The basic composition of magnetic ink

The basic composition of the magnetic ink is the same as the general ink, that is, it is composed of a pigment, a binder, a filler and an auxiliary material.

1, pigment

The pigments used in magnetic inks are not ordinary pigments, but are ferromagnetic materials that have the ability to retain magnetic properties after magnetic field treatment. The main components in the magnetic ink are magnetic pigments, and the best magnetic pigments are iron oxide black (Fe3O4) and iron oxide brown (Fe2O3). Most of these pigments are needle-shaped crystals smaller than 1 μm, and the size and shape of these particles make them extremely easy to align in the magnetic field, resulting in relatively high residual magnetism.

The ferromagnetic materials used for magnetic ink pigments mainly include magnetic elements such as iron (Fe), cobalt (Co), and nickel (Ni), alloys containing Fe-Mo and Fe-W ferromagnetic elements, and Mn-Al and Mn Alloys such as Ni-type crystal structures such as Bi. Most magnetic ink pigments are ferrite. Ferrite refers to an inorganic compound generally represented by XO-Fe2O3, wherein X is a divalent metal ion, and there are manganese-ferrite, iron-ferrite, copper-ferrite, etc. depending on the type of X. .

In the composition of iron oxide black, the content of ferrous oxide is generally between 18% and 26%, and the content of iron oxide is between 74% and 82%. Synthetic iron oxide black has excellent impermeability, chemical resistance (acid, antimony), light resistance, is almost non-toxic, and the dispersibility is between good and excellent. The heat resistance is better. Only when the temperature exceeds 177°C, the iron oxide black will be oxidized to red iron oxide. The iron oxide black has better particle consistency, and after diluting it has a clean blue-gray hue. Iron oxide black is generally a sexual reaction, and their particle shape is generally cubic or spherical.

2, the connection material

The fluidity, stickiness, dryness, and printability of the ink are all determined by the binder. The binder is part of the fluid in the ink. The magnetic ink binder is also the basis for the quality of the ink. The link material of the magnetic ink is similar to the link material of the general ink, and vegetable oil, animal oil, and mineral oil can be used, but more synthetic resin is used as the link material of the magnetic ink.

The basic chemical composition of vegetable oils is a mixture of glycerides of fatty acids, or triglycerides. All oils and fats can be regarded as the product of the reaction of various fatty acids and glycerol. If the grease is thinly spread on the glass, after a certain period of time, the thin oil film will gradually become thicker and more elastic due to the absorption of oxygen from the air, and finally form a solid state. This is the drying process of grease. The shorter this process, the better the oil's dryness. The dryness of grease depends on the number and location of unsaturated double bonds in the grease structure. The iodine value can be used to determine the degree of unsaturation of the oil. In general, the iodine value is between 140 and 200 dry oil, between 100 and 140 semi-dry oil, and less than 100 is dry oil. It can be seen that the more unsaturated double bonds, the better the dryness. In other words, the more unsaturated fatty acids, the better the dryness.

The use of synthetic resins in the ink industry is becoming more and more widespread, so various types of resin-based binders have become the main research content. The properties of the resin determine the properties of the binder. The main drawback of pure linseed vegetable oil type linking material is its relatively low molecular weight, so the produced ink is liable to cause emulsification in offset printing, which brings a series of ills, so that the printing cannot be performed smoothly, and the printing effect is not good. . The resin-based binder almost completely overcomes this defect, which greatly improves the quality of printing.

When the alkyd resin is used in a paste ink, a resin plasticizer may be considered. Because of its good adhesion and flexibility, the dryness and solidification time of the ink may also be adjusted. When an alkyd resin is used in an oil type ink, its reactivity with the pigment, the reactivity with the hard resin, and its film forming property should generally be considered. The wettability of the isocyanate alkyd resin is even more pronounced. When inks are formulated with linking materials made of alkyd resins and hard resins, attention should be paid to the pigments used. If the pigments absorb excessively low-molecular-weight binders, the balance of hard resins and alkyd resins in the binder should be taken into consideration.

General paste inks use mostly long oil (65%) alkyds. Oily long oils are also generally more soluble, so they are also widely used in screen (mesh) inks. This type of resin has good color retention when used in iron inks, has good light, and has excellent adhesion.

In order to achieve fast drying and bright light, the content of the resin in the magnetic ink is higher and the solid speed is faster, so that more of the binder is left on the surface, and the binder is required to have better water resistance and lubricity of the pigment. Filler can also reduce the amount of pigment in the magnetic ink, reduce the cost, but also can adjust the properties of the ink, such as thick, fluidity, etc., also improves the flexibility of formula design, and the additive in the magnetic ink can be pigment The additional part of the linking material can also be used as an additional part of the finished ink, depending on the characteristics of the product.