UV inkjet printing technology application (6)

1) Ink material

1 The material with low viscosity and excellent cured film properties is still small;
2 monomer irritability, toxicity, carcinogenicity and other safety issues;
3 odor and safety due to residual catalyst decomposition products and their use restrictions;
(4) The inability of the reaction to end due to oxygen inhibition causes the problem of volatilization and safety of the ink film.

2) Image quality 1100% reactive UV ink has a thick layer of ink.
2 Pixels with point pressure points are difficult to control.
3 When the solvent is contained due to the low viscosity of the ink, it is necessary to volatilize the solvent preferentially, which affects the device size, environmental measures, printing speed, and cost.

3) Image quality control when printing on non-absorbent substrates 1 In the case of non-absorbent materials, the material is very sensitive to chemical contamination and influences the image quality when forming the dots.
2 For this reason, from the viewpoint of quality management, it is necessary to remove fine dust and carry out corona treatment.
3 When using a special functional material as a coloring material, there are restrictions on the formulation.
4 need to choose a good print head. Use a special function material for the ink and prepare a print head that can eject the ink.
5 Because of the relationship between printing according to color sequence, the speed and position accuracy of UV irradiation need to be set more accurately.
In the above, all aspects of UV curing are described. Some important items in the above unsolved problems are further described below.

4) Printing by color sequence

From the standpoint of curing and image quality control, important topics in the printing process are wetting and penetration, and it involves the control of curing phenomena:

1 The dot size and image quality control and the curing are good when the non-absorbent substrate is printed.
2 Wetting between cured ink and uncured ink during color sequence printing.
3 Infiltration and curing of inks in the printing of absorbent materials.

· Control of wettability

When printing on a substrate that does not absorb ink, the shape of the droplets of ink on the substrate affects the diameter of the dots and also affects the curability and adhesion of the cured film. Therefore, strictly speaking, it is necessary to adjust the wettability of the ink depending on the printing material used.

Look again at the contact angle of the ink. High-energy surfaces like PET form flat, thin, large-diameter dots; while low-energy surfaces like PP, which are small in diameter, are raised to form high dots, which require monochromatic or resolution. Printing problems that are not high are not a problem, but the printing of multicolor images must be controlled.

• Water-based Hydrophilic compounds have relatively large contact angles and are easy to control. In the case of water-based UV inks, the printing of non-absorbent substrates can basically meet the requirements as long as the wetting properties are controlled.

5) Infiltration and curing of ink-absorbing material

When printing on ink-absorbing materials, the timing of ink absorption and curing must be controlled. Acrylic monomers have a good surface tension and exhibit a very fast penetration of paper that has been conventionally sized. For ink-jet papers with excellent absorption properties, the penetration is faster. Therefore, the rate of absorption becomes earlier than the time when the curing rate is faster or it enters the curing stage, and it becomes an obstacle to polymerization. Undoubtedly, since the penetration into the inside of the paper causes a decrease in the coloring property, good image quality cannot be obtained.

UV inkjet inks are not suitable for printing fast-absorbing materials. The UV inks currently on the market are suitable for the printed material with good wettability. For the printing of absorbent materials, water-based UV ink jets that can increase the surface tension are appropriate, which is one reason for the active research and development in this field.

6) Water-based UV inkjet ink

In the field of UV inkjet inks, the research on aspiration water is increasing. The use of water-containing UV inkjet inks does not necessarily require the forced removal of water when printing on paper, but it will lose some of its characteristics as a UV inkjet. For example, the reliability of the device due to the presence of volatile components is degraded and is generally similar to ink jet ink in the past. In addition, in order to maintain speed on commercial printing presses, water needs to be processed.

Despite the above-mentioned problems, on the other hand, there are also many benefits from this, as listed below.

1 Because of its hydrophilic nature, the use of water-based non-volatile materials has greatly reduced environmental pollution.
2 The selection of materials is extensive, especially when the reactive material is used in the form of an emulsion, which facilitates the use of high-viscosity materials.
3 The thickness of the solid ink layer is reduced, which will not damage the texture of the printed material.
4 can be suitable for high resolution print heads.
5 inhibition of oxygen barriers.
6 When printing on paper, it is possible to design an ink with a large surface tension, the dot gain is small, and the shape of the dots is good.
7 Prints that use 100% reactive inks are used for a wide range of applications such as interior decoration and packaging touched by human hands.

As for emulsion-based water-based UV inks, existing excellent industrial materials have been selected as the oligomer materials. But considering stability is the key. The difficulty in designing soluble water-based UV inks lies in the fact that there are few industrial materials with water solubility, especially photoinitiators dissolved in water, so new compounds are also formulated.

Photoinitiators are made water-soluble and have highly polar functional groups with strong intermolecular forces. As a result, volatility is greatly reduced, and odors and irritation that directly affect the human body are caused. Toxicity, skin irritation, etc. have also been reduced, but also eliminates the restrictions placed on the location of the printing press. This advantage is very important, and it is also a great sound for water-based.

7. Prospects for the future

UV inkjet technology is a rookie in the transition to on-demand digital processing. Not only the direct printing of characters and images, but also the use of UV ink jet resin properties for pre-printing, post-processing, etc. also compensate for the drawbacks of the original ink jet printing, and will more effectively function.

In many application attempts, small illumination devices that track the operation of the print head are needed. The UV ink jet printer is intended to expand its use, and it needs to develop a high-performance UV lamp, 2 develop the best print head, and 3 develop suitable materials. With the availability of these conditions, a new printing system will be created. The UV ink jet technology will be based on the torrent of digital technology development, and will use this as a driving force to gradually reduce the constraints on equipment and material selection.

Source: "Printing World" Author: Ding