Wallace W. Carr

An experimental study of drop-on-demand drop formation

The dynamics of drop-on-demand (DOD) drop formation have been studied experimentally using an imaging system with an interframe time of 1μs and a spatial resolution of 0.81μm∕pixel. Using a piezoelectrical actuated inkjet printhead with the nozzle orifice diameter of 53μm, experiments were conducted over a range of viscosities (1.0–5.0cP) and surface tensions (35–73mN∕m). The effects of the driving signal, which controls the piezoelectric transducer that produces the pressure pulse to drive the liquid from the reservoir through the orifice, have been examined along with those of liquid properties. The main stages of DOD drop formation, including ejection and stretching of liquid, pinch-off of liquid thread from the nozzle exit, contraction of liquid thread, breakup of liquid thread into primary drop and satellites, and recombination of primary drop and satellites, are analyzed based on the experimental results. The breakup time of liquid threads was found to be dependent mainly on the capillary time based...

Visualization of drop-on-demand inkjet: Drop formation and deposition

An apparatus developed for visualizing drop-on-demand (DOD) drop formation and impaction on substrates is described. Using a pulsed laser, a low-speed charge coupled device camera, and signal generators, an imaging system based on flash photography is shown to be able to obtain sharp images with a temporal resolution of 200ns and a spatial resolution of 0.81μm∕pixel. Several steps are taken to minimize the “first drop problem” so that excellent reproducibility is achieved; drop formation is reproducible with a positional variation of 1μm. The visualization system coupled with a motorized stage allows imaging of the impaction of micron-size drops on surfaces. A wave form generator and an amplifier are used to produce the required wave form for a given printhead and ejected liquid. Demonstration of the system for study of DOD micron-size drop formation and impaction on a substrate is presented. The effects of signal wave form on DOD drop formation are demonstrated using a Trident printhead driven by four di...

Frictional Characteristics of Apparel Fabrics

A study has been conducted to determine the frictional characteristics of several fabrics used in apparel. The objective was to generate fabric frictional data to help in developing automated assemblies for fabrics. The results revealed that the coefficients of static and dynamic friction between fabrics decreased as the normal force per unit area increased. Wilsons model relating frictional force to normal force and the apparent area of contact closely correlated the data.

Application of a Differential Interferometer to the Measurement of Heat Transfer Coefficients

The basic components and principles of operation of a differential interferometer are discussed. This type of interferometer is inexpensive, relatively insensitive to vibration, and does not require extensive alignment adjustments. For free convection to an ideal gas the differential interferometer produces a fringe shift that is a function of the temperature gradient. The interferometer described is capable of producing an infinite fringe pattern in which fringe lines correspond to lines of constant index of refraction gradient. These facts make the differential interferometer useful for the measurement of convective heat transfer coefficients and flow visualization, particularly in dynamic systems and in cases where there are rapid fluctuation in the flow structure. A derivation of an expression for the free convection heat transfer coefficient is presented as a function of fringe shift. Several interferograms are included.

A model of through-air drying of tufted textile materials

Abstract A transient two-dimensional mathematical model is developed to simulate the through-air drying process for tufted textile materials. The heat and mass transfer in a cylindrical porous medium and the air flowing around it are analyzed separately. First, thermal and mass circuits are used to analyze the simultaneous heat and mass transfer within the porous medium. Then, the equations of the conservation of mass and energy are written for the drying medium. The resulting system of three non-linear differential equations is numerically solved by an implicit finite difference method. The numerical solutions are compared with experimental drying results obtained using magnetic resonance imaging (MRI) and a laboratory through-air dryer (LTAD).

High-shear-rate capillary viscometer for inkjet inks

A capillary viscometer developed to measure the apparent shear viscosity of inkjet inks at high apparent shear rates encountered during inkjet printing is described. By using the Weissenberg-Rabinowitsch equation, true shear viscosity versus true shear rate is obtained. The device is comprised of a constant-flow generator, a static pressure monitoring device, a high precision submillimeter capillary die, and a high stiffness flow path. The system, which is calibrated using standard Newtonian low-viscosity silicone oil, can be easily operated and maintained. Results for measurement of the shear-rate-dependent viscosity of carbon-black pigmented water-based inkjet inks at shear rates up to 2 x 10(5) s(-1) are discussed. The Cross model was found to closely fit the experimental data. Inkjet ink samples with similar low-shear-rate viscosities exhibited significantly different shear viscosities at high shear rates depending on particle loading.

Image Quality of InkJet Printing on Polyester Fabrics

This paper is concerned with the image quality of lines that were inkjet printed on polyester woven fabric. Lines (ideal width of 0.1 mm) running in the warp and filling directions were inkjet printed on different fabrics, and print quality (line width, edge blurriness and edge raggedness) was assessed. The effects of fabric structural parameters (including fabric, yarn and fiber parameters), finishing (type and pick-up), and ink type on line image quality are discussed. Image quality depended on fabric construction, particularly for unfinished fabrics. The satin fabric had the worst image quality while the image quality on the plain fabric was best. Finishing can improve image quality; however, the type of finish was very important. Acrylic resin finish improved printing quality significantly, but results with polyurethane resin-finished fabric were not much better than for unfinished fabric. A volatile ink reduced wicking and improves line image quality; thus, image quality using the alcohol base ink was better than for the oil or glycol based inks.

Drop-on-demand drop formation of polyethylene oxide solutions

The dynamics of drop-on-demand (DOD) drop formation for solutions containing polyethylene oxide (PEO) have been studied experimentally. Using a piezoelectrical actuated inkjet printhead with the nozzle orifice diameter of 53 μm, experiments were conducted for a series of PEO aqueous solutions with molecular weights ranging from 14 to 1000 kg/mol, polydispersity from 1.02 to 2.5, and concentrations from 0.005 to 10 wt. %. The addition of a small amount of PEO can have a significant effect on the DOD drop formation process, increasing breakup time, decreasing primary drop speed, and decreasing the number of satellite drops in some cases. The effects depend on both molecular weight and concentration. At lower molecular weights (14 and 35 kg/mol), the effect of PEO over the dilute solution regime is insignificant even at concentrations large enough that the solution does not fall in the dilute regime. As PEO molecular weight increased, the effects became significant. For monodispersed PEO solutions, breakup t...

Development of an easily deinkable copy toner using soy-based copolyamides

To develop an easily deinkable toner for office copiers and laser printers, a series of homo- and copolyamide toner resins were synthesized via condensation polymerization of a soy-based dimer acid, 1,4-phenylenediamine, and L-tyrosine (an α-amino acid). The thermal properties of the resins were examined using differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA). It was found that the glass transition temperature (Tg), melting point (Tm), decomposition temperature (Td), and crystallinity of the copolyamides were remarkably decreased as the content of L-tyrosine was increased. By using both homo- and copolyamides as binders, respectively, two dual-component toners were developed. The triboelectrical charge, particle size, and particle-size distribution of these toners were examined. The printing trials demonstrated that the images of the soy-based toners are similar to those of commercially available toners. However, because of the low crystallinity and high water-uptake ability of the amino acid-containing polyamide, the copolymer is swellable in an alkaline solution. Initial results from flotation deinking suggest that the amino acid-containing toners are more easily deinked, likely due to their high swellability.

Effects of Moisture and Fiber Type on Infrared Absorption of Fabrics

A study of variations in IR absorption characteristics of fabrics with moisture regain and fiber type is discussed. Infrared spectral absorptivities of fabrics are measured over the range of wavelengths from 0.7 to 25 microns. These values are used with the normalized emission characteristics of blackbody emitters to calculate average absorptivities for blackbody emitter temperatures ranging from 500 to 3000 K. Overall radiant efficiencies of the blackbody emitters are calculated by multiplying average absorptivities by the radiant efficiencies of emitters in converting input power to IR radiant output power. The absorption characteristics of several fabrics such as polypropylene and wool are measured so that the behavior of hydrophilic and hydrophobic fibers can be compared. Correlation equations are presented for average absorptivities of several fabrics as a function of moisture regain.