Ultraviolet light-cured resin material for weld coating and preparation method thereof

Abstract

The application discloses a kind of weld coating with ultraviolet light curing resin material and preparation method thereof, it is related to ultraviolet light curing resin material technical field, weld coating with ultraviolet light curing resin material is calculated according to weight, including 60~75 parts of modified alicyclic epoxy acrylate, 10~25 parts of dimethylaminoethyl methacrylate, 2~5 parts of active diluent, 1~3 parts of curing agent, 0.5~1 part of drying agent, 3~5 parts of photoinitiator, 0.1~0.3 parts of defoaming agent, 5~10 parts of filler, modified alicyclic epoxy acrylate is grafted pentaerythritol triacrylate after being modified by silane first by alicyclic epoxy acrylate, finally introduce branched structure phosphate, resin material is obtained to horse-mouth iron high adhesion, ultraviolet light curing resin material protective coating resistant to damp heat by mixing, defoaming, roll coating, subsection ultraviolet irradiation and curing maintenance, especially suitable for the application of weld coating of iron printing package.

Description

Technical Field

[0001] This invention relates to the field of ultraviolet curable resin materials technology, specifically to an ultraviolet curable resin material for weld repair coating and its preparation method. Background Technology

[0002] In the tinplate packaging industry, the can body of can-type packaging containers is made of tinplate through printing, coating with varnish, rolling and welding. During the printing process, in order not to affect the welding quality of the weld, a 2-5 mm gap is left unprinted at the overlapping part of the can body. After welding, the weld is coated to protect the weld. After the coating is applied to the overlapping part of the can body, the can-type packaging containers need to be boiled in water for sterilization.

[0003] In existing technologies, such as patent 201410384711.3 (a new type of powder coating for repairing weld seams of metal cans), powder coatings are used. Although solid powder coatings have good adhesion to tinplate, the surface of the solid powder coating after spraying and curing is not smooth enough, has a granular feel, and produces a significant difference in feel compared to the printed area on the can body, affecting the usability of the can packaging container. Moreover, after the can packaging container is sterilized by boiling in water, the surface becomes hazy white, bubbly, and loses its gloss. During long-term storage, discontinuous rust spots appear at the joints of the can body. The reason for this is that the coating of solid powder coating is too hard and brittle, and has a high cross-linking density. When the tinplate expands violently, the coating of solid powder coating cannot deform in tandem, and shear stress will be generated at the interface, forming tiny peeling points. This provides space for water molecules to accumulate. The water molecules that penetrate in will quickly gather and nucleate at these micro-peeling points. Heating will increase the internal pressure of the bubbles, thus forming bubbles.

[0004] To address this, patent 202311258879.5 (A UV cationic weld repair coating liquid that can be brushed or sprayed and its preparation method) proposes a UV cationic weld repair coating material using low-viscosity alicyclic epoxy resin as the material. However, compared with free radical curing, UV cationic curing has a slow curing speed and a long complete curing time, often requiring several hours to achieve full performance, which affects the production efficiency of automated assembly line production of can-type packaging containers. The cured coating film is sensitive to moisture and alkaline substances, limiting its application on food and beverage cans in humid or alkaline environments. The absorption peaks of commonly used cationic photoinitiators are mainly concentrated in the short-wave ultraviolet region of 250~300nm, which has a relatively short absorption wavelength and poor matching with some common UV-LED light sources, affecting the initiation efficiency of photocuring.

[0005] Therefore, it is necessary to develop a UV-curable resin material for weld repair with excellent comprehensive performance, including a body structure resistant to humid and hot environments, good adhesion to tinplate, and short curing time, to meet the needs of tinplate weld repair in the tinplate printing and packaging industry. Summary of the Invention

[0006] To address the above problems, this invention proposes a UV-curable resin material for weld repair coating, as follows: A UV-curable resin material for weld repair coating, by weight comprising 60-75 parts of modified alicyclic epoxy acrylate, 10-25 parts of dimethylaminoethyl methacrylate, 2-5 parts of reactive diluent, 1-3 parts of curing agent, 0.5-1 part of drier, 3-5 parts of photoinitiator, 0.1-0.3 parts of defoamer, and 5-10 parts of filler; The modified alicyclic epoxy acrylate is prepared by the following steps: S1: Add the measured amount of bis(3,4-epoxycyclohexylmethyl)adipate to the reactor, start mechanical stirring at 250-300 rpm, continuously purge with nitrogen for 10-15 minutes, maintain a slight positive pressure nitrogen atmosphere throughout the process, raise the temperature to 75-85°C, add the dehydrated hydroxyl-terminated polydimethylsiloxane and dibutyltin dilaurate, stir at a constant temperature for 20-30 minutes until the system is homogeneous and transparent, raise the temperature of the reaction system to 115-125°C, continuously dehydrate under vacuum during the reaction process, react for 5-6 hours, and after the reaction is completed, cool to 80°C. Intermediate A of organosilicon-modified alicyclic epoxy resin was obtained at 0~90℃. Then, a measured amount of p-hydroxyanisole was added to the reactor and stirred until dissolved. Pentaerythritol triacrylate and triphenylphosphine were premixed and slowly added dropwise to the reactor through a dropping funnel for 60~90 min. After the addition was completed, the temperature was raised to 105~110℃ and reacted for 6~8 h under nitrogen protection throughout the process. After the reaction was completed, the temperature was lowered to 50~60℃ to obtain intermediate B of pentaerythritol triacrylate-grafted silicone-modified alicyclic epoxy resin. S2: The intermediate B obtained in step S1 is put into a low-temperature reactor, diluted with anhydrous dichloromethane, stirred evenly, and the air in the reactor is replaced with nitrogen. The system is cooled to 0~5℃ in an ice-water bath. The acid-binding agent with a molar ratio of 1:1 and the branched dichlorophosphate are simultaneously and slowly added to the reactor in a double-dropping manner for 2~3 hours. The molar ratio of the phosphorus-chlorine group of the branched dichlorophosphate to the hydroxyl group of the double-hydroxyl polydimethylsiloxane is (0.4~0.5):1. After the addition is completed, the reaction is carried out at a low temperature of 0~10℃ for 2~3 hours to generate an alicyclic epoxy resin intermediate containing phosphate ester. S3: At a temperature of 0~5℃, saturated ice water is slowly added dropwise for mild hydrolysis over a period of 30~60 minutes to completely convert the remaining phosphorus-chlorine bonds into stable phosphoric acid hydroxyl groups. The mixture is allowed to stand and separated. The organic phase is washed multiple times with saturated brine until the pH reaches 6~7 to remove hydrochloric acid. Anhydrous magnesium sulfate is then added to the organic phase and stirred to remove water. The magnesium sulfate is removed by vacuum filtration. The filtrate is then passed through a rotary evaporator at 20~30℃ under vacuum to remove dichloromethane. The product is the modified alicyclic epoxy acrylate.

[0007] Furthermore, the active diluent is one or both of isoborneol acrylate or tetrahydrofuran acrylate.

[0008] Furthermore, the drying agent is one or two of pentaerythritol tetrakis(3-mercaptopropionic acid) and polypentose polythiols.

[0009] Furthermore, the photoinitiator is one or both of 2-hydroxy-2-methyl-1-phenylpropanone or benzophenone.

[0010] Furthermore, the filler is one or both of nano-silica or nano-titanium oxide.

[0011] Furthermore, the curing agent is one or both of oxazolidine or 7-ethylbicyclooxazolidine.

[0012] Furthermore, the defoamer is one or more of BYK-054, BYK-024, or BYK-022.

[0013] Furthermore, in step S1, the dihydroxyl-terminated polydimethylsiloxane has a number-average molecular weight of 2000~3000 g / mol.

[0014] Further, in step S1, based on the input mass of bis(3,4-epoxycyclohexylmethyl)adipate, the mass percentage of hydroxyl-terminated polydimethylsiloxane is 20-30 wt%, the mass percentage of the catalyst dibutyltin dilaurate is 3-5 wt%, the mass percentage of p-hydroxyanisole is 0.03-0.05 wt%, the mass percentage of pentaerythritol triacrylate is 15-25 wt%, and the mass percentage of triphenylphosphine is 0.5-1 wt%.

[0015] Further, in step S2, the acid-binding agent is either triethylamine or pyridine.

[0016] Further, in step S2, the branched dichlorophosphate is one of isopropyl dichlorophosphate or dichlorophosphate (2-isopropoxyethyl) ester.

[0017] This invention also includes a method for preparing a UV-curable resin material for weld repair coating, comprising the following steps: (1) According to the mass ratio, the modified alicyclic epoxy acrylate, dimethyl aminoethyl methacrylate, reactive diluent, curing agent, drying agent, photoinitiator, defoamer and filler are stirred and mixed, and vacuum degassed in a vacuum container for 10~15min to obtain the mixture; (2) Apply the mixture to the weld surface of the overlapping part of the tank body by roller coating for 6~10 micrometers, and irradiate it with ultraviolet light at a wavelength of 365nm for 0.5~1s and at a wavelength of 395nm for 0.5~1s in a UV curing machine. (3) After coating, the product is placed in an indoor environment with a humidity of 45-55% for 24-48 hours to allow the coating to fully cross-link and cure.

[0018] This invention relates to a modified alicyclic epoxy acrylate, which is first modified with silane, then grafted with pentaerythritol triacrylate, and finally introduced with a branched phosphate ester. The resin material is mixed, degassed, roller coated, segmented UV irradiated and cured to obtain a UV-curable resin coating with high adhesion to tinplate and resistance to moisture and heat, which is especially suitable for the application of weld repair coating in tinplate packaging.

[0019] The present invention has the following beneficial effects: This invention uses bis(3,4-epoxycyclohexylmethyl) adipate with an alicyclic epoxy structure as the main structure of the photocurable resin, which has the advantages of high weather resistance, high heat resistance, low shrinkage, and resistance to yellowing. After modification with polydimethylsiloxane with double-terminated hydroxyl groups, Si-O-Si flexible chains are introduced, which further improves the hydrophobicity and water resistance of the photocurable resin, reduces epoxy internal stress, enhances water resistance and crack resistance, and prevents peeling and whitening after boiling in water at 100°C for 2 hours.

[0020] This invention utilizes the grafting reaction of pentaerythritol triacrylate with trifunctional acrylic acid, where the primary hydroxyl group of pentaerythritol triacrylate ring-opens with epoxy, anchoring the double bond of trifunctional acrylic acid to the molecule. This allows the resin to acquire the ability to cure rapidly with free radicals, thus solving the defects of surface stickiness and slow curing of pure cationic curing.

[0021] This invention introduces branched dichlorophosphate through phosphorylation modification. The branched dichlorophosphate is then incorporated into the resin, and the resin's active hydroxyl groups are used to perform low-temperature esterification with the branched dichlorophosphate, thereby partially introducing covalently bonded phosphate groups. Because the dichlorophosphate used has a sterically hindered branched structure, the low-temperature esterification process effectively controls the esterification of some of the chlorine in the dichlorophosphate. This results in the resin containing some phosphorus-chlorine bonds, which are then completely converted into stable phosphate hydroxyl groups through gentle hydrolysis, thus improving the resin's long-lasting and strong adhesion to metal materials.

[0022] This invention also effectively solves the problem of UV surface curing followed by deep internal curing of UV-curable resin materials for weld repair by setting oxazolidine or 7-ethylbicyclooxazolidine as a moisture-latent curing agent, thereby further improving the internal crosslinking density of the protective coating. Detailed Implementation

[0023] The present invention will be further described in detail below with reference to embodiments. It should also be understood that the following embodiments are only for further illustration of the present invention and should not be construed as limiting the scope of protection of the present invention. The specific mass, reaction time, temperature, process parameters, etc., in the examples are merely examples within a suitable range. Any non-essential improvements and adjustments made by those skilled in the art based on the above description of the present invention are within the scope of protection of the present invention.

[0024] In this embodiment, the bis(3,4-epoxycyclohexylmethyl) adipate used is a commercial product, specifically an alicyclic epoxy resin with the model number TTA-26 (epoxy equivalent of 200 g / mol).

[0025] In an embodiment of the present invention, the synthesis of standard bisphenol A epoxy acrylate is as follows: Under nitrogen protection, 19.6 g of epoxy resin E51 (epoxy equivalent of 196 g / mol) is added to a reactor. When the temperature rises to 90°C, acrylic acid containing 0.2 g of catalyst tetraethylammonium bromide and 0.04 g of polymerization inhibitor p-hydroxyanisole is added dropwise. The amount of acrylic acid used is 7.52 g. After the addition is complete, the temperature is raised to 100°C and reacted for 2 hours. Then the temperature is raised to 110°C, and the acid value is measured every half hour until the acid value of the product is lower than 2 mg KOH / g. The reaction is then stopped, and the temperature is lowered to 60°C for discharge. Example 1

[0026] A UV-curable resin material for weld repair coating, by weight, comprises 70 parts of modified alicyclic epoxy acrylate, 14 parts of dimethylaminoethyl methacrylate, 3 parts of isobornyl acrylate, 2.9 parts of 7-ethylbicyclooxazolidine, 1 part of pentaerythritol tetrakis(3-mercaptopropionic acid), 4 parts of 2-hydroxy-2-methyl-1-phenylpropanone, 0.1 parts of BYK-054, and 5 parts of nano-titanium oxide.

[0027] Modified alicyclic epoxy acrylates are prepared through the following steps: S1: Add 40g of TTA-26 to the reactor, start mechanical stirring at 300r / min, continuously purge with nitrogen for 15min, maintain slight positive pressure with nitrogen throughout, raise the temperature to 80℃, add 8g of dehydrated hydroxyl-terminated polydimethylsiloxane with a number average molecular weight of 2000g / mol and 1.6g of dibutyltin dilaurate, stir at constant temperature for 30min until the system is homogeneous and transparent, raise the temperature of the reaction system to 120℃, continuously dehydrate under vacuum during the reaction, react for 6h, and after the reaction is completed, cool down to 80℃. Intermediate A of organosilicon-modified alicyclic epoxy resin was obtained. Then, 0.016 g of p-hydroxyanisole was added to the reaction vessel and stirred until dissolved. 8 g of pentaerythritol triacrylate and 0.2 g of triphenylphosphine were premixed and slowly added dropwise to the vessel through a dropping funnel over a period of 90 min. After the addition was completed, the temperature was raised to 110 °C and reacted for 8 h under nitrogen protection throughout. After the reaction was completed, the temperature was lowered to 50 °C to obtain intermediate B of pentaerythritol triacrylate-grafted silicone-modified alicyclic epoxy resin. S2: The intermediate B obtained in step S1 is put into a low-temperature reactor, diluted with 60 ml of anhydrous dichloromethane, stirred evenly, and the air in the reactor is replaced with nitrogen. The system is cooled to 0°C in an ice-water bath. 0.126 g of pyridine and 0.258 g of isopropyl dichlorophosphoric acid (the molar ratio of pyridine to isopropyl dichlorophosphoric acid is 1:1) are added to the reactor simultaneously and slowly in a double-dropping manner for 3 h. The molar ratio of the phosphorus-chlorine group of isopropyl dichlorophosphoric acid to the hydroxyl group in the double-hydroxyl polydimethylsiloxane is 0.4:1. After the drop is added, the reaction is carried out at 5°C for 3 h to generate an alicyclic epoxy resin intermediate containing phosphate ester. S3: At a temperature of 3℃, 60 ml of saturated ice water was slowly added dropwise for gentle hydrolysis over a period of 60 min, completely converting the remaining phosphorus-chlorine bonds into stable phosphoric acid hydroxyl groups. The mixture was allowed to stand and separated. The organic phase was washed repeatedly with 50 ml of saturated saline solution until the pH reached 6-7 to remove hydrochloric acid. 2 g of anhydrous magnesium sulfate was added to the organic phase and stirred to remove water. The magnesium sulfate was removed by vacuum filtration. The filtrate was then passed through a rotary evaporator at 25℃ under vacuum to remove dichloromethane, yielding modified alicyclic epoxy acrylate 1.

[0028] A method for preparing a UV-curable resin material for weld repair involves mixing modified alicyclic epoxy acrylate 1, dimethylaminoethyl methacrylate, reactive diluent, curing agent, drier, photoinitiator, defoamer, and filler according to a mass ratio, and then vacuum degassing in a vacuum container for 15 minutes to obtain a mixture. A tinplate sheet with dimensions of 120mm × 50mm × 0.3mm is used to replace the weld surface at the overlap of the can body. The mixture is then rolled onto the surface to obtain a coating layer with a thickness of 8 micrometers. The coating is then irradiated for 1 second under a 365nm mercury lamp and 1 second under a 395nm UV-LED lamp in a UV curing machine. The coated tinplate sheet is then placed in an indoor environment with 50% humidity for 48 hours to allow complete cross-linking and curing of the coating, thus obtaining the protective coating 1 of the UV-curable resin material for weld repair. Example 2

[0029] A UV-curable resin material for weld repair coating, by weight, comprises 60 parts of modified alicyclic epoxy acrylate 2, 25 parts of dimethylaminoethyl methacrylate, 3 parts of tetrahydrofuran acrylate, 2 parts of oxazolidine, 0.5 parts of polypentose polythiol, 3 parts of benzophenone, 0.2 parts of BYK-024, and 6.3 parts of nano-silica. The preparation method of modified alicyclic epoxy acrylate 2 is the same as in Example 1, except that only the raw material ratio is adjusted. In step S1, based on 40g of TTA-26 alicyclic epoxy, the dihydroxyl-terminated polydimethylsiloxane is a dehydrated polydimethylsiloxane with a number average molecular weight of 3000g / mol, and its addition amount is 30wt% of TTA-26, which is 12g. The catalyst is 5wt% of dibutyltin dilaurate, which is 2.0g. The polymerization inhibitor is... 0.03wt% is equivalent to 0.012g of p-hydroxyanisole, 15wt% is equivalent to 6.0g of pentaerythritol triacrylate, and 1wt% is equivalent to 0.4g of triphenylphosphine. In step S2, the acid-binding agent is triethylamine, with an amount of 0.202g, and the branched dichlorophosphate is dichlorophosphate (2-isopropoxyethyl) ester, with an amount of 0.442g. The molar ratio of triethylamine to dichlorophosphate (2-isopropoxyethyl) ester is 1:1, and the molar ratio of the phosphorus-chlorine group of dichlorophosphate (2-isopropoxyethyl) ester to the hydroxyl group in the dihydroxyl-terminated polydimethylsiloxane is 0.5:1. Finally, modified alicyclic epoxy acrylate 2 is obtained. The coating preparation process of the material is the same as in Example 1, and a protective coating 2 of UV-curable resin material for weld repair is obtained. The film thickness of the protective coating 2 is 6 micrometers. Example 3

[0030] A UV-curable resin material for weld repair coating, by weight, comprises 75 parts of modified alicyclic epoxy acrylate 3, 10 parts of dimethylaminoethyl methacrylate, 2 parts of isobornyl acrylate, 2 parts of 7-ethylbicyclooxazolidine, 0.5 parts of pentaerythritol tetrakis(3-mercaptopropionic acid), 5 parts of 2-hydroxy-2-methyl-1-phenylpropanone, 0.3 parts of BYK-022, and 5.5 parts of nano-silica. The preparation method of modified alicyclic epoxy acrylate 2 is the same as in Example 1, except that only the raw material ratio is adjusted. In step S1, based on 40g of TTA-26 alicyclic epoxy, the dihydroxyl-terminated polydimethylsiloxane is a dehydrated polydimethylsiloxane with a number average molecular weight of 2000g / mol, and its addition amount is 20wt% of TTA-26, which is 8g. The agent is 3 wt% dibutyltin dilaurate (1.2 g), the polymerization inhibitor is 0.05 wt% p-hydroxyanisole (0.02 g), pentaerythritol triacrylate is 25 wt% (10 g), and triphenylphosphine is 0.7 wt% (0.28 g). In step S2, the acid-binding agent is pyridine (0.158 g), the branched dichlorophosphate is isopropyl dichlorophosphate (0.322 g), the molar ratio of pyridine to isopropyl dichlorophosphate is 1:1, and the molar ratio of the phosphorus-chlorine group of isopropyl dichlorophosphate to the hydroxyl group in the dihydroxyl-terminated polydimethylsiloxane is 0.5:1. Finally, modified alicyclic epoxy acrylate 3 is obtained. The coating preparation process of the material is the same as in Example 1, and a protective coating 3 of UV-curable resin material for weld repair is obtained. The film thickness of the protective coating 3 is 10 micrometers.

[0031] Comparative Example 1 A UV-curable resin material for weld repair coating, by weight, comprises 70 parts of standard bisphenol A epoxy acrylate, 14 parts of dimethylaminoethyl methacrylate, 3 parts of isobornyl acrylate, 2.9 parts of 7-ethylbicyclooxazolidine, 1 part of pentaerythritol tetrakis(3-mercaptopropionic acid), 4 parts of 2-hydroxy-2-methyl-1-phenylpropanone, 0.1 parts of BYK-054, and 5 parts of nano-silica. The coating preparation process of the material is the same as in Example 1, resulting in a protective coating A of the UV-curable resin material for weld repair coating, with a film thickness of 10 micrometers.

[0032] Comparative Example 2 A UV-curable resin material for weld repair coating is provided, with the same formulation as in Example 1, except that in the preparation step of the modified alicyclic epoxy acrylate, the dichlorophosphate ester is replaced with methyl dichlorophosphate without a branched structure, and the amount used is 0.238g. The coating preparation process of the material is the same as in Example 1, resulting in a protective coating B of the UV-curable resin material for weld repair coating, with a film thickness of 8 micrometers.

[0033] Comparative Example 3 A UV-curable resin material for weld repair coating is provided, with the same formulation as in Example 1, except that in the preparation step of the modified alicyclic epoxy acrylate, the molar ratio of the phosphorus-chlorine group of isopropyl dichlorophosphoric acid to the hydroxyl group of the double-terminated polydimethylsiloxane is 0.8:1, i.e., the amount of isopropyl dichlorophosphoric acid is 0.516g. The coating preparation process of the material is the same as in Example 1, resulting in a protective coating C of the UV-curable resin material for weld repair coating, with a film thickness of 9 micrometers.

[0034] The testing procedures for various properties of the UV-curable resin materials used for weld repair coating in Examples 1-3 and Comparative Examples 1-3 are as follows: Adhesion test: determined according to GB / T9286-2021 "Paints and Varnishes Cross-cut Test".

[0035] Moisture and heat resistance test: The tinplate coated with the protective coating was tested for 24 hours under constant temperature and humidity conditions of 25℃ and 50%. After testing, the tinplate with the protective coating was placed in a water bath with the protective coating side facing up and completely submerged below the water surface. The tinplate was fixed to prevent it from rolling over and boiled in 100℃ boiling water for 2 hours. The tinplate was then removed and the appearance of the protective coating was observed.

[0036] Hardness test: The hardness of paint film was determined according to the national standard GB / T6739-2022 "Determination of Hardness of Paint Film by Pencil Method".

[0037] The linear thermal expansion coefficient of the material was determined using the following method: Tinplate sheets coated with UV-curable resin material, measuring 120mm × 50mm × 0.3mm in length × width × thickness, were selected and conditioned for 24 hours under constant temperature and humidity conditions of 25℃ and 50%. Two parallel marking lines, 100mm apart, were etched at both ends of the coating using a utility knife. Two measurement points were marked on these parallel marking lines using a fine marker. The tinplate sheets were then placed on a constant temperature heating table (with a temperature accuracy of 1℃). The tinplate sheets were then placed on the measuring platform of an IM-8000 image dimension measuring instrument at constant temperatures of 25℃, 35℃, 45℃, 55℃, 65℃, and 75℃ to measure the two measurement points on the parallel marking lines. The measurement results are shown in Table 1.

[0038] Table 1

[0039] Plotting the measured length y as the ordinate and the temperature x as the abscissa, we fit the measurement results to a straight line and obtain: Protective coating 1 is y = 0.00531x + 99.878 (R 2 =0.999); Protective coating 2 is y = 0.00701x + 99.762 (R 2 =0.967); The protective coating 3 is y = 0.00561x + 99.624 (R 2 =0.998); The protective coating A is given by y = 0.00973x + 99.906 (R). 2 =0.993); The protective coating B is y = 0.00589x + 99.676 (R 2 =0.999); The protective coating C is y = 0.0052x + 99.906 (R 2 =0.997); Dividing both ends of the fitted line by the intercept yields a dilated fitted line of one unit length: The protective coating 1 has a ratio of y / 99.878 = 53.2 × 10⁻⁶. -6 x+1(R) 2 =0.999); thus, α1 = 53.2 × 10 -6 m / m·℃; The protective coating 2 is y / 99.762 = 70.3 × 10 -6 x+1(R) 2 =0.967); thus, α2 = 70.3 × 10 -6 m / m·℃; The protective coating 3 has a ratio of y / 99.624 = 56.3 × 10⁻⁶. -6 x+1(R) 2 =0.998); thus, α3 = 56.3 × 10 -6 m / m·℃; The protective coating A is y / 99.906 = 97.4 × 10⁻⁶. -6 x+1(R) 2 =0.993); thus, α was obtained. A =97.4×10 -6 m / m·℃; The protective coating B is y / 99.676 = 59.1 × 10⁻⁶. -6 x+1(R) 2 =0.999); thus, α was obtained. B =59.1×10 -6 m / m·℃; The protective coating C is y / 99.906 = 52.0 × 10⁻⁶. -6 x+1(R) 2 =0.997); thus, α was obtained. C =52.0×10 -6 m / m·℃; The linear thermal expansion coefficient of tinplate is α = 11.5 × 10⁻⁶. -6 m / m·℃.

[0040] Table 2

[0041] The results of the cross-cut adhesion test in Examples 1-3 of this invention show that the protective coating prepared in this invention has excellent adhesion to tinplate. The protective coating prepared in this invention has a small amount of phosphate hydroxyl groups. These small amounts of phosphate hydroxyl groups can form covalent adsorption with tinplate metal to achieve long-term stable adhesion. The covalently bonded phosphate hydroxyl groups achieve long-term adhesion to the metal, avoid the migration and hydrolysis of free phosphate esters, and do not produce rust spots during long-term storage. Compared with Comparative Example 1, the resin material does not have phosphate hydroxyl groups with strong adhesion to metal, and the adhesion effect is poor.

[0042] In embodiments 1-3 of this invention, the pencil with protective coating has moderate hardness, a smooth surface, no powder coating particle feel, and a consistent feel with the printed gloss layer on the can body. It takes into account both the flexibility and rigidity of the protective coating, has an excellent feel, and enhances the user experience.

[0043] The results of the damp heat resistance tests in Examples 1-3 of this invention show that the protective coating prepared in this invention has excellent damp heat resistance. Compared with bisphenol A epoxy acrylate, the resin of this invention, through the synergistic modification of phosphorus and silicon dual functions, significantly improves the water resistance of the protective coating, while retaining the advantages of alicyclic epoxy resins such as high resistance to yellowing and low shrinkage. The linear thermal expansion coefficient of the obtained protective coating is 53.2 × 10⁻⁶. -6 ~70.3×10 -6 This indicates that, compared to bisphenol A epoxy acrylate, the linear thermal expansion coefficient of the protective coating is closer to that of tinplate. Therefore, during the damp heat resistance test, when the tinplate expands violently, the expansion difference between the protective coating of this invention and the tinplate substrate is smaller. The shear stress generated at the interface during high-temperature sterilization is correspondingly lower, which effectively prevents water molecule attack and avoids micro-peeling, thus eliminating blisters and rust spots at the source. Therefore, it has good water boiling resistance.

[0044] Compared to Comparative Example 2, Embodiment 1 of this invention uses methyl dichlorophosphate without a branched structure. In Comparative Example 2, the steric hindrance of methyl dichlorophosphate is small in step S2 of the preparation of modified alicyclic epoxy acrylate. The chlorine in methyl dichlorophosphate and the hydroxyl groups in intermediate B of pentaerythritol triacrylate-grafted silicon-modified alicyclic epoxy resin both react, making it impossible to control the esterification of some of the chlorine in the dichlorophosphate. As a result, very few phosphorus-chlorine bonds are retained in the alicyclic epoxy resin intermediate of the obtained phosphate ester. In the subsequent step S3, the phosphate hydroxyl groups cannot be completely hydrolyzed and converted. Therefore, the strong adhesion to metal materials is poor.

[0045] Compared to Comparative Example 3, Embodiment 1 of this invention uses an excessive amount of isopropyl dichlorophosphate. Therefore, the modified alicyclic epoxy acrylate has a higher content of phosphate hydroxyl groups. Phosphate hydroxyl groups are hydrophilic groups. During the damp heat resistance test, the hydrolysis of phosphate ester groups actually worsens the damp heat resistance performance. Once hydrolysis occurs, small molecule alcohols and acids are generated at the interface, cutting off the entanglement of the protective coating on the surface of the metal substrate. Therefore, the water boiling resistance also deteriorates. Only when the molar ratio of the phosphorus-chlorine groups of the branched dichlorophosphate to the hydroxyl groups in the double-terminated polydimethylsiloxane is (0.4~0.5):1 can the photocurable resin adhere well to the metal substrate of the printed tin packaging material, and the material can also withstand the hydrolysis of phosphate ester groups during high-temperature sterilization.

[0046] This invention utilizes a resin with dual curing activity, introducing pentaerythritol triacrylate double bonds to achieve rapid free radical photocuring. Surface curing takes only 1-2 seconds, making it compatible with existing UV mass production lines' staged UV curing processes. It boasts strong compatibility and a wide range of applications. Combined with a moisture-latent curing agent, the protective coating not exposed to UV light undergoes slow cross-linking and complete curing through moisture, further increasing the cross-linking density within the protective coating. The moisture-latent curing process can be achieved during placement without affecting the production line process of tinplate packaging, thus making it suitable for high-speed tinplate packaging production lines.

[0047] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A UV-curable resin material for weld repair coating, characterized in that, By weight, it includes 60-75 parts of modified alicyclic epoxy acrylate, 10-25 parts of dimethylaminoethyl methacrylate, 2-5 parts of reactive diluent, 1-3 parts of curing agent, 0.5-1 part of drier, 3-5 parts of photoinitiator, 0.1-0.3 parts of defoamer, and 5-10 parts of filler. The modified alicyclic epoxy acrylate is prepared by the following steps: S1: Add the measured amount of bis(3,4-epoxycyclohexylmethyl)adipate to the reactor, start mechanical stirring at 250-300 rpm, continuously purge with nitrogen for 10-15 minutes, maintain a slight positive pressure nitrogen atmosphere throughout the process, raise the temperature to 75-85°C, add the dehydrated hydroxyl-terminated polydimethylsiloxane and dibutyltin dilaurate, stir at a constant temperature for 20-30 minutes until the system is homogeneous and transparent, raise the temperature of the reaction system to 115-125°C, continuously dehydrate under vacuum during the reaction process, react for 5-6 hours, and after the reaction is completed, cool to 80°C. Intermediate A of organosilicon-modified alicyclic epoxy resin was obtained at 0~90℃. Then, a measured amount of p-hydroxyanisole was added to the reactor and stirred until dissolved. Pentaerythritol triacrylate and triphenylphosphine were premixed and slowly added dropwise to the reactor through a dropping funnel for 60~90 min. After the addition was completed, the temperature was raised to 105~110℃ and reacted for 6~8 h under nitrogen protection throughout the process. After the reaction was completed, the temperature was lowered to 50~60℃ to obtain intermediate B of pentaerythritol triacrylate-grafted silicone-modified alicyclic epoxy resin. S2: The intermediate B obtained in step S1 is put into a low-temperature reactor, diluted with anhydrous dichloromethane, stirred evenly, and the air in the reactor is replaced with nitrogen. The system is cooled to 0~5℃ in an ice-water bath. The acid-binding agent with a molar ratio of 1:1 and the branched dichlorophosphate are simultaneously and slowly added to the reactor in a double-dropping manner for 2~3 hours. The molar ratio of the phosphorus-chlorine group of the branched dichlorophosphate to the hydroxyl group of the double-hydroxyl polydimethylsiloxane is (0.4~0.5):

1. After the addition is completed, the reaction is carried out at a low temperature of 0~10℃ for 2~3 hours to generate an alicyclic epoxy resin intermediate containing phosphate ester. S3: At a temperature of 0~5℃, saturated ice water is slowly added dropwise for mild hydrolysis over a period of 30~60 minutes to completely convert the remaining phosphorus-chlorine bonds into stable phosphoric acid hydroxyl groups. The mixture is allowed to stand and separated. The organic phase is washed multiple times with saturated brine until the pH reaches 6~7 to remove hydrochloric acid. Anhydrous magnesium sulfate is then added to the organic phase and stirred to remove water. The magnesium sulfate is removed by vacuum filtration. The filtrate is then passed through a rotary evaporator at 20~30℃ under vacuum to remove dichloromethane. The product is the modified alicyclic epoxy acrylate.

2. The UV-curable resin material for weld repair according to claim 1, characterized in that, The reactive diluent is one or two of isobornyl acrylate or tetrahydrofuran acrylate; the drying agent is one or two of pentaerythritol tetrakis(3-mercaptopropionic acid) or polypentose polythiol; the photoinitiator is one or two of 2-hydroxy-2-methyl-1-phenylpropanone or benzophenone; the filler is one or two of nano-silica or nano-titanium oxide; the curing agent is one or two of oxazolidine or 7-ethylbicyclooxazolidine; and the defoamer is one or more of BYK-054, BYK-024, or BYK-022.

3. The UV-curable resin material for weld repair according to claim 1, characterized in that, In step (1), the double-hydroxyl-terminated polydimethylsiloxane has a number-average molecular weight of 2000~3000 g / mol.

4. The UV-curable resin material for weld repair according to claim 1, characterized in that, In step S1, based on the input mass of bis(3,4-epoxycyclohexylmethyl)adipate, the mass percentage of hydroxyl-terminated polydimethylsiloxane is 20-30 wt%, the mass percentage of the catalyst dibutyltin dilaurate is 3-5 wt%, the mass percentage of p-hydroxyanisole is 0.03-0.05 wt%, the mass percentage of pentaerythritol triacrylate is 15-25 wt%, and the mass percentage of triphenylphosphine is 0.5-1 wt%.

5. The UV-curable resin material for weld repair according to claim 1, characterized in that, In step S2, the acid-binding agent is either triethylamine or pyridine.

6. The UV-curable resin material for weld repair according to claim 1, characterized in that, In step S2, the branched dichlorophosphate is one of isopropyl dichlorophosphate or dichlorophosphate (2-isopropoxyethyl) ester.

7. The method for preparing the UV-curable resin material for weld repair coating as described in any one of claims 1 to 6, characterized in that, Includes the following steps: (1) According to the mass ratio, the modified alicyclic epoxy acrylate, dimethyl aminoethyl methacrylate, reactive diluent, curing agent, drying agent, photoinitiator, defoamer and filler are stirred and mixed, and vacuum degassed in a vacuum container for 10~15min to obtain the mixture; (2) Apply the mixture to the weld surface of the overlapping part of the tank body by roller coating for 6~10 micrometers, and irradiate it with ultraviolet light at a wavelength of 365nm for 0.5~1s and at a wavelength of 395nm for 0.5~1s in a UV curing machine. (3) After coating, the product is placed in an indoor environment with a humidity of 45-55% for 24-48 hours to allow the coating to fully cross-link and cure.

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