Vinyl chloride (VC) - vinylidene chloride (VDC) copolymer
DATE：2023/1/13 8:36:11 / READ： / SOURCE：This station
2.3.11 Vinyl chloride-vinyl chloride copolymer
Vinyl chloride (VC) - vinylidene chloride (VDC) copolymer is one of the most widely used polyvinylidene chloride (PVDC) resins. This product has two forms: dried powder material and original water latex.
2.3.11.1 Performance of vinyl chloride-vinylidene chloride
Vinyl chloride-vinylidene chloride copolymer has high density, transparent products, good printability, low permeability of film products to liquid and gas, and high thermal shrinkage; The toughness and impact strength of the product are higher than that of PVC film; The product is flame resistant and free from bacteria and insects; Hydrogen chloride and other gases can be easily decomposed under the action of heat, ultraviolet ray, particle radiation (X ray, r ray), alkaline reagent, some metals or salts; The product is resistant to a variety of solvents and chemical reagents and oil, but it is easy to swell in chlorine and chlorinated solvents and decompose in concentrated sulfuric acid and nitric acid.Vinyl chloride-vinylidene chloride copolymer can be used to produce molded films by extrusion spinning, calendering and extrusion blow molding.
2.3.11.2 Key points of vinyl chloride-vinylidene chloride copolymer forming process
① When VC-VDC copolymer is used to form film or fiber, the resin with vinylidene chloride content of 80%~95% and produced by suspension method shall be selected; The lotion process shall be used as the copolymer for coating and adhesive, and the resin with vinylidene chloride content no more than 70% shall be used.② Due to the large crystallization tendency of VC-VDC copolymer, water cooling (10 ℃) should be carried out quickly after extrusion molding of film blank or drawing, and then enter the preheating bath. The membrane blank treated under this process condition is suitable for blowing bulging film.
③ In the process of extrusion resin, the raw material is easy to decompose and release hydrogen chloride (HCI) gas. The amount of heat stabilizer in the raw material formula should be appropriately increased.
④ For the film used for forming food packaging, non-toxic and odorless additives (plasticizers, heat stabilizers, etc.) should be added to the raw materials, such as plasticizers such as epoxy soybean oil.
⑤ In order to avoid or reduce the decomposition of resin in the high temperature of extrusion molding, the heat stabilizer with good performance should be selected.
⑥ Screw structure requirements in the extruder: the ratio of screw pitch to screw diameter should be within (0.8~1): 1, the thread depth of the feeding section should be 8~13 mm, the compression ratio should be about 4:1, and the length-diameter ratio D/L should be less than 10:1 (this is to shorten the residence time of molten material in the barrel).
⑦ The process temperature control of extruded products shall be stable, and the allowable value of temperature (barrel, mold and water bath) fluctuation control shall be ± 1 ℃.
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