Prevention of Curling

The ink is usually ejected to print on one surface of the recording medium during printing in the inlqet recording apparatus. Since the recording medium is shrunk only on its printed surface, it is presumed that a difference in shrinkage factor is caused between the printed surface and the non-printed surface, whereby the recording medium curls (56). 

Another conventional technique uses a colorless reaction solution instead of a salt in an ink. There, the ink consists of a colorant having an opposite charge to that of a salt used in the colorless reaction solution. Ion pairing is induced on the surface of paper during printing so as to cause an agglomeration phenomenon. The colorless reaction solution used in this case may include a polyvalent salt or a cationic pol uner. 

In these techniques, due to the fast reaction between the ink and a reaction solution having different ionic groups, many ink residues remain on the surface of paper, which leads to the formation of high resolution and high-quality images (58). 

However, since ink is in a liquid state due to the inherent characteristics of inlqet printing, the printing paper curls due to the moisture present in the ink after image printing. So a curling phenomenon occurs. A reaction solution including a polyvalent metal salt and a cationic polymer alone may not prevent such a paper curling. 

A special coating solution has been developed that includes a nonionic polymer, a monovalent metal salt and a water-soluble organic solvent (58). 

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