Thermoplastic polyurethane hot melt adhesive and preparation method thereof

Abstract

The invention discloses a thermoplastic polyurethane hot melt adhesive and a preparation method thereof, and the thermoplastic polyurethane hot melt adhesive comprises the following components in parts by mass: 70 to 80 parts of polyester glycol, 2 to 6 parts of a chain extender, 8 to 15 parts of diisocyanate, 8 to 15 parts of titanium dioxide, 0.001 to 0.1 part of a catalyst, 0.1 to 0.5 part of a dispersant, 0.1 to 1.0 part of an antioxidant and 0.1 to 1.0 part of a light stabilizing aid. Through screening and compounding of the raw materials and optimization of the production process, the prepared polyurethane hot melt adhesive has the advantages of high mechanical strength, excellent adhesion, good aging resistance and low activation temperature, can realize adhesion within a relatively low temperature range, does not damage a thermosensitive substrate, and still has good adhesion after aging.

Description

Technical Field

[0001] The present invention relates to polyurethane hot melt adhesive technology, in particular to an aging-resistant, low-activation-temperature thermoplastic polyurethane hot melt adhesive and a preparation method thereof. Background Art

[0002] Thermoplastic polyurethane hot-melt adhesives are linear polymers formed by reacting polymer diols, low-molecular-weight chain extenders, and diisocyanates. They offer excellent overall performance, simple operation, and are solvent-free and reusable. They are widely used in applications such as clothing, composite materials, woodworking, automotive, and aerospace. These applications place stringent demands on adhesives: excellent adhesion to prevent debonding; operation within a relatively low temperature range to avoid damaging heat-sensitive substrates; and ensuring that the composite material maintains good adhesion even after aging.

[0003] CN110903805B discloses a polyurethane hot melt adhesive, which is prepared by mixing thermoplastic polyurethane with SEBS / SEPS rubber powder. The hot melt adhesive has the advantages of low polarity, high rebound, and low thermal activation temperature. However, the addition of SEBS / SEPS rubber powder reduces the aging performance of the product, limiting its application. CN119708421A and CN117659348A disclose a polyurethane hot melt adhesive, which achieves both low initial flow temperature and high rebound performance of the material by using small molecule diamines with specific structures in thermoplastic polyurethane elastomers, but the hot melt adhesive does not solve the problem of aging resistance. CN117025158B discloses an anti-aging polyurethane adhesive, its preparation method and application, which solves the problem of polyurethane adhesive aging in hot and humid environments by introducing hindered phenol diols containing fluorine chains into the polyurethane adhesive; however, organic solvents are used in its production process, and the problem of low operating temperature is not solved.

[0004] Therefore, based on market demand, an aging-resistant, low activation temperature thermoplastic polyurethane hot melt adhesive is developed, which has excellent application prospects. Summary of the Invention

[0005] In order to solve the problems existing in the prior art, the present invention provides a thermoplastic polyurethane hot melt adhesive and a preparation method thereof, wherein the hot melt adhesive has the advantages of high strength, aging resistance, low activation temperature, and reusability.

[0006] The first aspect of the present invention provides a thermoplastic polyurethane hot melt adhesive comprising the following components in parts by mass: .

[0007] The polyester diol is formed by polycondensation of an aliphatic dicarboxylic acid and an aliphatic diol. The aliphatic dicarboxylic acid includes one or more of succinic acid, adipic acid, and sebacic acid. The aliphatic diol includes one or more of ethylene glycol, 1,4-butanediol, 1,6-hexanediol, and neopentyl glycol. The molecular weight of the polyester diol is 3,000-5,000.

[0008] The chain extender includes one or more of ethylene glycol, 1,4-butanediol, and 1,6-hexanediol.

[0009] The diisocyanate includes one or more of diphenylmethane diisocyanate (MDI), dicyclohexylmethane diisocyanate (HMDI), and hexamethylene diisocyanate (HDI).

[0010] The catalyst comprises one or more of dibutyltin dilaurate, stannous octoate and dibutyltin diacetate.

[0011] The antioxidant comprises a primary antioxidant and a secondary antioxidant. The primary antioxidant comprises one or more of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], triethylene glycol bis-[3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionate], diethylene thiobis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], octadecyl 3,5-di-tert-butyl-4-hydroxyphenylpropionate, isooctyl 3,5-di-tert-butyl-4-hydroxyphenylpropionate, and 2,6-di-tert-butyl-p-cresol; the secondary antioxidant comprises one or more of tris(2,4-di-tert-butylphenyl) phosphite, triphenyl phosphite, dilauryl β,β'-thiodipropionate, and distearyl β,β'-thiodipropionate.

[0012] The light stabilizing auxiliary agent consists of an ultraviolet absorber and a hindered amine light stabilizer. The ultraviolet absorber includes one or more of 2-(2'-hydroxy-3',5'-di-tert-butylphenyl)benzotriazole, 2-(2'-hydroxy-3'-tert-butyl-5'-methylphenyl)-5-chlorobenzotriazole, 2-(2'-hydroxy-3',5'-di-tert-butylphenyl)-5-chlorobenzotriazole, 2-(2'-hydroxy-3',5'-di-tert-amylphenyl)benzotriazole, and 2-(2'-hydroxy-3'-dodecyl-5'-methylphenyl)benzotriazole; the hindered amine light stabilizer includes one or more of bis(1,2,2,6,6-pentamethyl-4-piperidinyl)sebacate, poly(1-hydroxyethyl-2,2,6,6-tetramethyl-4-hydroxypiperidinyl)succinate, and bis(2,2,6,6-tetramethyl-4-piperidinyl)sebacate.

[0013] The titanium dioxide is nano-scale titanium dioxide with a particle size distribution of 1-10 nm.

[0014] The dispersant includes one or more of TEGO-700, TEGO-687, BYK-9076, and BYK-9077.

[0015] The ratio of the amount of the hydroxyl group substance of the polyester diol and the chain extender to the amount of the isocyanate group substance in the isocyanate is 1:(0.9-1.0).

[0016] A second aspect of the present invention provides a method for preparing a thermoplastic polyurethane hot melt adhesive, which is prepared using a twin-screw extruder and comprises the following steps: (1) Adding a chain extender, a dispersant, an antioxidant and a light stabilizer into a pre-dispersion kettle, heating and stirring (time t1), then adding titanium dioxide and continuing stirring (time t2) to obtain a mixed slurry; grinding the mixed slurry to obtain titanium dioxide slurry; (2) Polyester diol and catalyst are used as component A; diisocyanate is used as component B; (3) Component A and component B are added to the twin-screw extruder through the main feeding port of the front section of the twin-screw extruder respectively, and the mixture after the reaction of component A and component B enters the middle section; the titanium dioxide slurry is added to the twin-screw extruder through the side feeding port of the middle section of the twin-screw extruder to react with the mixture from the front section; and enters the back section of the twin-screw extruder for extrusion to obtain thermoplastic polyurethane hot melt adhesive.

[0017] Preferably, in step (1), the heating temperature is 40-100°C, the stirring speed is 400-800 rpm, the stirring time t1 is 15-60 min, and the stirring time t2 after adding titanium dioxide is 0.5-2 h to obtain a mixed slurry. The mixed slurry is ground in a grinder at a grinding speed of 2500-4000 rpm and a grinding time of 2-4 h.

[0018] Preferably, in step (2), the polyester diol is dehydrated before use. Preferably, the dehydration method is: add the polyester diol to a reaction kettle, heat to 100-130°C, stir evenly, and then vacuum dehydrate for 2-3 hours, and measure the moisture content to be less than 0.05%.

[0019] Preferably, in step (3), the temperature of the front section of the twin-screw extruder is set to 80-160°C; the temperature of the middle section is set to 140-220°C; and the temperature of the back section is set to 120-190°C.

[0020] The activation temperature of the thermoplastic polyurethane hot melt adhesive of the present invention is ≤70°C, preferably 65-70°C.

[0021] Compared with the prior art, the key technology of the present invention is: 1. Titanium dioxide has excellent UV shielding and transparency, effectively reflecting direct sunlight and possessing both high UV absorption and infrared reflectivity. The present invention fully premixes titanium dioxide with a chain extender, facilitating the formation of hydrogen bonds between the chain extender and the oxygen atoms in the titanium dioxide, ensuring uniform dispersion in the polyurethane hot melt adhesive. This improves the hot melt adhesive's infrared reflectivity and UV absorption, thereby enhancing the polyurethane hot melt adhesive's resistance to UV and thermal oxidative aging. 2. The present invention fully premixes the chain extender, antioxidant, light stabilizer, and titanium dioxide and then adds them together in the middle section of the twin-screw extruder. This addition helps regularize the polyurethane structure and reduces the heating time of the antioxidant and light stabilizer. Through improved raw material ratios and process, the hard segment structure of the thermoplastic polyurethane hot melt adhesive is enhanced and optimized, facilitating two-phase separation, improving the aging resistance of the hot melt adhesive, and lowering the activation temperature. 3. The hot melt adhesive prepared by the present invention has excellent bonding properties, good aging resistance, and a low activation temperature, making it particularly suitable for bonding heat-sensitive substrates and electronic devices. The preparation method of the present invention is simple and easy to implement, with high production efficiency, which is conducive to widespread promotion and application. DETAILED DESCRIPTION

[0022] The present invention will be further described in detail below with reference to examples, but the embodiments of the present invention are not limited thereto.

[0023] The twin-screw extruder of the embodiment and comparative example is divided into 15 zones, wherein zones 1-5 are the front section, with the temperature set at 80-160°C; zones 6-10 are the middle section, with the temperature set at 140-220°C; and zones 11-15 are the rear section, with the temperature set at 120-190°C.

[0024] Example 1

[0025] 14.7 kg of 1,4-butanediol, 1.0 kg of dispersant BYK-9076, 0.9 kg of 2,6-di-tert-butyl-p-cresol, 0.6 kg of tris(2,4-di-tert-butylphenyl) phosphite, 1.2 kg of 2-(2'-hydroxy-3',5'-di-tert-butylphenyl)benzotriazole, and 1.4 kg of bis(1,2,2,6,6-pentamethyl-4-piperidinyl) sebacate were added to a pre-dispersion kettle, heated to 50°C, adjusted to 500 rpm, and stirred for 30 minutes. Then, 54.9 kg of titanium dioxide was added and stirred for 1 hour to obtain a mixed slurry. The mixed slurry was added to a grinder at 2500 rpm and ground for 2.0 hours to obtain a titanium dioxide slurry. 500 kg of poly(1,6-hexanediol adipate) with a molecular weight of 3000 was added to a reactor, heated to 100°C, stirred evenly, and vacuum dehydrated for 3 hours. The moisture content was measured to be less than 0.05%. 25 g of dibutyl silicate was added and stirred evenly as component A. MDI diisocyanate was added to another reactor as component B. Components A and B were added to the twin-screw extruder through the main feed port at the front end of the extruder. The reaction mixture of components A and B entered the middle section. Titanium dioxide slurry was added to the twin-screw extruder through the side feed port at the middle section to react with the mixture from the front section. The mixture then entered the back end of the twin-screw extruder for extrusion to produce a thermoplastic polyurethane hot melt adhesive. The temperature settings for the twin-screw extruder are shown in Table 1. The ratio of hydroxyl groups to isocyanate groups in the raw materials was 1:0.98.

[0026] Example 2

[0027] 23.3 kg of 1,6-hexanediol, 1.1 kg of dispersant TEGO-700, 2.4 kg of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], 1.5 kg of dilauryl β,β'-thiodipropionate, 1.0 kg of 2-(2'-hydroxy-3'-dodecyl-5'-methylphenyl)benzotriazole, 0.9 kg of 2-(2'-hydroxy-3'-tert-butyl-5'-methylphenyl)-5-chlorobenzotriazole, and 1.8 kg of bis(2,2,6,6-tetramethyl-4-piperidinyl)sebacate were added to a pre-dispersion kettle, heated to 90°C, adjusted to 700 rpm, and stirred for 20 minutes. Then, 90.9 kg of titanium dioxide was added and stirred for 2 hours to obtain a mixed slurry. The mixed slurry was added to a grinder at 3000 rpm and ground for 3 hours to obtain titanium dioxide slurry.

[0028] Add 500 kg of polybutylene succinate sebacate diol with a molecular weight of 3800 into a reactor, heat to 120°C, stir evenly, and vacuum dehydrate for 2 hours. The moisture content is measured to be less than 0.05%. Add 40 g of stannous octoate and stir evenly as component A. Add diisocyanate MDI into another reactor as component B.

[0029] Components A and B were added to the twin-screw extruder through the main feed port at the front end of the extruder. The reaction mixture of components A and B entered the middle section. Titanium dioxide slurry was added to the twin-screw extruder through the side feed port at the middle section to react with the mixture from the front section. The mixture entered the back end of the twin-screw extruder for extrusion to produce a thermoplastic polyurethane hot melt adhesive. The temperature settings for the twin-screw extruder are shown in Table 1. The ratio of the amount of hydroxyl groups to the amount of isocyanate groups in the raw materials was 1:0.92.

[0030] Example 3

[0031] 11.9 kg 1,6-hexanediol, 6.2 kg ethylene glycol and 2.0 kg dispersant BYK-9077, 2.2 kg 3,5-di-tert-butyl-4-hydroxyphenylpropionic acid isooctyl ester, 1.7 kg β,β'-thiodipropionic acid distearyl ester, 1.8 kg 2-(2'-hydroxy-3',5'-di-tert-amylphenyl) benzotriazole, 1.8 kg poly (1-hydroxyethyl-2,2,6,6-tetramethyl-4-hydroxypiperidinyl) succinate were added to the pre-dispersion kettle, heated to 80 ° C, the speed was adjusted to 600 rpm, and the stirring time was 45 minutes. Then, 72.4 kg of titanium dioxide was added and stirred for 2 hours to obtain a mixed slurry. The mixed slurry was added to a grinder at a speed of 4000 rpm and the slurry was ground for 4 hours to obtain titanium dioxide slurry.

[0032] Add 500 kg of polyethylene glycol hexanediol sebacate with a molecular weight of 5000 into a reactor, heat to 105°C, stir evenly, and vacuum dehydrate for 3 hours. The moisture content is less than 0.05%. Add 200 g of dibutyltin diacetate and stir evenly as component A. Add diisocyanate HMDI into another reactor as component B.

[0033] Components A and B were added to the twin-screw extruder through the main feed port at the front end of the extruder. The reaction mixture of components A and B entered the middle section. Titanium dioxide slurry was added through a side feed port in the middle section of the twin-screw extruder to react with the mixture from the front section. The mixture then entered the back end of the twin-screw extruder for extrusion to produce a thermoplastic polyurethane hot melt adhesive. The twin-screw extruder temperature settings are shown in Table 1. The ratio of hydroxyl groups to isocyanate groups in the raw materials was 1:1.

[0034] Comparative Example 1

[0035] 500 kg of 3000 molecular weight poly (1,6-hexanediol adipate), 14.7 kg of 1,4-butanediol, 1.0 kg of dispersant BYK-9076, 0.9 kg of 2,6-di-tert-butyl-p-cresol, 0.6 kg of tris(2,4-di-tert-butylphenyl) phosphite, 1.2 kg of 2-(2'-hydroxy-3',5'-di-tert-butylphenyl)benzotriazole, and 1.4 kg of bis(1,2,2,6,6-pentamethyl-4-piperidinyl) sebacate were added to a reactor, heated to 100°C, stirred evenly, and vacuum dehydrated for 3 hours. The moisture content was measured to be less than 0.05%, and 25 g of dibutyl silicate was added and stirred evenly as component A. MDI diisocyanate was added to another reactor as component B. Component A and component B were respectively added to the twin-screw extruder through the main feeding port of the front section of the twin-screw extruder, and thermoplastic polyurethane hot melt adhesive was prepared by extrusion through the twin-screw extruder. The temperature setting of the twin-screw extruder is shown in Table 1. The ratio of the amount of hydroxyl group substance to the amount of isocyanate group substance in the raw material was 1:0.98.

[0036] Comparative Example 2

[0037] 500 kg of 3000 molecular weight poly(1,6-hexanediol adipate), 14.7 kg of 1,4-butanediol, 54.9 kg of titanium dioxide, 1.0 kg of dispersant BYK-9076, 0.9 kg of 2,6-di-tert-butyl-p-cresol, 0.6 kg of tris(2,4-di-tert-butylphenyl) phosphite, 1.2 kg of 2-(2'-hydroxy-3',5'-di-tert-butylphenyl)benzotriazole, and 1.4 kg of bis(1,2,2,6,6-pentamethyl-4-piperidinyl) sebacate were added to a reactor, heated to 100°C, stirred evenly, and vacuum dehydrated for 3 hours. The moisture content was measured to be less than 0.05%, and 25 g of dibutyl silicate was added and stirred evenly as component A. Diisocyanate MDI was added to another reactor as component B. Components A and B were added to a twin-screw extruder through the main feed port at the front end of the extruder. Thermoplastic polyurethane hot melt adhesive was produced by extrusion. The temperature setting for the twin-screw extruder is shown in Table 1. The ratio of the amount of hydroxyl groups to the amount of isocyanate groups in the raw materials was 1:0.98.

[0038] Comparative Example 3

[0039] 500 kg of 3000 molecular weight poly (1,6-hexanediol adipate), 54.9 kg of titanium dioxide, 1.0 kg of dispersant BYK-9076, 0.9 kg of 2,6-di-tert-butyl-p-cresol, 0.6 kg of tris(2,4-di-tert-butylphenyl) phosphite, 1.2 kg of 2-(2'-hydroxy-3',5'-di-tert-butylphenyl)benzotriazole, and 1.4 kg of bis(1,2,2,6,6-pentamethyl-4-piperidinyl) sebacate were added to a reactor, heated to 100°C, stirred evenly, and vacuum dehydrated for 3 hours. The moisture content was measured to be less than 0.05%, and 25 g of dibutyl silicate was added and stirred evenly as component A. MDI diisocyanate was added to another reactor as component B. Components A and B were added to the twin-screw extruder through the main feed port at the front end of the extruder. The reacted mixture of components A and B entered the middle section. 14.7 kg of 1,4-butanediol was added through a side feed port in the middle section of the twin-screw extruder to react with the mixture from the front section. The mixture then entered the back end of the twin-screw extruder for extrusion to produce a thermoplastic polyurethane hot melt adhesive. The twin-screw extruder temperature settings are shown in Table 1. The ratio of hydroxyl groups to isocyanate groups in the raw materials was 1:0.98.

[0040] Table 1 Twin-screw extruder temperature of Examples 1-3 and Comparative Examples 1-3

[0041] The polyurethane hot melt adhesives prepared in Examples 1-3 and Comparative Examples 1-3 were subjected to performance tests and bonding, respectively. The results are shown in Table 2.

[0042] The test conditions are as follows: Tensile strength and elongation: measured in accordance with GB / T 528-2009.

[0043] Activation temperature: Make the polyurethane hot melt adhesive into a film and heat it in an oven set at temperature T for 1 hour. Then, stack the two films staggered and lightly press the contact surface with your fingers. If the contact surfaces are completely fused and require obvious force to separate, the temperature T at this time is the activation temperature of the hot melt adhesive.

[0044] Bonding strength: After the polyurethane hot melt adhesive is bonded to PVC and placed for stability, the bonding strength is tested according to GB / T 2791-1995; Aging conditions: Determined in accordance with GB / T 14522-2008; place the polyurethane hot melt adhesive in a UV aging box and irradiate at 70°C and irradiance 1.0W / m2 for 30 days.

[0045] Table 2 Properties of polyurethane hot melt adhesives in Examples and Comparative Examples

[0046] By analyzing the performance test results of the embodiments and comparative examples, we found that the polyurethane hot melt adhesive prepared by the present invention through the screening and compounding of raw materials and the optimization of the production process has high mechanical strength, excellent adhesion, good aging resistance, and low activation temperature. It can achieve bonding within a relatively low temperature range without damaging heat-sensitive substrates and still has good adhesion after aging.

Claims

1. A thermoplastic polyurethane hot melt adhesive comprising the following components in parts by mass: 。 2. The thermoplastic polyurethane hot melt adhesive according to claim 1, characterized in that The polyester diol is formed by condensation of aliphatic dicarboxylic acid and aliphatic diol; preferably, the aliphatic dicarboxylic acid includes one or more of succinic acid, adipic acid, and sebacic acid, and the aliphatic diol includes one or more of ethylene glycol, 1,4-butanediol, 1,6-hexanediol, and neopentyl glycol.

3. The thermoplastic polyurethane hot melt adhesive according to claim 1, characterized in that The chain extender includes one or more of ethylene glycol, 1,4-butanediol, and 1,6-hexanediol.

4. The thermoplastic polyurethane hot melt adhesive according to claim 1, characterized in that: The diisocyanate includes one or more of diphenylmethane diisocyanate (MDI), dicyclohexylmethane diisocyanate (HMDI), and hexamethylene diisocyanate (HDI).

5. The thermoplastic polyurethane hot melt adhesive according to claim 1, characterized in that: The catalyst comprises one or more of dibutyltin dilaurate, stannous octoate and dibutyltin diacetate.

6. The thermoplastic polyurethane hot melt adhesive according to claim 1, characterized in that: The antioxidant is composed of a primary antioxidant and an auxiliary antioxidant; preferably, the primary antioxidant includes one or more of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, triethylene glycol bis-[3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionate], diethylene thiobis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], octadecyl 3,5-di-tert-butyl-4-hydroxyphenylpropionate, isooctyl 3,5-di-tert-butyl-4-hydroxyphenylpropionate, and 2,6-di-tert-butyl-p-cresol, and the auxiliary antioxidant includes one or more of tris(2,4-di-tert-butylphenyl) phosphite, triphenyl phosphite, dilauryl β,β'-thiodipropionate, and distearyl β,β'-thiodipropionate.

7. The thermoplastic polyurethane hot melt adhesive according to claim 1, characterized in that: The light stabilizing agent is composed of an ultraviolet absorber and a hindered amine light stabilizer; preferably, the ultraviolet absorber includes 2-(2'-hydroxy-3',5'-di-tert-butylphenyl)benzotriazole, 2-(2'-hydroxy-3'-tert-butyl-5'-methylphenyl)-5-chlorobenzotriazole, 2-(2'-hydroxy-3',5'-di-tert-butylphenyl)-5-chlorobenzotriazole, 2-(2'-hydroxy-3',5'-di-tert-butylphenyl)-5-chlorobenzotriazole, The hindered amine light stabilizer includes one or more of bis(1,2,2,6,6-pentamethyl-4-piperidinyl) sebacate, poly(1-hydroxyethyl-2,2,6,6-tetramethyl-4-hydroxypiperidinyl) succinate, and bis(2,2,6,6-tetramethyl-4-piperidinyl) sebacate.

8. The thermoplastic polyurethane hot melt adhesive according to claim 1, characterized in that: The titanium dioxide is nanometer-level titanium dioxide.

9. The thermoplastic polyurethane hot melt adhesive according to claim 1, characterized in that: The ratio of the amount of the hydroxyl group substance of the polyester diol and the chain extender to the amount of the isocyanate group substance in the isocyanate is 1:(0.9-1.0).

10. A method for preparing the thermoplastic polyurethane hot melt adhesive according to any one of claims 1 to 9, using a twin-screw extruder, comprising the following steps: (1) Adding a chain extender, a dispersant, an antioxidant and a light stabilizer into a pre-dispersion kettle, heating and stirring, then adding titanium dioxide and continuing to stir to obtain a mixed slurry; grinding the mixed slurry to obtain titanium dioxide slurry; (2) Polyester diol and catalyst are used as component A; Diisocyanate as component B; (3) Component A and component B are added to the twin-screw extruder through the main feeding port of the front section of the twin-screw extruder respectively, and the mixture after the reaction of component A and component B enters the middle section; The titanium dioxide slurry is fed into the twin-screw extruder through the side feed port in the middle section of the twin-screw extruder to react with the mixture from the front section; the titanium dioxide slurry enters the rear section of the twin-screw extruder for extrusion to obtain a thermoplastic polyurethane hot melt adhesive.

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