Application of extrusion foaming method
DATE：2022/4/29 8:48:56 / READ： / SOURCE：This station
Application of extrusion foaming method
According to the variety of extruded foam products and the scope of applicable polymers, it can be summarized into the following specific application fields.1、 Profile
Chemical foaming method or physical foaming method is widely used in the extrusion of foamed profile, which belongs to free expansion system. This kind of product can use the "seluka" method to control the foaming expansion. In this field, unplasticized PVC and PS are widely used, as well as a small amount of homopoly PP products. Carpet compounding equipment www.handern.com com
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Unplasticized PVC foamed profile products are the largest application field of commercial foamed profiles.
(1) Application and characteristics the biggest application field of unplasticized PVC foam profile is to replace wood. Because this product can have complex section shape, good processing performance and certain structural strength, the construction industry is particularly interested in it. This product can be used in high humidity environment, or as structural elements, decoration of internal instrument panels or seals. Two kinds of extrusion technologies are basically adopted for the commercial products of non increased early profile. Soft large surface (die) products can be produced by "shadow expansion extrusion" method, and small complex sections can be produced by ordinary free foaming technology. The latter technology requires longer cooling time or vacuum setting die sleeve can be used to improve its dimensional accuracy. When using the extrusion method of free foaming expansion, the main research topic is to increase the surface hardness of products and reduce the density, so as to meet the economy of wood. The average density of uninvolved PVC foam profile is 0.8 ~ 1.0g/cm. Such a high density makes PVC inferior, because the density of PS foam profile is 0.4 ~ 0.6g/m. Physical properties of typical unplasticized PVC extruded foamed profile products
For hard PVC, if its density is lower than 0.8g/cm, it will lead to the disadvantages of poor product stiffness and soft surface. This kind of surface is easily nicked. To solve this problem, extrusion technology. The basic method is to add surface additives (floating and proliferating rapidly during processing) or adopt co extrusion technology to allow PVC core layer to have low density, and make the physical properties of hard PVC foam profile adopting free foaming technology equal to PS foam profile and hard PVC foam profile produced by "seluka" method. However, the cost should be paid attention to in the production of rigid PVC foamed profile by this co extrusion free expansion method.
(2) As we all know, PVC melt has low melt elasticity and poor fluidity. The following factors have been proven to improve these properties. (i) Lower homopolymer. The sample polymer will obviously get poor physical properties of the final product. However, the rapid melting of this material system in the processing process can ensure the uniformity of its melt at the temperature at which the gas can be released.
(II) the flexibility of the acrylic foam wall to increase the impact strength of the product. However, another important function of modifier is to increase the elasticity of PVC melt and improve the bubble structure. The amount of this modifier is actually directly proportional to the surface and bubble quality of the final product. However, the cost economy of these formulations and the actual needs of product performance limit the amount of modifier added.
(III) lubricants for external or internal systems are based on acrylate and organic waxes (such as paraffin). Lubricants are usually used to increase the gelatinization of components in the screw and contribute to the formation of skin. This property is particularly suitable for free foaming technology.
(IV) foaming system the foaming system of controllable foaming technology is basically based on inorganic system (sodium bicarbonate), while free foaming technology and co extrusion technology are based on organic system. The choice of organic foaming system is related to the grade of polymer, but Azodicarbonamide (AC foaming agent for short) with better activation performance is usually selected. When selecting heat stabilizers and other additives, we should also pay attention to whether these additives interact with Azodicarbonamide to reduce its decomposition temperature. Composite carpet equipment com
It is feasible to adjust the density of foamed products with the addition of foaming agent to a certain extent. If the dosage is too small, it can not obtain sufficient foaming. On the contrary, if the dosage is too large, it can not increase the foaming ratio, but also cause obvious discoloration due to the residue of foaming agent, rough product surface, coarse pores and large bubbles and other quality problems. Therefore, when determining the dosage of foaming agent in the formula, the theoretical formula can be used for estimation. The technology is applicable to the chemical foaming system based on Azodicarbonamide. As a result of this matching, the auxiliary agent can not only play the role of heat stabilizer, but also play the role of dual nitrogen dicarbonamide as a chemical agent. Finally, the decomposition temperature of Azodicarbonamide in the processing range is reduced. This heat agent system includes zinc, lead or cadmium, inorganic salts or organic compounds, as well as the newly developed heat agent organotin compounds. The value of heat stabilizer is that it can stabilize bubbles in both free foaming technology and controllable foaming. In the latter extrusion technology, the use of thermal stability can affect the efficiency of process operation.
(VI) technical materials and pigments are of special value. Because fillers and pigments can not only control the surface quality of products and reduce the cost of products, but also play an auxiliary role as nucleating agent in the foaming process, the particle size of fillers or pigments used in foaming should be controlled and not too coarse. In addition, in chemical foaming, the selection of pigments also depends on the stability of pigments in the gas separated during processing, as shown in Figure 2 Carbon oxide, carbon monoxide, nitrogen, especially ammonia. Carpet compounding equipment www.handern.com com
Author：admin