Water-based defoaming agent for coating and preparation method of water-based defoaming agent

Abstract

The invention discloses a water-based defoaming agent for paint and a preparation method of the water-based defoaming agent, and relates to the technical field of paint assistants, the water-based defoaming agent comprises the following components: polyether modified polysiloxane of which the molecular weight of a polyether chain segment is in a range of 1000-5000; by introducing the natural antibacterial component chitosan quaternary ammonium salt, the effect of inhibiting mildew of the coating in a high-humidity environment is achieved, the chitosan quaternary ammonium salt is tightly combined with anion groups on the surfaces of microbial cells by virtue of a unique cation structure, breeding of molds and bacteria is effectively inhibited, stable quality of the coating in the high-humidity environment is guaranteed, and the coating has a good application prospect. The defoaming components are wrapped by a microencapsulation technology, the effect that the defoaming components can be released to repair defects when the coating is mechanically damaged after film forming is achieved, when the coating is mechanically impacted and microcapsules are broken, internal efficient defoaming components such as polyether modified polysiloxane and fatty alcohol-polyoxyethylene ether are rapidly released, newly generated foam is eliminated in time, and the coating has a good defoaming effect. The defects of pinholes, bubbles and the like of the coating caused by the failure of the defoaming agent are prevented.

Description

Technical Field

[0001] The present invention relates to the technical field of coating additives, and particularly to an aqueous defoamer for coatings and a preparation method thereof. Background Technique

[0002] A coating is a material used for decorative, protective or functional purposes, which can be coated on the surface of an object and form a firmly adhering film. It is widely used in many fields such as construction, industry, and household, playing a key role in improving the appearance and durability of products. During the production and application process of coatings, the generation of foam is an extremely troublesome problem. The existence of foam will not only leave defects such as pinholes and bubble marks on the appearance of the coating, resulting in an uneven coating surface and affecting the aesthetics, but also have a negative impact on the internal performance of the coating, such as reducing the adhesion between the coating and the substrate and weakening the corrosion resistance of the coating. An aqueous defoamer is an important part of coating additives, specifically used to eliminate the foam generated during the production, storage, and construction of aqueous coatings. In aqueous coatings, due to the presence of various surfactants, polymers and other components in the formulation, combined with process operations such as stirring and pumping, foam is very likely to be generated. The existence of foam will seriously affect the performance of the coating, such as causing pinholes and bubble marks on the coating, reducing the adhesion and gloss of the coating, and may also affect the construction efficiency and uniformity of the coating.

[0003] Traditional aqueous defoamers still have certain defects when in use. The aqueous defoamers in the prior art mainly focus on the defoaming function. However, in a special high-humidity environment, the coating is extremely vulnerable to microbial erosion and then mildew occurs. This not only seriously damages the quality of the coating and shortens its service life, but also may pose a health hazard due to microbial growth. In addition, during the actual use of the coating, once the film is mechanically damaged after film formation, the originally functioning defoamer may become ineffective, thus triggering new foam-related defects. Therefore, it is of great significance to develop an aqueous defoamer for coatings and a preparation method thereof. Summary of the Invention

[0004] The purpose of the present invention is to make up for the deficiencies of the prior art, and provides an aqueous defoamer for coatings and a preparation method thereof. It not only has excellent defoaming ability, but also has remarkable antibacterial efficacy, can well adapt to high-humidity environments, and more prominently, when the coating is mechanically damaged after film formation, the defoamer can achieve self-repair and maintain the defoaming performance of the coating.

[0005] In order to solve the above technical problems, the present invention provides the following technical solution: An aqueous defoamer for coatings, which comprises the following components: Polyether-modified polysiloxane, the molecular weight of its polyether chain segment is in the range of 1000 - 5000; Fatty alcohol polyoxyethylene ether, prepared by ethoxylation reaction; The natural antibacterial component chitosan quaternary ammonium salt is obtained by quaternary ammonium modification of chitosan, and a quaternary ammonium group is introduced into the molecule; The microcapsule internally encapsulates polyether-modified polysiloxane and fatty alcohol polyoxyethylene ether. The wall material of the microcapsule is gelatin and arabic gum, and the two form a wall film through complex coacervation method; The dispersant sodium polyacrylate has a linear molecular structure and ionizes sodium ions and polyacrylate ions in an aqueous system; The thickener hydroxyethyl cellulose contains hydroxyethyl groups in its molecule and is introduced onto the cellulose molecular chain through chemical modification.

[0006] Furthermore, the mass ratio of the polyether-modified polysiloxane, fatty alcohol polyoxyethylene ether and chitosan quaternary ammonium salt is (5 - 10):(3 - 8):(1 - 3).

[0007] Furthermore, the average particle size of the microcapsule is 1 - 10 μm.

[0008] Furthermore, in the molecular structure of the polyether-modified polysiloxane, the degree of polymerization of the siloxane chain segment is 50 - 150.

[0009] Furthermore, the degree of quaternization of the chitosan quaternary ammonium salt is 60% - 80%.

[0010] A preparation method of an aqueous defoamer for coatings is applicable to the above-mentioned aqueous defoamer for coatings, and this preparation method includes the following steps: Preparing a defoaming premix containing chitosan quaternary ammonium salt: adding chitosan quaternary ammonium salt into deionized water according to a ratio, using a mechanical stirring device to stir to make a chitosan quaternary ammonium salt solution, and slowly adding polyether-modified polysiloxane and fatty alcohol polyoxyethylene ether into the chitosan quaternary ammonium salt solution in a dropping manner according to the mass ratio, and continuously stirring to make a defoaming premix containing chitosan quaternary ammonium salt; Preparing microencapsulated defoaming components: adding gelatin and arabic gum into deionized water in different containers respectively, heating and stirring to completely dissolve them, mixing the polyether-modified polysiloxane and fatty alcohol polyoxyethylene ether evenly, and then slowly adding them into the gelatin solution, starting stirring to form a uniform dispersion. Under the condition of continuous stirring, slowly drop the arabic gum solution into the above dispersion by using a peristaltic pump, and at the same time use an acid-base regulator to adjust the pH value of the system to 4 - 5, control the temperature at 40 - 50 °C by using a constant temperature water bath device. After the reaction is completed, cool down and add a curing agent for curing operation to stabilize the microcapsule structure; Mixing and post-treatment: Transfer the prepared microcapsules and defoaming premix to the mixing equipment, start high-speed stirring to evenly disperse the microcapsules in the system, remove unreacted impurities and large particles from the mixed liquid through a filtration device, concentrate the filtrate with a vacuum concentration device, adjust the defoaming agent concentration range, and finally obtain a water-based defoaming agent product for coatings.

[0011] Furthermore, in the process of preparing the defoaming premix containing chitosan quaternary ammonium salt, the stirring speed of the mechanical stirring device is controlled at 200-500 rpm, and the stirring time is 30-60 minutes.

[0012] Furthermore, in the preparation process of the microencapsulated defoaming component, the concentration of the gelatin solution is 2%-5%, and the concentration of the gum arabic solution is 1%-3%.

[0013] Furthermore, in the mixing and post-processing steps, the pressure of the vacuum concentration is controlled at -0.08MPa-0.06MPa, and the temperature is controlled at 40-50°C.

[0014] Compared with the prior art, the aqueous defoamer for coatings and the preparation method thereof have the following beneficial effects: The invention achieves the effect of inhibiting the mildew of the coating in a high humidity environment by introducing the natural antibacterial ingredient chitosan quaternary ammonium salt. The chitosan quaternary ammonium salt is tightly combined with the anionic groups on the surface of microbial cells by virtue of its unique cationic structure, effectively inhibiting the growth of molds and bacteria, and ensuring the stable quality of the coating in a high humidity environment. The antifoaming component is wrapped by microencapsulation technology, so that the antifoaming component can be released to repair defects when the coating is mechanically damaged after film formation. When the coating is subjected to mechanical impact, the microcapsule is broken, and the internal high-efficiency antifoaming components such as polyether-modified polysiloxane and fatty alcohol polyoxyethylene ether are quickly released, so that newly generated foam is eliminated in time, and defects such as pinholes and bubbles in the coating caused by the failure of the defoamer are prevented.

[0015] Other advantages, objectives and features of the present invention will be set forth in part in the following description and, in part, will be apparent to those skilled in the art based on an examination of the following or may be taught from the practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the prior art descriptions are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention, and for ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0017] Figure 1It is a schematic flow diagram of a preparation method of an aqueous defoamer for coatings. Detailed implementation manners

[0018] To further elaborate on the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, the following will, in conjunction with the accompanying drawings and preferred embodiments, describe in detail the specific implementation manners, structures, features and their effects according to the present invention.

[0019] Example 1 Accurately weigh 7 g of polyether-modified polysiloxane (the molecular weight of its polyether chain segment is 3000, and the degree of polymerization of the siloxane chain segment is 100), 5 g of fatty alcohol polyoxyethylene ether, 2 g of chitosan quaternary ammonium salt (the degree of quaternization is 70%), 4 g of gelatin, 2 g of gum arabic, 0.1 g of sodium polyacrylate, 0.05 g of hydroxyethyl cellulose, sufficient deionized water, appropriate acid-base regulators and curing agents.

[0020] Add 2 g of chitosan quaternary ammonium salt to 100 g of deionized water, use a mechanical stirring device, set the stirring speed to 300 revolutions per minute, and stir for 40 minutes until the chitosan quaternary ammonium salt is completely dissolved to form a homogeneous solution. Then, according to the mass ratio, slowly drip 7 g of polyether-modified polysiloxane and 5 g of fatty alcohol polyoxyethylene ether into the chitosan quaternary ammonium salt solution through a dropping funnel, continuously stir during the dropping process, and continue to stir for 30 minutes after the dropping is completed to prepare a defoaming premix containing chitosan quaternary ammonium salt.

[0021] Add 4 g of gelatin to 100 g of deionized water, heat to 45 °C and stir until it is completely dissolved; add 2 g of gum arabic to 50 g of deionized water, also heat to 45 °C and stir until it is completely dissolved. After mixing 7 g of polyether-modified polysiloxane and 5 g of fatty alcohol polyoxyethylene ether evenly, slowly add them to the gelatin solution and start stirring to form a homogeneous dispersion.

[0022] Under the condition of continuous stirring, slowly drip the gum arabic solution into the above dispersion by using a peristaltic pump, at the same time use an acid-base regulator to adjust the pH value of the system to 4.5, use a constant temperature water bath device to maintain the temperature at 45 °C, after reacting for 2 hours, naturally cool to room temperature, and add an appropriate amount of curing agent for curing operation to stabilize the microcapsule structure.

[0023] Transfer the prepared microcapsules and the defoaming premix to a high-speed stirring device, stir at a speed of 1000 revolutions per minute for 30 minutes to make the microcapsules evenly dispersed in the system. The mixed solution is filtered through a filter membrane with a pore size of 0.45 μm to remove unreacted impurities and large particle substances, and vacuum concentration is carried out by using a rotary evaporator. Control the pressure at -0.07 MPa and the temperature at 45 °C, concentrate the filtrate, adjust the defoamer concentration, and finally obtain an aqueous defoamer product for coatings.

[0024] Defoaming performance test: In the laboratory, the production process of waterborne coatings was simulated. An antifoaming agent prepared in this example was added to a certain amount of waterborne coating base material. According to the standard test method, a high-speed stirrer was used to stir the coating, and the generation and disappearance of foam were observed. The results showed that after the addition of the antifoaming agent, the foam rapidly decreased within 30 seconds, and during the subsequent stirring process, the amount of foam generated was significantly lower than that of the control group without the addition of the antifoaming agent, indicating that the antifoaming agent has good defoaming performance.

[0025] Antibacterial performance test: The prepared antifoaming agent was added to the waterborne coating to make a coating sample plate, which was placed in a high-humidity (humidity 90%) environment for 7 days, and whether there was mildew on the coating surface was observed. At the same time, a coating sample plate without the addition of the antifoaming agent was set as a control. After 7 days, obvious mildew plaques appeared on the surface of the control group coating, while there were no obvious signs of mildew on the surface of the coating sample plate added with the antifoaming agent of this example, proving that the antifoaming agent can effectively inhibit the mildew of the coating in a high-humidity environment.

[0026] Self-healing performance test: The waterborne coating added with the antifoaming agent was coated on a sample plate. After the coating was dried into a film, a sharp object was used to scratch a wound on the coating surface to simulate mechanical damage, and then the situation at the wound was observed. It was found that no new bubbles were generated around the wound within 24 hours, while a large number of bubbles appeared at the wound in the control group without the addition of the microencapsulated antifoaming component, indicating that when the antifoaming agent encounters mechanical damage after the coating forms a film, it can release the antifoaming component to repair the defect.

[0027] Example 2 Accurately weigh 5 g of polyether-modified polysiloxane (the molecular weight of the polyether chain segment is 1000, and the degree of polymerization of the polysiloxane chain segment is 50), 3 g of fatty alcohol polyoxyethylene ether, 1 g of chitosan quaternary ammonium salt (the degree of quaternization is 60%), 2 g of gelatin, 1 g of gum arabic, 0.05 g of sodium polyacrylate, 0.02 g of hydroxyethyl cellulose, sufficient deionized water, an appropriate amount of acid-base regulator, and curing agent.

[0028] Slowly add 1 g of chitosan quaternary ammonium salt to 50 g of deionized water, start the mechanical stirring device, set the stirring speed to 200 revolutions per minute, and continuously stir for 30 minutes until the chitosan quaternary ammonium salt is completely dissolved to form a clear and transparent solution. During the stirring process, 5 g of polyether-modified polysiloxane and 3 g of fatty alcohol polyoxyethylene ether were slowly added dropwise to the chitosan quaternary ammonium salt solution through a separatory funnel, and the dropping speed was controlled at 30-40 drops per minute. After the dropping was completed, continue to stir for 30 minutes to make each component fully mixed and uniform, and an antifoaming premix containing chitosan quaternary ammonium salt was prepared. During the stirring process, it was observed that the solution gradually became uniform and there was no obvious layering phenomenon.

[0029] Add 2 g of gelatin to 50 g of deionized water, place it in a constant temperature water bath, heat it to 40 °C, and at the same time turn on the stirrer and stir at a speed of 150 revolutions per minute until the gelatin is completely dissolved to form a uniform gelatin solution. Similarly, add 1 g of gum arabic to 30 g of deionized water, heat it to 40 °C and stir until it is completely dissolved. After thoroughly mixing 5 g of polyether-modified polysiloxane and 3 g of fatty alcohol polyoxyethylene ether, slowly pour it into the gelatin solution and adjust the stirring speed to 200 revolutions per minute to form a uniform dispersion.

[0030] Under the condition of continuous stirring, use a peristaltic pump to slowly drip the gum arabic solution into the above dispersion, and control the dripping speed at 15 - 20 drops per minute. At the same time, use an acid-base regulator (dilute hydrochloric acid or sodium hydroxide solution) to adjust the pH value of the system to 4, and use a constant temperature water bath device to strictly control the temperature at 40 °C. After the reaction proceeds for 1.5 hours, stop heating, let it cool naturally to room temperature, and slowly add an appropriate amount of glutaraldehyde solution (mass fraction 2%) for curing operation to stabilize the microcapsule structure. During the reaction process, it can be observed that the solution gradually becomes turbid and a large number of tiny particles, that is, microcapsules, are formed.

[0031] Transfer the prepared microcapsules and defoaming premix to a high-speed stirring device, set the stirring speed at 800 revolutions per minute, and stir for 25 minutes to evenly disperse the microcapsules in the system. The mixed solution is filtered through a filter membrane with a pore size of 0.3 μm to remove unreacted impurities and large particle substances. During the filtration process, a small amount of insoluble substances can be seen remaining on the filter membrane. Use a rotary evaporator for vacuum concentration, control the pressure at -0.08 MPa and the temperature at 40 °C, and concentrate the filtrate until the appropriate defoamer concentration is reached, and finally obtain a water-based defoamer product. During the concentration process, it is observed that the volume of the solution gradually decreases and the concentration gradually increases.

[0032] After testing, in terms of defoaming performance, during the simulated stirring process of water-based paint production, the foam significantly decreases within 40 seconds; in terms of antibacterial performance, after being placed in a high-humidity environment for 5 days, there is no obvious mildew on the coating surface; during the self-healing performance test, very few bubbles are generated at the wound within 24 hours after mechanical damage, showing a certain self-healing ability.

[0033] Example Three Accurately measure 10 g of polyether-modified polysiloxane (the molecular weight of the polyether chain segment is 5000, and the degree of polymerization of the siloxane chain segment is 150), 8 g of fatty alcohol polyoxyethylene ether, 3 g of chitosan quaternary ammonium salt (the degree of quaternization is 80%), 5 g of gelatin, 3 g of gum arabic, 0.2 g of sodium polyacrylate, 0.1 g of hydroxyethyl cellulose, and sufficient deionized water, acid-base regulator, and curing agent.

[0034] 3g chitosan quaternary ammonium salt is added in 150g deionized water, use mechanical stirring device, setting stirring speed is 500 rev / min, stir 60 minutes, until chitosan quaternary ammonium salt dissolves completely, in whipping process, chitosan quaternary ammonium salt is gradually dispersed in water, solution is slightly viscous by becoming limpid, then, 10g polyether-modified polysiloxane and 8g fatty alcohol-polyoxyethylene ether are slowly dripped by constant pressure dropping funnel in proportion, rate of addition is controlled at 40-50 per minute, continues to stir in the dropping process, continues to stir 40 minutes after completion of dropwise addition, each component is fully mixed, obtains the defoaming premix containing chitosan quaternary ammonium salt.Now solution presents uniform milky white.

[0035] Dissolve 5 g of gelatin and 3 g of gum arabic in 100 g and 60 g of deionized water, respectively. Place the container containing the gelatin solution in a constant temperature water bath, heat to 50°C, and stir at 200 rpm until the gelatin is completely dissolved. Perform the same operation on the gum arabic solution, mix the polyether-modified polysiloxane and fatty alcohol polyoxyethylene ether evenly, and then slowly add them to the gelatin solution. Adjust the stirring speed to 250 rpm to form a uniform dispersion.

[0036] Under continuous stirring, the gum arabic solution was slowly added to the above dispersion using a peristaltic pump. At the same time, the pH value of the system was adjusted to 5 using an acid-base regulator (dilute sulfuric acid or ammonia water). The temperature was maintained at 50°C using a constant temperature water bath. After the reaction was carried out for 2.5 hours, the heating was stopped, the temperature was naturally cooled to room temperature, and an appropriate amount of epichlorohydrin (mass fraction of 3%) was added for curing operation to stabilize the microcapsule structure. During the reaction, the color of the solution gradually darkened and became more turbid.

[0037] Transfer the microcapsules and defoaming premix to the mixing equipment, set the stirring speed to 1200 rpm, and stir for 35 minutes to ensure that the microcapsules are evenly dispersed in the system. The mixed solution is filtered through a filter membrane with a pore size of 0.6 μm to remove unreacted impurities and large particles. After filtration, the filtrate becomes clear and transparent. Use a vacuum concentration device to concentrate, control the pressure at -0.06 MPa, and the temperature at 50°C. The filtrate is concentrated to obtain an aqueous defoaming agent product. During the concentration process, pay attention to the changes in the solution. When the viscosity of the solution reaches an appropriate range, stop concentrating.

[0038] In the defoaming performance test of the product of this embodiment, the foam generated by stirring was greatly reduced within 25 seconds; in terms of antibacterial performance, the coating was almost free of mildew after being placed in a high humidity environment for 10 days; in the self-repairing performance test, basically no new bubbles were generated at the wound within 12 hours after mechanical damage, and the self-repairing effect was good.

[0039] Embodiment 4 Accurately weigh 8 g of polyether modified polysiloxane (molecular weight of the polyether segment is 2500, degree of polymerization of the siloxane segment is 120), 6 g of fatty alcohol polyoxyethylene ether, 2.5 g of chitosan quaternary ammonium salt (quaternization degree 75%), 3 g of gelatin, 2 g of gum arabic, 0.15 g of sodium polyacrylate, 0.08 g of hydroxyethyl cellulose, sufficient deionized water, acid-base regulator and curing agent.

[0040] 2.5 g of chitosan quaternary ammonium salt was added to 120 g of deionized water, and a mechanical stirring device was started. The mixture was stirred at a speed of 400 rpm for 50 minutes to completely dissolve the chitosan quaternary ammonium salt. During the stirring process, the solution gradually became clear. Then, 8 g of polyether-modified polysiloxane and 6 g of fatty alcohol polyoxyethylene ether were slowly added dropwise through a dropping funnel. The dropping speed was controlled at 35-45 drops per minute. The mixture was continuously stirred during the dropping process. After the dropping was completed, the mixture was continuously stirred for 35 minutes to obtain a defoaming premix containing chitosan quaternary ammonium salt. At this time, the solution was uniformly translucent.

[0041] Dissolve 3g of gelatin and 2g of gum arabic in 80g and 50g of deionized water respectively, place the container containing the gelatin solution in a constant temperature water bath, heat to 45°C, and stir at 180 rpm until the gelatin is completely dissolved; perform the same operation on the gum arabic solution, mix the polyether-modified polysiloxane and fatty alcohol polyoxyethylene ether evenly, and then slowly add them to the gelatin solution. Adjust the stirring speed to 220 rpm to form a uniform dispersion.

[0042] Under continuous stirring, the gum arabic solution is slowly added to the above dispersion using a peristaltic pump. At the same time, the pH value of the system is adjusted to 4.5 using an acid-base regulator (acetic acid or potassium hydroxide solution). The temperature is controlled at 45°C using a constant temperature water bath. After reacting for 2 hours, the heating is stopped, the temperature is naturally cooled to room temperature, and an appropriate amount of glyoxal (mass fraction of 2.5%) is added for curing operation to stabilize the microcapsule structure. During the reaction, the solution gradually forms a delicate emulsion.

[0043] The microcapsules and defoaming premix were transferred to a mixing device, the stirring speed was set to 1000 rpm, and the mixture was stirred for 30 minutes to uniformly disperse the microcapsules in the system. The mixed solution was filtered through a filter membrane with a pore size of 0.5 μm to remove unreacted impurities and large particles. After filtration, the transparency of the filtrate was significantly improved. The filtrate was concentrated using a vacuum concentration device, the pressure was controlled at -0.07 MPa, and the temperature was controlled at 45°C. The filtrate was concentrated to obtain an aqueous defoaming agent product. During the concentration process, pay attention to the concentration changes of the solution to ensure that the ideal product concentration is achieved.

[0044] In the defoaming performance test, the foam generated by stirring significantly decreased within 30 seconds; in terms of antibacterial performance, after being placed in a high-humidity environment for 8 days, there was no obvious mildew on the coating; during the self-healing performance test, within 18 hours after mechanical damage, very few bubbles were generated at the wound, indicating good self-healing performance.

[0045] Comparative example Weigh 10 g of polyether-modified polysiloxane (the molecular weight of the polyether segment is 3000, and the degree of polymerization of the siloxane segment is 100), 8 g of fatty alcohol polyoxyethylene ether, 0.2 g of sodium polyacrylate, 0.1 g of hydroxyethyl cellulose, and sufficient deionized water. No chitosan quaternary ammonium salt and microencapsulation components were added in this comparative example.

[0046] Add polyether-modified polysiloxane, fatty alcohol polyoxyethylene ether, sodium polyacrylate, and hydroxyethyl cellulose to 200 g of deionized water. Use a mechanical stirring device, set the stirring speed to 500 revolutions per minute, and stir for 60 minutes to make them fully mixed and uniform, obtaining a defoamer for comparison. During the stirring process, the solution gradually became uniform, but there were no obvious change characteristics.

[0047] Defoaming performance test: According to the same test method as in the example, simulate the production process of waterborne coatings in the laboratory. Add 0.5 g of the defoamer for comparison to 100 g of the waterborne coating base material, and use a high-speed stirrer to stir at a speed of 3000 revolutions per minute for 5 minutes. Observe the generation and disappearance of foam. The results show that after adding the defoamer, the foam decreased within 40 seconds, but 5 minutes after the stirring stopped, there was still a large amount of foam, and during the subsequent stirring process, the amount of foam generated was significantly more than that of the defoamer in the example, indicating that the defoaming performance of this defoamer for comparison is relatively weak.

[0048] Antibacterial performance test: Add the defoamer for comparison to the waterborne coating to make a coating sample board with a coating thickness of 0.1 mm. Place the sample board in an environmental chamber with high humidity (humidity 90%, temperature 30 °C) for 5 days, and observe whether there is mildew on the coating surface. At the same time, set a coating sample board without the defoamer as a control. After 5 days, a large number of mold colonies appeared on the surface of the sample board coating, and the area of the colonies accounted for about 20% of the total area of the coating. Compared with the control group without the defoamer, the mildew situation was basically the same, proving that this defoamer for comparison does not have antibacterial performance.

[0049] Self-healing performance test: Uniformly coat the waterborne coating containing the defoamer for comparison on the sample board with a coating thickness of 0.15 mm. After the coating dries and forms a film, use a sharp object to scratch a wound with a length of 2 cm and a depth of about 0.05 mm on the coating surface to simulate mechanical damage. Then place the sample board in a normal environment to observe the situation at the wound, and record it every 6 hours. It was found that a large number of bubbles quickly appeared at the wound, and the number and size of the bubbles did not change significantly within 24 hours.

[0050]

[0051] As described in the above table, from the perspective of raw material parameters, in each example, the mass and molecular structure parameters of components such as polyether-modified polysiloxane, fatty alcohol polyoxyethylene ether, and chitosan quaternary ammonium salt are different, which will affect the performance of the defoamer. In terms of the preparation process parameters, there are differences in the stirring speed, stirring time, solution concentration, reaction pH value, temperature, and time in each example, and these differences will change the formation of microcapsules and the uniformity of the defoamer.

[0052] In terms of performance, Examples 1, 2, 3, and 4 all have good defoaming performance and can reduce foam in a short time. In terms of antibacterial performance, each example can effectively inhibit the mildew of the coating in a high-humidity environment. However, due to the absence of chitosan quaternary ammonium salt and microencapsulation components, the comparative example shows extremely poor antibacterial and self-repair performance, and the defoaming performance is also relatively weak, fully demonstrating the advantages of adding specific components and adopting a special preparation process in the present invention.

[0053] The above description is only the preferred embodiments of the present invention and does not impose any form of limitation on the present invention. Although the present invention has been disclosed above with preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some changes or modifications to equivalent embodiments with equivalent changes within the scope of the technical solution of the present invention. However, as long as it does not depart from the content of the technical solution of the present invention, any brief modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. An aqueous defoamer for coatings, characterized in that, It includes the following components: Polyether-modified polysiloxane, whose molecular weight of the polyether chain segment is in the range of 1000 - 5000; Fatty alcohol polyoxyethylene ether, prepared by ethoxylation reaction; Natural antibacterial ingredient chitosan quaternary ammonium salt, obtained by quaternization modification of chitosan, with quaternary ammonium groups introduced into the molecule; Microcapsules, internally encapsulating polyether-modified polysiloxane and fatty alcohol polyoxyethylene ether, and the microcapsule wall material is gelatin and arabic gum, and the two form a wall film through complex coacervation method; Dispersant sodium polyacrylate, having a linear molecular structure, ionizing sodium ions and polyacrylate ions in an aqueous system; Thickener hydroxyethyl cellulose, whose molecule contains hydroxyethyl groups, introduced into the cellulose molecular chain through chemical modification.

2. An aqueous defoamer for coatings according to claim 1, characterized in that, The mass ratio of the polyether-modified polysiloxane, fatty alcohol polyoxyethylene ether and chitosan quaternary ammonium salt is (5 - 10):(3 - 8):(1 - 3).

3. The aqueous defoamer for coatings according to claim 1, characterized in that, The average particle size of the microcapsules is 1 - 10 μm.

4. An aqueous defoamer for coatings according to claim 1, wherein In the molecular structure of the polyether-modified polysiloxane, the degree of polymerization of the siloxane chain segment is 50 - 150.

5. An aqueous defoamer for coatings according to claim 1, characterized in that, The quaternization degree of the chitosan quaternary ammonium salt is 60% - 80%.

6. A preparation method of an aqueous defoamer for coatings, applicable to the aqueous defoamer for coatings described in claims 1-5, characterized in that, The preparation method includes the following steps: Preparation of defoaming premix containing chitosan quaternary ammonium salt: Add chitosan quaternary ammonium salt to deionized water according to the proportion, stir with a mechanical stirring device to make a chitosan quaternary ammonium salt solution, and slowly add polyether-modified polysiloxane and fatty alcohol polyoxyethylene ether to the chitosan quaternary ammonium salt solution by dropping according to the mass ratio, and continuously stir to make a defoaming premix containing chitosan quaternary ammonium salt; Preparation of microencapsulated defoaming components: Add gelatin and arabic gum to deionized water in different containers respectively, heat and stir to completely dissolve them, mix polyether-modified polysiloxane and fatty alcohol polyoxyethylene ether evenly, and slowly add them to the gelatin solution, start stirring to form a uniform dispersion, under continuous stirring, slowly drip the arabic gum solution into the above dispersion by using a peristaltic pump, at the same time use an acid-base regulator to adjust the pH value of the system to 4 - 5, use a constant temperature water bath device to control the temperature at 40 - 50 °C, after the reaction is completed, cool down, and add a curing agent for curing operation to stabilize the microcapsule structure; Mixing and post-treatment: Transfer the prepared microcapsules and defoaming premix to a mixing device, start high-speed stirring to make the microcapsules evenly dispersed in the system, the mixed solution is filtered through a filtering device to remove unreacted impurities and large particle substances, and the filtrate is concentrated by a vacuum concentration device to adjust the defoamer concentration range, and finally a water-based defoamer product for coatings is prepared.

7. The aqueous defoamer for coatings and its preparation method according to claim 6, characterized in that During the preparation of the defoaming premix containing chitosan quaternary ammonium salt, the stirring speed of the mechanical stirring device is controlled at 200 - 500 revolutions per minute, and the stirring time is 30 - 60 minutes.

8. The aqueous defoamer for coatings and its preparation method according to claim 6, characterized in that, During the preparation of the microencapsulated defoaming components, the concentration of the gelatin solution is 2% - 5%, and the concentration of the arabic gum solution is 1% - 3%.

9. A water-based defoamer for coatings and its preparation method according to claim 6, characterized in that, In the mixing and post-treatment step, the pressure of vacuum concentration is controlled at -0.08 MPa - 0.06 MPa, and the temperature is controlled at 40 - 50 °C.

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