A tensile shear strength enhanced polyurethane adhesive, a preparation method and application thereof

Abstract

This invention discloses a tensile shear strength-enhanced polyurethane adhesive, its preparation method, and its application. The disclosed polyurethane adhesive includes a prepolymer, toluene triisocyanate (TTI), and a carboxyl modifier. The prepolymer is prepared by reacting isocyanate and polyester polyol. The isocyanate is selected from toluene diisocyanate (TDI) or diphenylmethane diisocyanate (MDI). The carboxyl modifier is a mixture of succinic acid and acrylic acid. This invention introduces carboxyl groups into the adhesive layer, resulting in a polyurethane adhesive suitable for bonding metals. The carboxyl groups can form stable chemical bonds with the oxide layer on the metal surface, improving interfacial adsorption.

Description

Technical Field

[0001] This invention relates to the field of chemical materials technology, specifically to a tensile shear strength enhanced polyurethane adhesive, its preparation method, and its application. Background Technology

[0002] Polyurethane adhesives are widely used in chemical, automotive, electronics, and construction industries due to their excellent comprehensive performance. Their core advantages include: wide applicability, capable of bonding various substrates such as metals, plastics, and wood; high bond strength, meeting the bonding needs of most structures; excellent flexibility and impact resistance, adapting to minor deformations of the substrate; good weather resistance and environmental stability, maintaining stable bonding performance in high and low temperature, humid environments; and flexible curing methods, allowing for room temperature curing or heat curing to suit different construction scenarios.

[0003] However, traditional polyurethane adhesives are prepared by direct reaction of isocyanates (such as MDI and TDI) with polyols. The molecular chains are predominantly linear with low branching and crosslinking degrees, resulting in limited tensile shear strength. The tensile shear strength of bonded metals is only 5-10 MPa, which is merely a common basic strength level. This makes it difficult to meet the bonding requirements of high-strength structures such as load-bearing metal components. Summary of the Invention

[0004] In view of the defects or deficiencies of the prior art, the present invention provides a polyurethane adhesive with enhanced tensile shear strength.

[0005] Therefore, the polyurethane adhesive provided by the present invention includes a prepolymer, toluene triisocyanate (TTI), and a carboxyl modifier;

[0006] The method for preparing the prepolymer includes: reacting isocyanate and polyester polyol to prepare the prepolymer; the isocyanate is selected from toluene diisocyanate (TDI) or diphenylmethane diisocyanate (MDI); the carboxyl modifier is a mixture of succinic acid and acrylic acid; The formulation of each component is as follows: 100 parts by weight of polyester polyol, 90-107 parts by weight of isocyanate, 0.5-10 parts by weight of TTI, and 1-10 parts by weight of carboxyl modifier.

[0007] An alternative approach is that the preparation of the prepolymer includes: preparing the prepolymer by mixing and reacting isocyanate and polyester polyol under inert gas protection and at 60-90°C.

[0008] Alternatively, the polyester polyol may be selected from polyester polyols with a number average molecular weight of 1000-3000 or polyether polyols with a number average molecular weight of 1000-2000.

[0009] An alternative is that the succinic acid content in the carboxyl modifier is 20%~70%, and the acrylic acid content is 30%~80%.

[0010] Alternatively, the polyurethane adhesive has a tensile shear strength of 12-14 MPa and an interfacial peel strength of 15-16 N / mm when bonding to a metal substrate, wherein the metal substrate is aluminum or steel.

[0011] The present invention also relates to a method for preparing the above-mentioned tensile shear strength enhanced polyurethane adhesive, the method comprising: mixing the prepolymer, TTI and carboxyl modifier uniformly under an inert atmosphere and then heating to 50-70°C to react and prepare the polyurethane adhesive.

[0012] This invention also relates to the application of the above-mentioned polyurethane adhesive for bonding metal substrates, wherein the metal substrate is aluminum or steel, and the application includes coating the surface of the metal substrate to be bonded with the polyurethane adhesive prepared by the method of claim 7, followed by curing. Optionally, the coating thickness is 0.1-0.5 mm. The curing is performed at 20-50°C for 24-48 hours.

[0013] The purpose of this invention is to overcome the problems of limited tensile shear strength of traditional polyurethane adhesives, poor interfacial adsorption of existing crosslinking modification technologies, and the limited resource utilization pathways for TNT. This invention introduces carboxyl groups through a carboxyl-containing modifier, solving the problem of decreased interfacial adsorption caused by high crosslinking degree. The carboxyl groups form stable chemical bonds with the metal oxide layer, improving interfacial bonding strength, making it suitable for bonding to metal substrates such as aluminum and steel. Detailed Implementation

[0014] The present invention will be described in detail below through specific embodiments, but the scope of protection of the present invention is not limited to the following embodiments.

[0015] The present invention will be further explained and illustrated below with reference to the embodiments. All raw materials used in the following embodiments are commercially available products. The technical effects of the present invention are verified through specific embodiments and comparative examples. Performance tests were conducted according to national standards: open time according to GB / T 13477.10-2017, tensile shear strength according to GB / T 7124-2023, interfacial peel strength according to GB / T2790-1995, and elongation at break according to GB / T 528-2009.

[0016] Example 1: The raw materials and steps for preparing the polyurethane adhesive in this embodiment are as follows: 100g of polyester polyol (number average molecular weight 2000) and 98g of MDI were added to the reactor, argon gas was introduced, the temperature was raised to 70℃, and the reaction was stirred for 3.5h to obtain MDI-based polyurethane prepolymer. Next, add 4g of TTI, stir at 400r / min for 15min, then add 4g of carboxyl modifier, which contains 57% succinic acid and 43% acrylic acid, and heat to 60℃ to react for 1h.

[0017] When using this adhesive precursor to bond metal parts, the specific operation is as follows: (1) Substrate pretreatment: The steel surface is treated by sandblasting or chemical degreasing to remove oil, rust and impurities, and the surface roughness Ra=0.8-3.2μm is controlled to increase the contact area between the adhesive layer and the substrate; (2) Coating and bonding: Apply the adhesive evenly to the surface of the metal substrate the day before, and control the coating thickness to be 0.1-0.5mm. Complete the precise bonding of the substrate to be bonded within an open time of 20-30min to avoid the degradation of adhesive performance due to time limit. (3) Curing and maintenance: Select the curing process according to the needs of the scenario. It can be put into use after complete curing.

[0018] Example 2: The difference between this embodiment and Embodiment 1 is that the raw materials for preparation in this embodiment are: 100g of polyester polyol, 90g of MDI, 10g of TTI, and 1g of carboxyl modifier, wherein the content of succinic acid is 30% and the content of acrylic acid is 70%.

[0019] Example 3: The difference between this embodiment and Example 1 is that the raw materials used in its preparation are: 100g of polyester polyol, 107g of MDI, 1g of TTI, and 10g of carboxyl modifier, wherein the succinic acid content is 70% and the acrylic acid content is 30%. The preparation steps of this embodiment are the same as those in Example 1.

[0020] Comparative Example 1: The difference between this comparative example and Example 1 is that the carboxyl modifier is only succinic acid.

[0021] Comparative Example 2: The difference between this comparative example and Example 1 is that the carboxyl modifier is only acrylic acid.

[0022] Comparative Example 3: The difference between this comparative example and Example 1 is that the carboxyl modifier is only citric acid.

[0023] Comparative Example 4: The difference between this comparative example and Example 1 is that the carboxyl modifier is replaced with citric acid instead of acrylic acid.

[0024] Comparative Example 5: The difference between this comparative example and Example 1 is that the carboxyl modifier is citric acid instead of succinic acid.

[0025] Comparative Example 6: The difference between this comparative example and Example 1 is that the carboxyl modifiers are succinic acid, acrylic acid, and citric acid, with the proportions of the three carboxyl modifiers being 40%, 40%, and 20%, respectively.

[0026] Comparative Example 7: This comparative example differs from Example 1 in that it does not contain a carboxyl modifier.

[0027] The performance evaluation of the adhesives in the above embodiments and comparative examples is shown in Table 1.

[0028] Table 1

[0029] The products prepared in Examples 1-3 meet the environmental protection standards required by GB / 18583-2008 and GB / 33372-2020.

[0030] The above embodiments and comparative examples show that this application improves the bulk strength of the adhesive at the molecular structure level by using TTI multifunctional crosslinking and optimizes the metal bonding force at the interfacial level by using succinic acid / acrylic acid compound carboxyl modification, thus achieving a dual improvement in "bulk strength + interfacial performance". The resulting adhesive not only has core bonding performance far exceeding that of traditional products and commercially available similar products, but also takes into account process flexibility, environmental friendliness and construction compatibility.

Claims

1. A polyurethane adhesive with enhanced tensile shear strength, characterized in that, The polyurethane adhesive comprises a prepolymer, toluene triisocyanate (TTI), and a carboxyl modifier; The method for preparing the prepolymer includes: reacting isocyanate and polyester polyol to prepare the prepolymer; the isocyanate is selected from toluene diisocyanate (TDI) or diphenylmethane diisocyanate (MDI); the carboxyl modifier is a mixture of succinic acid and acrylic acid; The formulation of each component is as follows: 100 parts by weight of polyester polyol, 90-107 parts by weight of isocyanate, 0.5-10 parts by weight of TTI, and 1-10 parts by weight of carboxyl modifier.

2. The polyurethane adhesive according to claim 1, characterized in that, The preparation of the prepolymer includes: reacting isocyanate and polyester polyol under inert gas protection and at 60-90°C to prepare the prepolymer.

3. The polyurethane adhesive according to claim 1, characterized in that, The polyester polyol is selected from polyester polyols with a number average molecular weight of 1000-3000 or polyether polyols with a number average molecular weight of 1000-2000.

4. The polyurethane adhesive according to claim 1, characterized in that, The carboxyl modifier contains 20% to 70% succinic acid and 30% to 80% acrylic acid.

5. The polyurethane adhesive according to claim 1, characterized in that, The polyurethane adhesive has a tensile shear strength of 12-14 MPa and an interfacial peel strength of 15-16 N / mm when bonding to a metal substrate, wherein the metal substrate is aluminum or steel.

6. The method for preparing the tensile shear strength enhanced polyurethane adhesive according to claim 1, characterized in that, The preparation method includes: under the protection of an inert atmosphere, the prepolymer, TTI and carboxyl modifier are mixed evenly and then heated to 50-70℃ to react and prepare the polyurethane adhesive.

7. The polyurethane adhesive prepared by the method of claim 6 is used for bonding metal substrates, wherein the metal substrate is aluminum or steel, characterized in that... The application includes coating the surface of the metal substrate to be bonded with the polyurethane adhesive prepared by the method of claim 7 and then curing it.

8. The application according to claim 7, characterized in that, The coating thickness is 0.1-0.5mm.

9. The application according to claim 7, characterized in that, The curing process involves curing at 20-50°C for 24-48 hours.

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