Application area of ​​acrylic resin (below)

2.2 Laminating adhesives

Except that the activation temperature of the adhesive is much lower than that of the heat-sealable adhesive, the laminating adhesive has almost the same function as the heat-sealable adhesive. Heat sealable adhesives require a temperature of 120 (250) for activation, and laminating adhesives are effective anywhere between room temperature and 90 (200). Recently, in the field of flexible packaging, new low-temperature curing type adhesives have replaced two-component solvent-based polyurethane adhesives to a certain extent. The use of low temperature curing acrylic polymers in the industry has also made considerable progress. It is generally applied to the lamination bonding of wood including ethylene adhesives and the adhesion of ethylene adhesives to ABS resin of automotive interior parts.

2.3 Pressure sensitive adhesive

Pressure-sensitive adhesive bonding is often referred to as "one-step" bonding. The adhesive is applied directly or transferably to the substrate. The adhesive is protected by an anti-adhesive pad until it is ready for use. When needed, the anti-adhesive pad is removed and the adhesive-coated substrate is adhered to another substrate using only pressure. Pressure actually acts as an activating adhesive, so this method is called pressure-sensitive adhesion. When the pressure is stabilized, the viscous adhesive substance is actually fluid and mechanically and chemically adheres to the other surface.
However, in order to be functional, the pressure-sensitive adhesive cannot only be viscous. Flypaper, for example, is highly viscous but lacks internal strength adhesion. Functional pressure-sensitive materials will have high viscosity and high cohesive strength, which is the most basic requirement for any adhesive.

Pressure-sensitive adhesives are used in many areas of tape, such as packaging, shielding, electrical repair, medicine, and installation. The field of print art includes plastic decal printing and special decorative films such as transparent metal-coated polyester films. These areas generally require a significant balance of these properties, which must be stable under stringent outdoor exposure and temperature extremes. Properties such as resistance to UV degradation and anti-plasticizer migration are essential. Adhesives in this area must be able to form a clear and colorless film, which determines the widespread use of acrylic polymers.

Solvent-based styrene acrylic (PSAs) copolymers have been used in these fields. Nowadays they have been replaced to varying degrees by their emulsions. However, they are still used in the industrial field where solvent systems are dominant, these include applications requiring heat resistance, water resistance, and solvent resistance.

3 ink

In the past 10 years, aqueous inks formulated with acrylic polymers have grown steadily. The main reason for the increase was that national regulations strengthened the restrictions on the solvents released by printers. Of course, the same reason also guarantees the growth of waterborne coatings and adhesives. The choice left for the printer is:

Install a solvent recovery-combustion system.
Develop high solid solvent inks that meet environmental regulations.
Develop water-based ink that meets usage requirements.

Because many printing companies have chosen the third option, our discussion will focus on this point.

In addition to pigments, aqueous acrylic inks generally consist of two types of acrylic polymers: one is an emulsion-polymerized acrylic resin, and the other is an alkali-soluble solid acrylic resin. Emulsion acrylic resins have an impact on the properties of the finished ink, such as film-forming properties, adhesion to plastic films, abrasion resistance, heat resistance, and alkali resistance. However, emulsion polymers are very poor pigment wetting agents. In addition, wheat has relatively poor flow characteristics compared to its solvent-based polymers. The alkali-soluble resin is a good pigment wetting agent, exhibits good rheology, and can prevent ink drying inside the cartridge when production stops in the printing line. Many different types of alkali soluble resins can be used with emulsion acrylic polymers.

Table 3 compares acrylic polymers and four other general types of polymers: maleic resins, shellac, proteins, and styrene-maleic acid copolymers.

Table III Comparison of Properties of Alkaline Soluble Acidic Resins

By combining the best properties of emulsion-polymerized acrylic polymers with alkali-soluble acrylic polymers, water-based inks that are environmentally friendly are gradually replacing traditional solvent-based inks. These water-based inks have been used in different fields of application for stamps, cigarette cardboard boxes, beer cans, cows' cardboard boxes, food packaging, wallpapers, grocery bags, newspapers and corrugated boxes.

Despite its successful application in these fields, water-based inks still have shortcomings and technical problems. The following questions are some of them:

Drying problem. In order to maintain the same production rate as solvent inks, a more efficient drying oven must be used.

Foaming. The use of suitable defoamers has greatly reduced this problem to a minimum.

Freeze-thaw stability. It depends on the formulation not to blame the trader must also consider the storage conditions in winter.
Soluble. Sometimes called dry in the printing industry, this requires careful balancing of the alkali soluble resin and the liquid sloshing polymer.

With the increase of research and development efforts, the performance improvement and the prospect of growth of water-based acrylic inks are very optimistic.

Source: China Tobacco Packaging Ink Information Network