Principle and equipment of melt blowing process
Melt-blown nonwoven technology is to use high speed hot air to draft the polymer melt which is extruded from the spinneret hole of the die head, thus forming superfine fiber and condensing on the screen curtain or roller, and forming nonwoven fabric by self-bonding
Comparison of melt-blown fiber and spun-bonded fiber
Fiber length: spun-bonded for filament, for short fibers
Fiber strength: spun-bonded fibre > melt-blown fiber strength.
Fiber fineness: melt-blown fiber finer than spun-bonded fibers
Melt - blown process flow
Polymer preparation → melt extrusion → metering pump → melt injection die head assembly → melt tensioning → cooling → receiving device
Main equipment: feeding machine, screw extruder, metering pump, melt injection die head assembly, air compressor, air heater, receiving device, winding device.
Production auxiliary equipment :mainly includes mould head cleaning furnace, electrostatic device and spray device.
Molten spray material
Theoretically, all thermoplastic (melting at high temperature, curing at low temperature) polymer chips can be used in melt blasting process. Polypropylene is one of the most widely used slicing materials in melt injection process. In addition, polymer slicing materials commonly used in melt injection process include polyester, polyamide, polyethylene, teflon, polystyrene, PBT, EMA, EVA, etc.
The type of polymer determines its melting point and rheological properties. For each kind of polymer raw materials, there are corresponding melt blowing process, such as heating temperature, screw length-diameter ratio, screw form, raw material drying process and other aspects are different.
The molecular weight and molecular weight distribution of polymer raw materials are the most important factors affecting the performance of melt-jet process and melt-jet nonwovens. It is generally considered that low molecular weight and narrow molecular weight distribution of polymer raw materials are beneficial to the uniformity of melt-blown fiber network. The lower the molecular weight of the polymer, the higher the MFI (melt flow index), the lower the melt viscosity, and the more suitable for the weak drafting of the melt process.
Structure and properties of melt-blown nonwovens
One of the characteristics of melt-blown nonwovens is that the fibers are smaller, usually less than 10 microns, and most fibers are between 1 and 4 microns.
The various forces on the whole spinning line from the spinneret hole of the melt injection die head to the receiving device cannot be balanced (the influence of the tension fluctuation of high temperature high-speed airflow, the speed and temperature of cooling air, etc.), resulting in the different sizes of the melt injection fibers.
The uniformity of fiber diameter in spun-bonded nonwovens is obviously better than that of melt-blown fibers. In spun-bonded process, the spinning process conditions are stable, and the drafting and cooling conditions change little.
Comparison between spun-bond method and melt injection method
Melt Blown Process
Raw material MFI
Short fibers of various lengths
Short fibers of various lengths
They vary in size, averaging less than 5 microns
Fraction of coverage
The intensity of the product
Thermal bonding, acupuncture, spines
Varieties of transformation
Spunbond products are high in strength but thick in fiber, while melt-blown products are fine in fiber but low in strength. The combination and complementation of the two meet the performance requirements. The products include SMS, spun-bonded/melt-blown/spun-bonded, SM, SMMS, SMSMS, etc
S —— Spun-bonded non-woven fabrics
M —— Melt-blown non-woven fabrics
The methods of compounding (combining) are on - line compounding and off - line compounding.
Online compounding: production is carried out by using spunbond/melt-jet compounding equipment.
Off-line compound: spunbond, melt - blown product compound.