In the previous article, we talked about “20 kinds of materials commonly used in composite food packaging bags”, then in this article, we will continue to talk about the related issues of packaging bag raw materials. In this article, we will talk about Basic performance requirements for plastic film materials. One of the requirements of the packaging bag for the film material – the appearance generally requires that the appearance is smooth and smooth, without wrinkles or only a small amount of loose folds, without obvious unevenness, black spots, impurities, crystal points and rigid blocks, and without streaks and spots. There are no bubbles, pinholes and cracks. The aluminized layer of the aluminized film should be uniform, and no obvious bright stripes, yin and yang surfaces, etc. are allowed. In addition, the surface of the film is also required to be clean and free from dust, oil, etc. The second requirement of the packaging bag for the film material – specifications and deviations The width, thickness and deviation of the plastic film should meet the requirements, and the thickness should be uniform, the thickness deviation between the horizontal and vertical directions is small, and the deviation distribution is relatively uniform. In addition, the thickness of the aluminized layer of the aluminized film should also meet the requirements. The third requirement of the packaging bag for the film material – physical and mechanical properties Since the plastic film is subjected to mechanical force during the printing and compounding process, the film material is required to have certain mechanical strength and flexibility. The physical and mechanical properties of plastic films mainly include tensile strength, elongation at break, tear strength, impact strength, etc. In addition, the firmness of the aluminized layer on the aluminized film should also meet the requirements. The fourth requirement of the packaging bag for the film material – physical and mechanical properties For the transparent plastic film, the light transmittance is required to be higher, which should generally reach more than 92%. For opaque plastic films, such as white film, it is required to have high whiteness and good opacity. In addition, the plastic film should also have good gloss. The fifth requirement of the packaging bag for the film material – surface tension In order to make the printing ink and composite adhesive have good wetting and adhesion on the surface of the plastic film, the surface tension of the film is required to reach a certain standard, otherwise it will be Affects the adhesion and adhesion of inks and adhesives on their surfaces, thereby affecting the quality of printed and composite products. For example, the surface tension of biaxially oriented polypropylene film and low-density polyethylene film is required to reach 3.8 * 10-2N/m or more, and the surface tension of nylon film, polyester film and polyester aluminized film is generally required to reach 4.5 * 10-2N /m or more. Generally speaking, plastic films must be surface-treated before printing or compounding to increase their surface tension, so that they can be printed and compounded smoothly. The sixth requirement of the packaging bag for the film material – the moisture permeability indicates the amount of water vapor transmission of the plastic film material under certain conditions, such as when the relative humidity is 90% and the temperature is 30 °C, the thickness within 24h is 25 The quality of the water vapor permeated by the μm plastic film per square meter represents the moisture resistance of the film material to a certain extent. The moisture permeability of various film materials is different, which also determines its application range. The seventh requirement of the packaging bag for the film material – the oxygen permeability indicates the oxygen permeability of the plastic film material under certain conditions, such as when the relative humidity is 90% and the temperature is 23 °C, the thickness within 24 hours is 25%. The volume of oxygen transmitted per square meter of plastic film in μm. The oxygen permeability of various film materials also varies. The eighth requirement for the film material of the packaging bag – chemical stability The plastic film is in contact with ink, adhesives and some organic solvents during the printing and lamination process. These are all chemical substances. Therefore, the plastic film must be sensitive to these Chemicals have some resistance so as not to be affected by them. The ninth requirement of packaging bags for film materials – geometric dimensional stability The plastic film must have a certain geometric dimensional stability, otherwise, its expansion rate is too large, and it is easy to expand and contract under the action of mechanical force or heat during the printing and lamination process. Deformation will not only affect the overprint accuracy, but also cause wrinkles, curling and other problems, seriously affecting product quality and production efficiency. Therefore, the composite packaging bag is also very important when selecting materials.
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