A plastic electroplating pretreatment solution containing a functionalized resin and a method for preparing the same

Abstract

The application discloses a plastic electroplating pretreatment liquid containing a functionalized resin, which comprises the following components: 20-35% of a functionalized polyurethane hybrid resin; 1.0-3.0% of reduced graphene oxide; a dispersing agent; 1.0-2.5% of a film-forming aid; 0.05-0.30% of a leveling agent; 0.03-0.20% of a rheological modifier; 0.05-0.10% of an antioxidant; deionized water; and the functionalized polyurethane hybrid resin comprises a polyurethane main skeleton, a compatibilizing segment and an interface functional segment; the compatibilizing segment comprises a styrene segment and / or an acrylonitrile segment and is bonded to a polyurethane side chain or a chain segment end in a copolymerization form; and the functional groups of the interface functional segment comprise one or more combinations of sulfur-containing functional groups, carboxylate, hydroxyl, amide group and ketone carbonyl. The plastic electroplating pretreatment liquid can obtain good substrate adhesion, coating-plating adhesion and electroplating deposition uniformity under the conditions of water-based, low temperature, low viscosity, low film thickness and long storage period.

Description

Technical Field

[0001] This invention belongs to the field of plastic electroplating pretreatment technology, and more specifically, relates to a plastic electroplating pretreatment solution containing functionalized resin and its preparation method. Background Technology

[0002] ABS, with its multiphase structure of acrylonitrile-styrene continuous phase and butadiene rubber dispersed phase, is widely recognized as one of the most suitable engineering plastics for plastic electroplating. Traditional ABS electroplating relies on chromic acid roughening to form a microporous structure, followed by sensitization, activation, and chemical plating to establish the metal layer adhesion interface. Although this route is mature, it suffers from problems such as long process, hexavalent chromium pollution, high palladium activation costs, and heavy waste liquid treatment burden, and it is increasingly difficult to meet the dual requirements of environmental compliance and low-cost manufacturing.

[0003] Existing one-step pretreatment technologies for plastic electroplating typically attempt to construct a conductive layer on the plastic surface using graphene, carbon nanomaterials, conductive polymers, or metal powders, aiming to omit traditional roughening and activation steps. However, existing solutions generally suffer from the following drawbacks: First, the conductive layer relies heavily on surface adhesion to the ABS substrate, making it difficult to simultaneously achieve low sheet resistance and high peel strength. Second, the conductive layer and subsequent metal plating layers often have a planar covering relationship, making it difficult for metal ions to penetrate into the near-surface area of ​​the coating, resulting in insufficient bonding between the plating layer and the conductive layer. Third, many systems rely on strong solvents, high-temperature crosslinking, or multi-component instantaneous reaction systems, which are incompatible with industrial conditions such as open baths, low-viscosity application, and hot air drying at 60–70°C. Fourth, while some systems may have good initial conductivity, they are prone to thickening, sedimentation, flocculation during storage, or swelling and instability in the electroplating solution, leading to decreased adhesion and coating defects.

[0004] When graphene dispersions are directly coated onto ABS substrates, the graphene conductive film alone is insufficient to reliably solve the problems of ABS interface adhesion and coating penetration. Existing graphene / WPU composite coatings do not have molecular design for ABS substrate compatibility and metal ion nucleation sites, making it difficult to simultaneously ensure substrate adhesion, coating-plating adhesion, and electroplating deposition uniformity.

[0005] Therefore, there is an urgent need to develop a new pretreatment solution for plastic electroplating that can achieve good substrate adhesion, coating-plating adhesion and electroplating deposition uniformity under conditions of water, low temperature, low viscosity, low film thickness and long storage period. Summary of the Invention

[0006] The purpose of this application is to overcome the above-mentioned deficiencies of the prior art and provide a plastic electroplating pretreatment solution containing functionalized resin, which can obtain good substrate adhesion, coating-plating adhesion and electroplating deposition uniformity under aqueous, low temperature, low viscosity, low film thickness and long storage period conditions.

[0007] To achieve the above-mentioned objectives, this application provides a plastic electroplating pretreatment solution comprising a functionalized resin, including the following components by weight percentage: Functionalized polyurethane hybrid resin 20-35%; Reduced graphene oxide 1.0–3.0%; A dispersant, wherein the dispersant is 0.5 to 1.5 times the mass of the reduced graphene oxide; Film-forming aid 1.0–2.5%; Leveling agent 0.05–0.30%; Rheology modifier 0.03–0.20%; Antioxidant 0.05-0.10%; Deionized water balance; The functionalized polyurethane hybrid resin comprises a polyurethane main skeleton, compatibilizing segments, and interfacial functional segments. The compatibilizing segments include styrene segments and / or acrylonitrile segments, which are copolymerized and bonded to the polyurethane side chains or segment ends. The functional groups of the interfacial functional segments include one or more combinations of sulfur-containing functional groups, carboxylates, hydroxyl groups, amide groups, and ketone carbonyl groups.

[0008] This invention achieves a technological breakthrough by leveraging the synergistic effect of functionalized polyurethane hybrid resin and rGO conductive filler, combined with precisely measured amounts of dispersants, film-forming aids, leveling agents, rheology modifiers, and antioxidants. This breakthrough results in a low-cost, high-adhesion, environmentally compliant pretreatment solution for plastic electroplating, eliminating the need for precious metals and strong acid roughening, enabling room-temperature film formation, and facilitating Cu-S chemical bonding. The functionalized polyurethane hybrid resin utilizes a three-segment molecular design: a polyurethane main skeleton (mechanical support), compatibilizing segments (plastic compatibility, no roughening required), and interfacial functional segments (Cu-S chemical bonding, hydrophilic guidance). Combined with a continuous rGO conductive network, this achieves penetrating deposition and chemical bonding, increasing copper layer adhesion by 3-5 times compared to traditional processes. Simultaneously, it eliminates roughening and activation processes, and is free of precious metals and heavy metal contamination.

[0009] Preferably, the pretreatment solution has a pH of 7.5–8.8, a viscosity of 20–180 mPa·s at 25°C, a solid content of 20–35%, and a particle size ≤300 nm. The four physical properties of this pretreatment solution—pH 7.5–8.8 (carboxylate stabilization + Cu-S bonding), viscosity 20–180 mPa·s (suitable for various coating processes), solid content 20–35% (single-pass film formation + cost-effectiveness), and particle size ≤300 nm (stability + density + penetration)—are synergistically optimized to achieve stable storage (≥6 months), uniform coating (1-5 μm controllable), full exposure of rGO, and copper ion penetration and deposition across the entire coating chain. This provides a high-adhesion (Grade 0), high-conductivity, and high-yield coating foundation for subsequent electroplating.

[0010] Preferably, the pretreatment solution is dried with hot air at 60–70°C to form a conductive functional layer with a thickness not exceeding 5 μm and a sheet resistance of less than 50 Ω / □. The low drying temperature protects the plastic substrate, allows for ultra-thin exposure of rGO, and enables direct electron access to the interface through high conductivity.

[0011] Preferably, the film-forming aid is one or more of dipropylene glycol methyl ether, tripropylene glycol methyl ether, and propylene glycol methyl ether; and / or, the dispersant is one or more of PVP and polyether nonionic dispersants; and / or, the leveling agent is polyether-modified silicone leveling agent BYK378; and / or, the rheology modifier is HEUR rheology modifier; and / or, the antioxidant is 2,6-di-tert-butyl-p-cresol or a water-based hindered phenolic antioxidant.

[0012] The above-mentioned additives have advantages such as low film-forming temperature, no cracking, excellent leveling, smooth and flat surface, stable dispersion, controllable viscosity, and long shelf life. At the same time, they have no risk of flocculation or gelation and are environmentally friendly with low VOCs.

[0013] Preferably, the polyurethane main skeleton in the functionalized polyurethane hybrid resin is one or two of polycarbonate diol, polyester diol, and polyether diol, and the isocyanate is one or two of IPDI, HDI, and H12MDI.

[0014] In this invention, the number-average molecular weight (Mn) of the functionalized polyurethane hybrid resin is controlled between 20,000 and 30,000 g / mol, the PDI is between 1.6 and 2.0, and the weight-average molecular weight (Mw) is controlled between 80,000 and 120,000 g / mol. This range balances the cohesive strength of the coating with film-forming permeability, providing sufficient mechanical support for electroplating without hindering the penetration of resin molecular chains into the plastic surface.

[0015] This application also provides a method for preparing a plastic electroplating pretreatment solution containing a functionalized resin, comprising the following steps: S1: After dehydrating the polyol, add isocyanate and catalyst under nitrogen protection, and react at 70-85℃ for 2-4 hours to obtain -NCO-terminated prepolymer; S2: Add a carboxyl-containing internal emulsifier to the prepolymer and react for 0.5-2 h. Then add a neutralizing agent to ionize the internal emulsifying groups, then add deionized water for dispersion, and then slowly add a 10-20% (w / w) EDA ethylenediamine aqueous solution for chain extension. The amount of EDA is 0.9-1.0 times the residual-NCO molar ratio to obtain the WPU dispersion. S3: Seed emulsion polymerization; pre-emulsify the monomers St, BA, DAAM, and MAA according to the formulation, add them dropwise to the WPU dispersion at 70-85℃, add persulfate initiator or redox initiation system at the same time, and add 3-mercaptopropionic acid as chain transfer agent, the amount of which accounts for 0.6-1.0% of the total mass of the above monomers, so that the monomers form a hybrid functional layer on the surface or inside of the WPU particles and introduce sulfur-containing bonding sites at the end of the polymer chain; S4: After the reaction is complete, keep warm for 1.5 to 2 hours, adjust the pH to 7.0 to 8.5, filter to remove the gel, add ADH crosslinking agent, stir for 30 minutes to obtain a functionalized polyurethane hybrid resin dispersion with a solid content of 28% to 33%. S5: Add reduced graphene oxide, dispersant and deionized water into a pre-dispersion vessel in proportion. After high-speed shearing for 20 to 40 minutes, introduce it into a sand mill and disperse it with 0.3 to 0.8 mm zirconia beads. Control the slurry temperature not to exceed 40℃ until there are no obvious coarse particles and agglomeration to obtain a reduced graphene oxide dispersion. S6: Compound the following components in the order of functionalized polyurethane hybrid resin dispersion, reduced graphene oxide dispersion, film-forming aid, leveling agent, rheology modifier, and antioxidant. Stir at low speed of 200–400 rpm for 20–60 min, and adjust the pH, viscosity, and solid content to the target values.

[0016] The above preparation method involves synthesizing an -NCO-terminated prepolymer from isocyanate and polyol, introducing hydrophilic groups through a carboxyl-containing internal emulsifier, neutralizing, dispersing in water, and chain-extending to obtain an aqueous polyurethane (WPU) dispersion. Based on this, an acrylate hybrid layer composed of styrene (St), butyl acrylate (BA), diacetone acrylamide (DAAM), and methacrylic acid (MAA) is grafted onto the surface or interior of the WPU particles via seed emulsion polymerization. This hybrid layer, mainly distributed on the particle surface, exhibits high hardness and good compatibility with subsequent electroless metallization. Furthermore, the ketone carbonyl groups provided by DAAM can undergo crosslinking reactions with adipic acid diazid (ADH) added in S4 at room temperature, further improving the resin's cohesive strength and chemical resistance. More importantly, the use of 3-mercaptopropionic acid as a chain transfer agent not only precisely controls the molecular weight of the acrylate hybrid layer (avoiding excessive crosslinking leading to gelation) but also introduces -S- (sulfur) bonding sites at the polymer chain ends. These sulfur atoms have a strong coordination adsorption capacity for metal ions (such as Pd ions, Ni ions, and Cu ions) in the subsequent electroplating solution, which can significantly improve the loading density and uniformity of the catalytic center, thereby accelerating chemical deposition and enhancing the adhesion between the coating and the plastic.

[0017] In this invention, the term "acrylate" is a broad industry term that refers to a polymer system that is primarily composed of (meth)acrylate monomers and may contain other vinyl comonomers.

[0018] In this invention, ADH can crosslink with the DAAM units in the resin at room temperature to form a dense network structure. This avoids premature curing of the treatment solution during storage (ADH reacts slowly with the ketone carbonyl group and is stable inside the container); on the other hand, it rapidly forms a high-strength film that is water-resistant and solvent-resistant after coating and drying, preventing the plating layer from peeling off due to the swelling of the resin by the electroplating solution.

[0019] Preferably, in S1, the isocyanate is IPDI isophorone diisocyanate with an NCO / OH index of 1.5–2.0, a prepolymer -NCO content of 3.5–4.5%, and the catalyst is DBTDL dibutyltin dilaurate, with the catalyst accounting for 0.05% of the total mass of the prepolymer. The IPDI hard segment imparts weather resistance, yellowing resistance, and high hardness; the appropriate -NCO content balances hydrophilicity and water resistance. Simultaneously, the WPU particles formed after prepolymer emulsification have the characteristics of "moderate hardness and surface active groups (carboxyl groups, urethane groups)," facilitating the swelling polymerization of acrylate monomers and the subsequent introduction of -S- bonding sites.

[0020] Preferably, in S2, the carboxyl-containing internal emulsifier is selected as DMPA (dimethylolpropionic acid), accounting for 3-4% of the prepolymer mass; the neutralizing agent is selected as TEA (triethylamine), with a neutralization degree of 85-100%; and the solid content of the WPU dispersion is 30-35%.

[0021] Preferably, in step S3, the monomers St, BA, DAAM, and MAA are pre-emulsified at a mass ratio of 20:18:3:1, wherein the amount of St is 15-25 wt% of the solid content of the WPU dispersion. The pre-emulsification process includes adding 1% by mass of allyloxy polyoxyethylene ether (such as "allyloxy polyoxyethylene ether (APEG-10, EO=10)") and an equal mass of water, followed by high-speed shearing at 2000-3000 rpm for 10-15 min to obtain a pre-emulsion. The pre-emulsion is then added dropwise to the WPU dispersion at 70-85°C, simultaneously adding a persulfate initiator over a time interval of 2-2.5 minutes. h. The above operations yielded a styrene-acrylic hybrid layer with uniform particle size, controllable surface chemical composition, and uniform internal molecular structure. A dropwise addition strategy was used to allow free radical polymerization to proceed at low monomer concentrations, forcing preferential chain transfer reactions in the growing chains. This efficiently utilized the active hydrogens pre-placed on the WPU backbone by S1 / S2 to chemically graft acrylate segments onto the WPU. Simultaneously, precise monomer ratios controlled the performance of the grafted chains, and low amounts of allyloxy polyoxyethylene ether and chain transfer agent ensured the effective introduction of -SH bonding sites. Ultimately, a hybrid resin with high grafting rate, uniform composition, and controllable chain length was obtained, providing an ideal interface with high conductivity, high adhesion, and resistance to electroplating solution corrosion for plastic pretreatment.

[0022] Preferably, in step S4, the ADH crosslinking agent is added slowly in a 10% aqueous solution prepared by DAAM:ADH = 1:1 molar ratio; and / or, in step S5, reduced graphene oxide, dispersant, and deionized water are added to a pre-dispersion vessel at a mass ratio of rGO:PVP:water = 5:3:92, and after high-speed shearing at 2000-3000 rpm for 20-40 min, the mixture is introduced into a sand mill and dispersed with 0.3-0.8 mm zirconia beads, controlling the slurry temperature not to exceed 40°C, until there are no obvious coarse particles and the particle size D90 ≤ 300 nm.

[0023] Step S4 employs a ketone-hydrazine post-crosslinking strategy, where ADH is prepared into a 10% aqueous solution at a precise DAAM:ADH molar ratio of 1:1 and then slowly added. This stoichiometric ratio ensures maximum crosslinking density and eliminates residual functional groups, while the slow addition of the dilute solution effectively prevents localized gelation, achieving uniform crosslinking.

[0024] In step S5, the combination of high-shear pre-dispersion and 0.3–0.8 mm zirconia bead milling process can efficiently exfoliate rGO to D90≤300 nm without damaging its sheet structure; the temperature is controlled at ≤40℃ throughout the process, which effectively prevents graphene from recombinizing and ensures dispersion quality.

[0025] The D90≤300 nm mentioned in this invention specifically refers to the equivalent hydrodynamic diameter (DD) measured by dynamic light scattering (DLS) in a liquid dispersion medium, i.e., the microscopic fineness of the dispersion slurry, rather than the absolute geometric size of the reduced graphene oxide (rGO) two-dimensional sheets. This invention achieves effective exfoliation of rGO stacks under non-destructive shearing. During this process, rGO is in a highly swollen and coated solvated state in the liquid phase, exhibiting an equivalent hydrodynamic diameter in the submicron range. This indicates that the rGO particles achieve excellent monodispersity and anti-entanglement in the liquid phase, ensuring the rheological stability and film uniformity of the pretreatment solution during storage and coating. During the film-forming process of coating drying, as moisture and volatile additives are removed, the rGO sheets coated with functionalized hybrid resin undergo self-assembly under the emulsion template effect. The two-dimensional sheet structure fully unfolds and oriented in three-dimensional space, efficiently constructing an "isolated" three-dimensional conductive network at the edges and grain boundaries of the polymer matrix. This allows the coating to overcome the percolation threshold with extremely low filler content, achieving ultra-low sheet resistance.

[0026] In this invention, rGO is selected with an initial flake diameter D50 ≤ 5 μm. By selecting rGO raw material with D50 ≤ 5 μm, combined with the resin and gentle milling process of this invention, the aim is to effectively peel off the rGO flakes through interlayer shearing rather than strong lattice fragmentation, thus converging the equivalent hydrodynamic particle size to D90 ≤ 300 nm. If the flake diameter is too large, it is prone to self-entanglement and wrinkling in water, making peeling difficult and easily clogging the grinding media and causing rapid settling.

[0027] In some embodiments of the present invention, if 2,6-di-tert-butyl-p-cresol is selected as the antioxidant, BHT can be dissolved in the monomer (such as styrene) during the monomer pre-emulsification stage of S3 to participate in polymerization dispersion, or BHT can be added in advance dissolved in the film-forming aid.

[0028] In some embodiments of the present invention, if pinholes or bubbles are subsequently found in the film formed by the pretreatment solution, 0.05-0.2% of defoamer (such as Tego-901W or BYK-024) can be added. Half of the defoamer can be added in stage S5 to eliminate grinding bubbles, and the remainder can be added during the final compounding in stage S6 to completely eliminate pinhole defects in the wet film.

[0029] In this invention, because the functionalized polyurethane hybrid resin contains thioether bonds and possibly residual thiol groups, it is prone to oxidation during hot air drying (60–70°C) and storage, leading to a decrease in the interfacial activity of the conductive layer. This invention incorporates 0.05–0.10% antioxidant (such as hindered phenols or phosphites) to effectively protect the sulfur-containing structure and maintain the coating's ability to adsorb and reduce metal ions.

[0030] In this invention, the pretreatment solution for plastic electroplating is applied to the surface of degreased ABS plastic, and after drying, it directly enters the subsequent chemical plating or electroplating process. During electroplating, metal ions enter the near-surface region and form penetrating deposition and fixation structures near the rGO conductive network and resin polar functional sites. The degreasing operation can be performed using conventional alkaline degreasing agents containing sodium hydroxide, trisodium phosphate, sodium carbonate, sodium silicate, and surfactants (such as OP-10). The temperature is controlled at 55-65°C for 5-15 minutes, removing oil stains through saponification and emulsification. This method is suitable for most ABS substrates.

[0031] Compared with the prior art, this application has the following technical effects: The plastic electroplating pretreatment liquid of the present invention is an integrated conductive primer that integrates three major functions, namely "plastic surface modification, conductive layer construction, and metal bonding promotion", into a one-step coating process. It is expected to replace the traditional complicated and highly polluting electroplating pretreatment process, and is especially suitable for high-quality plastic electroplating in the fields of 3C electronics, automotive decoration, and smart home appliances.

[0032] The functionalized polyurethane hybrid resin of this invention achieves penetrating deposition and chemical bonding through a three-segment molecular design of polyurethane main skeleton (mechanical support) + compatibilizing segment (plastic compatibility, no roughening required) + interface functional segment (Cu-S chemical bonding, hydrophilic guidance), combined with rGO continuous conductive network. This improves the copper layer adhesion by 3-5 times compared with traditional processes, while eliminating roughening and activation processes, and is free of precious metals and heavy metal pollution.

[0033] The preparation process of this invention enables the large-scale production of plastic electroplating pretreatment solution under mild conditions, low cost, easy scale-up, and environmentally friendly. All steps are carried out at normal pressure and ≤85°C, without the need for special equipment, with good batch stability, and the raw material cost is reduced by 40-60% compared with the traditional palladium activation system. Attached Figure Description

[0034] Figure 1 The infrared spectrum of the functionalized polyurethane hybrid resin prepared in Example 2 of this invention; Figure 2 The TGA image is of the functionalized polyurethane hybrid resin prepared in Example 2 of this invention; Figure 3The S 2p spectrum of the coating formed by the plastic electroplating pretreatment solution prepared in Example 2 of the present invention; Figure 4 This is the XPS spectrum of the surface (near the interface) after electroplating in Example 2 of the present invention, and the S 2p high-resolution spectrum. Figure 5 This is an optical microscope image of the cross-section after electroplating in Embodiment 2 of the present invention. Detailed Implementation

[0035] To enable those skilled in the art to better understand the present invention, the present invention will now be further described in conjunction with specific embodiments.

[0036] In the following description, the embodiments of this application are for illustrative purposes and not for limiting purposes, so as to provide a thorough understanding of the embodiments. However, those skilled in the art will understand that the embodiments of this application can also be implemented in other embodiments without these specific details. In other cases, detailed descriptions of well-known preparation methods have been omitted so as not to obscure the description of the embodiments of this application with unnecessary details. Unless otherwise specified, the raw materials used in the following embodiments are all commercially available.

[0037] It should also be understood that the terms "comprising," "including," "having," and their variations all mean "including but not limited to," unless otherwise specifically emphasized. Only content related to the inventive points is described here; other details can be obtained from related technologies and will not be elaborated further here. The following embodiments merely illustrate several implementations of this application, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of this patent application. It should be noted that those skilled in the art can make several modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

[0038] The specific implementation method is as follows: Example 1

[0039] A plastic electroplating pretreatment solution containing functionalized resin, the components and their weight percentages are as follows: Functionalized polyurethane hybrid resin (30% solids content) 25%; Reduced graphene oxide by 1.5%; Dispersant (PVP) 1.5% (i.e., 1.0 times the mass of reduced graphene oxide); Film-forming aid (dipropylene glycol methyl ether) 1.2%; Leveling agent (polyether-modified siloxane) 0.10%; Rheology modifier (HEUR type) 0.05%; Antioxidant (2,6-di-tert-butyl-p-cresol) 0.06%; Deionized water balance.

[0040] Preparation method: S1: 700 g of dehydrated polycarbonate diol (number average molecular weight: 800) was mixed with 300 g of isophorone diisocyanate (NCO / OH index 1.54) and 0.5 g of DBTDL dibutyltin dilaurate catalyst (0.05% of the total mass of the prepolymer) under nitrogen protection and reacted at 75 °C for 3 h to obtain a prepolymer with an -NCO content of approximately 4.0%.

[0041] S2: Add 35 g of dimethylolpropionic acid, which accounts for 3.5% of the prepolymer mass, react for 1 h, add 26.5 g of triethylamine to neutralize to 95% ionization, then add about 2325 g of deionized water for dispersion, and then slowly add 15% ethylenediamine aqueous solution (at a rate of 0.95 times the residual-NCO molar ratio) to obtain a WPU dispersion with a solid content of 32%.

[0042] S3: Pre-emulsify 162 g St, 146 g BA, 24.3 g DAAM, and 8.1 g MAA at a mass ratio of 20:18:3:1 (add 3.4 g of allyloxy polyoxyethylene ether APEG-10 and 340 g of deionized water, and shear at 2500 rpm for 12 min). Add the pre-emulsion dropwise to the WPU dispersion at 80°C, simultaneously adding 3.4 g of ammonium persulfate initiator (dissolve 3.4 g of ammonium persulfate in approximately 30–50 g of deionized water to prepare an initiator aqueous solution, and add it dropwise with the pre-emulsion). Dissolve 2.7 g of 3-mercaptopropionic acid in a portion of the pre-emulsion and add it dropwise with the initiator solution. The addition time is 2 h.

[0043] S4: After the reaction is complete, keep warm for 1.5 h, adjust the pH to 8.0, filter to remove the gel, add 125 g of 10% ADH aqueous solution at a DAAM:ADH molar ratio of 1:1, stir for 30 min to obtain the functionalized polyurethane hybrid resin dispersion.

[0044] S5: Add 25 g of reduced graphene oxide, 15 g of PVP and 460 g of deionized water to a pre-dispersion vessel at a mass ratio of rGO:PVP:water = 5:3:92. After high-speed shearing at 2500 rpm for 30 min, introduce the mixture into a sand mill and disperse it with 0.3-0.8 mm zirconia beads, controlling the temperature to ≤40℃, until D90 ≤300 nm.

[0045] S6: Add the functionalized polyurethane hybrid resin dispersion → reduced graphene oxide dispersion → film-forming aid → leveling agent → rheology modifier → antioxidant to the mixing tank in the following order, and stir at 300 rpm for 40 min. The antioxidant is pre-dissolved in the film-forming aid before being added.

[0046] Samples were then taken to test pH, viscosity, and solids content.

[0047] pH adjustment: Adjust to the target value using 10% ammonia or DMEA (dimethylethanolamine); Viscosity adjustment: Add deionized water (to reduce viscosity) or add HEUR rheology modifier diluent (to increase viscosity) to adjust to the target value; Solid content adjustment: Add deionized water or concentrate under reduced pressure to adjust to the target value.

[0048] After adjustment, continue stirring for 15 minutes, then filter through a 200-mesh filter before discharging.

[0049] Properties of the obtained pretreatment solution: It has a pH of 8.1, a viscosity of 95 mPa·s at 25℃, a solid content of 28.5%, and a particle size D90 of 260 nm. Example 2

[0050] A plastic electroplating pretreatment solution containing functionalized resin, the components and their weight percentages are as follows: Functionalized polyurethane hybrid resin (30% solids content) 30%; Reduced graphene oxide 2.0%; Dispersant (PVP) 1.6% (i.e., 0.8 times the mass of reduced graphene oxide); Film-forming aid (dipropylene glycol methyl ether) 1.5%; Leveling agent (polyether-modified siloxane) 0.15%; Rheology modifier (HEUR type) 0.08%; Antioxidant (2,6-di-tert-butyl-p-cresol) 0.08%; Deionized water balance.

[0051] Preparation method: The process is basically the same as in Example 1, except that: the reaction temperature in S1 is 80°C; the amount of chain transfer agent in S3 is 0.7% of the total mass of the monomer, and the dropping time is 2.2 h; in S5, the mixture is sand-milled to D90 = 245 nm; in S6, after compounding, the pH is adjusted to 8.0, the viscosity to 105 mPa·s, and the solid content to 30.2%, and the antioxidant is pre-dissolved in the film-forming aid before being added.

[0052] Properties of the obtained pretreatment solution: The pH is 8.0, the viscosity at 25℃ is 105 mPa·s, the solid content is 30.2%, and the particle size D90 is 245 nm. Example 3

[0053] A plastic electroplating pretreatment solution containing functionalized resin, the components and their weight percentages are as follows: Functionalized polyurethane hybrid resin (30% solids content) 35%; Reduced graphene oxide 2.8%; Dispersant (PVP) 3.36% (i.e., 1.2 times the mass of reduced graphene oxide); Film-forming aid (dipropylene glycol methyl ether) 2.0%; Leveling agent (polyether-modified siloxane) 0.25%; Rheology modifier (HEUR type) 0.15%; Antioxidant (water-based antioxidant 1010) 0.10%; Deionized water balance.

[0054] Preparation method: The process is basically the same as in Example 1, except that: in S1, the NCO / OH index is 1.6 and the prepolymer-NCO content is 4.5%; in S2, the WPU dispersion has a solid content of 35%; in S3, the chain transfer agent is used at 1.0% of the total monomer mass and the reaction temperature is 85°C; in S5, the mixture is sand-milled to D90 = 290 nm; and in S6, after compounding, the pH is adjusted to 7.9, the viscosity to 145 mPa·s, and the solid content to 33.5%.

[0055] Properties of the obtained pretreatment solution: The pH is 7.9, the viscosity at 25℃ is 145 mPa·s, the solid content is 33.5%, and the particle size D90 is 290 nm. Example 4

[0056] A plastic electroplating pretreatment solution containing functionalized resin, the components and their weight percentages are as follows: Functionalized polyurethane hybrid resin (30% solids content) 20%; Reduced graphene oxide 1.0%; Dispersant (PVP) 0.5% (i.e., 0.5 times the mass of reduced graphene oxide); Film-forming aid (dipropylene glycol methyl ether) 1.0%; Leveling agent (polyether-modified siloxane) 0.05%; Rheology modifier (HEUR type) 0.03%; Antioxidant (2,6-di-tert-butyl-p-cresol) 0.05%; Deionized water balance.

[0057] Preparation method: The reaction was basically the same as in Example 1, except that: the reaction temperature in S1 was 70°C; the amount of chain transfer agent in S3 was 0.6% of the total mass of the monomer, and the dropping time was 2.5 h; the pH in S4 was adjusted to 7.5; the mixture in S5 was milled to D90 = 210 nm; and after compounding in S6, the pH was adjusted to 8.3, the viscosity to 65 mPa·s, and the solid content to 24.5%.

[0058] Properties of the obtained pretreatment solution: It has a pH of 8.3, a viscosity of 65 mPa·s at 25℃, a solid content of 24.5%, and a particle size D90 of 210 nm. Example 5

[0059] A plastic electroplating pretreatment solution containing functionalized resin, the components and their weight percentages are as follows: Functionalized polyurethane hybrid resin (30% solids content) 28%; Reduced graphene oxide by 2.5%; Dispersant (PVP) 3.75% (i.e., 1.5 times the mass of reduced graphene oxide); Film-forming aid (dipropylene glycol methyl ether) 2.5%; Leveling agent (polyether-modified siloxane) 0.30%; Rheology modifier (HEUR type) 0.20%; Antioxidant (water-based antioxidant 1010) 0.09%; Deionized water balance.

[0060] Preparation method: The process is basically the same as in Example 1, except that: in S1, polyester diol is used and the reaction temperature is 85°C; in S3, the amount of chain transfer agent is 0.9% of the total mass of the monomers and the dropping time is 2 h; in S5, the mixture is sand-milled to D90=280 nm; and in S6, after compounding, the pH is adjusted to 7.8, the viscosity to 160 mPa·s, and the solid content to 32.0%.

[0061] Properties of the obtained pretreatment solution: The pH is 7.8, the viscosity at 25℃ is 160 mPa·s, the solid content is 32.0%, and the particle size D90 is 280 nm. Example 6

[0062] A plastic electroplating pretreatment solution containing functionalized resin, the components and their weight percentages are as follows: Functionalized polyurethane hybrid resin (30% solids content) 32%; Reduced graphene oxide 3.0%; Dispersant (PVP) 3.0% (i.e., 1.0 times the mass of reduced graphene oxide); Film-forming aid (dipropylene glycol methyl ether) 1.8%; Leveling agent (polyether-modified siloxane) 0.20%; Rheology modifier (HEUR type) 0.10%; Antioxidant (2,6-di-tert-butyl-p-cresol) 0.07%; Deionized water balance.

[0063] Preparation method: The process is basically the same as in Example 1, except that: in S1, polyether diol is used and the NCO / OH index is 1.7; in S3, the amount of chain transfer agent is 0.8% of the total mass of the monomers and the reaction temperature is 75°C; in S4, the pH is adjusted to 8.5; in S5, the mixture is milled to D90 = 295 nm; and in S6, after compounding, the pH is adjusted to 7.7, the viscosity to 175 mPa·s, and the solid content to 34.0%.

[0064] Properties of the obtained pretreatment solution: The pH is 7.7, the viscosity at 25℃ is 175 mPa·s, the solid content is 34.0%, and the particle size D90 is 295 nm. Comparative Example 1

[0065] Non-functionalized resin, using ordinary polyurethane.

[0066] Components: Ordinary polyurethane resin (30% solid content) 30%; reduced graphene oxide 2.0%; dispersant (PVP) 2.0%; film-forming aid 1.5%; leveling agent 0.15%; rheology modifier 0.08%; antioxidant 0.08%; deionized water balance.

[0067] Preparation method: Except for S1–S4, which do not undergo functionalization modification, the remaining steps are the same as in Example 2. Ordinary polyurethane resin is synthesized using IPDI and polycarbonate diol according to conventional methods, without introducing compatibilizing segments such as styrene and acrylonitrile, or sulfur-containing interfacial functional segments.

[0068] performance: pH 8.0, viscosity 100 mPa·s, solid content 29.5%, particle size D90 320 nm. Comparative Example 2

[0069] Non-reduced graphene oxide.

[0070] Components: Functionalized polyurethane hybrid resin (30% solid content) 30%; dispersant (PVP) 0%; film-forming aid 1.5%; leveling agent 0.15%; rheology modifier 0.08%; antioxidant 0.08%; deionized water balance (excluding rGO and dispersant).

[0071] Preparation method: Step S5 is omitted; the rest is the same as in Example 2.

[0072] performance: pH 8.2, viscosity 110 mPa·s, solid content 30.0%, particle size D90 260 nm. Comparative Example 3

[0073] Components: Conventional acrylic resin (30% solids content) 30%; reduced graphene oxide 2.0%; dispersant (PVP) 2.0%; film-forming aid 1.5%; leveling agent 0.15%; rheology modifier 0.08%; antioxidant 0.08%; deionized water balance.

[0074] Preparation method: The acrylic resin was prepared by conventional emulsion polymerization (St, BA, MMA copolymer, without DAAM, MAA and sulfur-containing chain transfer agents), without polyurethane-acrylic hybridization or functionalization modification. The remaining steps are the same as in Example 2.

[0075] performance: pH 8.0, viscosity 98 mPa·s, solid content 29.0%, particle size D90 280 nm. Comparative Example 4

[0076] Components and weight percentages: Same as Example 2: Functionalized polyurethane hybrid resin (sulfur-free) 30%; Reduced graphene oxide 2.0%; Dispersant (PVP) 1.6% (i.e., 0.8 times the mass of reduced graphene oxide); Film-forming aid (dipropylene glycol methyl ether) 1.5%; Leveling agent (polyether-modified siloxane) 0.15%; Rheology modifier (HEUR type) 0.08%; Antioxidant (2,6-di-tert-butyl-p-cresol) 0.08%; Deionized water balance.

[0077] Preparation method: It is basically the same as Example 2, except that: In S3: St, BA, DAAM, and MAA were pre-emulsified at a mass ratio of 20:18:3:1. The pre-emulsified solution was added dropwise to the WPU dispersion at 80°C, while ammonium persulfate initiator was added dropwise over a period of 2 hours. No 3-mercaptopropionic acid chain transfer agent was added (i.e., the polymer chain ends did not contain sulfur-containing functional groups). The remaining steps S1, S2, S4, S5, and S6 were the same as in Example 2. In S6, the pH was adjusted to 8.0, the viscosity to 108 mPa·s, and the solid content to 29.8%.

[0078] Performance results: The pH is 8.0, the viscosity at 25℃ is 108 mPa·s, the solid content is 29.8%, and the particle size D90 is 320 nm (obvious agglomeration is observed). Comparative Example 5

[0079] Components and weight percentages: Same as Example 2: Functionalized polyurethane hybrid resin (non-polar functional groups) 30%; Reduced graphene oxide 2.0%; Dispersant (PVP) 1.6%; Film-forming aid (dipropylene glycol methyl ether) 1.5%; Leveling agent (polyether-modified siloxane) 0.15%; Rheology modifier (HEUR type) 0.08%; Antioxidant (2,6-di-tert-butyl-p-cresol) 0.08%; Deionized water balance.

[0080] Preparation method: It is basically the same as Example 2, except that: In S3: St and BA are pre-emulsified at a mass ratio of 20:18 (without adding DAAM and MAA), meaning no amide groups (DAAM) and carboxylic acid groups (MAA) are introduced. Therefore, when ADH is added in S4, there are no cross-linking targets, and a ketone carbonyl cross-linking network cannot be formed. The remaining S1, S2, S4 (ADH does not actually react), S5, and S6 are the same as in Example 2. In S6, the pH is adjusted to 8.1, the viscosity to 112 mPa·s, and the solid content to 30.1%.

[0081] Performance results: pH 8.1, viscosity at 25℃ 112 mPa·s, solid content 30.1%, particle size D90 380 nm (severe agglomeration).

[0082] Performance testing: Pretreatment solution performance indicators: pH value was measured using a pH meter, viscosity was measured using a rotational viscometer (25℃), solid content was measured using an oven drying method (105℃, 2h), and particle size was measured using dynamic light scattering (DLS).

[0083] Pretreatment solution storage stability test Stability under normal temperature storage: 6 months at 25±2℃ under sealed conditions, GB / T 6753.3-1986; Stability under accelerated thermal storage: 30 days at 50±2℃, GB / T 6753.3-1986; Freeze-thaw stability: -5℃ for 24 hours → 25℃ for 24 hours, repeated 3 times, ASTM D2243-14. Test results are shown in Table 1.

[0084] Pretreatment solution coating sheet resistance test: The pretreatment solution was immersed in the ABS substrate surface and dried under 60-70℃ hot air for 2-5 minutes, with a coating thickness ≤5 μm. The surface resistivity (sheet resistance) of the coating was measured using a four-probe tester. The test results are shown in Table 1.

[0085] Post-electroplated performance indicators: The pretreatment solution was sprayed onto the ABS board and dried with hot air at 70℃ for 5 min (film thickness ≤ 5 μm). Then, acid copper plating (2 A / dm², 30 min) was performed, with a coating thickness of approximately 10 μm. Nickel / chromium plating can be continued as needed. The specific testing methods after electroplating are as follows.

[0086] I. Coating Appearance The applicable standard is GB / T 12609-2005, "Sampling Inspection of Electrodeposited Layers and Related Finishing Layers". During testing, visual observation is conducted at a distance of 30 cm from the sample under natural light or a D65 standard light source; simultaneously, a 20x optical microscope is used to scan the entire coating surface to check for microscopic defects. The judgment criteria are: the coating should be uniform, bright, free of pitting, pinholes, incomplete plating, burning, dendritic crystals, blistering, and peeling.

[0087] II. The Combination Force of the Grid Method The standard adopted is GB / T 9286-1998 "Cross-cut Test for Paints and Varnishes". During the test, a cross-cut tester (6 blades, 1 mm spacing) is used to cut 100 1×1 mm squares on the coating surface, applying enough force to penetrate the coating to the substrate. After removing the scratches with a soft brush, 3M 600 tape is applied to the marked area, and a rubber roller is used to press it firmly to remove air bubbles. Then, the tape is quickly and vertically pulled up. This process is repeated three times. The judgment index is grade 0, meaning the cut edge is completely smooth with no squares peeling off.

[0088] III. Thermal shock (thermal cycling) The applicable standards are GB / T 2423.22-2012 "Environmental Testing - Part 2: Test Methods - Test N: Temperature Change" and IPC-TM-650 2.6.7 "Thermal Shock Test". During testing, the electroplated sample is placed in an oven at 85±2℃ for 30 minutes, then immediately immersed in a 0±2℃ ice-water mixture (completely submerged) for 30 seconds. It is then removed and air-dried at room temperature (23±2℃) for 5 minutes. This constitutes one cycle, which is repeated 10 times. The plating condition is checked after every two cycles. The judgment criteria are: after 10 cycles, the plating should show no blistering, peeling, cracking, or discoloration. Slight discoloration at the edges is permissible, but blistering is not allowed.

[0089] IV. Thermal shock (high temperature and high humidity) The standard followed is GB / T 2423.3-2016 "Environmental Testing - Part 2: Test Methods - Cab: Constant Humidity and Heat Test". During testing, the electroplated samples are vertically suspended in a constant temperature and humidity chamber, with no contact between samples. The conditions are set at 85±2℃ and 85±3% RH for 96 hours. After removal, the samples are left at room temperature for 2 hours to recover, and then the appearance and adhesion of the coating are inspected. The judgment criteria are: after 96 hours, the coating shows no discoloration, no blistering, no rust, no peeling, and the cross-cut adhesion is not lower than grade 1.

[0090] V. Thermal Shock (Reflow Soldering Simulation) The applicable standards are J-STD-003C "Solderability Test of Printed Circuit Boards" (Reflow Solderability Section) and IPC-TM-6502.6.27 "Thermal Stress Test". During testing, the electroplated sample is passed through a reflow oven with a peak temperature of 260±5℃ held for 10 seconds. It is then removed and cooled to room temperature. This process is repeated three times, and the plating condition is checked after each pass. The criteria for evaluation are: no blistering, no delamination, no melting, and no cracks after three reflow soldering cycles. Slight discoloration is permissible, but blistering is not.

[0091] VI. Neutral Salt Spray Test The standard followed is GB / T 10125-2012 "Artificial Atmosphere Corrosion Test - Salt Spray Test". During the test, a 5±1% NaCl solution is prepared, with the pH adjusted to 6.5–7.2. The salt spray chamber temperature is controlled at 35±2℃, and the salt spray deposition rate is 1–2 mL / 80 cm²·h. The sample is placed at a 15–30° angle to the vertical direction, with the non-test surface sealed for protection. Continuous spraying is performed for 48 hours. After removal, the sample is rinsed with running water for 5 minutes and dried at room temperature for 2 hours before inspection. The judgment criteria are: after 48 hours, the corrosion area ≤5%, no blistering, no peeling, no rust, and slight discoloration at the edges is permissible.

[0092] VII. Coating Hardness The standard followed is GB / T 4340.1-2009 "Metallic Materials - Vickers Hardness Test - Part 1: Test Method". During testing, the electroplated sample is mounted and cured, and the surface is polished to a mirror finish. A micro Vickers hardness tester (25 g load, 10 s holding time) is used to measure the diagonal length of the indentation at five different locations on the plating cross-section (avoiding edges and defects). The HV value is calculated and the average value is taken. The judgment criterion is: the hardness of the copper plating is not less than 120 HV.

[0093] 8. Coating roughness The standard adopted is GB / T 1031-2009 "Geometric Specifications for Products (GPS) - Surface Roughness Parameters and Their Values ​​by Surface Structure Profilometry". During testing, a white light interferometer or a stylus-type profilometer is used. The sampling length is 0.8 mm, and the evaluation length is 5.0 mm. Five different areas on the sample surface are selected to measure the Ra value (arithmetic mean deviation of the profile), and the average value is taken. The judgment criterion is: Ra not greater than 0.3 μm.

[0094] IX. Electroplating Rate The industry-standard weighing method was used for testing. During testing, the ABS substrate was coated with a pretreatment solution and dried, then weighed using an analytical balance (accurate to 0.1 mg), and recorded as W0. Electroplating was then performed in an acidic copper plating solution at a current density of 2 A / dm² for 30 min. After electroplating, the sample was rinsed with deionized water, dried, and weighed again, recorded as W1. The electroplating rate was calculated using the formula (W1 - W0) / (plating area × 0.5 h), in g / dm²·h. The test was repeated three times, and the average value was taken. The judgment criterion was: an electroplating rate of not less than 0.45 g / dm²·h.

[0095] The test results are shown in Table 1. Comparative Example 2 could not be electroplated or subjected to subsequent performance tests due to the lack of reduced graphene oxide.

[0096] Table 1-1: Comparison of Test Results project Shear resistance (Ω / □) Coating appearance Cross-grid bonding force Salt spray 48h Coating hardness (HV) Roughness Ra (μm) Electroplating rate (g / dm²·h) Example 1 45 Even gloss Level 0 Corrosion <1% 128 0.22 0.52 Example 2 39 Even gloss Level 0 Corrosion <1% 135 0.18 0.58 Example 3 35 Even gloss Level 0 Corrosion <1% 142 0.15 0.62 Example 4 46 Glossy, with minor imperfections at the edges Level 0 2% corrosion 122 0.28 0.48 Example 5 37 Even gloss Level 0 Corrosion <1% 138 0.19 0.56 Example 6 32 Even gloss Level 0 Corrosion <1% 145 0.14 0.64 Comparative Example 1 95 Pockmarks, unevenness Level 2 15% corrosion 95 0.45 0.35 Comparative Example 2 <![CDATA[>10 6 ]]> Unable to be plated / / / / / Comparative Example 3 63 Localized plating defects Level 2 10% corrosion 102 0.38 0.38 Comparative Example 4 76 Unevenness, dullness Level 1-2 8% corrosion 98 0.42 0.32 Comparative Example 5 113 Severe plating defects Level 3 25% corrosion 88 0.55 0.25 Table 1-2: Comparison of Test Results project Thermal shock (85℃ / 0℃, 10 cycles) Thermal shock (85℃ / 85% RH, 96 h) Thermal shock (260℃ reflow soldering, 3 times) Storage stability at room temperature for 6 months Storage stability accelerated by thermal acceleration in 30 days Storage stability after 3 freeze-thaw cycles Example 1 No abnormalities No abnormalities No foaming No stratification, particle size +8%, viscosity +6%. Particle size +12%, viscosity +10% No demulsification, particle size 298 nm Example 2 No abnormalities No abnormalities No foaming No stratification, particle size +6%, viscosity +5%. Particle size +10%, viscosity +8% No demulsification, particle size 275 nm Example 3 No abnormalities No abnormalities No foaming No stratification, particle size +10%, viscosity +12%. Particle size +15%, viscosity +15% No demulsification, particle size 325 nm Example 4 Microbubbling at the edges Slight discoloration Slight bubbling at the edges (3rd time) No stratification, particle size +5%, viscosity +4%. Particle size +8%, viscosity +7% No demulsification, particle size 235 nm Example 5 No abnormalities No abnormalities No foaming No stratification, particle size +9%, viscosity +10% Particle size +14%, viscosity +14% No demulsification, particle size 318 nm Example 6 No abnormalities No abnormalities No foaming No stratification, particle size +11%, viscosity +14%. Particle size +18%, viscosity +18% No demulsification, particle size 342 nm Comparative Example 1 6th cycle of peeling Severe bubbling and discoloration First foaming Slight stratification, particle size +22% Significant sedimentation, particle size +35% Do not use if the milk has broken. Comparative Example 2 / / / No stratification, particle size +7% Particle size +11%, viscosity +9% No demulsification, particle size 285 nm Comparative Example 3 The bubbling intensifies in the 6th cycle. Localized blistering Second bubbling Slight precipitation, particle size +18% Layering, particle size +28% Do not use if the milk has broken. Comparative Example 4 The bubbling intensifies in the 5th cycle. Edge discoloration, microbubbles Second bubbling Slight aggregation, particle size +20% Precipitation, particle size +30% Breast breaking Comparative Example 5 Large-scale peeling during the third cycle Completely peeled off First erosion and spalling Clear stratification, particle size +30% Severe settlement, unusable Breast breaking As shown in Table 1, Example 2 has the best overall performance, Example 6 has the best conductivity but slightly lower stability, Examples 1 and 4 have the best storage stability but relatively weak conductivity, and Examples 3 and 5 are in between.

[0097] Comparative Example 1 uses ordinary polyurethane resin instead of functionalized polyurethane hybrid resin. Its sheet resistance is as high as 95 ohms per square, adhesion drops to level two, and peeling occurs after the sixth thermal cycle, indicating poor storage stability. The root cause is that ordinary polyurethane does not contain compatibilizing segments and interfacial functional segments, failing to effectively disperse reduced graphene oxide and unable to form sulfur-copper chemical bonds, resulting in a discontinuous conductive layer, poor adhesion, and easy delamination and precipitation. Comparative Example 2 does not add any reduced graphene oxide. Its sheet resistance is in an insulating state, making electroplating impossible. This proves that reduced graphene oxide is the sole source of conductivity. This comparative example actually has the best storage stability because it does not contain solid particles. Comparative Example 3 uses conventional acrylic resin instead of functionalized polyurethane hybrid resin. Its sheet resistance is 63 ohms per square, adhesion is level two, foaming occurs after the sixth thermal cycle, and storage stability is poor. The reason is that acrylic resin lacks a polyurethane backbone, resulting in insufficient film-forming properties and adhesion, poor compatibility with reduced graphene oxide, and inability to form a cross-linked network. Comparative Example 4 does not add trimercaptopropionic acid during synthesis, therefore the polymer does not contain sulfur-containing functional groups. Its sheet resistance is 76 ohms per square, adhesion is grade I to II, and it bubbles after the fifth thermal cycle. The root cause is that the lack of sulfur-containing functional groups reduces the dispersibility of the reduced graphene oxide and prevents the formation of sulfur-copper chemical bonds. The interfacial bonding relies solely on physical adsorption, making it prone to failure under thermal shock. Comparative Example 5 did not include DAAM and MAA monomers in its synthesis, therefore the resin lacks amide and carboxylic acid groups and cannot form a ketone carbonyl crosslinking network. Its performance deteriorates the most severely, with a sheet resistance as high as 113 ohms per square, adhesion grade II to III, complete peeling after the third thermal cycle, and extremely poor storage stability. This is because the lack of carboxylic acid groups leads to the loss of electrostatic stability, and the lack of amide and ketone carbonyl groups results in the absence of hydrogen bonds and crosslinking networks, causing the conductive layer structure to collapse. The reduced graphene oxide severely aggregates, failing to form an effective conductive pathway and interfacial bonding layer.

[0098] The functionalized polyurethane hybrid resin prepared in Example 2, which exhibited superior performance, was subjected to infrared and TGA tests. Simultaneously, the pretreatment solution from Example 2 formed a coating on the surface of an ABS substrate, and the S 2p spectrum of the coating surface was tested. Then, copper was further electroplated, followed by chromium plating. The XPS spectrum (S 2p high-resolution spectrum) of the copper and the coating surface (near the interface) after electroplating was tested, as well as a cross-sectional optical microscope image of the entire electroplated surface.

[0099] See Figure 1 The functionalized polyurethane hybrid resin prepared in Example 2 has the following core characteristic in its FTIR spectrum: ~1730 cm⁻¹ -1 Extremely strong C=O peak (ester / carbamate), ~3320 cm⁻¹ -1 Broad NH peak (polyurethane), ~1550 / 1400cm -1 Paired carboxylate peaks (successfully dispersed in water), ~1640 cm⁻¹ -1Amide peak (DAAM-ADH ketone hydrazine crosslinking), ~760 / 700 cm⁻¹ -1 Benzene ring bimodal (St), ~2550 cm⁻¹ -1 No thiol peak was observed (MPA has already reacted). See also Figure 2 The TGA curve shows two clear peaks for maximum weight loss rates: T_max1 (~300℃) is attributed to the decomposition of the hard segments of polyurethane, and T_max2 (~380-400℃) is attributed to the decomposition of the polyacrylate phase and the soft segments of polyurethane. This bimodal characteristic is direct evidence of the chemical hybridization (rather than physical blending) of polyurethane and acrylate and its microscopic phase separation structure, and also proves that the material possesses both flexibility (thermal shock resistance) and interfacial compatibility (anchoring with ABS).

[0100] like Figure 3 , Figure 4 As shown, Figure 3 The S 2p spectrum of the surface before electroplating is shown. The peak positions are consistent with those of the "sulfur-containing functional groups" (163~164 eV is CS, 164.7 eV is SS). Figure 4 The image shows the XPS spectrum of the surface (near the interface) after electroplating. The S 2p spectrum shows that the binding energy of sulfur shifts to 161.8 eV after electroplating. This position is a characteristic region of Cu-S bond, indicating that a chemical bond has been formed between sulfur and copper.

[0101] like Figure 5 As shown in the image, the structure consists of an ABS substrate (bottom layer), a conductive functional layer (approximately 3.5 μm thick at the junction with metallic copper), an electroplated copper layer (middle layer, approximately 10 μm thick), and a chromium layer approximately 4 μm thick above the copper layer. The conductive functional layer, approximately 3.5 μm thick, interpenetrates with the ABS substrate at its lower boundary, creating a blurred interface; its upper boundary is adjacent to the electroplated copper layer, with a transition zone visible at the interface. This indicates that sulfur-containing functional groups guide preferential copper nucleation, forming an interdiffusion interface.

[0102] Based on the disclosure and teachings of the foregoing specification, those skilled in the art can make changes and modifications to the above embodiments. Therefore, the present invention is not limited to the specific embodiments disclosed and described above, and some modifications and changes to the present invention should also fall within the protection scope of the claims of the present invention. Furthermore, although some specific terms are used in this specification, these terms are only for convenience of explanation and do not constitute any limitation on the present invention.

Claims

1. A pretreatment solution for plastic electroplating comprising functionalized resin, characterized in that, Includes the following components by weight percentage: Functionalized polyurethane hybrid resin 20-35%; Reduced graphene oxide 1.0–3.0%; A dispersant, wherein the dispersant is 0.5 to 1.5 times the mass of the reduced graphene oxide; Film-forming aid 1.0–2.5%; Leveling agent 0.05–0.30%; Rheology modifier 0.03–0.20%; Antioxidant 0.05-0.10%; Deionized water balance; The functionalized polyurethane hybrid resin comprises a polyurethane main skeleton, compatibilizing segments, and interfacial functional segments. The compatibilizing segments include styrene segments and / or acrylonitrile segments, which are copolymerized and bonded to the polyurethane side chains or segment ends. The functional groups of the interfacial functional segments include one or more combinations of sulfur-containing functional groups, carboxylates, hydroxyl groups, amide groups, and ketone carbonyl groups.

2. The plastic electroplating pretreatment solution containing functionalized resin as described in claim 1, characterized in that, The pretreatment solution has a pH of 7.5–8.8, a viscosity of 20–180 mPa·s at 25°C, a solid content of 20–35%, and a particle size of ≤300 nm.

3. The plastic electroplating pretreatment solution containing functionalized resin as described in claim 1, characterized in that, The pretreatment solution is dried with hot air at 60-70°C to form a conductive functional layer with a thickness of no more than 5 μm and a sheet resistance of less than 50 Ω / □.

4. The plastic electroplating pretreatment solution containing functionalized resin as described in claim 1, characterized in that, The film-forming aid is one or a combination of dipropylene glycol methyl ether, tripropylene glycol methyl ether, and propylene glycol methyl ether. And / or, The leveling agent is a polyether-modified silicone leveling agent. And / or, The dispersant is one or more of PVP and polyether nonionic dispersants; And / or, The rheology modifier used is HEUR rheology modifier; And / or, The antioxidant is selected from 2,6-di-tert-butyl-p-cresol or water-based hindered phenolic antioxidants.

5. The plastic electroplating pretreatment solution containing functionalized resin as described in claim 1, characterized in that, The polyurethane main skeleton in the functionalized polyurethane hybrid resin is one or two of polycarbonate diol, polyester diol, and polyether diol, and the isocyanate is one or two of IPDI, HDI, and H12MDI.

6. The method for preparing the pretreatment solution for plastic electroplating containing functionalized resin according to any one of claims 1 to 5, characterized in that, Includes the following steps: S1: After dehydrating the polyol, add isocyanate and catalyst under nitrogen protection, and react at 70-85℃ for 2-4 h to obtain -NCO-terminated prepolymer; S2: Add a carboxyl-containing internal emulsifier to the prepolymer and react for 0.5-2 h. Then add a neutralizing agent to ionize the internal emulsifying groups, then add deionized water for dispersion, and then slowly add a 10-20% EDA aqueous solution for chain extension. The amount of EDA is 0.9-1.0 times the residual-NCO molar ratio to obtain the WPU dispersion. S3: Seed emulsion polymerization; pre-emulsify the monomers St, BA, DAAM, and MAA according to the formulation, add them dropwise to the WPU dispersion at 70-85℃, add persulfate initiator or redox initiation system at the same time, and add 3-mercaptopropionic acid as chain transfer agent, the amount of which accounts for 0.6-1.0% of the total mass of the above monomers, so that the monomers form a hybrid functional layer on the surface or inside of the WPU particles and introduce sulfur-containing bonding sites at the end of the polymer chain; S4: After the reaction is complete, keep warm for 1.5 to 2 hours, adjust the pH to 7.0 to 8.5, filter to remove the gel, add ADH crosslinking agent, stir for 30 minutes to obtain a functionalized polyurethane hybrid resin dispersion with a solid content of 28% to 33%. S5: Add reduced graphene oxide, dispersant and deionized water into a pre-dispersion vessel in proportion. After high-speed shearing for 20 to 40 minutes, introduce it into a sand mill and disperse it with 0.3 to 0.8 mm zirconia beads. Control the slurry temperature not to exceed 40℃ until there are no obvious coarse particles and agglomeration to obtain a reduced graphene oxide dispersion. S6: Compound the following components in the order of functionalized polyurethane hybrid resin dispersion, reduced graphene oxide dispersion, film-forming aid, leveling agent, rheology modifier, and antioxidant. Stir at low speed of 200–400 rpm for 20–60 min, and adjust the pH, viscosity, and solid content to the target values.

7. The method for preparing the pretreatment solution for plastic electroplating containing functionalized resin as described in claim 6, characterized in that, In S1, the isocyanate is selected from IPDI, the NCO / OH index is 1.5 to 2.0, the NCO content of the prepolymer is 3.5 to 4.5%, the catalyst is selected from DBTDL, and the amount of catalyst accounts for 0.05% of the total mass of the prepolymer.

8. The method for preparing the pretreatment solution for plastic electroplating containing functionalized resin as described in claim 6, characterized in that, In S2, the carboxyl-containing internal emulsifier is selected from DMPA, accounting for 3-4% of the prepolymer mass; the neutralizer is selected from TEA, with a neutralization degree of 85-100%; and the solid content of the WPU dispersion is 30-35%.

9. The method for preparing the pretreatment solution for plastic electroplating containing functionalized resin as described in claim 6, characterized in that, In S3, the monomers St, BA, DAAM, and MAA are pre-emulsified at a mass ratio of 20:18:3:1, with the amount of St being 15–25 wt% of the solid content of the WPU dispersion. The pre-emulsification process includes adding 1% of the total monomer mass of allyloxy polyoxyethylene ether and an equal mass of water, followed by high-speed shearing at 2000–3000 rpm for 10–15 min to obtain a pre-emulsion. The pre-emulsion is then added dropwise to the WPU dispersion at 70–85°C, along with a persulfate initiator, over a period of 2–2.5 h.

10. The method for preparing the pretreatment solution for plastic electroplating containing functionalized resin as described in claim 6, characterized in that, As described in S4, ADH crosslinking agent is added slowly in a 10% aqueous solution of ADH prepared according to a DAAM:ADH molar ratio of 1:

1. And / or, In S5, reduced graphene oxide, dispersant, and deionized water are added to a pre-dispersion vessel at a mass ratio of rGO:PVP:water = 5:3:

92. After high-speed shearing at 2000-3000 rpm for 20-40 min, the mixture is introduced into a sand mill and dispersed with 0.3-0.8 mm zirconia beads. The slurry temperature is controlled to be no higher than 40℃ until there are no obvious coarse particles and the particle size D90 ≤ 300 nm.

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