High-toughness ultra-low voc waterborne epoxy emulsion and preparation method thereof

Abstract

The application discloses a kind of high toughness ultra-low VOC water-based epoxy emulsion, comprising: epoxy resin: 40-60 parts;SBS: 5-10 parts;Styrene: 2-5 parts;Acrylate monomer: 2-5 parts;Initiator: 1.5-3 parts;Polymerization inhibitor: 0.01-0.1 parts;Emulsifier: 3-5 parts;Water: 40-60 parts.It is modified by SBS with hard segment and soft segment in molecular chain to epoxy resin, on the basis of improving toughness, ensure the mechanical strength and heat aging resistance of modified epoxy.The application also discloses its preparation method, and the styrene and acrylate monomer used as copolymer bridging agent, also as the solvent of SBS and epoxy resin under the protection of polymerization inhibitor in the dissolution stage, so that the temperature does not need to be too high when dissolving, melting, the viscosity is moderate when dispersing and emulsifying, monomer copolymerization into polymer after emulsification, so that VOC can be reduced to almost zero.

Description

Technical Field

[0001] This invention belongs to the coatings industry in the chemical field, and relates to an environmentally friendly waterborne epoxy emulsion, and more particularly to a method for preparing a waterborne epoxy emulsion with high toughness. Background Technology

[0002] Currently, in the coatings and chemical industry, high-end equipment often uses two-component epoxy coatings as anti-corrosion primers due to their excellent adhesion, resistance to various media, salt spray resistance, and good mechanical properties. The performance of the coating film is realized after the epoxy resin and curing agent in waterborne epoxy coatings react and crosslink. As the degree of crosslinking increases, the hardness of the coating film increases, but the toughness decreases accordingly. This is especially true after later application or after heat aging treatment, when the degree of crosslinking reaches a very high level, resulting in a significant reduction in toughness. Therefore, the application of ordinary waterborne epoxy emulsions is limited in applications requiring high coating toughness.

[0003] Currently, the main methods used in the industry to improve the toughness of epoxy resin are physical mixing with the addition of low molecular weight liquid toughening agents or chemical modification with resins containing toughening groups. For example, patent CN113817289A discloses a method to improve the toughness of epoxy resin by adding toughening agents such as polyethers, polythiols, and liquid elastomers. While this method improves the toughness of epoxy resin after curing to some extent, this method of adding toughening agents suffers from poor compatibility, poor mechanical properties, and poor aging performance. Patent CN110698810B discloses a method to obtain core-shell toughened composite nanoparticles by chemically modifying silicone rubber and epoxy resin. Finally, the toughness of the final epoxy composition is improved by adding these nano-toughening particles. Although the compatibility between the modified toughening particles and epoxy resin is improved, the mixing process requires acetone solvent, and subsequent solvent removal steps also have an environmental impact and are cumbersome. Furthermore, although waterborne epoxy coatings have lower VOCs than oil-based epoxy coatings, ordinary waterborne epoxy emulsions still contain a certain amount of solvent. This is because a certain amount of solvent is needed during the production of epoxy emulsions to dissolve and melt the epoxy resin under heating conditions, allowing it to undergo subsequent emulsification operations at an appropriate low viscosity. This makes it difficult to further reduce the VOCs of waterborne epoxy coatings. Patent CN110776605A discloses a low-VOC waterborne epoxy emulsion and its preparation method. This epoxy emulsion first synthesizes a reactive emulsifier, and then ring-opening grafts are performed on epoxy resin, epoxy diluent, methyl vinyl dimethoxysilane, acrylate monomers, and an initiator to obtain the epoxy emulsion. This method improves the stability and flexibility of the waterborne epoxy emulsion, but the introduced flexible segment consumes epoxy groups, which leads to a decrease in the epoxy value of the product and affects the crosslinking degree of the subsequent coating film. At the same time, although the introduced epoxy diluent can participate in the reaction of the subsequent two-component coating, some of this diluent will also volatilize during the coating application stage, leading to an increase in VOCs. Summary of the Invention

[0004] The technical problem to be solved by this invention is to overcome the shortcomings and defects mentioned in the background art above, and to provide a high-toughness, ultra-low VOC waterborne epoxy emulsion and its preparation method. Using SBS as a toughening modifier and styrene and acrylate monomers as crosslinking agents, chemical grafting modification is performed with epoxy resin under the action of an initiator, thereby improving the toughness of the epoxy resin and enhancing the system compatibility. Simultaneously, during the dissolution stage, styrene and acrylate monomers act as solvents to dissolve SBS and epoxy resin. After emulsification, a polymer is formed through a polymerization grafting reaction, resulting in a final waterborne epoxy emulsion free of volatile solvents, significantly reducing the VOC content of the system.

[0005] To solve the above-mentioned technical problems, the technical solution proposed by this invention is as follows:

[0006] A high-toughness, ultra-low VOC waterborne epoxy emulsion, comprising the following components in parts by weight:

[0007] Epoxy resin: 40-60 parts;

[0008] Styrene-butadiene-styrene block copolymer (SBS): 5-10 parts;

[0009] Styrene: 2-5 parts;

[0010] Acrylate monomers: 2-5 parts;

[0011] Initiator: 1.5-3 parts;

[0012] Polymerization inhibitor: 0.01-0.1 parts;

[0013] Emulsifier: 3-5 parts;

[0014] Water: 40-60 parts.

[0015] Preferably, the epoxy resin in the above-mentioned high-toughness ultra-low VOC waterborne epoxy emulsion is one or a mixture of E51, CYD-011, NPES-904, and NPES-629.

[0016] Preferably, the styrene-butadiene-styrene block copolymer is one or a mixture of SBS1201, SBS1301, and SBS1401.

[0017] Preferably, the acrylate monomer is one or a mixture of isobornyl methacrylate, butyl acrylate, and dodecyl methacrylate.

[0018] Preferably, the initiator is one or a mixture of TBPO, AIBN, and TAPO.

[0019] Preferably, the polymerization inhibitor is one or a mixture of hydroquinone, tert-butylhydroquinone, and tert-butylcatechol.

[0020] Preferably, the emulsifier is one or a mixture of AEO-9, AEO-15, Maxemul 9107, and PE-6200.

[0021] The styrene, acrylate monomers, and polymerization inhibitors used in this invention are intended to enable the acrylate monomers to act as small molecule solvents to dissolve SBS and epoxy resins before emulsification, so that they can maintain low viscosity at low temperatures to facilitate subsequent dispersion and emulsification. At the same time, they can polymerize into high molecular weight polymers under the action of initiators after emulsification, thus preventing these monomers from becoming VOCs during the application of the coating.

[0022] Based on a general inventive concept, the present invention also provides a method for preparing the above-mentioned high-toughness ultra-low VOC waterborne epoxy emulsion, comprising the following steps:

[0023] Step 1: Add the epoxy resin, styrene-butadiene-styrene block copolymer, emulsifier, acrylate monomer, and polymerization inhibitor into the reactor, and heat while stirring until completely dissolved to obtain a solution.

[0024] Step 2: Transfer the solution obtained in Step 1 to a dispersion vessel for dispersion, and then slowly add water dropwise to the dispersion vessel to obtain a white emulsion;

[0025] Step 3: Mix and dissolve the styrene with the initiator in advance, and add the mixed solution to the white emulsion obtained in Step 2. After the addition is complete, continue to keep it dispersed, and after cooling, discharge to obtain a high-toughness, ultra-low VOC waterborne epoxy emulsion.

[0026] In the above preparation method, preferably, in step 1, the temperature is raised to 100-120°C while stirring.

[0027] Preferably, in step 2, the temperature is lowered to 80-90°C during dispersion, and the dispersion speed is controlled at 2000-3000 r / min; when water is slowly added to the dispersion vessel, water is added at a rate of 0.4-1.0 g / min to obtain a white emulsion.

[0028] Preferably, in step 3, the dispersion is maintained at 80-90°C for 3-4 hours, and then cooled to 30-40°C inside the vessel.

[0029] The technical principle of this invention is as follows: Epoxy resin exhibits high mechanical strength and hardness after curing, but lacks flexibility in applications requiring high toughness. Toughness can be improved by directly adding small-molecule liquid toughening agents or by adding asphalt, which softens the epoxy resin after curing. However, this softening comes at the expense of the epoxy resin's strength. Especially after the epoxy resin undergoes a heat aging process after curing, these small-molecule plasticizers may migrate or age and become brittle, losing their toughening effect. SBS, a block copolymer of styrene and butadiene, has a large molecular weight, strong resistance to heat aging, and its molecular chain structure contains both hard and soft segments, resulting in high toughness. Therefore, modification with SBS can improve the toughness of the epoxy resin without significantly reducing its post-curing strength. However, directly adding SBS to epoxy resin presents a problem of poor compatibility. After emulsification into water-based epoxy, it easily leads to delamination, and the poor compatibility also affects the improvement of the mechanical properties and toughness of the epoxy resin after curing. Therefore, this invention employs a chemical modification method, using SBS to chemically graft onto the epoxy resin molecular chain. SBS is chosen for chemical modification instead of resins that can undergo ring-opening reactions with the epoxy groups in the epoxy resin. This ensures that the epoxy groups of the epoxy resin are not consumed, thus maintaining the degree of cross-linking during subsequent curing. Furthermore, achieving a grafting reaction between SBS and epoxy resin is not straightforward, as both are macromolecules with a low reaction probability. Therefore, styrene and acrylate monomers are introduced for copolymerization to act as a bridging agent, improving the grafting effect between SBS and epoxy resin. Simultaneously, the selected epoxy is primarily a macromolecular solid epoxy, and SBS is also a solid particle. To emulsify them into an aqueous emulsion, they must first be dissolved into a homogeneous phase at an appropriate viscosity before subsequent emulsification can proceed. Conventional methods may add solvents to achieve compatibility, but this inevitably results in solvents remaining in the emulsion, leading to high VOC levels. Therefore, this invention innovatively uses acrylate monomers as a solvent under the protection of a polymerization inhibitor to homogenize the two phases and achieve subsequent emulsification at an appropriate viscosity. After emulsification, the monomers can be polymerized into a high molecular weight polymer under the action of an initiator to eliminate VOCs.

[0030] In other words, this invention achieves low-temperature phase dissolution of SBS and epoxy resin through process improvement, and improves the compatibility of the two phases through chemical modification, thereby improving toughness without introducing VOCs.

[0031] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0032] 1. The high-toughness, ultra-low VOC waterborne epoxy emulsion of the present invention uses SBS (styrene-butadiene block copolymer) with hard and soft segments in its molecular chain to modify the epoxy resin, thereby improving the toughness while ensuring the mechanical strength and heat aging resistance of the modified epoxy.

[0033] 2. The high-toughness, ultra-low VOC waterborne epoxy emulsion of the present invention uses SBS polymer molecules containing unsaturated bonds and epoxy resin molecules containing active hydrogen. Chemical copolymerization modification can be achieved under free radical conditions. However, due to the large molecular weight and steric hindrance of SBS and epoxy resin, direct reaction between the two is difficult. Therefore, styrene and acrylate monomers with high small molecule activity are added as copolymerization crosslinking agents, which can better achieve chemical grafting modification of SBS and epoxy resin, and greatly improve their compatibility.

[0034] 3. SBS modified epoxy resin is grafted copolymerized through the reaction between the unsaturated bonds in the SBS molecular chain and the active hydrogen and unsaturated bonds in the epoxy resin molecule and monomer. Therefore, it does not consume the epoxy groups in the epoxy resin. This ensures that the crosslinking degree of the subsequent epoxy coating will not be reduced when it reacts with the curing agent, thus resulting in better film durability.

[0035] 4. In the preparation method of the present invention, the styrene and acrylate monomers used not only serve as copolymerization crosslinking agents, but also act as solvents for SBS and epoxy resins under the protection of polymerization inhibitors during the dissolution stage. The process adopted is to first dissolve, melt, then emulsify, and then polymerize. This ensures that the temperature does not need to be too high during dissolution and melting, and the viscosity is moderate during dispersion and emulsification. After emulsification, the monomers copolymerize into polymers, thereby reducing VOCs to almost zero. Detailed Implementation

[0036] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to preferred embodiments in the specification, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0037] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0038] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0039] Example 1:

[0040] A high-toughness, ultra-low VOC waterborne epoxy emulsion, the composition of which is shown in Table 1 below:

[0041] Table 1: Components of the high-toughness, ultra-low VOC waterborne epoxy emulsion in Example 1 (unit: g)

[0042]

[0043]

[0044] The preparation method of the above-mentioned high-toughness ultra-low VOC waterborne epoxy emulsion is as follows:

[0045] Step 1: Add epoxy resin, SBS, emulsifier, acrylate monomers and polymerization inhibitor into the reactor, and heat to 100-120℃ while stirring, and continue stirring until completely dissolved.

[0046] Step 2: Transfer the solution obtained in Step 1 to a dispersion vessel and cool it to 80-90℃, controlling the speed of the disperser to 2000-3000 r / min;

[0047] Step 3: Use a peristaltic pump to slowly add water dropwise into the dispersion vessel at a rate of approximately 0.8 g / min to obtain a white emulsion;

[0048] Step 4: Mix and dissolve styrene and initiator in advance, and add the mixed solution to the white emulsion in Step 3;

[0049] Step 5: After adding the ingredients, continue to keep them dispersed and maintain the temperature at 80-90℃ for 3-4 hours.

[0050] Step 6: Cool to 30-40℃ inside the reactor. The resulting product is a high-toughness, ultra-low VOC waterborne epoxy emulsion.

[0051] Example 2:

[0052] A high-toughness, ultra-low VOC waterborne epoxy emulsion, the composition of which is shown in Table 2 below:

[0053] Table 2: Components of the high-toughness, ultra-low VOC waterborne epoxy emulsion in Example 2 (unit: g)

[0054] Epoxy resin E51:20, NPES-904:25 SBS SBS1201:3, SBS1401:3 styrene 4 acrylate monomers Isoborneol methacrylate: 3, Dodecyl methacrylate: 1 Initiator AIBN: 1, TAPO: 2 Polymerization inhibitor tert-Butylcatechol: 0.08 emulsifier AEO-9:3, Maxemul9107:2 water 50

[0055] The preparation method of the above-mentioned high-toughness ultra-low VOC waterborne epoxy emulsion is the same as that in Example 1.

[0056] Comparative Example 1:

[0057] The components of a common SBS-modified waterborne epoxy emulsion are shown in Table 3 below:

[0058] Table 3: Components of Comparative Example 1 (unit: g)

[0059]

[0060]

[0061] The preparation method of the above-mentioned ordinary SBS modified waterborne epoxy emulsion is as follows:

[0062] Step 1: Add epoxy resin, SBS, emulsifier, and xylene into the reactor, and heat to 100-120℃ while stirring. Continue stirring until completely dissolved.

[0063] Step 2: Transfer the solution obtained in Step 1 to a dispersion vessel and cool it to 80-90℃, controlling the speed of the disperser to 2000-3000 r / min;

[0064] Step 3: Use a peristaltic pump to slowly add water dropwise into the dispersion vessel at a rate of 0.4-1.0 g / min to obtain a white emulsion;

[0065] Step 4: Cool to 30-40℃ inside the reactor. The resulting product is a standard SBS-modified waterborne epoxy emulsion.

[0066] Comparative Example 2:

[0067] The components of a waterborne epoxy emulsion modified with a common plasticizer are shown in Table 4 below:

[0068] Table 4: Components of Comparative Example 2 (unit: g)

[0069] Epoxy resin E51:20, NPES-904:25 Liquid petroleum resin 5 Propylene glycol methyl ether 3 emulsifier AEO-9:2, Maxemul9107:2 water 42

[0070] The preparation method of the above-mentioned waterborne epoxy emulsion modified with common plasticizer is as follows:

[0071] Step 1: Add epoxy resin, liquid petroleum resin, emulsifier, and xylene into the reactor, and heat to 100-120℃ while stirring. Continue stirring until completely dissolved.

[0072] Step 2: Transfer the solution obtained in Step 1 to a dispersion vessel and cool it to 80-90℃, controlling the speed of the disperser to 2000-3000 r / min;

[0073] Step 3: Use a peristaltic pump to slowly add water dropwise into the dispersion vessel at a rate of 0.4-1.0 g / min to obtain a white emulsion;

[0074] Step 4: Cool to 30-40℃ inside the reactor. Then discharge the material to obtain a waterborne epoxy emulsion modified with a common plasticizer.

[0075] Performance comparison:

[0076] The properties of the high-toughness, ultra-low VOC waterborne epoxy emulsions and ordinary products prepared in Examples 1-2 of this invention are shown in Table 5 below:

[0077] Table 5: Performance of the high-toughness ultra-low VOC waterborne epoxy emulsions prepared in Examples 1-2 and ordinary products

[0078]

[0079]

[0080] The performance comparison of the above embodiments with comparative examples and commercially available products shows that the epoxy emulsion prepared by the present invention has extremely low VOC, which is far lower than that of the comparative products and commercially available products, among waterborne epoxy emulsions of the same specifications.

[0081] The epoxy emulsion obtained by this invention was used to prepare water-based iron oxide red epoxy paint according to the formula in Table 6, and the performance of the water-based iron oxide red epoxy primer was tested after being sprayed on a hardener plate, as shown in Table 7.

[0082] Table 6: Formulation of High-Toughness Ultra-Low VOC Waterborne Epoxy Emulsion

[0083] Serial Number raw material Amount added (g) 1 Waterborne epoxy emulsion 35 2 Dispersant BYK190 1 3 water 22.3 4 Defoamer 0.1 5 wetting agent 0.1 6 Bentonite 0.2 7 Zinc phosphate 3 8 Iron oxide red 8 9 Barium sulfate 16 10 Iron-titanium powder 12 11 Alcohol ester dodecyl 2 12 Thickener 0.3

[0084] Table 7: Performance test results of water-based iron oxide red epoxy primer after spraying with matching hardener

[0085]

[0086]

[0087] The performance comparison of the above embodiments, comparative examples, and commercially available products shows that the waterborne epoxy emulsion prepared by the present invention has significantly better coating performance than the comparative sample and commercially available samples after the same formulation is used for paint preparation. In particular, it has obvious advantages in adhesion, salt spray, toughness, and aging resistance.

Claims

1. A high-toughness, ultra-low VOC waterborne epoxy emulsion, characterized in that, It contains the following components in parts by mass: Epoxy resin: 40-60 parts; Styrene-butadiene-styrene block copolymer: 5-10 parts; Styrene: 2-5 parts; Acrylate monomers: 2-5 parts; Initiator: 1.5-3 parts; Polymerization inhibitor: 0.01-0.1 parts; Emulsifier: 3-5 parts; Water: 40-60 parts; The styrene-butadiene-styrene block copolymer is of type SBS1201, SBS1301, SBS1401 or a mixture thereof; the acrylate monomer is of type Isobornyl methacrylate, butyl acrylate, dodecyl methacrylate or a mixture thereof. The initiator is one or a mixture of TBPO, AIBN, and TAPO; The emulsifier is one or a mixture of AEO-9, AEO-15, Maxemul 9107, and PE-6200; The polymerization inhibitor is one or a mixture of hydroquinone, tert-butylhydroquinone, and tert-butylcatechol; The high-toughness, ultra-low VOC waterborne epoxy emulsion is prepared by the following method: the epoxy resin, styrene-butadiene-styrene block copolymer, emulsifier, acrylate monomer, and polymerization inhibitor are added to a reaction vessel, and the mixture is heated to 100-120°C while stirring. The stirring continues until the emulsion is completely dissolved. The resulting solution is transferred to a dispersion vessel for dispersion, and then water is slowly added dropwise to the dispersion vessel to obtain a white emulsion. The styrene and initiator are pre-mixed and dissolved, and the mixed solution is added to the white emulsion. After the addition is complete, dispersion is maintained, and the product is discharged after cooling to obtain the high-toughness, ultra-low VOC waterborne epoxy emulsion.

2. The high-toughness, ultra-low VOC aqueous epoxy emulsion according to claim 1, characterized in that, The epoxy resin is one or a mixture of E51, CYD-011, NPES-904, and NPES-629.

3. A method for preparing a high-toughness, ultra-low VOC aqueous epoxy emulsion as described in any one of claims 1-2, characterized in that, Includes the following steps: Step 1: Add the epoxy resin, styrene-butadiene-styrene block copolymer, emulsifier, acrylate monomer, and polymerization inhibitor into the reactor, and heat to 100-120°C while stirring. Continue stirring until completely dissolved to obtain a solution. Step 2: Transfer the solution obtained in Step 1 to a dispersion vessel for dispersion, and then slowly add water dropwise to the dispersion vessel to obtain a white emulsion; Step 3: Mix and dissolve the styrene with the initiator in advance, and add the mixed solution to the white emulsion obtained in Step 2. After the addition is complete, continue to keep it dispersed, and after cooling, discharge to obtain a high-toughness, ultra-low VOC waterborne epoxy emulsion.

4. The method for preparing the high-toughness ultra-low VOC waterborne epoxy emulsion according to claim 3, characterized in that, In step 2, the temperature is lowered to 80-90℃ during dispersion, and the dispersion speed is controlled at 2000-3000 r / min; when water is slowly added dropwise to the dispersion vessel, water is added at a rate of 0.4-1.0 g / min to obtain a white emulsion.

5. The method for preparing the high-toughness ultra-low VOC aqueous epoxy emulsion according to any one of claims 3-4, characterized in that, In step 3, the dispersion is maintained at 80-90℃ for 3-4 hours, and then cooled to 30-40℃ inside the vessel.

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