A kind of waterborne polyurethane topcoat and its preparation method and application

Abstract

The present invention relates to the field of coatings, and in particular to a waterborne polyurethane topcoat and a preparation method and application thereof, wherein the waterborne polyurethane topcoat comprises: 40-65 parts of hydroxy acrylic dispersion, 5-20 parts of water, 0.1-0.5 parts of defoamer, 1-5 parts of wetting dispersant, 0.3-0.6 parts of leveling agent, 0.4-1 parts of rheology control additive, 10-15 parts of pigment, and 10-20 parts of filler; the B component comprises: 20-30 parts of oily polyisocyanate curing agent, 20-30 parts of waterborne polyisocyanate curing agent, and 40-60 parts of cosolvent; the oily polyisocyanate curing agent is an aromatic polyisocyanate curing agent, and the waterborne polyisocyanate curing agent is an aliphatic polyisocyanate curing agent; the C component comprises: hydroxyethylethylenediamine and / or N,N'-bis(2-hydroxyethyl)ethylenediamine. The topcoat film of the present invention is smooth and has high hardness, impact resistance and excellent corrosion resistance.

Description

Technical Field

[0001] The invention relates to the field of coatings, and in particular to a waterborne polyurethane topcoat and a preparation method and application thereof. Background Art

[0002] The wet-on-wet spraying process of water-based paint has attracted widespread attention because it can shorten the coating cycle, but there are still many problems with paints suitable for the wet-on-wet spraying process.

[0003] Because the wet-on-wet spraying process is to spray the next coat of paint directly when the previous coat of paint is not completely dry, this construction method usually causes the quality of the topcoat surface to deteriorate, such as paint film defects such as loss of gloss and prickly heat. In addition, the paint film has poor adhesion, weather resistance and corrosion resistance.

[0004] In order to solve the problems of polyurethane topcoat such as loss of gloss and prickly heat in the wet-on-wet process, water-based hydroxy acrylic emulsion containing steric hindered groups is usually used as the resin part. However, the use of water-based hydroxy acrylic emulsion containing steric hindered groups will not only increase the cost of the resin component, but also significantly reduce the compatibility of the resin component and the curing agent component due to the large space occupied by the steric hindered groups and the strong mutual repulsion. In order to improve the compatibility, it is usually necessary to use a metal salt catalyst to catalyze the conversion of the oily polyisocyanate curing agent, which increases the complexity of the process and the difficulty of control. At the same time, the oily polyisocyanate curing agent is directly applied to the water-based polyurethane coating. Because the oily polyisocyanate curing agent has poor compatibility in the water phase, it will cause the gloss of the paint film to decrease or even become rough, which has a greater negative impact on the performance and appearance of the paint film. Summary of the invention

[0005] Therefore, the technical problem to be solved by the present invention is to overcome the deficiencies and defects in the prior art, thereby providing a water-based polyurethane topcoat with excellent paint film appearance, high hardness and impact resistance, good corrosion resistance, and low VOC content, as well as a preparation method and application thereof.

[0006] To solve the above problems:

[0007] The invention provides a waterborne polyurethane topcoat, comprising component A, component B and component C;

[0008] The component A comprises the following raw materials in parts by weight: 40-65 parts of hydroxy acrylic dispersion, 5-20 parts of water, 0.1-0.5 parts of defoamer, 1-5 parts of wetting dispersant, 0.3-0.6 parts of leveling agent, 0.4-1 parts of rheology control agent, 10-15 parts of pigment, and 10-20 parts of filler;

[0009] The B component includes the following raw materials in parts by weight: 20-30 parts of oily polyisocyanate curing agent, 20-30 parts of water-based polyisocyanate curing agent, and 40-60 parts of cosolvent;

[0010] The oily polyisocyanate curing agent is an aromatic polyisocyanate curing agent, and the water-based polyisocyanate curing agent is an aliphatic polyisocyanate curing agent;

[0011] The C component includes: hydroxyethylethylenediamine and / or N,N'-bis(2-hydroxyethyl)ethylenediamine.

[0012] When component C is hydroxyethylethylenediamine and N,N'-bis(2-hydroxyethyl)ethylenediamine, the mass ratio of the two is 1:1.

[0013] Preferably, the mass ratio of the oily polyisocyanate curing agent to the water-based polyisocyanate curing agent is (0.6-1.5):1, more preferably (0.8-1.2):1; the mass ratio of component A to component B is (3-5):1; the mass ratio of component C to component A is (0.02-0.1):1.

[0014] Preferably, the hydroxylated acrylic dispersion includes one or more of Bayhydrol A 2470, Shiquanxing 6470 and Bayhydrol A 2601.

[0015] In an optional embodiment, the solid content of the hydroxy acrylic dispersion is 43%-48%. In the polyurethane topcoat system, the higher the solid content of the hydroxy acrylic dispersion used, the better the film-forming property, the faster the drying speed, the thicker the paint film thickness, which is conducive to forming a dense and uniform paint film. However, too high a solid content will increase the difficulty of construction. The lower the solid content of the hydroxy acrylic dispersion used, the worse the film-forming property, the slower the drying speed, the thinner the paint film thickness, and it is difficult to form a dense and uniform paint film, which may cause the hardness and wear resistance of the paint film to decrease. In order to ensure the uniformity and density of the paint film and improve the hardness of the paint film, the solid content of the hydroxy acrylic dispersion in the present invention is 43%-48%.

[0016] In an optional embodiment, the hydroxyl content of the hydroxy acrylic dispersion is 3.5%-4%. When the hydroxyl content of the hydroxy acrylic dispersion used is reduced, the crosslinking density of the waterborne polyurethane topcoat will be reduced, thereby reducing the hardness of the paint film; the higher the hydroxyl content of the hydroxy acrylic dispersion used, the more conducive it is for the isocyanate curing agent to fully react with the hydroxyl group to form more crosslinking points, thereby increasing the crosslinking density and hardness of the paint film, thereby making the paint film denser and harder, and helping to improve the wear resistance and scratch resistance of the paint film. However, too high a hydroxyl content may cause defects such as bubbles and pinholes to form during the drying process of the paint film, reducing the medium resistance. When the hydroxyl content is 3.5%-4%, the hydroxy acrylic dispersion has good solvent resistance, water resistance and good pigment wetting properties.

[0017] Preferably, the wetting and dispersing agent comprises a copolymer dispersant containing pigment affinity groups and an organosilicon wetting and dispersing agent; the mass ratio of the copolymer dispersant containing pigment affinity groups and the organosilicon wetting and dispersing agent is (1-10):1; the rheology control additive comprises a polyurethane thickener and fumed silica; the mass ratio of the polyurethane thickener and fumed silica is 1:(1-1.5).

[0018] In an optional embodiment, the particle size of the fumed silica is 100-300 nm. Its nano-particle size and surface characteristics make it thixotropic and can change viscosity under shear force, which is helpful for the construction and leveling of the coating.

[0019] Preferably, the copolymer dispersant containing pigment affinity groups includes HY-755 and / or SDJ8002; the organosilicon wetting dispersant includes one or more of HTK-4011, Momentive Silwet L-77, TEGO Wet 270 and Efka 3777; the polyurethane thickener includes one or more of RHEOLATE 299, Rheovis PU1190, Vesmody U300 and RM-8W; the fumed silica includes one or more of R972, R812 and R974.

[0020] When there are two types of organosilicon wetting and dispersing agents, the mass ratio of the two is 2: 1. For example, when the organosilicon wetting and dispersing agents are TEGO Wet 270 and Efka 3777, the mass ratio of TEGO Wet 270 and Efka 3777 is 2:1.

[0021] When there are two types of polyurethane thickeners, the mass ratio of the two is 3:2. For example, when the polyurethane thickeners are RHEOLATE 299 and polyurethane thickener RM-8W, the mass ratio of RHEOLATE 299 and RM-8W is 3:2.

[0022] When there are two types of fumed silica, the mass ratio of the two is 1: 1. For example, when the fumed silica is R972 and R974, the mass ratio of R972 to R974 is 1:1.

[0023] Preferably, the aromatic polyisocyanate curing agent includes one or more of TL-75E, TT-150B, N-75 and DesmodurL75A CN; the aliphatic polyisocyanate curing agent includes one or more of PT-3100, Bayhydur 401-70 and S-208; the defoamer is an organic silicone water-based defoamer; the leveling agent is an organic silicone leveling agent; and the cosolvent is an organic solvent with a boiling point of 190-225°C.

[0024] The boiling point of the above-mentioned auxiliary solvent is the boiling point under the conditions of 25° C. and 101.325 kPa.

[0025] When there are two types of aliphatic polyisocyanate curing agents, the mass ratio of the two is 1: 1. For example, when the aliphatic polyisocyanate curing agents are Bayhydur 401-70 and S-208, the mass ratio of Bayhydur 401-70 and S-208 is 1:1.

[0026] Preferably, the silicone aqueous defoaming agent includes one or more of TEGO Foamex 810, TEGO Airex 901 W, TEGO Airex 902 W and TEGO Foamex 825; the silicone leveling agent includes one or more of LAG-8000, BYK-348, BY-9315 and OFX-0400; the organic solvent includes one or more of dipropylene glycol butyl ether, dipropylene glycol methyl ether, propylene glycol diacetate, diethylene glycol ethyl ether acetate and diethylene glycol ethyl ether; the pigment includes one or more of titanium dioxide, organic orange, phthalocyanine blue, carbon black, iron oxide red and iron oxide yellow; the filler includes one or more of precipitated barium sulfate, talc, calcium carbonate, kaolin, mica powder and mica iron oxide powder.

[0027] When there are two types of silicone water-based defoamers, the mass ratio of the two is 1: 1. For example, when the silicone water-based defoamers are TEGO Airex 902 W and TEGO Foamex 825, the mass ratio of TEGO Airex 902 W to TEGO Foamex825 is 1:1.

[0028] When there are two types of silicone leveling agents, the mass ratio of the two is 1: 1. For example, when the silicone leveling agents are BY-9315 and OFX-0400, the mass ratio of BY-9315 and OFX-0400 is 1:1.

[0029] When there are two kinds of organic solvents, the mass ratio of the two is 5:6. For example, when the organic solvents are propylene glycol diacetate and diethylene glycol ethyl ether, the mass ratio of propylene glycol diacetate and diethylene glycol ethyl ether is 5:6.

[0030] When there are two types of fillers, the mass ratio of the two is 1: 1. For example, when the fillers are kaolin and mica powder, the mass ratio of kaolin and mica powder is 1:1.

[0031] The present invention also provides a method for preparing the waterborne polyurethane topcoat, comprising the following preparation steps:

[0032] (1) Mix and stir water, a wetting and dispersing agent, a defoaming agent, a filler, a pigment, a rheology control agent, a hydroxy acrylic dispersion, and a leveling agent to obtain component A;

[0033] (2) Add component C and component B to component A, mix and stir to prepare a waterborne polyurethane topcoat.

[0034] The specific steps in step (1) include:

[0035] S1. Mix water and a copolymer dispersant containing a pigment affinity group, stir, then add a defoamer, adjust the stirring speed, continue stirring, and obtain a mixture;

[0036] S2. Add filler, pigment and fumed silica to the mixture, stir evenly, and grind to obtain a slurry;

[0037] S3. Add hydroxy acrylic dispersion, silicone wetting and dispersing agent, leveling agent and polyurethane thickener to the slurry, mix and stir to obtain component A.

[0038] Preferably, in step S1, the stirring time is 10-20 min, after adjusting the stirring speed, the stirring speed is 500-1000 r / min, and the continued stirring time is 15-30 min; the added amount of the copolymer dispersant containing the pigment affinity group is 0.5-4.5 parts.

[0039] Preferably, in step S2, the fineness of the slurry is less than 20 µm, and the amount of fumed silica added is 0.2-0.5 parts.

[0040] Preferably, the viscosity of the A component is 70-80 KU.

[0041] The specific steps in step (2) include: adding component C to component A, stirring evenly, adding component B, stirring evenly, and preparing a waterborne polyurethane topcoat;

[0042] First, components A and C are stirred evenly before adding component B, which is beneficial for component C to fully contact with the hydroxylated acrylic dispersion and the polyisocyanate curing agent, thereby enhancing the compatibility of components A and B.

[0043] The preparation method of the B component comprises:

[0044] The water-based polyisocyanate curing agent, the oil-based polyisocyanate curing agent and the cosolvent are mixed and stirred to obtain component B.

[0045] The present invention also provides the use of the above-mentioned waterborne polyurethane topcoat or the waterborne polyurethane topcoat prepared by the above-mentioned preparation method of the waterborne polyurethane topcoat in a wet-on-wet spraying process.

[0046] The technical solution of the present invention has the following advantages:

[0047] 1. The present invention provides a waterborne polyurethane topcoat, comprising component A, component B and component C;

[0048] The component A comprises the following raw materials in parts by weight: 40-65 parts of hydroxy acrylic dispersion, 5-20 parts of water, 0.1-0.5 parts of defoamer, 1-5 parts of wetting dispersant, 0.3-0.6 parts of leveling agent, 0.4-1 parts of rheology control agent, 10-15 parts of pigment, and 10-20 parts of filler; the component B comprises the following raw materials in parts by weight: 20-30 parts of oily polyisocyanate curing agent, 20-30 parts of water-based polyisocyanate curing agent, and 40-60 parts of cosolvent; the oily polyisocyanate curing agent is an aromatic polyisocyanate curing agent, and the water-based polyisocyanate curing agent is an aliphatic polyisocyanate curing agent; the component C comprises: hydroxyethylethylenediamine and / or N,N'-bis(2-hydroxyethyl)ethylenediamine.

[0049] In the present invention, the oily polyisocyanate curing agent is an aromatic polyisocyanate curing agent, and the water-based polyisocyanate curing agent is an aliphatic polyisocyanate curing agent. The aromatic polyisocyanate curing agent and the aliphatic polyisocyanate curing agent are used in combination to reduce the molecular structure susceptible to ultraviolet rays, and avoid the aging or yellowing of the paint film due to long-term exposure to sunlight, air and other environments and erosion by natural factors. The appearance and stability of the coating can be maintained.

[0050] The C component of the present invention includes: hydroxyethylethylenediamine and / or N,N'-bis(2-hydroxyethyl)ethylenediamine. Generally, hydroxyethylethylenediamine or N,N'-bis(2-hydroxyethyl)ethylenediamine is used as a curing agent for epoxy resin. In the system of the present invention, both are used as crosslinking agents. Since hydroxyethylethylenediamine and N,N'-bis(2-hydroxyethyl)ethylenediamine have both amino groups and hydroxyl groups in their structures, they have strong polarity. On the one hand, the amino groups and hydroxyl groups in the molecules can interact with the polar groups in the hydroxylated acrylic dispersion and the polyisocyanate curing agent, reduce the interfacial tension of the hydroxylated acrylic dispersion and the polyisocyanate curing agent, and help the hydroxylated acrylic dispersion and the polyisocyanate curing agent to merge with each other, thereby improving the compatibility between the hydroxylated acrylic dispersion and the polyisocyanate curing agent. On the other hand, it participates in the crosslinking reaction during the curing process, forms additional crosslinking points, promotes the formation of a crosslinking grid, and increases the crosslinking density of the paint film, thereby improving the water resistance, corrosion resistance and aging resistance of the topcoat. In addition, in waterborne polyurethane topcoats, pH adjusters are usually added to enhance the stability of the coating, but improper selection can easily affect the use effect and paint film performance. Hydroxyethylethylenediamine and N,N'-bis(2-hydroxyethyl)ethylenediamine can both effectively regulate the pH value of the coating, avoiding adverse phenomena such as stratification, precipitation, and gelation during storage or use of the coating, thereby enhancing the stability of the coating.

[0051] The present invention significantly improves the compatibility of component A and component B as well as topcoat and primer by adding component C, not only avoiding phase separation of the paint film during the drying process, thereby producing defects in appearance such as orange peel, uneven paint film, and matte, but also improving the crosslinking density and curing degree of the paint film, improving the hardness and impact strength of the paint film, and improving the corrosion resistance and durability of the paint film. In addition, component C replaces the conventional pH regulator, can effectively regulate the pH value of the coating, enhances the stability of the coating, and its high boiling point and non-volatile properties also reduce VOC.

[0052] Under the action of component C, aromatic oily polyisocyanate curing agent and aliphatic water-based polyisocyanate curing agent can be evenly dispersed in the water-based system after compounding, and form a coating with a tight cross-linking structure with the hydroxyl acrylic dispersion. It effectively blocks the erosion of various chemical substances such as acids, alkalis, and salts, and can make the paint film have good water resistance and chemical resistance. The cured coating also has high hardness and toughness, and is not prone to cracking, peeling and other problems, which prolongs the service life of the coating.

[0053] 2. The present invention further defines that the mass ratio of the oily polyisocyanate curing agent to the water-based polyisocyanate curing agent is (0.6-1.5): 1. When the oily polyisocyanate curing agent is used in the water-based polyurethane coating, the oily polyisocyanate curing agent has a low degree of crosslinking with the hydroxy acrylic dispersion and poor compatibility with the water phase, resulting in low gloss of the paint film and a bottom biting phenomenon between the topcoat and the primer, which affects the performance and appearance of the paint film; when the water-based polyisocyanate curing agent is used in the water-based polyurethane coating, although the VOC content is low, after the topcoat is cured into a film, the hydrophilic groups remaining on the surface of the paint film will reduce the water resistance of the paint film surface. The invention improves the adhesion to the substrate, increases the hydrophobicity of the waterborne polyurethane topcoat, moderates the reaction rate between the hydroxyl acrylic dispersion and the polyisocyanate curing agent, prolongs the cross-linking reaction time between the hydroxyl acrylic dispersion and the polyisocyanate curing agent, and then prolongs the open time of the paint film, provides a water volatilization channel for the primer, avoids paint diseases such as prickly heat and gloss loss of the paint film, and ensures the stability of the curing effect and the performance of the paint film.

[0054] The present invention further defines that the mass ratio of component C to component A is (0.02-0.1): 1. The component A and component B in the waterborne polyurethane topcoat provided by the present invention, as well as the topcoat and primer, have suitable compatibility, thereby avoiding the degradation of the paint film quality due to phase separation during the drying process of the topcoat, and at the same time, by participating in the curing process, the crosslinking density and curing degree of the paint film are improved, and the hardness and impact strength of the paint film are improved.

[0055] 3. The present invention further defines that the wetting dispersant includes a copolymer dispersant containing a pigment affinity group and an organosilicon wetting dispersant. Compared with other wetting dispersants, the copolymer dispersant containing a pigment affinity group can be specifically adsorbed on the surface of the pigment particles, and effectively improves the wettability and dispersibility of the pigment particles in the liquid through the hydrophilic and lipophilic groups on its molecular chain. The organosilicon wetting dispersant further reduces the surface tension of the liquid through its excellent surface activity and promotes the uniform dispersion of the pigment particles.

[0056] The present invention further defines that the mass ratio of the copolymer dispersant containing pigment affinity groups to the organosilicon wetting dispersant is (1-10): 1. Under this ratio, the composite use of the two can effectively prevent the agglomeration and sedimentation of pigment particles during the dispersion process, improve the stability and uniformity of the dispersion system; and can improve the gloss and tinting power of the coating, reduce defects such as floating color, blooming and fish eyes during the coating process, extend the storage life of the coating, and improve the performance of the coating.

[0057] The present invention further defines that the rheology control additive includes a polyurethane thickener and fumed silica. The polyurethane thickener forms a three-dimensional network structure through the entanglement and cross-linking of molecular chains, thereby increasing the viscosity of the system. Fumed silica increases the yield value of the liquid system, reduces the mobility of pigments and fillers, and thus prevents the sedimentation of pigments and fillers.

[0058] When polyurethane thickener is compounded with fumed silica, the viscosity, fluidity and thixotropy of the coating can be comprehensively improved, ensuring the thickness and uniformity of the paint film during one-time construction.

[0059] The present invention further defines that the mass ratio of the polyurethane thickener to the fumed silica is 1:(1-1.5). Under this ratio, after the polyurethane thickener and the fumed silica are compounded, the three-dimensional network structure of the polyurethane thickener is combined with the particle filling effect of the fumed silica, which can further enhance the consistency and viscosity of the coating and adjust the rheology and thixotropy of the coating.

[0060] 4. The present invention further defines that the defoamer is a water-based silicone defoamer, which has good compatibility with the hydroxy acrylic dispersion and the polyisocyanate curing agent system, and has the characteristics of low surface tension and can fully exert the effects of defoaming and anti-foaming.

[0061] The present invention further defines that the cosolvent is an organic solvent with a boiling point of 190-225°C. The high-boiling-point organic solvent can maintain the stability of the coating during storage and construction due to its low volatility, thereby extending the open time of the paint film and reducing the degradation of the paint film performance due to solvent volatilization. DETAILED DESCRIPTION

[0062] The following examples are provided for a better understanding of the present invention, but are not intended to limit the best mode of implementation, nor to limit the content and protection scope of the present invention. Any product identical or similar to the present invention obtained by anyone under the inspiration of the present invention or by combining the features of the present invention with other prior arts shall fall within the protection scope of the present invention.

[0063] If no specific experimental steps or conditions are specified in the examples, the conventional experimental steps or conditions described in the literature in the field can be used. If no manufacturer is specified for the reagents or instruments used, they are all conventional reagent products that can be obtained commercially.

[0064] Example 1

[0065] The present invention provides a waterborne polyurethane topcoat, comprising component A, component B and component C:

[0066] The raw materials of component A are calculated by weight and include: 40 parts of hydroxyl acrylic dispersion Bayhydrol A 2601, 5 parts of water, 0.1 parts of silicone water-based defoamer TEGO Foamex 810, 0.5 parts of copolymer dispersant SDJ8002 containing pigment affinity groups, 0.5 parts of silicone wetting dispersant HTK-4011, 0.3 parts of silicone leveling agent LAG-8000, 0.2 parts of polyurethane thickener RHEOLATE 299, 0.2 parts of fumed silica R972, 10 parts of iron oxide yellow (pigment), and 10 parts of talc (filler).

[0067] The raw materials of component B are calculated by weight and include: 20 parts of aromatic polyisocyanate curing agent TL-75E, 20 parts of aliphatic polyisocyanate curing agent PT-3100, and 40 parts of dipropylene glycol butyl ether (organic solvent).

[0068] Component C is hydroxyethylethylenediamine.

[0069] The mass ratio of component A to component B is 3:1; the mass ratio of component C to component A is 0.02:1.

[0070] The preparation method of the above-mentioned waterborne polyurethane topcoat comprises:

[0071] (1) Add water and a copolymer dispersant SDJ8002 containing pigment affinity groups into a dispersion tank, mix, and stir for 15 minutes. Then add a silicone water-based defoamer TEGO Foamex 810, adjust the speed to 800 r / min, and continue stirring for 25 minutes to obtain a mixture;

[0072] Add talcum powder (filler), yellow iron oxide (pigment) and fumed silica R972 to the mixture, stir evenly, transfer to a grinder, grind to obtain a slurry with a fineness of less than 20 μm;

[0073] Adding hydroxy acrylic dispersion Bayhydrol A 2601, silicone wetting and dispersing agent HTK-4011, silicone leveling agent LAG-8000 and polyurethane thickener RHEOLATE 299 to the slurry, mixing and stirring to obtain component A, wherein the viscosity of component A is 70KU;

[0074] Add aliphatic polyisocyanate curing agent PT-3100, aromatic polyisocyanate curing agent TL-75E and dipropylene glycol butyl ether (organic solvent) into a dispersion tank, mix and stir to obtain component B;

[0075] (2) Add hydroxyethylethylenediamine (component C) to component A and stir evenly, then add component B and stir evenly to prepare the waterborne polyurethane topcoat.

[0076] Example 2

[0077] The present invention provides a waterborne polyurethane topcoat, comprising component A, component B and component C:

[0078] The raw materials of component A are calculated by weight and include: 50 parts of hydroxyl acrylic dispersion Shiquanxing 6470, 10 parts of water, 0.3 parts of silicone water-based defoamer TEGO Foamex 810, 4.5 parts of copolymer dispersant HY-755 containing pigment affinity groups, 0.5 parts of silicone wetting dispersant HTK-4011, 0.5 parts of silicone leveling agent LAG-8000, 0.5 parts of polyurethane thickener RHEOLATE 299, 0.5 parts of fumed silica R972, 13 parts of iron oxide yellow (pigment), and 15 parts of precipitated barium sulfate (filler).

[0079] The raw materials of component B are calculated by weight and include: 24 parts of aromatic polyisocyanate curing agent N-75, 30 parts of aliphatic polyisocyanate curing agent PT-3100, and 50 parts of propylene glycol diacetate (organic solvent).

[0080] Component C is hydroxyethylethylenediamine.

[0081] The mass ratio of component A to component B is 4:1; the mass ratio of component C to component A is 0.04:1.

[0082] The preparation method of the above-mentioned waterborne polyurethane topcoat comprises:

[0083] (1) Add water and a copolymer dispersant HY-755 containing pigment affinity groups into a dispersion tank, mix, and stir for 15 minutes. Then add a silicone water-based defoamer TEGO Foamex 810, adjust the speed to 800 r / min, and continue stirring for 25 minutes to obtain a mixture;

[0084] Add precipitated barium sulfate (filler), yellow iron oxide (pigment) and fumed silica R972 to the mixture, stir evenly, transfer to a grinder, grind to obtain a slurry with a fineness of less than 20 μm;

[0085] Add hydroxyl acrylic dispersion Shiquanxing 6470, silicone wetting dispersant HTK-4011, silicone leveling agent LAG-8000 and polyurethane thickener RHEOLATE 299 to the slurry, mix and stir to obtain component A, wherein the viscosity of component A is 78KU;

[0086] Add aliphatic polyisocyanate curing agent PT-3100, aromatic polyisocyanate curing agent N-75 and propylene glycol diacetate (organic solvent) into a dispersion tank, mix and stir to obtain component B;

[0087] (2) Add hydroxyethylethylenediamine (component C) to component A and stir evenly, then add component B and stir evenly to prepare the waterborne polyurethane topcoat.

[0088] Example 3

[0089] The present invention provides a waterborne polyurethane topcoat, comprising component A, component B and component C:

[0090] The raw materials of component A are calculated by weight and include: 65 parts of hydroxyl acrylic dispersion Shiquanxing 6470, 20 parts of water, 0.5 parts of silicone water-based defoamer TEGO Foamex 810, 3.5 parts of copolymer dispersant HY-755 containing pigment affinity groups, 0.5 parts of silicone wetting dispersant HTK-4011, 0.3 parts of silicone leveling agent BY-9315, 0.3 parts of silicone leveling agent OFX-0400, 0.3 parts of polyurethane thickener RHEOLATE 299, 0.2 parts of polyurethane thickener RM-8W, 0.5 parts of fumed silica R974, 15 parts of phthalocyanine blue (pigment), 10 parts of kaolin (filler), and 10 parts of mica powder (filler).

[0091] The raw materials of component B are calculated by weight and include: 30 parts of aromatic polyisocyanate curing agent TL-75E, 25 parts of aliphatic polyisocyanate curing agent S-208, and 60 parts of diethylene glycol ethyl ether acetate (organic solvent).

[0092] Component C is N,N'-bis(2-hydroxyethyl)ethylenediamine.

[0093] The mass ratio of component A to component B is 5:1; the mass ratio of component C to component A is 0.1:1.

[0094] The preparation method of the above-mentioned waterborne polyurethane topcoat comprises:

[0095] (1) Add water and a copolymer dispersant HY-755 containing pigment affinity groups into a dispersion tank, mix, and stir for 15 minutes. Then add a silicone water-based defoamer TEGO Foamex 810, adjust the speed to 1000 r / min, and continue stirring for 25 minutes to obtain a mixture;

[0096] Add kaolin (filler), mica powder (filler), phthalocyanine blue (pigment) and fumed silica R974 to the mixture, stir evenly, transfer to a grinder, grind to obtain a slurry with a fineness of less than 20 μm;

[0097] Add hydroxyl acrylic dispersion Shiquanxing 6470, silicone wetting dispersant HTK-4011, silicone leveling agent BY-9315, silicone leveling agent OFX-0400, polyurethane thickener RHEOLATE 299 and polyurethane thickener RM-8W to the slurry, mix and stir to obtain component A, wherein the viscosity of component A is 80KU;

[0098] Add aliphatic polyisocyanate curing agent S-208, aromatic polyisocyanate curing agent TL-75E and diethylene glycol ethyl ether acetate (organic solvent) into a dispersion tank, mix and stir to obtain component B;

[0099] (2) Add N,N'-bis(2-hydroxyethyl)ethylenediamine (component C) to component A and stir evenly, then add component B and stir evenly to obtain the waterborne polyurethane topcoat.

[0100] Example 4

[0101] The present invention provides a waterborne polyurethane topcoat, comprising component A, component B and component C:

[0102] The raw materials of component A are calculated by weight and include: 45 parts of hydroxyl acrylic dispersion Shiquanxing 6470, 10 parts of water, 0.2 parts of silicone water-based defoamer TEGO Airex 901 W, 1 part of copolymer dispersant HY-755 containing pigment affinity groups, 0.1 parts of silicone wetting dispersant Momentive Silwet L-77, 0.4 parts of silicone leveling agent BYK-348, 0.2 parts of polyurethane thickener Vesmody U300, 0.3 parts of fumed silica R812, 13 parts of titanium dioxide (pigment), and 10 parts of calcium carbonate (filler).

[0103] The raw materials of component B are calculated by weight and include: 30 parts of aromatic polyisocyanate curing agent TT-150B, 20 parts of aliphatic polyisocyanate curing agent Bayhydur 401-70, and 45 parts of dipropylene glycol methyl ether (organic solvent).

[0104] C component raw materials: 50 parts of hydroxyethylethylenediamine and 50 parts of N,N'-bis(2-hydroxyethyl)ethylenediamine.

[0105] The mass ratio of component A to component B is 3.5:1; the mass ratio of component C to component A is 0.03:1.

[0106] The preparation method of the above-mentioned waterborne polyurethane topcoat comprises:

[0107] (1) Add water and a copolymer dispersant HY-755 containing pigment affinity groups into a dispersion tank, mix, and stir for 20 minutes. Then add a silicone water-based defoamer TEGO Airex 901 W, adjust the speed to 500 r / min, and continue stirring for 30 minutes to obtain a mixture.

[0108] Add calcium carbonate (filler), titanium dioxide (pigment) and fumed silica R812 to the mixture, stir evenly, transfer to a grinder, grind to obtain a slurry with a fineness of less than 20 μm;

[0109] Add hydroxy acrylic dispersion Shiquanxing 6470, silicone wetting dispersant MomentiveSilwet L-77, silicone leveling agent BYK-348 and polyurethane thickener Vesmody U300 to the slurry, mix and stir to obtain component A, wherein the viscosity of component A is 75KU;

[0110] Add aliphatic polyisocyanate curing agent Bayhydur 401-70, aromatic polyisocyanate curing agent TT-150B and dipropylene glycol methyl ether (organic solvent) into a dispersion tank, mix and stir to obtain component B;

[0111] (2) Add hydroxyethylethylenediamine (component C) and N,N'-bis(2-hydroxyethyl)ethylenediamine (component C) to component A and stir evenly, then add component B and stir evenly to prepare the waterborne polyurethane topcoat.

[0112] Example 5

[0113] The present invention provides a waterborne polyurethane topcoat, comprising component A, component B and component C:

[0114] The raw materials of component A are calculated by weight and include: 55 parts of hydroxy acrylic dispersion Bayhydrol A 2470, 15 parts of water, 0.2 parts of silicone water-based defoamer TEGO Airex 902 W, 0.2 parts of silicone water-based defoamer TEGO Foamex825, 2.4 parts of copolymer dispersant HY-755 containing pigment affinity groups, 0.2 parts of silicone wetting and dispersing agent TEGO Wet270, 0.1 parts of silicone wetting and dispersing agent Efka 3777, 0.5 parts of silicone leveling agent LAG-8000, 0.2 parts of polyurethane thickener Rheovis PU1190, 0.1 parts of fumed silica R972, 0.1 parts of fumed silica R974, 15 parts of titanium dioxide (pigment), and 20 parts of precipitated barium sulfate (filler).

[0115] The raw materials of component B are calculated by weight and include: 20 parts of aromatic polyisocyanate curing agent Desmodur L75ACN, 15 parts of aliphatic polyisocyanate curing agent Bayhydur 401-70, 15 parts of aliphatic polyisocyanate curing agent S-208, 25 parts of propylene glycol diacetate (organic solvent), and 30 parts of diethylene glycol ethyl ether (organic solvent).

[0116] Component C is hydroxyethylethylenediamine.

[0117] The mass ratio of component A to component B is 4.5:1; the mass ratio of component C to component A is 0.08:1.

[0118] The preparation method of the above-mentioned waterborne polyurethane topcoat comprises:

[0119] (1) Add water and a copolymer dispersant HY-755 containing pigment affinity groups into a dispersion tank, mix and stir for 10 minutes, then add an organic silicon water-based defoamer TEGO Foamex 825 and an organic silicon water-based defoamer TEGO Airex 902 W, adjust the speed to 1000 r / min, and continue stirring for 15 minutes to obtain a mixture;

[0120] Add precipitated barium sulfate (filler), titanium dioxide (pigment), fumed silica R972 and fumed silica R974 to the mixture, stir evenly, transfer to a grinder, grind to obtain a slurry with a fineness of less than 20 μm;

[0121] Adding hydroxy acrylic dispersion Bayhydrol A 2470, silicone wetting and dispersing agent TEGO Wet270, silicone wetting and dispersing agent Efka 3777, silicone leveling agent LAG-8000 and polyurethane thickener RheovisPU1190 to the slurry, mixing and stirring to obtain component A, wherein the viscosity of component A is 72KU;

[0122] Add aliphatic polyisocyanate curing agent Bayhydur 401-70, aliphatic polyisocyanate curing agent S-208, aromatic polyisocyanate curing agent Desmodur L75A CN, propylene glycol diacetate (organic solvent), and diethylene glycol ethyl ether (organic solvent) into a dispersion tank, mix and stir to obtain component B;

[0123] (2) Add hydroxyethylethylenediamine (component C) to component A and stir evenly, then add component B and stir evenly to prepare the waterborne polyurethane topcoat.

[0124] Comparative Example 1

[0125] This comparative example provides a water-based polyurethane topcoat, which differs from Example 2 in that the hydroxylated acrylic dispersion Shiquanxing 6470 is replaced with the same amount of hydroxylated acrylic dispersion YWH6030; the aliphatic polyisocyanate curing agent PT-3100 is not added, and the amount of the aromatic polyisocyanate curing agent N-75 is adjusted to 54 parts.

[0126] Among them, the solid content of the hydroxylated acrylic dispersion YWH6030 is 40±2% and the hydroxyl content is 3.0%.

[0127] Comparative Example 2

[0128] This comparative example provides a waterborne polyurethane topcoat, which differs from Example 2 in that component C is N,N-dimethylethanolamine.

[0129] Comparative Example 3

[0130] This comparative example provides a waterborne polyurethane topcoat, which differs from Example 2 in that the organic silicon wetting and dispersing agent HTK-4011 and the fumed silica R972 are not added, and the amount of the copolymer dispersant HY-755 containing the pigment affinity group is adjusted to 5 parts, and the amount of the polyurethane thickener RHEOLATE 299 is adjusted to 1 part.

[0131] Comparative Example 4

[0132] This comparative example provides a waterborne polyurethane topcoat, which differs from Example 2 in that the aromatic polyisocyanate curing agent N-75 is replaced by an equal amount of aliphatic polyisocyanate HT100.

[0133] Test Case

[0134] "Wet-on-wet" spraying construction process: spray 50-60µm of conventional water-based epoxy primer on the market, dry naturally for 20-30 minutes in a well-ventilated environment (temperature and humidity meet the requirements of water-based paint construction), and the paint film reaches a surface dry state. Apply the water-based polyurethane topcoat of Examples 1-5 and Comparative Examples 1-4, dry naturally for 20-30 minutes, and then put it into an 80°C oven for baking for 30 minutes to obtain different samples.

[0135] The conventional waterborne epoxy primer on the market is ZD800 (W).

[0136] The above samples were tested according to the specific requirements of HG / T 4761-2014 Waterborne Polyurethane Coatings and Construction Machinery. The test standards and qualified indicators of each test are shown in Table 1. The results of each test are shown in Table 2.

[0137] Table 1 Test standards and qualified indicators

[0138]

[0139] Table 2 Results of each performance test

[0140]

[0141]

[0142] As can be seen from Table 1 and Table 2, the waterborne polyurethane topcoat provided by the present invention has various properties that meet the specific requirements of HG / T 4761-2014. After wet-on-wet spraying, the paint film is flat and smooth with high fullness, and has high hardness, high impact strength, high adhesion, excellent corrosion resistance and durability, and has a long-term protective effect. At the same time, the VOC content of the paint film is low.

[0143] By comparing Example 2 with Comparative Example 1, it is found that after the oily polyisocyanate curing agent and the water-based polyisocyanate curing agent are mixed and cross-linked with the hydroxy acrylic dispersion of the present invention, the adhesion of the paint film to the substrate is improved. The prepared topcoat has a good appearance under the wet-on-wet process, and has outstanding hardness, impact strength, corrosion resistance, and resistance to artificial weathering, which can meet the requirements of the paint film gloss and color difference retention rate of engineering machinery under long-term exposure.

[0144] By comparing Example 2 with Comparative Example 2, it is found that the addition of component C not only avoids appearance defects such as unevenness and matte of the paint film, but also improves the hardness and impact strength of the paint film, improves the corrosion resistance and water resistance, salt spray resistance, and artificial weathering resistance of the paint film, and reduces VOC.

[0145] By comparing Example 2 with Comparative Example 3, it is found that the glossiness of the coating is increased, and the anti-sagging property and corrosion resistance are improved by the compounded wetting and dispersing agent and the compounded rheology control additive.

[0146] By comparing Example 2 with Comparative Example 4, it is found that after the aromatic oily polyisocyanate curing agent is compounded with the aliphatic water-based polyisocyanate curing agent, the paint film has good adhesion, flexibility, water resistance, salt spray resistance, and artificial weathering resistance.

[0147] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived therefrom are still within the scope of protection of the present invention.

Claims

1. A waterborne polyurethane topcoat, characterized in that: It includes component A, component B and component C; The component A is composed of the following raw materials in parts by weight: 40-65 parts of hydroxy acrylic dispersion, 5-20 parts of water, 0.1-0.5 parts of defoamer, 1-5 parts of wetting and dispersing agent, 0.3-0.6 parts of leveling agent, 0.4-1 parts of rheology control agent, 10-15 parts of pigment, and 10-20 parts of filler; the hydroxy acrylic dispersion includes one or more of Bayhydrol A 2470, Shiquanxing 6470 and Bayhydrol A 2601; the wetting and dispersing agent includes a copolymer dispersant containing pigment affinity groups and an organosilicon wetting and dispersant; the mass ratio of the copolymer dispersant containing pigment affinity groups to the organosilicon wetting and dispersant is (1-10):1; the rheology control agent includes a polyurethane thickener and fumed silica; the mass ratio of the polyurethane thickener to the fumed silica is 1:(1-1.5); The B component is composed of the following raw materials in parts by weight: 20-30 parts of oily polyisocyanate curing agent, 20-30 parts of water-based polyisocyanate curing agent, and 40-60 parts of cosolvent; the oily polyisocyanate curing agent includes one or more of TL-75E, TT-150B, N-75 and Desmodur L75A CN; the water-based polyisocyanate curing agent includes one or more of PT-3100, Bayhydur 401-70 and S-208; The C component is hydroxyethylethylenediamine and / or N,N'-bis(2-hydroxyethyl)ethylenediamine; The mass ratio of the oily polyisocyanate curing agent to the water-based polyisocyanate curing agent is (0.6-1.5):1; The mass ratio of component A to component B is (3-5):1; The mass ratio of the C component to the A component is (0.02-0.1):

1.

2. The waterborne polyurethane topcoat according to claim 1, characterized in that: The copolymer dispersant containing pigment affinity groups includes HY-755 and / or SDJ8002; The organosilicon wetting and dispersing agent includes one or more of HTK-4011, Momentive Silwet L-77 and TEGO Wet 270; The polyurethane thickener includes one or more of RHEOLATE 299, Rheovis PU1190, Vesmody U300 and RM-8W; The fumed silica includes one or more of R972, R812 and R974.

3. The waterborne polyurethane topcoat according to claim 1, characterized in that: The defoamer is a water-based silicone defoamer; The leveling agent is a silicone leveling agent; The cosolvent is one or more of dipropylene glycol butyl ether, dipropylene glycol methyl ether, propylene glycol diacetate, diethylene glycol ethyl ether acetate and diethylene glycol ethyl ether.

4. The waterborne polyurethane topcoat according to claim 3, characterized in that: The organosilicon-based aqueous defoaming agent includes one or more of TEGO Foamex 810, TEGO Airex 901 W, TEGO Airex 902 W and TEGO Foamex 825; The organosilicon leveling agent includes one or more of LAG-8000, BYK-348, BY-9315 and OFX-0400; The pigment includes one or more of titanium dioxide, organic orange, phthalocyanine blue, carbon black, iron oxide red and iron oxide yellow; The filler includes one or more of precipitated barium sulfate, talc, calcium carbonate, kaolin, mica powder and mica iron oxide powder.

5. The method for preparing the waterborne polyurethane topcoat according to any one of claims 1 to 4, characterized in that: The method comprises the following preparation steps: (1) Mix and stir water, a wetting and dispersing agent, a defoaming agent, a filler, a pigment, a rheology control agent, a hydroxy acrylic dispersion, and a leveling agent to obtain component A; (2) Add component C and component B to component A in sequence, mix and stir to prepare a waterborne polyurethane topcoat.

6. The method for preparing the waterborne polyurethane topcoat according to claim 5, characterized in that: The viscosity of the A component is 70-80 KU.

7. Use of the waterborne polyurethane topcoat according to any one of claims 1 to 4 in a wet-on-wet spraying process.

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