环境友好型达克罗处理技术的现状及研究进展

Present Situation and Research Progress of Environment-friendly Dacromet Treatment Technology

达克罗涂层的无氢脆、耐高温、强耐腐蚀性、附着力良好、高渗透性和强涂覆能力等特点使其近年来广泛用于汽车、家用电器、建筑、石油化工等领域。然而该涂层中的Cr^(6+)由于具有较强的致癌、致畸、致突变作用而受到限制,且其硬度仅有1~2H,抗划伤能力差,耐磨性低,因此使用该图层的工件不适用于硬度和耐磨性要求高的场合。本文先介绍了达克罗涂液的主要组成成分(金属粉末、溶剂、铬酸盐钝化剂和特殊有机物)及铬酸盐在达克罗涂层中的作用(钝化作用、黏结作用和自愈作用);接着从环境友好型达克罗防腐涂层的成膜物质-铬酸盐替代物(无铬钝化剂-含氧酸盐及氧化物、稀土盐和有机黏结剂-硅烷偶联剂、硅烷偶联剂+缓蚀剂、树脂+缓蚀剂)的选取、无铬钝化液的配方优化、纳米微粒增强达克罗涂层三方面分别综述了国内外关于提高环境友好型达克罗涂层的硬度和耐蚀性,指出了各种成膜物质的不足并指出进一步的研究方向;最后简要介绍了稀土改性达克罗处理技术的防腐蚀机理,对环境友好型达克罗涂层研究中存在的问题进行了归纳,并对其发展方向进行了展望。在总结与分析的基础上可知,随着环境保护要求的提高,开发由有机聚合物(硅烷或树脂)和稀土盐组成的具有钝化和自愈作用的复合成膜系统,以及纳米粒子将具有很大的发展潜力。

Dacromet coating is widely used in automobile,home appliance,architecture and petrochemical industry because of its non-hydrogen embrittlement,high temperature resistance,strong corrosion resistance,good adhesion,high permeability and strong coating ability.However,the Cr6+ content in the dacromet coating is limited due to its strong carcinogenic,teratogenic and mutagenic effects,and the hardness of dacromet coating is only 1H ~ 2H,the scratch resistance is poor,and the wear resistance is low.Therefore,the workpiece with such a coating is not suitable in the situation requiring high hardness and wear resistance.Under this background,the chromium-free dacromet technology is put forward.Chromium-free Zn/Al coating has become the trend of development.However,without chromate,the coating will lose self-repair capabilities,so the corrosion resistance is to be further improved.In addition,the hardness and wear resistance of chromium-free dacromet coating is not high enough,which limits the use of the coating.The chromium-free dacromet technology solves the pollution problem well,but the hardness and wear resistance of the coating are low,so the coating is easy to scratch.It is not possible to use chromium-free dacromet technology for workpieces requiring wear resistance.The workpiece is often scratched and worn during transportation,assembly and use.At the same time,the corrosion resistance of dacromet coating is also weakened in the high salt spray and high humidity environment,which affects the corrosion resistance of coating and the appearance of products.Therefore,it is urgent to improve the hardness and corrosion resistance of the coating by adding reinforcing phase to the non-chromium dacromet coating.In this work,the main components of dacromet coating solution(metal powders,solvents,chromate passivators and special organic compounds) and the effect of chromate(passivation,adhesion and self-healing) in dacromet coating were introduced.Then,the selection of chromate substitutes(non-chromate passivating agent-oxygen-containing salts and oxides,rare earth salts and organic binders-silane coupling agent,silane coupling agent + corrosion inhibitor,resin + corrosion inhibitor),and the formulation optimization of non-chromate passivating solution and nano-particle reinforced dacromet coatings were reviewed to improve the hardness and corrosion resistance of environment-friendly dacromet coatings in China and abroad.At present,there are many reinforcing phases including oxylate and oxide,rare earth salt,silane coupling agent,silane coupling agent + corrosion inhibitor,resin + corrosion inhibitor,which can improve the corrosion resistance of the coating.However,the research on nano-particles is limited.In the previous research,nano-particles can improve the hardness and wear resistance of coatings,but nano-ions have little effect on the corrosion resistance of coatings.Finally,the anti-corrosion mechanism of rare earth modified dacromet treatment technology is briefly introduced,the existing problems in the research of environment-friendly dacromet coatings are summarized,and the development trend of the dacromet coatings is prospected.On the basis of summary and analysis,it is pointed out that with the improvement of environmental protection requirements,the development of composite film-forming systems consisting of organic polymers(silane or resin) and rare earth salts with passivation and self-healing effects and nanoparticles will have great potential.