Preparation method of low modulus polyurethane hot melt adhesive for electronic screen bonding

Abstract

This invention relates to the field of polyurethane adhesive preparation technology, and discloses a method for preparing a low-modulus polyurethane hot melt adhesive for bonding electronic screens. The method includes: heating and mixing bifunctional hydroxyl-terminated polybutadiene and polyether polyol uniformly, then adding diisocyanate to react and prepare an isocyanate-terminated prepolymer A containing a long-chain polyolefin structure; heating and mixing polyester polyol and polytetrahydrofuran diol uniformly, then adding diisocyanate to react and synthesize an isocyanate-terminated prepolymer B; and mixing prepolymer A and prepolymer B uniformly in a certain proportion to prepare a reactive polyurethane hot melt adhesive for bonding electronic screen structures. Because the reactive polyurethane hot melt adhesive prepared by this invention contains a long-chain polyolefin structure, the cured adhesive has a low modulus and good flexibility, exhibiting excellent bonding performance for bonding electronic screens.

Description

Technical Field

[0001] This invention relates to the field of polyurethane adhesive preparation technology, specifically a method for preparing a low-modulus polyurethane hot melt adhesive for bonding electronic screens. Background Technology

[0002] Reactive polyurethane hot melt adhesive (PUR) is a 100% solids-content, environmentally friendly adhesive with excellent bonding strength to a variety of substrates. It initially generates tack through temperature changes from high to room temperature and the crystallization of some molecular segments. Later, it undergoes a chemical cross-linking reaction with moisture in the air and on the material surface to achieve higher bonding strength. It is gaining an increasingly large share in the adhesive industry. In the electronics, automotive, and home appliance industries, polyurethane hot melt adhesives are gradually replacing traditional double-sided tapes, solvent-based adhesives, and processes such as welding and screw fixing for assembling parts, significantly improving manufacturers' production efficiency and product reliability.

[0003] With the rapid pace of updates and iterations in consumer products such as 3C electronics and automobiles, the development of related electronic displays is also accelerating. PUR (Polyurethane Adhesive) is gradually replacing traditional tape and clip-on processes as a new technology for assembling screen components due to its advantages such as simple and efficient dispensing process and high bonding strength after curing. At the same time, the market's requirements for screen bonding are becoming increasingly stringent, such as withstanding 168 hours of dual 85 testing, high and low temperature impact testing (-40℃~80℃), roller testing, and higher requirements for waterproofing and dustproofing. Currently, most PUR on the market suffers from drawbacks such as high glue line modulus, high hardness, and poor elasticity after moisture curing, which easily leads to problems such as glue separation, decreased airtightness, and abnormal screen display during high and low temperature impact testing and roller testing. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing a low-modulus polyurethane hot melt adhesive for bonding electronic screens, so as to solve the problems mentioned in the background art.

[0005] To achieve the above objectives, the present invention provides a method for preparing a low-modulus polyurethane hot melt adhesive for bonding electronic screens, the method comprising:

[0006] (1) Add bifunctional hydroxyl-terminated polybutadiene and polyether polyol to a reactor at a temperature of 100-120℃, stir until the materials are mixed evenly, remove water under vacuum for 1-2 hours, cool to 90-110℃, add diisocyanate and react for 1-2 hours, and discharge to obtain isocyanate-terminated prepolymer A.

[0007] (2) Add polyester polyol and polytetrahydrofuran diol to a reactor at a temperature of 100-120℃, stir until the materials are evenly mixed, remove water under vacuum for 1-2 hours, cool down to 90-110℃, add diisocyanate and react for 1-2 hours, and discharge to obtain isocyanate-terminated prepolymer B.

[0008] (3) Add the prepolymer A and prepolymer B in a certain proportion in a reactor at a temperature of 100-120℃, stir for 15-30 minutes and then discharge the material to obtain a low-modulus, high-bonding-strength reactive polyurethane hot melt adhesive for bonding electronic screen structures.

[0009] Furthermore, by mass percentage, the percentage of each substance added in step (1) to the total mass of the mixture is as follows:

[0010] The content of difunctional hydroxyl-terminated polybutadiene is 30.0-45.0%; the content of polyether polyol is 30.0-45.0%; the content of diisocyanate is 10.0-30.0%; and the content of catalyst is 0.0-1.0%.

[0011] The total mass percentage of the added difunctional hydroxyl-terminated polybutadiene, polyether polyol, diisocyanate, and catalyst is 100%.

[0012] Furthermore, by mass percentage, the percentage of each substance added in step (2) to prepare isocyanate-terminated prepolymer B relative to the total mass of the mixture is as follows:

[0013] Polyester polyol: 30.0-40.0%; Polytetrahydrofuran diol: 30.0-45.0%; Diisocyanate: 20.0-35.0%; Catalyst: 0.0-1.0%;

[0014] The total mass percentage of the added polyester polyol, polytetrahydrofuran diol, diisocyanate and catalyst is 100%.

[0015] Furthermore, in step (3), the ratio of prepolymer A to prepolymer B in preparing the polyurethane hot melt adhesive is 40 / 60-60 / 40.

[0016] Furthermore, the structure of the difunctional polybutadiene described in step (1) is as follows:

[0017]

[0018] The molecular weight is 1000-3000, wherein structure a accounts for 30-50% of the molecular chain and structure b accounts for 50-70% of the molecular chain. The polyether polyol mentioned in step (1) is one or more of polypropylene glycol ether diol and polyethylene glycol ether diol, with a molecular weight of 1000-4000; the diisocyanate mentioned in steps (1) and (2) is one or more of a mixture of 4,4'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate and 4,4'-diphenylmethane diisocyanate; and the catalyst mentioned in steps (1) and (2) is bismorpholino diethyl ether.

[0019] Furthermore, the polyester polyol mentioned in step (2) is one or more of polybutylene adipate diol, polyhexane adipate diol PHA, polyhexane sebacate diol, polyneoprene adipate diol, and polydiethylene adipate diol, and the molecular weight of the polytetrahydrofuran diol mentioned in step (2) is 1000-3000.

[0020] Furthermore, the prepared polyurethane hot melt adhesive contains the following structure:

[0021]

[0022] Among them, a accounts for 30-50%, and b accounts for 50-70%.

[0023] Compared with the prior art, the beneficial effects of the present invention are:

[0024] This invention utilizes a compound of difunctional hydroxyl-terminated polybutadiene (HTPB) and polyether polyol to prepare prepolymer A. By leveraging the compliant carbon-carbon double bond backbone structure of the HTPB molecular chain, the in-segment cohesive energy and crosslinking density of the polyurethane molecular chain are significantly reduced, resulting in a hot melt adhesive with a low elastic modulus after moisture curing. Simultaneously, through the synergistic effect of the polyester polyol and polytetrahydrofuran diol in prepolymer B, the microphase separation structure of the system is effectively controlled while ensuring good adhesive strength, avoiding stress concentration problems caused by excessively high modulus after adhesive layer curing. Therefore, the polyurethane hot melt adhesive prepared by this invention can effectively absorb and buffer the thermal and mechanical stresses generated by electronic screens during harsh tests such as high and low temperature impacts and roller drops, effectively avoiding problems such as adhesive layer delamination, decreased airtightness, and abnormal screen display, significantly improving the long-term reliability and finished product yield of electronic screen components.

[0025] This invention employs a dual prepolymer blend design. HTPB and polyether polyol in prepolymer A impart excellent flexibility and low-temperature flexibility to the colloid, while crystalline polyester polyol and polytetrahydrofuran diol in prepolymer B provide strong cohesive strength and adhesion to polar substrates. When blended in a specific ratio, the hot melt adhesive rapidly forms initial physical crystalline tack during application and cooling, and then forms a chemical cross-linking network after moisture curing, giving the colloid high-strength adhesion to various commonly used electronic screen substrates such as glass, metal, PC, and PET. Simultaneously, the cured colloid possesses both moderate flexibility and cohesive strength, effectively resolving the technical contradiction of traditional PUR adhesives, which suffer from excessively high modulus and cannot simultaneously achieve both adhesive strength and impact resistance.

[0026] This invention effectively reduces the excessive sensitivity of the adhesive layer to moisture and its tendency to hydrolytic degradation through the non-polar hydrophobic backbone structure of HTPB. Simultaneously, the synergistic crosslinking structure of the dual prepolymer system exhibits good stability in humid and hot environments. The prepared hot melt adhesive can meet the stringent requirements of the dual 85 test (85℃ / 85%RH) for 168 hours and the high and low temperature shock cycle test from -40℃ to 80℃. After long-term aging, it maintains high bond strength, with no cracking or peeling of the adhesive layer, and its airtightness remains consistently stable, fully meeting the high standards of bonding reliability required by current 3C electronics and automotive displays. Attached Figure Description

[0027] Figure 1 This diagram illustrates the working steps of a method for preparing a low-modulus polyurethane hot melt adhesive for bonding electronic screens according to the present invention. Detailed Implementation

[0028] The present invention will be further described in detail below with reference to specific embodiments and comparative examples, in order to more clearly illustrate the technical solution, technical effect and protection scope of the present invention, rather than to limit the present invention. Experimental methods in this embodiment that do not specify specific conditions are generally carried out under conventional conditions or conditions recommended by the manufacturer; reagents, materials, etc., used, unless otherwise specified, are all conventional products that can be obtained through commercial channels.

[0029] The present invention will be further illustrated by the following examples, but the implementation of the present invention is not limited thereto.

[0030] In the following examples, the purity of the organic diisocyanate is above 99%, and the water content of the hydroxyl-terminated polybutadiene, polyether polyol, polyester polyol, polytetrahydrofuran diol and catalyst is required to be below 400 ppm.

[0031] The basic properties of the polyurethane hot melt adhesive in this invention were characterized using the following test methods.

[0032] Viscosity determination: The high-temperature viscosity of polyurethane hot melt adhesive was determined at 110℃ using a NDJ-1C rotational viscometer from Shanghai Changji Geological Instrument Co., Ltd., with a 27# rotor at 20 rpm.

[0033] Elastic modulus test: After melting the polyurethane hot melt adhesive at 110℃, it was placed in a polytetrafluoroethylene mold (standard dumbbell type, thickness 2mm, length 25mm, width 6mm) and cured for 48h. The tensile force and deformation data of the adhesive were tested using an electronic universal testing machine with a large deformation extensometer at a test speed of 500mm / min. The modulus data corresponding to 100% deformation was calculated. The average value of 5 sets of test data was taken.

[0034] Shear strength test: Polyurethane hot melt adhesive was evenly applied to the surfaces of two substrates (PC + ink glass containing 20% ​​glass fiber, with dimensions of 150mm×25mm×2mm) using a piezoelectric spray valve dispensing machine. The area of ​​the bonding zone was controlled to be 4mm×25mm and the adhesive layer thickness was 0.5mm. After pressure holding for 48 hours, the final shear strength was measured by an electronic universal testing machine (GC-WS-1000S). Five groups of samples were tested under each test condition, and the average value of the data was taken.

[0035] Bonding the phone frame and screen assembly: Apply PUR to the bonding area of ​​the phone screen frame using a piezoelectric spray valve dispensing machine, then cover with the screen panel, apply pressure for 48 hours using a special pressure-holding device, and then remove the pressure-holding device.

[0036] Double 85 test: The glued mobile phone screen and the shear test sample were placed in a constant temperature and humidity test chamber at 85℃ and 85% humidity for 168 hours. Then the test sample was taken out to test the shear strength and the glue separation of the glued parts of the mobile phone was examined with an electron microscope.

[0037] High and low temperature impact test: The bonded mobile phone screen and shear test sample were placed in a test chamber with a temperature range of -40℃ to 80℃, a temperature change rate of 10℃ / min, and a high and low temperature residence time of 30min for 168h. Then the test sample was taken out to test the shear strength and the bonding delamination of the bonded parts was examined with an electron microscope.

[0038] Roller test: The glued mobile phone screen and the shear test sample were placed in a roller with a diameter of 500mm and a rotation speed of 5r / min and dropped 100 times. Then the test sample was removed to test the shear strength and the glue separation of the glued parts was examined with an electron microscope.

[0039] Example 1

[0040] Preparation of prepolymer A1: Hydroxyl-terminated polybutadiene and polyether polyol were added to a glass reactor equipped with stirring and temperature monitoring and heated to 110°C. While stirring, water was removed under vacuum for 2 hours (vacuum degree ≤0.095MPa). Then, the temperature was lowered to 100°C, diisocyanate was added, and the reaction was maintained at 100°C for 1.5 hours. After that, the catalyst was added, and the reaction was continued for another 0.5 hours before the product was discharged. The specific amounts of each raw material are shown in Table 1.

[0041] Preparation of prepolymer B1: Polyester polyol and polytetrahydrofuran diol were added to a glass reactor equipped with stirring and temperature monitoring and heated to 120°C. While stirring, water was removed under vacuum for 2 hours (vacuum degree ≤0.095MPa). Then, the temperature was lowered to 100°C and diisocyanate was added. The reaction was maintained at 100°C for 1.5 hours. After that, the catalyst was added and the reaction was continued for another 0.5 hours before the product was discharged. The specific amounts of each raw material are shown in Table 1.

[0042] Preparation of polyurethane hot melt adhesive PUR1: Add 200g of prepolymer A1 and 300g of prepolymer B1 (A:B=40:60) to a reactor equipped with stirring and temperature monitoring, heat to 110℃ and stir for 20min, then discharge to obtain low modulus and high bonding strength reactive polyurethane hot melt adhesive PUR1 for bonding electronic screen structures.

[0043] Table 1: Raw Material Requirement List for Example 1

[0044]

[0045] Example 2

[0046] Preparation of polyurethane hot melt adhesive PUR2: Add 250g of prepolymer A1 and 250g of prepolymer B1 (A:B=50:50) to a reactor equipped with stirring and temperature monitoring, heat to 110℃ and stir for 20min, then discharge to obtain low modulus and high bonding strength reactive polyurethane hot melt adhesive PUR2 for bonding electronic screen structures.

[0047] Example 3

[0048] Preparation of polyurethane hot melt adhesive PUR3: Add 300g of prepolymer A1 and 200g of prepolymer B1 (A:B=40:60) to a reactor equipped with stirring and temperature monitoring, heat to 110℃ and stir for 20min, then discharge to obtain low modulus and high bonding strength reactive polyurethane hot melt adhesive PUR3 for bonding electronic screen structures.

[0049] Example 4

[0050] Preparation of prepolymer A4: Hydroxyl-terminated polybutadiene and polyether polyol were added to a glass reactor equipped with stirring and temperature monitoring and heated to 110°C. While stirring, water was removed under vacuum for 2 hours (vacuum degree ≤ 0.095 MPa). Then, the temperature was lowered to 100°C and diisocyanate was added. The reaction was maintained at 100°C for 1.5 hours. After that, the catalyst was added and the reaction was continued for another 0.5 hours before the product was discharged. The specific amounts of each raw material are shown in Table 1.

[0051] Preparation of prepolymer B4: Polyester polyol and polytetrahydrofuran diol were added to a glass reactor equipped with stirring and temperature monitoring and heated to 120°C. While stirring, water was removed under vacuum for 2 hours (vacuum degree ≤ 0.095 MPa). Then, the temperature was lowered to 100°C and diisocyanate was added. The reaction was maintained at 100°C for 1.5 hours. After that, the catalyst was added and the reaction was continued for another 0.5 hours before the product was discharged. The specific amounts of each raw material are shown in Table 2.

[0052] Preparation of polyurethane hot melt adhesive PUR4: Add 200g of prepolymer A4 and 300g of prepolymer B4 (A:B=40:60) to a reactor equipped with stirring and temperature monitoring. After heating to 110℃ and stirring evenly, the low-modulus, high-bonding-strength reactive polyurethane hot melt adhesive PUR4 for bonding electronic screen structures can be obtained.

[0053] Table 2: Raw Material Requirement Table for Example 4

[0054]

[0055] Example 5

[0056] Preparation of polyurethane hot melt adhesive PUR5: Add 250g of prepolymer A4 and 250g of prepolymer B4 (A:B=50:50) to a reactor equipped with stirring and temperature monitoring, heat to 110℃ and stir evenly before discharging to obtain low modulus and high bonding strength reactive polyurethane hot melt adhesive PUR5 for bonding electronic screen structures.

[0057] Example 6

[0058] Preparation of polyurethane hot melt adhesive PUR6: Add 300g of prepolymer A4 and 200g of prepolymer B4 (A:B=60:40) to a reactor equipped with stirring and temperature monitoring. After heating to 110℃ and stirring evenly, the low-modulus, high-bonding-strength reactive polyurethane hot melt adhesive PUR6 for bonding electronic screen structures can be obtained.

[0059] Comparative Example 1

[0060] Preparation of prepolymer A7: Polyether polyol was added to a glass reactor equipped with stirring and temperature monitoring and heated to 110°C. While stirring, water was removed under vacuum for 2 hours (vacuum degree ≤ 0.095 MPa). Then, the temperature was lowered to 100°C and diisocyanate was added. The reaction was maintained at 100°C for 1.5 hours. After that, the catalyst was added and the reaction was continued for another 0.5 hours before the product was discharged. The specific amounts of each raw material are shown in Table 3.

[0061] Preparation of prepolymer B4: Polyester polyol and polytetrahydrofuran diol were added to a glass reactor equipped with stirring and temperature monitoring and heated to 120°C. While stirring, water was removed under vacuum for 2 hours (vacuum degree ≤0.095MPa). Then, the temperature was lowered to 100°C and diisocyanate was added. The reaction was maintained at 100°C for 1.5 hours. After that, the catalyst was added and the reaction was continued for another 0.5 hours before the product was discharged. The specific amounts of each raw material are shown in Table 3.

[0062] Preparation of polyurethane hot melt adhesive PUR7: Add 250g of prepolymer A7 and 250g of prepolymer B7 (A:B=40:60) to a reactor equipped with stirring and temperature monitoring, heat to 110℃ and stir evenly to obtain low modulus and high bonding strength reactive polyurethane hot melt adhesive PUR7 for bonding electronic screen structures.

[0063] Table 3: Raw Material Consumption Table for Comparative Example 1

[0064]

[0065] The basic properties of polyurethane hot melt adhesive and the shear strength test results of the test samples are shown in Table 4. As can be seen from the data in the table, polyurethane containing long-chain polybutadiene structure has a low modulus and strong adhesive strength after hot melt curing. The test samples can still maintain high adhesive strength after undergoing double 85 test, high and low temperature impact test and roller test.

[0066] Table 4: Basic properties of polyurethane hot melt adhesive and test results of shear strength of test specimens

[0067]

[0068] The test results of bonding mobile phone screens with polyurethane hot melt adhesive are shown in Table 5. As can be seen from the data in the table, the screen samples bonded with polyurethane hot melt adhesive containing long-chain polybutadiene structure can still maintain excellent bonding performance after undergoing double 85 test, high and low temperature impact test and roller test. Moreover, the higher the content of long-chain polybutadiene segments, the better the bonding effect.

[0069] Table 5: Test Results of Polyurethane Hot Melt Adhesive Bonding to Mobile Phone Screens

[0070]

[0071] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a low-modulus polyurethane hot melt adhesive for bonding electronic screens, characterized in that, Includes the following steps: (1) Add bifunctional hydroxyl-terminated polybutadiene and polyether polyol to a reactor at a temperature of 100-120℃, stir until the materials are mixed evenly, remove water under vacuum for 1-2 hours, cool to 90-110℃, add diisocyanate and react for 1-2 hours, and discharge to obtain isocyanate-terminated prepolymer A. (2) Add polyester polyol and polytetrahydrofuran diol to a reactor at a temperature of 100-120℃, stir until the materials are evenly mixed, remove water under vacuum for 1-2 hours, cool down to 90-110℃, add diisocyanate and react for 1-2 hours, and discharge to obtain isocyanate-terminated prepolymer B. (3) Add the prepolymer A and prepolymer B in a certain proportion in a reactor at a temperature of 100-120℃, stir for 15-30 minutes and then discharge the material to obtain a low-modulus, high-bonding-strength reactive polyurethane hot melt adhesive for bonding electronic screen structures.

2. The method for preparing a low-modulus polyurethane hot melt adhesive for bonding electronic screens according to claim 1, characterized in that, The percentage by mass of each substance added in step (1) to prepare prepolymer A relative to the total mass of the mixture is as follows: The content of difunctional hydroxyl-terminated polybutadiene is 30.0-45.0%; the content of polyether polyol is 30.0-45.0%; the content of diisocyanate is 10.0-30.0%; and the content of catalyst is 0.0-1.0%. The total mass percentage of the added difunctional hydroxyl-terminated polybutadiene, polyether polyol, diisocyanate, and catalyst is 100%.

3. The method for preparing a low-modulus polyurethane hot melt adhesive for bonding electronic screens according to claim 1, characterized in that, The percentage by mass of each substance added in step (2) to prepare isocyanate-terminated prepolymer B relative to the total mass of the mixture is as follows: Polyester polyol: 30.0-40.0%; Polytetrahydrofuran diol: 30.0-45.0%; Diisocyanate: 20.0-35.0%; Catalyst: 0.0-1.0%; The total mass percentage of the added polyester polyol, polytetrahydrofuran diol, diisocyanate and catalyst is 100%.

4. The method for preparing a low-modulus polyurethane hot melt adhesive for bonding electronic screens according to claim 1, characterized in that, In step (3), the ratio of prepolymer A to prepolymer B in preparing the polyurethane hot melt adhesive is 40 / 60-60 / 40.

5. The method for preparing a low-modulus polyurethane hot melt adhesive for bonding electronic screens according to claim 1, characterized in that, The structure of the bifunctional polybutadiene described in step (1) is as follows: The molecular weight is 1000-3000, wherein structure a accounts for 30-50% of the molecular chain and structure b accounts for 50-70% of the molecular chain. The polyether polyol mentioned in step (1) is one or more of polypropylene glycol ether diol and polyethylene glycol ether diol, with a molecular weight of 1000-4000; the diisocyanate mentioned in steps (1) and (2) is one or more of a mixture of 4,4'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate and 4,4'-diphenylmethane diisocyanate; and the catalyst mentioned in steps (1) and (2) is bismorpholino diethyl ether.

6. The method for preparing a low-modulus polyurethane hot melt adhesive for bonding electronic screens according to claim 1, characterized in that, The polyester polyol mentioned in step (2) is one or more of polybutylene adipate diol, polyhexane adipate diol PHA, polyhexane sebacate diol, polyneoprene adipate diol, and polydiethylene adipate diol, and the molecular weight of the polytetrahydrofuran diol mentioned in step (2) is 1000-3000.

7. The method for preparing a low-modulus polyurethane hot melt adhesive for bonding electronic screens according to claim 1, characterized in that, The prepared polyurethane hot melt adhesive contains the following structure: Among them, a accounts for 30-50%, and b accounts for 50-70%.

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