Impact-resistant waterproof powder coating for electronic components and preparation process of impact-resistant waterproof powder coating

Abstract

The invention discloses an impact-resistant electronic component waterproof powder coating and a preparation process thereof, and relates to the technical field of electronic component coatings, the impact-resistant electronic component waterproof powder coating comprises epoxy resin, a curing agent, an inorganic filler, an organosilicon modified hyperbranched polyester flexibilizer and an auxiliary agent; the organic silicon modified hyperbranched polyester toughening agent is prepared by the following steps: carrying out melt polycondensation on a polyhydroxy compound and excessive polybasic acid anhydride which are used as raw materials to construct a carboxyl-terminated hyperbranched polyester core, and partially grafting the core by utilizing polysiloxane containing an epoxy group to introduce a flexible hydrophobic chain segment, so as to obtain the organic silicon modified hyperbranched polyester toughening agent. And carrying out end-capping modification on the residual end carboxyl group by using epoxy chloropropane under an alkaline condition. By constructing a chemically anchored rigid core-flexible shell topological structure, impact energy and thermal stress are effectively dispersed, excellent heat resistance and dimensional stability are maintained while the coating is prevented from cracking, phase separation and water vapor permeation are completely eradicated through a built-in compact hydrophobic network, and lasting and reliable mechanical protection and insulation guarantee are provided.

Description

Technical Field

[0001] This invention relates to the field of electronic component coating technology, specifically to an impact-resistant waterproof powder coating for electronic components and its preparation process. Background Technology

[0002] Electronic components are exposed to mechanical shocks, vibrations, and frequent temperature fluctuations caused by current switching during packaging and use. Currently, epoxy resin-based powder coatings are widely used as insulating encapsulation materials. However, due to the high density of the cross-linked network after epoxy resin curing, the material often exhibits significant internal stress and brittleness. When subjected to external physical impacts or rapid temperature changes, the mismatch in thermal expansion coefficients between the coating and the substrate can easily lead to microcracks or even brittle fracture in the cured layer, thereby compromising the integrity of the encapsulation structure and causing protection failure.

[0003] To address this issue, existing technologies typically employ the addition of rubber elastomers or physical plasticizers to enhance material flexibility. However, this often introduces new and difficult-to-resolve contradictions: the introduced flexible components disrupt the rigid network of the resin matrix, leading to a decrease in the material's heat resistance and glass transition temperature, making the coating prone to softening and deformation under high-temperature operating conditions. Furthermore, simple physical blending methods cannot guarantee long-term compatibility between components. During long-term use, modifiers are prone to agglomeration or migration to the interface, causing phase separation. This not only weakens the toughening effect but also provides a pathway for moisture penetration from the environment, ultimately leading to decreased insulation performance or short-circuit failures in electronic components. Summary of the Invention

[0004] The purpose of this invention is to provide an impact-resistant waterproof powder coating for electronic components and its preparation process, thereby solving the problems existing in the background art.

[0005] To solve the above-mentioned technical problems, the present invention provides an impact-resistant waterproof powder coating for electronic components, which is made of the following components in parts by weight: Epoxy resin: 40-70 parts; curing agent: 10-30 parts; inorganic filler: 10-40 parts; organosilicon-modified hyperbranched polyester toughening agent: 2-10 parts; additives: 0.5-3 parts; Organosilicon-modified hyperbranched polyester toughening agent is a core-shell structured epoxy-terminated polymer, which is prepared by melt polycondensation of a polyhydroxy compound and an excess of polybasic acid anhydride to construct a carboxyl-terminated hyperbranched polyester core. A flexible hydrophobic segment is introduced by partial grafting of an epoxy-containing polysiloxane onto the core. The remaining carboxyl groups are then capped with epichlorohydrin under alkaline conditions.

[0006] A process for preparing an impact-resistant waterproof powder coating for electronic components is also provided, comprising the following steps: Step 1: Preparation of organosilicon-modified hyperbranched polyester toughening agent: A polyhydroxy compound and a polybasic acid anhydride are added to a reaction vessel at a carboxyl to hydroxyl molar ratio of 1.5:1 to 2.5:1. Under nitrogen atmosphere protection and mechanical stirring, the temperature is gradually increased to a molten state at a speed controlled at 150–300 rpm. Nitrogen gas is continuously purged to assist in water removal at a flow rate controlled at 0.5–1.5 L / min for melt polycondensation until the acid value of the reaction system decreases to 120–180 mg KOH / g, yielding a carboxyl-terminated hyperbranched polyester core. After cooling, a polymer containing epoxy groups is added to the carboxyl-terminated hyperbranched polyester core. A ring-opening esterification grafting reaction was carried out on siloxane and esterification catalyst under isothermal conditions to introduce flexible hydrophobic segments. Subsequently, excess epichlorohydrin and phase transfer catalyst were added, and the mixture was heated to reflux to carry out the ring-opening reaction. Then, an alkaline solution was added to carry out the ring-closing reaction. After the reaction was completed, an organic solvent was added to the reaction system to dissolve the product. The by-product salts were removed by washing with water until no white precipitate was formed and the pH value was neutral when the washing liquid was tested with silver nitrate solution. The organic phase was collected by separation, and finally the organic solvent, unreacted epichlorohydrin and small molecule by-products were removed by vacuum distillation. The product was then vacuum dried to obtain an organosilicon-modified hyperbranched polyester toughening agent. Step 2, preparation of powder coating: Weigh epoxy resin, curing agent, inorganic filler, organosilicon-modified hyperbranched polyester toughening agent and additives according to the weight parts, and put them into a high-speed mixer for premixing treatment; feed the premixed material into a twin-screw extruder, and melt extrude and mix in the temperature range of 100℃~120℃. After the extrudate is cooled by pressing, it is ultra-finely pulverized and sieved to obtain an impact-resistant waterproof powder coating for electronic components.

[0007] Preferably, in step one, the polyhydroxy compound is pentaerythritol or trimethylolpropane, and the polybasic acid anhydride is phthalic anhydride or trimellitic anhydride. The gradient heating process involves first heating to 100℃~110℃ for melting and mixing, then heating to 140℃~160℃ and holding the temperature for 2~4 hours.

[0008] Preferably, in step one, the epoxy-containing polysiloxane is a double-epoxy-terminated polydimethylsiloxane or a single-epoxy-terminated polydimethylsiloxane, with a number-average molecular weight of 1000-5000 and an epoxy value of 0.05-0.3 mol / 100g, and the amount added is 20%-40% of the mass of the end-carboxyl hyperbranched polyester core; the esterification catalyst is tetrabutylammonium bromide or triphenylphosphine, and the amount added is 0.1%-0.5% of the total mass of the reactants; the ring-opening esterification grafting reaction temperature is 100℃-115℃, and the reaction time is 1-3 hours.

[0009] Preferably, in step one, the amount of epichlorohydrin added is 200% to 400% of the mass of the end-carboxyl hyperbranched polyester core; The reflux temperature is 110℃~120℃, and the reaction time is 3~5 hours; The vacuum degree of vacuum distillation is -0.08MPa to -0.098MPa, and the distillation temperature is 80℃ to 100℃.

[0010] Preferably, in step two, the epoxy resin is bisphenol A type epoxy resin or o-cresol epoxy resin; the curing agent is one or more of phenolic resin, dicyandiamide or adipate dihydrazide.

[0011] Preferably, in step two, the inorganic filler is one or more of fumed silica, talc, or mica powder that has been hydrophobically treated with silane coupling agent or titanate coupling agent; the additives include leveling agents, degassing agents, and pigments.

[0012] Preferably, in step two, the speed of the high-speed mixer is controlled at 500-1000 rpm, the mixing time is 3-10 minutes, and a 180-200 mesh sieve is used for sieving.

[0013] Compared with the prior art, the present invention has the following beneficial effects: The constructed coating system forms a unique stress-dispersing structure after curing. The rigid hyperbranched polyester core acts as an anchor point, effectively absorbing external impact energy and preventing the rapid propagation of cracks. The externally grafted flexible segments provide the molecular chains with space to move under drastic temperature changes, allowing the coating to dissipate stress through the coordinated movement of internal molecular chains when subjected to mechanical impacts or thermal cycles. This avoids cracking and peeling caused by mismatched coefficients of thermal expansion or localized stress concentration, ensuring the integrity of the encapsulation structure.

[0014] By utilizing end-group chemical reactions, molecular-level covalent bonding between the toughening component and the matrix resin is achieved, completely eliminating the risk of phase separation caused by physical blending. This ensures the long-term uniformity of the coating's internal structure and prevents the migration or precipitation of components during long-term use. The introduced hydrophobic flexible segments construct a dense water-blocking barrier in the cured network, effectively blocking the penetration of external water vapor and corrosive ions. This allows electronic components to maintain excellent adhesion and electrical insulation performance even in high-temperature and high-humidity environments.

[0015] The unique rigid core and flexible shell topology solves the technical problem that traditional toughening modification often sacrifices heat resistance. The high-density rigid skeleton provides strong mechanical support for the system, avoiding the problem of glass transition temperature drop caused by the introduction of flexible components. This allows the coating to maintain a high heat distortion temperature and hardness while achieving excellent impact resistance, ensuring that the encapsulation coating of electronic components will not soften or deform in size when the components are in a heated state. This achieves a balance between mechanical toughness and heat resistance rigidity. Detailed Implementation

[0016] Pre-mechanism model construction: Before optimizing the formal coating preparation process, this invention pre-established a dynamic correlation model between the acid value of the end-carboxyl hyperbranched polyester core and the organosilicon grafting efficiency to determine the optimal melt polycondensation endpoint control parameters in step one. Specifically, the model was established as follows: at a constant reaction temperature (140℃) and catalyst concentration, the acid value change of the polycondensation reaction system was monitored in real-time by sampling, and polycondensation was terminated at different acid value nodes (200, 180, 150, 120, 100 mg KOH / g). A quantitative polysiloxane grafting reaction was then carried out, and the amount of silicon element bound in the final product was measured. Regression analysis data showed that the acid value and grafting efficiency exhibited a non-linear, volcano-like correlation: steric hindrance effect range: when the acid value was greater than 180 mg KOH / g, the branching degree of the hyperbranched molecules was low, the end-carboxyl group density was too high and the arrangement was too tight, leading to large polysiloxane chains... The grafting efficiency is less than 15% because the segments cannot reach the reaction sites through the steric hindrance barrier. The optimal reaction window is when the acid value is controlled within the range of 120-180 mgKOH / g. At this time, the hyperbranched polyester core forms a moderately spherical cavity structure, and the spatial distribution of the terminal carboxyl groups tends to be more relaxed. At this time, the grafting efficiency reaches its peak (>90%), and the core-shell structure formed is the most stable. The risk range of gelation is when the acid value is less than 120 mgKOH / g. The viscosity of the system increases exponentially, the movement of molecular chain segments is restricted, and excessive cross-linking is prone to occur, leading to gelation, which seriously hinders subsequent chemical modification. Based on the above correlation model, this invention sets the acid value of the reaction system to 120-180 mgKOH / g as the key rheological control index for determining the endpoint of the melt polycondensation reaction. This index ensures that the subsequent flexible organosilicon segments can be anchored on the surface of the rigid polyester core with the best topological structure. Before detailing the specific embodiments, to clarify the applicable scope of the process parameters of the present invention, the general conditions involved in each step are explained as follows: In step one and subsequent treatments, the organic solvent is not limited to xylene in the examples, but may also be selected from aromatic hydrocarbons or ester solvents such as toluene, butyl acetate or methyl isobutyl ketone, depending on the actual dissolution requirements; the phase transfer catalyst, in addition to tetrabutylammonium bromide, may also be selected from quaternary ammonium salt catalysts such as tetraethylammonium bromide, benzyltriethylammonium chloride or octadecyltrimethylammonium chloride, and the amount used is usually 0.1% to 0.5% of the total mass of the reactants; In the closed-loop reaction stage, the preferred alkali solution is an aqueous solution of sodium hydroxide or potassium hydroxide with a mass fraction of 20% to 40%. To prevent side reactions caused by excessively high local concentrations, the dropping rate of the alkali solution must be strictly controlled. The dropping time is usually controlled at 1 to 2 hours, and the reaction is continued at a constant temperature for 1 to 3 hours after the dropping is completed. In addition, for the final vacuum distillation purification step, in order to efficiently remove the solvent while avoiding the thermal polymerization of terminal epoxy groups, the vacuum degree is preferably controlled at -0.09 MPa to -0.095 MPa, and the temperature is controlled at 85℃ to 95℃.

[0017] Example 1: This embodiment, as the preferred implementation of the present invention, aims to verify the modification effect under low toughening agent content. The specific formulation is as follows: 40 parts epoxy resin (bisphenol A type epoxy resin); 10 parts curing agent (phenolic resin); 10 parts inorganic filler (fumed silica with hydrophobic surface treatment); 2 parts organosilicon-modified hyperbranched polyester toughening agent; and 0.5 parts additives (leveling agent, degassing agent). The amount of organosilicon-modified hyperbranched polyester toughening agent added is at the low end of the range. This design aims to verify whether the rigid skeleton constructed by the carboxyl-terminated hyperbranched polyester core can effectively maintain the glass transition temperature of the coating under low modifier content, thus avoiding excessive softness of the coating due to toughening. The specific process parameters of this embodiment are as follows: In step one, a polyhydroxy compound (pentaerythritol) and a polybasic acid anhydride (phthalic anhydride) are added to the reactor at a carboxyl to hydroxyl molar ratio of 1.5:1. The lower limit of the molar ratio range of 1.5:1 is chosen here to construct a relatively loose hyperbranched structure, thereby reducing melt viscosity and ensuring rapid dispersion even at low addition levels. Under nitrogen atmosphere protection and mechanical stirring, a gradient heating process is performed: first, the temperature is raised to 100°C for melting and mixing, then raised to 140°C and held for 4 hours, with continuous nitrogen purging to assist in water removal. During this step, continuous... Nitrogen gas is used not only to prevent the raw materials from oxidizing and discoloring at high temperatures, but more importantly, to remove water molecules generated by the polycondensation reaction by utilizing the entrainment effect of the gas flow. This breaks the chemical equilibrium and drives the reaction toward the formation of high molecular weight polyester until the acid value of the reaction system drops to 120 mg KOH / g, resulting in a carboxyl-terminated hyperbranched polyester core. Here, the acid value is controlled at the lower limit of the specified range of 120 mg KOH / g. According to the aforementioned mechanism model, the polyester core has the largest molecular weight and the strongest molecular chain entanglement at this point. Although it is close to the risk zone of gelation, the strongest mechanical framework support is obtained through strict control of the nitrogen flow rate. After cooling, a polysiloxane containing epoxy groups (bi-epoxy polydimethylsiloxane with a number average molecular weight of 2000 and an epoxy value of 0.12 mol / 100 g, added at 20% of the mass of the carboxyl-terminated hyperbranched polyester core) and an esterification catalyst (tetrabutylammonium bromide, added at 0.1% of the total mass of the reactants) were added to the carboxyl-terminated hyperbranched polyester core. The ring-opening esterification grafting reaction was carried out at a constant temperature of 100℃ for 1 hour. During this stage, a low grafting ratio (20%) was controlled to retain most of the carboxyl sites for subsequent epoxy end-capping, ensuring the chemical compatibility of the toughening agent with the epoxy resin matrix. Subsequently, excess epichlorohydrin was added at 200% of the mass of the carboxyl-terminated hyperbranched polyester core, along with a phase transfer catalyst (tetrabutylammonium bromide). Ammonium bromide was heated to 110℃ and refluxed for a ring-opening reaction for 3 hours. Then, an alkaline solution (30% sodium hydroxide aqueous solution) was slowly added dropwise to initiate a ring-closing reaction. After the addition was complete, the reaction was maintained at the same temperature for another 2 hours. After the reaction was completed, the temperature was lowered to 60℃, and xylene (50% of the resin mass) was added to the system to dissolve the product. The product was transferred to a separatory funnel and washed 3-5 times with deionized water until the washing filtrate showed no turbidity or precipitation after the addition of 0.1 mol / L silver nitrate solution and the pH was neutral. The aqueous phase was discarded after separation. The organic phase was collected and subjected to vacuum distillation (vacuum degree -0.08 MPa, temperature 90℃) to remove xylene solvent, unreacted epichlorohydrin, and small molecule byproducts. The purified organosilicon-modified hyperbranched polyester toughening agent was obtained by vacuum drying. In step two, the above components are weighed according to their weight proportions and added to a high-speed mixer. The speed is controlled at 500 rpm, and the mixing time is 3 minutes for premixing. The premixed material is then fed into a twin-screw extruder and melt-extruded within a temperature range of 100°C. The extrusion temperature is strictly controlled at the lower limit of 100°C to prevent premature cross-linking of the B-stage curing system during extrusion, ensuring that the final powder coating still has excellent leveling properties after electrostatic spraying. After the extrudate is cooled by pressing, it is fed into an ACM air classifier mill or similar high-efficiency pulverizing equipment for ultra-fine pulverization. The particle size distribution is controlled by adjusting the speed of the classifier wheel to ensure that D50 ≤ 30 μm, preferably 20-25 μm. Then, it is sieved through a 180-200 mesh sieve to remove large particles, resulting in a waterproof powder coating for impact-resistant electronic components with uniform particle size and good fluidization performance. This embodiment demonstrates that even with the introduction of small amounts of flexible segments, the stress dispersion mechanism of hyperbranched structures can significantly improve the crack resistance of electronic components under mild thermal shock by combining a low modifier content, a low grafting ratio, and a high molecular weight core (low acid value). This reflects the high efficiency of the technical solution of this invention.

[0018] Example 2: This embodiment focuses on verifying the synergistic effect of a highly branched skeleton and a high-filler content; the specific formula is as follows: 70 parts epoxy resin (o-cresol epoxy resin); 30 parts curing agent (dicyandiamide); 40 parts inorganic filler (talc); 10 parts organosilicon-modified hyperbranched polyester toughening agent; and 3 parts additives (leveling agent, pigment). The specific process parameters are adjusted as follows: A polyhydroxy compound (trimethylolpropane) and a polybasic acid anhydride (triphenyltriglyceridate anhydride) are added to the reactor at a carboxyl to hydroxyl molar ratio of 2.5:1. The upper limit of the molar ratio range of 2.5:1 is chosen here to maximize the functionality of the carboxyl groups at the molecular ends, thereby constructing a highly dense spherical topology. Under nitrogen atmosphere protection and mechanical stirring at 250 rpm, a gradient temperature increase is carried out. Specifically, the temperature is first raised to 110℃ for melting and mixing, then raised to 160℃ and held for 2 hours, with continuous nitrogen flow to assist in water removal and melt polycondensation until the acid value of the reaction system decreases to 180 mg KOH / g, resulting in a carboxyl-terminated hyperbranched polyester core. In this step, the reaction temperature is set to the upper limit of 160℃ to overcome the huge steric hindrance caused by high branching degree, ensuring the reaction can proceed completely. Simultaneously, the acid value is controlled at the upper limit of 180 mg KOH / g to prevent premature gelation of the system and retain an appropriate molecular weight to match the high-filler system. After the reaction, an epoxy-containing polysiloxane (using mono-epoxylated polydimethylsiloxane with a number average molecular weight of 1500, an epoxy value of 0.08 mol / 100 g, and added at 40% of the mass of the carboxyl-terminated hyperbranched polyester core) and an esterification catalyst (triphenylphosphine, added at 0.5% of the total mass of the reactants) were added, and a ring-opening esterification grafting reaction was carried out at a constant temperature of 115℃ for 3 hours; subsequently, excess epichlorohydrin (added at 400% of the mass of the carboxyl-terminated hyperbranched polyester core) and a phase transfer catalyst (tetrabutyl) were added. Ammonium bromide was heated to 120°C and refluxed for a ring-opening reaction for 5 hours. Then, an alkaline solution (30% sodium hydroxide aqueous solution) was added dropwise to initiate a ring-closing reaction. After the reaction was completed, the temperature was lowered, and xylene was added to the system to dissolve the product. The mixture was washed repeatedly with deionized water until the aqueous phase was neutral and no precipitation reaction was detected by silver nitrate. The organic phase was collected by separation. Finally, the solvent, unreacted epichlorohydrin, and small molecule byproducts were removed by vacuum distillation (vacuum degree -0.098MPa, temperature 100°C). The product was then vacuum dried to obtain an organosilicon-modified hyperbranched polyester toughening agent. In this embodiment, the high content of flexible hydrophobic segments forms a denser hydrophobic network in the curing system, which is crucial for resisting water vapor penetration in high humidity environments. In addition, the high filling amount (40 parts) of inorganic fillers usually leads to the coating becoming brittle, but with the high content of organosilicon-modified hyperbranched polyester toughening agent, the large amount of free volume brought about by its hyperbranched structure effectively offsets the internal stress caused by the high filling, so that the coating has excellent impact resistance while maintaining high density.

[0019] Example 3: This embodiment aims to obtain a coating with balanced overall performance, and adopts the intermediate values ​​of each component and process parameter; the specific formula is as follows: 55 parts epoxy resin (bisphenol A type epoxy resin); 20 parts curing agent (mixture of phenolic resin and dicyandiamide); 25 parts inorganic filler (mixture of fumed silica and mica powder with hydrophobic surface treatment); 6 parts organosilicon modified hyperbranched polyester toughening agent; 1.5 parts additives (leveling agent, degassing agent, pigment); The specific process parameters are adjusted as follows: A polyhydroxy compound (pentaerythritol) and a polybasic acid anhydride (triphenylamine anhydride) are added to the reactor at a carboxyl to hydroxyl molar ratio of 2:1. The mixture is first heated to 105℃ for melting and mixing, then heated to 150℃ and held for 3 hours until the acid value decreases to 150 mg KOH / g. After cooling, a polysiloxane containing epoxy groups (bi-epoxy polydimethylsiloxane with a number average molecular weight of 2500 and an epoxy value of 0.09 mol / 100g, added at 30% of the mass of the carboxyl-terminated hyperbranched polyester core) and an esterification catalyst (tetrabutylammonium bromide, added at 0.3% of the total mass of the reactants) are added to the carboxyl-terminated hyperbranched polyester core. The ring-opening esterification grafting reaction is carried out at a constant temperature of 110℃ for 2 hours. The grafting temperature is selected at 110℃ to balance the reaction temperature. To balance the reaction rate and control side reactions, ensuring the grafting rate while avoiding thermal degradation of polysiloxane segments, this step utilizes bi-epoxy-terminated polysiloxanes to form a bridging structure, further enhancing the bonding force between the core-shell structure and the matrix. Subsequently, excess epichlorohydrin (300% of the mass of the end-carboxyl hyperbranched polyester core) and a phase transfer catalyst (tetrabutylammonium bromide) are added, and the mixture is heated to 115°C under reflux for a ring-opening reaction for 4 hours. Then, an alkaline solution (30% sodium hydroxide aqueous solution) is added dropwise to initiate a ring-closing reaction. After the reaction, a suitable amount of xylene is added to dissolve the product, and the mixture is washed with water to remove byproduct salts until neutral. The organic phase is then separated. Finally, the solvent and volatiles are removed by vacuum distillation (vacuum degree -0.09 MPa, temperature 90°C), and the product is vacuum dried to obtain the organosilicon-modified hyperbranched polyester toughening agent. In this embodiment, the three-dimensional spherical structure of the end-carboxyl hyperbranched polyester core is combined with an appropriate amount of flexible hydrophobic segments, maximizing the toughening and waterproofing effects without significantly reducing the coating hardness; the organosilicon-modified hyperbranched polyester toughening agent is uniformly dispersed in the epoxy resin matrix, and the risk of phase separation is eliminated through end-group chemical reaction; this structural design effectively suppresses the generation of internal microcracks when the coating undergoes repeated thermal expansion and contraction cycles.

[0020] Example 4: This embodiment focuses on examining the compatibility of curing agent types and the impact of end-capping process on product performance; the specific formulation is as follows: 60 parts epoxy resin (o-cresol epoxy resin); 15 parts curing agent (adipic acid dihydrazide); 30 parts inorganic filler (mica powder); 5 parts organosilicon-modified hyperbranched polyester toughening agent; 1 part additive (leveling agent). The specific process parameters are adjusted as follows: A polyhydroxy compound (trimethylolpropane) and a polybasic acid anhydride (phthalic anhydride) are added to the reactor at a carboxyl to hydroxyl molar ratio of 1.8:1. The mixture is first heated to 108℃ for melting and mixing, then heated to 145℃ and held for 3.5 hours until the acid value decreases to 140 mg KOH / g. After cooling, a polysiloxane containing epoxy groups (using mono-epoxylated polydimethylsiloxane with a number average molecular weight of 3000, an epoxy value of 0.05 mol / 100g, and added at 25% of the mass of the end-carboxyl hyperbranched polyester core) and an esterification catalyst (triphenylphosphine, added at 0.2% of the total mass of the reactants) are added. The ring-opening esterification grafting reaction is carried out at a constant temperature of 105℃ for 2.5 hours. Subsequently, excess epichlorohydrin (added at 25% of the mass of the end-carboxyl hyperbranched polyester core) is added. The polyester core (250% by mass) and phase transfer catalyst (tetrabutylammonium bromide) were heated to 112°C and refluxed for a ring-opening reaction for 3.5 hours. Then, an alkaline solution (30% sodium hydroxide aqueous solution) was added dropwise to initiate a ring-closing reaction. After the reaction was complete, an organic solvent (xylene) was added to dissolve the product. The generated sodium chloride salt and alkaline residue were removed by water washing and extraction until the aqueous phase was neutral. The organic phase was separated and retained. Subsequently, the solvent, unreacted epichlorohydrin, and small molecule byproducts were removed by vacuum distillation (vacuum degree -0.085MPa, temperature 85°C). In this step, the vacuum degree and temperature of vacuum distillation (85°C, on the low-temperature side of 80°C~100°C) were strictly controlled to prevent the thermal degradation or self-polymerization of the terminal epoxy groups formed during the solvent removal process, thus ensuring the high reactivity of the toughening agent. In this embodiment, adipic acid dihydrazide was selected as the curing agent, which has a certain degree of flexibility. Combined with organosilicon-modified hyperbranched polyester toughening agent, the impact resistance of the coating is further enhanced. The carboxyl-terminated hyperbranched polyester core is constructed by trimethylolpropane and phthalic anhydride. Compared with the pentaerythritol system, its crosslinking density is slightly lower, which gives the molecular chain better mobility. Combined with single-end grafted polysiloxane containing epoxy groups, the flexible hydrophobic segments are more easily enriched on the coating surface, so as to achieve good surface hydrophobic effect even with a low silicon content.

[0021] Example 5: This embodiment aims to verify the effect of high-shear mixing process on the dispersion state of toughening agent; the specific formulation is as follows: 50 parts epoxy resin (bisphenol A type epoxy resin); 25 parts curing agent (phenolic resin); 20 parts inorganic filler (hydrophobic fumed silica); 8 parts organosilicon modified hyperbranched polyester toughening agent; 2 parts additives (degassing agent, pigment); The specific process parameters are adjusted as follows: In the preparation of organosilicon-modified hyperbranched polyester toughening agent, the acid value is controlled to decrease to 160 mg KOH / g as the polycondensation endpoint; during the grafting stage, 35% of the dimethylsiloxane (number average molecular weight of 2200, epoxy value of 0.10 mol / 100g) is added, the amount of esterification catalyst is 0.4%, and the grafting temperature is controlled at 112℃; during the end-capping stage, the amount of epichlorohydrin added is 350%, and the reflux temperature is 118℃; after the ring-closing reaction is completed, solvent dissolution, water washing to desalination to neutrality and liquid separation steps are added; finally, the vacuum degree of vacuum distillation is controlled at -0.095 MPa and the temperature is 95℃. In the powder coating preparation in step two, the speed of the high-speed mixer is increased to 900 rpm, and the mixing time is extended to 8 minutes. Here, the speed is set to 900 rpm and the mixing time is 8 minutes. This high-intensity and long-term premixing treatment aims to use strong mechanical shear force to initially break down the high-viscosity organosilicon-modified hyperbranched polyester toughening agent and uniformly coat it on the surface of the resin particles, preventing the formation of enrichment islands during the subsequent extrusion process. The reason why the maximum speed of 1000 rpm was not selected is to avoid the resin softening and clumping during the premixing stage due to excessive frictional heat generation. The extrusion temperature was set at 115℃, and a 200-mesh sieve was used for sieving. In this embodiment, a toughening agent structure with high branching degree and hydrophobic segment density was constructed by adjusting the proportion of reactive monomers in the end-carboxyl hyperbranched polyester core and the grafting amount of polysiloxane containing epoxy groups. Experiments show that after high-speed premixing and fine sieving, the core-shell structure of the organosilicon-modified hyperbranched polyester toughening agent exhibits excellent compatibility at this ratio. The end-epoxy modification ensures that it can be firmly anchored in the solidified network, preventing the migration and precipitation of organosilicon components during long-term use, thereby ensuring the reliability of electronic components in long-term high temperature and high humidity environments.

[0022] Comparative Example 1: This comparative example provides a conventional epoxy powder coating as a blank control group; its only difference from Example 3 is that the organosilicon-modified hyperbranched polyester toughening agent of the present invention is not added, but the amount of epoxy resin is directly increased to make up the total parts; the specific formula is: 61 parts epoxy resin, 20 parts curing agent, 25 parts inorganic filler, and 1.5 parts additives; the preparation process parameters are completely consistent with those of Example 3; this comparative example aims to verify the inherent defects of the base resin system in terms of impact resistance and thermal cycling resistance in the absence of toughening agent introduction.

[0023] Comparative Example 2: This comparative example provides a physically blended modified powder coating as a structural verification group; its only difference from Example 3 is that an equal amount of ordinary end-carboxyl hyperbranched polyester is used, that is, the intermediate product of step one without subsequent organosilicon grafting and epoxy end-capping is used to replace the organosilicon-modified hyperbranched polyester toughening agent; the remaining components and preparation process parameters are consistent with Example 3; this comparative example aims to strip away the two key features of organosilicon flexible segments and end-epoxy chemical anchoring, and verify whether relying solely on the physical filling of the hyperbranched polyester core is sufficient to resolve the contradiction between waterproofing and toughening.

[0024] Comparative Example 3: This comparative example provides a powder coating with a commercially available toughening agent as a control group of existing technologies. The only difference between this example and Example 3 is that an equal amount of commercially available core-shell rubber toughening agent is used instead of the silicone-modified hyperbranched polyester toughening agent of the present invention. The remaining components and preparation process parameters are consistent with those of Example 3. This comparative example aims to compare the performance differences between the toughening agent of the present invention with a special rigid core-flexible shell structure and existing commercial toughening agents in electronic component packaging applications, and in particular to examine the degree of negative impact on the glass transition temperature.

[0025] Verification experiment: To fully verify the technical effect of the impact-resistant waterproof powder coating for electronic components of the present invention, the powder coatings prepared in Examples 1-5 and Comparative Examples 1-3 were electrostatically sprayed onto standard electronic component simulation samples and tinplate sheets, and performance tests were conducted after curing at 160°C for 20 minutes. Testing standards: Impact resistance: According to GB / T1732-1993 "Test Method for Impact Resistance of Coating Film", a 1kg hammer is dropped from a height of 50cm to impact the coating surface. A 10x magnifying glass is used to observe whether there are cracks or peeling at the impacted part of the coating and its edges. Thermal shock test: Referring to GJB150.5A-2009 "Laboratory Environmental Test Methods for Military Equipment Part 5: Temperature Shock Test", a severe cycle was set from -40℃ (held for 30 min) to 125℃ (held for 30 min), with a transition time of less than 10 seconds. After 500 cycles, the microcrack propagation on the coating surface and cross-section was observed using a metallographic microscope. Water resistance (PCT high pressure boiling test): According to JEDEC JESD22-A102 standard, the coating is boiled for 96 hours at 121℃, 100%RH, and 2atm saturated water vapor pressure. The coating appearance is observed to see if it blisters or turns white. The adhesion retention rate is tested according to GB / T9286-1998. Glass transition temperature (Tg): The temperature was measured using a differential scanning calorimeter at a heating rate of 10 °C / min under a nitrogen atmosphere, and the midpoint temperature of the second heating curve was taken. Specific testing process: Ten parallel samples were prepared for each set of examples and comparative examples for testing. The impact resistance and thermal shock test results were described by the mode. The PCT test and Tg test results were the average of three parallel measurements. Data processing was performed to two decimal places to ensure the statistical significance of the data. Data table: Table 1: Result analysis components: Analysis of Table 1 and related test results shows the following: Synergistic toughening mechanism: Comparing Examples 1-5 with Comparative Example 1, after introducing the silicone-modified hyperbranched polyester toughening agent, the impact resistance of the coating changed from cracking to passing and withstanding 500 cycles of thermal shock. This indicates that the end-carboxyl hyperbranched polyester core acts as a stress concentration point in the cured network, inducing crazing and absorbing impact energy, while the grafted flexible hydrophobic segments endow the molecular chains with mobility at low temperatures, effectively alleviating thermal mismatch stress. Waterproof reliability analysis: Comparing Example 3 with Comparative Example 2, although Comparative Example 2 also contains a hyperbranched structure, it showed severe blistering in the PCT high-pressure boiling test. This confirms that the dual mechanism of end-epoxy chemical anchoring and silicone hydrophobic shielding is crucial. The toughening agent in Comparative Example 2 lacks chemical bonding with the matrix, resulting in poor adhesion during humid heat aging. Phase separation occurs, and the lack of hydrophobic protection from organosilicon allows moisture to penetrate along the interface. In contrast, Example 3 utilizes terminal epoxy groups to achieve in-situ covalent bonding between the toughening agent and the epoxy body, locking the moisture transport channels. Regarding thermal stability: Compared to Comparative Example 3, which uses a commercially available CSR toughening agent, Comparative Example 3, while still exhibiting acceptable toughness, shows a significant decrease in Tg to 125.40℃. This is because the low modulus of the CSR rubber phase inevitably dilutes the crosslinking density of the matrix. In contrast, this invention, by precisely controlling the ratio of rigid to flexible hydrophobic segments in the terminal carboxyl hyperbranched polyester core, achieved a high Tg of 136.10℃ in Example 3. This demonstrates that the unique rigid core-flexible shell structure of this invention enhances toughness while maximizing the preservation of the coating's heat resistance rigidity, achieving the optimal balance between toughness, water resistance, and heat resistance.

[0026] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments that can be applied to other fields. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A waterproof powder coating for impact-resistant electronic components, characterized in that, It is made from the following components in parts by weight: Epoxy resin: 40-70 parts; curing agent: 10-30 parts; inorganic filler: 10-40 parts; organosilicon-modified hyperbranched polyester toughening agent: 2-10 parts; additives: 0.5-3 parts; Organosilicon-modified hyperbranched polyester toughening agent is a core-shell structured epoxy-terminated polymer, which is prepared by melt polycondensation of a polyhydroxy compound and an excess of polybasic acid anhydride to construct a carboxyl-terminated hyperbranched polyester core. A flexible hydrophobic segment is introduced by partial grafting of an epoxy-containing polysiloxane onto the core. The remaining carboxyl groups are then capped with epichlorohydrin under alkaline conditions.

2. A preparation process for an impact-resistant waterproof powder coating for electronic components as described in claim 1, characterized in that, Includes the following steps: Step 1: Preparation of organosilicon-modified hyperbranched polyester toughening agent: A polyhydroxy compound and a polybasic acid anhydride are added to a reaction vessel at a carboxyl to hydroxyl molar ratio of 1.5:1 to 2.5:

1. Under nitrogen atmosphere protection and mechanical stirring, the temperature is gradually increased to a molten state at a speed controlled at 150–300 rpm. Nitrogen gas is continuously purged to assist in water removal at a flow rate controlled at 0.5–1.5 L / min for melt polycondensation until the acid value of the reaction system decreases to 120–180 mg KOH / g, yielding a carboxyl-terminated hyperbranched polyester core. After cooling, a polymer containing epoxy groups is added to the carboxyl-terminated hyperbranched polyester core. A ring-opening esterification grafting reaction was carried out on siloxane and esterification catalyst under isothermal conditions to introduce flexible hydrophobic segments. Subsequently, excess epichlorohydrin and phase transfer catalyst were added, and the mixture was heated to reflux to carry out the ring-opening reaction. Then, an alkaline solution was added to carry out the ring-closing reaction. After the reaction was completed, an organic solvent was added to the reaction system to dissolve the product. The by-product salts were removed by washing with water until no white precipitate was formed and the pH value was neutral when the washing liquid was tested with silver nitrate solution. The organic phase was collected by separation, and finally the organic solvent, unreacted epichlorohydrin and small molecule by-products were removed by vacuum distillation. The product was then vacuum dried to obtain an organosilicon-modified hyperbranched polyester toughening agent. Step 2, preparation of powder coating: Weigh epoxy resin, curing agent, inorganic filler, organosilicon-modified hyperbranched polyester toughening agent and additives according to the weight parts, and put them into a high-speed mixer for premixing treatment; feed the premixed material into a twin-screw extruder, and melt extrude and mix in the temperature range of 100℃~120℃. After the extrudate is cooled by pressing, it is ultra-finely pulverized and sieved to obtain an impact-resistant waterproof powder coating for electronic components.

3. The preparation process of an impact-resistant waterproof powder coating for electronic components as described in claim 2, characterized in that, In step one, the polyhydroxy compound is pentaerythritol or trimethylolpropane, and the polybasic acid anhydride is phthalic anhydride or trimellitic anhydride. The gradient heating process involves first heating to 100℃~110℃ for melting and mixing, then heating to 140℃~160℃ and holding the temperature for 2~4 hours.

4. The preparation process of an impact-resistant waterproof powder coating for electronic components as described in claim 2, characterized in that, In step one, the epoxy-containing polysiloxane is either a di-epoxy-terminated polydimethylsiloxane or a mono-epoxy-terminated polydimethylsiloxane, with a number-average molecular weight of 1000–5000 and an epoxy value of 0.05–0.3 mol / 100g. The amount added is 20%–40% of the mass of the end-carboxyl hyperbranched polyester core. The esterification catalyst is tetrabutylammonium bromide or triphenylphosphine, and the amount added is 0.1%–0.5% of the total mass of the reactants. The ring-opening esterification grafting reaction temperature is 100℃–115℃, and the reaction time is 1–3 hours.

5. The preparation process of an impact-resistant waterproof powder coating for electronic components as described in claim 2, characterized in that, In step one, the amount of epichlorohydrin added is 200% to 400% of the mass of the end-carboxyl hyperbranched polyester core; The reflux temperature is 110℃~120℃, and the reaction time is 3~5 hours; The vacuum degree of vacuum distillation is -0.08MPa to -0.098MPa, and the distillation temperature is 80℃ to 100℃.

6. The preparation process of an impact-resistant waterproof powder coating for electronic components as described in claim 2, characterized in that, In step two, the epoxy resin is bisphenol A type epoxy resin or o-cresol epoxy resin; the curing agent is one or more of phenolic resin, dicyandiamide or adipate dihydrazide.

7. The preparation process of an impact-resistant waterproof powder coating for electronic components as described in claim 2, characterized in that, In step two, the inorganic filler is one or more of fumed silica, talc powder, or mica powder that has been hydrophobically treated with silane coupling agent or titanate coupling agent; the additives include leveling agents, degassing agents, and pigments.

8. The preparation process of an impact-resistant waterproof powder coating for electronic components as described in claim 2, characterized in that, In step two, the speed of the high-speed mixer is controlled at 500-1000 rpm, and the mixing time is 3-10 minutes; a 180-200 mesh sieve is used for sieving.

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