The production process of meltblown non-woven fabrics is to use high-speed hot air to draw the thin stream of polymer melt extruded from the orifice of the die, thereby forming ultra-fine fibers and condensing on the net curtain or roller, and relying on Bonds itself to become a non-woven fabric.
Comparison of meltblown fiber and spun-bond fiber:
- Fiber length: Spunbond is a filament, meltblown is a short fiber.
- Fiber strength: Spunbond fiber strength> Meltblown fiber strength.
- Fiber fineness: Meltblown fiber is thinner than spun-bond fiber.
Melt-blowing devices are divided into horizontal and vertical types according to their placement methods.
1. Process flow and equipment
Meltblown process
Polymer preparation→melt extrusion→metering pump→melt blowing die assembly→melt trickle stretching→cooling→receiving device
Equipment included in pp meltblown non-woven fabric production line
Main equipment: feeder, screw extruder, metering pump, meltblown die assembly, air compressor, air heater, receiving device, winding device. To produce polyester and other raw materials, a chip drying device is also required.
Auxiliary equipment: die cleaning furnace, electrostatic application device, and spray device, etc.
1. Feeder
Installed on the hopper of the extruder. The function of the feeder is to suck the polymer slices into the hopper of the screw extruder. It usually has an automatic function. The feeding amount per unit time can be set according to the output of the entire production line.
2. Screw extruder
3. Metering pump
4. Meltblown die head assembly
The die assembly is the most critical part of the meltblown equipment, mainly including:
- Polymer melt distribution system
- Die head system
Polymer melt distribution system
The polymer melt distribution system can ensure that the polymer melt flows uniformly along the length of the meltblown die and has a uniform residence time, thereby ensuring that the meltblown non-woven fabric has more uniform properties across the width.
Die system
The die head system is composed of the spinneret, gas plate, heating and heat preservation elements, etc.
The uniformity of meltblown products is closely related to the die. Generally, the processing accuracy of the meltblown die head is high, so the manufacturing cost of the die head is expensive.
5. Air heater
The meltblown process requires a lot of hot air. The compressed air output by the air compressor is dehumidified and filtered and then sent to the air heater for heating, and then sent to the meltblown die assembly. The air heater is a pressure vessel, and at the same time it must resist the oxidation of high-temperature air, so the material must be stainless steel.
6. Receiving device
The main types of meltblown process receiving devices are: roller type, flat-screen type
Three-dimensional molding (mandrel): device for producing filter elements
Adopt a three-dimensional receiving device, divided into intermittent receiving and continuous receiving.
Intermittent receiving device
The receiving device moves back and forth, and the fibers are wound on the mandrel in multiple layers; the receiving distance is changed to produce a filter element with a density gradient;
Change the size of the mandrel to produce filter elements with different inner diameters. After each filter element is made, the mandrel needs to be replaced, so the production efficiency is low.
Continuous receiving device
The receiving mandrel is in the form of a cantilever beam, and there is a transmission shaft for outputting the tubular filter element. The head end of the transmission shaft is threaded, and the tubular filter element is pulled out from the receiving mandrel and transported to the cutting system.
When producing filter elements with density gradients, multiple die heads with different receiving distances should be equipped.
7. Auxiliary equipment
The main auxiliary equipment of the meltblown production line is the die cleaning furnace. Hole blockage will occur after the meltblown die head is produced for some time. At this time, the meltblown die head needs to be replaced.
The replaced meltblown die needs to be fired to remove the polymer and impurities remaining in the die. Screws and spinnerets are usually roasted to remove residual polymers and impurities.
2. Raw materials used in meltblown
In theory, all thermoplastic (high-temperature melting, low-temperature solidification) polymer chip raw materials can be used in the meltblown process. Polypropylene is one of the most widely used chip materials for meltblown technology. Besides, the commonly used polymer chip materials for meltblown technology include polyester, polyamide, polyethylene, polytetrafluoroethylene, polystyrene, PBT, EMA, EVA, etc.
The type of polymer determines its melting point and rheological properties. For each polymer raw material, there is a corresponding melt blowing process, such as heating temperature, screw length-to-diameter ratio, screw form, raw material drying process, etc., there are certain differences.
Olefin polymer raw materials (such as polypropylene) have a high degree of polymerization, so the heating temperature is higher than its melting point 100 ℃ or higher can be meltblown smoothly, while the polyester heating temperature is slightly higher than its melting point can be meltblown. Olefin raw materials generally do not need to be dried. The polyester must be chip-dried.
The molecular weight and molecular weight distribution of polymer raw materials are the most important factors that affect the meltblown process and the performance of meltblown non-woven fabrics.
For the meltblown process, it is generally believed that the low molecular weight and narrow molecular weight distribution of the polymer raw materials are beneficial to the uniformity of the meltblown web. The lower the molecular weight of the polymer, the higher the melt flow index (MFI, melt flow index, refers to the weight of the melt that flows out in 10 minutes under certain pressure and temperature), and the lower the melt viscosity, the more suitable it is The meltblown process has a weaker drafting effect.
3.the structure and properties of meltblown non-woven fabrics
One of the characteristics of meltblown non-woven fabrics is that the fiber fineness is small, usually less than 10 μm, and most of the fiber fineness is 1 to 4 μm.
Various forces on the entire spinning line from the meltblown die nozzle to the receiving device cannot be balanced (the influence of the stretching force fluctuation of the high temperature and high-speed airflow, the speed, and temperature of the cooling air, etc.), which makes the meltblown fiber Different sizes of fineness.
The uniformity of the fiber diameter in the spun bond non-woven fabric web is significantly better than that of the meltblown fiber, because in the spun bond process, the spinning process conditions are stable, and the drafting and cooling conditions changeless.
The crystallinity and orientation of the meltblown fiber are smaller than that of the spun-bond method. Therefore, the strength of the meltblown fiber is poor, and the strength of the fiber web is also poor. The strength of several PP fibers is as follows:
Due to the poor strength of meltblown fibers, the practical application of meltblown non-woven fabrics is mainly due to the characteristics of its ultra-fine fibers.
4.the application of meltblown non-woven fabrics
At present, meltblown non-woven fabrics are mainly used for:
1 filter material
Filtration is the separation of particulate matter dispersed in gas or liquid.
Filtration mechanism: sieving deposition, electrostatic deposition, diffusion deposition, etc.
Are the particles larger than the pore size of the filter material to be sieved?
Studies have shown that: filter materials with a pore size of between ten and tens of microns can trap dust up to 1 µm. To improve the sedimentation effect of the sieve, it is necessary to reduce the pore size of the filter material, that is, to reduce the fiber fineness and increase the density of the material.
Meltblown non-woven materials have the advantages of fine fibers, many pores, and small pore size.
application:
Gas filtration: medical masks, filter materials for indoor air conditioners.
Liquid filtration: beverage filtration, water filtration.
To improve the filtering effect, the fiber fineness can be reduced and the density of the filter material can be increased, but it will cause a significant increase in the filtering resistance.
Therefore, let the meltblown non-woven material be electrostatically charged, and its filtering effect can be improved through the electrostatic effect, that is, electret treatment.
The electret-treated meltblown non-woven fabric has long-lasting static electricity and can rely on the electrostatic effect to trap fine dust, so it has the advantages of high filtration efficiency and low filtration resistance.
Polypropylene has high electrical resistivity (7×1010Ω·cm) and a large charge injection capacity. It is an ideal material for making electret fibers. Experiments show that after 1440 hours of storage of the electret-finished polypropylene meltblown non-woven fabric in a natural state, the filtration efficiency remains unchanged.
The influence of electret finishing on the filtration efficiency and resistance of meltblown non-woven fabrics
It can be seen that the filtration resistance of the meltblown non-woven fabric has not changed after electret finishing, but the filtration efficiency has been improved a lot, which is unmatched by other non-woven fabrics.
2. Medical and health materials
Medical mask: a composite material (SMS) made of spun-bond material on the inner and outer layers, and meltblown material in the middle.
3. Environmental protection materials (oil-absorbing materials)
Polypropylene meltblown non-woven fabric is a good oil-absorbing material due to its material properties and microfiber structure. It has been widely used in developed countries such as Europe, America, Japan, etc., such as marine oil spills, oil spills from factory equipment, and sewage treatment.
Polypropylene meltblown non-woven fabric has hydrophobic and lipophilic properties, is resistant to strong acids and alkalis, and has a lower density than water. After oil absorption, it can float on the water for a long time without deformation and can be recycled and stored for a long time. Polypropylene meltblown non-woven fabrics are made into oil-absorbing cords, oil-absorbing chains, oil-absorbing pillows, etc. The oil absorption can reach 10-50 times its weight.
4. Clothing materials (warm-keeping materials)
Thermal insulation materials should have good thermal insulation properties and can be used for a long time without changing their thermal insulation properties.
Experiments show that the fiber mesh structure is one of the main factors affecting the heat transfer performance of thermal insulation materials.
For the meltblown composite thermal insulation material, its thickness has little effect on the air permeability, while the air permeability of polyester fiber flakes increases rapidly as the thickness decreases. Therefore, the meltblown composite thermal insulation material has strong wind resistance.
5. Battery separator
The diaphragm material is an important component of the battery and is often placed between the positive and negative plates. The main function is to insulate the positive and negative plates to ensure the flow of the dielectric.
Polypropylene material has excellent acid and alkali resistance. Polypropylene meltblown diaphragm material has the characteristics of small pore size, large porosity, small resistance, and diverse product changes.
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