Low-temperature curing high-throwing-power cathode electrophoretic coating as well as preparation method and application thereof

Abstract

The invention discloses a low-temperature curing high-throwing-power cathode electrophoretic coating and a preparation method and application thereof, and belongs to the field of automobile coating materials, the coating is composed of epoxy resin, a fluorosilicone copolymerization type epoxy modifier, a polyamino siloxane-acrylic acid hybrid and other components, and performance improvement is achieved through the synergistic effect of the two brand-new modifiers. Wherein the fluorine-silicon copolymerization type epoxy modifier is prepared by taking bisphenol A epoxy resin as a framework, introducing fluorine-containing alkyl and siloxane groups and carrying out ultraviolet reaction, so that the surface energy is reduced, and low-temperature crosslinking is promoted; the polyamido siloxane-acrylic acid hybrid takes siloxane as a core, and acrylic acid and polyamido are bridged through isocyanate, so that the crosslinking density and the water solubility are enhanced. When the coating is prepared, the two modifiers are mixed with epoxy resin, a solvent and the like, and the coating is prepared through dispersion and dilution. The coating can be cured at low temperature, so that a uniform thick film is obtained in an inner cavity of a complex workpiece, and meanwhile, the coating has excellent corrosion resistance and adhesive force and is suitable for efficient and environment-friendly coating of an automobile body and parts.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of automobile coating materials, in particular to a low-temperature curing high-spread cathodic electrophoretic paint and a preparation method and application thereof. BACKGROUND

[0002] As one of the core technologies in the field of automobile coating, cathodic electrophoretic paint has long occupied the mainstream position of automobile body and parts coating due to its high spread, uniform film thickness and excellent corrosion resistance. Traditional cathodic electrophoretic paint needs to go through a high-temperature curing process in application, usually to complete the crosslinking reaction in a high-temperature environment. This process not only significantly increases the production energy consumption, but also easily causes thermal deformation of metal workpieces. Especially for complex automobile parts, thermal stress concentration may cause coating cracking or adhesion loss, limiting its further promotion in precision and lightweight automobile manufacturing.

[0003] The coating quality of complex workpieces is another key indicator to measure the performance of cathodic electrophoretic paint. Due to the complex structure and narrow inner cavity of automobile door hinges, wheel covers and other parts, the electric field distribution is uneven during the electrophoresis process, and the anion of the resin cannot effectively migrate to the inner cavity surface, resulting in a film thickness of less than 10 microns in the inner cavity, which cannot form an effective protective barrier. Although the traditional technology attempts to improve the electrophoresis behavior by adding surfactants, excessive use will weaken the chemical adhesion between the resin and the metal substrate. Some modification methods can improve the spread, but it is difficult to simultaneously solve the contradiction between curing temperature and corrosion resistance, and the comprehensive performance of the coating is limited.

[0004] In view of the above problems, the industry focuses on the modification of cathodic electrophoretic paint, but the existing technology still has significant bottlenecks. Epoxy resin as the main chain material of cathodic electrophoretic paint, its low-temperature crosslinking needs to rely on high-activity modifiers, and traditional modifiers are mostly designed with single functional groups (such as containing only fluorine or silicon elements), which are difficult to achieve multiple goals such as reducing surface energy to promote low-temperature curing, enhancing interface adhesion to improve spread, and improving corrosion resistance. In addition, the existing modification process often involves complex chemical reaction conditions or expensive raw materials, resulting in increased production cost of the paint, which is difficult to meet the needs of large-scale industrial application. Therefore, developing a new type of modified compound with low-temperature crosslinking activity, high spread promotion function and comprehensive corrosion resistance has become a key direction to break through the performance bottleneck of cathodic electrophoretic paint. SUMMARY

[0005] The purpose of the present application is to provide a low-temperature curing high-spread cathodic electrophoretic paint and a preparation method and application thereof, which solves the problems of high energy consumption of existing cathodic electrophoretic paint high-temperature curing, thin film thickness in the inner cavity of complex workpieces, and poor corrosion resistance.

[0006] The present application achieves the above-mentioned purposes through the following technical solutions: A low-temperature curing high-wetting cathode electrophoretic paint, comprising the following raw materials in parts by weight: epoxy resin: 500-600 parts by weight; fluorosilicon copolymer type epoxy modifier: 100-150 parts by weight; polyamine-based siloxane-acrylic hybrid: 50-80 parts by weight; glycol butyl ether: 200-250 parts by weight; dimethyl sulfoxide: 50-80 parts by weight; titanium white: 150-200 parts by weight; talc: 80-120 parts by weight; organic bentonite: 20-30 parts by weight; antifoaming agent: 3-5 parts by weight; polyether modified polydimethylsiloxane: 2-3 parts by weight; deionized water: 200-250 parts by weight; The preparation method of the fluorosilicon copolymer type epoxy modifier comprises the following steps: A1, dissolving bisphenol A epoxy resin in dimethylbenzene, and stirring and dissolving at a temperature of 120-122°C; sequentially adding perfluorooctyl acrylate and γ-glycidyl ether oxygen propyl trimethoxysilane; A2, adding 2,4,6-trimethylbenzoyl-diphenyl phosphine oxide and N,N-dimethyl aniline, and irradiating under ultraviolet light in nitrogen protection; and distilling under reduced pressure after the reaction is completed.

[0007] According to the preferred embodiment of the present application, the epoxy resin is purchased from Bluestar Chemical Co., Ltd., and the model number is E-44 (bisphenol A type epoxy resin, epoxy value 0.44 eq / 100g).

[0008] According to the preferred embodiment of the present application, the bisphenol A epoxy resin is purchased from Balin Petrochemical Co., Ltd., and the model number is E-20 (bisphenol A type epoxy resin, epoxy value 0.2 eq / 100g).

[0009] According to the preferred embodiment of the present application, the dimethylbenzene is purchased from Sinopec Shanghai Petrochemical Co., Ltd., and the model number is AR grade industrial dimethylbenzene (purity ≥ 99%).

[0010] According to the preferred embodiment of the present application, the perfluorooctyl acrylate is purchased from Zhejiang Juhua Group Fluorochemical Co., Ltd., and the model number is FAC-8 (perfluorooctyl acrylate, carbon number C8).

[0011] According to the preferred embodiment of the present application, the γ-glycidyl ether oxygen propyl trimethoxysilane is purchased from Hubei Wuda Organic Silicon New Material Co., Ltd., and the model number is KH-560 (γ-glycidyl ether oxygen propyl trimethoxysilane).

[0012] According to the preferred embodiment of the present application, the 2,4,6-trimethylbenzoyl-diphenylphosphine oxide is purchased from Beijing Yingli Science and Technology Development Co., Ltd., model TPO-L (photoinitiator, purity ≥ 98%).

[0013] According to the preferred embodiment of the present application, the N,N-dimethylaniline is purchased from Jiangsu Feixing Chemical Co., Ltd., model DMA (N,N-dimethylaniline, purity ≥ 99%).

[0014] According to the preferred embodiment of the present application, the ethylene glycol monobutyl ether is purchased from Jiangsu Yida Chemical Co., Ltd., model BCS (ethylene glycol monobutyl ether, purity ≥ 99.5%).

[0015] According to the preferred embodiment of the present application, the dimethyl sulfoxide is purchased from Liaoning Aoke Chemical Co., Ltd., model DMSO (dimethyl sulfoxide, purity ≥ 99.9%).

[0016] According to the preferred embodiment of the present application, the titanium dioxide is purchased from Longbai Group Co., Ltd., model BLR-996 (rutile titanium dioxide, TiO2content ≥ 96%).

[0017] According to the preferred embodiment of the present application, the talc powder is purchased from Liaoning Aihai Talc Co., Ltd., model AH-325 (talc powder, particle size ≤ 5 μm).

[0018] According to the preferred embodiment of the present application, the organic bentonite is purchased from Zhejiang Fenghong New Material Co., Ltd., model BENTON-38 (organically modified bentonite, gum price ≥ 70 mL / 15 g).

[0019] According to the preferred embodiment of the present application, the defoaming agent is purchased from Jiangsu Sixin Interface Agent Technology Co., Ltd., model SX-088 (water-based organic silicon defoaming agent, solid content ≥ 95%).

[0020] According to the preferred embodiment of the present application, the polyether modified polydimethylsiloxane is purchased from Shanghai Aladdin Biochemical Technology Co., Ltd., model PEG-2000 (polyether modified polydimethylsiloxane, HLB value 8-10).

[0021] According to the preferred embodiment of the present application, the deionized water is purchased from self-made deionized water (electrical conductivity ≤ 10 μS / cm, metal ion content ≤ 1 ppb).

[0022] In the present application, the synthesis of fluorosilicone copolymer type epoxy modifier takes bisphenol A epoxy resin as starting material, and first forms a uniform system by solvent dissolution, laying a foundation for subsequent functional group introduction. The epoxy group (-CH(O)CH-) on the molecular chain of bisphenol A epoxy resin has high reactivity, and can copolymerize with fluorine-containing monomer and silane group under heating. The double bond (-C=C-) in perfluorooctyl acrylate is activated under ultraviolet light initiation, and forms a covalent bond with the ring-opening reaction of the epoxy group, introducing a long-chain fluorocarbon structure (-C6F 13 ) into the epoxy resin skeleton; at the same time, the siloxane group (-Si-O-Si-) of γ-glycidyl ether oxypropyl trimethoxysilane is hydrolyzed to generate hydroxyl (-OH), and condenses with the epoxy group to form a stable siloxane bond (-Si-O-C-). The nitrogen protection environment avoids the quenching of oxygen on the free radical reaction, and the photoinitiator (2,4,6-trimethylbenzoyl-diphenyl phosphine oxide) decomposes to generate free radicals after absorbing ultraviolet light energy, accelerating the addition reaction of the double bond and the epoxy group. After the reaction is completed, the solvent is removed by reduced pressure distillation, and a copolymer type epoxy modifier containing fluorocarbon chain and siloxane chain segment is obtained. The long fluorocarbon chain of the modifier gives the coating low surface energy characteristics, and reduces the migration resistance of resin particles to the metal surface; the siloxane chain segment reduces the activation energy required for curing through the hydrogen bonding of the hydroxyl group and the epoxy group, and creates conditions for low-temperature curing.

[0023] According to the preferred embodiment of the present application, in step A1, the mass ratio of bisphenol A epoxy resin to xylene is 1: (2-2.2).

[0024] According to the preferred embodiment of the present application, in step A2, the amount of 2,4,6-trimethylbenzoyl-diphenyl phosphine oxide is 2-4% of the mass of the epoxy resin; the amount of N,N-dimethyl aniline is 1-2% of the mass of the epoxy resin; the wavelength of ultraviolet light irradiation is 365-370 nm, the power is 500-520 W, and the reaction time is 4-6 h.

[0025] According to the preferred embodiment of the present application, the preparation method of the polyamine-based siloxane-acrylic hybrid body comprises: B1, dissolving the terminal hydroxyl polydimethylsiloxane and isophorone diisocyanate in N,N-dimethyl formamide; heating to 70-72℃ to generate terminal isocyanate groups; B2, cooling to 50-52℃, adding hydroxyethyl acrylate to cap the reaction, to obtain an intermediate; and then adding a polyethylene polyamine and reacting at 80-82℃, and removing the unreacted amine under reduced pressure.

[0026] According to the preferred embodiment of the present application, the terminal hydroxyl polydimethylsiloxane is purchased from Hubei Xingfa Organic Silicon New Material Co., Ltd., and the model number is XH-201 (terminal hydroxyl polydimethylsiloxane, molecular weight 2000-3000).

[0027] According to the preferred embodiment of the present application, the isophorone diisocyanate is purchased from Wanhua Chemical Group Co., Ltd., with the model number of WANNATE 8012 (isophorone diisocyanate, purity ≥ 99.5%).

[0028] According to the preferred embodiment of the present application, the N,N-dimethylformamide is purchased from Jiangsu Feixiang Chemical Co., Ltd., with the model number of DMF-99.9 (N,N-dimethylformamide, industrial grade high purity, moisture ≤ 0.05%).

[0029] According to the preferred embodiment of the present application, the hydroxyethyl acrylate is purchased from Wanhua Chemical Group Co., Ltd., with the model number of WANLITE HEA-100 (hydroxyethyl acrylate, purity ≥ 99.0%).

[0030] According to the preferred embodiment of the present application, the polyethylene polyamine is purchased from Jiangsu Feixiang Chemical Co., Ltd., with the model number of DETA-80 (polyethylene polyamine, diethylene triamine content ≥ 80%).

[0031] In the present application, the preparation of the amine-silicone-acrylic hybrid uses a step-by-step addition reaction; the hydroxyl group (-OH) of the hydroxyl-terminated polydimethylsiloxane (PDMS-OH) reacts with the isocyanate group (-NCO) of the isophorone diisocyanate (IPDI) to generate an intermediate (PDMS-NCO) with an isocyanate group (-NCO) at the end, in which the carbon atom of the isocyanate group is attacked by the hydroxyl oxygen atom to form a stable carbamate bond (-NH-CO-O-). Subsequently, hydroxyethyl acrylate (HEA) is added, and its hydroxyl group reacts with the remaining isocyanate group to form an intermediate (PDMS-HEA) containing an acrylic segment (-CH2=CHCOO-) to avoid excessive hydrolysis of the isocyanate group. Finally, polyethylene polyamine (DETA) is added, and the amine group (-NH2) reacts with the unreacted isocyanate group in the intermediate to generate a urea bond (-NH-CO-NH-), forming a "silicone-polyurethane-acrylic" hybrid structure. In this structure, the polyamine group (-NH2) acts as a high-efficiency crosslinking point, which can undergo ring-opening reaction with the epoxy group of the epoxy resin at low temperature to form a dense crosslinking network; the silicone segment reduces the surface energy of the coating and improves the penetration power; and the acrylic segment enhances the water solubility to ensure the stability of the coating during the electrophoresis process.

[0032] According to the preferred embodiment of the present application, in step B1, the reaction time is 2-4 h.

[0033] According to the preferred embodiment of the present application, in step B2, the time for the end-capping reaction is 1-2 h, and the reaction time at 80-82°C is 3-4 h.

[0034] The application further provides a preparation method of the low-temperature curing high-penetration cathode electrophoretic paint. S1, the fluorosilicon copolymer type epoxy modifier is mixed with the epoxy resin, glycol butyl ether and dimethyl sulfoxide are added, and the temperature is raised to 80-82 DEG C and stirred; a polyamine-siloxane-acrylic hybrid is added, and the reaction is carried out at 60-62 DEG C; S2, titanium white, talcum powder, organic bentonite, defoaming agent, polyether modified polydimethylsiloxane are added, high-speed dispersion is carried out, deionized water is used for dilution, slurry is obtained, and filtration is carried out.

[0035] In the preparation process of the paint, the mixing reaction of the fluorosilicon copolymer type epoxy modifier and the epoxy resin is a key step. The epoxy groups in the modifier and the epoxy groups in the epoxy resin form an interpenetrating network structure through an oxygen bridge (-O-), and at the same time, the fluorocarbon chain and the siloxane chain in the modifier migrate to the surface of the paint, thereby reducing the surface tension of the system. The polyamine groups in the polyamine-siloxane-acrylic hybrid crosslink with the epoxy groups in the epoxy resin to form a three-dimensional network structure, thereby significantly improving the crosslinking density of the coating. In the dispersion stage, the pigments such as titanium white and talcum powder are uniformly suspended through the dispersion effect of the organic bentonite, and the defoaming agent and the leveling agent improve the construction performance of the paint. After dilution, the water-based paint formed in the electrophoresis process migrates to the metal workpiece, and the low surface energy of the fluorocarbon chain reduces the particle migration resistance, and the electric field distribution in the complex cavity area is more uniform, so that a uniform film layer is deposited on the surface of the cavity. In the curing stage, the crosslinking reaction of the epoxy groups and the amine groups is quickly completed under low temperature (120-150 DEG C), the silanol (-Si-OH) generated by the hydrolysis of the siloxane condenses with the hydroxyl groups (-OH) on the metal surface to form a siloxane bond (-Si-O-M-), thereby enhancing the adhesion between the coating and the substrate; the hydrophobicity of the fluorocarbon chain hinders the penetration of water vapor, and the polyamine crosslinking network reduces the porosity of the coating, and finally a high-penetration, corrosion-resistant cathode electrophoretic coating is formed.

[0036] According to the preferred embodiment of the application, in step S1, the temperature is raised to 80-82 DEG C and stirred for 2-3 h; and the reaction is carried out at 60-62 DEG C for 1-2 h.

[0037] According to the preferred embodiment of the application, in step S2, the rotation speed of high-speed dispersion is 10000-12000 rpm, and the time is 30-40 min; and the filter screen aperture for filtration is 100-110 mesh.

[0038] The application further provides the application of the low-temperature curing high-penetration cathode electrophoretic paint or the low-temperature curing high-penetration cathode electrophoretic paint prepared by the preparation method to automobiles.

[0039] The application has the following beneficial effects: In the present application, the fluorosilicon copolymer type epoxy modifier takes bisphenol A epoxy resin as the skeleton, introduces fluorine-containing alkyl and siloxane groups: the siloxane group is hydrolyzed to generate hydroxyl group in the curing process, forms hydrogen bond with the epoxy group, greatly reduces the reaction activation energy, and makes the curing temperature reduce to 120-150℃; the fluorine-containing alkyl reduces the surface energy of the coating, and promotes the migration of the resin particles to the metal surface. The polyamine-siloxane-acrylic hybrid takes siloxane as the core, and the acrylic acid is bridged with the polyamine group through the isocyanate, wherein the polyamine group acts as a high-efficiency crosslinking agent, can rapidly react with the epoxy group at low temperature, forms a dense crosslinking network, and avoids the loose film problem caused by incomplete crosslinking of the traditional low-temperature coating. The synergistic effect of the two realizes the efficient and complete crosslinking of the coating at low temperature, and solves the contradiction between "low-temperature curing" and "high crosslinking density" in the traditional process.

[0040] The improvement of the penetration of complex workpieces is another core advantage of the present application. Due to the complex structure and narrow inner cavity of automobile door hinges, wheel covers and other components, the electric field distribution is uneven in the traditional electrophoresis process, and the resin particles are difficult to migrate to the inner cavity surface, resulting in insufficient film thickness. In the present application, the fluorine-containing alkyl group of the fluorosilicon copolymer type epoxy modifier has extremely low surface energy, which can reduce the contact angle of the coating with the metal surface to below 40°, significantly reducing the particle migration resistance; the acrylic acid segment of the polyamine-siloxane-acrylic hybrid enhances the water solubility and ion stability of the coating, and the charged particles are more uniformly dispersed during the electrophoresis process, and the migration path is smoother.

[0041] The comprehensive performance of the coating of the present application also realizes a qualitative leap. The fluorine-containing segment and siloxane group of the fluorosilicon copolymer type epoxy modifier synergistically form a double protection: the hydrophobicity of the fluorocarbon chain reduces water vapor penetration, and the reaction of the siloxane with the hydroxyl group on the metal surface generates siloxane bond, enhancing the adhesion of the coating to the substrate; the dense network formed by the crosslinking of the polyamine group and the epoxy group of the polyamine-siloxane-acrylic hybrid reduces the porosity of the coating and hinders the penetration of corrosive media. DETAILED DESCRIPTION

[0042] The following detailed description is only used to further illustrate the present application, and cannot be understood as limiting the protection scope of the present application. Those skilled in the art can make some non-essential improvements and adjustments to the present application according to the above application content.

[0043] I. Examples Example 1 Firstly, the fluorosilicon copolymer type epoxy modifier was prepared: 100 g of bisphenol A epoxy resin was taken into a beaker, 210 g of dimethylbenzene was added, magnetic stirring was started and the temperature was raised to 121 °C, and stirring was continued until the bisphenol A epoxy resin was completely dissolved; 18 g of perfluorooctyl acrylate and 7 g of γ-glycidyl ether oxygen propyl trimethoxysilane were sequentially added to the solution, and stirring was continued for 10 minutes to uniformly mix the three; then 3 g of 2, 4, 6-trimethylbenzoyl-diphenyl phosphine oxide and 1.5 g of N, N-dimethyl aniline were added to the solution, the beaker was transferred to a nitrogen protection device, ultraviolet light irradiation (wavelength 365 nm, power 500 W) was started, the reaction temperature was maintained at 121 °C, and the reaction was carried out for 5 hours; after the reaction was completed, the solution was transferred to a reduced pressure distillation device, dimethylbenzene was removed by distillation at 50 °C and -0.09 MPa, and the fluorosilicon copolymer type epoxy modifier was collected.

[0044] Then, the polyamine-based siloxane-acrylic hybrid was prepared: 100 g of hydroxyl-terminated polydimethylsiloxane (molecular weight 2500) was taken into a three-necked flask with stirring device and thermometer, 174 g of isophorone diisocyanate was added, 200 g of N, N-dimethylformamide was added as a solvent, stirring was started and the temperature was raised to 71 °C, and the temperature was maintained for 3 hours to generate an isocyanate-terminated intermediate; the reaction system was cooled to 51 °C, 15 g of hydroxyethyl acrylate was added, and the reaction was continued for 1 hour to complete the capping to obtain the intermediate; 60 g of polyethylene polyamine was added to the intermediate, the temperature was raised to 81 °C, and the reaction was carried out for 3.5 hours; after the reaction was completed, the unreacted polyethylene polyamine was removed by distillation under reduced pressure, and the polyamine-based siloxane-acrylic hybrid was collected.

[0045] Finally, the low-temperature curing high-wetting power cathodic electrophoretic paint was prepared: 120 g of the fluorosilicon copolymer type epoxy modifier prepared above and 550 g of epoxy resin (E-44) were taken into a high-speed mixer, stirring was started, 220 g of ethylene glycol butyl ether and 60 g of dimethyl sulfoxide were added, the temperature was raised to 81 °C, and stirring was carried out for 2.5 hours; 60 g of the polyamine-based siloxane-acrylic hybrid was added to the mixed system, the temperature was reduced to 61 °C, and the reaction was carried out for 1.5 hours; then 170 g of titanium white, 100 g of talc, 25 g of organic bentonite, 4 g of defoaming agent, and 2.5 g of polyether modified polydimethylsiloxane were sequentially added to the system, a high-speed disperser was started to disperse at a speed of 11000 rpm for 35 minutes; after the dispersion was completed, deionized water was added to dilute the solid content to 48% (mass fraction), the mixed liquid was filtered through a 105 mesh filter screen to remove impurity particles, and finally the low-temperature curing high-wetting power cathodic electrophoretic paint was obtained.

[0046] Example 2 The specific embodiment is the same as example 1, except that the preparation of fluorosilicon copolymerized epoxy modifier: take bisphenol A epoxy resin 120 g dissolved in 250 g of xylene, heated to 122 ℃ stirring to dissolve; sequentially add perfluoro octyl acrylate 22 g and γ-glycidyl ether oxygen propyl trimethoxysilane 9 g, stirring uniform; add 2,4,6-trimethyl benzoyl-diphenyl phosphine oxide 4 g and N, N-dimethyl aniline 2 g, under the protection of nitrogen with 368 nm wavelength, 510 W power ultraviolet light irradiation reaction 5.5 h; remove xylene by distillation under reduced pressure, to obtain fluorosilicon copolymerized epoxy modifier.

[0047] The preparation of polyamine based siloxane-acrylic hybrid: take the end hydroxyl polydimethylsiloxane 120 g and isophorone diisocyanate 209 g dissolved in N, N-dimethyl formamide 240 g, heated to 72 ℃ reaction 3.5 h to generate end isocyanate intermediate; cooling to 52 ℃, add hydroxyethyl acrylate 18 g to cap reaction 1.5 h, to obtain intermediate; add polyethylene polyamine 70 g at 82 ℃ for 3.5 h, remove unreacted amine under reduced pressure, to obtain polyamine based siloxane-acrylic hybrid.

[0048] The preparation of low temperature curing high wetting power cathode electrophoretic coating: fluorosilicon copolymerized epoxy modifier 140 g and epoxy resin 600 g are mixed, add ethylene glycol butyl ether 250 g and dimethyl sulfoxide 70 g, heated to 82 ℃ stirring 3 h; add polyamine based siloxane-acrylic hybrid 70 g, reaction at 62 ℃ for 2 h; add titanium dioxide 200 g, talc 120 g, organic bentonite 30 g, defoaming agent 5 g, polyether modified polydimethylsiloxane 3 g, high speed dispersion for 40 min at 12000 rpm, dilute to 50% solid with deionized water, filter through 110 mesh screen to obtain coating.

[0049] Example 3 The specific embodiment is the same as example 1, except that the preparation of fluorosilicon copolymerized epoxy modifier: take bisphenol A epoxy resin 110 g dissolved in 230 g of xylene, heated to 121 ℃ stirring to dissolve; sequentially add perfluoro octyl acrylate 20 g and γ-glycidyl ether oxygen propyl trimethoxysilane 8 g, stirring uniform; add 2,4,6-trimethyl benzoyl-diphenyl phosphine oxide 3.5 g and N, N-dimethyl aniline 1.8 g, under the protection of nitrogen with 366 nm wavelength, 505 W power ultraviolet light irradiation reaction 5.2 h; remove xylene by distillation under reduced pressure, to obtain fluorosilicon copolymerized epoxy modifier.

[0050] Preparation of polyamine-silicone-acrylic hybrid: hydroxyl-terminated polydimethylsiloxane 110 g and isophorone diisocyanate 220 g were dissolved in N,N-dimethylformamide 220 g, and the temperature was raised to 71 °C for 3.2 h to form an isocyanate-terminated intermediate; the temperature was lowered to 51 °C, and hydroxyethyl acrylate 16 g was added for end-capping for 1.2 h to form the intermediate; polyvinyl polyamine 65 g was then added, and the temperature was raised to 81 °C for 3.8 h to form the polyamine-silicone-acrylic hybrid, and unreacted amine was removed by reduced pressure.

[0051] Preparation of low-temperature-cured high-sag cathodic electrophoretic paint: fluorosilicone copolymer epoxy modifier 130 g and epoxy resin 580 g were mixed, ethylene glycol butyl ether 230 g and dimethyl sulfoxide 65 g were added, and the temperature was raised to 81 °C for 2.8 h of stirring; polyamine-silicone-acrylic hybrid 65 g was added, and the temperature was raised to 61 °C for 1.8 h; titanium dioxide 180 g, talc 110 g, organic bentonite 28 g, defoamer 4.5 g, and polyether-modified polydimethylsiloxane 2.8 g were dispersed at 11500 rpm for 38 min, and deionized water was added to dilute the paint to a solid content of 49%, and the paint was filtered through a 108-mesh screen to obtain the paint.

[0052] Comparative Example 1 The specific implementation was the same as in Example 1, except that the polyamine-silicone-acrylic hybrid was prepared as follows: the procedure of Example 1 was followed to obtain 60 g of the polyamine-silicone-acrylic hybrid. The low-temperature-cured high-sag cathodic electrophoretic paint was prepared as follows: epoxy resin 550 g and polyamine-silicone-acrylic hybrid 60 g were mixed, ethylene glycol butyl ether 220 g and dimethyl sulfoxide 60 g were added, and the temperature was raised to 81 °C for 2.5 h of stirring; titanium dioxide 170 g, talc 100 g, organic bentonite 25 g, defoamer 4 g, and polyether-modified polydimethylsiloxane 2.5 g were dispersed at 11000 rpm for 35 min, and deionized water was added to dilute the paint to a solid content of 48%, and the paint was filtered through a 105-mesh screen to obtain the paint (without fluorosilicone copolymer epoxy modifier).

[0053] Comparative Example 2 The specific implementation was the same as in Example 1, except that the fluorosilicone copolymer epoxy modifier was prepared as follows: the procedure of Example 1 was followed to obtain 120 g of the fluorosilicone copolymer epoxy modifier. The low-temperature-cured high-sag cathodic electrophoretic paint was prepared as follows: fluorosilicone copolymer epoxy modifier 120 g and epoxy resin 550 g were mixed, ethylene glycol butyl ether 220 g and dimethyl sulfoxide 60 g were added, and the temperature was raised to 81 °C for 2.5 h of stirring; titanium dioxide 170 g, talc 100 g, organic bentonite 25 g, defoamer 4 g, and polyether-modified polydimethylsiloxane 2.5 g were dispersed at 11000 rpm for 35 min, and deionized water was added to dilute the paint to a solid content of 48%, and the paint was filtered through a 105-mesh screen to obtain the paint (without polyamine-silicone-acrylic hybrid).

[0054] Comparative Example 3 The specific implementation is the same as that of Example 1, except that the preparation of the low-temperature curing high-wet-through cathodic electrophoretic paint: take 550 g of epoxy resin, add 220 g of ethylene glycol butyl ether and 60 g of dimethyl sulfoxide, heat to 81℃ and stir for 2.5 h; add 170 g of titanium dioxide, 100 g of talc, 25 g of organic bentonite, 4 g of defoaming agent, 2.5 g of polyether modified polydimethylsiloxane, high speed dispersion at 11000 rpm for 35 min, dilute with deionized water to 48% solid content, filter through a 105 mesh filter to obtain the paint (without two modifiers).

[0055] II. Performance Test The insulating materials prepared in the above Examples 1-3 and Comparative Examples 1-3 are tested for performance according to the following method: 1. Curing temperature test: take 50 mm x 100 mm x 0.2 mm tin plate, evenly coat the paint on the surface of the tin plate with a wire bar applicator (dry film thickness 20-25 μm), and put it into a constant temperature oven. Start timing from 120℃, every 10℃ is a test point, record the lowest temperature at which the coating is completely cured (not sticky, pencil hardness ≥H).

[0056] 2. Wetting power test (Ford box method): prepare a Ford box model with an inner cavity size of 50 mm x 50 mm x 10 mm (stainless steel material), coat the paint on the outer surface of the model (dry film thickness 25-30 μm), and take out the model after curing according to the curing conditions of the paint. Measure the film thickness of the four sides and the top of the inner cavity with a vernier caliper, and take the average value as the inner cavity film thickness.

[0057] 3. Corrosion resistance test (neutral salt spray test): according to GB / T 10125-2012 standard, put the cured coating test piece (size 150 mm x 70 mm x 0.2 mm, film thickness 25-30 μm) into a salt spray chamber, test conditions are 5% NaCl solution (pH 6.5-7.2), temperature 35±2℃, continuous spraying. Observe the time when rust (red rust) appears on the surface of the coating, and record the time when the first rust appears.

[0058] 4. Adhesion test (crosshatch method): according to ISO 2409 standard, draw a 1 mm x 1 mm square grid (10 x 10 grid) on the surface of the cured coating with a crosshatch tool (spacing 1 mm), paste with 3M 600 type adhesive tape, and observe the grid shedding after tearing. Rating criteria: 0 level (no shedding), 1 level (≤5% shedding), 2 level (5%-15% shedding), 3 level (15%-35% shedding), 4 level (35%-65% shedding), 5 level (>65% shedding).

[0059] 5. Pencil hardness test (GB / T 6739-2006): using a Mitsubishi pencil hardness tester, from 9B to 9H, scratch the coating surface in turn (load 7.5N, 5 times per second), record the hardest pencil model that does not scratch the coating surface (such as 2H indicates that 2H pencil does not scratch, 3H pencil scratches).

[0060] 6. Performance test results: Table 1: Performance test results of each example and comparative example

[0061] As can be seen from Table 1, examples 1-3 effectively solve the problems of high energy consumption, uneven film thickness in the inner cavity of complex workpieces and poor corrosion resistance of existing cathodic electrophoretic coatings by the synergistic effect of two modifiers. From the performance test results, the curing temperature (125-130℃) of examples 1-3 is significantly lower than that of the comparative examples (178-195℃), indicating that the siloxane groups in the fluorosilicone copolymer epoxy modifier and the polyamine groups in the polyamine-based siloxane-acrylic hybrid body synergistically reduce the curing activation energy, achieve low-temperature curing, and greatly reduce energy consumption; the inner cavity film thickness (16.2-18.5μm) is much higher than that of the comparative examples (8.2-10.5μm), which benefits from the fluorocarbon chain of the fluorosilicone copolymer epoxy modifier to reduce the surface energy and promote the migration of the resin to the inner cavity, and the acrylic segment of the polyamine-based siloxane-acrylic hybrid body to enhance the water solubility and electrophoretic stability, which together improve the film thickness uniformity of the inner cavity of complex workpieces; the salt spray corrosion time (3500-4000h) is significantly longer than that of the comparative examples (1500-2000h), which is due to the hydrophobicity of the fluorosilicon chain to hinder water vapor penetration, the reaction of siloxane and the hydroxyl group on the metal surface to form a siloxane bond to enhance the bonding force, and the dense network formed by the crosslinking of the polyamine group to reduce the pores of the coating, which together improve the corrosion resistance. In addition, the adhesion (0 level) and pencil hardness (2H) of examples 1-3 are better than those of the comparative examples, which further verifies the improvement of the modified agent on the comprehensive performance of the coating.

[0062] The above examples only express several embodiments of the present application, and the description is more specific and detailed, but it cannot be understood as limiting the scope of the present patent. It should be noted that for ordinary skilled persons in the art, without departing from the concept of the present application, several modifications and improvements can be made, which are within the scope of protection of the present application.

Claims

1. Low temperature curing high throwing power cathodic electrophoretic coating, characterized in that: The composition comprises the following raw materials in parts by weight: Epoxy resin: 500-600 parts by weight; Fluorosilicone copolymer epoxy modifier: 100-150 parts by weight; Polyaminosiloxane-acrylic acid hybrid: 50-80 parts by weight; Ethylene glycol butyl ether: 200-250 parts by weight; Dimethyl sulfoxide: 50-80 parts by weight; Titanium dioxide: 150-200 parts by weight; Talc: 80-120 parts by weight; Organic bentonite: 20-30 parts by weight; Defoaming agent: 3-5 parts by weight; Polyether modified polydimethylsiloxane: 2-3 parts by weight; Deionized water: 200-250 parts by weight; The preparation method of the fluorosilicone copolymer epoxy modifier includes: A1, dissolving bisphenol A epoxy resin in xylene, heating to 120-122°C and stirring to dissolve; adding perfluorooctyl acrylate and γ-glycidyloxypropyltrimethoxysilane in sequence; A2, adding 2,4,6-trimethylbenzoyl-diphenylphosphine oxide and N,N-dimethylaniline, and irradiating with ultraviolet light under nitrogen protection to react; and distilling under reduced pressure after the reaction is completed.

2. The low-temperature curing high-throw-power cathodic electrophoretic coating according to claim 1, characterized in that: In step A1, the mass ratio of bisphenol A epoxy resin to xylene is 1:(2-2.2).

3. The low-temperature curing high throwing power cathodic electrophoretic coating according to claim 1, characterized in that: In step A2, the amount of 2,4,6-trimethylbenzoyl-diphenylphosphine oxide is 2-4% of the mass of the epoxy resin; the amount of N,N-dimethylaniline is 1-2% of the mass of the epoxy resin; the wavelength of ultraviolet light irradiation is 365-370 nm, the power is 500-520 W, and the reaction time is 4-6 h.

4. The low-temperature curing high-throw-power cathodic electrophoretic coating according to claim 1, characterized in that: The preparation method of the polyaminosiloxane-acrylic acid hybrid comprises the following steps: B1, dissolving terminal hydroxyl polydimethylsiloxane and isophorone diisocyanate in N,N-dimethylformamide; heating the mixture to 70-72°C for reaction to generate terminal isocyanate groups; B2, cooling the mixture to 50-52°C, adding hydroxyethyl acrylate for end-capping reaction to obtain an intermediate; then adding polyethylene polyamine, reacting the mixture at 80-82°C, and removing unreacted amines under reduced pressure.

5. The low-temperature curing high throwing power cathodic electrophoretic coating according to claim 4, characterized in that: In step B1, the reaction time is 2-4 h.

6. The low-temperature curing high throwability cathodic electrophoretic coating according to claim 4, characterized in that: In step B2, the end-capping reaction time is 1-2 hours; the reaction time at 80-82° C. is 3-4 hours.

7. A method for preparing a low-temperature curing high-throwing power cathodic electrophoretic coating according to any one of claims 1 to 6, characterized in that the steps include: S1. Mix a fluorosilicone copolymer epoxy modifier with an epoxy resin, add ethylene glycol butyl ether and dimethyl sulfoxide, raise the temperature to 80-82°C and stir; add a polyaminosiloxane-acrylic acid hybrid and react at 60-62°C; S2. Add titanium dioxide, talc, organic bentonite, defoamer, and polyether-modified polydimethylsiloxane, disperse at high speed, dilute with deionized water to obtain a slurry, and filter.

8. The preparation method according to claim 7, characterized in that In step S1, the temperature is raised to 80-82°C and the stirring time is 2-3 hours; the reaction time at 60-62°C is 1-2 hours.

9. The preparation method according to claim 7, characterized in that In step S2, the rotation speed of high-speed dispersion is 10000-12000 rpm, and the time is 30-40 minutes; the pore size of the filter is 100-110 mesh.

10. A use of the low-temperature curing high-throwing power cathodic electrophoretic coating according to any one of claims 1 to 6 or the low-temperature curing high-throwing power cathodic electrophoretic coating prepared by the preparation method according to any one of claims 7 to 9, characterized in that: Application of the low-temperature curing high-throw-power cathodic electrophoretic coating on automobiles.

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