Specific gravity and viscosity of PE stretch film

The specific gravity of the stretch film: the calculation of the weight and length of the PE stretch film are different, thinking that the length of each roll is different, its weight is also different, and the calculation formula is the same, but some units are converted, Everyone needs to pay special attention. The error of sometimes dividing, sometimes dividing into a decimal point, the result will be much worse, so everyone must pay special attention to it, then we will briefly explain it. The first important point is that PE stretch film has a fixed specific gravity, its specific gravity is 0.925, and the specific gravity of PVC is 1.325, but their calculation formulas are the same, there is another point I want to emphasize about For the conversion of thickness, we often hear customers say that I want a thick film of a few silks. This silk is also a measurement unit commonly used in the film industry, 1 silk u003d 0.01 mm u003d 10 microns.　　 Calculation formula: length * width * thickness (m*m*mm) * specific gravity u003d net weight, net weight + core weight u003d gross weight.　　Note: Conventional PE pipe cores are 0.3KG, 0.5KG, 1KG, while other films are generally calculated by gross weight, and the weight of the pipe core accounts for about 10% of the total weight. Simply put, we know its length, width and thickness, then we can accurately calculate the weight of this roll of PE stretch film by applying the above formula. On the contrary, knowing the weight, width and thickness can also calculate the length of a roll. , Let’s give an example of the theory below.　　1. PE stretch film with a width of 1 meter and thickness of 2.5 filaments. It is required to make 800 meters per roll, and the core is 1KG. What is the gross weight of this roll?　　 Answer: 1*0.025*800*0.925u003d18.5KG, 18.5+1u003d19.5KG.　　2. A film with a width of 50cm, a thickness of 2 filaments, a roll of 5kg gross weight, and a core weight of 0.6kg. What is the length of the roll?　　 Answer: (5-0.6)/0.925/0.02/0.5u003d475.7 meters.　　3. A film with a width of 7cm, a thickness of 3 filaments, and a roll weighs about 0.3KG. How many meters is a roll?　　 Answer: (0.3-0.3*0.1)/1.325/0.03/0.07u003d97 meters. Stretch film needs to have good viscosity: Polyethylene can provide good mechanical strength, excellent extensibility and better resilience for stretch film, but it cannot provide enough external viscosity, so polyethylene stretch film needs to use a tackifier A class of additives to obtain the surface viscosity of the film. In industrial consumption, low molecular weight polyisobutylene (PIB), ultra-low density polyethylene (VLDPE) and ethylene-vinyl acetate copolymer (EVA) with a density below 0.905 can be used as a tackifier for polyethylene stretch film. EVA is rarely used by manufacturers due to its pungent sour taste during processing, high price and low cost performance. VLDPE has the characteristics of good flexibility, high viscosity and high puncture resistance, but due to the low cost performance, it is rarely used in practice. PIB, as a tackifier for polyethylene stretch film, has a wide range of viscosity conditioning, convenient conditioning, and obvious comprehensive advantages in performance and price. PIB and its masterbatch are currently the most common tackifiers in the consumption of polyethylene stretch films. Because of their incompatible properties with polyethylene films, they will gradually migrate to the surface of the film to produce stickiness. The required adhesion of the stretch film must have both good peel adhesion and good lap adhesion. The higher the peeling viscosity, the less likely the tray is to be loosened, and the better the sealing of the film; the higher the lap viscosity, the less likely the film will be longitudinally displaced. Therefore, to obtain a strong package, the peeling viscosity and overlap of the stretch film are required The stickiness reaches a balance. 1. The molecular weight has different effects on the viscosity of the stretch film. The molecular weight will have different adhesive properties. PIB with high molecular weight makes the film have higher final peel adhesion, but as the molecular weight of the PIB increases, the lap adhesion will decrease; and the molecular weight is too high. If it is low, it will cause too short stickiness due to its relatively volatile content. Therefore, choosing PIB with appropriate molecular weight can make the stretch film have the best performance. The study showed that PIB with a number average molecular weight of about 1300 is more suitable for increasing the self-adhesiveness of stretch film. 2. The effect of the addition amount on the viscosity of the stretch film is positively correlated with the amount of PIB. However, after the participation of PIB exceeds 3%, the improvement of the self-adhesiveness of the stretch film becomes insignificant. If the participation of PIB continues to increase, the PIB will precipitate and form agglomerates on the surface of the film, forming uneven self-adhesiveness of the film, and even the film roll is very large. Difficult to open. In order to ensure the final performance of the stretch film and comprehensively consider the cost of raw materials, the amount of PIB added should be controlled between 1 and 3%. PIB has a process of exudation, and it usually takes about three days to stretch the surface of the film to produce enough viscosity. 3. The effect of the storage temperature of the stretch film on the viscosity The migration speed of PIB is related to the storage temperature. As the ambient temperature increases, the migration speed of PIB increases and the viscosity improves. Therefore, to reach the required viscosity, the stretch film should be stored at a higher temperature, and it should generally be avoided after a week to reach the application request. However, if stored in an environment higher than 30℃ for a long time, PIB will precipitate in a large amount, and it is easy to cause the film roll size or paper core to come off. Therefore, after reaching the viscosity request, it should be placed in an environment of -15℃~40℃. Store. PIB is a thin liquid substance. When PIB is co-extruded with polyethylene, the material cannot be extruded smoothly. Special extrusion equipment is required, such as an extruder with a forced feeder in the hopper, which is forced to feed LLDPE and PIB mixture, or use a special extruder that can be pumped into viscous liquid, and pump into PIB. In order to facilitate consumption, people have developed a high-concentration PIB tackifying masterbatch for the consumption of polyethylene wrapping film. This masterbatch is made by mixing PIB and polyethylene in a certain proportion, and it is used in the production of plastic products. The masterbatch is similar in shape, has good mobility, and is easy to use. Previous: What are the differences between PE POF heat shrinkable film and the next: Characteristics and application of PE stretch film