Tackling Autumn And Winter Printing Challenges: Prevention And Rectification Measures For Skinning And Stringing Defects Of Offset Printing Ink

Skinning and stringing of offset printing ink in autumn and winter result from the combined effects of climate, ink properties, production processes and equipment operation, with climate factors serving as the main trigger. A detailed analysis is as follows:

• Climate Factors: Low humidity accelerates solvent volatilization in offset printing ink, causing rapid drying of the ink layer surface and forming skinning, which is particularly obvious in dry northern regions. Low temperature increases ink viscosity and impairs fluidity, raising friction on ink rollers and hindering ink transfer, thus triggering stringing. In addition, large temperature fluctuations in workshops due to the big day-night temperature difference further increase the probability of defects.

• Ink-Related Factors: An unreasonable ink formulation (excessive resin content or an inappropriate proportion of desiccants) speeds up drying and easily causes skinning. Low-VOC environmentally friendly offset printing ink also tends to develop drying and stringing issues due to poor adaptability of its solvent volatilization rate to the autumn and winter environment. Improper storage (uncontrolled temperature and humidity, direct sunlight) leads to premature deterioration and clumping of ink, increasing the risk of defects.

• Production Process and Equipment Factors: Poorly sealed ink fountains and failure to protect ink promptly during shutdown expose ink directly to air and accelerate skinning. Excessive ink roller pressure or rotation speed, or aged and rough ink rollers, intensify ink extrusion and stretching, triggering stringing. Failing to protect ink during short shutdowns also causes skinning.

Based on the causes and frontline practical experience, pre-emptive prevention measures are formulated from four dimensions to reduce the incidence of defects at the source:

• Environmental Control: Maintain workshop humidity at 55%-65% and temperature at 18°C-25°C using humidifiers and constant-temperature air conditioners to avoid temperature and humidity fluctuations. Optimize ventilation and prevent direct strong wind from blowing on ink fountains and ink paths. Prioritize ink fountains with sealed lids, close the lids promptly during shutdown, or spray environmentally friendly anti-skinning agents (ensure compatibility with offset printing ink).

• Ink Selection and Storage Optimization: Prioritize low-viscosity, high-fluidity autumn and winter-specific offset printing ink. For conventional ink, add anti-skinning agents under professional guidance. Store ink in a constant-temperature warehouse at 15°C-20°C, away from direct sunlight and extreme temperatures. Acclimate ink in the workshop 24 hours before use, use it within 24-48 hours after opening, and seal unused ink for storage.

• Pre-production Process Adjustments: Before printing, add thinners at a ratio of 3%-5% based on temperature and humidity, stir thoroughly to reduce ink viscosity. Clean ink fountains and rollers before startup, replace aged rollers, and calibrate ink roller pressure to 0.1-0.3MPa to avoid defects caused by abnormal pressure.

• Standardized Operating Procedures: During short shutdowns (≤30 minutes), keep ink rollers idling or cover the ink with plastic film or damp gauze. Before long shutdowns (>1 hour), thoroughly clean the ink path and fountain. Conduct test printing to confirm quality before formal production resumption.

When defects occur during production, targeted rectification is required, combining immediate handling with root cause investigation. Specific measures are as follows:

• Rectification for Skinning: For minor skinning, stop production, clean the affected area with a special ink scraper, add no more than 2% anti-skinning agent and stir thoroughly, then resume production after passing test printing. For severe skinning, completely disassemble and clean the ink path and fountain, replace with new autumn and winter-specific offset printing ink, check seals, and restart after test printing.

• Rectification for Stringing: Immediately reduce printing press speed by 10%-15%, add thinners or ink adjusting oil to improve fluidity. For root cause investigation, inspect ink roller condition (replace if aged), calibrate roller pressure, replace with dedicated ink if the current ink is incompatible, and adjust workshop temperature and humidity.

• Post-Rectification Verification: Print 10-20 test sheets after restart for random inspection. Proceed to continuous production for 1-2 hours only if no defects are found, and conduct random inspections every 30 minutes to ensure no recurrence of defects. Re-investigate and rectify if defects reappear.

Three typical cases are selected with interpretations from industry experts for reference by enterprises:

• Case 1: A food packaging plant had a skinning failure rate of 70% due to low workshop humidity (35%-40%). By installing humidifiers, switching to autumn and winter-specific offset printing ink and standardizing operations, the skinning failure rate dropped by 80% within one month, reducing monthly losses by over 8,000 yuan.

• Case 2: A commercial printing house saw its print qualification rate drop to 85% due to aged ink rollers and high ink viscosity. After replacing the rollers and adjusting the dilution ratio, the qualification rate rose to 98%.

• Case 3: A small and medium-sized printing factory adopted a low-cost solution (covering ink fountains with gauze and adding anti-skinning agents), reducing the defect rate by 60% and effectively controlling costs.

Skinning and stringing of offset printing ink in autumn and winter are preventable and controllable, with the core being a three-in-one approach of environmental control, ink adaptation and standardized processes. Climate is an objective trigger, proper ink selection and storage form the foundation, and standardized operation is the key. As autumn and winter printing enters a critical period, enterprises are urged to prioritize equipment inspections, ink selection and environmental optimization, establish standardized processes and strengthen employee training. Meanwhile, industry exchanges and cooperation are encouraged to jointly promote high-quality development. We will continue to interpret other ink-related challenges in autumn and winter printing, so stay tuned.