Waterborne polyurethane, alkali-resistant protective glue as well as preparation method and application of alkali-resistant protective glue

Abstract

The invention discloses waterborne polyurethane, alkali-resistant protective glue as well as a preparation method and application of the alkali-resistant protective glue. The waterborne polyurethane comprises polyurethane obtained by carrying out reaction on polyester polyol, isocyanate and a chain extender; the chain extender comprises a first chain extender and a second chain extender; the first chain extender comprises at least one of 2, 2-dimethylolpropionic acid, dimethylolbutyric acid or polyethylene glycol; the second chain extender comprises at least one of glycerol and trimethylolpropane. By selecting the specific polyester polyol and the chain extender, the waterborne polyurethane with excellent alkali resistance, high transparency and good mechanical properties is realized. The protective glue further prepared on the basis of the waterborne polyurethane can give consideration to excellent mechanical properties and alkali resistance, effectively solves the technical problems that a traditional protective glue is prone to blistering, falling off and the like in an alkaline environment, and provides a brand-new solution for reliable protection of an aluminum plating material in a severe alkaline environment.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, specifically to an aqueous polyurethane, an alkali-resistant protective adhesive, its preparation method, and its application. Background Technology

[0002] Metallized materials are widely used in chemical product packaging, building material surface treatment, and many other fields due to their excellent barrier properties, decorative properties, and metallic luster. However, in actual use, the metallized layer often inevitably comes into contact with various alkaline substances, such as alkaline chemicals or alkaline substrates in building material environments. The metallized layer itself is chemically relatively reactive in alkaline media and is prone to corrosion, leading to a loss of its functionality and aesthetics. Therefore, a protective adhesive is usually applied to the surface of the metallized layer to isolate it from corrosive media and extend its service life. Currently, most metallized coating protective adhesives on the market are based on traditional polymer systems. Although these products may perform well under normal conditions, their protective effectiveness is significantly insufficient in long-term or continuous alkaline environments. Specifically, the coating is prone to blistering, cracking, and even peeling off from the substrate, failing to provide a durable and effective barrier for the metallized layer. This fundamental deficiency in alkali resistance severely limits the reliable application of metallized materials in harsh alkaline environments. Furthermore, many traditional formulations of protective adhesives with relatively good performance in existing technologies still involve a large amount of volatile organic solvents during preparation and use, which not only poses a potential threat to the health of production personnel, but also causes environmental pollution problems.

[0003] Therefore, developing an environmentally friendly, high-performance aluminized coating protective adhesive that can withstand alkaline corrosion for a long time is an important research direction in this field. Summary of the Invention

[0004] To overcome the shortcomings of the existing technology, the present invention aims to provide a waterborne polyurethane that combines excellent alkali resistance, high transparency and good mechanical properties.

[0005] Another objective of this invention is to provide a high-performance alkali-resistant protective adhesive that can be used for the protection of aluminum-plated coatings.

[0006] This invention is achieved through the following technical solution: In a first aspect, the present invention provides an aqueous polyurethane, comprising a polyurethane obtained by reacting a polyester polyol, an isocyanate and a chain extender. The chain extender includes a first chain extender and a second chain extender; The first chain extender includes at least one of 2,2-dimethylolpropionic acid (DMPA), dimethylolbutyric acid (DMBA), or polyethylene glycol (PEG); The second chain extender includes at least one of glycerol and trimethylolpropane (TMP).

[0007] Preferably, the mass ratio of the polyester polyol, isocyanate, first chain extender and second chain extender is 100:(20-35):(3-6):(1-3).

[0008] Preferably, the polyester polyol is selected from polycarbonate diol (PCDL); the number average molecular weight of the polyester polyol is 500-3000.

[0009] Preferably, the isocyanate is selected from at least one of isophorone diisocyanate (IPDI), hexamethylene diisocyanate (HDI), diphenylmethane diisocyanate (MDI), and toluene diisocyanate (TDI).

[0010] Preferably, the solid content of the waterborne polyurethane of the present invention is 30%-40%; and the pH of the waterborne polyurethane is 7-8.

[0011] Secondly, the present invention provides a method for preparing the aforementioned waterborne polyurethane, comprising the following steps: Polyester polyol, diisocyanate, first chain extender, and catalyst are added to a reaction vessel and reacted at 75-85℃ for 2-4 hours to obtain a polyurethane prepolymer with terminal -NCO. After the reaction system is cooled to 55-65℃, a second chain extender is added and reacted at this temperature for 1.5-3 hours. Then, N-methylpyrrolidone is added for dilution. After the reaction system is cooled to 40-50℃, a neutralizing agent and deionized water are added, and the reaction is carried out for 25-40 minutes. Finally, an amine chain extender is added, and the mixture is stirred and emulsified to prepare waterborne polyurethane.

[0012] Furthermore, in the polyurethane prepolymer reaction system, the amounts of each component, by mass percentage, are as follows: polyester polyol 60%-70%, isocyanate 20%-30%, first chain extender 8%-10%, and catalyst 0.02%-0.03%.

[0013] Furthermore, the NCO content of the polyurethane prepolymer is 0.8-1.5%. The NCO content is determined by titration.

[0014] Further, the amount of catalyst used is 0.02%-0.06% of the polyester polyol; the amount of N-methylpyrrolidone used is 25%-45% of the mass of the polyurethane prepolymer; the amount of neutralizing agent used is to adjust the pH of the system to 7-8; and the amount of amine chain extender used is 0.3%-1.2% of the mass of the polyurethane prepolymer.

[0015] Furthermore, the catalyst is selected from at least one of organotin catalysts and organobismuth catalysts; the neutralizing agent is selected from at least one of triethylamine (TEA) and dimethylethanolamine (DMEA); and the amine chain extender is selected from at least one of ethylenediamine (EDA) and diethylenetriamine (DETA).

[0016] Furthermore, the polyester polyol raw material is first subjected to vacuum dehydration. Preferably, the vacuum dehydration is carried out at a temperature of 90-110℃ and a vacuum degree of -0.095 MPa to -0.1 MPa for 1-3 hours.

[0017] Furthermore, the stirring speed for emulsification is 800-1500 rpm and the temperature is 40-50℃.

[0018] Furthermore, in the method for preparing the waterborne polyurethane, the reaction system is carried out under the protection of a dry inert gas.

[0019] Thirdly, the present invention provides an alkali-resistant protective adhesive, comprising the following components by weight: 30-50 parts of the waterborne polyurethane described in this invention; 10-20 parts titanium dioxide; Dispersant 0.5-4 parts; Leveling agent 0.5-2 parts; 1-3 parts isopropanol; 30-45 parts water.

[0020] Preferably, the titanium dioxide has an average particle size of 0.2-0.5 μm.

[0021] Preferably, the dispersant is selected from polyacrylate-based dispersants; the leveling agent is selected from polyacrylate-based leveling agents.

[0022] Furthermore, the alkali-resistant protective adhesive has a pH of 7-8, a solid content of 30%-40%, and a viscosity of 250-300 mPa·s (25℃). The viscosity was measured using a rotational viscometer.

[0023] Further, by weight, the alkali-resistant protective adhesive also includes 0.5-1.5 parts of defoamer. Preferably, the defoamer is selected from at least one of polyether-modified polysiloxane defoamers and organosilicon defoamers.

[0024] Fourthly, the present invention provides a method for preparing the alkali-resistant protective adhesive, comprising the following steps: According to the formula, first mix water and isopropanol evenly, then add the dispersant and stir at 300-500 rpm to fully dissolve the dispersant in the solvent; then add titanium dioxide and continue stirring at 300-500 rpm for 30-60 minutes, then increase the speed to 1000-1500 rpm for high-speed dispersion for 30-60 minutes; after dispersion, reduce the speed to 500-800 rpm, add waterborne polyurethane and leveling agent, stir for 20-30 minutes, filter with a sieve, and prepare the alkali-resistant protective adhesive.

[0025] Fifthly, the present invention provides the application of the aforementioned waterborne polyurethane or alkali-resistant protective adhesive in the preparation of aluminized coating protective materials.

[0026] The present invention has the following beneficial effects: This invention achieves a waterborne polyurethane with excellent alkali resistance, high transparency, and good mechanical properties by selecting specific polyester polyols and chain extenders.

[0027] This invention further utilizes a water-based polyurethane-formulated protective adhesive, which balances excellent mechanical properties and alkali resistance, effectively solving the technical problems of bubbling and peeling that traditional protective adhesives easily encounter in alkaline environments. Testing showed that aluminized plates coated with this invention remained intact and showed no abnormal changes after immersing in a 5% sodium hydroxide solution for 12 hours, demonstrating excellent long-term resistance to alkali corrosion. Furthermore, since the protective adhesive uses water as the primary dispersion medium, it significantly reduces the use and emission of volatile organic compounds, exhibiting remarkable environmental friendliness and providing a novel solution for reliable protection of aluminized materials in harsh alkaline environments. Detailed Implementation

[0028] The following embodiments are provided to better understand the present invention and are not limited to the preferred embodiments described. They do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the protection scope of the present invention.

[0029] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0030] Unless otherwise specified, the temperature in the embodiments of the present invention is room temperature or ambient temperature; room temperature or ambient temperature refers to 25±1℃. Example

[0031] This embodiment provides an aqueous polyurethane, the preparation steps of which are as follows: 100g of polycarbonate diol (PCDL, number average molecular weight 1000) was added to a four-necked flask. The system temperature was raised to 100℃ with stirring, and a vacuum pump was turned on. Dehydration was carried out at a vacuum of -0.1 MPa for 2 hours. After dehydration, the system was cooled to 80℃. Under dry nitrogen protection, 30g of isophorone diisocyanate (IPDI), 0.05g of organotin catalyst (Fomrez UL-28), and 5g of 2,2-dimethylolpropionic acid (DMPA) were slowly added to the flask. The reaction was carried out at a constant temperature of 80℃ for 3 hours to obtain a polyurethane prepolymer with terminal -NCO, and the NCO content was measured to be 1.2%. After cooling the reaction system to 60℃, 2g of trimethylolpropane (TMP) was added and the reaction was carried out at this temperature for 2 hours. Then, 40g of... N-methylpyrrolidone was diluted; after the reaction system was cooled to 40°C, 4g of triethylamine (TEA) was slowly added dropwise, followed by 200g of deionized water. The reaction was carried out for 30 minutes, and then 1.5g of ethylenediamine (EDA) was added. The mixture was stirred and emulsified at 40°C and 1500rpm to prepare waterborne polyurethane A with a solid content of 40%. Example

[0032] This embodiment provides an aqueous polyurethane, the preparation steps of which are as follows: 100g of polycarbonate diol (PCDL, number average molecular weight 1500) was added to a four-necked flask. With stirring, the system temperature was raised to 100℃, and a vacuum pump was turned on. Dehydration was carried out at -0.1 MPa for 2 hours. After dehydration, the system was cooled to 80℃. Under dry nitrogen protection, 25g of hexamethylene diisocyanate (HDI), 0.05g of organotin catalyst (Fomrez UL-28), and 4g of 2,2-dimethylolpropionic acid (DMPA) were slowly added to the flask. The reaction was carried out at a constant temperature of 80℃ for 3 hours to obtain a polyurethane prepolymer with terminal -NCO, and the NCO content was measured to be 1.2%. After cooling the reaction system to 60℃, 1.5g of glycerol was added and reacted at this temperature for 2 hours. Then, 35g of glycerol was added... Dilute with gN-methylpyrrolidone; after the reaction system is cooled to 40°C, slowly add 3g dimethylethanolamine (DMEA) and 180g deionized water, react for 30 minutes, then add 1g diethylenetriamine (DETA), stir and emulsify at 40°C and 1500rpm to prepare waterborne polyurethane B; the solid content is 41%.

[0033] Comparative Example 1 The only difference between this comparative example and Example 1 is that the polyol is a polyether polyol (PPG, number average molecular weight 1500), and all other aspects are the same as in Example 2; waterborne polyurethane C was prepared.

[0034] Comparative Example 2 The difference between this comparative example and Example 1 is that trimethylolpropane (TMP) is not added. The specific preparation steps are as follows:

[0035] 100g of polycarbonate diol (PCDL, number average molecular weight 1000) was added to a four-necked flask. With stirring, the system temperature was raised to 100℃, and a vacuum pump was turned on. Dehydration was carried out under a vacuum of -0.1 MPa for 2 hours. After dehydration, the system was cooled to 80℃. Under dry nitrogen protection, 30g of isophorone diisocyanate (IPDI), 0.05g of organotin catalyst (Fomrez UL-28), and 5g of [other chemicals] were slowly added to the flask. 2,2-Dimethylolpropionic acid (DMPA) was reacted at 80℃ for 3 hours to obtain a polyurethane prepolymer with terminal -NCO, and the NCO content was measured to be 1.2%. 40g of N-methylpyrrolidone was added for dilution. After the reaction system cooled to 40℃, 4g of triethylamine (TEA) was slowly added dropwise, followed by 200g of deionized water. The reaction was carried out for 30 minutes, and then 1.5g of ethylenediamine (EDA) was added. The mixture was stirred and emulsified at 40℃ and 1500rpm to prepare waterborne polyurethane D with a solid content of 40%.

[0036] The waterborne polyurethanes prepared in the examples and comparative examples were subjected to the following performance tests: (1) Alkali resistance test: The resin was coated on the PET film substrate, dried in an oven at 80°C, and then immersed in a 5% NaOH solution for 12 hours. The appearance of the coating was then observed.

[0037] (2) Transmittance test: The transmittance of waterborne polyurethane was tested using a spectrophotometer.

[0038] (3) Mechanical property test: The tensile test was conducted according to GB / T1040.3-2006 standard. PET film was used as the substrate and the specimens were cut into 15 mm wide and 50 mm gauge length using a dumbbell-shaped cutter. The specimens were placed at 23±2℃ for 24 h before the tensile test was performed.

[0039]

[0040] The above results show that the waterborne polyurethane of the present invention has high light transmittance (transmittance ≥85%) and high mechanical properties (tensile strength ≥15MPa), and excellent alkali resistance. According to the test, the aluminized plate coated with the protective adhesive of the present invention can still remain intact and without abnormal changes after being immersed in 5% sodium hydroxide solution for 12 hours, showing excellent long-term alkali corrosion resistance.

[0041] The aqueous polyurethane used in the examples and comparative examples was used to prepare a protective adhesive for aluminum plating. The specific preparation method is as follows: According to the proportions in Table 2, water and isopropanol were first added to a mixing tank and stirred at 400 rpm until homogeneous. Then, a dispersant was slowly added while stirring, and stirring was continued at 400 rpm for 12 minutes to fully dissolve the dispersant in the solvent. Then, titanium dioxide was slowly added while stirring at 400 rpm. After the addition was completed, stirring was continued for 40 minutes to initially disperse the titanium dioxide in the system. After the initial dispersion was completed, the speed was increased to 1200 rpm for high-speed dispersion for 45 minutes. After dispersion was completed, the speed was reduced to 600 rpm, and aqueous polyurethane and leveling agent were slowly added. At the same time, an antifoaming agent was added to eliminate the air bubbles introduced during stirring. Stirring was carried out at 600 rpm for 25 minutes, and the mixture was filtered through a 200-mesh filter to prepare an alkali-resistant protective adhesive.

[0042] The protective adhesives prepared in the application examples and application comparison examples were subjected to the following performance tests: (1) Solid content: The solid content was determined by drying and weighing method. A certain amount of protective latex was dried at 105℃ to constant weight and the solid content was determined.

[0043] (2) pH: Measured using a pH meter.

[0044] (3) Viscosity: Measured at 25°C using a rotational viscometer.

[0045] (4) Mechanical property testing: The tensile test was conducted according to GB / T1040.3-2006 standard. PET film was used as the substrate and the specimens were cut into 15 mm wide and 50 mm gauge length using a dumbbell-shaped cutter. The specimens were placed at 23±2℃ for 24 h before the tensile test was performed.

[0046] (5) Alkali resistance test: The protective adhesive is coated on the PET film substrate, dried in an oven at 80°C, and then immersed in a 5% NaOH solution for 12 hours. The appearance of the coating is then observed.

[0047]

[0048] The results above show that the protective adhesive formulated with water-based polyurethane according to the present invention can achieve both excellent mechanical properties and alkali resistance, effectively solving the technical problems of bubbling and peeling that are prone to occur in traditional protective adhesives in alkaline environments. Tests showed that the aluminized sheet coated with the protective adhesive of the present invention remained intact and showed no abnormal changes after being immersed in a 5% sodium hydroxide solution for 12 hours, demonstrating excellent long-term resistance to alkali corrosion.

[0049] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A waterborne polyurethane, characterized in that, This includes polyurethanes obtained by reacting polyester polyols, isocyanates, and chain extenders. The chain extender includes a first chain extender and a second chain extender; The first chain extender includes at least one of 2,2-dimethylolpropionic acid, dimethylolbutyric acid, or polyethylene glycol; The second chain extender includes at least one of glycerol and trimethylolpropane.

2. The waterborne polyurethane according to claim 1, characterized in that, The polyester polyol is selected from polycarbonate diols; the number average molecular weight of the polyester polyol is 500-3000; the isocyanate is selected from at least one of isophorone diisocyanate, hexamethylene diisocyanate, diphenylmethane diisocyanate, and toluene diisocyanate.

3. The waterborne polyurethane according to claim 1, characterized in that, The mass ratio of the polyester polyol, isocyanate, first chain extender and second chain extender is 100:(20-35):(3-6):(1-3).

4. The waterborne polyurethane according to claim 1, characterized in that, The solid content of the waterborne polyurethane is 30%-40%.

5. The method for preparing waterborne polyurethane according to any one of claims 1-4, characterized in that, Includes the following steps: Polyester polyol, diisocyanate, first chain extender, and catalyst are added to a reaction vessel and reacted at 75-85℃ for 2-4 hours to obtain a polyurethane prepolymer with terminal -NCO. After the reaction system is cooled to 55-65℃, a second chain extender is added and reacted at this temperature for 1.5-3 hours. Then, N-methylpyrrolidone is added for dilution. After the reaction system is cooled to 40-50℃, a neutralizing agent and deionized water are added, and the reaction is carried out for 25-40 minutes. Finally, an amine chain extender is added, and the mixture is stirred and emulsified to prepare waterborne polyurethane.

6. The method for preparing waterborne polyurethane according to claim 5, characterized in that, The NCO content of the polyurethane prepolymer is 0.8-1.5%.

7. The method for preparing waterborne polyurethane according to claim 5, characterized in that, The amount of catalyst used is 0.02%-0.06% of the polyester polyol; the amount of N-methylpyrrolidone used is 25%-45% of the mass of the polyurethane prepolymer; the amount of neutralizing agent used is to adjust the pH of the system to 7-8; and the amount of amine chain extender used is 0.3%-1.2% of the mass of the polyurethane prepolymer.

8. An alkali-resistant protective adhesive, characterized in that, By weight parts Includes the following components: 30-50 parts of the waterborne polyurethane according to any one of claims 1-4; 10-20 parts titanium dioxide; Dispersant 0.5-4 parts; Leveling agent 0.5-2 parts; 1-3 parts isopropanol; 30-45 parts water.

9. The method for preparing the alkali-resistant protective adhesive according to claim 8, characterized in that, Includes the following steps: According to the formula, first mix water and isopropanol evenly, then add the dispersant and stir at 300-500 rpm to fully dissolve the dispersant in the solvent; then add titanium dioxide and continue stirring at 300-500 rpm for 30-60 minutes, then increase the speed to 1000-1500 rpm for high-speed dispersion for 30-60 minutes; after dispersion, reduce the speed to 500-800 rpm, add waterborne polyurethane and leveling agent, and stir for 20-30 minutes to prepare the alkali-resistant protective adhesive.

10. The use of the waterborne polyurethane according to any one of claims 1-4 or the alkali-resistant protective adhesive according to claim 8 in the preparation of aluminized coating protective materials.

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