Preparation method and application of gemini-based low-foam ether ester nonionic surfactant

Abstract

The invention relates to a preparation method and application of a gemini-based low-foam ether ester nonionic surfactant, and the preparation method of the gemini-based low-foam ether ester nonionic surfactant comprises the following steps: 1, mixing linoleic acid and polyethylene glycol dilaurate, adding a catalyst A, adding a solvent B, carrying out nitrogen replacement, and carrying out a reaction to obtain a gemini-based low-foam ether ester nonionic surfactant; the reaction is finished until no water is generated in the reaction container, and a reaction solution is obtained; and step 2, evaporating out liquid from the reaction solution to obtain the gemini-based low-foam ether ester nonionic surfactant. The invention also discloses the application of the gemini-based low-foam ether ester nonionic surfactant in a coating. The gemini-based low-foam ether ester nonionic surfactant prepared by the method disclosed by the invention can solve the problem that the stability of the existing surfactant in an acid medium is slightly poor. And by adding the ether ester nonionic surfactant, the problems of poor water resistance, poor glossiness and the like of the coating are solved.

Description

Background Art

[0001] Surfactants are a class of substances that can effectively reduce surface (interface) tension and can form an ordered aggregate state at a certain concentration, realizing a variety of applications. Surfactants have important application value in the fields of fine chemicals due to their excellent dispersibility, wettability, emulsification and antistatic properties. With the development of society and the improvement of the degree of industrialization in the world, the scope of use of surfactants has gradually expanded from ordinary chemical products to antibacterial, food additives, new energy, pollutant treatment, biomedicine and other fields.

[0002] Compared with traditional surfactants, Gemini surfactants are a kind of "dimers" that connect traditional surfactants with a linking group, which can better reduce the surface tension of water and increase the tension of the oil-water interface. Gemini surfactants can also reduce the concentration of critical micelles, improve water solubility, emulsification, foaming, wettability, etc. Due to the high surface tension of water in aqueous systems, substrate wetting agents must be used, and their types include: organic small molecule surfactants, polyether-modified polysiloxanes, acetylene glycols and their derivatives, organic fluorine and their derivatives. The conditions of an ideal substrate wetting agent are: low surface tension; high wetting performance; good hydrolysis resistance; low foam or defoaming effect; wide versatility in coating formulations; no adverse effects on other properties of the coating.

[0003] Polyethylene glycol dilaurate is a widely used fatty acid ester, belonging to the high-performance ether ester nonionic surfactant. Its preparation method is mainly obtained by esterification reaction. The specific method is to react polyethylene glycol and lauric anhydride in the presence of an appropriate catalyst under certain temperature and pressure conditions for a period of time to form polyethylene glycol dilaurate. It has excellent lubrication, emulsification, solubilization, decontamination, penetration, hard water resistance and wetting properties, and has a certain defoaming ability. This compound has a wide HLB value, high activity and low toxicity, and can significantly improve the consistency of products in shampoos and conditioners. In cosmetics, it can play a role in solubilization, emulsification and moisturizing. In the food industry, as an additive, it can provide emulsification, defoaming, wetting, dispersion and antioxidant functions. In the textile industry, it is widely used in polyester oil. In addition, in the fields of medicine, pesticides, metal processing and leather, this compound also plays an important auxiliary role. Polyethylene glycol dilaurate is a Gemini surfactant with a specific structure, suitable for dynamic penetration and defoaming of water-based coatings, inks, and adhesives. Its hydrophobic carbon chain is prone to strong interaction due to the CH bond, which can improve its hydrophobicity, make its surface structure more compact, and lower its surface energy, showing good surface activity. However, its stability in acidic media is slightly poor, and the pH value must be controlled to be much greater than 4. In addition, it has high foam in aqueous solution, which affects its application in coatings.

[0004] The surfactants used in existing wood paints have high foaming properties, poor water resistance, cannot be cured with the coating, and are prone to migration, which affects the water resistance and adhesion of the coating. Summary of the invention

[0005] The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art, especially the poor stability of the surfactant in the prior art in an acidic medium, and to provide a method for preparing a gemini low-foam ether ester nonionic surfactant. The obtained gemini low-foam ether ester nonionic surfactant has good water resistance and defoaming and anti-foaming properties.

[0006] Another technical problem to be solved by the present invention is to overcome the deficiencies of the prior art and provide an application of a gemini low-foam ether ester nonionic surfactant, and apply the obtained gemini low-foam ether ester nonionic surfactant to coatings to improve the water resistance of the coating.

[0007] The technical solution adopted by the present invention to solve the technical problem is a method for preparing a gemini low-foam ether ester nonionic surfactant, comprising the following steps:

[0008] Step 1: adding linoleic acid and surfactant polyethylene glycol dilaurate into a reaction container and mixing, then adding catalyst A and a certain amount of solvent B, then performing nitrogen replacement, reacting at a certain temperature until no water is produced in the reaction container, the reaction is terminated, and a reaction solution is obtained;

[0009] Step 2: The reaction solution obtained in step 1 is evaporated at a certain pressure and a certain temperature until no liquid evaporates, thereby obtaining a gemini low-foam ether ester nonionic surfactant (LPEG).

[0010] Furthermore, in step 1, the reaction between linoleic acid and the surfactant polyethylene glycol dilaurate produces water, so whether the reaction is complete is determined by whether water is produced. Here, the reaction system cannot form an azeotrope with water, and the water in the system can be removed during the reaction by a water separator or by adding an azeotropic dehydrating agent.

[0011] Further, in step 1, linoleic acid and surfactant polyethylene glycol dilaurate are added to a reaction vessel in a molar ratio, and then catalyst A is added, and a certain amount of solvent B is added at the same time, and then nitrogen replacement is performed, and then a water separator filled with solvent B is connected, and the reaction is carried out at a certain temperature until there is no water in the water separator to obtain a reaction solution.

[0012] Further, in step 1, according to the ratio of the amount of substance, linoleic acid: polyethylene glycol dilaurate is 0.5 to 2:1. The catalyst A is 1 to 3% of the mass of the reaction system. The amount of solvent B added is more than 0.5 times the mass of the reaction system (preferably 0.8 to 1.5 times). The mass of the reaction system here refers to the sum of the total mass of linoleic acid, polyethylene glycol dilaurate, and catalyst A. Adding too little solvent B will affect the speed and progress of the reaction, and adding too much will not help the reaction much, and it will have to be evaporated later, resulting in waste of solvent and increased energy consumption, which is unnecessary.

[0013] Studies have shown that within a certain range, as the amount of linoleic acid increases, the degree of reaction becomes deeper, and when the molar ratio of linoleic acid to polyethylene glycol dilaurate is 2:1, the reaction is more complete (based on the acid value). The more catalyst is added, the faster the reaction speed.

[0014] Further, in step 1, catalyst A is p-toluenesulfonic acid, a solid-supported liquid acid (more preferably a solid-supported liquid acid BF 3 / Al 2 O 3 ), at least one of zeolite bar molecular sieves. Solvent B is at least one of cyclohexane, 4-methyl-2-pentanone, and trimethylpentane.

[0015] Furthermore, in step 1, the reaction temperature is 70-90°C. Stir during the reaction for 4-6 hours. Studies have shown that if the reaction temperature is too high, the vegetable oil will oxidize, hydrolyze and become rancid during long-term heating at high temperature, which will reduce the quality of the oil, cause a large loss of essential fatty acids, and produce harmful substances such as trans fatty acids. If the temperature is too low, the two substances will not react. The reaction is generally completed after a reaction time of 4-6 hours. If the reaction time is increased, the reaction will not continue. If the reaction time is too short, the reaction will not be complete.

[0016] Furthermore, in step 2, the liquid (solvent) is evaporated by rotary evaporation or reduced pressure distillation.

[0017] Further, in step 2, the rotary evaporation pressure is 0.09-0.1 MPa. The temperature is 30-50°C. The time is generally 2-4 hours. Studies have shown that if the rotary evaporation temperature is too high, bumping will occur, and if the temperature is too low, the solvent cannot be evaporated. Too high or too low pressure will cause the solvent to not evaporate.

[0018] The present invention uses the gemini low-foam ether ester nonionic surfactant, and adds the surfactant equivalent to 0.3%-2% of the coating mass into the coating.

[0019] The method of the present invention prepares a gemini low-foam ether ester nonionic surfactant, and uses linoleic acid to modify the surfactant polyethylene glycol dilaurate to obtain a polymer with good water resistance and defoaming and foam suppression properties. It can solve the problem that the existing surfactant has slightly poor stability in acidic media, and provide a new idea for the development and application of gemini low-foam wetting agents. By adding ether ester nonionic surfactants, the problems of poor water resistance and poor gloss of coatings are solved, and a new idea is provided for the development and application of gemini low-foam wetting agents.

[0020] Beneficial effects of the present invention:

[0021] (1) The raw materials used in the present invention are linoleic acid and surfactant polyethylene glycol dilaurate, both of which are environmentally friendly materials;

[0022] (2) The present invention grafts linoleic acid onto polyethylene glycol dilaurate to prepare a gemini low-foam ether ester nonionic surfactant composed of a linoleic acid single chain (hydrophobic part) and a bridging group (hydrophilic part), and the defoaming ability, static surface tension, coating wettability, and coating water resistance are gradually improved;

[0023] Linoleic acid (LA) is a long-chain unsaturated fatty acid of the octadecadienoic acid (18:2) type, which is found in vegetable oils, nuts and seeds. Linoleic acid is an important chemical raw material that can be used to produce products such as polyamides, polyesters and polyureas, and has broad application prospects in the fields of coatings and inks. Due to the presence of carboxyl groups, linoleic acid and normal fatty acids have complementary self-assembly activities. The conjugated double bonds of linoleic acid can eliminate the adverse effects caused by the undesirable position of the double bonds, so it has strong cross-linking activity. The present invention grafts linoleic acid onto the surfactant polyethylene glycol dilaurate through an esterification reaction, and the prepared ether ester surfactant has better performance than the currently mainly used ether ester surfactants.

[0024] (3) The present invention increases the length of the hydrophobic segment through esterification reaction, thereby solving the shortcomings of ether ester products that have high equilibrium surface tension and poor wetting on low surface energy substrates due to short hydrophobic chains;

[0025] (4) The present invention only needs to add a small amount of linoleic acid to modify the surfactant polyethylene glycol dilaurate, which can greatly change the performance of the surfactant polyethylene glycol dilaurate. It mainly introduces unsaturated fatty acid segments and increases the length of the segments in the structure.

[0026] The present invention esterifies the surfactant polyethylene glycol dilaurate with linoleic acid under the action of an acidic catalyst to obtain a low-foaming ether ester nonionic surfactant of the gemini-based type. The present invention adopts an ether ester nonionic surfactant with high activity to reduce the polymerization difficulty of linoleic acid, and esterifies the linoleic acid with high reactivity with the ether ester nonionic surfactant to prepare a reactive gemini-based wetting agent with low foam and good water resistance.

[0027] The gemini low-foam ether ester nonionic surfactant can be added to the coating at a mass concentration of 0.3%-2%. The surfactant provided by the present invention can achieve the effect by adding a small amount to the coating. In particular, during the curing process of the coating, the surfactant and the resin particles are further polymerized to form a dense film, which reduces the migration of the coating and improves the water resistance of the coating. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 The structural diagram of the gemini low foam ether ester nonionic surfactant described in the background technology of the present invention;

[0029] Figure 2 The gemini low-foam ether ester nonionic surfactant prepared in Examples 1-4 of the present invention was added to 100g of 0.1% sodium dodecylbenzene sulfonate solution, and the defoaming ability was compared before and after hand shaking 50 times (a: polyethylene glycol dilaurate; b: LPEG-1; c: LPEG-2; d: LPEG-3; e: LPEG-4);

[0030] Figure 3 This is a graph showing the glossiness test results of the coating prepared in Example 7 of the present invention;

[0031] Figure 4 This is a graph showing the contact angle test results of the coating prepared in Example 6 of the present invention. DETAILED DESCRIPTION

[0032] To make the present invention easier to understand, the present invention is further described below in conjunction with specific examples. It should be understood that these examples are only used to illustrate the present invention and are not used to limit the scope of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in the field without making creative work are within the scope of protection of the present invention. Unless otherwise defined, the professional terms used below are consistent with the meanings understood by professional and technical personnel in the field; unless otherwise specified, the raw materials and reagents involved in this article can be purchased from the market or prepared by known methods.

[0033] In this specification, unless otherwise specified, the percentages are percentages by mass.

[0034] It should be noted that the reaction of linoleic acid of the present invention and surfactant polyethylene glycol dilaurate is as follows:

[0035]

[0036] Embodiment 1:

[0037] Linoleic acid and surfactant polyethylene glycol dilaurate were added to a four-necked flask at a molar ratio of 0.5:1, and then p-toluenesulfonic acid as catalyst A was added, and the amount of p-toluenesulfonic acid added was 2% of the mass of the reaction system, and cyclohexane of 1 times the mass of the reaction system was added at the same time. The mass of the reaction system here refers to the sum of the total mass of linoleic acid, polyethylene glycol dilaurate, and catalyst A.

[0038] The nitrogen was replaced by a vacuum pump, and a water separator filled with solvent B cyclohexane was connected. The reaction temperature was set to 80°C, stirred, and refluxed for 5 hours until no more water was precipitated in the water separator. Finally, the reaction solution was rotary evaporated under 0.1 MPa and 40°C until all the liquid was completely evaporated to obtain a gemini low-foam ether ester nonionic surfactant (LPEG).

[0039] Embodiment 2:

[0040] Linoleic acid and surfactant polyethylene glycol dilaurate were added to a four-necked flask at a molar ratio of 1:1, and then p-toluenesulfonic acid, a catalyst A, was added in an amount of 2% of the mass of the reaction system, and cyclohexane was added in an amount of 1 times the mass of the reaction system. The mass of the reaction system here refers to the sum of the total mass of linoleic acid, polyethylene glycol dilaurate, and catalyst A.

[0041] The nitrogen was replaced by a vacuum pump, and a water separator filled with cyclohexane was connected. The reaction temperature was set to 80°C, stirred, and refluxed for 5 hours until no more water was precipitated in the water separator. Finally, the reaction solution was rotary evaporated under 0.1 MPa and 40°C until all the liquid was completely evaporated to obtain a gemini low-foam ether ester nonionic surfactant (LPEG).

[0042] Embodiment 3:

[0043] Linoleic acid and surfactant polyethylene glycol dilaurate were added to a four-necked flask at a molar ratio of 1.5:1, and p-toluenesulfonic acid was added in an amount of 2% of the mass of the reaction system, and cyclohexane was added in an amount of 1 times the mass of the reaction system. The mass of the reaction system here refers to the sum of the total mass of linoleic acid, polyethylene glycol dilaurate, and catalyst A.

[0044] The nitrogen was replaced by a vacuum pump, and a water separator filled with cyclohexane was connected. The reaction temperature was set to 80°C, stirred, and refluxed for 5 hours until no more water was precipitated in the water separator. Finally, the reaction solution was rotary evaporated under 0.1 MPa and 40°C until all the liquid was completely evaporated to obtain a gemini low-foam ether ester nonionic surfactant (LPEG).

[0045] Embodiment 4:

[0046] Linoleic acid and surfactant polyethylene glycol dilaurate were added to a four-necked flask at a molar ratio of 2:1, and p-toluenesulfonic acid was added. The amount of p-toluenesulfonic acid added was 2% of the mass of the reaction system, and cyclohexane was added at 1 times the mass of the reaction system. The mass of the reaction system here refers to the total mass of linoleic acid, polyethylene glycol dilaurate, and catalyst A.

[0047] The nitrogen was replaced by a vacuum pump, and a water separator filled with cyclohexane was connected. The reaction temperature was set to 80°C, stirred, and refluxed for 5 hours until no more water was precipitated in the water separator. Finally, the reaction solution was rotary evaporated under 0.1 MPa and 40°C until all the liquid was completely evaporated to obtain a gemini low-foam ether ester nonionic surfactant (LPEG).

[0048] Embodiment 5:

[0049] Linoleic acid and surfactant polyethylene glycol dilaurate were added to a four-necked flask at a molar ratio of 2:1, and then catalyst A immobilized liquid acid BF was added. 3 / Al 2 O 3 , Immobilized liquid acid BF 3 / Al 2 O 3 The amount of addition is 1% of the mass of the reaction system, and 4-methyl-2-pentanone is added in an amount of 1.5 times the mass of the reaction system. The mass of the reaction system here refers to the total mass of linoleic acid, polyethylene glycol dilaurate, and catalyst A.

[0050] The nitrogen was replaced by a vacuum pump, and a water separator filled with 4-methyl-2-pentanone was connected. The reaction temperature was set to 80°C, stirred, and refluxed for 4 hours until no more water was precipitated in the water separator. Finally, the reaction solution was rotary evaporated under 0.1 MPa and 40°C until all the liquid was completely evaporated to obtain a gemini low-foam ether ester nonionic surfactant (LPEG).

[0051] Embodiment 6:

[0052] Linoleic acid and surfactant polyethylene glycol dilaurate were added to a four-necked flask at a molar ratio of 2:1, and then zeolite bar molecular sieves were added, the amount of zeolite bar molecular sieves added was 3% of the mass of the reaction system, and trimethylpentane was added in an amount of 1.5 times the mass of the reaction system. The mass of the reaction system here refers to the sum of the total mass of linoleic acid, polyethylene glycol dilaurate, and catalyst A.

[0053] Nitrogen replacement was performed by a vacuum pump, and a water separator filled with trimethylpentane was connected. The reaction temperature was set to 80°C, stirred, and refluxed for 3 hours until no more water was precipitated in the water separator. Finally, the reaction solution was rotary evaporated under 0.1 MPa and 40°C until all the liquid was completely evaporated to obtain a gemini low-foam ether ester nonionic surfactant (LPEG).

[0054] Embodiment 7:

[0055] Take a 1000mL disposable beaker, weigh the hydroxy acrylic resin in proportion according to the evaluation formula, and place it in a disperser at 1500r / min for pre-dispersion, and add amine neutralizer, thickener, defoamer, film-forming aid, water, wetting and leveling agent, anti-crater aid, wetting agent components 1 to 4 (respectively, the gemini low-foam ether ester non-ionic surfactants prepared in Examples 1-4) in sequence, and the addition amount is equivalent to 1% of the coating mass. After dispersing at 600r / min for 30min, take out and filter after defoaming as a primer. Use a water-soluble hydroxy acrylic resin baking paint system as a topcoat. Use an Iwasaki w-101 (1.3 caliber) spray gun to spray on the wooden board. Spray the topcoat after the primer is completely dry, with a vertical distance of 20cm and a spray width of 20cm. Observe the board surface effect and test the glossiness, water resistance, etc.

[0056] Comparative Example 1

[0057] The difference between this comparative example and Example 4 is that linoleic acid is not added, and other parameters and steps are the same as Example 4.

[0058] Add the surfactant polyethylene glycol dilaurate to a four-necked flask, then add p-toluenesulfonic acid, the amount of which is 2% of the mass of the reaction system, and add cyclohexane at a mass of 1 times the mass of the reaction system. The mass of the reaction system here refers to the total mass of polyethylene glycol dilaurate and catalyst A.

[0059] The nitrogen was replaced by a vacuum pump, and a water separator filled with cyclohexane was connected. The reaction temperature was set to 80°C, and the mixture was stirred and refluxed for 5 hours until no more water was precipitated from the water separator. Finally, the reaction solution was rotary evaporated at 0.1 MPa and 40°C until all the liquid was completely evaporated.

[0060] Comparative Example 2

[0061] The difference between this comparative example and Example 4 is that the surfactant polyethylene glycol dilaurate is not added, and the other parameters and steps are the same as Example 4.

[0062] Add linoleic acid to a four-necked flask, then add p-toluenesulfonic acid, the amount of p-toluenesulfonic acid added is 2% of the mass of the reaction system, and add cyclohexane 1 times the mass of the reaction system. The mass of the reaction system here refers to the total mass of linoleic acid and catalyst A.

[0063] The nitrogen was replaced by a vacuum pump, and a water separator filled with cyclohexane was connected. The reaction temperature was set to 80°C, and the mixture was stirred and refluxed for 5 hours until no more water was precipitated from the water separator. Finally, the reaction solution was rotary evaporated at 0.1 MPa and 40°C until all the liquid was completely evaporated.

[0064] Comparative Example 3:

[0065] The difference between this comparative example and Example 7 is that no wetting agent is added, and other parameters and steps are the same as Example 7.

[0066] Take a 1000mL disposable beaker and weigh the hydroxy acrylic resin in equal proportion according to the evaluation formula, then place it in a disperser at 1500r / min for pre-dispersion, and add amine neutralizer, thickener, defoamer, film-forming aid, water, wetting and leveling agent, anti-crater aid components 1 to 12 in sequence, disperse at 600r / min for 30min, then take it out and filter it after defoaming as primer. Use water-soluble hydroxy acrylic resin baking paint system as topcoat. Use Iwasaki w-101 (1.3 caliber) spray gun to spray on the wooden board. Spray the topcoat after the primer is completely dry, with a vertical distance of 20cm and a spray width of 20cm. Observe the board surface effect and perform glossiness, water resistance and other tests.

[0067] Performance check and results analysis

[0068] The acid value of the gemini low foam ether ester nonionic surfactant prepared in Examples 1-6 and Comparative Examples 1-2 was measured. The decrease in the acid value indicates the successful synthesis of the gemini low foam ether ester nonionic surfactant.

[0069] Table 1 Acid value of Examples 1-6 before and after reaction, acid value of Comparative Examples 1-2

[0070]

[0071] In Table 1, the acid value of the system before reaction refers to the acid value of the system mixture measured after the raw materials in each embodiment and comparative example are added and before the reaction. The acid value of the system after reaction refers to the acid value of the system measured after the reaction is completed and all liquids are completely evaporated.

[0072] As can be seen from the results in Table 1, the acid value of the gemini low-foam ether ester nonionic surfactant (LPEG) obtained in Examples 1-6 of the present invention after modification is greatly reduced, which further proves that the grafting of linoleic acid is successful. With the increase of linoleic acid content, the acid values ​​of LPEG-1 (Example 1), LPEG-2 (Example 2), LPEG-3 (Example 3), and LPEG-4 (Example 4) are reduced by 76.78%, 84.71%, 87.53%, and 84.90%, respectively. The results show that due to the limitation of the Fisher esterification reaction, it is difficult to convert all linoleic acid completely, and there is still a small amount of linoleic acid in the system. However, this does not affect the application of gemini low-foam ether ester nonionic surfactant products. When the molar ratio of linoleic acid to polyethylene glycol dilaurate is 2:1, the acid value after the reaction is 84.9% lower than that before the reaction. The acid value reflects the content of linoleic acid in the system, indicating that the reaction is relatively complete.

[0073] 0.1 g of the Gemini low-foam ether ester nonionic surfactant prepared in Example 1-4 was added to 100 g of 0.3% sodium dodecylbenzene sulfonate solution, and the foam heights were compared after shaking for 50 times and standing for 5 minutes. The foam heights of the two test tubes were respectively before and after shaking (see Figure 2 and Table 2). Among them, the surfactant polyethylene glycol dilaurate ( Figure 2 a) The initial foam value is the highest, but the initial foam values ​​of the remaining four samples (b: LPEG-1; c: LPEG-2; d: LPEG-3; e: LPEG-4) are generally low, and the foam decreases by 10mL, 4mL, 5mL, and 3mL respectively in the same period of time. This proves that the synthesized gemini low-foam ether ester nonionic surfactant has low foam.

[0074] Table 2 Polyethylene glycol dilaurate and foam volume before and after defoaming of Examples 1-4

[0075] Before defoaming / mL After defoaming / mL Polyethylene glycol dilaurate Full Bubble 190.00 Example 1 120.00 110.00 Example 2 114.00 110.00 Example 3 112.00 107.00 Example 4 110.00 107.00

[0076] Through the foam comparison in Table 2, it is found that when the sample is added to 0.3% sodium dodecylbenzene sulfonate, the initial foam of polyethylene glycol dilaurate is the highest, but the initial foam values ​​of the remaining four samples are generally low, and the foam decreases in the same time are 10mL, 4mL, 5ml, and 3mL respectively. This is because the 18-carbon long carbon chain is grafted onto polyethylene glycol dilaurate and added to the foaming liquid. The hydrophobic carbon chain will be attracted by the hydrophobic end of the surfactant, making the hydrophobic carbon chain become hydrophilic and enter the water phase, thereby playing a defoaming role. And the LPEG droplet has an extremely low surface tension, and the foam liquid film will quickly form a local contact with it under the action of external force, so that the surface tension of the part in contact with the foam liquid film is reduced, but in the part that is not in contact with the defoamer droplet, its surface tension is basically unchanged. The foam liquid containing the defoamer droplet, because of its reduced surface tension, will produce a surface tension difference between the part with unchanged surface tension, so that the weaker connection is subjected to strong stretching and expansion, and finally causes the bubble liquid film to break to achieve the purpose of defoaming.

[0077] The coating prepared in Example 7 was immersed in water for 24h×7, the board surface effect was observed, and its water absorption rate was calculated by weighing. With the increase of linoleic acid content, the content of conjugated double bonds in the sample was increased, so that cross-linking and curing occurred during the drying film-forming process, the density of the sample film was improved, and then its water resistance was improved. When the molar ratio of linoleic acid to surfactant polyethylene glycol dilaurate was 2:1, the paint film did not bubble and had the best water resistance.

[0078] Table 3 Water absorption of the coating of Example 7 Gemini low foam ether ester nonionic surfactant and Comparative Example 2

[0079] sample Water absorption LPEG-1 (Example 1) 0.9％ LPEG-2 (Example 2) 0.8％ LPEG-3 (Example 3) 0.6％ LPEG-4 (Example 4) 0.5％ Comparative Example 2 1.5％

[0080] The glossiness of the coating prepared in Example 7 was measured. When the measuring angles were 20°, 60°, and 85°, the glossiness of the coating film with the addition of the gemini low-foam ether ester nonionic surfactant was improved compared with the blank coating film. Comprehensive comparison showed that the glossiness of the coating film was best improved when the molar ratio of oleic acid to polyethylene glycol dilaurate was 2:1. Figure 3 This is a graph showing the gloss test results of the coating prepared in Example 7 of the present invention. Wherein White is a paint film sample without the addition of a surfactant. When the measuring angle is 20°, the glossiness is improved by 0.7%, 0.5%, 1.3%, and 2.0% respectively compared with the White paint film. When the measuring angle is 60°, the glossiness is improved by 0.1%, 0.9%, 0.5%, and 1.2% respectively compared with the White paint film; when the measuring angle is 85°, the glossiness is improved by 1.0%, 1.6%, 1.2%, and 0.9% respectively compared with the White paint film. The test shows that the addition of LPEG can improve the glossiness of the coating. Comprehensive comparison shows that the glossiness of the paint film is best improved when the molar ratio of linoleic acid to polyethylene glycol dilaurate is 2:1.

[0081] The contact angle of the coating prepared in Example 7 was measured. It can be seen that the coating containing the surfactant polyethylene glycol dilaurate and the gemini low-foam ether ester nonionic surfactant can be considered to be relatively hydrophobic. The surface becomes a complex of the coating and water, resulting in an increase in the surface hydrophilicity. The presence of the gemini low-foam ether ester nonionic surfactant enhances the wettability of the film surface. The more water adsorbed, the lower the surface hydrophobicity, and the smaller the apparent contact angle of the droplet. The results show that the coating containing LPEG-4 has the smallest contact angle at 102°; the contact angle of the coating containing the gemini low-foam ether ester nonionic surfactant is always smaller than that of the coating containing the surfactant polyethylene glycol dilaurate. Figure 4 This is a graph showing the contact angle test results of the coating prepared in Example 6 of the present invention, wherein PEG is a paint film sample to which polyethylene glycol dilaurate surfactant is added.

[0082] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by any technician familiar with the art within the technical scope disclosed in the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be based on the protection scope of the claims.

Claims

1. A method for preparing a gemini low-foam ether-ester nonionic surfactant, characterized in that: The following steps are involved: Step 1: adding linoleic acid and surfactant polyethylene glycol dilaurate into a reaction container and mixing, then adding catalyst A and a certain amount of solvent B, then performing nitrogen replacement, reacting at a certain temperature until no water is produced in the reaction container, the reaction is terminated, and a reaction solution is obtained; Step 2: Distill the liquid from the reaction solution obtained in step 1 at a certain pressure and a certain temperature until no liquid is evaporated, thereby obtaining a gemini low-foam ether ester nonionic surfactant.

2. The method for preparing the gemini low-foam ether ester nonionic surfactant according to claim 1, characterized in that: In step 1, the reaction between linoleic acid and the surfactant polyethylene glycol dilaurate produces water. Here, the reaction system cannot form an azeotrope with water. The water in the system is removed during the reaction by using a water separator or adding an azeotropic dehydrating agent.

3. The method for preparing the gemini low foam ether ester nonionic surfactant according to claim 1 or 2, characterized in that: In step 1, linoleic acid and surfactant polyethylene glycol dilaurate are added to a reaction container in a molar ratio, and then catalyst A is added, and a certain amount of solvent B is added at the same time, and then nitrogen replacement is performed, and then a water separator filled with solvent B is connected, and the reaction is carried out at a certain temperature until there is no water in the water separator to obtain a reaction solution.

4. The method for preparing the gemini low foam ether ester nonionic surfactant according to claim 1 or 2, characterized in that: In step 1, according to the ratio of the amount of substance, linoleic acid: polyethylene glycol dilaurate is 0.5~2:1; and / or the catalyst A is 1~3% of the mass of the reaction system; and / or the amount of solvent B added is more than 0.5 times the mass of the reaction system; the mass of the reaction system here refers to the sum of the total mass of linoleic acid, polyethylene glycol dilaurate, and catalyst A.

5. The method for preparing the gemini low foam ether ester nonionic surfactant according to claim 1 or 2, characterized in that: In step 1, catalyst A is at least one of p-toluenesulfonic acid, solid-supported liquid acid, and zeolite molecular sieve strips.

6. The method for preparing the gemini low-foam ether ester nonionic surfactant according to claim 1 or 2, characterized in that: The solvent B is at least one of cyclohexane, 4-methyl-2-pentanone and trimethylpentane.

7. The method for preparing the gemini low-foam ether ester nonionic surfactant according to claim 1 or 2, characterized in that: In step 1, the reaction temperature is 70-90°C.

8. The method for preparing the gemini low-foam ether ester nonionic surfactant according to claim 1 or 2, characterized in that: In step 2, the liquid is evaporated by rotary evaporation or reduced pressure distillation.

9. The method for preparing the gemini low-foam ether ester nonionic surfactant according to claim 1 or 2, characterized in that: In step 2, the rotary evaporation pressure is 0.09-0.1 MPa; and / or the temperature is 30-50°C.

10. Use of a gemini low-foam ether ester nonionic surfactant prepared by the preparation method according to any one of claims 1 to 9, characterized in that: Add surfactant equivalent to 0.3%-2% of the coating mass to the coating.

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