Polyurethane adhesive as well as preparation method and application thereof

Abstract

The invention relates to the technical field of adhesives, in particular to a polyurethane adhesive as well as a preparation method and application thereof. The polyurethane adhesive comprises a component A and a component B, the component A comprises modified polyester polyol; the component B comprises a curing agent; the modified polyester polyol is prepared from the following raw materials: polyester polyol, aliphatic polyisocyanate and hydroxyl-terminated polybutadiene; the curing agent comprises isocyanate. According to the invention, the aliphatic polyisocyanate and the hydroxyl-terminated polybutadiene are adopted to carry out chain extension on the polyester polyol to prepare the modified polyester polyol, and the modified polyester polyol is combined with the curing agent, so that the overall performance of the adhesive layer is improved, and the adhesive layer can still maintain a good bonding effect and has excellent humidity and heat resistance after a hot working process.

Description

Technical Field

[0001] The present invention relates to the technical field of adhesives, and in particular to a polyurethane adhesive and a preparation method and application thereof. Background Art

[0002] Polyurethane adhesives (PU adhesives) refer to adhesives containing carbamate groups (-NHCOO-) or isocyanate groups (-NCO) in their molecular chains. These adhesives form excellent chemical bonds with materials containing active hydrogen, porous materials, and materials with smooth surfaces. They also exhibit excellent wear resistance, water resistance, oil resistance, solvent resistance, and ultra-low temperature resistance. Consequently, they are widely used in fields such as shoemaking, packaging, plastics processing, automotive, construction, healthcare, low-temperature environments, and the wood industry. However, polyurethane adhesives have poor heat resistance and readily degrade and lose strength at high temperatures, limiting their application in heat-resistant structural applications. Therefore, the development of heat-resistant polyurethane adhesives has significant potential and a broad market prospect. For example, using heat-resistant polyurethane adhesives in the preparation of wood-structure composite materials for construction, such as timber-framed housing and timber-structured components, can ensure that the wood composites maintain good mechanical strength even in the early stages of a fire, thereby increasing the chances of escape in the early stages of a fire. For example, when a car is placed outdoors for a long time, especially in summer, the temperature inside the car will be very high. Therefore, the polyurethane adhesive used in automotive parts must have certain heat resistance to prevent aging and cracking of the parts inside the car.

[0003] ABS plastic is a terpolymer of acrylonitrile, butadiene, and styrene. The relative proportions of the three monomers can be varied to create a variety of resins. ABS plastic combines the properties of all three components: acrylonitrile imparts chemical and heat resistance, along with a certain degree of surface hardness; butadiene imparts high elasticity and toughness; and styrene imparts the processing and molding characteristics of thermoplastics, while also improving electrical properties. Therefore, ABS plastic is a tough, hard, and rigid material with readily available raw materials, excellent overall performance, low price, and a wide range of applications. ABS plastic is widely used in the manufacturing industries, including machinery, electrical equipment, textiles, automobiles, aircraft, and ships, as well as in the chemical industry. However, as a thermoplastic, ABS material will deform at temperatures above 80°C. Ensuring that ABS maintains good adhesion to other substrates and exhibits no surface defects after high-temperature heat processing remains a topic of research.

[0004] Patent publication number CN106833496A discloses a polyurethane resin-based adhesive and its preparation method. Using polyester polyols, polyether polyols, acrylates, epoxy resins, ketone-aldehyde resins, 4,4-diphenylmethane diisocyanate, and toluene diisocyanate as primary raw materials, along with nano-silica, ultrafine carbon black, and additives, the patent addresses the shortcomings of traditional polyurethane adhesives in terms of water resistance and high-temperature resistance. However, the patent does not explore the impact of the molecular weight of the polyester polyol on performance, nor does it address the effects of thermal processing on bonding, making it difficult to guarantee product performance. Summary of the Invention

[0005] The present invention aims to at least partially address one of the technical problems in the related art. To this end, the present invention provides a polyurethane adhesive, its preparation method, and its application. This invention utilizes aliphatic polyisocyanates and hydroxyl-terminated polybutadiene to chain-extend polyester polyols to produce modified polyester polyols. This modified polyester polyol is then combined with a curing agent to improve the overall performance of the adhesive layer, enabling it to maintain good adhesion even after thermal processing and exhibiting excellent moisture and heat resistance.

[0006] To this end, the first aspect of the present invention provides a polyurethane adhesive, which includes component A and component B;

[0007] The component A comprises a modified polyester polyol; the component B comprises a curing agent;

[0008] The raw materials for preparing the modified polyester polyol include polyester polyol, aliphatic polyisocyanate, and hydroxyl-terminated polybutadiene;

[0009] The curing agent includes isocyanate.

[0010] The present invention adopts aliphatic polyisocyanate and terminal hydroxyl polybutadiene to chain extend polyester polyol to prepare modified polyester polyol, and combines it with a curing agent to improve the overall performance of the adhesive layer, so that it can still maintain a good bonding effect after thermal processing and has excellent moisture and heat resistance.

[0011] According to an embodiment of the present invention, the mass ratio of the modified polyester polyol to the curing agent is (5-10):1.

[0012] According to an embodiment of the present invention, the weight average molecular weight of the modified polyester polyol is 30,000-80,000, preferably 30,000-60,000.

[0013] According to an embodiment of the present invention, the hydroxyl value of the modified polyester polyol is 3-20 mgKOH / g, preferably 3-15 mgKOH / g.

[0014] According to an embodiment of the present invention, the acid value of the modified polyester polyol is ≤0.5 mgKOH / g.

[0015] According to an embodiment of the present invention, the mass ratio of the polyester polyol, the aliphatic polyisocyanate, and the hydroxyl-terminated polybutadiene is 100:(2-20):(20-100);

[0016] According to an embodiment of the present invention, the polyester polyol has a weight average molecular weight of 20,000-50,000, a hydroxyl value of 2-15 mgKOH / g, and an acid value of ≤0.5 mgKOH / g.

[0017] According to an embodiment of the present invention, the raw materials for preparing the polyester polyol include dibasic acid and diol.

[0018] According to an embodiment of the present invention, the dibasic acid includes an aromatic dibasic acid and an aliphatic dibasic acid, and the mass proportion of the aromatic dibasic acid in the dibasic acid is ≥50%, preferably 60%-80%.

[0019] According to an embodiment of the present invention, the aromatic dibasic acid includes at least one of isophthalic acid, terephthalic acid, naphthalene dicarboxylic acid, phthalic anhydride and ester compounds formed therefrom.

[0020] According to an embodiment of the present invention, the aliphatic dibasic acid includes at least one of adipic acid, azelaic acid, sebacic acid, succinic acid, glutaric acid, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, maleic anhydride and ester compounds formed therefrom.

[0021] According to an embodiment of the present invention, the diol includes at least one of ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, 1,6-hexanediol, neopentyl glycol, 2-methyl-2,4-pentanediol, 1,4-butanediol, 1,4-cyclohexanedimethanol, 1,9-nonanediol, 3-methyl-1,5-pentanediol, polycarbonate diol, polyolefin diol, acrylic diol, and polyurethane diol.

[0022] According to an embodiment of the present invention, the aliphatic polyisocyanate includes at least one of trimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, dimers and trimers of the above isocyanate monomers, or adducts of the above isocyanate monomers and small molecule polyols.

[0023] According to an embodiment of the present invention, the small molecule polyol includes at least one of glycerol, trimethylolpropane, and pentaerythritol.

[0024] According to an embodiment of the present invention, the weight average molecular weight of the hydroxyl-terminated polybutadiene is 2000-5000, preferably 2500-3500.

[0025] According to an embodiment of the present invention, the isocyanate includes at least one of aliphatic isocyanate and aromatic isocyanate.

[0026] According to an embodiment of the present invention, the isocyanate includes trimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, 1,2-propylene diisocyanate, 1,2-butylene diisocyanate, 2,3-butylene diisocyanate, 1,3-butylene diisocyanate, 2,4,4-trimethylhexamethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, 2,6-diisocyanatomethyl hexanoate, m-phenylenediisocyanate , p-phenylene diisocyanate, 4,4'-diphenyl diisocyanate, 1,5-naphthalene diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, 4,4'-toluidine diisocyanate, dimethoxyaniline diisocyanate, 4,4'-diphenyl ether diisocyanate and at least one of dimers, trimers, biuret and allophanate derived from the above isocyanate monomers.

[0027] The second aspect of the present invention provides a method for preparing the polyurethane adhesive according to the first aspect, comprising:

[0028] Mixing component A and component B to obtain the polyurethane adhesive;

[0029] Wherein, the solid content of the polyurethane adhesive is 20%-90%.

[0030] The polyurethane adhesive can be prepared by the preparation method provided by the present invention. The polyurethane adhesive still maintains a good bonding effect after a thermal processing process and can be used in scenarios requiring heat resistance and deformation requirements.

[0031] According to an embodiment of the present invention, the preparation method further comprises the following steps of preparing the modified polyester polyol:

[0032] Under an inert atmosphere, the polyester polyol, aliphatic polyisocyanate, and hydroxy-terminated polybutadiene are added stepwise and reacted until the isocyanate group content in the solution is 0, thereby obtaining the modified polyester polyol.

[0033] According to an embodiment of the present invention, the preparation of the modified polyester polyol is carried out at 30°C-90°C.

[0034] According to an embodiment of the present invention, the preparation method further comprises the following steps of preparing the polyester polyol:

[0035] Under an inert atmosphere, a dibasic acid, a diol, a catalyst, and an antioxidant are mixed and reacted once until the acid value is less than 30 mgKOH / g to obtain a precursor;

[0036] The precursor is subjected to a polycondensation reaction under vacuum conditions, with the vacuum degree controlled at 5 Pa-300 Pa, and the reaction is carried out for 3 h-5 h until the acid value is ≤0.5 mgKOH / g, thereby obtaining the polyester polyol.

[0037] According to an embodiment of the present invention, the catalyst includes at least one of tetrabutyl titanate, antimony acetate, stannous oxide, and germanium oxide.

[0038] According to an embodiment of the present invention, the antioxidant includes at least one of antioxidant 1010 , antioxidant 1076 , antioxidant 168 , and antioxidant 1098 .

[0039] According to an embodiment of the present invention, the temperature of the primary reaction is 160°C-260°C.

[0040] According to an embodiment of the present invention, the temperature of the polycondensation reaction is 180°C-280°C.

[0041] The third aspect of the present invention provides the use of the polyurethane adhesive described in the first aspect or the polyurethane adhesive obtained according to the preparation method described in the second aspect as an adhesive for thermoplastic plastics, wherein the thermoplastic plastics include at least one of ABS plastics, PS plastics, PC plastics, PP plastics, PET plastics, and PMMA plastics.

[0042] By using the polyurethane adhesive provided by the present invention as an adhesive for thermoplastic plastics, the composite film prepared from thermoplastic plastics can still maintain excellent bonding effect after high-temperature stretching and exhibit good moisture and heat resistance, and can be used in scenarios requiring heat resistance and deformation requirements.

[0043] The beneficial effects of the present invention compared to the prior art are as follows:

[0044] (1) The present invention uses aliphatic polyisocyanate and terminal hydroxyl polybutadiene to extend the chain of polyester polyol to prepare modified polyester polyol, and combines it with a curing agent, thereby improving the overall performance of the adhesive layer and being able to maintain a good bonding effect after the heat treatment process. Among them, the combination of aliphatic polyisocyanate and terminal hydroxyl polybutadiene provides a long carbon chain structure for the polyester polyol during the chain extension process, increases the molecular weight of the main agent, and gives the adhesive layer better flexibility and tensile properties.

[0045] (2) In the raw materials for preparing polyester polyols, aromatic dibasic acids account for more than 50% of the total mass of dibasic acids, thereby providing the adhesive with heat resistance and excellent bonding effect.

[0046] (3) By combining modified polyester polyols with specific molecular weight and hydroxyl value with curing agents, a polyurethane adhesive product with higher cross-linking density, excellent heat deformation resistance, and better heat and moisture resistance is obtained, thereby achieving the bonding of thermoplastic materials such as PMMA and ABS. After high-temperature stretching, a film product is obtained that still maintains excellent adhesion and heat and moisture resistance, which can be used in scenarios requiring heat resistance and deformation requirements.

[0047] Additional aspects and advantages of the present invention will be set forth in part in the description which follows and, in part, will be obvious from the description which follows, or may be learned by practice of the present invention. DETAILED DESCRIPTION

[0048] The embodiments of the present invention are described in detail below. The embodiments described below are exemplary and are only used to explain the present invention, and should not be understood as limiting the present invention.

[0049] It should be noted that the terms "first" and "second" are used for descriptive purposes only and should not be understood to indicate or imply relative importance or implicitly specify the number of the technical features indicated. Therefore, features defined as "first" or "second" may explicitly or implicitly include one or more of such features. Furthermore, in the description of the present invention, unless otherwise specified, "plurality" means two or more.

[0050] The endpoints of the ranges and any values disclosed herein are not limited to the precise ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0051] In order to make the present invention more easily understood, certain technical and scientific terms are specifically defined below. Unless otherwise clearly defined elsewhere in this document, all other technical and scientific terms used herein have the meaning commonly understood by those skilled in the art to which the present invention belongs.

[0052] In this document, the terms “include” or “comprising” are open expressions, that is, including the contents specified in the present invention, but not excluding other contents.

[0053] As used herein, the terms "optionally," "optional," or "optionally" generally mean that the subsequently described event or circumstance may but need not occur, and that the description includes instances where the event or circumstance occurs and instances where it does not.

[0054] According to an embodiment of the present invention, a first aspect of the present invention provides a polyurethane adhesive, wherein the polyurethane adhesive comprises component A and component B;

[0055] The component A comprises a modified polyester polyol; the component B comprises a curing agent;

[0056] The raw materials for preparing the modified polyester polyol include polyester polyol, aliphatic polyisocyanate, and hydroxyl-terminated polybutadiene;

[0057] The curing agent includes isocyanate.

[0058] The present invention utilizes aliphatic polyisocyanates and hydroxyl-terminated polybutadiene to chain-extend polyester polyols to produce modified polyester polyols. The aliphatic polyisocyanates and hydroxyl-terminated polybutadiene provide the polyester polyols with long carbon chains during the chain extension process, increasing their molecular weight and imparting improved flexibility and tensile properties to the adhesive layer. Combining the modified polyester polyols with a curing agent enhances the overall performance of the adhesive layer, maintaining good bonding even after thermal processing.

[0059] According to a specific embodiment of the present invention, the mass ratio of the modified polyester polyol to the curing agent is (5-10):1. As some specific examples, the mass ratio of the modified polyester polyol to the curing agent can be 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, etc. If the amount of modified polyester polyol added is too much, the excess hydroxyl groups fail to form effective crosslinking points, resulting in insufficient overall mechanical properties of the adhesive. If the amount of modified polyester polyol added is too little, the excess curing agent does not react completely, resulting in reduced adhesive strength and heat resistance.

[0060] According to a specific embodiment of the present invention, the weight-average molecular weight of the modified polyester polyol is 30,000-80,000. As some specific examples, the weight-average molecular weight of the modified polyester polyol can be 30,000, 40,000, 50,000, 60,000, 70,000, 80,000, etc., preferably 30,000-60,000. If the weight-average molecular weight (Mw) of the modified polyester polyol is too small, the polyurethane adhesive chain segments formed are too short and insufficient to provide sufficient mechanical properties. If the weight-average molecular weight of the modified polyester polyol is too large, the viscosity of the adhesive is too high, affecting actual operation.

[0061] According to a specific embodiment of the present invention, the method for measuring the weight average molecular weight of the modified polyester polyol is not particularly limited. As some specific examples, the method for measuring the weight average molecular weight of the modified polyester polyol includes but is not limited to gel permeation chromatography (GPC). The specific operation can be: using tetrahydrofuran as a solvent to measure the weight average molecular weight by gel permeation chromatography (GPC).

[0062] According to a specific embodiment of the present invention, the modified polyester polyol has a hydroxyl value of 3-20 mgKOH / g. As some specific examples, the hydroxyl value of the modified polyester polyol can be 3 mgKOH / g, 5 mgKOH / g, 10 mgKOH / g, 15 mgKOH / g, 20 mgKOH / g, etc., preferably 3-15 mgKOH / g. By combining a modified polyester polyol of a specific molecular weight and hydroxyl value with a curing agent, a polyurethane adhesive with a higher crosslink density, excellent heat deformation resistance, and improved moisture and heat resistance can be obtained.

[0063] According to a specific embodiment of the present invention, the acid value of the modified polyester polyol is ≤0.5 mgKOH / g. As some specific examples, the acid value of the modified polyester polyol may be 0.4 mgKOH / g, 0.3 mgKOH / g, 0.2 mgKOH / g, 0.1 mgKOH / g, 0.08 mgKOH / g, 0.05 mgKOH / g, etc.

[0064] According to a specific embodiment of the present invention, the mass ratio of the polyester polyol, the aliphatic polyisocyanate, and the hydroxyl-terminated polybutadiene is 100:(2-20):(20-100). As some specific examples, the mass ratio of the polyester polyol, the aliphatic polyisocyanate, and the hydroxyl-terminated polybutadiene may be 100:2:20, 100:3:30, 100:4:40, 100:5:50, 100:10:60, 100:20:100, etc.

[0065] According to a specific embodiment of the present invention, the polyester polyol has a weight-average molecular weight of 20,000-50,000, a hydroxyl value of 2-15 mgKOH / g, and an acid value of ≤0.5 mgKOH / g. As some specific examples, the weight-average molecular weight of the polyester polyol may be 20,000, 30,000, 40,000, 50,000, etc. If the weight-average molecular weight of the polyester polyol is too small, the resulting modified polyester polyol chain segments are too short, and thus insufficient to provide adequate mechanical properties when cross-linked with a curing agent. If the weight-average molecular weight of the polyester polyol is too large, the resulting modified polyester polyol has excessively high viscosity, affecting practical operation.

[0066] According to a specific embodiment of the present invention, the method for measuring the weight average molecular weight of the polyester polyol is not particularly limited, and can refer to the method for measuring the weight average molecular weight of the modified polyester polyol, that is, using gel permeation chromatography.

[0067] According to a specific embodiment of the present invention, the raw materials for preparing the polyester polyol are not particularly limited. As some specific examples, the raw materials for preparing the polyester polyol include dibasic acid and diol.

[0068] According to a specific embodiment of the present invention, the dibasic acid includes an aromatic dibasic acid and an aliphatic dibasic acid, and the weight percentage of the aromatic dibasic acid in the dibasic acid is ≥ 50%. As some specific examples, the weight percentage of the aromatic dibasic acid in the dibasic acid can be 50%, 60%, 70%, 80%, 90%, etc., preferably 60%-80%. If the weight percentage of the aromatic dibasic acid is less than 50%, the final hot working properties of the adhesive tend to be reduced.

[0069] According to a specific embodiment of the present invention, the type of the aromatic dibasic acid is not particularly limited. As some specific examples, the aromatic dibasic acid includes at least one of isophthalic acid, terephthalic acid, naphthalene dicarboxylic acid, phthalic anhydride and ester compounds formed therefrom.

[0070] According to a specific embodiment of the present invention, the type of the aliphatic dibasic acid is not particularly limited. As some specific examples, the aliphatic dibasic acid includes at least one of adipic acid, azelaic acid, sebacic acid, succinic acid, glutaric acid, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, maleic anhydride and ester compounds formed therefrom.

[0071] According to a specific embodiment of the present invention, the type of the diol is not particularly limited. As some specific examples, the diol includes at least one of ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, 1,6-hexanediol, neopentyl glycol, 2-methyl-2,4-pentanediol, 1,4-butanediol, 1,4-cyclohexanedimethanol, 1,9-nonanediol, 3-methyl-1,5-pentanediol, polycarbonate diol, polyolefin diol, acrylic diol, and polyurethane diol.

[0072] According to a specific embodiment of the present invention, the type of the aliphatic polyisocyanate is not particularly limited. As some specific examples, the aliphatic polyisocyanate includes trimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, and at least one of dimers and trimers of the above isocyanate monomers, or adducts of the above isocyanate monomers and small molecule polyols, preferably hexamethylene diisocyanate trimer.

[0073] According to a specific embodiment of the present invention, the type of the small molecule polyol is not particularly limited. As some specific examples, the small molecule polyol includes at least one of glycerol, trimethylolpropane, and pentaerythritol.

[0074] According to a specific embodiment of the present invention, the weight average molecular weight of the hydroxyl-terminated polybutadiene is 2000-5000. As some specific examples, the weight average molecular weight of the hydroxyl-terminated polybutadiene can be 2000, 2500, 3000, 3500, 4000, 4500, 5000, etc., preferably 2500-3500. If the weight average molecular weight of the hydroxyl-terminated polybutadiene is too small, its hydroxyl value is too high, the reaction rate is difficult to control, and the low molecular weight leads to a low carbon chain length, resulting in poor flexibility and mechanical strength of the formed adhesive. If the weight average molecular weight is too large, its viscosity is high, making it difficult to form a uniform reaction system, and the formed adhesive is too viscous and difficult to operate.

[0075] According to a specific embodiment of the present invention, the type of isocyanate is not particularly limited. As some specific examples, the isocyanate includes at least one of an aliphatic isocyanate and an aromatic isocyanate, such as trimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, 1,2-propylene diisocyanate, 1,2-butylene diisocyanate, 2,3-butylene diisocyanate, 1,3-butylene diisocyanate, 2,4,4-trimethylhexamethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate. At least one of diisocyanate, 2,6-diisocyanatomethyl hexanoate, m-phenylene diisocyanate, p-phenylene diisocyanate, 4,4'-diphenyl diisocyanate, 1,5-naphthalene diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, 4,4'-toluidine diisocyanate, dimethoxyaniline diisocyanate, 4,4'-diphenyl ether diisocyanate, and dimers, trimers, biuret, and allophanate derived from the above isocyanate monomers. The isocyanate is preferably a trimer derived from an isocyanate monomer, and more preferably an aromatic polyisocyanate.

[0076] According to an embodiment of the present invention, a second aspect of the present invention provides a method for preparing the polyurethane adhesive according to the first aspect, comprising:

[0077] Mixing component A and component B to obtain the polyurethane adhesive;

[0078] Wherein, the solid content of the polyurethane adhesive is 20%-90%.

[0079] The polyurethane adhesive can be prepared by the preparation method provided by the present invention. The polyurethane adhesive still maintains a good bonding effect after a thermal processing process and can be used in scenarios requiring heat resistance and deformation requirements.

[0080] According to a specific embodiment of the present invention, the preparation method further comprises: mixing component A and component B, and adding a diluent to obtain the polyurethane adhesive.

[0081] According to a specific embodiment of the present invention, the type of the diluent is not particularly limited. As some specific examples, the diluent includes but is not limited to ethyl acetate.

[0082] According to a specific embodiment of the present invention, the preparation method further comprises the following steps of preparing the modified polyester polyol:

[0083] Under an inert atmosphere, the polyester polyol, aliphatic polyisocyanate, and hydroxy-terminated polybutadiene are added stepwise and reacted until the isocyanate group content in the solution is 0, thereby obtaining the modified polyester polyol.

[0084] According to a specific embodiment of the present invention, the preparation of the modified polyester polyol is carried out at 30°C-90°C.

[0085] According to specific embodiments of the present invention, the method for detecting the isocyanate group content in the mixed solution is not particularly limited. As some specific examples, the method includes but is not limited to titration. The titration method can be specifically tested with reference to GB / T12009.4-2016 "Aromatic Isocyanates for the Production of Plastic Polyurethanes - Part 4: Determination of Isocyanate Content."

[0086] According to a specific embodiment of the present invention, the preparation method further comprises the following steps of preparing the polyester polyol:

[0087] Under an inert atmosphere, a dibasic acid, a diol, a catalyst, and an antioxidant are mixed and reacted once until the acid value is less than 30 mgKOH / g to obtain a precursor;

[0088] The precursor is subjected to a polycondensation reaction under vacuum conditions, with the vacuum degree controlled at 5 Pa-300 Pa, and the reaction is carried out for 3 h-5 h until the acid value is ≤0.5 mgKOH / g, thereby obtaining the polyester polyol.

[0089] According to a specific embodiment of the present invention, the type of the catalyst is not particularly limited. As some specific examples, the catalyst includes at least one of tetrabutyl titanate, antimony acetate, stannous oxide, and germanium oxide.

[0090] According to a specific embodiment of the present invention, the type of the antioxidant is not particularly limited. As some specific examples, the antioxidant includes at least one of antioxidant 1010, antioxidant 1076, antioxidant 168, and antioxidant 1098.

[0091] According to a specific embodiment of the present invention, the temperature of the primary reaction is 160°C-260°C. As some specific examples, the temperature of the primary reaction may be 160°C, 200°C, 210°C, 220°C, 240°C, 260°C, etc.

[0092] According to a specific embodiment of the present invention, the temperature of the polycondensation reaction is 180°C-280°C. As some specific examples, the temperature of the polycondensation reaction can be 180°C, 200°C, 220°C, 240°C, 260°C, 280°C, etc.

[0093] According to an embodiment of the present invention, the third aspect of the present invention provides the use of the polyurethane adhesive described in the first aspect or the polyurethane adhesive obtained according to the preparation method described in the second aspect as an adhesive for thermoplastic plastics, wherein the thermoplastic plastics include at least one of ABS plastics, PS plastics, PC plastics, PP plastics, PET plastics, and PMMA plastics.

[0094] By using the polyurethane adhesive provided by the present invention as an adhesive for thermoplastic plastics, the composite film prepared from thermoplastic plastics can still maintain excellent bonding effect after high-temperature stretching and exhibit good moisture and heat resistance, and can be used in scenarios requiring heat resistance and deformation requirements.

[0095] Below, the scheme of the present invention will be explained in conjunction with embodiment.It will be understood by those skilled in the art that the following examples are only used to illustrate the present invention and should not be regarded as limiting the scope of the present invention.In the embodiment, if specific technology or conditions are not indicated, the technology or conditions described in the literature in this area or the product instructions are used.The reagents or instruments used are not indicated by the manufacturer, and are all conventional products that can be obtained by commercial purchase.

[0096] The compounds used in the following examples and comparative examples are described as follows:

[0097] The preparation methods of polyester polyols ①-⑦ are as follows:

[0098] A dibasic acid, a diol, an antioxidant 1010, and a catalyst (tetrabutyl titanate) are placed in a reaction kettle, the air is removed by nitrogen replacement, the temperature is raised to 220°C with stirring, and the reaction is carried out until the acid value is less than 30 mgKOH / g and more than 80% of the theoretical water output is distilled off. The temperature is then raised to 250°C, and polycondensation is carried out with stirring under vacuum conditions. The vacuum degree is controlled at 5Pa-300Pa, and the reaction is carried out for 3h-5h until the acid value is ≤0.5mgKOH / g. Nitrogen is then introduced to eliminate the vacuum, and the material is discharged to obtain a polyester polyol.

[0099] The raw materials and dosage, molecular weight, hydroxyl value, and acid value of polyester polyols ①-⑦ are shown in Table 1. The meanings of the English abbreviations in Table 1 are as follows:

[0100] Diacids: PTA: purified terephthalic acid, AA: 1,6-adipic acid, IPA: isophthalic acid, SA: sebacic acid.

[0101] Diols: HDO: 1,6-hexanediol, MEG: ethylene glycol, MPD: 2-methyl-2,4-pentanediol, NPG: neopentyl glycol.

[0102] Table 1

[0103]

[0104]

[0105] Among them, “-” means no.

[0106] The preparation methods of modified polyester polyols A-1, A-2, A-3, A-4, A-5, A-6, A-7 and A-8 are as follows:

[0107] Polyester polyol and ethyl acetate were put into a reactor and dissolved into a solution with a solid content of 50% at 80°C. The air was replaced by nitrogen, and aliphatic polyisocyanate was added. The reaction was carried out at 80°C for 4 hours. Then, terminal hydroxyl polybutadiene was added and the reaction was continued with stirring until the isocyanate group content was titrated to 0. Ethyl acetate was added to adjust the solid content to 50%, and the material was cooled and discharged to obtain a modified polyester polyol solution with a solid content of 50%.

[0108] The titration method is carried out in accordance with GB / T 12009.4-2016 “Aromatic isocyanates for use in the production of plastic polyurethanes—Part 4: Determination of isocyanate content”.

[0109] Among them, the preparation raw materials and dosage, molecular weight, hydroxyl value, and acid value of modified polyester polyols A-1, A-2, A-3, A-4, A-5, A-6, A-7, and A-8 are shown in Table 2 (the masses of polyester polyols and modified polyester polyols in the table are all solid mass, and the addition amounts of aliphatic polyisocyanate and hydroxyl-terminated polybutadiene are calculated based on the hydroxyl value of the polyester polyol). The raw materials used in the table, "N3300" is the abbreviation of Covestro N3300, which is composed of hexamethylene diisocyanate isocyanurate trimer with a solid content of 100%; "L75" is the abbreviation of Covestro L75, which is an aromatic polyisocyanate prepolymer based on toluene diisocyanate, containing ethyl acetate as a solvent, and has a solid content of 75%; different models of hydroxyl-terminated polybutadiene products of Hongyuan New Materials are selected, and their molecular weights and hydroxyl values are different. The molecular weight of HTPB-I type to IV type gradually decreases, and the hydroxyl value gradually increases.

[0110] Table 2

[0111]

[0112] Examples 1-4 and Comparative Examples 1-5 each provide a polyurethane adhesive, and the preparation method is as follows:

[0113] The polyester polyol or modified polyester polyol and the curing agent are mixed according to a proportion, and ethyl acetate as a diluent is added to prepare an adhesive solution with a solid content of 30%, thereby obtaining a polyurethane adhesive coating liquid.

[0114] Among them, the preparation raw materials and amounts of Examples 1-4 and Comparative Examples 1-5 are shown in Table 3 (the mass of the modified polyester polyol in the table is the solid mass), wherein L75 represents Covestro L75.

[0115] Table 3

[0116] Sample number Main agent curing agent Example 1 Modified polyester polyol (A-1) 100g L75 20g Example 2 Modified polyester polyol (A-2) 100g L75 15g Example 3 Modified polyester polyol (A-3) 100g L75 10g Example 4 Modified polyester polyol (A-4) 100g L75 10g Comparative Example 1 Polyester polyol④100g L75 10g Comparative Example 2 Modified polyester polyol (A-5) 100g L75 10g Comparative Example 3 Modified polyester polyol (A-6) 100g L75 10g Comparative Example 4 Modified polyester polyol (A-7) 100g L75 10g Comparative Example 5 Modified polyester polyol (A-8) 100g L75 10g

[0117] Test Case

[0118] At room temperature, the polyurethane adhesive coating liquid prepared in the examples and comparative examples was applied to a polymethyl methacrylate (PMMA) film using a coating machine. The film was placed in an 80°C oven for 1 minute to allow the solvent to evaporate completely. The PMMA film coated with the adhesive was then composited with an ABS film at 100°C and 0.5 MPa pressure using a laminating machine. The film was then kept in an atmosphere of 60°C for 96 hours to allow the main agent and the curing agent to fully react, thereby obtaining a test film. The test film was tested for its 100-grid adhesion, appearance after high-temperature stretching, appearance after high-temperature stretching and aging, and 100-grid adhesion after high-temperature stretching and aging. The test results are shown in Table 4. The test method is as follows:

[0119] (1) 100-grid adhesion test:

[0120] The test film was subjected to a 100-grid adhesion test according to the test method of GB / T 9286-2021 "Paint and varnish cross-cut test", where 100% no drop was regarded as level 0.

[0121] (2) Appearance test after high temperature stretching:

[0122] The test film was cut into strips of 300 mm long and 25 mm wide, and the tensile properties were tested at 80°C on a high-temperature tensile testing machine. The film was stretched to 150% and the surface of the strip was observed for blistering or delamination. The strips without apparent changes were considered qualified.

[0123] (3) Appearance and 100-grid adhesion test after high-temperature stretching and aging:

[0124] The specimens stretched 150% were placed in an aging chamber at 85°C and 85% relative humidity (RH). After 96 hours, they were taken out and placed at room temperature to observe whether there was blistering or delamination on the surface. The specimens without apparent changes were judged to be qualified and the 100-grid adhesion was tested again.

[0125] Table 4

[0126]

[0127]

[0128] As can be seen from Table 4, since Comparative Example 1 uses unmodified polyester polyol ④ as the main agent, compared with the examples, in terms of the test performance of the coating film, Comparative Example 1 cannot pass the 85°C, 85% RH, 96h wet heat aging test after high temperature stretching, indicating that the unmodified polyester polyol cannot provide sufficient bonding strength, flexibility and wet heat aging resistance; the molecular weight of the polyester polyol in Comparative Example 2 is too large, resulting in a large molecular weight of the modified polyester polyol after chain extension, a small hydroxyl value, and insufficient cross-linking density, which deteriorates the final adhesive performance after wet heat aging, affecting the appearance and adhesion; in Comparative Example 3, when preparing the polyester polyol, the amount of aromatic dibasic acid used is less than 1% of the dibasic acid. The total amount of acid used is 50%, resulting in that although the adhesion of Comparative Example 3 is acceptable under normal conditions, the adhesion and appearance are significantly reduced after stretching 150% and wet-heat aging, indicating that the amount of aromatic dibasic acid used has a significant effect on the bonding strength and resistance to wet-heat aging; the molecular weight, hydroxyl value, etc. of the polyester polyol and modified polyester polyol in Comparative Example 4 are not within the scope of the technical solution provided by the present invention, the molecular weight is too small, and the hydroxyl value is too high, resulting in poor overall performance of the coating; in the preparation process of the modified polyester polyol in Comparative Example 5, aromatic polyisocyanate Covestro L75 is used instead of the aliphatic polyisocyanate required by the technical solution of the present invention, which makes the modified polyester polyol more rigid but less flexible, thereby affecting the final performance of the coating.

[0129] In the description of this specification, the reference terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and features of different embodiments or examples without contradiction.

[0130] Although the embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention.

Claims

1. A polyurethane adhesive, characterized in that: The polyurethane adhesive comprises component A and component B; The component A comprises a modified polyester polyol; the component B comprises a curing agent; The raw materials for preparing the modified polyester polyol include polyester polyol, aliphatic polyisocyanate, and hydroxyl-terminated polybutadiene; The curing agent includes isocyanate.

2. The polyurethane adhesive according to claim 1, characterized in that The mass ratio of the modified polyester polyol to the curing agent is (5-10):

1.

3. The polyurethane adhesive according to claim 1, characterized in that The weight average molecular weight of the modified polyester polyol is 30,000-80,000, preferably 30,000-60,000; Optionally, the modified polyester polyol has a hydroxyl value of 3-20 mgKOH / g, preferably 3-15 mgKOH / g; Optionally, the acid value of the modified polyester polyol is ≤0.5 mgKOH / g.

4. The polyurethane adhesive according to claim 1, characterized in that The mass ratio of the polyester polyol, aliphatic polyisocyanate and hydroxyl-terminated polybutadiene is 100:(2-20):(20-100); Optionally, the polyester polyol has a weight average molecular weight of 20,000-50,000, a hydroxyl value of 2-15 mgKOH / g, and an acid value of ≤0.5 mgKOH / g; Optionally, the raw materials for preparing the polyester polyol include dibasic acid and diol; Optionally, the dibasic acid comprises an aromatic dibasic acid and an aliphatic dibasic acid, and the mass proportion of the aromatic dibasic acid in the dibasic acid is ≥50%, preferably 60%-80%; Optionally, the aromatic dibasic acid includes at least one of isophthalic acid, terephthalic acid, naphthalene dicarboxylic acid, phthalic anhydride and ester compounds formed therefrom; Optionally, the aliphatic dibasic acid includes at least one of adipic acid, azelaic acid, sebacic acid, succinic acid, glutaric acid, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, maleic anhydride and ester compounds formed therefrom; Optionally, the diol includes at least one of ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, 1,6-hexanediol, neopentyl glycol, 2-methyl-2,4-pentanediol, 1,4-butanediol, 1,4-cyclohexanedimethanol, 1,9-nonanediol, 3-methyl-1,5-pentanediol, polycarbonate diol, polyolefin diol, acrylic diol, and polyurethane diol.

5. The polyurethane adhesive according to claim 1, characterized in that The aliphatic polyisocyanate includes at least one of trimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, dimers and trimers of the above isocyanate monomers, or adducts of the above isocyanate monomers and small molecule polyols; Optionally, the small molecule polyol includes at least one of glycerol, trimethylolpropane, and pentaerythritol; Optionally, the weight average molecular weight of the hydroxyl-terminated polybutadiene is 2000-5000, preferably 2500-3500.

6. The polyurethane adhesive according to claim 1, characterized in that The isocyanate includes at least one of an aliphatic isocyanate and an aromatic isocyanate; Optionally, the isocyanate includes trimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, 1,2-propylene diisocyanate, 1,2-butylene diisocyanate, 2,3-butylene diisocyanate, 1,3-butylene diisocyanate, 2,4,4-trimethylhexamethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, 2,6-diisocyanatomethyl hexanoate, m-phenylene diisocyanate, p-phenylene diisocyanate, at least one of diisocyanate, 4,4'-diphenyl diisocyanate, 1,5-naphthalene diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, 4,4'-toluidine diisocyanate, dimethoxyaniline diisocyanate, 4,4'-diphenyl ether diisocyanate, and dimers, trimers, biuret, and allophanate derived from the above isocyanate monomers.

7. A method for preparing the polyurethane adhesive according to any one of claims 1 to 6, characterized in that: include: Mixing component A and component B to obtain the polyurethane adhesive; Wherein, the solid content of the polyurethane adhesive is 20%-90%.

8. The preparation method according to claim 7, characterized in that The preparation method further comprises the following steps of preparing the modified polyester polyol: Under an inert atmosphere, the polyester polyol, aliphatic polyisocyanate, and hydroxy-terminated polybutadiene are added stepwise and reacted until the isocyanate group content in the solution is 0, thereby obtaining the modified polyester polyol; Optionally, the preparation of the modified polyester polyol is carried out at 30°C-90°C.

9. The preparation method according to claim 7, characterized in that The preparation method further comprises the following steps of preparing the polyester polyol: Under an inert atmosphere, a dibasic acid, a diol, a catalyst, and an antioxidant are mixed and reacted once until the acid value is less than 30 mgKOH / g to obtain a precursor; Under vacuum conditions, the precursor is subjected to a polycondensation reaction, the vacuum degree is controlled at 5 Pa-300 Pa, and the reaction is carried out for 3 h-5 h until the acid value is ≤0.5 mgKOH / g, thereby obtaining the polyester polyol; Optionally, the catalyst comprises at least one of tetrabutyl titanate, antimony acetate, stannous oxide, and germanium oxide; Optionally, the antioxidant includes at least one of antioxidant 1010, antioxidant 1076, antioxidant 168, and antioxidant 1098; Optionally, the temperature of the primary reaction is 160°C-260°C; Optionally, the temperature of the polycondensation reaction is 180°C-280°C.

10. Use of the polyurethane adhesive according to any one of claims 1 to 6 or the polyurethane adhesive obtained by the preparation method according to any one of claims 7 to 9 as an adhesive for thermoplastic plastics, characterized in that: The thermoplastic plastic includes at least one of ABS plastic, PS plastic, PC plastic, PP plastic, PET plastic, and PMMA plastic.

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