Q & A on the hottest soft plastic packaging techno

Q & A on flexible plastic packaging technology (I)

I. what is the heat sealing property of plastics? What are the characteristics of various heat sealing resins

answer: the heat sealing property of plastics refers to the thermal bonding property of plastics with itself or other kinds of plastics after heating to the molten state. This kind of thermal bonding performance is of great significance in the welding of plastic packaging materials and bag making. With the development of production to high-speed automation, the production speed of the original automatic filling and sealing packaging machine is only 20 ~ 30/min, up to now it can reach 150 ~ 200/min. The sealing property of plastic, that is, the requirements of thermal bonding property have been greatly improved, and the thermal sealing property of plastic can not meet the requirements of this high-speed automatic filling machine, It will not be able to produce high-quality commodity packaging

(I) heat sealing strength

sealing strength refers to the peel strength achieved after two layers of the same or different materials are thermally bonded together under a certain pressure at a certain melting temperature. According to jisz standard, heat sealing is the strength measured after 2 ~ 3 seconds of heat sealing time at a temperature of 130 ℃ ~ 140 ℃ and a pressure of 1kgf/cm2. There are many factors that affect the heat sealing strength, the main ones are: (1) the performance of resin; (2) The composition and amount of additives in the resin; (3) Processing conditions, especially the surface oxidation degree during extrusion coating processing; (4) In the case of composite film, the properties of other materials compounded with heat sealing resin are different, and the heat sealing strength and heat sealing temperature are also different; (5) The degree of surface treatment during composite operation, such as the size of corona treatment

when high-speed automatic packaging, it needs not only the heat sealing strength, but also the low-temperature heat sealing property, a wide range of heat sealing temperature and the hot peel strength during heat sealing, that is, the thermal adhesion of materials, but also the so-called inclusion heat sealing property that can be heat sealed with pollutants on the heat sealing interface

the heat sealing strength of polyethylene is also related to the thickness of polyethylene. With the increase of the thickness of heat sealing resin, such as PE, the heat sealing strength increases. For example, the test type of rubber tensile machine: when the thickness of LDPE heat sealing layer is 20 μ M, that is, the heat sealing strength is 1.0kgf/15mm wide, while 30 μ 1.5kgf/15mm when m thick, 40 μ 2.5kgf/15mm wide when m thick, 60 μ M thick, the peel strength can reach 4.2kgf/15mm wide. This is why PE or PP film, the inner sealing material of high-temperature cooking bags, should be between 60 and 70 μ M thickness

the performance of heat sealing resin is also closely related to the heat sealing strength: pt300#/ldpe20 μ For the composite film with thickness of M, under the pressure of 2kgf/cm2 and the heat sealing condition of 0.5 seconds, the heat sealing has the highest heat sealing strength at 150 ℃, mi=3.7g/10min, d=0.923g/cm3, and the heat sealing strength is 1.25kgf/15mm wide; Mi=3.0g/10min, d=z - Corrugated constant; 921g/cm3, the heat sealing strength is 1.4kgf/15mm wide; The heat sealing strength of mi=7.0g/10min, d=0.917g/cm3 is 1.75kgf/15mm wide; Mi=9.5g/10min, d=0.917g/cm3, heat sealing strength is 1.9kgf/15mm wide. It shows that the heat sealing strength increases with the increase of MI

(II) low temperature heat sealing

low temperature heat sealing is a measure of the ease of heat sealing, which represents the comprehensive factors of heat sealing start temperature and heat sealing strength. For LDPE resin, low temperature heat sealing is closely related to MI and density. LDPE with high MI and low density has excellent low-temperature heat sealing performance. For ethylene copolymers, the content of monomers copolymerized with ethylene and the properties of comonomers have a great influence on their low-temperature heat sealing properties. For example, the softening temperature of EVA decreases with the increase of VA content, and the low-temperature heat sealing property is good. With the increase of EVA density, the low-temperature heat sealing property improves and becomes better

(III) hot peel strength

hot peel strength refers to the heat sealing pressure of 2kgf/cm2, heat sealing time of 0.5 seconds, stripping angle of 22.5 °, stripping load of 90g/10mm wide, and the strength of heat sealing melt at the heat sealing temperature of 90 ℃ ~ 180 ℃. In Japan, it is generally expressed by the stripping distance between heat seals. The hot stripping distance is the same as the oxidation degree of the extruded coating film surface. 4. Automatic calibration: the system can automatically calibrate the accuracy of the indication It is directly proportional to the melting strength of the resin under heat sealing conditions, and inversely proportional to the amount of high melting point components in the resin and the high melting temperature. The smaller the stripping distance between heats, the better the heat sealing property of the resin, and the possibility of displacement of the heat sealed part under the mechanical force of heat sealing bag making. The larger the supporting area of the instrument base is, that is, the smaller the re stripping property that has been heat sealed, the better the initial adhesion of the heat sealing resin under melting

(IV) inclusion heat sealing property

this refers to a property that still has good heat sealing strength when the surface of the heat sealing layer is stained with dust, grease, sundries or package contents. The resins with this kind of inclusion heat sealing property include Surlyn resin, various adhesive resins and LLDPE

among various heat sealing resins, there are the following:

(I) LDPE: This is the most commonly used heat sealing resin. It can be produced into a film by extrusion blowing or extrusion salivation method, and then used with other films to form a composite film. It can also be co extruded into a composite film by other resins. Its melting point is between 105 ℃ ~ 120 ℃, and its heat sealing, transparency and non-toxic properties are good

(II) MDPE and HDPE: the melting point is between 120 ℃ ~ 135 ℃, and they also have good heat sealing property. The transparency is not as good as LDPE, the crystallinity is higher than LDPE, the film strength is greater than LDPE, and the heat sealing temperature is higher than LDPE. Generally speaking, the best heat sealing temperature of PE is 150 ℃ ~ 160 ℃, when there is the highest heat sealing strength

(III) copolymers of PE, such as PE and others α Olefins with high carbon atoms, such as copolymers of octene and pentene, Metallocene PE (MPE), LLDPE, VLDPE, as well as copolymers of ethylene with acrylate, ethylene with vinyl acetate, ethylene with maleic anhydride, etc. the common characteristics of these resins are good low-temperature heat sealing, high heat sealing strength and good heat adhesion

II. Dried tofu is packed with composite film of pet12/ldpe30. After vacuum packaging and placing for 3 months, the composite bag expands and all deteriorate. Why

answer: dried tofu is a substance rich in protein, which is easy to corrupt and produce bacteria. The vacuum packaging with pet12/ldpe30 structure cannot meet the packaging requirements, but should be steamed and sterilized at high temperature. After being fully sterilized at 100 ℃ for 30min, it can be stored for more than one year. In order to improve the tightness of the cooking bag, the inner LDPE thickness should be increased to μ m。 (plastic packaging)