Low-viscosity high-strength flame-retardant structural adhesive and preparation method thereof

Abstract

The invention provides a low-viscosity high-strength flame-retardant structural adhesive and a preparation method thereof.The low-viscosity high-strength flame-retardant structural adhesive is formed by mixing a component A and a component B. The component A comprises, by weight, 79-104 parts of epoxy resin, 6-12 parts of diluent and 3-10 parts of hyperbranched organic filler; the component B comprises the following components in parts by weight: 76-84 parts of phenolic aldehyde amine, 2-8 parts of a 593 curing agent, 0-4 parts of polyether amine and 5 parts of a promoting curing agent; and the component A and the component B in a mass ratio of (1-1.5): 1 are uniformly mixed to prepare the low-viscosity high-strength flame-retardant structural adhesive. Compared with the traditional structural adhesive, the structural adhesive disclosed by the invention has the advantages that through the molecular design of the hyperbranched compound and the synergistic effect of the phosphaphenanthrene group, the viscosity of the structural adhesive is lower, and meanwhile, the comprehensive performance in the aspects of tensile strength, viscosity, tensile shear strength and flame retardance is good.

Description

Technical Field

[0001] The present invention relates to the technical field of structural adhesives, and in particular to a low-viscosity, high-strength flame-retardant structural adhesive and a preparation method thereof. Background Art

[0002] With the acceleration of my country's urbanization and the rapid development of the construction industry, the demand for new materials and technologies is increasing, especially in key areas such as high-rise and super-high-rise buildings and bridge construction. Modern architecture not only places greater emphasis on structural safety and durability, but also places higher demands on construction efficiency. Against this backdrop, epoxy resin structural adhesives, thanks to their superior mechanical properties, durability, and bonding performance, are becoming an increasingly important choice in construction applications.

[0003] With the continuous advancement of epoxy resin technology and the continuous optimization of production processes, its cost has been significantly reduced, and construction techniques have become increasingly mature. The application prospects of epoxy resin structural adhesives are becoming increasingly broad. Especially in the critical stage of my country's construction industry's transition to green buildings and high-performance buildings, epoxy resin structural adhesives will surely play an irreplaceable and important role.

[0004] With further technological breakthroughs and continued cost reductions, the application of epoxy resin structural adhesives in the construction industry will become more extensive, providing solid support for the high-quality development of my country's construction industry and helping to achieve the green and intelligent transformation goals in the construction field.

[0005] However, the current traditional structural adhesives still have the following problems to be solved:

[0006] (1) The viscosity of the structural adhesives currently on the market is very high. The high viscosity is not conducive to the uniformity of the mixing of components A and B, and will affect the performance of the mixed structural adhesive. The structural adhesives on the market generally have a high viscosity, which leads to uneven mixing of the two-component structural adhesive or residual bubbles, affecting the strength of the structural adhesive after curing. The construction process requirements are relatively high. In addition, due to poor fluidity during construction, the colloid will remain in the tools or containers, making the utilization rate less than ideal.

[0007] (2) Traditional structural adhesives cannot take into account viscosity, tensile strength, shear strength and toughness at the same time, and their comprehensive performance is not strong. Existing structural adhesives have deficiencies in viscosity control and the coordinated optimization of strength and toughness. High-viscosity adhesives have high requirements for construction technology, and low-viscosity structural adhesives do not have the ideal tensile / shear strength. It is difficult to take into account the viscosity, tensile strength and shear strength of structural adhesives at the same time.

[0008] (3) Epoxy resins are widely used in various fields such as construction, coatings, and adhesives due to their excellent anti-corrosion and mechanical properties. However, since epoxy resins are flammable and mainly composed of hydrocarbon elements, they are not suitable for use in many cases, and their application is greatly limited. Therefore, improving the flame retardant properties of epoxy resins is of great significance to the promotion and application of epoxy resins.

[0009] Therefore, how to maintain the excellent performance of epoxy resin while also ensuring a certain degree of toughness and flame retardancy, and achieve a balanced performance of epoxy resin composite materials, is of great significance for the development of high-performance epoxy resin materials and meeting the requirements of epoxy resin materials in complex application scenarios. Summary of the Invention

[0010] The purpose of the present invention is to provide a low-viscosity, high-strength flame-retardant structural adhesive and a preparation method thereof, while taking into account the viscosity, tensile strength, shear strength and flame retardant properties of the structural adhesive, so that the structural adhesive has the characteristics of low viscosity, high strength and good flame retardant properties.

[0011] The above-mentioned purpose of the present invention is achieved through the following technical solutions:

[0012] The present invention provides a low-viscosity and high-strength flame-retardant structural adhesive, comprising a component A and a component B; the weight ratio of the component A to the component B is 1-1.5:1;

[0013] The A component includes the following components in parts by weight:

[0014] Epoxy resin 79-104 parts;

[0015] 6~12 parts of diluent;

[0016] 3 to 10 parts of hyperbranched organic filler

[0017] Furthermore, the epoxy resin is a mixture of bisphenol A epoxy resin and novolac epoxy resin in a weight ratio of 7 to 8.4:1. The bisphenol A epoxy resin can be a commercially available product, such as the E-51 epoxy resin with an epoxy equivalent of 184 to 194 and the E-44 epoxy resin with an epoxy equivalent of 44 to 100 from Guangzhou Fufei Chemical. The novolac epoxy resin can be a commercially available product, such as the novolac epoxy resin with an epoxy equivalent of 180 from Wuxi Jiunai Anticorrosion Materials Co., Ltd., which has phenolic hydroxyl groups inside.

[0018] Furthermore, the diluent is one or both of dodecyl glycidyl ether and mixed trimethylbenzene. Dodecyl glycidyl ether can be a commercially available product, such as the active diluent of Hubei Green Home Material Technology Co., Ltd.; mixed trimethylbenzene can be a commercially available product, such as the inert diluent of Shandong Longyu Chemical Co., Ltd.

[0019] Furthermore, the hyperbranched organic filler is a hyperbranched compound 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide-itaconic anhydride adduct, and its preparation method comprises the following steps:

[0020] Itaconic anhydride and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide are mixed in equal moles, and then tetrahydrofuran is added; a reflux reaction is carried out under constant temperature stirring and nitrogen protection; after the reaction, the mixture is vacuum evaporated to dryness of tetrahydrofuran, anhydrous ethanol is added to the residue, ultrasonic dispersion is performed, a solid product is separated by centrifugation, the solid product is repeatedly washed with anhydrous ethanol, and the solid product obtained after washing is dried to obtain the hyperbranched organic filler.

[0021] Furthermore, the reflux reaction under constant temperature stirring conditions and nitrogen protection is carried out at a constant temperature of 50° C., a stirring speed of 500 rpm and nitrogen protection for 6 hours.

[0022] The B component includes the following components in parts by weight:

[0023] 76-84 parts of phenalkamine;

[0024] 593 curing agent 2~8 parts;

[0025] Polyetheramine 0-4 parts;

[0026] Accelerator curing agent 5 parts.

[0027] Phenalkamine can be a commercially available product, such as Hensamine-1040 produced by Suzhou HNSAT Industrial Co., Ltd.; polyetheramine can be a commercially available product, such as C-16H produced by Suzhou HNSAT Industrial Co., Ltd., with an equivalent weight of 97. The primary and secondary amine groups contained in the molecular chains of these two products can alternately participate in the ring-opening reaction to regulate the curing speed and material properties.

[0028] Primary amine first reaction:

[0029] R-NH2+epoxy group (-CH2-CH(O)-) → R-NH-CH2-CH(OH)-+hydroxyl group (-OH)

[0030] Second reaction of primary amine:

[0031] R-NH-CH2-CH(OH)-+epoxy group (-CH2-CH(O)-)→RN(CH2-CH(OH)-)2

[0032] Secondary amine first reaction:

[0033] R1-NH-R2+epoxy group (-CH2-CH(O)-)→R1-N(CH2-CH(OH)-)-R2

[0034] The 593 curing agent can be the 593 curing agent with an H equivalent of 45 from Chuzhou Huisheng Electronic Materials Co., Ltd.

[0035] Furthermore, the accelerating curing agent is N-aminoethylpiperazine, which can be produced by Guangzhou Yihuisheng Chemical Co., Ltd., and can adjust the reaction rate of the resin and the curing agent. In addition, the nitrogen element therein can produce a PN synergistic effect with DOPO-ITA, thereby enhancing the crosslinking density and flame retardant properties of the epoxy resin.

[0036] The present invention also provides a method for preparing the above-mentioned low-viscosity and high-strength flame-retardant structural adhesive, comprising the following steps:

[0037] Preparation of component A: At room temperature, liquid epoxy resin and diluent are mixed evenly, and then hyperbranched organic filler is added, sheared, dispersed, and placed in a sealed container for standing to obtain component A;

[0038] Preparation of component B: After mixing and dispersing phenalkamine, 593 curing agent and polyetheramine, add curing agent to promote uniform mixing to obtain component B;

[0039] Preparation of low-viscosity and high-strength flame-retardant structural adhesive: Component A and component B are mixed and dispersed, placed in a sealed container and allowed to stand, thereby obtaining low-viscosity and high-strength flame-retardant structural adhesive.

[0040] This invention is based on molecular modular design, assembling different functional modules such as the epoxy curing unit amino group, the phosphorus element in the intumescent flame retardant system, and the triazine structure through synthetic chemistry to precisely construct a hyperbranched multifunctional flame retardant. The specific molecular construction method is: in itaconic anhydride (ITA) and DOPO (9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide), the DOPO group provides a phosphaphenanthrene structure (containing P=0 and P-0-Ph bonds), which imparts flame retardant activity. The anhydride group of ITA acts as a reaction site, forming a covalent bond with the epoxy group of the epoxy resin or an amine curing agent (such as DDM). The PH bond of DOPO undergoes ring-opening addition with the anhydride ring of ITA, integrating the phosphorus element into the network structure of the epoxy resin in the form of a covalent bond. This hyperbranched organic filler can impart excellent flame retardancy, good mechanical properties, and toughness to the structural adhesive.

[0041] The present invention selects specific types of epoxy resins, diluents, fillers and curing agents through systematic material screening and formula optimization experiments, and optimizes the synergistic effect between them by adjusting the ratio, thereby preparing a low-viscosity and high-strength flame-retardant structural adhesive.

[0042] This invention utilizes DOPO-ITA, through the synergistic effect of hyperbranched structural design and phosphaphenanthrene groups, to achieve synergistic optimization of the mechanical and flame retardant properties of epoxy resins: free volume regulation and rigid group-strengthening toughening and reinforcement. Gas-phase free radical quenching and a condensed-phase carbon barrier achieve high flame retardancy.

[0043] The present invention continuously optimizes the ratio of each component and the synergistic matching of each group in the curing agent and the resin, so that the viscosity of components A and B can be controlled below 1200cp, which is conducive to more uniform dispersion and stirring after the two components are mixed.

[0044] The present invention has the following beneficial effects:

[0045] (1) By adding the hyperbranched compound DOPO-ITA, phosphorus free radicals are released during high-temperature decomposition, capturing active free radicals in the flame and interrupting the combustion chain reaction. In addition, the anhydride groups of DOPO-ITA react with the epoxy groups of the epoxy resin to enhance interfacial bonding and further stabilize the carbon layer structure. The phosphorus element in DOPO-ITA can improve flame retardancy by releasing free radicals and promoting the formation of a condensed phase in the carbon layer. At the same time, it has good flame retardancy at low dosages, and a small amount of filler also improves mechanical properties to a certain extent.

[0046] (2) The present invention introduces functional groups to the surface of the filler, thereby enhancing the bonding between the components in the filler and the structural adhesive, resulting in a higher degree of cross-linking of the structural adhesive, and enabling components A and B to maintain good mechanical properties even at low viscosity. Furthermore, the three-dimensional dendritic structure of DOPO-ITA contains a large number of intramolecular cavities. The increase in free volume provides more space for the epoxy resin molecular segments to move, absorbing impact energy through segment movement under external forces and inhibiting crack propagation. The low viscosity ensures that DOPO-ITA is evenly distributed in the epoxy resin, which can not only bring out the excellent flame retardant properties of the filler, but also improve the strength and toughness of the structural adhesive. DETAILED DESCRIPTION

[0047] The present invention will be further described below in conjunction with specific preferred embodiments, but the scope of protection of the present invention is not limited thereby. The implementation cases described below are only part of the embodiments of the present invention, rather than all the embodiments.

[0048] Example 1 to Example 5

[0049] Use the formula shown in Table 1

[0050] The preparation method is as follows:

[0051] Preparation of Component A: At room temperature, mix the liquid epoxy resin and diluent, then add the hyperbranched organic filler, shear at 1000 rpm for 35 minutes, disperse in an ultrasonic disperser, and allow to stand in a sealed container for 5 minutes to obtain Component A.

[0052] The shearing is carried out in a high-speed shearing machine, which is a conventional equipment, and is a SRS500 high-speed shearing machine produced by Shanghai Xinle Electromechanical Technology Co., Ltd.; the dispersion is carried out in an ultrasonic disperser, which is a conventional equipment, and is a rps-20k 500W ultrasonic disperser produced by Hangzhou Gonglu Ultrasonic Equipment Co., Ltd.

[0053] The hyperbranched organic filler is a hyperbranched compound 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide-itaconic anhydride adduct (DOPO-ITA), and its preparation comprises the following steps:

[0054] (1) 13 g of itaconic anhydride (ITA) and 21.6 g of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) were added in equimolar amounts into a 250 mL three-necked flask, and then 100 mL of tetrahydrofuran (TFH) was added;

[0055] (2) Connect the three-necked flask to a mechanical stirring paddle, a reflux condenser, and a thermometer, and place the flask in a constant temperature oil bath set at 50°C.

[0056] (3) Start mechanical stirring at 500 rpm to ensure that the product is fully separated and to reduce impurity residues. Keep the reaction system under nitrogen protection to prevent DOPO oxidation or ITA ring opening. Reflux reaction for 6 hours.

[0057] (4) After the reaction, the mixture was transferred to a rotary evaporator and TFH was evaporated to dryness at 50 °C and 5 mbar vacuum;

[0058] (5) Add 100 mL of anhydrous ethanol to the residue, ultrasonically disperse for 5 minutes, and centrifuge at 8000 rpm for 10 minutes to separate the solid product. Repeat the anhydrous ethanol washing of the solid product to ensure that unreacted DOPO and ITA are removed;

[0059] (6) The solid product obtained after washing was transferred to a vacuum oven and dried at 50 °C and -0.1 MPa for 12 h to obtain the hyperbranched organic filler DOPO-ITA.

[0060] Preparation of component B:

[0061] Mix and disperse phenalkamine, 593 curing agent and polyetheramine, then add N-aminoethylpiperazine and mix evenly to obtain component B.

[0062] Preparation of low-viscosity and high-strength flame-retardant structural adhesive: Mix and disperse component A and component B, place them in a closed container and let them stand for 2 minutes to obtain a low-viscosity and high-strength flame-retardant structural adhesive.

[0063] The dispersion is carried out in an ultrasonic disperser, which is a conventional device, and is a model rps-20k 500W ultrasonic disperser produced by Hangzhou Gonglv Ultrasonic Equipment Co., Ltd.

[0064] Example 1 The weight ratio of component A to component B used is 1.5:1;

[0065] Example 2 The weight ratio of component A to component B used was 1.15:1;

[0066] Example 3 The weight ratio of component A to component B used was 1.27:1;

[0067] Example 4 The weight ratio of component A to component B used was 1.28:1;

[0068] Example 5 The weight ratio of component A to component B is 1:1.

[0069] The epoxy resin used in Example 1 is a mixture of bisphenol A epoxy resin and novolac epoxy resin, with a weight ratio of bisphenol A epoxy resin: novolac epoxy resin = 84:10;

[0070] The epoxy resin used in Example 2 is a mixture of bisphenol A epoxy resin and novolac epoxy resin, with a weight ratio of bisphenol A epoxy resin: novolac epoxy resin = 83:10;

[0071] The epoxy resin used in Example 3 is a mixture of bisphenol A epoxy resin and novolac epoxy resin, with a weight ratio of bisphenol A epoxy resin: novolac epoxy resin = 84:12;

[0072] The epoxy resin used in Example 4 is a mixture of bisphenol A epoxy resin and novolac epoxy resin, with a weight ratio of bisphenol A epoxy resin: novolac epoxy resin = 83:10;

[0073] The epoxy resin used in Example 5 is a mixture of bisphenol A epoxy resin and novolac epoxy resin, with a weight ratio of bisphenol A epoxy resin: novolac epoxy resin = 83:10;

[0074] The diluent used in Example 1 is dodecyl glycidyl ether;

[0075] The diluent used in Example 2 is a mixture of dodecyl glycidyl ether and mixed trimethylbenzene, with a weight ratio of dodecyl glycidyl ether: mixed trimethylbenzene = 2:5;

[0076] The diluent used in Example 3 is dodecyl glycidyl ether;

[0077] The diluent used in Example 4 is a mixture of dodecyl glycidyl ether and mixed trimethylbenzene, with a weight ratio of dodecyl glycidyl ether: mixed trimethylbenzene = 2:5;

[0078] The diluent used in Example 5 is a mixture of dodecyl glycidyl ether and mixed trimethylbenzene, with a weight ratio of dodecyl glycidyl ether: mixed trimethylbenzene = 2:5;

[0079] The hyperbranched organic fillers used in Examples 1 to 5 are all DOPO-ITA.

[0080] Table 1

[0081]

[0082] Comparative Example 1 to Comparative Example 3

[0083] Use the formula shown in Table 2

[0084] The preparation method is as follows:

[0085] Preparation of component A: At room temperature, mix the liquid epoxy resin and diluent, shear at 1000 rpm for 35 minutes using a shearing machine, disperse in an ultrasonic disperser, and let stand in a sealed container for 5 minutes;

[0086] The shearing is carried out in a high-speed shearing machine, which is a conventional equipment, and is a SRS500 high-speed shearing machine produced by Shanghai Xinle Electromechanical Technology Co., Ltd.; the dispersion is carried out in an ultrasonic disperser, which is a conventional equipment, and is a rps-20k 500W ultrasonic disperser produced by Hangzhou Gonglu Ultrasonic Equipment Co., Ltd.

[0087] Preparation of component B:

[0088] Component B can be obtained by mixing and dispersing phenalkamine, 593 curing agent and polyetheramine.

[0089] Preparation of structural adhesive: Component A and component B are mixed and dispersed in a weight ratio of component A to component B of 5:4, placed in a sealed container and allowed to stand for 2 minutes to obtain a comparative structural adhesive test block.

[0090] The dispersion is carried out in an ultrasonic disperser, which is a conventional device, and is a model rps-20k 500W ultrasonic disperser produced by Hangzhou Gonglv Ultrasonic Equipment Co., Ltd.

[0091] The epoxy resin used in Comparative Example 1 is a mixture of bisphenol A epoxy resin and novolac epoxy resin, with a weight ratio of bisphenol A epoxy resin: novolac epoxy resin = 80:20;

[0092] The epoxy resin used in Comparative Example 2 is a mixture of bisphenol A epoxy resin and novolac epoxy resin, with a weight ratio of bisphenol A epoxy resin: novolac epoxy resin = 80:20;

[0093] The epoxy resin used in Comparative Example 3 is a mixture of bisphenol A epoxy resin and novolac epoxy resin, with a weight ratio of bisphenol A epoxy resin: novolac epoxy resin = 80:20;

[0094] Table 2

[0095]

[0096] Comprehensive performance tests were conducted on Examples 1 to 5 and Comparative Examples 1 to 3, and the results are shown in Table 3. The tensile strength was measured in accordance with GB / T 2567-2021; the elongation at break was measured in accordance with GB / T 528-2009; the viscosity refers to the viscosity of the slurry immediately after components A and B are uniformly mixed using a single-cylinder rotational viscometer, measured in accordance with GB / T 2794-2022; the workable time is measured by the increase in viscosity during the mixing reaction of components A and B using a rotational viscometer, measured in accordance with GB / T 7123.1-2015; the tensile shear strength was measured in accordance with GB / T 7124-2008, the limiting oxygen index (LOI) was measured in accordance with GB / T 2406-1993, and the vertical combustion test of the sample was measured in accordance with GB / T 2794-1995.

[0097] Table 3

[0098]

[0099] As can be seen from Table 3, compared with Comparative Examples 1 to 3, Examples 1 to 5, by screening different types of epoxy resins and curing agents and combining them in specific ratios and preparation processes, produce finished products with a viscosity reduction of 400 to 900 cp, a 4- to 10-fold increase in tensile shear strength, and a 1- to 2-fold increase in tensile strength. After incorporating the hyperbranched organic filler DOPO-ITA, the flammability rating of the structural adhesives all reached V-0, and the limiting oxygen index all reached above 35%, making them suitable for high-safety applications.

[0100] The structural adhesive prepared by the invention has low viscosity, good permeability, good mechanical properties, good tensile shear strength and good flame retardant performance.

Claims

1. A low-viscosity, high-strength flame-retardant structural adhesive, characterized in that: Comprising component A and component B; the weight ratio of component A to component B is 1-1.5:1; The A component includes the following components in parts by weight: Epoxy resin 79-104 parts; 6~12 parts of diluent; 3-10 parts of hyperbranched organic filler; The hyperbranched organic filler is a hyperbranched compound 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide-itaconic anhydride adduct, and its preparation method comprises the following steps: Itaconic anhydride and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide are mixed in equal moles, and tetrahydrofuran is added; a reflux reaction is carried out under constant temperature stirring and nitrogen protection; after the reaction, the mixture is vacuum evaporated to dryness of tetrahydrofuran, anhydrous ethanol is added to the residue, ultrasonic dispersion is performed, a solid product is separated by centrifugation, the solid product is repeatedly washed with anhydrous ethanol, and the solid product obtained after washing is dried to obtain the hyperbranched organic filler; The B component includes the following components in parts by weight: 76-84 parts of phenalkamine; 593 curing agent 2~8 parts; Polyetheramine 0-4 parts; Accelerator curing agent 5 parts.

2. The low-viscosity, high-strength flame-retardant structural adhesive according to claim 1, characterized in that: The epoxy resin is a mixture of bisphenol A epoxy resin and novolac epoxy resin in a weight ratio of 7-8.4:

1.

3. The low-viscosity, high-strength flame-retardant structural adhesive according to claim 1, characterized in that: The diluent is one or two of dodecyl glycidyl ether and mixed trimethylbenzene.

4. The low-viscosity, high-strength flame-retardant structural adhesive according to claim 1, characterized in that: The accelerating curing agent is N-aminoethylpiperazine.

5. The low-viscosity, high-strength flame-retardant structural adhesive according to claim 1, characterized in that: The reflux reaction under the condition of constant temperature stirring and nitrogen protection is carried out at a constant temperature of 50° C., a stirring speed of 500 rpm and nitrogen protection for 6 hours.

6. The method for preparing a low-viscosity, high-strength flame-retardant structural adhesive according to claim 1, characterized in that: The following steps are involved: Preparation of component A: At room temperature, liquid epoxy resin and diluent are mixed evenly, and then hyperbranched organic filler is added, sheared, dispersed, and placed in a sealed container for standing to obtain component A; Preparation of component B: After mixing and dispersing phenalkamine, 593 curing agent and polyetheramine, add curing agent to promote uniform mixing to obtain component B; Preparation of low-viscosity and high-strength flame-retardant structural adhesive: Component A and component B are mixed and dispersed, placed in a sealed container and allowed to stand, thereby obtaining low-viscosity and high-strength flame-retardant structural adhesive.

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