Yellowing-resistant epoxy resin curing agent as well as preparation method and application thereof

Abstract

The invention discloses a yellowing-resistant epoxy resin curing agent as well as a preparation method and application thereof, and relates to the technical field of industrial coatings. According to the yellowing-resistant epoxy resin curing agent provided by the invention, by introducing the chain extender of which the molecular structure contains more than or equal to two epoxy groups, alicyclic amine forms a longer molecular chain, and meanwhile, alcoholic hydroxyl groups can be introduced into the molecular structure of the alicyclic amine. On the basis, tertiary carbonate and silane containing amido and / or alkoxy are introduced into a reaction system, silane and tertiary carbonate can be further grafted to alicyclic amine molecules through the reaction between functional groups, the steric hindrance of the curing agent is improved, and the chemical bond energy is reduced. The curing agent disclosed by the invention can form a compact cross-linked network with epoxy resin, so that ultraviolet rays and moisture are effectively shielded, and the yellowing resistance and salt spray resistance of the epoxy resin are greatly improved.

Description

Technical Field

[0001] This invention relates to the field of industrial coatings technology, specifically to a yellowing-resistant epoxy resin curing agent, its preparation method, and its application. Background Technology

[0002] Epoxy resins possess excellent mechanical properties, adhesive properties, and chemical resistance, making them widely used in coatings and other fields. However, traditional epoxy resins are prone to yellowing during use, especially under complex environmental conditions such as ultraviolet radiation, high temperature, and humidity, where the yellowing phenomenon is more pronounced. This is mainly because the aromatic rings in the epoxy resin molecular chain are oxidized to form quinone groups, which are chromophores. This type of yellowing not only affects the appearance of the product but also its functionality, reducing its lifespan.

[0003] Improving the curing agent of epoxy resin is a feasible way to enhance its resistance to yellowing. Chinese patent CN113527638B provides an epoxy curing agent synthesized by reacting salicylate, aldehyde compounds, and alicyclic diamines. This curing agent contains UV-absorbing groups (salicylate) in its molecular structure, which can prevent ultraviolet light from affecting the epoxy resin molecular chain. However, salicylate compounds themselves do not directly absorb ultraviolet light. Their absorption is achieved through a photochemical reaction under UV irradiation, generating compounds with strong UV absorption capabilities. Based on this reaction, epoxy resin cured with this curing agent cannot achieve long-term use. Chinese patent CN105482080B also improves the yellowing resistance of epoxy resin by introducing polyethers with a certain degree of polymerization into the conventional epoxy resin formulation. The polyethers reflect a large amount of ultraviolet light, thus improving the yellowing resistance of the epoxy resin. However, the polyether compounds severely affect the water resistance of the coating film. Therefore, it is of great significance to improve the yellowing resistance of epoxy resin by modifying the curing agent, while avoiding excessive negative impact on its water resistance and extending the service life of epoxy resin coating. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a yellowing-resistant epoxy resin curing agent, its preparation method, and its application.

[0005] The above-mentioned objective of this invention is achieved through the following technical solution: A yellowing-resistant epoxy resin curing agent, comprising the following raw materials in parts by weight: Alicyclic amine 50-70 parts, chain extender 10-20 parts, silane 10-40 parts, tertiary carbonate 0-50 parts; The silane includes silane A and / or silane B, and the molecular structures of silane A and silane B both contain functional groups. The functional groups of silane A include amino groups and alkoxy groups, and the functional groups of silane B include alkoxy groups. The amino group includes primary amino groups and / or secondary amino groups; The chain extender contains ≥2 epoxy groups in its molecular structure.

[0006] The yellowing-resistant epoxy resin curing agent provided by this invention introduces a chain extender containing ≥2 epoxy groups in its molecular structure, enabling the alicyclic amine to form a longer molecular chain. Simultaneously, the reaction between the chain extender and the alicyclic amine introduces hydroxyl groups into the molecular structure of the alicyclic amine. Furthermore, this invention introduces silane A containing both amino and alkoxy groups and / or silane B containing only alkoxy groups into the reaction system. Through the hydrolysis of the alkoxysilane or the reaction between the amino group and the residual hydroxyl groups at the end of the extended alicyclic amine, the silane can be further grafted onto the alicyclic amine molecule. Specific groups contained in tertiary carbonates, such as epoxy groups and vinyl groups, can also be grafted onto the alicyclic amine through reaction with amino groups. The curing agent prepared from the above raw materials can form a denser cross-linked network after reacting with epoxy resin. The silicon-oxygen bond has high bond energy and the tertiary carbonate structure has high steric hindrance. Both can increase the shielding performance of epoxy resin against moisture and oxygen, and improve its resistance to yellowing and water resistance. At the same time, the raw materials used in this invention are all introduced by chemical bonds, which can effectively avoid the risks of raw material migration that exist in physical mixing.

[0007] In a specific embodiment of the present invention, silane A and silane B further include non-functional groups, which include hydrogen and alkyl groups.

[0008] Preferably, the number of functional groups in the molecular structure of silane A is 2-5.

[0009] Preferably, the ratio of amino groups to alkoxy groups in the functional groups of silane A is (1-2):2.

[0010] Amine groups can react with vinyl or epoxy resin matrices in tertiary carbonates and epoxy groups on chain extenders. Therefore, compared to alkoxy groups, which can only react with -OH groups introduced by chain extenders, amine groups are more likely to form crosslinking sites and a denser network. However, the siloxane bonds formed by the reaction of Si-OR alkoxy groups and hydroxyl groups have better shielding properties against moisture and oxygen (chemical bonds with higher bond energy are less likely to break due to external influences). By controlling the ratio of amine to alkoxy groups in the functional groups of silane A to (1-2):2, it is beneficial to fully utilize the role of siloxane bonds while maintaining the density of the crosslinking structure.

[0011] Preferably, the molecular weight of silane A is 150-300 g / mol.

[0012] Preferably, the silane A comprises at least one of 3-aminopropylmethyldimethoxysilane, 3-aminopropylmethyldiethoxysilane, 3-(2-aminoethylamino)propylmethyldimethoxysilane, N-(2-aminoethyl)-3-aminopropylmethyldiethoxysilane, N-(piperazinylethyl)-3-aminopropylmethyldimethoxysilane, N-cyclohexyl-3-aminopropylmethyldimethoxysilane, and 3-(N-cyclohexylamino)propylmethyldimethoxysilane.

[0013] The silanes selected above are all dimethoxysilanes or diethoxysilanes, which are beneficial for obtaining linear polymers, improving the flexibility of the coating film, and avoiding resin gelation caused by the crosslinking of trimethoxy or triethoxysilanes, which would affect the yellowing resistance and salt spray resistance.

[0014] More preferably, the molecular weight of the silane A is 170-300 g / mol.

[0015] More preferably, the silane A comprises at least one of 3-aminopropylmethyldiethoxysilane, 3-(2-aminoethylamino)propylmethyldimethoxysilane, N-(2-aminoethyl)-3-aminopropylmethyldiethoxysilane, N-(piperazinylethyl)-3-aminopropylmethyldimethoxysilane, N-cyclohexyl-3-aminopropylmethyldimethoxysilane, and 3-(N-cyclohexylamino)propylmethyldimethoxysilane.

[0016] Preferably, the number of functional groups in the molecular structure of silane B is 1-3.

[0017] Preferably, the molecular weight of silane B is 175-300 g / mol.

[0018] Preferably, the silane B includes at least one of diphenyldimethoxysilane, diphenyldiethoxysilane, methylphenyldimethoxysilane, and methylphenyldiethoxysilane.

[0019] More preferably, the molecular weight of the silane B is 185-250 g / mol.

[0020] More preferably, the silane B includes at least one of diphenyldimethoxysilane and methylphenyldiethoxysilane.

[0021] More preferably, the silane is silane A.

[0022] Preferably, the molecular weight of the alicyclic amine is 100-200 g / mol.

[0023] Preferably, the alicyclic amine includes one of isophorone diamine, 1,4-cyclohexanediamine, 1,3-cyclohexanedimethylamine, and N-cyclohexyl-3-aminopropylmethyldimethoxysilane.

[0024] Preferably, the chain extender has a molecular weight of 150-400 g / mol.

[0025] Preferably, the chain extender comprises at least one of hydrogenated bisphenol A type epoxy resin, propylene glycol glycidyl ether, ethylene glycol glycidyl ether, diethylene glycol glycidyl ether, 1,4-butanediol glycidyl ether, 1,4-cyclohexanediethanol diglycidyl ether, and neopentyl glycol diglycidyl ether.

[0026] Preferably, the tertiary carbonate has a molecular weight of 175-250 g / mol.

[0027] Preferably, the tertiary carbonate includes at least one of glycidyl tertiary carbonate and vinyl tertiary carbonate.

[0028] Preferably, the raw materials for preparing the yellowing-resistant epoxy resin curing agent also include 5-15 parts of ultraviolet absorber.

[0029] More preferably, the ultraviolet absorber includes at least one of acrylonitrile, benzotriazole, 2,4,6-tris(2'-hydroxy-4'-hexyloxyphenyl)-1,3,5-triazine, 2-hydroxy-4-methoxybenzophenone, and p-tert-butylphenyl salicylate.

[0030] Preferably, the mass fraction of tertiary carbonate in the yellowing-resistant epoxy resin curing agent is 10-30 parts.

[0031] This invention also protects the preparation method of the above-mentioned anti-yellowing epoxy resin curing agent, comprising the following steps: S1. Disperse the alicyclic amine in a solvent, and add the chain extender dropwise at a stirring speed of 200-300 rpm and a temperature of 50-90℃ for 2-4 h; after the addition, keep the reaction at the temperature for 1-3 h to obtain the precursor; S2. Add the remaining components to the precursor obtained in step S1, and react at 160-220℃ for 2-8 h to obtain the yellowing-resistant epoxy resin curing agent.

[0032] Preferably, when the raw materials for preparing the yellowing-resistant epoxy resin curing agent include an ultraviolet absorber, in step S1, before adding the chain extender, the alicyclic amine and the ultraviolet absorber are dispersed in a solvent.

[0033] Preferably, the solvent includes at least one selected from methanol, ethanol, isopropanol, n-butanol, ethylene glycol monobutyl ether, propylene glycol methyl ether, propylene glycol propyl ether, benzyl alcohol, toluene, xylene, trimethylbenzene, acetone, cyclohexanone, and methyl isobutyl ketone (MEK).

[0034] This invention also protects the use of the above-mentioned yellowing-resistant epoxy resin curing agent in curing epoxy resins.

[0035] This invention also protects a method for curing epoxy resin, comprising the following steps: The yellowing-resistant epoxy resin curing agent is mixed with epoxy resin at a molar ratio of amine group to epoxy group of 1:(0.8-1.2), and cured at 20-30℃ for 5-24 h to obtain the product.

[0036] Compared with the prior art, the present invention has the following beneficial effects: The yellowing-resistant epoxy resin curing agent provided in this application can give the resin matrix good salt spray resistance and yellowing resistance after curing the epoxy resin. The failure time in the salt spray test is as high as 1200 h or more, and the gloss loss rate in the yellowing resistance test is as low as 13% or less. Detailed Implementation

[0037] The present invention will be further described below with reference to specific embodiments, but the embodiments do not limit the present invention in any way. Unless otherwise stated, the raw materials and reagents used in the embodiments of the present invention are conventionally purchased raw materials and reagents. The raw material information used in each embodiment and comparative example is as follows: Alicyclic amine-1: Isophorone diamine, molecular weight 170 g / mol.

[0038] Alicyclic amine-2: 1,3-cyclohexanedimethylamine, molecular weight 142 g / mol.

[0039] Alicyclic amine-3: 1,4-cyclohexanediamine, molecular weight 114 g / mol.

[0040] Chain extender-1: Hydrogenated bisphenol A type epoxy resin, with the structure shown in the formula below, containing 2 epoxy groups in its molecular structure, and a molecular weight of 352 g / mol. .

[0041] Chain extender-2: ethylene glycol glycidyl ether, with a molecular structure containing two epoxy groups and a molecular weight of 174 g / mol.

[0042] Chain extender-3: 1,4-cyclohexanediethanol diglycidyl ether, with a molecular structure containing 2 epoxy groups and a molecular weight of 256 g / mol.

[0043] Chain extender-4: 1,4-Butanediol glycidyl ether, with a molecular structure containing two epoxy groups and a molecular weight of 202 g / mol.

[0044] Tertiary carbonate-1: Vinyl tertiary carbonate, molecular weight 198 g / mol.

[0045] Tertiary carbonate-2: Tertiary glycidyl carbonate, molecular weight 228 g / mol.

[0046] Silane A1: N-cyclohexyl-3-aminopropylmethyldimethoxysilane, CAS 120218-28-2, molecular weight 245 g / mol, the molecular structure contains 1 secondary amino group and 2 methoxy groups.

[0047] Silane A2: 3-aminopropylmethyldiethoxysilane, with a molecular weight of 191 g / mol, contains one primary amino group and two ethoxy groups in its molecular structure.

[0048] Silane A3: 3-(2-aminoethylamino)propylmethyldimethoxysilane, CAS 3069-29-2, molecular weight 206 g / mol, the molecular structure contains 1 primary amino group, 1 secondary amino group and 2 methoxy groups.

[0049] Silane A4: N-(piperazinylethyl)-3-aminopropylmethyldimethoxysilane, CAS 128644-51-9, molecular weight 275 g / mol, the molecular structure contains 1 primary amine group, 1 secondary amine group and 2 methoxy groups.

[0050] Silane A5: N-[6-(diethoxymethylsilyl)hexyl]-1,6-hexanediamine, CAS 144006-73-5, molecular weight 322 g / mol, the molecular structure contains 1 primary amine group, 1 secondary amine group and 2 ethoxy groups.

[0051] Silane A6: 3-aminopropylmethyldimethoxysilane, with a molecular weight of 163 g / mol, contains one primary amino group and two methoxy groups in its molecular structure.

[0052] Silane A7: N-(2-aminoethyl)-N'-[3-(ethoxysilyl)propyl]-1,2-ethylenediamine, CAS 25294-80-8, molecular weight 219 g / mol, the molecular structure contains 1 primary amino group, 2 secondary amino groups and 1 ethoxy group.

[0053] Silane A8: 3-Diethylenetriaminepropyltrimethoxysilane, CAS 35141-30-1, molecular weight 265 g / mol, the molecular structure contains 1 primary amine group, 2 secondary amine groups and 3 methoxy groups.

[0054] Silane B1: Methylphenyldiethoxysilane, molecular weight 210 g / mol, containing 2 ethoxy groups in its molecular structure.

[0055] Silane B2: Diphenyldimethoxysilane, molecular weight 244 g / mol, containing 2 methoxy groups in its molecular structure.

[0056] Silane B3: Diphenyldiethoxysilane, molecular weight 272 g / mol, containing two ethoxy groups in its molecular structure.

[0057] Silane B4: Methylphenyl dimethoxysilane, molecular weight 182 g / mol, containing 2 methoxy groups in its molecular structure.

[0058] Silane B5: Tetraethoxysilane, molecular weight 208.33 g / mol, containing 4 ethoxy groups in its molecular structure.

[0059] Silane C1: N,N'-Di(2-methyl-2-propyl)silanediamine, CAS 186598-40-3, molecular weight 174 g / mol, the molecular structure contains 2 secondary amine groups.

[0060] Silane C2: 1,1-Dimethyl-N,N'-Disec-butylaminosilane, CAS 93777-98-1, molecular weight 202 g / mol, containing 2 secondary amino groups in its molecular structure.

[0061] Silane C3: N,N'-dimethyl-3-aminopropyltrimethoxysilane, CAS 2530-86-1, molecular weight 207 g / mol, the molecular structure contains 1 tertiary amine group and 3 methoxy groups.

[0062] Silane C4: N,N-diethyl-3-aminopropyltriethoxysilane, CAS 10049-42-0, molecular weight 277 g / mol, the molecular structure contains 1 tertiary amine group and 3 ethoxy groups.

[0063] UV absorber-1: Acrylonitrile.

[0064] UV absorber-2: benzotriazole.

[0065] Ultraviolet absorber-3: 2-hydroxy-4-methoxybenzophenone.

[0066] Examples 1-17 and Comparative Examples 1-4 This embodiment and the comparative example provide a series of epoxy resin curing agents, the raw materials for which are prepared are shown in Tables 1-3.

[0067] The preparation method of the curing agent in this embodiment and the comparative example includes the following steps: S1. Disperse the alicyclic amine and ultraviolet absorber (if any) in the organic solvent methanol, and add the chain extender dropwise at a stirring speed of 25 rpm and a temperature of 70°C for 3 h; after the addition, keep the reaction at the temperature for 2 h to obtain the precursor; S2. Add the remaining components to the precursor obtained in step S1, and react at 200°C for 6 h to obtain the yellowing-resistant epoxy resin curing agent.

[0068] Table 1. Table 2. Table 3. Performance testing Sample preparation: The curing agent obtained from the examples and comparative examples was mixed with hydrogenated bisphenol A epoxy resin at a molar ratio of amine groups to epoxy groups of 1:1, and cured at 25°C for 12 h to obtain the sample.

[0069] Yellowing resistance test: According to Section 6.19 of GB / T 9779-2015 Multi-layer architectural coatings, the gloss loss rate of the sample after aging for 1000 hours is tested; the higher the gloss loss rate, the higher the degree of yellowing and the worse the yellowing resistance.

[0070] Salt spray resistance test: The salt spray resistance of the cured coating was tested according to the method in GB / T 1771-2007. The test temperature was 35±1℃ and the settling rate was 1-2 mL / 80cm. 2 •h. Test results are expressed as failure time; the longer the failure time, the better the salt spray resistance.

[0071] The test results are shown in Table 4 below: Table 4. As can be seen from Table 1 above, the yellowing-resistant epoxy resin curing agent provided in this application can give the resin matrix good salt spray resistance and yellowing resistance after curing the epoxy resin. The failure time in the salt spray test is as high as 1200 h or more, and the gloss loss rate in the yellowing resistance test is as low as 13% or less.

[0072] According to Examples 1, 9-12, and 15-16, if the molecular weight of the silane used to modify the alicyclic amine is unsuitable, it will lead to a decrease in the performance of the epoxy resin after curing.

[0073] According to Examples 1 and 17, an excessive number of functional groups in silane also leads to a decrease in effectiveness. It is speculated that this is because excessive functional groups can easily affect the grafting of silane through steric hindrance.

[0074] According to Comparative Examples 1-4, silanes containing only amine groups, or silanes containing unsuitable types of amine groups, will cause silanes to fail to perform their corresponding functions.

[0075] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A yellowing-resistant epoxy resin curing agent, characterized in that, The raw materials include the following parts by weight: Alicyclic amine 50-70 parts, chain extender 10-20 parts, silane 10-40 parts, tertiary carbonate 0-50 parts; The silane includes silane A and / or silane B, and the molecular structures of silane A and silane B both contain functional groups. The functional groups of silane A include amino groups and alkoxy groups, and the functional groups of silane B include alkoxy groups. The amino group includes primary amino groups and / or secondary amino groups; The chain extender contains ≥2 epoxy groups in its molecular structure.

2. The yellowing-resistant epoxy resin curing agent as described in claim 1, characterized in that, The number of functional groups in the molecular structure of silane A is 2-5; And / or, the number of functional groups in the molecular structure of the silane B is 1-3.

3. The yellowing-resistant epoxy resin curing agent as described in claim 2, characterized in that, The ratio of amino groups to alkoxy groups in the functional groups of silane A is (1-2):

2.

4. The yellowing-resistant epoxy resin curing agent as described in claim 3, characterized in that, The molecular weight of the silane A is 170-300 g / mol; And / or, the molecular weight of the silane B is 185-250 g / mol.

5. The yellowing-resistant epoxy resin curing agent according to any one of claims 1-4, characterized in that, Includes at least one of the following (a)-(e): (a) The alicyclic amine includes one of isophorone diamine, 1,4-cyclohexanediamine, 1,3-cyclohexanedimethylamine, and N-cyclohexyl-3-aminopropylmethyldimethoxysilane; (b) The chain extender comprises at least one of hydrogenated bisphenol A type epoxy resin, propylene glycol glycidyl ether, ethylene glycol glycidyl ether, diethylene glycol glycidyl ether, 1,4-butanediol glycidyl ether, 1,4-cyclohexanediethanol diglycidyl ether, and neopentyl glycol diglycidyl ether. (c) The silane A comprises at least one of 3-aminopropylmethyldiethoxysilane, 3-(2-aminoethylamino)propylmethyldimethoxysilane, N-(2-aminoethyl)-3-aminopropylmethyldiethoxysilane, N-(piperazinylethyl)-3-aminopropylmethyldimethoxysilane, N-cyclohexyl-3-aminopropylmethyldimethoxysilane, and 3-(N-cyclohexylamino)propylmethyldimethoxysilane; (d) The silane B includes at least one of diphenyldimethoxysilane and methylphenyldiethoxysilane; (e) The tertiary carbonate includes at least one of glycidyl tertiary carbonate and vinyl tertiary carbonate.

6. The yellowing-resistant epoxy resin curing agent as described in claim 1, characterized in that, The raw materials used in the preparation also include 5-15 parts of ultraviolet absorber.

7. The yellowing-resistant epoxy resin curing agent as described in claim 6, characterized in that, The ultraviolet absorber includes at least one of acrylonitrile, benzotriazole, 2,4,6-tris(2'-hydroxy-4'-hexyloxyphenyl)-1,3,5-triazine, 2-hydroxy-4-methoxybenzophenone, and p-tert-butylphenyl salicylate.

8. The method for preparing the yellowing-resistant epoxy resin curing agent according to any one of claims 1-7, characterized in that, Includes the following steps: S1. Disperse the alicyclic amine in a solvent, and add the chain extender dropwise at a stirring speed of 200-300 rpm and a temperature of 50-90℃ for 2-4 h; after the addition, keep the reaction at the temperature for 1-3 h to obtain the precursor; S2. Add the remaining components to the precursor obtained in step S1, and react at 160-220℃ for 2-8 h to obtain the yellowing-resistant epoxy resin curing agent.

9. The use of the yellowing-resistant epoxy resin curing agent according to any one of claims 1-7 in curing epoxy resin.

10. A method for curing epoxy resin, characterized in that, Includes the following steps: The yellowing-resistant epoxy resin curing agent according to any one of claims 1-7 is mixed with epoxy resin at a molar ratio of amine group to epoxy group of 1:(0.8-1.2), and cured at 20-30℃ for 5-24 h to obtain the product.

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