Selection of ink rheological additives (1)
2024-09-09 06:01:03
Editor's note: This article reviews various rheology modifiers used in inks in terms of chemical composition, mechanism of action, and application performance.
The rheological additives discussed in this article range from organically modified clays to organic rheological additives such as castor oil derivatives, diamides, hydrophobically modified polyol polyethers (PEPO), hydrophobically modified polyurethanes (HEUR), and hydrophobic modifications. Acrylic copolymer (HASE). This article discusses the important application properties of each type of rheological agent in solvent-based, oil-based, waterborne, and UV-curable ink systems.
Overview Controlling the rheological behavior of printing inks has always been a challenge for ink manufacturers. In general, rheological additives are not the primary considerations in formulas when a chemist configures a new product. In general, the types of resins, solvents, and pigments have largely determined the rheological properties of the ink. The formulator always hopes that the rheological properties of the ink will meet the actual needs through the choice of resin type, which of course is very desirable. But the reality is that researchers have to choose rheological additives to further adjust the rheology of the product and improve the overall performance of the ink.
Rheology additives are one of the most important additives in printing ink formulations. The purpose of adding rheological agents is to adjust the rheology of the ink to meet the needs of different printing processes. Different ink printing methods determine the type of rheological agent in the ink formulation.
Oily and Solvent Inks In the lithographic printing process, the addition of rheological additives such as organoclay enables the ink to maintain a balanced concentration in printing. However, it is generally not necessary to add rheology additives that increase the viscosity of the ink during the relief, gravure, and ink jet printing processes.
Therefore, the role of rheology aids is to control the flowability, temperature stability, permeation and reverse osmosis properties of the ink, and to prevent settling of pigments and fillers in inks of lower viscosity.
Rheology is a science that describes the behavior of fluids. Understanding its basic theory is necessary for any formulator to design ink formulations. A typical rheological model is described as a rectangular body made up of very thin liquid sheets (Figure 1).
The rheological additives discussed in this article range from organically modified clays to organic rheological additives such as castor oil derivatives, diamides, hydrophobically modified polyol polyethers (PEPO), hydrophobically modified polyurethanes (HEUR), and hydrophobic modifications. Acrylic copolymer (HASE). This article discusses the important application properties of each type of rheological agent in solvent-based, oil-based, waterborne, and UV-curable ink systems.
Overview Controlling the rheological behavior of printing inks has always been a challenge for ink manufacturers. In general, rheological additives are not the primary considerations in formulas when a chemist configures a new product. In general, the types of resins, solvents, and pigments have largely determined the rheological properties of the ink. The formulator always hopes that the rheological properties of the ink will meet the actual needs through the choice of resin type, which of course is very desirable. But the reality is that researchers have to choose rheological additives to further adjust the rheology of the product and improve the overall performance of the ink.
Rheology additives are one of the most important additives in printing ink formulations. The purpose of adding rheological agents is to adjust the rheology of the ink to meet the needs of different printing processes. Different ink printing methods determine the type of rheological agent in the ink formulation.
Oily and Solvent Inks In the lithographic printing process, the addition of rheological additives such as organoclay enables the ink to maintain a balanced concentration in printing. However, it is generally not necessary to add rheology additives that increase the viscosity of the ink during the relief, gravure, and ink jet printing processes. Therefore, the role of rheology aids is to control the flowability, temperature stability, permeation and reverse osmosis properties of the ink, and to prevent settling of pigments and fillers in inks of lower viscosity.
Rheology is a science that describes the behavior of fluids. Understanding its basic theory is necessary for any formulator to design ink formulations. A typical rheological model is described as a rectangular body made up of very thin liquid sheets (Figure 1).
If the force F is applied to the area A of the fluid surface to generate a top lateral pull, this pull force is defined as the shear stress F/A.
When the fluid on the top layer begins to move under the action of shear stress, it will generate a pulling force on the second layer of fluid. Accordingly, the second layer will pull the third layer, and the third layer will pull the fourth layer again... If the fluid velocity of the top layer moves For V, the thickness of each layer of fluid is defined as X, then the viscosity gradient is defined as the shear rate (Figure 2).
In this way, the viscosity is defined as the "flow resistance" of the fluid, ie the ratio of the shear stress to the corresponding shear rate, ie: viscosity (fluid resistance) = shear stress (τ)/(γ).
There are different types of fluid flow, and the most important fluid types in the ink industry are Newtonian fluids, pseudoplastic fluids, and thixotropic fluids. The rheological profile of Newtonian fluids shows that the fluid viscosity remains constant at different shear rates (Figure 3).
The flow pattern of pseudoplastic fluids is the so-called shear thinning phenomenon. Many inks are pseudoplastic fluids, ie, the viscosity of the system decreases as the shear rate increases. Thixotropic fluids also exhibit shear thinning, but once the shear stress is removed, the viscosity of the thixotropic fluid takes a while to recover, and the viscosity and shear rate are plotted to form a hysteresis loop. The area of ​​the loop is The thixotropy of the fluid can be measured (Figure 4). (To be continued)
When the fluid on the top layer begins to move under the action of shear stress, it will generate a pulling force on the second layer of fluid. Accordingly, the second layer will pull the third layer, and the third layer will pull the fourth layer again... If the fluid velocity of the top layer moves For V, the thickness of each layer of fluid is defined as X, then the viscosity gradient is defined as the shear rate (Figure 2).
In this way, the viscosity is defined as the "flow resistance" of the fluid, ie the ratio of the shear stress to the corresponding shear rate, ie: viscosity (fluid resistance) = shear stress (τ)/(γ).
There are different types of fluid flow, and the most important fluid types in the ink industry are Newtonian fluids, pseudoplastic fluids, and thixotropic fluids. The rheological profile of Newtonian fluids shows that the fluid viscosity remains constant at different shear rates (Figure 3).
The flow pattern of pseudoplastic fluids is the so-called shear thinning phenomenon. Many inks are pseudoplastic fluids, ie, the viscosity of the system decreases as the shear rate increases. Thixotropic fluids also exhibit shear thinning, but once the shear stress is removed, the viscosity of the thixotropic fluid takes a while to recover, and the viscosity and shear rate are plotted to form a hysteresis loop. The area of ​​the loop is The thixotropy of the fluid can be measured (Figure 4). (To be continued)
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