Blown Film Line Research Articles

Rheology modifier additive for enhanced processability of polyethylene forblown‐Filmapplications

AbstractPolyethylene is a versatile polymer suitable for a large variety of flexible and rigid packaging applications. Its mechanical and rheological properties can be tuned across a wide range by controlling its molecular architecture, such as the amount and distribution of olefinic comonomers (short chain branching), long chain branching, and molecular weight distribution. Linear low‐density polyethylene (LLDPE) is known for its high toughness which enables downgauged film structures and low‐density polyethylene (LDPE) is known for its excellent shear thinning and melt strength which enables enhanced processability and high throughput, such as on blown film lines. In order to obtain a balance of toughness and processability on films produced on blown film lines, blends of LLDPE and LDPE are commonly used. In this paper, we describe additive‐based approaches, including a new product, DOWLEX™ (TM = trademark of the Dow Chemical Company (“Dow”) or an affiliated company of Dow) GM AX01, which enhances melt strength and other rheological properties of polyethylene, enabling fabrication of films with lower LDPE content while still maintaining excellent rheological properties and higher toughness versus conventional LLDPE/LDPE blends. The higher toughness enables downgauging without loss of mechanical properties, which in turn reduces consumption of polymer resulting in a more sustainable solution.

Structure of N-Layer Film Obtained by Developed Blow Molding Process

Aim of the work was obtaining of the composite in form of n-layer polymer film and investigation of the structure. Manufacturing of the film combine the advantages of individual layers in one production process to achieve multilayer composite. In the experiment LDPE was used as main material. Processing of material was done using blow molding process and final product was obtained if the form of thin film. Conventional blown film line contains one extruder, die head, cooling ring and calibration basket, collapsing frame and winding rolls. To develop structure unique blow film line has been used. Two another extruder were joined to existing one transferring material simultaneously to the die head where 3 materials were joined together to combine 3-layered film. This process gives possibility to design final product and control the structure in many various combinations.

A process-oriented scale-up/scale-down strategy for industrial blown film processes: Theory and experiments

To gain a competitive edge in developing innovative products, new multi-layer film manufacturers need to know whether laboratory-scale blown film line results reliably translate to large-scale production. This, however, is not always the case: Transferring process conditions and getting equal final film properties are not ensured. To address this problem, this paper presents a scale-independent scale-up/scale-down strategy to produce films with consistently similar properties regardless of a plant’s size and design. A second aim is to prove this strategy is applicable by comparing the reference and experimental film mechanical properties. Here, experimental scale-down runs were carried out based on a process-oriented scale-up/scale-down strategy for the blown film process. An industrial production process (>800 kg/h), successfully transferred to a laboratory-scale blown film line, was used as the reference. The introduced process-oriented scale-up/scale-down is based on geometric and dynamic similarity. In this context, blow-up ratio, draw-down ratio and process time have been identified as major scale-up/scale-down variables. Unlike existing scale-up strategies, the process-oriented approach is more flexible in practice. Film mechanical properties taken from the experimental runs were determined by tensile and puncture resistance tests. The compared results confirmed that process-oriented scale-up/scale-down is feasible for the applied material and under the existing plant-specific restrictions. The comparison indicated that most film properties produced on the laboratory-scale plant were comparable to those from the high-capacity blown film line.

Real-time crystalline orientation measurements during low-density polyethylene blown film extrusion using wide-angle X-ray diffraction

Real-time wide-angle X-ray diffraction studies were successfully used to investigate the effect of film blowing process parameter on the crystalline orientation development during the blown film extrusion of low-density polyethylene. Azimuthal distribution scans showed the evolution of crystalline orientation in the bubble from an isotropic state to an oriented state as inferred from (110) and (200) planes. These real-time X-ray diffraction measurements in a blown film line are consistent with prior observations using polarized Raman spectroscopy (Gururajan and Ogale, J. Raman Spectrosc., 40, 212 (2009)) and small-angle light scattering (Bullwinkel et al., Int. Polym. Proc., 16, 41 (2001)) that significant molecular orientation takes place past the frost-line height, even after the blown film diameter is locked into place. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers

Optimizing Blown Film Line Layouts for Improved Surface Treating Performance

Blown film processors, large and small, have limited resources in both capital and manpower to devote to optimizing their productivity. Yet avenues of improvement are open for even the most over-extended organization. And some of the most effective modifications cost little more than a small change in equipment orientation or procedures. A key aspect of optimizing a blown film layout is line footprint and determining how to minimize footprint and maximize output with each integral piece of equipment on the line. Multiple surface treatment systems are integral to every blown film line and can control product quality and line efficiencies. The objective of this work is to present best practices of blown film manufacturers ranging from multinationals to small privately owned operations relative to the most effective surface treatment system designs, their roll coverings, optimum power density settings, alternative treatment technologies, troubleshooting protocols, and model line layouts that optimize production output.

The Problem of Die Drool in the Extrusion of Recycled Polyethylene

Present understanding of the formation of die drool is reported in light of current developments in materials for blown film polyethylene (PE). Two series of samples were collected from a blown film line, and the material from the die drool and the die channel, or blown film, were analysed separately. The techniques used included thermal analysis, melt rheology, filtration of dissolved material, and X-ray diffraction. Die drool was found to consist of segregated material, with the segregation depending on the content of high-molecular-weight branched polyethylene or impurities. As the presence of these PE materials may increase, it might be advisable for processors of recycled PE film to take prior actions to limit problems.

Molecular orientation evolution during low‐density polyethylene blown film extrusion using real‐time Raman spectroscopy

AbstractReal‐time polarized Raman spectroscopy was used in this study to measure the molecular orientation evolution during blown film extrusion of low‐density polyethylene (LDPE). Spectra were obtained at different locations along the blown film line, starting from the molten state near the die and extending up to the solidified state near the nip rolls. The trans CC symmetrical stretching vibration of polyethylene (PE) at 1132 cm−1 was analyzed for films possessing uniaxial symmetry. For the given peak, the principal axis of the Raman tensor is coincident with the c‐axis of the orthorhombic crystal, and was used to solve a set of intensity ratio equations to obtain second (〈P2(cosθ)〉) and fourth (〈P4(cosθ)〉) moments of the orientation distribution function. The orientation parameters (P2, P4) were found to increase along the axial distance in the film line even past the frost‐line height (FLH). The P2 values also showed an increasing trend with crystalline evolution during extrusion, consistent with past observations that molecular orientation takes place even after the blown film diameter is locked into place. It was also found that the integral ratio (I1132/I1064) obtained from a single, ZZ‐back‐scattered mode can provide a reasonable estimate of molecular orientation. These results indicate the potential of real‐time Raman spectroscopy as a rapid microstructure monitoring tool for better process control during blown film extrusion. Copyright © 2008 John Wiley & Sons, Ltd.

Melt Strength, Maximum Output, and Physical Properties of SURPASS TM1 sLLDPE–LDPE Blends in Blown Film

The development of Advanced SCLAIRTECH TM2 dual reactor technology and a proprietary single-site catalyst by NOVA Chemicals Corporation provides unique opportunities for resin design. This results in single-site linear low-density polyethylene (sLLDPE) products with a unique set of properties. For blends of these sLLDPE with low density polyethylene (LDPE), several benefits arise. The melt strength is enhanced easily, which benefits maximum output on blown film lines. The equivalent crystallization temperatures of sLLDPE and LDPE are beneficial for processability and physical properties. Adding as little as 5% LDPE to sLLDPE results in a 50% increase in maximum output, while maintaining a high film performance.

Temperature gradients in blown film bubbles

AbstractIt is argued that the assumption of negligible temperature gradients across the thickness in blown film extrusion is not valid in the vicinity of the die exit. Numerical simulation of heat transfer involving convection and radiation shows significant temperature differences between the inside and outside film surfaces, which gradually decrease and eventually become negligible near the frost line. The differences are influenced by the magnitude of local heat transfer coefficients. In blown film lines having internal bubble cooling (IBC), temperature gradients in the thickness direction may be reduced, but still they cannot be considered negligible for typical production rates. © 2005 Wiley Periodicals, Inc. Adv Polym Techn 24:83–90, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20039

A Rheological Model for the Prediction of Polyethylene Blown Film Properties

In this paper, a model is presented that enables us to get a better understanding of the relationship between polymer type, machine parameters and blown film properties for PE. For the mechanical properties it appears that the key parameter is the stress at the freeze line. Validation of the model on different blown film lines has proven its reliability for LDPE. Furthermore, the model has been extended to binary LDPE/LLDPE blends, demonstrating its versatility for PE in general.

A Rheological Model for the Prediction of Polyethylene Blown Film Properties

Development of new or improved blown film products is an expensive and time-consuming exercise for converters. Often, many experiments and trial runs have to be performed, accompanied by evaluations of the resulting film samples. If no lab-scale blown film line is available, valuable production time is lost while seeking out optimum processing parameters. Utilization of model calculations relating polymer type and machine parameters to properties of films obviously is an interesting option to streamline the development process of films. The practical use of model calculations depends on reliability and versatility of the model used. In this paper, a Theological model is presented that was developed for low density polyethylene (LDPE), and relates rheological properties, processing conditions and die geometry to mechanical and optical properties of the films. Validation of the model on different blown film lines has proven its reliability for LDPE. Furthermore, the model has been extended to binary LDPE/LLDPE (linear low density polyethylene) blends, demonstrating its versatility for PE in general. An oversight is given of theoretical and experimental issues encountered during the development of the model, complemented with some instructive examples of practical usage.

Instrumentation development for sensing modes of bubble motion of a blown‐film process

AbstractWe have developed instrumentation using an internal‐bubble pressure transducer with a data acquisition system to sense LLDPE bubble stability on a commercial blown‐film line. Real‐time bubble instability was also recorded using a video camera at a speed of 30 frames/s. The pressure signal was analyzed using a fast‐Fourier‐transform (FFT) computer program to determine the frequency of bubble oscillation. Since bubble instability often consists of large‐scale oscillation and bubble flutter, and both motions affect gauge and layflat uniformity, the pressure signal was decomposed to determine the frequency of each oscillation mode. To obtain a stable bubble, the amplitudes of both oscillation modes must be reduced to a minimum. Under a single mode oscillation, the period of bubble‐diameter variation analyzed using videotape matches that of the pressure trace. The initial results indicated that the trace of the pressure can provide a warning to the stability of a blown‐film process.

Deformational history of LLDPE/LDPE blends on blown film equipment

AbstractA video camera tracer technique (T. A. Huang and G. A. Campbell, paper to be presented at ANTEC '85, Washington, D. C.) was used to obtain MD velocity profile and bubble shape above the air ring under industrial film blowing conditions. Subsequently, the velocity profile and bubble shape were utilized to calculate strain and strain rate histories for a fluid element before it solidified. The deformational history of a fluid element was compared between LDPE and LLDPE of similar melt index and density. Also, the study was extended to two groups of LLDPE/LDPE blends: blends rich in LLDPE and blends rich in LDPE. We used a 100‐mil die gap for extruding resins rich in LLDPE to avoid melt fracture. A 30‐mil die gap was used to process blends that were rich in LDPE. Under the same film blowing conditions and frost line height, LDPE exhibits higher peak strain rates than LLDPE and the peak strain rates for LDPE occur closer to the air ring. Moreover, the MD strain of LLDPE continues to increase above the frost line. Conversely, the MD strain profile of LDPE levels off quickly before the frost line. The observed differences in fluid element deformation between LLDPE and LDPE on the blown film line are attributed to the higher melt tension of LDPE. For LLDPE, a 10 wt % LDPE addition causes a significant increase in strain and strain rate at lower positions. Interestingly, a further addition up to 25 wt % LDPE causes little or no further change in deformational history. The increased strain rates associated with an increased strain results in a stabilized LLDPE bubble. For LDPE, only slight differences in strain and strain histories were observed with the addition of LLDPE up to 25%.

Design Parameters for LLDPE Film Resin Selection

A wide variety of LLDPE resins have been run on laboratory through commercial scale blown film lines. The film properties fit into two classes, butene copolymers in one, and higher alpha-olefins in a second, higher strength class. Within each class the film properties have been correlated with resin density and melt flow properties. These relationships can help converters to choose the optimum LLDPE resin for each specific application.