Application of acrylic resin in inks

Ink is one of the main consumables in the printing industry, and it is also a major factor that affects the copying effect of originals. The printing technology and the printing process continue to improve, and ink producers have also continuously improved the printability of inks. Ink producers also continue to improve the printability of inks. The binder is the fluid component of the ink. With the continuous development of modern industry, new types of ink binders have been used. From the initial vegetable oils, natural resins as the main component of the binder, to the present synthetic resin, The ink industry has made considerable progress. Among the existing synthetic resins, acrylic resins are the most widely used, and they can be found in UV-curable (UV) inks, electron beam-curable (EB) inks, and water-based inks. The role of acrylic resin in the above-mentioned inks The reaction mechanism is different. The following are examples to illustrate.
First, the application of acrylic resin in UV inks and EB inks UV inks are inks that change from a liquid state to a solid state under certain ultraviolet light irradiation. UV inks have wide printability and can be printed using offset, flexo, or screen printing. They have good printing performance on most substrates, and have fast ink drying and less organic volatiles (VOC), affecting the environment. Small, the print has strong fastness, good wear resistance, high gloss and so on. In recent years, UV inks have been widely used in lithographic offset printing, screen printing, and flexographic printing. Its market share has a high annual growth rate, and its growth rate far exceeds other types of printing inks.
The reaction mechanism of the UV ink is radical or cationic polymerization, and the composition of the UV ink is very important. The structure of the resin prepolymer and the activity of the functional groups in the formulation determine the speed of the entire cross-linking polymerization reaction. The resin used in the manufacture of UV inks is now dominated by acrylic resins. Due to the unsaturated double bond “C=C” present in the acrylic resin, the unsaturation activates the initiator under the irradiation of ultraviolet rays, thereby triggering the chain type. The reaction, polymerization into a solid resin, is widely used in the manufacture of UV inks. Acrylic resins used in the ink industry mainly include epoxy acrylate resins and urethane acrylate resins.
Epoxy acrylate resin is made by direct reaction between epoxy resin and acrylic acid. It has the characteristics of fast curing, high film hardness and good gloss. UV inks use epoxy acrylate resins to achieve faster curing speeds.
In addition, there is an epoxy acrylate resin which is an epoxidized oil acrylate resin obtained by reacting epoxidized soybean oil and epoxy linseed oil with acrylic acid. It has low viscosity, good fluidity, and good wetting and dispersing of pigments. Such characteristics, but the curing speed is slow, film formation is relatively soft, in the UV ink is generally only used as an auxiliary resin.
Polyester acrylate resin is obtained by direct esterification and dehydration of polyester polyol and acrylic acid, and has good adhesion to the material. More applications in UV inks. When the molecular weight is low, it can be used as a diluent, and the high molecular weight can be used as the main resin, but the polyester acrylate resin has a high viscosity. If the fatty acid is used for modification, the viscosity of the resin can be reduced, and the pigment can also be improved. Wet dispersibility.
The urethane acrylate resin is obtained by the condensation reaction of a polybasic acid with a diisopropyl ester and ethyl acrylate. The molecular weight of urethane acrylate resin can be adjusted, and the curing speed can also be adjusted to suit the different printing requirements of UV ink. The urethane acrylate resin has a strong urethane bond in its molecular structure, and thus has high adhesion to plastics, metals, and woodware, but the cost of the urethane internal acrylate resin is high. And the temperature will have a certain impact on the viscosity, which is more solid at room temperature, use and reactive diluents to use.
The following will combine a specific formula of UV ink, introduce the UV ink curing mechanism.
Sheet-fed lithographic UV ink formulation example: (See Table 1)

The drying mechanism of UV inks is that under the action of ultraviolet rays, the ink is excited by photoinitiators to generate free radicals or ions. These radicals or ions react with hydroxy polymers and unsaturated bonds in monomers to form monomer groups. These monomer groups then undergo a chain reaction to complete the curing process. Figure 1:

Light Source → Photoinitiator → Free Radical ───→ Vinyl Monomers and Prepolymers ───→Polymer Initiated Polymerization

During the reaction, the double bond in the molecular formula breaks down to perform polymerization reaction to form a polymeric macromolecular resin. Tetraethylene glycol diacrylate is used as a reactive diluent in inks and primarily functions to adjust the viscosity of the ink to adjust the printability of the acrylic ester resin.
Both EB ink and UV ink are reactive inks, and the drying mechanism is generally the same. In UV inks, ultraviolet light excites photosensitizers with photons and activates polymers to initiate double bond polymerization in resins and monomers. EB inks rely on high-energy electron beams to directly bombard resin prepolymers, causing double bond polymerization in resins and monomers. The resin prepolymer used in the EB ink, the requirements for the monomer and the UV curable ink, and the reaction mechanism are substantially the same, and will not be elaborated here.
Second, the use of acrylic resin in water-based inks Acrylic resin is not only used in UV inks and EB inks, but also widely used in water-based inks. Water based ink (water based ink) is an environmentally friendly ink that is increasingly being packaged and printed around the world due to its low volatile organic compounds (VOC) during the printing process, without compromising the health of printing operators, and having a low environmental impact. The community favored and began to expand to the press and printing industry.
Water-based ink refers to a type of liquid ink that uses water instead of organic solvents. The components mainly consist of color-changing agents, aqueous resins, alkali components, solvents, and additives. The alkali component is composed of organic amine components, solvents and additives. The alkali component is an organic amine or ammonia water, the solvent is water and a small amount of an alcohol, and the additives include an antifoaming agent, a dispersant and a wax. Water-based resin is an important component of water-based inks, which directly affects the ink's adhesion properties, drying speed, anti-sticking properties and heat resistance, as well as gloss and ink transfer properties. Therefore, the choice of suitable resin is the key to water-based inks, which must have easy formation of water-soluble salts, good affinity with colorants, high adhesion after printing film formation, wear resistance, scratch resistance, good heat resistance, glossiness High, and require printing and drying, water release, easy to cross-linked film and other properties. The commonly used connecting materials can be divided into three major categories: water-soluble binders, diffusive binders, and alkali-soluble binders. Resins used in the binders mainly include acrylics, polyamides, and polyesters, but acrylics are commonly used. Acrylic resin is a highly effective wetting agent and abrasive, which helps to disperse and color, has a good gloss, reduces the amount of pigments, and is environmentally friendly.
According to the practical application in aqueous inks, acrylic resins can be divided into two types: solution type, emulsion type. Compared with the latter, the former is more compatible and more stable than the latter.
The solution type acrylic resin generally has a molecular weight of 5000-10000 MW. It does not have the characteristics of an emulsion state, but has good solubility and gloss, and has good wettability as a carrier and dispersion of a pigment. However, its weaknesses are slow drying and poor film formation. Therefore, it is not generally used alone, but it is used together with other emulsions.
Emulsion acrylic resins are available in many varieties. However, the emulsion particles formed due to their different composition are also in different states. There are usually two kinds of colloidal dispersions and conjunctival emulsions in their physical and chemical properties.
Colloidal dispersions, mostly copolymers of acrylic acid and styrene, have a molecular weight between 15,000 and 40000 MW. Since the number of particles is less than the required limit of the emulsion, it is not a true emulsion, but it has a large particle size and can add a large amount of water. dilution. This type of emulsion is generally used in printing ink in corrugated boxes.
Conjunctival emulsions, due to their high molecular weight, are good in oil and water resistance and have good gloss. It has good adhesion to non-absorbent substrates, low glass transition temperature, good film formation and resistance, and is widely used in the printing of impermeable materials such as films and metal foils.
The following will be combined with a reference recipe: (see Table 2)

The drying of water-based inks is mainly volatilization drying and penetration drying. The drying mechanism is that the main resin in the binder contains carboxyl groups (-COOH) in the acrylic resin, and after adding a certain amount of amine-group (-NH2) alkaline substances The amine group reacts with the carboxyl group in the resin to form a water-soluble organic amine salt.
During the drying process of the ink, after the oxygen is volatilized, the resin in the ink is restored to a water-insoluble ink film, thereby completing the drying and curing of the ink. The amount of ammonia in the above formula needs to be strictly controlled and the pH of the ink is generally controlled.