Application of Dendrimers in UV Ink Jet Inks

In the 1980s, the dendrimer suddenly broke into the scientific lens, which caused widespread concern in the field of polymer science. This peculiar molecule has a beautiful and impressive structure, reminiscent of geometric fractals and corals in the sea, suggesting that there are still many virgin lands to be developed in the chemical field. Over the years, the potential application value and theoretical significance of dendrimers have exceeded the scope of chemists' research and entered the door of the ink coating industry.

Dendrimer Overview As the name suggests, a dendrimer is a macromolecule with a dendritic structure. There are two kinds of dendritic structures. One is perfect dendritic growth, and the other is dendritic growth with defects. The macromolecule with a perfect dendritic structure is the so-called dendrimer, and the defective one is Shaped polymers give it another name - hyperbranched polymers.

As early as 1952, it was proposed that highly branched polymers could be prepared from polyfunctional monomers. However, in the past few decades, highly branched polymers have not attracted people's attention. Until 1987, DuPont purposely synthesized a hyperbranched polymer, applied for the first patent on this, and announced the scientific research results at the National Chemical Conference held in Los Angeles in 1988. By the early 1990s, the nomenclature of dendrimers had been established, mainly based on the shape of the polymer, such as star-burst, arborol, and cascade dendrimer polymerizations. Things, and it has been strictly separated from the highly branched linear polymer at this time.

The difference between a dendrimer and an ordinary linear polymer lies in the special structure of this type of compound. Its molecular structure is highly spherical and symmetrical, and the functional group density on the surface of the molecule is extremely high. A synthesis method typical of "divergence" and "convergence" can synthesize a number of structurally specific dendrimers, and many chemists predict that they can be used in many fields.

In 1982, chemists began to consider the application of dendrimers. In 1987, Hall et al. studied the electrical conductivity of polyaniline dendrimers and found that their electrical conductivity was as high as 10-7/Ω·m. Subsequently, the former Soviet Union scientist Borisova et al. used a silicon-containing dendritic polymer as a gas separation membrane. The gas separation membrane can be used for the separation of gas mixtures, such as the preparation of high-purity nitrogen from oxygen-enriched air, and has better effect. In the future, a large number of nanomaterials, liquid-liquid extraction, liquid crystal materials, catalysts, light-responsive materials, energy conversion antennas, amphoteric polymers, chromatographic stationary phases, LB membranes, chiral molecules, sustained-release drug carriers, and PH switches were carried out. The application of research work, the results are generally better, but the application of the commodity is still rare.

UV inkjet ink Introduction UV ink is an environmentally friendly ink that has developed rapidly in recent years. It contains no volatile organic solvents and no solvent hazards. In order to eliminate the emission of solvent-based ink volatile organic compounds and meet the stringent requirements of air quality standards, the printing industry uses UV ink technology for printing. Therefore, UV inks quickly occupied the printing market. The advent of drop-on-demand inkjet (also called intermittent inkjet) nozzles has made its use in digital inkjet printing a reality. This not only broadens the range of applications of UV inks, but also promotes the development of inkjet technology. .

Using UV inkjet inks, even on uncoated substrates, they can be bright, tough, and long-lasting, eliminating the need for protective film when used outdoors. This allows reliable, efficient, and rapid creation of outdoor media such as poster boards, billboards, and banners. In addition, UV inkjet inks are free of volatile organics and can remain in a liquid state before UV exposure curing. This allows the inkjet head to stay dry for a long time and its maintenance requirements are also low. When the ink is exposed to ultraviolet light, curing on the substrate can be completed almost instantaneously. Due to its many advantages, UV inkjet inks are rapidly becoming the main ink for new generation of platform digital inkjet printers. These machines can perform inkjet printing on a variety of flexible and rigid materials. For example, Inca introduced a UV curable ink for its Inca Eagle44 flatbed inkjet printer. XAAR, UK, uses a 400-ink inkjet printer with piezoelectric drop-on-demand inkjet technology and UV inks. It is the first UV digital inkjet printer capable of inkjet printing on cylindrical objects. It can be used in beverage cans, etc. The object is directly inkjet printed. Its short-run, variable-volume inkjet printing capabilities provide users with better personalized service.

However, the UV ink itself has a higher viscosity, and ink jet printing requires a low viscosity ink. Therefore, how to reduce the ink viscosity becomes a key problem to be solved in the development of the UV ink jet ink. The usual solution is to increase the monomer content in the ink, but if the monomer content in the ink is high, there is a danger of skin allergies, which requires special care during the entire operation and storage. Therefore, it is an important trend for the development of UV ink jet inks to look for new types of UV-curable materials to reduce ink viscosity.

Use of Dendrimers in UV Ink Jet In contrast to linear polymers, dendrimers and hyperbranched polymers have the following structural features with similar average molecular weights. (1) High-density branch branches are many, branching degree is high, the radius of gyration of macromolecules is small, and the macromolecular chains are not easily tangled.

(2) It has a topological morphology with a high degree of branching of nanometer size and an approximately spherical structure system. The molecular size is generally between several nanometers and several tens of nanometers. It is a typical nanomaterial. (3) The structure containing a large number of terminal functional groups and polar groups makes dendritic and hyperbranched polymers possess a variety of excellent properties: good fluid mechanical properties; unique viscosity behavior; easy film formation; versatility; Not easy to crystallize. These performance advantages are very attractive for UV inkjet inks, especially at the same solids content, the viscosity of the solution is significantly lower than the ordinary polymer, this characteristic is the UV ink jet ink manufacturer dreams to achieve the goal. Therefore, the introduction of dendritic and hyperbranched polymers into UV inkjet inks should be very effective. Because of its low viscosity properties, dendrimers are extremely suitable for the preparation of coatings or coating additives with high solids content. In recent years, they have become a new type of coating resin that is of great interest. However, from an industrial point of view, the disadvantage of dendrimers is that their highly ordered molecular structure requires multiple repetitive synthesis during the manufacturing process, which leads to an increase in costs, and at each step of the synthesis The active group at the end of the core molecule must be completely reacted, and the product of each step must be thoroughly purified, so the yield obtained is very low, which greatly restricts the industrialized production of the dendrimer. The structure of the hyperbranched polymer is not required to be perfect, but it has a certain relative molecular mass distribution, and similar to the dendrimer, it can generally be synthesized by a one-step polymerization method, so it is easy for industrial production. This makes it advantageous for application in industrial production synthesis technology.

In theory, acrylic polymers with dendritic or hyperbranched structures have the potential to meet the needs of UV inkjet inks, especially its compact spherical structure makes the polymer chains less tangled and fluid ( The small size of the power) makes the viscosity of the solution at the same solid content much lower, and its high concentration of acrylic groups can also provide a lot of excellent physical properties. In addition, the dendrimer also has good compatibility and abundant modified end groups, which provides an opportunity for the dendrimer to be used in UV inkjet inks. For example, the terminal groups of polyamide (PAMAM) dendrimers are modified, and crystallizable segments are introduced to obtain a semi-solid semi-crystalline polymer that can be used as a UV powder coating. This paint contains no solvents, no VOC emissions, high raw material utilization, and easy operation.

The oligomers in UV inks are a significant component of the curing system, and acrylic polymers are generally used. We can introduce dendrimers into oligomers, that is, we need to prepare dendritic or hyperbranched acrylic oligomers. The oligomer can be prepared by esterification of a hydroxyl-functional polyhydric dendrimer and an acrylic compound, and can also be prepared by reacting a polyhydric dendrimer with an acryloyl halide. Researchers have prepared hyperbranched polyhydroxy polyesters containing 16 terminal hydroxyl groups by standard acrylate synthesis methods and concluded that the chance of conversion of terminal hydroxyl groups to acrylates can vary over a wide range, but if To maximize the advantages of hyperbranched structures, the conversion rate should be as high as possible.

At present, the speed of UV-curable ink-jet printing is mainly constrained by the curing speed of the ink used, which requires the ink material to have a very high curing speed. The cure speed of acrylic monomers and oligomers depends primarily on the functionality. It has been found through experiments that high concentration of reactive terminal groups in the hyperbranched acrylic oligomer can greatly increase the curing speed of the ink. Therefore, the application of dendrimers to UV inkjet inks is a feasible and effective approach, which not only broadens the field of application of dendrimers, but also enables UV inkjet inks to exert their greatest advantages. Not fun for it?

Conclusion Regardless of whether it is a dendrimer or a hyperbranched polymer, its unique structure and properties have shown broad application prospects in many fields and it has begun to be applied to the ink coating industry. However, there are few applications in inks, especially in the UV inkjet ink research is still in the laboratory stage, there are still many problems still to be solved, especially in theory need to further study.