I. Benzene-Free Gravure Compound Ink
Traditional solvent-based flexible packaging gravure inks are typically composed of chlorinated polymers. In the ink production process, solvents such as toluene, esters, and ketones are commonly used. Toluene serves two main purposes in the ink: (1) it exhibits excellent solubility for resins in the ink, and (2) it enhances printability and plate wetting. While most of these organic solvents evaporate during drying, residual amounts can still pose health hazards upon prolonged exposure, causing skin dryness, roughness, and potential chronic toxicity if absorbed into the bloodstream. Additionally, organic solvents can undergo chemical reactions with air, producing chlorobenzene and smoke, leading to significant air pollution and adverse effects on plant growth, disrupting ecological balance. Ink manufacturers have been striving to develop benzene-free gravure compound inks to replace toluene inks, mitigating health risks associated with benzene residues. Currently, benzene-free compound inks include:
Benzene-Free Ketone Polyurethane Compound Ink: This ink contains no benzene solvents but includes ketone solvents. It features vibrant colors, good solvent release, and excellent printability. Mainly used for printing on PET films and NY films. Adhesion may be slightly lower in OPP film printing but does not affect compound strength.
Alcohol Ester-Soluble Polyurethane Compound Ink: This ink has low odor and does not contain benzene or ketone solvents. Special attention is needed for the reproduction of light screen versions. Primarily used for printing PET films and NY films. Adhesion may be slightly lower in OPP film printing but does not affect compound strength.
Alcohol-Water Acrylic System Compound Ink: The main solvent is ethanol, with the option to add 10% water as a diluent, providing cost advantages. Currently, ink manufacturers mainly produce white inks. These can be used in conjunction with regular benzene-soluble chlorinated polypropylene compound inks. The initial colors are printed using regular compound inks to maintain vibrant colors, with the final layer of alcohol-water white ink applied to reduce solvent residues.
Alcohol-Water Polyurethane System Compound Ink: The main diluent is 95% ethanol. This ink does not contain benzene or ketone solvents, has low odor, vibrant colors, and is cost-effective with good printability. Suitable for printing on PET films, NY films, and OPP films. Successfully launched by Leitong Company in Zhuhai, it is identified as the GP39 series alcohol-soluble compound ink.
Benzene-free compound inks, like their benzene-containing counterparts, consist of binders, pigments, solvents, and small amounts of additives. Typically, multiple solvents are used in combination to improve solubility and drying performance. Quality control indicators for benzene-free compound inks include color, fineness, coloring power, gloss, viscosity, drying performance, adhesion, heat resistance, and freeze resistance. These indicators are crucial for plastic packaging printing.
II. Water-Based Ink
Water-based inks use water as the primary solvent with a small amount of alcohol as a co-solvent. The significant difference from solvent-based inks lies in the use of water and ethanol as solvents, resulting in extremely low volatile organic compound (VOC) content, minimizing environmental pollution. Advantages of water-based inks include:
Environmental and Safety Benefits: Many water-based inks can be formulated to be low or zero VOCs, providing environmental and safety advantages.
Stability and Low Flammability: Water-based inks offer stability and low flammability due to the low volatility of water, leading to better viscosity stability.
Ease of Cleaning: The new generation of water-based products is easier to clean than solvent systems. Simple cleaning with soapy water or weak alkaline cleaning solutions can efficiently clean printing machine components, improving production efficiency.
Compared to solvent-based inks, water-based inks have good flowability, can prepare high-pigment inks, and generally exhibit 30% to 50% higher color intensity while maintaining excellent flowability. However, due to the high surface tension of water, ink wetting is challenging, and water does not evaporate, limiting printing speed. To achieve the printing speed and quality of solvent-based inks, improvements are needed not only in water-based inks but also in gravure equipment and printing plate rollers. For example, converting corroded or electro-engraved plate rollers to laser-engraved rollers and using corrosion-resistant materials for printing plate rollers. Additionally, significant investments and time are required to retrofit printing machines with more powerful and effective ink drying systems and ink scrapers.