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Today, flexible packaging labels have long surpassed the role of a simple "information carrier" and become a key factor in brand differentiation competition, as well as an important barrier for product safety and compliance. Flexible packaging labels need to bend and rub along with the substrate without falling off, adapt to complex scenarios such as low-temperature refrigeration, high-temperature sterilization, and outdoor storage, and also eliminate safety hazards such as ink migration and solvent residue. This places more stringent requirements on the selection of printing inks than ordinary printing.
The selection of inks for flexible packaging labels needs to be based on substrate characteristics, printing processes, end-use scenarios, environmental regulations, etc. Combining years of practical industry experience, this article focuses on the core pain points in the selection of inks for flexible packaging labels, abandons theoretical and vague expressions, and provides practical and referential professional guidance to help industry practitioners select label printing inks suitable for their own needs, reduce production risks, and improve product competitiveness.
I. Core Principles for Selection
The selection of inks for flexible packaging labels is based on four core principles: "adaptability, safety, stability, and economy". Among them, adaptability is the premise, safety is the bottom line, stability is the guarantee, and economy is the core competitiveness.1 Adaptability Principle
Flexible packaging labels use a wide variety of substrates, and different substrates have significant differences in surface energy, polarity, and flexibility, which directly determine the adhesion and film-forming effect of the ink. At the same time, different printing processes (flexographic printing, gravure printing, digital printing, etc.) have different requirements for inks. Therefore, adaptability is the primary premise for selection.For example, non-polar substrates such as PE and PP have low surface energy, so attention should be paid to the adhesion of the ink. Polar substrates such as PET and NY have higher surface energy, and the adaptability of the ink is stronger, but attention should be paid to the compatibility between the ink and the substrate.
In terms of printing processes, flexographic printing requires inks with moderate viscosity (18-28s by Zahn cup) and good fluidity to adapt to the characteristics of quantitative ink supply by anilox rollers; gravure printing requires inks with good transferability and drying speed to adapt to high-speed printing (80-200m/min); digital printing requires special UV-curable inks to ensure color reproduction and printing accuracy.
2 Safety Principle
Flexible packaging labels, especially those used in food, pharmaceutical, and daily chemical fields, are in direct or indirect contact with products, so the safety of inks is crucial. They must strictly comply with global environmental regulations and safety standards, and eliminate safety hazards such as ink migration, solvent residue, and heavy metal exceeding the standard.It is necessary to control the content of harmful substances in inks, such as heavy metals, aromatic hydrocarbons, and volatile organic compounds (VOCs), and comply with standards such as EU REACH, US FDA, China GB 38507-2020, and GB 9685-2016. For food flexible packaging labels, food-grade inks must be selected to ensure that ink components will not migrate to food.
3 Stability Principle
During use, flexible packaging labels may experience various environments such as rubbing, bending, and temperature changes. Therefore, inks must have good stability. They should not cause screen clogging during printing, ensure uniform color and smooth transfer, not settle, stratify, or discolor during 6-12 months of storage, and not fade, fall off, or wear during use.4 Economy Principle
In the selection process, on the premise of meeting adaptability, safety, and stability, cost control should also be taken into account. There is a large price difference between different types of inks. For example, for high-end food and daily chemical product flexible packaging labels, high-performance UV inks or environmentally friendly water-based inks can be selected to improve label texture and safety; for mid-to-low-end product labels, cost-effective solvent-based inks (which must meet environmental standards) can be selected to control costs on the premise of meeting basic performance.
II. Main Types of Inks for Flexible Packaging Labels and Their Adaptation Schemes
At present, the main types of printing inks for flexible packaging labels are water-based inks, solvent-based inks, and UV inks. Each type of ink has significant differences in characteristics, advantages, disadvantages, and applicable scenarios, and should be reasonably selected according to actual needs. The specific adaptation schemes are as follows:1 Water-Based Inks: More Environmentally Friendly
Water-based inks have low VOC emissions (≤50g/L) and are the preferred inks for food and pharmaceutical flexible packaging labels. Their advantages are environmental compliance, no peculiar smell, and low migration; their disadvantage is slow drying speed and poor adhesion to non-polar substrates (PE, PP), which need to be used with corona treatment or primers.Applicable scenarios: Food, pharmaceutical flexible packaging labels, paper flexible packaging labels, environmentally friendly daily chemical labels;
Applicable substrates: PET, NY, paper substrates, PE, PP substrates;
Applicable processes: Flexographic printing, gravure printing.
2 Solvent-Based Inks: Cheaper
Solvent-based inks are the traditional mainstream inks for flexible packaging label printing. Their advantages are strong adhesion, fast drying speed, good printing effect, and adaptation to high-speed printing; their disadvantages are high VOC emissions, pungent odor, potential safety hazards from solvent residues, and great pressure on environmental compliance.Applicable scenarios: Mid-to-low-end food flexible packaging labels, daily chemical labels, outdoor labels, PE/PP flexible packaging labels;
Applicable substrates: PE, PP, PET, NY, composite substrates;
Applicable processes: Flexographic printing, gravure printing.
3 UV Inks: More High-End
UV inks are the preferred inks for high-end flexible packaging labels. Their advantages are high printing efficiency, excellent friction resistance and weather resistance, no solvent residue, and environmental friendliness between water-based and solvent-based inks; their disadvantages are high cost and potential migration risks of some photoinitiators.Applicable scenarios: High-end food, daily chemical flexible packaging labels, outdoor labels, personalized digital printing labels;
Applicable substrates: PET, NY, composite substrates, PE/PP;
Applicable processes: Flexographic printing, digital printing.
III. Practical Selection Process
The practical selection process of printing inks for flexible packaging labels can be divided into five steps to avoid production risks and cost waste caused by incorrect selection.Step 1: Clarify Core Requirements
Core requirements include: substrate type, printing process, end-use scenario, environmental compliance requirements, color and texture requirements, and cost budget.Clarify the usage conditions, such as whether it is in direct contact with food, whether high-temperature/low-temperature resistance is required, and whether there are environmental certification requirements.
For example, the core requirements for frozen food flexible packaging labels are "environmentally friendly and low migration, low-temperature resistance, and strong adhesion", and the usage conditions are compliance with FDA standards, adaptation to PE substrates, flexographic printing, and controllable cost.
