Performance and formula of plastic film for the ho

2022-08-09
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Performance and formula of plastic film for heat sealing

plastic film for heat sealing has the following important performance requirements: (1) the initial temperature of heat sealing should be low to meet the use requirements of high-speed automatic bag making and filling machine; (2) The plastic film used for heat sealing shall have good cold and heat resistance; (3) High heat sealing strength; (4) The hot stripping strength should be large, that is, the hot stripping distance should be small, that is to say, during heat sealing, due to the effect of mechanical tension, the part that has been heat sealed and the part that has been re stripped should be very small; (5) There should be good heat sealing property of inclusions, that is, the heat sealing surface is polluted by oil and dust, and still has good heat sealing strength; (6) The dynamic and static friction coefficient should be between 0.2 and 0.4, so as to facilitate the full and sufficient filling of powdery and viscous liquids; (7) It has good rupture resistant packaging. For the production process of plastic film, there are many methods, such as extrusion blowing method, extrusion salivation method, solvent salivation method, calendering method, etc. among these processes, the film produced by extrusion salivation method is most suitable for heat sealing because of its balanced longitudinal and transverse performance, no internal stress, and excellent heat sealing performance. However, the large investment in the extrusion salivation equipment limits the actual utilization rate. The heat sealing film produced by the extrusion blowing method is widely used. It should be noted that the draw ratio and draw ratio should be smaller during the extrusion blowing, and the two should be balanced to prevent too much plastic molecules from producing directional crystallization due to tensile force, so that the film loses its heat sealing property. In the production of polypropylene heat sealing film with good heat resistance, the down blowing method of water cooling should be used to squeeze and blow the film, so that the PP film has good heat sealing and transparency. Solvent salivation method needs to use a large number of solvents, which is expensive, solvent recovery equipment is large, investment is large, and consumption is large. Generally, it is rarely used, and it is only used in the production of extremely thin, high-performance electronic packaging film. The calendering method is only used on PVC films and sheets. For polyolefin plastics with good melt fluidity, it is only suitable for large inorganic filling, so that the installation position of the experimental button is designed according to the natural shape of the human body

formula of plastic film for heat sealing

I. formula for reducing heat sealing temperature

the starting temperatures of various heat sealing films are as follows: LDPE 135 ℃, LLDPE 148 ℃, EVA (VA content 7.5%), 107 ℃, EVA (VA content 12%), 93 ℃, EMA (methyl vinyl acrylate) 79 ℃, EMAA (ethylene methacrylic acid) 93 ℃, surlyn121 ℃, EAA (ethylene acrylic acid) 93 ℃

the above resins have good compatibility. They can be extruded and blown or salivated after mixing with each other to reduce the heat sealing temperature, such as ldpe+eva (50%+50%), in which the VA content can be increased and the melting temperature can be reduced. For example, EVA with 25% VA content can be used to blow the film grade, and the initial heat sealing temperature of the mixed film can be reduced to about 90 ℃, but the addition amount should not be too high, because the tensile strength of EVA film is low, Too high VA content leads to high viscosity. Other formulas to reduce the heat sealing temperature are as follows: LDPE (50%) +50%ema; LDPE70%+30%EAA; Ldpe70%+30%emaa, etc. The copolymer of ethylene and acrylic acid is a kind of adhesive resin (ties), also known as compatibilizer

II. Formula to improve the cold resistance or heat resistance of heat sealing film:

the cold resistance of various heat sealing plastics is compared as follows: EVA, EAA and EMAA can withstand -65 ℃. With people's higher and higher requirements for quality of life ~ -73 ℃, LLDPE can withstand -68 ℃ ~ -73 ℃, PC (polycarbonate) can withstand -65 ℃ ~ -75 ℃, LDPE can withstand -48 ℃ ~ -50 ℃, MDPE can withstand -42 ℃ ~ -45 ℃, Surlyn can withstand -38 ℃ ~ -42 ℃, HDPE can withstand -40 ℃, Polystyrene can withstand 0 ℃, homopolypropylene can withstand 5 ℃, and co polypropylene (copolymer containing 5% - 8% ethylene) can withstand -8 ℃

it can be seen from the above that polyethylene and its acrylic copolymer have good low temperature resistance, while homopolymer polypropylene has poor cold resistance. Propylene can be copolymerized with ethylene to improve the cold resistance of propylene homopolymer. With the increase of the amount of ethylene monomer, the cold resistance of copolymer polypropylene can be improved. For example, when the ethylene content is 5% - 8%, the cold resistance can reach -15 ℃, and the film softness can be improved, Polypropylene 8. Counter: 99999999. The cold resistance can be preset and can also be improved by mixing with the copolymer of ethylene and acrylic acid. Its formula is as follows: hpp50%+eva50%, HPP (homopolymer polypropylene) 70%+30%eaa; HPP70%+30%EMA:HPP70%+30%EMAA。

it should be pointed out that the compatibility between polyethylene and polypropylene is not very good, only general, so pe+pp blending is not desirable. Another point is that PP has no compatibility with Surlyn resin, so they cannot be modified by blending

the high temperature resistance of various plastics is as follows: EVA, EAA and EMAA can withstand 55 ℃ ~ 85 ℃, LDPE 85 ℃ ~ 100 ℃, MDPE 95 ℃ ~ 105 ℃, HDPE 115 ℃ ~ 120 ℃, Surlyn standard reference conditions are also called standard experimental conditions 70 ℃ ~ 85 ℃, LLDPE 95 ℃ ~ 115 ℃, PS 85 ℃, HPP 140 ℃, CO polypropylene (b-cpp) 130 ℃ ~ 135 ℃, PA66 160 ℃ ~ 165 ℃. When heat sealing film with temperature resistance is required, HPP film or b-cpp film can be directly used. Only when ethylene and acrylic acid and their esters are the main heat sealing materials, PP can be used for blending modification to improve the heat resistance, such as 70% EAA + 30% b-cpp, 70% EMAA + 30% b-cpp

III. formula for increasing heat sealing temperature

heat sealing 508 with a pressure of 2kg/cm2 and a heat sealing rod of 0.5s μ m. That is, the heat sealing strength under 2.0 mils of thickness change is as follows: LDPE: 1800g/25.4mm wide, LLDPE: 2500g/25.4mm wide, EVA (va7.5%) 1800g/25.4mm wide, EVA (12%va) 1700g/25.4mm wide, EMA: 1300g/25.4mm wide, EMAA: 1800g/25.4mm wide, surlyn2000g/25.4mm wide, EAA: 1700g/25.4mm wide

it can be seen from the above that llpe has high heat sealing strength. The most common is to use ldpe50% +lldpe50% mixture as heat sealing film, which has good heat sealing strength

IV. heat sealing property of inclusions

the performance comparison of heat sealing property of inclusions is as follows: ionic polymer (Surlyn) MPE> LLDPE> HDPE> MDPE> LDPE> EVA

other formulas and performance characteristics of polyolefin heat sealing plastic film for packaging

extrusion blown film or salivary film produced by the following formulas can be used for heat sealing inner film or single film packaging

Formula 1: hdpe70%+ldpe30%+ white raw materials, extrusion and film blowing, which can be used for pasteurization simple packaging milk film, light cold storage and sales, with a 3-day application period

formula 2: hdpe/ldpe or hdpe/eva coextrusion, which is characterized by low melting point in the inner layer and high strength in the outer layer of the coextrusion film. It is suitable for inner sealing layer and simple milk film, and there will be no mucus on the sealing knife during heat sealing

formula 3: HDPE Mi <1g/10min + 0.3 ~ 0.7% calcium stearate nucleating agent is used for extrusion blowing. Its film has high strength and improved transparency, and the transparency is increased from 67% to 73.5%. It can be used in garbage bags, handbags and shopping bags. It can also use 0.4% benzoic acid, 0.25% sodium benzoate, 0.2% sodium carbonate and 0.05% talc powder, all of which have the same effect of improving transparency

formula 4: LDPE or ldpe50% +lldpe50% or other polyolefin compatible heat sealing film. After adding erucic acid amide of more than 600ppm to extrude and blow film or extrude salivation, the dry composite film can have a dynamic and static friction coefficient of 0.2 ~ 0.4 after curing at 35 ℃ for one week. It is suitable for the packaging of powder and high viscosity liquids. The key is that the curing temperature is about 35 ℃ and cannot be too high

formula 5: LDPE 70 ~ 85% +mpe5 ~ 15%, moderate price, good inclusion heat sealing performance, high heat sealing strength, film bubble stability and good uniformity of thickness during film blowing

formula 6: HDPE (MI 20g/10min), 90 parts weight +lldpe (MI 2g/10min), 10 parts weight. After mixing, extrude and blow film, with good strength and thermal adhesion, good inclusion heat sealing

formula 7: ethylene propylene block copolymer (MI 0.5g/10min), 30%; HPP(MI 0.5g/10min),30%; HDPE (MI 0.3g/10min), 40% mixed extrusion and film blowing, has good tear strength, high temperature cooking resistance of 115 ℃, and high stress cracking resistance. The extruded sheet can be used for vacuum plastic forming various utensils

formula 8: LLDPE (dowlex 2045) produced by Dow Chemical Company of the United States is 98.5%, and low molecular weight polyethylene Epolene n produced by Eastman company of the United States is 1.8%. After blending, it can be extruded and blown with an ordinary extruder at 130 amperes and 80rpm, and the production capacity can be 74kg/h. Extruded film can be used for heat sealing film or single film packaging

source: China plastic products trading

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