Anti-cracking and anti-stripping coating and preparation method thereof

Abstract

The invention relates to an anti-cracking and anti-stripping coating and a preparation method thereof. The coating is prepared from the following components in parts by weight: 20 to 30 parts of acrylic acid modified epoxy resin, 15 to 25 parts of waterborne polyurethane dispersion, 5 to 10 parts of nano silicon dioxide, 3 to 8 parts of nano calcium carbonate, 10 to 15 parts of anti-crack microcapsules, 1 to 3 parts of silane coupling agent, 5 to 10 parts of polyether polyol, 0.2 to 1 part of defoaming agent, 2 to 5 parts of coalescing agent, 0.3 to 1 part of thickening agent, 0.1 to 0.5 part of flatting agent and 30 to 50 parts of deionized water. Wherein the capsule core of the anti-crack microcapsule is polyamic acid, the capsule wall of the anti-crack microcapsule is polyurea formaldehyde, a repairing material can be released when the coating cracks, and a three-dimensional network structure is formed through esterification reaction of carboxyl of the polyamic acid and hydroxyl of polyether polyol so as to repair cracks. After the nano filler is subjected to surface modification by the silane coupling agent, the binding force between the nano filler and a resin matrix is remarkably enhanced, and the crack resistance and the adhesive force of the coating are improved. Through the synergistic effect of the acrylic acid modified epoxy resin and the waterborne polyurethane, the coating has flexibility and wear resistance.

Description

Technical Field

[0001] The present invention relates to the technical field of coatings, and particularly to a crack-resistant and peeling-resistant coating and a preparation method thereof. Background Art

[0002] In the fields of construction, automobiles, ships, furniture, etc., coatings are widely used. Their function is not only for aesthetics, but more importantly, to protect the base material. However, in actual use, coatings often face the problems of cracking and peeling. For example, on the exterior walls of buildings, due to temperature changes, humidity fluctuations, deformation of the base material, and erosion from the external environment (such as rain, ultraviolet rays, chemical substances, etc.), cracks are likely to appear in the coating layer. Over time, the cracks will gradually expand, leading to coating peeling. This not only affects the appearance of the building, but also causes the base material to lose protection and suffer more serious damage, such as steel bar corrosion and wall seepage, shortening the service life of the building. In the automotive field, automotive coatings are exposed to the external environment for a long time, experiencing wind, sun, rain, snow, vibration, and impact during driving. The crack-resistant and peeling-resistant performance of the coating directly affects the aesthetics and durability of the automobile.

[0003] At present, there are already some crack-resistant and peeling-resistant coatings on the market. Some coatings add a large amount of elastic polymers to improve the flexibility of the coating layer, thereby reducing the generation of cracks. However, too much elastic polymer will reduce the hardness and wear resistance of the coating layer, and at the same time increase the cost. There are also some coatings that use a multi-layer coating system to improve the crack-resistant and peeling-resistant performance through the synergistic effect between layers. However, this method has a complex construction process and high requirements for construction conditions, making it difficult to be widely applied. In addition, the adhesion of some existing coatings to the surface of the base material is not strong enough, especially on some base materials with less than ideal surface treatment, and peeling is likely to occur. Therefore, it is of great practical significance to develop a coating with excellent crack-resistant and peeling-resistant performance, convenient construction, and reasonable cost. Summary of the Invention

[0004] The purpose of the present invention is to provide a crack-resistant and peeling-resistant coating and a preparation method thereof to solve the problems of insufficient crack-resistant and peeling-resistant performance, complex construction, and high cost of existing coatings as mentioned in the above background art.

[0005] To achieve the above object, the present application provides a crack-resistant and anti-stripping coating, which is characterized by comprising the following components in parts by weight: 20-30 parts of acrylic-modified epoxy resin, 15-25 parts of aqueous polyurethane dispersion, 5-10 parts of nano-silica, 3-8 parts of nano-calcium carbonate, 10-15 parts of crack-resistant microcapsules, 1-3 parts of silane coupling agent, 5-10 parts of polyether polyol, 0.2-1 part of defoaming agent, 2-5 parts of film-forming aid, 0.3-1 part of thickener, 0.1-0.5 part of leveling agent, and 30-50 parts of deionized water; the core of the crack-resistant microcapsules is polyamic acid, and the wall is polyurea formaldehyde.

[0006] Further, the acrylic-modified epoxy resin is prepared by free radical polymerization of acrylic monomers and epoxy resin, wherein the mass ratio of acrylic monomers to epoxy resin is (1:5)-(1:3).

[0007] Further, the silane coupling agent is one or a mixture of two of γ-methacryloxypropyltrimethoxysilane and γ-aminopropyltriethoxysilane.

[0008] Further, the crack-resistant microcapsules are prepared by in-situ polymerization method, and the in-situ polymerization method comprises the following steps: mixing urea, ammonium chloride, resorcinol and water to obtain a mixed solution; dropping polyamic acid into the mixed solution, adjusting the pH value to 3-4, and mixing with formaldehyde aqueous solution for in-situ polymerization reaction to obtain crack-resistant microcapsules, wherein the temperature of the in-situ polymerization reaction is 50-60 °C and the time is 4-6 h.

[0009] Further, the defoaming agent is one or a mixture of two of polyether-modified silicone defoaming agent and mineral oil defoaming agent.

[0010] Further, the film-forming aid is one or a mixture of two of propylene glycol butyl ether and dipropylene glycol methyl ether; the polyether polyol is one or a mixture of two of polyoxypropylene glycol, polytetrahydrofuran glycol, and tetrahydrofuran-oxypropylene copolymer glycol.

[0011] Further, the thickener is one or a mixture of two of hydroxyethyl cellulose and associative thickener; the leveling agent is one or a mixture of two of polydimethylsiloxane leveling agent and acrylate leveling agent.

[0012] Furthermore, the mass ratio of the polyether polyol to the crack-resistant microcapsule is 0.5 - 0.7:1. The purpose is to provide a suitable three-dimensional network structure. When the coating cracks, the crack-resistant microcapsules can release the repair material. The carboxyl groups in the released polyamic acid react with the hydroxyl groups of the polyether polyol to form an esterification reaction, connecting the chain-like reactants in the polyamic acid solution to each other to form a stable three-dimensional network polymer. If the content of the polyether polyol is too low, insufficient cross-linking points will be provided, resulting in insufficient cross-linking density of the polymer network structure, affecting the strength and stability of the three-dimensional network polymer and making the polymer network not tight enough. If the content of the polyether polyol is too high, over-crosslinking will occur, making the polymer network too dense, and the polymer is not easy to fill into the gaps, resulting in the loss of flexibility of the repaired coating and affecting the final repair effect.

[0013] The present invention also provides a preparation method of the anti-cracking and anti-peeling coating as described above, which is characterized by including the following steps:

[0014] S1, Add deionized water to the reaction kettle, start stirring at a stirring speed of 200 - 400 r / min, and sequentially add polyether polyol, defoamer, and leveling agent, and stir for 10 - 20 min to fully mix each component;

[0015] S2, Add nano-silica, nano-calcium carbonate, and crack-resistant microcapsules, and continue stirring for 30 - 60 min to fully disperse the fillers;

[0016] S3, Add a silane coupling agent and stir for 15 - 30 min to perform a surface modification treatment on the fillers;

[0017] S4, Add acrylic acid-modified epoxy resin and aqueous polyurethane dispersion, adjust the stirring speed to 100 - 200 r / min, and stir for 20 - 40 min to fully mix the resin and the fillers;

[0018] S5, Add a film-forming aid and a thickener, and stir for 10 - 20 min to adjust the viscosity and leveling property of the coating;

[0019] S6, Finally, perform filtration with a filtration accuracy of 100 - 200 mesh to obtain the anti-cracking and anti-peeling coating.

[0020] Furthermore, in step S3, the addition amount of the silane coupling agent is 1% - 3% of the total weight of nano-silica and nano-calcium carbonate; the mass ratio of the polyether polyol to the crack-resistant microcapsule is 0.5 - 0.7:1.

[0021] Compared with the prior art, the beneficial effects of the present invention are:

[0022] (1) Through reasonable formulation design, the crack-resistant and spalling-resistant coating of the present invention uses the compound of acrylic modified epoxy resin and aqueous polyurethane dispersion as the film-forming substance. The acrylic modified epoxy resin has good adhesion and chemical corrosion resistance. At the same time, the introduction of acrylic acid improves the flexibility and weather resistance of the resin; the aqueous polyurethane dispersion has excellent elasticity and wear resistance. The compound of the two endows the coating with good flexibility, adhesion and wear resistance, and can effectively resist the deformation of the substrate and the influence of the external environment, reducing the generation of cracks.

[0023] (2) Nano-silica and nano-calcium carbonate as fillers can not only improve the hardness and strength of the coating, but also fill the tiny pores in the coating, improve the structure of the coating, and further enhance the crack resistance. The silane coupling agent is used to modify the surface of the filler, improving the compatibility and bonding force between the filler and the resin, thereby enhancing the overall performance of the coating. The addition of auxiliaries such as dispersants, defoamers, film-forming aids, thickeners, and leveling agents improves the construction performance of the coating and the appearance quality of the coating, enabling the coating to be evenly coated during construction, forming a flat and smooth coating, improving the adhesion between the coating and the substrate, and reducing the occurrence of spalling. The preparation method of the present invention is simple, the process is controllable, and it is suitable for industrial production.

[0024] (3) The crack-resistant microcapsules can release repair materials when the coating cracks. The carboxyl groups in the released polyamic acid react with the hydroxyl groups of the polyether polyol to connect the chain-like reactants in the polyamic acid solution to each other, forming a stable three-dimensional network polymer. The cross-linking points in the three-dimensional network polymer are dense and evenly distributed, repairing the cracked part of the coating. At the same time, by optimizing the mass ratio of polyamic acid and polyether polyol, the three-dimensional network polymer exists more uniformly, which can further improve the flexibility and crack resistance of the coating. Detailed implementation manners

[0025] To make the purpose, technical solutions and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Those skilled in the art should understand that the embodiments are only for helping to understand the present invention and should not be regarded as specific limitations on the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative work belong to the scope of protection of the present invention. The process parameters without specific conditions noted in the following embodiments are usually in accordance with conventional conditions.

[0026] In the ranges disclosed in the present invention, the endpoints and any values are not limited to the exact ranges or values. These ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values, they can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed in the present invention.

[0027] Preparation of crack-resistant microcapsules:

[0028] First, at room temperature, 5.00 g of urea, 0.50 g of ammonium chloride, 0.50 g of resorcinol, and 200 mL of deionized water were added to a 1000 mL beaker and stirred evenly. After complete dissolution, the stirring speed of the stirrer was adjusted, and 1000 mL of the core material polyamic acid was slowly added dropwise. The pH value was adjusted to 3.5 with hydrochloric acid. After stabilization, 13 g of 40 wt% formaldehyde aqueous solution was added, and the mixture was heated in a constant temperature water bath at 50 °C for 5 h. The pH value was monitored with a pH meter and maintained at 3.3 - 3.7. After the reaction was completed, the reaction solution was allowed to cool naturally, and then solid-liquid separation (filtration), extraction with ethyl acetate, washing with water, and drying were carried out to prepare crack-resistant microcapsules with an average particle size of 90 - 140 μm and a wall thickness of 30 - 50 μm.

[0029] Example 1

[0030] A crack-resistant and anti-stripping coating, comprising the following components by weight: 25 parts of acrylic modified epoxy resin, 20 parts of aqueous polyurethane dispersion, 8 parts of nano-silica, 5 parts of nano-calcium carbonate, 12 parts of crack-resistant microcapsules, 2 parts of silane coupling agent (γ-methacryloxypropyltrimethoxysilane), 8 parts of polyether polyol (polypropylene glycol), 0.5 part of defoaming agent (polyether modified silicone defoaming agent), 3 parts of film-forming aid (propylene glycol monobutyl ether), 0.6 part of thickener (hydroxyethyl cellulose), 0.3 part of leveling agent (polydimethylsiloxane leveling agent), and 40 parts of deionized water.

[0031] The preparation method is as follows:

[0032] 40 parts of deionized water were added to the reaction kettle, and stirring was started at a stirring speed of 200 r / min. 8 parts of polyether polyol, 0.5 part of defoaming agent, and 0.3 part of leveling agent were added in sequence and stirred for 10 min to fully mix the components.

[0033] 8 parts of nano-silica, 5 parts of nano-calcium carbonate, and 12 parts of crack-resistant microcapsules were added, and stirring was continued for 30 min to fully disperse the fillers.

[0034] 2 parts of silane coupling agent were added and stirred for 15 min to perform surface modification treatment on the fillers.

[0035] Add 25 parts of acrylic modified epoxy resin and 20 parts of aqueous polyurethane dispersion, adjust the stirring speed to 100 r / min, and stir for 20 min to fully mix the resin and the filler.

[0036] Add 3 parts of film-forming aid and 0.6 part of thickener, stir for 10 min to adjust the viscosity and leveling property of the coating.

[0037] Finally, perform filtration with a filtration accuracy of 100 mesh to obtain the crack-resistant and spalling-resistant coating.

[0038] Example 2

[0039] The main difference between this comparative example and Example 1 is that the acrylic modified epoxy resin is 20 parts and the aqueous polyurethane dispersion is 25 parts, and the remaining steps and technical parameters are the same as those in Example 1.

[0040] Example 3

[0041] The main difference between this comparative example and Example 1 is that the acrylic modified epoxy resin is 30 parts and the aqueous polyurethane dispersion is 15 parts, and the remaining steps and technical parameters are the same as those in Example 1.

[0042] Comparative Example 1

[0043] The main difference between this comparative example and Example 1 is that there is no crack-resistant microcapsule in the coating, and the remaining steps and technical parameters are the same as those in Example 1.

[0044] Comparative Example 2

[0045] The main difference between this comparative example and Example 1 is that there is no silane coupling agent in the coating, and the remaining steps and technical parameters are the same as those in Example 1.

[0046] Comparative Example 3

[0047] The main difference between this comparative example and Example 1 is that there are 16 parts of crack-resistant microcapsules and 4 parts of polyether polyol in the coating, and the remaining steps and technical parameters are the same as those in Example 1.

[0048] Comparative Example 4

[0049] The main difference between this comparative example and Example 1 is that there are 11 parts of crack-resistant microcapsules and 9 parts of polyether polyol in the coating, and the remaining steps and technical parameters are the same as those in Example 1.

[0050] Comparative Example 5

[0051] The main difference between this comparative example and Example 1 is that the acrylic modified epoxy resin in the coating is replaced with ordinary epoxy resin, and the remaining steps and technical parameters are the same as those in Example 1.

[0052] The coatings in Examples 1-3 and Comparative Examples 1-5 were used as samples for testing: The samples were sprayed on a stainless steel plate by electrostatic spraying and baked at 120 °C for 10 min to prepare a coating film with a thickness of 100 μm. And the coating film was tested, and the test results are shown in Table 1:

[0053] Table 1

[0054]

[0055] From the experimental data in Examples 1-3, it can be seen that in Example 1, the ratio of acrylic-modified epoxy resin (strong adhesion) to waterborne polyurethane (high elasticity) is balanced, the cross-cut method is grade 0 (completely no peeling), and the elongation at break is 35%, reflecting the characteristic of "combining rigidity and flexibility", which is suitable for substrates with medium deformation. In Example 2, the amount of waterborne polyurethane increases, and the elasticity is increased to 45% (more adaptable to the expansion and contraction of the substrate), but the pencil hardness drops from 2H to 1H, indicating that part of the hardness is sacrificed for higher flexibility, which is suitable for easily deformed scenarios such as exterior walls. In Example 3, the proportion of epoxy resin increases, and the hardness is increased to 3H (suitable for industrial wear-resistant scenarios), but the adhesion drops to grade 1 (slight peeling), because the reduction of waterborne polyurethane leads to insufficient elasticity of the coating, and interfacial stress concentration occurs when the substrate deforms. The color difference ΔE of ultraviolet aging in Example 2 is 2.0 (better than that in Example 1), because the waterborne polyurethane contains an aliphatic structure and has slightly better ultraviolet resistance; in Example 3, ΔE = 3.0, because the epoxy resin still contains a benzene ring structure after modification and is prone to oxidation and discoloration under long-term ultraviolet irradiation.

[0056] From the data in Example 1 and Comparative Example 1, it can be seen that no anti-cracking microcapsules were added in Comparative Example 1. After cracks occurred, no polyamic acid was released and it could not be repaired by esterification reaction, verifying the necessity of the "mechanism of microcapsule rupture and release of repair materials" in the invention. The polyamic acid in the core of the microcapsule and the polyurea formaldehyde structure of the capsule wall ensure that the capsule wall ruptures when the crack propagates and accurately releases the repair components, which is the key to achieving "active anti-cracking".

[0057] From the data in Example 1 and Comparative Example 2, it can be seen that there is no silane coupling agent in Comparative Example 2. After the damp heat cycle, the adhesion drops from grade 0 to grade 3 (severe peeling) suddenly, because the surface of nano-silica / calcium carbonate is not modified and there is only physical adsorption between it and the resin, and water erosion leads to interfacial debonding. The silane coupling agent (such as γ-methacryloxypropyltrimethoxysilane) generates silanol by hydrolysis, condenses with the hydroxyl groups on the surface of the filler to form a Si-O-Si covalent bond, and at the same time the organic group at the other end reacts with the resin to form a chemical connection of "filler-coupling agent-resin", increasing the interfacial bonding force by more than 3 times.

[0058] It can be seen from Example 1 and Comparative Examples 3-4 that in Comparative Example 3 (insufficient polyether, 0.25:1), the tensile strength after repair only remained at 60%. Due to the excessive carboxyl groups of polyamic acid and insufficient hydroxyl crosslinking points, the three-dimensional network structure was loose and could not effectively fill the cracks. In Comparative Example 4 (excessive polyether, 0.82:1), the elongation at break decreased to 20%. Due to excessive crosslinking, the polymer network became rigid, and the flexibility of the coating was lost after repair, verifying the scientific nature of the "optimal ratio of 0.5-0.7:1" in the invention, ensuring a moderate crosslinking density and taking into account both strength and ductility.

[0059] At the same time, it can be seen from Example 1 and Comparative Example 5 that after replacing with ordinary epoxy resin, the elongation at break decreased from 35% to 20% (increased brittleness), and the ultraviolet aging color difference ΔE = 5.0 (far exceeding 2.5 of Example 1). Because the double bonds and polar groups (such as carboxylate groups) introduced by acrylic modification endow the resin with flexibility and ultraviolet absorption ability, while ordinary epoxy resin only contains a rigid benzene ring structure and is easily damaged by the external environment.

[0060] The above-described embodiments only represent several implementation manners of the present invention. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention patent shall be subject to the appended claims.

Claims

1. An anti-cracking and anti-spalling coating, characterized in that, It comprises the following components by weight: 20 - 30 parts of acrylic acid modified epoxy resin, 15 - 25 parts of aqueous polyurethane dispersion, 5 - 10 parts of nano - silica, 3 - 8 parts of nano - calcium carbonate, 10 - 15 parts of anti - cracking microcapsules, 1 - 3 parts of silane coupling agent, 5 - 10 parts of polyether polyol, 0.2 - 1 part of defoaming agent, 2 - 5 parts of film - forming auxiliary, 0.3 - 1 part of thickener, 0.1 - 0.5 part of leveling agent, and 30 - 50 parts of deionized water; the core of the anti - cracking microcapsules is polyamic acid, and the wall is polyurea formaldehyde.

2. The anti-cracking and anti-spalling coating according to claim 1, wherein The acrylic acid modified epoxy resin is prepared by free - radical polymerization reaction of acrylic acid monomer and epoxy resin, where the mass ratio of acrylic acid monomer to epoxy resin is (1:5)-(1:3).

3. The crack-resistant and spalling-resistant coating according to claim 1, wherein The silane coupling agent is one or a mixture of two of γ - methacryloxypropyltrimethoxysilane and γ - aminopropyltriethoxysilane.

4. The anti-cracking and anti-spalling coating according to claim 1, characterized in that, The anti - cracking microcapsules are prepared by in - situ polymerization method, and the in - situ polymerization method comprises the following steps: mix urea, ammonium chloride, resorcinol and water to obtain a mixed solution; drop polyamic acid into the mixed solution, adjust the pH value to 3 - 4, and mix with aqueous formaldehyde solution for in - situ polymerization reaction to obtain anti - cracking microcapsules. The temperature of the in - situ polymerization reaction is 50 - 60 °C, and the time is 4 - 6 h.

5. The anti-cracking and anti-spalling coating according to claim 1, wherein The defoaming agent is one or a mixture of two of polyether - modified silicone defoaming agent and mineral oil defoaming agent.

6. The anti-cracking and anti-spalling coating according to claim 1, wherein The film - forming auxiliary is one or a mixture of two of propylene glycol butyl ether and dipropylene glycol methyl ether; the polyether polyol is one or a mixture of two of polyoxypropylene glycol, polytetrahydrofuran glycol, and tetrahydrofuran - propylene oxide copolymer glycol.

7. The crack-resistant and spalling-resistant coating according to claim 1, characterized in that, The thickener is one or a mixture of two of hydroxyethyl cellulose and associative thickener; the leveling agent is one or a mixture of two of polydimethylsiloxane leveling agent and acrylate leveling agent.

8. The anti-cracking and anti-spalling coating according to claim 1, characterized in that, The mass ratio of the polyether polyol to the anti - cracking microcapsules is 0.5 - 0.7:

1.

9. A preparation method of the crack and spalling resistant coating according to any one of claims 1-8, characterized in that, It comprises the following steps: S1, Add deionized water into the reaction kettle, start stirring with a stirring speed of 200 - 400 r / min, and successively add polyether polyol, defoaming agent, and leveling agent, and stir for 10 - 20 min to fully mix each component. S2, Add nano - silica, nano - calcium carbonate, and anti - cracking microcapsules, and continue stirring for 30 - 60 min to fully disperse the fillers. S3, Add the silane coupling agent and stir for 15 - 30 min to perform surface modification treatment on the fillers. S4, Add acrylic acid modified epoxy resin and aqueous polyurethane dispersion, adjust the stirring speed to 100 - 200 r / min, and stir for 20 - 40 min to fully mix the resin and the fillers. S5, Add the film - forming auxiliary and thickener, and stir for 10 - 20 min to adjust the viscosity and leveling property of the coating. S6, Finally, perform filtration with a filtration accuracy of 100 - 200 mesh to obtain the anti - cracking and anti - spalling coating.

10. The preparation method according to claim 9, characterized in that, The addition amount of the silane coupling agent in step S3 is 1% - 3% of the total weight of nano - silica and nano - calcium carbonate.

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