Waterborne polyurethane-styrene-acrylic composite waterproof coating and preparation method thereof

Abstract

The invention provides a waterborne polyurethane-styrene-acrylic composite waterproof coating and a preparation method thereof, and belongs to the technical field of waterborne waterproof coatings. The waterborne polyurethane-styrene-acrylic composite waterproof coating is prepared from the following raw materials in parts by weight: 35 to 45 parts of waterborne polyurethane emulsion containing a catechol structure, 40 to 60 parts of styrene-acrylic emulsion containing hydrogen bond crosslinking sites, 20 to 30 parts of water, 0.5 to 1.5 parts of a de-foaming agent, 0.5 to 1.5 parts of a dispersing agent, 65 to 105 parts of filler, 0.5 to 1 part of a sterilizing agent and 0.3 to 1 part of a thickening agent, a hydrogen bond crosslinking site of the styrene-acrylic emulsion is provided by an acrylate functional monomer containing a hydroxyl functional group.

Description

Technical Field

[0001] The present invention belongs to the technical field of waterborne waterproof coatings, and particularly relates to a waterborne polyurethane-styrene-acrylic composite waterproof coating and a preparation method thereof. Background Art

[0002] In recent years, with the increasing attention to environmental issues, waterborne emulsion coatings have become materials that have attracted much attention in the coating industry due to their low cost, convenient construction, wide applicability, and non-toxic and environmentally friendly advantages. Among them, acrylic emulsions have advantages such as good film-forming properties, low price, stain resistance, and weather resistance, and are widely used in products such as architectural waterproof coatings, wood coatings, peelable coatings, anticorrosive coatings, and waterborne amino baking varnishes. However, waterborne acrylic acid has poor water resistance and mechanical properties due to the influence of hydrophilic monomers and external emulsifiers. Waterborne polyurethane materials have excellent mechanical adjustability due to their special molecular structure with cross-distribution of hard and soft segments, but their price is relatively high and the application environment is limited. Therefore, in order to obtain a waterproof coating with better comprehensive performance and low cost, combining the advantages of acrylic acid and polyurethane, using waterborne polyurethane-acrylic composite emulsions to prepare waterproof coatings has become a research hotspot. For example, an acrylic polyurethane coating has good anti-aging properties and good anti-discoloration properties, but the flexibility of this coating is poor and the elongation at break is low. Or, an acrylic-polyurethane waterproof coating, its preparation method and application, this waterproof coating has excellent mechanical properties, but its copolymerization synthesis process is relatively complex. Summary of the Invention

[0003] In view of the above technical problems, the present invention provides a waterborne polyurethane-styrene-acrylic composite waterproof coating and a preparation method thereof, in order to at least partially solve the above technical problems. The specific technical solutions provided by the present invention are as follows.

[0004] As a first aspect of the present invention, there is provided a waterborne polyurethane-styrene-acrylic composite waterproof coating, comprising the following raw materials in parts by weight: 35-45 parts of a waterborne polyurethane emulsion containing catechol structure, 40-60 parts of a styrene-acrylic emulsion containing hydrogen bond crosslinking sites, 20-30 parts of water, 0.5-1.5 parts of a defoaming agent, 0.5-1.5 parts of a dispersant, 65-105 parts of a filler, 0.5-1 part of a bactericide, and 0.3-1 part of a thickener; wherein, the hydrogen bond crosslinking site is a hydroxyl structure contained in an acrylic monomer unit.

[0005] As a second aspect of the present invention, a preparation method of an aqueous polyurethane-styrene-acrylic composite waterproof coating is provided, including: adding an aqueous polyurethane emulsion containing catechol structure and a styrene-acrylic emulsion containing hydrogen bond crosslinking sites into water and mixing them, then adding an antifoaming agent and a dispersant and mixing them to obtain a mixed liquid material; adding a filler to the mixed liquid material and mixing them, then adding a thickening agent and a bactericide and mixing them to obtain the aqueous polyurethane-styrene-acrylic composite waterproof coating.

[0006] In an embodiment of the present invention, the aqueous polyurethane-styrene-acrylic composite waterproof coating provided by the present invention is prepared from an aqueous polyurethane emulsion containing catechol structure and a styrene-acrylic emulsion containing hydrogen bond crosslinking sites. Among them, the catechol structure in the aqueous polyurethane emulsion and the hydrogen bond crosslinking sites of the styrene-acrylic emulsion form a dense molecular crosslinking network, and the prepared aqueous polyurethane-styrene-acrylic composite waterproof coating has excellent physical and mechanical properties, water resistance and weather resistance. The preparation method of the aqueous polyurethane-styrene-acrylic composite waterproof coating provided by the present invention only needs to add raw materials in sequence and mix them. The preparation process is simple, without strict preparation conditions and equipment, and is suitable for large-scale industrial promotion. Detailed implementation mode

[0007] To make the purpose, technical solution and advantages of the present invention clearer, the following further describes the present invention in detail with reference to specific embodiments.

[0008] To provide a waterproof coating that has both excellent water resistance and excellent mechanical properties, the present invention provides an aqueous polyurethane-styrene-acrylic composite waterproof coating, which is obtained by blending an aqueous polyurethane emulsion containing catechol structure and a styrene-acrylic emulsion containing hydrogen bond crosslinking sites.

[0009] Specifically, as a first aspect of the present invention, an aqueous polyurethane-styrene-acrylic composite waterproof coating is provided, including the following raw materials in parts by weight: 35-45 parts of an aqueous polyurethane emulsion containing catechol structure, 40-60 parts of a styrene-acrylic emulsion containing hydrogen bond crosslinking sites, 20-30 parts of water, 0.5-1.5 parts of an antifoaming agent, 0.5-1.5 parts of a dispersant, 65-105 parts of a filler, 0.5-1 part of a bactericide, and 0.3-1 part of a thickening agent; among them, the hydrogen bond crosslinking site is a hydroxyl structure contained in an acrylic monomer unit.

[0010] In an embodiment of the present invention, the aqueous polyurethane-styrene-acrylic composite waterproof coating provided by the present invention is prepared from an aqueous polyurethane emulsion containing catechol structure and a styrene-acrylic emulsion containing hydrogen bond crosslinking sites. Among them, the catechol structure in the aqueous polyurethane emulsion and the hydrogen bond crosslinking sites of the styrene-acrylic emulsion form a dense molecular crosslinking network, and the prepared aqueous polyurethane-styrene-acrylic composite waterproof coating has excellent physical and mechanical properties, water resistance and weather resistance.

[0011] According to an embodiment of the present invention, the aqueous polyurethane emulsion containing catechol structure is made from the following raw materials in parts by weight: 50-100 parts of polyether diol, 20-40 parts of diisocyanate, 0.1-0.5 part of catalyst, 1-10 parts of diol linear chain extender, 4-20 parts of functional chain extender, 2-10 parts of functional neutralizer, and 120-240 parts of solvent. Among them, the polyether diol includes at least one of polypropylene glycol, polyethylene glycol, and polytetrahydrofuran. The diisocyanate includes at least one of toluene diisocyanate, isophorone diisocyanate, diphenylmethane diisocyanate, dicyclohexylmethane diisocyanate, hexamethylene diisocyanate, and lysine diisocyanate. The catalyst is dibutyltin dilaurate (DBTDL). The diol linear chain extender includes at least one of 1,4-butanediol, 1,6-hexanediol, 1,5-hexanediol, and furan-2,5-diol. The functional chain extender includes 3-dimethylamino-1,2-propanediol and trimethylolpropane, with the proportion of 3-dimethylamino-1,2-propanediol being 2-10 parts and the proportion of trimethylolpropane being 2-10 parts. The functional neutralizer is 3,4-dihydroxybenzoic acid. The solvent includes acetone and water, with the proportion of acetone being 30-40 parts and the proportion of water being 80-200 parts.

[0012] According to an embodiment of the present invention, the styrene-acrylic emulsion is made from the following raw materials in parts by weight: 25-35 parts of styrene, 30-50 parts of acrylic soft monomer, 5-15 parts of acrylic hard monomer, 2-4 parts of acrylic functional monomer, 0.5-4 parts of emulsifier, 0.2-1.5 parts of pH buffer, 0.15-0.6 part of initiator, and 100 parts of deionized water. Among them, the acrylic hard monomer includes at least one of methyl methacrylate, ethyl methacrylate, and acrylonitrile. The acrylic soft monomer includes at least one of butyl acrylate, isooctyl acrylate, lauryl acrylate, and lauryl methacrylate. The acrylic functional monomer includes at least one of 2-hydroxyethyl methacrylate, hydroxyethyl acrylate, and hydroxypropyl methacrylate. The emulsifier includes at least one of anionic emulsifier and non-ionic emulsifier; the anionic emulsifier includes at least one of sodium dodecyl sulfonate, sodium dodecyl sulfate (SDS), and sodium dodecylbenzenesulfonate (SDBS); the non-ionic emulsifier includes at least one of polyoxyethylene octylphenol ether (OP-10) and sorbitan monolaurate (Span20). The pH buffer includes at least one of dipotassium hydrogen phosphate and sodium carbonate. The initiator includes at least one of persulfate initiator, organic peroxide initiator, and redox initiator; the persulfate initiator includes at least one of sodium persulfate, ammonium persulfate, and potassium persulfate; the organic peroxide initiator includes at least one of benzoyl peroxide and dicumyl peroxide; the redox initiator includes at least one of ammonium persulfate-sodium bisulfite initiator and hydrogen peroxide-ferrous salt initiator.

[0013] In an embodiment of the present invention, when synthesizing the aqueous polyurethane emulsion, 3-dimethylamino-1,2-propanediol and 3,4-dihydroxybenzoic acid undergo electrostatic interaction to form an aqueous polyurethane emulsion containing a catechol structure. Specifically, the carboxyl group (-COOH) contained in 3,4-dihydroxybenzoic acid reacts with the tertiary amine group contained in 3-dimethylamino-1,2-propanediol to form a carboxylic acid-quaternary ammonium salt structure. Through the electrostatic interaction between the positive and negative charges of the salt ions, small molecules with a catechol structure are grafted onto the polyurethane chain while emulsifying. The hydroxyl group structure contained in the acrylic functional monomer makes the styrene-acrylic emulsion contain multiple hydrogen bond crosslinking sites. Therefore, after mixing the aqueous polyurethane emulsion and the styrene-acrylic emulsion, the strong intermolecular or intramolecular hydrogen bond forces result in the formation of a dense molecular crosslinking network in the obtained aqueous polyurethane-styrene-acrylic composite waterproof coating. At the same time, due to the cationic polymer property of the synthesized aqueous polyurethane, the cation-π interaction between the quaternary ammonium salt structure on the side chain of the polyurethane molecule and the benzene ring on the molecular chain of the styrene-acrylic emulsion can serve as a secondary force to enhance the crosslinking force between the molecular crosslinking networks in the aqueous polyurethane-styrene-acrylic composite waterproof coating.

[0014] According to the embodiments of the present invention, the defoamer includes at least one of polyether defoamers, silicone defoamers, non-silicone defoamers, and polyether-modified silicone defoamers. The dispersant includes at least one of anionic dispersants and non-ionic dispersants; the anionic dispersant includes at least one of sodium oleate, carboxylates, sulfate esters, and sulfonates; the non-ionic dispersant includes at least one of the adduct of fatty acid and ethylene oxide, polyethylene glycol type polyols, and polyethyleneimine derivatives. The bactericide includes at least one of benzisothiazolinone bactericides and isothiazolinone bactericides; the benzisothiazolinone bactericides include at least one of 1,2-benzisothiazolin-3-one and 2-butyl-1,2-benzisothiazolin-3-one; the isothiazolinone bactericides include at least one of methylisothiazolinone bactericide and Kathon bactericide. The thickener includes at least one of hydroxyethyl cellulose, carboxymethyl cellulose, and hydroxypropyl methyl cellulose. The filler includes heavy calcium carbonate, titanium dioxide, and barium sulfate. The proportion of heavy calcium carbonate is 50-65 parts, the average particle size of heavy calcium carbonate is 20-80 μm, the proportion of titanium dioxide is 5-10 parts, and the proportion of barium sulfate is 10-30 parts.

[0015] As the second aspect of the present invention, a preparation method of an aqueous polyurethane-styrene-acrylic composite waterproof coating is provided, including: adding the aqueous polyurethane emulsion containing a catechol structure and the styrene-acrylic emulsion containing hydrogen bond crosslinking sites into water and mixing them, then adding a defoamer and a dispersant and mixing them to obtain a mixed liquid material; adding a filler to the mixed liquid material and mixing them, then adding a thickener and a bactericide and mixing them to obtain the aqueous polyurethane-styrene-acrylic composite waterproof coating.

[0016] In an embodiment of the present invention, the preparation method of the waterborne polyurethane-styrene-acrylic composite waterproof coating provided by the present invention only needs to add raw materials in sequence for mixing. The preparation process is simple, without strict preparation conditions and equipment, and is suitable for large-scale industrial promotion.

[0017] According to an embodiment of the present invention, the waterborne polyurethane emulsion containing catechol structure is prepared by the following method: After mixing polyether diol, diisocyanate, and catalyst, react at 75-85 °C for 2-3 h to obtain a first polymerization product; after adding 3-dimethylamino-1,2-propanediol and acetone to the first polymerization product, react at 65-75 °C for 1-2 h to obtain a second polymerization product; after adding a diol linear chain extender and trimethylolpropane to the second polymerization product, react at 60-80 °C for 2-3 h to obtain a third polymerization product; after adding a functional neutralizer and water to the third polymerization product, shear and emulsify evenly and then remove acetone to obtain a waterborne polyurethane emulsion containing catechol structure.

[0018] According to an embodiment of the present invention, the styrene-acrylic emulsion containing hydrogen bond crosslinking sites is prepared by the following method: Take 40-50 parts of deionized water and mix it with an emulsifier, then add styrene, acrylic soft monomer, acrylic hard monomer, and acrylic functional monomer respectively and mix evenly to obtain an acrylic monomer emulsion; add 50-60 parts of deionized water to the polymerization kettle, heat up to 80-90 °C, then add a pH buffer solution, and then slowly dropwise add the acrylic monomer emulsion and the initiator solution. After the dropping is completed, keep the temperature at 80-90 °C and react for 2-3 h to obtain a styrene-acrylic emulsion containing hydrogen bond crosslinking sites.

[0019] Specifically, the method for preparing the styrene-acrylic emulsion containing hydrogen bond crosslinking sites includes: Mix 40-50 parts of deionized water and an emulsifier, then add the acrylic monomers required for the reaction and mix to obtain an acrylic monomer emulsion; Prepare a 10 wt% first initiator solution and a 1 wt% second initiator solution, where the initiators used in the first initiator solution and the second initiator solution are the same or different, and the proportions of the initiators in the first initiator solution and the second initiator solution are 0.1-0.4 parts and 0.05-0.2 parts respectively; Add the first initiator solution, pH buffer, and 5-15 parts of the acrylic monomer emulsion (it should be understood that part of the acrylic monomer emulsion added here can also be replaced with the prepared styrene-acrylic emulsion containing hydrogen bond crosslinking sites, acting as the seed in the polymerization reaction) to water at 80-90 °C; Slowly dropwise add the remaining acrylic monomer emulsion and the second initiator solution so that they end the dropping at the same time. After the dropping is completed, react at 80-90 °C for 2-3 h. After the reaction is completed, cool to room temperature and dropwise add ammonia water to adjust the pH value of the system to meet the usage requirements of different environments to obtain a styrene-acrylic emulsion containing hydrogen bond crosslinking sites.

[0020] The present invention will be further illustrated by the following examples and related test experiments. In the following detailed description, for the sake of explanation, numerous specific details are set forth in order to provide a thorough understanding of the embodiments of the present invention. However, it is obvious that one or more embodiments can be implemented without these specific details. Moreover, without conflict, the details in the following embodiments can be combined arbitrarily to form other feasible embodiments. All instruments, consumables, reagents, etc. in the following examples can be obtained from commercial sources without special instructions.

[0021] Example 1

[0022] In this Example 1, an acrylic seed emulsion was prepared for subsequent use. Among them, the types and contents of the raw materials for synthesizing the acrylic seed emulsion are shown in Table 1.

[0023] Table 1 Types and Contents of Raw Materials for Synthesizing Acrylic Seed Emulsion in Example 1

[0024]

[0025] The specific method for synthesizing the acrylic seed emulsion is as follows.

[0026] (1) Add 53.52 g of deionized water and an emulsifier to the monomer stirring kettle; add acrylic monomers and disperse them evenly at a rotation speed of 150 rpm to obtain an acrylic monomer emulsion.

[0027] (2) Add the remaining deionized water to the polymerization reaction kettle and heat its temperature to 80 °C, then turn on the nitrogen source and the condensation device.

[0028] (3) Add the prepared 10 wt% initiator solution, pH buffer, and 7 wt% acrylic monomer emulsion to the system in (2).

[0029] (4) Adjust the speeds of the two rate-controlled feeding devices to drip the 1 wt% initiator solution and the remaining acrylic monomer emulsion into (3) respectively and ensure that the dripping ends simultaneously.

[0030] (5) After all the acrylic monomer emulsion and the 1 wt% initiator solution are added dropwise, react at 80 °C for 3 h.

[0031] (6) After the reaction is completed, cool to room temperature and add ammonia water dropwise to adjust the required pH value of the system to obtain an acrylic seed emulsion.

[0032] Example 2

[0033] In this Example 2, a waterborne polyurethane-styrene-acrylic composite waterproof coating was prepared.

[0034] Among them, the types and contents of the raw materials for synthesizing the waterborne polyurethane emulsion are shown in Table 2.

[0035] Table 2 Types and Contents of Raw Materials for Synthesizing Aqueous Polyurethane Emulsion in Example 2

[0036]

[0037] The aqueous polyurethane emulsion is prepared by the following method.

[0038] (1) Add the dehydrated polyether diol and diisocyanate into a reaction flask, and add a catalyst to the reaction system. Carry out a polymerization reaction at 80 °C for 3 h.

[0039] (2) Slowly add 3-dimethylamino-1,2-propanediol dropwise to the system in (1), and react at 70 °C for 1.5 h. Add acetone as needed during the reaction to adjust the viscosity of the system.

[0040] (3) Slowly add the diol linear chain extender and trimethylolpropane dropwise to the system in (2), and react at 80 °C for 3 h.

[0041] (4) Wait for the reaction system in (3) to cool down, add the functional neutralizer 3,4-dihydroxybenzoic acid and deionized water, and increase the stirring speed to 1600 rpm, and stir for 0.5 h.

[0042] (5) Use a rotary evaporator to remove the residual acetone in the system in (4) to obtain the aqueous polyurethane emulsion.

[0043] The types and contents of raw materials for synthesizing styrene-acrylic emulsion are shown in Table 3.

[0044] Table 3 Types and Contents of Raw Materials for Synthesizing Styrene-Acrylic Emulsion in Example 2

[0045]

[0046] The specific method for synthesizing the styrene-acrylic emulsion is as follows.

[0047] (1) Add 50.28 g of deionized water and an emulsifier into a monomer stirring kettle; add monomers and disperse them evenly at a rotation speed of 150 rpm to obtain an acrylic monomer emulsion.

[0048] (2) Add the remaining deionized water into the polymerization reaction kettle and heat its temperature to 80 °C, and turn on the nitrogen source and the condensation device.

[0049] (3) Add the prepared 10 wt% initiator solution, pH buffer and the acrylic seed emulsion in Example 1 into the system in (2).

[0050] (4) Adjust the speeds of the two controlled-speed feeding devices so that they are used to separately dropwise add the 1 wt% initiator solution and the remaining acrylic monomer emulsion into (3) and ensure that the dropping ends simultaneously.

[0051] After the addition of all acrylic monomer emulsions and 1 wt% initiator solution was completed, the reaction was carried out at 80 °C for 3 h.

[0052] (6)After the reaction, the temperature was lowered to room temperature, and ammonia water was added dropwise to adjust the pH value required for the system to obtain a styrene-acrylic emulsion.

[0053] Furthermore, a waterborne polyurethane-styrene-acrylic composite waterproof coating was synthesized using the above-mentioned waterborne polyurethane emulsion and styrene-acrylic emulsion, and the specific method is as described below.

[0054] (1)40 parts of waterborne polyurethane emulsion and 60 parts of styrene-acrylic emulsion were mixed, 30 parts of water, 0.5 part of defoamer (BYK-1786 of BYK Chemie) and 0.5 part of dispersant (BYK-110 of BYK Chemie) were added and stirred evenly to obtain a mixed liquid material.

[0055] (2)65 parts of heavy calcium carbonate, 10 parts of titanium dioxide and 25 parts of barium sulfate were added to the above-mentioned mixed liquid material and stirred for 10 min until the powder was evenly dispersed.

[0056] (3)0.3 part of thickener (hydroxyethyl cellulose) and 0.5 part of fungicide (KATHON LXE) were added to the material in (2) and mixed evenly to obtain a waterborne polyurethane-styrene-acrylic composite waterproof coating.

[0057] Unless otherwise specified, the preparation process of the following examples was carried out according to the method of Example 2, except for the differences in the formulations of the waterborne polyurethane emulsion and styrene-acrylic emulsion.

[0058] Example 3

[0059] In this Example 3, a waterborne polyurethane-styrene-acrylic composite waterproof coating was prepared.

[0060] Among them, the types and contents of the raw materials for synthesizing the waterborne polyurethane emulsion are shown in Table 4.

[0061] Table 4 Types and Contents of Raw Materials for Synthesizing Waterborne Polyurethane Emulsion in Example 3

[0062]

[0063] The types and contents of the raw materials for synthesizing the styrene-acrylic emulsion are shown in Table 5.

[0064] Table 5 Types and Contents of Raw Materials for Synthesizing Styrene-Acrylic Emulsion in Example 3

[0065]

[0066] Example 4

[0067] In this Example 4, a waterborne polyurethane-styrene-acrylic composite waterproof coating was prepared.

[0068] Among them, the types and contents of the raw materials for synthesizing the aqueous polyurethane emulsion are shown in Table 6.

[0069] Table 6 Types and Contents of Raw Materials for Synthesizing Aqueous Polyurethane Emulsion in Example 4

[0070]

[0071] The types and contents of the raw materials for synthesizing the styrene-acrylic emulsion are shown in Table 7.

[0072] Table 7 Types and Contents of Raw Materials for Synthesizing Styrene-Acrylic Emulsion in Example 4

[0073]

[0074] Comparative Example 1

[0075] In this Comparative Example 1, an aqueous polyurethane waterproof coating was prepared. The difference from the aqueous polyurethane-styrene-acrylic composite waterproof coating in Example 2 is that 100 parts of the aqueous polyurethane emulsion were added, and no styrene-acrylic emulsion was added.

[0076] Comparative Example 2

[0077] In this Comparative Example 2, a styrene-acrylic emulsion waterproof coating was prepared. The difference from the aqueous polyurethane-styrene-acrylic composite waterproof coating in Example 2 is that 100 parts of the styrene-acrylic emulsion were added, and no aqueous polyurethane emulsion was added.

[0078] Comparative Example 3

[0079] In this Comparative Example 3, an aqueous polyurethane-styrene-acrylic composite waterproof coating was prepared. The difference from the aqueous polyurethane-styrene-acrylic composite waterproof coating in Example 2 is that the monomers used in preparing the styrene-acrylic emulsion do not have a hydroxyl structure. The specific formula of the styrene-acrylic emulsion is shown in Table 8.

[0080] Table 8 Types and Contents of Raw Materials for Synthesizing Styrene-Acrylic Emulsion in Comparative Example 3

[0081]

[0082] Comparative Example 4

[0083] In this Comparative Example 4, an aqueous polyurethane-styrene-acrylic composite waterproof coating was prepared. The difference from the aqueous polyurethane-styrene-acrylic composite waterproof coating in Example 2 is that the prepared aqueous polyurethane emulsion does not have a functional catechol structure. The specific formula of the aqueous polyurethane emulsion is shown in Table 9.

[0084] Table 9 Types and Contents of Raw Materials for Synthesizing Aqueous Polyurethane Emulsion in Comparative Example 4

[0085]

[0086] Furthermore, the acrylic seed emulsions or styrene-acrylic emulsions obtained in the above Examples 1-4 and Comparative Example 3 were tested and characterized, and the test and characterization results are shown in Table 10. The specific test methods are as follows.

[0087] (1) Solids content test: Sample preparation and testing were carried out according to the non-volatile matter test of GB / T 20623-2006. Bake a flat-bottomed disc (diameter about 75 mm) in a forced-air drying oven at (150 ± 2) °C for 15 min, cool it to room temperature in the drying oven, weigh (m0) accurately to 1 mg, weigh about 1 g of the sample (m1) in the disc with the same accuracy and ensure that the sample is evenly dispersed in the disc. Place the weighed sample in a preheated forced-air drying oven at (150 ± 2) °C for 15 min, put the disc in a desiccator, and weigh (m2) accurately to 1 mg after cooling to room temperature. The solids content is calculated according to Equation (1).

[0088] Equation (1).

[0089] In Equation (1): w—the solids content of the sample (%); m0—the mass of the disc, in grams (g); m1—the mass of the sample before heating, in grams (g); m2—the mass of the sample and the disc after heating, in grams (g).

[0090] Perform two parallel determinations, and the difference between the two test results should not be greater than 1%. The test results are expressed as the average of the two measured values, accurate to one decimal place.

[0091] (2) pH value test: After thoroughly stirring the sample, place it in a 50 mL beaker, and measure the pH value of the sample at (23 ± 2) °C with a pH meter with a precision of 0.01. Perform 3 parallel determinations, and the results are expressed as the average of the 3 measured values, accurate to one decimal place.

[0092] (3) Particle size test: The test instrument is Zetasizer Nano ZS90. The particle size distribution of the emulsion sample is measured using a nano particle size and zeta potential analyzer. Before testing, dilute the emulsion sample with distilled water to about 0.01 wt%, and perform three parallel experiments for each sample.

[0093] (4) Tg test: The test instrument is Q2000. The glass transition temperature of the sample is tested by a differential scanning calorimeter. Take an appropriate amount of the emulsion sample in a polytetrafluoroethylene mold, place it in a forced-air drying oven at 150 °C and bake it to absolute dryness. Take 3 - 8 mg of the dried sample for the differential scanning calorimeter test. The test temperature range is -50~180 °C, and the heating rate is 10 °C / min. The test is carried out under the condition of a stable nitrogen flow.

[0094] (5) Gel content test: After synthesizing the styrene-acrylic emulsion, take out the gel remaining on the stirring paddle and the kettle wall, place it on a weighing pan (m0), accurate to 1 mg, and place it in a preheated blast drying oven at (150 ± 2) °C for 30 min. Place the pan in a desiccator, and after cooling to room temperature, weigh it (m1), accurate to 1 mg. The total gel content is calculated according to Equation (II).

[0095] Equation (II).

[0096] In Equation (II): g—the gel content of the sample (%); m0—the mass of the disc, in grams (g); m1—the mass of the gel and the disc after heating, in grams (g); M—the total amount of the synthesized emulsion, in grams (g).

[0097] Table 10 Test characterization results of acrylic seed emulsion or styrene-acrylic emulsion in Examples 1-4 and Comparative Example 3

[0098]

[0099] As can be seen from Table 10, the solid contents of the styrene-acrylic emulsions in Examples 2-4 and Comparative Example 3 are all around 50%, which is relatively stable. This indicates that these styrene-acrylic emulsions have good consistency in terms of solid content, and when used subsequently to prepare waterborne polyurethane-styrene-acrylic composite waterproof coatings, they can provide a relatively stable film-forming substance basis. The pH values of the styrene-acrylic emulsions in Examples 2-4 are between 7.2 and 7.7, within the range of weak alkalinity. This shows that these styrene-acrylic emulsions are relatively moderate in terms of acidity and alkalinity, which is beneficial to the stable storage and subsequent processing and use of the emulsion. The particle size affects the film-forming performance of the styrene-acrylic emulsion. Larger particle sizes (such as in Example 2) cause different stacking patterns between the particles during the film-forming process of the styrene-acrylic emulsion, and the formed coating film may be relatively loose, but it is easier to spread during construction. The coating film formed by the styrene-acrylic emulsion with smaller particle sizes (such as in Example 3) is denser. When preparing waterproof coatings, styrene-acrylic emulsions with different particle sizes will affect the performance of the coating film such as air permeability and water permeability. Negative T g values indicate that these styrene-acrylic emulsions are in a highly elastic state at room temperature, which is a very ideal property for waterproof coatings because waterproof coatings need to have good flexibility to adapt to the deformation of the base layer, such as the settlement of buildings and the expansion and contraction caused by temperature changes. The lower T g value enables the coating film to maintain a certain elasticity at low temperatures and is not easily brittle and cracked, thus effectively maintaining the waterproof function. A lower gel content indicates better stability of the styrene-acrylic emulsion. When synthesizing the emulsion, less gel content means a higher proportion of effective components in the styrene-acrylic emulsion, which can better exert its performance.

[0100] Furthermore, the properties of the waterborne polyurethane-styrene-acrylic composite waterproof coatings obtained in the above Examples 2-4 and Comparative Examples 1-4 were tested, and the test results are shown in Table 11.

[0101] The specific test methods are as follows.

[0102] (1) Mechanical property test (tensile testing machine): Specimens were prepared and tested according to Chapter 9 of GB / T 16777-2008, with a tensile speed of 500 mm / min. The tensile strength and elongation at break before treatment and after immersion were tested.

[0103] Calculated according to the following formula: Tensile strength retention rate (average of 5 data) = (tensile strength before treatment - tensile strength after immersion) / tensile strength before treatment × 100%, Elongation at break retention rate (average of 5 data) = (elongation at break before treatment - elongation at break after immersion) / elongation at break before treatment × 100%, and the results are shown in Table 11.

[0104] (2) Bond strength: The test was carried out according to Method A in 7.1 of GB / T 16777-2008. Calculated according to the following formula: Bond strength retention rate (average of 5 data) = (bond strength before treatment - bond strength after immersion) / bond strength before treatment × 100%. The results are shown in Table 11.

[0105] (3) Low-temperature flexibility: Specimens were prepared and tested according to Chapter 14 of GB / T 16777-2008, and the low-temperature chamber was adjusted to -20 °C in advance.

[0106] Table 11 Test results of the waterproof coating properties of Examples 2-4 and Comparative Examples 1-4

[0107]

[0108] As can be seen from Table 11, the elongation at break of the waterproof coatings in Examples 2-4 are 487%, 587% and 525% respectively, and the values are relatively high, indicating that the waterproof coating has good ductility and can adapt to large deformations of the base layer without cracking; the retention rate after 7 days of immersion is between 72% and 77%, indicating that the waterproof coating can still maintain a certain ductility after immersion and has good water resistance. The tensile strengths of the waterproof coatings in Examples 2-4 are 3.02 MPa, 2.79 MPa and 2.88 MPa respectively, indicating that the waterproof coating has a certain mechanical strength and can withstand a certain tensile force without being damaged; the retention rate after 7 days of immersion is between 85% and 88%, showing that the waterproof coating can still maintain a relatively high tensile strength after immersion, further proving its good water resistance and mechanical stability. The tensile strength, elongation at break and retention rate of Comparative Examples 1-4 are all lower than those of the Examples, proving that the cross-linking effect between the polyurethane molecules with catechol structure and the acrylate molecular chains with hydroxyl groups is beneficial to providing enhanced mechanical properties and waterproof properties for the waterproof coating. The bond strengths of the waterproof coatings in Examples 2-4 are 1.47 MPa, 1.54 MPa and 1.44 MPa respectively, and the bond strengths are relatively high, indicating that the waterproof coating has good adhesion to the base layer and can firmly adhere to the base layer; the retention rate after 7 days of immersion is between 90% and 92%, indicating that the adhesion performance of the waterproof coating can still be well maintained after immersion, further proving its reliability in a humid environment. The bond strength results of Comparative Examples 1-4 are slightly lower than those of the Examples, mainly because the acrylate molecules with catechol structure in the Examples have a stronger bonding force to the substrate, and the strong cross-linking network helps the anchoring effect of the bonding layer and the "adhesive nails". All three Examples have no cracks when bent at -20°C, while Comparative Examples 2-4 have cracks under low-temperature bending, indicating that the waterborne polyurethane-acrylate composite waterproof coating has good low-temperature toughness and can be used in cold regions without the waterproof layer cracking and failing due to low temperature. This is very important for some regions with cold winters or occasions that require construction in low-temperature environments, ensuring the applicability and reliability of the waterproof coating under different temperature conditions.

[0109] The specific embodiments described above further elaborate on the purpose, technical solutions and beneficial effects of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not used to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A waterborne polyurethane-styrene acrylic composite waterproof coating, comprising the following raw materials in parts by weight: 35-45 parts of aqueous polyurethane emulsion containing catechol structure; 40-60 parts of styrene acrylic emulsion containing hydrogen bond crosslinking sites; 20-30 parts water; Defoaming agent 0.5-1.5 parts; Dispersant 0.5-1.5 parts; 65-105 parts of filler; 0.5-1 part of fungicide; Thickener 0.3-1 part; in, The hydrogen bond cross-linking site is the hydroxyl structure contained in the acrylic acid monomer unit.

2. The waterproof coating according to claim 1, wherein: The aqueous polyurethane emulsion containing catechol structure is made from the following raw materials in parts by weight: Polyether diol 50-100 parts; 20-40 parts of diisocyanate; Catalyst 0.1-0.5 parts; 1-10 parts of diol linear chain extender; 4-20 parts of functional chain extender; Functional neutralizer 2-10 parts; 120-240 parts of solvent; The diol linear chain extender includes at least one of 1,4-butanediol, 1,6-hexanediol, 1,5-hexanediol, and furan-2,5-diol; The functional chain extender includes 3-dimethylamino-1,2-propylene glycol and trimethylolpropane, wherein the proportion of the 3-dimethylamino-1,2-propylene glycol is 2-10 parts, and the proportion of the trimethylolpropane is 2-10 parts.

3. The waterproof coating according to claim 2, wherein: The polyether diol includes at least one of polypropylene glycol, polyethylene glycol, and polytetrahydrofuran; The diisocyanate includes at least one of toluene diisocyanate, isophorone diisocyanate, diphenylmethane diisocyanate, dicyclohexylmethane diisocyanate, hexamethylene diisocyanate, and lysine diisocyanate; The catalyst is dibutyltin dilaurate; The functional neutralizer is 3,4-dihydroxybenzoic acid; The solvent includes acetone and water, wherein the acetone accounts for 30-40 parts and the water accounts for 80-200 parts.

4. The waterproof coating according to claim 1, wherein: The styrene-acrylic emulsion is made from the following raw materials in parts by weight: Styrene 25-35 parts; 30-50 parts of acrylic soft monomer; 5-15 parts of acrylic hard monomer; 2-4 parts of acrylic acid functional monomer; Emulsifier 0.5-4 parts; pH buffer 0.2-1.5 parts; Initiator 0.15-0.6 parts; 100 parts of deionized water; Wherein, the acrylic functional monomer includes at least one of 2-hydroxyethyl methacrylate, hydroxyethyl acrylate, and hydroxypropyl methacrylate.

5. The waterproof coating according to claim 4, wherein: The acrylic soft monomer includes at least one of butyl acrylate, isooctyl acrylate, lauryl acrylate, and lauryl methacrylate; The acrylic hard monomer includes at least one of methyl methacrylate, ethyl methacrylate, and acrylonitrile; The emulsifier includes at least one of an anionic emulsifier and a nonionic emulsifier; The pH buffer comprises at least one of dipotassium hydrogen phosphate and sodium carbonate; The initiator includes at least one of a persulfate initiator, an organic peroxide initiator, and a redox initiator.

6. The waterproof coating according to claim 5, wherein: The anionic emulsifier includes at least one of sodium dodecyl sulfonate, sodium dodecyl sulfate, and sodium dodecylbenzene sulfonate; The nonionic emulsifier includes at least one of polyoxyethylene octylphenol ether and sorbitan monolaurate; The persulfate initiator includes at least one of sodium persulfate, ammonium persulfate and potassium persulfate; The organic peroxide initiator includes at least one of benzoyl peroxide and dicumyl peroxide; The redox initiator includes at least one of an ammonium persulfate-sodium bisulfite initiator and a hydrogen peroxide-ferrous salt initiator.

7. The waterproof coating according to claim 1, wherein: The defoamer includes at least one of a polyether defoamer, a silicone defoamer, a non-silicon defoamer, and a polyether-modified silicone defoamer; The dispersant includes at least one of an anionic dispersant and a nonionic dispersant; The fungicide includes at least one of a benzisothiazolinone fungicide and an isothiazolinone fungicide; The thickener includes at least one of hydroxyethyl cellulose, carboxymethyl cellulose and hydroxypropyl methyl cellulose; The filler includes heavy calcium carbonate, titanium dioxide and barium sulfate, wherein the heavy calcium carbonate accounts for 50-65 parts, the titanium dioxide accounts for 5-10 parts, and the barium sulfate accounts for 10-30 parts.

8. A method for preparing a waterproof coating as claimed in any one of claims 1 to 7, comprising: A water-based polyurethane emulsion containing a catechol structure and a styrene-acrylic emulsion containing a hydrogen bond cross-linking site are added into water and mixed, and then a defoamer and a dispersant are added and mixed to obtain a mixed liquid material; After adding filler into the mixed liquid and mixing, adding thickener and fungicide and mixing, a waterborne polyurethane-styrene acrylic composite waterproof coating is obtained.

9. The method according to claim 8, wherein: The aqueous polyurethane emulsion containing catechol structure is prepared by the following method: After mixing the polyether diol, diisocyanate and catalyst, reacting at 75-85° C. for 2-3 hours to obtain a first polymerization product; After adding 3-dimethylamino-1,2-propylene glycol and acetone to the first polymerization product, reacting at 65-75° C. for 1-2 hours to obtain a second polymerization product; adding a diol linear chain extender and trimethylolpropane to the second polymerization product, and reacting at 60-80° C. for 2-3 hours to obtain a third polymerization product; A functional neutralizing agent and water are added to the third polymer product, and the acetone is removed after shearing and emulsification to obtain a waterborne polyurethane emulsion containing a catechol structure.

10. The method according to claim 8, wherein: The styrene-acrylic emulsion containing hydrogen bond crosslinking sites is prepared by the following method: After mixing water and an emulsifier, styrene, acrylic soft monomer, acrylic hard monomer and acrylic functional monomer are added and mixed respectively to obtain an acrylic monomer emulsion; After adding the pH buffer into 80-90° C. water, slowly dropwise add the acrylic monomer emulsion and the initiator solution, and after the dropwise addition, heat-retaining and reacting at 80-90° C. for 2-3 hours to obtain a styrene-acrylic emulsion containing hydrogen bond cross-linking sites.

Images