Studies On The Viscoelastic Behaviors And Printing Performance Of Printing Paste

As an integral part of color paste, the paste, whose rheological properties are the major factors that affect printing results, determines the shade, color yield, sharp definition, print uniformity and feel of printed fabrics to a large extent. Most pastes fall into the non-Newtonian fluid and their rheological properties are extremely complicated. What kind of rheological pastes should be chosen to fulfill different print requirements has become a common concern.Regarding to the rheological behaviors of printing paste, static method is commonly employed both in domestic and abroad to explore the interrelationship between viscosity and shear stress, viscosity and temperature as well as the thixotropic property of paste. Paste is a macromolecular compound with the performance between solid and liquid and the trait of viscoelasticity. Although static method can partly reflect the paste's rheological properties, it is not able to manifest the paste's viscoelastic behaviors. However, the dynamic method can be employed to represent the paste's viscoelastic behaviors by measuring the characteristics of paste's storage modulus, loss modulus, loss angle and complex viscosity under the conditions of varying shear stress, frequency and strain.By means of the static method and dynamic method, steady shear and dynamic scanning tests, this paper studies three aspects:the viscoelastic behaviors of sodium alginate (SA) and xanthan gum; the influence of metal ions on SA's viscoelastic behaviors; the interrelationship between printing reactive dyes'viscoelastic behaviors and printing performance.Steady shear tests show that compared with SA, xanthan gum has high viscosity at low concentrations and low shear rates, and exhibits prominent shear-thinning behaviors of pseudoplastic fluids. With the increase of the paste's concentration or molecular weight, the paste's pseudoplasticity becomes more significant.Dynamic scanning tests indicate that SA is more viscous and performs more liquidlike behavior while xanthan gum more elastic effect and more solidlike behavior. The two pastes with similar viscosity perform totally different viscoelastic behaviors by the actions of shear stress, frequency or strain. With the increase of shear stress or strain, SA shows stable viscoelasticity. Its loss modulus is always higher than storage modulus and the loss angle is greater than 45°, and SA mainly shows viscous behavior. While xanthan gum's viscoelasticity shows a mutational change from high elasticity to viscosity. Before the change its storage modulus is higher than loss modulus and the loss angle is less than 45°, and xanthan gum exhibits distinctive elastic behavior. When the shear stress increases to a higher level, SA still shows stable viscoelasticity while xanthan gum approximates the behavior of liquid. With the increase of frequency, the properties of SA show transformations from high viscosity to high elasticity and then to the viscosity while xanthan gum shows relatively stable viscoelasticity. In the process of the SA's transformation, the elasticity will reach to its maximum and the loss angle is nearly 0°while xanthan gum's storage modulus is constantly higher than loss modulus and the loss angle is less than 45°. With the increase of the paste's concentration or molecular weight, the paste's elastic effect will gradually become stronger and the paste's viscoelasticity more steady.Calcium ion, copper ion and ferric ion influence the viscoelastic properties of SA more strongly than magnesium ion does. Within low frequency, when the concentration is higher than 300 ppm, the metalion paste's resilience is greater than the blank sample paste's and its elastic effect will be gradually strengthened with the increase of the metal ions'concentration. Urea, sodium bicarbonate and reactive dye have little effect on SA's viscoelasticity while reservehao S can enhance SA's elastic effect. Calcium ion influences the printing paste's viscoelasticity most prominently. When the concentration is higher than 100 ppm, the printing paste's elasticity is stronger than the blank sample printing paste's and with the increase of the concentration printing paste's elastic effect will be reinforced little by little.The paste's viscoelastic behaviors are closely related to printing performance. In the production we should select the paste with weaker elasticity, stronger viscosity and relatively steady viscoelasticity even in the action of external forces. The concentration of calcium ion should not surpass 300ppm; otherwise a large quantity of partial gel will be formed in the printing paste, thus affecting permeability of the printing paste and sharp definition of the textile.