Recently, mask materials have received a lot of attention, and our polymer workers have not been hindered in this battle against the epidemic. Today we will introduce how melt blown PP material is produced.
Market demand for high melting point PP
The melt flowability of polypropylene is closely related to its molecular weight. The weight average molecular weight of commercial polypropylene resin prepared by conventional Ziegler Natta catalytic system is generally between 3 × 105 and 7 × 105. The melt index of these conventional polypropylene resins is generally low, which limits their application range.
With the rapid development of the chemical fiber industry and textile machinery industry, the non-woven fabric industry has risen rapidly. The series of advantages of polypropylene make it the preferred raw material for non-woven fabrics. With the development of society, the application fields of non-woven fabrics tend to be broad: in the field of medical and health, non-woven fabrics can be used to manufacture isolation gowns, masks, surgical gowns, women’s sanitary napkins, baby diapers, and so on; As a building and geotechnical material, non-woven fabrics can be used for roof waterproofing, road construction, and water conservancy projects, or advanced roof felt can be produced using spunbond and needle punched composite technology. Its service life is 5-10 times longer than traditional asphalt felt; Filter materials are also one of the fastest developing products in non-woven fabrics, which can be used for gas and liquid filtration in industries such as chemical, pharmaceutical, and food, and have great market potential; In addition, non-woven fabrics can be used for the manufacturing of synthetic leather, bags, clothing linings, decorative fabrics, and wiping cloths in daily life and household use.
Due to the continuous development of non-woven fabrics, the requirements for their production and application are constantly increasing, such as melt blown, high-speed production, and thin products. Therefore, the requirements for the processing performance of polypropylene resin, the main raw material for non-woven fabrics, have also correspondingly increased; In addition, the production of high-speed spinning or fine denier polypropylene fibers also requires polypropylene resin to have good melt flow properties; Some pigments that cannot withstand high temperatures require processing of polypropylene as a carrier at relatively lower temperatures. All of these require the use of ultra-high melt index polypropylene resin as raw material that can be processed at lower temperatures.
The special material for meltblown fabrics is high melt index polypropylene. The melt index refers to the mass of molten material passing through a standard die capillary every 10 minutes. The larger the value, the better the processing fluidity of the material. The higher the melt index of polypropylene, the finer the fibers blown out, and the better the filtration performance of the produced melt blown fabric.
Method for preparing high melt index polypropylene resin
One is to control the molecular weight and molecular weight distribution of polypropylene by controlling the polymerization reaction process, such as using methods to increase the concentration of inhibitors such as hydrogen to reduce the molecular weight of the polymer, thereby increasing the melt index. This method is limited by factors such as catalytic system and reaction conditions, making it difficult to control the stability of the melt index and implement.
Yanshan Petrochemical has been using metallocene catalysts for direct polymerization of melt blown materials with a melt index of over 1000 in the past few years. Due to the difficulty in controlling stability, large-scale polymerization has not been carried out. Since the outbreak of the epidemic this year, Yanshan Petrochemical has adopted the controllable degradation polypropylene melt blown material production technology developed in 2010 to produce polypropylene melt blown non-woven fabric special material on February 12th. At the same time, industrial tests were conducted on the device using metallocene catalysts. The product has been produced and is currently being sent to downstream users for trial.
Another method is to control the degradation of polypropylene obtained through conventional polymerization, reducing its molecular weight and increasing its melt index.
In the past, high-temperature degradation methods were commonly used to reduce the molecular weight of polypropylene, but this high-temperature mechanical degradation method has many drawbacks, such as loss of additives, thermal decomposition, and unstable processes. In addition, there are methods such as ultrasonic degradation, but these methods often require the presence of solvents, which increases the difficulty and cost of the process. In recent years, the method of chemical degradation of polypropylene has gradually been widely applied.
Production of high melt index PP by chemical degradation method
The chemical degradation method involves reacting polypropylene with chemical degradation agents such as organic peroxides in a screw extruder, causing the molecular chains of polypropylene to break and reduce their molecular weight. Compared with other degradation methods, it has the advantages of complete degradation, good melt flowability, and simple and feasible preparation process, making it easy to carry out large-scale industrial production. This is also the most commonly used method by modified plastic manufacturers.
Equipment requirements
High melting point refers to equipment that is completely different from ordinary PP modification equipment. The equipment used for spraying molten materials requires a longer aspect ratio and a vertical machine head, or uses underwater granulation (Wuxi Huachen has a similar underwater cutting); The material is very thin and needs to come into contact with water immediately after coming out of the machine head for easy cooling;
The production of conventional polypropylene requires an extruder cutting speed of 70 meters per minute, while high melting point polypropylene requires a cutting speed of over 120 meters per minute. In addition, due to the fast flow rate of high melting point polypropylene, its cooling distance also needs to be increased from 4 meters to 12 meters.
The machine for making melt blown materials requires continuous mesh changing, usually using a dual station mesh changer. The motor power requirement is much higher, and more shear blocks are used in the screw components;
1： Ensure smooth feeding of materials such as PP and DCP;
2： Determine the appropriate aspect ratio and axial position of the opening based on the half-life of the composite formula (which has evolved to the third generation to ensure smooth extrusion of CR-PP reaction);
3： To ensure a high yield of melted fingers within the tolerance range (more than 30 finished strips have a higher cost-effectiveness and blending basis compared to only a dozen strips);
4： Special underwater mold heads must be equipped. The melt and heat should be evenly distributed, and the amount of waste should be minimal;
5： It is recommended to equip a mature cold granulator for meltblown materials (which has a good reputation in the industry) to ensure the quality of the finished granules and a higher yield rate;
6： If there is online detection feedback, it would be even better.
In addition, the degradation initiator added to the side feed with liquid requires higher accuracy due to the small addition ratio. For side feeding equipment such as imported Brabenda, Kubota, and domestically produced Matsunaga.
The degradation catalyst currently used
1: Di-t-butyl peroxide, also known as di tert butyl peroxide, initiator a and vulcanizing agent dTBP, is a colorless to slightly yellow transparent liquid that is insoluble in water and miscible with organic solvents such as benzene, toluene, and acetone. Highly oxidizing, flammable, relatively stable at room temperature, insensitive to impact.
2: DBPH, abbreviated as 2,5-dimethyl-2,5-bis (tert butylperoxy) hexane, has a molecular weight of 290.44. Light yellow liquid, paste like and milky white powder, with a relative density of 0.8650. Freezing point 8 ℃. Boiling point: 50-52 ℃ (13Pa). Refractive index 1.418~1.419. The liquid viscosity is 6.5 mPa. s. Flash point (open cup) 58 ℃. Soluble in most organic solvents such as alcohols, ethers, ketones, esters, and aromatic hydrocarbons, insoluble in water.
3: Finger melting test
The melt finger test needs to be conducted in accordance with GB/T 30923-2014 Polypropylene Melt Spray Special Materials; Ordinary melt finger testers cannot be tested. High melting point refers to the use of volume method rather than mass method for testing.
Dongguan Liansheng Non woven Technology Co., Ltd. was established in May 2020. It is a large-scale non-woven fabric production enterprise integrating research and development, production, and sales. It can produce various colors of PP spunbond non-woven fabrics with a width of less than 3.2 meters from 9 grams to 300 grams.
Post time: Nov-08-2024