Asia Paper Manufacturing in the Republic of Korea had an ambitious target to improve the board strength values. They invested in OptiSizer Hard. Compared to conventional sizers, it pushes starch deeper into the board web improving the overall strength values.
Recycle, recycle, recycle. It is easy to say but a bit harder to execute when it comes to board making; recycled fibers lose their quality and strength when recycled repeatedly. That was the case at Sihwa Mill of Asia Paper Manufacturing. The mill needed to lower the raw material costs without losing the strength values of their container and gypsum board grades.
To improve strength properties, Asia Paper decided to invest in a new sizer. However, more starch doesn’t directly mean more strength. Most of the starch remain ineffective when positioned wrongly in the paper. That means that by applying more starch, you might just end up wetting the sheet and wasting the starch, and thus strength improvement potential.
The key was to increase nip load with Valmet’s OptiSizer Hard. The new sizer was successfully started up in 2021 and the results are promising. “Machine directional tensile strength of back liner has increased by about 11%. Compressive strength of reinforced corrugated board has increased by about 5%. In the production of gypsum board, we do not use a separate calender. Instead, the hard nip sizer delivers similar results: smoothness has increased by 15%.”, summarizes Chang-Ho Lee, Mill Manager.
Because the size application is contactless, recirculated starch is never in contact with recycled fiber. The customer has found it very important. When asked if they have had any issues with the stickies etc. from OCC, the answer is short and simple: “None.”
Porosity is an important property in the production of gypsum board. If the board is not porous enough, water in gypsum will not be able to exit in the following production phases. According to the customer porosity values are similar before and after starch application. Size application amount is easy to control, and the porosity values do not decrease at the current application amount.