The "Hardcore" Technology of Special Films: An In-depth Analysis of the Core Processes of High-Performance Film Materials

In modern industrial systems, film materials have evolved from their traditional role of simple packaging to an advanced material system integrating functionality, structure, and intelligence. Special films, in particular, as "high-end players" in the film family, not only play a significant role in the food, pharmaceutical, electronics, and automotive industries, but also

play an irreplaceable role in the new materials technology revolution.

From transparency and corrosion resistance to self-adhesion and heat transfer printing, and further to properties such as barrier properties, conductivity, anti-static properties, and thermal stability, the diverse performance of special films is supported by a series of advanced production processes known as "hardcore"—casting, biaxial stretching, blown film, coating, multilayer co-extrusion, surface treatment, etc. These processes play a decisive role in the manufacturing of different types of films such as transfer films, wrapping films, label films, and rust-proof films.

I. Special Films: Leading Representatives of Functional Materials

So-called "special films" are not traditional plastic films, but functional films with unique functions, high-performance indicators, and customized application scenarios. These films are no longer simply packaging layers, but incorporate the ability to respond to and control factors such as light, heat, water vapor, oxygen, and chemical corrosion at the material level.

According to application functions, special films can include, but are not limited to:

1. High-barrier films (water, oxygen, oil barrier, etc.)
2. Heat transfer films, cold transfer films (such as transfer films)
3. Self-adhesive protective films, wrapping films (used for packaging and surface protection)
4. Label films (labels, information identification)
5. Rust-proof films, anti-corrosion films (used for metal surface protection)
6. Electronic functional films (such as flexible circuit substrates, conductive films, optical films)
7. Medical films, biofilms (breathable, antibacterial, biodegradable, etc.)

The key to achieving these functions lies not in the inherent properties of the material itself, but in precise process control.

II. Core Process Analysis

1.  Casting process ( Cast Film Process )

Casting is a high-precision extrusion film-forming technology suitable for thermoplastic materials, widely used in the preparation of films requiring high transparency, flatness, and uniformity.

Process principle:

After the resin is heated and melted, the melt is cast onto a high-speed rotating cooling roller through an extrusion die head to quickly form a film. After cooling, drawing, and winding, a high-quality film is obtained.

Key control points:

1. Die head temperature uniformity: affects thickness consistency
2. Cooling roller temperature control accuracy: determines crystal structure and surface smoothness
3. Film thickness control system (such as automatic thickness measurement feedback system)

Application scenarios:

1) Carrier substrate for transfer films (such as PET film)

2) High-transparency label films (such as BOPET label base film)

3) Medical coating films

4) Base material for precision electronic films

2.  Biaxial stretching process ( BOP: Biaxially Oriented Process )

Biaxial stretching is a process that stretches the film in the longitudinal ( MD ) and transverse ( TD ) directions, causing the molecular chains to rearrange in two directions, improving its mechanical strength, transparency, rigidity, and thermal stability.

Stretching process:

1) Extrusion of primary film (thick film)

2) Preheat to orientation temperature

3) First, longitudinal stretching ( 2-5 times)

4) Then transverse stretching ( 3-10 times)

times) Heat setting, stabilize film structure, eliminate stress

Advantages:

1) High strength: improves tear resistance and puncture resistance

2) High transparency and optical properties

3) Strong Size stability (suitable for label printing, packaging)

Typical applications:

1) Label film base material (such as BOPP 、 BOPET )

2) Rust-proof film (stable structure, can be coated with rust inhibitor)

3) High-performance wrapping film (biaxially enhanced)

4) Capacitor film, lithium battery separator

3.  Blown film process ( Blown Film )

Blown film is the most traditional and flexible method in plastic film production, especially suitable for single-layer or multi-layer polyethylene and polypropylene films.

Process characteristics:

1) The film is inflated into a bubble shape by gas and then cooled and set.

2) Multi-layer co-extrusion can be easily achieved (such as ABC 、 ABCDE structure)

3) Low cost and mature technology

Application direction:

1) Wrapping film (such as LLDPE/LDPE high-elasticity film)

2) Rust preventive film ( PE film plus rust preventive masterbatch)

3) Some low-end labels or packaging materials

4.  Coating and composite technology

Many special films (especially transfer films, rust preventive films, and label films) need to have multiple functions, so they need to be coated on cast or stretched films, such as:

1) Rust preventive oil layer, moisture-proof layer

2) Hot melt adhesive layer, pressure-sensitive adhesive layer

3) Anti-stick layer, release layer

4) Ink carrying layer, transfer layer

Composite technology is used for the structural assembly of multiple functional film layers, such as PE+PET+ Release film and other multi-layer structures.

III. Typical Special Films and Their Technical Analysis

1.  Transfer film ( Transfer Film )

Transfer film is a functional film material that can "transfer" patterns, text, images, etc., from the surface of the film material to other substrates (such as leather, plastic, metal), often used in hot transfer and cold transfer technologies.

Structural composition:

1) Base film layer ( PET/OPP ): Provides a stable carrier, generally prepared by casting or biaxial stretching process

2) Release layer: Ensures smooth pattern transfer

3) Pattern layer: Ink printing

4) Adhesive layer / Hot melt layer: Controls bonding

Core technical points:

1) Base film surface tension control (conducive to printing and peeling)

2) Uniformity of multi-layer coating (affects transfer effect)

3) Resistance to temperature change and size stability (prevents pattern deformation)

2.  Wrapping film ( Stretch Film )

Wrapping films are widely used in logistics packaging, cargo packaging, and industrial dust protection. Its main technical indexes include tensile strength, elongation at break, and self-adhesion.

Manufacturing process:

Blown film method: Good thickness uniformity and strong self-adhesion

Casting method (mainstream): Multi-layer co-extrusion (such as LLDPE/LDPE/EVA structure), interlayer control adhesion performance

Technical characteristics:

1) Strong elasticity, puncture resistance

2) Single-sided or double-sided adhesion can be designed

3) Supports pre-stretching function to improve material utilization rate

3.  Label film ( Label Film )

Label film is a functional film used for label printing, barcodes, and information identification. It requires good printability, size stability, and durability.

Mainstream substrates:

1) BOPP 、 BOPET : Biaxially oriented, with good flatness

2) PE 、 PVC : Used for soft labels or special scenarios

Process requirements:

1) Surface energy control (conducive to ink adhesion)

2) Good thermal stability (suitable for high-speed printing)

3) Can be compounded with adhesive layer and release paper

4.  Rust preventive film ( VCI Film )

Rust preventive films add volatile corrosion inhibitors ( VCI ) to the film, releasing rust-preventing molecules when packaging metal products to form a molecular protective layer, effectively preventing oxidation and rust.

Typical structure:

  PE or BOPP Film + Rust preventive masterbatch / Coating layer

Production process:

1) Blown film or cast film process and masterbatch blending

2) Or use online / Offline coating technology

Technical difficulties:

1) Control and uniform distribution of volatile corrosion inhibitors

2) Maintain film strength and durability

3) Adapt to different metal types (iron, copper, aluminum)

IV. Future Trends and Innovation Directions

The field of specialty films is exhibiting the following technological evolution trends:

1.  Multifunctional Composite Trend

Traditional single-function films are gradually being replaced by multilayer, multi-effect integrated films. For example, rust prevention + Water resistance + Electrostatic shielding integrated packaging film.

2.  Environmental Protection and Biodegradability

PLA 、 PBS 、 PCL Bio-based materials such as these are entering the market for transfer films and label films, replacing traditional petrochemical-based materials with green materials.

3.  Intelligent Functional Films

High-end film materials with temperature response, conductivity, flame retardancy, self-healing, and other intelligent functions will become a research focus.

4.  High-Precision Manufacturing

Automatic thickness control ( ATC ), online optical detection, and digital coating technology improve the consistency and controllability of film materials.

The "hardcore" technology of specialty films is not only a reflection of the technological level but also the core support for material innovation and industrial upgrading. From casting, stretching to blown film and coating, every process is a precise refinement of performance. From the pattern accuracy of transfer films to the stretching ability of winding films, and to the optical properties of label films and the gas phase control of rust-proof films, specialty films are no longer just a combination of "thin" and "film," but a high-level embodiment of modern functional materials.

In the future, with the further development of materials science, intelligent manufacturing, and green processes, specialty films will extend unlimited possibilities in a more intelligent, efficient, and sustainable form.