Melt Blowing & Spunbonding Technologies II

Imerys, a mining company who produces specialty inorganic materials for the Plastic Market, conducted trials last year at TANDEC to establish the feasibility of using high loadings in spunbond products. The results confirmed that up to 25% of a mineral additive, such as calcium carbonate, could be added to standard polypropylene spunbond webs. The current study repeated the additive experiments in melt blown media. Melt blown webs typically contain very small diameter, poorly bonded fibers resulting in low strength properties, but potentially high barrier properties and absorption capacity. The melt blown webs, containing up to 25% calcium carbonate, exhibited higher filtration efficiency and opacity than unfilled webs with the same basis weight. The spunbond trials were conducted with resin/mineral concentrates since the spunbond resins were pelletized. The melt blown resins used in this project were powders so dry calcium carbonate powder was added directly. All of the process conditions and physical property results will be presented to justify the recommended additives and loadings.

A high speed camera was used to record the motion of a fiber below both a melt blowing slot die and a melt blowing swirl die.  These recorded images were processed to determine the frequency and amplitude of fiber motion during melt blowing.  The operating variables investigated included polymer flow rate, air flow rate, polymer temperature, and air temperature.  A crossover counting method was developed to determine the frequency of fiber motion. The frequencies determined from this counting method favorably compared with frequencies determined by taking fast Fourier transforms of the fiber displacement data.  Experimental results for frequency and amplitude were compared to predictions from a three dimensional mathematical model for the melt blowing process. 

At Saxon Textile Research Institute extensive experimental investigations for the production of spunbonded nonwovens made of hollow filaments were accomplished at lab-scale spunbond pilot lines according to the suction/compressed air principle type Reicofilâ4, and injection/compressed air principle type Lurgi.

Polypropylene (PP), Metallocene Polypropylene (MPP) and Polyester (PET) were chosen polymers. Four different configurations of spinning  nozzles ("double C" with different slot and bar width, "three C") were used at the injectors pilot line. For the investigations on the Reicofilâ4 line the configuration "double C" was selected with slot and bar width of 0.15 mm. Nonwovens were bonded by calandering, by spunlacing/hydroentanglement and needle-punching.

The most important variables regarding formation of the hollow structure are polymer viscosity at spinning nozzle, throughput per nozzle hole, cooling conditions of the filaments and the nonwoven bonding parameters.
Evaluation of test results is based on microscopic investigations of filament cross sections, process reliability during spinning as well as textile-physical characteristics of filaments and spunbonded fabrics.

Best hollow structures were achieved with PP and MPP at low cooling temperatures. Fast freezing of the hollow filaments right underneath spinning nozzle is probably one reason. Filament speed has relatively small influence on the hollow structure.
With calandering and spunlacing slight filament deformations towards oval cross sections was noticed. Needle-punching should be carefully accomplished, in order to largely avoid filament destruction during the process.

Kraton polymers are high performance thermoplastic elastomers engineered for a wide spectrum of end uses. The versatility of Kraton polymers is due to their distinctive styrenic block copolymer molecular structure, which can be precisely controlled and tailored to perform in specific applications. The unique structure of these polymers impart flexibility and elasticity to a wide range of personal care applications including disposable diapers, adult incontinence products, wipes, and many other industrial film and non-woven products.

New high melt flow Kraton polymer grades have been designed specifically for continuous yarns, spunbond and melt blown nonwoven applications. The grades developed are to be used as the core in bicomponent fiber structures to produce elastic and strong yarns and nonwoven fabrics. The Kraton materials have excellent process stability and do not require drying. They are compatible with polyolefins and can also be combined with other materials in multi-layer structures. The Kraton based spun bond nonwovens are elastic and strong. The Kraton polymer based melt blown nonwovens are very soft, have a high elongation at break (100-500%), good set and almost isotropic properties. The nonwoven properties are very stable in time.