I. Prologue to meltblown nonwoven innovation
- Meltblown strategy
The meltblown strategy is a creation innovation wherein a polymer liquefy is blown through a high velocity, high temperature air stream, so the dissolve stream is exposed to outrageous extending to shape super fine filaments, which then, at that point, combine to frame a fiber network on a permeable drum or into a net drape, which is then built up by its own holding or warm clinging to make a non-woven texture.
- Meltblown nonwovens process attributes
Short meltblown process, straightforward hardware (no compelling reason to set the fiber network gear), high creation productivity; energy utilization, significant expenses, the extension of its application regions have a specific adverse consequence; incredibly fine filaments (fiber measurement up to micron or even nanometer level), huge explicit surface region, high porosity of the fiber organization, great consistency of the fiber organization, delicate and feathery, particularly for filtration, fluid retention and warm materials; low strength of strands and fiber organization, low direction, unfortunate wear obstruction.
Second, meltblown nonwoven creation hardware
Take the programmed meltblown creation line of Qingdao Ruijie Company for instance.
The entire arrangement of meltblown hardware comprises of the fundamental machine, warming framework, grease framework, water powered framework, cooling framework, electrical control framework, and so on The primary machine fundamentally comprises of taking care of framework, screw extruder, sifting gadget, metering siphon, meltblown pass on head get together, getting gadget and winding component. While creating meltblown non-woven materials, for example, polyester and polyamide, cutting drying and pre-crystallization are additionally required.
- Taking care of framework
The taking care of framework is a three-stage canister metering and blending arrangement of type P-320-38G. The taking care of framework comprises of 3 drums: 1 principle material drum and 2 helper material drums. The vitally material drum adds the polymer chips and the two helper material drums add the masterbatches and useful masterbatches separately, and the proportion and taking care of amount of the primary material, masterbatches and antistatic specialist are naturally constrained by PLC/SBBL.
Schematic outline of the three-stage canister metering and blending framework
Planned quantitative taking care of to meet the prerequisites of the expulsion volume and programmed control of the proportion of cuts, masterbatches and practical masterbatches through the PLC/SBBL control framework; each drum has a material level marker to show the tallness of the material in the metering drum, which is checked by the program. The blending activity is additionally blended in a blending and metering drum with a winding stirrer, which combines the different granules as one and afterward takes care of them into the screw extruder through the taking care of cylinder.
- Screw extruder
At the feed end of the screw extruder, the polymer chips are to be blended in with added substances, for example, stabilizers and brightening specialists and the fundamental unrefined components, for example, masterbatches, after intensive blending into the screw extruder and warmed into a dissolve.
A solitary screw extruder is utilized.
- Sifting gadget (screen)
A twofold cylinder sifting gadget is utilized to guarantee that the screen can be changed web based during creation.
The screen is a composite screen comprising of 5 layers, the surface layer with a low lattice count and the center layer with a high cross section count. Assuming that the tension arrives at a set worth, the expulsion volume diminishes altogether or the power utilization of the screw extruder expands, the screen ought to be supplanted on schedule.
- Metering siphons
The capacity is to precisely meter and persistently transport the polymer soften to the turning pass on head and to create a foreordained strain to guarantee that the dissolve can defeat the opposition of the parts and the spinneret and be shot out from the spinneret to shape a fine stream of liquefy. The metering siphon comprises of 1 sets of unequivocally fit cog wheels, 3 siphon plates, 2 wheel shafts and 1 coupling.
- Meltblown pass on head get together
The pass on head get together (turning gathering) is the most basic piece of hardware in a meltblown line and comprises of the polymer dissolve conveyance framework, the bite the dust head framework, the extending hot air funneling channels (hot wind stream spouts and blade valves) and the warming and protection components.
(1) Polymer liquefy appropriation framework
Work: To guarantee uniform progression of the polymer dissolve all through the length of the meltblown bite the dust head.
By and large two circumstances should be met.
(I) the soften stream time is just about as short and indistinguishable as could really be expected.
② The strain drop in the soften stream is just about as little and indistinguishable as conceivable to keep away from exorbitant warm debasement; unreasonable warm corruption of the polymer because of dead space in the liquefy stream is additionally stayed away from.
Factors influencing the consistency of dissolve circulation.
① Manifold slant point: as the slant point of the complex builds, the powerful pace of the polymer liquefy in the focal point of the conveyance framework will in general diminish, while the stream rate on the two sides increments fundamentally.
② The polymer soften itself: the fiber-shaping polymer liquefy for the most part displays non-Newtonian conduct, which should be worked on through the sub-atomic load of the polymer and its dissemination and the choice of a higher temperature to work on its rheological properties.
Schematic graph of the holder type polymer dissolve dispersion framework
(2) Mold head framework (tip of the shape head)
Comprises of a channel layer, a preform layer and a turning plate. The sifting layer is comprised of a few layers of screens compounded with an aluminum combination guide edge to channel the dissolve and keep debasements from obstructing the spinneret opening; the preform layer and turning plate are in a bad way together and fixed with PTFE to permit the soften to stream flawlessly into the spinneret opening; the bite the dust tip is outfitted with little openings on the two sides for the establishment of projectile radiators and temperature sensors to warm the pass on tip to keep up with the expected temperature.
Parts of the kick the bucket head tip
1 – Screen 2 – Preform plate 3 – Spinneret 4 – PTFE seal
The spinnerets utilized in the meltblown technique vary from other turning strategies in that the spinnerets should be fixed up in an orderly fashion with high speed wind stream ejector openings on the two sides. The meltblown spinneret has a gap of 0.3-0.4mm and a spinneret dividing of 12-16 openings/cm.
Construction of the spinneret
1-Heating component 2-Melt 3-Hot air 4-Spinnerette 5-Hot air ejector opening
With the cut spinnerette kick the bucket, the spinnerette openings are at this point not individual openings, but instead a consistent cut like the hole from which the hot air is shot out. Since the dissolve expelled from the cut structures a slim film, to have the option to create a solitary fiber, the divider on one side of the cut is notched; the other divider is lower than the side with the depressions. Benefits: it can decrease the stopping up of the spinneret opening, lessen upkeep costs and further develop use.
(4) Hot wind current spouts and blade valves
Dissolve splash turning is the polymer liquefy from the spinneret opening expulsion, by high temperature and high velocity hot air fly and finished, so the bite the dust head all through the width of each place of the wind current speed should be equivalent to far as could really be expected, any other way it can not guarantee that the silk. The hot wind current spouts are introduced on the two sides of the kick the bucket head and the warmed wind current enters the hot air channel by means of the blade valve. To guarantee an even conveyance of the wind current, every channel pipe is outfitted with a blade valve.
Schematic graph of the construction of the air fly pipe
1 Die head 2 Die tip 3 Nozzle edge 4 Airflow change valve
The guideline and setting of the air channels straightforwardly impact the heading of the hot air fly and decide the nature of the strands. The change boundaries of the channel are predominantly the spout width W (0 to 13.5 mm) and the distance H (0 to 3 mm) from the kick the bucket tip to the spout edge.
- Getting gadget (web arrangement framework)
The spinneret is set evenly and the web is shaped on a roundabout assortment drum; the spinneret is set upward and the web is coagulated on an even moving web framing shade.
- Cutting and winding
Prior to winding, the crude edges of the meltblown texture are cut off on the two sides.
The cut edges are.
(I) straightforwardly reused; (ii) handled as a semi-completed natural substance into an end result. The managed texture is twisted in full width or in a few sections.
- Getting done or unique wrapping up
The physical and mechanical properties of the completed item can be essentially adjusted and new items created by rolling out suitable improvements in the meltblown nonwoven fabric meltblown cycle, which can likewise be a benefit of the adaptability of the meltblown nonwovens process. In the hot wind current into the wind current containing short strands or wood mash filaments, so that the meltblown texture has better flexibility, adsorption, strength, and so on; with super-spongy polymer powder or actuated carbon particles blown into the hot wind current to work on the adsorption or filtration productivity of the meltblown texture.
Three, meltblown technique for the primary creation process boundaries (factors influencing item execution)
- Melt index (MFI)
The lower the molecular weight of the polymer, the higher the melt flow index (MFI), the lower the viscosity of the melt, the more suitable for the meltblown process weaker drafting effect. The smaller the molecular weight, the better the flow properties and the higher the MFI. The melt index reflects not only the flowability of the polymer itself, but also the physical and mechanical properties of the fibres and nets made from it. The crystallinity and orientation of meltblown fibres are smaller than those of spunbond. Therefore, the strength of meltblown fibres is poorer and so is the strength of the fibre web. Under the same process conditions as the screw speed, PP chips with high MFI can increase the output by 1/3; as the hot air temperature can be reduced, the energy consumption is also reduced accordingly.
- The temperature of each zone of the screw extruder
The temperature of each zone of the screw extruder will not only affect whether the spinning process can be carried out smoothly, but also has a great impact on the feel and mechanical properties of the final product. Improper temperature settings can result in clogging of the nozzle, wear and tear of the spinnerets, increased fabric blemishes and flying flowers.
- Hot air velocity
This has a direct effect on the linear density of the fibres and the physical properties of the product.
Under the same conditions of temperature, screw speed and receiving distance.
① hot air speed increases, fiber diameter decreases, non-woven feel from hard to soft, fiber entanglement increases, fiber network dense, smooth, strength increases
② But the airflow speed is too large, easy to appear flying flowers, seriously affect the appearance of the fabric.
- Hot air injection angle
The angle between the airflow and the bottom of the die head. High temperature and high speed draft hot air is ejected from the air channel of the meltblown combination die head, and the two air streams collide, forming a complex flow field. This mainly affects the stretching effect and the fibre morphology. At angles close to 90° the hot air jet will produce highly dispersed turbulence, causing the fibres to form an irregular distribution on the forming curtain; the smaller the angle, the easier it is to form parallel fibre bundles.
- Receiving distance (DCD)
DCD increases the longitudinal and transverse strength decreases, the bending strength decreases, the non-woven fabric feels fluffy and soft, if used as a filter material, the filtering efficiency and filtering resistance decreases. dcd decreases, the hot air cooling and diffusion is not sufficient, the bonding effect is improved, the fluffiness of the product decreases (the fibres are more agglomerated), the strength increases.
- Extrusion volume of the polymer melt
In the case of constant temperature: extrusion volume increases, meltblown cloth increased quantitatively, the strength increased (reached the peak after the reduction) when the extrusion volume is too large, the strength of meltblown cloth but decreased, especially when the MFI is more than 1000 more obvious: may be due to the extrusion volume is too high, the silk strip stretching is not sufficient, and silk serious, the fabric surface bonded fibers reduced.
Four, the meltblown method of product applications
- Filter material
The main use of its ultra-fine fibre structure, which is also its earliest and largest application area; the demand for new filter materials is also the main driving force behind the development of meltblown nonwovens. Filtration with meltblown fabrics results in purified gases or liquids without the short pile of filter material shedding. About 20,000 tonnes of meltblown filter media are currently used worldwide each year, of which
① 65% for liquid filtration, e.g. beverage and food hygiene filtration, water filtration, precious metal recovery filtration, filtration of chemical products such as paints and coatings.
②35% is used for gas filtration, such as: indoor air conditioning unit filtration, gas-water separation filtration, clean room filtration, etc.
- Medical materials
Currently the second largest application area for meltblown fabrics, with an annual usage of more than 10,000 tons worldwide.
In this field, the largest amount is used for surgical gowns, operating room drapes and sterile dressings, and a small amount is used for elastic bandages, adhesive tapes, anti-inflammatory and pain relief films, etc.
- Hygienic materials
- Oil-absorbing materials
PP meltblown non-woven fabric is hydrophobic and oleophilic, resistant to strong acids and alkalis, with a density smaller than that of water, and can float on water for a long time without deformation after oil absorption, and can be recycled and stored for a long time.
The meltblown fabric is generally stuffed into a long mesh tube knitted from PET filaments as a floating water barrier for oil blocking and oil absorption at sea; an oil collection device made of PP meltblown fabric can also be installed at the head of an offshore tug to continuously remove oil from the sea surface.
PP meltblown non-woven fabric is made into oil-absorbing ropes, oil-absorbing chains and oil-absorbing pillows, etc. The oil-absorbing capacity can reach 10-50 times of its own weight.
- Clothing materials
①Special meltblown fabric developed by 3M in the United States: PET staple fibres are mixed in the meltblown fibre formation process to form an air-warm structure consisting of elastic PET staple fibres and PP superfine fibres.
②Domestic Tianjin TEDA Clean Materials Co., Ltd. took the lead in developing meltblown thermal insulation materials, bringing about the peak of meltblown non-woven fabric development in China.
- Wiping cloth
Using the natural oil-absorbing properties of PP, a variety of wiping cloths are made for use in oil-polluted working environments.
With appropriate humidifying additives, PP meltblown wiping cloths with hydrophilic properties can be made for use in hospitals, high clean rooms, precision machines, instruments, computer rooms and other places.
- Sound-absorbing and sound-insulating materials
The meltblown two-component sound-absorbing material is a non-woven material consisting of meltblown ultra-fine fibres with a diameter of 1-4μm and short fibres with a diameter of 3-7 dtex.
When sound waves vibrate through the pores of the meltblown two-component material, the energy of the sound passing through is converted into heat under the effect of friction loss and so on, thus playing the effect of sound insulation and sound absorption.