Analysis Of Plastic Co-extrusion Process
A variety of methods can be used to produce multi component composite products, and the co-extrusion process is the most simple and convenient method. It has become one of the most advanced plastic forming processing methods. High polymer co-extrusion process is a process that uses several extruders to supply different melt streams, and a total of composite products are extruded at a compound head. It can make the layers with different characteristics in the extrusion process of composite materials with each other together, so that the product has excellent properties of different materials, are complementary in character, so as to obtain the special requirements of
performance and appearance, such as anti oxygen and moisture barrier ability, coloring, heat preservation, heat molding and thermal bonding ability and strength, stiffness, hardness and other mechanical properties. These multilayer composites with comprehensive properties have been widely applied in many fields. In addition, the utility model can greatly reduce the cost of the product, simplify the process and reduce the investment of the equipment, and the composite process does not use solvent and produces no waste material. Therefore, co-extrusion technology is widely used in the production of composite films,plates, pipes, profiles and wires and cables.
The following are focused on the technology of co-extrusion of composite pipes,
composite films, flat film and casting film, PVC core layer foamed composite tube, plate and profile.
Co-extrusion of composite pipe
Plastic composite pipe has the advantages of plastic and metal as a whole, has the advantages of corrosion resistance, non-toxic, smooth, light texture, high strength, good heat resistance, low brittle temperature, convenient installation, beautiful appearance, long service life, can be used to transport the ground and the cold and hot water and drinking water pipes, heating pipelines, gas the pipeline, oil chemical industry in the corrosive liquid and corrosive gases, compressed air transportation and food industry, beverage wine and milk and other liquid delivery, in the near future may gradually replace the galvanized pipe, copper pipe, plastic pipe. In industrial developed countries, aluminum plastic composite pipe in the pipe in the market share of about 15%. The technology proposed in 1974 by British engineers ItzhakBarnoach patent, and Holland Kitech company, Germany Unicor company and company of gram Lao Bo has made the improvement to the pipe structure, processing equipment and manufacturing technology, make its performance improvement, began commercial application in Europe and Australia in early 1990s. In the middle of 1990s, China began to introduce aluminum plastic composite pipe production line technology, and began the production and application of aluminum plastic composite pipe.
Aluminum plastic composite pipe is composed of 5 layers (polyethylene, hot melt adhesive, hot melt adhesive, aluminum foil, polyethylene), with cross-linked polyethylene (XLPE) as the inner layer, the middle layer is welded tubes to increase the strength of the tube, and the plastic layer of adhesive bonding to the outer surface of the aluminum coating, through co-extrusion molding.
Flat film and casting film co-extrusion.
The casting film forming principle is that the plastic melt is extruded through the T mold head in the extruder, and then enters the water solution or quench roller directly. After the cooling and traction, the casting film is obtained. This method can give full play to the performance of the material to be machined while maintaining the best dimensional accuracy. Most thermoplastic films can be produced by tape casting. This is especially true for semi crystalline thermoplastics.
The forming principle of flat film extrusion is that the plastic melt which has been plasticized in the extruder has been extruded from the flat film head and cooled and solidified by contact with the cooling roller. Finally, the film is cut into a certain width film and rolled into a coil. The structure of each layer coextrusion film can be symmetric or asymmetric, when the adhesion between the two layers of film is poor, we need to add a thin layer of adhesive layer between the two layers, in order to improve the sealing performance and adhesion properties of the boundary.
There are three types of co-extrusion heads for flat film and casting film, that is multi channel co-extrusion head, co-extrusion head with feeding block, and co-extrusion head with multi channel head and feed block.
(1) multi channel co-extrusion die: flow channel comprises a plurality of extrusion melt extruder from a multi channel head feed end respectively into the width and thickness of the set, each layer of melt in the die in composite molding. With this method, people can choose plastic materials with different melting point and melting point to produce composite products. But the number of composite layers can not be too much, otherwise the extrusion head is too large.
(2) with co-extrusion die: the feed block comprises a plurality of extrusion melt extrusion machine by feeding block shunt, melt flow rate through the internal setting of the ratio control valve and the thickness of the adjusting bolt adjustment, and then join into the coat hanger die extrusion. This method allows people to produce more layers of composite films, the extrusion head is small and precise. The disadvantage is that only plastics with similar flowability and processing temperature can be combined with each other, and the processing range is narrow.
(3) A co-extrusion head with a multi channel head and a feeding block. It is by the German ReifenhSer company developed specifically for processing more than five layers of thermal sensitive material co-extrusion die.
Plastic profile co-extrusion aims to make different kinds of polymers into different parts of the same section of the profile to give special functional requirements or get the best performance and price ratio, so that the diversified or multi-functional products, to improve product quality and reduce cost.
The co-extrusion process of profiled material can be divided into two categories, pre co-extrusion and post extrusion, according to the forming state of co-extrusion material. Pre co-extrusion refers to the two materials in the process of incomplete molding to achieve composite forming; after co-extrusion is a material has been fully formed, and then with another material to achieve composite molding. The advantage of co-extrusion is that it can make good use of waste material and has better economic performance.
According to the extrusion material, it can be divided into two categories: Organic co extrusion and inorganic Co extrusion. The same material contains organic co-extrusion before (such as fine material and mixed with recycled materials before extrusion) and different materials before extrusion (such as PMMA and PVC pre and post co-extrusion) and PVC; inorganic co-extrusion can be divided into plastic composite extrusion and plastic composite extrusion.
In this paper, extrusion extrusion, aluminum plastic composite extrusion, steel plastic composite extrusion and PVC color coextrusion technology are emphasized.
Post co-extrusion (referred to as PCE below) technology is an advanced advanced molding technology developed by Austrian in the late 1980s. It is the latest development of co-extrusion technology. Compared with traditional co extrusion (referred to as FCE below) technology, it has the remarkable characteristics of simple process, flexible application, low waste rate, easy recovery and controllable adhesive strength. At present, the technology is mainly used in the manufacture of special-shaped materials for doors and windows with sealing strips.
Traditional FCE technology is a molding technology. The molten material by extrusion machine more than two sets of molds to the same extrusion with different rheological behaviors or different colors, the melt flow in the respective flow passage forming die, extrusion die and in the confluence, and the vacuum in the shaping sleeve, cooling and shaping. In this process, due to differences in melt viscosity and pressure and velocity of each layer of material confluence in the die, not easy to produce stable laminar flow, caused by irregular, uneven composite interface, a model of each layer is easy to separate. In addition, the difference of melt viscosity also makes the extrusion melt difficult to form in vacuum cooling molding (such as plugging into the setting sleeve easily), which makes the process more complex and difficult to control. Therefore, it is necessary to design and manufacture complex molds and skilled operation techniques to ensure the quality of molding.
Tongxiang long Cheng Plastic Co., Ltd. has nearly 20 years experience on PVC granule research,development and granulation production. With product of two-color co-extrusion profile special PVC pellets in good extrusion processing properties, fluidity and surface gloss; thermal stability and processing cycle of the host product matching; integration, excellent weathering resistance, tear resistance.Professional and technical service team can provide one-stop system solution for customers.
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