Gd Martin

Inkjet printing - the physics of manipulating liquid jets and drops

Over the last 30 years inkjet printing technology has been developed for many applications including: product date codes, mailing shots, desktop printing, large-area graphics and, most recently, the direct writing of materials to form electronic, biological, polymeric and metallic devices. The new non-graphical applications require higher print rates, better resolution and higher reliability while printing more complex, non-Newtonian and heavily solids-loaded liquids. This makes the understanding of the physics involved in the precise manipulation of liquid jets and drops ever more important. The proper understanding and control of jet formation and subsequent motion of the jetted materials requires physical studies into material properties at very high shear rates, acoustic modes in print heads, instabilities of jets, drop formation, drop motion, stretching of fluid ligaments, the role of polymers in jet break up, electrical charging of drops and the aerodynamic and electrostatic interaction of jets and drops in flight. Techniques for observation, measurement and analysis are evolving to assist these studies. This paper presents some examples of the application of physics to understanding and implementing inkjet printing, including recent work at the Cambridge Inkjet Research Centre.

Inkjet printing for pharmaceutics – A review of research and manufacturing

Global regulatory, manufacturing and consumer trends are driving a need for change in current pharmaceutical sector business models, with a specific focus on the inherently expensive research costs, high-risk capital-intensive scale-up and the traditional centralised batch manufacturing paradigm. New technologies, such as inkjet printing, are being explored to radically transform pharmaceutical production processing and the end-to-end supply chain. This review provides a brief summary of inkjet printing technologies and their current applications in manufacturing before examining the business context driving the exploration of inkjet printing in the pharmaceutical sector. We then examine the trends reported in the literature for pharmaceutical printing, followed by the scientific considerations and challenges facing the adoption of this technology. We demonstrate that research activities are highly diverse, targeting a broad range of pharmaceutical types and printing systems. To mitigate this complexity we show that by categorising findings in terms of targeted business models and Active Pharmaceutical Ingredient (API) chemistry we have a more coherent approach to comparing research findings and can drive efficient translation of a chosen drug to inkjet manufacturing.

A simple large-scale droplet generator for studies of inkjet printing

UNLABELLED A simple experimental device is presented, which can produce droplets on demand or in a continuous mode and provides a large-scale model for real inkjet printing systems. Experiments over different regimes of Reynolds and Weber number were carried out to test the system. The ranges of Reynolds and Weber numbers were adjusted by modifying the liquid properties or the jetting parameters. Reynolds numbers from 5.6 to 1000 and Weber numbers from 0.5 to 160 were obtained using water/glycerol mixtures in the drop-on-demand mode and Reynolds numbers from 30 to 5500 and Weber numbers from 20 to 550 for the continuous jet mode. The nozzle diameter can be varied from 0.15 to 3.00 mm and drop velocities were achieved in the range from 0.3 to 6.0 ms depending on the jetting parameters and the driving mode. KEYWORDS Droplet, printer nozzle, drop on demand and continuous jet.

Atomization patterns produced by the oblique collision of two Newtonian liquid jets

This paper reports a detailed experimental investigation of the formation, destabilization, and atomization of the liquid sheets created by the oblique impact of two laminar jets of a Newtonian liquid. Glycerol-water mixtures with viscosities between 4 and 30 mPa s were used to investigate the effects of viscosity and jet velocity. The jets were ejected from parallel cylindrical nozzles with an internal diameter of 0.85 mm. Collision of the jets resulted in various regimes of behavior which depend on the jet velocities and the liquid properties. We focus on the regime where the impinging jets form a liquid sheet which then breaks up into a regular succession of ligaments and droplets, a so-called “fishbone” pattern. We use short-duration, single-flash illumination combined with high-resolution digital photography to study the evolution of the sheet, its shape, and the form, size, and spacing of resulting ligaments and drops. Unexpectedly, we found fishbone regimes corresponding to lower Reynolds and Weber...

A novel method to produce small droplets from large nozzles.

This work presents a new method to generate droplets with diameters significantly smaller than the nozzle from which they emerge. The electrical waveform used to produce the jetting consists of a single square negative pulse. The negative edge of the pressure wave pulls the meniscus in, overturning the surface in such a way that a cavity is created. This cavity is then forced to collapse under the action of the positive edge of the pressure wave. This violent collapse produces a thin jet that eventually breaks up and produces droplets. Four droplet generator prototypes that demonstrate the capabilities of this novel mechanism are described. It is also shown that the proposed mechanism extends the existing limits of the commonly accepted inkjet operating regime.

Printing stable liquid tracks on a surface with finite receding contact angle.

We have used high-speed imaging to study the formation of liquid tracks on a surface with nonzero receding contact angle, by the sequential deposition of liquid drops. For small drop spacing we found good agreement with the track morphology predicted by an existing line stability model. In addition, we confirmed definitively the preferential drop-to-bead fluid flow and the predicted drop spreading variation in the scalloped line and paired bead formation regimes. However, we found that without accounting for drop impact inertia, the model underestimated the maximum drop spreading radii and, hence, the instantaneous track width. In addition, the printed track became stable at larger drop spacing, in contrast to the expected behavior. We believe that the destabilizing effect of a receding contact line may be minimized when track radii, as predicted by volume conservation and drop-bead coalescence dynamics, converge as the drop spacing increases. An increase in viscous dissipation and a reduction of the capillary-driven flow may be the additional stabilization mechanisms. The latter may also be responsible for achieving a stable and symmetrical track when printing with a shorter interval (higher print frequency) at a given drop spacing.

Development of High‐Throughput Glass Inkjet Devices for Pharmaceutical Applications

The application of the inkjet method to pharmaceutical products is promising. To make this realistic, not only does the throughput of this method need to be increased, but also the components should be inert to pharmaceutical preparations. We present designs of glass-based inkjet devices that are capable of producing droplets at high rates. To achieve this, inkjet devices from glass capillary tubes were manufactured with orifice diameters of 5, 10 and 20 μm and were actuated with diaphragm piezoelectric disks. Also, a pressure capsule was formed by creating a manifold at a distance from the orifice tip. Placing the piezoelectric disk at 0.5 mm distance from the tip allowed the formation of a jet at 3.2 MHz in certain designs, but for a short period of time because of overheating. The length of the pressure capsule, its inlet diameter, and the nozzle tip geometry were crucial to lower the required power. Actuating an inkjet device with 10 μm orifice diameter comfortably at 900 kHz and drying the droplets from 1% salbutamol sulphate solution allowed the formation of particles with diameters of 1.76 ± 0.15 μm and the geometric standard deviation of 1.08. In conclusion, optimising internal design of glass inkjet devices allowed the production of high-throughput droplet ejectors.

Optimizing the primary particle size distributions of pressurized metered dose inhalers by using inkjet spray drying for targeting desired regions of the lungs

Abstract Conventional suspension pressurized metered dose inhalers (pMDIs) suffer not only from delivering small amounts of a drug to the lungs, but also the inhaled dose scatters all over the lung regions. This results in much less of the desired dose being delivered to regions of the lungs. This study aimed to improve the aerosol performance of suspension pMDIs by producing primary particles with narrow size distributions. Inkjet spray drying was used to produce respirable particles of salbutamol sulfate. The Next Generation Impactor (NGI) was used to determine the aerosol particle size distribution and fine particle fraction (FPF). Furthermore, oropharyngeal models were used with the NGI to compare the aerosol performances of a pMDI with monodisperse primary particles and a conventional pMDI. Monodisperse primary particles in pMDIs showed significantly narrower aerosol particle size distributions than pMDIs containing polydisperse primary particles. Monodisperse pMDIs showed aerosol deposition on a single stage of the NGI as high as 41.75 ± 5.76%, while this was 29.37 ± 6.79% for a polydisperse pMDI. Narrow size distribution was crucial to achieve a high FPF (49.31 ± 8.16%) for primary particles greater than 2 µm. Only small polydisperse primary particles with sizes such as 0.65 ± 0.28 µm achieved a high FPF with (68.94 ± 6.22%) or without (53.95 ± 4.59%) a spacer. Oropharyngeal models also indicated a narrower aerosol particle size distribution for a pMDI containing monodisperse primary particles compared to a conventional pMDI. It is concluded that, pMDIs formulated with monodisperse primary particles show higher FPFs that may target desired regions of the lungs more effectively than polydisperse pMDIs.

Meniscus Motion Inside A DoD Inkjet Print-Head Nozzle

This is the author accepted manuscript. The final version is available from the Society for Imaging Sciences and Technology via http://www.ingentaconnect.com/contentone/ist/nipdf/2016/00002016/00000001/art00087