A new degreasable urethane film for temporary lubrication

摘要

A lubricative coated steel sheet having organic lubricative film on the surface has widely been in practical use to eliminate oiling and degreasing in press-forming line. Because of its excellent lubricity due to added lubricant into the film, the lubricative coated steel sheet can be deep-drawn and continuously press-formed without oiling. The lubricative film has commonly been permanent type, and it remains on the steel sheet after an alkaline degreasing process and contributes to primary corrosion protection. Meanwhile, there are some problems that the remaining film may disturb weldability or impair its appearance depending on the use of the steel sheets. Considering these circumstances, we have developed a new degreasable film for temporary lubrication that has good press-formability without oiling and at the same time can be easily degreased or delaminated in the alkaline degreasing process before painting. We focused on urethane resin and tried to design new resins to achieve good degreasability and high modulus at the high metal temperature (for example, about 130℃) to keep integrity of the steel surface even in continuous press-forming process. We have found that the key points of the resin design to achieve these performances are 1) kind and amount of a functional group to form alkaline salt, 2) optimizing of neutralizing agents, 3) resin structure. It is shown that the degreasable lubricative film composed of the designed resin and lubricants shows good press-formability without oiling, in particular anti-galling and anti-powdering properties and also good degreasability compared with conventional acrylic degreasable lubricative film.