A moisture-curable polyurethane hot melt adhesive and a method for preparing the same

Abstract

This invention discloses a moisture-curing polyurethane hot melt adhesive and its preparation method. The moisture-curing polyurethane hot melt adhesive of this invention, by weight, comprises the following components: 30-50 parts of crystalline polyester polyol, 20-40 parts of liquid polyester polyol, 10-15 parts of thermoplastic resin, 10-15 parts of isocyanate, 0.1-0.5 parts of heat stabilizer, and 0.03-0.1 parts of catalyst; wherein the heat stabilizer is a compound heat stabilizer with a carbon-centered free radical scavenger as its core. The moisture-curing polyurethane hot melt adhesive of this invention exhibits good high-temperature stability, that is, its viscosity remains relatively stable for a relatively long time under high-temperature conditions above 130°C.

Description

Technical Field

[0001] This invention relates to the field of adhesive technology, and to a moisture-curing polyurethane hot melt adhesive and its preparation method, particularly to a moisture-curing polyurethane hot melt adhesive with good high-temperature stability and its preparation method. Background Technology

[0002] Moisture-curing polyurethane hot melt adhesives are NCO-terminated adhesives produced by the reaction of polyester or polyether polyols and isocyanates. After molten application, they gradually transition to a high-viscosity or solid state, providing initial bond strength. Subsequently, the NCO groups in the system react with moisture in the air to form a cross-linked network structure, significantly improving bond strength and solvent resistance. Compared to traditional thermoplastic hot melt adhesives, moisture-curing polyurethane hot melt adhesives offer better cold resistance, heat resistance, solvent resistance, aging resistance, and stronger final bond strength, making them widely used in industries such as textiles, electronics, automotive, woodworking, construction, footwear, and bookbinding.

[0003] Moisture-curing polyurethane hot melt adhesives are polyurethane prepolymers, end-capped with NCO groups. The system contains a certain proportion of NCO groups, which undergo side reactions with urethane esters under high-temperature conditions. The application temperature for moisture-curing polyurethane hot melt adhesives is typically above 100℃. At application temperatures of 100-130℃, the viscosity increase after 3 hours in traditional systems is usually less than 30%. However, at application temperatures above 130℃, the viscosity increase after 3 hours is much faster; for example, at 140℃, the viscosity increase can reach 50-60%. This viscosity increase affects the normal application process, such as reducing the amount of adhesive dispensed and preventing the spiral or spraying process from proceeding smoothly and systematically, severely impacting production cycle time, especially in industries with strict requirements for production cycle time, such as the automotive and electronics sectors.

[0004] CN107236512A discloses a method for preparing a moisture-curable polyurethane hot melt adhesive modified with refractory kaolin fibers, relating to the field of adhesive preparation. Specifically, the method involves: first, preparing modified kaolin fibers; then, adding polyester polyol and polyether polyol to a three-necked flask, vacuum dehydrating at 120°C for 30 minutes, releasing the vacuum, cooling to 100°C, and adding a tackifying resin and an antioxidant to the three-necked flask under nitrogen protection, stirring and mixing for 30-50 minutes; subsequently, adding diisocyanate, modified kaolin fibers, and a catalyst to the three-necked flask, mixing thoroughly, and reacting at 100°C for 1-2 hours; after the reaction, adding a chain extender to the three-necked flask, and continuing the reaction for another hour; finally, transferring the resulting mixture to aluminum foil, heat-sealing, and curing at 80°C to obtain the polyurethane hot melt adhesive. The hot melt adhesive prepared by this invention exhibits good bonding performance and excellent high-temperature resistance. However, this hot melt adhesive also exhibits good bonding performance at temperatures up to 100°C, and it is difficult to guarantee stability at temperatures exceeding 100°C.

[0005] CN111909650A discloses a moisture-curing polyurethane hot melt adhesive and its preparation method. The adhesive comprises the following raw material components by weight: 80-100 parts of polyester polyol with a hydroxyl value of 37-112 mgKOH / g, 10-20 parts of highly crystalline polyester polyol with a hydroxyl value of 56-112 mgKOH / g, 20-50 parts of isocyanate, 1-2 parts of chain extender, 1-10 parts of additives, and 0.01-0.1 parts of catalyst. A method for preparing the adhesive is also provided. This invention's moisture-curing polyurethane hot melt adhesive exhibits high initial and final peel strength, with an initial 180° peel strength ≥50 N / 25 mm and a final 180° peel strength ≥600 N / 25 mm. It can be applied to bonding automotive polyolefin materials for components such as headlights, armrests, and door panels. However, the thermal stability of this invention's moisture-curing polyurethane hot melt adhesive at temperatures above 130°C needs further improvement.

[0006] Therefore, it is necessary to develop a moisture-curing polyurethane hot melt adhesive with good high-temperature stability and its preparation method. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the present invention aims to provide a moisture-curing polyurethane hot melt adhesive and its preparation method. The moisture-curing polyurethane hot melt adhesive of the present invention has good high-temperature stability, that is, the viscosity can remain relatively stable for a long time under high-temperature conditions above 130°C.

[0008] One of the objectives of this invention is to provide a moisture-curing polyurethane hot melt adhesive. To achieve this objective, the invention employs the following technical solution:

[0009] A moisture-curing polyurethane hot melt adhesive, comprising the following components by weight:

[0010]

[0011] The heat stabilizer is a compound heat stabilizer with a carbon-centered free radical scavenger as its core.

[0012] The moisture-curing polyurethane hot melt adhesive of the present invention uses crystalline polyester polyol, liquid polyester polyol, thermoplastic resin, isocyanate, heat stabilizer, and catalyst as raw materials. Under high temperature conditions above 130°C, the stabilizer used in the present invention contains a highly efficient carbon-center free radical scavenger, which can effectively inhibit the side reaction of NCO and urethane to generate urethane, thereby inhibiting the increase in viscosity. This ensures that the viscosity of the moisture-curing polyurethane hot melt adhesive remains relatively stable under high temperature conditions above 130°C, significantly improving the problem of reduced adhesive output or abnormal spiral or spray dispensing caused by increased viscosity during use, and ensuring normal and orderly production.

[0013] Specifically, the moisture-curing polyurethane hot melt adhesive comprises the following components by weight:

[0014] The crystalline polyester polyol has a weight of 30-50 parts, for example, 30 parts, 31 parts, 32 parts, 33 parts, 34 parts, 35 parts, 36 parts, 37 parts, 38 parts, 39 parts, 40 parts, 41 parts, 42 parts, 43 parts, 44 parts, 45 parts, 46 parts, 47 parts, 48 ​​parts, 49 parts, 50 parts, etc.

[0015] The liquid polyester polyol has a weight of 20-40 parts, for example, 20 parts, 21 parts, 22 parts, 23 parts, 24 parts, 25 parts, 26 parts, 27 parts, 28 parts, 29 parts, 30 parts, 31 parts, 32 parts, 33 parts, 34 parts, 35 parts, 36 parts, 37 parts, 38 parts, 39 parts, 40 parts, etc.

[0016] The thermoplastic resin is in parts by weight of 10-15, for example, 10, 11, 12, 13, 14, 15, etc.

[0017] The isocyanate is in parts by weight of 10-15, for example, 10, 11, 12, 13, 14, 15, etc.

[0018] The heat stabilizer is used in amounts of 0.1-0.5 parts by weight, such as 0.1, 0.2, 0.3, 0.4, or 0.5 parts. Too little heat stabilizer will not significantly inhibit side reactions, while too much will not substantially improve the inhibitory effect and will increase costs.

[0019] The catalyst is present in parts by weight of 0.03-0.1 parts, for example, 0.03 parts, 0.04 parts, 0.05 parts, 0.06 parts, 0.07 parts, 0.08 parts, 0.09 parts, 0.1 parts, etc.

[0020] It should be noted that the high-temperature stability referred to in this invention means that the viscosity of the adhesive can remain relatively stable for a relatively long time (e.g., 3 hours) under high-temperature conditions above 130°C.

[0021] The heat stabilizer is a compound heat stabilizer with a carbon-center free radical scavenger as its core, wherein the structure of the carbon-center free radical scavenger is as follows:

[0022]

[0023] The number average molecular weight of the crystalline polyester polyol is 3000-4000 g / mol, for example, 3000 g / mol, 3100 g / mol, 3200 g / mol, 3300 g / mol, 3400 g / mol, 3500 g / mol, 3600 g / mol, 3700 g / mol, 3800 g / mol, 3900 g / mol, 4000 g / mol, etc.

[0024] Preferably, the polyester polyol comprises any one or a mixture of at least two of the following: hexanediol adipate, hexanediol dodecanoate, and hexanediol sebacate.

[0025] The number average molecular weight of the liquid polyester polyol is 2000-5500 g / mol, for example, 2000 g / mol, 2500 g / mol, 3000 g / mol, 3500 g / mol, 4000 g / mol, 4500 g / mol, 5000 g / mol, 5500 g / mol, etc.

[0026] Preferably, the liquid polyester polyol comprises poly(hexamethylene adipate-hexanediol-neopentyl glycol) and / or poly(hexamethylene adipate-hexanediol-neopentyl glycol).

[0027] The thermoplastic resin comprises polycaprolactone and / or TPU.

[0028] Preferably, the number average molecular weight of the polycaprolactone is 40,000-80,000 g / mol, for example, 40,000 g / mol, 45,000 g / mol, 50,000 g / mol, 55,000 g / mol, 60,000 g / mol, 65,000 g / mol, 70,000 g / mol, 75,000 g / mol, 80,000 g / mol, etc.; and the softening point of the TPU is 70-100℃, for example, 70℃, 75℃, 80℃, 85℃, 90℃, 95℃, 100℃, etc.

[0029] The isocyanate is one of 4,4′-diphenylmethane diisocyanate and 2,4′-diphenylmethane diisocyanate.

[0030] The catalyst is an aliphatic amine catalyst.

[0031] Preferably, the aliphatic amine catalyst is bismorpholino diethyl ether.

[0032] A second objective of this invention is to provide a method for preparing the moisture-curing polyurethane hot melt adhesive described in the first objective, comprising the following steps:

[0033] (1) Add crystalline polyester polyol, liquid polyester polyol and thermoplastic resin to a reaction vessel and dehydrate under vacuum;

[0034] (2) Cool down, add isocyanate under nitrogen protection, and wait for the temperature to stabilize before reacting under controlled temperature.

[0035] (3) Add heat stabilizer and catalyst to the material after reaction in step (2) to react and obtain the moisture-curing polyurethane hot melt adhesive.

[0036] In step (1), the vacuum degree of the vacuum dehydration is below -0.09 MPa.

[0037] Preferably, the vacuum dehydration temperature is 120-130℃, for example, 120℃, 121℃, 122℃, 123℃, 124℃, 125℃, 126℃, 127℃, 128℃, 129℃, 130℃, etc.; the vacuum dehydration time is 1.5-2h, for example, 1.5h, 1.6h, 1.7h, 1.8h, 1.9h, 2h, etc.

[0038] In step (2), the temperature after cooling is 100-110℃, for example, 100℃, 101℃, 102℃, 103℃, 104℃, 105℃, 106℃, 107℃, 108℃, 109℃, 110℃, etc.

[0039] Preferably, in step (2), the temperature of the temperature-controlled reaction is 115-120℃, for example, 115℃, 116℃, 117℃, 118℃, 119℃, 120℃, etc., and the time is 1.5-2h, for example, 1.5h, 1.6h, 1.7h, 1.8h, 1.9h, 2h, etc.

[0040] Preferably, in step (3), the reaction time is 0.5-1h, for example, 0.5h, 0.6h, 0.7h, 0.8h, 0.9h, 1h, etc.

[0041] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0042] The moisture-curing polyurethane hot melt adhesive of this invention exhibits excellent high-temperature stability. Specifically, at temperatures above 130°C, its viscosity remains relatively stable for a considerable period. The viscosity increase after 1 hour at high temperature is less than 6%, less than 10%, and less than 17%. Specifically, the viscosity increase after 1 hour at 140°C is 2.12-5.2%, after 2 hours at 140°C is 4.3-9.4%, and after 3 hours at 140°C is 13.2-16.2%. Detailed Implementation

[0043] The technical solution of the present invention will be further illustrated below through specific embodiments.

[0044] Unless otherwise specified, all raw materials used in this invention are commercially available or can be prepared using conventional methods in the art.

[0045] The experimental materials used in the embodiments and comparative examples of this invention are as follows:

[0046] (1) Crystalline polyester polyol: The grade is HDPOL-6640, and the number average molecular weight is 3750 g / mol;

[0047] (2) Liquid polyester polyols: HDPOL-323, number average molecular weight is 2300 g / mol; HDPOL-325, number average molecular weight is 5500 g / mol;

[0048] (3) Thermoplastic resin: CAPA6500;

[0049] (4) Polyisocyanates: 4,4'-diphenylmethane diisocyanate (MDI);

[0050] (5) Catalyst: Bismorpholino diethyl ether;

[0051] (6) Heat stabilizers: U-5068L.

[0052] Example 1

[0053] The moisture-curing polyurethane hot melt adhesive of this embodiment contains the following components by weight:

[0054]

[0055] The preparation method of the moisture-curing polyurethane hot melt adhesive in this embodiment includes the following steps:

[0056] (1) Add crystalline polyester polyol, liquid polyester polyol and thermoplastic resin to the reaction vessel according to the ratio, and dehydrate under vacuum at 125℃ for 2 hours. The vacuum degree is below -0.09MPa.

[0057] (2) Cool down to 105℃, add isocyanate under nitrogen protection, and after the temperature stabilizes, react at 120℃ for 2 hours;

[0058] (3) Add heat stabilizer and catalyst to the material after reaction in step (2) and react for 1 hour to obtain moisture-curing polyurethane hot melt adhesive.

[0059] Example 2

[0060] The moisture-curing polyurethane hot melt adhesive of this embodiment contains the following components by weight:

[0061] The preparation method of the moisture-curing polyurethane hot melt adhesive in this embodiment is the same as that in Embodiment 1.

[0062] Example 3

[0063] The moisture-curing polyurethane hot melt adhesive of this embodiment contains the following components by weight:

[0064] The preparation method of the moisture-curing polyurethane hot melt adhesive in this embodiment is the same as that in Embodiment 1.

[0065] Comparative Example 1

[0066] The moisture-curing polyurethane hot melt adhesive in this comparative example contains the following components by weight:

[0067]

[0068]

[0069] The preparation method of the moisture-curing polyurethane hot melt adhesive in this comparative example is the same as that in Example 1.

[0070] Comparative Example 2

[0071] The moisture-curing polyurethane hot melt adhesive in this comparative example contains the following components by weight:

[0072] The preparation method of the moisture-curing polyurethane hot melt adhesive in this comparative example is the same as that in Example 1.

[0073] Comparative Example 3

[0074] The moisture-curing polyurethane hot melt adhesive in this comparative example contains the following components by weight:

[0075]

[0076]

[0077] The preparation method of the moisture-curing polyurethane hot melt adhesive in this comparative example is the same as that in Example 1.

[0078] The moisture-curing polyurethane hot melt adhesives prepared in Examples 1-3 and Comparative Examples 1-3 were subjected to the following performance tests:

[0079] (1) Viscosity: The unit is mPa·s@130℃, and the test is carried out according to the method specified in standard GB / T 2794-2013;

[0080] (2) High temperature stability test: The hot melt adhesive was heated at 140℃ for 1 hour, 2 hours and 3 hours respectively, and its viscosity change was tested and the viscosity growth rate was recorded. The specific data are shown in Table 1.

[0081] Table 1

[0082]

[0083] As can be seen from Table 1, the wet-curing polyurethane hot melt adhesive of the present invention has good high-temperature stability, that is, the viscosity growth rate can be controlled at a low level after continuous high temperature of 140°C for 3 hours.

[0084] In Comparative Example 1, the absence of a heating stabilizer caused the hot melt adhesive to increase in viscosity rapidly within three hours, with a three-hour growth rate reaching 50.2%. This increase in viscosity reduced the amount of adhesive dispensed during use, thus affecting the application process and efficiency.

[0085] In Comparative Example 2, using too much heat stabilizer will keep the viscosity growth rate essentially unchanged, increasing costs.

[0086] In Comparative Example 3, the heat stabilizer was replaced with phosphoric acid. Although phosphoric acid has the effect of inhibiting side reactions, it cannot effectively suppress the side reactions in the polyurethane prepolymer under high temperature conditions.

[0087] This invention illustrates the detailed process equipment and process flow through the above embodiments. However, this invention is not limited to the detailed process equipment and process flow described above, meaning that this invention does not necessarily depend on the detailed process equipment and process flow to be implemented. Those skilled in the art should understand that any improvements to this invention, equivalent substitutions of raw materials for the product of this invention, addition of auxiliary components, and selection of specific methods, all fall within the protection scope and disclosure scope of this invention.

[0088] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0089] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

[0090] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A moisture-curing polyurethane hot melt adhesive, characterized in that, By weight, it contains the following components: The heat stabilizer is U-5068L.

2. The moisture-curing polyurethane hot melt adhesive according to claim 1, characterized in that, The number-average molecular weight of the crystalline polyester polyol is 3000-4000 g / mol.

3. The moisture-curing polyurethane hot melt adhesive according to claim 2, characterized in that, The crystalline polyester polyol comprises any one or a mixture of at least two of the following: hexanediol adipate, hexanediol dodecanoate, and hexanediol sebacate.

4. The moisture-curing polyurethane hot melt adhesive according to claim 1, characterized in that, The number-average molecular weight of the liquid polyester polyol is 2000-5500 g / mol.

5. The moisture-curing polyurethane hot melt adhesive according to claim 4, characterized in that, The liquid polyester polyol comprises poly(hexamethylene adipate-hexanediol-neopentyl glycol) and / or poly(hexamethylene adipate-hexanediol-neopentyl glycol) ester.

6. The moisture-curing polyurethane hot melt adhesive according to claim 1, characterized in that, The thermoplastic resin comprises polycaprolactone and / or TPU.

7. The moisture-curing polyurethane hot melt adhesive according to claim 6, characterized in that, The polycaprolactone has a number-average molecular weight of 40,000-80,000 g / mol, and the TPU softening point is 70-100℃.

8. The moisture-curing polyurethane hot melt adhesive according to claim 1, characterized in that, The isocyanate is one of 4,4′-diphenylmethane diisocyanate and 2,4′-diphenylmethane diisocyanate.

9. The moisture-curing polyurethane hot melt adhesive according to claim 1, characterized in that, The catalyst is an aliphatic amine catalyst.

10. The moisture-curing polyurethane hot melt adhesive according to claim 9, characterized in that, The aliphatic amine catalyst is bismorpholino diethyl ether.

11. A method for preparing a moisture-curing polyurethane hot melt adhesive as described in any one of claims 1-10, characterized in that, Includes the following steps: (1) Add crystalline polyester polyol, liquid polyester polyol and thermoplastic resin to a reaction vessel and dehydrate under vacuum; (2) Cool down, add isocyanate under nitrogen protection, and wait for the temperature to stabilize before reacting under controlled temperature. (3) Add heat stabilizer and catalyst to the material after reaction in step (2) to react and obtain the moisture-curing polyurethane hot melt adhesive.

12. The preparation method according to claim 11, characterized in that, In step (1), the vacuum degree of the vacuum dehydration is below -0.09 MPa.

13. The preparation method according to claim 11, characterized in that, The vacuum dehydration temperature is 120-130℃, and the vacuum dehydration time is 1.5-2h.

14. The preparation method according to claim 11, characterized in that, In step (2), the temperature after cooling is 100-110℃.

15. The preparation method according to claim 11, characterized in that, In step (2), the temperature of the temperature-controlled reaction is 115-120℃ and the time is 1.5-2h.

16. The preparation method according to claim 11, characterized in that, In step (3), the reaction time after adding the heat stabilizer and catalyst is 0.5-1h.

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