[peculiar smell caused by molecular weight distribution of plastic materials]
Due to the limitation of synthetic technology and the need of processing, the molecular weight of plastic resin used in extrusion composite plastic packaging raw materials is not single, but has a normal distribution from small to large, also known as molecular weight distribution. Different normal distribution curves, that is, different molecular weight distribution, lead to different properties of plastic resin. If the proportion of small and medium molecules in the molecular weight distribution of plastic resin is high, in the processing process, if the temperature is too high, small molecules will volatilize and produce the flavor of paraffin. In addition, the residue of unreacted and side reactants and catalyst in the polymerization process of plastic resin will volatilize and escape during processing, which will also produce peculiar smell.
[peculiar smell caused by thermal decomposition and thermal oxidation of plastic resin]
When extruding and laminating, it is necessary to melt the granular plastic resin at high temperature, compound it with other base materials through the die, and then cool it to form. If the temperature is too high, the plastic resin will decompose. Here is mainly the odor produced by thermal decomposition of polyethylene, because polyethylene is generally the inner thermal seal layer of extruded composite film bag, and directly contacts with the contents of the package. If the food is packaged with this material, the flavor of the food will also change.
According to the analysis, the components of odor produced by the decomposition of polyethylene can be roughly divided into aliphatic hydrocarbons and aromatic hydrocarbons. According to the research, LDPE thermal decomposition into c3-c28 saturated or unsaturated hydrocarbons, of which C3-C6 produced by short branched chain has the greatest impact on the content.
In addition, when plastic resin is processed under high temperature and high shear force, in addition to thermal decomposition, especially after it comes out of the extruder die, it will react with oxygen in the air to produce the so-called "resin oxidation odor". This oxidation produces substances that can also cause odors.
[odor caused by plastic additives]

In order to improve the processability of plastic resin or improve and change the properties of composite film, it is often necessary to add various additives into the plastic resin in the process of extrusion composite film. Such as antioxidants, anti ultraviolet agents, lubricants, mouth opening agents, antistatic agents, antifogging agents, etc.; in addition, due to the cost or to improve the light resistance of the film, some functional inorganic fillers, such as calcium carbonate, kaolin, talcum powder, silicon oxide, etc., will be added; in order to increase the solubility of these inorganic fillers and resins, some dispersants, coupling agents, etc. should be added Various organic pigment masterbatch and titanium white masterbatch are added; these additives with various varieties and ingredients are also one of the main factors causing odor, which will produce a lot of volatile substances when heated, resulting in the extrusion of composite film to produce odor. In addition, some additives and plastic resin reaction products will also produce odor.

[peculiar smell caused by plastic aging]
If a variety of plastic resins or composite films are stored for a long time, the oxygen, ozone and moisture in the air will cause decomposition and oxidation under the action of ultraviolet rays, which will make the materials aging and produce peculiar smell. In addition, the additives in plastic materials and the plastic resin itself, under the action of oxygen and ultraviolet, cause oxidation and odor.
[measures to reduce odor generation]
For the extrusion composite film, the following measures should be taken to control the most important odor: resin selection, resin decomposition and the precipitation of additives.
[selection of plastic resin in extrusion compounding]
Choose the brand of plastic resin correctly, understand the variety and function of additives added to the plastic resin purchased. If the production is normal, try not to change the brand of plastic resin. If it is necessary to change the brand of plastic resin temporarily due to various reasons, it is necessary to conduct a small test first, and then put it into production if there is no problem. In order to avoid the loss of return caused by problems. Sometimes, although it is the same brand of plastic resin, its molecular weight distribution is slightly different with different production batches. Therefore, the processing conditions of different plastic resins of the same brand and batch need to be adjusted.
[decomposition of plastic resin in extrusion compounding]
In extrusion compound, the temperature of extrusion die is very high, at such a high temperature, the resin is easy to thermal decomposition, and at the same time thermal oxidation occurs with oxygen in the air, which will produce peculiar smell. In order to reduce the odor, the resin temperature should be appropriately reduced when possible, and the air gap can also be appropriately reduced, that is, the distance between the die lip and the composite roller can be shortened. However, if the air gap is too small, it is easy to reduce the composite fastness, so the air gap should be appropriate. Different resins produce different odor sizes, PP odor is slightly smaller, PE type is larger, EVA is more likely to produce odor due to poor thermal stability. There are also a large number of additives in the resin, such as antioxidant, smooth agent, etc., which are also the important reasons for the odor. The suitable resin type and masterbatch type should be selected.
[other aspects]
During bag making, due to heating and sealing, the plastic will degrade and produce peculiar smell. Therefore, on the one hand, the heat sealing temperature should be reduced as much as possible; on the other hand, the prepared bags should be placed for a while before being bagged and packed.
In addition, a large number of organic solvents, such as ethyl acetate and butanone, need to be used in the gravure printing of plastic extrusion composites. According to the process requirements, these solvents should be volatilized in the production process. However, in the actual production, due to various reasons, more or less solvents are not completely volatilized, which is the so-called "residual solvent". The "residual solvent" is usually a few solvents When the content of "residual solvent" is lower than a certain value, people's sense of smell will not feel its existence, and it will not affect the taste of packaged food. When the content of "residual solvent" is higher than a certain value, people's olfactory sense of its existence. When consumers open the food packaged with such high "residual solvent" packaging material, they may smell it To "smell.". At this time, the reason should be found in the printing process, such as the selection of appropriate printing ink and solvent, improve the drying ability of the printing machine, and control the amount of residual solvent.
Dongguan Beite packaging materials Co., Ltd. - located in Dongguan City, the world's manufacturing city, is a subsidiary of Beite packaging (China) Co., Ltd., with a plant area of 6000 square meters. It is a flexible packaging enterprise integrating R & D, production and sales. It has a complete set of domestic advanced production equipment, a scientific and humanized management system and a group of experienced technical personnel For backing, to provide customers with quality products and first-class service.
The company produces composite bags, roll film, fruit bags, aluminum foil bags, suction mouth bags, self-supporting bags, zipper bags, anti-static bags, special-shaped bags, etc., which are suitable for the internal and external packaging of food, daily chemicals, electronics, toys, medicine, cosmetics, industrial products and other industries.
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