Composite defoaming agent and preparation method thereof

Abstract

The invention relates to the technical field of water-based paint defoaming agents, in particular to a composite defoaming agent and a preparation method thereof.The composite defoaming agent is prepared by compounding the following raw materials: modified polysiloxane, an emulsifier, nano silicon dioxide, a defoaming auxiliary agent, other auxiliary agents, a cosolvent and water, and has better chemical stability and thermal stability; a stable defoaming effect can be kept in an alkaline environment; the defoaming aid is added for synergistic effect, liquid surface tension is changed, foam stability is reduced, new foam can be prevented from being generated, the thickening effect is achieved, the viscosity of the system is increased, the product is more stable, and the excellent effect is still achieved under the condition that the content of the modified polysiloxane and the defoaming aid in the system is low; and the addition amount of the emulsifier is reduced for mixed use. The composite defoaming agent can be used for eliminating foam of a water-containing system, is high in defoaming speed, excellent in dispersing performance, long in foam inhibition time, high in efficiency and low in dosage, and is particularly suitable for water-based paint 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, represented by polyvinyl alcohol and its various modified products. In addition, there are water-soluble alkyd resins, water-soluble epoxy resins, and inorganic polymer water-based resins. Water-dilutable paints refer to paints prepared with post-emulsified emulsions as film-forming materials. Solvent-based resins are dissolved in organic solvents, and then with the help of emulsifiers, the resins are dispersed in water by strong mechanical stirring to form an emulsion, which is called post-emulsified emulsion. The resulting paint can be diluted with water during construction. Water-dispersible paints mainly refer to paints prepared with synthetic resin emulsions as film-forming materials.

[0003] During the production and use of water-based paints, bubbles will inevitably be generated due to mixing, stirring, pumping and other processes. If these bubbles are not eliminated in time, they will affect the uniformity and appearance quality of the paint, causing unevenness and defects on the surface after coating. By adding defoamers, the number of bubbles in the paint can be reduced and the uniformity and stability of the paint can be improved. The amount of defoamer added is also an important factor affecting the performance of water-based paints. Excessive defoamers may cause problems such as decreased leveling and weakened adhesion of the paint.

[0004] In order to achieve better defoaming effect, the existing silicone defoamer adds a large amount of polysiloxane, which is not easily soluble in water and needs to be mixed with more emulsifiers. However, the defoaming effect becomes worse, and 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 the 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 defoamer.

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

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

[0008]

[0009] This composite defoamer uses special modified polysiloxane as the main defoaming raw material. The special modified polysiloxane molecules further improve the stability and activity of its molecular structure, so that it can better interact with the bubble surface and has better chemical stability and thermal stability. It can maintain a stable defoaming effect in different environments, and will quickly gather on the bubble surface to form a layer of film-like structure. By interacting with the tension on the bubble surface, it can destroy the balance of the bubble surface and make the bubble lose stability; adding defoaming additives synergistically 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 and improving The overall effect is that the modified polysiloxane and the defoaming agent still have excellent effects when the content in the system is low, and then the amount of emulsifier added is reduced for mixed use, and it is not easy to demulsify and float oil after dilution; the added nano-silicon dioxide is dispersed in water, and its tiny particle size and stable hydrogen bond three-dimensional network structure enable it to be evenly and stably distributed in the system, thereby increasing the viscosity of the defoaming agent 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 mixed with water to improve the stability of the system. In addition, the cosolvent can reduce the concentration of surfactants in the surface layer, and it will also dissolve into the surfactant adsorption layer to reduce the tightness between surfactant molecules, thereby weakening the stability of the foam. The composite defoamer can be used to eliminate the foam of the water-containing system, with fast defoaming speed, excellent dispersibility, long anti-foaming time, high efficiency, and low dosage. It is particularly suitable for water-based coatings in alkaline environments.

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

[0011] (R1), take 60-80 parts of dihydroxy polydimethylsiloxane, 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;

[0012] (R2), after hot air drying of dihydroxy polydimethylsiloxane and vacuum drying of rare earth lanthanum metal alkoxide, under nitrogen protection, dihydroxy polydimethylsiloxane, rare earth lanthanum metal alkoxide and organic solvent are mixed, the temperature is raised to 40-50° C. and dissolved uniformly under ultrasonic and stirring conditions to obtain a mixed solution;

[0013] (R3), under nitrogen protection, the temperature was raised to 70-90° C., a catalyst was added to the mixed solution, the mixture was stirred for reaction for 2-4 hours, and the mixture was allowed to stand for 1 hour to obtain a reaction product;

[0014] (R4), distilling and filtering the reaction product to remove impurities, thereby obtaining modified polysiloxane.

[0015] By adopting the above technical scheme, 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, and contains silicon-oxygen bonds in its molecular structure, which endows it with both the lipophilicity of organic matter and the hydrophilicity of inorganic matter. The introduction of rare earth metals further improves the stability and activity of its molecular structure, so that it can better interact with the bubble surface, has better chemical stability and thermal stability, and can maintain a stable defoaming effect under different environments. The presence of rare earth metals can also enhance the inhibitory effect of the defoamer on foam, prevent the re-formation of foam, and make the foam more easily broken, which can significantly improve the defoaming performance, enhance stability, and broaden the scope of application. In step (R2), the dihydroxy polydimethylsiloxane is dried by hot air, and the rare earth lanthanum metal alkoxide is dried by vacuum, and 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 scheme is adopted to catalyze the coordination reaction of dihydroxy polydimethylsiloxane and rare earth lanthanum metal alkoxide, introduce most of the rare earth lanthanum metal into the dihydroxy polydimethylsiloxane, and the triethylamine or dimethylaniline is easy to remove 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 acylated ethylenediamine.

[0022] By adopting the above technical scheme, the mixture of polyethylene glycol and distearic acid acylated ethylenediamine and the modified polysiloxane synergistically change the surface tension of the liquid, reduce the stability of the foam, can prevent the generation of new foam, and also have a thickening effect. The polyethylene glycol itself also has a high viscosity, forms a network structure in the system, increases the viscosity of the system, makes the product more stable, thereby extending the service life of the product and improving the overall effect, so that the modified polysiloxane and the defoaming aid still have excellent effects when the content is low in the system. More preferably, the defoaming aid is a mixture of polyethylene glycol and distearic acid acylated ethylenediamine in a weight ratio of 5-7:1.

[0023] Preferably, the other adjuvants include fungicides.

[0024] Using the above technical solution, more preferably, the fungicide is at least one of dodecyltrimethylammonium chloride, dodecyldimethylbenzylammonium chloride and dodecyldimethylbenzylammonium bromide.

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

[0026] By adopting the above technical solution, the above cosolvent is mixed with water to improve the stability of the system. In addition, the cosolvent can reduce the surfactant concentration in the surface layer and also dissolve into the surfactant adsorption layer to reduce the tightness between the 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-mentioned composite defoamer comprises the following steps:

[0028] (S1), taking modified polysiloxane, emulsifier, nano silicon dioxide, defoaming agent, other additives, cosolvent and water according to weight parts for later use;

[0029] (S2), uniformly mixing the modified polysiloxane, the cosolvent and water to obtain a blended liquid;

[0030] (S3), adding emulsifier, nano silicon dioxide, defoaming agent and other additives to the blended liquid, stirring for 5-10 minutes, and homogenizing for 3-5 minutes to obtain a composite defoaming agent.

[0031] The beneficial effects of the present invention are as follows: the composite defoamer of the present invention uses special modified polysiloxane as the main defoaming raw material, and the special modified polysiloxane molecule further improves the stability and activity of its molecular structure, so that it can better interact with the bubble surface and has better chemical stability and thermal stability, and can maintain a stable defoaming effect under different environments, and will quickly gather on the bubble surface to form a layer of film-like structure, which can destroy the balance of the bubble surface through the tension interaction with the bubble surface, so that the bubble loses stability; adding a defoaming auxiliary agent synergistically changes the liquid surface tension, 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 product The service life is improved, and the overall effect is improved, so that the modified polysiloxane and defoaming aid still have excellent effects when the content in the system is low, thereby reducing the amount of emulsifier added for mixed use, and it is not easy to demulsify and float oil after dilution; the added nano-silicon dioxide is dispersed in water, and its tiny particle size and stable hydrogen bond three-dimensional network structure enable it to be evenly and stably distributed in the system, thereby increasing the viscosity of the defoaming agent 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 mixed with water to improve the stability of the system. In addition, the cosolvent can reduce the surfactant concentration in the surface layer, and it will also dissolve into the surfactant adsorption layer, reduce the tightness between the surfactant molecules, and thus weaken the stability of the foam. The composite defoamer can be used to eliminate the foam of the water-containing system, with fast defoaming speed, excellent dispersibility, long anti-foaming time, high efficiency, and low dosage. It is particularly suitable for water-based coatings in alkaline environments.

[0032] The preparation method of the invention has the advantages of simple operation, convenient control, high production efficiency and low production cost, and can be used for large-scale production. DETAILED DESCRIPTION

[0033] In order to facilitate the understanding of those skilled in the art, the present invention is further described below in conjunction with embodiments, and the contents mentioned in the implementation modes are not intended to limit the present invention.

[0034] Example 1

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

[0036]

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

[0038] (R1), take 70 parts of dihydroxy polydimethylsiloxane, 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 dihydroxy polydimethylsiloxane for 2 hours and vacuum drying the rare earth lanthanum metal alkoxide for 2 hours, under nitrogen protection, mixing the dihydroxy polydimethylsiloxane, the rare earth lanthanum metal alkoxide and the organic solvent, heating to 45° C. and dissolving them uniformly under ultrasonic and stirring conditions to obtain a mixed solution;

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

[0041] (R4), distilling and filtering the reaction product to remove impurities, thereby obtaining modified polysiloxane.

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

[0043] The general structural formula of the rare earth lanthanum metal alkoxide is La(OR)3, wherein 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 silicon dioxide is 35nm.

[0046] The defoaming aid is prepared by mixing polyethylene glycol and distearate ethylenediamine in a weight ratio of 6:1.

[0047] The other auxiliary agents include a bactericide, and the bactericide is dodecyltrimethylammonium chloride.

[0048] The cosolvent is ethanol.

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

[0050] (S1), taking modified polysiloxane, emulsifier, nano silicon dioxide, defoaming agent, other additives, cosolvent and water according to weight parts for later use;

[0051] (S2), uniformly mixing the modified polysiloxane, the cosolvent and water to obtain a blended liquid;

[0052] (S3), adding emulsifier, nano silicon dioxide, defoaming agent and other additives to the blended liquid, stirring for 8 minutes, and homogenizing for 4 minutes to obtain a composite defoaming agent.

[0053] Example 2

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

[0055]

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

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

[0058] (R2), after hot air drying the dihydroxy polydimethylsiloxane for 2 hours and vacuum drying the rare earth lanthanum metal alkoxide for 2 hours, under nitrogen protection, mixing the dihydroxy polydimethylsiloxane, the rare earth lanthanum metal alkoxide and the organic solvent, heating to 40° C. and dissolving them uniformly under ultrasonic and stirring conditions to obtain a mixed solution;

[0059] (R3), under nitrogen protection, the temperature was raised to 75° C., a catalyst was added to the mixed solution, the mixture was stirred for reaction for 2 h, and the mixture was allowed to stand for 1 h to obtain a reaction product;

[0060] (R4), distilling and filtering the reaction product to remove impurities, thereby obtaining modified polysiloxane.

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

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

[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 silicon dioxide is 35nm.

[0065] The defoaming aid is prepared by mixing polyethylene glycol and distearate acylated ethylenediamine in a weight ratio of 5:1.

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

[0067] The cosolvent is ethanol.

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

[0069] (S1), taking modified polysiloxane, emulsifier, nano silicon dioxide, defoaming agent, other additives, cosolvent and water according to weight parts for later use;

[0070] (S2), uniformly mixing the modified polysiloxane, the cosolvent and water to obtain a blended liquid;

[0071] (S3), adding emulsifier, nano silicon dioxide, defoaming agent and other additives to the blended liquid, stirring for 8 minutes, and homogenizing for 4 minutes to obtain a composite defoaming agent.

[0072] Example 3

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

[0074]

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

[0076] (R1), take 78 parts of dihydroxy polydimethylsiloxane, 40 parts of rare earth lanthanum metal alkoxide, 120 parts of organic solvent and 2 parts of catalyst by weight, and set aside;

[0077] (R2), after hot air drying the dihydroxy polydimethylsiloxane for 2 hours and vacuum drying the rare earth lanthanum metal alkoxide for 2 hours, under nitrogen protection, mixing the dihydroxy polydimethylsiloxane, the rare earth lanthanum metal alkoxide and the organic solvent, heating to 50° C. and dissolving them uniformly under ultrasonic and stirring conditions to obtain a mixed solution;

[0078] (R3), under nitrogen protection, the temperature was raised to 90° C., a catalyst was added to the mixed solution, the mixture was stirred for reaction for 4 h, and the mixture was allowed to stand for 1 h to obtain a reaction product;

[0079] (R4), distilling and filtering the reaction product to remove impurities, thereby obtaining modified polysiloxane.

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

[0081] The general structural formula of the rare earth lanthanum metal alkoxide is La(OR)3, wherein 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 silicon dioxide is 35nm.

[0084] The defoaming aid is prepared by mixing polyethylene glycol and distearate acylated ethylenediamine in a weight ratio of 7:1.

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

[0086] The cosolvent is ethanol.

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

[0088] (S1), taking modified polysiloxane, emulsifier, nano silicon dioxide, defoaming agent, other additives, cosolvent and water according to weight parts for later use;

[0089] (S2), uniformly mixing the modified polysiloxane, the cosolvent and water to obtain a blended liquid;

[0090] (S3), adding emulsifier, nano silicon dioxide, defoaming agent and other additives to the blended liquid, stirring for 8 minutes, and homogenizing for 4 minutes to obtain a composite defoaming agent.

[0091] Example 4

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

[0093]

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

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

[0096] (R2), after hot-air drying of dihydroxy polydimethylsiloxane for 2 hours and vacuum drying of rare earth lanthanum metal alkoxide for 2 hours, dihydroxy polydimethylsiloxane, rare earth lanthanum metal alkoxide and organic solvent are mixed under nitrogen protection, the temperature is raised to 43° C. and dissolved uniformly under ultrasonic and stirring conditions to obtain a mixed solution;

[0097] (R3), under nitrogen protection, the temperature was raised to 80° C., a catalyst was added to the mixed solution, the mixture was stirred for reaction for 3 h, and the mixture was allowed to stand for 1 h to obtain a reaction product;

[0098] (R4), distilling and filtering the reaction product to remove impurities, thereby obtaining modified polysiloxane.

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

[0100] The general structural formula of the rare earth lanthanum metal alkoxide is La(OR)3, wherein 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 silicon dioxide is 35nm.

[0103] The defoaming aid is prepared by mixing polyethylene glycol and distearate ethylenediamine in a weight ratio of 6:1.

[0104] The other auxiliary agents include a bactericide, and the bactericide is dodecyltrimethylammonium chloride.

[0105] The cosolvent is ethanol.

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

[0107] (S1), taking modified polysiloxane, emulsifier, nano silicon dioxide, defoaming agent, other additives, cosolvent and water according to weight parts for later use;

[0108] (S2), uniformly mixing the modified polysiloxane, the cosolvent and water to obtain a blended liquid;

[0109] (S3), adding emulsifier, nano silicon dioxide, defoaming agent and other additives to the blended liquid, stirring for 8 minutes, and homogenizing for 4 minutes to obtain a composite defoaming agent.

[0110] Comparative Example 1

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

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

[0113] Comparative Example 2

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

[0115] The defoaming aid is polyoxyethylene alcohol.

[0116] Comparative Example 3

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

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

[0119]

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

[0121] Comparative Example 4

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

[0123] Performance Testing

[0124] The defoamers of Examples 1-4 and Comparative Examples 1-4 were respectively tested for stability, defoaming and antifoaming properties of the alkaline surfactant system under the same conditions. The test methods are as follows:

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

[0126] The alkaline surfactant aqueous solution is prepared by mixing the following components in weight percentage: 0.5% sodium dialkylbenzene sulfonate, 0.5% nonylphenol polyoxyethylene (10) ether, 1% sodium hydroxide and the balance deionized water;

[0127] (1) Stability test

[0128] Use two 10mL graduated centrifuge test tubes to measure 8mL of the sample respectively, place them symmetrically in a 80-2 low-speed electric centrifuge, and rotate continuously at a speed of 3000r / min for 15min. Take out the test 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 100mL stoppered measuring cylinder to take 50mL of alkaline surfactant aqueous solution, add 0.05g of sample, and keep the temperature in a water bath at 25℃ and 60℃ respectively. Cover the bottle with a stopper, and shake the measuring cylinder vertically up and down 10 times at a frequency of 2 times / s and an amplitude of (30-35)cm. Let it stand and start timing with a stopwatch, recording the time taken for the foam to disappear and the liquid surface to appear.

[0131] (3) Antifoaming performance

[0132] Use a lubricating oil (defoaming agent) foam property tester that meets the test requirements of GB / T 12579. Turn on and debug the foam property tester, and test the air flow rate at 100mL / min. Take 100mL of alkaline surfactant aqueous solution, add 0.1g of sample to the alkaline surfactant aqueous solution, stir evenly, and then pour into a clean bubbler measuring cylinder, and keep the temperature constant at 25℃ and 60℃ respectively. Turn on the flow pump, start the test, record the foam volume (mL) after 30min of air blowing, and express the result as the foam volume corresponding to 30min of air blowing.

[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 can better interact 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 aid 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 and improving the overall effect, so that the modified polysiloxane and the defoaming aid still have excellent effects when the content in the system is low, and then reduce the amount of emulsifier added for mixed use, and it is not easy to demulsify and float oil after dilution; the added cosolvent is blended with water to improve the stability of the system. The composite defoamer can be used to eliminate the foam of the aqueous system, has a fast defoaming speed, excellent dispersibility, a long foam suppression time, high efficiency, and low dosage, and is particularly suitable for water-based coatings in alkaline environments.

[0136] The above embodiments are preferred implementation schemes of the present invention. In addition, the present invention may also be implemented in other ways. Any obvious replacement 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: The invention comprises the following raw materials in parts by weight:

2. A composite defoamer according to claim 1, characterized in that: The preparation method of each modified polysiloxane comprises the following steps: (R1), take 60-80 parts of dihydroxy polydimethylsiloxane, 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 of dihydroxy polydimethylsiloxane and vacuum drying of rare earth lanthanum metal alkoxide, under nitrogen protection, dihydroxy polydimethylsiloxane, rare earth lanthanum metal alkoxide and organic solvent are mixed, the temperature is raised to 40-50° C. and dissolved uniformly under ultrasonic and stirring conditions to obtain a mixed solution; (R3), under nitrogen protection, the temperature was raised to 70-90° C., a catalyst was added to the mixed solution, the mixture was stirred for reaction for 2-4 hours, and the mixture was allowed to stand for 1 hour to obtain a reaction product; (R4), distilling and filtering the reaction product to remove impurities, thereby obtaining modified polysiloxane.

3. A composite defoamer according to claim 2, characterized in that: 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.

4. A composite defoamer according to claim 2, characterized in that: The general structural formula of the rare earth lanthanum metal alkoxide is La(OR)3, wherein R is methyl, ethyl, propyl or isopropyl.

5. A composite defoamer according to claim 2, characterized in that: The catalyst is triethylamine or dimethylaniline.

6. A 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 silicon dioxide is 30-40nm.

7. A composite defoamer according to claim 1, characterized in that: The defoaming aid is a mixture of polyethylene glycol and distearic acid acylated ethylenediamine.

8. A composite defoamer according to claim 1, characterized in that: The other adjuvants include fungicides.

9. A composite defoamer according to claim 1, characterized in that: The co-solvent is at least one of octanol, ethanol and propanol.

10. A method for preparing the composite defoamer according to any one of claims 1 to 9, characterized in that: The steps include: (S1), taking modified polysiloxane, emulsifier, nano silicon dioxide, defoaming agent, other additives, cosolvent and water according to weight parts for later use; (S2), uniformly mixing the modified polysiloxane, the cosolvent and water to obtain a blended liquid; (S3), adding emulsifier, nano silicon dioxide, defoaming agent and other additives to the blended liquid, stirring for 5-10 minutes, and homogenizing for 3-5 minutes to obtain a composite defoaming agent.

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