Why is calcium carbonate added to paper?

Calcium carbonate is used as a less expensive filler and coating pigment used in alkaline paper manufacturing. It acts as a brightener since it is very white (and less expensive than titanium dioxide). Titanium dioxide is a white pigment used in ink and paint bases. Calcium carbonate is water soluble and can dissolve into the dampening solution, interfering with the acids and gum resulting in the image areas of the plate and ink rollers becoming hydrophilic (attracts water). Calcium and gum bonding to the image area of the plate and repelling ink causes plate blinding. Fountain solution adhering to the ink rollers will cause ink emulsification and roller stripping. Paper sizing must be water resistant and the printer needs to run a minimum of fountain solution to keep the calcium from dissolving.

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