Low temperature operating high temperature resistant hot melt adhesive

Abstract

The application relates to a high-temperature-resistant hot melt adhesive operated at low temperature and relates to the technical field of hot melt adhesive preparation, and comprises the following components in mass fraction: 60-80 parts of silane-modified polypropylene, 40-60 parts of maleic anhydride-modified propylene copolymer, 10-30 parts of a plasticizer, 10-20 parts of a polyisocyanate and 0.1-1 part of an antioxidant; the silane-modified polypropylene has a melting point of 140-160 DEG C and is used for improving the adhesion of the hot melt adhesive and improving the softening point of the hot melt adhesive; the maleic anhydride-modified propylene copolymer has a melting point of 130-140 DEG C and is used for improving the adhesion of the hot melt adhesive at high temperature; the plasticizer is an organic compound containing a hydroxyl group and is used for forming polyurethane together with the polyisocyanate to improve the softening point of the hot melt adhesive; through modification of the polypropylene, the adhesion at high temperature of the hot melt adhesive is improved and the operation temperature is reduced while the high-temperature-resistant property of the polypropylene is maintained.

Description

Technical Field

[0001] This application relates to the technical field of hot melt adhesive preparation, and in particular to a high-temperature resistant hot melt adhesive with a relatively low operating temperature. Background Technology

[0002] Hot melt adhesive is a type of plastic adhesive that melts at high temperatures for easy application and solidifies at low temperatures to bond objects. It is non-toxic, odorless, and an environmentally friendly chemical product with advantages such as simple production process, high added value, strong bonding strength, and fast bonding speed.

[0003] Compared to traditional resin-based hot melt adhesives, the biggest advantage of polypropylene hot melt adhesives is their lower price. Furthermore, polypropylene's more stable chemical properties and higher heat resistance make it a promising candidate for hot melt adhesive applications.

[0004] Currently, polypropylene is typically formulated into hot melt adhesives by combining it with waxes and tackifying resins. Chinese Patent Publication No. CN116042135A discloses a polypropylene hot melt adhesive comprising: 45–65 wt% ternary copolymer polypropylene; 15–25 wt% ethylene-acrylate-maleic anhydride copolymer; 5–10 wt% copolyamide; 5–30 wt% ethylene-propylene rubber; and an antioxidant. The antioxidant is present at a mass of 0.3–0.5% of the total mass of the ternary copolymer polypropylene, ethylene-acrylate-maleic anhydride copolymer, copolyamide, and ethylene-propylene rubber. The polypropylene hot melt adhesive provided by this invention improves the high-temperature resistance of polypropylene heat shrinkable tape. The polypropylene hot melt adhesive and its heat shrinkable tape for steel oil pipelines provided by this invention can withstand temperatures up to 130°C. The polypropylene hot melt adhesive provided by this invention reduces the installation temperature of polypropylene heat shrink tape, making construction easier. The polypropylene heat shrink tape provided by this invention can be installed at 130°C, shortening the heating time and avoiding the risk of epoxy coating carbonization. However, the heat resistance temperature of 130°C is difficult to maintain the adhesive performance of the hot melt adhesive in some higher temperature application scenarios, leading to adhesive failure.

[0005] Chinese Patent Publication No. CN113462332A discloses a hot melt adhesive for vertical bonding of air filters and its preparation method. The hot melt adhesive for vertical bonding of air filters provided by this invention is composed of the following components: 3-20 parts high-temperature polyethylene wax, 3-20 parts linear low-density polyethylene, 15-40 parts metallocene-catalyzed polypropylene, 5-30 parts random polyolefin, 15-50 parts petroleum resin, and 0.1-2 parts antioxidant. The ratio of linear low-density polyethylene to metallocene-catalyzed polypropylene is 1:(1.5-4). The hot melt adhesive for vertical bonding of air filters provided by this invention can replace traditional hot melt adhesive products for vertical bonding on production lines. This product has a softening point of 120 degrees Celsius, is not easily carbonized, and does not require ultra-high temperature use; however, a softening point of 120 degrees Celsius makes it difficult to apply in higher temperature scenarios. To meet the bonding requirements at higher temperatures, the heat resistance temperature of the polypropylene hot melt adhesive still needs to be increased. Summary of the Invention

[0006] To address the problem of insufficient heat resistance temperature of polypropylene hot melt adhesives, this application provides a low-temperature operating high-temperature resistant hot melt adhesive that can improve heat resistance temperature while minimizing the increase in operating temperature.

[0007] Firstly, the low-temperature operating high-temperature resistant hot melt adhesive provided in this application adopts the following technical solution: A low-temperature operating high-temperature resistant hot melt adhesive comprises the following components in parts by weight: 60-80 parts of silane-modified polypropylene, 40-60 parts of maleic anhydride-modified propylene copolymer, 10-30 parts of plasticizer, 10-20 parts of polyisocyanate, and 0.1-1 parts of antioxidant; the silane-modified polypropylene has a melting point of 140-160℃ and a melt index of 18-52 g / 10min, and is used to improve the adhesion of the hot melt adhesive and increase its softening point; Maleic anhydride-modified propylene copolymer has a melting point of 130-140℃ and a melt index of 2-15g / 10min, and is used to improve the adhesion of hot melt adhesives at high temperatures. Plasticizers are organic compounds containing hydroxyl groups, used to combine with polyisocyanates to form polyurethane and increase the softening point of hot melt adhesives.

[0008] By adopting the above technical solution, since polypropylene lacks adhesive ability and its melting point is usually around 155℃, the softening point of the hot melt adhesive prepared after mixing with plastic substances such as paraffin and resin will be further reduced. At a temperature of 150℃, it cannot meet the requirement of strong adhesion. By grafting silane groups onto polypropylene, silane-modified polypropylene can, on the one hand, increase the intermolecular forces by increasing the branching, so that the polymer molecules can no longer be neatly arranged, improving the flexibility of the molecules and thus increasing the adhesive ability of polypropylene. On the other hand, silane can form various molecular bonds with the adhesion surface, reducing the surface energy between the adhesion surface and the hot melt adhesive, thereby enhancing the adhesion performance of the hot melt adhesive. While maintaining the anti-aging, high temperature resistance, and wear resistance properties of the original chemical stability of polypropylene, the adhesion performance is increased. By grafting maleic anhydride onto propylene copolymer, the propylene copolymerization... The grafted material contains polar hydroxyl groups, which enhance intermolecular forces, making the molecules less prone to crystallization and improving flexibility. Hydroxyl groups also improve the wetting properties of the hot melt adhesive on the adhesion surface, enhancing adhesion. Furthermore, the stability of hydroxyl groups at high temperatures allows the hot melt adhesive to maintain its adhesion at high temperatures. The softening point of silane-modified polypropylene and maleate-modified propylene copolymers decreases after modification. The polyurethane generated by the reaction of plasticizers and polyisocyanates can interweave between the silane-modified polypropylene and maleate-modified propylene copolymers, improving the bonding between the components of the hot melt adhesive. This allows the softening point of the hot melt adhesive to remain at a high temperature after improving adhesion, maintaining adhesion ability at 150℃. Antioxidants protect the hot melt adhesive from external oxides after use, preventing discoloration, peeling, and other phenomena, ensuring the hot melt adhesive maintains its normal adhesion performance.

[0009] Optionally, the silane-modified polypropylene includes atactic polypropylene, olefin-based silane, dioctyl phthalate and benzoyl peroxide, with a mass ratio of atactic polypropylene, olefin-based silane, dioctyl phthalate and benzoyl peroxide of 30:(25-45):(10-20):(0.5-2).

[0010] By adopting the above technical solution, atactic polypropylene contains a small amount of ethylene, which is attached to the polypropylene main chain. Compared with homopolymer polypropylene, it has better heat resistance. Olefin-based silanes can graft organosilanes onto the polypropylene main chain. The higher amount of olefin-based silanes can attach more silane groups to the polypropylene main chain, which is beneficial to improving the adhesion performance of hot melt adhesive. Dioctyl phthalate can be well compatible with organic matter and is used to improve the plasticity of organic matter. Benzoyl peroxide is used as an initiator to initiate the reaction between atactic polypropylene and olefin-based silanes.

[0011] Optionally, the molecular weight of the random polypropylene is 10,000-30,000, the glass transition temperature is -20-0℃, and the number of α-olefins in a single molecule of the olefin-based silane is 2-4, which is used to improve the grafting degree of silane-modified polypropylene.

[0012] By adopting the above technical solution, atactic polypropylene with a smaller molecular weight is selected, and olefin-based silanes with more α-olefins are selected. This allows the olefin-based silanes to extend the length of the main chain and shorten the length of the side chains while grafting onto the main chain of polypropylene, thereby reducing the influence of the side chains on the main chain. This helps to reduce the decrease in the softening point temperature of polypropylene after silane modification, enabling silane-modified polypropylene to maintain good heat resistance.

[0013] Optionally, the preparation method of silane-modified polypropylene includes the following steps: (S11) Heat dioctyl phthalate and stir until melted, then add atactic polypropylene and benzoyl peroxide and stir until evenly mixed; (S12) In step (S1), olefin-based silane is added dropwise at a rate of 5-8 drops / min. Stirring is maintained during the dropwise addition. After the dropwise addition is completed, the temperature is maintained and the mixture is allowed to stand to obtain silane-modified polypropylene.

[0014] By adopting the above technical solution, dioctyl phthalate and organic matter have good compatibility. Melting dioctyl phthalate first can accelerate the melting speed of subsequent atactic polypropylene. Since the preparation of silane-modified polypropylene involves an addition reaction, an initiator is required. By adding the initiator first and then adding the olefin silane dropwise, the intensity of the reaction can be controlled, and the organosilane can be uniformly grafted onto the polypropylene main chain.

[0015] Optionally, the maleic anhydride-modified propylene copolymer includes copolymer PP, maleic anhydride, SEBS elastomer and diisophenyl propylene peroxide, wherein the mass ratio of copolymer PP, maleic anhydride, SEBS elastomer and diisophenyl propylene peroxide is 70:(0.3-1.5):(12-20):(0.05-0.15).

[0016] By adopting the above technical solution, the copolymer PP is a polypropylene with a high ethylene content. By polymerizing ethylene on the polypropylene main chain, the copolymer PP has better flexibility. By grafting maleic anhydride, the adhesion ability at high temperature can be improved. SEBS elastomer is a plastic material that can increase heat resistance and aging resistance in maleic anhydride modified propylene copolymer. Diisophenyl propylene peroxide acts as an initiator to trigger the reaction between copolymer PP and maleic anhydride, which helps to rapidly synthesize maleic anhydride modified propylene copolymer.

[0017] Optionally, the copolymer PP has an ethylene content of 8-12%, a molecular weight of 50,000-80,000, a melt index of 2-8 g / 10 min, and a glass transition temperature of -20-0℃.

[0018] By adopting the above technical solution, a copolymer PP with a high ethylene content and a high molecular weight is selected, so that the maleic anhydride-propylene copolymer after reaction with maleic anhydride has a longer branch chain, which is beneficial to increase the intermolecular forces. This allows the hot melt adhesive to quickly reach the molten state after reaching the softening point, which is beneficial to reducing the operating temperature of the hot melt adhesive.

[0019] Optionally, the preparation method of maleic anhydride-modified propylene copolymer includes the following steps: Heating and stirring the copolymerized PP to a molten state, then adding maleic anhydride, SEBS elastomer and diisophenylene peroxide, and stirring continuously until uniformly mixed, and cooling to obtain maleic anhydride modified propylene copolymer.

[0020] By adopting the above technical solution, the amount of copolymer PP used is the largest and the melting point is the highest. By melting the copolymer PP first, the subsequent mixing process is more convenient. Due to the high molecular weight and long main chain of copolymer PP, maleic anhydride can be uniformly grafted onto the copolymer PP under the action of molecular steric hindrance. There is no need to control the addition rate of maleic anhydride. Thus, by adding each component together for reaction, the preparation process can be simplified and the preparation efficiency can be improved.

[0021] Optionally, the plasticizer is one or more of the following: polycaprolactone diol, poly(phthalic anhydride) neopentyl glycol, poly(hexyl adipate) diol, polytetrahydrofuran diol, and poly(neopentyl terephthalate). The polyisocyanate is one or more of toluene diisocyanate, isophorone diisocyanate, diphenylmethane diisocyanate, dicyclohexylmethane diisocyanate, hexamethylene diisocyanate, and lysine diisocyanate; The antioxidant is one of the following: sodium tripolyphosphate, trinonyldiphenylamine, dithiocarbamate, dinitrosopeptimethylenetetramine, 2,6-di-tert-butyl-p-cresol, N-phenyl-α-naphthylamine, pentaerythritol ester, and octadecyl ester.

[0022] By adopting the above technical solution, polyols and acid anhydrides, as plasticizers, can react with polyisocyanates to prepare polyurethane. Since the components of the synthesized polyurethane are all small molecules with relatively low molecular weights, the large-molecule polyurethane is formed by linking the silane-modified polypropylene and maleic anhydride-modified propylene copolymer. This allows for a high degree of interweaving within a short mixing time. While improving the plasticity of the hot melt adhesive, more heat is required to allow the macromolecular chains to slide, thereby increasing the softening temperature of the hot melt adhesive. This is beneficial for maintaining the adhesive properties of the hot melt adhesive at high temperatures. The aforementioned antioxidants are suitable for use in the preparation of organic polymers such as plastics, rubber, and resins. In hot melt adhesives, they can prevent external oxides from corroding the hot melt adhesive and prevent discoloration, peeling, and other phenomena during use.

[0023] Secondly, the preparation method for the above-mentioned low-temperature operating high-temperature resistant hot melt adhesive provided in this application adopts the following technical solution: A method for preparing the above-mentioned low-temperature operating high-temperature resistant hot melt adhesive includes the following steps: (S01) Mix silane-modified polypropylene and maleic anhydride-modified propylene copolymer, heat to 160-180℃, stir until uniform, and stir for 2-4 hours under vacuum of 70-90kPa and stirring speed of 100-200rpm. (S02) Remove the vacuum, add the plasticizer and mix evenly, then add the polyisocyanate in batches while stirring. Stir at a vacuum of 70-90 kPa and a stirring speed of 100-200 rpm for 20-40 minutes. Add the antioxidant and stir for 1-2 hours to obtain the hot melt adhesive.

[0024] By adopting the above technical solution, silane-modified polypropylene and maleic anhydride-modified propylene copolymer are first mixed, and water is removed by vacuum stirring. In a short time, the water inside the molten silane-modified polypropylene and maleic anhydride-modified propylene copolymer is completely removed. After adding plasticizer, polyisocyanate is added in batches, which helps the polyurethane to be dispersed by stirring while the molecular chain is extended in the polycondensation reaction. This improves the bonding degree between the synthesized polyurethane and the silane-modified polypropylene and maleic anhydride-modified propylene copolymer, which is beneficial to improving the heat resistance and adhesion of hot melt adhesive. Since the polyurethane polycondensation reaction produces water, the water is quickly removed during the reaction by vacuum stirring. This not only ensures the quality of hot melt adhesive, but also accelerates the polyurethane polycondensation reaction by removing reactants, which is beneficial to the efficient preparation of hot melt adhesive.

[0025] In summary, this application includes at least one of the following beneficial technical effects: 1. Silane-modified polypropylene and maleic anhydride-modified propylene copolymer, as the main components of hot melt adhesive, utilize the adhesive ability of hydroxyl groups provided by silane and maleic anhydride while maintaining the high-temperature resistance of polypropylene itself. This allows the prepared hot melt adhesive to maintain good adhesion performance even at high temperatures. Furthermore, the modified polypropylene backbone with a large number of branches has increased intermolecular forces, and the polyurethane interwoven between the silane-modified polypropylene and maleic anhydride-modified propylene copolymer has good thermoplasticity. This allows the hot melt adhesive to soften rapidly upon reaching its softening point, achieving the purpose of processing at lower temperatures. 2. By synthesizing silane-modified polypropylene with shorter branches from random polypropylene with lower molecular weight, and synthesizing maleic anhydride-modified propylene copolymer with longer branches from copolymer PP with higher molecular weight, the softening point of the hot melt adhesive can be controlled by controlling the relationship of intermolecular forces, thereby maintaining heat resistance while reducing the operating temperature. Detailed Implementation

[0026] The present application will be further described in detail below with reference to embodiments and comparative examples.

[0027] In the examples and comparative examples, the random polypropylene used had a molecular weight of 15,000-20,000 and a glass transition temperature of (-20)-(-18)℃. The olefinic silane was dimethoxydivinylsilane. The copolymer PP had a molecular weight of 70,000-75,000 and a glass transition temperature of (-20)-(-18)℃. The plasticizer was polycaprolactone diol, CAS: 36890-68-3, with a molecular weight of 3,800-4,000. The polyisocyanate was toluene diisocyanate, and the antioxidant was pentaerythritol ester. Silane-modified polypropylene and maleic anhydride-modified propylene copolymers were prepared by the preparation examples, and high-temperature resistant hot melt adhesives were prepared by the examples.

[0028] Preparation Examples 1-3: Preparation of silane-modified polypropylene.

[0029] Preparation Example 1 The preparation of silane-modified polypropylene includes the following steps: (a) Take 15g of dioctyl phthalate and heat it to 180°C. Stir until the dioctyl phthalate is in a molten state. Add 30g of atactic polypropylene and 1.2g of benzoyl peroxide. Keep the temperature at 180°C and stir until the mixture is homogeneous.

[0030] (b) Take 35g of dimethoxydivinylsilane and add it dropwise to the mixture prepared in step (a) at a rate of 6 drops / min. Keep stirring during the dropwise addition process. After the dropwise addition is completed, keep stirring for another 10min and let it stand for 1h to obtain silane-modified polypropylene.

[0031] Preparation Example 2 The preparation of silane-modified polypropylene includes the following steps: (a) Take 10g of dioctyl phthalate and heat it to 180°C. Stir until the dioctyl phthalate is in a molten state. Add 30g of atactic polypropylene and 0.5g of benzoyl peroxide. Keep the temperature at 180°C and stir until the mixture is homogeneous.

[0032] (b) Take 25g of dimethoxydivinylsilane and add it dropwise to the mixture prepared in step (a) at a rate of 6 drops / min. Keep stirring during the dropwise addition process. After the dropwise addition is completed, keep stirring for another 10min and let it stand for 1h to obtain silane-modified polypropylene.

[0033] Preparation Example 3 The preparation of silane-modified polypropylene includes the following steps: (a) Take 20g of dioctyl phthalate and heat it to 180°C. Stir until the dioctyl phthalate is in a molten state. Add 30g of atactic polypropylene and 2g of benzoyl peroxide. Keep at 180°C and stir until the mixture is homogeneous.

[0034] (b) Take 45g of dimethoxydivinylsilane and add it dropwise to the mixture prepared in step (a) at a rate of 6 drops / min. Keep stirring during the dropwise addition process. After the dropwise addition is completed, keep stirring for another 10min and let it stand for 1h to obtain silane-modified polypropylene.

[0035] Preparation Examples 4-6: Preparation of maleic anhydride-modified propylene copolymers.

[0036] Preparation Example 4 The preparation of maleic anhydride-modified propylene copolymers includes the following steps: Take 70g of copolymer PP, heat to 170℃, stir until melted, add 11g of maleic anhydride, 16g of SEBS elastomer and 0.9g of diisophenyl propylene peroxide while stirring, maintain temperature and stir for 1.5h, and after cooling, maleic anhydride modified propylene copolymer is obtained.

[0037] Preparation Example 5 The preparation of maleic anhydride-modified propylene copolymers includes the following steps: Take 70g of copolymer PP, heat to 170℃, stir until melted, add 8g of maleic anhydride, 12g of SEBS elastomer and 0.7g of diisophenylene peroxide while stirring, maintain temperature and stir for 1.5h, and after cooling, maleic anhydride modified propylene copolymer is obtained.

[0038] Preparation Example 6 The preparation of maleic anhydride-modified propylene copolymers includes the following steps: Take 70g of copolymer PP, heat to 170℃, stir until melted, add 14g of maleic anhydride, 20g of SEBS elastomer and 1.1g of diisophenyl propylene peroxide while stirring, maintain temperature and stir for 1.5h, and after cooling, maleic anhydride modified propylene copolymer is obtained.

[0039] Example: Preparation of hot melt adhesive.

[0040] Example 1 The preparation of hot melt adhesive includes the following steps: (c) Take 70g of the silane-modified polypropylene prepared in Preparation Example 1 and 50g of the maleic anhydride-modified propylene copolymer prepared in Preparation Example 4, heat to 180°C, stir until uniformly mixed, and vacuum dehydrate for 3h under a vacuum of 80kPa and a stirring speed of 150rpm. (d) Remove the vacuum state, add 20g of polycaprolactone diol to the mixture prepared in step (c), mix evenly, keep stirring and add 15g of toluene diisocyanate in batches, stir for 30min under a vacuum of 80kPa and a stirring speed of 150rpm, add 0.5g of pentaerythritol ester, stir for 2h to obtain hot melt adhesive.

[0041] Example 2 The preparation of hot melt adhesive includes the following steps: (c) Take 60g of the silane-modified polypropylene prepared in Preparation Example 1 and 40g of the maleic anhydride-modified propylene copolymer prepared in Preparation Example 4, heat to 180°C, stir until uniformly mixed, and vacuum dehydrate for 3h under a vacuum of 80kPa and a stirring speed of 150rpm. (d) Remove the vacuum state, add 10g of polycaprolactone diol to the mixture prepared in step (c), mix evenly, keep stirring and add 10g of toluene diisocyanate in batches, stir for 30min under a vacuum of 80kPa and a stirring speed of 150rpm, add 0.1g of pentaerythritol ester, stir for 2h to obtain hot melt adhesive.

[0042] Example 3 The preparation of hot melt adhesive includes the following steps: (c) Take 80g of the silane-modified polypropylene prepared in Preparation Example 1 and 60g of the maleic anhydride-modified propylene copolymer prepared in Preparation Example 4, heat to 180°C, stir until uniformly mixed, and vacuum dehydrate for 3h under a vacuum of 80kPa and a stirring speed of 150rpm. (d) Remove the vacuum state, add 30g of polycaprolactone diol to the mixture prepared in step (c), mix evenly, keep stirring and add 20g of toluene diisocyanate in batches, stir for 30min under a vacuum of 80kPa and a stirring speed of 150rpm, add 1g of pentaerythritol ester, stir for 2h to obtain hot melt adhesive.

[0043] Example 4 The difference from Example 1 is that the silane-modified polypropylene prepared in Preparation Example 2 and the maleic anhydride-modified propylene copolymer prepared in Preparation Example 5 were used.

[0044] Example 5 The difference from Example 1 is that the silane-modified polypropylene prepared in Preparation Example 2 and the maleic anhydride-modified propylene copolymer prepared in Preparation Example 5 were used.

[0045] Comparative Example 1 The difference from Example 1 is that silane-modified polypropylene is not added; instead, an equal mass of maleic anhydride-modified propylene copolymer is added as a substitute.

[0046] Comparative Example 2 The difference from Example 1 is that maleic anhydride-modified propylene copolymer is not added; instead, an equal mass of silane-modified polypropylene is added as a substitute.

[0047] Comparative Example 3 The difference from Example 1 is that in step (d), polycaprolactone diol and toluene diisocyanate are not added, but an equal mass of polyurethane with a molecular weight of 2000-3000 is added instead.

[0048] The following performance tests were performed on Examples 1-5 and Comparative Examples 1-3; Softening point test: The softening point of the prepared hot melt adhesive is tested according to GB / T 15332-1994; High temperature resistance: Place the hot melt adhesive prepared above in a 150°C sample box and observe whether the coated sample peels off after 24 hours.

[0049] Table 1. Test results of Examples 1-5 and Comparative Examples 1-3 Example 1 173 No curling Example 2 176 Slightly upturned Example 3 174 No curling Example 4 175 No curling Example 5 168 No curling Comparative Example 1 159 Severely raised Comparative Example 2 182 No curling Comparative Example 3 164 Severely raised As can be seen from the above embodiments, the softening point of the hot melt adhesive prepared in Examples 1-5 is in the range of 168℃ and 176℃. Within this range, the hot melt adhesive can reach an operable temperature of around 180℃. Among Examples 1-5, only the hot melt adhesive prepared in Example 2 showed slight curling in the high temperature resistance test, indicating that the hot melt adhesive in Examples 1-5 can maintain a small change in physical state at a high temperature of 150℃, thereby maintaining good adhesion performance, remaining stable at a high temperature of 150℃, and reaching the softening point at around 170℃. The hot melt adhesive in Examples 1-5 can maintain high temperature resistance while the operating temperature does not rise too much, which is beneficial for the construction and use of hot melt adhesive.

[0050] Comparing Example 1, Comparative Example 1, and Comparative Example 2, the difference lies in the addition of an equal mass of maleic anhydride-modified propylene copolymer to replace silane-modified polypropylene in Comparative Example 1, and an equal mass of silane-modified polypropylene to replace maleic anhydride-modified propylene copolymer in Comparative Example 2. It can be seen that the softening point of Comparative Example 1 decreased significantly, indicating that the maleic anhydride-modified propylene copolymer causes a decrease in the softening point of the hot melt adhesive. A hot melt adhesive with a significantly decreased softening point cannot maintain high-temperature resistance at 150°C. Comparative Example 2 showed a significant increase in softening point, which, while maintaining high-temperature resistance at 150°C, necessitates a further increase in operating temperature, hindering the application of the hot melt adhesive. Comparing Example 1, Comparative Example 1, and Comparative Example 2 demonstrates that silane-modified polypropylene and maleic anhydride-modified propylene copolymer can work together to maintain the softening point of the hot melt adhesive at a temperature that balances high-temperature resistance at 150°C with a suitable operating temperature. This facilitates hot melt adhesive application while maintaining stable performance at high temperatures.

[0051] Comparing Example 1 and Comparative Example 3, the difference is that Comparative Example 3 added an equal mass of polyurethane to replace polycaprolactone diol and toluene diisocyanate. It can be seen that the softening point of Comparative Example 3 decreased, and severe warping occurred in the high temperature resistance test. This indicates that using polycaprolactone diol and toluene diisocyanate to prepare polyurethane in the case of a mixture of silane-modified polypropylene and maleic anhydride-modified propylene copolymer is more beneficial to maintaining the high temperature stability of hot melt adhesive than adding polypropylene alone.

[0052] The embodiments described herein are preferred embodiments of this application and are not intended to limit the scope of protection of this application. Identical components are indicated by the same reference numerals. Therefore, all equivalent changes made to the structure, shape, and principle of this application should be included within the scope of protection of this application.

Claims

1. A low-temperature operating, high-temperature resistant hot melt adhesive, characterized in that, It includes the following components in parts by weight: 60-80 parts of silane-modified polypropylene, 40-60 parts of maleic anhydride-modified propylene copolymer, 10-30 parts of plasticizer, 10-20 parts of polyisocyanate and 0.1-1 parts of antioxidant; The silane-modified polypropylene has a melting point of 140-160℃ and a melt index of 18-52 g / 10min, and is used to improve the adhesion of hot melt adhesive and increase the softening point of hot melt adhesive. The silane-modified polypropylene comprises atactic polypropylene, olefin-based silane, dioctyl phthalate, and benzoyl peroxide, wherein the mass ratio of the atactic polypropylene, olefin-based silane, dioctyl phthalate, and benzoyl peroxide is 30:(25-45):(10-20):(0.5-2). The random polypropylene has a molecular weight of 10,000-30,000 and a glass transition temperature of (-20)-0℃. The number of α-olefins in a single molecule of the olefin-based silane is 2-4, which is used to improve the grafting degree of silane-modified polypropylene. The maleic anhydride-modified propylene copolymer has a melting point of 130-140℃ and a melt index of 2-15g / 10min, and is used to improve the adhesion of hot melt adhesives at high temperatures. The maleic anhydride-modified propylene copolymer comprises copolymer PP, maleic anhydride, SEBS elastomer, and diisophenylene peroxide, wherein the mass ratio of the copolymer PP, maleic anhydride, SEBS elastomer, and diisophenylene peroxide is 70:(0.3-1.5):(12-20):(0.05-0.15). The copolymer PP has an ethylene content of 8-12%, a molecular weight of 50,000-80,000, a melt index of 2-8 g / 10 min, and a glass transition temperature of (-20)-0℃. The plasticizer is polycaprolactone diol, which is used to combine with the polyisocyanate to form polyurethane and increase the softening point of the hot melt adhesive.

2. The low-temperature operation high-temperature resistant hot melt adhesive according to claim 1, characterized in that, The preparation method of the silane-modified polypropylene includes the following steps: (S11) Heat dioctyl phthalate and stir until melted, then add atactic polypropylene and benzoyl peroxide and stir until evenly mixed; (S12) In step (S1), olefin-based silane is added dropwise at a rate of 5-8 drops / min. Stirring is maintained during the dropwise addition. After the dropwise addition is completed, the temperature is maintained and the mixture is allowed to stand to obtain silane-modified polypropylene.

3. The low-temperature operation high-temperature resistant hot melt adhesive according to claim 1, characterized in that, The preparation method of the maleic anhydride modified propylene copolymer includes the following steps: Heat and stir the copolymerized PP to a molten state, add maleic anhydride, SEBS elastomer and diisophenylene peroxide, continue stirring until uniformly mixed, and cool to obtain maleic anhydride modified propylene copolymer.

4. The low-temperature operation high-temperature resistant hot melt adhesive according to claim 1, characterized in that, The polyisocyanate is one or more selected from toluene diisocyanate, isophorone diisocyanate, diphenylmethane diisocyanate, dicyclohexylmethane diisocyanate, hexamethylene diisocyanate, and lysine diisocyanate. The antioxidant is one of the following: sodium tripolyphosphate, trinonyldiphenylamine, dithiocarbamate, dinitrosopeptimethylenetetramine, 2,6-di-tert-butyl-p-cresol, N-phenyl-α-naphthylamine, pentaerythritol ester, and octadecyl ester.

5. A method for preparing a low-temperature operating high-temperature resistant hot melt adhesive as described in any one of claims 1-4, characterized in that, Includes the following steps: (S01) Mix the silane-modified polypropylene and maleic anhydride-modified propylene copolymer, heat to 160-180℃, stir until uniform, and stir for 2-4 hours under vacuum of 70-90kPa and stirring speed of 100-200rpm. (S02) Remove the vacuum, add plasticizer and mix evenly, add polyisocyanate in batches while stirring, stir for 20-40 minutes at a vacuum of 70-90 kPa and a stirring speed of 100-200 rpm, add antioxidant and stir for 1-2 hours to obtain hot melt adhesive.