A two-component polyurethane structural adhesive with high insulation and a secondary curing process and its preparation method

Abstract

This invention belongs to the field of adhesive technology and relates to a two-component polyurethane structural adhesive with high insulation and a secondary curing process, as well as its preparation method. The structural adhesive, by weight, comprises: Component A: 30.4-45.6 parts of blocked prepolymer; 4.8-7.2 parts of polyurethane prepolymer; 12.8-19.2 parts of low-density polyethylene powder; 16-24 parts of silica powder; Component B: 8-12 parts of castor oil; 4.8-7.2 parts of polyether polyol; 16-24 parts of castor oil-modified polyol; 1.08-1.61 parts of silane coupling agent; 16-24 parts of low-density polyethylene powder; 3.1-4.66 parts of water-absorbing agent; 12-18 parts of calcium carbonate powder; and 0.05-0.15 parts of catalyst; the volume ratio of Component A to Component B is 1:1. The structural adhesive of this invention has a certain initial adhesive strength, can be cured by heating, and also provides the product with the characteristics of disassembly and repair, while possessing excellent adhesive and electrical insulation properties.

Description

Technical Field

[0001] This invention belongs to the field of adhesive technology, and particularly relates to a two-component polyurethane structural adhesive with high insulation and a method for its preparation. Background Technology

[0002] In the industrial manufacturing sector, the curing strength of conventional polyurethane structural adhesives gradually increases over time, reaching a final bond strength. Due to this high bond strength after curing, it is difficult to disassemble or repair product components without damage. Often, a single defective unit module can render the entire product unusable, making non-destructive disassembly or repair impossible. This results in a high scrap rate, potentially causing secondary pollution and increasing manufacturing costs. Summary of the Invention

[0003] To address the shortcomings of the existing technology, this invention provides a two-component polyurethane structural adhesive with secondary curing and its preparation method. The specific technical solution is as follows:

[0004] The first objective of this invention is to provide a two-component polyurethane structural adhesive with high insulation that requires two-stage curing, comprising component A and component B, in parts by weight:

[0005] Component A:

[0006] Closed-cell prepolymer 30.4-45.6 parts; polyurethane prepolymer 4.8-7.2 parts; low-density polyethylene powder 12.8-19.2 parts; silica powder 16-24 parts;

[0007] The closed-type prepolymer structure is shown in Formula 1:

[0008]

[0009] Where R is any structure;

[0010] Component B:

[0011] Castor oil 8-12 parts; polyether polyol 4.8-7.2 parts; castor oil-modified polyol 16-24 parts; silane coupling agent 1.08-1.61 parts; low-density polyethylene powder 16-24 parts; water absorbent 3.1-4.66 parts; calcium carbonate powder 12-18 parts; catalyst 0.05-0.15 parts;

[0012] The volume ratio of component A to component B is 1:1.

[0013] The two-component polyurethane structural adhesive of this invention, which requires two-stage curing, can achieve two-stage curing:

[0014] One-time curing: RN=C=O+R'-OH→RNHCOOR', the unclosed isocyanate groups of the polyurethane prepolymer react with the hydroxyl groups to generate urethane, the structural adhesive chemically cross-links and cures, producing a certain bonding strength to fix the product components and meet the handling conditions.

[0015] Secondary curing: In the closed-cell prepolymer, the blocked isocyanate groups undergo a reverse reaction under heating conditions, releasing the active isocyanate groups again. These groups then react with the free hydroxyl groups of component B to crosslink and cure, achieving a secondary curing reaction and reaching the final cured strength. The reaction mechanism is as follows:

[0016] First-order reaction:

[0017] Second-order reaction: RN=C=O + R'-OH → RNHCOOR'.

[0018] When using the two-component polyurethane structural adhesive of this invention, which is cured in a secondary manner, the initial stage achieves the bonding strength required by the production process through low cross-linking curing. If the product is unqualified, it is heated at 85-90℃ to melt and flow the low-density polyethylene powder, softening the adhesive layer and making it easy to disassemble. If the final assembly test is qualified, a heating process at 100-110℃ is used to unblock the closed isocyanate groups, further cross-linking and curing, providing higher bonding strength.

[0019] Furthermore, the blocked prepolymer is prepared by reacting a polyether polyol with a molecular weight of 2000, polymeric MDI, and blocking agent 2,4-dimethylimidazole in a mass ratio of 100:(67-75):(53-60), and the NCO content before blocking is 12%.

[0020] Further, the preparation method of the closed prepolymer is as follows: a polyether polyol with a molecular weight of 2000 is heated to 100-110°C, vacuumed to remove water, then cooled to 45-55°C, and polymeric MDI is added. The reaction is carried out under nitrogen protection, heated to 85-90°C and stirred continuously for 2-3 hours, then cooled to 40-45°C and 2,4-dimethylimidazole is added slowly. The reaction is carried out under nitrogen protection for 1-3 hours to obtain the closed prepolymer.

[0021] Furthermore, the polyurethane prepolymer is prepared by reacting a polyether polyol with a molecular weight of 5000 in a mass ratio of 100:(19-25) with polymeric MDI; the NCO content is 4%.

[0022] Further, the preparation method of the polyurethane prepolymer is as follows: a polyether polyol with a molecular weight of 5000 is heated to 100-110°C, vacuumed to remove water, then cooled to 45-55°C, and polymeric MDI is added. The reaction is carried out under nitrogen protection, heated to 80-85°C and stirred continuously for 2-3 hours until the NCO value no longer changes, and then cooled to room temperature to obtain the polyurethane prepolymer.

[0023] Furthermore, the D50 particle size of the low-density polyethylene powder (LDPE) is 25-40 μm.

[0024] Low-density polyethylene powder is a high-insulation material. On the one hand, it improves the electrical insulation performance of the product. On the other hand, if disassembly or repair is required, it can be heated to its melting point at 85-90℃ and held at this temperature. The low-density polyethylene powder melts and flows, and the colloidal layer softens, thereby breaking the contact surface between the colloidal layer and the adhesive substrate. This allows the components to be disassembled with a lower strength of external force for recycling.

[0025] Furthermore, the castor oil is castor oil from Ito Chemical Industry Co., Ltd., with a hydroxyl value of 160 mg KOH / g.

[0026] Furthermore, the polyether polyol is MN-700 from Shandong Lanxing Dongda Chemical Co., Ltd.

[0027] Furthermore, the castor oil modified polyol is URIC H-1823 from Ito Chemical Industry Co., Ltd., with a hydroxyl value of 100-200 mg KOH / g.

[0028] Castor oil-modified polyols have the advantages of being hydrophobic, having high adhesive strength, and being resistant to aging.

[0029] Furthermore, the water absorbent is 3A molecular sieve; the catalyst is organotin catalyst T12; and the silane coupling agent is KH-560.

[0030] The second objective of this invention is to provide a method for preparing the above-mentioned secondary curing high-insulation two-component polyurethane structural adhesive, comprising the following steps:

[0031] D1. The closed-cell prepolymer, polyurethane prepolymer, low-density polyethylene powder, and silica powder are mixed at a temperature ≤60℃, and component A is obtained by degassing.

[0032] D2. Castor oil, polyether polyol, castor oil-modified polyol, silane coupling agent, low-density polyethylene powder, water absorbent, calcium carbonate powder and catalyst are mixed at a temperature ≤55℃, and component B is obtained by degassing.

[0033] The beneficial effects of this invention are as follows:

[0034] This invention provides a two-stage curing high-insulation two-component polyurethane structural adhesive. Initially, low-crosslinking curing achieves the required bond strength for the production process. Utilizing the secondary curing property: if the product fails to meet standards, heating to 85-90℃ melts and flows the low-density polyethylene powder, softening the adhesive layer for easy disassembly and recycling. Once the product passes testing or is properly handled and installed, heating to 100-110℃ de-sealed the adhesive with a blocking curing agent further crosslinks and cures, providing even higher bond strength and reaching the final cured strength. Simultaneously, the low-density polyethylene powder exhibits better compatibility within the system after secondary curing, providing superior electrical insulation performance. It is suitable for bonding engineering plastics, aluminum alloys, and other substrates. Detailed Implementation

[0035] The principles and features of the present invention are described below with reference to embodiments. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0036] Low-density polyethylene powder (LDPE): D50 particle size is 30μm;

[0037] Castor oil: Castor oil from Ito Chemical Industry Co., Ltd., with a hydroxyl value of 160 mg KOH / g;

[0038] Polyether polyol: MN-700 from Shandong Lanxing Dongda Chemical Co., Ltd.;

[0039] Castor oil modified polyol: URIC H-1823 from Ito Chemical Industry Co., Ltd., with a hydroxyl value of 100-200 mg KOH / g;

[0040] Water absorbent: 3A molecular sieve;

[0041] Catalyst: Organotin catalyst T12;

[0042] Silane coupling agent: KH-560.

[0043] The above substances were used in the preparation of the structural adhesives in the following examples and comparative examples.

[0044] Example 1

[0045] 1. Preparation of closed-cell prepolymers:

[0046] 100g of polyether polyol with a molecular weight of 2000 was added to a flask and heated to 100°C. The mixture was then evacuated to remove water, cooled to 50°C, and 71g of polymeric MDI was added. The mixture was reacted under nitrogen protection, heated to 90°C and stirred continuously for 2.5h. After cooling to 45°C, 56.7g of 2,4-dimethylimidazole was added in a slow release. The mixture was stirred under nitrogen protection for 1.5h to obtain a closed prepolymer.

[0047] 2. Preparation of polyurethane prepolymer:

[0048] 100g of polyether polyol with a molecular weight of 5000 was added to a flask and heated to 100°C. The water was removed by vacuuming and then cooled to 50°C. 21g of polymeric MDI was added and reacted under nitrogen protection. The mixture was heated to 80°C and stirred continuously for 2.5h until the NCO value did not change. The mixture was then cooled to room temperature to obtain polyurethane prepolymer.

[0049] 3. Preparation of two-component polyurethane structural adhesive:

[0050] D1. 38g of closed-cell prepolymer, 6g of polyurethane prepolymer, 16g of low-density polyethylene powder, and 20g of silica powder are mixed at room temperature using a planetary mixer to remove bubbles and obtain component A.

[0051] D2. 10g castor oil, 6g MN-700, 20g URIC H-1823, 1.34g KH-560, 20g low-density polyethylene powder, 2.88g 3A molecular sieve, 15g calcium carbonate powder, and 0.08g T12 were mixed at room temperature using a planetary mixer to remove bubbles and obtain component B.

[0052] Example 2

[0053] 1. Preparation of closed-cell prepolymer: Same as in Example 1, and will not be repeated here;

[0054] 2. Preparation of polyurethane prepolymer: Same as in Example 1, and will not be repeated here;

[0055] 3. Preparation of two-component polyurethane structural adhesive:

[0056] D1. 45.6g of closed-cell prepolymer, 4.8g of polyurethane prepolymer, 16g of low-density polyethylene powder, and 20g of silica powder are mixed at room temperature using a planetary mixer to remove bubbles and obtain component A.

[0057] D2. 10g castor oil, 6g MN-700, 20g URIC H-1823, 1.34g KH-560, 20g low-density polyethylene powder, 2.88g 3A molecular sieve, 15g calcium carbonate powder, and 0.08g T12 were mixed at room temperature using a planetary mixer to remove bubbles and obtain component B.

[0058] Example 3

[0059] 1. Preparation of closed-cell prepolymer: Same as in Example 1, and will not be repeated here;

[0060] 2. Preparation of polyurethane prepolymer: Same as in Example 1, and will not be repeated here;

[0061] 3. Preparation of two-component polyurethane structural adhesive:

[0062] D1. 30.4g of closed-cell prepolymer, 7.2g of polyurethane prepolymer, 16g of low-density polyethylene powder, and 20g of silica powder are mixed at room temperature using a planetary mixer to remove bubbles and obtain component A.

[0063] D2. 10g castor oil, 6g MN-700, 20g URIC H-1823, 1.34g KH-560, 20g low-density polyethylene powder, 2.88g 3A molecular sieve, 15g calcium carbonate powder, and 0.08g T12 were mixed at room temperature using a planetary mixer to remove bubbles and obtain component B.

[0064] Comparative Example 1

[0065] 1. Preparation of closed-cell prepolymer: Same as in Example 1, and will not be repeated here;

[0066] 2. Preparation of polyurethane prepolymer: Same as in Example 1, and will not be repeated here;

[0067] 3. Preparation of two-component polyurethane structural adhesive:

[0068] D1. 30g of closed-cell prepolymer, 7.5g of polyurethane prepolymer, 16g of low-density polyethylene powder, and 20g of silica powder are mixed at room temperature using a planetary mixer to remove bubbles and obtain component A.

[0069] D2. 10g castor oil, 6g MN-700, 20g URIC H-182320g, 1.34g KH-560, 20g low-density polyethylene powder, 2.88g 3A molecular sieve, 15g calcium carbonate powder, and 0.08g T12 were mixed at room temperature using a planetary mixer to remove bubbles and obtain component B.

[0070] Comparative Example 2

[0071] 1. Preparation of closed-cell prepolymer: Same as in Example 1, and will not be repeated here;

[0072] 2. Preparation of polyurethane prepolymer: Same as in Example 1, and will not be repeated here;

[0073] 3. Preparation of two-component polyurethane structural adhesive:

[0074] D1. 46g of closed-cell prepolymer, 4.4g of polyurethane prepolymer, 16g of low-density polyethylene powder, and 20g of silica powder are mixed at room temperature using a planetary mixer to remove bubbles and obtain component A.

[0075] D2. 10g castor oil, 6g MN-700, 20g URIC H-1823, 1.34g KH-560, 20g low-density polyethylene powder, 2.88g 3A molecular sieve, 15g calcium carbonate powder, and 0.08g T12 were mixed at room temperature using a planetary mixer to remove bubbles and obtain component B.

[0076] Comparative Example 3

[0077] 1. Preparation of polyurethane prepolymer:

[0078] 100g of polyether polyol with a molecular weight of 5000 was added to a flask and heated to 100°C. The flask was then evacuated to remove water, and the temperature was lowered to 50°C. 64g of polymeric MDI was added, and the mixture was reacted under nitrogen protection. The mixture was heated to 80°C and stirred continuously for 2.5 hours until the NCO value remained unchanged. The mixture was then cooled to room temperature to obtain polyurethane prepolymer D.

[0079] 2. Preparation of two-component polyurethane structural adhesive:

[0080] D1. Polyurethane prepolymer D44g, low-density polyethylene powder 16g, silica powder 20g, are mixed at room temperature using a planetary mixer to remove bubbles and obtain component A.

[0081] D2. 10g castor oil, 6g MN-700, 20g URIC H-1823, 1.34g silane coupling agent, 20g low-density polyethylene powder, 2.88g water absorbent, 15g calcium carbonate powder, and 0.08g T12 were mixed at room temperature using a planetary mixer to remove bubbles and obtain component B.

[0082] Comparative Example 4

[0083] 1. Preparation of closed-cell prepolymer: Same as in Example 1, and will not be repeated here;

[0084] 2. Preparation of polyurethane prepolymer: Same as in Example 1, and will not be repeated here;

[0085] 3. Preparation of two-component polyurethane structural adhesive:

[0086] D1. 38g of closed-cell prepolymer, 6g of polyurethane prepolymer, 12g of low-density polyethylene powder, and 20g of silica powder are mixed at room temperature using a planetary mixer to remove bubbles and obtain component A.

[0087] D2. 10g castor oil, 6g MN-700, 20g URIC H-1823, 1.34g KH-560, 15g low-density polyethylene powder, 2.88g 3A molecular sieve, 15g calcium carbonate powder, and 0.08g T12 were mixed at room temperature using a planetary mixer to remove bubbles and obtain component B.

[0088] test

[0089] The two-component polyurethane structural adhesives prepared in the examples and comparative examples were subjected to the following performance tests, and the results are shown in Table 1.

[0090] 1. Mechanical testing

[0091] GB / T7124-2008 Determination of tensile shear strength of adhesives

[0092] 2. CPK analysis was conducted through actual workpiece testing, including DV vibration testing and insulation resistance testing.

[0093] The results showed that when the adhesive strength was ≥0.5 MPa, interface material damage occurred on the workpiece surface during disassembly. Therefore, for process considerations, non-destructive disassembly should be performed when the actual requirement is an adhesive strength <0.42 MPa.

[0094] If the bonding strength is greater than 5 MPa, it will pass the DV vibration test.

[0095] Table 1. Comparison of test data between the examples and the comparative examples.

[0096]

[0097] As shown in Table 1, the two-component polyurethane structural adhesive of this invention, through heating, de-encapsulates the closed prepolymer and further cross-links and cures, providing higher adhesive strength and achieving secondary curing; it also gives the product the characteristics of disassembly and repair. Simultaneously, the two-component polyurethane structural adhesive of this invention has higher electrical insulation properties. In Comparative Example 3, without the addition of a closed prepolymer, secondary curing cannot be achieved.

[0098] 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 two-component polyurethane structural adhesive with high insulation and secondary curing properties, characterized in that, Including components A and B, by weight: Component A: Closed-cell prepolymer 30.4-45.6 parts; polyurethane prepolymer 4.8-7.2 parts; low-density polyethylene powder 12.8-19.2 parts; silica powder 16-24 parts; The structural formula of the closed-type prepolymer is shown in Formula 1: Where R is any structure; Component B: Castor oil 8-12 parts; polyether polyol 4.8-7.2 parts; castor oil-modified polyol 16-24 parts; silane coupling agent 1.08-1.61 parts; low-density polyethylene powder 16-24 parts; water absorbent 3.1-4.66 parts; calcium carbonate powder 12-18 parts; catalyst 0.05-0.15 parts; The volume ratio of component A to component B is 1:1; The closed prepolymer is prepared by reacting a polyether polyol with a molecular weight of 2000, polymeric MDI, and a blocking agent 2,4-dimethylimidazole in a mass ratio of 100:(67-75):(53-60); the polyurethane prepolymer is prepared by reacting a polyether polyol with a molecular weight of 5000 and polymeric MDI in a mass ratio of 100:(19-25).

2. The secondary curing high-insulation two-component polyurethane structural adhesive according to claim 1, characterized in that, The method for preparing the closed prepolymer is as follows: a polyether polyol with a molecular weight of 2000 is heated to 100-110°C, vacuumed to remove water, then cooled to 45-55°C, and polymeric MDI is added. The reaction is carried out under nitrogen protection, heated to 85-90°C and stirred continuously for 2-3 hours, then cooled to 40-45°C and 2,4-dimethylimidazole is added slowly. The reaction is carried out under nitrogen protection for 1-3 hours to obtain the closed prepolymer.

3. The secondary curing high-insulation two-component polyurethane structural adhesive according to claim 2, characterized in that, The preparation method of the polyurethane prepolymer is as follows: heat a polyether polyol with a molecular weight of 5000 to 100-110℃, remove water by vacuum, then cool to 45-55℃, add polymeric MDI, react under nitrogen protection, heat to 80-85℃ and stir continuously for 2-3 hours until the NCO value no longer changes, then cool to room temperature to obtain the polyurethane prepolymer.

4. The secondary curing high-insulation two-component polyurethane structural adhesive according to claim 1, characterized in that, The D50 particle size of the low-density polyethylene powder is 25-40 μm.

5. The secondary curing high-insulation two-component polyurethane structural adhesive according to claim 1, characterized in that, The castor oil is castor oil from Ito Chemical Industry Co., Ltd., with a hydroxyl value of 160 mg KOH / g; the castor oil modified polyol is URIC H-1823 from Ito Chemical Industry Co., Ltd., with a hydroxyl value of 100-200 mg KOH / g.

6. The secondary curing high-insulation two-component polyurethane structural adhesive according to claim 1, characterized in that, The polyether polyol is MN-700 from Shandong Lanxing Dongda Chemical Co., Ltd.

7. The secondary curing high-insulation two-component polyurethane structural adhesive according to claim 1, characterized in that, The water absorbent is 3A molecular sieve; the catalyst is organotin catalyst T12; and the silane coupling agent is KH-560.

8. A method for preparing a two-component polyurethane structural adhesive with secondary curing as described in any one of claims 1-7, characterized in that, Includes the following steps: D1. The closed-cell prepolymer, polyurethane prepolymer, low-density polyethylene powder, and silica powder are mixed at a temperature ≤60℃, and component A is obtained by degassing. D2. Castor oil, polyether polyol, castor oil-modified polyol, silane coupling agent, low-density polyethylene powder, water absorbent, calcium carbonate powder and catalyst are mixed at a temperature ≤55℃, and component B is obtained by degassing.

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