This paper describes the rheology of printing inks. Several kinds of pigments-linseed oil suspensions and commercial inks were used as the samples. For many years flow requirements of printing inks for various types of printing processes have been determined by skilled workers through experience rather than through experiments. However, it is very important for advances in printing or coating engineering that technical skills obtained emperically are confirmed theoretically or by scientific methods. The ink on a printing machine undergo various types of shear strain and complex deformations and flow processes. The optimum printing conditions and printability of inks are closely associated with their rheological properties. Therefore, we investigated the non-linear viscoelastic phenomena of printing ink under complicated rheological processes such as stress relaxation under large deformation, stress growth and relaxation following initiation and cessation of steady flow, non-linear creep and creep recovery. The equilibrium modulus in the long time region was observed in the stress relaxation curve. This phenomenon may be attributed to the formation of temporary network structure due to the association of suspended particles. Shear stress development after sudden initiation of steady shear flow showed an overshoot and approached an equilibrium value. The transient phenomena seem to be caused by the break down of the structure of dispersed particles. Disperse systems of pigments such as printing inks show remarkable thixotropy, rheopexy, pseudo-plastic flow, and structural viscosity attributed to a denser network structure of suspended pigments. In order to provide new concepts for these phenomena, creep compliance and creep recovery were measured under the conditions of various flow histories. The elastic properties of the network structure of suspended particles can be evaluated also from the creep experiments. The yield stress can also be determined from the relationship between recoverable strain and shear stress under steady flow. The formation of the temporary network structure of suspended particles were also investigated by an acoustical technique.
Torsional shear tests were performed with a cone and plate type rheometer on a 7.5vol% Bentonite slurry. To acquire real distortion and stress breakdown phenomena of the slurry, photographic visualizations were carried out simultaneously with the shear tests using lines marked on the sample surface as markers. The sample were elastic within small strain of less than 0.1, irrespective of the strain history. Stress increased with increasing strain beyond the elastic limit and exhibited an overshoot. The extent of the stress overshoot depended greatly on the rate of strain. The phenomenon corresponded with the fact that the width of sliding layer in the sample increased with increasing strain rate. Therefore, under a limiting strain rate, the breakdown of the sample took place only in a limited region but not in the whole specimen. Above a certain critical strain-rate, the sample exhibited thixotropic behavior. The sliding layer became narrower with time and finally became very thin at steady state. Stress-strain rate curve at steady state showed a different characterstics below and above this limiting strain rate. Stress hysteresis was also observed in the region slightly above the yield point.
The rheological behavior of flocculated Kaolin and Calcium Carbonate were examined by a torsional shearing test on a cone-and-plate rheometer. All of these sol type solutions behaved more or less like rigid bodies within small shear and suddenly broken down with increasing shear at several points in the slurries. Break down was progressed intermittently to give a step-wise stress overshoot. When shear rate was less than a limiting value, sliding layer was developed near the solid surface. The phenomenon was supposedly due to the dilatant nature of the slurry. Over the limiting shear rate, stress break-down occurred at once and as a whole without any stress overshoot, that is quite similar to a Binghammodel fluid. Steady state properties also varied at this limiting shear rate.
The entanglement molecular weight Me was evaluated from the relaxation modulus over the range of concentration 0.02≤c/g cm-3≤0.08 for polystyrene in chlorinated biphenyl. The result was consistent with the earlier result c1.4Me=1.23x104 (g cm-3)1.4 obtained from the relaxation time characterizing the nonlinear property of relaxation modulus in finite shear. The effect of concentration on the maximum relaxation time τ10 could be accounted for with the aid of the blob model of de Gennes if the observed effect of concentration on Me is employed for the determination of the exponent representing the excluded volume effect.
The inherent error involved in the measurement of dynamic mechanical properties of viscoelastic materials by a conventional forced-vibration method is theoretically evaluated by considering propagation of strain and stress waves in a sample. The frequency f and the sample length l must satisfy the criterion fl<0.12(|E*|/ρ)1/2, when the dynamic modulus and loss angle have to be determined within 10% error. Here, E* is the complex modulus and ρ is the sample density. For an ordinary polymer sample of a few centimeter length, the criterion sets the limit of applicable frequency below a few hundred Hz. To avoid these difficulties, we propose a new method of viscoelastic spectroscopy hopefully applicable in the audio frequency range, employing a technique of the mechanical impedance measurement. The new method involves the following procedures: Two equivalent vibraters are attatched to the both ends of a specimen. The vibraters are operated simultaneously with the phase difference θ of 0, π/2, π, and 3π/2, or only one vibrater is operated with the other end fixed (without operating the second vibrater). The impedance Z(θ) or Zfix is measured by an impedance meter attached to the end of the specimen. Then, the complex modulus E* can be estimated by one of several simple algebraic relations among the Z. One of such relations, for example, is E*=Z(0)Z(π)/ρA2, where ρ and A are the density and the cross-sectional area of the specimen, respectively.
Experimental investigation was carried out on the effect of carbon powder, which was generated in metallurgical furnace, on flow and mechanical properties of polypropylene. The effect of evacuation treatment during the blending process was also examined. The evacuation treatment results in decrease in melt vicosity and improved mechanical properties of the carbon-filled polypropylene. Suitable filler content was found to be 10%wt.
A continuous pulse oscillation method was devised modifying the sing-around method to determine the ultrasonic velocity (V) of a dilute suspension of rabbit red blood cells (RBC) in SF60 (60% glycerol solution) in the temperature range from 20°C to 40°C. The density (ρ) of the sample was also measured by a vibrational density meter. V and ρ are related to compressibility (B) by B=1/(ρV2). The difference in ultrasonic velocity between the RBC suspension and the medium decreased with raising temperature, while the difference in density increased. On the other hand, the RBC compressibility approached to that of the medium with raising temperature.