A silicon chain-modified polyurethane-acrylic three-protection coating agent and a preparation method thereof

Abstract

The present application relates to the technical field of water-based leather finishing material, in particular to a kind of silicon chain modified polyurethane-acrylic three-proofing finishing agent and preparation method thereof.First, flexible polysiloxane microgel main network is formed by hydroxyl-terminated polydimethylsiloxane and methyl triethoxysilane, then surface amination is carried out by pre-hydrolyzed 3-amino propyl triethoxysilane;Microgel is added into water-dispersed isocyanate group-terminated polyurethane prepolymer before chain extension of ethylenediamine, and polyurethane seed anchor type microgel dispersion is obtained;2.0%~5.0% of the first part of monomer in total mass of acrylic monomer is added, kept at 40℃ for 60min, and 2,2'-azobis(2,4-dimethylpentyl nitrile) at 58℃ is used to initiate preliminary polymerization, then the remaining monomer and ammonium persulfate are added at 75℃ to complete polymerization.The present application helps to reduce the loss of silicon component during wet state friction, so that the finished leather maintains good water resistance, oil resistance and stain resistance, while the adhesion and folding resistance of coating are also considered.

Description

Technical Field

[0001] This invention relates to the field of water-based leather finishing materials technology, specifically to a silicon chain modified polyurethane-acrylic three-proof coating agent and its preparation method. Background Technology

[0002] Waterborne polyurethane-acrylic composite emulsions combine the flexibility and adhesion of polyurethane with the weather resistance of polyacrylates, and are commonly used for leather surface finishing. Leather is repeatedly bent during wear and use, and may come into contact with water, oil, and wet friction. In this application, high-performance waterproof coatings, in addition to reducing the surface energy of the coating, should also possess good adhesion and folding resistance, and maintain surface component stability during wet friction. Introducing polysiloxanes into waterborne polyurethane or polyurethane-acrylic systems is a common approach to reducing coating surface energy and improving waterproof performance.

[0003] Patent CN103981716A discloses a method for introducing hydroxyl silicone oil into waterborne polyurethane leather finishing materials; patent CN105622891A discloses the introduction of polysiloxane microsphere emulsions during the emulsification process of waterborne polyurethane; patent CN108467463A discloses organosilicon-modified waterborne polyurethane-polyacrylate emulsions, and polymerizes acrylic monomers after pre-swelling in the polyurethane emulsion; patent CN113801271A discloses the addition of silica sol to a polyurethane aqueous dispersion and subsequent polymerization of acrylic monomers. These methods can improve the surface hydrophobicity and abrasion resistance of coatings through reactive organosilicon, silicon-containing particle or seed emulsion polymerization, etc.

[0004] However, when silicon components exist as linear chains or physically dispersed particles, they are prone to migration and loss during repeated wet friction, resulting in a decrease in waterproof performance. While increasing the degree or content of silicon phase crosslinking is beneficial for stabilizing hydrophobic components, it may also increase the local rigidity of the coating, reducing its adhesion and folding resistance during leather bending. Existing technologies still struggle to maintain waterproof performance while simultaneously ensuring the adhesion and flexibility of the leather coating after wet friction. Summary of the Invention

[0005] Existing waterborne polyurethane-acrylic coatings containing silicon are prone to silicon component migration and loss during wet friction; simply increasing the degree of cross-linking of the silicon phase can easily increase local rigidity, thus making it difficult to balance waterproof retention, adhesion, and folding resistance after wet friction.

[0006] For the reasons mentioned above, this invention provides a method for preparing a silicon chain modified polyurethane-acrylic conformal coating agent, comprising the following steps: S1, hydroxyl-terminated polydimethylsiloxane and methyltriethoxysilane are sequentially subjected to acid-catalyzed hydrolysis and alkali-catalyzed condensation in an aqueous phase to form a flexible polysiloxane microgel host network. Then, 3-aminopropyltriethoxysilane that has been pre-hydrolyzed by acid catalysis is added to the flexible polysiloxane microgel host network for alkali-catalyzed condensation. The free amine is removed by washing and filtration to obtain a surface-aminated flexible polysiloxane microgel dispersion. S2, prepare an isocyanate-terminated polyurethane prepolymer using polymeric diol, dimethylolpropionic acid and isophorone diisocyanate, neutralize and disperse the polyurethane prepolymer in water, add the surface-aminated flexible polysiloxane microgel dispersion obtained in step S1 before adding ethylenediamine, so that the amino groups on the surface of the microgel react with the isocyanate groups in the polyurethane prepolymer, and then add ethylenediamine for aqueous chain extension to obtain a polyurethane seed-anchored flexible polysiloxane microgel dispersion. S3, the first part of acrylic monomers, accounting for 2.0%~5.0% of the total mass of acrylic monomers, is mixed with 2,2'-azobis(2,4-dimethylpentanonitrile) and added to the dispersion obtained in step S2. The mixture is kept at 40°C for 60 min, then heated to 58°C for 2 h, and then heated to 75°C. A portion of ammonium persulfate aqueous solution is added first, and then the remaining acrylic monomer pre-emulsion and the remaining ammonium persulfate aqueous solution are added dropwise simultaneously. After the addition is completed, polymerization continues to obtain the silicon chain modified polyurethane-acrylic three-proof coating agent.

[0007] Preferably, in step S1, based on 100.0 parts by weight of hydroxyl-terminated polydimethylsiloxane, the following components are used: 600 parts by weight of deionized water, 2.5 parts by weight of fatty alcohol polyoxyethylene ether AEO-9, 0.8 parts by weight of sodium dodecyl sulfate, 5.0 parts by weight of methyltriethoxysilane, and 4.0 parts by weight of 3-aminopropyltriethoxysilane; the kinematic viscosity of the hydroxyl-terminated polydimethylsiloxane at 25°C is 1000 mmHg. 2 / s, with a hydroxyl content of 0.058 mol / kg.

[0008] Preferably, in step S1, the pH of the polysiloxane microemulsion is adjusted to 4.50 and reacted at 30°C for 2 hours, then the pH is adjusted to 9.50 and reacted at 50°C for 3 hours; 3-aminopropyltriethoxysilane is pre-hydrolyzed at pH 4.50 and 25°C for 30 minutes, and the resulting pre-hydrolyzed solution is added to the flexible polysiloxane microgel dispersion and reacted at pH 9.50 and 50°C for 2 hours; the solution is washed and filtered until the free amine content in the permeate is less than 0.01 mmol / L, and the solid content is adjusted to 20.0%.

[0009] Preferably, the Z-average particle size of the surface-aminated flexible polysiloxane microgel obtained in step S1 is 101~153 nm, the polydispersity index is 0.14~0.16, the gel fraction is 72.7%~82.3%, the amount of surface-accessible amino groups is 0.080~0.121 mmol / g, and the equilibrium liquid absorption is 1.10~1.44 g / g.

[0010] Preferably, in step S2, 80.0 parts by mass of polycarbonate diol with a number average molecular weight of 1000 and a hydroxyl value of 112 mg KOH / g and 40.0 parts by mass of polytetrahydrofuran diol with a number average molecular weight of 1000 and a hydroxyl value of 112 mg KOH / g are dehydrated, and then reacted with 8.0 parts by mass of dimethylolpropionic acid, 53.9 parts by mass of isophorone diisocyanate and 0.05 parts by mass of bismuth neodecanoate at 80°C for 3 hours to obtain a polyurethane prepolymer with an isocyanate group mass fraction of 2.90%.

[0011] Preferably, 40 parts by weight of acetone and 5.7 parts by weight of triethylamine are added to the polyurethane prepolymer for neutralization, followed by 320 parts by weight of deionized water for dispersion. Before adding ethylenediamine, 40.0 parts by weight of a surface-aminated flexible polysiloxane microgel dispersion with a solid content of 20.0% is added to the polyurethane seed dispersion, reacted at 25°C for 20 min, and then 3.75 parts by weight of ethylenediamine is added for chain extension to obtain a polyurethane seed-anchored flexible polysiloxane microgel dispersion with a solid content of 30.7%.

[0012] Preferably, in step S3, the first portion of acrylic monomer accounts for 5.0% of the total mass of acrylic monomer and is composed of butyl acrylate and methyl methacrylate in a mass ratio of 60:40; the mass of 2,2'-azobis(2,4-dimethylpentanonitrile) is 0.8% of the mass of the first portion of acrylic monomer.

[0013] Preferably, in step S3, based on 650 parts by mass of the polyurethane seed-anchored flexible polysiloxane microgel dispersion obtained in step S2, the first part of the acrylic monomer is composed of 4.5 parts by mass of butyl acrylate and 3.0 parts by mass of methyl methacrylate, and the 2,2'-azobis(2,4-dimethylpentanonitrile) is 0.06 parts by mass; the remaining acrylic monomer preemulsion is prepared by 85.5 parts by mass of butyl acrylate, 57.0 parts by mass of methyl methacrylate, 0.8 parts by mass of sodium dodecyl sulfate and 50 parts by mass of deionized water, and 0.45 parts by mass of ammonium persulfate is dissolved in 20 parts by mass of deionized water; after heating to 75°C, 2.0 parts by mass of ammonium persulfate aqueous solution is added first, and then the remaining acrylic monomer preemulsion and the remaining ammonium persulfate aqueous solution are added dropwise simultaneously within 150 min. After the addition is completed, the reaction continues at 75°C for 60 min.

[0014] Furthermore, the present invention also provides a silicon chain modified polyurethane-acrylic conformal coating agent, which is prepared by the aforementioned preparation method.

[0015] Preferably, the silicon chain modified polyurethane-acrylic conformal coating agent has a solid content of 35.1% and a pH value of 8.00.

[0016] Furthermore, the present invention also provides a leather finishing method, wherein the silicon chain modified polyurethane-acrylic three-proof coating agent is diluted with deionized water to a solid content of 25.0%, and sprayed onto the leather surface in two coats, with each coat having a wet coating amount of 40 g / m². 2 After each coat, dry at 60°C for 5 minutes, and after the second coat, continue drying at 60°C for 15 minutes.

[0017] Beneficial effects (1) In this invention, a microgel host network with hydroxyl-terminated polydimethylsiloxane as flexible segments is first formed, and then pre-hydrolyzed 3-aminopropyltriethoxysilane is condensed in the network to obtain a flexible polysiloxane microgel with amino groups on its surface. Compared with linear polysiloxanes or microgels without surface amino groups, this structure can reduce the migration tendency of silicon components and retain the flexibility of polysiloxane segments, which helps to reduce the loss of silicon components during wet friction.

[0018] (2) Before the chain extension of ethylenediamine, the surface-aminated flexible polysiloxane microgel is added to the isocyanate-terminated polyurethane prepolymer, so that the microgel first forms a connection with the polyurethane seed, and then the remaining isocyanate groups are consumed by ethylenediamine. This addition order helps to avoid the microgel being dispersed in the continuous phase only by physical blending, improves the retention of the silicon phase in the polyurethane seed, and improves the waterproof performance and adhesion of the coating after wet friction.

[0019] (3) In the polyurethane seed-anchored microgel dispersion, a first portion of monomers, accounting for 2.0% to 5.0% of the total mass of acrylic monomers, is first added. After being kept at 40°C, a preliminary polymerization is carried out using an oil-soluble low-temperature initiator. Then, ammonium persulfate is used to complete the polymerization of the remaining monomers. The pre-swelling and preliminary polymerization of the first portion of monomers helps the subsequent acrylic polymers to distribute around the connected microgels and polyurethane seeds, reducing silicon loss during wet friction and maintaining the continuity of the coating interface.

[0020] (4) The degree of crosslinking, the amount of amino groups that can be accessed on the surface, and the amount added are coordinated with the segmented acrylic acid polymerization process to reduce the local rigidity increase caused by excessive silicon particles. The resulting coating maintains a high water contact angle and adhesion after wet friction. No visible cracks appeared in any of the 9 test pieces after 50,000 bends. The static water absorption rate was low 24 hours after bending. In the liquid paraffin penetration test and the water-based carbon black stain removal test, it also showed a long oil penetration time and a low color difference after removal. It can achieve a balance between waterproof, oil-proof, stain-proof, adhesion and folding resistance. Detailed Implementation

[0021] I. Preparation Example Preparation Example 1: Surface-Aminated Flexible Polysiloxane Microgel Add 2.5g of fatty alcohol polyoxyethylene ether AEO-9 and 0.8g of sodium dodecyl sulfate to 600g of deionized water and stir at 25°C until dissolved. Mix 100.0g of hydroxyl-terminated polydimethylsiloxane and 5.0g of methyltriethoxysilane, wherein the kinematic viscosity of the hydroxyl-terminated polydimethylsiloxane at 25°C is 1000 mmHg. 2 The hydroxyl content was 0.058 mol / kg. The resulting mixture was sheared at 10000 r / min, then the aqueous phase was added, and the mixture was sheared for another 10 min. The mixture was then homogenized twice at 30 MPa to obtain a polysiloxane fine emulsion.

[0022] The pH of the polysiloxane microemulsion was adjusted to 4.50 using a 10.0% acetic acid aqueous solution and reacted at 30°C for 2 hours. The pH was then adjusted to 9.50 using a 10.0% ammonia solution, and the mixture was heated to 50°C and reacted for 3 hours to form the polysiloxane microgel matrix network.

[0023] 4.0 g of 3-aminopropyltriethoxysilane was added to 16 g of deionized water, and the pH was adjusted to 4.50 with a 10.0% acetic acid aqueous solution. Pre-hydrolyzing was carried out at 25 °C for 30 min. The resulting pre-hydrolyzed solution was added to the polysiloxane microgel dispersion within 20 min, and the pH was maintained at 9.50. The reaction was continued at 50 °C for 2 h. After cooling to 25 °C, the pH was adjusted to 8.20 with a 10.0% acetic acid aqueous solution. Continuous washing and filtration were performed using a hollow fiber membrane with a molecular weight cutoff of 100 kDa until the free amine content in the permeate was lower than 0.01 mmol / L. Deionized water was added to adjust the solid content to 20.0%, and the solution was passed through a 100 μm wet sieve to obtain a surface-aminated flexible polysiloxane microgel dispersion.

[0024] Preparation Example 2: Low-crosslinking surface-aminated flexible polysiloxane microgels Except for changing the amount of methyltriethoxysilane added to 2.5g, the amount of 3-aminopropyltriethoxysilane added to 2.6g, changing the formation conditions of the polysiloxane microgel main network to pH 9.30, reaction at 48℃ for 2.5h, and changing the reaction time after adding the pre-hydrolyzed solution to 1.5h, the other raw materials, dosages and preparation conditions were the same as in Preparation Example 1, and a low-crosslinked surface-aminated flexible polysiloxane microgel dispersion with a solid content of 20.0% was obtained.

[0025] Preparation Example 3: Highly Crosslinked Surface-Aminated Flexible Polysiloxane Microgels Except for changing the amount of methyltriethoxysilane added to 7.5g, the amount of 3-aminopropyltriethoxysilane added to 6.0g, changing the formation conditions of the polysiloxane microgel main network to pH 9.70, reaction at 52℃ for 4h, and changing the reaction time after adding the pre-hydrolyzed solution to 2.5h, the other raw materials, dosages and preparation conditions were the same as in Preparation Example 1, and a highly cross-linked surface-aminated flexible polysiloxane microgel dispersion with a solid content of 20.0% was obtained.

[0026] Preparation Example 4: Flexible polysiloxane microgels without surface amino groups Except for changing the amount of methyltriethoxysilane added to 8.2g, omitting the preparation and addition steps of 3-aminopropyltriethoxysilane pre-hydrolyzed solution, and changing the formation time of the polysiloxane microgel main network to 5h, the other raw materials, dosages and preparation conditions are the same as in Preparation Example 1, and a flexible polysiloxane microgel dispersion without surface amino groups with a solid content of 20.0% is obtained.

[0027] Preparation Example 5: Polyurethane Seed-Anchored Flexible Polysiloxane Microgel Dispersion 80.0 g of polycarbonate diol with a number average molecular weight of 1000 and a hydroxyl value of 112 mg KOH / g and 40.0 g of polytetrahydrofuran diol with a number average molecular weight of 1000 and a hydroxyl value of 112 mg KOH / g were added to a reactor and dehydrated at 110 °C and -0.09 MPa for 1 h. The temperature was then lowered to 75 °C, and 8.0 g of dimethylolpropionic acid, 53.9 g of isophorone diisocyanate, and 0.05 g of bismuth neodecanoate were added. The mixture was then heated to 80 °C under nitrogen protection and reacted for 3 h to obtain a polyurethane prepolymer with an isocyanate group mass fraction of 2.90%.

[0028] Cool the polyurethane prepolymer to 55°C, add 40g of acetone and stir for 10 minutes; continue cooling to 45°C, add 5.7g of triethylamine and react for 20 minutes. Adjust the material temperature to 25°C, and add 320g of deionized water at 20°C within 10 minutes while stirring at 1500r / min, and continue dispersing for 10 minutes.

[0029] Before adding ethylenediamine, 40.0 g of the surface-aminated flexible polysiloxane microgel dispersion obtained in Preparation Example 1 was added to the above polyurethane seed dispersion within 10 min, and the reaction was continued at 25 °C for 20 min. 3.75 g of ethylenediamine was dissolved in 33.75 g of deionized water and added within 10 min at 20 °C, and the reaction was continued for 30 min. Acetone was then removed at 45 °C and -0.08 MPa, and deionized water was added to a total mass of 650 g. The pH was adjusted to 7.80 with 10.0% ammonia solution, and the mixture was passed through a 100 μm wet sieve to obtain a polyurethane seed-anchored flexible polysiloxane microgel dispersion with a solid content of 30.7%.

[0030] Preparation Example 6: Low-content polyurethane seed-anchored flexible polysiloxane microgel dispersion Except for replacing 40.0g of the microgel dispersion obtained in Preparation Example 1 with 17.5g of the microgel dispersion obtained in Preparation Example 2, changing the amount of ethylenediamine added to 3.77g, and adding deionized water to a total mass of 635g after removing acetone, the other raw materials, amounts, and preparation conditions were the same as in Preparation Example 5, resulting in a low-content polyurethane seed-anchored flexible polysiloxane microgel dispersion with a solid content of 30.7%.

[0031] Preparation Example 7: High-content polyurethane seed-anchored flexible polysiloxane microgel dispersion Except for replacing 40.0g of the microgel dispersion obtained in Preparation Example 1 with 70.0g of the microgel dispersion obtained in Preparation Example 3, changing the amount of ethylenediamine added to 3.70g, and adding deionized water to a total mass of 669g after removing acetone, the other raw materials, amounts, and preparation conditions were the same as in Preparation Example 5, resulting in a high-content polyurethane seed-anchored flexible polysiloxane microgel dispersion with a solid content of 30.7%.

[0032] II. Implementation Examples Example 1 Step (1): Add 650g of the polyurethane seed-anchored flexible polysiloxane microgel dispersion obtained in Preparation Example 5 to the reactor, purge with nitrogen for 20min, and heat to 40℃. Mix 4.5g of butyl acrylate, 3.0g of methyl methacrylate and 0.06g of 2,2'-azobis(2,4-dimethylpentanonitrile), wherein the butyl acrylate and methyl methacrylate together account for 5.0% of the total mass of acrylic monomers; add to the reactor within 5min, and maintain stirring at 600r / min for 60min.

[0033] Step (2): Heat the system to 58℃ and react for 2 hours. Shear emulsify 85.5g butyl acrylate, 57.0g methyl methacrylate, 0.8g sodium dodecyl sulfate, and 50g deionized water for 5 minutes to obtain the remaining monomer pre-emulsion; dissolve 0.45g ammonium persulfate in 20g deionized water. Heat the system to 75℃, add 2.0g of ammonium persulfate aqueous solution first, and then simultaneously add the remaining monomer pre-emulsion and the remaining ammonium persulfate aqueous solution over 150 minutes. After the addition is complete, maintain the reaction at 75℃ for 60 minutes.

[0034] Step (3): Cool the system to 55℃, add an aqueous solution prepared with 0.12g of 70% tert-butyl hydrogen peroxide and 5g of deionized water, and an aqueous solution prepared with 0.10g of sodium bisulfite and 5g of deionized water, and react at 55℃ for 30min. Cool to 25℃, adjust the pH to 8.00 with 10.0% ammonia water, add deionized water to a total mass of 1000g, and pass through a 100μm wet sieve to obtain a silicon chain modified polyurethane-acrylic conformal coating agent with a solid content of 35.1%.

[0035] Example 2 Step (1): Add 635g of the low-content polyurethane seed-anchored flexible polysiloxane microgel dispersion obtained in Preparation Example 6 to the reactor, purge with nitrogen for 20min, and heat to 40℃. Mix 1.9g of butyl acrylate, 1.2g of methyl methacrylate and 0.03g of 2,2'-azobis(2,4-dimethylpentanonitrile), wherein the butyl acrylate and methyl methacrylate together account for 2.0% of the total mass of acrylic monomers; add to the reactor within 5min, and maintain stirring at 600r / min for 60min.

[0036] Step (2): Heat the system to 58°C and react for 2 hours. Shear emulsify 90.8 g butyl acrylate, 60.6 g methyl methacrylate, 0.8 g sodium dodecyl sulfate, and 50 g deionized water for 5 minutes; dissolve 0.46 g ammonium persulfate in 20 g deionized water. Polymerize the remaining acrylic monomers at 75°C following the dropwise addition method in Step (2) of Example 1.

[0037] Step (3): Perform residual monomer treatment, pH adjustment, water replenishment and filtration according to step (3) of Example 1 to obtain a silicon chain modified polyurethane-acrylic three-proof coating agent with a solid content of 35.1%.

[0038] Example 3 Step (1): Add 669g of the high-content polyurethane seed-anchored flexible polysiloxane microgel dispersion obtained in Preparation Example 7 to the reactor, purge with nitrogen for 20min, and heat to 40℃. Mix 4.2g of butyl acrylate, 2.8g of methyl methacrylate and 0.06g of 2,2'-azobis(2,4-dimethylpentanonitrile), wherein butyl acrylate and methyl methacrylate together account for 4.9% of the total mass of acrylic monomers; add to the reactor within 5min, and maintain stirring at 600r / min for 60min.

[0039] Step (2): Heat the system to 58°C and react for 2 hours. Shear emulsify 82.2g butyl acrylate, 54.8g methyl methacrylate, 0.8g sodium dodecyl sulfate, and 50g deionized water for 5 minutes; dissolve 0.43g ammonium persulfate in 20g deionized water. Polymerize the remaining acrylic monomers at 75°C following the dropwise addition method in Step (2) of Example 1.

[0040] Step (3): Perform residual monomer treatment, pH adjustment, water replenishment and filtration according to step (3) of Example 1 to obtain a silicon chain modified polyurethane-acrylic three-proof coating agent with a solid content of 35.1%.

[0041] Example 4 Step (1): Add 650g of the polyurethane seed-anchored flexible polysiloxane microgel dispersion obtained in Preparation Example 5 to the reactor, purge with nitrogen for 20min, and heat to 40℃. Mix 3.2g of butyl acrylate, 2.1g of methyl methacrylate and 0.04g of 2,2'-azobis(2,4-dimethylpentanonitrile), wherein the butyl acrylate and methyl methacrylate together account for 3.5% of the total mass of acrylic monomers; add to the reactor within 5min, and maintain stirring at 600r / min for 60min.

[0042] Step (2): Heat the system to 58°C and react for 2 hours. Shear emulsify 86.8g butyl acrylate, 57.9g methyl methacrylate, 0.8g sodium dodecyl sulfate, and 50g deionized water for 5 minutes; dissolve 0.45g ammonium persulfate in 20g deionized water. Polymerize the remaining acrylic monomers at 75°C following the dropwise addition method in Step (2) of Example 1.

[0043] Step (3): Perform residual monomer treatment, pH adjustment, water replenishment and filtration according to step (3) of Example 1 to obtain a silicon chain modified polyurethane-acrylic three-proof coating agent with a solid content of 35.1%.

[0044] III. Comparative Example Comparative Example 1 Step (1): Mix 90.0g butyl acrylate, 60.0g methyl methacrylate, 0.8g sodium dodecyl sulfate and 50g deionized water, and shear at 3000r / min for 5min to obtain acrylic monomer preemulsion; dissolve 0.45g ammonium persulfate in 20g deionized water to obtain ammonium persulfate aqueous solution.

[0045] Step (2): Add 650g of the polyurethane seed-anchored flexible polysiloxane microgel dispersion obtained in Preparation Example 5 to the reactor, purge with nitrogen for 20min, and heat to 75℃. First add 2.0g of ammonium persulfate aqueous solution, then simultaneously add all the acrylic monomer pre-emulsion and the remaining ammonium persulfate aqueous solution over 150min. After the addition is complete, maintain the reaction at 75℃ for 60min.

[0046] Step (3): Perform residual monomer treatment, pH adjustment, water replenishment and filtration according to step (3) of Example 1 to obtain a silicon chain modified polyurethane-acrylic three-proof coating agent with a solid content of 35.1%.

[0047] Comparative Example 2 A comparative polyurethane seed dispersion was prepared according to Preparation Example 5, with the following differences: 8.0 g of dihydroxybutyl polydimethylsiloxane was added during the preparation of the polyurethane prepolymer, wherein the hydroxyl content of the dihydroxybutyl polydimethylsiloxane was 0.50 mmol / g; the amount of isophorone diisocyanate added was changed to 54.5 g; no polysiloxane microgel dispersion was added; the amount of ethylenediamine added was changed to 3.82 g; and after removing acetone, deionized water was added to bring the total mass to 650 g. 650 g of the obtained comparative polyurethane seed dispersion was taken and a coating agent was prepared according to the acrylic polymerization steps of Comparative Example 1, wherein the amounts of butyl acrylate and methyl methacrylate added were changed to 89.6 g and 59.7 g, respectively, to obtain a silicone-chain modified polyurethane-acrylic conformal coating agent.

[0048] Comparative Example 3 A comparative polyurethane seed dispersion was prepared according to Preparation Example 5, the difference being that 36.75 g of the flexible polysiloxane microgel dispersion without surface amino groups obtained in Preparation Example 4 and 0.65 g of linear amino polydimethylsiloxane with an amino value of 1.50 mmol / g were sheared and dispersed for 5 min, and the resulting mixture replaced 40.0 g of the microgel dispersion obtained in Preparation Example 1. 650 g of the obtained comparative polyurethane seed dispersion was taken and a coating agent was prepared according to the acrylic polymerization steps of Comparative Example 1 to obtain a silicone-chain modified polyurethane-acrylic conformal coating agent.

[0049] Comparative Example 4 A comparative polyurethane seed dispersion was prepared according to Preparation Example 5, the difference being that after the polyurethane prepolymer was dispersed in water, 3.77 g of ethylenediamine was first added to complete the aqueous chain extension and react for 30 min, and then 40.0 g of the surface-aminated flexible polysiloxane microgel dispersion obtained in Preparation Example 1 was added and stirred for 20 min. 650 g of the obtained comparative polyurethane seed dispersion was taken and a coating agent was prepared according to the acrylic polymerization steps of Comparative Example 1 to obtain a silicon-chain modified polyurethane-acrylic three-proof coating agent.

[0050] Comparative Example 5 Except that after adding the first part of acrylic monomer and 2,2'-azobis(2,4-dimethylpentanonitrile) to the polyurethane seed-anchored flexible polysiloxane microgel dispersion, the temperature was directly raised to 58°C for 2 hours instead of being kept at 40°C for 60 minutes, the other raw materials, dosages and preparation conditions were the same as in Example 1, and a silicon chain modified polyurethane-acrylic three-proof coating agent was obtained.

[0051] Comparative Example 6 A comparative polyurethane seed dispersion was prepared according to Preparation Example 5, the difference being that 40.0 g of the surface-aminated flexible polysiloxane microgel dispersion obtained in Preparation Example 1 was replaced with 40.0 g of the non-surface-aminated flexible polysiloxane microgel dispersion obtained in Preparation Example 4, and the amount of ethylenediamine added was changed to 3.77 g. 650 g of the obtained comparative polyurethane seed dispersion was taken and subjected to the first part of monomer pre-swelling, preliminary polymerization, and residual monomer polymerization according to Example 1 to obtain a silicon-chain modified polyurethane-acrylic conformal coating agent.

[0052] Comparative Example 7 Except for changing the amount of butyl acrylate, methyl methacrylate and 2,2'-azobis(2,4-dimethylpentanonitrile) added in step (1) of Example 1 to 5.8g, 3.8g and 0.08g respectively, so that the first part of acrylic monomer accounts for 6.4% of the total mass of acrylic monomer, and changing the amount of the remaining butyl acrylate and methyl methacrylate added in step (2) to 84.2g and 56.2g respectively, the other raw materials, dosages and preparation conditions are the same as in Example 1, and a silicone chain modified polyurethane-acrylic three-proof coating agent is obtained.

[0053] IV. Performance Testing 1. Polysiloxane microgel state The microgel dispersions obtained in each preparation example were diluted with deionized water to a solid content of 0.05%, and the Z-mean particle size and polydispersity index were determined by dynamic light scattering. The microgel dispersions were freeze-dried, the dried solids were weighed, and extracted with toluene using a Soxhlet extractor for 24 h. The insoluble matter after extraction was dried at 80 °C to constant weight, and the gel fraction was calculated as the percentage of the mass of the insoluble matter to the mass of the dry solids before extraction.

[0054] The amount of amino groups approaching the surface of the microgel was determined using the 2,4,6-trinitrobenzenesulfonic acid colorimetric method. A standard curve was prepared using glycine. The test pH was 8.50, the reaction temperature was 40℃, and the reaction time was 60 min. The particle turbidity was corrected using the dispersion from Preparation Example 4 with the same dry solids concentration. 1.00 g of dry microgel solids was added to 20.0 g of a mixture of butyl acrylate and methyl methacrylate in a mass ratio of 60:40. The mixture was kept at 25℃ for 24 h, centrifuged at 20000×g for 30 min, the supernatant was discarded, and the residual liquid on the inner wall of the centrifuge tube was removed before weighing. The equilibrium liquid absorption volume was calculated as the ratio of the increase in microgel weight to the initial dry solids mass. Each determination was performed in triplicate, and the average value was taken. The results are shown in Table 1.

[0055] In Table 1, an accessible amino group of less than 0.005 mmol / g indicates that the result is below the limit of quantitation of the method.

[0056] Table 1. Main states of polysiloxane microgels obtained in each preparation example.

[0057] 2. Waterproofing performance and silicone loss after wet friction Each coating agent was poured into a polytetrafluoroethylene (PTFE) film-forming tank and dried at 25°C for 24 hours, followed by drying at 60°C for 12 hours to prepare a free film with a thickness of 100±5 μm. The free film was then conditioned in an environment with a temperature of 23±2°C and a relative humidity of 50±5% for 48 hours. The initial water contact angle was determined according to GB / T30693-2014 "Measurement of Water Contact Angle of Plastic Films". The water droplet volume was 5 μL, and the result was read 10 seconds after the water droplet contacted the coating. Five different positions were measured for each free film.

[0058] The free membrane was fixed on a reciprocating friction test bench. A cotton cloth friction head with a diameter of 20 mm was used, with a load of 4.9 N, a friction stroke of 60 mm, a frequency of 30 times / min, and 500 reciprocating friction cycles. During the friction process, deionized water was added to the friction area at a rate of 0.5 mL / min. After the friction was completed, the friction head and friction area were rinsed with 20 mL of deionized water. The friction fluids were combined and diluted to 100 mL. After digestion with nitric acid, the silicon content was determined using inductively coupled plasma atomic emission spectrometry (ICP-AES), and the silicon loss was calculated based on the area of ​​the friction area.

[0059] The free membrane after wet friction was placed in an environment of 23±2℃ and 50±5% relative humidity for 2 hours. The water contact angle after wet friction was measured according to the initial water contact angle measurement conditions, and the contact angle retention rate was calculated. Another free membrane treated with the same wet friction was dried at 50℃ to constant weight, and its mass m0 was obtained. It was then immersed in deionized water at 23℃ for 24 hours. After removing it and absorbing the surface moisture, its mass m1 was obtained. The water absorption rate after 24 hours of wet friction was calculated as (m1-m0) / m0×100%. Three free membranes were prepared in parallel for each sample, and the results were averaged. The results are shown in Table 2.

[0060] Table 2. Waterproofing performance of the coatings obtained in each embodiment and comparative example after wet friction.

[0061] 3. Coating adhesion and folding resistance Use light-colored full-grain cowhide shoe upper raw leather from the same batch as the flexible substrate. Dilute each coating agent with deionized water to a solid content of 25.0%, and spray in two coats, with each coat having a wet coating weight of 40 g / m². 2 After each coat, dry at 60℃ for 5 minutes, and after the second coat, continue drying at 60℃ for 15 minutes. Then, acclimate in an environment with a temperature of 23±2℃ and a relative humidity of 50±5% for 24 hours.

[0062] The initial coating adhesion was determined according to GB / T39452-2020 "Leather Physical and Mechanical Tests - Determination of Coating Adhesion Fastness". Separately, coated leather samples were subjected to wet rubbing according to the load, stroke, frequency, number of reciprocations, and dripping rate specified in Section 2 of this document. After being placed in an environment of 23±2℃ and 50±5% relative humidity for 2 hours, the coating adhesion after wet rubbing was determined, and the adhesion fastness retention rate was calculated.

[0063] According to GB / T39368.1-2025 "Determination of flexural strength of leather - Part 1: Deflection tester method", coated leather was subjected to 50,000 bends, and the number of specimens with visible cracks among the nine specimens was recorded. Another specimen treated with the same bending method was used, and the static water absorption rate 24 hours after bending was determined according to GB / T4689.21-2008 "Physical and mechanical tests of leather - Determination of static water absorption". Adhesion strength and static water absorption rate were measured in triplicate, and the results were averaged (see Table 3).

[0064] Table 3. Adhesion and folding resistance of the coatings obtained in each embodiment and comparative example.

[0065] 4. Oil and stain repellency Finished leather was prepared using the same batch of raw leather, spraying amount, drying, and conditioning conditions as described in item 3, and 50mm × 50mm test pieces were cut. For the oil resistance test, the test piece was placed flat with the leather side facing up. A 20mm inner diameter polytetrafluoroethylene ring was placed in the center of the test piece, and 0.20mL of liquid paraffin containing 0.02% Oil Red O was added to the ring. The flesh side of the test piece was observed from the start of sample addition, and the time when the first red oil spot appeared on the flesh side was recorded as the liquid paraffin penetration time; the longer the penetration time, the better the oil resistance. Three test pieces were tested in parallel for each sample.

[0066] For stain resistance testing, 1.0 g carbon black, 0.2 g AEO-9, and 98.8 g deionized water were dispersed at 3000 r / min for 10 min to obtain an aqueous carbon black stain solution. A 20 mm diameter test area was defined in the center of the test piece using a positioning ring. 0.20 mL of the stain solution was added and allowed to stand for 30 min. Residual liquid was first absorbed with a dry nonwoven cloth, then the sample was wiped 10 times under a 4.9 N load using a cotton cloth moistened with deionized water. The sample was then left to stand at room temperature for 2 h. The CIE L of the test area before and after staining was measured using a colorimeter. a b Value, calculate the color difference ΔE after stain removal. ab; The smaller the color difference, the better the anti-fouling performance. Three test pieces were measured in parallel for each sample, and the average value of the results was taken, as shown in Table 4.

[0067] Table 4. Oil and stain repellency of the coatings obtained in each example and comparative example.

[0068] V. Results Analysis The Z-average particle sizes of the microgels obtained in Preparation Example 1 and Preparation Example 4 were 153 nm and 156 nm, respectively; the gel fractions were 82.3% and 82.1%, respectively; the equilibrium liquid uptake was 1.10 g / g and 1.08 g / g, respectively; and the accessible amino groups were 0.121 mmol / g and less than 0.005 mmol / g, respectively. The particle size, gel fraction, and monomer liquid uptake capacity of the two microgels were similar; the main difference lay in the accessible amino group content on the microgel surface.

[0069] The microgel obtained in Preparation Example 2 had a gel fraction of 72.7% and an equilibrium liquid uptake of 1.44 g / g; the microgel obtained in Preparation Example 3 had a gel fraction increased to 89.2% and an equilibrium liquid uptake decreased to 0.63 g / g. Increasing the degree of condensation of the microgel network reduces its absorption of acrylic monomers and creates a difference in flexibility in the subsequent coating.

[0070] Comparative Example 1 used a surface-aminated flexible polysiloxane microgel, which was added to the polyurethane seed dispersion before ethylenediamine chain extension; Comparative Example 2 used a linear polysiloxane diol incorporated into the polyurethane prepolymer. After wet rubbing, Comparative Example 1 showed a water contact angle of 98.2° and a silica loss of 12.0 mg / m³. 2 It is superior to Comparative Example 2's 87.6° and 22.9 mg / m³, respectively. 2 Meanwhile, the adhesion strength after wet rubbing increased from 4.2N / 10mm to 5.4N / 10mm.

[0071] Comparative Example 3 involved the co-addition of a microgel without surface amino groups and an equal amount of linear amino polydimethylsiloxane. After wet rubbing, the water contact angle was 91.1°, and the silicon loss was 20.4 mg / m³. 2 After 50,000 bending cycles, 5 test pieces developed cracks. In Comparative Example 1, after adding reactive amino groups to the surface of the flexible polysiloxane microgel, the retention of silicon components and flexural strength after wet rubbing were improved.

[0072] Comparative Examples 1 and 4 used the same surface-aminated flexible polysiloxane microgel, the difference being that the microgel was added before or after ethylenediamine chain extension. When added before chain extension, the water contact angle after wet rubbing increased from 89.4° to 98.2°, and the silicon loss decreased from 27.2 mg / m³. 2 Reduced to 12.0 mg / m³ 2 After wet rubbing, the adhesion strength increased from 3.5 N / 10 mm to 5.4 N / 10 mm, indicating that the microgel entering the polyurethane seed formation stage can improve its retention in the coating film.

[0073] Both Example 1 and Comparative Example 1 used the polyurethane seed-anchored flexible polysiloxane microgel dispersion obtained in Example 5. The difference was that Example 1 further underwent pre-swelling and pre-polymerization of the first batch of monomers. Using this process, the water contact angle after wet rubbing increased from 98.2° to 104.0°, and the silicon loss decreased from 12.0 mg / m³. 2 Reduced to 6.7 mg / m³ 2 The number of cracked specimens after 50,000 bends decreased from 2 to 0.

[0074] The difference between Example 1 and Comparative Example 5 lies in whether the first monomer was kept at 40°C for 60 minutes after addition. After pre-swelling, the water contact angle after wet rubbing increased from 98.3° to 104.0°, and the silicon loss decreased from 10.4 mg / m³. 2 Reduced to 6.7 mg / m³ 2 After wet rubbing, the adhesion strength increased from 5.0 N / 10 mm to 5.9 N / 10 mm.

[0075] Comparative Example 6 used a flexible polysiloxane microgel without surface amino groups, and fully implemented the retention and pre-polymerization of the monomers in the first part. Its water contact angle after wet rubbing was 92.1°, and the silicon loss was 21.0 mg / m³. 2 After wet rubbing, the adhesion strength was 3.8 N / 10 mm. In Example 1, after performing the same process on a microgel already connected to polyurethane seeds, the above indicators reached 104.0° and 6.7 mg / m³, respectively. 2 The values ​​of 5.9 N / 10 mm indicate that the effect of prepolymerization is related to the pre-connection state of the microgel.

[0076] In the oil and stain resistance tests, the liquid paraffin in Comparative Example 1 had a penetration time of 228 minutes, and the color difference ΔE after stain removal was [not specified]. ab was 3.9; the penetration times of liquid paraffin in Comparative Examples 2, 3, and 4 were 128 min, 146 min, and 112 min, respectively, and the color difference ΔE after stain removal was [missing value]. The ab values ​​were 7.1, 6.3, and 7.6, respectively. Considering the structural differences among the comparative examples, the surface-aminated flexible polysiloxane microgels entered the polyurethane seed formation process before ethylenediamine chain extension, which helps to delay the penetration of oily media into the leather base and reduce the residue after water-based carbon black stain removal.

[0077] Example 1 involves pre-swelling and preliminary polymerization of the first monomer in the aforementioned connected state. The liquid paraffin penetration time is 336 minutes, and the color difference ΔE after stain removal is [not specified]. The ab value was 2.3; for Comparative Example 5, which omitted the 40℃ holding step, the time was 244 min and 4.1 min, respectively; for Comparative Example 6, which did not form a surface amino pre-linked state, the time was 138 min and 6.8 min, respectively. These results indicate that when the first monomer pre-swelling and preliminary polymerization establish a microgel pre-linked state, the oil and dirt resistance of the coating can be further improved.

[0078] In Example 2, after reducing the amount of microgel added and using a microgel with a lower degree of cross-linking, only one sample developed a crack after 50,000 bending cycles. However, the water contact angle after wet rubbing was 95.0°, and the silicon loss was 14.8 mg / m³. 2 Lower microgel addition and gel fraction are beneficial for maintaining folding resistance, but have a weaker effect on maintaining water resistance after wet rubbing.

[0079] In Example 3, by increasing the amount of microgel added, the gel fraction, and the amount of surface-accessible amino groups, the water contact angle after wet rubbing reached 105.7°, and the silicon loss decreased to 6.1 mg / m³. 2 The adhesion strength after wet rubbing was 4.4 N / 10 mm, and cracks appeared in 4 test pieces after 50,000 bends. Excessive addition of microgel and excessive degree of cross-linking will increase local rigidity, which is not conducive to maintaining both coating adhesion strength and flexural strength.

[0080] In Example 4, the first portion of monomer weighed 5.3 g, accounting for 3.5% of the total mass of acrylic acid monomers. After wet rubbing, the water contact angle and silicone loss were 101.0° and 8.8 mg / m³, respectively. 2 Comparative Example 7 increased the mass of the first monomer component to 9.6 g, accounting for 6.4% of the total mass of acrylic acid monomers, and further reduced the silicon loss to 5.8 mg / m³. 2 However, after wet rubbing, the adhesion strength decreased to 4.7 N / 10 mm, and the number of cracked specimens increased to 4. An excessively high monomer ratio in the first part increases the amount of acrylic polymer around the microgel, which is detrimental to the coating's folding resistance.

[0081] The surface-aminated flexible polysiloxane microgel enters the polyurethane seeding process before conventional diamine chain extension. This allows it to maintain microgel flexibility while limiting the loss of silicon components during wet friction, delaying the penetration of oily media, and reducing residues after water-based stain removal. Performing the first-part monomer pre-swelling and pre-polymerization in this connected state further improves waterproof, oil-proof, and stain-resistant properties, while also ensuring coating adhesion and folding resistance with appropriate monomer amounts.

Claims

1. A method for preparing a silicon-chain modified polyurethane-acrylic conformal coating agent, characterized in that, Includes the following steps: S1, hydroxyl-terminated polydimethylsiloxane and methyltriethoxysilane are sequentially subjected to acid-catalyzed hydrolysis and alkali-catalyzed condensation in an aqueous phase to form a flexible polysiloxane microgel host network. Then, 3-aminopropyltriethoxysilane that has been pre-hydrolyzed by acid catalysis is added to the flexible polysiloxane microgel host network for alkali-catalyzed condensation. The free amine is removed by washing and filtration to obtain a surface-aminated flexible polysiloxane microgel dispersion. S2, prepare an isocyanate-terminated polyurethane prepolymer using polymeric diol, dimethylolpropionic acid and isophorone diisocyanate, neutralize and disperse the polyurethane prepolymer in water, add the surface-aminated flexible polysiloxane microgel dispersion obtained in step S1 before adding ethylenediamine, so that the amino groups on the surface of the microgel react with the isocyanate groups in the polyurethane prepolymer, and then add ethylenediamine for aqueous chain extension to obtain a polyurethane seed-anchored flexible polysiloxane microgel dispersion. S3, the first part of acrylic monomers, accounting for 2.0%~5.0% of the total mass of acrylic monomers, is mixed with 2,2'-azobis(2,4-dimethylpentanonitrile) and added to the dispersion obtained in step S2. The mixture is kept at 40°C for 60 min, then heated to 58°C for 2 h, and then heated to 75°C. A portion of ammonium persulfate aqueous solution is added first, and then the remaining acrylic monomer pre-emulsion and the remaining ammonium persulfate aqueous solution are added dropwise simultaneously. After the addition is completed, polymerization continues to obtain the silicon chain modified polyurethane-acrylic three-proof coating agent.

2. The preparation method according to claim 1, characterized in that, In step S1, based on 100.0 parts by weight of hydroxyl-terminated polydimethylsiloxane, the following components are used: 600 parts by weight of deionized water, 2.5 parts by weight of fatty alcohol polyoxyethylene ether AEO-9, 0.8 parts by weight of sodium dodecyl sulfate, 5.0 parts by weight of methyltriethoxysilane, and 4.0 parts by weight of 3-aminopropyltriethoxysilane; the kinematic viscosity of the hydroxyl-terminated polydimethylsiloxane at 25°C is 1000 mmHg. 2 / s, with a hydroxyl content of 0.058 mol / kg.

3. The preparation method according to claim 1, characterized in that, In step S1, the pH of the polysiloxane microemulsion was adjusted to 4.50 and reacted at 30°C for 2 hours. Then, the pH was adjusted to 9.50 and reacted at 50°C for 3 hours. 3-Aminopropyltriethoxysilane was pre-hydrolyzed at pH 4.50 and 25°C for 30 minutes. The resulting pre-hydrolyzed solution was added to the flexible polysiloxane microgel dispersion and reacted at pH 9.50 and 50°C for 2 hours. The solution was washed and filtered until the free amine content in the permeate was less than 0.01 mmol / L, and the solid content was adjusted to 20.0%.

4. The preparation method according to claim 1, characterized in that, The Z-average particle size of the surface-aminated flexible polysiloxane microgels obtained in step S1 is 101~153 nm, the polydispersity index is 0.14~0.16, the gel fraction is 72.7%~82.3%, the amount of accessible amino groups on the surface is 0.080~0.121 mmol / g, and the equilibrium liquid absorption is 1.10~1.44 g / g.

5. The preparation method according to claim 1, characterized in that, In step S2, 80.0 parts by mass of polycarbonate diol with a number average molecular weight of 1000 and a hydroxyl value of 112 mg KOH / g and 40.0 parts by mass of polytetrahydrofuran diol with a number average molecular weight of 1000 and a hydroxyl value of 112 mg KOH / g are dehydrated and then reacted with 8.0 parts by mass of dimethylolpropionic acid, 53.9 parts by mass of isophorone diisocyanate and 0.05 parts by mass of bismuth neodecanoate at 80°C for 3 hours to obtain a polyurethane prepolymer with an isocyanate group mass fraction of 2.90%.

6. The preparation method according to claim 5, characterized in that, 40 parts by weight of acetone and 5.7 parts by weight of triethylamine were added to the polyurethane prepolymer for neutralization, followed by the addition of 320 parts by weight of deionized water for dispersion. Before adding ethylenediamine, 40.0 parts by weight of a surface-aminated flexible polysiloxane microgel dispersion with a solid content of 20.0% was added to the polyurethane seed dispersion and reacted at 25°C for 20 min. Then, 3.75 parts by weight of ethylenediamine were added for chain extension to obtain a polyurethane seed-anchored flexible polysiloxane microgel dispersion with a solid content of 30.7%.

7. The preparation method according to claim 1, characterized in that, In step S3, the first part of acrylic monomers accounts for 5.0% of the total mass of acrylic monomers and is composed of butyl acrylate and methyl methacrylate in a mass ratio of 60:40; the mass of 2,2'-azobis(2,4-dimethylpentanonitrile) is 0.8% of the mass of the first part of acrylic monomers.

8. The preparation method according to claim 7, characterized in that, In step S3, based on 650 parts by mass of the polyurethane seed-anchored flexible polysiloxane microgel dispersion obtained in step S2, the first part of the acrylic monomer consists of 4.5 parts by mass of butyl acrylate and 3.0 parts by mass of methyl methacrylate, and the 2,2'-azobis(2,4-dimethylvaleronitrile) is 0.06 parts by mass; the remaining acrylic monomer preemulsion is made of 85.5 parts by mass of butyl acrylate, 57.0 parts by mass of methyl methacrylate, 0.8 parts by mass of sodium dodecyl sulfate and 50 parts by mass of deionized water, and 0.45 parts by mass of ammonium persulfate is dissolved in 20 parts by mass of deionized water; After heating to 75°C, 2.0 parts by mass of ammonium persulfate aqueous solution were added first, and then the remaining acrylic monomer preemulsion and the remaining ammonium persulfate aqueous solution were added dropwise simultaneously over 150 min. After the addition was completed, the reaction was continued at 75°C for 60 min.

9. A silicone-chain modified polyurethane-acrylic conformal coating agent, characterized in that, It is prepared by the preparation method according to any one of claims 1 to 8.

10. The silicon-chain modified polyurethane-acrylic conformal coating agent according to claim 9, characterized in that, The silicon-chain modified polyurethane-acrylic conformal coating agent has a solid content of 35.1% and a pH value of 8.00.

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