Ink Compatibility in Inkjet Printing | How Does Viscosity Affect Inkjet Technology? The Importance of High Viscosity

Ink Compatibility in Inkjet Printing

 

Concept of Ink Compatibility

Ink compatibility refers to the performance of the ink that matches the printing conditions and is suitable for printing operations. It mainly includes viscosity, adhesion, thixotropy, drying properties, etc.

Ink Viscosity

Viscosity refers to the internal friction characteristics of the ink while flowing, which is a measure of how resistant the liquid is to flow. It is the physical quantity that measures the ink's viscosity.

The faster the speed of the inkjet printer/press, the greater the ink flowability required, and the lower the viscosity needed.

Ink viscosity can be adjusted using ink additives or diluents.

For more information on printing ink, refer to the article:
"Types and Composition of Traditional Printing Inks"

★ Tips

cp: Centipoise (cP) is the smallest unit of dynamic viscosity. Dynamic viscosity is the measurement of internal friction force in a liquid as it flows under a certain shear stress. Its value is the ratio of the applied shear stress to the shear rate, and it is typically expressed in Pa·s in the SI unit system, but commonly used as cP.
1 cP = 10^-3 Pa·s = 1 mPa·s
1 cP = 100 Poise

Common Fluid Viscosity Values

Unit: centipoise (cP)

Viscosity refers to the flowability (or resistance to flow) of a substance, with the measurement unit being centipoise (cP).

• Water at 20°C has a viscosity of 1 cP, which is very easy to flow.
  
  

• Molasses has a viscosity of 100,000 cP, which is very thick.
  
  

• 1 cP = the viscosity of water; 10,000 cP = the viscosity of honey.
  
  

• 500 cP = the viscosity of vegetable oil.
  
  

• 100,000 cP = the viscosity of molasses.
  
  

• 2,500 cP = the viscosity of motor oil.
  
  

Ink Adhesion

Ink adhesion refers to the ability of the ink to resist breaking during the process of transferring from the ink reservoir to the ink roller, printing plate, and eventually to the substrate (such as rubber blankets). The physical quantity that measures ink adhesion is called the "Tack" value.

Ink adhesion can be adjusted using adhesion agents or ink additives.

Ink Thixotropy

At a certain temperature, ink's flowability improves when stirred or subjected to mechanical force, which decreases the viscosity. When left standing, the flowability deteriorates, and the viscosity increases again. This property is called thixotropy.

For information on ink formulation ratios and process characteristics, refer to these articles:

• "Inkjet Printing Conductive Ink Process Performance and Application Fields"
  
  

• "Basic Ingredients of UV Curing Ink Formulas"
  
  

• "10 Common Water-Based Ink Formulations and Process Parameters"
  
  

• "Water-Based Inks for Enhancing Sustainability in Textile Printing"
  
  

Ink Drying Properties

Ink drying is a complex process and mainly involves the following three forms:

• Absorption Drying: Some of the binder in the ink penetrates into the substrate, while the remaining part, along with the pigment, bonds to the surface of the substrate and dries.
  
  

• Oxidative Polymerization Drying: The binder in the ink reacts with oxygen in the air, polymerizes, and forms a film on the substrate surface, drying in the process.
  
  

• Evaporation Drying: Some of the binder in the ink evaporates into the air, while the remaining binder and pigment remain on the substrate surface, causing the ink to dry.
  
  

 

How Does Viscosity Affect Inkjet Technology? The Importance of High Viscosity

How Does Viscosity Affect Inkjet Technology? 

Viscosity is a measure of a fluid’s resistance to flow and describes the internal friction that occurs when a fluid is in motion.

Fluids with higher viscosity resist flow due to their molecular structure, resulting in greater internal friction. In contrast, fluids with lower viscosity flow more easily and generate less friction during movement.

Viscosity is influenced by multiple factors, including temperature, the base viscosity of the material, and particle loading.

Traditionally, the recommended nominal jetting viscosity for industrial inkjet printing applications has been 6–15 centipoise (cP). This range is also affected by printhead design, flow rate, operating temperature, and the fluid-handling capability of the system.

Fluids with higher particle loading inherently exhibit higher base viscosity.

However, current inkjet technologies are now capable of stably jetting fluids with higher particle concentration and density, enabling the use of higher-viscosity materials in applications such as photopolymer jetting.

 

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The Importance of High Viscosity

The ability to print high-viscosity fluids significantly expands the range of materials that can be used in drop-on-demand inkjet printing.

By increasing particle loading or using larger particles, it is possible to achieve a wider color gamut and higher opacity in single-pass printing, while also reducing ink consumption and improving energy efficiency.

As viscosity increases, printed colors become more vibrant, with stronger contrast between white and black. This exceptional ability to achieve high opacity—especially white—in single-pass printing is particularly valuable for many label printing and direct-to-shape packaging applications.

Single-pass jetting of liquids or inks provides label and packaging printers with opportunities to increase production efficiency and throughput, while enabling innovative finishes on a wider variety of packaging substrates.

The process is also more sustainable, as printing can be performed at room temperature without the need for additional high-temperature heating.

High-viscosity jetting enables thick varnish and coating effects, adding texture, visual appeal, and functional properties to labels, packaging, or even primary packaging and products themselves (such as glass bottles), while ensuring durability during handling and washing.

In 3D printing and additive manufacturing, printing high–molecular-weight polymers results in parts that are stronger, more elastic, and more flexible.

Additionally, jetting higher-viscosity fluids reduces droplet spreading before curing (referred to as dot gain in analog printing), thereby improving edge sharpness on non-porous substrates.