Printing paint for color-coated aluminum plate and preparation method of printing paint

Abstract

The invention discloses a printing coating for a color-coated aluminum plate and a preparation method of the printing coating, and belongs to the technical field of color-coated aluminum plate coatings. The coating comprises the following components: fluorocarbon resin, modified polyester resin, an HDI tripolymer curing agent, flake mica powder, nano # imgabs0 #, an inorganic pigment, an ultraviolet light absorber, a hindered amine light stabilizer, an organosilicon leveling agent, nano cerium oxide, a mixed solvent of xylene and butyl acetate, and a silane coupling agent. The preparation method of the coating comprises the following steps: S1, preparing the modified polyester resin; s2, pretreating the raw materials; s3, preparing main slurry of the coating; and S4, adding an auxiliary agent to prepare the printing paint for the color-coated aluminum plate. Nano cerium oxide and fluorocarbon resin cooperate, cerium oxide neutralizes free radicals, and # imgabs 1 # and # imgabs 2 # are cyclically generated, so that resin degradation is inhibited, and the absorption effect on ultraviolet rays is further improved; a vacuum defoaming process and ultrasonic dispersion are adopted, so that gaps of the coating are reduced, and the corrosion resistance of the coating is enhanced.

Description

Technical Field

[0001] The present invention relates to the technical field of color-coated aluminum sheet coatings, and particularly to a printing coating for color-coated aluminum sheets and a preparation method thereof. Background Art

[0002] Color aluminum coatings are mainly divided into polyester resins and fluorocarbon resins. Polyester resins are formed by the polycondensation of polyols and polyacids to form a high molecular polymer with an ester bond in the main chain, having good adhesion and flexibility, and are suitable for interior decoration and advertising boards. Its production cost is low and the coating process is mature. The basic anti-UV performance can be achieved by adding alkyd resins and ultraviolet absorbers (such as benzotriazoles). Fluorocarbon resins have a C-F bond as the core structure, and can absorb and shield ultraviolet rays with the characteristics of high bonds.

[0003] At present, the ester bonds in polyester resin-based coatings on the market are easily attacked by free radical chain reactions caused by ultraviolet rays, resulting in coating yellowing, powdering and other aging conditions. During the film-forming process of polyester coatings, micron-sized pores are formed due to solvent volatilization, and the chloride ion permeability is high in a salt spray environment, which easily causes pitting corrosion of the substrate aluminum. In areas with sufficient sunlight, the energy of ultraviolet rays is easily higher than the bond energy of resin chemical bonds, and the generated ROO· attacks resin molecules, continuously generating new free radicals, causing the aging of the coating layer to be cyclically amplified. Summary of the Invention

[0004] The present invention provides a printing coating for color-coated aluminum sheets and a preparation method thereof, aiming to solve the defects that polyester resin-based coatings in the prior art are prone to aging and are eroded by a salt spray environment, while fluorocarbon resins as resin matrices have high costs.

[0005] On the one hand, the present invention provides a printing coating for color-coated aluminum sheets, including the following components: 30-40 parts of modified polyester resin, 6-8 parts of flaky mica powder, nano 8-10 parts, 1.5-2 parts of ultraviolet absorber, 1-1.5 parts of hindered amine light stabilizer, 0.3-0.5 parts of silicone leveling agent, 1-1.2 parts of nano-ceria, and 35-40 parts of a mixed solvent of xylene and butyl acetate; the modified polyester resin includes the following components: 8-12 parts of trimethylolpropane, 25-30 parts of isophthalic acid, 10-15 parts of oxalic acid, 0.03-0.05 parts of monobutyltin oxide, and 20-25 parts of a mixed solution of xylene and propylene glycol monomethyl ether.

[0006] Further, the printing coating for color-coated aluminum sheet further comprises 50-60 parts of fluorocarbon resin, 18-22 parts of HDI trimer curing agent, 6-7 parts of inorganic pigment, and 0.5-1 part of silane coupling agent. The modified polyester resin contains hydroxyl groups and further comprises 35-49 parts of neopentyl glycol and 5-8 parts of thiophthalic anhydride. The molar ratio of the isocyanate groups in the HDI trimer curing agent to the hydroxyl groups in the modified polyester resin is 1.1:1. The particle size of the flaky mica powder is 5-15 μm, the molar concentration of the ultraviolet absorber is 0.05-0.07 mol / kg, the molar concentration of the hindered amine light stabilizer is 0.03-0.05 mol / kg, the ratio of xylene to butyl acetate is 7:3, and the ratio of xylene to propylene glycol methyl ether is 7:3.

[0007] On the other hand, the present invention provides a preparation method of a printing coating for color-coated aluminum sheet, comprising the following preparation steps: adding neopentyl glycol, trimethylolpropane, isophthalic acid, oxalic acid and monobutyltin oxide into a prepared reaction kettle for preliminary reaction, adding thiophthalic anhydride and excessive trimethylolpropane and keeping the temperature for reaction, cooling to a predetermined temperature, adding a premixed solvent of xylene and propylene glycol methyl ether to dilute to a preset value, and filtering to remove impurities to obtain a modified polyester resin; performing activation treatment on the fluorocarbon resin and the modified polyester resin, preparing a mixed solution of xylene and butyl acetate, performing hydrophobic treatment on nano-silica, and performing preliminary dispersion on the inorganic pigment; adding the activated fluorocarbon resin and modified polyester resin into the reaction kettle, stirring at a low speed to form a resin matrix, slowly adding a premixed solvent of xylene and butyl acetate in the first stage, heating to make the resin fully compatible, slowly adding the hydrophobically treated nano-silica into the resin matrix for first-stage dispersion, adding nano-cerium oxide, and using the and cycle to weaken the oxidation of the ultraviolet rays to the coating for second-stage dispersion to obtain a main slurry; sequentially adding an ultraviolet absorber, a hindered amine light stabilizer, and an organosilicon leveling agent, stirring, activating the HDI trimer curing agent through the premixed solvent of xylene and butyl acetate in the second stage, slowly adding the activated HDI trimer curing agent into the main slurry, mixing and adjusting the viscosity, and filtering and defoaming to obtain the printing coating for color-coated aluminum sheet.

[0008] Further, under nitrogen protection, the reaction kettle is heated to 180-190 °C within 4-6 h, and the esterification reaction is maintained until the acid value drops to 15-20 mgKOH / g.

[0009] Further, the preparation method of the premixed solvent of xylene and propylene glycol methyl ether is as follows: After adding xylene into a prepared container, stir at a low speed of 50 r / min, slowly add propylene glycol methyl ether, and increase the stirring speed to 200 r / min. After stirring for 10 min, let it stand for defoaming for standby; Add thiophthalic anhydride by means of titration monitoring, with a predetermined acid value of less than 5 mgKOH / g, and an additional 3 - 5 parts of excessive trimethylolpropane. After adding trimethylolpropane, keep it warm at 160 - 170 °C for 1 hour to ensure that the unreacted trimethylolpropane hydroxyl groups cap the main chain ends. The predetermined temperature for cooling is 120 °C, and add the premixed solvent of xylene and propylene glycol methyl ether to dilute to a solid content of 60 - 65% to obtain the modified polyester resin.

[0010] Further, the activation method of the fluorocarbon resin and the modified polyester resin is as follows: Place the fluorocarbon resin and the modified polyester resin respectively in a preheated oven at 50 - 60 °C for 2 hours; The preparation method of the mixed solution of xylene and butyl acetate is as follows: Mix xylene and butyl acetate in a ratio of 7:3, stir for 10 min, and then let it stand for defoaming for standby to obtain the pre-prepared mixed solution of xylene and butyl acetate.

[0011] Further, the method for hydrophobic treatment of the nano-silica is as follows: Ultrasonically disperse the nano-silica and 0.5% silane coupling agent in ethanol for 30 minutes, and dry at 80 °C; The method for pre-dispersion of inorganic pigments is as follows: Mix the inorganic pigments and propylene glycol methyl ether in a ratio of 1:1, and treat with a high-speed disperser at 3000 r / min for 20 minutes.

[0012] Further, the fluorocarbon resin and the modified polyester resin are stirred at a low speed of 200 - 300 r / min. The premixed solvent of xylene and butyl acetate in the first stage is 30% of the total amount of the premixed solvent of xylene and butyl acetate. The temperature for heating to make the resins fully compatible is 50 - 60 °C and keep it for 1 hour; The method for dispersion in the first stage is as follows: Increase the rotation speed to 1200 r / min, disperse for 40 min until the fineness ≤ 20 μm, sequentially add flaky mica powder and pre-dispersed inorganic pigments, and maintain high-speed stirring and dispersion for 30 minutes; The method for dispersion in the second stage is as follows: Switch to ultrasonic dispersion with a frequency of 40 kHz and a power of 500 W, disperse for at least 15 minutes to eliminate nano-agglomeration.

[0013] Further, the stirring method is as follows: adjust the rotation speed of the reaction kettle to 500 r / min; the activation treatment method of the HDI trimer curing agent is: dilute the HDI trimer curing agent with the premixed solvent of xylene and butyl acetate in the second stage at a ratio of 1:1 to avoid direct contact with moisture; the mixing method of the HDI trimer curing agent and the main slurry is: control the temperature ≤ 35°C, mix at a rotation speed of 400 r / min for 20 minutes to ensure that the NCO:OH ratio is 1.1:1; the method of adjusting the viscosity is: make the viscosity of the coating reach 60 - 80 s in a coating cup at room temperature, and perform post-treatment on the coating.

[0014] Further, the premixed solvent of xylene and butyl acetate in the second stage is 70% of the total amount of the premixed solvent of xylene and butyl acetate; the method of filtering and defoaming the coating is: filter through a 10-μm filter bag and place it in an environment with a vacuum degree of -0.08 MPa for 30 minutes of negative pressure defoaming.

[0015] The printing coating for color-coated aluminum sheets provided by the present invention synergizes nano-ceria and fluorocarbon resin. Cerium oxide neutralizes free radicals, and the cyclic generation of [missing part] inhibits resin degradation, further improves the ultraviolet absorption effect, and has a better anti-aging effect.

[0016] The hydroxyl value of the modified polyester resin can be gradient-matched with the surface of the fluorocarbon resin, reducing the stress concentration between the coating and the aluminum sheet substrate; increasing the interfacial bonding between the coating and the aluminum substrate, and reducing the peeling of the coating.

[0017] Flaky mica powder in the coating can delay the diffusion rate of corrosive media. The vacuum defoaming process plus ultrasonic dispersion is used to reduce the voids in the coating, and nano-particles are used to fill the microscopic defects to block the penetration of water and oxygen, compensating for the impact of the reduction of fluorocarbon resin on corrosion resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following drawings are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0019] Figure 1 It is a schematic flow chart of the preparation method of a printing coating for color-coated aluminum sheets of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0020] To make the objectives, technical solutions, and advantages of the present invention clearer, the following will clearly and completely describe the technical solutions in the present invention in conjunction with the accompanying drawings in the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present invention without making creative efforts fall within the scope of protection of the present invention.

[0021] The HDI trimer curing agent used in the following examples and comparative examples is of the type Bayer N3390, and the manufacturer is Covestro AG, Germany.

[0022] The benzotriazole ultraviolet absorber used in the following examples and comparative examples is of the type Tinuvin 1130, and the hindered amine light stabilizer is of the type Tinuvin 292. The manufacturer is BASF SE, Germany.

[0023] The silicone leveling agent used in the following examples and comparative examples is of the type BYK-331, and the manufacturer is BYK-Chemie GmbH, Germany.

[0024] The silane coupling agent used in the following examples and comparative examples is of the type KH-570, and the manufacturer is Wuhan Jiyesheng Chemical Co., Ltd.

[0025] As mentioned above, the ester bonds in polyester resin-based coatings are vulnerable to attack by free radical chain reactions initiated by ultraviolet light, leading to aging conditions such as yellowing and powdering of the coating. During the film-forming process of the polyester coating, micron-sized pores are formed due to solvent evaporation, and the penetration rate of chloride ions in a salt spray environment is high, easily triggering pitting corrosion of the substrate aluminum. The price of fluorocarbon resin is 3 to 5 times that of fluorocarbon resin, and using only fluorocarbon resin as the matrix resin of the coating results in a high cost.

[0026] In response to this, the present invention provides a printing coating for color-coated aluminum sheets, enabling it to synergize with fluorocarbon resin through nano-ceria. Ceria neutralizes free radicals, inhibits resin degradation, further enhances the ultraviolet absorption effect, and has a better anti-aging effect. The hydroxyl value of the modified polyester resin matches the surface energy gradient of the fluorocarbon resin, reducing stress concentration between the coating and the aluminum sheet substrate. Using a combination of polyester resin and fluorocarbon resin reduces the amount of fluorocarbon resin used, saving costs. The flaky mica powder delays the diffusion rate of corrosive media in the coating. The vacuum defoaming process combined with ultrasonic dispersion reduces the voids in the coating. The nano-particles fill the microscopic defects, block the penetration of water and oxygen, and make up for the impact of the reduction in fluorocarbon resin on corrosion resistance. It includes the following components in weight percentages: Fluorocarbon resin (FEVE) 50 - 60 parts, hydroxyl-containing modified polyester resin 30 - 40 parts, Bayer N3390 type HDI trimer curing agent 18 - 22 parts, flaky mica powder with a particle size of 5 - 15 μm 6 - 8 parts, nano 8 - 10 parts, 6 - 7 parts of inorganic pigment, 1.5 - 2 parts of Tinuvin 1130 benzotriazole ultraviolet absorber with a molar concentration of 0.05 - 0.07 mol / kg, 1 - 1.5 parts of Tinuvin 292 hindered amine light stabilizer (HALS) with a molar concentration of 0.03 - 0.05 mol / kg, 0.3 - 0.5 parts of BYK - 331 silicone leveling agent, 1 - 1.2 parts of nano - cerium oxide, 35 - 40 parts of a mixed solvent of xylene and butyl acetate with a ratio of xylene / butyl acetate = 7:3, 0.5 - 1 part of silane coupling agent; Among them, the modified polyester resin includes the following components: 35 - 49 parts of neopentyl glycol (NPG), 8 - 12 parts of trimethylolpropane (TMP), 25 - 30 parts of isophthalic acid (IPA), 10 - 15 parts of oxalic acid (AA), 0.03 - 0.05 parts of monobutyltin oxide, 5 - 8 parts of thiophthalic anhydride (HHPA), 20 - 25 parts of a mixed solution of xylene and propylene glycol methyl ether with a ratio of xylene / propylene glycol methyl ether = 7:3.

[0027] Based on the same general inventive concept, the present invention also protects a preparation method of a printing coating for color - coated aluminum sheets. As Figure 1 shown, it may include the following steps: S1. Prepare the modified polyester resin; S2. Pretreat the raw materials; S3. Prepare the main slurry of the coating; S4. Add additives to prepare the printing coating for color - coated aluminum sheets.

[0028] The above steps may include: S1. Add neopentyl glycol, trimethylolpropane, isophthalic acid, oxalic acid and monobutyltin oxide into a prepared reaction kettle, gradually heat up to 180 - 190 °C under nitrogen protection, maintain the esterification reaction until the acid value drops to 15 - 20 mgKOH / g (4 - 6 h), add thiophthalic anhydride, continue the reaction until the acid value is less than 5 mgKOH / g, then add an additional 3 - 5 parts of trimethylolpropane as the excessive trimethylolpropane, keep it warm at 160 - 170 °C for 1 hour to ensure that the unreacted trimethylolpropane hydroxyl - terminates the main chain end, cool down to 120 °C. Prepare a premixed solvent of xylene and propylene glycol methyl ether: Add xylene into a prepared container, stir at a low speed of 50 r / min, slowly add propylene glycol methyl ether, and increase the stirring speed to 200 r / min. After stirring for 10 min, let it stand to defoam and reserve. Add the prepared premixed solvent of xylene and propylene glycol methyl ether to dilute the mixed solution to a solid content of 60 - 65%, filter to remove unreacted impurities to obtain a transparent viscous liquid, and finally control the hydroxyl value at 80 - 100 mgKOH / g (tested by GB / T12009.2). The content (hydroxyl value) of the polyester resin content (hydroxyl value) and that of the fluorocarbon resin The group enhances the interfacial bonding through hydrogen bonding. By adjusting the proportion of trimethylolpropane, the hydroxyl value gradient is matched to make the surface energy of the fluorocarbon resin reach 25 - 30 mN / m. The rigid benzene ring structure of isophthalic acid is introduced to form physical entanglement with the rigid chain segments of the fluorocarbon resin. A silane coupling agent is added to improve the interfacial bonding force between the two-phase resins; S2. Place the fluorocarbon resin and the modified polyester resin in an oven at 50 - 60 °C for preheating for 2 hours (to reduce viscosity for subsequent mixing) for matrix resin activation. Mix xylene and butyl acetate in a ratio of 7:3, stir for 10 minutes, let it stand for defoaming and reserve, to make a mixed solution of xylene and butyl acetate. Ultrasonically disperse nano-silica and 0.5% silane coupling agent in ethanol for 30 minutes, and dry at 80 °C for hydrophobic treatment. Rutile titanium dioxide and propylene glycol methyl ether are mixed in a ratio of 1:1 and processed in a prepared high-speed disperser at 3000 r / min for 20 minutes for pre-dispersion of titanium dioxide; S3. Add the activated fluorocarbon resin and the modified polyester resin into the reaction kettle, start low-speed stirring at 200 - 300 r / min, slowly add 30% of the total amount of the pre-mixed solvent of xylene / butyl acetate, raise the temperature to 50 - 60 °C and keep for 1 hour to make the resins fully compatible. Gradually add the hydrophobic-treated nano-silica into the resin matrix, raise the stirring speed of the reaction kettle to 1200 r / min, disperse for 40 minutes until the fineness ≤ 20 μm, and use a Hegman plate to detect the fineness. Sequentially add flaky mica powder and pre-dispersed titanium dioxide, maintain dispersion at 1200 r / min for 30 minutes, add nano-ceria and switch to ultrasonic dispersion to disperse at a power of 500 W and a frequency of 40 kHz for 15 minutes to eliminate nano-agglomeration; S4. After the prepared main slurry is cooled to below 40 °C, sequentially add benzotriazole ultraviolet absorber, hindered amine light stabilizer, and silicone leveling agent, control the stirring speed of the reaction kettle at 500 r / min to avoid shear damage to the molecular structure of the additives. Dilute the HDI trimer curing agent and the remaining 70% of the mixed solution of xylene and butyl acetate in a ratio of 1:1 to avoid direct contact with moisture for activation treatment of the HDI trimer curing agent. Slowly add the diluted curing agent into the main slurry, control the temperature of the reaction kettle ≤ 35 °C, and mix at a speed of 400 r / min for 20 minutes. Detect the NCO:OH ratio by titration method to ensure the ratio is 1.1:1, and make the coating viscosity reach 60 - 80 s of the No. 4 cup at room temperature, filter through a 10-μm filter bag to remove undispersed particles, and remove air bubbles under negative pressure in a vacuum environment of -0.08 MPa for 30 minutes.

[0029] The bond energy of the C-F bond in the main chain of FEVE fluorocarbon resin is high, about 485 kJ / mol, which is significantly better than the C-C bond of traditional polyester (about 347 kJ / mol). Nano-ceria at high temperature passes through Redox cycling quenches free radicals.

[0030] Among them, there are oxygen vacancies in the crystal structure of nano-ceria ( ), and on the surface coexist to form a dynamic redox pair: , and the existence of oxygen vacancies ( ) can promote the adsorption and activation of oxygen, enhance the free radical capture ability, by accepting the electrons of free radicals, reducing them to stable products, reacting with oxygen or peroxides in the environment to regenerate , and completing the cycle. As follows: ; .

[0031] The mechanism of coating aging under ultraviolet light is as follows: Resin degradation chain reaction (taking fluorocarbon resin as an example): The energy of ultraviolet light (200~400nm) is higher than the bond energy of the resin chemical bond (C-F bond 485kJ / mol). Initiation stage (photoexcitation and free radical generation): RH R· + H·; Propagation stage: R· OO·; ROO· attacks other resin molecules, continuously generating new free radicals, causing cyclic amplification: ROO· + RH ROOH + R·.

[0032] The mechanism of nano-ceria against ultraviolet aging is as follows: Free radical scavenging reaction mechanism: Neutralization of superoxide free radicals ( ): ; Reduces to hydrogen peroxide and oxidizes itself to , cutting off the chain reaction initiated by and inhibiting the formation of peroxides.

[0033] Neutralization of hydroxyl free radicals (·OH): +·OH + ; Reduces ·OH to hydroxide ions ( ), and reduces itself to , neutralizing the strongly oxidizing ·OH and preventing it from attacking the resin backbone.

[0034] And it can also block the chain reaction cycle: Capture chain growth free radicals ( OO·): , terminate the free radical propagation, making the chain reaction unable to continue, and Theoretically recyclable, with extremely low loss due to agglomeration or poisoning.

[0035] The flaky mica powder is arranged in parallel, extending the diffusion path of the corrosive medium, and the permeability is reduced by 40 - 60%. The nano forms a dense network, making the water absorption rate of the coating < 1.5% (ASTM D570). It is detected that the crosslinking density of this coating is greater than (DMA test), ensuring that the coating hardness ≥ 2H (pencil hardness), the elongation at break > 80% (ASTM D638), and adapting to the thermal expansion and contraction of the aluminum plate.

[0036] The coating density is 1.2 g / , and the aluminum plate substrate using this kind of coating can be chromated (film weight 15 - 25 mg / ), the coating method adopts electrostatic spraying, the film thickness ≥ 25 μm (two coats and one bake), and the curing conditions are baking at 230 - 250 °C for 10 - 15 min (PMT).

[0037] Example 1: (1) Add 35 parts of neopentyl glycol, 8 parts of trimethylolpropane, 25 parts of isophthalic acid, 10 parts of oxalic acid, and 0.03 part of monobutyltin oxide into a reaction kettle equipped with at least stirring and heating functions. Gradually heat up to 180 °C under nitrogen protection. Maintain the esterification reaction for 4 hours until the acid value drops to 15 - 20 mgKOH / g. Add 5 parts of thiophthalic anhydride and continue the reaction until the acid value is less than 5 mgKOH / g. Then add an additional 3 parts of trimethylolpropane and keep it at 160 °C for 1 hour to ensure that the unreacted trimethylolpropane hydroxyl groups cap the main chain ends. Cool down to 120 °C, add 20 parts of a premixed solvent of xylene and propylene glycol methyl ether to dilute the mixture to a solid content of 60, filter to remove unreacted impurities, obtain a transparent viscous liquid, and add 0.2 part of silane coupling agent to enhance the interfacial bonding force between the two-phase resins; (2) Preheat the fluorocarbon resin and the modified polyester resin in a 50 °C oven for 2 hours. Mix xylene and butyl acetate in a ratio of 7:3, stir for 10 minutes, let it stand for defoaming and reserve, and make a mixed solution of xylene and butyl acetate. Ultrasonically disperse nano-silica and 0.2 part of 0.5% silane coupling agent in ethanol for 30 minutes, dry at 80 °C for hydrophobic treatment. Mix rutile titanium dioxide and propylene glycol methyl ether in a ratio of 1:1 and treat it in a high-speed disperser at 3000 r / min for 20 minutes for pre-dispersion of titanium dioxide; (3) Add 50 parts of activated fluorocarbon resin and 30 parts of modified polyester resin into the reaction kettle, start low-speed stirring at 200 r / min, slowly add 10.5 parts of xylene / butyl acetate mixed solvent, heat up to 50 °C and keep for 1 hour to make the resins fully compatible. Gradually add 8 parts of hydrophobically treated nano-silica into the resin matrix, increase the stirring speed of the reaction kettle to 1200 r / min, disperse for 40 minutes until the fineness is ≤ 20 μm. Then add 6 parts of flaky mica powder and 6 parts of pre-dispersed titanium dioxide in sequence, maintain the dispersion at 1200 r / min for 30 minutes, add 1 part of nano-ceria and switch to ultrasonic dispersion, disperse at a power of 500 W and a frequency of 40 kHz for 15 minutes to eliminate nano-agglomeration; (4) After the prepared main slurry is cooled to below 40 °C, add 1.5 parts of benzotriazole ultraviolet absorber, 1 part of hindered amine light stabilizer, and 0.3 part of silicone leveling agent in sequence. Control the stirring speed of the reaction kettle at 500 r / min. Dilute 18 parts of HDI trimer curing agent with 24.5 parts of xylene / butyl acetate mixed solution at a ratio of 1:1 for activation treatment of the HDI trimer curing agent. Slowly add the diluted curing agent into the main slurry, control the temperature of the reaction kettle not to exceed 35 °C, mix at a speed of 400 r / min for 20 minutes, measure the ratio of NCO:OH to be 1.1:1, and the coating viscosity reaches 60 s in a No. 4 cup at room temperature. Filter through a 10-μm filter bag to remove undispersed particles and perform negative pressure defoaming.

[0038] Example 2: (1) Add 49 parts of neopentyl glycol, 12 parts of trimethylolpropane, 30 parts of isophthalic acid, 15 parts of oxalic acid, and 0.05 part of monobutyltin oxide into a prepared reaction kettle with at least stirring and heating functions. Gradually heat up to 190 °C under nitrogen protection. Maintain the esterification reaction for 6 hours until the acid value drops to 15 - 20 mgKOH / g. Add 8 parts of thiophthalic anhydride and continue the reaction until the acid value is less than 5 mgKOH / g. Then add an additional 5 parts of trimethylolpropane and keep it at 170 °C for 1 hour to ensure that the unreacted trimethylolpropane hydroxyl-caps the main chain end. Cool down to 120 °C, add 25 parts of a premixed solvent dilution mixture of xylene and propylene glycol monomethyl ether to a solid content of 65%, filter to remove unreacted impurities to obtain a modified polyester resin, and then add 0.3 part of silane coupling agent to enhance the interfacial bonding force of the two-phase resin; (2) Preheat the fluorocarbon resin and the modified polyester resin in an oven at 60 °C for 2 hours. Mix xylene and butyl acetate in a ratio of 7:3, stir for 10 minutes, let it stand for defoaming and reserve, to prepare a mixed solution of xylene and butyl acetate. Ultrasonically disperse nano-silica and 0.8 parts of 0.5% silane coupling agent in ethanol for 30 minutes, dry at 80 °C for hydrophobic treatment. Mix rutile titanium dioxide and propylene glycol methyl ether in a ratio of 1:1, and treat it at 3000 r / min in a prepared high-speed disperser for 20 minutes for pre-dispersing the titanium dioxide. (3) Add 60 parts of the activated fluorocarbon resin and 40 parts of the modified polyester resin into the reaction kettle, start low-speed stirring at 300 r / min, slowly add 12 parts of the xylene / butyl acetate mixed solvent, heat up to 60 °C and keep it for 1 hour to make the resins fully compatible. Gradually add 10 parts of the hydrophobic-treated nano-silica into the resin matrix, increase the stirring speed of the reaction kettle to 1200 r / min, disperse for 40 minutes until the fineness is ≤ 20 μm. Add 8 parts of flaky mica powder and 7 parts of pre-dispersed titanium dioxide in sequence, maintain dispersion at 1200 r / min for 30 minutes, add 1.2 parts of nano-ceria and switch to ultrasonic dispersion to disperse at a power of 500 W and a frequency of 40 kHz for 15 minutes to eliminate nano-agglomeration. (4) After the prepared main slurry is cooled to below 40 °C, add 2 parts of benzotriazole ultraviolet absorber, 1.5 parts of hindered amine light stabilizer, and 0.5 part of silicone leveling agent in sequence. Control the stirring speed of the reaction kettle at 500 r / min. Dilute 22 parts of HDI trimer curing agent and 28 parts of xylene / butyl acetate mixed solution in a ratio of 1:1 for activating the HDI trimer curing agent. Slowly add the diluted curing agent into the main slurry, control the temperature of the reaction kettle not to exceed 35 °C, mix at a speed of 400 r / min for 20 minutes, measure the ratio of NCO:OH to be 1.1:1, and the coating viscosity reaches 80 s in a No. 4 cup at room temperature. Filter through a 10-μm filter bag to remove undispersed particles and perform negative pressure defoaming.

[0039] Example 3: (1) Add 42 parts of neopentyl glycol, 10 parts of trimethylolpropane, 27 parts of isophthalic acid, 13 parts of oxalic acid, and 0.04 part of monobutyltin oxide into a prepared reaction kettle with at least stirring and heating functions. Gradually heat up to 185°C under nitrogen protection. Maintain the esterification reaction for 5 hours until the acid value drops to 15 - 20 mgKOH / g. Add 6 parts of thiophthalic anhydride and continue the reaction until the acid value is less than 5 mgKOH / g. Then add an additional 4 parts of trimethylolpropane and keep it at 165°C for 1 hour to ensure that the unreacted trimethylolpropane hydroxyl-caps the main chain end. Cool down to 120°C and add 23 parts of a premixed solvent of xylene and propylene glycol methyl ether to dilute the mixed solution to a solid content of 63%. Filter to remove unreacted impurities to obtain a modified polyester resin. Add 0.25 part of silane coupling agent to enhance the interfacial bonding force between the two-phase resins; (2) Place the fluorocarbon resin and the modified polyester resin in an oven at 55°C and preheat for 2 hours. Mix xylene and butyl acetate in a ratio of 7:3, stir for 10 minutes, let it stand to defoam and set aside to prepare a mixed solution of xylene and butyl acetate. Ultrasonically disperse nano-silica and 0.5 part of 0.5% silane coupling agent in ethanol for 30 minutes, dry at 80°C for hydrophobic treatment. Mix rutile titanium dioxide and propylene glycol methyl ether in a ratio of 1:1 and treat it at 3000 r / min in a prepared high-speed disperser for 20 minutes for pre-dispersion of titanium dioxide; (3) Add 55 parts of the activated fluorocarbon resin and 35 parts of the modified polyester resin into the reaction kettle. Start low-speed stirring at 250 r / min and slowly add 11 parts of the xylene / butyl acetate mixed solvent. Heat up to 55°C and keep it for 1 hour to make the resins fully compatible. Gradually add 9 parts of the hydrophobic-treated nano-silica into the resin matrix, increase the stirring speed of the reaction kettle to 1200 r / min, disperse for 40 minutes until the fineness ≤ 20 μm. Sequentially add 7 parts of flaky mica powder and 6.5 parts of pre-dispersed titanium dioxide, maintain dispersion at 1200 r / min for 30 minutes, add 1.1 parts of nano-ceria and switch to ultrasonic dispersion to disperse at a power of 500 W and a frequency of 40 kHz for 15 minutes to eliminate nano-agglomeration; (4) After the prepared main slurry is cooled down to below 40°C, sequentially add 1.7 parts of benzotriazole ultraviolet absorber, 1.3 parts of hindered amine light stabilizer, and 0.4 part of silicone leveling agent. Control the stirring speed of the reaction kettle at 500 r / min. Dilute 20 parts of HDI trimer curing agent and 27 parts of the xylene / butyl acetate mixed solution in a ratio of 1:1 for activation treatment of the HDI trimer curing agent. Slowly add the diluted curing agent into the main slurry, control the temperature of the reaction kettle not to exceed 35°C, mix at a speed of 400 r / min for 20 minutes, measure the ratio of NCO:OH to be 1.1:1, and the coating viscosity reaches 70 s in a cup 4 at room temperature. Filter through a 10 - μm filter bag to remove undispersed particles and perform negative pressure defoaming.

[0040] Comparative Example 1: Add 45 parts of polyester resin, 10 parts of hexamethoxymethylmelamine, 20 parts of R-type titanium dioxide, 0.5 part of leveling agent, and 0.3 part of defoaming agent into the reaction kettle in sequence, stir at a speed of 800 r / min for 30 min to mix all components evenly, slowly add 24.2 parts of xylene into the reaction kettle, and at the same time raise the temperature to 60 °C, continue stirring until all components are completely dissolved, grind the mixed solution through a sand mill to make the particle size of the coating ≤ 20 μm, ensure the fineness and uniformity of the coating, filter the ground coating with a 200-mesh filter screen to remove impurities and large particle substances in it, and obtain a polyester resin coating. Among them, hexamethoxymethylmelamine is used as a cross-linking agent, and xylene is used as a solvent to dissolve other components and adjust the viscosity of the coating.

[0041] Comparative Example 2: Add 50 parts of FEVE fluorocarbon resin, 10 parts of isocyanate curing agent, and 15 parts of nano-titanium dioxide into the reaction kettle, stir at a speed of 1000 r / min for 45 minutes to fully disperse all components evenly, then add 24.2 parts of butyl acetate and 0.8 part of fluorocarbon surfactant into the reaction kettle, and at the same time raise the temperature to 55 °C, continue stirring until all components are completely dissolved, and further disperse the solution at 2000 r / min through a high-speed disperser to ensure that nano-particles are evenly distributed in the coating to improve the performance of the coating, filter the dispersed coating with a 300-mesh filter screen to remove impurities and large particle substances in it, and obtain a solvent-based fluorocarbon resin coating.

[0042] Comparative Example 3: (1) Add 42 parts of neopentyl glycol, 10 parts of trimethylolpropane, 27 parts of isophthalic acid, 13 parts of oxalic acid, and 0.04 part of monobutyltin oxide into a pre-prepared reaction kettle with at least stirring function and heating function, gradually raise the temperature to 185 °C under nitrogen protection, maintain the esterification reaction within 5 hours until the acid value drops to 15 - 20 mgKOH / g, add 6 parts of thiophthalic anhydride, continue the reaction until the acid value is less than 5 mgKOH / g, then add an additional 4 parts of trimethylolpropane, keep it warm at 165 °C for 1 hour to ensure that the unreacted trimethylolpropane hydroxyl-caps the end of the main chain, cool down to 120 °C, add 23 parts of a premixed solvent of xylene and propylene glycol methyl ether to dilute the mixed solution to a solid content of 63%, filter to remove unreacted impurities, obtain a modified polyester resin, and add 0.25 part of silane coupling agent to enhance the interfacial bonding force between the two-phase resins; (2) Preheat the fluorocarbon resin and the modified polyester resin in an oven at 55 °C for 2 hours. Mix xylene and butyl acetate in a ratio of 7:3, stir for 10 minutes, let it stand for defoaming and reserve, to make a mixed solution of xylene and butyl acetate. Ultrasonically disperse nano-silica and 0.5 parts of 0.5% silane coupling agent in ethanol for 30 minutes, dry at 80 °C for hydrophobic treatment. Mix rutile titanium dioxide and propylene glycol methyl ether in a ratio of 1:1, and disperse in a prepared high-speed disperser at 3000 r / min for 20 minutes for pre-dispersion of titanium dioxide to obtain pre-treated raw materials; (3) Add 55 parts of activated fluorocarbon resin and 35 parts of modified polyester resin into the reaction kettle, start low-speed stirring at 250 r / min, slowly add 11 parts of xylene / butyl acetate mixed solvent, heat up to 55 °C and keep for 1 hour to make the resins fully compatible. Gradually add 9 parts of hydrophobic-treated nano-silica into the resin matrix, increase the stirring speed of the reaction kettle to 1200 r / min, disperse for 40 minutes until the fineness ≤ 20 μm, add 7 parts of flaky mica powder and 6.5 parts of pre-dispersed titanium dioxide, and maintain dispersion at 1200 r / min for 30 minutes; (4) After the prepared main slurry is cooled to below 40 °C, add 1.7 parts of benzotriazole ultraviolet absorber, 1.3 parts of hindered amine light stabilizer, and 0.4 parts of silicone leveling agent in sequence. Control the stirring speed of the reaction kettle at 500 r / min. Dilute 20 parts of HDI trimer curing agent and 27 parts of xylene / butyl acetate mixed solution in a ratio of 1:1 for activation treatment of the HDI trimer curing agent. Slowly add the diluted curing agent into the main slurry, control the temperature of the reaction kettle not to exceed 35 °C, mix at 400 r / min for 20 minutes, filter and remove undispersed particles, and perform negative pressure defoaming to obtain the coating.

[0043] Prepare 6 aluminum plates with dimensions of 150 mm × 70 mm, spray or use a rubber roller to print coat the 6 kinds of coatings of Example 1, Example 2, Example 3, Comparative Example 1, Comparative Example 2, and Comparative Example 3 on the six aluminum plates respectively to make 6 color-coated aluminum samples with standard dimensions.

[0044] Test Example 1: After cleaning the surfaces of the 6 color-coated aluminum samples with alcohol and drying, put the samples into a QUV aging test chamber, use UVA-340 lamps, set the temperature in the chamber at 60 °C, continuously irradiate for 500 hours, regularly observe the changes of the samples, and after the test, use a color difference meter to measure the color difference of the samples before and after the test , and use a gloss meter to measure the gloss retention rate for ultraviolet aging test.

[0045] Test Example 2: Weigh the above 6 color-coated aluminum samples respectively to obtain the mass 、 、 、 , , , prepare a sulfuric acid solution with pH = 4, completely immerse the sample plate in it, soak for 72 hours at room temperature, keep the pH of the solution stable during this period, take out the sample plate, rinse it clean with ionized water and dry it, weigh the mass again, and obtain the masses of 6 groups of corresponding color-coated aluminum sample plates , , , , , . Calculate the coating weight loss rate: ( ) / × 100% (where n = 1, 2, 3, 4, 5, 6), and observe the surface changes of the sample plate to conduct the acid rain erosion test.

[0046] Test Example 3: Conduct the aging test of Test Example 1 on the above 6 color-coated aluminum sample plates. After the test, gently brush the surface of the sample plate with a soft brush, evaluate the degree of coating powdering according to the standard of GB / T 14826-1993, and conduct the coating powdering test.

[0047] Test Example 4: Scan the samples of 6 groups before and after the aging test respectively through an infrared spectrum analyzer, record the characteristic absorption peaks, compare the intensity changes of the characteristic absorption peaks of the C-O-C bond before and after the test, calculate the bond breakage rate, and conduct the resin degradation test.

[0048] Test Example 5: For 6 groups of samples, use a sharp tool to cut 10×10 squares with a spacing of 1 mm on the coating surface of the sample plate to reach the aluminum plate substrate. Gently brush away the debris in the cutting area with a soft brush, closely paste the tape on the scribed grid area, and then quickly pull the tape at a 90° angle. According to the rating standard of the scribed grid result in the standard of GB / T 9286-1998, evaluate the coating adhesion strength grade and conduct the coating adhesion strength test.

[0049] Test Example 6: After 6 groups of sample plates are aged by ultraviolet rays and eroded by acid rain, observe the blistering and peeling conditions on the surface of the sample plates under natural light or other suitable lights, count the number of blisters, calculate the blister density, record whether there is peeling at the blistering positions, and conduct the grade assessment of the blistering and peeling conditions of 6 groups of sample plates according to the standard ASTM D714-02, and conduct the coating blistering / peeling test.

[0050] Table 1 Detection results of multiple physical and chemical properties of the coating

[0051] From the comparison of the experimental data of Examples 1 to 3 and Comparative Examples 1 to 3 in Table 1, it can be found that the coating prepared by the present invention has a color difference after ultraviolet aging Lower, higher gloss retention rate, and stronger ability to resist acid rain erosion.

[0052] By comparison, it can be found that in Comparative Example 3, nano cerium oxide was not added to cooperate with the fluorocarbon resin, and there was no cerium oxide to neutralize free radicals, inhibit resin degradation, and the absorption effect of ultraviolet rays was poor, and the anti-ultraviolet aging effect was not good. At the same time, the silane coupling agent added in Examples 1 to 3 acted as a bridge, hydrolyzed to form Si-OH groups, and reacted with Al-OH of aluminum to form Si-O-Al chemical bonds. At the same time, it combined with the resin hydroxyl group to enhance the interfacial adhesion, and the modified polyester resin hydroxyl value (80~100mgKOH / g) was gradient matched with the fluorocarbon resin surface energy (25~30mN / m), reducing the stress concentration between the coating and the aluminum plate substrate.

[0053] Comparing Example 3 with Examples 1 and 2, the flaky mica powder (diameter-to-thickness ratio>50) in the coating slows down the diffusion rate of the corrosive medium. Comparing Examples 1, 2, and 3 with Comparative Example 3, the vacuum defoaming process plus ultrasonic dispersion reduces the voids in the coating, and the nanoparticles fill the microscopic defects, blocking the penetration of water and oxygen, thereby achieving better corrosion resistance.

[0054] It is obvious to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the present invention can be implemented in other specific forms without departing from the spirit or essential features of the present invention. Therefore, the embodiments should be regarded as exemplary and non-restrictive from any point of view, and the scope of the present invention is not limited by the above description, and it is intended that all changes falling within the meaning and scope of equivalent elements are included in the present invention.

Claims

1. A printing coating for color-coated aluminum plate, characterized in that: It includes the following components: 30-40 parts of modified polyester resin, 6-8 parts of flaky mica powder, nano 8-10 parts, ultraviolet absorber 1.5-2 parts, hindered amine light stabilizer 1-1.5 parts, silicone leveling agent 0.3-0.5 parts, nano cerium oxide 1-1.2 parts, mixed solvent of xylene and butyl acetate 35-40 parts; The modified polyester resin comprises the following components: 8-12 parts of trimethylolpropane, 25-30 parts of isophthalic acid, 10-15 parts of oxalic acid, 0.03-0.05 parts of monobutyltin oxide, and 20-25 parts of a mixed solution of xylene and propylene glycol methyl ether.

2. The printing coating for color-coated aluminum sheet according to claim 1, characterized in that: The printing coating for color-coated aluminum plate also includes 50-60 parts of fluorocarbon resin, 18-22 parts of HDI trimer curing agent, 6-7 parts of inorganic pigment, and 0.5-1 part of silane coupling agent. The modified polyester resin contains hydroxyl groups. The modified polyester resin also includes 35-49 parts of neopentyl glycol and 5-8 parts of sulfhydrylphthalic anhydride. The molar ratio of isocyanate groups in the HDI trimer curing agent to hydroxyl groups in the modified polyester resin is 1.1:

1. The particle size of the flaky mica powder is 5-15 μm, the molar concentration of the ultraviolet absorber is 0.05-0.07 mol / kg, the molar concentration of the hindered amine light stabilizer is 0.03-0.05 mol / kg, the ratio of xylene to butyl acetate is 7:3, and the ratio of xylene to propylene glycol methyl ether is 7:

3.

3. A method for preparing a printing coating for a color-coated aluminum plate according to any one of claims 1 to 2, characterized in that: The method comprises the following preparation steps: (1) Preparation of modified polyester resin: neopentyl glycol, trimethylolpropane, isophthalic acid, oxalic acid and monobutyltin oxide are added to a prepared reactor for preliminary reaction, sulfhydrylphthalic anhydride and an excess of trimethylolpropane are added and the reaction is carried out at a temperature-insulated state, and after the temperature is lowered to a predetermined temperature, a premixed solvent of xylene and propylene glycol methyl ether is added to dilute the mixture to a predetermined value, and impurities are removed by filtration to obtain a modified polyester resin; (2) Raw material pretreatment: activating fluorocarbon resin and modified polyester resin, preparing a mixed solution of xylene and butyl acetate, hydrophobizing nano-silica, and pre-dispersing inorganic pigments; (3) Preparation of main slurry: Add activated fluorocarbon resin and modified polyester resin into the reactor, stir at low speed to form a resin matrix, slowly add a premixed solvent of xylene and butyl acetate, raise the temperature to make the resin fully compatible, slowly add hydrophobic treated nano-silica into the resin matrix, disperse it in one stage, add nano-cerium oxide, and use the nano-cerium oxide to and The cyclic generation weakens the oxidation of the coating by ultraviolet rays, and a two-stage dispersion is performed to obtain the main slurry; (4) Adding additives: adding ultraviolet absorber, hindered amine light stabilizer and silicone leveling agent in sequence, and activating the HDI trimer curing agent with a second-stage premixed solvent of xylene and butyl acetate after stirring, and slowly adding the activated HDI trimer curing agent into the main slurry, mixing and adjusting the viscosity, filtering and defoaming to obtain the printing coating for the color-coated aluminum plate.

4. The method for preparing the printing coating for color-coated aluminum plate according to claim 3, characterized in that: The preliminary reaction method of step (1) is: under nitrogen protection, the temperature of the reactor is raised to 180-190° C. within 4-6 hours, and the esterification reaction is maintained until the acid value drops to 15-20 mgKOH / g.

5. The method for preparing the printing coating for color-coated aluminum plate according to claim 3, characterized in that: The method for preparing the premixed solvent of xylene and propylene glycol methyl ether in step (1) is as follows: after adding xylene into a prepared container, stirring at a low speed of 50 r / min, slowly adding propylene glycol methyl ether, and increasing the stirring speed to 200 r / min, stirring for 10 minutes and then standing to defoam for standby use; Step (1) adds sulfhydrylphthalic anhydride by titration monitoring, the predetermined acid value is less than 5 mgKOH / g, the excess trimethylolpropane is an additional 3-5 parts, and after adding the trimethylolpropane, the temperature is kept at 160-170°C for 1 hour to ensure that the unreacted trimethylolpropane hydroxyl terminates the main chain end, the predetermined temperature for cooling is 120°C, and a premixed solvent of xylene and propylene glycol methyl ether is added to dilute to a solid content of 60-65%, thereby obtaining a modified polyester resin.

6. The method for preparing the printing coating for color-coated aluminum plate according to claim 3, characterized in that: In step (2), the activation method of the fluorocarbon resin and the modified polyester resin is: preheating the fluorocarbon resin and the modified polyester resin in a prepared oven at 50-60° C. for 2 hours; The preparation method of the mixed solution of xylene and butyl acetate is as follows: xylene and butyl acetate are mixed in a ratio of 7:3, stirred for 10 minutes, and then allowed to stand for defoaming and standby to obtain a prefabricated mixed solution of xylene and butyl acetate.

7. The method for preparing the printing coating for color-coated aluminum plate according to claim 3, characterized in that: The method for hydrophobic treatment of nano-silica in step (2) is: ultrasonically disperse nano-silica and 0.5% silane coupling agent in ethanol for 30 minutes, and dry at 80°C; The method for pre-dispersing the inorganic pigment is as follows: the inorganic pigment and propylene glycol methyl ether are mixed in a ratio of 1:1 and processed at 3000 r / min in a high-speed disperser for 20 minutes.

8. The method for preparing the printing coating for color-coated aluminum plate according to claim 3, characterized in that: In step (3), the fluorocarbon resin and the modified polyester resin are stirred at a low speed of 200-300 r / min, the premixed solvent of xylene and butyl acetate in the first stage is 30% of the total amount of the premixed solvent of xylene and butyl acetate, and the temperature is raised to 50-60° C. so that the resins are fully compatible, and maintained for 1 hour; The method of one-stage dispersion is: increase the speed to 1200r / min, disperse for 40min until the fineness is ≤20μm, add flaky mica powder and pre-dispersed inorganic pigment in sequence, and maintain high-speed stirring and dispersion for 30 minutes; The second-stage dispersion method is: switch to ultrasonic dispersion with a frequency of 40 kHz and a power of 500 W for at least 15 minutes to eliminate nano-agglomerates.

9. The method for preparing a printing coating for a color-coated aluminum plate according to claim 3, characterized in that: The stirring method in step (4) is as follows: adjusting the speed of the reaction kettle to 500 r / min; The method for activating the HDI trimer curing agent is as follows: dilute the HDI trimer curing agent with the second-stage premixed solvent of xylene and butyl acetate at a ratio of 1:1 to avoid direct contact with moisture; The method of mixing the HDI trimer curing agent and the main slurry is: control the temperature ≤35°C, rotate at 400r / min for 20 minutes, and ensure that the NCO:OH ratio is 1.1:1; The method for adjusting the viscosity is to make the viscosity of the paint at room temperature reach 60~80s for coating 4 cups, and post-process the paint.

10. The method for preparing a printing coating for a color-coated aluminum plate according to claim 8, characterized in that: The premixed solvent of xylene and butyl acetate in the second stage is 70% of the total amount of the premixed solvent of xylene and butyl acetate; The method for filtering and defoaming the paint is: filter through a 10μm filter bag and place it in a -0.08MPa vacuum environment for negative pressure defoaming for 30 minutes.

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