Research Progress of Water-based Acrylic Resin for Ink (Part Two)

In the past 20 years, emulsion polymerization technology has achieved rapid development, and many new emulsion polymerization methods have emerged, such as reversed-phase polymerization, non-aqueous normal-phase emulsion polymerization, latex interpenetrating network polymerization (IPN), and nuclear-shell structure emulsion polymerization. , radiation polymerization, directional polymerization, etc., and Okubo Masaru et al. proposed a new concept of “particle design” based on molecular design.

Acrylic resin emulsion is used as a binder for water-based inks. Its minimum film forming temperature (MFT) is closely related to its glass transition temperature (Tg) value. High glass transition temperature resins cannot form films at room temperature, but low vitrification. The temperature of the resin has better film formation. The main factors influencing the glass transition temperature are the flexibility of the molecular chain, the geometric orientation, the intermolecular forces, the molecular weight, and the experimental rate. The glass transition temperature of the copolymer resin can be calculated according to the following addition formula based on the glass transition temperature of each monomer, and the desired glass transition temperature can be designed.

In the formula, W1, W2, ?, Wn are the mass of each monomer in the copolymer: Tg1, Tg2, ?, Tgn are the glass transition temperature (absolute temperature) of each monomer.

3. Outlook

Water-based acrylic resin is used as a binder for water-based inks, and it has always been the main binder for water-based inks due to its excellent printability. However, its water-swelling property after drying, easy peeling of the film and poor adhesion to plastics, and the water-soluble acrylic resin volatilizes ammonia during the drying process, etc., all of which restrict the quality of the produced aqueous ink. The application and performance improvement of acrylic resin in water-based ink can be started from several aspects:

1) Reduce the volatilization of amines. Usually aqueous ammonia is used to dissolve acrylic resins and other water-soluble resins. There are two ways to reduce the ammonia odor. First, we replaced a small portion of ammonia with less volatile, odorless amines: Second, no ammonia or amines were used at all. For example: A unique system consisting of a sulfonated polyester resin and a water-soluble acrylic resin produces aqueous ammonia-free amine-based inks.

2) The use of polymerized acrylic resin instead of the commonly used low molecular weight polymer, the biggest advantage of polymerized acrylic resin is that migration does not occur, and low molecular weight polymer usually produces a certain degree of migration, from the ink film into the substrate and packaging Products make ink more environmentally friendly.

3) Improve gloss and alkali resistance by reducing the molecular weight and acid value of the water-based acrylic resin during polymerization while maintaining the following properties: drying speed, viscosity, transparency, color density, dirty print, resistance to rubbing, resistance ( Scratch, water, grease, acid, heat).

4) Developed a low water absorption aqueous acrylic resin for use in printing "wet" packaging such as fruit and vegetable packaging, and film-forming acrylic resins with low moisture vapour permeability, which is not allowed to allow water vapor to pass freely package of.

5) The introduction of functional groups or surfactants in waterborne acrylic resins improves their adhesion to plastics or other non-absorbent substrates, resulting in a wider print range for aqueous inks, eg in PE, PP. , polyester film and metal foil printing.