| Because of the advantages of energy-saving,environmental protection,economic performance,high efficiency and wide adaptability,photocurable coating have been widely used in the fields of wood,paper,plastic and printing.However,in the field of metal-based substrates(such as metal coils),the application of photocurable coatings is limited due to the poor adhesion and the poor corrosion resistance between photocurable coating and metal substrates.Among a varities of resins,bisphenol A type epoxy resin is characteristic of low cost,stable synthesis process,excellent performance and wide application.Thus,it is of great economic significance to study the modification of bisphenol A type epoxy resin to synthesize photocurable resin and apply it to metal substrates.In this paper,bisphenol A type epoxy resin(E51)was used as the main resin and a variety of diacids were used to modify epoxy resin to synthesize a series of modified UV curable epoxy acrylate resin,and this paper will explore the application of the resin in UV metallic coatings.In the first part of this paper,the investigation was carried out on the influence of different main chain structure on the properties of epoxy acrylate resin.The bisphenol A epoxy resin(E51)was expanded by diacid(succinic acid,adipic acid,octanic acid,sebacic acid)with four different alkane chain lengths,and then four modified epoxy acrylates with different alkane chain lengths on the main chan were synthesized by using acrylic acid as epoxy group capping agent.The modified epoxy acrylate resin were characterized by proton nuclear magnetic resonance spectroscopy,Fourier Infrared spectroscopy and gel permeation chromatograph,and it is used as the main resin to build UV curing coating.Water contact angle,water absorption test,basic coating performance test,dynamic mechanical analysis,electrochemical impedance test and salt spray test were performed to investigate water resistance,mechanical properties,film properties and corrosin resistance.The results showed that with the increase of the alkane chain length in the main chain of the modified epoxy acrylate,the water resistance,adhesion and flexibility of the UV curable coating are improved,and the corrosion resistance of the coating is also improved.However,when the alkane chain length is too long,the crosslinking density and hardness of the cured coating decreased,and the corrosion resistance of the coating will be reduced.The energy storage modulus and glass transition temperature(Tg)of the cured coatings decreased with the increase of alkane chain length.The second part of this paper explores the influence of different side chain structures on the properties of epoxy acrylate resin.The modified epoxy acrylates with different side groups were synthesized by the mercaptosuccinic acid(MSA)and acrylates through the reaction of thiol-Michael addition.The diacid with different structures and modified epoxy acrylate were characterized by ~1H NMR and Fourier transform infrared spectroscopy.The viscosity of the modified resin was tested by rotating rheometer.The photocurable coating was constructed by using modified epoxy acrylate with different side chain structure as the main resin.The water resistance,mechanical properties and corrosion resistance of the coating were investigated by basic property test,tensile test,dynamic mechanical analysis,water absorption test and electrochemical impedance test.The results showed that:(1)The viscosity of the modified resin increased with the introduction of benzene ring structure,glass transition temperature and tensile modulus of the photocurable film increased,elongation at break decreased,surface hardness of the photocurable coating increased,adhesion and water absorption of the coating decreased,and corrosion resistance increased.(2)With the increase of branching degree(n-butyl,isobutyl,tert-butyl)of the resin side chain structure,the tensile modulus of the photocurable film increased,elongation at break decreased,and water absorption and corrosion resistance of the photocurable film increased.(3)Compared with the aliphatic ring structure,when the side chain structure of the resin was a straight chain,the water absorption and adhesion of the photocurable film increased,while the electrochemical impedance performance decreased,which may be due to the decrease of the crosslinking density of the film.Due to the fast curing rate of the photocurable coating,the large shrinkage stress between the coating and the metal interface in the curing process leads to the poor adhesion of the coating to the metal substrate.However,the UV/thermal dual curing can integrate the advantages of the photocurable and thermal curing,so that the coating has excellent adhesion and surface hardness.So in the third part of this paper,a kind of UV/thermal dual curing epoxy resin(E51-IA)was synthesized by reacting the itaconic acid(IA)and bisphenol A type epoxy resin(E51)through one-step synthesis.In order to solve the shortcoming of fast curing rate,large shrinkage stress and poor adhesion in the process of photocuring,the coating prepared with this resin forms pre-curing film through photocuring first,and then achieves complete curing degree through thermal curing.The prepared itaconic acid modified epoxy resin(E51-IA)was characterized by gel penetration chromatography,Fourier transform infrared spectroscopy and ~1H NMR.The succinic acid(SA)without double bond was used to replace itaconic acid and synthesize succinic acid modified epoxy resin(E51)under the same conditions as the contrast reference group.The solidified samples containing E51-IA and E51-SA were characterized by means of gel content,tensile test and dynamic mechanics analysis.The results show that,after photothermal curing,the cured film containing E51-IA modified resin has higher crosslinking density,and its’Young’s modulus,storage modulus,coating hardness and adhesion are higher,thus it can be better applied to the photocurable metal coatings. |
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