Deinkability of toner prints

Dry toner printing processes have their widest use in laser printers and copiers. There are different ways to create the latent image but without significant influence on deinkability. These electrophotographic processes commonly use powdered toners with a particle size of typically 5 µm to 10 microns.^1,2 Most toners contain the general components listed in Table 1.³

Table 1. Toner components ³

Component material		Function
Colourant	Pigment or dye	Colour
Base binder resin	Blend of monomers: styrene acrylates, polyesters, epoxy-type resins	Fusing of toner particles
Modifier resin	Natural material: abietic acid, resin, wax	Enhance strength of toner/paper interface
Charge control agents	Quaternary ammonium salts, sulfonates, zinc complexes	Provide toner particle with electrostatic charge necessary for development

After printing, fixation and repulping, the dry toner particle sizes range from 25 µm to 250 µm.⁴ Their prints are usually well deinkable. The left part of Figure 1 shows that with one exception all other dry toner prints achieve the deinkability assessment “good”. The exception is a print with an unusual combination of toner and substrate.

High quality, high resolution print jobs sometimes use a liquid electrophotographic process. The technical advantage of this process is that the particle size of the toner is only about 1 µm.¹ After printing, the toner films are very cohesive and flexible; they are not sufficiently during pulping. A significant proportion of the particles are above 500 µm. Therefore, because of the very high content of dirt particles in the deinked pulp, typically the samples of liquid toner prints fail to reach a positive deinkability score. There are so many toner particles left in the deinked pulp that in two cases even the ink elimination receives a negative assessment. But two liquid toner prints received a positive deinkability result. They belonged to a test series of 9 samples on different paper grades. The two papers with positive Deinkability Score were woodfree uncoated papers. The investigations will be continued.

In the Deinkability Scores the negative scores are limited to the same absolute values as the positive scores. Therefore, the difference in dirt speck area between dry and liquid toner prints is not as prominent as implied by the raw data. Figure 2 shows the large, visible dirt specks above 250 µm particle size in deinked pulp from toner prints. Common dry toner prints have a dirt speck area in this size class between near zero until close to the threshold of 600 mm²/m² with an average of 72 mm²/m². Only one deinked pulp sample of liquid toner prints was below the threshold. Most of the samples were in a range between 15 000 and 20 000 mm²/m². For particles above 250 µm circle equivalent diameter in deinked pulp from liquid toner prints the average dirt particle area was 10.805 mm²/m², 18 times above the threshold.

Source https://forestbiofacts.com/