Guidelines On Prohibited Combinations And Standardized Processes For Matching UV Varnish Ink And Water-Based Varnish Ink With Printing Inks

With the high-end, refined and eco-friendly upgrading of the printing industry, market requirements for finished product appearance, protective performance and environmental indicators keep rising, making over-varnishing an essential value-adding finishing process for printed products. At present, UV varnish ink and water-based varnish ink have fully replaced traditional solvent-based varnish ink and are widely adopted in the production of various printed goods. Nevertheless, small and medium-sized printing enterprises generally suffer from inadequate process control. Most only focus on equipment and material procurement without complete compatibility standards, and frontline operations rely heavily on experience, resulting in arbitrary material selection, cross-system mixing and non-standard working procedures.

Practitioners commonly hold a misconception that printed and over-varnished products are qualified as long as the two procedures are completed, overlooking the physical and chemical differences and compatibility boundaries between different printing inks and varnish inks. Long-term irregular matching makes system mismatch a frequent quality pain point in printing. In terms of quality, it easily leads to colour shift and fading, blurred dots, blistering and mottling on the plate surface, and ink layer peeling. In terms of performance, the finished products fail to meet standards for abrasion resistance, folding resistance and weather resistance, and are prone to damage during storage and transportation. High-end packaging and premium printed products allow minimal tolerance for defects; once mass flaws occur, large-scale rework and scrapping are inevitable, increasing production costs, delaying delivery schedules and directly damaging enterprises’ market credibility.

1. Core Prohibitions for Matching Water-Based Varnish Ink with Printing Ink

Strictly prohibited from mixing with printing inks poor in alkali resistanceMainstream water-based varnish ink is weakly alkaline (pH 8.0–9.2). Alkali-sensitive colour printing inks such as reflex blue, golden red, violet and peach red will undergo chemical reactions when exposed to alkaline varnish ink, destroying the pigment colour development structure. The finished products will quickly turn yellow, suffer colour shift, dimness and partial fading, with colour aberration worsening during storage — this is a core operational red line.

Strictly prohibited from mixing with oil-based printing inksWater-based varnish ink adopts a water-based emulsion system, while oil-based printing ink relies on an organic solvent system; the two are completely incompatible. Coating water-based varnish ink on oil-based ink layers will trigger emulsification, delamination and repellent cratering, causing ink layer agglomeration and uneven spreading and curing of varnish ink, which results in plate surface contamination and full-batch product scrapping.

Forbidden to perform over-varnishing before printing ink is fully driedWater-based printing ink solidifies via water evaporation. If over-varnishing is carried out when the ink layer is not thoroughly dried, residual water will be sealed inside the coating layers and separate out gradually later, triggering plate surface blistering, bulging and delamination, drastically reducing ink layer adhesion. The finished products are highly susceptible to ink peeling and shedding, shortening their service life.

Exercise caution with non-special additives and diluentsGeneral diluents and miscellaneous-brand additives will disrupt the acid-base balance and emulsion stability of water-based varnish ink, leading to ink colour bleeding, dot blooming, plate mottling, uneven gloss and reduced abrasion resistance. During production, only special supporting auxiliary materials from manufacturers must be used; random blending is forbidden.

2. Core Prohibitions for Matching UV Varnish Ink with Printing Ink

Strictly prohibited from mixing with uncured general offset printing inkUV varnish ink contains highly active acrylic monomers with strong solvent erosion, which will directly dissolve and swell the resin of uncured general offset printing ink layers, resulting in dot diffusion, blurred patterns, colour mixing and bleeding, complete damage to images and mass scrapping.

Random mixing of different UV printing inks is prohibitedUV colour ink, gold and silver ink, and fluorescent ink feature vastly different formula systems. Mixing metallic pigments in UV gold/silver ink with ordinary colour ink will break system stability, causing sharp viscosity rise, premature gelation and poor fluidity of printing ink. Defects such as particles, pinholes and loss of gloss emerge after printing, and mixed ink cannot be stored for reuse.

Over-varnishing on semi-cured printing ink is forbiddenUV printing ink requires full crosslinking and curing under ultraviolet light to form a stable ink layer. If over-varnishing is performed under semi-cured or surface-dry conditions, the varnish ink will block ultraviolet rays, leading to incomplete curing of the underlying printing ink and uneven drying of the top varnish ink layer. Subsequent problems include skinning, cracking, edge warping, failed adhesion and large-area ink peeling and shedding.

Mixing non-UV special diluents is prohibitedOrdinary water/oil diluents will damage the photoinitiator system of UV varnish ink and inhibit crosslinking reactions, triggering a chain of faults including incomplete curing and sticky surface of varnish ink, plate surface fogging and gloss loss, as well as printing ink colour change. Only special diluents are allowed for UV systems.

Inherent conflicts in physical and chemical properties of systemsWater-based, oil-based and UV systems adopt entirely different carriers and resin structures: water-based materials are alkali-biased and hydrophilic, oil-based materials are hydrophobic, and UV systems feature high activity and strong erosion. Cross-system mixing inevitably causes physical faults such as delamination, emulsification, dissolution and repellency, which serve as the fundamental cause of quality issues.

Irreversible chemical reactions causing material damageAlkaline varnish ink decomposes alkali-sensitive pigments, and active UV monomers corrode resins in ordinary ink layers. Such chemical reactions are irreversible, directly leading to fading, ink peeling and image damage, leaving no room for rework and recovery of finished products.

Non-standard timing and operation of working proceduresInsufficient drying and curing time of printing ink traps residual solvents and water under the varnish ink, forming hidden internal hazards. Mismatched curing parameters and disordered procedure connection will undermine interlayer adhesion and induce blistering, delamination, peeling and other defects.

Unprofessional material selectionMost enterprises select materials merely based on price and gloss while ignoring core parameters such as acid and alkali resistance, solvent resistance and curing compatibility. Disconnection between procurement and production leads to recurring compatibility faults caused by long-term general mixing of materials, which cannot be fundamentally solved.

Adhere strictly to the principle of matching within the same systemWater-based varnish ink shall only be matched with alkali-resistant water-based printing ink; oil-based printing ink and alkali-sensitive colour ink are forbidden. UV varnish ink shall only be matched with fully cured UV printing ink and special cured offset printing ink; cross-system mixing must be eliminated to avoid compatibility risks at the source.

Conduct sample testing before mass productionFor new materials, new formulas and new orders, full-process proofing, curing and over-varnishing shall be completed in accordance with formal processes before mass production. After standing for 24 hours, tests on colour, dots, adhesion, flatness and curing status shall be carried out. Mass production can only be launched if no colour bleeding, blistering, delamination or sticky surface is detected.

Strictly control procedure timing and equipment parametersEnsure full drying and curing of the underlying printing ink before over-varnishing. For water-based processes, reasonably regulate drying temperature and paper running speed to guarantee complete water volatilization. For UV processes, calibrate UV lamp power and curing speed to achieve thorough curing of both coating layers, eliminating construction under false-dry or semi-cured conditions.

Standardize specifications for auxiliary material useOnly original supporting special diluents and additives shall be used for all printing inks and varnish inks. Standardize mixing ratios and blending procedures to avoid mixing general solvents, stabilize system performance and prevent derivative quality defects.

Improve material warehousing and management systemsUV materials shall be stored at low temperature and away from light to prevent premature curing; water-based materials shall be sealed and stored at constant temperature to avoid emulsion deterioration. Establish material ledgers and validity period control; expired materials are prohibited, and random mixing of materials of different brands and models is banned to unify production standards.

Three core principles must be followed in printing over-varnishing production: matching within the same system, testing prior to mass production, and strict control of process parameters. Extensive production modes relying solely on experience shall be completely abandoned, and standardized control shall be adopted to avoid mismatch risks and stabilize product quality.

Enterprises shall establish ledgers recording prohibited combinations of printing ink and varnish ink, standardize full-process specifications covering procurement, storage, blending, printing and inspection, and organize special training for operators regularly to popularize compatibility knowledge and operational red lines. Quality shall be controlled comprehensively from personnel, system and process dimensions.

Refinement and standardization will be the mainstream development trend of the industry. Standardizing matching rules for varnish ink and printing ink and avoiding basic process errors can effectively reduce defective rates, cut material waste, improve production efficiency, help enterprises boost quality, lower costs and raise efficiency amid competition for high-end orders, and build stable production competitiveness.

The over-varnishing process determines the appearance texture and protective performance of finished printed products, and compatibility control between varnish ink and printing ink is the core of post-finishing quality management. Most mass printing defects are not complex technical problems, but stem from mismatched materials and non-standard operations. By strictly abiding by the prohibited use rules of two types of varnish ink and implementing standardized processes, enterprises can eliminate most post-finishing defects at the source, reduce rework losses and improve finished product stability and market competitiveness. Against the backdrop of industrial upgrading, refined processes and standardized operations will become the core foundation for long-term sustainable development of printing enterprises.