Poly(methyl methacrylate-co methacrylic acid) for UV-sensitive aqueous-base developable lithographic plate

Abstract

Syntheses of the copolymer of methyl methacrylate and methacrylic acid were carried out by free-radical polymerization, in the presence of benzoyl peroxide (BPO) as an initiator. The effects of the monomer ratio and reaction time on polymerization were investigated. Thermal properties were investigated by DSC, the Mw, Mn and polydispersity by GPC, the CHO composition by EA, and the characteristic functional groups by FT-IR and NMR. These copolymers were used as the binder of UV coating formulation. Different ratios of the copolymer were mixed with TPGDA and TMPEOTA, Darocur 1173 and Darocur BP, and anthraquinone. The photosensitive coating was coated onto the anodized aluminium substrate by spin coating, which formed a smooth film and was then overcoated by PVA solution. Plate control wedge was assembled on the plate, and exposed to UV radiation at different exposure time. The exposed plate was developed in an alkaline developer. The resulting plate was evaluated for reproduction properties at 40, 50 and 60% dot areas, resolution at microline, and wettability by contact angle between image/non-image areas, and adhesion test by a standard tape. The optimum condition for the binder preparation was 75% w/w isopropyl alcohol, 25% w/w monomer with a ratio of MMA:MAA at 80:20, 1% w/w BPO, the agitation rate was 295 rpm for the reaction temperature and time of 70 ํC and 16 hours, respectively. The copolymers were transparent and rigid like a glass and had the following properties: the glass transition temperature (Tg) 163.4 ํC; average molecular weight of 1x10x10x10x10x10x10. The plates were evaluated in terms of appropriate exposure, surface properties and adhesion tape test. The result indicates that the formulation chemistry can be used for coating of a negative working offset plate that is developable in aqueous alkaline developer. This research elucidates the effects of parameters on the product qualities