Processing and performance testing of plastic film

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Abstract: This paper compares the moisture resistance, air permeability, heat sealing, tensile strength and ink adhesion fastness of various plastic films used in salt packaging bags, in order to provide a reference for selecting a suitable plastic film, and discusses the principle of surface treatment, for example, when the inlet temperature of crude oil at the tube side of the overhead condenser of a German crude oil distillation tower is 50 (6) degrees Methods and detection methods

1 preface <1 generally, we recommend customers to use electronic universal testing machine for material testing below 30 tons/p>

with the improvement of people's living standards, the state forces residents to eat iodized salt, and puts forward corresponding requirements for the production and packaging of salt. As the packaging bag of salt belongs to food packaging, the hygiene requirements are high. Generally, non-toxic or low toxic PE, pet, PP and PVC (only used as the outer composite film) films are selected. Their characteristics are described below

2 comparison of plastic film properties

2.1 polyethylene (PE) film

pe film has greater air permeability, and its air permeability decreases with the increase of density. PE film has moisture resistance and low moisture permeability

polyethylene film (PE) can produce products with different properties such as low-density, medium density, high-density polyethylene and cross-linked polyethylene according to different manufacturing methods and control means

(1) low density polyethylene (LDPE). Its density is about 0.92g/cm3. Low density polyethylene film has good transparency and heat sealing, and can be waterproof and moisture-proof; The tensile strength is low, the tensile elongation is large, and it is easy to wrinkle. For films below 0.03mm, the tension control should be small, and the tension everywhere should be constant, especially when heated, it is easier to deform, resulting in difficulty in chromaticity. Therefore, when drying, the surface temperature of the film should not be too high (within 55 ℃). According to different film-forming processes, it can be divided into blown film (IPE), salivary film (CPE), low foaming film, etc. IPE film has better tensile strength and opening than CPE film. It adopts front printing and can be used as food bags, clothing bags, etc; CPE film has uniform thickness, better surface gloss, transparency and heat sealing than IPE, and can be printed on both sides, but the production cost is high; CPE film is mainly used as the inner layer of composite bags and the packaging of cosmetics, pickles and cakes; Low foaming film has good decoration, thick texture, and is not easy to stretch and deform. It is printed on the front and used as New Year pictures, trademarks, hand bags, etc

(2) medium density polyethylene (MDPE). Its density is about 0.93 ~ 0.94g/cm3, and its performance is between high density and low density polyethylene

⑶ high density polyethylene (HDPE). The density is 0.94 ~ 0.965g/cm3. The heat resistance and mechanical strength of high-density polyethylene film are better than that of low-density polyethylene film, and the tensile elongation is small. The film thickness is generally more than 0.03mm, but the transparency is poor. Printed on the front, it is mainly used as vest bag, garbage bag and lining bag

⑷ cross linked polyethylene (CLPE). Because it has higher heat resistance, tensile strength, heat shrinkage and barrier than other polyethylene products, its use is further expanded. At present, it is mostly used as heat shrinkable packaging film

generally speaking, with the increase of density, the mechanical properties and barrier properties will be improved correspondingly, and the heat resistance is also good. Polyethylene with the same density also has different properties due to different film-forming processes. This is because the salivation method can be cooled quickly, with low crystallinity, high transparency and low turbidity, but the molecular arrangement tends to be irregular, so the barrier property is small, that is, the transmittance is large, the elongation is low, and the tear resistance is poor

2.2 polyester (polyethylene terephthalate, PET) film

biaxially stretched polyester film (PET) has a very high mechanical strength and rigidity, and has become an important new material industry base in China; Good heat resistance, high transparency, good gloss, good drug resistance; Water vapor and oxygen permeability is small, with good fragrance retention, which is unmatched by other plastic films. In addition, its surface energy is low. It needs surface treatment before printing, and it is not easy to stretch and deform. It has good printing operability. The requirements of tension control are lower than polyethylene film, but its heat sealing property is poor. It is used as cooking bags, cosmetic packaging bags, etc

polyester film (PET) has excellent insulation, which is easy to generate static electricity in the printing process and is not easy to disappear. In serious cases, the film will be adsorbed on the roller and cannot be printed. Therefore, static electricity elimination equipment must be set in high-speed printing. The drying temperature of polyester film (PET) can be set higher, but its surface temperature should not exceed 85 ℃. When winding, the film should be fully cooled to room temperature to prevent ink adhesion

2.3 polypropylene (PP) film

polypropylene film (PP) has better transparency, heat resistance and printing operability than polyethylene film (PE), and its ink adhesion is also poor. Before printing, surface treatment is required to improve the adhesion of ink, and the critical surface tension of surface treatment should be controlled at 40 ~ 44mn/m

bopp film has small tensile deformation, not easy to wrinkle, good printing operability, good transparency and light when the machine is idle, excellent moisture resistance, but poor heat sealing and tear resistance; CPP film has good heat sealing property, but it is easy to stretch and deform during printing, so the tension control value is lower than BOPP, and it can be used as the heat sealing layer of candy paper and composite materials; The tensile deformation and heat sealing properties of iPP film are between BOPP film and CPP film, with good transparency and gloss, but the thickness uniformity is worse than BOPP and CPP film. It is suitable for front printing and can be used as the packaging of textiles

2.4 polyvinyl chloride (PVC) film

polyvinyl chloride film (PVC) has good transparency, gloss and printability. Generally, there is no need to carry out surface treatment before printing, and it has good adhesion to the ink. Its disadvantages are poor heat resistance, cold resistance and toxicity. Pay attention to its safety and hygiene when packaging food. According to the amount of plasticizer, PVC film can be divided into hard, semi-hard and soft, and its properties are slightly different

soft PVC film contains a large number of plasticizers, which will precipitate into the ink layer, causing discoloration, adhesion and ink migration failures, and it is very easy to stretch and deform, resulting in wrinkles, causing inaccurate overprint, so the tension control should be light. In addition, it is easier to stretch after heating, which makes it difficult to print. Soft PVC film has good self adhesion when it is thin enough, and is often used in fruit and vegetable packaging

it can be seen from table 1 that considering the requirements of salt package on tensile strength, moisture resistance, heat sealing and impact strength, it is better to use CPP and HDPE as the inner membrane of packaging, which not only has good heat sealing property, but also can provide sufficient strength and moisture resistance. As an outer film, pet and OPP with high strength, moisture resistance and low elongation are better. Considering the price factor, PVC is also an available film for packaging outer film

(to be continued)

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