Experience sharing of production and commissioning of melt blown clothDue to the particularity of the melt-blown cloth production process, as a raw material for melt-blown cloth, it must meet the following requirements. The high melt index should be greater than 400g/min, leaving a narrow ash with a relatively low molecular weight distribution. The melt index of the melt blown raw material is too low, the melt viscosity is large, and the extruder needs to provide a large pressure to smoothly extrude it from the spinneret hole, which requires greater energy consumption, and the melt blown equipment is subjected to greater pressure and the melt After being extruded from the spinneret hole, it cannot be fully drawn and refined, and ultra-fine fibers cannot be formed. Therefore, only materials with a high melt index can meet the requirements of the melt-blown process, produce qualified ultra-fine fiber melt-blown cloth, and reduce energy consumption.
1. Heat treatment of polypropylene raw materials
According to the practical experience of Jingong customers, the extended treatment time at different temperatures of polypropylene has the same change law. The crystallinity continues to increase. When the heat treatment time is reached, it almost reaches the maximum value at that temperature. If the treatment time is extended, the crystallinity changes Prolonging the treatment time at less than 90℃ does not have much effect on the crystallinity of polypropylene. The effect of increasing the treatment temperature on the crystallinity of polypropylene with sufficient treatment time also has the same change rule. The heat treatment temperature is lower than 90℃, crystallization There is no obvious change in the degree. When the heat treatment temperature exceeds 90℃, the crystallinity rises sharply. At 140℃, the crystallinity is greatly improved, which can be increased by nearly 10% compared with the original sample. Through practice, it was found that the polypropylene melt-blown cloth will partially melt above 140°C, and the structure of the cloth will be destroyed.
2. Process parameters corresponding to various problems:
Melt temperature: It determines the flow rate of the melt. During the production process, the melt temperature should be adjusted according to the melt index of the raw materials and the actual situation to ensure that the melt is within a flow rate that is more suitable for spinning.
Air source equipment: It mainly provides high-pressure air flow for the melt-blown cloth production line to blow out the molten polypropylene. Here, air source equipment with stable air volume and pressure is required, generally 70-80Kpa, and different production lines are equipped with different air volumes. Practice has proved that Roots blower is the most economical and stable melt jet source equipment. First, the pressure of the air compressor is too high, and the second is that oil lubrication is required during the working process. Even if the air compressor is called "oil-free", only an oil-gas separator is added inside, and a small amount of oil mist will still be ejected with the air flow. The odor caused by the melt-blown cloth is obvious when it is made into a mask, and the detection fails.
Roots blower working principle diagram
Hot air volume and temperature: It mainly affects the drafting and cutting of the melt, determines the fiber formation, and affects the strength and softness of the meltblown fabric. The reasonable configuration of hot air volume and pressure plays an important role in normal production. In the case of a certain amount of melt extrusion, the temperature and pressure of hot air will affect the fineness of the melt blown fiber, especially the speed of drawing hot air directly affects Meltblown fiber diameter. The temperature of the hot air is constant, the drawing hot air speed is too high or the hot air pressure is constant, and the hot air temperature is too high, which will cause the excessive stretching of the melt-blown filaments, forming ultra-short and ultra-fine fibers that are scattered into the air and cannot be collected. That is, the phenomenon of "flying flowers and flying flocs" occurs, and the reasonable configuration of the temperature and pressure parameters of hot air is also of positive significance for reducing energy consumption.
Screw speed: The faster the screw speed, the greater the amount of extrusion per unit time. Under the same hot air drafting conditions, the fiber is formed thicker, the fiber content of the product with the same gram weight is reduced, and the strength of the fiber web is reduced.
Receiving distance: It is an important parameter that affects the performance of the fiber web. Generally, with the change of the receiving distance, the longitudinal and transverse strength of the melt-blown cloth, the bending stiffness, and the fiber diameter will also change. The larger the receiving distance, the longer the cooling time of the drawn fibers, the reduced the bonding points between the fibers, the more fluffy and soft the product, and the lower the breaking strength.
Rotation speed of the receiving drum: The rotation speed determines the orientation of the fibers in the finished cloth. The faster the rotation speed, the more the fibers are oriented in the direction of rotation of the receiving device, and the greater the difference between the vertical and horizontal directions of the finished cloth.
Here is a list of Jingong’s 30g meltblown process parameters, please refer to it.
3. Electret treatment
Electret time, electret voltage and electret distance are three important process parameters that affect the effect of electret. As the electret time increases, the equivalent surface charge density of the deposit increases and the potential of the electret surface increases. The adsorption and polarization of the electret are enhanced, but as the electret time increases again, when the surface potential of the filter material is sufficiently high, the charge below the needle tip will be repelled to move to other places with a lower charge density. When the electret ends, its charge surface density reaches saturation, so when the electret time increases again, the filtration efficiency of the filter material does not change significantly.
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