Predictive modelling of film blowing: A 1-D approach

Journal of Coatings Technology and Research, 2013

The objective of this work is to investigate the feasibility of extending the velocity boundary during the slot die casting of a polymer film, by studying the dynamics of entrained bubbles as they transition from the fluid to the solid phase. The solution of interest is a relatively high viscosity non-Newtonian solution. A 2D computational fluid dynamics model, using ANSYS FLUENT 13.0 software, was developed to analyze this behavior. The volume of fluid method and enthalpyporosity technique were used to track the air (i.e., entrained bubbles) and fluid phases and the solidification of the solution, respectively. It has been found that for this class of solution, bubbles that are entrained in the fluid phase will not diffuse out of the fluid due to the stresses formed during solidification. Thus, for relatively high viscosity non-Newtonian solution, the upper boundary of the casting window cannot be extended after a defect has originated in the film during the casting process.

Metalurgija, 2005

Explosive crystallization of thin amorphous films is an auto-catalytic process driven by the internal heat release at the transformation front. The phase front propagate unusually fast – one to tens meters per second. The process is controlled by the competition between heat production at the front, and, heat removal by conduction. A sufficiently high front temperature is required to maintain front velocity kinetics. This, in turn, requires fast enough front to achieve a high rate of heat release at the front. In this paper we review the current state of modeling and experiments and analyze some simple solutions. The simple planar-front homogeneous model qualitatively explains experimental observations that explosive crystallization can be realized only in a limited range of background (substrate) temperatures and film thickness. However, quantitative predictions require more sophisticated models.

Extrusion in its simplest definition is a continuous process of conversion of polymeric substances either pellets or powder through shearing and melting as they are conveyed through single or twin screw extruder to form a pressurized melt. The pressurized melt is then made to flow through a properly shaped orifice or die and is then pulled with pressure to convert into the final product. Today extrusion is used to form various products such as pipe/tubing, weather-stripping, fencing, deck railings, window frames, plastic films and sheeting, thermoplastic coatings, and wire insulation. The first of its kind extrusion process was patented by Joseph Bramah in 1797 for converting soft metal into pipes. I will concentrate on plastic sheet extrusion process using T-type die for manufacturing of ‘Air Bubble Sheet’ or LDPE Sheet. Air Bubble sheets are transparent and flexible in nature sheets having evenly distributed air pockets to provide cushioning effect and to offer water and scratch resistance as well. Mainly it is used as a packaging material and now days a new application has emerged as a low-cost water proofing material.

Mesoporous Biomaterials, 2014

Bubbles arise at the intersection of gases with other phases. Their role in the formation and applications of thin films and porous materials is complex. At times they are to be avoided. In other cases they are essential to the desired properties and outcomes. In many cases their function, form and production are misunderstood or disregarded. This review seeks to connect a diverse array of technical and fundamental aspects of bubbles so as to facilitate more control and understanding of their functions and utility.

International Journal of Heat and Mass Transfer, 2013

The effect of polyolefin extensional rheology on the non-isothermal film blowing process stability and minimum achievable final film thickness has been investigated experimentally as well as theoretically utilizing variational principle model for the film blowing operation. It has been revealed experimentally as well as theoretically that the relationship between film blowing stability window size (and/or minimum achievable final film thickness) and the extensional strain hardening is non-monotonic in character for a given range of melt strengths, i.e. there is existence of the optimal values for both variables to reach maximum stability window size and/or the smallest minimum achievable final film thickness.

Polymer Engineering & Science, 2011

During the extrusion coating process, a polymer film is extruded through a flat die, stretched in air, then coated on a substrate (steel sheet in our case) in a laminator consisting of a chill roll and a flexible pressure roll. The nip, i.e., the area formed by the contact between the pressure and the chill rolls, constitutes the very heart of the extrusion coating process. Indeed, in this region, some of the most critical properties, such as adhesion, barrier properties, optical properties, are achieved. The thermomechanical analysis of Sollogoub et al., Polym. Eng. Sci., 48, 1634, was used to study the origin of the bubble defect appearing during the extrusion coating process. First, we investigate the influence of process parameters on the bubble defect. Then, we compute the thermomechanical parameters of the process, and finally, we derive a realistic bubble defect appearance criterion. POLYM. ENG. SCI., 00:000-000, FIG. 11. Effect of the steel sheet surface roughness: steel sheet 1 (a: Sample 1A) and steels sheet 2 (b: Sample 10A).

European Polymer Journal, 2016

The on-line morphological development during film blowing of 2 different linear low density polyethylenes (LLDPE) and a blend of LLDPE with low density polyethylene (LDPE) has been investigated, for the first time, using synchrotron Small Angle X-Ray Scattering (SAXS). The processing conditions, blow-up ratio and takeup ratio, have been varied and the resulting lamellar thickness, linear crystallinity and orientation evolution in machine direction is obtained from a detailed analysis of SAXS data. Ex-situ SAXS and wide angle Xray Diffraction (WAXD) confirmed the effect of molecular structure and composition on structure evolution observed in the on-line experiments. The results obtained provide a valuable set of data for the understanding of the film blowing process and can be used to extend and improve numerical model.

ACS Applied Polymer Materials, 2019

The influences of both temperature and external flow field on film blowing have been studied with a combination of a custom-built film blowing device and in-situ synchrotron radiation small-and wide-angle X-ray scattering techniques (SR-SAXS/WAXS). Polyethylene (PE) with different structural topologies, namely linear (MPE) and long-chain branched polyethylene (LPE), were used here with different responses to temperature and flow. The MPE film shows a spherulite-like superstructure with low orientation independent of take-up ratio (TUR), while the LPE has a typical row-nucleated structure at high TUR. But for LPE film obtained at low TUR, it exhibits the combination of both crystal morphologies. Further analysis of the microscopic structural evolution of PE during film blowing by synchrotron X-ray scattering reveals three different types of network evolution: i) the temperature-induced crystallization (TIC) dominated process (MPE); ii) the flow-induced crystallization

2007

A two dimensional molecular dynamic (atomistic) simulation model was used to investigate the relationship between the nano-structure and the deposition parameters; namely, substrate temperature, deposition rate, angle of incidence, surface roughness. Qualitative agreements with the predictions of the structure zone model (SZM) and the theoretical results of Srolovitze and coworkers (1988), as well as expectations through changes in the activated processes during film growth due to changes in deposition parameters (Grovenor and coworkers (1984)) are obtained. It is shown that by enhancing the atomic mobility (i.e., increasing the substrate temperature or/and lowering the deposition rate) films of higher density with fewer voids are produced. By increasing the deposition angle, the nano-structure of the film changes from a dense film with few voids, to a nano-structure with columns/boundless inclined with the same angle (β) towards the incidence atoms with elongated voids. The angle β increases with increasing the deposition angle (α), and in agreement with the tangent rule (Dirks and Leamy (1977)). The angle of bundles (or the angle of the formation of the voids between atomic bundles), and columnar structure are caused by shadowing effects. Results showed that β decreases slowly with increasing surface mobility (i.e., increasing the substrate temperature or/and reducing the deposition rate). In general, the model provides almost all predicted results and agrees well with observations.

Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, 2003

Atomic-scale control and manipulation of the microstructure of polycrystalline thin films during kinetically limited low-temperature deposition, crucial for a broad range of industrial applications, has been a leading goal of materials science during the past decades. Here, we review the present understanding of film growth processes—nucleation, coalescence, competitive grain growth, and recrystallization—and their role in microstructural evolution as a function of deposition variables including temperature, the presence of reactive species, and the use of low-energy ion irradiation during growth.