Water-based paint is an environmentally friendly paint advocated by the state, but some properties are not as good as the corresponding solvent-based paint, which affects its development. Graphene has unique properties that can improve the performance of water-based paints, promote their development, and bring new expectations to paint workers. The first application of graphene in coatings is to modify solvent-based coatings, but there has also been significant progress in modifying water-based coatings. The modification method can be modified by blending method, or can be modified by in-situ polymerization and sol-gel technology, and can also be modified by coupling agent, and different functional modifications can be carried out at the same time.

1 Modification of water-dispersed modified graphene with titanate coupling agent

According to the general method, graphite is made into graphene oxide, and titanate and hydrazine hydrate are respectively added to the graphene oxide dispersion liquid, and the reaction occurs under the heating method in a water bath, so that the graphene oxide is reduced and the titanate coupling agent is grafted at the same time. molecular. The obtained mixed solution is subjected to post-treatment and vacuum drying to obtain powdery modified graphene.

Because the titanate coupling agent has carried out surface modification on graphene oxide, no agglomeration occurs, so the graphene aqueous dispersion has high stability, can be stored for a long time, and is suitable for the preparation of composite materials and coating materials. The preparation process is simple, the production efficiency is high, and the production process and products can meet the requirements of environmental protection.

2 Graphene and matrix resin blend composite water-based coating

2.1 Water-based conductive coatings

Graphene/polyester resin composite water-based conductive coating. Graphene oxide is prepared by Hummers method, and an aqueous solution of graphene modified by organic molecules is obtained by a two-step chemical reduction method. Polyester, auxiliary agent, cross-linking agent and catalyst are added, and the water-based conductive graphene coating is prepared by liquid blending. The coating has high electrical conductivity and mechanical properties, can be used in electromagnetic shielding, anti-static, anti-corrosion, heat dissipation, wear resistance and electronic circuits and other fields, and has a wide range of application values.

2.2 Graphene-modified water-based epoxy resin wear-resistant glass coating
The graphene-modified wear-resistant water-based glass coating consists of two components, the first component is a matrix film-forming material, and the second component is a curing agent. The first component includes 20% to 40% of modified epoxy resin, 0.5% to 7% of additives, 0.1% to 5% of graphene oxide, 1% to 2% of coupling agent, and the rest is water (all by mass). fraction); the second component is an amine curing agent. The two components are mixed before use, wherein the second component accounts for 3% to 30% of the mass fraction of the mixture. The coating has high hardness, good wear resistance, strong affinity and adhesion with glass substrates, good water resistance and ethanol resistance, and meets environmental protection requirements. In addition, the preparation method is simple and has important commercial application value.

2.3 Graphene-modified acrylate polymer cement waterproof coating

The graphene oxide prepared by the Hummers method is added to the acrylate polymer emulsion, the selected auxiliary agent is added, the cement is added in proportion, and the mixture is stirred and dispersed to prepare a graphene oxide-modified polymer cement waterproof coating. The coating significantly increases the tensile strength of acrylic polymer emulsion films; improves water resistance; in addition, the rich oxygen-containing functional groups of graphene oxide can regulate the growth of cement hydration product crystals and improve its tensile strength and toughness . Therefore, graphene oxide-modified polymer cement waterproof coatings have good durability, impermeability and physical and mechanical properties, and have broad application prospects.

2.4 Graphene-modified polyurethane resin composite water-based coating

2.4.1 Graphene/Waterborne Polyurethane Nanocomposite Emulsion

Polyether polyol (N210) dehydrated in vacuum was reacted with TDI to prepare polyurethane prepolymer, dimethylolpropionic acid was added to introduce hydrophilic carboxyl groups, triethylamine was added to neutralize the base, and graphene oxide aqueous solution was added to remove Ionized water and ethylenediamine are subjected to an emulsification reaction, and after acetone is distilled off under reduced pressure, a vitamin C solution is added dropwise to perform an in-situ reduction reaction to obtain graphene/aqueous polyurethane nanocomposite latex resin. The latex resin can be applied to the fields of electrostatic protection, anti-corrosion coating, architectural coatings, etc. The process of the invention is simple, environmentally friendly, and suitable for large-scale production.

2.4.2 Graphene/TiO2 composite modified waterborne polyurethane antibacterial coating

As a kind of photocatalytic nanomaterials, nano-TiO2 has antibacterial and sterilization effect, but its absorption rate for visible light is low, and nanoparticles tend to aggregate, which greatly reduces its sterilization effect. In the antibacterial coating containing nano-TiO2, the introduction of graphene below 5% can significantly improve the visible light absorption rate of the coating, and strengthen the photocatalytic activity and antibacterial and sterilization capabilities of nano-TiO2, so that the modified water-based polyurethane can be used for antibacterial and sterilization. The overall performance has been greatly improved. And has good surface properties, water resistance and mechanical properties.

3 Graphene/polyurethane in-situ polymerized water-based conductive coatings

Compared with traditional carbon-based conductive fillers (carbon black, graphite, carbon nanotubes, carbon fibers, etc.), graphene has better electrical conductivity and mechanical properties.

Graphene oxide was modified by amination with diamine, and then the conjugated conductive system of graphene was restored by chemical reduction. The graphene-containing water-based polyurethane was polymerized in situ by -NH and -NCO-terminated on the surface of graphene to obtain graphene-containing waterborne polyurethane conductive coatings.

The conductive coating has the properties of anti-radiation, anti-static, anti-corrosion, wear-resisting, etc., and can be used for the surface of polymer materials, metal materials, textile materials and the like.

4 Preparation of modified graphene/waterborne polyurethane nanocomposite coatings by sol-gel technology

Xin Wang et al. of University of Science and Technology of China published their research paper in "Surface & Coatings Technology" in 2012: Preparation of modified graphene/water-based polyurethane composite nanocoatings by sol-gel technology, divided into 3 parts: (1) Silane-modified graphene Preparation of nanofilms. Graphene oxide (GO) was prepared by Hummers method, followed by chemical reduction of GO aqueous dispersion with hydrazine hydrate to GNS, followed by DCC (N,N'-dicyclohexylcarbodiimide) and 3-aminopropyltriethyl The functional modification of oxysilane (APTES) was carried out by ultrasonic dispersion for 1 h, and the reaction was stirred at 70 °C for 24 h. After post-treatment, the graphene nanofilm f-GNS modified with APTES function was obtained.

(2) Preparation of silane APTES-terminated waterborne polyurethane (WPU). Use isophorone diisocyanate (IPDI), polyoxypropylene glycol, diethylene glycol and trimethylolpropane mixed polyol to synthesize PU prepolymer, then react with dimethylolpropionic acid, and then add APTES

After the reaction, APTES-terminated water-based polyurethane (WPU) was obtained with a yield of 86.3% and a number-average molecular weight of 28 600 (determined by GPC).

(3) f-GNS/WPU nanocomposite coatings were prepared by sol-gel technology. The f-GNS powder was dispersed in deionized water with the help of ultrasonic wave to make a suspension, the APTES-terminated WPU was added to it and mixed together, and the pH value was adjusted with triethylamine to prepare the f-GNS/WPU nanocomposite coating.
The structures of GO and f-GNS were characterized by 1H-NMR, FTIR, XPS, GPC, AFM, HRTEM, etc., which basically verified the molecular structure and reaction process shown in Figure 1, and the product structure of f-GNS/WPU nanocomposite coatings and composition. T1, T2, and T3 in the nanocomposites represent mono-, di-, and trisubstituted silane linkages, confirming the polycondensation reaction between APTES-terminated WPU and f-GNS adjacent siloxane molecules, forming covalent bonds.

5.1 Graphene has unique properties, and the research and development boom is booming around the world

Graphene is the "thinest" crystalline material found in the world today, with a thickness of only 1 carbon atom. It is also one of the "hardest" materials, and has high electrical conductivity and high thermal conductivity. Prediction has immeasurable application prospects in aerospace, space exploration, marine development, national defense industry, and national economy.

5.2 Graphene shows new prospects in modifying coating properties
It has very attractive potential prospects for graphene in functional coatings such as electrical conductivity, anticorrosion, flame retardant, thermal conductivity and high strength.

Graphene and various coating resins are compounded by physical blending, in-situ polymerization and sol-gel technology; or modified with coupling agents, or in-situ polymerization and other processes. These processes have been proved feasible in modified waterborne coatings, and the performance improvement is obvious. The performance of water-based coatings modified by graphene is expected to "go to the next level", and its further development can be expected.
5.3 The pace of research and development of graphene-modified coatings is in the early stages. To correctly promote the development of graphene production and application, the development boom will continue to heat up, but it should be treated calmly.

For production enterprises, there is a lot of technical work to be done to determine whether the graphene production technology reaches the most advanced in the world, whether it meets the requirements of clean and civilized production process, and whether the cost is reasonable. The application of graphene in coatings has a lot of research work and patents published in China. There is a lot of room for research and development in the composite method of graphene and coating resin, the selection of additives, and the improvement of functionality. Most of the work and patents published in China for graphene-modified water-based coatings are laboratory results. To achieve practicality and industrialization, more investment is required, and there is a lot of research and development work to be done.

Content source: China Corrosion and Protection Network