Summer features concentrated high temperature, high humidity and rainy weather, which is a peak period for various faults in offset printing. Offset production is highly sensitive to ambient temperature and humidity. Hot and humid conditions directly alter core printability of offset printing ink such as viscosity, drying rate and fluidity. Meanwhile, they also affect the performance of supporting materials including paper, fountain solution and ink rollers, frequently causing quality defects like print set-off, slow ink drying, false drying and re-adhesion, faded dots and dull ink tone. Such faults not only raise product rejection rates, increase waste of consumables like ink and paper and push up production costs, but also lead to order delays and customer complaints, undermining corporate production benefits. Combining the production characteristics of summer, this paper analyzes the root causes of three major frequent ink faults from four aspects: environment, ink, equipment and operation. It also sorts out practical ink mixing techniques and process control schemes, providing operational references for printing enterprises to stabilize printing quality in summer.
I. Core Impacts of High Temperature and High Humidity on Offset Printing Ink
Stable temperature and humidity are the foundation for normal application of offset printing ink. The hot and humid environment in summer impairs the printability of offset printing ink in multiple ways and triggers a chain of production faults. In high humidity conditions, water vapor in the air permeates the ink system, diluting ink concentration. It also disrupts the oxidative conjunctiva drying mechanism of oil-based ink and inhibits ink polymerization and film formation, which easily leads to excessive ink emulsification and reduced adhesion, further causing set-off and ink detachment. Sustained high temperature lowers ink viscosity, enhances fluidity and weakens thixotropy. During printing, the ink tends to spread and diffuse, resulting in faded dots and blurred outlines. In addition, high temperature accelerates the volatilization of surface solvents of the ink, forming a state of surface dry but inner wet (false drying), which seriously affects post-processing procedures such as film lamination and die cutting.
Furthermore, hot and humid conditions cause abnormalities in supporting materials. Moisture-absorbed paper suffers unbalanced water content and is prone to deformation. The concentration and pH value of fountain solution become difficult to stabilize, directly resulting in out-of-control ink-water balance. The superposition of multiple problems is the key reason for unstable printing quality and frequent faults in offset printing in summer.
II. Three Major Frequent Faults: Symptoms, Causes and Solutions
(1) Print Set-off (Back Set-off and Pile Smudging)
Fault Symptoms: After printed products are stacked for storage, incompletely dried ink adheres to the back of paper, causing smudges, ink spots and blurred images. Minor defects affect appearance, while severe cases lead to rejection of entire batches. This fault is most common in mass production of books, periodicals and color packaging printing, and ranks among the costliest printing faults in summer.
Root Causes: High humidity greatly reduces the oxidative drying rate and film-forming speed of ink. Operators add excessive ink mixing oil, resulting in overly thin ink with insufficient solid content. Overly high paper piles create a sealed and poorly ventilated space where heat and moisture accumulate and hinder ink drying. Meanwhile, excessive water supply of fountain solution in high humidity environment triggers severe ink emulsification and completely undermines the drying stability of ink.
Solutions: Optimize ink mixing ratio. Add dedicated fast-drying additives and drying oil as required to accelerate oxidative film formation of ink, and strictly control the dosage of ink mixing oil to maintain stable ink concentration and performance. Standardize on-site operations: reduce the stacking height of paper for each batch and reserve ventilation space. Keep dehumidifiers and exhaust fans running regularly in the workshop to lower ambient humidity. Refine process control: follow the summer principle of minimal water volume and stable ink-water balance, precisely control the dosage of fountain solution, regularly test fountain solution parameters and avoid excessive ink emulsification.
(2) Slow Ink Drying and False Drying with Re-adhesion
Fault Symptoms: The printed surface seems dry, while the internal ink is not fully cured. When products proceed to subsequent processes such as film lamination, box pasting and hot stamping, problems including ink detachment, re-adhesion, blistering and peeling of laminated films tend to occur, resulting in rework and rejection and seriously delaying production progress.
Root Causes: Water vapor in the air blocks the contact between ink and air and inhibits oxidative film-forming reactions. High temperature accelerates volatilization and failure of driers in ink, disabling the drying system. Most printing plants continue to use universal ink formulas all year round without adjusting auxiliary ingredient ratios for summer working conditions. Lack of standardized temperature and humidity control in the workshop further aggravates drying problems in hot and enclosed environments.
Solutions: Prioritize low-emulsification and moisture-resistant fast-drying special offset printing ink for summer use. Add driers in small quantities and multiple times to prevent crusting and plate clogging caused by excessive dosage. Establish a standardized environmental control system: keep the workshop temperature at 22-28℃ and relative humidity at 45%-65%, and discharge hot and humid air via linked equipment. Optimize production and circulation procedures: extend the drying time properly for products with large solid ink areas, and adopt batch production and batch circulation to prevent incompletely dried prints from entering post-processing stages.
(3) Faded Dots, Pale Ink Tone and Incomplete Dots
Fault Symptoms: Printed dots are incomplete with blurred edges and dull appearance, and the layered sense of images is lost. Solid areas suffer uneven ink distribution, insufficient color saturation and poor color reproduction. This problem is particularly prominent in high-end color printing and fine picture book printing, making it hard to meet sample standards.
Root Causes: High temperature reduces ink viscosity, and excessive fluidity leads to dot diffusion and collapse as well as poor ink holding performance. Water vapor in high humidity causes ink emulsification and dilution, resulting in pale and dull ink tone. Long-term operation of equipment raises the temperature of ink rollers. In addition, misalignment of ink-water roller pressure and unbalanced ratio lead to uneven ink and water transfer, eventually causing incomplete dots and dim colors.
Solutions: Optimize ink mixing process in a targeted manner. Add a small amount of thickening additives to improve ink viscosity and thixotropy, enhance ink adhesion and ensure complete reproduction of fine dots. Implement refined equipment commissioning: calibrate the pressure of ink-water rollers and impression rollers before startup every day, thoroughly remove impurities on ink rollers and plates, control the operating temperature of equipment and shut down for cooling in a timely manner. Standardize color control: abandon the improper operation of excessive water and insufficient ink. Reasonably adjust ink supply on the premise of stable ink-water balance, and precisely control the color layers of light screens and fine images to ensure full and even ink tone on the printing surface.
III. General Prevention and Ink Mixing Specifications for Offset Printing in Summer
Standardize selection of consumables: Replace universal ink with moisture-resistant, low-emulsification and fast-drying special offset printing ink in summer. Add auxiliary materials such as ink mixing oil, driers and diluents quantitatively as required, and avoid random proportioning to keep the overall performance of the ink system stable and adaptable to hot and humid production environments.
Regular environmental control: Implement a three-time daily inspection system for workshop temperature and humidity, and monitor environmental data in real time. Turn on dehumidification, ventilation and cooling equipment immediately when temperature and humidity exceed standards to prevent the workshop from being hot and enclosed. This can eliminate most seasonal ink faults from the source and guarantee stable printing quality.
Refined ink-water control: Adhere to the core summer principle of balanced ink and water, preferring dry over wet. Strictly control the water supply of fountain solution, regularly test its concentration, conductivity and pH value, and replace aged solution in a timely way to prevent excessive ink emulsification and stabilize ink drying performance and printability.
Routine equipment maintenance: Clean ink paths, ink rollers, water rollers and plates before daily startup to remove residual ink skin, dust and accumulated water, so as to ensure uniform ink and water transfer. Calibrate equipment pressure and temperature parameters and check the wear and aging of ink rollers every week, and replace worn parts timely to maintain stable equipment operation.
To sum up, faults such as set-off, slow drying and faded dots of offset printing ink caused by high temperature and high humidity in summer are not simply problems with ink quality. They are seasonal issues resulting from the combined effects of climatic conditions, ink proportioning, operational techniques and equipment status. Printing enterprises do not need to blindly purchase high-priced consumables or renovate equipment. By adjusting ink mixing formulas, standardizing workshop temperature and humidity management, refining ink-water processes and implementing equipment maintenance in line with summer production features, enterprises can effectively eliminate various ink faults, greatly cut product rejection rates and production costs, stabilize printing quality and production efficiency, and get through the peak production period in summer smoothly.
