Why can't paper mills do without calcium carbonate

Walking into any paper mill, you will see something piled up more than pulp - white stone powder. It is not an auxiliary material, but one of the main raw materials in the papermaking formula. It is calcium carbonate stone, also known as small square calcite in the industry. Why do paper mills need it and can they do without it?

One sentence, first come to the conclusion

Without calcium carbonate, paper will become more expensive, yellow, and worse, and the printing effect will be greatly reduced.

It is one of the three basic raw materials for papermaking (fiber, water, filler), not optional, but mandatory.

Calcium carbonate plays two roles in papermaking

The first item: as a filler, mixed into the pulp. Grinding calcium carbonate into powder and mixing it into pulp in a certain proportion. Pulp is made of fibers, and pure fiber papermaking has three problems: high cost, insufficient whiteness of paper, and transparent printing.

The cost comes down directly -341 tons of fiber, several hundred yuan per ton of calcium carbonate, filled in 15% -20%, saving a lot of cost per ton of paper raw materials

Whiter paper - Calcium carbonate itself has a higher whiteness, which increases the whiteness of the paper and improves its appearance

Printing opaque characters - increase opacity, double-sided printing does not interfere with each other, and the quality is fully enhanced

More uniform ink absorption - ink is distributed more evenly on paper, resulting in cleaner printing effects

The second step is to apply the pigment onto the paper surface. Why is copperplate paper slippery and shiny? Because the surface is coated with a layer of calcium carbonate coating.

After coating: the paper surface is smoother and more delicate

Better gloss

Printing colors are more vibrant and layers are clearer

Why is it just a small square puzzle stone?

There are two types of calcium carbonate used in papermaking: heavy (ground natural ore) and light (chemically synthesized).

The raw material for heavy calcium carbonate is small square calcite, which is directly ground from natural ore. It has low cost, high output, and simple process, and is the preferred raw material for the vast majority of paper mills.

What are the advantages of using small square stones to solve problems

·High whiteness: High quality mineral whiteness can reach over 90, resulting in paper white without the need for additional bleaching

·Less impurities: Iron, manganese and other components that affect whiteness are low, resulting in more stable paper quality

·Good particle size adjustment: 400 mesh, 800 mesh, 1250 mesh can be made, coarse mesh is used for fillers, fine mesh is used for coatings, and one set of mineral covers multiple paper types

·Suitable for neutral papermaking: Nowadays, papermaking mostly adopts neutral/alkaline processes, and calcium carbonate is the standard filler. The paper has a longer lifespan (can be stored for decades without yellowing), and equipment corrosion is also smaller

That's why the industry says that papermaking may not have many things, but it cannot do without calcium carbonate.