PP wetting tension KV/m is 31, compatibility is 8.1, fatigue-resistant bending can reach 100,000 times, brittle temperature is -35Â°C, oxygen permeability is 1.50, water absorption is 0.005 or less, water vapor permeability is 0.6g/ M2hr/mm, high shrinkage, slightly imperceptible aroma, high ultraviolet (366nm) permeability, good oil impermeability, poor gas impermeability, thermal blocking, non-charged .
Another major factor affecting the quality of packaging is transparency. In order to accelerate the crystallization of PP, the crystal structure of the surface of the product is made uniform to form a fine spherulite structure. Normally, 0.01%-0.05% DBS nucleating agent and antimony trioxide anti-flame retardant are added. The price of domestically produced SKG-Y5988 is not only lower than 2/5 of that of foreign countries, and its quality can be comparable to it.
Stretching (orienting) in PP means that the free surface of its internal structural units (such as talons or grains, etc.) is oriented, following some preferential directions, rather than being completely random. Because it gets a certain degree of orientation when it flows and deforms. Orientation is an important aspect of the structure of the molecule that reflects the state of aggregation. But its performance shows an anisotropy. Properly adjusting the orientation can change the properties and uses of PP stretch film in a wide range - fiber, monofilament, tape, narrow-band orientation and tear film. When we stretch orientation above the melting point and above the glass transition temperature, The quasicrystal obtained due to quenching (low crystallinity) is unstable, while the progressive cooling crystallinity is relatively high and accordingly is stable.
For example, it can be transformed into monoclinic crystals at 70Â°C; only half of the transformations occur at 110Â°C, while most of the transformations occur at 145Â°C, whereas monoclinic crystals begin to melt at 170Â°C. Production always involves the extrusion and stretching of sheets. The orientation is put together because the stretching temperature is set at a temperature between the maximum rate of crystallization and the melting point of -120-150Â°C. Although ordinary PP can greatly improve weatherability and transparency, branching degree and gloss retention after adding a nucleating agent, it is more important that the crystallization rate in the PP system doubles. As the number of crystal growth increases in the same system and the size of the crystal decreases, the result is that the crystal is smaller than the wavelength of visible light to allow light to pass through, thereby enhancing the transparency and greatly reducing the surface defects of its products. However, the effective temperature of domestically produced SKG-Y5988 is 185-260Â°C. Then, in practice, we need to mix and disperse the PP resin after it is dispensed. Otherwise, the purpose of adding organic nucleating agents cannot be achieved.
Second, we have a stretch ratio of about 7 in the stretching process. The draw ratio also has a problem of control of the ambient humidity and stretching temperature of the shop. For example, at Shijiazhuang Marine Plastics Packaging Co., Ltd., although at a high draw ratio, the strength of the product can be improved, the residual elongation can be made smaller, but the transparency is affected.
3 The application of additives has marked the practice of packaging technology in recent years. It has proved that there are no packaging materials without additives and no additives without materials. Therefore, in addition to the above examples of the use of additives, we will also introduce the following functions and dosages of additives.
3.1.1 Organic salts, organic tin, and pure organic compounds in stabilizers are divided into:
1 long-term heat stabilizer, the amount is generally 1% -3%, the main use of MW30N-1200 molecular weight;
2 Zinc stearate, calcium stearate, strontium stearate and the like.
3.1.2 Light Stabilizer: The dosage is 0.01%-0.05%, and the ultraviolet ray absorption agent OV-P, UV-326, UV-327 and so on.
3.1.3 The main antioxidant; The amount of 0.1% -0.5%.
1 General use of DLTP, namely phenolic antioxidants;
2 auxiliary antioxidants: The amount of 0.1% -0.5%, while the use of DSTP to make the white turbidity trend of PP (that is, sulfide esters);
3 can use tetradecyl ester;
4 Sandunovr3212 can also be added to improve the oxygen-absorption properties of metal inks.
3.1.4 Biocides: The amount of 0.1%-0.2%, there are more than 300 kinds of chemicals used for antimicrobial erosion, but PP material has not been successfully reported in this area.
3.1.5 In addition to the three major categories already described, there are light shielding agents, quenchers, and free radical accelerators.
3.2 Characteristic additives.
3.2.1 Characteristics Additives; dosage of 100%-30%, the market is often divided into inorganic and organic fillers such as calcium, wood flour, white carbon black, talcum powder and so on. 3.2.2 enhancer: dosage 10% -40%, support mother, wollastonite, silicon carbide flakes, talcum powder, glass fiber, carbon fiber and so on.
3.2.3 coupling agent: often referred to as modifier, the amount of 0.1% -5%. Commercially available points:
1 silicon organic silanes, organic aluminum acid esters, etc.;
2 oximes: organic phthalates, organic aluminates;
3 phosphate ester system.
3.2.4 plasticizer and reactive plasticizer: The amount of 0.1% -1%.
1 monomer molecular weight between 200-600.
2 The polymerization type is between 1000 and 8000. Yixiu Industry is divided into: Phosphoric acid esters, phthalic acid, aliphatic dibasic acid esters, epoxy compounds, polyesters, chlorine compounds, all Benzoic acid esters, trioctyl trimellitate and other 11 series. However, most of the PP materials used are phthalate or polyvinyl chloride resins. (to be continued)
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