6 challenges of gravure reverse water-based ink
Date: Apr 29 2025 From: Star Color Views:
Gravure reverse water-based ink has gradually become the mainstream in the printing industry due to its environmental protection and safety features. However, in the actual production process, it often faces six major core problems: substandard drying speed, insufficient composite peel strength, fluctuations in printing color difference, defects in ink stability, printing adaptability issues, and challenges in environmental compliance. These problems not only affect product quality but also increase production losses.
1. Substandard Drying Speed
During the gravure printing process, substandard drying speed can lead to a series of serious problems. Sticking of printed film rolls is a common symptom. When the residual moisture is ≥ 0.8%, during the winding process, the moisture fails to evaporate in time, causing the film layers to stick together, which seriously affects subsequent processing and use. Blurred graphics and texts after winding is also a typical symptom. When the solid density ΔE > 3, it means there are significant deviations in the color and clarity of the printed graphics and texts, reducing the visual effect and quality standard of the products.
Causes and Countermeasures
The drying speed is affected by various factors. Optimizing traditional parameters can significantly improve drying efficiency.
- Oven Temperature: The traditional three-stage heating at 60 - 80°C cannot precisely meet the drying requirements of water-based ink. It is optimized to gradient heating (50°C→75°C→95°C). Preheating at a lower temperature first allows the moisture in the ink to evaporate slowly, preventing the ink surface from forming a film too quickly due to a sudden temperature increase, which could hinder the volatilization of internal moisture. Then, gradually increasing the temperature accelerates moisture evaporation, and the drying efficiency is increased by 42%.
- Wind Speed Distribution: The uniform air supply method results in uneven wind speed distribution, and some areas are not fully dried. The eddy current pressurization design is adopted, with the wind speed difference controlled within ±2m/s, ensuring that all parts of the ink are fully dried during the printing process, and the residual moisture is ≤ 0.3%.
- Resin Glass Transition Temperature: Using resins with a glass transition temperature of 60 - 70°C traditionally leads to a slow surface drying speed. Selecting an acrylic resin with a Tg of 85°C enables the resin to quickly form a solid film layer at a lower temperature, shortening the surface drying time to 18 seconds.
2. Insufficient Composite Peel Strength
Composite peel strength is crucial for products such as food packaging and retort pouches. According to the GB 8808 standard, the composite peel strength of food packaging should be ≥ 3.5N/15mm to ensure that the packaging does not delaminate easily during transportation and storage. Since retort pouches need to withstand high-temperature retort processes, their composite peel strength requirements are even higher, requiring ≥ 8.0N/15mm.
Enhancement Solutions
- Primer Treatment: Corona treatment of the substrate surface and coating of the primer are key to improving composite peel strength. Using equipment to increase the corona value to ≥ 42 dynes can effectively increase the polarity and roughness of the substrate surface, enhancing the adhesion between the ink and the substrate. Coating 0.3g/㎡ of silane coupling agent, one end of the silane coupling agent molecule reacts with the hydroxyl groups on the substrate surface, and the other end reacts with the resin in the ink, forming a chemical bond connection and further enhancing the adhesion.
- Ink Modification: Adding 5% epoxy-modified polyester to the ink, the epoxy groups can cross-link with the substrate and other resins, enhancing the internal cohesion of the ink and its bonding force with the substrate. With a 0.8% dosage of nano SiO₂ dispersion, the nano SiO₂ particles are uniformly dispersed in the ink, filling the tiny voids inside the ink, increasing the ink's hardness and wear resistance, and simultaneously improving the composite peel strength.
3. Fluctuations in Printing Color Difference (ΔE > 2.5)
Fluctuations in printing color difference seriously affect product consistency and aesthetics. Through the intelligent upgrading of links such as ink viscosity, dot transfer rate, and color detection, printing accuracy can be greatly improved.
- Ink Viscosity: The traditional manual measurement of ink viscosity using a Zahn cup has large errors and low efficiency. Using an online rotational viscometer, with the measurement accuracy controlled within ±5cP, and monitoring the ink viscosity change in real-time, the color density fluctuation is ≤ 0.08, ensuring the stability of the printed color.
- Dot Transfer Rate: Estimating the dot transfer rate based on experience cannot guarantee printing consistency. Using laser engraving technology (200LPI±2 lines), precisely controlling the shape, size, and depth of the dots, the transfer consistency reaches 98.5%, ensuring that the ink transfer amount is the same in each printing, thus reducing color differences.
- Color Detection: Offline spectrophotometer detection has a time-lag problem. The X-ray online monitoring system can detect the printed color in real-time, control ΔE within ≤ 1.2, and immediately issue an alarm and automatically adjust the printing parameters once the color difference exceeds the range.
4. Defects in Ink Stability
Defects in ink stability affect the continuity of the printing process and product quality. When the pH value fluctuates by > 0.8 after 4 hours of printing, it will change the rheological properties of the ink and affect printing adaptability. When the foam thickness is > 2cm, it indicates an imbalance in the dynamic surface tension, prone to printing defects such as bubbles and pinholes.
Optimization of the Stabilizer Formula
- Defoamer: The traditional 0.3% mineral oil-based defoamer is prone to delamination, affecting the defoaming effect. The new composite solution uses 0.1% silicone + 0.05% polyether. Silicone has good defoaming performance, and polyether can prevent the defoamer from delaminating, ensuring that the ink has no delamination within 72 hours and maintaining a good defoaming effect.
- pH Regulator: Adjusting the pH value with single ammonia water is unstable and prone to fluctuations. Using a buffer system of triethanolamine + AMP - 95 can effectively stabilize the pH value, with the pH fluctuation ≤ 0.3, ensuring the stability of the ink.
- Dispersant: The dispersing effect of sodium polyacrylate dispersant is limited. The hyperbranched polymer (BYK - 2013) has a unique molecular structure, which can better disperse pigment particles, making the particle size D50 ≤ 0.5μm and improving the dispersion stability of the ink and printing quality.
5. Printing Adaptability Issues
Doctor blade lines and plate blocking are common frequent defects in gravure printing. When there are ≥ 3 doctor blade lines per kilometer, it seriously affects the clarity and aesthetics of the printed graphics and texts. The plate blocking phenomenon requires the machine to be shut down for cleaning during 4 hours of operation, reducing production efficiency and increasing production costs.
Fine-tuning of Process Parameters
- Doctor Blade Angle: When the doctor blade angle is at 55±5°, doctor blade lines are likely to occur. Adjusting it to 62±2° and installing a pressure feedback system to monitor the doctor blade pressure in real-time ensures that the contact pressure between the doctor blade and the plate cylinder is uniform, reducing the occurrence of doctor blade lines.
- Ink Viscosity: The traditional control of ink viscosity at 18±5s (measured with a No. 4 cup) is prone to plate blocking. Controlling the ink viscosity to 22±0.5s and equipping an automatic circulation system maintains the stability of the ink viscosity and prevents the ink from drying and blocking the cells on the plate cylinder.
- Plate Cylinder Linear Speed Ratio: A plate cylinder linear speed ratio of 1:1.2 is likely to cause uneven ink transfer. Adjusting it to 1:1.05 and installing servo tension control precisely controls the speed matching between the plate cylinder and the printing substrate, ensuring uniform ink transfer and reducing printing defects.
6. Challenges in Environmental Compliance
Mandatory Standards in 2024
With the continuous improvement of environmental protection requirements, the gravure printing industry faces strict environmental protection standards. The EU Reach SVHC list requires zero detection of 18 substances to ensure product compliance in the EU market. The Chinese standard GB 38507 - 2020 stipulates that VOC ≤ 30g/L, reducing the emission of volatile organic compounds and protecting the environment and human health.
Technical Paths to Compliance
- Raw Material Substitution: Replacing ethylene glycol ethers with propylene glycol methyl ether (PMA), PMA has lower toxicity and volatility, meeting environmental protection requirements. Replacing heavy metal pigments with azo condensation type color powders reduces the pollution of heavy metals to the environment.
- Testing and Certification: Conducting SGS VOC full-item detection (EPA Method 24) to accurately detect the content of volatile organic compounds in the ink.
Through in-depth analysis of the six major problems of gravure reverse water-based ink and the implementation of targeted solutions, enterprises can effectively solve practical problems in the production process, improve product quality and production efficiency, meet environmental compliance requirements at the same time, and gain a competitive advantage in the market.
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