Meltblown die head and spinneret

Meltblown nonwoven fabrics are the "heart" of medical surgical masks and N95 masks.

Medical surgical masks and N95 masks generally adopt a multi-layer structure, referred to as the SMS structure: a single layer of spunbond layer (S) on both sides, and a melt-blown layer (M) in the middle.

The middle meltblown layer is an electret-treated meltblown nonwoven fabric, which has good filterability, shielding properties, heat insulation and oil absorption, and is the core raw material for the production of masks.

S layer: polypropylene special resin

M Layer: polypropylene resin with high melt index

An ordinary plane mask needs about 1g meltblown cloth + 2g spunbond cloth; and an N95 mask needs about 3 ~ 4g meltblown cloth + 4g spunbond cloth.

Cut a used medical mask, you will find that the mask has three layers, (inner layer) moisture absorption layer, (middle layer) core filter layer, and (outer layer) water blocking layer.

The medical mask contains at least 3 layers of non-woven fabric (N95 grade mask, the structure is optimized: (middle layer) the core filter layer has more layers and thicker thickness).

Meltblown cloth, commonly known as the "heart" of the mask, is the filter layer in the middle of the mask, which can filter bacteria and prevent the spread of germs. Melt-blown cloth is a film made of polypropylene with a high melt index. It is a film formed by laminating many criss-cross fibers in random directions. The fiber diameter ranges from 0.5 to 10 microns, and the fiber diameter is about 30 cents of the hair thread. one.
The following picture is a photograph of the structure of the meltblown cloth:

Although the size of the new coronavirus is very small, about 100 nanometers (0.1 micrometers), the virus cannot exist independently. Its transmission route mainly includes secretions and droplets when sneezing. The size of the droplets is about 5 micrometers. One, second, the meltblown cloth is essentially a fiber filter. When the droplets containing the virus are close to the meltblown cloth, they will also be electrostatically adsorbed on the surface and cannot penetrate. In the production process of masks and melt-blown non-woven fabrics, one of the most indispensable core components is the melt-blown die head. In the melt-blown equipment, the melt-blown die head is one of the core components to realize the wire drawing of the polymer. The design and accuracy directly affect the length, uniformity, toughness, fineness and other aspects of the wire drawing, thus affecting the quality of the final coil. Have a decisive impact. The core part of the main machine of the melt-blown production equipment is the spinneret (spinneret), which has many spinneret holes for the melt to pass through. Its production and processing are crucial, which is related to the production efficiency and quality of the melt-blown cloth , Which in turn affects the protective performance of the mask.

Ⅰ. Micro-hole machining principle of melt-blown spinneret

The machine tool uses the principle of electrical discharge to process high precision, high finish precision micropores. It is used to process precision micro-holes of various types of fuel injection nozzle parts. The range of processing precision circular micro-holes is generally ￠ 0.1 ~ ￠ 0.5mm. The machine tool uses round elongated wire electrodes. The re-feeding mechanism with elongated wire electrode realizes the servo feeding and loss compensation of the electrode during processing. Processing generally uses deionized water working fluid. The machine tool is composed of a host, an electric control box and a working fluid system. The electric control box is composed of an industrial control computer, a special high-frequency pulse power supply for electric spark micro-finishing, a detection servo control unit and machine tool electrical components.

The special machine tool of the spinneret spinneret adopts round and long wire electrode. The re-feeding mechanism with elongated wire electrode realizes the servo feeding and loss compensation of the electrode during processing. Processing generally uses deionized water working fluid.

Ⅱ. Structure of melt-blown cloth spinneret

According to the shape of the spinneret, the structure of the spinneret can be divided into three forms: round, sector and rectangle. At present, round and rectangular plates are mostly used at home and abroad. To suit different chemical fiber spinning occasions, the round spinneret is divided into flat type, flange flat type, flat ring, flange ring, etc .: the rectangular spinneret is divided into flange rectangle and flange groove rectangle, etc. , Mostly used for short fiber spinning with more holes

Meltblown fabric is a non-woven fabric formed by meltblown method, which mainly uses polypropylene as the main raw material. The actual production process of meltblown fabric is more complicated, and the requirements for production equipment are also higher. Its production mainly passes through "melt preparation- "Filtration-metering-melt extrusion from the spinneret hole-melt fine flow drafting and cooling-network" and other six processes. The core component of the main machine of the melt-blown production equipment is the spinneret (spinneret), which has many spinneret holes for the melt to pass through. Its production and processing are crucial, which is related to the production efficiency of the melt-blown cloth and quality. At present, the domestic production of melt-blown cloth production equipment has been achieved in China, but the production of core components such as spinnerets still depends on the supply of foreign manufacturers. In extraordinary times, it is very important to be able to provide melt-blown cloth production equipment manufacturers with a spinneret that can meet the needs of high-protection mask melt-blown cloth production.

The processed part is the core part of the die of the melt blown cloth extruder. Each piece of work is distributed with more than 300 ~ 2000 micropores according to the size of the die. Depending on the application level of the meltblown cloth, the pore size of the micropores also differs in size (Φ0.2mm micropore molds are used in N95 masks)

 The medical surgical mask structure has at least three layers, the outermost layer is PP nonwoven fabric (common layer), the middle is meltblown fabric (main filter layer), and the inner layer is skin-friendly nonwoven fabric (waterproof treatment).

Its working principle is: the polypropylene PP special material is plasticized and enters the melt-blown die head flow channel, and is evenly distributed before entering the spinneret.