Co-extruded barrier multilayer composite film

Co-extruded barrier multilayer laminated films are usually made of polyolefin resins, with polyethylene, polypropylene and other plastics being the most widely used. In addition to the moisture-proof function, they often also play the role of heat sealing layer and carrier layer.

1. Polyethylene

Polyethylene is the most commonly used resin in co-extruded barrier multilayer laminated films. According to the different densities, polyethylene is divided into low-density polyethylene (LDPE, density 0.925g/cm or less), medium-density polyethylene (MDPE, density 0.925~0.940g/cm3) and high-density polyethylene (HDPE, density 0.940g/cm3 or more), and people often refer to the medium polyethylene together with the low-density polyethylene as low-density polyethylene. Polyethylene is divided into low-density polyethylene (LDPE, density 0.940g/cm3 or less) and high-density polyethylene (HDPE. Density 0.940g/ctn or more) two broad categories.

(1) the general characteristics of polyethylene film

(1) has good mechanical properties

Polyethylene film tensile strength are more than 10MPa, some grades up to 20MPa or more.

② has a wide range of operating temperatures

Polyethylene film has excellent low-temperature resistance, can be used in -40 ℃ below the low humidity environment for long-term use, at the same time, polyethylene also has good heat resistance, even if the heat resistance of low-density polyethylene film, its long-term use of the temperature is also in the 60 ℃ or more, heat-resistant high density polyethylene film can withstand 121 ℃ cooking sterilization treatment.

③Water resistance, moisture resistance

Water resistance, moisture-proof performance is excellent and has a certain degree of oxygen barrier, oil resistance.

④ Good heat sealing performance

Polyethylene film generally has good heat sealing performance, can be convenient, inexpensive ordinary heat sealing process, the polyethylene film into bags of products.

⑤ Good chemical stability

Except for a few kinds of strong oxidizing acids, polyethylene films are highly resistant to a variety of common acids, alkalis, salts and many kinds of chemical substances.

⑥Excellent hygienic performance

Polyethylene resin itself is non-toxic, odorless and tasteless, with reliable hygienic performance, and can be used for food and medicine packaging. The main defect in the performance of polyethylene packaging film is the poor barrier to oxygen, carbon dioxide and other non-polar gases permeability, in the packaging of oxygen-insulated storage of goods (processed foods, etc.), it is necessary to use a composite film containing polyethylene film layer and barrier film layer.

(2) Polyethylene Properties by Theory

① low-density polyethylene (LDPE) basic characteristics of the application of a wide range of temperatures (between -60 ~ 60 ℃); LDPE film has a good heat sealing performance, but in the presence of debris, LDPE film heat sealing is poor; LDPE film has a better brightness (light transmission rate of up to 80% or higher, haze can be in about 5%); LDPE Thin strength is poor (tensile strength is generally only a dozen MPa, but low melt flow rate grades of polyethylene has a high tensile strength, up to 20 MPa or more.

② Basic characteristics of high-density polyethylene (HDPE)

Compared with low-density polyethylene, high-density polyethylene has the following characteristics: the use of a wider range of temperatures, it can be used for both frozen food packaging, but also can be used at higher temperatures, when the density is high enough, polyethylene film can even be subjected to sterilization treatment (121 ℃ cooking treatment); with high mechanical strength (tensile strength of up to more than two times that of the LDPE packaging film); has a Excellent moisture resistance and good oil resistance. High-density polyethylene is commonly used packaging film in the barrier to water vapor performance is one of the best varieties, its oil resistance is not as good as nylon and other barrier-type film, but in the polyethylene film is the best varieties. Rigidity is better, but less flexible; less transparent, significantly lower than LDPE packaging film.

③ Basic characteristics of linear low-density polyethylene (LLDPE)

Puncture resistance, high tear propagation strength, outstanding resistance to stress cracking; heat sealing performance is significantly better than ordinary HDPE and LDPE, with good inclusions can be sealed and high heat sealing strength; the mechanical strength of the film is higher, between ordinary HDPE LDPE, close to the high-density polyethylene.