Types of flexible plastic packaging ink and the advantages of alcohol-soluble polyurethane flexible packaging ink

September 9, 2022 Longchang Chemical

Types of flexible plastic packaging ink and the advantages of alcohol-soluble polyurethane flexible packaging ink

Plastic flexible packaging ink is the ink used for printing on plastic films, such as PET, OPP, PE and other films, which are widely used in the packaging of food, pharmaceuticals and hygiene products. Flexible packaging inks are mainly composed of color fillers, connecting resins, additives (including leveling agents, defoamers, UV absorbers, wax additives, etc.) and solvents. According to the different solvent systems, the flexible packaging ink on the market can be divided into benzene-soluble ink, ester-soluble ink, alcohol-soluble ink and water-based ink. Solvent-based inks have been phased out because of the benzene, ketones and other hazardous components; water-based inks as a new generation of environmentally friendly ink without VOC, in the national policy and the development of technology to promote the rapid development. However, due to the impact of technology, cost and equipment and other factors, water-based ink has not been widely used in the market. Therefore, alcohol-soluble ink (especially alcohol-soluble polyurethane ink) will remain an important choice for packaging companies in the coming period of time.

First, the type of alcohol-soluble ink and performance.

Alcohol-soluble ink refers to the use of alcohol solvents can be dissolved and diluted ink. Ink can be dissolved with alcohol solvents, connecting material resin plays a decisive role. Currently on the market commonly used alcohol-soluble ink according to the resin connection material can be divided into acrylic alcohol-soluble ink, polyamide alcohol-soluble ink and polyurethane alcohol-soluble ink.

1, acrylic alcohol-soluble ink. Acrylic resin has good transparency, high mechanical strength, good adhesion to the film and other characteristics, and can be compatible with a variety of resins, such as nitrocellulose, cellulose acetate butyrate, vinyl resin, etc.. The gravure or flexo surface printing inks prepared with them are characterized by good color development, abrasion resistance, and strong adhesion to substrates. However, because the acrylic resin often contains incomplete reaction of acrylic monomer, resulting in a large odor.

2, polyamide-based alcohol-soluble ink. Polyamide resin has high gloss, good abrasion resistance, good toughness and other characteristics, but also with a variety of resins, such as fumaric acid resin, nitrocellulose and other mixed use. The ink prepared with polyamide resin has excellent color, good fastness and abrasion resistance, and is often used as gravure or flexographic surface printing ink and varnish. However, polyamide resin temperature resistance is poor, low temperature resistance to freezing performance and high temperature resistance to cooking performance are not good, so polyamide alcohol-soluble ink is commonly used in ordinary light packaging.

3, polyurethane type alcohol-soluble ink. Polyurethane resin has excellent flexibility, strength and temperature resistance. Polyurethane can also be used with polyketone resins, acrylic resins, nitrocellulose, vinyl resins and many other resins mixed. The alcohol-soluble ink prepared by polyurethane resin has good flexibility, good temperature resistance, low odor, and good fastness of the substrate. It can be used not only for ordinary light packaging, but also for high-temperature cooking and low-temperature freezing packaging.

Second, the role of polyurethane resin in the alcohol-soluble ink characteristics. The characteristics and ratio of soft and hard segments in the molecular structure of polyurethane resin determine the different properties and uses of the resin. Polyurethane resin ink connection material in the alcohol-soluble ink plays the following roles.

1、Improve flexibility. Some nitrocellulose, acrylic resin as a connecting material for the ink, the film is often hard and brittle, not suitable for use in flexible packaging ink alone, the need to add plasticizers or plasticizing resin to improve the flexibility of the resin. Most plasticizers are banned from use in food packaging inks due to the health hazards they pose to humans. Polyurethane resin has excellent plasticizing properties, can replace plasticizers to increase the flexibility of nitrocellulose ink, so that it can be used in a variety of plastic packaging substrates, and polyurethane resin is safe and environmentally friendly, in line with national food safety regulations.

2、Improve adhesion. The molecular structure of polyurethane resin contains a large number of COO-, -NHCOO- and -NHCONH- polar groups, which can form intermolecular hydrogen bonds with -OH, -NH- on the surface of corona treated PET, PE, NY and other substrates to improve the adhesion of the ink on plastic substrates.

3、Improve temperature resistance. There are a large number of polar groups in the molecular structure of polyurethane, which can improve the cohesive strength and thermal stability of the resin, so that the ink can be used in high-temperature cooking-resistant packaging.

4、Improve solubility. Alcohol-soluble polyurethane resin has good solubility, and it can be completely dissolved and diluted with alcohol solvents. Its use in alcohol-soluble ink can well improve the re-solubility of the ink and prevent the blocking phenomenon in the printing process.

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