Material properties of transparent plastic signs

Writer：admin Time：2023-06-14 11:33 Browse：℃

　　Plastic signs have the advantages of light weight, good toughness, easy molding, low cost, etc. Therefore, in modern industrial and daily products and sign LOGO, more and more transparent plastics are used to replace glass products, especially in Optical instrument and packaging industry, with rapid development. However, due to the requirements of good transparency, high wear resistance, and good impact toughness, the composition of plastic, as well as the entire injection molding process, equipment, molds, etc., must be accurately controlled to ensure that these plastic labels (transparent plastic products) used to replace glass products have good surface quality and meet the requirements for use.

　　At present, transparent plastics commonly used in the market include polymethyl methacrylate, (PMMA is commonly known as acrylic or plexiglass), polycarbonate (PC), polyethylene terephthalate (PET), transparent nylon, acrylonitrile styrene copolymer (AS), polysulfone (PSF), etc. Among them, PMMA, PC and PET are the three plastics that we are most exposed to. The following will take these three plastics as examples to discuss the properties of transparent plastics and injection molding precautions.

　　1、 Performance

　　Transparent plastic signs must first have high transparency, followed by a certain degree of strength and wear resistance, impact resistance, good heat resistance, excellent chemical resistance, low water absorption, and all of the above properties in order to meet the transparency requirements of the sign and remain unchanged for a long time.

　　Comparison of transparent plastic properties

　　Performance density

　　(g/am2) Tensile strength

　　(MPa) Notch impact

　　(J/m2) Transparency

　　(%) Deformation temperature

　　(℃) Allowable water content shrinkage rate, wear resistance, chemical resistance

　　PMMA 1.18 75 1200 92 95 0.04 0.5 Poor

　　PC 1.20 66 1900 90 137 0.02 0.6 Zhongliang

　　PET 1.37 165 1030 86 120 0.03 2 Liangyou

　　From the data, it can be seen that PC is an ideal choice, but due to its expensive raw materials and difficult injection molding process, PMMA is still the main choice (for plastic label products with general requirements), while RET is often used in packaging and containers because it requires stretching to obtain good mechanical properties.

　　2、 Precautions during the injection molding process of transparent plastic labels!

　　Transparent plastic, due to its high transmittance, inevitably requires strict surface quality requirements for plastic labels, without any defects such as spots, pores, whitening, haze, black spots, discoloration, and poor gloss. Therefore, strict or even special requirements must be paid attention to and put forward for the design of raw materials, equipment, molds, and even products throughout the entire injection molding process. Secondly, due to the high melting point and poor fluidity of transparent plastics, in order to ensure the surface quality of the product, it is often necessary to make slight adjustments to process parameters such as high temperature, injection pressure, and injection speed, so as not to generate internal stress and cause product deformation and cracking.