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How to see the quality of meltblown cloth? After reading it, you will become an expert!

文章出处:wingadmin 人气:发表时间:2020-05-28 16:16

 

一、Preliminary identification of the quality of meltblown cloth

Now the market is flooded with counterfeit products made of non-woven fabrics or composite melt-blown fabrics. We cannot distinguish the filtration rate of melt-blown fabrics by naked eyes alone, which requires professional machine inspection. But you can first make a preliminary judgment through the following identification methods
(1) Can't light a fire
(2) Tear up static electricity and can be adsorbed on 90 ° upright glass or steel surface
(3) Looking at the texture, first determine whether it is a meltblown cloth. The tensile toughness, light transmittance, and size of the web of the melt-blown fabric can be roughly judged whether the quality is good or bad, but the specific efficiency cannot be seen by the naked eye.
 

二、Meltblown cloth parameter index

The main structure of the mask is a three-layer non-woven fabric, or SMS structure.
Mask structure
The inner S layer is ordinary non-woven fabric, mainly for moisture absorption;
 

The outer S layer is a non-woven fabric with a waterproof treatment, which is mainly used to isolate the liquid sprayed by the patient and has the effect of preventing spray;
 
The middle M layer uses melt-blown non-woven fabric after electret treatment, which can filter bacterial suspended particles and is the most important core layer.
 
Meltblown cloth, commonly known as the "heart" of the mask. Its main raw material is polypropylene, a film composed of many criss-cross fibers stacked in random directions. The fiber diameter ranges from 0.5 to 10 microns, and the fiber diameter is about one-third of the hair diameter.

Photo of meltblown fabric structure

The following picture is a photograph of the structure of the meltblown cloth
 
 Meltblown fabric fiber diameter


Seeing this, are you a bit puzzled? With such a large gap in the meltblown cloth, how do you filter viruses in the environment?
 
Take the new coronavirus as an example. Although the size of the new coronavirus is very small, about 100 nanometers (0.1 micrometers), the virus cannot exist independently. Its transmission routes mainly include secretions and droplets when sneezing. Around 5 microns, this is one;
Second, the melt-blown cloth is essentially a fiber filter. When the droplets containing the virus are close to the melt-blown cloth, they will also be electrostatically adsorbed on the surface and cannot penetrate.
Schematic diagram of fiber filtration mechanism
Schematic diagram of fiber filtration mechanism

 
Although the raw materials of the S layer and M layer of the mask are all polypropylene-specific resins, there are some differences in the production process of the special materials for melt-blown cloth and other non-woven fabric materials. For example, the M layer has a modified plastic. Link.
 
Petroleum → Atmospheric pressure device / Secondary coking hydrogenation naphtha / Hydrocracking light naphtha → Ethylene cracking device → Ethylene / propylene → Ethylene oxide / Polypropylene (special resin)
 
S layer (spunbond layer): special resin for polypropylene → sent to non-woven fabric factory to produce S layer → sent to mask factory
 
M layer (meltblown layer): special resin for polypropylene → sent to modified plastics factory to produce special material for meltblown cloth → sent to meltblown nonwoven fabric factory to make M layer → sent to mask factory
 
Where did the meltblown cloth come from?
The special material for meltblown cloth is polypropylene with high melt index. The higher the melt index of polypropylene, the finer the fibers melt-blown, and the better the filterability of the melt-blown cloth.
 
Meltblown cloth application scope

(1) Medical and sanitary cloths: surgical gowns, protective clothing, sterilization wraps, masks, diapers, sanitary napkins, etc .;
 
(2) Fabrics for home decoration: wall stickers, tablecloths, bed sheets, bed covers, etc .;
 
(3) Cloth for clothing: lining, adhesive lining, flakes, shaped cotton, various synthetic leather base fabrics, etc .;
 
(4) Industrial fabrics: filter materials, insulating materials, cement bags, geotextiles, covering fabrics, etc .;
 
(5) Agricultural cloth: crop protection cloth, seedling raising cloth, irrigation cloth, thermal insulation curtain, etc .;
 
(6) Others: space cotton, thermal insulation and sound insulation materials, linoleum, cigarette filter, tea bags, etc.
 
The melt-blown filter material is composed of polypropylene microfibers randomly distributed and bound together. The appearance is white, smooth and soft. The material fiber fineness is 0.5-1.0μm. The random distribution of fibers provides more thermal bonding between fibers Chance, so that the melt-blown gas filter material has a larger specific surface area and a higher porosity (≥75%). After high-pressure electret filtration efficiency, the product has the characteristics of low resistance, high efficiency, high dust capacity and so on.
 
Main specifications of meltblown cloth
Weight: 18g-500g
 
Wide width: generally 600cm, 1200cm, 1600cm and (can also be determined according to customer needs)
 
Melt-blown cloth is a high-speed hot air flow to draw a thin stream of polymer melt extruded from the die orifice, thereby forming ultra-fine fibers and collecting them on the condensed screen or roller, while bonding themselves to become Meltblown nonwoven fabric.
 
The production process of meltblown cloth is mainly as follows:
 
1. Melt preparation
 
2. Filter
 
3. Measurement
 
4. Melt is extruded from the spinneret
 
5. Melt flow drafting and cooling
 
6. Netting
 
Meltblown cloth use
Meltblown fabrics use polypropylene as the main raw material, and the fiber diameter can reach 0.5-10 microns. These ultrafine fibers with unique capillary structure increase the number and surface area of ​​fibers per unit area, thereby making the meltblown fabrics have good air filtration properties. Is a good mask material. In large, medium and small medical institutions, in earthquake- and flood-affected areas, during the high season of SARS, avian influenza and H1N1 virus, melt-blown filter paper plays an irreplaceable role with its strong filtering performance effect.
 
The main use of meltblown cloth is:
 
1. Filter material
 
2. Medical and health materials
 
3. Environmental protection materials
 
4. Clothing materials
 
5. Battery separator material
 
6. Wipe the material
 
How to identify the authenticity of melt-blown cloth
We can easily identify the inferior products on the two floors. A useful medical mask must have three layers, with spunbond nonwoven fabric on both sides and a melt-blown fabric of sufficient weight in the middle. The picture shows the meltblown cloth, and the filtering effect is related to its weight (grams per square meter). This range is 18-500g, and the filtering effect above 40-50g is good. Don't buy a mask without meltblown cloth! Identify true and false meltblown masks. "Good meltblown fabrics look white rather than transparent due to their sufficient weight, and they are obviously different from the spunbond nonwoven fabrics on both sides. Like paper. If it looks different but is obviously thin, it is a melt-blown cloth with a small grammage. The thinner the melt-blown cloth, the worse the effect.
 
Simple identification method:
 
First, as the name implies, the meltblown layer will melt when it encounters fire, but will not burn. Paper will burn when it encounters fire.
 
Second, there is static electricity in the meltblown layer. If you tear the meltblown layer into strips, you will obviously feel the electrostatic adsorption effect, and you can also adsorb the meltblown layer on the stainless steel. You can remove the used mask and check it to avoid wearing a fake mask ~
 
How many masks can be produced per ton of meltblown cloth
A ton of meltblown cloth can make a mask about one-time without loss of about 1.05 million, KN95 600,000, medical N95 400,000, according to the actual productivity can increase the output appropriately.
 
Does the meltblown cloth carry static electricity
In order to make breathing as smooth as possible, and at the same time to meet the protection requirements, qualified masks with melt-blown cloth will go through the electret process. The surface of the fiber after the electret has a large amount of charge, and intercepts fine particles through the electrostatic adsorption effect. We can also use the classic physical characteristic of electrostatic adsorption to verify whether the meltblown fabric is charged. The non-woven fabric passing through the electret will have obvious attraction to hair and iron filings. Although the amount of meltblown cloth in a single mask is small, the effect of absorbing hair may not be obvious, but the presence of electric charge can also make it adsorb on the wall. Despite the melt-blown cloth in some of the inferior masks, they did not pass through the electret, or because the electret technology was not closed, and the storage time was too long, which caused a large amount of charge to dissipate, and its protection performance naturally fell short of the standard.

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