Oleic acid-resistant bio-based reactive polyurethane hot melt adhesive and preparation method thereof

Abstract

The invention provides an oleic acid-resistant bio-based reactive polyurethane hot melt adhesive and a preparation method thereof. The reactive polyurethane hot melt adhesive is prepared from the following raw materials in parts by weight: 10 to 15 parts of silicon-based diisocyanate, 10 to 12 parts of phenyl diisocyanate, 50 to 60 parts of bio-based polymer dihydric alcohol, 10 to 20 parts of multi-arm polyethylene glycol, 5 to 10 parts of acrylic resin, 1 to 2 parts of coupling agent and 0.2 to 0.5 part of catalyst. The silicon-based diisocyanate is prepared by carrying out a hydrosilylation reaction on bifunctional hydrogen-containing silane and monoalkenyl unsaturated isocyanate according to a molar ratio of 1: (2.1-2.15); si-O-Si bonds which are not easy to hydrolyze are introduced, so that the breakage of a polyurethane molecular main chain is stopped, and the oleic acid resistance and the damp-heat aging resistance are improved; the cross-linking density of the hot melt adhesive is improved by multi-arm polyethylene glycol, and a polyurethane molecular chain is protected from being eroded by oleic acid and damp heat; the silicon-based diisocyanate and the multi-arm polyethylene glycol cooperate to improve oleic acid resistance and damp-heat aging resistance of the hot melt adhesive.

Description

Technical Field

[0001] The invention belongs to the technical field of polyurethane hot melt adhesives, and in particular relates to an oleic acid resistant bio-based reactive polyurethane hot melt adhesive and a preparation method thereof. Background Art

[0002] Consumer electronics have become an important part of modern people's lives. Mobile phones, tablets, smart wearables and other electronic devices integrate the most advanced semiconductor and electronic technologies of the time, greatly enriching people's lives and influencing the development of society. Adhesives play a huge role in the development of electronic products, enabling the rapid assembly and production of electronic equipment, and undertake functions such as bonding, sealing, laminating, protection and assembly to meet increasingly rich functions and needs.

[0003] Reactive polyurethane hot melt adhesive is a one-component, solvent-free, hot melt structural adhesive, which is mainly a prepolymer prepared from polyester / polyether polyol and diisocyanate, with an isocyanate group at the end. Reactive polyurethane hot melt adhesive can be bonded in the form of molten liquid at a relatively low temperature (105-120°C), and after cooling, it first provides a certain initial strength, and after a moisture curing process in the air, it forms a polymer with high cohesion, excellent bonding properties and impact resistance. It has become one of the most widely used adhesives in the field of electronic products such as mobile phones.

[0004] Reactive polyurethane hot melt adhesive can be used with advanced dispensing equipment to bond parts with narrow gaps such as the frames and back covers of electronic products. It can reduce the gap between the glass panel and the substrate of electronic products from the millimeter level to 0.3-0.5mm, or even 0.2mm. It also has the advantages of high assembly efficiency, high degree of automation, and easy repair. Mobile phones, tablets, smart wearables and other electronic products are in long-term contact with the human body. The sweat secreted by the sweat glands and the oleic acid in the oil secreted by the sebaceous glands will corrode the polyurethane hot melt adhesive, resulting in a decrease in bonding strength and even debonding. Researchers have conducted a lot of research on this issue. For example, patent CN112662368B discloses a high-performance polyurethane hot melt adhesive and its preparation method, which is composed of the following raw materials by mass: 50-80 parts of polyester polyol, 10-30 parts of terminal hydroxyl polybutadiene acrylonitrile, 1-5 parts of multi-arm star terminal hydroxyl polyester polyol, 0.05-0.1 parts of catalyst, and 10-20 parts of diphenylmethane diisocyanate; patent CN112795350B discloses an oleic acid-resistant reactive polyurethane hot melt adhesive, which is a 100% solid single-component adhesive, and its formula includes polyol, p-phenylene diisocyanate, chain extender, antioxidant, coupling agent and catalyst. The polyols include polycarbonate diols, polyester diols and polyether diols. The above patented technology introduces multi-arm star-terminated hydroxyl polyester polyol or a suitable amount of polycarbonate diol into the polyurethane hot melt adhesive to improve its oleic acid resistance by increasing the crosslinking density or increasing the polarity difference with oleic acid. However, there are a large number of easily hydrolyzed groups on the multi-arm star-terminated hydroxyl polyester polyol or polycarbonate diol. Although increasing the crosslinking density or increasing the polarity difference with oleic acid can block or slow down the hydrolysis of carbamate or the weakening of intermolecular interaction caused by the penetration of oleic acid, it will result in poor resistance to moisture and heat aging.

[0005] Therefore, it is necessary to develop a reactive polyurethane hot melt adhesive having both excellent oil acid resistance and resistance to wet heat aging. Summary of the invention

[0006] In order to solve the above technical problems, the present invention provides an oleic acid resistant bio-based reactive polyurethane hot melt adhesive and a preparation method thereof. The polyurethane hot melt adhesive contains a silicon-based diisocyanate prepared by a silylation reaction using difunctional hydrogen-containing silane and monoethylenic unsaturated isocyanate as raw materials. Si-O-Si bonds that are not easily hydrolyzed are introduced into the molecular chain segments of the polyurethane hot melt adhesive prepared using the silicon-based diisocyanate as raw materials, which can stop the breakage of the main chain of the polyurethane molecule caused by the breakage of the carbamate bond, thereby improving the oleic acid resistance and the wet heat aging resistance from a chemical perspective. The multi-arm polyethylene glycol has the function of increasing the cross-linking density of the hot melt adhesive, and protects the polyurethane molecular chain from the corrosion of oleic acid and wet heat from a physical perspective. Under the synergistic effect of the physical protection and chemical protection of the silicon-based diisocyanate and the multi-arm polyethylene glycol, the oleic acid resistance and the wet heat aging resistance of the polyurethane hot melt adhesive are significantly improved.

[0007] In order to achieve the above purpose, the following technical solutions are adopted:

[0008] The invention discloses an oleic acid resistant bio-based reactive polyurethane hot melt adhesive, comprising the following raw materials in parts by weight: 10-15 parts of silicon-based diisocyanate, 10-12 parts of phenyl diisocyanate, 50-60 parts of bio-based polymer diol, 10-20 parts of multi-arm polyethylene glycol, 5-10 parts of acrylic resin, 1-2 parts of coupling agent and 0.2-0.5 parts of catalyst. The silicon-based diisocyanate is prepared by hydrosilylation reaction of difunctional hydrogen-containing silane and monoethylenic unsaturated isocyanate in a molar ratio of 1:2.1-2.15.

[0009] The bifunctional hydrogen-containing silane is selected from one or a combination of two of 1,1,3,3-tetramethyldisiloxane, 1,1,3,3,5,5-hexamethyltrisiloxane, 1,1,5,5-tetramethyl-3,3-diphenyltrisiloxane, 1,1,3,5,5-pentamethyl-3-phenyltrisiloxane, 1,1,1,3,5,7,7,7-octamethyltetrasiloxane, and octamethyltetrasiloxane. Preferably, it is 1,1,5,5-tetramethyl-3,3-diphenyltrisiloxane; the monoethylenically unsaturated isocyanate is selected from one or a combination of two or more of allyl isocyanate, 3-isopropyl-dimethylbenzyl isocyanate, and methacryloyl isocyanate. Preferably, it is allyl isocyanate.

[0010] The silicon-based diisocyanate is prepared by a method comprising the following steps:

[0011] Under an inert atmosphere, difunctional hydrogen-containing silane, monoethylenically unsaturated isocyanate and organic solvent are added into a reaction kettle and mixed evenly, the temperature is raised, a catalyst is added to react, and after the reaction is completed, reduced pressure distillation is performed to obtain silicon-based diisocyanate.

[0012] The organic solvent is selected from one or a combination of two or more of n-butyl ether, diphenyl ether, chloroform and carbon tetrachloride. The catalyst is a solution prepared by chloroplatinic acid and isopropanol with a concentration of 0.05-0.2 mol / L, and the amount of chloroplatinic acid in the catalyst is 5-10‰ of the molar amount of the difunctional hydrosilane and the monoethylenically unsaturated isocyanate. The temperature is raised to 60-100°C, and the reaction time is 2-6h. The reduced pressure distillation is to collect the 180-200°C / -0.098MPa fraction.

[0013] The multi-arm polyethylene glycol has a weight average molecular weight of 3000-5000 and is selected from one or a combination of two or more of four-arm polyethylene glycol, six-arm polyethylene glycol and eight-arm polyethylene glycol, preferably eight-arm polyethylene glycol with a weight average molecular weight of 5000.

[0014] The introduction of Si-O-Si bonds that are not easily hydrolyzed into the molecular chain segments of polyurethane hot melt adhesives can stop the breakage of the main chain of the polyurethane molecule caused by the breakage of the urethane bonds, thereby improving the oleic acid resistance and the heat and humidity aging resistance from a chemical perspective; multi-arm polyethylene glycol has the effect of increasing the cross-linking density of the hot melt adhesive, and physically protects the polyurethane molecular chains from the corrosion of oleic acid and heat and humidity. Under the synergistic effect of physical protection and chemical protection, the oleic acid resistance and heat and humidity aging resistance of the polyurethane hot melt adhesive can be significantly improved; however, the relative amounts of silicon-based diisocyanate and multi-arm polyethylene glycol need to be reasonably regulated.

[0015] Because silicon-based diisocyanate improves the flexibility of the polyurethane hard segment, excessive use of it will excessively weaken the rigid structure of the hard segment and reduce the shear strength; although increasing the amount of multi-arm polyethylene glycol is beneficial to improving the shear strength and oleic acid resistance, excessive use will significantly enhance its water absorption performance and significantly reduce its hydrothermal aging resistance. Therefore, the optimal ratio is strictly controlled to ensure good oleic acid resistance while taking into account the shear strength and moisture-heat aging resistance of the material.

[0016] Bio-based polymer diol refers to a polymer with a diol structure that is produced from renewable resources (such as crops, straw and other plants) through a series of chemical conversion processes, such as fermentation, transesterification, polymerization and other reactions. The bio-based polymer diol has a weight average molecular weight of 1000-2000 and is selected from one or a combination of bio-based polyether diol and bio-based polyester diol. Bio-based polyether diol is preferred.

[0017] The coupling agent is not particularly limited and can be commonly used in the art, and is selected from one or a combination of two or more of γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane, N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane, N-(β-aminoethyl)-γ-aminopropyltriethoxysilane, anilinemethyltriethoxysilane, anilinepropyltriethoxysilane, γ-glycidyletherpropyltrimethoxysilane, γ-mercaptopropyltrimethoxysilane, γ-mercaptopropyltriethoxysilane, γ-isocyanatepropyltrimethoxysilane and γ-isocyanatepropyltriethoxysilane.

[0018] The catalyst is selected from one or a combination of two or more of an organic tin catalyst, an organic bismuth catalyst, and an organic amine catalyst.

[0019] The weight average molecular weight of the acrylic resin is 30,000-60,000.

[0020] The phenyl diisocyanate is selected from one or a combination of two or more of toluene diisocyanate, diphenylmethane diisocyanate, naphthalene diisocyanate, p-phenylene diisocyanate, xylylene diisocyanate, tetramethyl meta-xylylene diisocyanate, and dimethyl biphenyl diisocyanate, preferably diphenylmethane diisocyanate.

[0021] The present invention also provides a method for preparing the above-mentioned oleic acid resistant bio-based reactive polyurethane hot melt adhesive, comprising the following steps:

[0022] 1) adding bio-based polymer diol, multi-arm polyethylene glycol and acrylic resin into a reaction kettle, heating and vacuuming to dehydrate, cooling and setting aside;

[0023] 2) adding silicon-based diisocyanate and phenyl diisocyanate, stirring and heating under vacuum conditions to react, releasing the pressure with nitrogen, adding a catalyst and a coupling agent, and continuing the reaction to obtain an oleic acid-resistant bio-based reactive polyurethane hot melt adhesive.

[0024] In step 1), the temperature is raised to 130-150°C, the vacuum dehydration is performed under a vacuum degree of 0.01-0.1 MPa for 1-3 hours, and the temperature is lowered to 70-90°C.

[0025] Step 2) The vacuum condition is a vacuum degree of 0.01-0.1 MPa. The temperature is raised to 100°C-120°C, the reaction time is 1-1.5 hours, and the continued reaction time is 15-30 minutes.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] The polyurethane hot melt adhesive of the present invention contains a silicon-based diisocyanate prepared by a silicon-hydrogen addition reaction with difunctional hydrogen-containing silane and monoethylenic unsaturated isocyanate as raw materials. Si-O-Si bonds that are not easily hydrolyzed are introduced into the molecular chain segments of the polyurethane hot melt adhesive prepared with the silicon-based diisocyanate as raw materials, so that the breakage of the main chain of the polyurethane molecule caused by the breakage of the carbamate bond can be stopped, and the oleic acid resistance and the wet heat aging resistance are improved from a chemical perspective. The multi-arm polyethylene glycol has the function of increasing the crosslinking density of the hot melt adhesive, and protects the polyurethane molecular chain from the corrosion of oleic acid and wet heat from a physical perspective. Under the synergistic effect of the physical protection and chemical protection of the silicon-based diisocyanate and the multi-arm polyethylene glycol, the oleic acid resistance and the wet heat aging resistance of the polyurethane hot melt adhesive are significantly improved.

[0028] Part of the raw materials of the polyurethane hot melt adhesive of the present invention are derived from bio-based materials, which is green, environmentally friendly and sustainable. DETAILED DESCRIPTION

[0029] The present invention will be further described below in conjunction with specific embodiments, but is not limited to the contents of the specification. Unless otherwise specified, the "parts" described in the embodiments of the present invention are all parts by weight. The reagents used are all commercially available reagents in the art.

[0030] Japanese Mitsubishi acrylic resin BR113, weight average molecular weight 30000.

[0031] Eight-arm polyethylene glycol, with a weight average molecular weight of 3000 and 5000, was purchased from NobiPure (Shanghai) Chemical Co., Ltd.

[0032] Four-arm polyethylene glycol, with a weight average molecular weight of 5000, was purchased from NobiPure (Shanghai) Chemical Co., Ltd.

[0033] Bio-based polyether diol was purchased from Allessa GmbH, with the brand name Velvetol H2000 and a weight average molecular weight of 2000; and the brand name Velvetol H1000 and a weight average molecular weight of 1000.

[0034] Example 1

[0035] 1) Under nitrogen atmosphere, add 1 mol 1,1,5,5-tetramethyl-3,3-diphenyltrisiloxane, 2.1 mol allyl isocyanate and 850 mL diphenyl ether to the reactor and mix well. Heat to 80°C, add 0.0775 L of a catalyst solution prepared by 0.2 mol / L chloroplatinic acid and isopropanol to react for 6 h. After the reaction is completed, distill under reduced pressure at 180-185°C / -0.098 MPa to obtain silicon-based diisocyanate.

[0036] 2) Add 60g Velvetol H2000, 20g eight-arm polyethylene glycol with a weight average molecular weight of 5000, and 10g acrylic resin BR113 into a reaction kettle, heat to 130°C, evacuate to a vacuum degree of 0.085MPa, dehydrate for 3h, cool to 70°C, and set aside;

[0037] 3) Add 15 g of silicon-based diisocyanate and 10 g of diphenylmethane diisocyanate, stir under vacuum conditions of 0.085 MPa and heat to 120 ° C for reaction for 60 min, release the pressure with nitrogen, add 0.5 g of dibutyltin dilaurate and 1 g of γ-isocyanatepropyltrimethoxysilane, and continue to react to obtain an oleic acid-resistant bio-based reactive polyurethane hot melt adhesive.

[0038] Example 2

[0039] The rest is the same as Example 1, except that in step 1), 1,1,3,5,5-pentamethyl-3-phenyltrisiloxane is used in an equal molar amount to replace 1,1,5,5-tetramethyl-3,3-diphenyltrisiloxane.

[0040] Example 3

[0041] The rest is the same as Example 1, except that in step 1), an equimolar amount of 3-isopropyl-dimethylbenzyl isocyanate is used instead of allyl isocyanate.

[0042] Example 4

[0043] The rest is the same as Example 1, except that in step 2), an equal mass of eight-arm polyethylene glycol with a weight average molecular weight of 3000 is used to replace the eight-arm polyethylene glycol with a weight average molecular weight of 5000.

[0044] Example 5

[0045] The rest is the same as Example 1, except that in step 2), an equal amount of four-arm polyethylene glycol with a weight average molecular weight of 5000 is used to replace the eight-arm polyethylene glycol with a weight average molecular weight of 5000.

[0046] Example 6

[0047] The rest is the same as Example 1, except that in step 2), the amount of eight-arm polyethylene glycol used is 10 g.

[0048] Example 7

[0049] The rest is the same as Example 1, except that in step 3), the amount of silicon-based diisocyanate used is 10 g.

[0050] Example 8

[0051] 1) Under nitrogen atmosphere, add 1 mol 1,1,5,5-tetramethyl-3,3-diphenyltrisiloxane, 2.15 mol allyl isocyanate and 850 mL diphenyl ether to the reactor and mix well. Heat to 80°C, add 0.079 L of a catalyst solution prepared by 0.2 mol / L chloroplatinic acid and isopropanol to react for 6 h. After the reaction is completed, distill under reduced pressure at 180-185°C / -0.098 MPa to obtain silicon-based diisocyanate.

[0052] 2) Add 60g Velvetol H1000, 20g eight-arm polyethylene glycol with a weight average molecular weight of 5000, and 5g acrylic resin BR113 into a reaction kettle, heat to 130°C, evacuate to a vacuum degree of 0.085MPa, dehydrate for 3h, cool to 70°C, and set aside;

[0053] 3) Add 15 g of silicon-based diisocyanate and 12 g of diphenylmethane diisocyanate, stir under vacuum conditions of 0.085 MPa and heat to 120 ° C for reaction for 60 min, release the pressure with nitrogen, add 0.5 g of dibutyltin dilaurate and 1 g of γ-isocyanatepropyltrimethoxysilane, and continue to react to obtain an oleic acid-resistant bio-based reactive polyurethane hot melt adhesive.

[0054] Comparative Example 1

[0055] The rest is the same as Example 1, except that in step 3), an equal mass of diphenylmethane diisocyanate is used to replace silicon-based diisocyanate.

[0056] Comparative Example 2

[0057] The rest is the same as Example 1, except that in step 2), the amount of eight-arm polyethylene glycol with a weight average molecular weight of 5000 is 25 g.

[0058] Comparative Example 3

[0059] The rest is the same as Example 1, except that in step 3), the amount of silicon-based diisocyanate used is 20 g.

[0060] The reactive polyurethane hot melt adhesive prepared in the above examples and comparative examples was cured for 168 hours at 25°C and 50% and then subjected to the following performance tests:

[0061] Shear strength: Prepare specimens according to standard GB / T 7124-2008 for shear strength test, bonding substrate PC / PC.

[0062] Oleic acid aging resistance: Under the environment of 60°C and 90% humidity, the bonded PC / PC shear-resistant specimens were immersed in 60°C oleic acid for one week, and then the shear strength was re-measured, and the shear strength attenuation rate was calculated.

[0063] Double 85 test: place the bonded PC / PC shear-resistant specimens in an aging test box at 85°C and 85% humidity for 1000 hours, re-measure the shear strength, and calculate the shear strength attenuation rate.

[0064] Table 1 Performance test results

[0065]

[0066] It can be seen from Table 1 that the reactive polyurethane hot melt adhesive prepared in the present invention has excellent mechanical properties, oleic acid resistance and moisture-heat aging resistance.

[0067] The above detailed description is a specific description of one feasible embodiment of the present invention. The embodiment is not intended to limit the patent scope of the present invention. Any equivalent implementation or modification that does not deviate from the present invention should be included in the scope of the technical solution of the present invention.

Claims

1. An oleic acid resistant bio-based reactive polyurethane hot melt adhesive, characterized in that: The invention comprises the following raw materials in parts by weight: 10-15 parts of silicon-based diisocyanate, 10-12 parts of phenyl diisocyanate, 50-60 parts of bio-based polymer diol, 10-20 parts of multi-arm polyethylene glycol, 5-10 parts of acrylic resin, 1-2 parts of coupling agent and 0.2-0.5 parts of catalyst. The silicon-based diisocyanate is prepared by hydrosilylation reaction of difunctional hydrogen-containing silane and monoethylenic unsaturated isocyanate in a molar ratio of 1:2.1-2.

15.

2. The oleic acid resistant bio-based reactive polyurethane hot melt adhesive according to claim 1, characterized in that: The bifunctional hydrogen-containing silane is selected from one or a combination of two of 1,1,3,3-tetramethyldisiloxane, 1,1,3,3,5,5-hexamethyltrisiloxane, 1,1,5,5-tetramethyl-3,3-diphenyltrisiloxane, 1,1,3,5,5-pentamethyl-3-phenyltrisiloxane, 1,1,1,3,5,7,7,7-octamethyltetrasiloxane, and octamethyltetrasiloxane; preferably 1,1,5,5-tetramethyl-3,3-diphenyltrisiloxane.

3. The oleic acid resistant bio-based reactive polyurethane hot melt adhesive according to claim 1, characterized in that: The monoethylenically unsaturated isocyanate is selected from one or a combination of two or more of allyl isocyanate, 3-isopropyl-dimethylbenzyl isocyanate, and methacryloyl isocyanate; preferably allyl isocyanate.

4. The oleic acid resistant bio-based reactive polyurethane hot melt adhesive according to claim 1, characterized in that: The silicon-based diisocyanate is prepared by a method comprising the following steps: Under an inert atmosphere, difunctional hydrogen-containing silane, monoethylenically unsaturated isocyanate and organic solvent are added into a reaction kettle and mixed evenly, the temperature is raised, a catalyst is added to react, and after the reaction is completed, reduced pressure distillation is performed to obtain silicon-based diisocyanate.

5. The oleic acid resistant bio-based reactive polyurethane hot melt adhesive according to claim 4, characterized in that: The organic solvent is selected from one or a combination of two or more of n-butyl ether, diphenyl ether, chloroform and carbon tetrachloride.

6. The oleic acid resistant bio-based reactive polyurethane hot melt adhesive according to claim 4, characterized in that: The catalyst is a solution prepared by chloroplatinic acid and isopropanol with a concentration of 0.05-0.2 mol / L. The amount of chloroplatinic acid in the catalyst is 5-10‰ of the sum of the molar amounts of the difunctional hydrogen-containing silane and the monoethylenic unsaturated isocyanate.

7. The oleic acid resistant bio-based reactive polyurethane hot melt adhesive according to claim 4, characterized in that: The reduced pressure distillation is to collect the 180-200°C / -0.098MPa fraction.

8. The oleic acid resistant bio-based reactive polyurethane hot melt adhesive according to claim 1, characterized in that: The multi-arm polyethylene glycol has a weight average molecular weight of 3000-5000 and is selected from one or a combination of two or more of four-arm polyethylene glycol, six-arm polyethylene glycol and eight-arm polyethylene glycol; preferably, the eight-arm polyethylene glycol has a weight average molecular weight of 5000.

9. The oleic acid resistant bio-based reactive polyurethane hot melt adhesive according to claim 1, characterized in that: The bio-based polymer diol has a weight average molecular weight of 1000-2000, and is selected from one or a combination of bio-based polyether diols and bio-based polyester diols; preferably, it is a bio-based polyether diol; the acrylic resin has a weight average molecular weight of 30,000-60,000; the phenyl diisocyanate is selected from one or a combination of two or more of toluene diisocyanate, diphenylmethane diisocyanate, naphthalene diisocyanate, p-phenylene diisocyanate, xylene diisocyanate, tetramethyl-m-xylene diisocyanate, and dimethylbiphenyl diisocyanate; preferably, it is diphenylmethane diisocyanate.

10. The method for preparing the oleic acid resistant bio-based reactive polyurethane hot melt adhesive according to any one of claims 1 to 9, characterized in that: The steps include: 1) adding bio-based polymer diol, multi-arm polyethylene glycol and acrylic resin into a reaction kettle, heating and vacuuming to dehydrate, cooling and setting aside; 2) adding silicon-based diisocyanate and phenyl diisocyanate, stirring and heating under vacuum conditions to react, releasing the pressure with nitrogen, adding a catalyst and a coupling agent, and continuing the reaction to obtain an oleic acid-resistant bio-based reactive polyurethane hot melt adhesive.

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