Polyurethane hot melt adhesive based on recyclable raw materials and preparation method therefor

Abstract

The present invention provides a polyurethane hot melt adhesive based on recyclable raw materials. Raw materials for preparing the polyurethane hot melt adhesive include: a polyester polyol based on recycled PET, a polyol based on a recyclable polylactic acid, a petroleum-based polyol and / or tackifying resin, a silane coupling agent containing a secondary amine group, and an isocyanate. The content of the polyester polyol based on recycled PET is 50-70% by weight relative to the total weight of the polyurethane hot melt adhesive, and the addition amount of the isocyanate is such that the molar ratio of NCO / OH is within a range of 2 to 5. In the present invention, the polyols based on the recyclable materials are used to the maximum extent, and the polyurethane hot melt adhesive is synthesized by means of bulk polymerization. The content of recyclable components in the hot melt adhesive can reach 20% or more. The main application direction of the polyurethane hot melt adhesive synthesized by the present invention is the electronics industry, and the damp-heat aging resistance of the polyurethane hot melt adhesive and the bonding performance of the polyurethane hot melt adhesive to metal substrates and plastic substrates are both superior to those of petroleum-based hot melt adhesives on the market.

Description

A polyurethane hot melt adhesive based on recyclable raw materials and preparation method thereof Technical Field

[0001] The present invention relates to the technical field of polyurethane adhesives, in particular to a polyurethane hot melt adhesive based on recyclable raw materials and a preparation method thereof. Background Art

[0002] In recent years, with growing awareness of sustainable development, cost savings, and environmental health, there has been growing interest in utilizing biomass, renewable, and recyclable resources to produce polymer materials. Studies have shown that polymer synthesis based on recycled resources is equivalent to saving 7%-15% of oil and natural gas usage. Therefore, there is an urgent need for extensive innovative research into polymer synthesis based on recycled resources to gradually reduce dependence on petroleum-based materials and contribute positively to environmental protection. At the same time, many international companies are increasingly emphasizing the concept of reducing the carbon footprint of their chemical products, which suggests that materials derived from biomass and recyclable sources have a broad market application.

[0003] ISCC (International Sustainability & Carbon Certification) recognizes environmentally friendly raw materials, which mainly include the following four categories: (i) biomass raw materials, which refer to products made from agricultural raw materials (such as corn); (ii) recyclable raw materials, which come from non-biomass waste or residues (such as plastic waste); (iii) biomass-recyclable raw materials, which come from biomass waste or residues (such as recycled waste cooking oil); (iv) renewable energy raw materials, which refer to non-biomass raw materials produced using renewable energy.

[0004] In adhesive technology, polyurethane adhesives represent one of the most promising areas for expansion and are also one of the most widely used types of solvent-free adhesives. They offer excellent adhesion to porous surfaces like ceramics, as well as smooth surfaces like metal foil, glass, and polymer films, and are widely used. Research on the synthesis and application of bio-based polyurethane adhesives derived from renewable resources such as modified vegetable oils, polysaccharides, and lignin derivatives is continuously emerging, and these bio-based adhesives demonstrate performance comparable to or even superior to commercial petroleum-based adhesives.

[0005] For example, patent 202210712666.4 discloses a method for preparing a degradable bio-based polyurethane adhesive, which is derived from renewable biomass raw materials such as tannin, polylactic acid and 2,5-furan dimethanol. The specific synthesis process is to first synthesize tannin-modified polyol and polylactic acid-2,5-furan dimethanol ester polyol in sequence, and then polymerize them with isocyanate in xylene solvent, and finally remove the solvent and impurities by reduced pressure distillation to obtain bio-based polyurethane. By composting the obtained polyurethane, it was found that it can be completely degraded after 360 days without any weight residue. The key point of this patent is the synthesis of degradable bio-based polyurethane adhesives. It is worth mentioning that there are differences in performance and purity between the raw material monomers extracted from biomass and the same raw material monomers extracted from petroleum-based waste, and thus the performance of the synthetic products based on the extracted monomers will also be different. In addition, the polymerization reaction described in the patent is completed in a solvent medium, and the solvent is xylene, which is easily toxic. Compared with the more common bulk method for synthesizing polyurethane hot melt adhesives, this solvent synthesis method has no advantages.

[0006] Therefore, the development of a polyurethane hot melt adhesive prepared by bulk polymerization using environmentally friendly raw materials that comply with ISCC certification has become a research hotspot in the field of polyurethane adhesive technology. Summary of the Invention

[0007] This invention proposes a design concept for a polyurethane hot-melt adhesive produced by bulk polymerization using recycled raw materials. Using recycled raw materials derived from non-biomass waste or residues, the resulting polyurethane hot-melt adhesive has a recycled content exceeding 20%. Furthermore, the performance of this recycled content polyurethane hot-melt adhesive is compared with comparable petroleum-based products on the market, demonstrating that this recycled content polyurethane hot-melt adhesive can replace common petroleum-based hot-melt adhesives.

[0008] By selecting recyclable upstream raw materials, preparing the target polyol, adjusting the final formula, and performing specific product modifications, the present invention endows the polyurethane hot melt adhesive based on recyclable raw materials with excellent bonding properties, such as for metal materials, polyimide, and other plastic substrates, while also improving the polyurethane hot melt adhesive's resistance to moisture and heat aging.

[0009] In order to achieve the above effects, the technical solutions of the present invention are as follows:

[0010] A polyurethane hot melt adhesive based on recyclable raw materials. The raw materials for preparing the polyurethane hot melt adhesive include: polyester polyol based on recycled PET, polyol based on recyclable polylactic acid, petroleum-based polyol and / or tackifying resin, silane coupling agent containing secondary amine group, and isocyanate.

[0011] The content of the recycled PET polyester polyol is between 50% and 70% by weight relative to the total weight of the polyurethane hot melt adhesive. The use of a large proportion of recycled PET polyester polyol in the hot melt adhesive of the present invention has the advantage that recycled PET polyester polyols contain a large number of aromatic ring structures in their molecular structure, which provides good adhesion to metal substrates and highly polar polyimide materials. Due to the rigid structure of the aromatic rings, the presence of a large number of aromatic ring structures in the hot melt adhesive can improve the heat resistance of the hot melt adhesive. Compared with aliphatic polyurethanes, aromatic polyurethanes also have better water resistance. When the weight proportion of recycled PET polyester polyol is greater than or equal to 50%, the hot melt adhesive's bond strength to anodized aluminum or stainless steel is significantly increased, and the hot melt adhesive's resistance to double 85 aging is also significantly improved. However, the use of a large proportion of recycled PET polyester polyol has a problem: compared with aliphatic crystalline polyols of the same molecular weight and hydroxyl number, at the same NCO / OH ratio, the polyurethane hot melt adhesive synthesized using recycled PET polyester polyol has a higher viscosity. In the electronics industry, polyurethane hot melt adhesives (PHAs) are often formulated with low viscosity to achieve narrow adhesive lines and smooth dispensing. Therefore, when formulating PHAs using large amounts of recycled PET-based polyester polyols, the NCO to OH ratio is increased to reduce the adhesive's viscosity.

[0012] The molecular weight of the recycled PET polyester polyol is 2000-3500. In the formulation design of the present invention, recycled PET polyester polyols are used in a larger proportion. If low-molecular-weight polyester polyols are selected, they tend to form soft polyurethane foam-like materials with obvious foaming after reaction with isocyanates, but lack the performance characteristics of polyurethane hot melt adhesives. Therefore, the molecular weight of recycled PET polyester polyols is preferably 2000-3500, corresponding to a hydroxyl value of 27-62 mg / KOH. Available commercial brands include HOOPOL F-39037 and HOOPOL F-39032 from Hook Chemicals of Spain, which have a recycled content of 38%; and 51041-2000 from Changxing Chemicals, which has a hydroxyl value of 50-65 mg / KOH and a recycled content of 40%.

[0013] The polyol based on recyclable polylactic acid is independently prepared, with a hydroxyl value of 20-140 mg / KOH. Its preparation process is as follows:

[0014] 1) Adding recycled polylactic acid into the reactor and raising the temperature to 160-190°C to obtain molten polylactic acid;

[0015] 2) Evacuate the reactor at a vacuum of -0.1 MPa for 30 minutes; break the vacuum and introduce inert gas into the reactor to replace the air for 20 minutes;

[0016] 3) Add small molecule diol and catalyst to the reactor in sequence, stir for 5-15 minutes, and replace with inert gas again for 20 minutes;

[0017] 4) Control the temperature to 180-190°C and react for 4-10 hours under inert gas protection;

[0018] 5) Control the temperature at 180±5°C and evacuate at -0.1 MPa for 30 minutes to remove a small amount of unreacted small molecule diol;

[0019] 6) Cooling to 120±5°C and discharging the material to obtain the polyol based on recyclable polylactic acid.

[0020] The recycled polylactic acid is Luminy® rPLA, a commercial product launched by Total Corbion PLA, with a recycled content of 20%. The small molecule diols include one or more of diethylene glycol, butanediol, ethylene glycol, and propylene glycol, with butanediol and / or diethylene glycol being preferred. The catalyst includes any one of tetrabutyl titanate, tetraisopropyl titanate, antimony trioxide and zinc acetate, and any one of zinc lactate, stannous lactate, zinc oxide, and stannous oxide, in combination. Preferably, the synthesized recycled polylactic acid-based polyol has a hydroxyl value of 56-62 mgKOH / g. The recycled polylactic acid-based polyol enhances the wettability of the hot melt adhesive in the formulation, counteracting the rapid dry-down characteristics of the recycled PET-based polyester polyol, which accounts for a large proportion of the formulation. Maximizing the use of recycled polylactic acid-based and recycled PET-based polyester polyols can increase the recycled content of the hot melt adhesive.

[0021] The secondary amine-containing silane coupling agent contains only a single secondary amine group, including but not limited to one or more of N-n-butyl-3-aminopropyltrimethoxysilane, bis(trimethoxysilylpropyl)amine, bis-[3-(triethoxysilyl)propyl]amine, and N-ethyl-3-trimethoxysilane-2-methylpropylamine. Typical commercial brands include Degussa Dynasylan 1189 and Dynasylan 1124. Silane coupling agents containing secondary amine groups are used to chemically modify polyurethane hot melt adhesives. The secondary amine groups react with excess NCO groups in the hot melt adhesive, thereby grafting them onto the polyurethane prepolymer backbone. Since secondary amine-containing silane coupling agents lack the more reactive primary amino groups and contain only a single secondary amine group, the reaction process is relatively smooth, without causing a sudden increase in viscosity or localized gelation. In summary, the use of silane coupling agents containing secondary amine groups can, on the one hand, react with the active NCO groups in the chemical chain of the polyurethane prepolymer without significantly increasing the viscosity of the hot melt adhesive, reducing the problem of bubbles in the hot melt adhesive during the later curing process. On the other hand, the silane grafted onto the polyurethane prepolymer undergoes a cross-linking reaction with water. The Si-C and Si-O bonds of the silane itself are non-hydrolyzable and have high bond energies, making them resistant to high temperatures. The aromatic rings in the polyester polyols based on recycled PET have a steric hindrance effect on the hydrolysis of the ester bonds, and the aromatic ring structure is more resistant to high temperatures than the aliphatic chain structure. In summary, the modification of silane coupling agents containing secondary amine groups, in conjunction with the terephthalic anhydride chemical bond structure of the large amount of PET in the hot melt adhesive, can significantly improve the wet heat aging resistance of the polyurethane hot melt adhesive.

[0022] The amount of isocyanate added is such that the NCO / OH molar ratio, denoted as (R), is in the range of 2-5. Generally speaking, the larger the R value, the more free isocyanate in the system and the lower the viscosity of the resulting polyurethane prepolymer. The isocyanate is an aromatic diisocyanate, including but not limited to one or more of 4,4'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate, 2,2'-diphenylmethane diisocyanate, and carbodiimide-modified diphenylmethane diisocyanate.

[0023] The petroleum-based polyol can be a crystalline polyester polyol, which is prepared by condensing one or more of succinic acid, adipic acid, sebacic acid, and dodecanedioic acid with one or more of ethylene glycol, butanediol, and hexanediol. Typical commercial brands include Dynacoll 7360, Dynacoll 7361, and Dynacoll 7330 from EVONIK Chemicals, HOOPOL F-911 and HOOPOL from Hook Chemicals of Spain. F-932; it can also be a liquid polyester polyol, which is prepared by condensation reaction of one or more of succinic acid, adipic acid, sebacic acid, maleic acid, fumaric acid, and cyclohexanediol, and one or more of ethylene glycol, butanediol, hexanediol, diethylene glycol, neopentyl glycol, and 1,5-pentanediol. Typical commercial brands include Dynacoll 7250, Dynacoll 7230, and Dynacoll 7210 from EVONIK Chemical. It can also be a polyether polyol, including polyethylene glycol, polypropylene oxide glycol, and polytetramethylene glycol. Typical commercial brands include PEG-1000 from Kunshan Guodu Chemical, VORANOL 2110TB and VORANOL 2120 from Dow Chemical, and PTMEG-1000 from Hyosung Chemical.

[0024] The tackifying resin can be an acrylic resin, typical commercial brands such as Japan Mitsubishi acrylic resin MB-2595, MB-2592; it can be a petroleum resin, typical commercial brands such as France Cray Valley W-85, W-100; it can also be APAO (amorphous α-olefin copolymer), typical commercial brands such as EVONIK VESTOPLAST 508, VESTOPLAST 708, VESTOPLAST 750.

[0025] The raw materials used to prepare the polyurethane hot melt adhesive also include additives, which include one or more of a defoamer, a fluorescent agent, a water scavenger, an antioxidant, and an amine catalyst. Defoamers are preferably acrylate defoamers, with typical commercial brands such as BYK-A535, BYK-088, and BYK-1790 from BYK Chemical, with BYK-A535 being preferred. Fluorescent agents enhance the resolution of the hot melt adhesive, with typical commercial brands such as BASF Ciba® UVITEX OB and BASF CBS-X, with UVITEX being preferred. OB; the main function of the dehydrating agent is to react with the trace moisture in the hot melt adhesive and improve the stability of the hot melt adhesive. Optional dehydrating agents include but are not limited to toluenesulfonyl isocyanate PTSI, 3-isocyanatepropyltrimethoxysilane, 3-isocyanatepropyltriethoxysilane, preferably toluenesulfonyl isocyanate PTSI; the function of the antioxidant is to reduce the yellowing phenomenon of the polyurethane hot melt adhesive and slow down the thermal aging of the hot melt adhesive. Optional antioxidants include but are not limited to antioxidant 1010, antioxidant 264, antioxidant 168, antioxidant 1076, preferably antioxidant 1010; the function of the amine catalyst is to promote the curing reaction of the polyurethane hot melt adhesive and moisture. Optional amine catalysts include but are not limited to bis(2-dimethylaminoethyl) ether DMDEE, bis(2-dimethylaminoethyl) ether, N,N-dimethylcyclohexylamine, triethylenediamine, N-ethylmorpholine, preferably bis(2-dimethylaminoethyl) ether.

[0026] A method for preparing a polyurethane hot melt adhesive based on recyclable raw materials, characterized by comprising the following steps:

[0027] 1) Prepare a molten polyol mixture by the following raw materials:

[0028] a) at least one polyester polyol based on recycled PET;

[0029] b) at least one polyol based on recycled polylactic acid;

[0030] c) Petroleum-based polyols or tackifying resins;

[0031] 2) adding isocyanate and a polyol mixture to carry out polymerization to obtain a polyurethane prepolymer, wherein the molar ratio of NCO in the isocyanate to OH in the polyol mixture is 2-5;

[0032] 3) Adding a silane coupling agent containing a secondary amine group and grafting it onto the main chain of the polyurethane prepolymer to obtain a polyurethane hot melt adhesive based on recyclable raw materials.

[0033] Preferably, an auxiliary agent is added between step 1) and step 2); and / or an auxiliary agent is added between step 2) and step 3).

[0034] Preferably, the preparation process of the polyurethane hot melt adhesive based on recyclable raw materials is as follows:

[0035] 1) Adding polyester polyol based on recycled PET, polyol based on recyclable polylactic acid, petroleum-based polyol and / or tackifying resin into a reactor, stirring and melting at 120-160° C. to a uniform molten state;

[0036] 2) Then add one or more of fluorescent agent, defoaming agent and antioxidant and stir evenly;

[0037] 3) Turn on the vacuum and dehydrate at a vacuum degree of -0.1 MPa for 1-2 hours;

[0038] 4) Lowering the system temperature to 80±2°C, adding isocyanate; reacting at 80-100°C for 30 minutes without applying external heating; applying external heating to control the temperature to about 110°C, simultaneously turning on the vacuum, and degassing and reacting at a vacuum degree of -0.1 MPa for 30 minutes;

[0039] 5) adding a desiccant and a catalyst in sequence, reacting at 110° C. for 10 minutes to prepare a polyurethane prepolymer while maintaining the melt;

[0040] 6) Lowering the temperature of the reaction system to 90° C., adding a secondary amino group-containing silane coupling agent, and controlling the temperature at 90±5° C. to react for 20 minutes; turning on the vacuum, and degassing the reaction at a vacuum degree of -0.1 MPa for 10 minutes;

[0041] 7) breaking the vacuum and discharging the material under the protection of inert gas to prepare the final polyurethane hot melt adhesive product.

[0042] A polyurethane hot melt adhesive based on recyclable raw materials, wherein the components of the polyurethane hot melt adhesive are as follows, in parts by weight:

[0043] 50-70 parts of polyester polyol based on recycled PET,

[0044] 10-30 parts of polyol based on recycled polylactic acid,

[0045] Petroleum-based polyol 0-10 parts, tackifying resin 0-10 parts,

[0046] 2-15 parts of silane coupling agent containing secondary amine group,

[0047] 10-30 parts of isocyanate,

[0048] The weight parts of the petroleum-based polyol and the tackifying resin are not both 0,

[0049] The total weight parts of the polyurethane hot melt adhesive is 100 parts.

[0050] Preferably, the polyurethane hot melt adhesive further comprises the following components: 0.07-3.5 parts of an auxiliary agent. Beneficial effects

[0051] The present invention maximizes the use of polyols based on recyclable materials and synthesizes polyurethane hot melt adhesive through a bulk polymerization method, and the content of recyclable components in the hot melt adhesive can reach more than 20%.

[0052] The polyurethane hot melt adhesive based on recycled materials of the present invention is mainly applicable to the electronics industry. Its resistance to moisture and heat aging and its adhesion performance to metal substrates and plastic substrates are superior to petroleum-based hot melt adhesives on the market.

[0053] Since the large-scale use of polyester polyols based on recycled PET will increase the viscosity of the hot melt adhesive, the viscosity is reduced by increasing the amount of isocyanate, and then a secondary amino silane coupling agent is used to consume some of the excess NCO groups introduced by the isocyanate. Ultimately, the hot melt adhesive has no obvious foaming after curing, thus balancing the control of viscosity and post-curing bubble problems. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] The present invention will be further described below with reference to the accompanying drawings and examples.

[0055] Figure 1 is the infrared spectrum of polyol PLA-1 based on recyclable polylactic acid. DETAILED DESCRIPTION

[0056] In the context of the present invention, the term "xy" is understood to mean an interval including the boundaries x and y. For example, the range "molecular weight 2000-3500" specifically includes the values ​​2000 and 3500.

[0057] The present invention will now be described in the following examples, which are given by way of illustration only and should not be construed as limiting the scope of the invention.

[0058] 1. Preparation of polyols based on recyclable polylactic acid

[0059] Two polyols based on recycled polylactic acid were prepared: PLA-1 with a recycled content of 14% and PLA-2 with a recycled content of 13.3%.

[0060] Preparation of PLA-1:

[0061] 1) Add 100 parts of recycled polylactic acid Luminy® rPLA into the reactor and raise the temperature to 160-190°C to obtain molten polylactic acid;

[0062] 2) Evacuate the reactor at a vacuum of -0.1 MPa for 30 minutes; break the vacuum and introduce nitrogen into the reactor to replace the air for 20 minutes;

[0063] 3) Add 20 parts of butanediol, 0.2 parts of tetrabutyl titanate, and 0.3 parts of stannous lactate to the reactor in sequence, stir for 10 minutes, and replace the atmosphere with nitrogen again for 20 minutes;

[0064] 4) Control the temperature to 180-190°C and react for 4-10 hours under nitrogen protection;

[0065] 5) Control the temperature at 180°C and evacuate at -0.1 MPa for 30 minutes to remove a small amount of unreacted small molecule diol;

[0066] 6) Cooling to 120° C. and discharging the material to obtain a polyol based on recyclable polylactic acid, which is denoted as PLA-1. Based on mass conversion, its recyclable content is approximately 14%.

[0067] Preparation of PLA-2:

[0068] 1) Add 100 parts of recycled polylactic acid Luminy® rPLA into the reactor and raise the temperature to 160-190°C to obtain molten polylactic acid;

[0069] 2) Evacuate the reactor at a vacuum of -0.1 MPa for 30 minutes; break the vacuum and introduce nitrogen into the reactor to replace the air for 20 minutes;

[0070] 3) Add 23.55 parts of diethylene glycol, 0.2 parts of tetraisopropyl titanate, and 0.3 parts of zinc lactate to the reactor in sequence, stir for 10 minutes, and replace the atmosphere with nitrogen again for 20 minutes;

[0071] 4) Control the temperature to 180-190°C and react for 4-10 hours under nitrogen protection;

[0072] 5) Control the temperature at 180°C and evacuate at -0.1 MPa for 30 minutes to remove a small amount of unreacted small molecule diol;

[0073] 6) Cooling to 120° C. and discharging the material to obtain a polyol based on recyclable polylactic acid, which is recorded as PLA-2. Based on mass conversion, its recyclable content is about 13.3%.

[0074] 2. Synthesis of polyurethane hot melt adhesive based on recyclable raw materials

[0075] Example 1

[0076] 1) Add 50 parts of recycled PET-based polyester polyol F-39037, 10 parts of recycled polylactic acid-based polyol PLA-1, and 15.15 parts of petroleum-based polyol Dynacoll 7360 into a reactor and stir and melt at 120°C until a uniform melt state is achieved;

[0077] 2) Then add 0.1 parts of defoamer BYK-A535 and 0.05 parts of fluorescent agent UVITEX OB and stir evenly;

[0078] 3) Turn on the vacuum and dehydrate at a vacuum degree of -0.1 MPa for 1.5 hours;

[0079] 4) The system temperature was lowered to 80° C., and 20.5 parts of 4,4′-diphenylmethane diisocyanate was added thereto; the reaction was allowed to proceed naturally for 30 minutes without applying external heating; external heating was applied to control the temperature to about 110° C., and vacuum was turned on at the same time, and degassing reaction was carried out at a vacuum degree of -0.1 MPa for 30 minutes;

[0080] 5) adding 0.1 parts of catalyst DMDEE and 0.1 parts of water scavenger PTSI in sequence, and reacting at 110° C. for 10 minutes to prepare a polyurethane prepolymer while keeping the prepolymer molten;

[0081] 6) Lowering the temperature of the reaction system to 90° C., adding 4 parts of a secondary amino group-containing silane coupling agent, Dynasylan 1189, and reacting at 90° C. for 20 minutes; turning on the vacuum, and degassing and reacting at a vacuum degree of -0.1 MPa for 10 minutes;

[0082] 7) breaking the vacuum and discharging the material under nitrogen protection to obtain a polyurethane hot melt adhesive based on recyclable raw materials.

[0083] Example 2

[0084] 1) Add 55 parts of recycled PET-based polyester polyol F-39037, 10 parts of recycled polylactic acid-based polyol PLA-2, and 6.5 parts of petroleum-based polyol Dynacoll 7230 into a reactor and stir and melt at 120° C. until a uniform molten state is achieved;

[0085] 2) Then add 0.1 parts of antioxidant 1010 and 0.05 parts of fluorescent agent UVITEX OB and stir evenly;

[0086] 3) Turn on the vacuum and dehydrate at a vacuum degree of -0.1 MPa for 1.5 hours;

[0087] 4) The system temperature was lowered to 80° C., and 22.15 parts of 4,4′-diphenylmethane diisocyanate was added thereto; the reaction was allowed to proceed naturally for 30 minutes without applying external heating; external heating was applied to control the temperature to about 110° C., and vacuum was turned on at the same time, and degassing reaction was carried out at a vacuum degree of -0.1 MPa for 30 minutes;

[0088] 5) adding 0.1 parts of catalyst DMDEE and 0.1 parts of water scavenger PTSI in sequence, and reacting at 110° C. for 10 minutes to prepare a polyurethane prepolymer while keeping the prepolymer molten;

[0089] 6) Lowering the temperature of the reaction system to 95° C., adding 6 parts of a secondary amino group-containing silane coupling agent, Dynasylan 1124, and reacting at 95° C. for 20 minutes; turning on the vacuum, and degassing and reacting at a vacuum degree of -0.1 MPa for 10 minutes;

[0090] 7) breaking the vacuum and discharging the material under nitrogen protection to obtain a polyurethane hot melt adhesive based on recyclable raw materials.

[0091] Example 3

[0092] 1) 30 parts of recycled PET-based polyester polyol F-39037, 20 parts of recycled PET-based polyester polyol 51041-2000, 10 parts of recycled polylactic acid-based polyol PLA-1, 9 parts of petroleum-based polyol VORANOL 2120, and 5.15 parts of tackifying resin acrylic resin MB-2595 were added to a reactor and stirred and melted at 130° C. until a uniform molten state was achieved;

[0093] 2) Then add 0.1 parts of defoamer BYK-088 and 0.05 parts of fluorescent agent UVITEX OB and stir evenly;

[0094] 3) Turn on the vacuum and dehydrate at a vacuum degree of -0.1 MPa for 1.5 hours;

[0095] 4) The system temperature was lowered to 78° C., and 20.5 parts of 4,4′-diphenylmethane diisocyanate was added thereto; the reaction was allowed to proceed naturally for 30 minutes without applying external heating; external heating was applied to control the temperature to about 110° C., and vacuum was simultaneously turned on, and degassing reaction was carried out at a vacuum degree of -0.1 MPa for 30 minutes;

[0096] 5) adding 0.1 parts of catalyst DMDEE and 0.1 parts of water scavenger PTSI in sequence, and reacting at 110° C. for 10 minutes to prepare a polyurethane prepolymer while keeping the prepolymer molten;

[0097] 6) Lowering the temperature of the reaction system to 90° C., adding 5 parts of a secondary amino group-containing silane coupling agent, Dynasylan 1189, and reacting at 90° C. for 20 minutes; turning on the vacuum, and degassing and reacting at a vacuum degree of -0.1 MPa for 10 minutes;

[0098] 7) breaking the vacuum and discharging the material under nitrogen protection to obtain a polyurethane hot melt adhesive based on recyclable raw materials.

[0099] Example 4

[0100] 1) 40 parts of recycled PET-based polyester polyol F-39032, 10 parts of recycled PET-based polyester polyol 51041-2000, 10 parts of recycled polylactic acid-based polyol PLA-2, 10 parts of petroleum-based polyol F-932, and 5 parts of tackifying resin APAO resin 508 were added to a reactor and stirred and melted at 140° C. until a uniform molten state was achieved;

[0101] 2) Then add 0.1 parts of antioxidant 1010 and stir evenly;

[0102] 3) Turn on the vacuum and dehydrate at a vacuum degree of -0.1 MPa for 1.5 hours;

[0103] 4) The system temperature was lowered to 82° C., and 20.7 parts of 4,4′-diphenylmethane diisocyanate was added thereto; the reaction was allowed to proceed naturally for 30 minutes without applying external heating; external heating was applied to control the temperature to about 110° C., and vacuum was simultaneously turned on, and a degassing reaction was carried out at a vacuum degree of -0.1 MPa for 30 minutes;

[0104] 5) adding 0.1 parts of catalyst DMDEE and 0.1 parts of water scavenger 3-isocyanatepropyltrimethoxysilane in sequence, and reacting at 110° C. for 10 minutes to prepare a polyurethane prepolymer while keeping the prepolymer in a molten state;

[0105] 6) Lowering the temperature of the reaction system to 95° C., adding 4 parts of a secondary amino group-containing silane coupling agent, Dynasylan 1124, and reacting at 95° C. for 20 minutes; turning on the vacuum, and degassing the reaction at a vacuum degree of -0.1 MPa for 10 minutes;

[0106] 7) breaking the vacuum and discharging the material under nitrogen protection to obtain a polyurethane hot melt adhesive based on recyclable raw materials.

[0107] Comparative Example

[0108] The preparation methods, components and weight parts of the auxiliary agents of Comparative Examples 1-7 are the same as those of Example 1. The other components and weight parts are described in the form of a table as follows:

[0109]

[0110] In addition, a petroleum-based polyurethane hot melt electronic adhesive EH9650 with certain versatility on the market was selected for comparison. The physical properties and performance tests of Examples 1-4, Comparative Examples 1-7, and EH9650 are as follows:

[0111]

[0112] Test item description:

[0113] Recyclable component content of hot melt adhesive: refers to the content of net recyclable components in the glue component, specifically the weighted sum of the content of recyclable components in each recyclable raw material component, as a percentage of the total formula by mass.

[0114] Viscosity test: Use a Brookfield DV2T viscometer with a No. 28 rotor to test the viscosity of the hot melt adhesive at 100°C.

[0115] Open time: Use molten hot melt adhesive at 120°C, scrape a 200μm thick film on the release paper, and use kraft paper to test the film's viscosity. If the kraft paper breaks when it is torn after bonding, the time is within the open time. If the kraft paper can be completely torn off after bonding, it means that the film has become ineffective and this period of time is the open time of the glue.

[0116] Glue line curing status: Use the Nordson PJ-30 jet dispensing system to dispense 1mm wide glue lines. After curing for 24 hours, observe the foaming of the glue lines.

[0117] PC-PC lap shear: PC is a polycarbonate substrate, and the bonding area is 25mm*12.5mm*0.25mm (length*width*thickness). After curing for 24 hours, the shear strength is tested using an electronic universal testing machine at a tensile speed of 10mm / min.

[0118] DT4-AlAn lap shear: DT4 is galvanized stainless steel, AlAn is anodized aluminum, the bonding area is 25mm*12.5mm*0.25mm (length*width*thickness), and after curing for 72 hours (metal has better barrier properties to water vapor than plastic, so the glue in the middle needs to cure longer, with an empirical value of 72 hours), the shear strength is tested using an electronic universal testing machine at a tensile speed of 10mm / min.

[0119] PI-PI 180° peel strength: PI is a polyimide substrate with a bonding width of 25.04 mm (i.e. 1 in) and a coating thickness of 100 μm. After curing for 24 hours, the 180° peel strength is tested using an electronic universal testing machine at a tensile speed of 50 mm / min.

[0120] Double 85-7 days after aging strength attenuation rate: Prepare PC-PC lap shear specimens and test their shear strength after being placed in an aging box at 85℃-85RH% for 7 days, compared with the normal PC-PC shear strength attenuation rate.

[0121] in conclusion:

[0122] From Examples 1-4, it can be seen that the amount of recycled PET-based polyester polyol in the hot melt adhesive formula is designed to be 50% or more, and the content of recyclable components in the hot melt adhesive is above 20%; from the performance data, it can be seen that the bonding strength and PI-PI 180° peel strength of the hot melt adhesive to DT4-AlAn are significantly higher than those of the commercial petroleum-based EH9650, and the bonding strength to the common plastic substrate PC is comparable to that of EH9650; in the evaluation of the wet heat aging performance, the strength decay rate of the hot melt adhesive after double 85-7 days of aging is lower than that of EH9650. Example 2 uses a larger amount of PET-based polyol and secondary amino silane coupling agent, and its wet heat aging resistance performance is the best.

[0123] In terms of balancing the viscosity of the hot melt adhesive and the problem of bubbles after curing, since the large-scale use of polyester polyols based on recycled PET will increase the viscosity of the hot melt adhesive, Examples 1-4 reduce the viscosity of the hot melt adhesive by increasing the amount of isocyanate, and then use a secondary amino silane coupling agent to consume some of the excess NCO groups introduced by the isocyanate, limiting the R value to the range of 2-5. The viscosity of the obtained hot melt adhesive is moderate, and the glue line does not foam after curing.

[0124] Comparative Examples 1-7 are control examples of Example 1. In Comparative Example 1, the content of polyol based on recycled PET is less than 50%, and the PC-PC lap shear, DT4-AlAn lap shear, and PI-PI 180° peel strengths of the hot melt adhesive are lower than those of Examples 1-4.

[0125] Comparative Example 2, in which no polyol based on recyclable polylactic acid was added, had an open time similar to that of Example 1. A characteristic of polyurethane hot melt adhesives is that the polyol portion primarily affects the open time of the hot melt adhesive. The difference in the polyol portion between the two formulations is that Example 1 uses PLA-1, while Comparative Example 2 uses liquid polyol Dynacoll 7250. This suggests that the synthesized polyol based on recyclable polylactic acid has the ability to regulate the open time of the hot melt adhesive, similar to a liquid polyol. Comparative Example 2 uses a petroleum-based liquid polyol, and the content of recyclable components in the hot melt adhesive is less than 20%.

[0126] In Comparative Example 3, no recycled PET-based polyol was added, and a larger amount of polylactic acid-based polyol was used, resulting in a significantly longer open time for the hot melt adhesive. Because the formula did not contain PET-based polyol with an aromatic ring structure, the hot melt adhesive exhibited poor bonding strength to both metal and polyimide substrates, with a higher strength decay rate after aging for 85-7 days than that of Examples 1-4.

[0127] In Comparative Example 4, the R value was 1.95, indicating a low isocyanate content. Consequently, the free NCO content in the resulting hot melt adhesive was reduced, controlling the bubble problem after curing. However, the hot melt adhesive had a high viscosity of 23,740 cp / 100°C, making it unsuitable for use as an electronic adhesive. For bonding, the PC-PC lap shear, DT4-AlAn lap shear, and PI-PI 180° peel strengths were low, and the strength degradation was severe after aging for 85-7 days.

[0128] In Comparative Example 5, the R value was 5.16, and the viscosity of the prepared hot melt adhesive was 2277 cp. The large amount of free NCO in the hot melt adhesive caused foaming of the hot melt adhesive after curing. The foaming of the adhesive line directly affected the bonding strength of the hot melt adhesive to the substrate, resulting in a decrease in the bonding strength. The PC-PC lap shear, DT4-AlAn lap shear, and PI-PI 180° peel strengths were very low. In addition, the substrate fell off after aging for 85-7 days, and the hot melt adhesive lost its adhesion.

[0129] The silane coupling agent in Comparative Example 6 contains two secondary amino groups. After addition, the reaction is violent, resulting in increased viscosity, poor adhesion and resistance to wet heat aging.

[0130] The silane coupling agent in Comparative Example 7 contains primary amino groups, which gel after being added, and the prepared hot melt adhesive has gel particles.

[0131] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art will be able to modify the technical solutions described in the aforementioned embodiments or substitute equivalents for some of the technical features. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A polyurethane hot melt adhesive based on recyclable raw materials, characterized in that: The raw materials for preparing the polyurethane hot melt adhesive include: polyester polyol based on recycled PET, polyol based on recyclable polylactic acid, petroleum-based polyol and / or tackifying resin, silane coupling agent containing secondary amine group, isocyanate; Relative to the total weight of the polyurethane hot melt adhesive, the content of the polyester polyol based on recycled PET is 50 wt % to 70 wt %; The molecular weight of the polyester polyol based on recycled PET is 2000-3500; The amount of isocyanate added is such that the NCO / OH molar ratio, denoted as (R), is in the range of 2-5.

2. The polyurethane hot melt adhesive according to claim 1, characterized in that: The hydroxyl value of the polyester polyol based on recycled PET is 27-62 mg / KOH, and the hydroxyl value of the polyol based on recyclable polylactic acid is 20-140 mg / KOH.

3. The polyurethane hot melt adhesive according to claim 1, characterized in that: The preparation method of the polyol based on recyclable polylactic acid is: 1) Adding recycled polylactic acid into the reactor, raising the temperature to 160-190°C to obtain molten polylactic acid; 2) Evacuate the reactor at a vacuum degree of -0.1Mpa for 30 minutes; break the vacuum and introduce inert gas into the reactor to replace the air therein for 20 minutes; 3) Add small molecule diol and catalyst into the reactor in sequence, stir for 5-15 minutes, and replace with inert gas again for 20 minutes; 4) Control the temperature to 180-190°C and react for 4-10 hours under inert gas protection; 5) Control the temperature at 180±5℃ and evacuate at -0.1Mpa for 30 minutes to remove a small amount of unreacted small molecule diol; 6) Cooling to 120±5°C and discharging the material to obtain the polyol based on recyclable polylactic acid.

4. The polyurethane hot melt adhesive according to claim 1, characterized in that: The petroleum-based polyol is one or more of crystalline polyester polyol, liquid polyester polyol and polyether polyol.

5. The polyurethane hot melt adhesive according to claim 1, characterized in that: The tackifying resin is one or more of acrylic resin, petroleum resin and amorphous α-olefin copolymer.

6. The polyurethane hot melt adhesive according to claim 1, characterized in that: The isocyanate is an aromatic diisocyanate, which is one or more of 4,4'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate, 2,2'-diphenylmethane diisocyanate, and carbodiimide-modified diphenylmethane diisocyanate.

7. The polyurethane hot melt adhesive according to claim 1, characterized in that: The secondary amine group-containing silane coupling agent contains only a single secondary amine group.

8. The polyurethane hot melt adhesive according to claim 7, characterized in that: The secondary amine-containing silane coupling agent is one or more of N-n-butyl-3-aminopropyltrimethoxysilane, bis-[3-(trimethoxysilane)-propyl]-amine, bis-[3-(triethoxysilane)-propyl]-amine, and N-ethyl-3-trimethoxysilane-2-methylpropylamine.

9. The polyurethane hot melt adhesive according to claim 1, characterized in that: The raw materials for preparing the polyurethane hot melt adhesive also include auxiliary agents, and the auxiliary agents are one or more of defoaming agents, fluorescent agents, dewatering agents, antioxidants, and amine catalysts.

10. The polyurethane hot melt adhesive according to any one of claims 1 to 8, characterized in that: In parts by weight, the components of the polyurethane hot melt adhesive are as follows: 50-70 parts of polyester polyol based on recycled PET, 10-30 parts of polyol based on recycled polylactic acid, Petroleum-based polyol 0-10 parts, 0-10 parts of tackifying resin, 2-15 parts of silane coupling agent containing secondary amine group, Isocyanate 10-30 parts, The weight parts of the petroleum-based polyol and the tackifying resin are not both 0, The total weight parts of the polyurethane hot melt adhesive is 100 parts.

11. The polyurethane hot melt adhesive according to claim 10, characterized in that: The polyurethane hot melt adhesive also includes 0.07-3.5 parts of an auxiliary agent.

12. A method for preparing a polyurethane hot melt adhesive based on recyclable raw materials, characterized in that: The following steps are involved: 1) Prepare a molten polyol mixture by the following raw materials: a) at least one polyester polyol based on recycled PET; b) at least one polyol based on recycled polylactic acid; c) Petroleum-based polyols or tackifying resins; 2) adding isocyanate and a polyol mixture for polymerization to obtain a polyurethane prepolymer, wherein the molar ratio of NCO in the isocyanate to OH in the polyol mixture is 2-5; 3) Add a secondary amine-containing silane coupling agent and graft it onto the main chain of the polyurethane prepolymer to obtain a polyurethane hot melt adhesive based on recyclable raw materials.

13. The method for preparing the polyurethane hot melt adhesive according to claim 12, characterized in that: The following steps are also included: Adding an auxiliary agent between step 1) and step 2); or / and adding an auxiliary agent between step 2) and step 3).

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