What are the thin film materials used in packaging bags?

Packaging bags are typically made of composite films, where multiple materials are layered and combined. Bags made from a single material are also common, but they must possess heat-sealing properties, such as PE and CPP films.

Composite films usually include several types, such as PET+NY+AL+PE, PET+AL+PE, PET+NY+AL+CPP, and it's noticeable that they all contain PE and CPP. This is primarily for heat-sealing purposes, so they are placed on the innermost layer of the packaging material, coming into direct contact with the packaged items, ensuring excellent heat-sealing performance. Common materials for composite films include LDPE, LLDPE, MLLDPE, CPP, VMCPP, EVA, EAA, E-MAA, EMA, EBA, etc.

The thickness of these composite films typically ranges from 70 micrometers to 220 micrometers, and based on functionality, they can be categorized into the base layer, functional layer, and heat-sealing layer. The base layer is mainly for aesthetics and is suitable for printing, providing moisture barrier functions, etc., using materials like BOPP, BOPET, BOPA, MT, KOP, KPET, etc. The functional layer is responsible for light avoidance and imparting required physical properties such as burst resistance, tear resistance, high/low-temperature resistance, increased flexibility, etc., with materials like VMPET, AL, EVOH, PVDC, etc.

Various materials exhibit different characteristics:

• PET: Excellent printing, transparency, gloss, good airtightness, moderate moisture resistance, and superior mechanical properties.
• NY: Puncture resistance, high impact strength, high bending strength, good gas barrier properties, low oxygen permeability, strong toughness, providing better protection against bag damage.
• AL: Excellent mechanical strength, lightweight, no heat bonding, metallic luster, good light shielding, strong light reflection, corrosion resistance, good barrier properties, moisture-proof, waterproof, and strong airtightness.
• PE: Used as the inner layer material, it has excellent heat-sealing properties.
• CPP: Used as the inner layer material, it has excellent heat-sealing properties, high-temperature resistance, and is suitable for high-temperature cooking.

The selection and combination of these various materials aim to meet diverse packaging requirements, ensuring optimal functionality and performance of the packaging.

LDPE and LLDPE are two common polyethylene resins that play a significant role in the packaging industry. Polyethylene (PE) is a common polymer with excellent electrical insulating properties, making it frequently used as a material to provide fundamental insulation performance in electrical insulating films.

LDPE stands for low-density polyethylene, and it exhibits good flexibility and extensibility, making it easy to bend and deform. This type of film demonstrates good impact resistance and has relatively good resistance to chemicals. Typically, LDPE is blended with LLDPE in certain proportions to enhance overall performance. LLDPE, with its more linear molecular structure, contributes to increased strength, toughness, and tear resistance.

In the production of LDPE and LLDPE, coating-grade LDPE resins include IC7A, L420, 19N430, 7500, etc., which are used for coating applications. Film-grade LDPE resins, such as Q200, Q281, F210-6, 0274, etc., are suitable for the blown film process. LLDPE resins like 218w, 218F, FD21H, etc., are widely used in the packaging industry, especially in the preparation of thin films.

The selection of these polyethylene resins depends on the specific requirements and applications of the packaging.

CPP film and CPE film have emerged in response to the expanding range of packaging materials. For certain products, such as expanded foods and cereals, there is a growing demand for transparency. Simultaneously, with the increasing popularity of boiling and high-temperature sterilization products, the requirements for packaging materials are correspondingly heightened. Traditional inner layer materials like LDPE and LLDPE find it challenging to meet the diverse needs of these products.

CPP material, known as Cast Polypropylene Film, has found extensive use in the packaging industry due to its resistance to oil, transparency, high-temperature resistance, flexibility, high strength, chemical resistance, moisture resistance, and moisture-proofing, along with its excellent heat-sealing performance. Building upon this, aluminum-coated CPP has been developed, adding a metallic luster for enhanced aesthetics. Moreover, owing to its remarkable barrier properties, it can be swiftly and widely employed.

Additionally, Chlorinated Polyethylene (CPE) produced through the casting process has gained attention. CPE offers tear resistance in one direction, low-temperature heat-sealing capabilities, good transparency, and a certain degree of thermal stability, maintaining its physical properties within a specific temperature range. CPE's versatility in addressing various packaging needs makes it a valuable solution in the field.

MLLDPE resin, short for Medium-Low Density Linear Polyethylene, is a polymer with intermediate density. DOW Chemical Company in the United States employs metallocene catalysis to synthesize MLLDPE. Notable resin types include APFINITY, POP1880, 1881, 1840, and 1450. Following this, other major players in the industry, such as Exxon in the United States, Mitsui in Japan, and Phillips in the United States, have also ventured into the production of MLLDPE.

Exxon offers variations like EX-CEED350D60 and 350D65, while Mitsui's E-VOLVE series includes SP0540 and SP2520. Philips contributes to the market with MPACT D143 and D139. These MLLDPE resins exhibit diverse properties and are tailored to meet specific application requirements. As the industry continues to evolve, the production and utilization of MLLDPE contribute significantly to the versatility and performance of various packaging materials.

The history of packaging materials dates back to the early 1920s when one of the initial forms of plastic film, nitrocellulose film, was introduced by the Shell Company. This film was utilized for packaging candies and tobacco. The widespread application of plastic films and significant technological advancements occurred primarily in the latter half of the 20th century. During this period, various plastic materials such as polyethylene, polypropylene, and polyvinyl chloride were developed for packaging films.

Production techniques, including extrusion, blown film, and coating, underwent substantial improvements, leading to enhanced efficiency in manufacturing. In the early to mid-1980s, China initiated the introduction of extruders, blown film machines, and printing machines for independent production. The focus was primarily on manufacturing two-layer or multilayer composite materials. This involved the production of extrusion-composite films like BOPP+PE, paper+PE, PP+PE, dry composite films such as BOPP+PE, PET+PE, as well as laminated films like BOPP+AL+PE and PET+AL+PE. This period marked a crucial phase in the evolution of packaging materials, laying the foundation for diverse and innovative packaging solutions.

Main Applications in Various Industries:

Anti-static Aluminum Foil Bags:

Suitable for industries such as PCBs, IC integrated circuits, electronic components, SMT patching in various LED industries, packaging for light bars, precision hardware, automotive parts, and other industrial products.

Food Packaging:

Includes packaging for rice, meat products, dried fish, seafood products, waxed meats, roasted duck, roast chicken, roast pork, frozen foods, ham, cured meat products, sausages, and cooked meat products.

Medical Packaging:

Utilized for packaging chemicals and pharmaceuticals.

Common Applications of PE:

Everyday items like plastic bags, cling film, bottles, containers, toys, etc.

Mainly used in the packaging of convenience foods such as instant noodles, biscuits, pickled vegetables, etc.

LLDPE:

Combining the flexibility of LDPE and the strength of LLDPE, it is widely used in film, garbage bags, agricultural films, pipes, conveyor belts, etc.

CPP:

Known for its moisture resistance and moisture resistance, commonly used in food packaging. Its hygienic properties make it suitable for medical supplies packaging.

CPE:

Due to its electrical insulation, it can be used in electrical and electronic applications.

Exhibits good flexibility, maintaining elasticity at low temperatures, suitable for products requiring high flexibility like seals, flooring materials, etc.

Resistant to acidic and alkaline substances, making it excellent for chemical, construction, and pipeline applications.

MLLDPE Resin:

Medium-Low Density Linear Polyethylene produced using metallocene catalysis.

Used in various products by companies like DOW, Exxon, Mitsui, and Phillips.

These diverse materials find applications in industries such as packaging for frozen and refrigerated foods, shampoos, oils, vinegar, soy sauce, detergents, etc. The specific combination of materials addresses issues like packaging speed, breakage, leakage, and permeability during production and transportation. For liquid packaging in cups, considerations include shelf life, heat seal strength between the lid and the cup, and consumer convenience. This requires adhesion strength between the inner layer material of the lid and the cup, and materials like modified EVA resin are commonly used for this purpose. Examples include DuPont's APPEEL53007, TOPCO L-3388 from Japan's TOYO, LOTRYL 20MA 08 from France, and HIRO.DINE's WT231 from Japan. The structure can include combinations such as PET/PE/HM, BOPA/PE/HM, PET/VMPET/PE/HM, PET/AL/PE/HM, paper/PE/AL/PE/HM. Specific materials for lids, such as LDPE or EAA for HDPE cups, CPP film for PP cups, and modified PET film for sealing pesticide PET bottles, have been successfully developed.

Advantages and Disadvantages of Various Materials:

LDPE, a recyclable material, aligns with the growing trend of environmental awareness. However, single-layer LDPE or LDPE blended with other resins results in limited performance, failing to meet the modern packaging demands. To address this, co-extruded films produced using co-extrusion blown film or co-extrusion cast film equipment offer advantages. Co-extruded blown film, in particular, allows for the realization of multi-layer structures, with flexible material and performance choices for each layer to meet diverse packaging needs.

Improvements in comprehensive performance, including mechanical strength, heat-sealing capabilities, sealing temperature, barrier properties, easy opening, and anti-contamination, become crucial. Excellent openability, referring to the ease with which users can open or tear the packaging without significant resistance or difficulty, is vital for various applications such as food and commodity packaging.

For instance, the H-layer co-extruded blown film with hot melt adhesive (PE+HM) reduces the demand for liquid glue and simplifies the production process, enhancing packaging seal durability. Electrical insulation film (PE+EAA) provides wear resistance and chemical resistance, while MLLDPE offers low-temperature heat-sealing capabilities. Other variations include EVA lid films, anti-static films, and slick films in co-extruded cast films.

Co-extruded cast films, such as H-layer co-extruded cast polypropylene (CPP) and unmodified PP + heat-sealable PP, showcase additional options. Multi-layer structures, like three-layer and five-layer nylon co-extruded films, and five-layer and seven-layer EVOH and PVDC high barrier films, are typically transparent or slightly yellowish. They possess characteristics such as water and air barrier properties, addressing issues like changes in the physical texture of packaged materials due to water molecule entry.

These advancements contribute to maintaining the quality of packaged materials, preventing oxidation, spoilage, decay, and the transmission of odors. The transparency of these films helps in solving problems caused by water molecules entering the packaging and altering the physical characteristics of the contents. Furthermore, the barrier properties prevent food or pharmaceutical products from oxidation, deterioration, and spoilage, preserving the original flavor and aroma and extending the shelf life of products.

Conclusion:

The development of inner films in composite flexible packaging, evolving from LDPE, LLDPE, CPP, MLLDPE, to the prevalent use of co-extruded films, has substantially achieved functional and personalized packaging. These innovations effectively meet the preservation, processing, transportation, and storage requirements of packaged contents. As society progresses and demands grow, the continuous introduction of new materials and advancements in production technology and equipment will drive the rapid development of functional and environmentally friendly packaging films. Examples include water-soluble polyvinyl alcohol (PVA) films, combining environmental safety, degradability, and excellent heat-sealing properties to meet evolving societal needs.