Waterproof and corrosion-resistant modified epoxy resin packaging coating and preparation method thereof

Abstract

The application relates to the technical field of coatings, in particular to a waterproof and corrosion-resistant modified epoxy resin packaging coating and a preparation method thereof, which comprises components A and B in terms of mass parts; the component A comprises the following components in terms of mass parts: DOPO-HQ modified epoxy resin 100 parts, talcum powder 12 to 20 parts, precipitated barium sulfate 8 to 14 parts, hydrophobic nano silicon dioxide 1 to 4 parts, silane coupling agent KH-560 1 to 3 parts, dispersant 0.4 to 1 part, defoaming agent 0.2 to 0.5 part, leveling agent 0.2 to 0.5 part, dimethylbenzene 8 to 16 parts and n-butanol 4 to 8 parts. The application grafts DOPO-HQ onto the main chain of the epoxy resin, so that the phosphorus-containing anticorrosion function exists in the form of intramolecular chemical bonds, and the problems of cavitation and osmotic pressure caused by the dissolution of granular pigments are fundamentally eliminated.

Description

Technical Field

[0001] This invention relates to the field of coating technology, specifically to a waterproof and corrosion-resistant modified epoxy resin packaging coating and its preparation method. Background Technology

[0002] Corrosion protection of metal products during storage and transportation is a crucial requirement in the packaging industry, especially in scenarios such as export packaging of electromechanical products, warehousing of automotive parts, and sealing of precision instruments. Packaging coatings play a key role in isolating corrosive media and providing long-term protection. Epoxy resin coatings, due to their excellent adhesion, chemical resistance, and low shrinkage, have become the mainstream choice for metal packaging coatings.

[0003] To impart active corrosion protection to epoxy coatings, current technologies commonly employ the addition of phosphate-based rust-inhibiting pigments, with zinc phosphate being the most widely used environmentally friendly rust-inhibiting pigment. The corrosion protection mechanism of zinc phosphate relies on its slow dissolution: when moisture penetrates into the coating, the zinc phosphate particles dissolve, releasing Zn. 2+ and PO4 3- Ions migrate to the interface between the coating and the metal substrate, reacting with the metal surface to form a FePO4 passivation film and a basic zinc carbonate inhibition layer.

[0004] However, this mechanism has a fundamental technical contradiction: while the dissolution of zinc phosphate particles provides corrosion-inhibiting ions, it inevitably leaves microcavities in the coating.

[0005] These cavities become new shortcuts for moisture and corrosive ions to penetrate into the substrate, while the soluble salts produced during dissolution create an osmotic pressure difference within the coating, leading to osmotic blistering. The weak interfacial bonding between zinc phosphate particles and epoxy resin becomes a delamination initiation point during moisture penetration. Therefore, while providing active anti-corrosion protection, zinc phosphate anti-rust pigments also create conditions that accelerate the coating's own failure, namely the pigment dissolution-cavitation paradox as described in this invention. This paradox explains the phenomenon that epoxy zinc phosphate anti-rust paints initially perform well but then experience a sharp decline in performance after 6 to 12 months; this long-standing technical contradiction has not yet been fundamentally resolved in the field.

[0006] CN109943169B discloses a nanocomposite marine anticorrosive coating that introduces an aminated modified iron oxide, titanium dioxide and hexagonal boron nitride hybrid composite material into an acrylic and epoxy composite resin. The labyrinthine shielding effect of the nanomaterial blocks the penetration path of corrosive media. However, this solution still uses traditional anti-rust pigments and does not address the problems of cavitation and penetration bubbling caused by pigment dissolution.

[0007] CN116837383B discloses a composite vapor phase corrosion inhibitor for carbon steel, comprising sodium dodecyl sulfonate, bismorpholine methyl urea, and benzotriazole. The corrosion inhibitor has limited compatibility with organic coatings, rapidly migrates to the surface in the coating film and evaporates, resulting in a short protection cycle and affecting the appearance of the coating.

[0008] Existing technologies have attempted to alleviate pigment dissolution problems through various approaches: modifying the surface of zinc phosphate particles with silane coupling agents to improve their interfacial bonding with epoxy resin and reduce interfacial porosity. However, surface modification can only slow down the dissolution rate and cannot fundamentally eliminate dissolution and void formation.

[0009] Alternatively, zinc phosphate can be encapsulated in mesoporous silica nanocarriers to achieve controlled ion release during corrosion inhibition. However, the encapsulation process is complex and costly, and the carrier itself is still particulate, which still creates weak points at the interface in the coating.

[0010] Bio-based alternatives such as lignin phosphate are used to replace pigments, but they are still essentially granular soluble pigments, and the problems of dissolution and cavitation still exist. Summary of the Invention

[0011] The primary objective of this invention is to provide a waterproof and corrosion-resistant modified epoxy resin packaging coating and its preparation method.

[0012] A further objective of this invention is to provide a waterproof and corrosion-resistant modified epoxy resin packaging coating and its preparation method.

[0013] A further objective of this invention is to provide a waterproof and corrosion-resistant modified epoxy resin packaging coating, comprising, by weight, component A and component B; wherein component A comprises, by weight, 12 to 20 parts of talc powder, 8 to 14 parts of precipitated barium sulfate, 1 to 4 parts of hydrophobic nano-silica, 1 to 3 parts of silane coupling agent KH-560, 0.4 to 1 part of dispersant, 0.2 to 0.5 parts of defoamer, 0.2 to 0.5 parts of leveling agent, 8 to 16 parts of xylene, and 4 to 8 parts of n-butanol; Component B is a cashew phenol amine curing agent, whose C15 long-chain alkyl group in its molecular structure endows the cured product with inherent hydrophobicity; the mass ratio of component A to component B is 100:22 to 100:30. The DOPO-HQ modified epoxy resin is prepared by grafting DOPO-HQ with bisphenol A type epoxy resin in the presence of triphenylphosphine catalyst. The amount of DOPO-HQ added is 6% to 14% of the mass of bisphenol A type epoxy resin. The chemical name of DOPO-HQ is 10-hydroquinone-9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, with a molecular weight of 324.27. Its molecular structure contains a rigid phenanthrene ring skeleton and two phenolic hydroxyl groups. Under the grafting reaction conditions, DOPO-HQ forms an ether bond by reacting one of its phenolic hydroxyl groups with the epoxy group of the epoxy resin, thus grafting it onto the epoxy resin in a suspended manner. On the resin side chain, the phenanthrene ring structure of DOPO-HQ after grafting is connected to the polymer side chain via POC ether bonds rather than embedded in the main chain. These POC ether bonds can undergo slow hydrolysis under alkaline conditions at the interface between the coating and the metal matrix after the coating is cured, releasing phosphorus-containing species to form a phosphorus-containing passivation protective layer on the metal surface. In the coating, DOPO-HQ exists on the epoxy resin side chain in an intramolecular chemical bond manner. The other phenolic hydroxyl group of DOPO-HQ mainly remains in an unreacted state under the grafting reaction conditions due to steric hindrance and the molar ratio of DOPO-HQ to epoxy groups being less than 1:10, ensuring that DOPO-HQ is grafted in a suspended manner rather than a crosslinking manner.

[0014] Preferably, the amount of DOPO-HQ added is 8% to 12% of the mass of bisphenol A type epoxy resin.

[0015] Preferably, the bisphenol A type epoxy resin is E-51 type, with an epoxy equivalent of 184 to 194 g / eq and a viscosity of 11,000 to 14,000 mPa·s at 25°C; the DOPO-HQ has a purity of not less than 98% and a phenolic hydroxyl value of 345 to 365 mg KOH / g.

[0016] Preferably, the cashew phenol amine curing agent has an amine value of 260 to 280 mg KOH / g and a viscosity of 3000 to 5000 mPa·s at 25°C; the hydrophobic nano-silica particles have a particle size of 15 to 25 nm, are surface-treated with hexamethyldisilazane, and have a specific surface area of ​​150 ± 25 m². 2 / g.

[0017] Preferably, the DOPO-HQ is grafted onto the epoxy resin side chain in a suspended manner, and the POC ether bond, the C15 long-chain alkyl group of the cashew phenol amine curing agent, and the hydrophobic surface of the hydrophobic nano silica together constitute a controlled hydrolysis release-hydrophobic barrier-micropore filling waterproof and anti-corrosion system in the coating.

[0018] A method for preparing the aforementioned waterproof and corrosion-resistant modified epoxy resin packaging coating includes the following steps: Step 1: DOPO-HQ and bisphenol A type epoxy resin are added to a reactor and heated to 130°C to 150°C under nitrogen protection. Triphenylphosphine catalyst is added, and the reaction is maintained at this temperature for 2 to 3 hours to obtain DOPO-HQ modified epoxy resin. This step is a pre-grafting step. DOPO-HQ is grafted onto the side chain of epoxy resin in a suspended manner through the addition reaction of phenolic hydroxyl groups and epoxy groups to form POC ether bonds. This pre-grafting is a prerequisite for the subsequent controlled hydrolysis of POC bonds to release phosphorus-containing species. If DOPO-HQ is added by physical blending, it is in a free state in the coating and dissolves rapidly when water penetrates, which not only fails to achieve controlled release but also leaves voids after dissolution, thus aggravating the deterioration of the coating. Step 2: Add the DOPO-HQ modified epoxy resin obtained in Step 1 to the mixing tank, and add xylene and n-butanol in sequence while stirring at 400 r / min to 600 r / min. Stir for 15 min to 20 min until the resin is completely dissolved. Step 3: Add dispersant and silane coupling agent KH-560, and disperse at a high speed of 800 r / min to 1200 r / min for 5 min to 10 min; Step 4: Add talc powder, precipitated barium sulfate and hydrophobic nano silica in sequence, and disperse at a high speed of 1200 r / min to 1500 r / min for 25 min to 35 min until the fineness is no greater than 30 μm; Step 5: Reduce the stirring speed to 400 r / min to 600 r / min, add defoamer and leveling agent, and stir for 10 min to 15 min to obtain component A; Step 6: Before construction, mix component A with cashew phenol amine curing agent at a mass ratio of 100:22 to 100:30, stir evenly, and let it mature for 20 to 30 minutes to obtain the finished coating.

[0019] Preferably, in step one, the amount of triphenylphosphine added is 0.2% to 0.5% of the mass of bisphenol A epoxy resin, the reaction temperature is 135°C to 145°C, and the reaction time is 2h to 2.5h.

[0020] Preferably, the amount of DOPO-HQ added in step one is 8% to 12% of the mass of bisphenol A epoxy resin.

[0021] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention grafts DOPO-HQ onto epoxy resin, allowing the phosphorus-containing anti-corrosion function to exist through intramolecular chemical bonds, effectively eliminating the voids and osmotic pressure problems caused by the dissolution of particulate pigments.

[0022] 2. This invention uses DOPO-HQ as an intramolecular phosphorus-containing functional source. The two phenolic hydroxyl groups in the DOPO-HQ molecule react with the epoxy groups of the epoxy resin to form ether bonds for grafting, covalently grafting the phosphorus-containing phenanthrene ring structure onto the polymer. After the grafted DOPO-HQ is cured, it is uniformly distributed in the cross-linked network, and there are no migratable or soluble particulate phases. When moisture penetrates to the interface between the coating and the metal substrate, the slow hydrolysis of the POC bonds under alkaline conditions releases phosphorus-containing species. The phosphorus-containing species form a phosphorus-containing passivation protective layer on the metal surface, achieving active protection of the corrosion initiation site.

[0023] 3. The rigid skeleton of the phenanthrene ring in the DOPO-HQ molecule of this invention provides the coating with dual benefits. The rigidity of the phenanthrene ring increases the effective crosslinking density of the crosslinking network, thereby improving the glass transition temperature and hardness. The phenanthrene ring reduces the free volume of the polymer chain segments, thereby reducing the diffusion channels of water in the coating and significantly reducing the water absorption rate.

[0024] 4. This invention uses cashew phenol amine as a curing agent. The C15 long-chain alkyl group in the cashew phenol molecule endows the cured product with inherent hydrophobicity. It works synergistically with the phenanthrene ring rigid skeleton of DOPO-HQ to make the water contact angle of the coating surface reach 94.2 to 97.9, which shows excellent waterproof performance.

[0025] 5. This invention forms a synergistic anti-corrosion and waterproof mechanism: the POC ether bonds of DOPO-HQ suspended grafts undergo controlled hydrolysis under alkaline conditions at the coating-metal interface, releasing phosphorus-containing species and achieving active passivation protection of the metal surface. This mechanism is fundamentally different from the dissolution-diffusion-film formation mechanism of particulate pigments. The C15 long-chain alkyl group in the cashew phenol aldehyde amine curing agent molecule forms a hydrophobic barrier on the coating surface, reducing the water penetration rate and matching the hydrolysis rate of the POC bonds, ensuring that the release of phosphorus-containing species is synchronized with water penetration. The hydrophobic nano-silica fills the nanoscale micropores in the coating, blocking the penetration path of corrosive media. This, combined with the effect of the phenanthrene ring rigid skeleton reducing free volume, reduces the water absorption rate of the coating to 0.81% to 0.95%.

[0026] 6. In the preparation method of this invention, the pre-grafting step of DOPO-HQ and epoxy resin ensures that the phosphorus-containing function is grafted onto the resin in a covalent manner. This pre-grafting is a prerequisite for the controlled hydrolysis of POC bonds to release phosphorus-containing species. If DOPO-HQ is added to the coating system in a physical blending manner, it is in a free state in the coating and dissolves rapidly when water penetrates. This not only fails to achieve controlled release but also leaves voids after dissolution, which aggravates the deterioration of the coating.

[0027] 7. The suspension grafting method of DOPO-HQ in this invention is fundamentally different from the cross-linking grafting method of direct reaction of DOPO: DOPO molecules react directly with epoxy groups through PH bonds, and DOPO molecules act as cross-linking points to connect two polymer chain segments simultaneously through PC bonds. The phosphorus-containing DOPO ring is tightly wrapped by the two polymer chains, and the steric hindrance is significantly increased. Water has difficulty approaching the POC bond to cause hydrolysis. Therefore, although the direct reaction of DOPO can introduce phosphorus into the resin, it cannot achieve the preservative function of controlled hydrolysis to release phosphorus-containing species. In contrast, after grafting, DOPO-HQ is suspended on the polymer side chain only through one phenolic hydroxyl ether bond, and the other phenolic hydroxyl group remains unreacted or forms a single-point connection with different resin molecules. The phenanthrene ring structure is exposed in the gaps between polymer chain segments, with less steric hindrance, and water can more easily approach the POC bond to trigger controlled hydrolysis. Detailed Implementation

[0028] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] The sources of raw materials used in the following examples and comparative examples are as follows: Bisphenol A type epoxy resin E-51, epoxy equivalent 184 to 194 g / eq, viscosity at 25℃ 11000 to 14000 mPa·s, Nantong Xingchen Synthetic Materials Co., Ltd. DOPO-HQ, chemical name 10-hydroquinone-9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, molecular weight 324.27, purity not less than 98%, phenolic hydroxyl value 350 to 360 mgKOH / g, Shanghai Caigu International Trade Co., Ltd.; DOPO, purity not less than 99%, Shanghai Caigu International Trade Co., Ltd.; Triphenylphosphine, purity not less than 99%, catalytic grade, Sinopharm Chemical Reagent Co., Ltd. Cashew phenolic amine curing agent, amine value 260 to 280 mgKOH / g, viscosity at 25℃ 3000 to 5000 mPa·s, Wansheng Co., Ltd. WSCM-1206; talc powder, 1250 mesh, Liaoning Aihai Talc Co., Ltd. Precipitated barium sulfate, 800 mesh, Guizhou Hongxing Development Co., Ltd.; hydrophobic nano-silica, particle size 15 to 25 nm, surface treated with hexamethyldisilazane, specific surface area 150 ± 25 m². 2 / g, Wacker Chemie HDK H20; Silane coupling agent KH-560, γ-glycidoxypropyltrimethoxysilane, purity not less than 98%, Jingzhou Jianghan Fine Chemical Co., Ltd.; Dispersant BYK-163, polymer block copolymer, BYK Chemical. Defoamer BYK-066, silicone-based, BYK Chemical; Leveling agent BYK-306, polyether-modified polysiloxane, BYK Chemical; Xylene and n-butanol, industrial grade, commercially available; zinc phosphate, particle size 3 to 5 μm, Guangxi Chemical Research Institute Co., Ltd.

[0030] Example 1: Preparation of DOPO-HQ modified epoxy resin: 100g of bisphenol A type epoxy resin E-51 and 10g of DOPO-HQ were added to a 250mL four-necked flask, heated to 140℃ under nitrogen protection, 0.3g of triphenylphosphine catalyst was added, and the reaction was maintained at this temperature for 2.5h to obtain DOPO-HQ modified epoxy resin.

[0031] Preparation of Component A of the coating: The above-mentioned DOPO-HQ modified epoxy resin was added to a mixing tank. 12g of xylene and 6g of n-butanol were added sequentially while stirring at 500r / min, and the mixture was stirred for 15min until the resin was completely dissolved. 0.6g of dispersant BYK-163 and 1.5g of silane coupling agent KH-560 were added, and the mixture was dispersed at 1000r / min for 8min. 16g of talc, 10g of precipitated barium sulfate, and 2g of hydrophobic nano-silica were added sequentially, and the mixture was dispersed at 1300r / min for 30min until the fineness was no greater than 30μm. The stirring speed was reduced to 500r / min, and 0.3g of defoamer BYK-066 and 0.3g of leveling agent BYK-306 were added. The mixture was stirred for 12min to obtain Component A.

[0032] Before application, mix component A with cashew phenol amine curing agent at a mass ratio of 100:26, stir evenly, and allow to mature for 25 minutes to obtain the finished coating.

[0033] Example 2: Preparation of DOPO-HQ modified epoxy resin: 100g of bisphenol A type epoxy resin E-51 and 8g of DOPO-HQ were added to a 250mL four-necked flask, heated to 135℃ under nitrogen protection, 0.3g of triphenylphosphine catalyst was added, and the reaction was maintained at this temperature for 2.5h to obtain DOPO-HQ modified epoxy resin.

[0034] Preparation of Component A of the coating: The above-mentioned DOPO-HQ modified epoxy resin was added to a mixing tank. 12g of xylene and 6g of n-butanol were added sequentially while stirring at 500r / min, and the mixture was stirred for 15min until the resin was completely dissolved. 0.6g of dispersant BYK-163 and 1.5g of silane coupling agent KH-560 were added, and the mixture was dispersed at 1000r / min for 8min. 16g of talc, 10g of precipitated barium sulfate, and 2g of hydrophobic nano-silica were added sequentially, and the mixture was dispersed at 1300r / min for 30min until the fineness was no greater than 30μm. The stirring speed was reduced to 500r / min, and 0.3g of defoamer BYK-066 and 0.3g of leveling agent BYK-306 were added. The mixture was stirred for 12min to obtain Component A.

[0035] Before application, mix component A with cashew phenol amine curing agent at a mass ratio of 100:26, stir evenly, and allow to mature for 25 minutes to obtain the finished coating.

[0036] Example 3: Preparation of DOPO-HQ modified epoxy resin: 100g of bisphenol A type epoxy resin E-51 and 12g of DOPO-HQ were added to a 250mL four-necked flask, heated to 145℃ under nitrogen protection, 0.3g of triphenylphosphine catalyst was added, and the reaction was maintained at this temperature for 2.5h to obtain DOPO-HQ modified epoxy resin.

[0037] Preparation of Component A of the coating: The above-mentioned DOPO-HQ modified epoxy resin was added to a mixing tank. 12g of xylene and 6g of n-butanol were added sequentially while stirring at 500r / min, and the mixture was stirred for 15min until the resin was completely dissolved. 0.6g of dispersant BYK-163 and 1.5g of silane coupling agent KH-560 were added, and the mixture was dispersed at 1000r / min for 8min. 16g of talc, 10g of precipitated barium sulfate, and 2g of hydrophobic nano-silica were added sequentially, and the mixture was dispersed at 1300r / min for 30min until the fineness was no greater than 30μm. The stirring speed was reduced to 500r / min, and 0.3g of defoamer BYK-066 and 0.3g of leveling agent BYK-306 were added. The mixture was stirred for 12min to obtain Component A.

[0038] Before application, mix component A with cashew phenol amine curing agent at a mass ratio of 100:26, stir evenly, and allow to mature for 25 minutes to obtain the finished coating.

[0039] Comparative Example 1: Preparation of Component A of the coating: 100g of unmodified bisphenol A type epoxy resin E-51 was added to a mixing tank. 12g of xylene and 6g of n-butanol were added sequentially while stirring at 500r / min, and the mixture was stirred for 15min until the resin was completely dissolved. 0.6g of dispersant BYK-163 and 1.5g of silane coupling agent KH-560 were added, and the mixture was dispersed at 1000r / min for 8min. 16g of talc, 10g of precipitated barium sulfate, and 2g of hydrophobic nano-silica were added sequentially, and the mixture was dispersed at 1300r / min for 30min until the fineness was no greater than 30μm. The stirring speed was reduced to 500r / min, and 0.3g of defoamer BYK-066 and 0.3g of leveling agent BYK-306 were added. The mixture was stirred for 12min to obtain Component A.

[0040] Before application, mix component A with cashew phenol amine curing agent at a mass ratio of 100:26, stir evenly, and allow to mature for 25 minutes to obtain the finished coating.

[0041] Comparative Example 2: Preparation of Component A of the coating: 100g of unmodified bisphenol A type epoxy resin E-51 was added to a mixing tank. 12g of xylene and 6g of n-butanol were added sequentially while stirring at 500r / min, and the mixture was stirred for 15min until the resin was completely dissolved. 10g of DOPO-HQ was added, and the mixture was stirred at 80℃ for 30min until the DOPO-HQ was uniformly dissolved. 0.6g of dispersant BYK-163 and 1.5g of silane coupling agent KH-560 were added, and the mixture was dispersed at 1000r / min for 8min. 16g of talc, 10g of precipitated barium sulfate, and 2g of hydrophobic nano-silica were added sequentially, and the mixture was dispersed at 1300r / min for 30min until the fineness was no greater than 30μm. The stirring speed was reduced to 500r / min, and 0.3g of defoamer BYK-066 and 0.3g of leveling agent BYK-306 were added. The mixture was stirred for 12min to obtain Component A.

[0042] Before application, mix component A with cashew phenol amine curing agent at a mass ratio of 100:26, stir evenly, and allow to mature for 25 minutes to obtain the finished coating.

[0043] Comparative Example 3: Preparation of DOPO modified epoxy resin: 100g of bisphenol A type epoxy resin E-51 and 7.2g of DOPO were added to a 250mL four-necked flask, heated to 150℃ under nitrogen protection, and kept at this temperature for 3h to obtain DOPO modified epoxy resin.

[0044] In DOPO, the PH bond reacts directly with the epoxy group, and the DOPO molecule acts as a crosslinking point to connect two polymer chain segments simultaneously through the PC bond.

[0045] Preparation of Component A of the coating: The above-mentioned DOPO modified epoxy resin was added to a mixing tank, and 12g of xylene and 6g of n-butanol were added sequentially under stirring at 500r / min. The mixture was stirred for 15min until the resin was completely dissolved. 0.6g of dispersant BYK-163 and 1.5g of silane coupling agent KH-560 were added, and the mixture was dispersed at 1000r / min for 8min. 16g of talc, 10g of precipitated barium sulfate and 2g of hydrophobic nano-silica were added sequentially, and the mixture was dispersed at 1300r / min for 30min until the fineness was no greater than 30μm. The stirring speed was reduced to 500r / min, and 0.3g of defoamer BYK-066 and 0.3g of leveling agent BYK-306 were added. The mixture was stirred for 12min to obtain Component A.

[0046] Before application, mix component A with cashew phenol amine curing agent at a mass ratio of 100:26, stir evenly, and allow to mature for 25 minutes to obtain the finished coating.

[0047] Comparative Example 4: Preparation of Component A of the coating: 100g of unmodified bisphenol A type epoxy resin E-51 was added to a mixing tank. 12g of xylene and 6g of n-butanol were added sequentially while stirring at 500r / min, and the mixture was stirred for 15min until the resin was completely dissolved. 0.6g of dispersant BYK-163 and 1.5g of silane coupling agent KH-560 were added, and the mixture was dispersed at 1000r / min for 8min. 16g of talc, 10g of precipitated barium sulfate, 6g of zinc phosphate, and 2g of hydrophobic nano-silica were added sequentially, and the mixture was dispersed at 1300r / min for 30min until the fineness was no greater than 30μm. The stirring speed was reduced to 500r / min, and 0.3g of defoamer BYK-066 and 0.3g of leveling agent BYK-306 were added. The mixture was stirred for 12min to obtain Component A.

[0048] Before application, mix component A with cashew phenol amine curing agent at a mass ratio of 100:26, stir evenly, and allow to mature for 25 minutes to obtain the finished coating.

[0049] Comparative Example 5: Preparation of modified zinc phosphate: 6g of zinc phosphate powder was added to 200mL of ethanol aqueous solution with a volume ratio of 3:1, ultrasonically dispersed for 30min, 0.3g of KH-560 silane coupling agent was added, and the mixture was stirred at 500r / min at 70℃ for 2h. After filtration, it was dried at 100℃ for 2h to obtain KH-560 modified zinc phosphate.

[0050] Preparation of Component A of the coating: 100g of unmodified bisphenol A type epoxy resin E-51 was added to a mixing tank. 12g of xylene and 6g of n-butanol were added sequentially while stirring at 500r / min, and the mixture was stirred for 15min until the resin was completely dissolved. 0.6g of dispersant BYK-163 and 1.5g of silane coupling agent KH-560 were added, and the mixture was dispersed at 1000r / min for 8min. 16g of talc, 10g of precipitated barium sulfate, 6g of modified zinc phosphate, and 2g of hydrophobic nano-silica were added sequentially, and the mixture was dispersed at 1300r / min for 30min until the fineness was no greater than 30μm. The stirring speed was reduced to 500r / min, and 0.3g of defoamer BYK-066 and 0.3g of leveling agent BYK-306 were added. The mixture was stirred for 12min to obtain Component A.

[0051] Before application, mix component A with cashew phenol amine curing agent at a mass ratio of 100:26, stir evenly, and allow to mature for 25 minutes to obtain the finished coating.

[0052] Comparative Example 6: Preparation of Component A of the coating: 100g of unmodified bisphenol A type epoxy resin E-51 was added to a mixing tank. 12g of xylene and 6g of n-butanol were added sequentially while stirring at 500r / min, and the mixture was stirred for 15min until the resin was completely dissolved. 10g of DOPO was added, and the mixture was stirred at 80℃ for 30min until the DOPO was uniformly dissolved. 0.6g of dispersant BYK-163 and 1.5g of silane coupling agent KH-560 were added, and the mixture was dispersed at 1000r / min for 8min. 16g of talc, 10g of precipitated barium sulfate, 6g of zinc phosphate, and 2g of hydrophobic nano-silica were added sequentially, and the mixture was dispersed at 1300r / min for 30min until the fineness was no greater than 30μm. The stirring speed was reduced to 500r / min, and 0.3g of defoamer BYK-066 and 0.3g of leveling agent BYK-306 were added. The mixture was stirred for 12min to obtain Component A.

[0053] Before application, mix component A with cashew phenol amine curing agent at a mass ratio of 100:26, stir evenly, and allow to mature for 25 minutes to obtain the finished coating.

[0054] Comparative Example 7: Preparation of DOPO-HQ modified epoxy resin: Same as in Example 1.

[0055] Preparation of Component A of the coating: The above-mentioned DOPO-HQ modified epoxy resin was added to a mixing tank, and 12g of xylene and 6g of n-butanol were added sequentially under stirring at 500r / min. The mixture was stirred for 15min until the resin was completely dissolved. 0.6g of dispersant BYK-163 and 1.5g of silane coupling agent KH-560 were added, and the mixture was dispersed at 1000r / min for 8min. 16g of talc, 10g of precipitated barium sulfate, 6g of zinc phosphate, and 2g of hydrophobic nano-silica were added sequentially, and the mixture was dispersed at 1300r / min for 30min until the fineness was no greater than 30μm. The stirring speed was reduced to 500r / min, and 0.3g of defoamer BYK-066 and 0.3g of leveling agent BYK-306 were added. The mixture was stirred for 12min to obtain Component A.

[0056] Before application, mix component A with cashew phenol amine curing agent at a mass ratio of 100:26, stir evenly, and allow to mature for 25 minutes to obtain the finished coating.

[0057] Performance testing: The coatings prepared in each embodiment and comparative example were applied to sandblasted Q235 steel plates, with a dry film thickness of 80±5μm. Performance tests were conducted after curing at room temperature for 7 days.

[0058] Pencil hardness was determined according to GB / T 6739-2006; Impact strength was determined according to GB / T 1732-1993; Flexibility was determined according to GB / T 1731-1993; Dry adhesion was determined according to GB / T 9286-1998; The 24-hour water absorption rate was determined according to GB / T 1738-1979; The water contact angle was determined using the static drop method on a contact angle measuring instrument. Salt spray resistance was determined according to GB / T 1771-2007. The time when the first blister appeared on the coating was recorded, and the width of unidirectional rust propagation at the scratch was measured after 1000 hours. Wet adhesion is the adhesion of the sample after immersion in deionized water for 168 hours, as determined by GB / T 9286. Electrochemical impedance spectroscopy was performed by immersing the three-electrode system in 3.5% sodium chloride solution for 500 hours to determine the low-frequency impedance modulus. The test frequency range was 100 kHz to 0.01 Hz, and the sinusoidal wave amplitude was 10 mV.

[0059] Table 1. Results of Physical Performance Tests: Test methods: Pencil hardness was determined according to GB / T 6739-2006, impact strength was determined according to GB / T 1732-1993, flexibility was determined according to GB / T 1731-1993, and dry adhesion was determined according to the cross-cut test method of GB / T 9286-1998.

[0060] Results Analysis: Examples 1 to 3 showed pencil hardness of 2H to 3H, impact strength of 41 to 51 kg·cm, and dry adhesion of 13.1 to 14.8 MPa, indicating that the phenanthrene ring rigid skeleton after DOPO-HQ graft modification effectively improved the coating hardness and adhesion. In Example 3, the DOPO-HQ addition increased to 12%, the pencil hardness remained at 3H, but the impact strength decreased to 41 kg·cm. In contrast, Example 2 (DOPO-HQ 8%) had an impact strength of 51 kg·cm, and Example 1 (DOPO-HQ 10%) had an impact strength of 48 kg·cm. The monotonically decreasing trend of impact strength with increasing DOPO-HQ dosage is consistent with the strengthening-embrittlement transition law of the phenanthrene ring rigid skeleton increasing crosslinking density while reducing toughness. The increased decrease at 12% dosage indicates that excessive introduction of the rigid skeleton leads to increased embrittlement. Comparative Examples 4 and 6, containing zinc phosphate pigment, had impact strengths of 43 and 38 kg·cm, respectively. Comparative Example 5, containing modified zinc phosphate, had an impact strength of 43 kg·cm. Comparative Example 7, with zinc phosphate added to DOPO-HQ grafted modification, had an impact strength of 46 kg·cm, lower than the 48 kg·cm of Example 1. The weak interface between the zinc phosphate particles and the resin became stress concentration points during impact. This indicates that the bonding between the zinc phosphate particles and the resin interface is weak, becoming stress concentration points during impact. The DOPO-HQ grafting modification helps maintain the impact resistance of the coating.

[0061] Table 2. Waterproof and corrosion-resistant performance test results: Test methods: Water absorption rate was determined according to GB / T 1738-1979; water contact angle was measured using the static drop method on a contact angle measuring instrument; salt spray resistance was determined according to GB / T 1771-2007, and the initial immersion time was recorded; rust spread width was determined according to ISO 12944-6 after 1000 hours of salt spray testing; wet adhesion was determined according to GB / T 9286 after immersion in deionized water for 168 hours; electrochemical impedance spectroscopy was performed using a three-electrode system after immersion in 3.5% sodium chloride solution for 500 hours, measuring the low-frequency impedance modulus at 0.01 Hz. Five tests were performed for each group, and the average value was taken.

[0062] Results analysis: The 24-hour water absorption rate of Examples 1 to 3 was 0.81% to 0.95%, the water contact angle was 94.2% to 97.9%, the salt spray resistance was 1240 to 1500 hours, and the low-frequency impedance modulus was 1.7 × 10⁹ to 4.0 × 10⁹ Ω·cm. 2It exhibits excellent waterproof and corrosion-resistant properties.

[0063] Example 3 had the highest DOPO-HQ addition (12%), the lowest water absorption (0.81%), the longest salt spray resistance (1500h), and the highest impedance (4.0×109 Ω·cm2). However, its impact strength decreased by 5 kg·cm compared to Example 1, indicating that there is a performance balance window for the DOPO-HQ addition amount. 8% to 10% is the preferred range that balances mechanical properties and corrosion resistance.

[0064] Comparative Example 1 contains neither DOPO-HQ nor zinc phosphate, has a water absorption rate as high as 2.67%, withstands salt spray for 480 hours, and has a low-frequency impedance of 8.6 × 10⁶ Ω·cm. 2 This indicates that epoxy coatings without active protection have poor corrosion resistance.

[0065] Comparative Example 2 uses physical blending of DOPO-HQ instead of grafting, resulting in a water absorption rate of 1.79%, salt spray resistance of 680 h, and impedance of 1.1 × 10⁸ Ω·cm. 2 The values ​​were all significantly lower than in Example 1, indicating that the physically blended DOPO-HQ dissolved out during water penetration and left voids in the coating, making controlled release impossible and exacerbating coating degradation, thus proving the necessity of the grafting reaction.

[0066] In Comparative Example 3, DOPO was directly reacted with epoxy. Since the pH bond of DOPO reacts directly with the epoxy group, the DOPO molecule acts as a crosslinking point, connecting two polymer chains simultaneously through the PC bond. The phosphorus-containing DOPO ring is tightly wrapped by the two polymer chains, significantly increasing steric hindrance, making it difficult for water to approach the POC bond and cause hydrolysis. In contrast, after DOPO-HQ grafting, it is suspended on the polymer side chain only through one phenolic hydroxyl ether bond, while the other phenolic hydroxyl group remains unreacted. The steric hindrance is small, and water can more easily approach the POC bond to trigger controlled hydrolysis and release phosphorus-containing species.

[0067] Therefore, Comparative Example 3 has a water absorption rate of 1.58%, a salt spray resistance of 750 h, and a impedance of 2.3 × 10⁸ Ω·cm. 2 Although it has better shielding performance than Comparative Example 2 due to the DOPO cross-linked embedded network (impedance is higher than 1.1 × 10⁸ Ω·cm of Comparative Example 2), 2 However, because it cannot achieve active passivation protection against phosphorus-containing species released by controlled hydrolysis of POC bonds, its impedance is still much lower than the 3.5 × 10⁹ Ω·cm of Example 1. 2 This study demonstrates that the suspended grafting mechanism provided by the phenolic hydroxyl bridging structure in the DOPO-HQ molecule is key to the controlled hydrolysis of POC bonds to release phosphorus-containing species. The cross-linked structure formed by the direct reaction of DOPO is difficult to release phosphorus-containing species due to excessive steric hindrance.

[0068] Therefore, Comparative Example 3 has a water absorption rate of 1.58%, a salt spray resistance of 750 h, and a impedance of 4.2 × 10⁷ Ω·cm. 2 Compared to Example 1, this demonstrates that the suspended grafting method provided by the phenolic hydroxyl bridging structure in the DOPO-HQ molecule is the key to achieving controlled hydrolysis of POC bonds to release phosphorus-containing species. The cross-linked structure formed by the direct reaction of DOPO is difficult to release phosphorus-containing species due to excessive steric hindrance.

[0069] Comparative Example 4 used a zinc phosphate pigment scheme, with the same amounts of talc and precipitated barium sulfate (16g talc, 10g precipitated barium sulfate) as Example 1, except that 6g of zinc phosphate was added to eliminate the influence of differences in filler ratios. Comparative Example 4 withstood salt spray for 880 hours, but its wet adhesion was only 5.0MPa, and its impedance was 9.2×10⁶Ω·cm. 2 This is significantly lower than the 11.1 MPa and 3.5 × 10⁹ Ω·cm of Example 1. 2 This indicates that, under the same total filler content, the voids and osmotic pressure generated by the dissolution of zinc phosphate still severely weaken the long-term protective performance and wet adhesion of the coating.

[0070] Comparative Example 5 used KH-560 modified zinc phosphate, with the same amounts of talc and precipitated barium sulfate as Example 1. Its performance was improved compared to Comparative Example 4, with a salt spray resistance of 960 hours, but its impedance remained only 2.8 × 10⁷ Ω·cm. 2 The wet adhesion was 5.8 MPa. Even with surface modification, zinc phosphate could not eliminate the dissolution-cavitation problem, indicating that surface modification can only slow down the pigment dissolution rate and cannot fundamentally eliminate the pigment dissolution-cavitation paradox.

[0071] Comparative Example 6 involved the simultaneous addition of DOPO physical blend and zinc phosphate pigment. The amounts of talc and precipitated barium sulfate were the same as in Example 1. The water absorption rate was 2.08%, the salt spray resistance was only 540 hours, and the low-frequency impedance was 4.5 × 10⁶ Ω·cm. 2 Its low-frequency impedance is the lowest among all comparative examples. The voids generated by the dissolution of DOPO during physical blending and the voids generated by the dissolution of zinc phosphate form a double degradation. The superposition of the two known functions leads to a sharp decline in coating performance.

[0072] Comparative Example 7 still added zinc phosphate pigment to the DOPO-HQ grafted modified epoxy resin. The amounts of talc and precipitated barium sulfate were the same as in Example 1. The surface contact angle of 89.7° was lower than that of Example 1 (96.8°), and the dry adhesion of 13.4 MPa was slightly lower than that of Example 1 (14.0 MPa). However, the salt spray resistance of 930 h and the impedance of 6.3 × 10⁷ Ω·cm were better. 2 This is far lower than the 1460h and 3.5×10⁹ Ω·cm of Example 1. 2The addition of zinc phosphate particles still disrupted the dense network structure of the DOPO-HQ modified epoxy resin, resulting in a decrease in impedance modulus of nearly two orders of magnitude.

[0073] This is because the dissolution of zinc phosphate particles in the coating still generates cavitation and osmotic pressure. These defects disrupt the dense network structure that DOPO-HQ modified epoxy resin should have, resulting in a decrease in impedance modulus by nearly two orders of magnitude.

[0074] The results indicate that adding particulate phosphate pigments to the DOPO-HQ grafting modification system of this invention is not only useless but also harmful. The replacement of particulate pigments with intramolecular phosphorus-containing functions in this invention is not a simple choice, but a necessary technical path to solve the pigment dissolution-cavitation paradox.

[0075] The amounts of talc and precipitated barium sulfate in Comparative Examples 4 to 7 were consistent with those in Example 1 (16g and 10g, respectively). An additional 6g of zinc phosphate was added (total filler 34g) to eliminate interference from differences in the talc / barium sulfate ratio, ensuring that performance differences could be attributed to the fundamental difference in the way the rust-preventive function is provided (intramolecular phosphorus versus particulate pigment). The additional filler amount of zinc phosphate contributed to the physical properties of the coating, but in terms of corrosion and water resistance, the comparative examples containing zinc phosphate were still significantly lower than those without zinc phosphate, further demonstrating the superiority of intramolecular phosphorus.

[0076] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention.

Claims

1. A waterproof and corrosion-resistant modified epoxy resin packaging coating, characterized in that, The product comprises, by weight, component A and component B; component A comprises, by weight, 12 to 20 parts of talc, 8 to 14 parts of precipitated barium sulfate, 1 to 4 parts of hydrophobic nano-silica, 1 to 3 parts of silane coupling agent KH-560, 0.4 to 1 part of dispersant, 0.2 to 0.5 parts of defoamer, 0.2 to 0.5 parts of leveling agent, 8 to 16 parts of xylene, and 4 to 8 parts of n-butanol, based on 100 parts by weight of the DOPO-HQ modified epoxy resin product. Component B is a cashew phenol amine curing agent, whose C15 long-chain alkyl group in its molecular structure endows the cured product with inherent hydrophobicity; the mass ratio of component A to component B is 100:22 to 100:

30. The DOPO-HQ modified epoxy resin is prepared by grafting DOPO-HQ with bisphenol A type epoxy resin in the presence of triphenylphosphine catalyst. The amount of DOPO-HQ added is 6% to 14% of the mass of bisphenol A type epoxy resin. The chemical name of DOPO-HQ is 10-hydroquinone-9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, with a molecular weight of 324.

27. Its molecular structure contains a rigid phenanthrene ring backbone and two phenolic hydroxyl groups. Under the grafting reaction conditions, DOPO-HQ reacts with the epoxy group of the epoxy resin through one of its phenolic hydroxyl groups to form an ether bond, which is then grafted onto the side chain of the epoxy resin in a suspended manner. After grafting, the phenanthrene ring structure of DOPO-HQ is connected to the polymer side chain through POC ether bonds instead of being embedded in the main chain. After the coating is cured, the POC ether bonds can undergo slow hydrolysis under alkaline conditions at the interface between the coating and the metal substrate, releasing phosphorus-containing species to form a phosphorus-containing passivation protective layer on the metal surface. In the coating, DOPO-HQ exists on the epoxy resin side chain via intramolecular chemical bonds. The other phenolic hydroxyl group of DOPO-HQ remains in an unreacted state under the grafting reaction conditions due to steric hindrance and the molar ratio of DOPO-HQ to epoxy group being less than 1:10, ensuring that DOPO-HQ is grafted in a suspended manner rather than a crosslinking manner.

2. The waterproof and corrosion-resistant modified epoxy resin packaging coating as described in claim 1, characterized in that: The amount of DOPO-HQ added is 8% to 12% of the mass of bisphenol A type epoxy resin.

3. The waterproof and corrosion-resistant modified epoxy resin packaging coating as described in claim 1, characterized in that: The bisphenol A type epoxy resin is E-51 type, with an epoxy equivalent of 184 to 194 g / eq and a viscosity of 11,000 to 14,000 mPa·s at 25°C; the DOPO-HQ has a purity of not less than 98% and a phenolic hydroxyl value of 345 to 365 mgKOH / g.

4. The waterproof and corrosion-resistant modified epoxy resin packaging coating as described in claim 1, characterized in that: The cashew phenol amine curing agent has an amine value of 260 to 280 mg KOH / g and a viscosity of 3000 to 5000 mPa·s at 25°C; the hydrophobic nano-silica particles have a particle size of 15 to 25 nm, are surface-treated with hexamethyldisilazane, and have a specific surface area of ​​150 ± 25 m². 2 / g.

5. The waterproof and corrosion-resistant modified epoxy resin packaging coating as described in claim 1, characterized in that: The DOPO-HQ is grafted onto the epoxy resin side chain in a suspended manner. The POC ether bond, the C15 long-chain alkyl group of the cashew phenol amine curing agent, and the hydrophobic surface of the hydrophobic nano silica together constitute a controlled hydrolysis release-hydrophobic barrier-micropore filling waterproof and anti-corrosion system in the coating.

6. A method for preparing a waterproof and corrosion-resistant modified epoxy resin packaging coating as described in any one of claims 1 to 5, characterized in that, Includes the following steps: Step 1: Add DOPO-HQ and bisphenol A type epoxy resin to a reaction vessel, heat to 130℃ to 150℃ under nitrogen protection, add triphenylphosphine catalyst, and keep the reaction at this temperature for 2 to 3 hours to obtain DOPO-HQ modified epoxy resin. This step is a pre-grafting step. DOPO-HQ is grafted onto the epoxy resin side chain in a suspended manner through the addition reaction of phenolic hydroxyl groups and epoxy groups to form POC ether bonds. This pre-grafting is a prerequisite for the subsequent controlled hydrolysis of POC bonds to release phosphorus-containing species. If DOPO-HQ is added in a physical blending manner, it is in a free state in the coating and dissolves rapidly when water penetrates. This not only fails to achieve controlled release but also leaves voids after dissolution, which exacerbates the deterioration of the coating. Step 2: Add the DOPO-HQ modified epoxy resin obtained in Step 1 to the mixing tank, and add xylene and n-butanol in sequence while stirring at 400 r / min to 600 r / min. Stir for 15 min to 20 min until the resin is completely dissolved. Step 3: Add dispersant and silane coupling agent KH-560, and disperse at a high speed of 800 r / min to 1200 r / min for 5 min to 10 min; Step 4: Add talc powder, precipitated barium sulfate and hydrophobic nano silica in sequence, and disperse at a high speed of 1200 r / min to 1500 r / min for 25 min to 35 min until the fineness is no greater than 30 μm; Step 5: Reduce the stirring speed to 400 r / min to 600 r / min, add defoamer and leveling agent, and stir for 10 min to 15 min to obtain component A; Step 6: Before construction, mix component A with cashew phenol amine curing agent at a mass ratio of 100:22 to 100:30, stir evenly, and let it mature for 20 to 30 minutes to obtain the finished coating.

7. The method for preparing the waterproof and corrosion-resistant modified epoxy resin packaging coating as described in claim 6, characterized in that: In step one, the amount of triphenylphosphine added is 0.2% to 0.5% of the mass of bisphenol A epoxy resin, the reaction temperature is 135°C to 145°C, and the reaction time is 2h to 2.5h.

8. The method for preparing the waterproof and corrosion-resistant modified epoxy resin packaging coating as described in claim 6, characterized in that: In step one, the amount of DOPO-HQ added is 8% to 12% of the mass of bisphenol A epoxy resin.

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