Nowadays, most of the coatings used are water-soluble or water-emulsion and other polymer materials as binders or as the main film-forming substances, where the thickeners used are water-soluble substances such as cellulose or polyacrylates, which are the objective conditions for mold reproduction. Especially in the summer, in a certain temperature and humidity environment, paint products are easy to mold, black, odor can not be used.
Graham used bisphenol A bis-2-hydroxypropyl ether as the epoxy acrylate cross-linked network segment model. After long-term UV irradiation, the photolysis products were analyzed by GC-MS and found that a large amount of acetone was produced. It is speculated that the 4′-(2-hydroxypropoxy) biphenol produced by the photolysis of the model compound of its photolysis process is easily oxidized and becomes a darker colored quinone product. Another angle explains the photo-aging yellowing behavior of the double-attached A epoxy acrylate cross-linking system. In addition, Minor conducted a photodegradation study on epoxy crosslinking system model compound 1,3-diphenoxyisopropanol [P hOCH, CH(OH) CHgO Ph] as early as the 1950s [201, found a model compound The degradation mechanism is wavelength-dependent. When irradiated by 254nm short-wave UV, it is decomposed into phenol and phenoxyacetone. The latter can be further photodegraded into phenol or Fries rearranged into acetomethylphenol. These phenol degradation products are easily oxidized into dark quinones. Structure is the main cause of yellowing. When irradiated with 280nm ultraviolet light for photolysis, the model compound is mainly cleaved to produce phenyl formate and minor phenoxyacetic acid, the latter continues to be converted into phenolic products by photolysis.
Fatty ether structure: The aliphatic ether structure in the cross-linked network is easily attacked by oxygen molecules under the cooperation of free radicals, and oxidatively decomposes into peroxides, esters, alcohols and other structures, accompanied by a decarbonylation process.
Polyurethane acrylate: The cured film of urethane acrylate is characterized by a large number of urethane bonds. During the photoaging process, the aliphatic polyurethane mainly undergoes the hydrogen loss reaction of the urethane bond N-orthogonal CH2, and is attacked by oxygen molecules, and the urethane is overoxidized. The intermediates can evolve into imide structures. The photolysis process of aromatic polyurethane is more complicated. On the one hand, light-induced Fries rearrangement occurs, sasol wax a1 generating both chromophores and aromatic ring structures that help chromophores, and the yellowness deepens [?11; on the other hand, urethanes are prone to occur. The direct photocleavage of the bond produces a quinone-imide structure, which is also an important source of yellowing. Regarding the photodegradation process of polyurethane acrylate curing system, the photodegradation of polyurethane acrylate based on MDI may be more serious than that of TDI. Since two benzene rings are connected through a methylene group, a larger total can be formed during the photoaging process. The reaction process of the degradation product of diquinoneimine with yoke structure and stronger light absorption.
Leave a message
We’ll get back to you soon