Water-based ink is mainly a uniform paste composed of binders, pigments, additives and other substances. The binder is the core component of water-based ink. It not only serves to disperse colorants but is also a key factor influencing the performance of ink, determining its adhesion, water resistance, washability and solvent resistance, among other properties. There are three common types of water-based ink binders, namely water-soluble resins, water-soluble sol resins and water-dispersed resins. Their properties vary. In the process of ink formulation, the three resins are usually compounded for use.

Water-soluble resins can dissolve in water but have poor water resistance. Water-based inks prepared with such resins cannot be applied in environments that come into direct contact with water, and their application is restricted. Therefore, water-soluble resins cannot be used as the main raw material for water-based ink binders. Due to its advantages such as low relative molecular weight, small particles and good uniformity, it is mainly used to adjust the viscosity and fluidity of water-based inks and disperse pigments.

Water-soluble sol resin is prepared by neutralizing acidic resin with low-molecular-weight amines to form salts and generate hydrophilic groups. It can also be called alkali-soluble resin. This resin has a fast drying and film-forming speed. This type of resin includes shellac, ethyl carbamate resin, waterborne amino resin and water-soluble acrylic resin.

Water-dispersed resin is also known as emulsion resin. Using this type of resin as the water-based binder, the ink has good dilutability, fast drying speed, excellent water resistance of the coating film, and the emulsion has low viscosity and high solid content, which can form high-performance coatings. However, water-based inks prepared with emulsion resins have the disadvantages of poor resolubility and difficulty in cleaning.

The formula of water-based printing ink is generally composed of acrylate copolymer emulsion, solid acrylic resin, pigments, wetting agents and defoamers. Acrylate copolymer emulsion is the main binder, and solid acrylic resin serves as the pigment dispersant, also known as the dispersion resin. The solid acrylic resins used are mostly alkali-soluble resins, which contain about 30% acrylic acid or methacrylic acid in their composition. They dissolve in alkali and immediately convert into macromolecular surfactants with emulsifying, wetting and dispersing functions. They have excellent adhesion to a variety of low-polarity substrates such as PE films, PP films and aluminum-coated films. Therefore, solid acrylic resin is an important functional additive throughout the entire water-based ink preparation process. It is not only widely used in the preparation of emulsion binders but also in considerable amounts during the ink formulation process. Another major function of waterborne solid acrylic resin is to provide dispersibility for a variety of difficult-to-disperse pigments, improving color development and film-forming properties. Therefore, in the field of water-based brush ink manufacturing, water-based solid acrylic resin is an excellent pigment dispersion binder.

Waterborne solid acrylic resin is also called alkali-soluble acrylic resin. The glass transition temperature of the resin is related to the film-forming performance. When the glass transition temperature is high, the resin has high hardness, gloss and weather resistance, but it cannot form a continuous film. When the glass transition temperature of the resin is relatively low, the formed film is soft and prone to adhesion. Therefore, waterborne solid acrylic resins with different molecular weights and their distributions, acid values and glass transition temperatures can be synthesized according to different actual demands.

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