Ink type and influence of deinking method

Many papers or processed papers are used after different printing, such as newspapers, magazine papers, photocopying papers, and the like. Therefore, the type and characteristics of the ink and the printing method all have a great influence on the disposal process of the waste paper, especially on the flotation deinking operation. This is described separately as follows.

First, the type and characteristics of ink

A wide variety of inks can be classified in various ways such as printing method, drying method, ink characteristics, ink composition, and use.

1. Water based ink Aniline flexo printing water based inks are water soluble liquids and are commonly used in newspaper printing. They have a density of 0.96-1.0 g/cm2, a viscosity (before dilution) of 15 Pa·s, and a boiling point of 100-110°C. Its chemical composition is shown in Table 1.
Table 1 Chemical composition of aniline relief printing water-based inks w/%
Water 40-60
Resin Polymer 15-30
Pigments 10-25
Amine Compound <5
Glycol ether 4-8
It can be seen from Table 1 that the water content in the water-based ink is about half.
When the water-based ink is heated to 100-150°C, the weight loss reaches 30%-40%. Mass spectrometry analysis shows that this system does not bind water. When the temperature continues to rise to 400-500°C, the weight loss reaches 32%. Mass spectrometry analysis proves that this is a decomposition of polystyrene. The product, which is hydrophobic; when the temperature continues to rise to 690-760°C, the weight loss is about 15%, and the phosphotungstic acid tungstate pigment is proved by mass spectrometry analysis.

Since most newspaper printing has been changed to color offset printing, the ink used has gradually shifted to oil based offset cold/offset heat inks.

2. Oil-based offset cold and offset thermosetting inks

The chemical composition of offset and offset thermoset inks is very similar and consists of vegetable or mineral oils, pigments, and resins. They are liquid at room temperature, have a density of about 0.96-1.1 g/cm2, and a viscosity of 15-25 Pa.s. However, due to the type and amount of oil used, such as offset printing cold-set inks often contain w=60% vegetable oil (soybean oil), while offset thermosetting inks often contain w=35% to 45% of mineral oil (deodorizing etc. Distill oil) so their pyrolytic properties are different. For example, the anti-counterfeiting temperature of offset thermosetting inks is larger, about 230-370°C, while the boiling point of offset cold-set inks is 270-315°C. In nitrogen atmosphere, offset cold-setting inks are from 80°C to 320°C. The weight loss of the product (wax and dry oil) was 18%. Mass spectrometry analysis of the evaporant proved that it was mainly saturated hydrocarbon. When the temperature was increased from 320°C to 500°C, the vegetable oil in the ink was quickly isolated and the weight loss was about 60%. When the temperature is further increased from 550°C to 600°C, the binder resin in the ink is decomposed and the weight loss is about 5%. Offset thermosetting inks contain more w=45% low-boiling saturated oils. They decompose when heated from 60°C to 260°C to form hydrocarbons. When the temperature is raised from 350°C to 500°C, the ink has a mass fraction of 35. % of thermoset resin is further decomposed.

3, photocopying and laser printing ink

Photolithographic and laser printing inks (ie, toners, or pigments) are dry black powders having densities of 1.21 g/cm<3> and 1.48 g/cm<3> respectively and an average particle size of about 15 [mu]m and 25 [mu]m, respectively.

Similar chemical composition, with styrene-acrylate copolymer as its linking agent, mass fraction of 60% to 90%. The main difference between them is that the laser printing toner contains w = 35% of iron oxide as the pigment, and the photocopying toner contains w = 12% of carbon black as the pigment. See Table 2 for details.
Table 2 Chemical composition of photocopies and laser printing ink w/%
Chemical Composition Photocopy Laser Printing Acrylic Styrene Carbon Black Iron Oxide 1
Amorphous silica stearate 85～90
10 to 15
-
<1
<1 60 to 70
-
30~40
-
-

Note 1: Some photocopying inks also use iron oxide as a pigment. Since pyrolysis of carbon black and iron oxide does not decompose, the pyrolysis curves of photolithographic and laser printing inks are very similar. They all have a single temperature between 350 and 460°C. The decomposition peaks of the decomposed products are considered to be the same by mass spectrometry, and are both dimers and trimers and acrylates of styrene, α-methylstyrene, base, methyl acrylate, benzene, acrylic acid, and styrene. The printed toner also has about w=20% residues after decomposition. The decomposition temperature of photoprinting and laser printing toners is lower than the decomposition temperature of pure polystyrene, which may be due to pigments and metal additives in the toner.
Although the types of inks are numerous, it has been found that the main product after the ink is decomposed is non-extractable compounds such as hydrocarbons. Therefore, these inks are originally hydrophobic, ie they have a larger contact angle (>80°) for water, see Table 3. The larger the contact angle, the greater the hydrophobicity and the more favorable it is to be floated from the fiber suspension.
Table 3 Contact angle materials for some inks Contact Angle/°
Non-printed newsprint oil based black ink New aniline letterpress printing ink New laser printing ink 0.0
81.2
93.0
91.5

These hydrophobic inks are easily separated from hydrophilic cellulose fibers during flotation.