The use of EB ink characteristics and applications

Electron beam curing ink (EB ink) is an ink that can rapidly change from a liquid to a solid state under the irradiation of a high-energy electron beam. It is a new environmentally-friendly ink. The main advantage of EB ink is that it does not pollute the environment. Its components also do not contain harmful organic volatile substances. It has low operating costs, high production efficiency, low energy consumption, stable printing quality, good reproducibility, and high print glossiness. Feeling strong.

1. Composition of EB ink

The composition of EB ink is similar to that of general ink, and is mainly composed of pigments, binders, auxiliary agents and the like.

Pigments are the color materials of inks. The quality of the ink determines the quality of the ink. The following principles should be observed in the selection of pigments: 1) Since it is mainly used for food packaging, the selection of pigments must first be non-toxic. 2) In addition, since the ink is dried using a high-energy electron beam, the color of the pigment should not change under the electron beam irradiation. 3) The pigment concentration should be high and the color should be bright. It must have excellent dispersion and sufficient coloring power. 4) The ink cannot be gelled within the effective storage period after the pigments are mixed. 5) When the pigments are used together, the amount of each pigment in the ink must be accurate.

In the selection of binders, EB inks have special requirements. The main components are acrylic resins and reactive monomers involved in the reaction.
The properties of the prepolymer (low molecular weight polymer containing unsaturated functional groups) used in the EB ink determine the physical properties of the ink after curing, such as abrasion resistance, adhesion, elasticity, hardness, chemical resistance, solvent resistance, and The color difference of pigments and other properties. Inks prepared from different prepolymers exhibit different physical properties. The prepolymer used in the EB ink is generally an acrylic oligomer with good fluidity. Common prepolymers include epoxy acrylic resins, polyester acrylic resins, acrylic polyurethanes, chlorinated polyester acrylic resins, and the like.

Reactive diluent monomer is used in the EB ink vehicle. The role of the reactive diluent in the ink is: 1) to adjust the viscosity of the high viscosity prepolymer. 2) Adjust the ink adhesion. 3) Strengthen the ink film strength. 4) Accelerate curing speed. There are many types of reactive diluent monomers. In general, reactive diluents can be divided into three categories: monofunctional, bifunctional, and multifunctional reactive diluents. In actual production, EB inks generally use a variety of monomer combinations have been able to obtain satisfactory curing speed, viscosity, adhesion, elasticity, hardness, impact strength, solvent resistance and other properties.

2. Curing mechanism

The curing mechanism of EB inks is basically similar to that of UV inks, except that EB inks do not require photoinitiators. The specific drying mechanism can be described as follows: Acrylic resins have a high degree of unsaturation. When they are exposed to high-energy electron beams, the molecules change from the ground state to the excited state, and unsaturated double bonds are opened to generate free radicals or ions. Then, by the initiation of the free radicals, a growing polymerization reaction of the chain occurs, crosslinking polymerization occurs between the oligomer and the monomer molecules, a network-like polymer is formed, and the ink rapidly cures the conjunctiva. Throughout the drying process, the role of electron radiation is like a special initiator. Its main role is in the initiation phase of the chain. Once the polymerization begins, the reaction is normal to the polymerization reaction as the reaction of each step is independent of the radiation. Learn the law. The whole process can be completed instantaneously under the irradiation of the electron beam, so the drying speed of the EB ink is particularly fast, and curing is usually completed in 1/200 second.

3. The advantages of EB ink

From the above curing mechanism, it can be known that the EB ink has many advantages over the general ink, specifically in five aspects.

1) Environmental protection and safety. From the EB ink composition point of view, EB ink does not contain harmful organic volatiles, its components do not contain solvents, no pollution to the environment, packaging, print odor smaller than the use of UV inks. Since the ink does not contain VOCs, the damage to workers is minimal. At present, the application of EB ink in food packaging and printing is very promising.

2) Fast curing speed and good curing quality. EB ink curing in the electron beam only takes 1/200 seconds, which is much faster than the UV ink curing speed. This makes it possible to perform on-line operations such as printing, coating, and compounding, which can greatly increase production efficiency. Moreover, the electron beam has a strong penetrating ability and can penetrate the ink layer to completely cure the ink. In addition, the abrasion resistance and chemical resistance of the ink film are also better and the emitted odor is small.

3) Curing produces less heat. Electron beam machining is a cold process that generates less heat than the UV ink cures. In particular, printing on a substrate such as a heat-sensitive film or the like, excessive heat causes the substrate to be deformed during the printing process, resulting in deterioration of print quality and occurrence of print failure. Therefore, EB ink is better than UV ink in this respect, and electron beam has no negative effect on the plastic film substrate. This provides a broad space for its application in the field of flexible packaging printing.

4) Easy to store. The EB ink does not need to insulate the air during storage, unlike ordinary inks. Ordinary ink is the surface crust, and the dark reaction of EB ink occurs first at the bottom of the ink tank and slowly solidifies from the bottom. Once the bottom has cured, the entire tank of ink loses its value. The shelf life of general EB ink is 1 year.

5) Can be converted into UV ink. From the viewpoint of the composition of the EB ink mentioned above, the EB ink is basically similar in composition to the UV ink. Only UV inks require a photoinitiator to initiate. This is because the energy of the ultraviolet rays is lower than that of the electron beam. If a certain amount of photoinitiator is added to the EB ink, UV curing can be performed.

4. Use of EB ink

Although EB ink has many advantages, there are also deficiencies. For example, EB ink printing still requires inactive gas printing, or the curing effect is poor, and the ink layer is sticky and yellow. Therefore, in order to better play its advantages, the following points should be noted during use.

1) The use of EB inks requires a relatively high level of curing equipment. Although electron beam curing requires only one ion cathode tube (installed after the last color unit), the active gas content in the curing chamber must be strictly controlled. Oxygen in the air will inhibit the activity of free radicals in the ink layer, which is not conducive to the chain-growth polymerization reaction. Therefore, the curing chamber is usually filled with nitrogen to ensure that the oxygen content in the curing chamber is lower than a certain amount.

2) EB inks require high control over the viscosity and adhesion of inks. Due to the high-speed multi-color printing, the ink is superposed in a wet and wet state. Therefore, in order to allow the ink to be superimposed smoothly and to avoid the occurrence of color mixing, the viscosity of the ink in the actual printing operation is reduced according to the printing color sequence, but the difference in viscosity between the two color sequences cannot be too different. Can affect the ink transfer performance and transfer ink volume. EB inks also require lower viscosity in turn. However, compared with common inks, the difference is that there is a significant gap between their differences, otherwise a series of failures will occur.

3) EB inks have certain requirements on the pH and conductivity of the wetting fluid during use. It is generally considered that the pH is controlled between 3.8 and 4.1, and the conductivity is controlled between 1000 and 2800s/m.

4) EB ink cleaning. The EB ink should be cleaned with a special cleaning solution, usually a mixture of solvents such as isopropyl alcohol and n-heptane. EB inks have certain erosion effects on rubber sticks and blankets. Therefore, corresponding rubber sticks and blankets should be used.

5. Analysis of market prospects

EB ink is favored by users because of its advantages of no volatile solvent, no VOC, little harm to operator's health, small odor, no need of photoinitiator, online direct drying and online operation. Compared to UV inks, EB inks do not require photoinitiators, cure faster, cure more completely, and have a smaller odor, which further increases the development space of EB inks, so EB inks along with EB ink raw materials and The price reduction of the supporting equipment and the further maturation of the design formula will become practical and economical inks that can be vigorously promoted. EB inks are now growing in flexible packaging. The superior performance and high production efficiency of EB inks provide it with a broader market. It is believed that the scope of EB ink application will be further expanded and become an important new type of environmentally friendly ink in the future.

Source: Xinhua Printing Network