Bio-based polythiol curing agent as well as preparation method and application thereof

Abstract

The invention relates to the field of high polymer materials, and particularly provides a bio-based polythiol curing agent and a preparation method and application thereof.The bio-based polythiol curing agent is obtained through reaction of polyether polyol, epoxy chloropropane and a sulfhydrylation reagent, the epoxy chloropropane is prepared from bio-based raw materials, and the sulfhydrylation reagent is prepared from polyether polyol. The invention relates to epoxy chloropropane, in particular to epoxy chloropropane prepared by a glycerin method, and the mass content of 2, 3-epoxypropane methyl ether in the epoxy chloropropane is less than 0.4%. By controlling the content of 2, 3-epoxypropane methyl ether in the bio-based epoxy chloropropane, the humidity and heat resistance of a polythiol adhesive system applied to the downstream can be improved. The epoxy adhesive prepared from the epoxy resin has the advantages of higher humidity and heat resistance, higher adhesive property, higher glass transition temperature and longer service life, can reduce the maintenance cost, and is widely applied to the fields of electronic and electrical appliances, automobile manufacturing, aerospace, architectural decoration and the like.

Description

Technical Field

[0001] The present invention relates to the field of polymer materials, and in particular to a bio-based polythiol curing agent, a preparation method thereof, and an application thereof. Background Art

[0002] With the urgent global demand for sustainable development, the adhesives industry is facing pressure to transition from traditional petroleum-based raw materials to green, renewable resources. Adhesive systems are formulated using polythiol as a curing agent, a certain amount of accelerator, and epoxy resin, which cures at room temperature. Polythiol compounds are synthesized using epichlorohydrin as a base raw material. Traditional epichlorohydrin (ECH) is primarily produced through the high-temperature chlorination of propylene, which relies heavily on petroleum resources. Its production process has high carbon emissions and is non-renewable, making it difficult to meet international environmental regulations (such as EU REACH and China's "dual carbon" goals) and consumer expectations for low-carbon products. Furthermore, this method produces a relatively high number of impurities, further impacting the performance of the adhesive, especially in the electronics, aerospace, and other fields where adhesive performance is demanding.

[0003] In recent years, bio-based epichlorohydrin has garnered significant attention for its environmental and sustainability considerations. Glycerol-based epichlorohydrin, a green alternative using bio-based glycerin as a raw material, has become a key technology for green upgrading in the adhesives industry. However, the glycerol-based production of epichlorohydrin contains an impurity, 2,3-propylene oxide methyl ether, which has a certain impact on the synthesis and application of polythiols, making it difficult to fully meet the needs of the adhesives industry. Therefore, how to effectively control these impurities in epichlorohydrin produced by the glycerol-based process to ensure its application in adhesives has become an urgent challenge in this field. Summary of the Invention

[0004] In order to solve the problems of poor moisture and heat resistance, low bonding strength and glass transition temperature of bio-based polythiol curing agents in the prior art, the present invention provides a bio-based polythiol curing agent, a preparation method and application thereof. The bio-based polythiol curing agent is obtained by reacting polyether polyol, epichlorohydrin and a thiol-forming agent. The epichlorohydrin is prepared from bio-based raw materials, more specifically, the epichlorohydrin is prepared by the glycerol method, and the mass content of 2,3-epoxypropylene methyl ether in the epichlorohydrin is less than 0.4%.

[0005] In the epichlorohydrin prepared by the glycerol method, the inventors controlled the content of 2,3-epoxypropylene methyl ether by artificial addition to meet the above-mentioned standards. By controlling the 2,3-epoxypropylene methyl ether content in bio-based epichlorohydrin, the moisture and heat resistance of the downstream polythiol adhesive system can be improved. This bio-based polythiol adhesive can be cured with epoxy resin in the presence of accelerators and additives to prepare an epoxy adhesive, either alone or mixed with other thiol compounds. This adhesive has strong moisture and heat resistance, strong bonding properties, and a higher glass transition temperature. It has a long service life and can reduce maintenance costs. It is widely used in the fields of electronics, automobile manufacturing, aerospace, architectural decoration, etc.

[0006] The present invention first provides a bio-based polythiol curing agent, which is obtained by reacting polyether polyol, epichlorohydrin and a thiol-forming agent. The epichlorohydrin is prepared by a glycerol method, and the mass content of 2,3-epoxypropylene methyl ether in the epichlorohydrin is less than 0.4%.

[0007] Preferably, the mass content of 2,3-epoxypropylene methyl ether in the epichlorohydrin is ≤0.1%.

[0008] By controlling the mass content of 2,3-epoxypropylene methyl ether in epichlorohydrin, a bio-based polythiol curing agent is prepared, and the epoxy adhesive composition is prepared using the bio-based polythiol curing agent, which can significantly improve the strength and moisture and heat resistance of the epoxy adhesive composition.

[0009] The sulfhydrylation reagent is selected from one of sodium sulfide, sodium hydrosulfide, thiourea and sodium polysulfide.

[0010] Preferably, the molar ratio of epichlorohydrin to polyether polyol is (0.5-6):1.

[0011] Preferably, the molar ratio of the thiol-forming agent to epichlorohydrin is (1-5):1, more preferably (1-3):1.

[0012] The present invention further provides a method for preparing the bio-based polythiol curing agent, comprising the following steps: (1) Add polyether polyol and catalyst to a reaction vessel, then slowly drop epichlorohydrin into it, then add thiol reagent and phase transfer catalyst in sequence, and fill with protective gas to keep the reaction warm; The polyether polyol used has a hydroxyl value of 300-600 mgKOH / g and a viscosity of 300-500 mPa.s. (2) After the reaction is completed, the aqueous phase is removed, 1.5-3 times the weight of water is added to the organic phase, and then dilute sulfuric acid is added to adjust the pH to 3-5, and the mixture is stirred for 1-8 hours, preferably 5 hours. The mixture is allowed to stand for separation, and then 1.5-3 times the weight of water is added to the organic phase, and the mixture is washed with water for 1-8 hours, preferably 5 hours. The separated liquid is subjected to rotary evaporation to obtain a bio-based polythiol curing agent; the rotary evaporation temperature is 60-95°C, and the rotary evaporation time is 1-5 hours.

[0013] Preferably, the catalyst is selected from one of tin tetrachloride, stannous octoate, tributyltin chloride, boron trifluoride, and boron trifluoride ether, and the amount of the catalyst is 0.05-6% of the mass of the polyether polyol, more preferably 0.3-5%; in step (1), the dropping temperature and the dropping time of epichlorohydrin are controlled, the dropping temperature is 28-80°C, more preferably 40-72°C, and the dropping time is 3-15 h, more preferably 5-9 h.

[0014] As a further preference, after the dropwise addition, the mixture is kept at 55-75° C. for 1-5 hours to allow the reaction to be more complete.

[0015] Preferably, the reaction temperature of the insulation reaction in step (1) is 70-130°C, more preferably 80-120°C; Preferably, the reaction time of the insulation reaction in step (1) is 3-10 h, more preferably 3-7 h.

[0016] Preferably, the reaction pressure of the insulation reaction in step (1) is 0.1-10 MPa, more preferably 0.1-6 MPa.

[0017] Preferably, the phase transfer catalyst is selected from one of tetrabutylammonium chloride, tetrabutylammonium bromide, polyethylene glycol, and glycerol; the mass of the phase transfer catalyst is 0.5-25% of the mass of the polyether polyol; and the protective gas is selected from one of carbon dioxide, nitrogen, hydrogen sulfide, and argon.

[0018] As further preferred, the protective gas is nitrogen or hydrogen sulfide, the phase transfer catalyst is selected from tetrabutylammonium bromide or polyethylene glycol, and the mass of the phase transfer catalyst is 5-10% of the mass of the polyether polyol.

[0019] The present invention further provides an epoxy adhesive composition, which comprises, by weight, 10-90 parts of the bio-based polythiol curing agent, 10-90 parts of epoxy resin, and 0.1-15 parts of accelerator.

[0020] Preferably, the contents of the components in the epoxy adhesive composition are as follows, by weight: 30-60 parts of bio-based polythiol curing agent, 30-60 parts of epoxy resin, and 2-9 parts of accelerator.

[0021] Among them, the epoxy resin is selected from one or two of glycidyl ether epoxy resins, glycidyl ester epoxy resins, glycidyl amine epoxy resins, alicyclic epoxy resins, epoxidized olefin epoxy resins, hydantoin epoxy resins, imide epoxy resins, silicone epoxy resins, and organic iron epoxy resins; preferably, it is a combination of one or more glycidyl ether epoxy resins and glycidyl ester epoxy resins.

[0022] The accelerator is selected from ethylenediamine, 1,2-diaminopropane, 1,3-diaminopropane, 1,5-diaminopentane, hexamethylenediamine, tetramethylenediamine, trimethylhexamethylenediamine, 2-methyl-1,5-diaminopentane, polyetherdiamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, diethylenepropylamine, polyamide, isophoronediamine, N-aminoethylpiperazine, m-phenylenediamine, diaminodiphenylmethane, diaminodiphenylsulfone, m-phenylenediamine, dicyandiamide, adipic acid dihydrazide, dipropylenetriamine, bis(hexamethylene)triamine, 2,4,6-tris(dimethylamino)methyl One or more of: 1,2-dimethylamino-2-methyl-1-phenylphenol, 2,4,6-tris(dimethylaminomethylphenol)tris(2-ethylhexanoate), 2,4,6-tris(dimethylaminomethylphenol)trioleate, benzyldimethylamine, ethylenediamine, triethanolamine, o-hydroxybenzyldimethylamine, acetylacetonate metal salt, triphenylphosphine and its phosphonate salt, active tris(2-ethylhexanoate)chromium, organic acid salt amine complex, 1,8-diaza-bicyclo(5,4,0)-7-undecene, 2-thiolbenzothiazole, thiourea and its derivatives, cycloalkylimidazoline, 2-imidazoline, epoxy-containing aromatic tertiary amine, and phthalate accelerator; The accelerator is further preferably one of 2,4,6-tris(dimethylaminomethyl)phenol, benzyldimethylamine, ethylenediamine, triethanolamine, o-hydroxybenzyldimethylamine, triphenylphosphine, diethylenetriamine, triethylenetetramine, and tetraethylenepentamine.

[0023] Compared with the existing technology, the biggest feature of this application is that the mass content of 2,3-epoxypropylene methyl ether in the bio-based epichlorohydrin is controlled to be less than 0.4%; when the mass content of 2,3-epoxypropylene methyl ether in the bio-based epichlorohydrin is greater than or equal to 0.4%, the cross-linking strength of the adhesive will be seriously reduced, and the moisture and heat resistance of the adhesive will be affected, affecting its bonding strength.

[0024] In summary, the present invention provides a bio-based polythiol curing agent and a preparation method thereof, and further provides an epoxy adhesive composition. The adhesive has strong moisture and heat resistance, strong bonding performance, and a higher glass transition temperature, has a long service life, and can reduce maintenance costs. It is widely used in the fields of electronics and electrical appliances, automobile manufacturing, aerospace, architectural decoration, etc., and has very good application prospects. DETAILED DESCRIPTION

[0025] The technical solution of the present invention will be further described below in conjunction with specific embodiments. These embodiments are only used to illustrate the technical solution of the present invention in more detail and should not be construed as limiting the scope of protection of the present invention.

[0026] The detection methods used in the following embodiments are as follows: 1. Adhesive performance test Use a universal testing machine to test the shear strength before and after damp heat aging in accordance with GB / T 7124-2008 "Test method for tensile shear strength of adhesives" at a temperature of 25°C and a shear strength of 10 mm / min. The shear strength (unit: MPa) before and after damp heat aging is tested, and the attenuation rate (unit: %) before and after damp heat aging is calculated.

[0027] 2. Test of moisture and heat resistance Use a high-temperature, high-humidity environmental chamber set at 85°C and 85% RH. Place the sample for 336 hours and then take it out and place it for 6 hours. Use a universal testing machine to test the shear strength according to GB / T 7124-2008 "Test method for tensile shear strength of adhesives" at a temperature of 25°C and a shear rate of 10 mm / min. Calculate the rate of change in %.

[0028] 3. Glass transition temperature Tg test, tested according to GB / T 19466.2-2004; The adhesive sample was placed in an aluminum crucible and heated at a rate of 10°C / min. The glass transition temperature of the adhesive material was determined based on the obtained test curve. The testing instrument used was a METTLER-DSC3 model.

[0029] The mass content of 2,3-epoxypropylene methyl ether in epichlorohydrin was detected by gas chromatography. In the following examples, the different contents of 2,3-epoxypropylene methyl ether in epichlorohydrin were achieved by artificial addition, and then the mercaptan reaction in the following examples was carried out.

[0030] Example 1 A method for preparing a bio-based polythiol curing agent, the specific steps are as follows: (1) 150.00 g of polyether polyol (R2302 from Yantai Wanhua Chemical Group Co., Ltd.) and 0.74 g of catalyst SnCl4•5H2O were added to the reaction vessel, and 180.45 g of epichlorohydrin (purity 99.30%) was slowly added dropwise. The content of 2,3-epoxypropylene methyl ether was found to be 0.3 wt%; the addition temperature was 60 °C and the addition time was about 5 h; the molar ratio of the above-mentioned epichlorohydrin to polyether polyol was 3.9:1; after the addition was completed, the temperature was raised to 65 °C and kept warm for 2 h, and then 297.80 g of NaHS solution (44 wt%) and 16.53 g of tetrabutylammonium chloride were added in sequence. The molar ratio of the above-mentioned thiol reagent to epichlorohydrin was 1.2:1; protective gas H2S (pressure 0.5 MPa) was filled in and the reaction was kept warm at 100 °C for 5 h.

[0031] (2) After the reaction, the aqueous phase was separated and removed. Then, 600.00 g of water was added to the organic phase, and then dilute sulfuric acid was added to adjust the pH to 3. The mixture was stirred for 5 h. The aqueous phase was separated and then 600.00 g of water was added to the organic phase. The mixture was washed with water for 5 h and separated. The organic phase was subjected to rotary evaporation at 85 °C for 2 h to obtain 273.00 g of bio-based polythiol curing agent.

[0032] Example 2 Preparation method of bio-based polythiol curing agent, the specific steps are as follows: (1) 150.00 g of polyether polyol (DMN-500 from Zibo Dexin Federal Chemical Industry Co., Ltd.) and 1.15 g of stannous octoate catalyst were added to the reaction vessel, and 108.77 g of epichlorohydrin (99.55% purity) was slowly added dropwise to the bottle. The content of 2,3-propylene oxide methyl ether was found to be 0.05 wt%. The addition temperature was 50 °C and the addition time was about 6 h. After the addition was completed, the temperature was raised to 70 °C and kept warm for 2 h. Then, 245.70 g of NaHS solution (32 wt%) and 12.94 g of glycerol were added in sequence, and the protective gas N2 (pressure 0.6 MPa) was filled in. The reaction was kept warm at 90 °C for 7 h. In the above reaction, the molar ratio of epichlorohydrin to polyether polyol is 3.9:1, and the molar ratio of thiol-forming agent to epichlorohydrin is 1.2:1.

[0033] (2) After the reaction is completed, the aqueous phase is separated and removed. Then, 600.00 g of water is added to the organic phase, and then dilute sulfuric acid is added to adjust the pH to 5. The mixture is stirred for 5 h, and the aqueous phase is removed after standing. Then, 600.00 g of water is added to the organic phase, and the mixture is washed with water for 5 h. The organic phase is separated and subjected to rotary evaporation at 90 °C for 1 h to obtain 275.00 g of bio-based polythiol curing agent.

[0034] Example 3 Preparation method of bio-based polythiol curing agent, the specific steps are as follows: (1) Add 150.00 g of polyether polyol (DMN-450 from Zibo Dexin Federal Chemical Industry Co., Ltd.) and 1.48 g of tributyltin chloride catalyst into the reaction vessel, slowly drop 146.98 g of epichlorohydrin (purity 99.50%) into the bottle, the content of 2,3-epoxypropylene methyl ether was found to be 0.1 wt% by weight, the dropping temperature was 50 ° C, the dropping time was about 7 h, after the dropping was completed, the temperature was raised to 70 ° C and kept warm for 3 h; then, 321.97 g of NaHS solution (33 wt%) and 14.85 g of tetrabutylammonium bromide were added in sequence, the protective gas H2S (pressure 0.3 MPa) was filled in, and the reaction was kept warm at 110 ° C for 3 h; In the above reaction, the molar ratio of epichlorohydrin to polyether polyol is 3.85:1, and the molar ratio of thiol-forming agent to epichlorohydrin is 1.2:1.

[0035] (2) After the reaction, the aqueous phase was separated and removed. Then, 600.00 g of water was added to the organic phase, and then dilute sulfuric acid was added to adjust the pH to 3. The mixture was stirred for 5 h. The aqueous phase was separated and then 600.00 g of water was added to the organic phase. The mixture was washed with water for 5 h and separated. The organic phase was subjected to rotary evaporation at 80 °C for 4 h to obtain 278.00 g of bio-based polythiol curing agent.

[0036] Example 4 The preparation method of a bio-based polythiol curing agent is as follows: (1) 150.00 g of polyether polyol (DMN-530 from Zibo Dexin Federal Chemical Industry Co., Ltd.) and 0.78 g of catalyst SnCl4·5H2O were added to the reaction vessel, and 164.80 g of epichlorohydrin (purity 99.59%) was slowly added dropwise to the bottle. The content of 2,3-epoxypropylene methyl ether was found to be 0.01 wt% by weight. The addition temperature was 55 °C and the addition time was about 5 h. After the addition was completed, the temperature was raised to 60 °C and kept warm for 2 h. Then, 372.27 g of NaHS solution (32 wt%) and 15.74 g of tetrabutylammonium bromide were added in sequence, and protective gas CO2 (pressure 0.6 MPa) was introduced. The reaction was kept warm at 120 °C for 3 h. In the above reaction, the molar ratio of epichlorohydrin to polyether polyol is 3.93:1, and the molar ratio of thiol-forming agent to epichlorohydrin is 1.2:1.

[0037] (2) After the reaction is completed, the aqueous phase is separated and removed. Then, 600.00 g of water is added to the organic phase, and then dilute sulfuric acid is added to adjust the pH to 4. The mixture is stirred for 5 h, and the aqueous phase is removed after standing. Then, 600.00 g of water is added to the organic phase, and the mixture is washed with water for 5 h. The organic phase is separated and subjected to rotary evaporation at 95 °C for 0.5 h to obtain 268.00 g of bio-based polythiol curing agent.

[0038] Example 5 Preparation method of bio-based polythiol curing agent, the specific steps are as follows: (1) 150.00 g of polyether polyol (GP-303 from Nantong Chenrun Chemical Co., Ltd.) and 0.80 g of catalyst SnCl4·5H2O were added to the reaction vessel, and 164.80 g of epichlorohydrin (purity 99.60%) was slowly added dropwise to the bottle. The content of 2,3-epoxypropylene methyl ether was found to be 0.005 wt%. The addition temperature was 60 °C and the addition time was about 6 h. After the addition was completed, the temperature was raised to 55 °C and kept warm for 3 h. Then, 372.27 g of NaHS solution (32 wt%) and 15.74 g of tetrabutylammonium bromide were added in sequence, and protective gas H2S (pressure 0.5 MPa) was introduced. The reaction was kept warm at 120 °C for 5 h. In the above reaction, the molar ratio of epichlorohydrin to polyether polyol is 3.93:1, and the molar ratio of thiol-forming agent to epichlorohydrin is 1.2:1.

[0039] (2) After the reaction is completed, the aqueous phase is separated and removed. Then, 600.00 g of water is added to the organic phase, and then dilute sulfuric acid is added to adjust the pH to 5. The mixture is stirred for 5 h, and the aqueous phase is removed after standing. Then, 600.00 g of water is added to the organic phase, and the mixture is washed with water for 5 h. The organic phase is separated and subjected to rotary evaporation at 85 °C for 1.5 h to obtain 269.50 g of bio-based polythiol curing agent.

[0040] Example 6 Preparation method of bio-based polythiol curing agent, the specific steps are as follows: (1) 150.00 g of polyether polyol (DMN-450 from Zibo Dexin Federal Chemical Industry Co., Ltd.) and 0.85 g of catalyst SnCl4·5H2O were added to the reaction vessel, and 147.00 g of epichlorohydrin (purity 99.599%) was slowly added dropwise to the bottle. The content of 2,3-epoxypropylene methyl ether was found to be 0.001 wt% by weight. The addition temperature was 62 °C and the addition time was about 8.5 h. After the addition was completed, the temperature was raised to 65 °C and kept warm for 2 h. Then, 332.03 g of NaHS solution (32 wt%) and 14.85 g of tetrabutylammonium bromide were added in sequence, and protective gas H2S (pressure 0.5 MPa) was introduced. The reaction was kept warm at 100 °C for 5 h. In the above reaction, the molar ratio of epichlorohydrin to polyether polyol is 3.85:1, and the molar ratio of thiol-forming agent to epichlorohydrin is 1.2:1.

[0041] (2) After the reaction is completed, the aqueous phase is separated and removed. Then, 600.00 g of water is added to the organic phase, and then dilute sulfuric acid is added to adjust the pH to 3. The mixture is stirred for 5 h, and the aqueous phase is removed after standing. Then, 600.00 g of water is added to the organic phase, and the mixture is washed with water for 5 h. The organic phase is separated and subjected to rotary evaporation at 90 °C for 1.5 h to obtain 268.70 g of bio-based polythiol curing agent.

[0042] Comparative Example 1 Compared with Example 6, except for the epichlorohydrin used (purity 98.9 wt %, 2,3-epoxypropylene methyl ether content of 1 wt %), other conditions were the same as those in Example 6, and 269.19 g of bio-based polythiol curing agent was obtained.

[0043] Comparative Example 2 Compared with Example 6, except for the epichlorohydrin used (purity 99.3 wt %, 2,3-epoxypropylene methyl ether content 0.5 wt %), other conditions were the same as those in Example 6, and 267.59 g of bio-based polythiol curing agent was obtained.

[0044] Comparative Example 3 Compared with Example 6, except for the use of epichlorohydrin (purity 99.1 wt %, 2,3-epoxypropylene methyl ether content of 0.7 wt %), other conditions were the same as those in Example 6, and 267.32 g of bio-based polythiol curing agent was obtained.

[0045] Comparative Example 4 Compared with Example 6, except for the use of epichlorohydrin (purity 99 wt %, 2,3-epoxypropylene methyl ether content of 0.9 wt %), other conditions were the same as those in Example 6, and 266.70 g of bio-based polythiol curing agent was obtained.

[0046] Comparative Example 5 Compared with Example 6, except for the use of epichlorohydrin (purity 99.4 wt %, 2,3-epoxypropylene methyl ether content of 0.4 wt %), other conditions were the same as those in Example 6, and 267.40 g of bio-based polythiol curing agent was obtained.

[0047] Application Example 1 At a constant temperature of 25°C and 50% RH, 50 g of the liquid bio-based polythiol curing agent prepared in Example 1 (the product prepared in Example 1) and 2.5 g of 2,4,6-tris(dimethylaminomethyl)phenol were mixed, and 50 g of epoxy resin E51 was added. The mixture was pre-mixed with a spatula for 20 seconds to obtain an epoxy adhesive composition. The mixture was then cured at room temperature for 24 hours to obtain a cured adhesive having a diameter of approximately 5 cm and a thickness of 0.6 cm.

[0048] Then the Tg, shear strength and shear strength after aging were tested.

[0049] Application Examples 2-6 The method in Application Example 1 was adopted, with other conditions unchanged, and the bio-based polythiol curing agent in Application Example 1 was replaced by the products in Examples 2-6, respectively. After preparing the cured adhesive, its Tg, shear strength and shear strength after aging were tested.

[0050] Application Example 7 The method in Application Example 1 was adopted, with other conditions unchanged, the epoxy resin E51 in Application Example 1 was replaced by epoxy resin E44, and the accelerator 2,4,6-tris(dimethylaminomethyl)phenol was replaced by benzyldimethylamine. After mixing and curing, a cured adhesive was obtained, and then its Tg, shear strength and shear strength after aging were tested.

[0051] Application Example 8 The method in Application Example 1 was adopted, with other conditions unchanged, the epoxy resin E51 in Application Example 1 was replaced by epoxy resin E55, and the accelerator 2,4,6-tris(dimethylaminomethyl)phenol was replaced by triethanolamine. After mixing and curing, a cured adhesive was obtained, and then its Tg, shear strength and shear strength after aging were tested.

[0052] Application Example 9 The method in Application Example 1 was adopted, with other conditions unchanged, the epoxy resin E51 in Application Example 1 was replaced by epoxy resin E42, and the accelerator 2,4,6-tris(dimethylaminomethyl)phenol was replaced by diethylenetriamine. After mixing and curing, a cured adhesive was obtained, and then its Tg, shear strength and shear strength after aging were tested.

[0053] Application Example 10 The method in Application Example 1 was adopted, with other conditions unchanged, the epoxy resin E51 in Application Example 1 was replaced by epoxy resin E20, and the accelerator 2,4,6-tris(dimethylaminomethyl)phenol was replaced by triethylenetetramine. After mixing and curing, a cured adhesive was obtained, and then its Tg, shear strength and shear strength after aging were tested.

[0054] Comparative Application Examples 1-5 Using the method described in Application Example 1, with all other conditions unchanged, the bio-based polythiol curing agent in Example 1 was replaced with the product described in Comparative Examples 1-5. Cured adhesives were prepared and their Tg, shear strength, and shear strength after aging were tested. The performance test results for Application Examples 1-10 and Comparative Examples 1-5 are shown in Table 1.

[0055] Table 1 Performance test results of adhesive cured products of application examples 1-10 and application comparative examples 1-5 Example Thiol curing agent / g Mass content of 2,3-propylene oxide methyl ether in epichlorohydrin / % Epoxy resin / g Accelerator / g Tg Initial shear strength / MPa Aging shear strength / MPa Shear strength attenuation rate / % Application Example 1 50.01 0.3 50.02 2.51 44.2 16.23 13.50 16.8 Application Example 2 50.00 0.05 50.03 2.52 48.5 18.77 16.09 11.1 Application Example 3 50.10 0.1 50.00 2.51 46.1 17.06 15.00 14.3 Application Example 4 50.13 0.01 50.12 2.50 48.2 18.52 16.50 8.3 Application Example 5 50.05 0.005 50.09 2.53 49.8 19.12 18.41 3.7 Application Example 6 50.03 0.001 50.02 2.54 50.1 20.03 19.24 3.9 Application Example 7 50.00 0.001 50.03 2.53 50.6 20.10 19.33 3.8 Application Example 8 50.12 0.001 50.15 2.54 50.8 20.32 19.08 6.1 Application Example 9 50.04 0.001 50.20 2.51 50.2 20.55 19.23 6.4 Application Example 10 50.09 0.001 50.05 2.53 50.5 20.09 19.15 4.7 Comparative Application Example 1 50.12 1.0 50.04 2.53 30.3 10.11 5.01 50.4 Application Comparative Example 2 50.08 0.5 50.08 2.50 38.4 14.32 9.24 35.5 Application Comparative Example 3 50.11 0.7 50.21 2.51 37.8 13.25 8.56 38.4 Comparative Application Example 4 50.02 0.9 50.19 2.52 34.1 12.29 6.50 47.1 Application Comparative Example 5 50.03 0.4 50.04 2.55 40.0 14.00 10.01 28.5 As can be seen from Table 1, the effects of Examples 4-10 are significantly better than those of Examples 1-3, which in turn are significantly better than those of Comparative Examples 1-5. This indicates that by controlling the content of 2,3-propylene oxide methyl ether in the bio-based raw material epichlorohydrin, the moisture and heat resistance of the downstream polythiol adhesive system can be improved. This bio-based polythiol curing agent can be cured with epoxy resin in the presence of a accelerator and an auxiliary agent to prepare an epoxy adhesive, either alone or in combination with other thiol compounds. This adhesive not only has strong moisture and heat resistance and a long service life, but also reduces maintenance costs and is widely used in fields such as electronics, automotive manufacturing, aerospace, and architectural decoration. However, the curing agents of Comparative Examples 1-5 do not possess these characteristics.

[0056] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any equivalent replacement, modification, etc. made by technicians in this field without any creative work within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A bio-based polythiol curing agent obtained by reacting polyether polyol, epichlorohydrin and a thiol-forming agent, characterized in that: The epichlorohydrin is epichlorohydrin prepared by a glycerol method, and the mass content of 2,3-propylene oxide methyl ether in the epichlorohydrin is less than 0.4%.

2. The bio-based polythiol curing agent according to claim 1, characterized in that The mass content of 2,3-epoxypropylene methyl ether in the epichlorohydrin is ≤0.1%.

3. The bio-based polythiol curing agent according to claim 1 or 2, characterized in that The thiolating agent is selected from one of sodium sulfide, sodium hydrosulfide, thiourea and sodium polysulfide, the molar ratio of epichlorohydrin to polyether polyol is (0.5-6):1; the molar ratio of the thiolating agent to epichlorohydrin is (1-5):

1.

4. The bio-based polythiol curing agent according to claim 1 or 2, characterized in that The molar ratio of the thiol-forming agent to epichlorohydrin is (1-3):

1.

5. The method for preparing the bio-based polythiol curing agent according to claim 1, characterized in that: The following steps are involved: (1) Add polyether polyol and catalyst to a reaction vessel, then slowly drop epichlorohydrin into it, then add thiol reagent and phase transfer catalyst in sequence, and fill with protective gas to keep the reaction warm; The polyether polyol used has a hydroxyl value of 300-600 mgKOH / g and a viscosity of 300-500 mPa.s. (2) After the reaction is completed, the aqueous phase is removed, 1.5-3 times the weight of water is added to the organic phase, and then dilute sulfuric acid is added to adjust the pH to 3-5, and the mixture is stirred for 1-8 hours. The mixture is allowed to stand for separation, and then 1.5-3 times the weight of water is added to the organic phase, and the mixture is washed with water for 1-8 hours. The separated liquid is subjected to rotary evaporation to obtain a bio-based polythiol curing agent; the rotary evaporation temperature is 60-95°C, and the rotary evaporation time is 1-5 hours.

6. The method for preparing the bio-based polythiol curing agent according to claim 5, characterized in that: The catalyst in step (1) is selected from one of tin tetrachloride, stannous octoate, tributyltin chloride, boron trifluoride, and boron trifluoride ether, and the amount of the catalyst is 0.05-6% of the mass of the polyether polyol; in step (1), the dropping temperature is controlled to be 28-80° C., and the dropping time is 3-15 hours; after the dropping, the temperature is kept at 55-75° C. for 1-5 hours.

7. The method for preparing the bio-based polythiol curing agent according to claim 5, characterized in that: The reaction temperature of the insulation reaction in step (1) is 70-130° C., the reaction time is 3-10 h, and the reaction pressure is 0.1-10 MPa; the phase transfer catalyst in step (1) is selected from one of tetrabutylammonium chloride, tetrabutylammonium bromide, polyethylene glycol, and glycerol; the mass of the phase transfer catalyst is 0.5-25% of the mass of the polyether polyol; and the protective gas is selected from one of carbon dioxide, nitrogen, hydrogen sulfide, and argon.

8. The method for preparing the bio-based polythiol curing agent according to claim 7, characterized in that: The protective gas is nitrogen or hydrogen sulfide, the phase transfer catalyst is selected from tetrabutylammonium bromide or polyethylene glycol, and the mass of the phase transfer catalyst is 5-10% of the mass of the polyether polyol.

9. An epoxy adhesive composition, characterized in that Calculated by weight, the composition comprises 10-90 parts of the bio-based polythiol curing agent according to claim 1, 10-90 parts of epoxy resin and 0.1-15 parts of accelerator.

10. The epoxy adhesive composition according to claim 9, characterized in that: The epoxy resin is selected from one or two of glycidyl ether epoxy resins, glycidyl ester epoxy resins, glycidyl amine epoxy resins, alicyclic epoxy resins, epoxidized olefin epoxy resins, hydantoin epoxy resins, imide epoxy resins, organosilicon epoxy resins, and organoferric epoxy resins; The accelerator is selected from ethylenediamine, 1,2-diaminopropane, 1,3-diaminopropane, 1,5-diaminopentane, hexamethylenediamine, tetramethylenediamine, trimethylhexamethylenediamine, 2-methyl-1,5-diaminopentane, polyetherdiamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, diethylenepropylamine, polyamide, isophoronediamine, N-aminoethylpiperazine, m-phenylenediamine, diaminodiphenylmethane, diaminodiphenylsulfone, m-phenylenediamine, dicyandiamide, adipic acid dihydrazide, dipropylenetriamine, bis(hexamethylene)triamine, 2,4,6-tris(dimethylamino)methyl One or more of: 1,2-dimethylamino-2-methylphenol, 2,4,6-tris(dimethylaminomethylphenol)tris(2-ethylhexanoate), 2,4,6-tris(dimethylaminomethylphenol)trioleate, benzyldimethylamine, ethylenediamine, triethanolamine, o-hydroxybenzyldimethylamine, acetylacetonate metal salt, triphenylphosphine and its phosphonate salt, active tris(2-ethylhexanoate)chromium, organic acid salt amine complex, 1,8-diaza-bicyclo(5,4,0)-7-undecene, 2-thiolbenzothiazole, thiourea and its derivatives, cycloalkylimidazoline, 2-imidazoline, aromatic tertiary amine containing epoxy group, phthalate ester accelerator.