Johann Philipp Dilo, CEO of Dilo Group, examines developments in needling technology and how they compare with hydroentanglement solutions.
In recent decades, significant progress has been made in the development of needling technology for staple fibre production. Machine builders have achieved notable advancements in web formation and consolidation, leading to considerable improvements in product quality, particularly homogeneity, production capacity and efficiency. However, public awareness of the importance of needling, based on statistical production data from a wide range of applications, was not always evident.
For many years, there was a close competition between nonwovens produced from staple fibre and those made from continuous filaments, as reflected in the respective production data. A similar rivalry existed between the consolidation technologies of hydroentanglement and needling. The market was divided between needled products and those that were hydroentangled. Needling, due to its ability to be applied to any fibre material across a wide range of weights and fibre fineness, predominantly controlled the higher weight range, typically over 100 gsm.
In contrast, hydroentanglement excelled in the lower weight range of 30 gsm to 100 gsm, especially in fine fibre applications. This success was fuelled by the growing demand for hygiene products, where hydroentanglement has dominated and recently surpassed the production volume of needled products. For a long period, it appeared that intensive needling could not penetrate this crucial lightweight sector.
Sustainable requirements
Recently, the rising cost of energy – particularly electricity and gas – combined with increasing water shortages, has prompted a re-evaluation of production methods. Now, economic considerations are increasingly tied to the environmental impact of industrial production. For Dilo, as a specialist in needling, this presented an opportunity to reconsider the potential of needling technology to better serve the fine and lightweight sectors. Key aspects of intensive needling were analysed and partially revised.
The necessary high advance per stroke – approximately 50 mm per stroke – requires extremely high stitching densities to achieve sufficient abrasion resistance in the final product. This necessitates a significant increase in the number of needles per board. Simulations indicated that the needle count would need to rise from around 20,000 needles/m/board to 45,000 needles/m/board. At the same time, Dilo’s needle modules had to be housed in specially designed needle boards, allowing for precise arrangement and quick exchange when necessary.
The entire needling zone was modified using “wire plates,” which replaced the previously used drilled or slotted stitching plates. These design changes were showcased at ITMA 2023 in Milan, where the company demonstrated that intensive needling, employing high needle densities at high advances per stroke, could be effectively applied.
Economy vs environment
The economics of needling are significantly influenced by current high electricity costs, which drive the high-pressure pumps used in hydroentangling, as well as by the cost of gas required to dry water from the entangled fleece. The global water shortage will further impact the economics of needling compared to hydroentangling.
In addition to economic factors, environmental considerations are becoming increasingly important. For instance, hygiene wipes should be made from biodegradable fibres to ensure they can decompose in an environmentally friendly manner after single use. To achieve this, the industry must aim to eliminate polyester or polypropylene from single-use lightweight products and instead use fibres such as viscose, cotton, or other natural fibres and biopolymers. An added benefit of using viscose and natural fibres is their ability to absorb and retain moisture, an essential quality in hygiene applications. However, this same characteristic becomes a disadvantage when hydroentangled nonwovens need to be dried in ovens.
The throughput rate of carded viscose and natural fibres is considerably lower than that of polyester or polypropylene fibres. As a result, both the ecological and economic aspects of hydroentangling and needling need to be carefully evaluated.
MicroPunch cost reductions
Simulations and production cost calculations suggest that cost reductions of up to 50% can be achieved when needling is used instead of hydroentangling, though these figures must be verified on a case-by-case basis, factoring all fibre and production parameters. Production tests can be conducted on the Dilo research and development (R&D) and demonstration line to assess these variables.
Typically, nonwoven production lines for wipes operate at working widths of approximately 3.6-3.8 metres. In such lines, when hydroentangling is used, the electrical power required is more than double that of needling. This extra power is necessary to operate the high-pressure pumps, filter the recirculated water, and vacuum the soaked fleece. In contrast, the mechanical needling process does not require water or heating gas for drying and, as it is easier to recycle, needling produces less fibre waste.
Hydroentangling lines require high-pressure pumps to create a stable jet capable of penetrating the fleece. However, unlike steel needles, which can endure several hundred million strokes, the kinetic energy of the water jet is lost after it penetrates the fleece once.
Technical aspects
“MicroPunch” intensive needling technology should ideally incorporate random carding, a process that benefits from the use of random and condenser rollers, which have been available from Spinnbau for decades. The choice of line configuration, whether with or without a cross-lapper, significantly impacts fibre throughput. Lines that include cross lappers naturally experience reduced maximum line speeds. To mitigate this, only state-of-the-art cross-lapping technology should be employed, featuring high layering precision and the fastest web infeed speeds – particularly when the layering width is below four metres, which is common in many lines.
This requirement is best met by DILO’s HYPERLAYER technology. In this process, the web is handled between two screen aprons that transport it from infeed to the layering point with minimal dimensional changes, ensuring low MD (machine direction) draft and CD (cross direction) shrinkage. As a result, hyperlayering delivers optimal layering precision and lapper joints, allowing for maximum nominal speeds of up to approximately 200 m/min, depending on larger layering widths.
CycloPunch kinematics enables advances of approximately 50-65 mm per stroke, resulting in throughput speeds of 50-65 m/min at 1000 strokes/min in the needling line. Depending on the draft during needling and in the end-of-line components – including configurations of drafting units – a nominal throughput speed range of approximately 125-160 m/min at 2500 strokes/min can be expected. Draft ratios further increase this speed before winding. A longitudinal draft of 15-30% can be applied, potentially raising throughput speeds to around 180-200 m/min, with one card providing a web mass of approximately 30-40 gsm, or more when two cards are used in-line.
The economics of a complete line depend heavily on production capacity, as production per hour is crucial in determining fixed costs per kilogram of fibre mass in the final product. When calculating the economics, it is essential to account for the impact of different fibre types on fibre throughput in the carding units. For instance, production rates tend to be lower when using viscose and natural fibres, as compared to polyester. Moreover, the higher the proportion of viscose or natural fibres in a blend, the greater the water retention in the fleece. This, in turn, affects the amount of gas needed for drying after hydroentanglement.
When using 100% viscose fibre, end-of-line speeds are generally limited to approximately 210-230 m/min at the winder. This relationship highlights the economic limitations of hydroentanglement lines, given their production capacities, and demonstrates how the production speeds of “MicroPunch” needling technology – at around 170-200 m/min – have come very close to the 220 m/min achieved by hydroentanglement lines when processing viscose only. As a result, the total cost per kilogram of nonwoven material from a needling line is significantly lower than that from a hydroentanglement line, primarily due to the substantial savings in electricity and the complete elimination of water and gas.
Through technological research at the DILO Technical Research Centre, product development for various “MicroPunch” needling applications can be carried out, enabling economic questions relating to different fibre materials and combinations to be addressed.
Efficient fibre suction and filtration for the needle looms are critical, and DiloTemafa’s suction filter station (TFS) effectively fulfils this requirement. The range of “MicroPunch” nonwovens is extensive, with possible weights ranging from 30-100 gsm or even up to 120-150 gsm – these specifics can be verified through tests and trials.