Method for improving adhesion between a metallization layer and an ozone-etched plastic

Abstract

A method for metallizing a plastic part includes the steps of: (a) etching the plastic part by immersing it in an acidic ozone etching aqueous solution; (b) metallizing the ozone-etched plastic part; and (c) heating the metallized part in an oven at an elevated temperature for a certain period of time. After heating in the oven, the ozone-etched and metallized plastic part exhibits increased peel strength and improved adhesion.

Description

Technical Field

[0001] The present invention relates generally to a method for improving the adhesion between a plastic component and a metallization layer applied thereon. Background Technology

[0002] The plating of non-conductive components (i.e., plastics) with metal for various purposes is well known in the art. The production of molded plastic parts is relatively inexpensive, and metal-plated plastic parts are used in many applications. For example, metal-plated plastics are used for decoration and in the manufacture of electronic devices. Examples of decorative applications include automotive parts, such as trim strips. Examples of electronic applications include printed circuits, where the metal plated in selective patterns includes the conductors of the printed circuit board, and metal-plated plastics for EMI shielding. ABS resin is one of the most common types of plated plastics used for decorative purposes, while phenolic and epoxy resins are the most common types used for manufacturing printed circuit boards.

[0003] Preparing plastics for subsequent coating is a multi-step process, and typical steps include: 1) Etch the components; 2) Neutralize the etched surface with a neutralizing solution; 3) Activate the etched surface; 4) Acceleration steps; and 5) Deposit one or more layers of electroless metal plating (such as electroless copper and / or electroless nickel), and then electrolyze the deposited metal (such as copper and / or nickel) layers.

[0004] The etching step introduces micro-roughness onto the surface of the component to provide mechanical adhesion for subsequent metal coatings and to provide a suitable surface for adsorbing the catalytic layer (typically palladium, applied by immersing colloidal palladium particles in a solution). A catalyst is applied to catalyze the deposition of an initial metal layer from a self-catalytic plating bath (such as a nickel- or copper-containing plating bath). Subsequently, an additional metal layer is applied by electroplating, which comprises one or more of, for example, copper, nickel, and / or chromium.

[0005] For the durability of metal layers deposited on plastic parts and surfaces, it is important to achieve a high level of adhesion of the metal layer to the plastic part. To produce plastic parts with a firmly bonded metal coating, the plastic part is typically pre-treated before metal deposition, which usually requires an etching step. Plastic parts often undergo etching / pretreatment steps, during which the surface of the plastic part is treated to increase the adhesion characteristics of the metal layer subsequently deposited on it.

[0006] For example, plastic parts can be chemically etched to create pores on their surface, which roughens the surface. The etching step introduces micro-roughness into the part surface to provide mechanical adhesion for subsequent metal coatings and to provide a suitable surface for adsorbing a catalytic layer (typically palladium, applied by immersing colloidal palladium particles in solution). A catalyst is then applied to catalyze the deposition of the initial metal layer from an autocatalytic nickel or copper plating method.

[0007] The resulting pores serve as anchors for the subsequently deposited metal layer, and it is presumed that the adhesion of the deposited metal layer is caused by this anchoring effect. Furthermore, partial oxidation of the polymer chains in the plastic component can also trigger functionalization of the plastic component, which induces chemical and / or physical interactions with the deposited metal layer (e.g., through the formation of covalent or ionic bonds or through van der Waals forces), thereby causing adhesion between the two phases.

[0008] Etching is understood to refer to changes in the chemical and physical properties of the surface of a plastic part treated with an etching solution, which also removes stains and inorganic contaminants. In addition to surface changes, these changes include (1) chemical erosion or dissolution of the plastic article, (2) functionalization of the plastic surface, i.e., by introducing hydroxide or carboxylic ester groups and related changes in the polarity of the plastic surface, and (3) changes in the physical properties of the treated plastic surface in terms of charge distribution, polymer structure or surface structuring.

[0009] In a typical method, plastic parts are treated with an etching solution containing sulfuric acid and chromium (VI). It is presumably that when the plastic part comes into contact with the chromium-sulfuric acid etchant, pores are created on the surface of the plastic part due to the erosion of unsaturated hydrocarbons on the plastic surface. However, the surface may also be eroded due to oxidation.

[0010] Chromium (VI) compounds are suspected of being carcinogenic, and because they are classified as substances of very high concern under the EU's Registration, Evaluation, Authorization and Restriction of Chemicals (REACH) regulation, the use of acidic chromium (VI) etch solutions is only permitted under special licenses. Given the potential hazards posed by compounds that release chromium (VI), a complete ban on the commercial use of chromium (VI) compounds is also possible.

[0011] Alternatives to chromium (VI) etch solutions used for plastic parts include, for example, permanganate-based etch solutions, including those based on alkali metal permanganates (including potassium permanganate) and inorganic acids (such as phosphoric acid). These etch solutions exhibit good etching performance on plastic surfaces; however, the alkaline permanganates used in the solutions undergo rapid self-decomposition, rendering the etching effect of alkaline permanganate etch solutions insufficient after several hours. Furthermore, manganese dioxide may undesirably deposit on the plastic surface, negatively impacting further coating processes.

[0012] U.S. Patent No. 5,160,600 to Patel et al. (the subject matter of which is incorporated herein by reference in its entirety) describes a method for chemical plating of plastics, which is carried out in an environment free of chromium ions by the following sequential steps: roughening and activating the surface of the plastic by contacting it with an aqueous solution of concentrated sulfuric acid, concentrated nitric acid, or concentrated phosphoric acid in the presence of noble metal ions and an oxidizing agent (selected from the group consisting of nitric acid, hydrogen peroxide, and persulfate), and then applying Pd... 0 It is suspended in an aqueous suspension and then chemically metallized.

[0013] EP3414364, granted to Biconex GmbH (the subject matter of which is incorporated herein by reference in its entirety), describes a method for pretreating the surface of plastic parts for metallization, such as electroplating by contacting the parts with an oxidizing agent, such as a peroxide compound. The plastic parts can be contacted with non-dehydrating peroxide compounds, including ozone. However, peroxide-etched plastic parts typically have low peel strength values. Therefore, to achieve higher desired peel strength, special heat treatment steps are usually performed, which typically require several days to achieve good results.

[0014] WO2022136377, granted to Delta Engineering & Chemistry GmbH (the subject matter of which is incorporated herein by reference in its entirety), describes a method for etching plastic parts using ozone. The etched plastic parts are subjected to a post-treatment to remove the ozone, which involves contacting the etched plastic parts with an alkaline post-treatment solution containing ammonia. While the post-treatment step is known to have a positive impact on methods of metallizing plastic parts, the peel strength values ​​after post-treatment remain relatively low.

[0015] Therefore, there is a need in the art for an improved method of preparing plastic parts for receiving metal plating thereon, which includes an improved method of treating ozone-etched plastic parts, which increases the adhesion of the metallization layer to the underlying plastic surface and exhibits improved peel strength. Summary of the Invention

[0016] One object of the present invention is to provide an improved method for preparing plastic parts for receiving metal plating thereon.

[0017] Another object of the present invention is to provide an improved method for preparing plastic parts for receiving metal plating thereon, the method comprising a post-processing step to improve the adhesion of the metallization layer to the plastic part.

[0018] Another objective of this invention is to improve the peel strength of metallized plastic parts.

[0019] Another object of the present invention is to improve the peel strength of metallized plastic parts comprising two or more different types of plastics positioned adjacent to each other.

[0020] Therefore, in one embodiment, the present invention relates to a method for metallizing plastic parts, the method comprising the following steps: a. Etching the plastic parts by introducing them into an acidic ozone etching solution. b. Metallizing ozone-etched plastic parts, and c. Heat the ozone-etched and metallized plastic parts in an oven at elevated temperatures for a certain period of time. Attached Figure Description

[0021] Figure 1 A graph depicts the adhesion strength of ABS panels dried for different times at a defined temperature in a laboratory oven.

[0022] Figure 2 A graph depicts the adhesion strength of ABS panels dried for different times at a defined temperature in a technical oven.

[0023] Figure 3 A graph depicting the adhesion strength of an ABS panel to an etchant containing chromium (VI). Detailed Implementation

[0024] This invention relates to a method for subjecting ozone-etched, metallized plastic parts to a drying oven for a certain period of time to increase adhesion. The inventors unexpectedly discovered that, compared to the initial peel strength under unheated conditions, drying ozone-etched and metallized plastic parts in a drying oven at a defined temperature for a defined period of time after the metallization step can increase the peel strength by at least three times, at least four times, or at least five times or more.

[0025] In one embodiment, after metallization, the ozone-etched plastic part is heated to an elevated temperature for a certain period of time to achieve a peel strength of at least about 5.0 N / cm or at least about 5.5 N / cm, or at least about 6.0 N / cm, or at least about 6.5 N / cm, or at least about 7.0 N / cm, or at least about 7.5 N / cm, or at least about 8.0 N / cm, or at least about 8.5 N / cm, or at least about 9.0 N / cm, or at least about 9.5 N / cm, or at least about 10 N / cm, according to ASTM Test Method B533-85 (re-approved in 2019) Procedure A (incorporated herein in its entirety by reference).

[0026] In another embodiment, after metallization, the ozone-etched plastic part is heated in an oven at a temperature maintained in the range of about 60°C to about 90°C, more preferably about 65°C to about 85°C, more preferably about 70°C to about 80°C, more preferably about 75°C to about 78°C, for about 10 minutes to about 120 minutes, preferably about 15 minutes to about 90 minutes, preferably about 20 minutes to about 75 minutes, more preferably about 30 minutes to about 60 minutes, to achieve a peel strength of at least about 5.0 N / cm or at least about 5.5 N / cm, or at least about 6.0 N / cm, or at least about 6.5 N / cm, or at least about 7.0 N / cm, or at least about 7.5 N / cm, or at least about 8.0 N / cm, or at least about 8.5 N / cm, or at least about 9.0 N / cm, or at least about 9.5 N / cm, or at least about 10 N / cm, according to ASTM Test Method B533-85 (re-approved in 2019) Procedure A.

[0027] As used herein, unless the context clearly indicates otherwise, “a,” “an,” and “the” refer to both singular and plural references.

[0028] As used herein, the term “about” refers to a measurable value, such as a parameter, quantity, duration, etc., and is intended to include variations of + / -15% or less, preferably + / -10% or less, more preferably + / -5% or less, even more preferably + / -1% or less, and even more preferably + / -0.1% or less, provided such variations are suitable for implementation in the invention described herein. Furthermore, it should be understood that the values ​​referred to by the modifier “about” are themselves specifically disclosed herein.

[0029] As used herein, for ease of description, spatial relative terms such as “below,” “under,” “lower,” “above,” and “upper” are used to describe the relationship between one element or feature and one or more other elements or features, as shown in the figure. It should also be understood that the terms “before” and “after” are not intended to be restrictive and are intended to be interchangeable where appropriate.

[0030] As used herein, the term "comprising and / or including" specifies the presence of the stated features, integers, steps, operations, elements, and / or components, but does not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0031] As used herein, unless otherwise defined for a specific element or compound, the terms "substantially free" or "largely free" mean that a given element or compound cannot be detected by conventional analytical methods using bath analysis familiar to those skilled in the art of metal plating. Such methods typically include atomic absorption spectrometry, titration, ultraviolet-visible analysis, secondary ion mass spectrometry, and other commonly used analytical methods.

[0032] In one embodiment, and as described herein, the invention relates throughout to a method for metallizing a plastic part, the method comprising the following steps: a. Etching the plastic parts by introducing them into an acidic ozone etching solution. b. Metallizing ozone-etched plastic parts, and c. Heat the ozone-etched and metallized plastic parts in an oven at elevated temperatures for a certain period of time.

[0033] Various methods can be used to etch plastic parts with ozone, including those described in WO2022 / 136377 (the contents of which are incorporated herein by reference in their entirety).

[0034] Gaseous ozone is introduced into an acidic aqueous solution to provide an acidic ozone etching solution. Ozone can be generated from oxygen using a high-voltage discharge, which produces an ozone-oxygen gas mixture. Ozone can also be generated using an ozone generator, and methods for generating ozone using an ozone generator are known to those skilled in the art.

[0035] The resulting ozone-oxygen gas mixture is preferably introduced into an acidic aqueous solution under pressure. The gas mixture is distributed in the water, for example by means of a static mixer, and the ozone dissolves in the acidic aqueous solution to form an acidic ozone etching aqueous solution.

[0036] The acidic ozone etching aqueous solution may contain one or more acids, preferably selected from the group consisting of sulfuric acid, phosphoric acid, acetic acid, hydrofluoric acid, sulfonic acid, phosphonic acid, toluenesulfonic acid, citric acid, and mixtures thereof. In one embodiment, the acidic ozone etching aqueous solution contains one or more acids, selected from the group consisting of sulfuric acid, phosphoric acid, and mixtures thereof.

[0037] In one embodiment, the pH value of the acidic ozone etching aqueous solution is preferably less than about 6.5, more preferably less than about 4.5, and even more preferably less than about 2.0. In one embodiment, the pH value of the acidic ozone etching aqueous solution is less than about 2.0, more preferably less than about 1.9, more preferably less than about 1.8, more preferably less than about 1.7, more preferably less than about 1.6, and even more preferably less than about 1.5. In one embodiment, the pH value of the acidic ozone etching aqueous solution is between about 0.1 and about 1.9, more preferably between about 0.2 and about 1.8, and even more preferably between about 0.3 and about 1.7. In another embodiment, the pH value of the acidic ozone etching aqueous solution is at most about 1.0, preferably less than about 1.0. In another embodiment, the pH value of the acidic ozone etching aqueous solution is between about 1.0 and about 2.0, more preferably between about 1.0 and about 1.9, and even more preferably between about 1.0 and about 1.8.

[0038] The concentration of acid in the acidic ozone etching aqueous solution can be as high as about 10.0 mol / L. The acid concentration is preferably between about 0.1 mol / L and about 5.5 mol / L. In one embodiment, the acid concentration is between about 0.1 mol / L and about 10 mol / L, preferably between about 1 mol / L and about 8 mol / L.

[0039] The ozone concentration of the acidic ozone etching aqueous solution can be in the range of about 2 mg / L to about 120 mg / L, or in the range of about 5 mg / L to about 100 mg / L, preferably between about 10 mg / L and about 50 mg / L, more preferably between about 20 mg / L and about 50 mg / L, and more preferably between about 30 mg / L and about 40 mg / L. In one embodiment, the ozone concentration of the acidic ozone etching aqueous solution is between about 2 mg / L and about 35 mg / L.

[0040] The acidic ozone etching aqueous solution is also at least substantially free of manganese compounds and at least substantially free of chromium compounds.

[0041] The phrase "at least substantially free of chromium compounds" means that the chromium content in the solution is less than 0.20 mmol / L, preferably less than 0.020 mmol / L, and more preferably less than 0.002 mmol / L, as measured by atomic absorption spectrometry (AAS).

[0042] Alternatively, chromium content can also be determined using inductively coupled plasma optical emission spectrometry (ICP-OES). In both methods, the quantification of chromium is independent of its oxidation state. In each case, the total amount of dissolved chromium (total chromium) is determined.

[0043] The phrase "at least substantially free of manganese compounds" means that the acidic ozone etching aqueous solution contains less than 0.03 mmol / L of manganese, preferably less than 0.01 mmol / L, more preferably less than 0.003 mmol / L, and even more preferably less than 0.001 mmol / L, as measured by AAS. Manganese compounds include manganese with oxidation states from +1 to +VII, including those with oxidation states of +II, +III, +IV, +VI, and +VII. Alternatively, the manganese content can also be determined using ICP-OES. In both methods, the quantification of manganese is independent of its oxidation state.

[0044] Methods for the quantitative determination of chromium and manganese using AAS and ICP-OES are generally known to those skilled in the art.

[0045] In one embodiment, the acidic ozone etching aqueous solution further comprises hydrogen peroxide in concentrations ranging from about 0.001 mol / L to about 0.1 mol / L, preferably from about 0.001 to about 0.05 mol / L, and more preferably from about 0.001 mol / L to about 0.02 mol / L. It is presumed that some of the ozone dissolved in the acidic ozone etching aqueous solution forms hydroxyl radicals together with the hydrogen peroxide, and that the etching occurs not only through the ozone decomposition of the C / C double bonds of unsaturated hydrocarbons on the surface of the plastic part to be etched, but also through the erosion by hydroxyl radicals.

[0046] Plastic materials treated in the manner described herein can be chemically plated to provide a uniformly coated plastic surface with exceptionally high adhesion properties. In one embodiment, the plastic component to be etched comprises a plastic having an unsaturated hydrocarbon compound. For example, the plastic component can be a plastic selected from the group consisting of: acrylonitrile butadiene styrene copolymer (ABS), acrylonitrile butadiene styrene copolymer / polycarbonate (ABS / PC), polycarbonate (PC), polyamide (PA), butadiene styrene methacrylate (MBS), polybutylene terephthalate (PBT), styrene-acrylonitrile copolymer (SAN), polyphenylene sulfide (PPS), polyester (PE), polyethylene terephthalate (PET), polyether ether ketone (PEEK), polylactide (PLA), polybutylene succinate (PBS), polylactide / polybutylene succinate (PI-A / PBS), aromatic polymers (LCPs) (such as aromatic polyamides), and combinations thereof. ABS / PC is a mixture of two plastics, ABS and PC. ABS / PC can contain different weight ratios of ABS and PC. The proportion of ABS in ABS / PC plastic is preferably between 30% and 60% by weight, more preferably between 35% and 55% by weight, based on the total weight of the ABS / PC plastic in each case. The proportion of PC in ABS / PC plastic is preferably between 40% and 70% by weight, more preferably between 45% and 65% by weight, based on the total weight of the ABS / PC plastic in each case.

[0047] Examples of commercially available ABS / PC plastics include, but are not limited to, Bayblend. ® T45 PG, Bayblend ® T65 PG and Bayblend ® T65 HI (available from Covestro AG, Leverkusen). Bayblend ® T45 PG contains 45% PC and 55% ABS, Bayblend ® T65 PG and T65 HI contain 65% PC and 35% ABS by weight. PLA / PBS is a mixture of two plastics, PLA and PBS. PLA / PBS can contain different weight ratios of PLA and PBS. In one embodiment, the plastic part to be etched comprises a plastic selected from the group consisting of ABS, MBS, and ABS / PC, preferably ABS.

[0048] The surfaces of any of the aforementioned plastics are etched by contact with an acidic ozone etching solution as described herein. It is presumed that ozone chemically erodes the carbon-carbon double bonds of unsaturated hydrocarbon compounds on the surface of the plastic part to be etched, causing bond breakage (ozone decomposition). Surprisingly, the reaction rate of bond breakage caused by the acidic ozone etching solution varies considerably in the aforementioned types of plastics and in the case of copolymers and mixtures of various plastics. Therefore, the method described herein can be used for selective etching of both plastic parts containing only one type of plastic and plastic parts containing two or more different types of plastics positioned adjacent to each other. Plastic parts containing two or more different types of plastics positioned adjacent to each other are referred to as 2K, 3K, or multi-component plastic parts, depending on whether they contain two, three, or more types of plastics positioned adjacent to each other. Selective etching of a single type of plastic in 2K, 3K, or multi-component plastic parts can be achieved by adjusting the reaction conditions of the etching method, such as temperature, concentration of ozone dissolved in the etching solution, concentration of acid in the ozone etching solution, and etching time. Then, in the metallization step, one or more metal layers can be used to selectively coat the selectively etched 2K, 3K, or multi-component plastic parts.

[0049] In one embodiment, the plastic part to be etched is a 2K, 3K, or multi-component plastic part. In another embodiment, the plastic part to be etched is a two-component plastic part, preferably a two-component plastic part made of ABS and ABS / PC or ABS and PC.

[0050] For example, consider a two-component plastic part made of ABS and ABS / PC, where the two plastics, ABS and ABS / PC, exist side-by-side. The ABS plastic is the component to be metallized, and the ABS / PC plastic is a so-called "selective" component that is not selectively metallized. If the plastic part undergoes a method according to the steps described herein, only the ABS component is selectively coated in the subsequent metallization, and the selective component is not metallized. The edges between the two plastics positioned adjacent to each other are also clearly defined in the metallization step.

[0051] In addition to plastics, or in the case of 2K, 3K, or multi-component plastic parts, the plastic parts to be etched may contain fillers such as glass fibers, carbon fibers, or minerals, in addition to at least two or more types of plastics positioned adjacent to each other. Such fillers are known to those skilled in the art.

[0052] In one embodiment, the method further includes a pretreatment step on the plastic part to be etched or already etched. However, it should be noted that the pretreatment step is not required, and the method described herein can be performed without a pretreatment step.

[0053] In one embodiment, the plastic part to be etched is pretreated to clean the plastic surface and activate the plastic surface for etching. In one embodiment, the pretreatment step includes contacting the plastic part to be etched with an activation solution, typically an aqueous solution. Various methods can be used to contact the plastic part with the activation solution, including immersing the plastic part in the activation solution or spraying the activation solution onto the surface of the plastic part.

[0054] In one embodiment, the activating solution is an acidic activating solution containing at least one inorganic acid, such as sulfuric acid, hydrochloric acid, or persulfate. In another embodiment, the activating solution is an alkaline activating solution containing an inorganic base (such as sodium hydroxide or potassium hydroxide). The activating solution may also contain at least one surfactant. In one embodiment, the activating solution containing an inorganic base may be a solution commonly used in degreasing baths. In one embodiment, the alkaline activating solution contains ammonia and / or contains at least one organic alkaline compound, which may include, for example, an amine or amide, such as, by way of example and not limitation: ethylamine, propylamine, tetraethylenepentamine, 1,3-bis(aminomethyl)cyclohexane, pyrimidine, imidazole, oxazole, ethanolamine, propanolamine, diethanolamine, acetamide, or hexamethylenetetramine.

[0055] An example of a suitable alkaline activating solution is a pre-soaking solution, such as HSO Vortauchlösung KU, which is available from HSO Herbert Schmidt GmbH & Co KG.

[0056] In one embodiment, the method also optionally, but preferably, includes a post-treatment step for the etched plastic part, comprising removing residual ozone from the etched plastic part prior to metallization. If used, the post-treatment step also serves to condition the surface for subsequent metallization process steps.

[0057] In one embodiment, the etched plastic part is contacted with a post-treatment solution, such as by immersing the etched part in the post-treatment solution or by spraying the post-treatment solution onto the surface of the etched plastic part. The post-treatment solution is preferably an aqueous solution, more preferably an alkaline solution comprising one or more of sodium hydroxide, potassium hydroxide, ammonia, amines, amides, phosphates, and mixtures thereof, and even more preferably, the post-treatment solution comprises one or more of ethylamine, propylamine, tetraethylenepentamine, 1,3-bis(aminomethyl)cyclohexane, pyrimidine, imidazole, oxazole, ethanolamine, propanolamine, diethanolamine, acetamide, and hexamethyleneamide. In one embodiment, the alkaline post-treatment solution particularly preferably contains ammonia. The concentration of the aforementioned substances or mixtures thereof in the alkaline post-treatment solution can be between about 0.01 mol / L and about 5 mol / L, preferably between about 0.05 mol / L and about 1 mol / L. Furthermore, the alkaline post-treatment solution preferably does not contain anionic surfactants and / or nonionic surfactants.

[0058] In one embodiment, when the post-treatment solution is brought into contact with the etched plastic part, the temperature of the post-treatment solution is preferably between about 20°C and about 70°C, and more preferably between about 30°C and about 70°C. The contact time between the etched plastic part and the post-treatment solution is preferably between about 1 minute and about 60 minutes, and more preferably between about 3 minutes and about 20 minutes.

[0059] In one embodiment, the alkaline post-treatment solution is an aqueous ammonia solution. Surprisingly, it has been shown that post-treatment with an ammonia solution produces particularly good coating results, and the alkaline post-treatment solution may contain ammonia at a concentration of about 0.5 mol / L to about 1.5 mol / L, preferably about 0.7 mol / L to about 1.2 mol / L, and more preferably about 1.0 mol / L. The etched plastic part can be contacted with the aforementioned ammonia solution used for post-treatment. When the aqueous ammonia solution is contacted with the etched plastic part, the temperature of the aqueous ammonia solution is preferably between about 10°C and about 50°C, more preferably between about 15°C and about 45°C, more preferably between about 20°C and about 40°C, and most preferably at about 35°C.

[0060] After treatment with the alkaline post-treatment solution described above, oxidation products on the surface of the etched plastic parts were effectively cleaned, and residual ozone on the components was effectively neutralized. As a result, the palladium activator exhibited uniform crystal growth without any uncovered areas or other inhomogeneities.

[0061] In one embodiment, an alkaline ammonia post-treatment solution is preferred because it has been observed that the adhesion of the metal coating on plastic parts post-treated with an ammonia solution is improved compared to the adhesion of the metal coating on plastic parts that have been treated with other alkaline post-treatment solutions. Similarly, no frame metallization occurs.

[0062] Alternatively, the post-treatment solution can be a solution containing a reducing agent (such as sodium dithionite, sodium bisulfite, or hydroxyl ammonium sulfate), or it can be an acidic aqueous solution of hydrogen peroxide.

[0063] In one implementation, the etched plastic part can be irradiated with ultraviolet light for post-processing, which removes any residual ozone from the etched plastic part. If used, the ultraviolet light typically has a wavelength between 240 nm and 320 nm. At wavelengths below 240 nm, ozone is formed from oxygen in the air, which should be avoided during subsequent processing.

[0064] Furthermore, it has been shown that the type of post-treatment has a positive impact on the method of metallizing plastic parts, and can also have a positive impact on the efficiency of subsequent metallization of etched plastic parts in electroless nickel plating.

[0065] In the method according to the invention, after the step of etching the plastic part, one or more metal layers are applied to the etched plastic part, the one or more metal layers may include one or more electroplating layers, autocatalytic layers, chemical plating layers and / or electroplating layers, as commonly known to those skilled in the art.

[0066] In one embodiment, the metallization step includes a first step of contacting the etched plastic part with an activator to deposit a metal nucleus onto the etched surface. Such methods for applying the metal nucleus are generally known to those skilled in the art, and typical metals include, for example, palladium, platinum, silver, and / or ruthenium. The activator typically contacts the etched surface as a colloid. In one embodiment, the activator comprises Pd containing between about 0.001% w / w and about 5% w / w of the activator. 0 Aqueous suspension.

[0067] Following the activation step, electroless metallization is typically performed by reduction from a metal salt to form a metal layer or metal alloy layer, including but not limited to nickel, copper, cobalt, copper / nickel, nickel / cobalt, or gold. Then, after electroless metallization, additional metal layers, including electroplated metal layers, may be applied, comprising, for example, one or more of copper, nickel, and / or chromium. In one embodiment, the metallization step includes electroless deposition of nickel, followed by electrolytic nickel deposition, and then electrolytic chromium deposition. In another embodiment, electrolytic copper, electrolytic nickel, and electrolytic chromium layers follow electrolytic deposition of nickel.

[0068] Subsequently, the metallized and ozone-etched plastic parts were transferred to a drying oven. The inventors of this invention unexpectedly discovered that drying the metallized and ozone-etched plastic parts at elevated temperatures for a certain period of time has a profound effect on the adhesion of the metallized coating to the plastic parts, as evidenced by the increased peel strength of metallized and ozone-etched plastic parts dried in a drying oven compared to those without post-treatment or those treated by different methods.

[0069] In one embodiment, the drying oven is maintained at a temperature ranging from about 40°C to about 120°C, more preferably from about 50°C to about 100°C, and even more preferably from about 60°C to about 90°C. In another embodiment, the temperature of the drying oven is maintained at a temperature between about 70°C and about 80°C, or between about 75°C and about 80°C, or between about 75°C and about 78°C, or between about 70°C and about 73°C. The ozone-etched and metallized plastic parts are maintained in the drying oven for a certain period of time. In one embodiment, this period of time is in the range of about 10 minutes to about 120 minutes, preferably between about 30 minutes and about 90 minutes, or between about 30 minutes and about 60 minutes, or between about 45 minutes and about 60 minutes.

[0070] The drying temperature and time will depend in part on the type of plastic being plated and the one or more metal layers applied thereon. Importantly, the drying temperature and time must be sufficient to increase the adhesion of the metallization layer on the ozone-etched plastic part. In one embodiment, according to ASTM Test Method B533-85 (2019 Re-approved) Procedure A, the peel strength is greater than about 5 N / cm, or greater than about 6.0 N / cm, or greater than about 6.5 N / cm, or greater than about 7.0 N / cm, or greater than about 7.5 N / cm, or greater than about 8 N / cm, or greater than about 8.5 N / cm, or greater than about 9.0 N / cm, or greater than about 9.5 N / cm, or greater than about 10.0 N / cm. For example, according to ASTM Test Method B533-85 (2019 Re-approved) Procedure A, the metallized ozone-etched plastic part can be heated in an oven at a temperature range of 75°C–78°C for 30–60 minutes to achieve a peel strength greater than 7.0 N / cm. In one embodiment, it has been found that, compared with the initial peel strength under unheated conditions, a drying step in a drying oven at the temperatures and times described herein can increase the peel strength by three times or more, or four times or more, or five times or more.

[0071] In one embodiment, the method for metallizing a plastic part according to the present invention includes the following steps: - Ozone etching of plastic parts; - A metal core is deposited onto the etched plastic part using an activator; - Chemical plating deposition is performed on the first metal layer; - Optionally, one or more additional metal layers are deposited by chemical plating and / or electroplating; and - Heat in an oven at 40°C to 100°C for 30 to 90 minutes.

[0072] The invention will now be described with reference to the following non-limiting embodiments. The embodiments provided in the drawings and examples are not intended to limit the scope of the invention in any way.

[0073] Example : Comparative Example 1 : Following the steps described in WO2022136377, an acidic ozone etching solution containing 100 mL / L sulfuric acid and 40 mg / L ozone was used to etch the surface of an ABS plastic part that is 2.5 mm thick, 10 cm wide, and 15 cm long.

[0074] The ABS plastic panel is subjected to the following steps:

[0075] The electrolytic deposition step following electroless nickel plating includes a thick nickel plating layer, followed by acidic copper plating, which is performed at a current density of about 4 A / dm² in a dye-free acidic copper electrolyte to a thickness of up to 40 μm.

[0076] Subsequently, the metallized ABS plastic parts are exposed to compressed air or dried at 25°C for 15 minutes.

[0077] The peel strength of ABS components was measured according to ASTM Test Method B533-85 (re-approved in 2019) Procedure A. ABS panels were determined to have a peel strength of less than 1 N / cm.

[0078] Example 2 : The ABS components were processed according to the steps outlined in Comparative Example 1. Subsequently, all components were placed in a laboratory oven maintained at a constant temperature of 70°C for varying durations from 15 to 60 minutes, as shown in the table below.

[0079] The peel strength of the ABS components was measured according to ASTM Test Method B533-85 (re-approved in 2019) Procedure A. The results are as follows: Figure 1 As shown in the figure, this graph depicts the adhesion strength of a 10×15cm ABS plastic part using different drying times in a laboratory oven.

[0080]

[0081] Example 3 : The ABS parts were processed according to the steps outlined in Comparative Example 1. Subsequently, all parts were placed in a technical oven maintained at a temperature ranging from 75°C to 78°C for different durations of 15 to 60 minutes, as shown in the table below. The results are as follows: Figure 2 As shown in the figure, this graph depicts the adhesion strength of a 10×15cm ABS plastic part using different drying times in a technical oven.

[0082]

[0083] Comparative Example 4 : The ABS panel is treated with a conventional chromium (VI) etching solution instead of the acidic ozone etching solution described above.

[0084] The ABS plastic panel is subjected to the following steps:

[0085] The ABS surface was etched using a chromium (VI) etchant. The initial peel strength of 6 N / cm was significantly higher than that achieved with non-metallic etchants. Subsequently, the parts were annealed in ovens maintained at different temperatures (50°C, 70°C, and 85°C) for 30 to 90 minutes. Figure 3 As shown, at 70°C, a 1.2-fold increase in peel strength was achieved within one hour compared to the initial value. In contrast, ABS etched with an acidic ozone etching solution that had undergone heat treatment at 70°C showed a much higher increase in peel strength compared to the initial value.

[0086] This embodiment demonstrates that the combination of an acidic ozone etching aqueous solution with a heat treatment step following metallization produces adhesion comparable to that achieved with prior art chromium (VI) etching solutions in a more environmentally friendly manner.

[0087] Comparative Example 5 : The steps in the method described in Comparative Example 1 were replaced to determine whether optimization of other steps in the method (including changes in processing time and / or temperature and changes in process steps) produced the same results as the heat treatment steps after metallization, and the results are shown in the table below.

[0088]

[0089] As can be seen from this embodiment, the combination of the heat treatment step alone and the acidic ozone aqueous solution etching step can significantly increase adhesion and thus improve peel strength. In other words, attempts to optimize other steps in the method described herein for metallizing plastic parts have been observed to fail to significantly improve peel strength and have not significantly contributed to increasing adhesion.

Claims

1. A method for metallizing a plastic part, the method comprising the following steps: a. Etching the plastic component by introducing it into an acidic ozone etching aqueous solution. b. Metallizing ozone-etched plastic parts, and c. Heat the ozone-etched and metallized plastic parts in an oven at elevated temperatures for a certain period of time.

2. The method of claim 1, wherein the plastic component is selected from the group consisting of: acrylonitrile butadiene styrene copolymer (ABS), acrylonitrile butadiene styrene copolymer / polycarbonate (ABS / PC), polycarbonate (PC), polyamide (PA), butadiene styrene methacrylate (MBS), polybutylene terephthalate (PBT), styrene-acrylonitrile copolymer (SAN), polyphenylene sulfide (PPS), polyester (PE), polyethylene terephthalate (PET), polyether ether ketone (PEEK), polylactide (PLA), polybutylene succinate (PBS), polylactide / polybutylene succinate (PI-A / PBS), aromatic polymers (LCP), and combinations thereof.

3. The method of claim 2, wherein the plastic component comprises ABS.

4. The method of claim 2, wherein the plastic component comprises ABS / PC.

5. The method of claim 2, wherein the plastic component is a two-component or three-component plastic component comprising two or more types of plastics.

6. The method of claim 1, wherein the elevated temperature is between about 40°C and about 100°C.

7. The method of claim 6, wherein the elevated temperature is between about 70°C and about 80°C.

8. The method of claim 1, wherein the time period is between about 30 minutes and about 90 minutes.

9. The method of claim 8, wherein the time period is between about 45 minutes and about 60 minutes.

10. The method of claim 1, wherein metallization step b) comprises electroless metallization with one or more layers of nickel, copper, cobalt, copper / nickel, nickel / cobalt, or gold.

11. The method of claim 10, wherein the metallization step b) comprises electroplating one or more metal layers on one or more electroless metallization layers.

12. The method of claim 1, further comprising treating the ozone-etched plastic part with an alkaline post-treatment solution prior to the metallization step, optionally wherein the alkaline post-treatment solution is an alkaline ammonium-containing solution.

13. The method of claim 12, further comprising the step of activating the ozone-etched plastic component prior to the metallization step, wherein the step of activating the ozone-etched plastic component comprises contacting the ozone-etched plastic component with an activation solution.

14. The method of claim 1, wherein the ozone-etched and metallized plastic component exhibits a peel strength of at least about 7.0 N / cm, as measured according to ASTM Test Method B533-85 (re-approved in 2019) Procedure A.

15. The method of claim 14, wherein the ozone-etched and metallized plastic component exhibits a peel strength of at least about 8.0 N / cm, as measured according to ASTM Test Method B533-85 (re-approved in 2019) Procedure A.

16. The method of claim 15, wherein the ozone-etched and metallized plastic component exhibits a peel strength of at least about 9.0 N / cm, as measured according to ASTM Test Method B533-85 (re-approved in 2019) Procedure A.

17. The method of claim 16, wherein the ozone-etched and metallized plastic component exhibits a peel strength of at least about 10 N / cm, as measured according to ASTM Test Method B533-85 (re-approved in 2019) Procedure A.

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