Polyurethane adhesive, process for its preparation and use

Abstract

The application discloses a polyurethane adhesive as well as a preparation method and application thereof. The polyurethane adhesive comprises a polyester polyol and an isocyanate trimer; the polyester polyol comprises a phenyl group; the isocyanate trimer comprises a siloxane group; and the mass ratio of the polyester polyol to the isocyanate trimer is (10-20):1. Thus, under the synergistic effect of the polyester polyol and the isocyanate trimer, the polyurethane adhesive with higher crosslinking density, excellent heat deformation resistance and good wet heat resistance can be obtained.

Description

Technical Field

[0001] This application relates to the field of adhesives, and more specifically, to polyurethane adhesives, their preparation methods, and applications. Background Technology

[0002] In the adhesive industry, polyurethane adhesives are one of the most widely used categories. However, traditional polyurethane adhesives are prone to molecular chain degradation under high temperature and high humidity conditions, which leads to a significant decrease in bond strength. This makes it difficult for polyurethane adhesives to meet the requirements of more demanding application scenarios, severely limiting their further widespread use.

[0003] It should be noted that the above statements are only used to provide background information related to this application and do not necessarily constitute prior art. Summary of the Invention

[0004] In a first aspect of this application, a polyurethane adhesive is provided, comprising a polyester polyol and an isocyanate trimer; the polyester polyol comprises a phenyl group; the isocyanate trimer comprises a siloxane group; and the mass ratio of the polyester polyol to the isocyanate trimer is (10-20):1.

[0005] The phenyl groups in polyester polyols impart structural rigidity to polyurethane adhesives, thereby improving their hardness and tensile strength. Simultaneously, the stable conjugated structure of the benzene ring enhances the heat resistance of the polyurethane adhesive. The isocyanate trimer exhibits a high crosslinking density, further increasing the tensile strength of the polyurethane adhesive. Furthermore, the siloxane groups in the isocyanate trimer hydrolyze to generate silanols (-Si-OH), which, through self-condensation, form a Si-O-Si network structure, thus enhancing the hydrolysis resistance and adhesion of the polyurethane adhesive. Therefore, by controlling the mass ratio of polyester polyol to isocyanate trimer within the aforementioned range, and through the synergistic effect of the two components, a polyurethane adhesive with higher crosslinking density, excellent heat distortion resistance, and good resistance to damp heat can be obtained.

[0006] In some embodiments, the polyester polyol satisfies one or two of the following conditions: the weight-average molecular weight of the polyester polyol is 20,000-50,000; and the hydroxyl value of the polyester polyol is 10 mg KOH / g-20 mg KOH / g. Therefore, by independently controlling the weight-average molecular weight and the hydroxyl value of the polyester polyol within the aforementioned ranges, the molecular chain segments of the polyester polyol can be controlled within an appropriate range. This not only improves the mechanical properties of the polyurethane adhesive but also controls its viscosity within an appropriate range, thereby reducing the impact on construction efficiency.

[0007] In some embodiments, the polyester polyol comprises, by weight parts: 80-180 parts aliphatic diol, 40-80 parts aliphatic diacid, and 50-100 parts aromatic diacid. The aromatic diacid imparts a phenyl group to the polyester polyol. The phenyl group can give the polyurethane adhesive structural rigidity, thereby improving the hardness and tensile strength of the polyurethane adhesive. Simultaneously, the benzene ring has a stable conjugated structure, which can improve the heat resistance of the polyurethane adhesive. The aliphatic molecular chains of the aliphatic diol and aliphatic diacid can provide a long carbon chain structure, thereby improving the hydrolysis resistance and flexibility of the polyester polyol. Therefore, by controlling the weight parts of each raw material in the polyester polyol within the aforementioned range, a polyester polyol with a weight-average molecular weight and a hydroxyl value within the range defined in this application can be obtained.

[0008] In some embodiments, one or more of the following conditions are met: the aliphatic diol includes one or more of ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, and 3-methyl-1,5-pentanediol; the aliphatic dicarboxylic acid includes one or more of oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, and sebacic acid; and the aromatic dicarboxylic acid includes one or more of phthalic acid, isophthalic acid, and terephthalic acid. Therefore, by independently controlling the types of aliphatic diacids and aliphatic diols within the aforementioned range, the aliphatic molecular chains of the aliphatic diacids and aliphatic diols can provide long carbon chain structures, thereby improving the hydrolysis resistance and flexibility of polyester polyols. Similarly, by controlling the types of aromatic diacids within the aforementioned range, aromatic diacids impart phenyl groups to polyester polyols. The phenyl groups can give polyurethane adhesives structural rigidity, thereby improving the hardness and tensile strength of polyurethane adhesives. Simultaneously, the stable conjugated structure of the benzene ring can improve the heat resistance of polyurethane adhesives.

[0009] In some embodiments, the molar ratio of siloxane groups to isocyanate groups in the isocyanate trimer is 3:(2-4). The siloxane groups hydrolyze to generate silanols (-Si-OH), which, after self-condensation, form a Si-O-Si network structure, thereby enhancing the hydrolysis resistance and adhesion of the polyurethane adhesive. Therefore, controlling the molar ratio of siloxane groups to isocyanate groups within the aforementioned range not only effectively enhances the hydrolysis resistance and adhesion of the polyurethane adhesive but also allows for control of the isocyanate dosage to regulate curing speed and cost.

[0010] In some embodiments, the isocyanate trimer comprises, by weight, 40-100 parts isocyanate and 10-30 parts silane coupling agent. Therefore, by controlling the weight percentages of each raw material in the isocyanate trimer within the aforementioned range, the mass ratio of siloxane groups to isocyanate groups in the isocyanate trimer can be controlled within the range defined in this application. This not only effectively enhances the hydrolysis resistance and adhesion of the polyurethane adhesive, but also allows for control of the isocyanate dosage to regulate curing speed and cost.

[0011] In some embodiments, one or two of the following conditions are met: the isocyanate includes one or more of toluene diisocyanate, isophorone diisocyanate, and hexamethylene diisocyanate; the silane coupling agent includes one or more of γ-aminopropyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-mercaptopropyltrimethoxysilane, and γ-mercaptopropyltriethoxysilane. Therefore, controlling the type of isocyanate within the aforementioned range is one of the fundamental conditions for preparing isocyanate trimers; controlling the type of silane coupling agent within the aforementioned range allows the isocyanate trimer to contain siloxane groups. The siloxane groups can hydrolyze to generate silanols (-Si-OH), and the silanols can form a Si-O-Si network structure after self-condensation, thereby enhancing the hydrolysis resistance and adhesion of the polyurethane adhesive.

[0012] In a second aspect, this application provides a method for preparing a polyurethane adhesive, comprising: S1. Mix aliphatic diol, aliphatic diacid, and aromatic diacid, and sequentially carry out esterification and polycondensation reactions to obtain the polyester polyol. S2. The isocyanate and silane coupling agent are mixed and subjected to nucleophilic addition and trimerization reactions in sequence to obtain the isocyanate trimer. S3. The polyester polyol and the isocyanate trimer are mixed to obtain the polyurethane adhesive; the mass ratio of the polyester polyol and the isocyanate trimer is (10-20):1.

[0013] The -OH group of aliphatic diols and the -COOH group of diacids (aliphatic and aromatic diacids) undergo dehydration, resulting in esterification to form ester bonds (-COO-), thus forming polyester oligomers containing active functional groups at both ends. Subsequently, these oligomers undergo polycondensation to repeatedly remove small water molecules, forming long-chain polymers, ultimately resulting in polyester polyols with a main chain containing numerous ester bonds (-COO-). The -NCO group in isocyanates undergoes nucleophilic addition reactions with amino, thiol, or epoxy groups in silane coupling agents, thus initially modifying the isocyanate to introduce siloxane groups. Subsequently, the modified isocyanate undergoes trimerization to form isocyanate trimers. The resulting isocyanate trimers include siloxane groups. Therefore, by controlling the mass ratio of polyester polyol and isocyanate trimer within the aforementioned range, a polyurethane adhesive with higher crosslinking density, excellent heat deformation resistance, and good resistance to humid heat can be obtained under the synergistic effect of the two components of polyester polyol and isocyanate trimer.

[0014] In some implementations, one or more of the following conditions are met: The esterification reaction is carried out at a temperature of 180℃-240℃ and for a reaction time of 3h-5h. The reaction temperature of the polycondensation reaction is 180℃-240℃; the reaction time of the polycondensation reaction is 3h-5h. The polycondensation reaction is carried out under vacuum conditions; The steps of esterification and polycondensation further include adding a first catalyst, which includes one or more of antimony acetate, calcium acetate, zinc acetate, manganese acetate, cobalt acetate, magnesium acetate, tetrabutyl titanate, isopropyl titanate, and organotin compounds. The nucleophilic addition reaction is carried out at a temperature of 65℃-85℃ and for a time of 1h-1.5h. The trimerization reaction temperature is 65℃-85℃; the trimerization reaction time is 5h-6h. The step of the trimerization reaction further includes the addition of a second catalyst, which comprises potassium acetate and octanoic acid. Potassium One or more of the amine-based delayed catalysts DABCO TMR-3.

[0015] Therefore, by independently controlling the parameters in the preparation of polyurethane adhesives within the aforementioned range, the degree of reaction at each stage can be controlled to obtain polyurethane adhesives with higher crosslinking density, excellent heat deformation resistance, and good resistance to humid heat.

[0016] In a third aspect, this application provides the application of the aforementioned polyurethane adhesive, or the polyurethane adhesive prepared by the aforementioned method, in high-temperature or humid environments. Detailed Implementation

[0017] The embodiments of this application are disclosed in detail below. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of actually identical structures may be omitted. This is to avoid making the following description unnecessarily lengthy and to facilitate understanding by those skilled in the art.

[0018] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is also expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0019] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0020] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0021] Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used in this application is for the purpose of describing particular embodiments only and is not intended to limit this application; unless otherwise stated, the values ​​of the parameters mentioned in this application can be measured using various measurement methods commonly used in the art (e.g., they can be tested according to the methods given in the embodiments of this application).

[0022] In the description of this application, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. "First feature" and "second feature" may include one or more of the indicated feature.

[0023] In the description of this application, "A and / or B" can include any of the cases of A alone, B alone, or A and B, where A and B are merely examples and can be any technical feature connected by "and / or" in this application.

[0024] In related technologies, polyurethane adhesives (PU adhesives) can be used as adhesives between interior trim films and substrates. They have the advantages of low toxicity and good biocompatibility, meet environmental protection requirements, and can also firmly bond interior trim films and substrates through abundant polar groups on the molecular chain, thereby improving the long-term aesthetics and structural stability of interior trim films. This makes them one of the important choices for interior trim film and substrate composites.

[0025] However, traditional polyurethane adhesives are prone to molecular chain degradation under high temperature and high humidity conditions, leading to a significant decrease in bond strength. In the application of automotive interior films, this performance limitation directly causes delamination failure between the interior film and the substrate in high temperature or high humidity environments. This not only damages the appearance integrity of the automotive interior film but also reduces the structural stability of interior components and shortens their service life, severely restricting the further application of interior films in the production of high-quality automotive interiors.

[0026] Based on this, in a first aspect, this application provides a polyurethane adhesive comprising a polyester polyol and an isocyanate trimer; Polyester polyols include phenyl groups; isocyanate trimers include siloxane groups; The mass ratio of polyester polyol to isocyanate trimer is (10-20):1.

[0027] The phenyl groups in polyester polyols can impart structural rigidity to polyurethane adhesives, thereby improving their hardness and tensile strength. Simultaneously, the stable conjugated structure of the benzene ring can enhance the heat resistance of polyurethane adhesives. The high crosslinking density of isocyanate trimers can improve the tensile strength of polyurethane adhesives. Furthermore, the hydrolysis of the siloxane groups in the isocyanate trimers can generate silanols (-Si-OH), which, after self-condensation, can form a Si-O-Si network structure, thereby enhancing the hydrolysis resistance and adhesion of polyurethane adhesives.

[0028] However, if there is too much polyester polyol, the hydroxyl groups will not react completely, resulting in insufficient crosslinking density and thus insufficient heat resistance of the finished interior film. If there is too little polyester polyol, there will be too few crosslinking sites that can react with isocyanate groups. In addition to insufficient crosslinking density leading to insufficient heat resistance of the interior film, excessive isocyanate trimer will also react with moisture in the air or further self-polymerize, resulting in the overall performance of the film being too hard and lacking weather resistance.

[0029] Therefore, by controlling the mass ratio of polyester polyol and isocyanate trimer within the aforementioned range, a polyurethane adhesive with higher crosslinking density, excellent heat deformation resistance, and good resistance to humid heat can be obtained under the synergistic effect of the two components of polyester polyol and isocyanate trimer.

[0030] As an example, the mass ratio of polyester polyol to isocyanate trimer can be 10:1, 10.5:1, 11:1, 11.5:1, 12:1, 12.5:1, 13:1, 13.5:1, 14:1, 14.5:1, 15:1, 15.5:1, 16:1, 16.5:1, 17:1, 17.5:1, 18:1, 18.5:1, 19:1, 19.5:1, 20:1, or a range of any two of the above values.

[0031] In some embodiments, the weight-average molecular weight of the polyester polyol is 20,000-50,000.

[0032] Therefore, by controlling the weight-average molecular weight of polyester polyol within the aforementioned range, the molecular chain segments of polyester polyol can be controlled within an appropriate range. This not only improves the mechanical properties of polyurethane adhesives but also controls the viscosity of polyurethane adhesives within an appropriate range, thereby reducing the impact on construction efficiency.

[0033] The weight-average molecular weight of polyester polyols can be tested using the following methods. For example, gel permeation chromatography can be used.

[0034] As an example, the weight-average molecular weight of polyester polyols can be 20,000, 25,000, 30,000, 35,000, 40,000, 45,000, 50,000, etc., or a range consisting of any two of the above values.

[0035] In some embodiments, the hydroxyl value of the polyester polyol is 10 mg KOH / g-20 mg KOH / g.

[0036] The hydroxyl value of polyester polyols refers to the mass of potassium hydroxide (KOH) corresponding to the amount of hydroxyl groups (-OH) in 1 gram of polyester polyol, expressed in mg KOH / g. The hydroxyl value of polyester polyols can be tested using methods commonly used in the field, such as the acetic anhydride-pyridine acylation method.

[0037] Therefore, by controlling the hydroxyl value of the polyester polyol within the aforementioned range, the crosslinking density of the polyester polyol can be controlled within an appropriate range. This not only improves the mechanical properties of the polyurethane adhesive but also controls the viscosity of the polyurethane adhesive within an appropriate range, thereby reducing its impact on construction efficiency.

[0038] As an example, the hydroxyl value of the polyester polyol can be 10 mgKOH / g, 11 mgKOH / g, 12 mgKOH / g, 13 mgKOH / g, 14 mgKOH / g, 15 mgKOH / g, 16 mgKOH / g, 17 mgKOH / g, 18 mgKOH / g, 19 mgKOH / g, 20 mgKOH / g, etc., or a range consisting of any two of the above values.

[0039] In some embodiments, the polyester polyol comprises the following raw materials by weight: 80-180 parts aliphatic diols, 40-80 parts aliphatic dicarboxylic acids, and 50-100 parts aromatic dicarboxylic acids.

[0040] Aromatic diacids impart phenyl groups to polyester polyols. Phenyl groups can give polyurethane adhesives structural rigidity, thereby improving the hardness and tensile strength of polyurethane adhesives. At the same time, the benzene ring has a stable conjugated structure, which can improve the heat resistance of polyurethane adhesives. The aliphatic molecular chains of aliphatic diols and aliphatic diacids can provide long carbon chain structures, thereby improving the hydrolysis resistance and flexibility of polyester polyols.

[0041] Therefore, by controlling the weight proportions of each raw material in the polyester polyol within the aforementioned range, a polyester polyol with a weight-average molecular weight and a hydroxyl value within the range defined in this application can be obtained.

[0042] As an example, aliphatic diols can be 80 parts, 90 parts, 100 parts, 110 parts, 120 parts, 130 parts, 140 parts, 150 parts, 160 parts, 170 parts, 180 parts, etc., or a range of any two of the above values.

[0043] As an example, the aliphatic dicarboxylic acid can be 40 parts, 45 parts, 50 parts, 55 parts, 60 parts, 65 parts, 70 parts, 75 parts, 80 parts, etc., or a range consisting of any two of the above values.

[0044] As an example, the aromatic dicarboxylic acid can be 50 parts, 55 parts, 60 parts, 65 parts, 70 parts, 75 parts, 80 parts, 85 parts, 90 parts, 95 parts, 100 parts, etc., or a range consisting of any two of the above values.

[0045] In some embodiments, the aliphatic diols include one or more of ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, and 3-methyl-1,5-pentanediol.

[0046] Therefore, by controlling the types of aliphatic diols within the aforementioned range, the aliphatic molecular chains of the aliphatic diols can provide long carbon chain structures, thereby improving the hydrolysis resistance and flexibility of polyester polyols.

[0047] In some embodiments, the aliphatic dicarboxylic acid includes one or more of oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, and sebacic acid.

[0048] Therefore, by controlling the types of aliphatic dicarboxylic acids within the aforementioned range, the aliphatic molecular chains of the aliphatic dicarboxylic acids can provide long carbon chain structures, thereby improving the hydrolysis resistance and flexibility of polyester polyols.

[0049] In some embodiments, the aromatic dicarboxylic acid includes one or more of phthalic acid, isophthalic acid, and terephthalic acid.

[0050] Therefore, by controlling the types of aromatic dicarboxylic acids within the aforementioned range, the aromatic dicarboxylic acids impart phenyl groups to the polyester polyols. The phenyl groups can give the polyurethane adhesives structural rigidity, thereby improving the hardness and tensile strength of the polyurethane adhesives. At the same time, the benzene rings have a stable conjugated structure, which can improve the heat resistance of the polyurethane adhesives.

[0051] In some embodiments, the molar ratio of siloxane groups to isocyanate groups in the isocyanate trimer is 3:(2-4).

[0052] The hydrolysis of siloxane groups can generate silanols (-Si-OH), which can then undergo self-condensation to form a Si-O-Si network structure, thereby enhancing the hydrolysis resistance and adhesion of polyurethane adhesives. Therefore, controlling the mass ratio of siloxane groups to isocyanate groups within the aforementioned range can not only effectively enhance the hydrolysis resistance and adhesion of polyurethane adhesives, but also control the amount of isocyanate used to regulate curing speed and cost.

[0053] As an example, the mass ratio of siloxane groups to isocyanate groups can be 3:2, 3:2.5, 3:3, 3:3.5, 3:4, or a range of any two of the above values.

[0054] In some embodiments, the isocyanate trimer comprises the following raw materials in parts by weight: 40-100 parts isocyanate and 10-30 parts silane coupling agent.

[0055] Therefore, by controlling the weight proportions of each raw material in the isocyanate trimer within the aforementioned range, the mass ratio of siloxane groups and isocyanate groups in the isocyanate trimer can be controlled within the range defined in this application. This not only effectively enhances the hydrolysis resistance and adhesion of polyurethane adhesives, but also controls the amount of isocyanate used to control the curing speed and cost.

[0056] In some embodiments, the isocyanate includes one or more of toluene diisocyanate, isophorone diisocyanate, and hexamethylene diisocyanate.

[0057] Therefore, controlling the types of isocyanates within the aforementioned range is one of the fundamental conditions for preparing isocyanate trimers.

[0058] In some embodiments, the silane coupling agent includes one or more of γ-aminopropyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-mercaptopropyltrimethoxysilane, and γ-mercaptopropyltriethoxysilane.

[0059] Therefore, by controlling the type of silane coupling agent within the aforementioned range, the isocyanate trimer can contain siloxane groups. The siloxane groups can be hydrolyzed to generate silanols (-Si-OH). After self-condensation, the silanols can form a Si-O-Si network structure, thereby enhancing the hydrolysis resistance and adhesion of polyurethane adhesives.

[0060] In a second aspect, this application provides a method for preparing a polyurethane adhesive, comprising the following steps: S1. Aliphatic diols, aliphatic diacids, and aromatic diacids are mixed and subjected to esterification and polycondensation reactions in sequence to obtain polyester polyols.

[0061] First, the -OH group of aliphatic diols and the -COOH group of diacids (aliphatic and aromatic diacids) undergo dehydration, resulting in esterification to form ester bonds (-COO-), which in turn forms polyester oligomers containing active functional groups at both ends. Then, the polyester oligomers containing active functional groups at both ends undergo polycondensation to repeatedly remove small molecule water, forming long-chain polymers, and finally forming polyester polyols with a main chain containing a large number of ester bonds (-COO-).

[0062] In some embodiments, the esterification reaction temperature is 180℃-240℃; the esterification reaction time is 3h-5h.

[0063] Therefore, by controlling the reaction temperature and reaction time of the esterification reaction within the range specified in this application, not only can the reaction rate of the esterification reaction be increased, but also the production cost can be controlled.

[0064] As an example, the reaction temperature for esterification can be 180℃, 185℃, 190℃, 195℃, 200℃, 205℃, 210℃, 215℃, 220℃, 225℃, 230℃, 235℃, 240℃, or a range of any two of the above values.

[0065] As an example, the reaction time for esterification can be 3h, 3.2h, 3.4h, 3.6h, 3.8h, 4h, 4.2h, 4.4h, 4.6h, 4.8h, 5h, or any range of two of the above values.

[0066] In some embodiments, the reaction temperature of the polycondensation reaction is 180℃-240℃; the reaction time of the polycondensation reaction is 3h-5h.

[0067] Therefore, by controlling the reaction temperature and reaction time of the polycondensation reaction within the range specified in this application, not only can the reaction rate of the polycondensation reaction be increased, but also the production cost can be controlled.

[0068] As an example, the reaction temperature of the polycondensation reaction can be 180℃, 185℃, 190℃, 195℃, 200℃, 205℃, 210℃, 215℃, 220℃, 225℃, 230℃, 235℃, 240℃, or a range of any two of the above values.

[0069] As an example, the reaction time of polycondensation can be 3h, 3.2h, 3.4h, 3.6h, 3.8h, 4h, 4.2h, 4.4h, 4.6h, 4.8h, 5h, or any range of two of the above values.

[0070] In some implementations, the polycondensation reaction is carried out under vacuum conditions.

[0071] Therefore, vacuum conditions can disrupt the reversible equilibrium of the polycondensation reaction, thereby promoting the growth of polyester polyol molecular chains and increasing the weight-average molecular weight of polyester polyols.

[0072] In some embodiments, the steps of esterification and polycondensation further include adding a first catalyst, which includes one or more of antimony acetate, calcium acetate, zinc acetate, manganese acetate, cobalt acetate, magnesium acetate, tetrabutyl titanate, isopropyl titanate, and organotin compounds.

[0073] Therefore, the first catalyst within the aforementioned range can increase the polycondensation reaction rate and improve the weight-average molecular weight of the polyester polyol.

[0074] In some embodiments, the esterification and polycondensation reactions are carried out under a first inert atmosphere.

[0075] Therefore, the introduction of the first inert gas into the reaction system can remove the small water molecules generated in the reaction, while isolating moisture in the air, thus promoting the forward esterification and polycondensation reactions to increase the esterification rate and the degree of polymerization of the polycondensation products.

[0076] In some embodiments, the first inert atmosphere may include one or both of nitrogen and argon.

[0077] S2. The isocyanate and silane coupling agent are mixed and subjected to nucleophilic addition and trimerization reactions in sequence to obtain isocyanate trimer.

[0078] First, the -NCO group in the isocyanate undergoes a nucleophilic addition reaction with the amino / thiol / epoxy group in the silane coupling agent, thereby initially modifying the isocyanate to introduce siloxane groups. Then, the modified isocyanate undergoes a trimerization reaction to form an isocyanate trimer. The resulting isocyanate trimer includes siloxane groups.

[0079] In some embodiments, the nucleophilic addition reaction is carried out at a temperature of 65°C-85°C and for a reaction time of 1-1.5 hours.

[0080] Therefore, by controlling the reaction temperature and reaction time of the nucleophilic addition reaction within the range specified in this application, not only can the reaction rate of the nucleophilic addition reaction be increased, but production costs can also be controlled.

[0081] As an example, the reaction temperature for nucleophilic addition reactions can be 65℃, 67℃, 69℃, 71℃, 73℃, 75℃, 77℃, 79℃, 81℃, 83℃, 85℃, or a range of any two of the above values.

[0082] As an example, the reaction time for a nucleophilic addition reaction can be 1 h, 1.1 h, 1.2 h, 1.3 h, 1.4 h, 1.5 h, or a range of any two of the above values.

[0083] In some embodiments, the trimerization reaction temperature is 65°C-85°C; the trimerization reaction time is 5h-6h.

[0084] Therefore, by controlling the reaction temperature and reaction time of the trimerization reaction within the range specified in this application, not only can the reaction rate of the trimerization reaction be increased, but also the production cost can be controlled.

[0085] As an example, the reaction temperature for trimerization can be 65℃, 67℃, 69℃, 71℃, 73℃, 75℃, 77℃, 79℃, 81℃, 83℃, 85℃, or a range of any two of the above values.

[0086] As an example, the reaction time for trimerization can be 5h, 5.2h, 5.4h, 5.6h, 5.8h, 6h, or any range of two of the above values.

[0087] In some embodiments, the trimerization step further includes the addition of a second catalyst, which may include potassium acetate or octanoic acid. Potassium One or more of the amine-based delayed catalysts DABCO TMR-3.

[0088] Therefore, the second catalyst within the aforementioned range can increase the trimer reaction rate, thereby increasing the crosslinking degree of the isocyanate trimer.

[0089] In some embodiments, after the nucleophilic addition reaction and trimerization reaction occur sequentially, a quencher is added.

[0090] Therefore, the quencher can terminate the trimer reaction, thereby controlling the degree of crosslinking of the isocyanate trimer.

[0091] In some implementations, the quenching agent may include benzoyl chloride.

[0092] In some embodiments, the nucleophilic addition reaction and trimerization reaction are carried out under a second inert atmosphere.

[0093] Therefore, the second inert atmosphere can isolate moisture and oxygen in the air, thereby reducing the degree of side reactions in the reaction system.

[0094] In some embodiments, the second inert atmosphere may include one or both of nitrogen and argon.

[0095] S3. Mix polyester polyol and isocyanate trimer to obtain polyurethane adhesive; the mass ratio of polyester polyol to isocyanate trimer is (10-20):1.

[0096] Therefore, by controlling the mass ratio of polyester polyol and isocyanate trimer within the aforementioned range, a polyurethane adhesive with higher crosslinking density, excellent heat deformation resistance, and good resistance to humid heat can be obtained under the synergistic effect of the two components of polyester polyol and isocyanate trimer.

[0097] In a third aspect, this application provides an application of a polyurethane adhesive prepared by the aforementioned method or the aforementioned polyurethane adhesive in a high-temperature or humid environment.

[0098] The polyurethane adhesive of this application exhibits excellent heat deformation resistance and good resistance to damp heat, making it suitable for use in environments with temperatures not exceeding 80°C and relative humidity not exceeding 80%. For example, as a bonding material, the polyurethane adhesive of this application can be used in high-quality automotive interiors, outdoor decorative products, and other similar applications.

[0099] Example The following specific embodiments illustrate the solution of this application. It should be noted that these embodiments are for illustrative purposes only and should not be considered as limiting the scope of this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0100] Example 1 The preparation of polyurethane adhesives includes the following steps: S1. Preparation of polyester polyols: 22g of ethylene glycol, 100g of 3-methyl-1,5-pentanediol, 58g of adipic acid, 68g of terephthalic acid, 32g of isophthalic acid, and 0.04g of antimony acetate were added to a reaction vessel. Under a nitrogen atmosphere, the temperature was raised to 240℃ and the esterification reaction was carried out for 3 hours. Then, the vacuum pump was turned on to gradually increase the vacuum degree inside the reaction vessel. After reacting for another 5 hours, the product was discharged to obtain polyester polyol.

[0101] The weight-average molecular weight of the obtained polyester polyol was 42,000; the hydroxyl value of the polyester polyol was 15 mg KOH / g.

[0102] S2. Preparation of isocyanate trimer: 53.3 g of toluene diisocyanate and 22.1 g of γ-aminopropyltriethoxysilane were added to a reaction vessel and heated to 70 °C under a nitrogen atmosphere. The mixture was stirred for 1.5 h. Then, butyl acetate and 0.04 g of potassium acetate were added and the mixture was kept at this temperature for 5 h. Finally, benzoyl chloride was added and the mixture was kept at this temperature for 1 h. The mixture was then cooled to obtain the isocyanate trimer.

[0103] In the obtained isocyanate trimer, the molar ratio of siloxane groups to isocyanate groups is 3:2.5.

[0104] S3. Mix polyester polyol and isocyanate trimer at a mass ratio of 10:1 until homogeneous, and dilute with an appropriate amount of ethyl acetate to obtain a two-component polyurethane adhesive.

[0105] Examples 2-9 The difference between Example 2 and Example 1 is that the polyester polyol and isocyanate trimer are mixed at a mass ratio of 16:1.

[0106] The difference between Example 3 and Example 1 is that the polyester polyol and isocyanate trimer are mixed at a mass ratio of 20:1.

[0107] The difference between Example 4 and Example 1 is that terephthalic acid is replaced with phthalic acid in the preparation of polyester polyol.

[0108] The difference between Example 5 and Example 1 is that the weight-average molecular weight of the polyester polyol is 20,000.

[0109] The difference between Example 6 and Example 1 is that the weight-average molecular weight of the polyester polyol is 50,000.

[0110] The difference between Example 7 and Example 1 is that, in the process of preparing the isocyanate trimer, γ-aminopropyltriethoxysilane silane is replaced with γ-glycidoxypropyltrimethoxysilane.

[0111] The difference between Example 8 and Example 1 is that when preparing the isocyanate trimer, the mass of toluene diisocyanate added is 43.5g, and the molar ratio of siloxane groups to isocyanate groups in the obtained isocyanate trimer is 3:2.

[0112] The difference between Example 9 and Example 1 is that when preparing the isocyanate trimer, the mass of toluene diisocyanate added is 78.4g, and the molar ratio of siloxane groups to isocyanate groups in the obtained isocyanate trimer is 3:4.

[0113] Comparative Examples 1-4 The difference between Comparative Example 1 and Example 1 is that the equal mass of isocyanate trimer was replaced with the equal mass of hexamethylene diisocyanate trimer N3300.

[0114] The difference between Comparative Example 2 and Example 1 is that the polyester polyol and isocyanate trimer were mixed at a mass ratio of 8:1.

[0115] The difference between Comparative Example 3 and Example 1 is that the polyester polyol and isocyanate trimer were mixed at a mass ratio of 22:1.

[0116] The difference between Comparative Example 4 and Example 1 is that terephthalic acid and isophthalic acid are not added during the preparation of the polyester polyol.

[0117] Performance testing: After coating the substrate film (PMMA) with polyurethane adhesive, the solvent was dried in an 80°C oven. Then, the interior film (ABS) was laminated with the substrate film (PMMA) on a laminating machine at 100°C and 0.5MPa pressure. The film was then cured at 60°C for 72 hours to obtain the test film.

[0118] The test film was cut into strips 300mm long and 25mm wide. Tensile tests were conducted at 80℃ using a high-temperature tensile testing machine. The test was stopped when the strips were stretched to 150% of their initial length. Ten sets of tests were conducted for each sample. The surface of the strips was observed for bubbling or delamination. Strips without any apparent changes were considered qualified. The number of qualified strips was recorded.

[0119] After stretching to 150% of the initial length and achieving acceptable appearance, the specimens were placed in an aging chamber at 85℃ and 85%RH. After 96 hours, they were removed and placed at room temperature. Ten samples were tested for each example, and the surface was observed for blistering or delamination. Specimens without apparent changes were considered acceptable, and the number of acceptable specimens was recorded.

[0120] The test results of the examples and comparative examples are shown in Table 1.

[0121] Table 1

[0122] As shown in Table 1, compared to Example 1, the polyurethane adhesive coated with hexamethylene diisocyanate trimer N3300 in Comparative Example 1 all passed the appearance test after stretching at 80°C, but some of the samples failed the appearance test after stretching at 85°C and 85%RH for 96 hours. This indicates that siloxane groups can provide sufficient flexibility and resistance to humid heat aging for polyurethane adhesives.

[0123] In Comparative Examples 2 and 3, the mass ratio of polyester polyol to isocyanate trimer was not within the range specified in this application, and the results were poor when performing tensile tests at 80°C, 85°C, and 85%RH×96h.

[0124] In Comparative Example 4, no aromatic dicarboxylic acid was added during the preparation of the polyester polyol, resulting in insufficient adhesion of the polyurethane adhesive. Consequently, the appearance after stretching at 80°C, 85°C, and 85%RH×96h were all poor.

[0125] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A polyurethane adhesive, characterized in that, Including polyester polyols and isocyanate trimers; The polyester polyol includes phenyl groups; the isocyanate trimer includes siloxane groups. The mass ratio of the polyester polyol to the isocyanate trimer is (10-20):

1.

2. The polyurethane adhesive according to claim 1, characterized in that, The polyester polyol satisfies one or two of the following conditions: The weight-average molecular weight of the polyester polyol is 20,000-50,000; The hydroxyl value of the polyester polyol is 10mgKOH / g-20mgKOH / g.

3. The polyurethane adhesive according to any one of claims 1 or 2, characterized in that, The polyester polyol comprises the following raw materials in parts by weight: 80-180 parts aliphatic diols, 40-80 parts aliphatic dicarboxylic acids, and 50-100 parts aromatic dicarboxylic acids.

4. The polyurethane adhesive according to claim 3, characterized in that, One or more of the following conditions must be met: The aliphatic diols include one or more of ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, and 3-methyl-1,5-pentanediol; The aliphatic dicarboxylic acids include one or more of oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, and sebacic acid; The aromatic dicarboxylic acid includes one or more of phthalic acid, isophthalic acid, and terephthalic acid.

5. The polyurethane adhesive according to any one of claims 1-4, characterized in that, The molar ratio of siloxane groups to isocyanate groups in the isocyanate trimer is 3:(2-4).

6. The polyurethane adhesive according to any one of claims 1-5, characterized in that, The isocyanate trimer comprises the following raw materials in parts by weight: 40-100 parts isocyanate and 10-30 parts silane coupling agent.

7. The polyurethane adhesive according to claim 6, characterized in that, One or two of the following conditions must be met: The isocyanate includes one or more of toluene diisocyanate, isophorone diisocyanate, and hexamethylene diisocyanate; The silane coupling agent includes one or more of γ-aminopropyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-mercaptopropyltrimethoxysilane, and γ-mercaptopropyltriethoxysilane.

8. A method for preparing the polyurethane adhesive according to any one of claims 1-7, characterized in that, include: S1. Mix aliphatic diol, aliphatic diacid, and aromatic diacid, and sequentially carry out esterification and polycondensation reactions to obtain the polyester polyol. S2. The isocyanate and silane coupling agent are mixed and subjected to nucleophilic addition and trimerization reactions in sequence to obtain the isocyanate trimer. S3. The polyester polyol and the isocyanate trimer are mixed to obtain the polyurethane adhesive; the mass ratio of the polyester polyol and the isocyanate trimer is (10-20):

1.

9. The method according to claim 8, characterized in that, One or more of the following conditions must be met: The esterification reaction is carried out at a temperature of 180℃-240℃ and for a reaction time of 3h-5h. The reaction temperature of the polycondensation reaction is 180℃-240℃; the reaction time of the polycondensation reaction is 3h-5h. The polycondensation reaction is carried out under vacuum conditions; The steps of esterification and polycondensation further include adding a first catalyst, which includes one or more of antimony acetate, calcium acetate, zinc acetate, manganese acetate, cobalt acetate, magnesium acetate, tetrabutyl titanate, isopropyl titanate, and organotin compounds. The nucleophilic addition reaction is carried out at a temperature of 65℃-85℃ and for a time of 1h-1.5h. The trimerization reaction temperature is 65℃-85℃; the trimerization reaction time is 5h-6h. The step of the trimerization reaction further includes the addition of a second catalyst, which comprises potassium acetate and octanoic acid. Potassium One or more of the amine-based delayed catalysts DABCO TMR-3.

10. The application of a polyurethane adhesive as described in any one of claims 1-7, or a polyurethane adhesive prepared by the method as described in any one of claims 8-9, in a high-temperature or humid environment.

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