Control of permeability in ‘Art’ ink-jet grades
22 January 2010
Background
The client wished to develop a variant of their fine-paper grades specifically for the high resolution inkjet 'art' market. The problem was that to increase the ink holdout they needed to close up the sheet. Increasing the refining energy would have reduced bulk and stiffness. They were unwilling to change the furnish in the well-founded belief that this would undermine the 'quality' feel and appearance of the sheet. The hydrophobicity of the sheet was well balanced between wet end and surface sizing so adding an excess of hydrophobic polymer would have caused loss of image quality. What to do?
Method
A laboratory size press and calender were used to surface treat base stock samples supplied by the mill. It was known that the application of a low percentage (2-35 dry basis) of a high-aspect ratio mineral filler at the size press reduced the permeability of the sheet. By judicious experimentation,
a combination of filler grade, starch and hydrophobic polymer was evolved, which could give holdout of the inkjet ink together with control of edge raggedness, interbleed and minimal mottle. The method also had the merit of increasing ash content and saving fibre. It did not affect the surface texture and optical properties as a continuous coating was not produced. Rather, the filler particles were deposited in the rugosity of the surface and so occluded the pores, which we termed ''stopping up the holes with rocks ©''.
Outcome
The paper maker developed a new grade on the basis of our advice, which enjoyed market success.
See Also
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