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Calcium Carbonate designed for PP spunmelt and dry-laid nonwovens Omya
Omya is a global producer of calcium carbonate for industrial applications. It is a privately owned Swiss company with more than 175 plants and own mineral deposits around the world.
Calcium carbonate can be found everywhere in daily life. It is used widely as a coating agent for paper and paperboard as well as for paints, as an additive in food/-pharma and cosmetics, as a soil fertilizer in agriculture, for water remineralization, for flue gas desulfurization and many other applications.
In plastics the first applications date back in the 50s of the last century when Omya introduced the first surface coated calcium carbonate for PVC applications. Since then the mineral has become an integral part of many formulations for wire and cables, pipes, conduits and profiles. Later, more and more applications in other polymers such as PS, UP, PUR, PA, ABS or PET were established.
Polyolefins are also a major application of calcium carbonate. Sheets for thermoforming, PP raffia tapes and injection molded articles typically contain up to 40 per cent of mineral. Shopping bags or T-shirt bags used in packaging are loaded with 5 per cent to 30 per cent. The improved performance with calcium carbonate is used to downgauge film thickness. BOPP films take advantage of the cavitation functionality of the carbonate particles. Voids created with 7 per cent to 25 per cent calcium carbonate particles help to reduce density down to 0.5 g/cm3 and boost the opacity of the films. If the addition rate of calcium carbonate is increased further to 40 per cent to 60 per cent, an open cell structure can be achieved. This effect is used to produce breathable hygiene films for baby diapers and adult incontinence products. The membrane function is characterized by a high water vapor transmission rate (WVTR) in combination with a good water column even for very thin films down to 8 g/m².
Such demanding applications require specific properties of calcium carbonate powder. It is therefore essential to develop tailormade solutions to fulfill the specific requirements of these markets. Omya relentlessly pushes the boundaries of established applications and introduces novel products to open new markets. Key to our success has been addressing all aspects along the value chain from raw materials, formulations, compounding, converting down to the requirements of the end application.
A good example of Omya’s perseverance in innovation is the development of the new Omyafiber® 800 calcium carbonate for PP spunmelt and dry-laid nonwoven fabrics. This product is specifically designed to provide an attractive solution which creates value for our customers. It is a fine ground calcium carbonate that is naturally very pure. The particle size and the particle size distribution are tailored to achieve outstanding processability and fiber properties. A new and improved proprietary surface treatment is applied to the calcium carbonate to achieve excellent dispersion of the mineral particles in the polymer matrix. It allows enhanced processability and optimized compatibility. The product is food contact approved according FDA and actual EU regulations and for further regulatory requests Omya can give an appropriate answer.
To successfully apply the new product, the whole value chain must be considered. Omyafiber® 800 is produced by Omya as a calcium carbonate powder. To apply this mineral to PP nonwovens, a masterbatch concentrate must be produced in an intermediate compounding step. To ensure good processability and product quality, the compounding technology needs to provide perfect dispersion of the mineral. To dilute the masterbatch concentrate pellets must be mixed with virgin PP and fed to the nonwoven process. A typical formulation may contain around 14 per cent masterbatch with Omyafiber® 800. The PP is typically a homopolymer with a melt flow rate (MFR) of 25 to 35 g/10 min at 230°C and 2.16 kg. The whole processing chain is shown in figure 1.
100% Omyafiber® Masterbatch Compounding
70% Omyafiber® in PP masterbatch Fiber & Nonwoven production
Virgin PP plus Omyafiber® imasterbatch
Omyafiber® 800 provides value that pays off. Raw material savings are substantial. But cost savings are not the only attraction. In spunlace and carded nonwoven fabrics it creates natural cotton like haptics and softness. At high and low basis weight fabrics it improves tensile strength and elongation. Higher whiteness with Omyafiber® 800 allows savings in titanium dioxide (TiO2). During processing and on the final fabric the static charge is reduced. Omyafiber® 800 is also beneficial from sustainability perspective as it has a substantially lower carbon footprint then PP resin; it improves the CO2 balance.
The value proposition is not only seen in internal lab investigations. Extensive technical evaluations have been done with wellknown research institutes. In recent years processing trials have been done at the European Centre of Innovative Textiles (CETI) in Tourcoing, France. Further trials on a Reicofil 4 nonwoven line have been conducted at the Sächsische Textilforschungsinstitut (STFI) in Chemnitz, Germany.
The successful trials were essential to ensure the outstanding processability of Omyafiber® 800 on industrial lines. The trials were conducted with different technologies. Spunbond nonwovens have been produced with thermal calendering. Further trials with spunlacing or hydroentanglement as bonding step have been conducted. Trials with PP staple fibers which were carded and hydro-entangled have been done. In all trials 10 per cent Omyafiber® 800 was incorporated in the nonwovens via the addition of 14 per cent masterbatch. Scanning electron micrographs of PP multifilaments containing 10 per cent Omyafiber® 800 are shown in figure 2.
Figure 2: PP multifilament fibers containing 10% Omyafiber® 800 showing perfect mineral dispersion
Figure 3: Close collaboration of all stakeholder along the value chain is key for a successful product introduction
The trials proved that Omyafiber® 800 caused no die build-up at the spinneret nor any extrusion pressure evolution during processing. The processes ran stable without fiber breakage. The evaluations helped to establish the know-how to optimize the process. More detailed technical results are available from Omya for further discussion.
To realize all beneficial features with Omyafiber® 800 it is important to ensure high quality along the value chain from raw material producer via the compounders to the nonwoven producers. Therefore, it is crucial that all stakeholders work together to make the development a success. Omya is committed to support our partners during this implementation and optimization phase. They can count on the technical advice from our dedicated and experienced scientists and engineers. Our technical experts rely on state of the art technical centers around the globe. Their technical service is based on application-related and analytical tests in Omya’s laboratories. It also includes hands-on support in our customer’s production sites. n
