In order to reduce the transparency of the paper, it is usually necessary to add a moderate amount of filler to the paper. Because fillers have smaller particles, higher hardness, better optical properties than fibers, and cannot form hydrogen bonds compared to fibers, these can affect the properties of the paper. Let's take a look at the various effects of packing on paper performance today.

1. Increase the paper's opacity

The addition of filler particles changes the interface between fibers and air established by the original plant fibers. The number of interfaces between fibers and air, filler particles and air, fibers and filler particles increases, and multi-layer refraction increases the paper opacity.

The filler particles are small, have a large specific surface area, and have a large refractive index, increase the scattering coefficient (ie, diffusion) of the paper, and increase the opacity of the paper. The improvement of opacity is related to the type of filler particles (refractive index), particle size, and particle shape. The effect of increasing the refractive index to increase the opacity is good, the effect of small particles is better than that of large particles, and the shape of the particles is mostly spherical.

As the proportion of filler in the paper increases, the opacity of the paper rapidly increases and then gradually stabilizes; that is, the opacity does not increase any more by increasing the fill rate.

2. Effect of Filler Addition on Paper Brightness

When the type of pulp and filler is constant, when the degree of beating of the pulp is low, the brightness of the paper is decreased when the pulp is beaten. When the degree of beating of the pulp is high, the filling of the paper increases the brightness of the paper, which may be related to the fact that beating changes the binding or distribution state of the plant fibers and filler particles.

When the brightness of the filler is higher than the brightness of the pulp, when the brightness of the pulp is low, the brightness of the paper is increased (larger); when the brightness of the pulp is high, the brightness of the paper is less improved. When the brightness of the filler is lower than the brightness of the pulp, when the brightness of the pulp is low, the brightness of the paper is reduced less when the filling is performed. When the brightness of the pulp is high, the brightness of the paper is slightly higher.

3. Effect of Filler on Paper Surface Smoothness and Printing Performance

The addition of fillers generally improves the smoothness of the paper after calendering. Under the influence of the calendering rollers, finer particles tend to redirect and fill the voids of the fibers, making the paper surface smoother. After filling, the paper is denser and has better shape stability. The smooth and dense surface of the paper makes the graphics more clearly printed, and the better absorption of the ink by the filler makes the printing better.

Due to overfilling or other improper operations causing the paper to fall out of powder, it will have an adverse effect on printing, which should be taken into account in production.

4. Effect of Filler on Paper Strength

The filler particles occupy the fiber voids and fiber spaces, hindering the binding between the plant fibers and the fibers, and decreasing their strength. When the loading amount is relatively small, the impact on the tensile strength, breaking strength, and bending strength is less; when the filler amount is increased, the tensile strength, breaking strength, and bending strength are greatly reduced.

Adding small amounts of filler will increase the bulk of the paper; at high levels, most paper will lose bulk.