Silk-screen printing process of aluminum veneer

Abstract

The invention relates to the technical field of silk-screen printing ink, in particular to a silk-screen printing process of an aluminum veneer. Comprising the following steps: preparing a composite chain extender; preparing a modified waterborne polyurethane emulsion; and carrying out a silk-screen printing process on the aluminum veneer. The ethylene carbonate, the hexamethylenediamine and the phenyl phosphate are compounded to prepare the chain extender, the ethylene carbonate and the phenyl phosphate can react with the hexamethylenediamine, bifunctional groups perform synergistic chain extension, and the phenyl phosphate is connected to a chain extender molecule through a chemical bond. The migration and precipitation of small molecules sheared during the reaction of ethylene carbonate and hexamethylenediamine are avoided, so that the molecular chain length and the crosslinking degree are improved, the hardness of the silk-screen printing ink prepared from the polypropylene oxide glycol and epoxidized soybean oil blended waterborne polyurethane emulsion is improved, and meanwhile, the hardness of the silk-screen printing ink is ensured not to be attenuated during long-term use.

Description

Technical Field

[0001] The invention relates to the technical field of silk screen ink, and in particular to a silk screen printing process for an aluminum veneer. Background Art

[0002] Aluminum veneer is a sheet material made of aluminum alloy. Its flat surface is suitable for billboards and signage. Various designs and text can be displayed on the surface of the aluminum veneer through screen printing. The specific process of screen printing aluminum veneer involves designing the desired pattern, creating a screen printing plate, selecting an ink suitable for aluminum veneer, and transferring the pattern onto the surface through the screen.

[0003] Screen printing inks include water-based inks and oil-based inks. The raw materials of water-based inks include water-based polyurethane emulsions. Water-based polyurethane emulsions have good adhesion, allowing them to stably adhere to the surface of aluminum veneers. They are also environmentally friendly, have no irritating odor, and emit low amounts of volatile organic compounds, complying with environmental regulations. However, the molecular chain of water-based polyurethane emulsions contains many hydrophilic segments. Therefore, screen printing inks with water-based polyurethane emulsions as the main raw material tend to absorb moisture in the air and expand over long periods of use, causing the ink layer printed on the surface of the aluminum veneer to wrinkle and deform, shortening its service life. In addition, its physical hardness is also limited by the molecular chain segments and is relatively general. After the screen printing process is completed, inks with higher hardness can avoid being scratched during use. Therefore, improving the hardness of screen printing inks in the screen printing process of aluminum veneers and extending their service life is an urgent problem that needs to be solved.

[0004] Therefore, the present invention provides a screen printing process for aluminum veneer, which pre-treats the aluminum veneer and makes a screen plate, and also prepares a screen printing ink with higher hardness and longer service life, and transfers it to the aluminum veneer through the screen plate to solve the above problems. Summary of the Invention

[0005] In view of the shortcomings of the prior art, the present invention aims to provide a screen printing process for aluminum veneer.

[0006] A screen printing process for aluminum veneer comprises the following steps: S1: Preparation of composite chain extender Weighing ethylene carbonate and hexamethylenediamine, mixing them in dichloromethane, then adding a catalyst, stirring, and heating to react. Subsequently, the product is distilled under reduced pressure to remove dichloromethane, and then phenyl phosphate and a catalyst are added, and heating and stirring are performed to prepare a composite chain extender. S2: Preparation of modified waterborne polyurethane emulsion Add polyoxypropylene glycol and ring-opened epoxy soybean oil to a reaction flask, then add hexafluoroisopropyl ketone and isophorone diisocyanate, stir, then add a composite chain extender and N-methylpyrrolidone, heat and stir after reaction, then dropwise add acetone and 1,4-butanediol, then add a catalyst and deionized water for emulsification to prepare a polyoxypropylene glycol and epoxy soybean oil blended waterborne polyurethane emulsion, then add a silane coupling agent and trimethylolpropane to prepare a modified waterborne polyurethane emulsion; S3: Screen printing process for aluminum veneer The modified water-based polyurethane emulsion and pigment are weighed, and deionized water is added and ground to obtain water-based polyurethane screen printing ink. The surface of the aluminum veneer is cleaned, polished and passivated, and then a screen is made. The screen is stretched on the screen frame, and then a photosensitive adhesive is evenly coated on the screen. After drying, it is exposed and developed to obtain a screen. The aluminum veneer and the screen are installed on a printing press, and water-based polyurethane screen printing ink is added. The pattern on the screen is transferred to the surface of the aluminum veneer by a scraper, dried and cured to obtain a printed aluminum veneer, and the screen printing process of the aluminum veneer is completed.

[0007] Furthermore, step S1 of preparing a composite chain extender comprises the following steps: Ethylene carbonate and hexamethylenediamine are weighed and mixed in dichloromethane in a mass ratio of 1:(1-3), and the mixture is heated to 60-80°C. Then, 1-2% of the mass of the system catalyst is added, and the mixture is stirred at a speed of 150-200 r / min for 4-6 hours. After the reaction system is stable, the temperature is increased to 95-100°C, and the mixture is reacted for 3-3.5 hours to remove excess ethylene carbonate in the system. Subsequently, the product is distilled under reduced pressure to remove the solvent dichloromethane, and an equal mass of phenyl phosphate is added and completely dissolved in dichloromethane. Then, 1-2% of the mass of the system catalyst is added, and the mixture is heated to 80-100°C. The mixture is stirred at a speed of 150-200 r / min for 6-8 hours. After the reaction is completed, the dichloromethane is removed by distillation under reduced pressure, and the precipitate is precipitated with ethanol. The precipitate is collected, washed, and dried to obtain a composite chain extender.

[0008] Furthermore, step S2 of preparing a modified aqueous polyurethane emulsion comprises the following steps: S2.1: Add 1-3 parts by mass of polyoxypropylene glycol and 2-6 parts by mass of ring-opened epoxidized soybean oil to a reaction flask, heat to 120-125°C, and vacuum dry for 12-13 hours. Then, control the temperature in the reaction flask to 50-60°C, add 10-12 parts by mass of hexafluoroisopropyl ketone, and stir at 250-300 r / min for 10-12 minutes. Then, raise the temperature of the reaction flask to 80-85°C, add 1-4 parts by mass of isophorone diisocyanate, and stir at 300-350 r / min for 2-2.5 hours. S2.2: Lower the temperature to 60-65°C while stirring. Add 2-6 parts by weight of a composite chain extender and 0.5-1 part by weight of N-methylpyrrolidone. After reacting for 15-20 minutes, raise the temperature to 80-85°C and stir for 2-2.5 hours. Then, control the temperature to 40-45°C and dropwise add 5-10 parts by weight of acetone while cooling. Stir at 400-450 r / min for 1-1.5 hours. Add 1-3 parts by weight of 1,4-butanediol dropwise while stirring. S2.3: The speed is then increased to 900-950 rpm, and 1-2% by weight of the catalyst and 30-50% by weight of deionized water are added. Emulsification is performed for 10-15 minutes. After emulsification, the acetone is removed to obtain a water-based polyurethane emulsion blended with polyoxypropylene glycol and epoxy soybean oil. S2.4: Add silane coupling agent and trimethylolpropane to the aqueous polyurethane emulsion blended with polyoxypropylene glycol and epoxy soybean oil, the mass ratio of the aqueous polyurethane emulsion blended with polyoxypropylene glycol and epoxy soybean oil, the silane coupling agent and trimethylolpropane is 10: (4-6): (1-3), and then add 1-2% of the system mass of the catalyst, stir at a speed of 800-900r / min, react for 10-15min, and obtain a modified aqueous polyurethane emulsion.

[0009] Furthermore, step S3 performs a screen printing process on the aluminum veneer, including the following steps: S3.1: Weigh 10-15 parts by weight of the modified waterborne polyurethane emulsion and 2-3 parts by weight of the pigment, disperse and grind them in a mortar, add 5-8 parts by weight of deionized water, and grind for 20-40 minutes to obtain a waterborne polyurethane screen printing ink; S3.2: Clean the surface of the aluminum veneer, remove oil and dust, polish and passivate, then make a silk screen, stretch the silk screen on the screen frame, and then evenly apply photosensitive glue on the silk screen, dry it in the dark, expose and develop it with a UV lamp to obtain a silk screen, fix the aluminum veneer on the printing press, install the silk screen on the printing press, and add the water-based polyurethane silk screen ink prepared in step S3.1. Use a scraper to evenly scrape the water-based polyurethane silk screen ink to transfer the pattern to the surface of the aluminum veneer, dry and solidify it to obtain the printed aluminum veneer and the ink layer on the surface of the aluminum veneer, and complete the silk screen printing process of the aluminum veneer.

[0010] Furthermore, the phenyl phosphate is specifically triphenyl phosphate.

[0011] Furthermore, the silane coupling agent is specifically silane coupling agent KH550, the main component of which is γ-aminopropyltriethoxysilane.

[0012] Furthermore, the catalyst in step S1 and step S2 is triethylamine.

[0013] Compared with the prior art, the present invention has at least the following beneficial effects: 1. The present invention uses ethylene carbonate, hexamethylenediamine and phenyl phosphate to prepare a chain extender. The amino group of hexamethylenediamine nucleophilically attacks the carbonyl carbon of ethylene carbonate, triggering a ring-opening reaction and extending the polymer main chain. In addition, the diol / amine compound generated by the reaction of the two contains active hydroxyl and secondary amine groups, which can be used as a chain extender to react with isocyanate or carboxyl groups. The prepared chain extender can play a role in adjusting the hardness of polyurethane in the preparation of polyurethane. Subsequently, phenyl phosphate is introduced for esterification and phosphorylation. The groups in the phenyl phosphate react with the hydroxyl groups of the hydroxyethylated hexamethylenediamine to form a chemical bond. With the generation of amine phosphate, the chain is extended to the molecular chain of polyurethane through the generated chemical bonds during the chain extension process of polyurethane, and flame retardant properties are brought to polyurethane. At the same time, ethylene carbonate and phenyl phosphate can react with hexamethylenediamine, and the two functional groups synergistically extend the chain. Phenyl phosphate is connected to the chain extender molecule through a chemical bond, which avoids the migration and precipitation of small molecules sheared during the reaction of ethylene carbonate and hexamethylenediamine, thereby increasing the molecular chain length and the degree of cross-linking, and increasing the hardness of the screen printing ink prepared by the water-based polyurethane emulsion blended with polyoxypropylene glycol and epoxy soybean oil, while ensuring that the hardness of the screen printing ink does not decay during long-term use.

[0014] 2. The present invention uses polyoxypropylene glycol and ring-opened epoxidized soybean oil as raw materials and prepares a polyoxypropylene glycol and epoxy soybean oil blended waterborne polyurethane emulsion with the assistance of auxiliary agents such as a composite chain extender and a catalyst. The ether bond of the polyoxypropylene glycol and the ester bond of the ring-opened epoxidized soybean oil promote microphase separation due to the polarity difference between the ether bond and the ester bond. In addition, the ester bond of the ring-opened epoxidized soybean oil and the ether bond of the polyoxypropylene glycol can form a weak hydrogen bond, which can reversibly break / reorganize under dynamic load and dissipate energy. Through microscopic effects, the dynamic fatigue properties of the prepared polyoxypropylene glycol and epoxy soybean oil blended waterborne polyurethane material are improved, thereby extending the service life of the screen printing ink prepared from the polyoxypropylene glycol and epoxy soybean oil blended waterborne polyurethane.

[0015] 3. The present invention uses a compound of a silane coupling agent and trimethylolpropane to perform surface modification on an aqueous polyurethane emulsion blended with polyoxypropylene glycol and epoxy soybean oil. The hydroxyl group of the trimethylolpropane can react with the aqueous polyurethane emulsion and serve as a bridge to increase crosslinking points on the polyurethane molecular chain that can combine with the silane coupling agent KH550, thereby allowing the amino group of KH550 to be introduced into the polyurethane molecular chain through the trimethylolpropane, thereby forming a richer crosslinked molecular long-chain structure. At the same time, the alkoxy group thereof is hydrolyzed and condensed with the hydroxyl group on the surface of the inorganic filler to form a chemical bridge. As a result, the molecular chain structure inside the prepared modified aqueous polyurethane emulsion has a high crosslinking density and bonding strength, and is not easily dispersed or decomposed due to external forces. The modified aqueous polyurethane emulsion is prepared into a screen printing ink with better physical hardness and longer service life. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The accompanying drawings, which are incorporated herein and constitute a part of the specification, illustrate embodiments of the present disclosure and, together with the description, further serve to explain the principles of the present disclosure and to enable one skilled in the relevant art to make and use the present disclosure.

[0017] Figure 1 This is a flow chart of the screen printing process of an aluminum veneer used in an embodiment of the present invention. DETAILED DESCRIPTION

[0018] The following describes in detail a screen printing process for aluminum veneer provided by the present invention, with reference to the accompanying drawings and specific embodiments. It is also noted that, for the sake of completeness, the following embodiments are optimal and preferred embodiments, and those skilled in the art may employ alternative methods for implementing known technologies. Furthermore, the accompanying drawings are intended only to provide a more detailed description of the embodiments and are not intended to limit the present invention. Example

[0019] A screen printing process for aluminum veneer, such as Figure 1 As shown, the following steps are included: S1: Preparation of composite chain extender Ethylene carbonate and hexamethylenediamine were weighed and mixed in dichloromethane in a mass ratio of 1:1, and the mixture was heated to 60°C. Then, 1% of the mass of the system catalyst triethylamine was added and stirred at a speed of 150 r / min for 4 hours. After the reaction system was stable, the temperature was raised to 95°C and the reaction was carried out for 3 hours to remove excess ethylene carbonate in the system. The product was then distilled under reduced pressure to remove the solvent dichloromethane, and an equal mass of triphenyl phosphate was added and completely dissolved in dichloromethane. Then, 1% of the mass of the system catalyst was added, and the mixture was heated to 80°C and stirred at a speed of 150 r / min for 6 hours. After the reaction was completed, the dichloromethane was removed by distillation under reduced pressure, and the precipitate was precipitated with ethanol. The precipitate was collected, washed and dried to obtain a composite chain extender.

[0020] S2: Preparation of modified waterborne polyurethane emulsion S2.1: Add 1 part by mass of polyoxypropylene glycol and 2 parts by mass of ring-opened epoxidized soybean oil to a reaction flask, heat to 120°C, and vacuum dry for 12 hours. Then, control the temperature in the reaction flask to 50°C, add 10 parts by mass of hexafluoroisopropyl ketone, and stir at 250 r / min for 10 minutes. Then, raise the temperature of the reaction flask to 80°C, add 1 part by mass of isophorone diisocyanate, and stir at 300 r / min for 2 hours. S2.2: The temperature was then lowered to 60°C while stirring. 2 parts by mass of a composite chain extender and 0.5 parts by mass of N-methylpyrrolidone were added. After reacting for 15 minutes, the temperature was raised to 80°C and stirred for 2 hours. The temperature was then controlled at 40°C. During the cooling process, 5 parts by mass of acetone were added dropwise. The mixture was stirred at 400 r / min for 1 hour. During the stirring process, 1 part by mass of 1,4-butanediol was added dropwise. S2.3: The speed is then increased to 900 rpm, and 1% by weight of the catalyst triethylamine and 30% by weight of deionized water are added. Emulsification is performed for 10 minutes. After emulsification, acetone is removed to obtain a water-based polyurethane emulsion blended with polyoxypropylene glycol and epoxidized soybean oil. S2.4: Add silane coupling agent KH550 and trimethylolpropane to the aqueous polyurethane emulsion blended with polyoxypropylene glycol and epoxy soybean oil, the mass ratio of the aqueous polyurethane emulsion blended with polyoxypropylene glycol and epoxy soybean oil, the silane coupling agent and trimethylolpropane is 10:4:1, and then add 1% of the system mass of catalyst triethylamine, stir at a speed of 800r / min, react for 10 minutes, and obtain a modified aqueous polyurethane emulsion.

[0021] S3: Screen printing process for aluminum veneer S3.1: Weigh 10 parts by mass of the modified waterborne polyurethane emulsion and 2 parts by mass of the pigment, disperse and grind them in a mortar, add 5 parts by mass of deionized water, and grind for 20 minutes to obtain a waterborne polyurethane screen printing ink; S3.2: Clean the surface of the aluminum veneer, remove oil and dust, polish and passivate, then make a silk screen, stretch the silk screen on the screen frame, and then evenly apply photosensitive glue on the silk screen, dry it in the dark, expose and develop it with a UV lamp to obtain a silk screen, fix the aluminum veneer on the printing press, install the silk screen on the printing press, and add the water-based polyurethane silk screen ink prepared in step S3.1. Use a scraper to evenly scrape the water-based polyurethane silk screen ink to transfer the pattern to the surface of the aluminum veneer, dry and solidify it to obtain the printed aluminum veneer and the ink layer on the surface of the aluminum veneer, and complete the silk screen printing process of the aluminum veneer. Example

[0022] A screen printing process for aluminum veneer, such as Figure 1 As shown, the following steps are included: S1: Preparation of composite chain extender Ethylene carbonate and hexamethylenediamine were weighed and mixed in dichloromethane in a mass ratio of 1:3, and the mixture was heated to 60°C. Then, 2% of the mass of the catalyst triethylamine was added and stirred at a speed of 150 r / min for 4 hours. After the reaction system was stable, the temperature was raised to 95°C and the reaction was carried out for 3 hours to remove excess ethylene carbonate in the system. The product was then distilled under reduced pressure to remove the solvent dichloromethane, and an equal mass of triphenyl phosphate was added and completely dissolved in dichloromethane. Then, 2% of the mass of the catalyst was added and the mixture was heated to 80°C and stirred at a speed of 150 r / min for 6 hours. After the reaction was completed, the dichloromethane was removed by distillation under reduced pressure, and the precipitate was precipitated with ethanol. The precipitate was collected, washed and dried to obtain a composite chain extender.

[0023] S2: Preparation of modified waterborne polyurethane emulsion S2.1: Add 3 parts by mass of polyoxypropylene glycol and 6 parts by mass of ring-opened epoxidized soybean oil to a reaction flask, heat to 120°C, and vacuum dry for 12 hours. Then, control the temperature in the reaction flask to 50°C, add 12 parts by mass of hexafluoroisopropyl ketone, and stir at 250 r / min for 10 minutes. Then, raise the temperature of the reaction flask to 80°C, add 4 parts by mass of isophorone diisocyanate, and stir at 300 r / min for 2 hours. S2.2: The temperature was then lowered to 60°C while stirring. 6 parts by weight of a composite chain extender and 1 part by weight of N-methylpyrrolidone were added. After reacting for 15 minutes, the temperature was raised to 80°C and stirred for 2 hours. The temperature was then controlled at 40°C. During the cooling process, 10 parts by weight of acetone was added dropwise. The mixture was stirred at 400 r / min for 1 hour. During the stirring process, 3 parts by weight of 1,4-butanediol was added dropwise. S2.3: The speed is then increased to 900 rpm, and 2% by weight of the catalyst triethylamine and 50% by weight of deionized water are added. Emulsification is performed for 10 minutes. After emulsification, acetone is removed to obtain a water-based polyurethane emulsion blended with polyoxypropylene glycol and epoxidized soybean oil. S2.4: Add silane coupling agent KH550 and trimethylolpropane to the aqueous polyurethane emulsion blended with polyoxypropylene glycol and epoxy soybean oil, the mass ratio of the aqueous polyurethane emulsion blended with polyoxypropylene glycol and epoxy soybean oil, the silane coupling agent and trimethylolpropane is 10:6:3, and then add 2% of the system mass of catalyst triethylamine, stir at a speed of 800r / min, react for 10 minutes, and obtain a modified aqueous polyurethane emulsion.

[0024] S3: Screen printing process for aluminum veneer S3.1: Weigh 15 parts by mass of the modified waterborne polyurethane emulsion and 3 parts by mass of the pigment, disperse and grind them in a mortar, add 8 parts by mass of deionized water, and grind for 20 minutes to obtain a waterborne polyurethane screen printing ink; S3.2: Clean the surface of the aluminum veneer, remove oil and dust, polish and passivate, then make a silk screen, stretch the silk screen on the screen frame, and then evenly apply photosensitive glue on the silk screen, dry it in the dark, expose and develop it with a UV lamp to obtain a silk screen, fix the aluminum veneer on the printing press, install the silk screen on the printing press, and add the water-based polyurethane silk screen ink prepared in step S3.1. Use a scraper to evenly scrape the water-based polyurethane silk screen ink to transfer the pattern to the surface of the aluminum veneer, dry and solidify it to obtain the printed aluminum veneer and the ink layer on the surface of the aluminum veneer, and complete the silk screen printing process of the aluminum veneer. Example

[0025] A screen printing process for aluminum veneer, such as Figure 1 As shown, the following steps are included: S1: Preparation of composite chain extender Ethylene carbonate and hexamethylenediamine were weighed and mixed in dichloromethane in a mass ratio of 1:1, and the mixture was heated to 80°C. Then, 1% of the mass of the system catalyst triethylamine was added and stirred at a speed of 200 r / min for 6 hours. After the reaction system was stable, the temperature was raised to 100°C and the reaction was carried out for 3.5 hours to remove excess ethylene carbonate in the system. The product was then distilled under reduced pressure to remove the solvent dichloromethane, and an equal mass of triphenyl phosphate was added and completely dissolved in dichloromethane. Then, 1% of the mass of the system catalyst was added, and the mixture was heated to 100°C and stirred at a speed of 200 r / min for 8 hours. After the reaction was completed, the dichloromethane was removed by distillation under reduced pressure, and the precipitate was precipitated with ethanol. The precipitate was collected, washed and dried to obtain a composite chain extender.

[0026] S2: Preparation of modified waterborne polyurethane emulsion S2.1: Add 1 part by mass of polyoxypropylene glycol and 2 parts by mass of ring-opened epoxidized soybean oil to a reaction flask, heat to 125°C, and vacuum dry for 13 hours. Then, control the temperature in the reaction flask to 60°C, add 10 parts by mass of hexafluoroisopropyl ketone, and stir at 300 r / min for 12 minutes. Then, raise the temperature of the reaction flask to 85°C, add 1 part by mass of isophorone diisocyanate, and stir at 350 r / min for 2.5 hours. S2.2: The temperature was then lowered to 65°C while stirring. 2 parts by mass of a composite chain extender and 0.5 parts by mass of N-methylpyrrolidone were added. After reacting for 20 minutes, the temperature was raised to 85°C and stirred for 2.5 hours. The temperature was then controlled at 45°C. During the cooling process, 5 parts by mass of acetone were added dropwise. The mixture was stirred at 450 r / min for 1.5 hours. During the stirring process, 1 part by mass of 1,4-butanediol was added dropwise. S2.3: The speed is then increased to 950 rpm, and 1% by weight of the catalyst triethylamine and 30% by weight of deionized water are added. Emulsification is performed for 15 minutes. After emulsification, acetone is removed to obtain a water-based polyurethane emulsion blended with polyoxypropylene glycol and epoxidized soybean oil. S2.4: Add silane coupling agent KH550 and trimethylolpropane to the aqueous polyurethane emulsion blended with polyoxypropylene glycol and epoxy soybean oil, the mass ratio of the aqueous polyurethane emulsion blended with polyoxypropylene glycol and epoxy soybean oil, the silane coupling agent and trimethylolpropane is 10:4:1, and then add 1% of the system mass of catalyst triethylamine, stir at a speed of 900 r / min, react for 15 minutes, and obtain a modified aqueous polyurethane emulsion.

[0027] S3: Screen printing process for aluminum veneer S3.1: Weigh 10 parts by mass of the modified waterborne polyurethane emulsion and 2 parts by mass of the pigment, disperse and grind them in a mortar, add 5 parts by mass of deionized water, and grind for 40 minutes to obtain a waterborne polyurethane screen printing ink; S3.2: Clean the surface of the aluminum veneer, remove oil and dust, polish and passivate, then make a silk screen, stretch the silk screen on the screen frame, and then evenly apply photosensitive glue on the silk screen, dry it in the dark, expose and develop it with a UV lamp to obtain a silk screen, fix the aluminum veneer on the printing press, install the silk screen on the printing press, and add the water-based polyurethane silk screen ink prepared in step S3.1. Use a scraper to evenly scrape the water-based polyurethane silk screen ink to transfer the pattern to the surface of the aluminum veneer, dry and solidify it to obtain the printed aluminum veneer and the ink layer on the surface of the aluminum veneer, and complete the silk screen printing process of the aluminum veneer.

[0028] Comparative Example 1: Compared with Example 1, the difference of Comparative Example 1 is that triphenyl phosphate is not added in step S1. Specifically, "ethylene carbonate and hexamethylenediamine are weighed in a mass ratio of 1:1, mixed in dichloromethane, and heated to 60°C, and then 1% of the system mass of catalyst triethylamine is added, and stirred at a speed of 150 r / min for 4 hours. After the reaction system is stable, the temperature is raised to 95°C, and the reaction is carried out for 3 hours to remove excess ethylene carbonate in the system. The product is then distilled under reduced pressure to remove the solvent dichloromethane, precipitated with ethanol, collected, washed and dried to obtain a composite chain extender", and the remaining steps remain unchanged. The prepared printed aluminum veneer is recorded as Comparative Example 1.

[0029] Comparative Example 2: Compared with Example 1, the difference of Comparative Example 2 is that no ethylene carbonate is added in step S1. Specifically, "weigh triphenyl phosphate and hexamethylenediamine in a mass ratio of 1:1, mix them in dichloromethane, and heat them to 60°C, then add 1% of the system mass of catalyst triethylamine, and stir at a speed of 150r / min for 4h. After the reaction system is stable, raise the temperature to 95°C, react for 3h to remove excess ethylene carbonate in the system, then distill the product under reduced pressure to remove the solvent dichloromethane, precipitate with ethanol, collect the precipitate, wash and dry to obtain a composite chain extender," and the remaining steps remain unchanged. The prepared printed aluminum veneer is recorded as Comparative Example 2.

[0030] Comparative Example 3: Compared with Example 1, the difference of Comparative Example 3 is that, in step S2.1, polyoxypropylene glycol is not added, but polyoxypropylene glycol is completely replaced by open-ring epoxidized soybean oil, specifically "S2.1: take 3 parts by mass of open-ring epoxidized soybean oil and add it to a reaction bottle, and heat it to 120°C, vacuum dry it for 12 hours, then control the temperature in the reaction bottle at 50°C, add 10 parts by mass of hexafluoroisopropyl ketone, and then stir at a speed of 250r / min for 10 minutes, raise the temperature of the reaction bottle to 80°C, and then add 1 part by mass of isophorone diisocyanate, and stir at a speed of 300r / min for 2 hours", and the other steps remain unchanged. The prepared printed aluminum veneer is recorded as Comparative Example 3.

[0031] Comparative Example 4: Compared with Example 1, the difference of Comparative Example 4 is that, in step S2.1, ring-opened epoxidized soybean oil is not added, but polyoxypropylene glycol is used to completely replace the ring-opened epoxidized soybean oil, specifically "S2.1: take 3 parts by mass of polyoxypropylene glycol and add it to a reaction bottle, and heat it to 120°C, vacuum dry it for 12 hours, then control the temperature in the reaction bottle at 50°C, add 10 parts by mass of hexafluoroisopropyl ketone, and then stir at a speed of 250r / min for 10 minutes, raise the temperature of the reaction bottle to 80°C, and then add 1 part by mass of isophorone diisocyanate, and stir at a speed of 300r / min for 2 hours", and the other steps remain unchanged. The prepared printed aluminum veneer is recorded as Comparative Example 4.

[0032] Comparative Example 5: Compared with Example 1, the difference of Comparative Example 5 is that the silane coupling agent KH550 is not added in step S2.4. Specifically, "S2.4: add trimethylolpropane to the aqueous polyurethane emulsion blended with polyoxypropylene glycol and epoxy soybean oil, the mass ratio of the aqueous polyurethane emulsion blended with polyoxypropylene glycol and epoxy soybean oil to trimethylolpropane is 10:1, and then add 1% of the system mass of catalyst triethylamine, stir at a speed of 800 r / min, react for 10 minutes, and obtain a modified aqueous polyurethane emulsion". The other steps remain unchanged, and the prepared printed aluminum veneer is recorded as Comparative Example 5.

[0033] Comparative Example 6: Compared with Example 1, the difference of Comparative Example 6 is that trimethylolpropane is not added in step S2.4, specifically "S2.4: adding silane coupling agent KH550 to the aqueous polyurethane emulsion blended with polyoxypropylene glycol and epoxy soybean oil, the mass ratio of the aqueous polyurethane emulsion blended with polyoxypropylene glycol and epoxy soybean oil and the silane coupling agent KH550 is 10:4, and then adding 1% of the system mass of catalyst triethylamine, stirring at a speed of 800 r / min, and reacting for 10 minutes to obtain a modified aqueous polyurethane emulsion", and the other steps remain unchanged, and the prepared printed aluminum veneer is recorded as Comparative Example 6.

[0034] Comparative Example 7: Compared with Example 1, the silk screen printing ink of Comparative Example 7 is a commercial silk screen printing ink. The commercial silk screen printing ink is poured on the silk screen screen, and the water-based polyurethane silk screen printing ink is scraped onto the surface of the aluminum veneer with a scraper, dried and solidified to obtain a printed aluminum veneer, completing the silk screen printing process of the aluminum veneer. The prepared printed aluminum veneer is recorded as Comparative Example 7.

[0035] The hardness of the ink layer on the surface of the aluminum veneer of Examples 1-3, Comparative Examples 1-2 and Comparative Examples 5-7 was tested using the method in GB / T 6739-2022 "Determination of paint film hardness by pencil method for paints and varnishes", as shown in Table 1.

[0036] The ink layer on the surface of the aluminum veneer of Examples 1-3 and Comparative Examples 3-7 was tested for aging resistance using the xenon arc lamp aging test chamber standard in GB / T 16422.2-2022 "Plastics Laboratory Light Source Exposure", as shown in Table 2.

[0037] The water resistance of the ink layer on the surface of the aluminum veneer of Examples 1-3 and Comparative Examples 3-7 was tested using GB / T 1733-1993 “Determination of water resistance of paint films”, as shown in Table 3.

[0038] Table 1 Pencil hardness Example 1 5H Example 2 5H Example 3 5H Comparative Example 1 3H Comparative Example 2 3H Comparative Example 5 4H Comparative Example 6 4H Comparative Example 7 4H Table 2 Initial appearance 800h xenon arc lamp irradiation Example 1 Smooth and flat No change Example 2 Smooth and flat No change Example 3 Smooth and flat No change Comparative Example 3 Smooth and flat No whitening or cracking Comparative Example 4 Smooth and flat No whitening or cracking Comparative Example 5 Smooth and flat Whitening and cracking Comparative Example 6 Smooth and flat Whitening and cracking Comparative Example 7 Smooth and flat Whitening and cracking Table 3 Initial appearance After immersion test Example 1 Smooth and flat No change Example 2 Smooth and flat No change Example 3 Smooth and flat No change Comparative Example 3 Smooth and flat wrinkles Comparative Example 4 Smooth and flat wrinkles Comparative Example 5 Smooth and flat wrinkles Comparative Example 6 Smooth and flat wrinkles Comparative Example 7 Smooth and flat wrinkles As can be seen from Table 1, the pencil hardness of the ink layers of Examples 1-3 is all 5H, while the pencil hardness of the ink layers of Comparative Examples 1 and 2 is only 3H. Comparative Example 7 is a commercially available product, and the hardness of its ink layer is 4H. This shows that the chain extender prepared by the present invention is prepared by combining ethylene carbonate, hexamethylenediamine, and phenyl phosphate. Ethylene carbonate and phenyl phosphate react with hexamethylenediamine together, and the bifunctional groups synergistically extend the chain, thereby improving the hardness of the screen printing ink prepared from the aqueous polyurethane emulsion blended with polyoxypropylene glycol and epoxy soybean oil. The hardness of the ink layer of Comparative Examples 5 and 6 is 4H, indicating that the hardness of the ink layer can also be improved by combining a silane coupling agent and trimethylolpropane for modification.

[0039] As can be seen from Table 2, after the 800-h xenon arc lamp aging test, the surfaces of the ink layers of Examples 1-3 can still remain smooth and flat, without any obvious changes, and without any whitening or cracking. However, comparative examples 3-6 all exhibit cracking to varying degrees or simultaneous whitening and cracking. This shows that the present invention uses polyoxypropylene glycol and ring-opened epoxidized soybean oil as raw materials for blending, and the two raw materials have a synergistic effect, which is better than the use of only one of the raw materials in the anti-aging effect and has a longer service life. The modified use of a silane coupling agent and trimethylolpropane in combination can also extend the service life of the ink layer. Comparative example 7 is a commercially available product, which also exhibits cracking and whitening after the 800-h xenon arc lamp aging test. This shows that the present invention has better anti-aging performance than existing products.

[0040] As can be seen from Table 3, the surfaces of the ink layers of Examples 1-3 remained smooth and flat after the water immersion test, while the surfaces of Comparative Examples 3-7 began to wrinkle, indicating that the ink layers prepared using the raw material combinations and process steps of the present invention have better water resistance. Good water resistance means that they are less likely to wrinkle during long-term use and have a longer service life than commercially available products.

[0041] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the present invention. Anyone skilled in the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by one of ordinary skill in the art without departing from the spirit and technical principles disclosed herein are intended to be covered by the claims of the present invention.

Claims

1. A screen printing process for aluminum veneer, characterized in that: The steps include: S1: Preparation of composite chain extender Weighing ethylene carbonate and hexamethylenediamine, mixing them in dichloromethane, then adding a catalyst, stirring, and heating to react. Subsequently, the product is distilled under reduced pressure to remove dichloromethane, and then phenyl phosphate and a catalyst are added, and heating and stirring are performed to prepare a composite chain extender. S2: Preparation of modified waterborne polyurethane emulsion Add polyoxypropylene glycol and ring-opened epoxy soybean oil to a reaction flask, then add hexafluoroisopropyl ketone and isophorone diisocyanate, stir, then add a composite chain extender and N-methylpyrrolidone, heat and stir after reaction, then dropwise add acetone and 1,4-butanediol, then add a catalyst and deionized water for emulsification to prepare a polyoxypropylene glycol and epoxy soybean oil blended waterborne polyurethane emulsion, then add a silane coupling agent and trimethylolpropane to prepare a modified waterborne polyurethane emulsion; S3: Screen printing process for aluminum veneer The modified water-based polyurethane emulsion and pigment are weighed, and deionized water is added and ground to obtain water-based polyurethane screen printing ink. The surface of the aluminum veneer is cleaned, polished and passivated, and then a screen is made. The screen is stretched on the screen frame, and then a photosensitive adhesive is evenly coated on the screen. After drying, it is exposed and developed to obtain a screen. The aluminum veneer and the screen are installed on a printing press, and water-based polyurethane screen printing ink is added. The pattern on the screen is transferred to the surface of the aluminum veneer by a scraper, dried and cured to obtain a printed aluminum veneer, and the screen printing process of the aluminum veneer is completed.

2. The screen printing process of aluminum veneer according to claim 1, characterized in that: Step S1: preparing a composite chain extender, comprising the following steps: Ethylene carbonate and hexamethylenediamine are weighed and mixed in dichloromethane in a mass ratio of 1:(1-3), and the mixture is heated to 60-80°C. Then, 1-2% of the mass of the system catalyst is added, and the mixture is stirred at a speed of 150-200 r / min for 4-6 hours. After the reaction system is stable, the temperature is increased to 95-100°C, and the mixture is reacted for 3-3.5 hours to remove excess ethylene carbonate in the system. Subsequently, the product is distilled under reduced pressure to remove the solvent dichloromethane, and an equal mass of phenyl phosphate is added and completely dissolved in dichloromethane. Then, 1-2% of the mass of the system catalyst is added, and the mixture is heated to 80-100°C. The mixture is stirred at a speed of 150-200 r / min for 6-8 hours. After the reaction is completed, the dichloromethane is removed by distillation under reduced pressure, and the precipitate is precipitated with ethanol. The precipitate is collected, washed, and dried to obtain a composite chain extender.

3. The screen printing process of aluminum veneer according to claim 2, characterized in that: Step S2 prepares a modified aqueous polyurethane emulsion, comprising the following steps: S2.1: Add 1-3 parts by mass of polyoxypropylene glycol and 2-6 parts by mass of ring-opened epoxidized soybean oil to a reaction flask, heat to 120-125°C, and vacuum dry for 12-13 hours. Then, control the temperature in the reaction flask to 50-60°C, add 10-12 parts by mass of hexafluoroisopropyl ketone, and stir at 250-300 r / min for 10-12 minutes. Then, raise the temperature of the reaction flask to 80-85°C, add 1-4 parts by mass of isophorone diisocyanate, and stir at 300-350 r / min for 2-2.5 hours. S2.2: Lower the temperature to 60-65°C while stirring. Add 2-6 parts by weight of a composite chain extender and 0.5-1 part by weight of N-methylpyrrolidone. After reacting for 15-20 minutes, raise the temperature to 80-85°C and stir for 2-2.5 hours. Then, control the temperature to 40-45°C and dropwise add 5-10 parts by weight of acetone while cooling. Stir at 400-450 r / min for 1-1.5 hours. Add 1-3 parts by weight of 1,4-butanediol dropwise while stirring. S2.3: The speed is then increased to 900-950 rpm, and 1-2% by weight of the catalyst and 30-50% by weight of deionized water are added. Emulsification is performed for 10-15 minutes. After emulsification, the acetone is removed to obtain a water-based polyurethane emulsion blended with polyoxypropylene glycol and epoxy soybean oil. S2.4: Add silane coupling agent and trimethylolpropane to the aqueous polyurethane emulsion blended with polyoxypropylene glycol and epoxy soybean oil, the mass ratio of the aqueous polyurethane emulsion blended with polyoxypropylene glycol and epoxy soybean oil, the silane coupling agent and trimethylolpropane is 10: (4-6): (1-3), and then add 1-2% of the system mass of the catalyst, stir at a speed of 800-900r / min, react for 10-15min, and obtain a modified aqueous polyurethane emulsion.

4. The screen printing process of aluminum veneer according to claim 3, characterized in that: Step S3 performs screen printing on the aluminum veneer, including the following steps: S3.1: Weigh 10-15 parts by weight of the modified waterborne polyurethane emulsion and 2-3 parts by weight of the pigment, disperse and grind them in a mortar, add 5-8 parts by weight of deionized water, and grind for 20-40 minutes to obtain a waterborne polyurethane screen printing ink; S3.2: Clean the surface of the aluminum veneer, remove oil and dust, polish and passivate, then make a silk screen, stretch the silk screen on the screen frame, and then evenly apply photosensitive glue on the silk screen, dry it in the dark, expose and develop it with a UV lamp to obtain a silk screen, fix the aluminum veneer on the printing press, install the silk screen on the printing press, and add the water-based polyurethane silk screen ink prepared in step S3.

1. Use a scraper to evenly scrape the water-based polyurethane silk screen ink to transfer the pattern to the surface of the aluminum veneer, dry and solidify it to obtain the printed aluminum veneer and the ink layer on the surface of the aluminum veneer, and complete the silk screen printing process of the aluminum veneer.

5. The screen printing process of aluminum veneer according to claim 3, characterized in that: The phenyl phosphate is specifically triphenyl phosphate.

6. The screen printing process of aluminum veneer according to claim 3, characterized in that: The silane coupling agent is specifically silane coupling agent KH550, the main component of which is γ-aminopropyltriethoxysilane.

7. The screen printing process of aluminum veneer according to claim 3, characterized in that: The catalyst in step S1 and step S2 is triethylamine.

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