Those who are familiar with membrane panel switches know that PC and PET are currently the more mainstream manufacturing raw materials. But in addition to these two types of plastic films, there are many more. Today we will summarize the characteristics of various plastic films.

There are many methods for forming plastic films, among which the three processes of casting, extrusion, and blow molding are more common.

Casting method: to produce a non-stretched, non-oriented flat-extrusion film, through the melt casting quenching process

Extrusion method: The high polymer material is first heated and melted and extruded into a thick sheet through an extruder, and then stretched by a stretching machine to a certain multiple in the longitudinal direction and the transverse direction within an appropriate temperature range. The molecular chains are oriented in a plane parallel to the film and arranged in an orderly manner, and then heat-set under tension to fix the oriented macromolecular structure, and finally form a film after cooling and subsequent processing.

Blow molding method: the material is plasticized and extruded to form a tube blank for inflation molding, and then cooled, hauled, and coiled. The blown film is oriented. The film-forming process of blow molding is simple and is the most commonly used film-forming process.

Characteristics of 12 Common Films 

1. HDPE

HDPE films are known as geomembranes or impermeable membrane. Its melting point is about 110℃-130℃, and the relative density is 0.918-0.965kg/cm3. It is a kind of thermoplastic resin with high crystallinity and non-polarity. The appearance of the original HDPE is milky white, and the thin section is translucent to a certain extent. It has good high and low temperature resistance and impact resistance, even at low temperatures of -40F.

Its chemical stability, rigidity, toughness, mechanical strength and tear resistance are excellent. As the density increases, the mechanical properties, barrier properties, tensile strength and heat resistance will increase accordingly. It is resistant to corrosion by acids, alkalis, and organic solvents. It is widely used in environmental protection, horticulture, agriculture, and breeding fields.

Identification method: mostly opaque, with wax-like feel. There is a rustle when rubbing or rubbing the plastic bag.

2. LDPE

LDPE film has low density, softness, low temperature resistance, impact resistance and good chemical stability. In general, it is resistant to acid (except strong oxidizing acid), alkali, salt corrosion, and has good electrical insulation.

LDPE is mostly used in plastic bags. Its products are mostly used in civil engineering and agricultural fields, such as geomembrane and agricultural film. Its recycled materials, scraps, etc. can be made into trash cans, tool boxes, bicycle mats, trash carts and other flexible plastic re-products.

Identification method: Plastic bags made of LDPE are softer. The outer packaging plastic film is soft and easy to tear is LDPE, and the more brittle and hard is PVC or PP film.

3. PP

Ordinary PP film is blow-molded, with simple process and low cost, but its optical performance is slightly lower than that of CPP and BOPP.

The biggest feature of PP is high temperature resistance (approximately -20℃~120℃), and its melting point is as high as 167℃. It is suitable for filling soy milk, rice milk and other products that require steam sterilization. Its hardness is higher than PE, and it is mostly used to make container caps.

Identification method: Generally, PP has a higher hardness and a shiny surface, and does not produce irritating odor when burned, while PE has a heavier candle smell.

4. CPP

Cast polypropylene film (CPP) is a non-stretched, non-oriented flat extrusion film produced by melt casting quenching.

It is characterized by fast production speed, high output, and good film transparency, gloss, barrier properties, flexibility, and thickness uniformity. It can withstand high temperature cooking (the cooking temperature is above 120°C) and low temperature heat sealing (the heat sealing temperature is less than 125°C), and the balance of various properties is excellent.

Follow-up work such as printing and compounding is convenient. It is widely used in the packaging of textiles, food and daily necessities. It can be used as the inner substrate of composite packaging to extend the shelf life of food and increase the aesthetics.

5. BOPP

Biaxially oriented polypropylene film (BOPP) is a transparent flexible packaging material developed in the 1960s. A special production line is used to mix polypropylene raw materials and functional additives, melt and knead to form a sheet, and then stretch it into a film.

This film not only has the original advantages of low density, corrosion resistance, and good heat resistance of PP resin, but also has good optical properties, high mechanical strength, rich source of raw materials, and excellent printing performance. It can be compounded with paper, PET and other substrates. At the same time, it has high definition and gloss, excellent ink absorption and coating adhesion, high tensile strength, excellent grease barrier properties, low electrostatic characteristics, etc.

It is widely used in the packaging of food, candy, cigarettes, tea, juice, milk, textiles, etc.

6. PVC

The advantages of PVC film and PET are similar. They are transparent, airtight, and resistant to acids and alkalis. In the past, PVC film was usually used as cling film, but PVC cling film is easy to precipitate and increase when it is heated or used in contact with oily food. Plasticizers are brought into the human body with food and cause certain harm to the human body. Therefore, PVC cling film can only be used to keep fresh fruits and vegetables, etc., and it has been gradually replaced by cling film of other materials.

Nowadays, PVC film is mostly used in daily necessities.

7. PS

Polystyrene (PS) has many advantages such as high transparency, non-toxicity, easy welding, convenient molding and processing, and low cost, but it is brittle.

The biggest feature of polystyrene film is that it has excellent electrical properties. The dielectric loss is the smallest of the existing films. It has outstanding water resistance and is suitable for high-frequency insulating films.

The main purpose of polystyrene film is to use its superior electrical properties as telecommunications equipment in the defense industry and cutting-edge technology, such as variable capacitors and high-frequency cable insulation. It can also be used as food packaging film, especially suitable for packaging vegetables, fish, meat, etc. where ventilation is required.

8. PET

Polyester film (PET) is a thermoplastic engineering plastic. It is a film material made of thick sheets by extrusion and then biaxially stretched.

PET film is characterized by excellent mechanical properties, high rigidity, hardness and toughness. Puncture resistance, abrasion resistance, high and low temperature resistance, chemical resistance, printability, oil resistance, air tightness and fragrance retention are good. It is one of the commonly used barrier composite film substrates. But the corona resistance is poor and the price is higher.

The thickness of the film is generally 0.12mm, and it is commonly used as the outer layer material, tape, and film of food packaging.

9. PA

There are many varieties of nylon plastic film at present, among which the main varieties used to produce the film are nylon 6, nylon 12, nylon 66 and so on.

Nylon film is a very tough film with good transparency and good gloss. Tensile strength, tensile strength, high and low temperature resistance, oil resistance, organic solvent resistance, abrasion resistance and puncture resistance are all good. In addition, the film is relatively soft and has excellent oxygen barrier properties, but has poor water vapor barrier properties, greater moisture absorption and moisture permeability, and poor heat sealability.

It is suitable for packaging hard items, such as greasy food, fried food, vacuum packaged food, steamed food, etc.

10. PVA

Polyvinyl alcohol (PVA) high-barrier composite film is a film with extremely high barrier properties formed by coating a modified polyvinyl alcohol water-soluble liquid on the substrate with polyethylene plastic as the base material.

PVA is the only vinyl polymer that can be used by bacteria as a carbon source and energy source. Under the action of bacteria and enzymes, it can degrade 75% in 46 days. It is a kind of biodegradable polymer material, usually formed by casting, low price, and has unique advantages in food and medicine packaging.

11. EVA

EVA film, also known as environmental protection film, is a film produced from EVA raw materials through casting and extrusion. It is a new generation of green and environmentally friendly degradable materials, which will not cause harm to the environment when discarded or burned. It has high heat-adhesive properties and can be heat-adhered to the surface of polyester, nylon, and canvas. It has high transparency, water resistance and organic solvent resistance.

12. Aluminized film

Aluminized film is a composite flexible packaging material formed by coating an extremely thin layer of metal aluminum on the surface of a plastic film using a special process. Common packaging films such as PE, BOPP, CPP can be made into aluminized film, of which PET and CPP aluminized film are the most used.

Aluminized film combines the characteristics of plastic film and metal. The function of aluminum plating on the surface of the film is to shield light and prevent ultraviolet radiation, which not only extends the shelf life of the contents, but also improves the brightness of the film. To a certain extent, it replaces aluminum foil, and it also has low price, beautiful appearance and better barrier properties. Therefore, the application of aluminized film in composite packaging is very wide, mainly used in dry and puffed food packaging such as biscuits, and outer packaging of medicine and cosmetics.