Weather-resistant self-stratifying coating and use method thereof

Abstract

The invention belongs to the technical field of coatings, and particularly relates to a weather-resistant self-stratifying coating and a use method thereof. According to the paint disclosed by the invention, the acrylic resin is migrated to the surface of the coating by utilizing the difference of the acrylic resin and the epoxy resin in surface tension, so that good hydrophobicity, hardness and weather resistance are provided, and the epoxy resin is downwards migrated to the bottom surface of the formed self-layering coating, so that the adhesive force between the self-layering coating and a base material and the overall weather resistance are increased; and finally, a good self-layering structure is formed. The coating is simple in use process and convenient to construct; two continuous coatings with different functions can be rapidly and spontaneously formed through one-time coating, the coating has good waterproof, antifouling and weather-resistant performance, after the coating is soaked in seawater for one month, the surface appearance does not change obviously, and the phenomena of discoloration, blistering, falling and the like are not found; and tests show that the adhesive force of the self-stratified coating is 14 MPa or above, the service life of the coating is prolonged, and the requirement of the high-performance coating on multiple aspects can be met.

Description

Technical Field

[0001] The present invention belongs to the technical field of coatings, and particularly relates to a weather-resistant self-stratifying coating and a method for using the same. Background Art

[0002] After applying a coating on the surface of a substrate, a self-stratifying coating can spontaneously form a multi-layer or gradient structure in a single process, thereby achieving the effect of combining the top and bottom layers, and at the same time having the excellent properties of both the surface coating and the bottom coating. In the existing self-stratifying coating system, the self-stratifying phenomenon is usually achieved by relying on the surface energy difference of the coating resin system. After the coating is applied, as the solvent evaporates, the resin with low surface energy will migrate to the surface of the coating, providing excellent aesthetics, durability, scratch resistance, and water and stain resistance; while the resin with high surface energy will migrate to the substrate interface, effectively improving the weather resistance of the coating and the adhesion to the substrate.

[0003] CN105482027A discloses an acrylic-modified polysiloxane resin and its application in a self-stratifying coating. The self-stratifying coating consists of component A and component B. The weight percentages of component A include: 15%-70% acrylic-modified polysiloxane resin, 5%-40% pigment and filler, 0.5%-2% additives, and 10%-45% solvent; component B is a curing agent, usually a coupling agent or an amino silane containing an isocyanate group. The acrylic-modified polysiloxane resin provided by this technical solution has two cross-linkable groups, allowing different curing agents to be selected for curing according to performance requirements. In addition, the self-stratifying coating has a fast surface drying speed, a low surface energy, and good hydrophobic and anti-fouling properties. However, the weather resistance and mechanical properties of the acrylic-modified polysiloxane are relatively weak, which reduces the weather resistance and mechanical properties of the coating and limits its wide application in coatings.

[0004] CN106867359A discloses a fluorine-containing block acrylate-epoxy resin weather-resistant and anti-corrosion self-stratifying coating and a preparation method thereof. The coating consists of component A and component B, and the specific formula is: component A includes 100 parts of epoxy resin, 10-30 parts of fluorine-containing block acrylate copolymer, 20-30 parts of pigment and filler, 1-2 parts of dispersant, and 60-80 parts of organic solvent I; component B includes 30-80 parts of amide curing agent and 20-60 parts of organic solvent II. By introducing fluorine groups, this technical solution makes the acrylate have a low surface energy and can migrate to the surface of the coating, while the epoxy resin migrates to the bottom surface of the coating, thereby achieving the self-stratifying effect. The coating can not only quickly stratify or form a gradient structure, improve the painting efficiency and reduce the cost, but also has good weather resistance and anti-corrosion properties. However, due to the use of fluorine groups, it may have a certain impact on the environment, which limits its application in coatings with high current environmental protection requirements.

[0005] In the prior art, self - stratifying coating systems generally suffer from problems such as poor weather resistance, insufficient mechanical properties, environmental pollution, and unstable stratification structures. These defects prevent the coating from achieving the desired ideal stratification effect after being sprayed onto the substrate. Usually, frequent adjustments and experiments are required, resulting in large deviations in actual applications, thus seriously affecting the use effect and wide application of the coating. Therefore, there is an urgent need to develop a self - stratifying coating with good and stable stratification effect, high adhesion, and good weather resistance after coating. Summary of the Invention

[0006] Aiming at the deficiencies in the prior art, the purpose of the present invention is to provide a weather - resistant self - stratifying coating and its use method. This self - stratifying coating can spontaneously form a stable stratification structure after coating, has excellent adhesion, and exhibits excellent weather resistance.

[0007] A weather - resistant self - stratifying coating, the raw material components are calculated by mass fraction, including 20 - 60 parts of resin binder, 45 - 75 parts of mixed solvent, 5 - 10 parts of curing agent, and 1 - 3 parts of defoamer.

[0008] The resin binder is composed of epoxy resin and acrylic resin with a mass ratio of 1 - 5:1; the curing agent is an aliphatic amine curing agent.

[0009] The mixed solvent includes butyl acetate, m - xylene, and methyl isobutyl ketone; among them, the mass ratio of m - xylene to methyl isobutyl ketone is 2 - 4:1; the mass ratio of butyl acetate to the curing agent is 1:2 - 3.

[0010] The mixed solvent used in the present invention is composed of butyl acetate, m - xylene, and methyl isobutyl ketone. Among them, the mass ratio of m - xylene to methyl isobutyl ketone is 2 - 4:1, and its functions include: 1) fully dissolving the epoxy resin and acrylic resin binder to ensure the homogeneity of the mixed system; 2) by reducing the polarity and solvent evaporation rate of the mixed system, extending the resin phase separation time window, and promoting the directional stratification of epoxy resin and acrylic resin. Methyl isobutyl ketone is a co - solvent for epoxy resin and acrylic resin, while m - xylene can only dissolve acrylic resin and has very low solubility for epoxy resin. In addition, the evaporation rate of methyl isobutyl ketone is greater than that of m - xylene. Therefore, based on the differences in solubility and evaporation rate of the two solvents for the resin, in the mixed system, methyl isobutyl ketone will evaporate first, and the epoxy resin phase will precipitate. At this time, the acrylic resin is still dissolved in the xylene solvent. Coupled with the fact that the surface tension of epoxy resin is greater than that of acrylic resin, it will first settle and cure at the bottom of the coating. Finally, as the methyl isobutyl ketone solvent evaporates, the acrylic resin will be enriched on the surface of the coating.

[0011] Therefore, the present invention screens the specific types and proportions of resin binders in a directional manner. Based on the difference in surface tension of the two resins, during the film-forming process of the self-stratifying coating, the acrylic resin with low surface energy can migrate to the surface of the self-stratifying coating to provide good hydrophobicity and weather resistance, while the epoxy resin with high surface energy migrates downward to the bottom surface of the self-stratifying coating to increase its adhesion to the substrate and overall weather resistance, forming a good self-stratifying structure. The combined solvents of m-xylene and methyl isobutyl ketone are used to utilize the differences of the two solvents, so that the coating after the coating is cured has better weather resistance, mechanical properties, environmental pollution, and multiple excellent properties of stable stratified structure.

[0012] Furthermore, the defoamer is BYK-110 defoamer.

[0013] The method for using the weather-resistant self-stratifying coating is as follows:

[0014] Step 1: Mix two solvents, m-xylene and methyl isobutyl ketone, at room temperature to obtain a mixed solvent.

[0015] Step 2: Completely dissolve the epoxy resin in half of the mixed solvent prepared in step 1 to obtain a mixed solution A.

[0016] Completely dissolve the acrylic resin in the other half of the mixed solvent prepared in step 1 to obtain a mixed solution B.

[0017] Step 3, the mixed solution A obtained in step 2 is mixed with the mixed solution B for the first time; then a defoamer is added for a second mixing; and then a mixture of a curing agent and butyl acetate is added for a third mixing to obtain a weather-resistant self-stratifying coating.

[0018] The weather-resistant self-stratifying coating is mixed according to the usage method, sprayed on the surface of the substrate and cured to obtain the coating.

[0019] Furthermore, the curing temperature is room temperature and the curing time is at least 4 hours.

[0020] The present invention also provides a method of use based on its own technical characteristics, which fully utilizes the characteristics of the mixed solvent in multiple steps. The slurry during use can better exert its own characteristics, so that the cured coating can efficiently achieve the technical purpose.

[0021] In summary, the coating of the present invention utilizes the difference in surface tension between acrylic resin and epoxy resin. The acrylic resin migrates to the surface of the coating, providing good hydrophobicity, hardness and weather resistance. The epoxy resin migrates downward to the bottom surface of the formed self-stratifying coating, increasing the adhesion between the self-stratifying coating and the substrate and the overall weather resistance, and finally forming a good self-stratifying structure. The coating of the present invention has a simple use process and convenient construction; a single coating can quickly and spontaneously form two continuous coatings with different functions, having good waterproof, anti-fouling and weather resistance properties. After being immersed in seawater for one month, the surface morphology has not changed significantly, and no discoloration, blistering, peeling and other phenomena have been found; and after testing, the adhesion of the self-stratifying coating is above 14 MPa, increasing the service life of the coating and meeting the requirements for various aspects of high-performance coatings. Description of the Drawings

[0022] Figure 1 It is the characterization of the coating cross-section image under an optical microscope for Example 1.

[0023] Figure 2 It is the SEM spectrum of the cross-section of Example 1.

[0024] Figure 3 It is the Fourier transform attenuated total reflection infrared spectrum FTIR-ATR of the surface and bottom surface of the coating for Example 1.

[0025] Figure 4 The surface energy comparison diagram of Example 3 and Comparative Example 1.

[0026] Figure 5 It is the Tafel polarization curve diagram for the comparative analysis of the electrochemical corrosion of Comparative Example 1 and Example 1 in an environment with a 3.5 wt% NaCl concentration. Detailed Description of the Invention

[0027] The present invention will be further described in detail below in conjunction with specific examples and drawings.

[0028] Example 1

[0029] A weather-resistant self-stratifying coating, the raw material components are calculated by mass fraction, including: 8 parts of acrylic resin, 16 parts of epoxy resin, 10 parts of curing agent, 0.1 part of defoaming agent, 3 parts of butyl acetate, 6.65 parts of m-xylene and 6.65 parts of methyl isobutyl ketone.

[0030] The use method of the weather-resistant self-stratifying coating is as follows:

[0031] Step 1: Mix m-xylene and methyl isobutyl ketone to obtain a mixed solvent.

[0032] Step 2: Mix 8 parts of acrylic resin with half of the mixed solvent prepared in Step 1 to obtain a mixture A.

[0033] Mix 16 parts of epoxy resin with the other half of the mixed solvent prepared in Step 1 to obtain Mixture B.

[0034] Step 3: First mix the mixed liquid A prepared in Step 2 with Mixture B at 500 r / min for 20 minutes; then add 0.1 part by weight of defoamer and mix at 500 r / min for 15 minutes for the second mixing; then add a mixture of 10 parts by weight of curing agent and 3 parts by weight of butyl acetate for the third mixing to obtain the weather-resistant self-stratifying coating.

[0035] Step 4: Spray the weather-resistant self-stratifying coating obtained in Step 3 onto a tinplate substrate with a spray gun, let it stand at 25 °C for 4 h, and then dry and cure at 60 °C for 4 h to obtain the self-stratifying coating.

[0036] Example 2

[0037] A weather-resistant self-stratifying coating, the raw material components are calculated by mass fraction, including: 5 parts of acrylic resin, 15 parts of epoxy resin, 9.38 parts of curing agent, 0.1 part of defoamer, 5 parts of butyl acetate, 2.5 parts of m-xylene, and 2.5 parts of methyl isobutyl ketone.

[0038] The usage process and coating preparation process of the weather-resistant self-stratifying coating are exactly the same as those in Example 1.

[0039] Example 3

[0040] A weather-resistant self-stratifying coating, the raw material components are calculated by mass fraction, including: 4 parts of acrylic resin, 16 parts of epoxy resin, 9.38 parts of curing agent, 0.1 part of defoamer, 3 parts of butyl acetate, 10 parts of m-xylene, and 10 parts of methyl isobutyl ketone.

[0041] The usage process and coating preparation process of the weather-resistant self-stratifying coating are exactly the same as those in Example 1.

[0042] Example 4

[0043] A weather-resistant self-stratifying coating, the raw material components are calculated by mass fraction, including: 3 parts of acrylic resin, 15 parts of epoxy resin, 9.38 parts of curing agent, 0.1 part of defoamer, 3 parts of butyl acetate, 6.65 parts of m-xylene, and 6.65 parts of methyl isobutyl ketone.

[0044] The usage process and coating preparation process of the weather-resistant self-stratifying coating are exactly the same as those in Example 1.

[0045] Comparative Example 1

[0046] This comparative example provides a method for preparing and using a coating, which is only different from Example 1 in that 8 parts of acrylic resin in the raw material components are not added, and other conditions are the same as those in Example 1.

[0047] The self-stratifying coatings provided in the above-mentioned examples and comparative examples were tested, and the specific test methods are as follows:

[0048] Stratification effect: An optical microscope, a scanning electron microscope, and Fourier transform attenuated total reflection infrared spectroscopy (FTIR-ATR) were used to analyze and determine whether the self-stratifying coatings provided in the examples and comparative examples had a stratification phenomenon.

[0049] Adhesion: Tested in accordance with GB / T 5210-2006.

[0050] Contact angle: The water contact angle was measured in accordance with GB / T 30693-2014.

[0051] Surface energy: Calculated by the Neumann-Sell experimental formula for surface energy.

[0052] Electrochemical corrosion behavior test: Under a 3.5 wt% NaCl solution, the Tafel polarization curve was measured to obtain the corrosion parameters.

[0053] Weather resistance: After the self-stratifying coatings and coatings provided in the examples and comparative examples were immersed in seawater for one month, the surface morphology was observed and no obvious changes occurred. If there were no discoloration, blistering, or peeling phenomena, it was recorded as "qualified"; otherwise, it was recorded as "unqualified".

[0054] The test results are shown in Table 1 below:

[0055]

[0056]

[0057] In Table 1, " / " represents that this test item was not carried out.

[0058] As can be seen from the content of Table 1, the self-stratifying coatings provided in Examples 1-3 can form coatings with a self-stratifying structure. The adhesion of the self-stratifying coatings is above 14 MPa, and the surface energy is 20.81-23.31 MJ·m -2 , having good waterproof, antifouling, and weather resistance properties, and having good protective properties.

[0059] Figure 1 and Figure 2 are the OM diagram and SEM diagram of the cross-section of the self-stratifying coating provided in Example 1, Figure 3 are the FTIR-ATR characterization results of the surface and bottom surface of the self-stratifying coating in Example 1. It can be seen that the surface area of the coating mainly exhibits the characteristic absorption peaks of acrylic resin, that is, 1730 cm -1 (stretching vibration of C=O bond); relatively, the bottom region of the coating exhibits characteristic absorption peaks of epoxy resin, specifically 1509 cm - 1 (C=C skeletal vibration of benzene ring) and 828 cm - 1 (δ(C-H) para-substitution of benzene ring), and there are almost no characteristic absorption peaks of acrylic resin on the bottom surface of the coating. It is Figures 1 - 3 clearly shown that the coating has undergone self-stratification behavior, with the upper layer of the coating mainly being acrylic resin and the lower layer being epoxy resin.

[0060] Figure 4 Figure showing the comparison of surface energies of the self-stratifying coating provided in Example 3 and the coating provided in Comparative Example 1. The surface energy of the self-stratifying coating provided in Example 3 is the lowest.

[0061] Figure 5 Figure showing the comparison of electrochemical corrosion behaviors of Example 1 and Comparative Example 1. It can be seen that the corrosion potential value (-0.144 V) of the self-stratifying coating in Example 1 is significantly positively shifted from the corrosion potential value (-0.102 V) of the coating in Comparative Example 1. Therefore, the coating with a self-stratifying coating structure has better electrochemical corrosion resistance than the single-layer coating.

[0062] Comparing Examples 1-3, it can be seen that with the decrease in the addition amount of acrylic resin, the adhesion decreases, the water contact angle increases, and the surface energy decreases. This is mainly because the concentration difference between epoxy resin and acrylic resin increases, resulting in an increase in the surface tension difference, causing more intense Marangoni convection, promoting the migration of acrylic resin to the surface and forming a more complete enrichment layer, and promoting coating stratification.

[0063] Comparing with Examples 1-3, further reducing the content of acrylic resin (Example 4), that is, the ratio of epoxy resin to acrylic resin is 5:1, the stratification effect of the prepared self-stratifying coating is unstable, and both the water contact angle and the surface energy decrease, and the weather resistance is unqualified. From this, it can be seen that the ratio of epoxy resin to acrylic resin is 2:1 (Example 1), 3:1 (Example 2), and 4:1 (Example 3) is the best.

Claims

1. A weather-resistant self-stratifying coating, characterized in that: The raw material components include 20-60 parts of resin binder, 45-75 parts of mixed solvent, 5-10 parts of curing agent and 1-3 parts of defoaming agent by mass fraction; The resin adhesive is composed of epoxy resin and acrylic resin in a mass ratio of 1-5:1; the curing agent is an aliphatic amine curing agent; The mixed solvent comprises butyl acetate, m-xylene and methyl isobutyl ketone; wherein the mass ratio of m-xylene to methyl isobutyl ketone is 2-4:1; and the mass ratio of butyl acetate to curing agent is 1:2-3.

2. The weather-resistant self-stratifying coating according to claim 1, characterized in that: The defoamer is BYK-110 defoamer.

3. The method for using the weather-resistant self-stratifying coating according to claim 1, characterized in that: The specific steps are as follows: Step 1, mixing two solvents, m-xylene and methyl isobutyl ketone, at room temperature to obtain a mixed solvent; Step 2, completely dissolving the epoxy resin in half of the mixed solvent prepared in step 1 to obtain a mixed solution A; Completely dissolving the acrylic resin in the other half of the mixed solvent prepared in step 1 to obtain a mixed solution B; Step 3, the mixed solution A obtained in step 2 is mixed with the mixed solution B for the first time; then a defoamer is added for a second mixing; and then a mixture of a curing agent and butyl acetate is added for a third mixing to obtain a weather-resistant self-stratifying coating.

4. A weather-resistant self-stratifying coating, characterized in that: The weather-resistant self-stratifying coating described in any one of claims 1-2 is mixed evenly according to the method described in claim 3, and then sprayed on the surface of the substrate and cured to obtain the coating.

5. The weather-resistant self-stratifying coating according to claim 4, characterized in that: The curing temperature is room temperature and the curing time is at least 4 hours.

6. The weather-resistant self-stratifying coating according to claim 4, characterized in that: The curing process is to first stand at room temperature for 4 hours, and then dry and cure at a temperature of 50-60° C. for at least 2 hours.

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