Fabrication of UV-curable fluorosilicone coatings with impressive hydrophobicity and solvent resistance

https://doi.org/10.1016/j.porgcoat.2020.105633Get rights and content

Highlights

  • Apply UV light curing technology to the field of fluorosilicone resins.

  • Prepare PCB protective coatings with excellent solvent resistance and hydrophobicity.

  • Reveal the relationship between surface properties and chemical structures of the coatings.

  • Characterization of the thermal decomposition process of the coatings.

Abstract

Novel UV-curable methacrylate functionalized fluorosilicone resin (MAFSR) and sulfhydryl functionalized fluorosilicone resin (SFSR) were synthesized respectively. The molecular structure, UV curing process, thermal properties and surface properties were studied. Further application as protective coatings in the field of printed circuit board (PCB) was explored. Results show that the MAFSR with more than 30 wt % SFSR possess a high carbon-carbon double bonds conversion above 95 % after 15 s UV exposure. Besides, the surface energy of the coatings is as low as 11.5 mN/m, showing excellent hydrophobicity. The XPS results further reveal that the migration and orientation of the fluorine groups to the surface is an intrinsic reason for low surface energy. In addition, the coatings also demonstrate excellent heat resistance and solvent resistance. This study shows that UV-curable fluorosilicone resins are presumably promising special protective coatings for PCB.

Introduction

Silicone resins are an attractive class of tridimensional, highly branched organosilicon polymers with excellent properties [1], including impressive thermal stability and anti-weatherability, remarkable electrical insulation and hydrophobicity [[2], [3], [4], [5]]. They have been widely used in many fields, especially in electronics industry, for instance, in pressure sensitive adhesives [6], electronics packaging (e.g. LED encapsulation) [7], or thermal management solutions (e.g. thermal conductive adhesives) [8], as well as in insulating and protective coatings [9]. However, most kind of silicone resins have poor solvent resistance. The modification of silicone resins with fluorine groups provide one of valuable methods to overcome this disadvantage, which combine the good processability of silicone resins with the excellent solvent resistance of fluororesins [10]. This novel fluorosilicone resins exhibit great potential in electronics industry as special protective coatings.

Considerable research efforts have been devoted to synthetic methods of fluorosilicone resins, including the physical blending method [11], the chemical grafting method [12], and the hydrolysis-polycondensation method [13]. By contrast, the hydrolysis-polycondensation method from alkoxysilane precursors is more environmentally friendly [14], such as low solvent consumption, no organometallic catalysts requirement, and no acid wastewater discharge [15,16]. But unfortunately, the requirement of high temperature or organo-metallic catalysts in crosslinking chemistries limit the applications of fluorosilicone resins in thermo-sensitive and low permittivity fields [17], such as in the protection of PCB. UV curing technology is one of promising methods to accomplish room temperature curing of fluorosilicone resins [18].

The applications of UV curing technology in the field of silicone resins have received more and more attention due to its distinct advantages, for instance, low-energy consumption, ambient temperature operation, high efficiency, and environmentally friendly [19]. These characteristics distinguish UV curing silicone resins from traditional curing systems, and promote many new applications, such as special coatings, opto-electronic devices packaging resins and 3D printing materials [[20], [21], [22], [23]]. Therefore, most researchers focus on introducing epoxy, acrylate, methacrylate, or allyl groups into silicone resins as active points to achieve rapid curing of silicone resins at room temperature in tens of seconds [[24], [25], [26]]. This modification strategy can also be applied in the fluorosilicone resins to overcome its drawbacks in curing process. Despite UV curing technology is a promising method in the applications of fluorosilicone resins, there are relatively few studies devoted to synthesis and applications in this domain.

In this study, methacrylate functionalized fluorosilicone resins (MAFSR) and sulfhydryl functionalized fluorosilicone resin (SFSR) were synthesized respectively via hydrolysis-polycondensation method from n-propyltrimethoxysilane (MPMS), 1H,1H,2H,2H-Perfluorooctyltrimethoxysilane (POTS), 3-methacryloxypropyltrimethoxysilane (KH570), and trimethoxysilylpropanethiol (KH590). The effects of hexamethyldisilazane (HMDS) on the residual silicon hydroxyl groups in fluorosilicone resins were investigated. The UV curing process and conversion ratio of Cdouble bondC bonds were studied. The thermostability and thermal decomposition process, surface energy, hydrophobic and oleophobic mechanism were discussed. Furthermore, acid, alkali and solvent resistance in the application of PCB protection were also preliminarily explored. The synthesis routes of UV curing fluorosilicone resins and their applications in PCB protection were shown in Fig. 1.

Section snippets

Materials

N-Propyltrimethoxysilane (MPMS), 1H,1H,2H,2H-Perfluorooctyltrimethoxysilane (POTS), 3-methacryloxypropyltrimethoxysilane (KH570), trimethoxysilylpropanethiol (KH590), hexamethyldisilazane (HMDS) were obtained from Qufu Chenguang Chemical Co., Ltd. (China). Absolute ethyl alcohol, n-heptane, p-hydroxyanisole (MEHQ) and diiodomethane were obtained from Aladdin Reagent Shanghai Co., Ltd. (China). Concentrated hydrochloric acid (38 wt %) was supplied by Yongfeng Chemical Reagent Jiangsu Co., Ltd.

Synthesis and structural characterization of MAFSR and SFSR

MAFSR and SFSR were synthesized respectively via hydrolysis-polycondensation method from alkoxy silane precursors including POTS, MPMS, KH570 and KH590 (shown in Fig. 1). However, large amount of silanol groups reserved in MAFSR and SFSR were harmful for surface properties of the UV curing coatings. Thus, HMDS was applied in the end of the synthetic process to eliminate the unreacted silanol groups [30]. The molecular structure of MAFSR and SFSR were confirmed by FTIR and 1H NMR. The molecular

Conclusion

In summary, we have synthesized the UV-curable fluorosilicone resins with methacryloxy groups (MAFSR) and sulfhydryl groups (SFSR) respectively, and then prepared UV-curable fluorosilicone coatings to research the relationship between formulation, structure and performance. Moreover, we have started initial research of these coatings for the protection of PCB. Results show that the addition of SFSR can observably increase the conversion of the double bonds in MAFSR and reduce the oxygen

CRediT authorship contribution statement

Xiaoqiang Zheng: Conceptualization, Methodology, Investigation, Writing - original draft, Writing - review & editing. Ai-min Pang: Resources, Project administration, Funding acquisition. Yu Wang: Writing - original draft. Wei Wang: Investigation. Yongping Bai: Conceptualization, Supervision, Project administration.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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