A composite defoamer and its preparation method

Abstract

The present invention relates to the technical field of water-based paint defoamers, and specifically relates to a composite defoamer and a preparation method thereof. The composite defoamer comprises the following raw materials in combination: modified polysiloxane, emulsifier, nano-silica, defoaming aid, other additives, cosolvent and water. It has better chemical stability and thermal stability, and can maintain a stable defoaming effect in an alkaline environment; by adding a defoaming aid to act synergistically, it changes the surface tension of the liquid, reduces the stability of the foam, can prevent the generation of new foam, and also has a thickening effect to increase the viscosity of the system, making the product more stable, so that the modified polysiloxane and the defoaming aid still have excellent effects even when their contents in the system are relatively low, thereby reducing the amount of emulsifier used in combination. This composite defoamer can be used to eliminate the foam in water-containing systems, has a fast defoaming speed, excellent dispersion performance, a long foam suppression time, high efficiency, low dosage, and is particularly suitable for water-based paints in an alkaline environment.

Description

Technical Field

[0001] The invention relates to the technical field of water-based coating defoamers, and in particular to a composite defoamer and a preparation method thereof. Background Art

[0002] Water-based paints include three types: water-soluble paints, water-dilutable paints, and water-dispersible paints (latex paints). Water-soluble paints use water-soluble resins as film-forming materials, with polyvinyl alcohol and its various modifications being the most representative. In addition, there are water-soluble alkyd resins, water-soluble epoxy resins, and inorganic polymer water-based resins. Water-dilutable paints refer to paints formulated with post-emulsified emulsions as film-forming materials. Solvent-based resins are dissolved in organic solvents, and then, with the help of emulsifiers, strong mechanical stirring is used to disperse the resin in water to form an emulsion, called a post-emulsified emulsion. The resulting paint can be diluted with water during construction. Water-dispersible paints mainly refer to paints formulated with synthetic resin emulsions as film-forming materials.

[0003] During the production and use of water-based paints, bubbles inevitably form due to mixing, stirring, and pumping processes. If these bubbles are not promptly eliminated, they can affect the uniformity and appearance of the paint, resulting in unevenness and defects on the painted surface. Adding a defoamer can reduce the number of bubbles in the paint, improving its uniformity and stability. The amount of defoamer added is also a key factor influencing the performance of water-based paints. Excessive use of defoamer can lead to problems such as reduced leveling and adhesion.

[0004] In order to achieve better defoaming effect, existing silicone defoamers require a large amount of polysiloxane added. However, polysiloxane is not easily soluble in water and needs to be mixed with more emulsifiers. However, the defoaming effect is actually worsened. Moreover, when used in water-based paints, it is easy to destroy the original emulsification balance, resulting in stratification and reduced defoaming effect. Water-based paints are mostly alkaline. If the silicone defoamer is in an alkaline environment for a long time, it is also easy to cause a decrease in defoaming effect. Summary of the Invention

[0005] In order to overcome the shortcomings and deficiencies in the prior art, one of the purposes of the present invention is to provide a composite defoaming agent.

[0006] The second object of the present invention is to provide a method for preparing a composite defoaming agent, which has simple operation, convenient control, high production efficiency, low production cost, and can be used for large-scale production.

[0007] One of the objectives of the present invention is achieved through the following technical solution: A composite defoamer comprises the following raw materials in parts by weight:

[0008]

[0009] This composite defoamer uses a special modified polysiloxane as the main defoaming raw material. The molecular structure of this special modified polysiloxane has further improved its stability and activity, enabling it to better interact with the bubble surface, having better chemical and thermal stability, and being able to maintain a stable defoaming effect in different environments. It will quickly aggregate on the bubble surface to form a structure similar to a thin film. By interacting with the surface tension of the bubble, it can disrupt the balance of the bubble surface and make the bubble lose stability. Adding defoaming aids for synergistic effect can change the surface tension of the liquid, reduce the stability of the foam, prevent the generation of new foam, and also has a thickening effect to increase the viscosity of the system, making the product more stable, thereby extending the service life of the product and improving the overall effect, so that the modified polysiloxane and defoaming aids still have excellent effects even when their contents in the system are relatively low, and then reducing the addition amount of emulsifiers when used in combination, and being not easily demulsified and floating oil after dilution. The added nano-silica is dispersed in water. Its tiny particle size and stable three-dimensional hydrogen bond network structure enable it to be evenly and stably distributed in the system, thereby increasing the viscosity of the defoamer and preventing sedimentation. Its tiny particles can effectively reduce the surface tension of the liquid and prevent the formation of bubbles. The added cosolvent is blended with water to improve the system stability. In addition, the cosolvent can reduce the surfactant concentration in the surface layer and also dissolve into the surfactant adsorption layer, reducing the tightness between surfactant molecules, thereby weakening the stability of the foam. This composite defoamer can be used to eliminate the foam in aqueous systems, with fast defoaming speed, excellent dispersion performance, long foam suppression time, high efficiency, low dosage, and is especially suitable for water-based coatings in alkaline environments.

[0010] Preferably, the preparation method of each portion of the modified polysiloxane comprises the following steps:

[0011] (R1), take 60 - 80 parts by weight of dihydroxypolydimethylsiloxane, 30 - 40 parts of rare earth lanthanum metal alkoxide, 120 parts of organic solvent, and 1 - 3 parts of catalyst, and set aside;

[0012] (R2), after hot air drying the dihydroxypolydimethylsiloxane and vacuum drying the rare earth lanthanum metal alkoxide, under nitrogen protection, mix the dihydroxypolydimethylsiloxane, rare earth lanthanum metal alkoxide, and organic solvent, heat up to 40 - 50 °C and dissolve evenly under ultrasonic and stirring conditions to obtain a mixed solution;

[0013] (R3), under nitrogen protection, heat up to 70 - 90 °C, add the catalyst to the mixed solution, stir and react for 2 - 4 h, and let it stand for 1 h to obtain a reaction product;

[0014] (R4), distill and filter the reaction product to remove impurities to obtain the modified polysiloxane.

[0015] By adopting the above technical solution, dihydroxy polydimethylsiloxane and rare earth lanthanum metal alkoxide react in combination under nitrogen protection, at a temperature of 70-90°C and under the action of a catalyst, and most of the rare earth lanthanum metal is introduced into the dihydroxy polydimethylsiloxane. The dihydroxy polydimethylsiloxane combines the excellent properties of rare earth metals and polysiloxane. The molecular structure contains silicon-oxygen bonds, which endows it with both the lipophilicity of organic matter and the hydrophilicity of inorganic matter. The introduction of the rare earth metal further improves the stability and activity of its molecular structure, enabling it to better interact with the bubble surface, have better chemical stability and thermal stability, and maintain a stable defoaming effect under different environments. The presence of the rare earth metal can also enhance the inhibitory effect of the defoamer on foam, prevent the re-formation of foam, and make the foam more easily broken, thereby significantly improving the defoaming performance, enhancing stability, and broadening the scope of application. In step (R2), the dihydroxy polydimethylsiloxane is dried by hot air, and the rare earth lanthanum metal alkoxide is vacuum dried. Steps (R2) and (R3) are performed under nitrogen protection to prevent the rare earth lanthanum metal alkoxide from reacting with water and oxygen to affect the product yield.

[0016] Preferably, the viscosity (25°C) of the dihydroxy polydimethylsiloxane is 20-40 mm 2 / s, the hydroxyl content is 6-12wt%; the organic solvent is toluene and / or xylene.

[0017] Preferably, the general structural formula of the rare earth lanthanum metal alkoxide is La(OR)3, wherein R is methyl, ethyl, propyl or isopropyl.

[0018] Preferably, the catalyst is triethylamine or dimethylaniline.

[0019] The above technical solution is used to catalyze the coordination reaction between dihydroxy polydimethylsiloxane and rare earth lanthanum metal alkoxide, introduce most of the rare earth lanthanum metal into the dihydroxy polydimethylsiloxane, and facilitate the removal of triethylamine or dimethylaniline after the reaction.

[0020] Preferably, the emulsifier is at least one of fatty alcohol polyoxyethylene ether, Tween-80 and Span 40; and the average particle size of the nano-silicon dioxide is 30-40 nm.

[0021] Preferably, the defoaming aid is a mixture of polyethylene glycol and distearate acylethylenediamine.

[0022] With the above technical solution, the mixture of polyethylene glycol and N,N'-distearylethylenediamine acts synergistically with the modified polysiloxane to change the surface tension of the liquid, reduce the stability of the foam, prevent the generation of new foam, and also has a thickening effect. Polyethylene glycol itself also has a relatively high viscosity, forming a network structure in the system, increasing the viscosity of the system, making the product more stable, thereby extending the service life of the product, improving the overall effect, so that the modified polysiloxane and the defoaming aid still have excellent effects even when their contents in the system are relatively low. More preferably, the defoaming aid is a mixture of polyethylene glycol and N,N'-distearylethylenediamine mixed in a weight ratio of 5-7:1.

[0023] Preferably, the other additives include a bactericide.

[0024] With the above technical solution, more preferably, the bactericide is at least one of dodecyl trimethyl ammonium chloride, dodecyl dimethyl benzyl ammonium chloride, and dodecyl dimethyl benzyl ammonium bromide.

[0025] Preferably, the co-solvent is at least one of octanol, ethanol, and propanol.

[0026] With the above technical solution, the above co-solvent is blended with water to improve the stability of the system. In addition, the co-solvent can reduce the surfactant concentration in the surface layer and also dissolve into the surfactant adsorption layer, reducing the tightness between surfactant molecules, thereby weakening the stability of the foam.

[0027] The second object of the present invention is achieved by the following technical solution: The preparation method of the above composite defoaming agent includes the following steps:

[0028] (S1) Weigh and take the modified polysiloxane, emulsifier, nano-silica, defoaming aid, other additives, co-solvent, and water by weight parts for standby;

[0029] (S2) Mix the modified polysiloxane, co-solvent, and water evenly to obtain a blend;

[0030] (S3) Add the emulsifier, nano-silica, defoaming aid, and other additives to the blend, stir for 5-10 min, and then homogenize for 3-5 min to obtain the composite defoaming agent.

[0031] The beneficial effects of the present invention are as follows: The composite defoamer of the present invention uses a special modified polysiloxane as the main defoaming raw material. The molecular structure of this special modified polysiloxane has further improved its stability and activity, enabling it to better interact with the bubble surface, having better chemical stability and thermal stability, being able to maintain a stable defoaming effect in different environments, quickly aggregating on the bubble surface to form a structure similar to a thin film, and by interacting with the surface tension of the bubble surface, it can disrupt the balance of the bubble surface and make the bubble lose stability; adding defoaming aids to act synergistically, changing the surface tension of the liquid, reducing the stability of the foam, being able to prevent the generation of new foam, and also having a thickening effect to increase the viscosity of the system, making the product more stable, thereby extending the service life of the product and improving the overall effect, so that the modified polysiloxane and defoaming aids still have excellent effects even when their contents in the system are relatively low, and further reducing the addition amount of emulsifiers when used in combination, and being not easily demulsified and floating oil after dilution; the added nano-silica is dispersed in water, and its tiny particle size and stable three-dimensional hydrogen bond network structure enable it to be evenly and stably distributed in the system, thereby increasing the viscosity of the defoamer and preventing sedimentation, and its tiny particles can effectively reduce the surface tension of the liquid and prevent the formation of bubbles; the added cosolvent is blended with water to improve the stability of the system. In addition, the cosolvent can reduce the concentration of surfactants in the surface layer and also dissolve into the surfactant adsorption layer, reducing the tightness between surfactant molecules, thereby weakening the stability of the foam. This composite defoamer can be used to eliminate the foam in aqueous systems, has a fast defoaming speed, excellent dispersion performance, a long foam suppression time, high efficiency, low dosage, and is particularly suitable for water-based coatings in an alkaline environment.

[0032] The preparation method of the present invention is simple to operate, convenient to control, has high production efficiency and low production cost, and can be used for large-scale production. Detailed implementation mode

[0033] For the convenience of understanding by those skilled in the art, the present invention will be further described below in conjunction with embodiments. The content mentioned in the implementation mode does not limit the present invention.

[0034] Embodiment 1

[0035] A composite defoamer, comprising raw materials in the following parts by weight:

[0036]

[0037] The preparation method of each part of the modified polysiloxane comprises the following steps:

[0038] (R1) Weigh 70 parts of dihydroxypolydimethylsiloxane, 35 parts of rare earth lanthanum metal alkoxide, 120 parts of organic solvent and 2 parts of catalyst by weight, and set aside;

[0039] (R2) After hot air drying the dihydroxypolydimethylsiloxane for 2 h and vacuum drying the rare earth lanthanum metal alkoxide for 2 h, under nitrogen protection, the dihydroxypolydimethylsiloxane, the rare earth lanthanum metal alkoxide and the organic solvent are mixed, heated to 45 °C and dissolved uniformly under ultrasonic and stirring conditions to obtain a mixed solution;

[0040] (R3) Under nitrogen protection, the temperature is raised to 80 °C, a catalyst is added to the mixed solution, and the mixture is stirred and reacted for 3 h and then allowed to stand for 1 h to obtain a reaction product;

[0041] (R4) The reaction product is distilled and filtered to remove impurities to obtain a modified polysiloxane.

[0042] The viscosity (25 °C) of the dihydroxypolydimethylsiloxane is 30 mm 2 / s, and the hydroxyl content is 9 wt%; the organic solvent is toluene.

[0043] The structural general formula of the rare earth lanthanum metal alkoxide is La(OR)3, where R is ethyl.

[0044] The catalyst is triethylamine.

[0045] The emulsifier is a mixture of fatty alcohol polyoxyethylene ether and Tween-80 in a weight ratio of 1:1; the average particle size of the nano-silica is 35 nm.

[0046] The defoaming auxiliary agent is a mixture of polyethylene glycol and N,N'-distearoylethylenediamine in a weight ratio of 6:1.

[0047] The other auxiliary agent includes a bactericide, and the bactericide is dodecyl trimethyl ammonium chloride.

[0048] ] The co-solvent is ethanol.

[0049] The preparation method of the composite defoamer includes the following steps:

[0050] (S1) Take the modified polysiloxane, emulsifier, nano-silica, defoaming auxiliary agent, other auxiliary agent, co-solvent and water by weight parts and set aside;

[0051] (S2) The modified polysiloxane, co-solvent and water are mixed uniformly to obtain a blend;

[0052] (S3) Add the emulsifier, nano-silica, defoaming auxiliary agent and other auxiliary agent to the blend, stir for 8 min, and then homogenize for 4 min to obtain the composite defoamer. [[ID= forty-three]]

[0053] Example 2

[0054] A composite defoamer, comprising the following raw materials in parts by weight:

[0055]

[0056] The preparation method of each of the modified polysiloxanes comprises the following steps:

[0057] (R1) Take 60 parts by weight of dihydroxypolydimethylsiloxane, 30 parts of rare earth lanthanum metal alkoxide, 120 parts of organic solvent and 2 parts of catalyst, and set aside;

[0058] (R2) After subjecting dihydroxypolydimethylsiloxane to hot air drying treatment for 2 h and rare earth lanthanum metal alkoxide to vacuum drying treatment for 2 h, under nitrogen protection, mix dihydroxypolydimethylsiloxane, rare earth lanthanum metal alkoxide and organic solvent, heat up to 40 °C and dissolve evenly under ultrasonic wave and stirring conditions to obtain a mixed solution;

[0059] (R3) Under nitrogen protection, heat up to 75 °C, add the catalyst to the mixed solution, stir and react for 2 h, and let stand for 1 h to obtain a reaction product;

[0060] (R4) Distill and filter the reaction product to remove impurities to obtain the modified polysiloxane.

[0061] The viscosity (25 °C) of the dihydroxypolydimethylsiloxane is 25 mm 2 / s, and the hydroxyl content is 7 wt%; the organic solvent is xylene.

[0062] The structural general formula of the rare earth lanthanum metal alkoxide is La(OR)3, wherein R is methyl.

[0063] The catalyst is triethylamine.

[0064] The emulsifier is a mixture of fatty alcohol polyoxyethylene ether and Tween-80 in a weight ratio of 1:1; the average particle size of the nano-silica is 35 nm.

[0065] The defoaming auxiliary agent is a mixture of polyethylene glycol and N,N'-di(stearoyl)ethylenediamine in a weight ratio of 5:1.

[0066] The other auxiliary agents include a bactericide, and the bactericide is dodecyltrimethylammonium chloride.

[0067] The co-solvent is ethanol.

[0068] The preparation method of the composite defoamer comprises the following steps:

[0069] (S1) Take the modified polysiloxane, emulsifier, nano-silica, defoaming auxiliary agent, other auxiliary agents, co-solvent and water by weight, and set aside;

[0070] (S2) Mix the modified polysiloxane, co-solvent and water evenly to obtain a blend.

[0071] (S3) Add emulsifier, nano-silica, defoaming aid and other additives to the blend, stir for 8 min, and then homogenize for 4 min to obtain the composite defoamer.

[0072] Example 3

[0073] A composite defoamer, comprising the following raw materials in parts by weight:

[0074]

[0075] The preparation method of each part of the modified polysiloxane comprises the following steps:

[0076] (R1) Weigh 78 parts of dihydroxypolydimethylsiloxane, 40 parts of rare earth lanthanum metal alkoxide, 120 parts of organic solvent and 2 parts of catalyst for standby;

[0077] (R2) After drying the dihydroxypolydimethylsiloxane by hot air for 2 h and the rare earth lanthanum metal alkoxide by vacuum for 2 h, under nitrogen protection, mix the dihydroxypolydimethylsiloxane, rare earth lanthanum metal alkoxide and organic solvent, heat up to 50 °C and dissolve evenly under ultrasonic and stirring conditions to obtain a mixed solution;

[0078] (R3) Under nitrogen protection, heat up to 90 °C, add the catalyst to the mixed solution, stir and react for 4 h, and let stand for 1 h to obtain a reaction product;

[0079] (R4) Distill and filter the reaction product to remove impurities to obtain the modified polysiloxane.

[0080] The viscosity (25 °C) of the dihydroxypolydimethylsiloxane is 40 mm 2 / s, and the hydroxyl content is 10 wt%; the organic solvent is toluene.

[0081] The structural general formula of the rare earth lanthanum metal alkoxide is La(OR)3, where R is ethyl.

[0082] The catalyst is triethylamine.

[0083] The emulsifier is a mixture of fatty alcohol polyoxyethylene ether and Tween-80 in a weight ratio of 1:1; the average particle size of the nano-silica is 35 nm.

[0084] The defoaming aid is a mixture of polyethylene glycol and N,N'-distearoylethylenediamine in a weight ratio of 7:1.

[0085] The other additives include a bactericide, and the bactericide is dodecyltrimethylammonium chloride.

[0086] The co-solvent is ethanol.

[0087] The preparation method of the composite defoamer comprises the following steps:

[0088] (S1) Weigh and take modified polysiloxane, emulsifier, nano-silica, defoaming auxiliary, other auxiliaries, cosolvent and water according to parts by weight, and set aside;

[0089] (S2) Mix the modified polysiloxane, cosolvent and water evenly to obtain a blend;

[0090] (S3) Add the emulsifier, nano-silica, defoaming auxiliary and other auxiliaries to the blend, stir for 8 min, and then homogenize for 4 min to obtain the composite defoamer.

[0091] Example 4

[0092] A composite defoamer, comprising raw materials in the following parts by weight:

[0093]

[0094] The preparation method of each part of the modified polysiloxane comprises the following steps:

[0095] (R1) Weigh and take 72 parts of dihydroxypolydimethylsiloxane, 36 parts of rare earth lanthanum metal alkoxide, 120 parts of organic solvent and 2 parts of catalyst according to parts by weight, and set aside;

[0096] (R2) After subjecting the dihydroxypolydimethylsiloxane to hot air drying treatment for 2 h and the rare earth lanthanum metal alkoxide to vacuum drying treatment for 2 h, under nitrogen protection, mix the dihydroxypolydimethylsiloxane, rare earth lanthanum metal alkoxide and organic solvent, heat up to 43 °C and dissolve evenly under ultrasonic wave and stirring conditions to obtain a mixture;

[0097] (R3) Under nitrogen protection, heat up to 80 °C, add the catalyst to the mixture, stir and react for 3 h, and let stand for 1 h to obtain a reaction product;

[0098] (R4) Subject the reaction product to distillation and filtration to remove impurities to obtain the modified polysiloxane.

[0099] The viscosity (25 °C) of the dihydroxypolydimethylsiloxane is 28 mm 2 / s, and the hydroxyl content is 8 wt%; the organic solvent is toluene.

[0100] The structural general formula of the rare earth lanthanum metal alkoxide is La(OR)3, where R is ethyl.

[0101] The catalyst is dimethylaniline.

[0102] The emulsifier is a mixture of fatty alcohol polyoxyethylene ether and Tween-80 in a weight ratio of 1:1; the average particle size of the nano-silica is 35 nm.

[0103] The defoaming aid is a mixture of polyethylene glycol and N,N'-distearyl ethylenediamine in a weight ratio of 6:1.

[0104] The other additives include a bactericide, and the bactericide is dodecyl trimethyl ammonium chloride.

[0105] The co-solvent is ethanol.

[0106] The preparation method of the composite defoamer includes the following steps:

[0107] (S1) Weigh and take modified polysiloxane, emulsifier, nano-silica, defoaming aid, other additives, co-solvent and water by weight parts for standby;

[0108] (S2) Mix the modified polysiloxane, co-solvent and water evenly to obtain a blend;

[0109] (S3) Add the emulsifier, nano-silica, defoaming aid and other additives to the blend, stir for 8 min, and then homogenize for 4 min to obtain the composite defoamer.

[0110] Comparative Example 1

[0111] The difference between this comparative example and Example 1 is that:

[0112] The modified polysiloxane is polyether-modified polysiloxane, selected from the model Evonik TEGOPREN 5863.

[0113] Comparative Example 2

[0114] The difference between this comparative example and Example 1 is that:

[0115] The defoaming aid is polyvinyl alcohol.

[0116] Comparative Example 3

[0117] The difference between this comparative example and Example 1 is that:

[0118] The composite defoamer includes the following raw materials by weight parts:

[0119]

[0120] That is, the composite defoamer does not add defoaming aid.

[0121] Comparative Example 4

[0122] A polyether-modified polysiloxane emulsion defoamer, selected from the model RianPont8405.

[0123] Performance Test

[0124] Take the defoamers of Examples 1-4 and Comparative Examples 1-4, and conduct performance tests on the stability, defoaming property and foam inhibition property of the alkaline surfactant system under the same conditions respectively. The test methods are as follows:

[0125] Specimen: Take the silicone defoamers of Examples 1-4 and Comparative Examples 1-4, dilute them with deionized water respectively (the volume ratio of added deionized water to defoamer is 1:2), heat them in an oil bath at 100 °C respectively, and then cool them to obtain specimens;

[0126] The alkaline surfactant aqueous solution is composed of the following components mixed by weight percentage: 0.5% sodium dialkylbenzenesulfonate, 0.5% nonylphenol polyoxyethylene (10) ether, 1% sodium hydroxide and the balance deionized water;

[0127] (1) Stability Test

[0128] Use two 10 mL graduated centrifuge tubes to measure 8 mL of the specimen respectively, symmetrically place them in an 80-2 type low-speed electric centrifuge, rotate continuously at a speed of 3000 r / min for 15 min, take out the tubes, read the volume of the stratified liquid, and take the arithmetic mean of the two measured values as the measurement result.

[0129] (2) Defoaming Performance

[0130] Use a 100 mL stoppered graduated cylinder to take 50 mL of the alkaline surfactant aqueous solution, add 0.05 g of the specimen, thermostatically control it to 25 °C and 60 °C respectively in a water bath, cover the bottle stopper, shake the graduated cylinder vertically up and down at a frequency of 2 times / s and a swing amplitude of (30-35) cm for 10 times, let it stand and start timing with a stopwatch, and record the time taken for the foam to disappear until the liquid surface appears.

[0131] (3) Foam Inhibition Performance

[0132] Adopt a lubricating oil (defoamer) foam property tester that meets the requirements of GB / T 12579. Turn on and debug the foam property tester, and the test gas flow rate is 100 mL / min. Take 100 mL of the alkaline surfactant aqueous solution, add 0.1 g of the specimen to the alkaline surfactant aqueous solution, stir evenly, then pour it into a clean bubbling apparatus graduated cylinder, and thermostatically control it to 25 °C and 60 °C respectively. Turn on the flow pump, start the test, and record the foam volume (mL) for 30 min of air bubbling. The result is represented by the foam volume corresponding to 30 min of air bubbling.

[0133] The test results are shown in Table 1 below:

[0134]

[0135] As can be seen from Table 1 above, the composite defoamer of the present invention enables it to interact better with the bubble surface, has better chemical stability and thermal stability, and can maintain a stable defoaming effect in an alkaline environment; the addition of a defoaming auxiliary has a synergistic effect, changes the surface tension of the liquid, reduces the stability of the foam, can prevent the generation of new foam, and also has a thickening effect to increase the viscosity of the system, making the product more stable, thereby extending the service life of the product, improving the overall effect, so that the modified polysiloxane and the defoaming auxiliary still have excellent effects even when their contents in the system are low, and further reducing the addition amount of the emulsifier and mixing them, and it is not easy to break emulsion and float oil after dilution; the added cosolvent is mixed with water to improve the system stability. This composite defoamer can be used to eliminate the foam in the water-containing system, has a fast defoaming speed, excellent dispersion performance, a long foam suppression time, high efficiency, and low dosage, and is particularly suitable for water-based coatings in an alkaline environment.

[0136] The above embodiments are the preferred implementation schemes of the present invention. In addition, the present invention can also be implemented in other ways. Any obvious substitution without departing from the concept of the present invention is within the protection scope of the present invention.

Claims

1. A composite defoamer, characterized in that, It comprises raw materials in the following parts by weight: Modified polysiloxane: 10 - 20 parts Emulsifier: 1 - 5 parts Nano-silica: 0.1 - 0.8 part Defoaming auxiliary agent: 3 - 8 parts Other auxiliary agents: 1 - 3 parts Cosolvent: 5 - 10 parts Water: 100 parts; The preparation method of each part of the modified polysiloxane comprises the following steps: (R1)Take 60 - 80 parts of dihydroxypolydimethylsiloxane, 30 - 40 parts of rare earth lanthanum metal alkoxide, 120 parts of organic solvent and 1 - 3 parts of catalyst by weight, and set aside; (R2)After hot air drying the dihydroxypolydimethylsiloxane and vacuum drying the rare earth lanthanum metal alkoxide, under nitrogen protection, mix the dihydroxypolydimethylsiloxane, rare earth lanthanum metal alkoxide and organic solvent, heat up to 40 - 50 °C and dissolve evenly under ultrasonic and stirring conditions to obtain a mixed solution; (R3)Under nitrogen protection, heat up to 70 - 90 °C, add the catalyst to the mixed solution, stir and react for 2 - 4 h, and let it stand for 1 h to obtain a reaction product; (R4)Distill and filter the reaction product to remove impurities to obtain the modified polysiloxane.

2. The composite defoamer according to claim 1, characterized in that: The viscosity of the dihydroxypolydimethylsiloxane at 25 °C is 20-40 mm 2 / s, and the hydroxyl content is 6-12 wt%; the organic solvent is toluene and / or xylene.

3. The composite defoamer according to claim 1, characterized in that: The structural general formula of the rare earth lanthanum metal alkoxide is La(OR)3, where R is methyl, ethyl or propyl.

4. A composite defoamer according to claim 1, characterized in that: The catalyst is triethylamine or dimethylaniline.

5. The composite defoamer according to claim 1, characterized in that: The emulsifier is at least one of fatty alcohol polyoxyethylene ether, Tween - 80 and Span 40; the average particle size of the nano-silica is 30 - 40 nm.

6. The composite defoamer according to claim 1, characterized in that: The defoaming auxiliary agent is a mixture of polyethylene glycol and di(stearoyl)ethylenediamine.

7. A composite defoamer according to claim 1, characterized in that: The other auxiliary agents include a bactericide.

8. The composite defoamer according to claim 1, wherein: The cosolvent is at least one of octanol, ethanol and propanol.

9. A preparation method of the composite defoamer according to any one of claims 1-8, characterized in that, It comprises the following steps: (S1)Take the modified polysiloxane, emulsifier, nano-silica, defoaming auxiliary agent, other auxiliary agents, cosolvent and water by weight, and set aside; (S2)Mix the modified polysiloxane, cosolvent and water evenly to obtain a blend; (S3)Add the emulsifier, nano-silica, defoaming auxiliary agent and other auxiliary agents to the blend, stir for 5 - 10 min, and then homogenize for 3 - 5 min to obtain a composite defoamer.

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