Epoxy-terminated polyurethane flexibilizer as well as preparation method and application thereof

Abstract

The invention provides an epoxy-terminated polyurethane flexibilizer and a preparation method and application thereof, and belongs to the technical field of epoxy composites.The epoxy-terminated polyurethane flexibilizer is prepared from polyol, isocyanate, a chain extender, a catalyst, metal salt and epoxy resin, and the chain extender comprises hydroxybenzoxazine. The epoxy-terminated polyurethane toughening agent provided by the invention contains carbamate groups, benzoxazine groups and five-membered oxazolidinone structures, the groups have strong polarity, and due to the introduction of the five-membered oxazolidinone and the benzoxazine groups, the toughening agent has excellent stability at a high temperature and in a salt mist old chemical process, so that the toughness of the toughening agent is improved, and the service life of the toughening agent is prolonged. The toughening agent is added into the epoxy resin structural adhesive, the adhesion of the epoxy resin structural adhesive to metal materials can be improved while the glass transition temperature is not reduced, and the toughening agent further contains a polyether chain segment which can improve the low-temperature impact resistance of the epoxy resin structural adhesive.

Description

Technical Field

[0001] This invention belongs to the field of epoxy composite material technology, and relates to an epoxy-terminated polyurethane toughening agent, its preparation method, and its application. Background Technology

[0002] Epoxy resin adhesives are epoxy composite materials prepared under strict conditions by controlling the proportions of resin, toughening agent, filler, additives, and curing accelerator. These adhesives possess high temperature resistance, high strength, and resistance to high and low temperature impacts. Epoxy resin structural adhesives are characterized by their resistance to high and low temperature impacts, oil resistance, thermochemical stability, low shrinkage, and excellent adhesion. They are widely used in the automotive and electronics industries, especially with the widespread application of new energy vehicles. Single-component epoxy resin structural adhesives are now used in high-speed motors, high-temperature structural bonding of silicon steel sheets, composite body structures, and steel-aluminum and aluminum-aluminum composite bonding to reduce vehicle weight and increase structural strength. However, after curing, epoxy resin exhibits high brittleness and poor impact resistance, which limits its widespread application.

[0003] CN119529218A discloses polyurethane-modified epoxy, which uses -NCO-terminated polyurethane prepolymer to modify epoxy. The E44 / E51 / E55 used in this method contains a large number of hydroxyl groups, with a hydroxyl molar content of 0.09-0.40. The hydroxyl groups consume a large number of -NCO groups. Furthermore, the urea bonds generated by the reaction of hydroxyl groups and -NCO will continue to consume -NCO groups at high temperatures, which seriously affects the reaction to generate stable five-membered oxazolidinone high-temperature resistant units. CN108976381A also does not generate five-membered oxazolidinones due to issues with temperature, epoxy, and process selection.

[0004] CN119119411A discloses the production of modified polyurethane toughening agents using the reaction of hydroxyl groups and -NCO, but these agents are not heat-resistant. Foreign manufacturers such as Adeka and Baxenden produce Blocked-PU toughening agents using thermal deblocking of modified epoxy resins under high-temperature conditions; however, epoxy adhesives prepared using this technology have limited storage stability. Foreign manufacturers such as CVC use carboxyl-terminated nitrile butadiene rubber to modify epoxy resins, exhibiting excellent room-temperature shear peel resistance and aging resistance; however, their products have low low-temperature impact peel resistance and low high-temperature tensile strength. Foreign manufacturers such as DOW, Kaneka, and Wacker use core-shell structure modified toughening epoxy resins, producing products that are heat-resistant, do not reduce Tg, and have good impact resistance; however, their low-temperature impact peel performance is poor.

[0005] With the upgrading of national demand and industry capabilities in the fields of new energy vehicles and electronics, the market's requirements for lightweight and high-strength automobiles are becoming increasingly stringent. Motor speeds are rising, and centrifugal forces are increasing, demanding high strength, high toughness, and high oil resistance alongside high-temperature resistance. Therefore, developing an epoxy resin structural adhesive for use in the new energy vehicle field—one that can enhance vehicle body structure, replace weld joints, strengthen structural toughness, meet impact resistance requirements, control vehicle weight, and facilitate bonding of steel-aluminum hybrid structures and all-aluminum structures—and for use in high-speed motors, achieving impact resistance at -40℃ while maintaining high shear and peel strength at 150~180℃, presents a new challenge in this field. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide an epoxy-terminated polyurethane toughening agent, its preparation method, and its application. Applying the epoxy-terminated polyurethane toughening agent provided by this invention to epoxy resin structural adhesives solves the problem that polyurethane toughening of single-component epoxy resin structural adhesives, while improving impact performance, is incompatible with high-temperature shear and high-temperature impact peeling.

[0007] To achieve this objective, the present invention adopts the following technical solution:

[0008] In a first aspect, the present invention provides an epoxy-terminated polyurethane toughening agent, wherein the raw materials for preparing the epoxy-terminated polyurethane toughening agent include: polyol, isocyanate, chain extender, catalyst, metal salt, and epoxy resin.

[0009] The chain extender includes hydroxybenzoxazine.

[0010] The epoxy-terminated polyurethane toughening agent provided by this invention involves the synergistic interaction of various raw materials, particularly the introduction of a specific type of chain extender. This results in the presence of urethane groups, benzoxazine groups, and a five-membered oxazolidinone structure in the toughening agent. These groups exhibit strong polarity. The introduction of the five-membered oxazolidinone and benzoxazine groups enhances the toughening agent's excellent stability during high-temperature and salt spray aging processes. It improves the adhesion of epoxy resin structural adhesives to metal materials without lowering the glass transition temperature. The toughening agent also contains polyether segments, which can improve the low-temperature impact resistance of epoxy resin structural adhesives. When this epoxy-terminated polyurethane toughening agent is used in epoxy resin structural adhesives, it can improve the bonding performance between epoxy resin structural adhesives and reinforcing materials such as ceramics and carbon fibers.

[0011] Preferably, the polyol comprises polyester polyol and / or polyether polyol.

[0012] Preferably, the polyester polyol comprises polycarbonate diol (PCDL).

[0013] Preferably, the polyether polyol comprises any one or a combination of at least two of polytetrahydrofuran ether diol (PTMEG), polypropylene glycol (PPG), and 1,4-butanediol / 2-methyl-1,3-propanediol copolyether polyol (BDO / MPO copolyether polyol). The polyether polyol used in this invention exhibits excellent stability at high temperatures.

[0014] Preferably, the present invention uses flexible segments of BDO / MPO copolyether polyol or PCDL to synthesize polyurethane toughening agents, which not only have good resistance to heat and oxygen aging, but also have excellent low-temperature performance.

[0015] Preferably, the molecular weight of the polyol is 1000~8000, such as 1000, 2000, 3000, 4000, 5000, 6000, 7000, 8000, etc.

[0016] Preferably, the isocyanate comprises any one or a combination of at least two of hexamethylene diisocyanate (HDI), pentamethylene diisocyanate, phenylenediamine diisocyanate (XDI), 1,5-naphthalene diisocyanate (NDI), norbornene diisocyanate (DMDCI), and dimethylbiphenyl diisocyanate (TODI). A mixture of HDI and TODI, or a mixture of pentamethylene diisocyanate and DMDCI, is preferred. This design primarily aims to balance low-temperature and high-temperature performance, where HDI and pentamethylene diisocyanate provide flexibility and contribute to low-temperature impact resistance, while DMDCI and TODI provide high-temperature stability.

[0017] Preferably, the isocyanate is a mixture of HDI and TODI in a mass ratio of 2:1 or a mixture of pentamethylene diisocyanate and DMDCI in a mass ratio of 2.2:1.

[0018] Preferably, the hydroxybenzoxazine includes hydroxybisphenol F type benzoxazine and / or hydroxybisphenol A type benzoxazine.

[0019] The structural formula of the hydroxybisphenol F type benzoxazine is shown below: .

[0020] The structural formula of the hydroxybisphenol A type benzoxazine is shown below: .

[0021] Preferably, the catalyst comprises any one or a combination of at least two of organotin, chelated tin, organoplatinum, organocopper, and organocopper-copper neodecanoate, with organoplatinum and / or organocopper being more preferred. Organotin catalysis leads to higher material temperatures during the synthesis process, so organoplatinum and / or organocopper are preferred. This catalyst exhibits milder activity at 80-95°C, is slower than chelated tin, has a smaller temperature rise, and allows for better control of byproducts. Furthermore, the molecular chain segments are uniform, preventing excessively high localized temperature rises due to catalyst addition, and avoiding cross-linking reactions of some isocyanate groups and urethane bonds that could affect the final -NCO equivalent.

[0022] Preferably, the metal salt comprises any one or a combination of at least two of aluminum acetylacetonate, copper acetylacetonate, zinc acetylacetonate, and iron acetylacetonate, with aluminum acetylacetonate and / or zinc acetylacetonate being more preferred. This is important because aluminum acetylacetonate and zinc acetylacetonate are excellent heat stabilizers; using them instead of tertiary amines and organophosphorus compounds can prevent the self-polymerization of isocyanate groups at high temperatures.

[0023] Preferably, the epoxy resin is a high-purity epoxy resin, and the content of hydroxyl groups in the epoxy resin is <0.01mol / mol, for example, 0.008mol / mol, 0.006mol / mol, 0.005mol / mol, 0.002mol / mol, etc.

[0024] Preferably, the epoxy equivalent of the epoxy resin is 140~160 g / eq, such as 140 g / eq, 143 g / eq, 145 g / eq, 148 g / eq, 150 g / eq, 153 g / eq, 155 g / eq, 156 g / eq, 160 g / eq, etc.

[0025] Preferably, the epoxy resin includes naphthol epoxy resin and / or bisphenol F type epoxy resin.

[0026] Preferably, the epoxy resin comprises a naphthol epoxy resin with an epoxy equivalent of 143 g / eq, a bisphenol F type epoxy resin with an epoxy equivalent of 156 g / eq, and a mixed epoxy resin of naphthol epoxy resin and bisphenol F type epoxy resin with an epoxy equivalent of 150 g / eq. Most common epoxy resins contain hydroxyl groups, which preferentially react with isocyanates, reducing the reaction between epoxy groups and isocyanates, which has a significant adverse effect on the reaction products. Therefore, this invention preferentially selects a 1:1 molar ratio of naphthol epoxy resin and bisphenol F type epoxy resin, which can improve adhesive strength while reducing viscosity.

[0027] Preferably, the molar ratio of the polyol to the isocyanate is (0.8~1.2):1, for example, 0.8:1, 0.9:1, 1:1, 1.1:1, 1.2:1, etc.

[0028] Preferably, the amount of the chain extender is 1 wt.% to 10 wt.% of the amount of polyol, for example, 1 wt.%, 2 wt.%, 3 wt.%, 5 wt.%, 8 wt.%, 10 wt.%, etc.

[0029] Preferably, the amount of catalyst used is 10 to 50 ppm of the amount of polyol used, such as 10 ppm, 15 ppm, 20 ppm, 25 ppm, 30 ppm, 35 ppm, 40 ppm, 45 ppm, 50 ppm, etc.

[0030] Preferably, the amount of the metal salt is 20 to 40 ppm of the amount of polyol, such as 20 ppm, 25 ppm, 30 ppm, 35 ppm, 40 ppm, etc.

[0031] Preferably, the amount of epoxy resin used is 10wt.% to 20wt.% of the amount of polyol used, for example, 10wt.%, 12wt.%, 13wt.%, 15wt.%, 18wt.%, 20wt.%, etc.

[0032] In a second aspect, the present invention provides a method for preparing an epoxy-terminated polyurethane toughening agent as described in the first aspect, the method comprising the following steps:

[0033] A terminal-NCO prepolymer was synthesized from polyol and isocyanate under the catalysis of a catalyst. Then, a polyurethane prepolymer was synthesized using hydroxybenzoxazine as a chain extender. Finally, the polyurethane prepolymer was end-capped by the epoxy groups of an epoxy resin under the catalysis of a metal salt to obtain the epoxy-end-capped polyurethane toughening agent.

[0034] As a preferred technical solution of the present invention, the preparation method specifically includes the following steps:

[0035] (1) The polyol was dehydrated under vacuum, then isocyanate was added, then chain extender was added, stirred, then catalyst was added, reaction was carried out, and -NCO equivalent was tested to obtain polyurethane prepolymer;

[0036] (2) Mix the polyurethane prepolymer and epoxy resin, heat up, then add metal salt, heat up again, react, take a sample and use infrared detection to detect -NCO residue. If there is no -NCO characteristic peak, it indicates that the isocyanate reaction is complete. When the reaction ends, titrate the epoxy equivalent and test the degree of reaction to obtain the epoxy-terminated polyurethane toughening agent.

[0037] This invention utilizes the reaction of polyether polyols and / or polyester polyols with isocyanates to obtain isocyanate-terminated polyurethane prepolymers. After chain extension with benzoxazine, the chain-extended -NCO-terminated polyurethane prepolymers and epoxy groups are further reacted at high temperature to obtain epoxy-terminated polyurethane toughening agents. The entire preparation process is carried out logically, without the generation of complex small molecules or waste gas and waste liquid, and belongs to green industrial production processes.

[0038] Preferably, the vacuum dehydration temperature in step (1) is 100~120℃, such as 100℃, 105℃, 110℃, 115℃, 120℃, etc., and the vacuum dehydration time is 90~120min, such as 90min, 100min, 110min, 120min, etc.

[0039] Preferably, after vacuum dehydration of the polyol in step (1), an inert gas is introduced and the temperature is lowered to 60~70℃, for example, 60℃, 65℃, 70℃, etc., and then isocyanate is added.

[0040] Preferably, the method of adding isocyanate in step (1) includes dropwise addition, and the dropwise addition time is controlled at 30~45min, for example 30min, 35min, 40min, 45min, etc.

[0041] Preferably, the stirring temperature in step (1) is 70~90℃, for example 70℃, 75℃, 80℃, 85℃, 90℃, etc., and the stirring time is 20~40min, for example 20min, 25min, 30min, 35min, 40min, etc.

[0042] Preferably, the reaction temperature in step (1) is 90~100℃, for example 90℃, 95℃, 100℃, etc., and the reaction time is 80~100min, for example 80min, 85min, 90min, 95min, 100min, etc.

[0043] Preferably, the temperature rise in step (2) is to 90~110℃, such as 90℃, 95℃, 100℃, 105℃, 110℃, etc.

[0044] Preferably, the reheating in step (2) is to raise the temperature to 130~150℃, for example, 130℃, 135℃, 140℃, 145℃, 150℃, etc.

[0045] Preferably, the reaction temperature in step (2) is 130~150℃, for example 130℃, 135℃, 140℃, 145℃, 150℃, etc., and the reaction time is 40~60min, for example 40min, 45min, 50min, 55min, 60min, etc.

[0046] Thirdly, the present invention provides an epoxy resin structural adhesive, wherein the epoxy resin structural adhesive comprises the following components by weight:

[0047] 20-30 parts of isocyanate-modified epoxy;

[0048] 20-30 parts epoxy resin;

[0049] 15-35 parts of polyurethane toughening agent;

[0050] 5-10 parts of phosphated epoxy resin;

[0051] 10-15 parts of filler;

[0052] 4-6 parts of curing accelerator;

[0053] The polyurethane toughening agent includes the epoxy-terminated polyurethane toughening agent as described in the first aspect or the epoxy-terminated polyurethane toughening agent prepared according to the preparation method described in the second aspect.

[0054] The epoxy resin structural adhesive provided by this invention introduces a specific type of polyurethane toughening agent. After the epoxy resin structural adhesive is cured, flexible high and low temperature resistant segments are introduced into the curing system, which can significantly improve the toughness of the matrix resin, greatly enhance the low temperature resistance and impact peel strength of the matrix resin, and at the same time, the heat resistance of the cured product is not reduced, and a high glass transition temperature can be maintained.

[0055] The epoxy resin structural adhesive provided by this invention has excellent low-temperature impact resistance and peel strength, and can maintain good mechanical properties in high-temperature areas, thus meeting the performance requirements under extreme low-temperature weather conditions.

[0056] In this invention, the amount of isocyanate-modified epoxy in the epoxy resin structural adhesive can be 20 parts, 22 parts, 24 parts, 25 parts, 26 parts, 28 parts, 30 parts, etc., by weight.

[0057] In this invention, the amount of epoxy resin used in the epoxy resin structural adhesive can be 20 parts, 22 parts, 24 parts, 25 parts, 26 parts, 28 parts, 30 parts, etc., by weight.

[0058] In this invention, the amount of polyurethane toughening agent used in the epoxy resin structural adhesive can be 15 parts, 16 parts, 18 parts, 20 parts, 22 parts, 24 parts, 25 parts, 26 parts, 28 parts, 30 parts, 32 parts, 34 parts, 35 parts, etc., by weight.

[0059] In this invention, the amount of phosphated epoxy resin used in the epoxy resin structural adhesive can be 5 parts, 6 parts, 7 parts, 8 parts, 9 parts, 10 parts, etc., by weight.

[0060] In this invention, the amount of filler used in the epoxy resin structural adhesive can be 10 parts, 12 parts, 14 parts, 15 parts, etc., by weight.

[0061] In this invention, the amount of curing accelerator used in the epoxy resin structural adhesive can be 4 parts, 5 parts, 6 parts, etc., by weight.

[0062] Preferably, the isocyanate-modified epoxy comprises any one or a combination of at least two of isophorone diisocyanate (IPDI) modified epoxy, diphenylmethane diisocyanate (MDI) modified epoxy, and phenyl dimethylene diisocyanate (XDI) modified epoxy.

[0063] Preferably, the epoxy resin comprises any one or a combination of at least two of CYD-134, DER-663U, E10P, and NC-513, and more preferably a mixture of CYD-134, DER-663U, E10P, and NC-513 in a mass ratio of 6:3:0.5:0.5. This epoxy resin is mainly used as the host resin, which can improve interfacial wetting ability and promote adhesion.

[0064] Preferably, the phosphated epoxy resin comprises any one or a combination of at least two of the following: pentavalent phosphorus-modified epoxy resin, vinyl dimethyl phosphate-modified epoxy resin, vinyl diethyl phosphate-modified epoxy resin, and propyl phosphoric anhydride-modified epoxy resin. Only pentavalent phosphorus can be used as the phosphate ester, as it possesses the ability to chelate metal ions, which can enhance the electrochemical reaction of the epoxy resin structural adhesive during salt spray aging and inhibit corrosion.

[0065] Preferably, the filler comprises any one or a combination of at least two of the following: fumed silica (e.g., Evonik fumed silica R8200, fumed silica R972), wollastonite (e.g., wollastonite 0200M, aspect ratio 50-100), spherical nano-alumina, and nano-zinc phosphate; more preferably, a mixture of fumed silica, wollastonite, spherical nano-alumina, and nano-zinc phosphate in a mass ratio of 2:9:7:2. Nanofillers can improve the bulk strength of epoxy resin structural adhesives, and materials with a high aspect ratio can improve the impact resistance of epoxy resin structural adhesives.

[0066] Preferably, the curing accelerator comprises a mixture of dicyandiamide (DICY) and a urea accelerator. The amount of dicyandiamide used is 0.08 to 0.088 times the equivalent of the epoxy resin, and the amount of the urea accelerator is 1 / 4 to 1 / 5 of the weight of the dicyandiamide.

[0067] This invention does not limit the preparation method of the epoxy resin structural adhesive. Exemplarily, the epoxy resin structural adhesive is prepared by the following method:

[0068] Each component is added to a planetary mixer and first dispersed at a speed of 10-30 Hz, then stirred at a speed of 40-50 Hz. The mixture is cooled and kept below 45°C, and dispersed and stirred for 40-60 minutes. The mixture is then vacuum filtered to obtain the epoxy resin structural adhesive.

[0069] Compared with the prior art, the present invention has the following beneficial effects:

[0070] The epoxy-terminated polyurethane toughening agent provided by this invention involves the synergistic interaction of various raw materials, particularly the introduction of a specific type of chain extender. This results in the presence of urethane groups, benzoxazine groups, and a five-membered oxazolidinone structure in the toughening agent. These groups exhibit strong polarity. The introduction of the five-membered oxazolidinone and benzoxazine groups enhances the toughening agent's excellent stability during high-temperature and salt spray aging processes. It improves the adhesion of epoxy resin structural adhesives to metal materials without lowering the glass transition temperature. The toughening agent also contains polyether segments, which can improve the low-temperature impact resistance of epoxy resin structural adhesives. When this epoxy-terminated polyurethane toughening agent is used in epoxy resin structural adhesives, it can improve the bonding performance between epoxy resin structural adhesives and reinforcing materials such as ceramics and carbon fibers. Detailed Implementation

[0071] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0072] Unless otherwise specified, information on some of the raw materials used in the following preparation examples of this invention is as follows:

[0073] BDO / MPO copolyether polyol: molecular weight 2000, purchased from Shandong Sciore;

[0074] Polyester polyol: PCDL, molecular weight 1000, purchased from Wuxi Shuyu;

[0075] Isocyanate 1 mixture: a mixture of HDI and TODI in a mass ratio of 2:1, wherein both HDI and TODI were purchased from Hunan Daochen Technology.

[0076] Hydroxybisphenol F benzoxazine and hydroxybisphenol A benzoxazine: both purchased from Honshu Chemical Co., Ltd.

[0077] Organic copper-copper neodecanoate: copper content 5%, purchased from Sinopharm Chemicals;

[0078] Organic platinum, with a platinum content of 3000 ppm, was purchased from Shanghai Jingri New Materials.

[0079] Aluminum acetylacetone and zinc acetylacetone: both purchased from Maclean Chemical Technology;

[0080] High-purity epoxy resin: Naphthol epoxy resin and bisphenol F type epoxy resin in a molar ratio of 1:1, wherein both the naphthol epoxy resin and the bisphenol F type epoxy resin were purchased from Xi'an Zhilun Technology.

[0081] Dimethyl vinyl phosphate: purchased from Guangdong Jiatu Technology;

[0082] n-Propylphosphine: Purchased from Jiangxi Weida Pharmaceutical Co., Ltd.

[0083] Preparation Example 1

[0084] This preparation example provides an epoxy-terminated polyurethane toughening agent, the preparation method of which includes the following steps:

[0085] 1000 g of BDO / MPO copolyether polyol with a molecular weight of 2000 Da was added to a 2-liter four-necked glass flask. The oil bath was turned on and heated to 110°C. The vacuum oil pump was turned on and the mixture was vacuum dehydrated for 100 min. The vacuum was turned off, the nitrogen valve was opened, and the mixture was ventilated and cooled to 70°C. 200 g of isocyanate 1 mixture was added dropwise over a time of 40 min. 34 g of bisphenol F type benzoxazine chain extender was added, and the temperature was maintained at 80°C. The mixture was stirred for 30 min, and then 15 ppm equivalent of an organic platinum catalyst (based on the total liquid volume of the reactants) was added. The mixture was reacted at 95°C for 90 min to obtain the polyurethane prepolymer.

[0086] 145 g of dehydrated high-purity epoxy resin was dropped into the above polyurethane prepolymer, heated to 100°C, and then 0.035 g of aluminum acetylacetonate was added and melted. The temperature was then raised to 145°C within 45 min and maintained for 60 min to obtain the epoxy-terminated polyurethane toughening agent, denoted as PU-EP-1, with an activity equivalent of 1620 g / mol.

[0087] Preparation Example 2

[0088] This preparation example provides an epoxy-terminated polyurethane toughening agent, the preparation method of which includes the following steps:

[0089] 600g of BDO / MPO copolyether polyol with a molecular weight of 2000Da and 200g of PCDL polyester polyol with a molecular weight of 1000Da were added to a 2L four-necked glass flask. The oil bath was turned on and heated to 110°C. Vacuum dehydration was carried out for 100min with a vacuum oil pump. The vacuum was turned off, the nitrogen valve was opened, and the mixture was ventilated and cooled to 70°C. 200g of isocyanate 1 mixture was added dropwise over a time of 40min. 36g of bisphenol A type benzoxazine chain extender was added, and the temperature was maintained at 80°C. The mixture was stirred for 30min, and then 17ppm equivalent of an organocopper-neodecanone catalyst (based on the total liquid volume of reactants) was added dropwise. The mixture was reacted at 95°C for 90min to obtain a polyurethane prepolymer.

[0090] 145 g of dehydrated high-purity epoxy resin was dropped into the above polyurethane prepolymer, heated to 100°C, and then 0.037 g of zinc acetylacetone was added and melted. The temperature was then raised to 145°C within 45 min and maintained for 60 min to obtain the epoxy-terminated polyurethane toughening agent, denoted as PU-EP-2, with an activity equivalent of 1360 g / mol.

[0091] Comparative Preparation Example 1

[0092] The only difference between this comparative preparation example and preparation example 1 is that the bisphenol F type benzoxazine chain extender is replaced with an equimolar amount of 1,4-butanediol, and the resulting epoxy-terminated polyurethane toughening agent is denoted as PU-EP-3.

[0093] Preparation Example 3

[0094] This preparation example provides a phosphated epoxy resin, the preparation method of which includes the following steps:

[0095] 136 g of dimethyl vinyl phosphate was added to a 1 L flask and heated to 120 °C. Then, 3 g of trifluoromethylbenzenesulfonic acid catalyst was added and the mixture was refluxed under nitrogen. After that, 790 g of E51 epoxy resin was added dropwise and the mixture was refluxed for 3 hours. The temperature was then raised to 150 °C and vacuumed for 60 min. The mixture was then cooled and discharged to obtain 926 g of the phosphated epoxy resin, which was designated as phosphated epoxy resin P1.

[0096] Preparation Example 4

[0097] This preparation example provides a phosphated epoxy resin, the preparation method of which includes the following steps:

[0098] 104.5 g of n-propylphosphoric anhydride was diluted in 150 g of toluene, and then 1 g of 2-ethyl-4-methylimidazole accelerator was added to prepare a mixed liquid.

[0099] 772 g of epoxy resin (128E epoxy resin) was added to a 2 L four-necked flask and heated to 105 °C. Then, 255.5 g of the above mixed liquid was added dropwise. The mixture was refluxed at 105 °C under nitrogen protection. The product was then added dropwise to E51 epoxy resin over 70 min. After the addition was complete, the mixture was reacted at 110 °C for 60 min. The temperature was then raised to 120 °C, and the toluene solvent was removed under vacuum of -0.095 kPa for 60 min. The mixture was then cooled and discharged to obtain 877 g of the phosphated epoxy resin, denoted as phosphated epoxy resin P2.

[0100] Unless otherwise specified, the raw material information used in the following embodiments and comparative examples of the present invention is as follows:

[0101] YER-3310 isocyanate-modified epoxy: purchased from Guangdong Guangshan Chemical Co., Ltd.

[0102] Epoxy resin M: a mixture of CYD-134, DER-663U, E10P and NC-513 in a mass ratio of 6:3:0.5:0.5, wherein CYD-134 was purchased from Kunshan Guodu Chemical, DER-663U was purchased from Aolin Chemical, E10P was purchased from Hansoh Hexion, and NC-513 was purchased from Cardley Fine Chemicals;

[0103] Polyurethane toughening agents: PU-EP-1 and PU-EP-2 provided in Preparation Example 1 and Preparation Example 2; PU-EP-3 provided in Comparative Preparation Example 1;

[0104] Other toughening agents: QR-9466, 86840, MX154;

[0105] Phosphated epoxy resins: Phosphated epoxy resin P1 and phosphated epoxy resin P2 provided in Preparation Example 3 and Preparation Example 4;

[0106] Filler: A mixture of gaseous silica, wollastonite, spherical nano-alumina, and nano-zinc phosphate in a mass ratio of 2:9:7:2. Among them, the gaseous silica is Evonik gaseous silica R8200, the wollastonite is wollastonite 0200M with an aspect ratio of 50-100, purchased from Guangyuan Chemical, the spherical nano-alumina is purchased from Lianrui New Materials, and the nano-zinc phosphate is purchased from Guangdong Xindi Chemical.

[0107] Curing accelerator: A mixture of dicyandiamide and urea accelerator, wherein the dicyandiamide is purchased from complexing chemistry and the urea accelerator is Alzchem's UR800 urea-based accelerator, and the amount of urea accelerator is 1 / 4 of the weight of dicyandiamide.

[0108] Example 1

[0109] This embodiment provides an epoxy resin structural adhesive, the specific components and amounts (parts by weight) of which are shown in Table 1.

[0110] The preparation method includes the following steps:

[0111] According to the formula, each component is added to a planetary mixer, first dispersed at a speed of 20 Hz, then stirred at a speed of 45 Hz until uniformly mixed, cooled and kept at a temperature below 45 ℃, and then vacuum filtered to obtain the epoxy resin structural adhesive.

[0112] Examples 2-7, Comparative Examples 1-5

[0113] The only difference from Example 1 is that the specific components and / or amounts are different, as shown in Tables 1 and 2.

[0114] Table 1

[0115]

[0116] Table 2

[0117]

[0118] The performance of the epoxy resin structural adhesives provided in the embodiments and comparative examples of the present invention was tested using the following methods:

[0119] 1. Shear strength at 25℃: All test pieces used were 38CrSi steel pieces (100mm×25mm×1.6mm). The test pieces were cleaned with ethyl acetate, and the adhesive thickness was controlled to be 200μm. According to GB / T 7124 standard, epoxy resin structural adhesive was adhered between two test pieces. After curing the fixed test pieces at 180℃ for 30min, they were removed and placed at room temperature for 24h. Shear strength was then tested at 23±1℃, with a tensile speed of 10mm / min. The unit is expressed in MPa.

[0120] 2. High-temperature shear strength test, specifically at 90℃: 8CrSi steel specimens (100mm×25mm×1.6mm) were cleaned with ethyl acetate, and the adhesive thickness was controlled to be 200μm. Epoxy structural adhesive was applied between the two specimens according to GB / T 7124 standard. After curing the fixed specimens at 180℃ for 30 minutes, they were removed and left at room temperature for 24 hours. The shear strength test was then conducted at 90±1℃ with a tensile speed of 10mm / min.

[0121] 3. Low-temperature impact peel strength: The test piece was a CRS 14O3 carbon steel test piece (90mm×20mm×1.0mm). The test piece was cleaned with ethyl acetate. According to ISO 11343 standard, epoxy resin structural adhesive was adhered between the two test pieces. The fixed test pieces were cured at 180℃ for 30 minutes and then removed. After cooling at room temperature for 24 hours, the impact peel strength test was carried out at -40℃ with a loading speed of 2m / s. The unit is expressed as N / mm.

[0122] 4. Salt spray aging retention rate: Performed according to GB / T 10125 standard. Shear plates are prepared according to Test 1 above, and then placed in a neutral salt spray aging test chamber for 2000h of cyclic testing. After the test, the difference in mechanical strength between the aged shear plate and the blank shear plate is tested, and the remaining value is calculated. The larger the retention rate, the better the salt spray resistance.

[0123] 5. High and low temperature cycling retention rate: In accordance with GB31241-2014 standard, the temperature is -40℃ to 105℃ for cyclic impact, and the cycle test is carried out for 1000 hours. After the test, the difference in mechanical strength between the aged shear sheet and the blank shear sheet is tested, and the remaining value is calculated. The larger the retention, the better the temperature impact resistance.

[0124] 6. The 85% aging retention rate was tested according to GB / T 2423.50-2019 standard, in an environment of 85℃ and 85% humidity, for 1000 hours continuously. After the test, the difference in mechanical strength between the aged shear sheet and the blank shear sheet was tested, and the remaining strength was calculated. The higher the retention rate, the better the 85% aging resistance.

[0125] 7. Tensile strength, tested in accordance with GB / T 1040.1-2025.

[0126] 8. Peel strength, tested in accordance with GB / T 2790.

[0127] 9. Low-temperature impact peel strength under baking: The test piece is a CRS 14O3 carbon steel test piece (90mm×20mm×1.0mm). The test piece is cleaned with ethyl acetate. According to ISO 11343 standard, epoxy resin structural adhesive is adhered between two test pieces. The fixed test pieces are cured at 150℃ for 30 minutes and then removed. After cooling at room temperature for 24 hours, the impact peel strength test is carried out at -40℃ with a loading speed of 2m / s. The unit is expressed as N / mm.

[0128] 10. Low-temperature impact peel strength after baking: The test piece is a CRS 14O3 carbon steel test piece (90mm×20mm×1.0mm). The test piece is cleaned with ethyl acetate. According to ISO 11343 standard, epoxy resin structural adhesive is adhered between two test pieces. The fixed test pieces are cured at 200℃ for 45 minutes and then removed. After cooling at room temperature for 24 hours, the impact peel strength test is carried out at -40℃ with a loading speed of 2m / s. The unit is expressed as N / mm.

[0129] 11. Glass transition temperature (Tg) was tested using a DMA-QA-800 instrument with a programmed temperature rise of 2 times, a scanning range of -20℃ to 150℃, and a heating rate of 10℃ / minute.

[0130] The performance test results are shown in Table 3.

[0131] Table 3

[0132]

[0133] As shown in Table 3, compared with Comparative Examples 1-5, Examples 1-7, through the selection and specific proportions of epoxy resin, polyurethane toughening agent, phosphated epoxy resin, curing accelerator, and filler, produced epoxy resin structural adhesives with a shear strength of no less than 36 MPa and a maximum of 43 MPa at 25°C, and a shear strength of no less than 26 MPa and a maximum of 32 MPa at 90°C, far exceeding the toughening performance of structural adhesives using QR-9466, 86840, and MX154 as toughening agents. The epoxy resin structural adhesives provided in Examples 1-7 also exhibited an impact peel strength of no less than 30 N / mm and a maximum of 56 N / mm at -40°C, demonstrating excellent shear strength at both high and low temperatures while maintaining superior peel strength.

[0134] By comparing Comparative Example 3 with Example 3, it can be seen that Comparative Example 3 does not contain phosphated epoxy resin, and its salt spray resistance is poor. Therefore, it can be found that phosphated epoxy resin can improve the salt spray aging resistance of the adhesive.

[0135] The epoxy resin structural adhesive provided by this invention is suitable for structural bonding of parts such as automobile doors and hoods, motor silicon steel sheets, engines, brake motors, and powertrains.

[0136] The applicant declares that this invention illustrates the epoxy-terminated polyurethane toughening agent, its preparation method, and its application through the above embodiments. However, this invention is not limited to the above embodiments, meaning that this invention does not necessarily rely on the above embodiments for implementation. Those skilled in the art should understand that any improvements to this invention, equivalent substitutions of the raw materials used in this invention, additions of auxiliary components, and selection of specific methods all fall within the protection and disclosure scope of this invention.

Claims

1. An epoxy-terminated polyurethane flexibilizer characterized in that, The raw materials for preparing the epoxy-terminated polyurethane toughening agent include: polyol, isocyanate, chain extender, catalyst, metal salt, and epoxy resin. The chain extender includes hydroxybenzoxazine.

2. The epoxy-terminated polyurethane flexibilizer of claim 1, wherein, The polyols include polyester polyols and / or polyether polyols; Preferably, the polyester polyol comprises polycarbonate diol; Preferably, the polyether polyol includes any one or a combination of at least two of the following: polytetrahydrofuran ether diol, polypropylene glycol, and 1,4-butanediol / 2-methyl-1,3-propanediol copolyether polyol. Preferably, the molecular weight of the polyol is 1000~8000; Preferably, the isocyanate includes any one or a combination of at least two of hexamethylene diisocyanate, pentamethylene diisocyanate, phenyldimethyl diisocyanate, 1,5-naphthalene diisocyanate, norbornene diisocyanate, and dimethylbiphenyl diisocyanate.

3. The epoxy-terminated polyurethane flexibilizer according to claim 1 or 2, characterized in that, The hydroxybenzoxazine includes hydroxybisphenol F benzoxazine and / or hydroxybisphenol A benzoxazine; Preferably, the catalyst comprises any one or a combination of at least two of organotin, chelated tin, organoplatinum, organocopper, and organocopper-copper neodecanoate.

4. The epoxy-terminated polyurethane toughening agent according to any one of claims 1-3, characterized in that, The metal salt includes any one or a combination of at least two of aluminum acetylacetonate, copper acetylacetonate, zinc acetylacetonate, and iron acetylacetonate. Preferably, the epoxy resin is a high-purity epoxy resin, and the content of hydroxyl groups in the epoxy resin is <0.01 mol / mol; Preferably, the epoxy equivalent of the epoxy resin is 140~160 g / eq; Preferably, the epoxy resin includes naphthol epoxy resin and / or bisphenol F type epoxy resin.

5. The epoxy-terminated polyurethane toughening agent according to any one of claims 1-4, characterized in that, The molar ratio of the polyol to the isocyanate is (0.8~1.2):1; Preferably, the amount of the chain extender is 1 wt.% to 10 wt.% of the amount of polyol. Preferably, the amount of catalyst used is 10-50 ppm of the amount of polyol used; Preferably, the amount of the metal salt is 20-40 ppm of the amount of polyol used; Preferably, the amount of epoxy resin used is 10wt.% to 20wt.% of the amount of polyol used.

6. A method for preparing an epoxy-terminated polyurethane toughening agent as described in any one of claims 1-5, characterized in that, The preparation method includes the following steps: A terminal-NCO prepolymer was synthesized from polyol and isocyanate under the catalysis of a catalyst. Then, a polyurethane prepolymer was synthesized using hydroxybenzoxazine as a chain extender. Finally, the polyurethane prepolymer was end-capped by the epoxy groups of an epoxy resin under the catalysis of a metal salt to obtain the epoxy-end-capped polyurethane toughening agent.

7. The preparation method according to claim 6, characterized in that, The preparation method specifically includes the following steps: (1) The polyol was dehydrated under vacuum, then isocyanate was added, then chain extender was added, stirred, then catalyst was added, reaction was carried out, and -NCO equivalent was tested to obtain polyurethane prepolymer; (2) Mix the polyurethane prepolymer and epoxy resin, heat the mixture, add a metal salt, heat the mixture again, and react to obtain the epoxy-terminated polyurethane toughening agent.

8. The preparation method according to claim 7, characterized in that, The vacuum dehydration temperature in step (1) is 100~120℃, and the vacuum dehydration time is 90~120min; Preferably, after vacuum dehydration of the polyol in step (1), an inert gas is introduced and the temperature is lowered to 60~70°C before isocyanate is added; Preferably, the method of adding isocyanate in step (1) includes dropwise addition, and the dropwise addition time is controlled within 30~45 min; Preferably, the stirring temperature in step (1) is 70~90℃ and the stirring time is 20~40min; Preferably, the reaction temperature in step (1) is 90~100℃ and the reaction time is 80~100min; Preferably, the temperature rise in step (2) is to 90~110℃; Preferably, the reheating in step (2) is to raise the temperature to 130~150℃; Preferably, the reaction temperature in step (2) is 130~150℃ and the reaction time is 40~60min.

9. An epoxy resin structural adhesive, characterized in that, The epoxy resin structural adhesive comprises the following components by weight: 20-30 parts of isocyanate-modified epoxy; 20-30 parts epoxy resin; 15-35 parts of polyurethane toughening agent; 5-10 parts of phosphated epoxy resin; 10-15 parts of filler; 4-6 parts of curing accelerator; The polyurethane toughening agent includes the epoxy-terminated polyurethane toughening agent as described in any one of claims 1-5 or the epoxy-terminated polyurethane toughening agent prepared according to the preparation method as described in any one of claims 6-8.

10. The epoxy resin structural adhesive according to claim 9, characterized in that, The isocyanate-modified epoxy includes any one or a combination of at least two of isophorone diisocyanate-modified epoxy, diphenylmethane diisocyanate-modified epoxy, and phenylmethylene diisocyanate-modified epoxy. Preferably, the epoxy resin includes any one or a combination of at least two of CYD-134, DER-663U, E10P, and NC-513; Preferably, the phosphated epoxy resin includes any one or a combination of at least two of the following: pentavalent phosphorus-modified epoxy resin, vinyl dimethyl phosphate-modified epoxy resin, vinyl diethyl phosphate-modified epoxy resin, and propyl phosphoric anhydride-modified epoxy resin. Preferably, the filler comprises any one or a combination of at least two of the following: gaseous silica, wollastonite, spherical nano-alumina, and nano-zinc phosphate; Preferably, the curing accelerator comprises a mixture of dicyandiamide and a urea accelerator.

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