The core of mask production: melt blown die head, spinneret, melt blown air heater!

- May 11, 2020-

The global epidemic situation is severe, and there is still a large gap of anti epidemic materials mainly for masks. As everyone knows, the melt blown cloth is the core raw material for the production of masks. As a filter layer, it is the heart of masks. It used to be a very partial raw material, which was not known by many people or understood by many people. However, an epidemic situation made the world look at it with great admiration and became a hot product in an instant. With the continuous production of masks, the raw materials and equipment involved in their production have become popular.

 

Now, melt blown die head, spinneret and melt blown air heater are in short supply,

 

01Mask

The mask mainly has three layers of structure, including the outer waterproof non-woven fabric, the middle filter layer, and the inner layer of gauze or non-woven fabric. The production of the outer layer and the inner layer is relatively simple, and the most important is the middle filter layer, which is a special melt blown cloth made of polypropylene material. It is a superfine fiber with a unique capillary structure and has good filtering and shielding functions.

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Mask structure

02

 

PP is the main raw material of melt blown cloth, and the fiber diameter can reach 1-5 μ M. There are many gaps, fluffy structure and good anti wrinkle ability. These ultra-fine fibers with unique capillary structure increase the number and surface area of fibers per unit area, so that the melt blown cloth has good filtration, shielding, heat insulation and oil absorption. It can be used in the fields of air, liquid filter material, isolation material, absorption material, mask material, heat preservation material, oil absorption material and wiping cloth.

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 Manufacturing process of melt blown cloth

 

The core of the whole mask is melt blown nonwovens. The melt blown nonwovens is a kind of ideal mask material. Because of the dense melt blown layer, the linear density of the fibers is very small, and they are basically superfine fibers, which can reach 0.01-0.05 dtex, about 1% of the linear density of ordinary spunbond fibers.

 

The fiber of the melt blown fiber mesh is very thin, and the fiber mesh is very even. When the liquid contacts with it, the liquid is not easy to penetrate because of the surface tension; because the gap formed by the connection between the microfibers is quite small, the dust and bacteria are blocked. Large specific surface area and irregular arrangement of nonwovens solve the contradiction between filtration effect and suction resistance.

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Melt blown fabric structure

 

03

熔喷布的生产原理

The production principle of melt blown cloth is mainly to use hot air jet to extrude hot polypropylene from the orifice of the spinneret of the spinneret to make it extend like fiber, and then gather on the conveyor belt to form a fiber network according to its self fusibility. There are many small nozzles arranged on the spinneret with a diameter of only 0.15mm. The melt polypropylene flow from the nozzle extends through the high-speed air flow and concentrates on the moving conveyor belt to obtain the melt spray cloth.

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Melt blown fiber forming

 

04

熔喷布生产工艺

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At present, this process is still the mainstream production process widely used in melt blown nonwovens industry, which is characterized by adopting single row of spinneret holes, drawing with hot air flow, and drawing hot air flow blowing out from both sides of spinneret at a certain angle.

 

The production process of melt blown nonwovens is to use polymer chips with high melt index (referred to as MFI for short) to extrude, heat and melt into high-temperature melts with good flow performance, then use high-temperature and high-speed hot air flow to blow the melt from spinneret into fine fibers, gather and integrate the fiber nets on the receiving device (such as mesh forming machine), and use their own residual heat to bond with each other Production process of cloth.

 

It has the characteristics of short process flow (only 10 minutes from feeding to product formation), simple equipment (such as the general production line does not need the equipment of consolidating fiber mesh), fine fiber (fiber diameter reaches micron or even sub nanometer level), and diversified product performance.

 

At present, melt blown method is an important process for manufacturing fine filter materials and high barrier materials, and it is also a method for manufacturing nano materials, which is still developing rapidly.

 

At present, the widely used nonwoven SMS mask is produced by the combination of spunbond and melt blown processes. It concentrates the high strength of spunbond nonwovens (s) and the small difference between the vertical and horizontal strength, as well as the high shielding and water-proof performance of melt blown nonwovens (m) on one material, forming a mask with strong water-proof performance, good air permeability and efficient isolation performance.图片6

Composite process

 

One step:

In one production line, there are two spunbonded spinnerets and one melt blown spinneret. The fibers ejected from them fall on the same screen successively to form a three-layer fiber network; then, after the hot rolling machine, they form a composite nonwovens with only one point of adhesion.

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One step process equipment

The top two sides of the mesh laying machine are spunbond die heads, and the middle is melt blown die heads. A line has two processes of spunbond and melt blown, and three die heads. It is a multi head spinning and melt blown nonwovens equipment.

 

Two steps:

The spunbond cloth and melt blown cloth are produced in the spunbond production line and melt blown production line in advance, and are compounded by lamination or other processes. After three sets of equipment, the S-layer and m-layer are obtained, and a layer of melt blown cloth is sandwiched between the two layers of spunbond, and the three-layer composite SMS is hot-rolled and bonded on a special hot-rolled composite mill.

 

05

Components of melt blown cloth equipment

Key equipment such as melt nozzle, automatic loading system equipment components, ultrasonic cleaning machine, air heater, centrifugal fan, screw extruder, melt spray mesh forming machine, melt spray off-line winding machine, melt spray off-line cutting machine, etc.

06

Core parts of melt blown cloth equipment

 

Melt blown die head

The die head includes the die head main body, spinneret and air plate. The spinneret and air plate are detachably installed in the die head main body. The spinneret is provided with a spinneret hole, and there are several caulking grooves between the spinneret and the air plate. The die head main body is also provided with a number of gas flow channels, which are connected with the caulking grooves. The outer wall of the die head main body is provided with a gas pipe connection end, and the gas flow channel is connected with the caulking groove  The connecting end of the pipe is connected with the gas collecting chamber through the gas transmission pipe, one end face of the spinneret hole of the spinneret plate is fixedly connected with the spacing flow stabilizing part, the other end face of the spinneret hole is fixedly connected with the pipe connecting device, and the spinneret hole is connected with the discharge port of the screw extruder through the pipe connecting device.

 

In the melt blown equipment, the melt blown die head is one of the core components to realize the drawing and forming of polymers. The design and precision directly affect the length, uniformity, toughness, fineness and many other aspects of the drawing, thus having a decisive impact on the final coil quality.

 

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Structure of melt blown die head


Spinneret

Spinneret for melt spinning is a representative spinneret for the manufacture of synthetic fibers such as polyester and nylon. It is a spinning method that the thermoplastic resin is heated and melted, extruded through spinneret in air or water at a certain speed, cooled and solidified into fibers.

 

The core technology is the small nozzle on the spinneret. This nozzle is not only small in size, but also 0.15mm In addition, it is very difficult to process the complex pass on such a small nozzle. The process of nozzle processing takes several months. If the processing accuracy is not high, the final production of the melt blown cloth can not meet the corresponding technical requirements, which will affect the protective performance of the mask.

 

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The structure of melt blown cloth spinneret


According to the shape of spinneret, the structure of spinneret can be divided into three forms: circular, fan-shaped and rectangular. At present, circular plate and rectangular plate are widely used at home and abroad. In order to adapt to different kinds of chemical fiber spinning occasions, circular spinneret can be divided into plate type, flange plate type, plate ring type, flange ring type, etc.; rectangular spinneret can be divided into flange rectangle and flange groove rectangle, etc., which are mostly used for short fiber spinning with more holes.

 

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Structure of melt blown cloth spinneret


Meltblown air heater

That is to say, the pipeline heater is composed of two parts: the body and the control system. The heating element is made of stainless steel pipe as the protective sleeve, high temperature resistance alloy wire, crystal magnesia powder. The control part is formed by compression process. The advanced digital circuit, integrated circuit trigger, high back pressure thyristor are used as the adjustable temperature measurement and constant temperature system to ensure the normal operation of the electric heater.

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Meltblown air heater

 

 

Polypropylene material is extracted from petroleum. At present, Sinopec and other enterprises can produce it in large quantities, but the equipment for melt blown polypropylene production, especially the core parts of spinneret, mainly depends on imports. These suppliers mainly include Japan's Carson spinneret, Germany enka, Japan spinneret and other enterprises. Japanese suppliers play the most important role. At present, the output of several enterprises is far from meeting the market demand.

 

Therefore, the production capacity of the mask ultimately depends on the production of the melt blown cloth production equipment, while the production of the spinneret nozzle, the core of the melt blown cloth production equipment, is very difficult. The processing time will take several months. In a short period of time, the production capacity cannot be greatly improved, and the production capacity is very limited, which also makes the mask production can only maximize the use of the current equipment, by extending the working time of the production line Increase production.