Polyurethane hot melt adhesive and preparation method thereof

Abstract

The invention belongs to the technical field of hot melt adhesives, and particularly relates to a polyurethane hot melt adhesive and a preparation method thereof, the polyurethane hot melt adhesive comprises the following components by weight: 10-20 parts of a hydroxymethyl-terminated polydimethylsiloxane-polyether compound; 25 to 40 parts of crystalline polyester polyol; 10 to 20 parts of polyether polyol; 1 to 10 parts of tackifying resin; 25 to 35 parts of diisocyanate; 0.1 to 1 part of a catalyst; 0-1 part of an auxiliary agent; and 0-1 part of a coupling agent. The invention provides a non-ultraviolet (UV) cured reactive polyurethane hot melt adhesive, which overcomes the inherent defect that the traditional UV cured adhesive is difficult or incomplete to cure in a complex structure, in a shadow area or on the surface of an ultraviolet opaque material, and has the advantages of high curing speed and high curing speed through unique component design. According to the polyurethane hot melt adhesive, the balance between extremely low modulus and relatively high bonding strength of the polyurethane hot melt adhesive is realized, stress can be effectively buffered, impact can be effectively absorbed, and reliable fixing and sealing can be provided.

Description

Technical Field

[0001] This invention relates to a polyurethane hot melt adhesive and its preparation method, belonging to the field of hot melt adhesive technology. Background Technology

[0002] With the rapid development of mobile electronics technology, mobile phones and various wearable electronic devices have become an indispensable part of people's daily lives, and their product designs continue to evolve towards thinner, lighter, and more aesthetically pleasing designs. Polyurethane hot melt adhesives, with their excellent flexibility, weather resistance, and bonding strength, have been widely used in wearable electronic products.

[0003] However, with the upgrading of electronic product structural design and the continuous improvement of functional requirements, the performance of traditional polyurethane hot melt adhesives can no longer fully meet the needs of emerging application scenarios. For example, in specific applications such as screen backing support and sealing bonding of internal cavities in mobile phones, a special hot melt adhesive with low modulus, rapid establishment of initial bond strength, and easy rework at room temperature is required. Existing technologies mostly use ultraviolet (UV) curing to achieve rapid curing, but this method has obvious limitations, especially in areas not covered by light (such as shaded areas or inside complex three-dimensional structures), where the curing effect is severely affected, leading to a limited range of applications.

[0004] Therefore, developing a polyurethane hot melt adhesive that combines low modulus, high bonding strength, and does not rely on UV curing has become an urgent technical problem to be solved in this field. Summary of the Invention

[0005] To address the aforementioned deficiencies in the prior art, this invention provides a polyurethane hot melt adhesive and its preparation method.

[0006] The technical solution of the present invention to solve the above-mentioned technical problems is as follows: One objective of this invention is to provide a polyurethane hot melt adhesive, comprising the following components in parts by weight: 10-20 parts of hydroxymethyl-terminated polydimethylsiloxane-polyether compound; 25-40 parts of crystalline polyester polyol; 10-20 parts of polyether polyol; 1-10 parts of tackifying resin; 25-35 parts of diisocyanate; Catalyst 0.1 to 1 part; 0-1 part of auxiliary agent; 0-1 part of coupling agent.

[0007] The core inventive concept of this invention lies in achieving a balance between low modulus and high strength through the synergistic formulation of specific structural components: Introducing hydroxymethyl-terminated polydimethylsiloxane-polyether compounds: This component is key to reducing the system's modulus and surface energy. The terminal hydroxymethyl (-CH2OH) ensures its smooth participation in the polyurethane polymerization reaction. The polydimethylsiloxane (PDMS) segments endow the molecular chains with excellent flexibility and low surface energy, significantly reducing the modulus of the colloid and improving wettability to low surface energy substrates. The embedded polyether segments ensure good compatibility between the compound and the system, allowing it to be uniformly dispersed and intercalated into the polyurethane network backbone.

[0008] Long-chain aliphatic diisocyanates are selected, with dimer diisocyanate (DDI) being the preferred choice. DDI has a flexible dimer backbone of up to 36 carbon atoms. This long-chain structure introduces flexible spacers into the hard segments of polyurethane, effectively reducing the overall modulus of the material. Simultaneously, its aliphatic long-chain structure provides excellent hydrolysis resistance, while the dimer backbone itself has good affinity for various substrates, contributing to improved adhesive strength.

[0009] A blend of crystalline polyester polyols and polyether polyols: Crystalline polyester polyols provide initial bond strength and final cohesive strength; polyether polyols further enhance the flexibility and low-temperature resistance of the colloid. Together with the two key components mentioned above, they construct a polymer network that combines rigidity and flexibility with excellent viscoelastic properties.

[0010] Furthermore, the crystalline polyester polyol is selected from at least one of polycaprolactone diol (PCL), polycarbonate diol (PCDL), adipic acid-based polyester diol, and phthalic anhydride polyester diol, and the number average molecular weight is preferably 1500-3500.

[0011] Furthermore, the number average molecular weight of the hydroxymethyl-terminated polydimethylsiloxane-polyether compound is 2000-3000, preferably 2200 (such as Momentive 2812, Shin-Etsu KF-6001) or 2800.

[0012] Furthermore, the polyether polyol is at least one of polypropylene glycol (PPG) with a molecular weight of 1000 to 5000.

[0013] Furthermore, the diisocyanate is a dimeric acid diisocyanate (DDI, Liming Chemical Research Institute).

[0014] Furthermore, the catalyst is bismorpholino diethyl ether (DMDEE).

[0015] Furthermore, the tackifying resin is a hydrogenated hydrocarbon resin. The tackifying resin used in this invention is primarily used to provide good initial tack; preferably, it is a hydrogenated C5 petroleum resin, such as Eastman's F100.

[0016] Furthermore, the coupling agent is selected from any one of γ-aminopropyltriethoxysilane, γ-(2,3-epoxypropoxy)propyltrimethoxysilane, or γ-mercaptopropyltrimethoxysilane; preferably KH-550, KH-560, or KH-590.

[0017] Furthermore, the adjuvant is an antioxidant, preferably pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (antioxidant 1010).

[0018] The polyurethane hot melt adhesive of the present invention has a tensile modulus as low as 1-5 MPa after curing at 25°C for 7 days, while its shear strength against various plastic substrates (such as PC) can reach more than 2 MPa, achieving an excellent combination of low modulus and high strength.

[0019] A second objective of this invention is to provide a method for preparing the polyurethane hot melt adhesive as described above, comprising the following steps: S1. Mix hydroxymethyl-terminated polydimethylsiloxane-polyether compound, crystalline polyester polyol, polyether polyol, tackifying resin and additives, and heat to dehydrate under vacuum conditions; S2. Cool down, add diisocyanate, and react at 100-120°C for 1-3 hours under inert gas protection; S3. Add catalyst and coupling agent to the reaction system, and continue stirring to mix evenly to obtain the polyurethane hot melt adhesive.

[0020] Furthermore, in step S1, the dehydration temperature is 110–130°C, the vacuum degree is -0.10–-0.09 MPa, and the dehydration time is 1–3 hours.

[0021] Furthermore, in step S2, the temperature is lowered to 85-95°C before adding diisocyanate.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention provides a non-UV curable reactive polyurethane hot melt adhesive, which fundamentally overcomes the inherent defects of traditional UV curing adhesives, such as difficulty or incomplete curing in complex structures, shaded areas, or on surfaces of materials that are opaque to UV light, thus expanding its application range in scenarios with shielding requirements, such as precision electronic assembly.

[0023] This invention constructs a rigid-flexible polyurethane network by synergistically designing hydroxymethyl-terminated polydimethylsiloxane-polyether compounds with long-chain flexible dimer diisocyanate (DDI). This design enables the resulting adhesive to maintain high shear bond strength (e.g., over 2 MPa for PC substrates) while possessing a low tensile modulus (2.9–4.1 MPa, effectively buffering stress and absorbing impact), thus resolving the technical contradiction that low-modulus materials often suffer from insufficient strength.

[0024] The preparation method of this invention has simple steps, mild and controllable reaction conditions (with a clear range of temperature and vacuum), and does not require special light or complex post-processing equipment, making it easy to achieve stable and efficient industrial production. Detailed Implementation

[0025] The principles and features of the present invention are described below through specific embodiments. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0026] Example 1 This embodiment provides a method for preparing polyurethane hot melt adhesive. The following substances were used: Hydroxymethyl-terminated polydimethylsiloxane-polyether compound (Momentive 2812, Mn=2200): 10 parts Polycaprolactone diol (PCL, Mn=2000): 40 parts Polypropylene glycol (PPG, Mn=1000): 10 parts Tackifying resin (Eastman F100): 4 parts Antioxidant 1010: 0.3 parts Diisocyanate dimer (DDI): 35 parts Catalyst DMDEE: 0.6 parts Coupling agent KH-550: 0.5 parts The preparation of the polyurethane hot melt adhesive specifically includes the following steps: S1. Add PCL, PPG, hydroxymethyl-terminated polydimethylsiloxane-polyether compound, F100, and antioxidant 1010 to a dry reaction vessel and dehydrate for 2 hours at 120°C and -0.095MPa vacuum.

[0027] S2. After dehydration, cool to 90°C and add DDI under nitrogen protection. Raise the temperature to 115°C and maintain the reaction for 3 hours.

[0028] S3. Add DMDEE and KH-550, continue stirring for 30 minutes, discharge, cool, and obtain polyurethane hot melt adhesive.

[0029] Example 2 Unlike Example 1, this example increases the hydroxymethyl-terminated polydimethylsiloxane-polyether compound (Mn=2200) to 15 parts, reduces PCL (Mn=3000) to 30 parts, reduces DDI to 30 parts, increases F100 to 5 parts, increases antioxidant 1010 to 0.5 parts, and uses 0.5 parts of catalyst DMDEE. The preparation method is the same as in Example 1.

[0030] Example 3 Unlike Example 1, this example replaces the hydroxymethyl-terminated polydimethylsiloxane-polyether compound with a similar product of Mn=2800, using 20 parts; PCL (Mn=3000) 25 parts; PPG replaced with a product of Mn=4000; DDI 25 parts; F100 6 parts; catalyst DMDEE 0.3 parts; coupling agent 0.6 parts. The preparation method is the same as in Example 1.

[0031] Comparative Example 1 Unlike Example 1, this comparative example does not use hydroxymethyl-terminated polydimethylsiloxane-polyether compounds, but instead uses an equal amount of PPG (Mn=2000). The preparation method is the same as in Example 1.

[0032] Comparative Example 2 Unlike Example 1, this comparative example does not use DDI, but instead uses an equal amount of hexamethylene diisocyanate (HDI). The preparation method is the same as in Example 1.

[0033] Comparative Example 3 Unlike Example 1, this comparative example uses an equal amount of PPG (Mn=2000) instead of the hydroxymethyl-terminated polydimethylsiloxane-polyether compound, and an equal amount of HDI instead of DDI. The preparation method is the same as in Example 1.

[0034] Performance testing The hot melt adhesive samples obtained from the above embodiments and comparative examples were tested as follows: Tensile modulus: The sample was prepared into a standard dumbbell-shaped specimen (approximately 0.2 mm thick) and cured for 7 days at 25°C and 50% relative humidity. The tensile modulus was tested at 25°C using a dynamic thermomechanical analyzer (DMA).

[0035] Shear strength: Based on polycarbonate (PC) sheet, according to national standard GB / T 7124 In 2008 (Determination of Tensile Shear Strength of Adhesives), lap shear specimens (bonded area 12.5 mm × 25 mm) were prepared and cured for 7 days under the same conditions. The shear strength was then tested using a universal testing machine at a tensile rate of 10 mm / min.

[0036] The test results are shown in Table 1.

[0037] Table 1. Performance test data of hot melt adhesives in the examples and comparative examples.

[0038] As can be seen from the data in Table 1: The hot melt adhesives prepared in Examples 1 to 3 of this invention all achieved a good combination of low modulus (2.9 to 4.1 MPa) and high shear strength (2.1 to 2.6 MPa).

[0039] Comparative Example 1, the polydimethylsiloxane-polyether compound without hydroxymethyl end-capping, showed a significantly increased modulus (7.8 MPa) and a substantial decrease in shear strength (1.3 MPa). This demonstrates that hydroxymethyl end-capped polydimethylsiloxane-polyether compounds play an irreplaceable and crucial role in simultaneously reducing modulus and improving bond strength.

[0040] Comparative Example 2 used HDI instead of DDI. Although the shear strength was comparable to that of the Example (2.7 MPa), the modulus increased sharply to 10.2 MPa, and the low modulus characteristics were lost. This demonstrates that the long-chain flexible structure of DDI is crucial for reducing the modulus.

[0041] Comparative Example 3, lacking both key components, exhibited the worst performance, yet had the highest modulus (13.2 MPa) and no advantage in strength. This further confirms the synergistic effect between the hydroxymethyl-terminated polydimethylsiloxane-polyether compound and DDI in the system of this invention, jointly achieving the technical objectives.

[0042] In summary, this invention, by carefully selecting and combining siloxane-modified polyols (hydroxymethyl-terminated polydimethylsiloxane-polyether compounds) with specific structures and long-chain diisocyanates, synergistically regulates the microstructure of the polyurethane network, and successfully develops a high-performance low-modulus, high-strength polyurethane hot melt adhesive, which is particularly suitable for precision bonding and sealing of high-end electronic products.

[0043] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A polyurethane hot melt adhesive, characterized in that, Based on parts by weight, it comprises the following components: 10-20 parts of hydroxymethyl-terminated polydimethylsiloxane-polyether compound; 25-40 parts of crystalline polyester polyol; 10-20 parts of polyether polyol; 1-10 parts of tackifying resin; 25-35 parts of diisocyanate; Catalyst 0.1 to 1 part; 0-1 part of auxiliary agent; 0-1 part of coupling agent.

2. The polyurethane hot melt adhesive according to claim 1, characterized in that, The crystalline polyester polyol is selected from at least one of polycaprolactone diol, polycarbonate diol, adipic acid-based polyester diol, and phthalic anhydride polyester diol.

3. The polyurethane hot melt adhesive according to claim 1, characterized in that, The number-average molecular weight of the hydroxymethyl-terminated polydimethylsiloxane-polyether compound is 2000-3000.

4. The polyurethane hot melt adhesive according to claim 1, characterized in that, The polyether polyol is at least one of polyoxypropylene glycol with a molecular weight of 1000 to 5000.

5. The polyurethane hot melt adhesive according to claim 1, characterized in that, The diisocyanate is a dimeric acid diisocyanate.

6. The polyurethane hot melt adhesive according to claim 1, characterized in that, The catalyst is bismorpholino diethyl ether.

7. The polyurethane hot melt adhesive according to claim 1, characterized in that, The tackifying resin is a hydrogenated hydrocarbon resin.

8. The polyurethane hot melt adhesive according to claim 1, characterized in that, The coupling agent is selected from any one of γ-aminopropyltriethoxysilane, γ-(2,3-epoxypropoxy)propyltrimethoxysilane, or γ-mercaptopropyltrimethoxysilane; the adjuvant is an antioxidant.

9. A method for preparing a polyurethane hot melt adhesive as described in any one of claims 1 to 8, characterized in that, Includes the following steps: S1. Mix hydroxymethyl-terminated polydimethylsiloxane-polyether compound, crystalline polyester polyol, polyether polyol, tackifying resin and additives, and heat to dehydrate under vacuum conditions; S2. Cool down, add diisocyanate, and react at 100-120°C for 1-3 hours under inert gas protection; S3. Add catalyst and coupling agent to the reaction system, and continue stirring to mix evenly to obtain the polyurethane hot melt adhesive.

10. The method for preparing polyurethane hot melt adhesive according to claim 9, characterized in that, In step S1, the dehydration temperature is 110-130℃, the vacuum degree is -0.10--0.09MPa, and the dehydration time is 1-3 hours; in step S2, the temperature is lowered to 85-95℃ before diisocyanate is added.

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