Preparation method and application of ADH / E-44 epoxy resin modified acrylate emulsion

Abstract

The invention relates to the technical field of water-based paint, in particular to a preparation method for double-modified acrylate emulsion through adipic acid dihydrazide and E-44 epoxy resin and application of the emulsion in paint, and is characterized in that firstly, the E-44 epoxy resin is used for modifying the acrylate emulsion; e-44 epoxy resin modified acrylate emulsion is obtained, on the basis, adipic acid dihydrazide and diacetone acrylamide serving as curing agents are introduced into a synthesis system, and multiple crosslinking occurs in the emulsion curing process. The problems of low hardness, poor adhesive force, weak water resistance, low glass transition temperature and the like of a traditional waterborne acrylate emulsion can be solved, on the premise of avoiding high-epoxy-content implosion, the crosslinking density can be remarkably improved, environmental protection and performance balance are achieved, and therefore the requirements of metal protection / building coatings for high hardness and high weather resistance are met.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of water-based coatings, in particular to a method for modifying an acrylate emulsion by adipic acid dihydrazide (ADH) and E-44 epoxy resin, and application of the emulsion in coatings. BACKGROUND

[0002] Traditional solvent-based coatings use organic solvents, resulting in excessive volatile organic compounds, which not only wastes resources, but also causes great harm to human health and the environment. With increasing environmental awareness, low-VOC (volatile organic compound) or VOC-free environmentally friendly coatings are gaining more and more attention. Water-based coatings are one of the research hotspots of green and environmentally friendly coatings in recent years, and water-based acrylic emulsion is a commonly used coating.

[0003] Acrylic coatings are a kind of high molecular weight polymers formed by free radical polymerization of acrylate or methacrylate, which have excellent weather resistance, acid and alkali resistance, and chemical resistance, but also have the disadvantages of low hardness, poor adhesion, and poor water resistance. In view of the characteristics of acrylate emulsion, chemical modification methods are often used to overcome the shortcomings of water-based acrylic resin, and epoxy modification is one of the modification methods.

[0004] Epoxy resin (EP) refers to a high molecular polymer containing two or more epoxy groups in the molecule, which has the characteristics of small density, good corrosion resistance, excellent electrical insulation, and excellent mechanical properties, and is widely used in aerospace, nuclear energy, national defense, and other fields. E-44 epoxy resin has excellent performance due to its high activity of aliphatic hydroxyl and ether bond functional groups, so E-44 epoxy resin is one of the commonly used epoxy resins. In the literature Appl. Polym. Sci., 2022, 139, 51441, a stable epoxy-acrylate composite emulsion was successfully prepared by emulsion polymerization of modified epoxy-acrylic acid (EPAC) oligomer and acrylate monomer. In the literature Coatings, 2021, 11, 1422, a new synthesis method was used to prepare a water-based epoxy-styrene-acrylate composite emulsion, which has good stability and corrosion resistance. In the literature Polym. Mater. Sci. Eng., 2014, 30, 1, amine was also used to open the ring of epoxy-acrylic acid copolymer to prepare a WPU dispersion, which improves the mechanical properties, weather resistance, and other properties of the film.

[0005] The existing traditional acrylate emulsion has defects such as low hardness (≤2H), poor water resistance (contact angle ≤70°), insufficient adhesion (≥2 levels), and low glass transition temperature (Tg). Although single epoxy resin modification can improve some performance, the crosslinking density is insufficient, and high addition amount (>15wt%) can easily lead to explosive polymerization. The epoxy-acrylate composite emulsion prepared in the document Appl. Polym. Sci., 2022, 139, 51441 and the epoxy-styrene-acrylate emulsion prepared in the document Coatings, 2021, 11, 1422 improve stability, but do not solve the problem of balancing multiple crosslinking density and mechanical properties. The prior art does not disclose the specific ratio of ADH curing agent and E-44 epoxy resin for modifying acrylate and the multiple crosslinking mechanism. SUMMARY

[0006] The present application aims to overcome the shortcomings of the prior art and provide an ADH / E-44 epoxy resin modified acrylate emulsion that can overcome the problems of low hardness, poor adhesion, weak water resistance, and low glass transition temperature of traditional water-based acrylate emulsion, significantly improve the crosslinking density under the premise of avoiding high epoxy content explosive polymerization, achieve environmental protection and performance balance, and meet the demand for high hardness and strong weather resistance of metal protection / architectural coatings.

[0007] To solve the above technical problems, the present application is implemented as follows:

[0008] A preparation method of an ADH / E-44 epoxy resin modified acrylate emulsion, comprising the following components by total mass percentage:

[0009] E-44 epoxy resin: 5-15wt%;

[0010] Methyl acrylate (MAA): 1.5-7.5wt%;

[0011] Adipic acid dihydrazide (ADH): 2-6wt%;

[0012] Acrylate monomer: 70-85wt%;

[0013] Initiator: 0.1-0.6wt%.

[0014] Further, the acrylate monomer includes methyl methacrylate (MMA), styrene (St), and butyl acrylate (BA) in a mass ratio of 0.5-1:1-1.5:1-1.5.

[0015] Further, the E-44 epoxy resin is used in an amount of 12-15wt%; the methyl acrylate (MAA) is used in an amount of 5-7.5wt%; and the adipic acid dihydrazide (ADH) is used in an amount of 5-6wt%.

[0016] Further, the initiator is a redox initiation system, comprising tert-butyl hydroperoxide (TBHP), sodium formaldehyde sulfoxylate (SFS), ferrous sulfate (FeS04), and the mass ratio is 1.8-2.2:0.9-1.1:0.01-0.03, respectively.

[0017] The preparation method of the ADH / E-44 epoxy resin modified acrylate emulsion comprises the following steps:

[0018] (a) Preparation of pre-emulsion: add acrylate monomers (MMA, St, BA), E-44 epoxy resin, and methacrylic acid (MAA) into a container, stir at 400±50 rpm for 15 min until completely dissolved; add emulsifier sodium dodecyl sulfate (SDS) and water, continue to stir for 30 min to obtain a first emulsion;

[0019] (b) Ultrasonic treatment: ultrasonically treat the first emulsion in step a at a temperature ≤55℃ for 15 min to obtain a second emulsion;

[0020] (c) Initiation of polymerization: transfer the second emulsion to a four-necked flask and heat to 65-67℃; first, add an aqueous solution containing sodium formaldehyde sulfoxylate (SFS) and ferrous sulfate (FeSO4); after 1 h, start adding an aqueous solution of tert-butyl hydroperoxide (TBHP);

[0021] (d) Post-treatment: after the addition is complete, incubate for 1-2 h, and cool to room temperature; adjust the pH to 7-8 with ammonia water, filter through a 200-mesh filter screen to obtain a modified emulsion;

[0022] (e) Multiple crosslinking: prepare adipic acid dihydrazide (ADH) into a 10wt% aqueous solution, and stir at room temperature to add to the filtered emulsion, and continue to stir for 30 min.

[0023] Further, the amount of the emulsifier SDS in step (a) is 0.8-1.2wt% of the total mass of the monomers; and the mass ratio of tert-butyl hydroperoxide (TBHP), sodium formaldehyde sulfoxylate (SFS), and ferrous sulfate (FeSO4) in the initiator in step (c) is 1.8-2.2:0.9-1.1:0.01-0.03, respectively.

[0024] The coating film formed after curing of the ADH / E-44 epoxy resin modified acrylate emulsion has the following properties: when the E-44 epoxy resin is ≥10wt% and the adipic acid dihydrazide is ≥4wt%, the pencil hardness is ≥4H; the adhesion grade is ≤1 grade; the glass transition temperature is ≥55℃; the contact angle is ≥85°; and the 24h water absorption rate is ≤3wt%.

[0025] Furthermore, after curing at 120°C for 30 min, the crosslinking network comprises: an open-ring graft structure of E-44 epoxy resin and acrylate monomer; amide bond crosslinking formed by adipic acid dihydrazide and epoxy groups; and hydrazide bond crosslinking formed by adipic acid dihydrazide and carboxyl groups of methacrylic acid.

[0026] The above-mentioned ADH / E-44 epoxy resin modified acrylate emulsion is used in coatings, wherein the coating is a metal protective coating or a building exterior wall coating; after being applied to the substrate, it is cured at 100-120℃ for 20-40 minutes.

[0027] A coating composition comprising the above-mentioned modified acrylic emulsion; pigment filler: 10-30 wt%; leveling agent: 0.5-2 wt%. The leveling agent may be selected from silicone-based or acrylic-based agents. Specifically, 25 wt% rutile TiO2 and 1.5 wt% acrylic leveling agent are used.

[0028] Synthesis mechanism of ADH / E-44 epoxy resin modified acrylate emulsion:

[0029] Epoxy resin (EP) refers to a polymeric prepolymer containing two or more epoxy groups in its molecular structure. Epoxy resin-modified acrylates not only possess good elasticity and flexibility, but also exhibit mechanical properties and water resistance due to the three-dimensional cross-linked network formed by epoxy grafting. This invention, based on the synthesis of acrylate emulsions, introduces E-44 epoxy resin to synthesize E-44 epoxy resin-modified acrylate emulsions. The reaction mechanism for the synthesis of E-44 epoxy resin-modified acrylate emulsions is as follows:

[0030]

[0031] Based on this, by introducing the curing agent ADH into the synthesis system, multiple crosslinking occurs during the emulsion curing process, increasing the emulsion crosslinking density and further improving the emulsion performance. The mechanism of action is as follows:

[0032]

[0033] This invention aims to overcome the problems of low hardness, poor adhesion, weak water resistance, and low glass transition temperature of traditional waterborne acrylic emulsions. A graft copolymerization method is employed to graft E-44 epoxy resin onto the waterborne acrylic emulsion, thereby modifying the emulsion. Based on this, by introducing ADH into the synthesis system, multiple crosslinking reactions occur during the curing process, increasing the crosslinking density of the emulsion, while avoiding explosive polymerization at high epoxy content. The synthesized samples were characterized and their performance tested. This modified emulsion combines the film-forming properties of acrylic esters, the corrosion resistance of epoxy, and the stability brought by ADH crosslinking, resulting in significant improvements in the hardness, adhesion, weather resistance, chemical resistance, and water resistance of the coating film.

[0034] When the content of E-44 epoxy resin is 15wt%, MAA is 7.5wt%, and ADH is 6wt%, the resulting ADH / E-44 epoxy resin modified waterborne acrylic resin emulsion exhibits improved hardness and water resistance. The cured coating has a water absorption rate of 2.1wt%, a contact angle that increases from 60° to 90°, a pencil hardness of 5H, zero adhesion, and a glass transition temperature that increases from 39.50℃ to 61.23℃. The modified acrylic emulsion demonstrates improved performance to varying degrees and shows promising application prospects in the coatings industry. Attached Figure Description

[0035] The present invention will now be described in detail through specific embodiments. These embodiments are provided to enable a more thorough understanding of the invention and to fully convey the scope of the invention to those skilled in the art. As used throughout the specification and claims, the terms "comprising" or "including" are open-ended and are interpreted as "comprising but not limited to". The following description is a preferred embodiment for carrying out the invention; however, this description is intended to illustrate the general principles of the specification and is not intended to limit the scope of the invention. The scope of protection of the invention is determined by the appended claims. Unless otherwise specified, all reagents and materials used in the present invention are commercially available.

[0036] Figure 1 The particle size distribution curves of the samples with E-44 epoxy resin added at (A) 0 wt%, (B) 5 wt%, (C) 10 wt%, and (D) 15 wt% are shown.

[0037] Figure 2 The particle size distribution curves are for samples with MAA additions of (A) 1.5 wt%, (B) 3.5 wt%, (C) 5.0 wt%, and (D) 7.5 wt%.

[0038] Figure 3The particle size distribution curves of the samples with ADH addition of (A) 2wt%, (B) 3wt%, (C) 4wt%, (D) 5wt%, and (E) 6wt% are shown.

[0039] Figure 4 The FTIR spectra of ADH (a), acrylate emulsion (b), E-44 epoxy resin acrylate emulsion (c), and ADH\E-44 epoxy resin modified acrylate emulsion (d) of the present invention are shown.

[0040] Figure 5 The DSC curves (A) and TG curves (B) of the acrylic latex film, the E-44 epoxy resin modified acrylic latex film, and the ADH / E-44 epoxy resin modified acrylic latex film of the present invention are shown.

[0041] Figure 6 SEM images of the acrylic latex film (A), the E-44 epoxy resin modified acrylic latex film (B), and the ADH / E-44 epoxy resin modified acrylic latex film (C) of the present invention.

[0042] Figure 7 The results of water absorption and chemical resistance tests are for the acrylic latex film, the E-44 epoxy resin modified acrylic latex film, and the ADH / E-44 epoxy resin modified acrylic latex film of this invention.

[0043] Figure 8 These are contact angle images of the acrylate coating (A), the E-44 epoxy resin modified acrylate coating (B), and the ADH / E-44 epoxy resin modified acrylate coating (C) of the present invention. Detailed Implementation

[0044] To enable those skilled in the art to better understand the technical solutions of this invention, the invention will be further described below with reference to specific embodiments. Obviously, the described embodiments are merely a part of the embodiments of this invention, and not all of them. These embodiments should be understood as being used only to illustrate the invention and not to limit the scope of protection of the invention. After reading the contents of this invention, all other embodiments obtained by making various modifications or alterations to the invention based on the technical solutions and embodiments of this invention also fall within the scope of protection of the claims of this invention.

[0045] The methyl methacrylate (MAA, AR), styrene (St, AR), butyl acrylate (BA, AR), and methacrylic acid (MAA, AR) used in this invention were purchased from Anhui Zesheng Technology Co., Ltd.; E-44 epoxy resin (AR) was purchased from Nantong Xingchen Synthetic Materials Co., Ltd.; sodium dodecyl sulfate (SDS, AR), tert-butyl hydroperoxide (TBHP, AR), and formaldehyde-synthesized sodium bisulfate (SFS, AR) were purchased from Shanghai Bide Pharmaceutical Technology Co., Ltd.; adipic acid dihydrazide (ADH, AR) and diacetone acrylamide (DAAM, AR) were purchased from Beijing Innocare Technology Co., Ltd.; and FeSO4 (AR) was purchased from Shandong Keji Biochemical Co., Ltd. All chemical reagents were directly usable in the experiment without any purification.

[0046] Example:

[0047] 1. Raw materials for E-44 epoxy resin modified acrylate emulsion

[0048] MAA and St were selected as hard monomers to improve the resin's hardness, weather resistance, water resistance, and adhesion; BA was selected as a soft monomer to enhance the resin's flexibility and film formation; MAA and E-44 epoxy resin were selected as functional monomers. MAA enhances the resin's chemical resistance, flexibility, and cohesive strength, while E-44 epoxy resin improves the resin's hardness, gloss, weather resistance, and adhesion, increases crosslinking density, and enhances the overall performance of the emulsion. A pre-emulsified semi-continuous emulsion polymerization synthesis method (CN202210863339.9) was used to prepare an aqueous acrylate emulsion in a 500ml four-necked flask equipped with a mechanical stirrer, thermometer, spherical condenser, and constant-pressure dropping funnel. The basic components of the synthesized aqueous polyacrylate emulsion are shown in Table 1.

[0049] Table 1. Basic Components of Acrylic Emulsions

[0050]

[0051] 2. Preparation of E-44 epoxy resin modified acrylate emulsion

[0052] Add each monomer from Table 1 to a 500 ml round-bottom flask and stir at 400 rpm for 15 min until the monomer is completely dissolved. Add emulsifier (SDS) and water, and continue stirring at 400 rpm for 30 min to obtain the first emulsion. Sonicate the first emulsion for 15 min (temperature not exceeding 55℃) to obtain the second emulsion. Heat the second emulsion to 65–67℃, add the pre-prepared FeSO4 solution, and then begin adding SFS solution dropwise. After 1 h of dropwise addition, begin adding TBHP solution dropwise. After the dropwise addition is complete, maintain the reaction temperature for 1–2 h, cool to room temperature, adjust the pH to 7–8 using ammonia, filter through a 200-mesh filter, collect the emulsion, and record it as CO.

[0053] Based on this, different mass fractions of E-44 epoxy resin were added during the pre-emulsification preparation stage, and E-44 epoxy resin modified acrylate emulsion was synthesized using the same method, denoted as Cn (n represents the mass fraction of E-44 epoxy resin added to the synthesis system).

[0054] 3. Coating preparation

[0055] The coating was prepared using an AFA-V type automatic coating machine manufactured by Shanghai Tianchen Modern Environmental Protection Technology Co., Ltd. The prepared sample was uniformly coated onto the surface of a dry and clean tinplate substrate using a 1.5 μm coating strip, resulting in a coating thickness of 1.5 μm. The tinplate substrate coated with the emulsion was cured at 120℃ for 30 min to obtain the coating.

[0056] 4. Preparation of latex film

[0057] Take a small amount of emulsion with a dropper and drop it into a mold made of polytetrafluoroethylene. Let it stand at room temperature for 24 hours until the moisture evaporates. Then, place it in a forced-air drying oven and heat-treat it in an air atmosphere at 100°C for 10 hours to obtain a latex film.

[0058] 5. Characterization

[0059] Fourier transform infrared (FTIR) spectroscopy was performed using an FTIR-660+610 infrared microspectroscopy instrument manufactured by Agilent Technologies, Inc., USA. Scanning electron microscopy (SEM) images were obtained using a SU8010 field emission scanning electron microscope, manufactured by Japan. Glass transition temperature (Tg) was measured using a Q20 differential scanning calorimeter manufactured by TA Instruments, Inc., USA. Zeta potential and particle size of the emulsion were determined using a Nano ZS90 nanolaser particle size analyzer manufactured by Malvern Instruments Ltd., UK. Thermogravimetric (TG) data were measured using a TGA thermogravimetric analyzer manufactured by Mettler Toledo, Switzerland. Contact angle was measured using a DSA100 water contact angle meter manufactured by Kruss, Germany.

[0060] 6. Performance Testing

[0061] Water resistance test

[0062] The water resistance of the coating was determined according to GB / T1733-93. Two-thirds of the tinplate coated with polyacrylate resin was immersed in deionized water at room temperature for 24 hours. After immersion, the tinplate was removed, the water was absorbed with filter paper, and the presence of phenomena such as loss of gloss, whitening, blistering, wrinkling, peeling, and rusting of the coating was recorded by visual inspection, and its water resistance was evaluated.

[0063] Water absorption test

[0064] Water absorption rate is also used to evaluate the water resistance of latex films. The latex film is cut into squares (2cm × 2cm), weighed (m0), soaked in deionized water at room temperature for 24 hours, and the surface moisture is absorbed with filter paper. The film is then weighed again (m1). This measurement is repeated three times, and the average value is taken. The water absorption rate is calculated using the following formula:

[0065]

[0066] Contact angle test

[0067] The water contact angle of the coating was measured using a DSA100 water contact angle meter at room temperature via static droplet measurement. The volume of the test water droplet used in the experiment was 3 μl. The contact angle was taken as the average of five measurements taken at different locations on the same coating.

[0068] Crosslinking degree test

[0069] Weigh the sample and record the weight as m0. Place the sample in a stainless steel mesh bag, suspend the sample package in the reaction flask, and reflux at 140℃ for 5 hours using xylene as solvent. After cooling, remove the sample and dry it in air at 140℃ for 3 hours. After cooling, weigh the sample and record the weight as ml. Calculate the degree of crosslinking of the sample according to the crosslinking degree test formula. The formula for calculating the degree of crosslinking is:

[0070]

[0071] Coating hardness test

[0072] Referring to GB / T6739-2006, the hardness of CMA-modified acrylic emulsion coatings was tested using Zhonghua brand pencils from the same batch. The pencil grades ranged from 6B to 6H, meaning a 6B grade indicated a softer coating and a 6H grade indicated the highest hardness. During testing, the pencil was held at a 45° angle to the coating, and the surface was observed for scratches, abrasions, or chipping, as these defects could be caused by the pencil lead. Each sample was tested three times until no pencil-induced damage was observed on the coating surface, and the coating hardness grade was recorded.

[0073] Coating adhesion test

[0074] The adhesion of the coating was determined according to GB / T9286-98. A cross-cut adhesion tester was used to cut the coating in a right-angled grid pattern, penetrating to the substrate to assess the adhesion level. The tester was applied perpendicularly to the coating surface, first making several parallel cuts 1mm apart, parallel to the coating, ensuring the cuts made contact with the tinplate. Then, the coating was cut in the opposite direction to create a standardized right-angled grid. The test area was gently cleaned with a suitable soft brush, and then the entire grid area was covered with adhesion testing tape. The tape was gently pressed to ensure full contact between the tape and the coating. After five minutes, the tape was quickly removed, and the area of ​​coating damage on the tinplate was immediately observed using a magnifying glass. The adhesion level was graded from 0 to 5, with grade 0 being the highest and grade 5 the lowest.

[0075] 7. Effect of E-44 epoxy resin dosage on synthesis results

[0076] In this synthesis process, the dosage of E-44 epoxy resin was first investigated. Table 2 shows that a relatively stable emulsion (Zeta potential between 30 and 60 mV) could be synthesized when the E-44 epoxy resin dosage was between 0 wt% and 15 wt%. Within this range, as the E-44 epoxy resin content increased, the coating adhesion improved from grade 2 to grade 0, and the hardness increased from 2H to 4H. When the E-44 epoxy resin dosage was 20 wt%, explosive polymerization occurred. Particle size analysis was performed on samples within this range, and the particle size distribution is shown in the figure. Figure 1 As shown in the figures, when the E-44 epoxy resin content is 0 wt% and 10 wt% (Figures A and C), two peaks appear, indicating a relatively broad particle size distribution. When the E-44 epoxy resin content is 5 wt% and 15 wt% (Figures B and D), the particle size distribution is more concentrated. When the E-44 epoxy resin content is low, the synthesized product has a smaller particle size, and the emulsion stability is better. As the E-44 content increases, the emulsion particle size may increase, and beyond a certain amount, the emulsion stability may decrease.

[0077] Table 2E-44 Effect of epoxy resin dosage on emulsion properties

[0078]

[0079] 8. Effect of MAA dosage on synthesis results

[0080] The effect of the amount of MAA on the synthesized product was investigated during the synthesis process. The synthesis results are shown in Table 3 and... Figure 2As shown in the table, a relatively stable emulsion can be obtained within the range of 1.5wt% to 7wt% MAA dosage. Within this range, the emulsion adhesion and hardness remain unchanged with increasing MAA dosage. Within the range of 1.5wt% to 5wt% MAA dosage, the average particle size does not differ significantly (Figures A, B, and C). When the MAA dosage increases to 7.5wt% (Figure D), the average particle size increases to 222.1 nm. When the MAA dosage increases to 9wt%, the synthesized product fails to form an emulsion, exhibiting stratification and demulsification. Therefore, a MAA dosage of 1.5wt% to 7.5wt% and a Zeta potential within the range of 30 to 60 mV indicate that the emulsion has good stability. The particle size distribution curves for different MAA contents are shown below. Figure 2 As shown:

[0081] Table 3 Effect of MAA dosage on emulsion properties

[0082]

[0083] 9. Effect of ADH dosage on synthesis results

[0084] The dosage of ADH was also investigated in this system, and the synthesis results are shown in Table 4 and... Figure 3 As shown in the table, when the ADH dosage is in the range of 2wt% to 6wt%, a milky white emulsion with good flowability can be obtained, and the average particle size and adhesion remain basically unchanged. With increasing ADH dosage, the hardness gradually increases from 3H to 5H. When the ADH dosage is in the range of 2wt% to 5wt%, the Zeta potential is in the range of 30 to 40 mV, indicating that the emulsion has good stability. When the ADH dosage is 6wt%, the potential is 57.83 mV, and the emulsion stability decreases. When the ADH dosage is 7wt%, the synthesized product is viscous and no emulsion is formed.

[0085] Table 4 Effect of ADH dosage on emulsion properties

[0086]

[0087]

[0088] 10. Crosslinking degree analysis of acrylate emulsions before and after ADH / E-44 epoxy resin modification

[0089] Based on the above investigation of the component dosages in a series of synthesis processes, an emulsion with good performance was finally synthesized under the conditions of 15wt% E-44 epoxy resin, 7.5wt% MAA, and 6wt% ADH. Latex films were prepared from the unmodified acrylate emulsion, the E-44 epoxy resin-modified acrylate emulsion, and the ADH / E-44 epoxy resin-modified acrylate emulsion (method referred to section 4. Preparation of Latex Films), and their characterization and testing were performed. First, the crosslinking degree of these three samples was tested, and the results are shown in Table 5. As can be seen from the table, the crosslinking degree of the E-44 epoxy resin-modified acrylate emulsion was significantly increased, while the crosslinking degree of the ADH / E-44 epoxy resin-modified acrylate emulsion was further increased compared to the E-44 epoxy resin-modified acrylate emulsion.

[0090] Table 5. Degree of crosslinking of latex films modified with acrylate C0, E-44 epoxy resin and ADH / E-44 epoxy resin (MAA: 7.5 wt% / ADH: 6 wt%)

[0091] 10. Infrared analysis of acrylate emulsions before and after ADH / E-44 epoxy resin modification

[0092] FTIR characterization was performed on ADH, acrylate emulsion, E-44 epoxy-modified acrylate emulsion, and ADH / E-44 epoxy resin-modified acrylate emulsion. Figure 4 It can be seen that all four samples exhibited stretching vibration absorption peaks of -CH3 and -CH2 at 2950 cm⁻¹, 2930 cm⁻¹, and 2870 cm⁻¹, and a stretching vibration absorption peak of C=O at 1731 cm⁻¹. The acrylate emulsion, E-44 epoxy-modified acrylate emulsion, and ADH\E-44 epoxy resin-modified acrylate emulsion exhibited characteristic absorption peaks of NH at 3451 cm⁻¹ and 1389 cm⁻¹. When E-44 epoxy resin was introduced, the absorption peak at 1040 cm⁻¹ was the stretching vibration absorption peak of COC, which is due to the ring-opening reaction of the epoxy groups. The ADH\E-44 epoxy resin-modified acrylate emulsion sample only showed an absorption peak at 1534 cm⁻¹, consistent with the FTIR spectrum of ADH, but other characteristic absorption peaks of ADH were not observed. This may be because all ADH in the synthetic system participated in the cross-linking reaction.

[0093] 11. DSC and TG analysis of acrylate latex films before and after ADH / E-44 epoxy resin modification

[0094] Figure 5 These are the DSC curves (A) and TG curves (B) for these three samples. Figure 5(A) It is known that the glass transition temperature of the unmodified acrylate emulsion is 39.50℃. After modification with E-44 epoxy resin, the glass transition temperature increases to 45.15℃. This is because the epoxy in the E-44 modified polyacrylate exists in the main chain form. The hydroxyl, epoxy groups, and ether bonds in the epoxy can not only undergo ring-opening reactions with acrylate monomers, but also improve the cohesive force between the entire resin molecules. Based on the E-44 epoxy resin modification, the addition of curing agent ADH to undergo a crosslinking reaction can achieve a glass transition temperature of up to 61.23℃. Before curing, the molecular chains have a certain degree of freedom of movement. After the epoxy resin and curing agent undergo a crosslinking and curing reaction, the molecular chains are connected by chemical bonds to form a three-dimensional network structure. This crosslinking network greatly restricts the movement of the molecular chains, making it more difficult for the molecular chains to move and relax at higher temperatures. Therefore, a higher temperature is required for the molecular chains to transition from the glassy state to the elastic state, i.e., the glass transition temperature increases. However, due to... Figure 5 (B) It can be seen that the thermal decomposition temperature of the unmodified acrylate emulsion and the acrylate emulsion modified with E-44 epoxy resin did not change significantly, but after adding 6wt% ADH, the sample underwent slow decomposition at 210℃~380℃.

[0095] 12. SEM analysis of acrylate latex films before and after ADH / E-44 epoxy resin modification

[0096] Figure 6 These are SEM images of three samples. As shown in the images, the cross-section of the unmodified acrylate latex film is relatively smooth, while the cross-section of the E-44 epoxy-modified acrylate latex film becomes rougher, exhibiting an uneven surface. This is related to the presence of epoxy groups in the structure of epoxy resin, which can undergo ring-opening reactions with acrylate monomers, increasing the cross-linking density. The cross-section roughness of the ADH / E-44 epoxy-modified acrylate latex film is relatively increased, and it exhibits texture. This is because the epoxy groups undergo cross-linking under the action of the curing agent ADH, increasing the cohesive force between resin molecules and further increasing the cross-linking density, generating a complex interpenetrating network structure with an epoxy resin cross-linked network as the backbone and methacrylic resin penetrating through it.

[0097] 13. Analysis of water absorption and chemical resistance of ADH / E-44 epoxy resin modified acrylic latex film

[0098] The synthesized sample underwent performance testing, and the test results are as follows: Figure 7As shown in the figure, the water resistance and chemical resistance of the E-44 epoxy resin modified acrylate latex film and the ADH / E-44 epoxy resin modified acrylate latex film are significantly improved. Especially in terms of water resistance, this is consistent with their contact angle data (shown in Table 6). The contact angle data shows that the unmodified acrylate coating has a contact angle of 64.4°. After adding E-44 epoxy modification, the contact angle increases to 74.9°. Furthermore, with the addition of ADH curing agent for composite modification, the contact angle reaches 91.9°. The difference in water resistance and chemical resistance among these three latex films can be attributed to the cross-linking reaction between the epoxy groups in the added E-44 epoxy resin and the acrylate, forming a tighter three-dimensional network structure, reducing the gaps between molecules, and making it difficult for water molecules to penetrate. Based on epoxy modification, the curing agent ADH undergoes composite modification. ADH contains multiple hydrazine groups (-NH-NH2), which can react with the epoxy groups of epoxy resin and the carboxyl or hydroxyl groups in acrylate to form a denser cross-linked network, reducing intermolecular gaps and hindering water molecule penetration. In the composite system, polar groups (such as hydroxyl groups) are partially converted into nonpolar or weakly polar structures (such as amide bonds) through cross-linking reactions, reducing the latex film's affinity for water and further reducing water absorption. The formed dense cross-linked structure makes it difficult for chemicals such as acids, alkalis, and solvents to diffuse into the latex film, reducing damage to the molecular chains. The amide bonds and ether bonds formed by the reaction of ADH with epoxy and acrylate have strong chemical stability and can resist the erosion of chemical substances; at the same time, the chemical resistance of epoxy itself and the cross-linking enhancement effect of ADH work synergistically to improve the overall corrosion resistance of the latex film.

[0099] Table 6. Contact angles of emulsion coatings of acrylate C15 modified with acrylate C0, E-44 epoxy resin and ADH / E-44 epoxy resin modified acrylate C15 (MAA: 7.5 wt% / ADH: 6 wt%)

[0100]

[0101] The content of this invention is not limited to the embodiments listed. Any equivalent modifications made by those skilled in the art to the technical solutions of this invention by reading this specification are covered by the claims of this invention.

Claims

1. An ADH / E-44 epoxy resin-modified acrylate emulsion, characterized by, By total mass percentage, comprising the following components: E-44 epoxy resin: 5-15wt%; Methyl methacrylate: 1.5-7.5wt%; Adipic acid dihydrazide: 2-6wt%; Acrylate monomer: 70-85wt%; Initiator: 0.1-0.6wt%.

2. The ADH / E-44 epoxy resin-modified acrylate emulsion according to claim 1, characterized in that: The acrylate monomer includes methyl methacrylate, styrene, butyl acrylate, and their mass ratio is 0.5-1:1-1.5:1-1.5, respectively.

3. The ADH / E-44 epoxy resin-modified acrylate emulsion according to claim 2, characterized in that: The amount of E-44 epoxy resin is 12-15wt%; the amount of methyl methacrylate is 5-7.5wt%; the amount of adipic acid dihydrazide is 5-6wt%.

4. The ADH / E-44 epoxy resin-modified acrylate emulsion according to claim 2, characterized in that: The initiator is a redox initiation system, which includes t-butyl hydroperoxide, sodium formaldehyde sulfoxylate, and ferrous sulfate, and their mass ratio is 1.8-2.2:0.9-1.1:0.01-0.03, respectively.

5. The method for preparing the ADH / E-44 epoxy resin-modified acrylate emulsion according to any one of claims 1 to 4, characterized by, Including the following steps: (a) Preparation of pre-emulsion: add acrylate monomer, E-44 epoxy resin, and methyl methacrylate into a container, stir at 400±50 rpm for 15 min until completely dissolved; add emulsifier sodium dodecyl sulfate and water, continue stirring for 30 min to obtain a first emulsion; (b) Ultrasonic treatment: ultrasonically treat the first emulsion in step a at a temperature ≤55℃ for 15 min to obtain a second emulsion; (c) Initiation of polymerization: transfer the second emulsion to a four-necked flask and heat to 65-67℃; first add an aqueous solution containing sodium formaldehyde sulfoxylate and ferrous sulfate; after 1 h, start adding t-butyl hydroperoxide aqueous solution; (d) Post-treatment: after the addition is complete, incubate for 1-2 h, cool to room temperature; adjust the pH to 7-8 with ammonia water, filter through a 200 mesh filter screen to obtain a modified emulsion; (e) Multiple crosslinking: prepare a 10wt% aqueous solution of adipic acid dihydrazide and stir it into the filtered emulsion at room temperature, continue stirring for 30 min.

6. The method for preparing the ADH / E-44 epoxy resin modified acrylate emulsion according to claim 5, characterized in that: In step (a), the amount of emulsifier SDS is 0.8-1.2wt% of the total mass of monomers; in step (c), the mass ratio of t-butyl hydroperoxide, sodium formaldehyde sulfoxylate, and ferrous sulfate in the initiator is 1.8-2.2:0.9-1.1:0.01-0.03, respectively.

7. A coating film formed after curing of the ADH / E-44 epoxy resin-modified acrylate emulsion according to any one of claims 1 to 4, characterized by It has the following properties: when E-44 epoxy resin ≥10wt% and adipic acid dihydrazide ≥4wt%, the pencil hardness is ≥4H; the adhesion grade is ≤1 grade; the glass transition temperature is ≥55℃; the contact angle is ≥85°; the 24h water absorption rate is ≤3wt%.

8. The coated film according to claim 7, characterized by: After curing at 120℃ for 30 min, the crosslinked network contains: ring-opening graft structure of E-44 epoxy resin and acrylate monomer; amide bond crosslinking formed by adipic acid dihydrazide and epoxy group; hydrazine bond crosslinking formed by adipic acid dihydrazide and methyl methacrylate carboxyl group.

9. Use of the ADH / E-44 epoxy resin-modified acrylate emulsion according to any one of claims 1 to 4 in a coating, characterized in that: The coating is a metal protective coating or an architectural exterior wall coating; after being coated on a substrate, it is cured at 100-120℃ for 20-40 min.

10. A coating composition characterized in that, It contains the ADH / E-44 epoxy resin modified acrylate emulsion of any one of claims 1-4; pigment filler: 10-30wt%; leveling agent: 0.5-2wt%.

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