A UV-curable PUR hot melt adhesive for bonding metals and a method for producing the same

Abstract

The application discloses a kind of UV cured PUR hot melt adhesive of bonding metal and preparation method thereof, using solution method, with PPG polyether as medium, acrylic acid (or methacrylic acid), 2-3 different methacrylic ester, methacrylic acid hydroxyl ester as monomer, synthesis polyacrylate with hydroxyl group;Again with the polyacrylate as core raw material, with MDI, polyester polyol, methacrylic acid hydroxyl ester, by melting mixing, reaction polymerization preparation obtains UV cured PUR hot melt adhesive.The prepared PUR hot melt adhesive has low softening point, high initial adhesion, can realize UV light curing and moisture curing dual curing, has excellent bonding strength and stability to white cast iron, aluminum and other metals, can perfectly adapt to the rapid bonding production scene of metal product, and the whole preparation process is solvent emission-free, energy saving and environmental protection, practicality is extremely strong, with wide industrial application prospect and popularization value.

Description

Technical Field

[0001] This invention belongs to the field of hot melt adhesive preparation technology, specifically relating to a method for preparing a UV-curable PUR hot melt adhesive for bonding metals. It is particularly suitable for bonding, encapsulating, and fixing metal products such as white cast iron, aluminum, and various aluminum alloys, and can be widely used in multiple industrial fields such as automotive parts processing, electronic equipment manufacturing, and metal jewelry production. Background Technology

[0002] PUR (Polyurethane Reactive Hot Melt Adhesive) is widely used in the bonding field due to its advantages such as being solvent-free, environmentally friendly, having high bonding strength, and being resistant to high and low temperatures. Among them, PUR hot melt adhesives for metal bonding need to meet the requirements of low softening point (easy to apply), high initial tack (fast positioning), excellent metal bonding performance, and rapid curing to meet the needs of industrial production.

[0003] However, existing PUR hot melt adhesives on the market currently have many obvious technical defects in metal bonding applications, which seriously limit their promotion and application in the field of metal product processing: First, the softening point is too high. The softening point of existing PUR hot melt adhesives is usually above 80℃. Heating and melting them requires more energy, increasing production costs. Moreover, they are prone to embrittlement at low temperatures, seriously affecting the stability and service life of the bonded parts. Second, the initial tack is insufficient. When bonding metal components, due to the smooth metal surface, the initial tack of existing PUR hot melt adhesives cannot meet the requirements for rapid positioning, easily leading to slippage of the bonded parts. Issues such as detachment reduce production efficiency; third, poor adhesion to metals (especially metals with low surface polarity such as white cast iron and aluminum). Metal surfaces are usually smooth and have low polarity, and the intermolecular forces between existing PUR hot melt adhesives and metal surfaces are weak, making them prone to delamination and cracking during long-term use, thus failing to guarantee long-term bonding stability; fourth, the curing method is singular. Most existing PUR hot melt adhesives rely solely on moisture curing, which takes a long time, usually more than 72 hours to fully cure, making them unsuitable for rapid processing scenarios of metal products with high production efficiency requirements, thus limiting their application scope.

[0004] UV curing technology, as a highly efficient and environmentally friendly curing method, boasts significant advantages such as rapid curing speed, low energy consumption, environmental friendliness, and excellent curing effect. Combining UV curing technology with PUR hot melt adhesives to achieve a dual curing mode can effectively compensate for the shortcomings of a single moisture curing method, improving the curing efficiency and bonding performance of hot melt adhesives. However, most existing UV-curable PUR hot melt adhesives on the market are designed and developed for non-metallic materials such as plastics, wood, and paper, without fully considering the surface characteristics and bonding requirements of metallic materials. These adhesives suffer from poor adhesion to metals, difficulty in balancing initial tack and softening point, and poor synergistic effects of dual curing, failing to meet the bonding requirements of metal products. Therefore, developing a PUR hot melt adhesive preparation method with a low softening point, high initial tack, excellent adhesion to metals, and the ability to achieve dual curing via UV light and moisture curing, to overcome the shortcomings of existing technologies, has significant practical implications and broad industrial application value. Summary of the Invention

[0005] The purpose of this invention The purpose of this invention is to overcome the shortcomings of existing PUR hot melt adhesives, such as high softening point, insufficient initial tack, poor metal bonding performance, and single curing method. It provides a method for preparing a UV-curable PUR hot melt adhesive for bonding metals. The prepared hot melt adhesive has a low softening point, high initial tack, and can achieve dual curing by UV and moisture. It has excellent bonding performance to metals such as white cast iron and aluminum, thus solving the problems existing in the prior art.

[0006] Technical solution of the present invention To achieve the above objectives, the present invention adopts the following technical solution: a UV-curable PUR hot melt adhesive for bonding metals, the raw material composition by mass parts including: 10-15 parts MDI, 20-30 parts polyester polyol, 40-60 parts hydroxyl-containing polyacrylate, and 8-10 parts hydroxyl methacrylate; the hydroxyl-containing polyacrylate is synthesized by solution method, using PPG polyether as the reaction medium, and the monomers are acrylic acid or methacrylic acid, methacrylate, and hydroxyl methacrylate. After the reaction, the hydroxyl-containing polyacrylate is obtained; the UV-curable PUR hot melt adhesive for bonding metals has a softening point of 65-75℃, initial tack ≥180N / 25mm, UV curing energy ≤800mj / cm², moisture curing time of 24-48h, and peel strength to white cast iron and aluminum ≥180N.

[0007] The hydroxyl-containing polyacrylate comprises, by mass, the following monomers: 5-8 parts acrylic acid or methacrylic acid, 40-60 parts methacrylate, 2-15 parts hydroxyl methacrylate; and 40-60% PPG polyether by mass of the total mass of the hydroxyl-containing polyacrylate reaction system; the hydroxyl-containing polyacrylate has an acid value of 8-10, a hydroxyl value of 8-10 mgKOH / g, a number average molecular weight of 25000-35000, and a glass transition temperature of 60-65℃.

[0008] The methacrylate is obtained by mixing 2-3 of methyl methacrylate, ethyl methacrylate, and butyl methacrylate in any proportion; the PPG polyether is PPG2000, or a combination of PPG1000 and PPG4000.

[0009] The polyester polyol is a crystalline polyester polyol with a hydroxyl value strictly controlled at 20-30 mgKOH / g and a number-average molecular weight of 1000-2000.

[0010] The polyester polyol is one or two of polyethylene adipate polyol and polybutylene adipate polyol mixed in any proportion.

[0011] The raw materials also include 0.1-0.3% of a polymerization inhibitor, which is either p-hydroxyanisole (HEMQ) or hydroquinone.

[0012] The method for preparing the UV-curable PUR hot melt adhesive for bonding metals includes the following steps: Step 1: Synthesize polyacrylate with hydroxyl groups using a solution method with PPG polyether as the reaction medium. The monomers are mixed evenly and reacted. After the reaction is complete, polyacrylate with hydroxyl groups is obtained. Step 2: Prepare UV-curable PUR hot melt adhesive. Add polyester polyol and the hydroxyl-containing polyacrylate synthesized in Step 1 to the reaction apparatus, heat to 100-120℃, and stir until completely melted and mixed. Add MDI, control the temperature at 100-120℃, and react at a constant temperature for 2-3 hours. Then add hydroxy methacrylate and continue to react at a constant temperature for 1-2 hours, stirring continuously during the reaction. After the reaction is completed, seal and discharge the material under a nitrogen atmosphere, and cool to room temperature to obtain UV-curable PUR hot melt adhesive.

[0013] The specific process for solution synthesis is as follows: PPG polyether is added to a reactor equipped with an electric stirrer, precise temperature control, and nitrogen protection device. The temperature is slowly raised to 80-90℃, and stirred until the PPG polyether is completely melted and becomes transparent and uniform. Dry nitrogen is introduced throughout the process to prevent the monomers from being oxidized. Then, acrylic acid or methacrylic acid, methacrylate, and hydroxyethyl methacrylate are added slowly in sequence. The mixture is stirred for 30-60 minutes until all components are completely mixed and uniform. Alternatively, an initiator may be added. The reaction temperature is strictly controlled to be stable at 85-95℃, and the reaction is carried out at a constant temperature for 4-6 hours to ensure that the polymerization reaction proceeds fully, ultimately yielding a transparent and uniform polyacrylate product. The initiator is one of azobisisobutyronitrile (AIBN) or benzoyl peroxide (BPO), and the amount added is 0.5-1.0% of the total mass of all monomers.

[0014] The application of the UV-curable PUR hot melt adhesive for bonding metals in the bonding, encapsulation and fixing of metal products.

[0015] Beneficial effects 1. The prepared UV-curable PUR hot melt adhesive has a low softening point, controlled within the range of 65-75℃, which significantly reduces the energy consumption required during melting, effectively saving production costs. It also exhibits good flexibility and stability over a wide temperature range of -20℃ to 80℃, and is not prone to embrittlement or cracking. It can adapt to the metal bonding needs under different environmental conditions and has a wider range of applications.

[0016] 2. High initial adhesion, reaching ≥180N / 25mm, enables rapid positioning and immediate fixation when bonding metal components, effectively avoiding problems such as slippage and detachment of the bonded parts, significantly improving the production efficiency of metal products and reducing the scrap rate in the production process.

[0017] 3. Excellent adhesion to metals (especially white cast iron and aluminum), with peel strength ≥180N for both white cast iron and aluminum, ensuring strong adhesion. It effectively solves the defects of existing PUR hot melt adhesives, such as poor adhesion to metals and easy delamination after long-term use, ensuring the long-term stability and service life of the bonded parts.

[0018] 4. It achieves dual curing modes of UV curing and moisture curing. UV curing is fast and can meet the needs of rapid production, while moisture curing can further improve the bonding strength. It achieves an organic combination of short-term efficient curing and long-term stable bonding, which broadens the application scenarios of hot melt adhesives and can be adapted to metal processing scenarios with different production efficiency requirements.

[0019] 5. The entire preparation process adopts a solvent-free process with no solvent emissions, which meets environmental protection requirements. Moreover, the preparation process is simple and easy to operate, and the process parameters are easy to control, which facilitates large-scale industrial production and has broad industrial application prospects and promotion value. Detailed Implementation

[0020] All raw materials used in this invention are qualified industrial products, not limited to specific manufacturers, and are all commercially available conventional products; throughout the patent application, the following terms have specific meanings:

[0021] The present invention will be further described in detail below with reference to the embodiments. The embodiments are only used to explain the present invention and are not intended to limit the scope of protection of the present invention.

[0022] A method for preparing a UV-curable PUR hot melt adhesive for bonding metals includes the following two core steps: synthesizing a hydroxyl-containing polyacrylate and preparing the UV-curable PUR hot melt adhesive, with specific details as follows: Step 1: Synthesize polyacrylate with hydroxyl groups by solution polymerization using PPG polyether as the reaction medium. The monomer composition is acrylic acid or methacrylic acid, 2-3 different types of methacrylate and hydroxy methacrylate. By precisely controlling key process parameters such as reaction temperature and reaction time, the polymerization reaction is ensured to be full and uniform. After the reaction is completed, a polyacrylate product with stable performance is obtained. Step 2: Prepare UV-curable PUR hot melt adhesive. By mass percentage, add 10-15% MDI, 20-30% polyester polyol, 40-60% of the polyacrylate synthesized in Step 1, and 8-10% hydroxyl methacrylate sequentially to the reaction apparatus. After a series of process steps including melt mixing, vacuum cleaning to remove moisture and impurities, reaction at a constant temperature of 100-120℃ for 2-3 hours, and sampling inspection to ensure performance compliance, the UV-curable PUR hot melt adhesive is finally obtained. The key performance indicators of the polyacrylate synthesized in Step 1 are strictly controlled as follows: acid value 8-10, hydroxyl value 8-10 mgKOH / g, number average molecular weight 25000-35000, and glass transition temperature 60-65℃. This range of indicators is the core foundation for ensuring sufficient reaction with MDI and polyester polyol, and for the final hot melt adhesive to possess excellent metal bonding performance.

[0023] Further technical details Preferably, in step 1, the mass ratio of each monomer is precisely controlled as follows: 5-8 parts acrylic acid, 40-60 parts methacrylate, and 2-15 parts hydroxy methacrylate; wherein the amount of PPG polyether added is 40-60% of the total mass of the reaction system. The methacrylate is preferably 2-3 of methyl methacrylate, ethyl methacrylate, and butyl methacrylate mixed in any proportion. The mixture can be flexibly combined according to the required flexibility, adhesion, and other performance requirements of the polyacrylate, thereby adjusting the overall performance of the product to better suit the bonding needs of different metal materials.

[0024] As a preferred option, the solution synthesis process in step 1 is as follows: PPG polyether is added to a reactor equipped with an electric stirrer, precise temperature control, and nitrogen protection. The temperature is slowly raised to 80-90℃, and stirred until the PPG polyether is completely melted and becomes transparent and uniform. Dry nitrogen is introduced for protection throughout the process to prevent monomer oxidation during the reaction. Then, acrylic acid or methacrylic acid, methacrylate, and hydroxyethyl methacrylate are added slowly in sequence. After stirring for 30-60 minutes until all components are completely mixed, an initiator is added. The reaction temperature is strictly controlled and stabilized at 85-95℃, and the reaction is carried out at a constant temperature for 4-6 hours to ensure that the polymerization reaction proceeds fully, ultimately yielding a transparent and uniform polyacrylate product. Nitrogen protection effectively prevents monomer oxidation during the reaction, ensuring product purity and performance stability. Controlling the reaction temperature and time allows for precise regulation of the molecular weight, acid value, and hydroxyl value of the polyacrylate, ensuring its reactivity with MDI and polyester polyols, laying the foundation for the preparation of high-performance hot melt adhesives.

[0025] Preferably, the initiator is selected from azobisisobutyronitrile (AIBN) or benzoyl peroxide (BPO), and the amount added is 0.5-1.0% of the total mass of all monomers. The addition of the initiator can effectively start the polymerization reaction of the monomers. Controlling the amount of initiator within the above range can avoid the problems of excessive initiator leading to excessively fast reaction rate and uneven molecular weight distribution of the product, or insufficient initiator leading to incomplete reaction and substandard product performance, thus ensuring the stability of the polyacrylate product.

[0026] As a preferred choice, a PPG polyether with a molecular weight of PPG 2000 is generally appropriate. Of course, a combination of polyethers, such as PPG 1000 and PPG 4000, can also be selected. The specific choice should be based on the reasonable range of relevant hydroxyl values.

[0027] Preferably, in step 2, the polyester polyol is a crystalline polyester polyol with a hydroxyl value strictly controlled at 20-30 mg KOH / g and a number-average molecular weight of 1000-2000. It is preferably one or a mixture of two of polyethylene adipate polyol and polybutylene adipate polyol in any proportion. The addition of crystalline polyester polyol can significantly improve the initial tack and bonding strength of the hot melt adhesive. Precise control of its hydroxyl value and molecular weight ensures sufficient reaction with MDI and polyacrylate to form a stable polyurethane molecular structure, thereby improving the overall performance of the hot melt adhesive.

[0028] Preferably, step 2 involves the following process: Polyester polyol and the polyacrylate synthesized in step 1 are added to a reactor, and the temperature is slowly raised to 100-120°C. Stirring is continued for 60-90 minutes until both components are completely melted and uniformly mixed. Then, MDI is added, and the reaction temperature is maintained at 100-120°C for 2-3 hours to ensure sufficient prepolymerization of the polyurethane. Next, hydroxyl methacrylate is added, and the reaction continues for 1-2 hours with continuous stirring to ensure uniform reaction of all components. After the reaction, the product is sealed and discharged under a nitrogen atmosphere, poured into a special mold, and allowed to cool naturally to room temperature to obtain the UV-cured PUR hot melt adhesive. This step-by-step reaction ensures sufficient reaction of all components, avoiding uneven product performance due to incomplete local reactions. Sealing the product under a nitrogen atmosphere prevents premature reaction with moisture in the air, ensuring the storage stability and performance of the hot melt adhesive.

[0029] Preferably, in step 2, 0.1-0.3% of a polymerization inhibitor can be added according to actual production needs. The polymerization inhibitor is selected from either p-hydroxyanisole (HEMQ) or hydroquinone, and is added simultaneously with the addition of hydroxymethyl methacrylate. The role of the polymerization inhibitor is to effectively prevent the self-polymerization reaction of hydroxymethyl methacrylate during the high-temperature reaction process, ensuring that it can successfully undergo a grafting reaction with polyurethane molecules, thereby improving the UV curing performance of the hot melt adhesive and ensuring the synergistic effect of the dual curing modes.

[0030] As a preferred option, the final UV-curable PUR hot melt adhesive meets the following key performance indicators: softening point of 65-75℃, initial tack ≥180N / 25mm, UV curing energy ≤800mj / cm², moisture curing time of 24-48h, and peel strength ≥180N for both white cast iron and aluminum. These performance indicators perfectly meet the bonding requirements of metal products. The low softening point significantly reduces melting energy consumption, the high initial tack enables rapid positioning and immediate fixation of metal parts, the dual curing method balances curing efficiency and long-term stability, and the excellent peel strength ensures strong adhesion, meeting long-term usage requirements.

[0031] Preferably, the metal includes white cast iron, aluminum and various aluminum alloys. This UV-curable PUR hot melt adhesive can be widely used in various scenarios such as bonding, encapsulation and fixing of metal products, such as splicing of automotive metal parts, encapsulation of metal shells for electronic devices, bonding of metal ornaments, fixing of hardware products, etc. It has a wide range of applications and can meet the metal bonding needs of different industries.

[0032] Example 1 A method for preparing a UV-curable PUR hot melt adhesive for bonding metals, specifically including the following steps: Step 1: Synthesize polyacrylates with hydroxyl groups Accurately weigh the following components according to the mass ratio: 6 parts acrylic acid, 25 parts methyl methacrylate, 27 parts butyl methacrylate, and 5 parts hydroxyethyl methacrylate, totaling 63 parts by mass. Simultaneously, add 63 parts PPG2000 polyether, representing 50% of the total mass of the reaction system. Add the PPG polyether to a reactor equipped with an electric stirrer, precise temperature control, and nitrogen protection. Slowly heat to 85°C and stir until the polyether is completely melted and transparent and homogeneous. Purge with dry nitrogen for continuous protection. Then, slowly add acrylic acid, methyl methacrylate, butyl methacrylate, and hydroxyethyl methacrylate sequentially. Stir for 40 minutes until all components are completely and evenly mixed. Finally, add AIBN. 0.63 parts (1.0% of the total monomer mass) were used, and the reaction temperature was strictly controlled at 90℃ for 5 hours to ensure that the polymerization reaction was fully carried out, finally yielding a transparent and uniform polyacrylate product. According to professional testing, the polyacrylate has an acid value of 9, a hydroxyl value of 9 mgKOH / g, a number average molecular weight of 30,000, and a glass transition temperature of 62℃, which fully meets the performance requirements of this invention.

[0033] Step 2: Preparation of UV-curable PUR hot melt adhesive Accurately weigh 14% MDI, 25% polyethylene adipate polyol, 50% polyacrylate synthesized in step 1, and 10.8% hydroxyethyl methacrylate by weight percentage, and add the above raw materials to the reactor in sequence. First, add the polyester polyol and polyacrylate to the reactor, heat to 110°C, and stir continuously for 70 minutes until the two components are completely melted and mixed evenly. Then add MDI, keep the reaction temperature stable at 110°C, and react at a constant temperature for 2.5 hours to ensure that the polyurethane prepolymerization reaction is complete. Then add hydroxyethyl methacrylate and 0.2% HEMQ, and continue to react at a constant temperature for 1.5 hours, stirring continuously to ensure that the components react evenly. After the reaction is completed, seal and discharge the product under a nitrogen protective atmosphere, pour the product into a special mold, and let it cool naturally to room temperature to obtain the UV-cured PUR hot melt adhesive product.

[0034] Example 2 A method for preparing a UV-curable PUR hot melt adhesive for bonding metals, specifically including the following steps: Step 1: Synthesize polyacrylates with hydroxyl groups Accurately weigh the following components according to the mass ratio: 5 parts methacrylic acid, 28 parts ethyl methacrylate, 20 parts butyl methacrylate, and 2 parts hydroxyethyl methacrylate, totaling 55 parts by mass. Simultaneously, add 24 parts PPG1000 and 20 parts PPG4000 polyether, representing 44% of the total mass of the reaction system. Add the polyether to a reactor equipped with an electric stirrer, precise temperature control, and nitrogen protection device. Slowly heat to 80°C and stir until the polyether is completely melted and transparent and homogeneous. Purge with dry nitrogen for continuous protection. Then, slowly add methacrylic acid, ethyl methacrylate, butyl methacrylate, and hydroxyethyl methacrylate sequentially. Stir for 30 minutes until all components are completely and evenly mixed. Finally, add BPO. 0.275 parts (0.5% of the total monomer mass) were used, and the reaction temperature was strictly controlled to be stable at 85℃. The reaction was carried out at a constant temperature for 6 hours to ensure that the polymerization reaction was fully carried out, and finally a transparent and uniform polyacrylate product was obtained. According to professional testing, the acid value of the polyacrylate was 8, the hydroxyl value was 8 mgKOH / g, the number average molecular weight was 25000, and the glass transition temperature was 60℃, which fully met the performance requirements of this invention.

[0035] Step 2: Preparation of UV-curable PUR hot melt adhesive Accurately weigh 10.9% MDI, 20% polybutylene adipate polyol, 60% polyacrylate synthesized in step 1, and 9% hydroxyethyl methacrylate by weight percentage, and add the above raw materials to the reactor in sequence. First, add the polyester polyol and polyacrylate to the reactor, heat to 100°C, and stir continuously for 90 minutes until the two components are completely melted and mixed evenly. Then add MDI, keep the reaction temperature stable at 100°C, and react at a constant temperature for 3 hours to ensure that the polyurethane prepolymerization reaction is sufficient. Then add hydroxyethyl methacrylate and 0.1% hydroquinone, and continue to react at a constant temperature for 2 hours, stirring continuously to ensure that the components react evenly. After the reaction is completed, seal the material under a nitrogen protective atmosphere, pour the product into a special mold, and let it cool naturally to room temperature to obtain the UV-cured PUR hot melt adhesive product.

[0036] Example 3 A method for preparing a UV-curable PUR hot melt adhesive for bonding metals, specifically including the following steps: Step 1: Synthesize polyacrylates with hydroxyl groups Accurately weigh the following components according to the mass ratio: 8 parts acrylic acid, 20 parts methyl methacrylate, 20 parts ethyl methacrylate, and 15 parts hydroxyethyl methacrylate, totaling 63 parts by mass. Simultaneously, add 94.5 parts PPG2000 polyether, representing 60% of the total mass of the reaction system. Add the PPG2000 polyether to a reactor equipped with an electric stirrer, precise temperature control, and nitrogen protection. Slowly heat to 90°C and stir until the PPG2000 polyether is completely melted and transparent and homogeneous. Purge with dry nitrogen for continuous protection. Then, slowly add acrylic acid, methyl methacrylate, ethyl methacrylate, and hydroxyethyl methacrylate sequentially, stirring for 60 minutes until all components are completely and evenly mixed. Finally, add AIBN. 0.441 parts (0.7% of the total monomer mass) were used, and the reaction temperature was strictly controlled at 95℃ for 4 hours to ensure that the polymerization reaction was fully carried out, finally yielding a transparent and uniform polyacrylate product. According to professional testing, the polyacrylate has an acid value of 10, a hydroxyl value of 10 mgKOH / g, a number average molecular weight of 35000, and a glass transition temperature of 65℃, which fully meets the performance requirements of this invention.

[0037] Step 2: Preparation of UV-curable PUR hot melt adhesive Accurately weigh 15% MDI, 15 parts polyethylene adipate polyol, 15 parts polybutylene adipate polyol (the two polyester polyols total 30%), 44.7% polyacrylate synthesized in step 1, and 10% hydroxyethyl methacrylate by weight percentage. Add the above raw materials to the reactor in sequence. First, add the two polyester polyols and the polyacrylate synthesized in step 1 to the reactor, heat to 120°C, and stir continuously for 60 minutes until all components are completely melted and mixed evenly. Then add MDI, keep the reaction temperature stable at 115-120°C, and react at a constant temperature for 2 hours to ensure that the polyurethane prepolymerization reaction is sufficient. Then add hydroxyethyl methacrylate and 0.3% HEMQ, and continue to react at a constant temperature for 1 hour, stirring continuously to ensure that all components react evenly. After the reaction is completed, seal and discharge the product under a nitrogen protective atmosphere, pour the product into a special mold, and let it cool naturally to room temperature to obtain the UV-cured PUR hot melt adhesive product.

[0038] Example 4. Comparative Example Using existing conventional PUR hot melt adhesive preparation methods, without adding the self-made polyacrylate of this invention, PUR hot melt adhesive is prepared directly from MDI, polyester polyol, ordinary polyacrylate, and polyether polyol PPG2000 as raw materials, following existing conventional process steps.

[0039] Example 5 Performance Testing The UV-curable PUR hot melt adhesive products prepared in Examples 1, 2, and 3, as well as the existing conventional metal bonding PUR hot melt adhesive (control group Example 4), were subjected to performance tests according to the following standards: 1. Softening point: Tested using the ring and ball method; 2. Initial tack: Tested using the rolling ball method, unit: N / 25mm; 3. UV curing energy: The minimum energy required to achieve a curing degree of ≥80% under 385nm LED-UV ultraviolet light, in mJ / cm²; 4. Moisture curing time: The time required for complete curing under conditions of 25℃ and 50% humidity; 5. Metal peel strength: For bonding white cast iron and aluminum sheets respectively, the peel strength is tested using the 90-degree peel test according to GB / T 2790-1995 standard, in N.

[0040] The test results are shown in the table below:

[0041] By comparing the performance data of Examples 1-3 of the present invention with those of the comparative examples, it can be seen that the UV-curable PUR hot melt adhesive prepared by the present invention is significantly superior to the existing conventional PUR hot melt adhesive in terms of key performance indicators such as softening point, initial tack, metal bonding performance, and curing speed. It can effectively solve many defects of the existing technology, perfectly meet the rapid bonding requirements of metal products, and has significant technical advantages and industrial application value.

[0042] The test results show that the UV-curable PUR hot melt adhesive prepared by this invention has a significantly lower softening point than the control group, and its initial tack is increased by more than 50%. It has excellent UV curing and moisture curing performance, and its peel strength to white cast iron and aluminum is 1.7-1.8 times that of the control group. The bonding performance is greatly improved, which fully meets the industrial requirements of metal bonding. It is also environmentally friendly and easy to apply, and is superior to existing conventional PUR hot melt adhesives.

Claims

1. A UV-curable PUR hot melt adhesive for bonding metals, characterized in that, The raw material composition, by weight, includes: 10-15 parts MDI, 20-30 parts polyester polyol, 40-60 parts hydroxyl-containing polyacrylate, and 8-10 parts hydroxyl methacrylate. The hydroxyl-containing polyacrylate is synthesized by solution method, using PPG polyether as the reaction medium, with acrylic acid or methacrylic acid, methacrylate, and hydroxyl methacrylate as monomers. The hydroxyl-containing polyacrylate is obtained after the reaction. The UV-curable PUR hot melt adhesive for bonding metals has a softening point of 65-75℃, initial tack ≥180N / 25mm, UV curing energy ≤800mj / cm², moisture curing time 24-48h, and peel strength to white cast iron and aluminum ≥180N.

2. The UV-curable PUR hot melt adhesive for bonding metals according to claim 1, characterized in that, The hydroxyl-containing polyacrylate comprises, by mass, the following monomers: 5-8 parts acrylic acid or methacrylic acid, 40-60 parts methacrylate, 2-15 parts hydroxyl methacrylate; and 40-60% PPG polyether by mass of the total mass of the hydroxyl-containing polyacrylate reaction system; the hydroxyl-containing polyacrylate has an acid value of 8-10, a hydroxyl value of 8-10 mgKOH / g, a number average molecular weight of 25000-35000, and a glass transition temperature of 60-65℃.

3. The UV-curable PUR hot melt adhesive for bonding metals according to claim 2, characterized in that, The methacrylate is obtained by mixing 2-3 of methyl methacrylate, ethyl methacrylate, and butyl methacrylate in any proportion; the PPG polyether is PPG2000, or a combination of PPG1000 and PPG4000.

4. The UV-curable PUR hot melt adhesive for bonding metals according to claim 1, characterized in that, The polyester polyol is a crystalline polyester polyol with a hydroxyl value strictly controlled at 20-30 mgKOH / g and a number-average molecular weight of 1000-2000.

5. The UV-curable PUR hot melt adhesive for bonding metals according to claim 1, characterized in that, The polyester polyol is one or two of polyethylene adipate polyol and polybutylene adipate polyol mixed in any proportion.

6. The UV-curable PUR hot melt adhesive for bonding metals according to claim 1, characterized in that, The raw materials also include 0.1-0.3% of a polymerization inhibitor, which is either p-hydroxyanisole (HEMQ) or hydroquinone.

7. A method for preparing the UV-curable PUR hot melt adhesive for bonding metals according to any one of claims 1 to 6, characterized in that, Includes the following steps: Step 1: Synthesize polyacrylate with hydroxyl groups using a solution method with PPG polyether as the reaction medium. The monomers are mixed evenly and reacted. After the reaction is complete, polyacrylate with hydroxyl groups is obtained. Step 2: Prepare UV-curable PUR hot melt adhesive. Add polyester polyol and the hydroxyl-containing polyacrylate synthesized in Step 1 to the reaction apparatus, heat to 100-120℃, and stir until completely melted and mixed. Add MDI, control the temperature at 100-120℃, and react at a constant temperature for 2-3 hours. Then add hydroxy methacrylate and continue to react at a constant temperature for 1-2 hours, stirring continuously during the reaction. After the reaction is completed, seal and discharge the material under a nitrogen atmosphere, and cool to room temperature to obtain UV-curable PUR hot melt adhesive.

8. The method according to claim 7, characterized in that, The specific process of solution synthesis is as follows: PPG polyether is added to a reactor equipped with an electric stirrer, precise temperature control, and nitrogen protection device. The temperature is slowly raised to 80-90℃ and stirred until the PPG polyether is completely melted and becomes transparent and uniform. Dry nitrogen is introduced for protection throughout the process to prevent the monomer from being oxidized during the reaction. Then, acrylic acid or methacrylic acid, methacrylate, and hydroxyethyl methacrylate are added slowly in sequence and stirred for 30-60 minutes until all components are completely mixed and uniform. Alternatively, an initiator may be added. The reaction temperature is strictly controlled to be stable at 85-95℃ and the reaction is carried out at a constant temperature for 4-6 hours to ensure that the polymerization reaction is fully carried out, and finally a transparent and uniform polyacrylate product is obtained.

9. The method according to claim 8, characterized in that, The initiator is one of azobisisobutyronitrile (AIBN) or benzoyl peroxide (BPO), and the amount added is 0.5-1.0% of the total mass of all monomers.

10. The application of the UV-curable PUR hot melt adhesive for bonding metals as described in any one of claims 1 to 6 in the bonding, encapsulation and fixing of metal products.

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