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Abstract: Printing ink is a core material in the fields of graphic reproduction, packaging decoration, and functional printing. It can be divided into two systems based on the type of dispersion medium: traditional solvent based oil-based ink and environmentally friendly water-based ink. There are essential differences between the two types of inks in terms of formulation composition, dispersion state, film-forming mechanism, interfacial wetting behavior, rheological properties, printing adaptability, coating microstructure, durability, and environmental attributes. Oil based ink uses organic solvents as the continuous phase, with resin completely dissolved and a uniform and stable system. It has the advantages of strong wetting ability, fast drying speed, dense film formation, high glossiness, and wide substrate adaptability. It has long occupied the high-end film printing and fine graphic printing market; However, there are prominent issues such as high VOC emissions, flammability and explosiveness, solvent residue, environmental pollution, and human harm. Water based ink is mainly dispersed in deionized water, supplemented with a small amount of water-soluble solvents and environmentally friendly additives. It has the characteristics of low VOC, low odor, safe flame retardant, green low-carbon, and extremely low residue, which is in line with modern green printing industry policies and is the mainstream upgrading direction of the packaging printing industry. However, water-based inks have technical shortcomings such as high surface tension, difficulty in wetting low-energy substrates, significant influence of temperature and humidity on film formation, high drying energy consumption, easy foaming during high-speed printing, and weak water and wear resistance of coating films. This article conducts a comparative study from multiple dimensions, including system architecture, film formation mechanism, interface wetting, rheological properties, printing process adaptation, coating physical and chemical properties, environmental protection and safety, engineering application limitations and development trends. It deeply analyzes the performance advantages and inherent defects of the two types of inks, clarifies the material selection criteria under different printing scenarios, and provides theoretical basis and technical reference for the industrial application of water-based ink performance modification, process optimization, and replacement of traditional oil-based inks.

1 Introduction

The printing industry is an important supporting industry for packaging, cultural and creative industries, and light manufacturing. With the implementation of the national dual carbon policy, continuous upgrading of VOC control standards, and increasingly strict food packaging safety regulations, traditional high pollution and high-risk solvent based printing materials are facing comprehensive quality upgrades. Ink, as the core functional material in the printing process, directly determines the printing clarity, color saturation, dot restoration accuracy, coating adhesion, and product durability. For a long time, oil-based (solvent based) printing inks have dominated the fields of plastic flexible packaging, laminated paper products, metal printing, and high-end color printing due to their excellent interfacial wetting ability, stable rheological properties, rapid drying, and high film-forming quality. However, a large amount of organic solvents evaporate during its production and printing process, which not only causes serious air pollution and exacerbates the greenhouse effect, but also poses multiple risks such as workshop flammability and explosiveness, occupational health hazards for operators, and excessive solvent residue in packaging products, making it difficult to meet the modern needs of safe, environmentally friendly, and green industrial development.

Water based printing ink uses pure water as the main dispersing medium, replacing traditional petroleum based organic solvents and significantly reducing the VOC content of the system. It has significant advantages such as production safety, low toxicity and residue, low exhaust emissions, and simple post-treatment. It is currently recognized as a green and environmentally friendly printing material in the industry. In recent years, with the continuous iteration of water-based resin synthesis technology, wetting and dispersing agent modification technology, and drying and curing process, the printing stability, film density, wear resistance and weather resistance of water-based inks have been greatly improved. They have been widely industrialized in fields such as carton printing, paper packaging, textile printing, and food outer packaging. However, due to the inherent characteristics of high surface tension, slow evaporation rate, and dependence on environmental temperature and humidity for film formation, water-based ink still cannot completely replace traditional oil-based ink in high-speed fine printing, low surface energy thin film substrates, and high gloss and high wear resistant printing scenarios.

At present, the comparison between the two types of inks in the industry mostly remains at the level of environmental friendliness and simple performance, lacking a systematic academic review of micro film formation mechanisms, interface wetting differences, rheological adaptation laws, and the causes of process defects. Based on this, this article comprehensively, deeply, and systematically compares the system differences, performance mechanisms, process adaptability, and application limitations of oil-based ink and water-based ink, clarifies the core advantages and technical bottlenecks of the two types of ink, and provides complete theoretical support for subsequent ink formula modification, additive screening, printing process optimization, and green printing upgrade.

Differences in formula system and micro dispersion morphology

2.1 Characteristics of Oil based Printing Ink System

Oil based ink is mainly composed of organic solvents, alcohol ester ketone mixed solvents, solid synthetic resins, organic/inorganic pigments, and functional additives. Nitrocellulose resin, acrylic resin, chlorinated polypropylene resin, etc. in the system can be completely dissolved in organic solvents, forming a molecular level uniform true solution system; The pigment particles are uniformly dispersed in the resin solution through wetting and dispersing agents, and the dispersion medium is continuous and stable without particle phase separation. The overall viscosity of the system is controllable and the storage stability is extremely strong. It is not easy to separate, flocculate, emulsify, or coarsen after long-term storage. The auxiliary system mainly consists of solvent based wetting and dispersing agents, leveling agents, anti settling agents, and desiccants, which have excellent compatibility with the system. There is no involvement of water, and there are no problems such as hydrolysis, freeze-thaw emulsion breaking, or microbial deterioration.

Oil based ink belongs to a homogeneous dissolution system, where resin, additives, and solvents are completely miscible, pigments are evenly dispersed, and the microstructure is continuous and dense, laying the structural foundation for high gloss, high flatness, and high wear resistant coatings.

2.2 Characteristics of water-based printing ink system

Water based ink uses deionized water as the main dispersing medium, combined with a small amount of ethylene glycol, propylene glycol, and alcohol ether co solvents, with no high VOC organic solvents in the system. Film forming resins are mostly water-based acrylic lotion, water-based polyurethane dispersion, and water-based rosin modified resin. The resin is not dissolved in water, but suspended and dispersed in the water phase in the form of nano latex particles, belonging to a multiphase colloidal dispersion system. The system includes multiple additives such as pigment powder, wetting and dispersing agents, thickening and rheological agents, defoamers, moisturizers, and fungicides. The system has complex components, multiple phase interfaces, and weaker thermodynamic stability than oil-based systems.

Due to the significant difference in polarity between water and resin, as well as the high surface energy of pigment powder, water-based systems are prone to problems such as pigment aggregation, system layering, storage coarsening, low-temperature emulsion breaking, mold and deterioration. They are much more sensitive to the compatibility of additives, pH stability, and temperature environment than oil-based inks.

3. Film formation mechanism and microstructure differences

3.1 Mechanism of solvent evaporation and film formation in oil-based ink

The film formation of oily ink belongs to the process of single solvent evaporation and solidification. After printing and transferring onto the surface of the substrate, the low boiling point organic solvents in the system preferentially evaporate rapidly, while the high boiling point solvents evaporate slowly. The resin completely dissolved in the solvent gradually precipitates, accumulates, and tightly arranges as the solvent decreases, enveloping the pigment particles to form a continuous, dense, and smooth solid coating film. The entire film-forming process does not require particle fusion, cross-linking reaction, or residual moisture, and the film-forming rate is completely controllable under solvent formulation and environmental ventilation conditions.

After film formation, the resin molecular chains are tightly wrapped and stacked, with very few pores inside the coating and a dense and uniform structure. Therefore, oil-based inks generally have excellent physical properties such as high gloss, high hardness, high wear resistance, high water resistance, and low permeability.

3.2 Mechanism of water-based ink latex particle fusion film formation

The film formation of water-based ink belongs to a multi-stage composite process of water evaporation, latex particle extrusion fusion, and polymer chain diffusion entanglement. The first stage is the rapid evaporation of surface free water, resulting in an increase in system concentration and viscosity; The second stage involves latex particles approaching each other, squeezing and deforming, and particle interface fusion; The third stage is the mutual diffusion, entanglement, and recombination of polymer segments, forming a continuous overall coating film. The film-forming of water-based ink must meet the minimum film-forming temperature (MFFT) of the resin. Low ambient temperature and high humidity can cause incomplete fusion of latex particles, leaving a large number of micropores and cracks inside the coating, resulting in loose coating, decreased gloss, and decreased water and wear resistance.

Compared to oil-based inks, water-based inks have stronger dependence on the environment, longer film-forming cycles, higher drying energy consumption, and are easily affected by air humidity to produce film-forming defects.

Differences in Interface Wetting and Printing Forming Performance

4.1 Comparison of Wetting Ability of Substrate

Oil based ink with organic solvents has extremely low surface tension and natural excellent wetting and spreading ability for low surface energy non-polar plastic substrates such as PET, BOPP, PE, PP, etc. After ink droplets fall to the ground, they quickly spread without shrinkage, serrations, or shrinkage holes. The dots are full and round, and the graphic and text edges are clear, suitable for high-precision film printing. Regardless of whether the substrate has undergone corona treatment, oil-based ink can achieve good wetting and adhesion, and the substrate has a very high fault tolerance rate.

Water based ink uses water as the medium, and the static surface tension of pure water is as high as 72 mN/m, far higher than the critical surface tension of plastic substrates, with extremely poor natural wetting ability. If there is no high-quality wetting agent regulation, ink droplets are prone to printing defects such as shrinkage, agglomeration, incomplete dot, edge burrs, and exposed bottom and flower. Only by relying on alkynediol, organosilicon, and non-ionic wetting agents to reduce dynamic surface tension can it barely adapt to plastic printing, and strict requirements are placed on corona treatment and substrate surface energy.

4.2 Differences in adaptability of high-speed printing

The oil-based ink system has no foam risk, stable viscosity, controllable solvent volatilization, uniform transfer under high-speed gravure printing, flexographic printing, and silk screen printing conditions, stable ink layer, and is not easy to block and fly ink. The continuous production stability is extremely strong, and it is suitable for high-volume, high-speed, and high-precision industrial printing.

There are many surface active additives in water-based ink system, and micro foam is easily produced during high-speed shear mixing and high-speed printing. Micro bubbles will cause printing white spots, ink shortage, color spots and ink break defects; At the same time, water evaporates slowly, and high-speed printing is prone to problems such as slow drying, overlapping adhesion, and back smudging. Strong hot air drying and low foaming additive systems must be matched, and the difficulty of process control is much higher than that of oil-based inks.

Comparison of Physical and Chemical Properties and Durability of Coating Films

5.1 Adhesion and Weather Resistance

Oil based ink resin has good compatibility with non-polar substrates, with dense film formation and strong interfacial bonding. It is not easy to peel, peel off, or bubble after long-term use, and has excellent weather resistance, moisture and heat resistance, and aging resistance. It is suitable for packaging and graphic printing for long-term outdoor use.

Water based ink has weak adhesion to untreated plastic substrates, and residual additives and micro pore defects in the coating will further reduce the interfacial bonding strength. In long-term humid and hot environments, the coating is prone to whitening, foaming, and peeling, and the overall outdoor weather resistance is weaker than that of oil-based systems.

5.2 Water resistance and friction resistance

After the formation of oily ink film, there is no residual hydrophilic group, and the overall coating is hydrophobic and dense. It has strong resistance to immersion, rainwater erosion, and sweat erosion, and outstanding wear and scratch resistance.

The residual part of water-based ink is hydrophilic wetting and dispersing agent, and the initial coating has strong hydrophilicity. After complete drying and curing, the water resistance gradually improves, but there is still a gap compared to oil-based systems; When the film is not fully formed, the internal micropores are interconnected, making it easy for water to absorb and penetrate, resulting in a decrease in friction and washing resistance.

5.3 Glossiness and Color Performance

Oil based ink coating is smooth and dense, with few micro defects, uniform light reflection, and can easily achieve high gloss mirror effect. It has high color saturation, pure color rendering, and delicate layers, and has significant advantages in high-end color printing.

Water based inks are affected by the fusion of latex particles, residual additives, and micro pores, resulting in low coating flatness and generally dominated by matte and semi matte colors. High gloss water-based inks have difficulty in formulation, high cost, poor stability, and slightly lower color fineness than oil-based inks.

6 Differences in Environmental Protection, Safety, Production Technology, and Operation and Maintenance Costs

6.1 Environmental Protection and Safety Characteristics

Oil based ink contains a large amount of volatile organic solvents, with extremely high VOC values. The production and printing process emits large amounts of exhaust gas, which is flammable and explosive. The workshop has high safety risks, and the residual organic solvents cannot be completely eliminated. It is strictly prohibited to use it for direct contact with food packaging. The investment and operation costs of exhaust gas treatment equipment are high.

Water based ink uses water as the medium, with extremely low VOC, no risk of open flame combustion, greatly improved workshop safety, light odor, non-toxic residue, and meets the requirements of food packaging, infant and toddler products, and green packaging regulations. It has simple exhaust gas treatment and low operation and maintenance costs, and is the core development direction of green printing.

6.2 Production energy consumption and cleaning operation and maintenance

Oil based ink has a fast drying speed, does not require high-power hot air drying, and has low production energy consumption; However, specialized organic solvents must be used for equipment cleaning, which has high cleaning costs, high pressure for waste liquid and hazardous waste treatment, and serious environmental pollution.

Water based ink can directly clean equipment with clean water, and the waste liquid treatment is simple and environmentally friendly; But the drying speed is slow, relying on hot air drying, higher production energy consumption, difficult production in high humidity and rainy environments, and the yield rate decreases.

7 Applicable Scenarios and Industry Application Positioning

7.1 Mainstream application scenarios of oil-based ink

Suitable for high-end plastic flexible packaging, composite film printing, laminated paper, metal substrate printing, high gloss color printing, outdoor weather resistant printing, high-precision fine graphic printing and other industrial scenarios with extremely high requirements for wear resistance, water resistance, gloss, and clarity. It is currently an irreplaceable material for high-end packaging printing.

7.2 Mainstream application scenarios of water-based ink

Widely used in fields such as food cardboard boxes, paper packaging, textile printing, advertising printing, children’s product printing, and environmentally friendly cultural and creative printing that require high safety, low residue, low odor, and environmental protection levels, it is the absolute mainstream of civilian green packaging.

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