, amine-borane.

19. The method according to claim 1 or 2, wherein the metal is Ag, the electroless plating solution contains copper, and the reducing agent is selected from formaldehyde or amine borane.

20. A conductive metal surface comprising a non-conductive substrate subjected to hydrophilic conditioning, an activated metal seed, a metal surface on which metal is deposited by electroless deposition, and an electroplated metal surface.

21. The conductive metal surface on a non-conductive substrate according to claim 20, wherein the density of the activated metal seeds is sufficient to produce a bond strength of 10 N / cm or more when tested in accordance with ASTM B533.

22. A conductive metal surface comprising a non-conductive substrate subjected to hydrophilic conditioning, an activated metal seed, a metal surface from which metal has been deposited electrolessly, and an electroplated metal surface, manufactured according to claim 1 or 2.

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