news

Abstract: Pigment based inkjet printing ink has become the mainstream consumable for high-end digital printing, office printing, advertising printing, and digital coloring of textiles due to its excellent light resistance, strong weather resistance, high color fidelity, and resistance to fading. However, pigment powder has a large specific surface area and high surface energy, making it prone to agglomeration and sedimentation in water-based ink systems. At the same time, ink on low surface energy substrates has printing defects such as uneven spreading, droplet shrinkage, bleeding, and incomplete dots. Wetting agents, as key functional additives for inkjet inks, play multiple roles in wetting and depolymerizing pigment powders, regulating system surface tension, dynamically spreading substrates, and improving printing accuracy. Their selection and adaptability directly determine ink storage stability, nozzle smoothness, and final printing quality. In response to the common engineering problems of insufficient grinding fineness, long-term storage coarsening, nozzle clogging, printing color difference, and low dot reduction rate in current inkjet inks, this paper systematically screened four commonly used wetting agents: anionic, nonionic, organosilicon, and alkynediol. The effects of different wetting agents on pigment wetting efficiency, system dynamic surface tension, particle size distribution, storage stability, and printing adaptability were compared to clarify the optimal wetting system and addition range for pigment based inkjet inks, and to reveal the structure-activity relationship between wetting agent structure and inkjet system performance. The test results show that the low foam alkyne glycol type wetting additives have excellent dynamic wetting ability and low foam characteristics, can rapidly reduce the dynamic surface tension of the system, effectively improve the wetting and dispersion effect of organic pigments and carbon black powder, significantly improve the ink drop spreading uniformity and dot reduction accuracy, and do not affect the ink viscosity and spray stability of the nozzle. They are the best wetting additives for high-performance pigment inkjet inks. This study can provide experimental basis and theoretical support for the formulation optimization, additive screening, and industrial production of high-end pigment inkjet inks.

1 Introduction

Digital inkjet printing technology, with its advantages of high precision, high efficiency, low pollution, and flexible and controllable patterns, is widely used in fields such as graphic printing, textile digital printing, decorative board printing, and image output. According to the coloring medium, inkjet ink can be divided into two categories: dye type and pigment type. Compared with dye ink, pigment type ink uses inorganic and organic solid pigments as coloring components, which have excellent UV resistance, water washing resistance, and friction resistance, outstanding long-term color stability, and are the core development direction in the high-end printing field. However, the inherent agglomeration characteristics of pigment powders and poor interface compatibility with water-based systems have always constrained the quality improvement of pigment inkjet inks.

Pigment ink-jet ink is a nano dispersion system with high precision and high stability requirements. It not only needs ultra-fine and uniform pigment particle size, but also needs to meet the strict indicators of low viscosity, low dynamic surface tension, no foam, no sedimentation, plug prevention, and high-speed spray stability. During the ink preparation and grinding stage, a large amount of air is adsorbed on the surface of the dried pigment powder, making it difficult for aqueous media to quickly infiltrate the micropores of the powder, resulting in low grinding efficiency, incomplete powder depolymerization, and the presence of large particle residues in the system; In the printing application stage, the surface energy of substrates such as paper, polyester, PET film, etc. is low, and the surface tension of pure water systems is too high. Ink droplets are prone to shrinkage, non spreading, edge serrations, color bleeding and diffusion after landing, which seriously reduces the printing clarity and color uniformity.

Wetting agents can significantly reduce the static and dynamic surface tension of the system by adsorbing at the solid-liquid and liquid gas interfaces. On the one hand, they can replace the air on the pigment surface, achieve rapid wetting of the powder, assist in depolymerization and dispersion, and improve grinding fineness and system uniformity; On the other hand, it enhances the dynamic spreading ability of ink on various substrate surfaces, optimizes ink droplet formation and dot reduction effects. However, the molecular structure of different types of wetting agents varies greatly, and the anionic wetting agent foam is on the high side, and the dynamic wetting lags behind; Ordinary organic silicon wetting agents are prone to migration, causing surface shrinkage, poor recoating properties, and long-term storage delamination; Non ionic wetting agents have weak wetting efficiency and limited adaptability, and blind selection can easily lead to quality problems such as ink clogging, ink breakage, foaming, and storage coarsening. Based on this, this article conducts a special screening experiment on multiple types of wetting agents, systematically exploring the influence of wetting agent types and amounts on the comprehensive performance of pigment inkjet inks, and determining the optimal wetting scheme suitable for inkjet systems.

2 Experimental section

2.1 Experimental raw materials and additives

The experiment uses commonly used industrial pigment systems, including difficult to disperse carbon black pigments, phthalocyanine blue organic pigments, and iron oxide inorganic pigments; The dispersion medium is a composite solvent of deionized water, ethylene glycol, and propylene glycol, which is suitable for the moisturizing, anti drying, and anti clogging requirements of inkjet systems; Four mainstream additives were selected for comparative screening: anionic sulfonate wetting agent, ordinary fatty alcohol non-ionic wetting agent, polyether modified organosilicon wetting agent, and alkyne diol low foaming wetting agent; Supporting additives such as polymer dispersants, moisturizers, and fungicides are added, and all raw materials meet the production standards of high-precision inkjet ink with low impurities, low residues, and high stability.

2.2 Ink preparation process

Preparation of pigment inkjet ink using a process of pre dispersion, high-speed sanding, and low-speed blending. Firstly, mix deionized water, composite moisturizing solvent, wetting agent, and dispersant evenly to form a uniform transparent additive system; Batch feeding of pigment powder, high-speed pre dispersion to break down large aggregates; Transfer to the sand mill for ultrafine grinding, control the grinding speed and time, and monitor the particle size and fineness of the system in real time; After grinding to meet the standard, low-speed mixing, filtering, and static defoaming are carried out to obtain the finished pigment inkjet ink, which is sealed and cured for future use.

2.3 Testing and characterization methods

Dynamic surface tension testing: The maximum bubble pressure method is used to test the dynamic surface tension of inks with different additive systems and evaluate the interfacial wetting ability under high-speed spraying conditions;

Pigment particle size and dispersion stability testing: Laser particle size analyzer is used to test the ink D50 and D90 particle sizes, and the settling, coarsening, and layering of the system are observed through constant temperature standing and high-temperature thermal storage;

Foam performance test: test the foam height and defoaming speed of the system with high-speed oscillation method, and evaluate the adaptability of additives to low foam;

Printing performance testing: Test the smoothness of ink ejection, nozzle patency, dot restoration, and ink droplet spreading uniformity on the machine, and observe whether there are defects such as ink breakage, ink flying, bleeding, and color difference;

Rheological viscosity test: detect changes in ink viscosity before and after the addition of wetting agents to ensure compatibility with nozzle spray parameters.

3 Experimental results and screening analysis of additives

3.1 The influence of different wetting agents on surface tension and dynamic wetting performance

Dynamic wetting performance is the core indicator of inkjet ink, which directly determines the droplet forming and substrate spreading effects under high-speed printing conditions. The experimental results indicate that there is a significant difference in the ability of the four types of wetting agents to reduce surface tension. The static surface tension reduction effect of polyether modified silicone wetting agent is the best, but the dynamic response lags behind. The interface tension control is unstable during high-speed spraying, which can easily cause uneven ink droplet size and uneven printing dot density; At the same time, organic silicon molecules are prone to migration and enrichment at the system interface, and long-term storage can lead to surface oil film and shrinkage defects, which affect the printing quality.

Anionic wetting agents have moderate wetting efficiency, but strong foaming ability. During grinding and high-speed printing processes, a large number of microbubbles are easily generated. Bubbles mixed with ink can cause ink breakage, ink flying, and white spots in the print head, seriously damaging the continuity of printing; Ordinary non-ionic aliphatic alcohol wetting agent has low foam and stable system, but its molecular interface activity is weak, and its dynamic wetting ability is insufficient. Ink drops have poor spread on the surface of low surface energy substrate, which is prone to problems such as ink drop shrinkage, zigzag pattern edges, and decreased clarity.

Acetylene glycol based wetting agents exhibit the best comprehensive performance, with symmetrical molecular structures and fast interfacial adsorption rates, which can quickly reduce the dynamic surface tension of the system and meet the high-speed instantaneous wetting requirements of inkjet printing; At the same time, the self foaming property is extremely low, the defoaming speed is fast, and there is no foam accumulation in the grinding and spraying process, which perfectly adapts to the strict requirements of bubble free construction and stable spraying of the inkjet system.

3.2 Influence on wetting dispersion and particle size stability of pigments

Pigment inkjet ink requires ultra-fine particle size and long-term stability, with D90 typically controlled within 100 nm. Large particles and particle coarsening are the core causes of nozzle clogging. Without the addition of high-quality wetting agents, the pigment powder is not fully wetted, and the air inside the aggregates cannot be effectively discharged. Mechanical grinding is difficult to completely break the particles, leaving a large number of submicron sized aggregated particles in the system. Short term storage can lead to particle size increase, powder settling, and bottom thickening.

Acetylene glycol wetting agent can quickly penetrate into the pores of pigment aggregates, displace air on the surface of particles, significantly reduce solid-liquid interfacial tension, assist dispersants to achieve complete depolymerization of pigment particles, and significantly improve grinding efficiency and particle size uniformity. At the same time, this type of additive has excellent compatibility with polymer dispersants, which can synergistically enhance the surface coating effect of pigments, suppress particle Brownian motion and agglomeration, effectively solve the problem of long-term storage and coarsening of carbon black and organic pigments, ensure the long-term stability of ink particle size, and reduce the probability of nozzle clogging from the source.

3.3 Analysis of foam performance and spray stability

Ink jet printing belongs to high-precision micro jet system, which is extremely sensitive to foam. Micro bubbles can cause jet interruption, ink shortage and printing defects. Anionic wetting agent foam has strong persistence, small bubbles that are difficult to eliminate naturally, and cannot adapt to high-speed inkjet working conditions; Although the organic silicon wetting agent has a low foam, it is easy to cause system interface defects and abnormal wetting of the nozzle, resulting in ink droplet jet deviation.

The alkyne glycol wetting agent has unique characteristics of low foam, foam suppression and rapid defoaming. The molecule has no side chain hydrophobic enrichment structure, which makes it difficult to form a stable interface foam film. There is no foam accumulation under the conditions of high-speed mixing and high-pressure spraying. The ink system is pure and stable, and the jet is smooth and continuous, without ink break, flying ink, plug and other failures, which can meet the needs of industrial continuous high-speed printing production.

3.4 Comparison of Printing Quality and Substrate Adaptation Performance

There is a significant difference in the printing quality of ink prepared with different wetting agents. A system with insufficient wetting ability causes ink droplets to shrink and aggregate on the surface of the substrate, resulting in small dot diameters, incomplete edges, uneven spreading, and large areas of color blocks showing exposed bottoms, blurred areas, and color differences; In systems with excessive wetting or strong migration of additives, ink droplets spread uncontrollably, causing severe bleeding, dot expansion, pattern blurring, and significant loss of details.

The optimal alkyne diol wetting system can achieve precise and controllable wetting, with ink droplets evenly spreading, regular morphology, high dot reduction, clear pattern edges, high color saturation, and uniform color difference after landing. It can simultaneously adapt to various types of printing substrates such as paper, polyester fabrics, PET films, acrylic, etc., and has excellent broad-spectrum compatibility with substrates.

4. Mechanism and compatibility rules of wetting agents

In the pigment inkjet ink system, wetting agents and dispersants undertake differentiated functions: dispersants are mainly responsible for pigment particle adsorption stability, anti aggregation and anti redeposition; Wetting agents are mainly responsible for wetting the solid-liquid interface, air displacement, surface tension control of the system, and dynamic spreading of the substrate, which work together to achieve ink stability. High quality ink-jet special wetting agent shall meet the five core requirements of high dynamic interfacial activity, low foam, low migration, high compatibility and no residue.

The symmetrical structure of alkynediol molecules gives it both hydrophilic and hydrophobic equilibrium properties, allowing it to quickly adsorb at the interface between pigments and gas-liquid in a very short period of time. It can efficiently wet ultrafine pigment powders, assist in nanoscale dispersion, and accurately regulate the dynamic surface tension of ink, achieving stable formation and precise spreading of ink droplets under high-speed spraying. At the same time, this additive does not have compatibility conflicts with anionic dispersants, moisturizers, and fungicides in the system, does not affect the rheological viscosity and storage stability of ink, and has no post migration or precipitation problems, perfectly adapting to high-precision inkjet systems.

5 Key Control Points for Formula Application

Based on the screening test results, the application of pigment ink-jet ink wetting additives should be strictly controlled in two aspects: first, the selection of additives should give priority to low foam alkyne diols, prohibit high foam anions and high migration ordinary silicone wetting agents, and avoid foam, plug and image quality defects from the source; The second is to strictly control the amount of wetting agent added. Insufficient addition of wetting agent can lead to insufficient wetting, low grinding efficiency, and poor printing spreading. Excessive addition can cause low surface tension of ink, excessive spreading of ink droplets, severe bleeding, and improve the hydrophilic residue of the system, reducing printing water resistance. The optimal addition range for the project is 0.2% to 0.6% of the total system mass, which can be fine tuned according to the type of pigment and substrate.

If you need relevant technical guidance, please contact our technical personnel by leaving a message on the website

You can also contact us through the following ways:

Whatsapp:+86 18068723597

Mail:  sandy2000@huidechemical.com