Long open time, short dwell time reactive polyurethane hot melt adhesive and preparation method thereof

Abstract

The application relates to a long-open-time and short-pressure-maintenance-time reactive polyurethane hot melt adhesive and a preparation method thereof, and belongs to the technical field of reactive polyurethane hot melt adhesives. The adhesive comprises the following components in parts by weight: liquid polyol 10-25 parts, crystalline polyol 10-25 parts, hydroxyl-terminated liquid polybutadiene resin containing SIS 15-25 parts, tackifying resin 2-5 parts, isocyanate 10-20 parts and catalyst 0.2-0.5 parts. The adhesive has long open time, good wettability after 5 minutes of hot melt adhesive application and pressure bonding, the bonding strength after 3 minutes of hot melt adhesive application is higher than 0.5 MPa, short pressure maintenance time can be realized, and the demand of large-size products for open time of about 5 minutes is met.

Description

Technical Field

[0001] This invention relates to a reactive polyurethane hot melt adhesive with a long open time and a short holding time, and its preparation method, belonging to the technical field of reactive polyurethane hot melt adhesives. Background Technology

[0002] Currently, in the production line process of hot melt adhesive encapsulation, rapid positioning is commonly used for positioning and encapsulation, resulting in low production efficiency. Furthermore, the open time of traditional rapid positioning hot melt adhesives is relatively short, typically around 2 minutes, which cannot meet the requirement of approximately 5 minutes for large-size products. Therefore, developing a reactive polyurethane hot melt adhesive with a long open time and short holding time, along with its preparation method, has become an urgent problem to be solved in this field. Summary of the Invention

[0003] To address the shortcomings of the prior art, this invention provides a reactive polyurethane hot melt adhesive with a long open time and a short holding time, and a method for preparing the same.

[0004] The technical solution of the present invention to solve the above-mentioned technical problems is as follows: A reactive polyurethane hot melt adhesive with a long open time and a short holding time is characterized by comprising, by weight, the following components: 10-25 parts of liquid polyol, 10-25 parts of crystalline polyol, 15-25 parts of hydroxyl-terminated liquid polybutadiene resin containing SIS, 2-5 parts of tackifying resin, 10-20 parts of isocyanate, and 0.2-0.5 parts of catalyst.

[0005] The synthesis method of the hydroxyl-terminated liquid polybutadiene resin containing SIS is as follows: Hydroxyl-terminated liquid polybutadiene and SIS are added to a reaction vessel, heated to 130°C for 2 hours under nitrogen protection, cooled to 85°C, BPO is added under nitrogen protection, the reaction is carried out for 4 hours, and the product is discharged and sealed for storage when cooled to 50°C.

[0006] Furthermore, the SIS-containing hydroxyl-terminated liquid polybutadiene resin has the following characteristics:

[0007] Where x, y, and z are the mole fractions of the structural units in the formula, x is 5-20 mol%, y is 50-80 mol%, z is 5%-20%, and (m+p):n is 2:8-6:4.

[0008] Furthermore, the liquid polyol is an aromatic polyester polyol with a molecular weight of 1000-3000.

[0009] Furthermore, the crystalline polyol is one or both of hexanediol adipate and hexanediol sebacate with a molecular weight of 2000-5000.

[0010] Furthermore, the tackifying resin is hydrogenated C5 petroleum resin.

[0011] Furthermore, the isocyanate is diphenylmethane-4,4'-diisocyanate (MDI).

[0012] Furthermore, the catalyst is organozinc and bismorpholine diethyl ether.

[0013] A method for preparing a reactive polyurethane hot melt adhesive with a long open time and a short holding time, comprising the following steps: Step 1: Add liquid polyol, crystalline polyol, and hydroxyl-terminated liquid polybutadiene resin containing SIS to the reaction vessel, heat until the crystalline polyol dissolves, and then start stirring. Step 2: Add tackifying resin, start vacuuming when the temperature reaches 120℃, maintain for 60 minutes, then cool down to 80℃; Step 3: Add isocyanate under nitrogen protection, heat to 120°C, and react for 1 hour under a vacuum below -0.09 MPa; Step 4: Add the catalyst under nitrogen protection and continue stirring at 120°C and a vacuum of less than -0.09 MPa for 30 minutes; Step 5: Discharge the material under nitrogen protection; The vacuum level in step two is below -0.09 MPa.

[0014] The beneficial effects of the invention are: it has a long open time, and the bonding still has good wettability after 5 minutes of pressing after application of adhesive; the bonding strength is higher than 0.5MPa after 3 minutes of application of adhesive, and a short holding time can be achieved, which meets the requirement of large-size products for an open time of about 5 minutes. Detailed Implementation

[0015] The principles and features of the present invention are described below. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0016] A reactive polyurethane hot melt adhesive with a long open time and a short holding time, comprising the following components by weight: 10-25 parts liquid polyol, 10-25 parts crystalline polyol, 15-25 parts hydroxyl-terminated liquid polybutadiene resin containing SIS, 2-5 parts tackifying resin, 10-20 parts isocyanate, and 0.2-0.5 parts catalyst.

[0017] The synthesis method of the hydroxyl-terminated liquid polybutadiene resin containing SIS is as follows: Hydroxyl-terminated liquid polybutadiene and SIS are added to a reaction vessel, heated to 130°C for 2 hours under nitrogen protection, cooled to 85°C, BPO is added under nitrogen protection, the reaction is carried out for 4 hours, and the product is discharged and sealed for storage when cooled to 50°C.

[0018] The hydroxyl-terminated liquid polybutadiene resin containing SIS has the following characteristics:

[0019] Where x, y, and z are the mole fractions of the structural units in the formula, x is 5-20 mol%, y is 50-80 mol%, z is 5%-20%, and (m+p):n is 2:8-6:4.

[0020] The beneficial effects of adopting the above-mentioned further scheme are as follows: the hydroxyl-terminated liquid polybutadiene resin containing SIS, when added to the formulation of reactive polyurethane hot melt adhesive, the large presence of SIS improves the adhesive strength of the system in the first 3 minutes and prolongs the open time. Due to the methyl side chain characteristics of the SIS mesoblock polyisoprene structure, it has good cohesive force and excellent adhesive properties, as well as good compatibility with other additives.

[0021] The liquid polyol is an aromatic polyester polyol with a molecular weight of 1000-3000.

[0022] The beneficial effects of adopting the above-mentioned further scheme are: since SIS contains a benzene ring structure, according to the principle of similar compatibility, liquid polyols containing cyclic structures are selected to increase compatibility, and they are liquid with low viscosity and long open time.

[0023] The crystalline polyol is one or both of hexanediol adipate and hexanediol sebacic acid diol with a molecular weight of 2000-5000.

[0024] The beneficial effects of adopting the above-mentioned further solution are: the presence of crystalline polyols shortens the holding time of the system, and crystallization improves the density of the system after curing, thereby enhancing the final bonding strength of the product.

[0025] The tackifying resin is hydrogenated C5 petroleum resin.

[0026] The beneficial effects of adopting the above-mentioned further solutions are: improved adhesion to a variety of substrates and extended open time.

[0027] The isocyanate is diphenylmethane-4,4'-diisocyanate (MDI).

[0028] The beneficial effects of adopting the above-mentioned further scheme are: the diphenylmethane-4,4'-diisocyanate has a symmetrical structure, uniform curing, is not prone to foaming, has a high benzene ring content, and a high crosslinking density, thus resulting in high hardness and high strength.

[0029] The catalyst is organozinc and bismorpholine diethyl ether.

[0030] The beneficial effect of adopting the above-mentioned further scheme is that the combined use of organic zinc and amine catalysts increases the reaction rate of isocyanate groups with moisture in the system.

[0031] A method for preparing a reactive polyurethane hot melt adhesive with a long open time and a short holding time, comprising the following steps: Step 1: Add liquid polyol, crystalline polyol, and hydroxyl-terminated liquid polybutadiene resin containing SIS to the reaction vessel, heat until the crystalline polyol dissolves, and then start stirring. Step 2: Add tackifying resin, start vacuuming when the temperature reaches 120℃, maintain for 60 minutes, then cool down to 80℃; Step 3: Add isocyanate under nitrogen protection, heat to 120°C, and react for 1 hour under a vacuum below -0.09 MPa; Step 4: Add the catalyst under nitrogen protection and continue stirring at 120°C and a vacuum of less than -0.09 MPa for 30 minutes; Step 5: Discharge the material under nitrogen protection; The vacuum level in step two is below -0.09 MPa.

[0032] The mechanism by which the reactive polyurethane hot melt adhesive of the present invention achieves a long open time and a short holding time is as follows: SIS hot melt pressure-sensitive resin and hydroxyl-terminated liquid polybutadiene resin are used as composite modifiers, and the two work synergistically. The hydroxyl-terminated liquid polybutadiene resin, with its special molecular functional structure, has active functional groups whose double bonds can undergo polymerization and grafting reactions with the SIS hot melt pressure-sensitive resin, improving SIS compatibility and effectively enhancing the hot melt pressure sensitivity of the hot melt adhesive, thereby achieving the functions of a long open time and a short holding time. The hydroxyl groups participate in the reaction with isocyanate to generate a strong, dense, three-dimensional macromolecule, thus obtaining the final high strength. Example

[0033] Add 10 parts of liquid polyol, 25 parts of crystalline polyol, and 15 parts of hydroxyl-terminated liquid polybutadiene resin containing SIS to the reaction vessel. Heat until the crystalline polyol dissolves, then start stirring. Add 5 parts of hydrogenated C5 petroleum resin as a thickening resin. When the temperature reaches 120°C, start vacuuming, maintaining a vacuum level below -0.09 MPa for 1 hour. Cool down to 80°C, and add 10 parts of diphenylmethane-4,4'-diisocyanate under nitrogen protection. Heat to 120°C and react for 1 hour under a vacuum level below -0.09 MPa. Then, add 0.02 parts of organic zinc catalyst and 0.2 parts of bismorpholine diethyl ether under nitrogen protection. Continue stirring at 120°C and a vacuum level below -0.09 MPa for 30 minutes, and then discharge under nitrogen protection. Example

[0034] Add 25 parts of liquid polyol, 10 parts of crystalline polyol, and 25 parts of hydroxyl-terminated liquid polybutadiene resin containing SIS to the reaction vessel. Heat until the crystalline polyol dissolves and then start stirring. Add 2 parts of hydrogenated C5 petroleum resin as a thickening resin. When the temperature reaches 120℃, start evacuating the vacuum to a level below -0.09MPa and maintain this vacuum for 1 hour. Cool down to 80℃ and add 20 parts of diphenylmethane-4,4'-diisocyanate under nitrogen protection. Heat to 120℃ and react for 1 hour under a vacuum below -0.09MPa. Then, add 0.04 parts of organic zinc catalyst and 0.5 parts of bismorpholine diethyl ether under nitrogen protection. Continue stirring at 120℃ and a vacuum below -0.09MPa for 30 minutes. Finally, discharge the product under nitrogen protection. Example

[0035] Add 17.5 parts of liquid polyol, 17.5 parts of crystalline polyol, and 20 parts of hydroxyl-terminated liquid polybutadiene resin containing SIS to the reaction vessel. Heat until the crystalline polyol dissolves, then start stirring. Add 3.5 parts of hydrogenated C5 petroleum resin as a thickening resin. When the temperature reaches 120°C, start vacuuming, maintaining a vacuum level below -0.09 MPa for 1 hour. Cool down to 80°C, and add 15 parts of diphenylmethane-4,4'-diisocyanate under nitrogen protection. Heat to 120°C and react for 1 hour under a vacuum level below -0.09 MPa. Then, add 0.03 parts of organic zinc catalyst and 0.35 parts of bismorpholine diethyl ether under nitrogen protection. Continue stirring at 120°C and a vacuum level below -0.09 MPa for 30 minutes, and then discharge under nitrogen protection.

[0036] Comparative Example 1 Add 10 parts of liquid polyol and 40 parts of crystalline polyol to the reaction vessel. Heat until the crystalline polyol dissolves and then start stirring. Add 5 parts of hydrogenated C5 petroleum resin as a thickening resin. When the temperature reaches 120℃, start evacuating the vacuum to a level below -0.09MPa and maintain this vacuum for 1 hour. Cool down to 80℃ and add 10 parts of diphenylmethane-4,4'-diisocyanate under nitrogen protection. Heat to 120℃ and react for 1 hour under a vacuum below -0.09MPa. Then, add 0.02 parts of organic zinc catalyst and 0.2 parts of bismorpholine diethyl ether under nitrogen protection. Continue stirring at 120℃ and a vacuum below -0.09MPa for 30 minutes. Finally, discharge the product under nitrogen protection.

[0037] Testing: The reactive polyurethane hot melt adhesives generated in Examples 1-3 and Comparative Example 1 were tested. Test 1: Opening Hours The reactive polyurethane hot melt adhesives of Examples 1-3 and Comparative Example 1 were placed in the sleeve of a dispensing machine and heated to 110°C. Adhesive lines were applied to the PC sheet with a width of 1 mm. Paper strips were pressed into the adhesive strips at regular intervals. The paper strips were removed after the adhesive strips were no longer bonded. The open time was calculated based on the time without fiber tearing.

[0038] Test 2: 3-minute shear strength The reactive polyurethane hot melt adhesives of Examples 1-3 and Comparative Example 1 were placed in the sleeve of a dispensing machine and heated to 110°C. The dispensing lines were pressed together on a PC sheet used for shear strength testing, with an adhesive layer thickness of 0.1 mm. Then, a 3 kg weight was used to press them together for 1 minute. After standing for 2 minutes, the shear strength was tested according to the test method of GB-T 7124-2008.

[0039] Test 3: Final Shear Strength The reactive polyurethane hot melt adhesives of Examples 1-3 and Comparative Example 1 were placed in the sleeve of a dispensing machine and heated to 110°C. The adhesive lines were then pressed together on a PC sheet used for shear strength testing, with an adhesive layer thickness of 0.1 mm. A 3 kg weight was then used to press them together for 1 minute. After 2 minutes, the sheets were placed under standard conditions (25°C, 50% RH) for curing for 7 days, followed by shear strength testing according to GB-T 7124-2008.

[0040] The test results are shown in Table 1: Table 1 Test Results of Reactive Polyurethane Hot Melt Adhesive Opening hours (min) 6.1 4.8 5.0 1.5 3-minute shear strength (PC / PC MPa) 0.55 0.64 0.60 0.2 Final shear strength (PC / PC MPa) 12.54 11.86 12.23 9.65 As can be clearly seen from Table 1, the open time of Examples 1, 2, and 3 is longer than that of Comparative Example 1, all exceeding 4.8 minutes, while the open time of Comparative Example 1 is only 1.5 minutes. The shear strength at 3 minutes is greater than 0.55, while the strength of Comparative Example 1 is only 0.2. Therefore, Examples 1 and 3 have a long open time, good wettability after 5 minutes of adhesive application, and an adhesive strength of over 0.5 MPa after 3 minutes of adhesive application. This allows for a short holding time and meets the requirement of an open time of about 5 minutes for large-size products.

[0041] 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 reactive polyurethane hot melt adhesive with a long open time and a short holding time, characterized in that: The raw materials, by weight, include the following components: 10-25 parts liquid polyol, 10-25 parts crystalline polyol, 15-25 parts SIS-containing hydroxyl-terminated liquid polybutadiene resin, 2-5 parts tackifying resin, 10-20 parts isocyanate, and 0.2-0.5 parts catalyst. The hydroxyl-terminated liquid polybutadiene resin containing SIS has the following characteristics: ； Where x, y, and z are the mole fractions of the structural units in the formula, x is 5-20 mol%, y is 50-80 mol%, z = 5%-20%, and (m+p):n = 2:8~6:4; The liquid polyol is an aromatic polyester polyol with a molecular weight of 1000-3000; The crystalline polyol is one or both of hexanediol adipate and hexanediol sebacic acid diol with a molecular weight of 2000-5000.

2. The reactive polyurethane hot melt adhesive with long open time and short holding time according to claim 1, characterized in that: The synthesis method of the hydroxyl-terminated liquid polybutadiene resin containing SIS is as follows: Hydroxyl-terminated liquid polybutadiene and SIS are added to a reaction vessel, heated to 130°C for 2 hours under nitrogen protection, cooled to 85°C, BPO is added under nitrogen protection, the reaction is carried out for 4 hours, and the product is discharged and sealed for storage when cooled to 50°C.

3. The reactive polyurethane hot melt adhesive with long open time and short holding time according to claim 1, characterized in that: The tackifying resin is hydrogenated C5 petroleum resin.

4. The reactive polyurethane hot melt adhesive with long open time and short holding time according to claim 1, characterized in that: The isocyanate is diphenylmethane-4,4'-diisocyanate (MDI).

5. The reactive polyurethane hot melt adhesive with long open time and short holding time according to claim 1, characterized in that: The catalyst is organozinc and bismorpholine diethyl ether.

6. The method for preparing a reactive polyurethane hot melt adhesive with a long open time and short holding time according to claim 1, characterized in that: The steps include: Step 1: Add liquid polyol, crystalline polyol, and hydroxyl-terminated liquid polybutadiene resin containing SIS to the reaction vessel, heat until the crystalline polyol dissolves, and then start stirring. Step 2: Add tackifying resin, start vacuuming when the temperature reaches 120℃, maintain for 60 minutes, then cool down to 80℃; Step 3: Add isocyanate under nitrogen protection, heat to 120°C, and react for 1 hour under a vacuum below -0.09 MPa; Step 4: Add the catalyst under nitrogen protection and continue stirring at 120°C and a vacuum of less than -0.09 MPa for 30 minutes; Step 5: Discharge the material under nitrogen protection.

7. The method for preparing a reactive polyurethane hot melt adhesive with a long open time and short holding time according to claim 6, characterized in that: The vacuum level in step two is below -0.09 MPa.

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