Enhancement of antistatic properties of conductive carbon black/waterborne polyurethane UV-curable coatings by metal-organic framework materials

UV curable waterborne polyurethane (UV-WPUA) is an environmentally friendly and high performance polymeric coating suitable for a wide range of substrates including plastics, metals, paper, leather, etc. However, waterborne polyurethanes are insulating and the surface of the coating tends to collect static charges and can cause electrostatic discharge (ESD), which can damage contacting electronic equipment. Therefore, it is necessary to use coatings that can prevent ESD for electronic and electrical products, as well as for any equipment that needs to prevent dust particles from adhering to it, such as aerospace, petroleum storage and chemical engineering [9]. This is why the addition of antistatic properties to waterborne polyurethanes has become a hot topic today.

In this study, conductive carbon black (CB) was employed as a conductive filler for UV-WPUA in order to prepare UV-curable coatings with antistatic properties. Subsequently, MOF-801, a metal-organic framework material with varying contents, was introduced in order to further reduce the surface resistance of the coating. Fourier transform infrared spectroscopy (FT-IR) and nuclear magnetic resonance hydrogen spectroscopy (H NMR) were employed to ascertain the structural composition of UV-WPUA. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were utilised to characterise the structural and microscopic morphology of MOF-801 and the dispersion of MOF-801-CB/UV-WPUA coating.

The acetone method was employed to ascertain the synthesis of UV-WPUA substances via Fourier transform infrared spectroscopy (FT-IR) and nuclear magnetic resonance hydrogen spectroscopy (H NMR). (ii) The synthesis of MOF-801 material was determined by hydrothermal method using FT-IR, scanning electron microscope (SEM), and X-ray diffractometer (XRD). (iii) In the laboratory at a constant temperature of 25 ℃ and constant humidity of 67%, CB/UV-WPUA composite coating, the mass ratio of CB was increased from 10% to 15%, and the surface resistivity of the composite conductive filler was reduced from 2. The electrical resistance of the coating ranged from 5×10 Ω to 2.3×10 Ω, exceeding the penetration threshold. The conductive particles were sufficiently mobile to contact each other and form numerous conductive pathways, resulting in the formation of a conductive network within the coating's inner layer. This network was established in a three-dimensional space. In addition, the CB 15 wt%/UV-WPUA composite coating exhibits superior basic properties, including adhesion grade 0, pencil hardness B, and pendulum hardness 269s. (iv) In the laboratory, the surface resistance of the MOF-801-CB/UV-WPUA composite coating was tested at a constant temperature of 25 ℃ and humidity of 67%. The mass ratio of CB was fixed at 15%, while the mass ratio of MOF-801 was varied. At a MOF-801 mass ratio of 1%, the surface resistivity of the MOF-801-CB/UV-WPUA composite coating was the lowest, at 1.7×10⁵ Ω. It was observed that the mechanical properties of the composite coatings were decreased when the mass ratio of MOF-801 was increased to 2.5%.(v)At a constant temperature of 25℃ and varying ambient humidity, the surface resistance of the MOF-801 1 wt%-CB 15 wt%/UV-WPUA composite coatings exhibited a rapid decline with increasing relative humidity, thereby demonstrating the dependence of The results demonstrated that the MOF-801 composite coating exhibited a reduction in surface resistance with an increase in humidity. This reduction was attributed to the formation of intact hydrogen-bonding networks facilitated by the absorption of water molecules within the MOF-801 framework. These hydrogen-bonding networks were found to facilitate proton conduction, which in turn reduced the surface resistance of the composite coating. However, at a relative humidity of 98%, the resistance of the composite coating increases rather than decreases, and a thin film of water on the coating can be observed to hinder the conduction of charge carriers. When the relative humidity is 75%, the surface resistance reaches a minimum value of 1.2 × 10⁵ Ω. Meanwhile, the MOF-801 1 wt%-CB 15 wt%/UV-WPUA composite coating demonstrated superior basic performance under varying humidity conditions. (vi) In the MOF-801 1 wt%-CB 15 wt%/WPUA composite coating, the CB particles and MOF particles were uniformly dispersed. (vii) The double bond conversion rate of both the MOF-801 1 wt%-CB 15 wt%/UV-WPUA coating and the CB 15 wt%/UV-WPUA coating was 70%, with more complete curing and superior thermal stability.

The synthesis of UV-curable waterborne polyurethane (UV-WPUA) and MOF-801 materials was successfully achieved. The CB 15 wt%/UV-WPUA composite material exhibited a surface resistivity of 2.3×10 Ω, good dispersion, and a higher conversion rate of the double bond. The basic performance of the coating was also enhanced.MOF-801 1 wt%/CB 15 wt%/UV-WPUA composite.The surface resistance of the coating was reduced to 1.7×10 Ω, which is one order of magnitude lower than that of the CB 15 wt%/UV-WPUA coating. The composite performance is excellent and it can be applied to antistatic coatings. The surface resistance of the MOF-801 1 wt%–CB 15 wt%/UV-WPUA composite coating was found to decrease with the increase of relative humidity. Furthermore, the surface resistance of the coating was observed to be dependent on the ambient relative humidity following the addition of MOF-801.