Waterborne epoxy resin emulsifier and waterborne epoxy resin composition

Abstract

A waterborne epoxy resin emulsifier, the molecular structure thereof comprises: a structure derived from a first compound; and a structure derived from an epoxy resin, wherein the molecular structure of the first compound comprises a benzene ring and a dibasic carboxyl group, wherein the molecular structure of the epoxy resin comprises two or more epoxy groups, wherein the waterborne epoxy resin emulsifier is prepared by reacting the first compound with the epoxy resin, wherein the first compound is prepared by subjecting a diester containing a benzene ring structure to an esterification reaction with polyethylene glycol, and then reacting with an acid anhydride compound capable of forming a dibasic carboxyl group. The waterborne epoxy resin emulsifier of the present invention is suitable for emulsifying oil-based epoxy resin into a water phase. The present invention also relates to a waterborne epoxy resin composition.

Description

[Technical Field]

[0001] This invention relates to an aqueous epoxy resin emulsifier, and more particularly to an aqueous epoxy resin emulsifier whose molecular structure comprises a structure derived from a first compound and a structure derived from an epoxy resin. This invention also relates to an aqueous epoxy resin composition. [Previous Technology]

[0002] Waterborne epoxy resin is a thermosetting polymer material that retains the characteristics of traditional solvent-based epoxy resins: corrosion resistance, high adhesion, high mechanical strength, and low shrinkage. Compared with traditional solvent-based epoxy resins, waterborne epoxy resins are easier to handle, dilute, and clean, and have lower volatile organic compound (VOC) content, improving the safety of transportation and construction. In recent years, with increasing emphasis on environmental protection and health, and with stricter requirements for VOC limits in coatings from various countries, the demand for waterborne epoxy resins has risen accordingly.

[0003] However, early waterborne epoxy resins were prepared by using emulsifiers in a homogenizer with high-speed stirring to form epoxy resin emulsions. These waterborne epoxy resins often suffered from uneven emulsification, with average particle sizes exceeding 1000 nm, leading to agglomeration and precipitation, resulting in low storage stability. To improve the quality of waterborne epoxy resins, using emulsifiers to enhance stability has become a mainstream approach. In recent years, various epoxy resin emulsifier structures have been developed, most of which utilize the reaction of polyethylene glycol amine compounds with epoxy resins to form emulsifiers. However, the presence of active hydrogen on the amine groups may react with epoxy functional groups, raising concerns about storage stability. Furthermore, most epoxy resin emulsifiers are non-reactive and do not participate in subsequent cross-linking reactions, resulting in emulsifier release after curing and a decrease in coating surface strength. Previous emulsifiers were mostly only able to emulsify epoxy resins with low epoxy equivalent weight (EEW ​​< 200); or they could emulsify epoxy resins with high epoxy equivalent weight, but only at low solid content (≤ 20%). They were insufficient in terms of operating conditions and resin selection. For high-molecular-weight epoxy resins, there is still a lack of suitable emulsifiers in China. [Summary of the Invention]

[0004] Traditional epoxy resin emulsifiers still have room for improvement. Therefore, in one embodiment of the present invention, recycled polyethylene terephthalate (PET) is used as raw material. By using chemical depolymerization and modification, the aromatic ring structure is retained, and a reactive epoxy resin emulsifier with epoxy groups is designed without concerns about residual active hydrogen. The goal is to emulsify commercially available oily epoxy resins into an aqueous phase to produce a stable and high-performance emulsion.

[0005] To achieve the above and other objectives, the present invention provides an aqueous epoxy resin emulsifier, the molecular structure of which comprises: a structure derived from a first compound; and a structure derived from an epoxy resin, wherein the molecular structure of the first compound comprises a benzene ring and a dicarboxyl group, wherein the molecular structure of the epoxy resin comprises two or more epoxy groups, wherein the aqueous epoxy resin emulsifier is prepared by reacting the first compound with the epoxy resin, wherein the first compound is prepared by esterifying a diester containing a benzene ring structure with polyethylene glycol, and then reacting it with an anhydride compound that can form a dicarboxyl group.

[0006] In one embodiment of the present invention, the waterborne epoxy resin emulsifier may have a structure as shown in formula (I), formula (II) or formula (III): In formula (I), formula (II), formula (III), R represents an alkyl or sulfonyl group having 1 to 3 carbon atoms; R' represents a benzene ring structure containing 0 to 4 alkyl groups; m and n represent the number of repeating units.

[0007] In one embodiment of the present invention, m may be between 1 and 5; and n may be between 13 and 70.

[0008] In the structures of formulas (I), (II), and (III) above, only the epoxy resin has an OH group at the ring-opening position. Its reactivity is low, requiring temperatures above 100 degrees Celsius to react with the epoxy group. It does not affect storage at room temperature. In contrast, emulsifiers in the prior art commonly use amines that react with acid anhydrides, resulting in -CO-NH- functional groups in their chain segments. The hydrogen in the residual NH is active hydrogen, which, although less reactive than typical primary amines, still exhibits reactivity, leading to reduced storage stability.

[0009] In one embodiment of the present invention, the diester containing a benzene ring structure may be selected from the group consisting of terephthalic acid, phthalic acid, isophthalic acid, dimethyl terephthalate, diethylene terephthalate and polyethylene terephthalate.

[0010] In one embodiment of the present invention, the diester containing the benzene ring structure may be recycled polyethylene terephthalate.

[0011] In one embodiment of the present invention, the number average molecular weight of the polyethylene glycol may be between 600 and 3000.

[0012] In one embodiment of the present invention, the anhydride compound capable of forming a dicarboxyl group is selected from the group consisting of succinic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, and phthalic anhydride. Among them, hexahydrophthalic anhydride belongs to aliphatic anhydride compounds and has a cyclic structure. Compared with linear anhydride compounds, it can make the waterborne epoxy resin emulsifier of the present invention have better heat resistance.

[0013] In one embodiment of the present invention, the anhydride compound that can form a dicarboxyl group may be hexahydrophthalic anhydride.

[0014] To achieve the above and other objectives, the present invention also provides an aqueous epoxy resin composition comprising: 5 to 20 parts by weight of the aqueous epoxy resin emulsifier as described above; 30 to 50 parts by weight of epoxy resin, wherein the molecular structure of the epoxy resin comprises two or more epoxy groups; and 45 to 55 parts by weight of deionized water.

[0015] In one embodiment of the present invention, the D50 particle size of the aqueous epoxy resin composition may be less than 500 nm.

[0016] The waterborne epoxy resin emulsifier of the present invention, through its unique molecular structure, can emulsify bisphenol A type epoxy resins with medium to high epoxy equivalent weight (EEW=650) to form a stable waterborne epoxy resin composition. Furthermore, the waterborne epoxy resin emulsifier of the present invention is also applicable to low molecular weight epoxy resin BE188 (epoxy equivalent weight EEW~190). Here, epoxy equivalent weight (EEW) refers to the number of grams of epoxy resin required to produce 1 mole of epoxy groups, expressed in grams per equivalent weight. A high epoxy equivalent weight indicates a higher molecular weight of the epoxy resin, which allows for the calculation of the correct mixing ratio of the epoxy system and the curing agent.

[0017] The waterborne epoxy resin composition of the present invention, by adding the waterborne epoxy resin emulsifier of the present invention, exhibits good coating storage stability and mechanical properties after curing, even under conditions of high solids content (>50wt%). Commercially available emulsions typically have a solids content of around 50%, which manufacturers then dilute according to usage requirements. Higher solids content increases the likelihood of emulsion stratification, reducing storage stability. Therefore, a stable high-solids-content epoxy resin composition helps manufacturers save storage space and simplify application.

Implementation Method

[0018] To fully understand the purpose, features, and effects of the present invention, the present invention will be described in detail below with reference to the specific embodiments described in the following description:

[0019] An exemplary preparation process of the waterborne epoxy resin emulsifier of the present invention is shown in the following reaction formula (A): Reaction formula (A)

[0020] This invention relates to the technical development of emulsifiers for epoxy resins, aiming to improve the emulsification problems of epoxy resins. In reaction formula (A), terephthalic acid (ester) or polyethylene terephthalate (PET) is modified, and polyethylene glycol is added for esterification to obtain a hydrophilic intermediate. This hydrophilic intermediate is then reacted with an acid anhydride to obtain a first compound. Finally, the first compound is reacted with epoxy resin to obtain the epoxy resin emulsifier of this invention. In terms of structural design, the epoxy resin emulsifier of this invention incorporates the benzene ring structure of terephthalic acid (ester) to improve its compatibility with epoxy resin, thus contributing to the emulsification effect and stability of the epoxy resin. The use of an acid anhydride to react with the epoxy resin avoids residual active hydrogen, which could affect the storage stability of waterborne epoxy resins. Furthermore, the terminal epoxy groups are retained, allowing them to react with the hardener, thus avoiding concerns about emulsifier residue after curing.

[0021] In embodiments using polyethylene terephthalate (PET), the method for depolymerizing PET is an alcoholysis reaction with polyethylene glycol. For example, the depolymerization of PET can be performed by referring to the relevant method disclosed in patent application No. TWI788008B and the range of PET raw material types used therein, but the present invention is not limited thereto.

[0022] This invention relates to the structural design of an emulsifier for an epoxy resin, wherein each molecule can be obtained by mixing and reacting an epoxy resin having at least two epoxy groups with a hydrophilic compound containing a carboxyl group, wherein the hydrophilic compound can be obtained by reacting terephthalic acid (ester), polyethylene glycol and an acid anhydride.

[0023] Example 1: Synthesis of epoxy resin emulsifier S1

[0024] Take 1 kg of polyethylene glycol (PEG) with a molecular weight of 2000, add 64 g of diethylene glycol terephthalate (bis(2-Hydroxyethyl) terephthalate (BHET)) and 0.72 g of catalytic tetrabutyl titanate to the reaction vessel, heat the mixture from 120 °C to 260 °C and perform a polymerization reaction under vacuum for 6 hours. After the reaction time is reached, cool down to 100 °C and add 5 g of antioxidant to form a hydrophilic polyester intermediate. Take out 1 kg of the hydrophilic polyester intermediate and under nitrogen atmosphere at 100 °C, add 50.8 g of succinic anhydride and 0.38 g of triphenylphosphine to the reaction vessel, heat the mixture from 100 °C to 150 °C and react under nitrogen atmosphere for 6 hours. Then, the temperature was lowered to 100°C, and 455 g of epoxy resin (BE188) and 2.1 g of triphenylphosphine were added to the reaction vessel. The mixture was then heated from 100°C to 120°C and reacted under nitrogen atmosphere for 3 hours to obtain epoxy resin emulsifier S1.

[0025] Example 2: Synthesis of epoxy resin emulsifier S2

[0026] Based on the experimental conditions of Example 1, but replacing succinic anhydride with 77.3 g of tetrahydrophthalic anhydride, epoxy resin emulsifier S2 was obtained by reaction.

[0027] Example 3: Synthesis of epoxy resin emulsifier S3

[0028] Based on the experimental conditions of Example 1, but replacing succinic anhydride with 75.3 g of phthalic anhydride, the reaction yielded epoxy resin emulsifier S3.

[0029] Example 4: Synthesis of epoxy resin emulsifier S4

[0030] Based on the experimental conditions of Example 1, but replacing diethylene terephthalate with 48g of polyethylene terephthalate (PET) and replacing succinic anhydride with 77.3g of tetrahydrophthalic anhydride, epoxy resin emulsifier S4 was obtained by reaction.

[0031] Example 5: Synthesis of epoxy resin emulsifier S5

[0032] Based on the experimental conditions of Example 1, but replacing the 2000 molecular weight polyethylene glycol with 1 kg of 1000 molecular weight polyethylene glycol, and adding 127 g of diethylene terephthalate, 98.6 g of succinic anhydride, and 883 g of BE188, the epoxy resin emulsifier S5 was obtained.

[0033] Example 6: Synthesis of epoxy resin emulsifier S6

[0034] Based on the experimental conditions of Example 5, but replacing succinic anhydride with 150 g of tetrahydrophthalic anhydride, epoxy resin emulsifier S6 was obtained by reaction.

[0035] Example 7: Synthesis of epoxy resin emulsifier S7

[0036] Based on the experimental conditions of Example 5, but replacing succinic anhydride with 146 g of phthalic anhydride, epoxy resin emulsifier S7 was obtained by reaction.

[0037] Example 8: Synthesis of epoxy resin emulsifier S8

[0038] Based on the experimental conditions of Example 4, but replacing the 2000 molecular weight polyethylene glycol with 1 kg of 1000 molecular weight polyethylene glycol, and adding 127 g of diethylene terephthalate, 98.6 g of succinic anhydride, and 883 g of BE188, the epoxy resin emulsifier S5 was obtained.

[0039] Comparative Example 1: Synthesis of epoxy resin emulsifier C1 as a comparison

[0040] Take 1 kg of polyethylene glycol with a molecular weight of 2000, add 105 g of succinic anhydride and 0.53 g of triphenylphosphine to the reaction vessel, and heat the mixture from 100 ℃ to 150 ℃, reacting for 6 hours under nitrogen atmosphere. Then, cool down to 100 ℃, add 940 g of BE188 and 2.2 g of triphenylphosphine to the reaction vessel, and heat the mixture from 100 ℃ to 120 ℃, reacting for 3 hours under nitrogen atmosphere to obtain epoxy resin emulsifier C1.

[0041] The formulations of Examples 1-8 and Comparative Example 1 are summarized in Table 1 below.

[0042] Table 1 Example 1 2 3 4 5 Product Number S1 S2 S3 S4 S5 PEG PEG2000 PEG2000 PEG2000 PEG2000 PEG1000 PEG weight (g) 1000 1000 1000 1000 1000 BHET (g) 64 64 64 127 PET (g) 48 Titanium catalyst (g) 0.72 0.72 0.72 0.72 0.72 acid anhydride type Succinic anhydride Tetrahydrophthalic anhydride Phthalic anhydride Tetrahydrophthalic anhydride Succinic anhydride Weight of acid anhydride (g) 50.8 77.3 75.3 77.3 98.6 BE188 (g) 455 455 455 455 883 TPP (g) 0.38 / 2.1 0.38 / 2.1 0.38 / 2.1 0.38 / 2.1 0.38 / 2.1 Epoxy Equivalent of Product 780 790 790 790 540

[0043] Table 1 (continued) Example 6 7 8 Comparative Example 1 Product Number S6 S7 S8 C1 PEG PEG1000 PEG1000 PEG1000 PEG2000 PEG weight (g) 1000 1000 1000 1000 BHET (g) 127 127 PET (g) 96 Titanium catalyst (g) 0.72 0.72 0.72 acid anhydride type Tetrahydrophthalic anhydride Phthalic anhydride Tetrahydrophthalic anhydride Succinic anhydride Weight of acid anhydride (g) 150 146 150 105 BE188 (g) 833 833 833 940 Titanium Catalyst 0.72 0.72 0.72 TPP (g) 0.38 / 2.1 0.38 / 2.1 0.38 / 2.1 0.53 / 2.2 Epoxy Equivalent of Product 530 530 530

[0044] The main difference between the waterborne epoxy resin emulsifier C1 of Comparative Example 1 and the waterborne epoxy resin emulsifiers S1 to S8 of Examples 1 to 8 lies in whether an aromatic core structure is introduced. Specifically, waterborne epoxy resin emulsifiers S1, S2, S3, S5, S6, and S7 use diethylene terephthalate (bis(2-Hydroxyethyl) terephthalate (BHET), while S4 and S8 use polyethylene terephthalate (PET) as a starting material and react it with polyethylene glycol (PEG), followed by reaction with acid anhydrides. In contrast, the waterborne epoxy resin emulsifier C1 of Comparative Example 1 directly reacts polyethylene glycol (PEG) with acid anhydrides, and its structure does not contain aromatic ring segments.

[0045] The test results of Examples 9 to 16 and Comparative Example 2 below show that, for the epoxy resin NPES902, which is rich in benzene rings and has a high molecular weight, the waterborne epoxy resin emulsifiers S1 to S8, which introduce aromatic core structures, have better emulsification effects. In contrast, the waterborne epoxy resin emulsifier C1, which does not contain aromatic ring segments in its structure, has poor emulsification effects.

[0046] Example 9: Preparation of waterborne epoxy resin composition S9 using epoxy resin emulsifier S1

[0047] 15 g of the epoxy resin emulsifier S1 synthesized as described above was mixed with 40 g of bisphenol A epoxy resin (purchased from Nan Ya Plastics, trade name NPES902, epoxy equivalent 620), and 10 g of butanone was added and mixed evenly. Then, under stirring at 600 rpm, 45 g of deionized water was added to carry out an emulsification process of phase inversion dispersion in water. After emulsification, butanone was removed under reduced pressure to obtain an aqueous epoxy resin composition S9.

[0048] Examples 10 to 16: Preparation of waterborne epoxy resin compositions S10 to S16 using epoxy resin emulsifiers S2 to S8

[0049] The reaction steps are the same as in Example 9. The only difference is that the epoxy resin emulsifiers S2 to S8 synthesized as described above are used to prepare the waterborne epoxy resin compositions S10 to S16.

[0050] Comparative Example 2: Preparation of waterborne epoxy resin composition C2 using C1

[0051] The reaction steps are the same as in Example 9. The only difference is that the epoxy resin emulsifier C1 synthesized as described in Comparative Example 1 is used to prepare the waterborne epoxy resin compound C2.

[0052] The formulations and test results of the waterborne epoxy resin compositions of Examples 9 to 16 and Comparative Example 2 are summarized in Table 2 below.

[0053] Table 2 Example 9 10 11 12 13 Product Number S9 S10 S11 S12 S13 Emulsifier number S1 S2 S3 S4 S5 Weight (g) of S1-S8, C1 15 15 15 15 15 NPES902 (g) 40 40 40 40 40 Butanone (g) 10 10 10 10 10 Deionized water (g) 45 45 45 45 45 Solid content (%) 55 55 55 55 55 Emulsification test Can Can Can Can Can Adhesion test 5B 5B 5B 5B 5B Particle size (D50) (nm) 489 323 385 323 800

[0054] Table 2 (continued) Example 14 15 16 Comparative Example 2 Product Number S14 S15 S16 C2 Emulsifier number S6 S7 S8 C1 Weight (g) of S1-S8, C1 15 15 15 15 NPES902 (g) 40 40 40 40 Butanone (g) 10 10 10 10 Deionized water (g) 45 45 45 45 Solid content (%) 55 55 55 55 Emulsification test Can Can Can fail Adhesion test 5B 5B 5B No data Particle size (D50) (nm) 339 345 339 No data

[0055] The emulsification test in Table 2 is used to observe whether the waterborne epoxy resin composition containing the waterborne epoxy resin emulsifier and epoxy resin can be uniformly dissolved in water, without visual separation, and can be stably stored for more than 30 days. From the emulsification test results in Table 2, it can be observed that Examples 9 to 16 are all "acceptable," except for Comparative Example 2, which failed. Furthermore, according to the particle size analysis experiment, except for Example 13, the D50 particle size of Examples 9 to 16 is all below 500 nm. Generally speaking, the smaller the particle size, the better the stability of the waterborne epoxy resin composition.

[0056] The adhesion test in Table 2 was performed on coating compositions S9 to S16 and C2. The adhesion test was performed according to ASTM-D3359. The test method is as follows: a grid pattern with 6 or 11 cuts is cut in each direction on the film on the substrate, and pressure-sensitive tape is applied to the grid. After the pressure-sensitive tape is removed, the adhesion is evaluated by comparison. The test results can be divided into 6 levels: 5B (the cut edges are completely smooth; no squares are separated); 4B (small patches of coating peel off at the intersections of the scribing lines, but the affected area is less than 5%); 3B (small patches of coating peel off at the edges and intersections of the scribing lines, affecting an area of ​​5% to 15%); 2B (small patches of coating peel off at the edges and inside of the square grids, affecting an area of ​​15% to 35%); 1B (the coating peels off in strips along the edges of the scribing lines, and the entire square grid also shows signs of peeling off, affecting an area of ​​35% to 65%); and 0B (the phenomenon of peeling or detachment is worse than level 1B).

[0057] As shown in Table 2, in the adhesion test according to ASTM-D3359, the edges of each cut in Examples 9 to 16 were completely smooth. No square grids separated. Comparative Example 2 was not subjected to an adhesion test because it failed the water test.

[0058] The waterborne epoxy resin emulsifier of the present invention can use recycled PET as raw material, introduce a benzene ring structure into a nonionic hydrophilic structure for reaction, and graft epoxy resin to obtain a reactive epoxy resin emulsifier. Introducing a benzene ring structure increases the compatibility of the epoxy resin and retains epoxy groups, allowing it to react with a hardener for curing, thus avoiding concerns about the emulsifier becoming free after curing. In contrast, most non-reactive emulsifiers in the prior art are designed to be obtained by reacting fatty alcohols with acid anhydrides, resulting in a structure without benzene rings; or they have an amine structure, which is significantly different from the structure of the waterborne epoxy resin emulsifier of the present invention. Furthermore, most reactive emulsifiers in the prior art involve a direct reaction between polyethylene glycol and epoxy resin, unlike the grafting of acid anhydrides followed by reaction with epoxy resin in the present invention.

[0059] As shown in Table 2, compared to Comparative Example 1, the waterborne epoxy resin emulsifiers of Examples 1 to 8 of the present invention can emulsify bisphenol A type epoxy resins with medium to high epoxy equivalent (EEW=650) to form the waterborne epoxy resin compositions of Examples 9 to 16. Compared to Comparative Example 2, the waterborne epoxy resin compositions of Examples 9 to 16 exhibit good coating storage stability and mechanical properties after curing under high solids content (>50wt%) conditions.

[0060] The present invention has been disclosed above with reference to preferred embodiments. However, those skilled in the art should understand that these embodiments are only used to describe the present invention and should not be construed as limiting the scope of the present invention. It should be noted that all variations and substitutions equivalent to these embodiments should be included within the scope of the present invention. Therefore, the scope of protection of the present invention shall be determined by the claims.

Claims

1. A waterborne epoxy resin emulsifier, the molecular structure comprising: a structure derived from a first compound; and a structure derived from an epoxy resin, wherein, The molecular structure of the first compound includes a benzene ring and a dicarboxyl group, wherein the benzene ring is derived from a diester containing a benzene ring structure, and the dicarboxyl group is derived from an anhydride compound that can form a dicarboxyl group. The molecular structure of the epoxy resin includes two or more epoxy groups. The waterborne epoxy resin emulsifier is prepared by reacting the first compound with the epoxy resin. The first compound is prepared by esterifying a diester containing a benzene ring structure with polyethylene glycol, and then reacting it with an anhydride compound that can form a dicarboxyl group.

2. The waterborne epoxy resin emulsifier as described in claim 1, having a structure as shown in formula (I), formula (II), or formula (III): In formula (I), formula (II), formula (III), in formulas (I) to (III), R represents an alkyl or sulfonyl group having 1 to 3 carbon atoms; R' represents a benzene ring structure containing 0-4 alkyl groups; m and n represent the number of repeating units, wherein... The m-series ranges from 1 to 5; and the n-series ranges from 13 to 70.

3. The waterborne epoxy resin emulsifier as described in claim 1, wherein, The diester containing the benzene ring structure is selected from the group consisting of dimethyl terephthalate, diethylene terephthalate and polyethylene terephthalate.

4. The waterborne epoxy resin emulsifier as described in claim 3, wherein, The diester containing the benzene ring structure is recycled polyethylene terephthalate.

5. The waterborne epoxy resin emulsifier as described in claim 1, wherein, The number average molecular weight of this polyethylene glycol is between 600 and 3000.

6. The waterborne epoxy resin emulsifier as described in claim 1, wherein, The anhydride compounds that can form dicarboxyl groups are selected from the group consisting of succinic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, and phthalic anhydride.

7. The waterborne epoxy resin emulsifier as described in claim 6, wherein, The anhydride compound that can form a dicarboxyl group is hexahydrophthalic anhydride.

8. An aqueous epoxy resin composition comprising: 5 to 20 parts by weight of an aqueous epoxy resin emulsifier as described in any one of claims 1 to 7; 30 to 50 parts by weight of an epoxy resin, wherein the epoxy resin has a molecular structure comprising two or more epoxy groups; and 45 to 55 parts by weight of deionized water.

9. The waterborne epoxy resin composition as described in claim 8, wherein, The D50 particle size of this waterborne epoxy resin composition is less than 500 nm.