Polyethylene terephthalate (PET) is a polymer made of t […]
Polyethylene terephthalate (PET) is a polymer made of terephthalic acid and ethylene glycol through the direct phenolization method or the exchange method of dimethyl terephthalate and ethylene glycol. Although the history of development is not long, with the rapid development of the packaging industry, the application of PET materials in my country has soared year by year, especially in terms of films and sheets, which also led to the development of PET sheet thermoforming technology. The thermoforming of PET sheet is generally produced on the original positive pressure, negative pressure or positive and negative pressure molding (blister) machine. The products produced are called thermoformed products, which are non-toxic, tasteless and do not pollute the environment. "Green packaging materials" can replace PVC, PS, PP and other materials used in the outer packaging of eggs, fruits, vegetables, packaging cartons, independent packaging and heat-resistant packaging of food, and simple packaging of tools (such as nails, nuts, screws) )Wait. Therefore, the prospect of PET thermoforming processing technology is very broad, and the market prospect of thermoforming products is very promising.
Physical and mechanical properties of PET sheet for thermoforming. PET is a milky white translucent or colorless transparent body. It belongs to a thermoplastic resin. The relative density is 1.38, the refractive index is 1.655, and the light transmittance is 5%. PET is a medium barrier material. The permeability coefficient of oxygen is 50 per tap. Lining·～plus 2·d.MPa, the permeability coefficient for carbon dioxide is 180. m3·～and 2·MPa, the water absorption rate is 0.6%, and the water absorption is relatively large. Compared with other materials, PET has a high tensile strength, comparable to aluminum foil, 9 times that of PE-HD and 3 times that of PC and PA; it has good barrier properties, dimensional stability, high transparency, high impact strength, and no Toxic and tasteless, easy to thermoform, PET sheet can be made into thermoformed products with complex shapes. The commonly used PET sheet is amorphous PETP resin, with a characteristic dryness of 0.6 to 0.7dl, electricity. PET sheet can be produced by extrusion casting method. Amorphous transparent sheet, also called APET sheet, extruded by a T-head and quenched, has a thickness of 0.2mm to 0.6~. APET sheet can be used as various transparent thermoformed packaging products. The crystalline modified PET sheet (CPET) also has the characteristics of high temperature resistance (150-200℃). Usually the thickness is 0.20～一1.00? CPET cast sheet can be used as thermoformed products. The crystalline modified PET sheet (CPET) also has the characteristics of high temperature resistance (150-200℃). Usually the thickness is 0.20～一1. The ~, CPET cast sheet can be used as thermoformed products. The requirements of thermoforming for materials are as follows: ① It must have good heating extensibility, a higher height to diameter ratio (ie stretch ratio), and good elongation; ② It must have sufficiently high tensile strength, impact strength and needle resistance Porosity; ③Products with composite requirements need to have good thermal strength; ④Good transparency and gloss, which is convenient for the exhibition and sale of the packaged goods; ⑤Waste packaging is easy to handle; ⑥Products used for food and medical packaging It should have non-toxic, tasteless or low-odor requirements; ⑦Products with color printing requirements should be corona treated. The general physical and mechanical properties of PErr sheet suitable for thermoforming are shown in the table.