What is Soft Packaging Manufacturing Process

An In-Depth Analysis of Soft Packaging Manufacturing Process: A Precision Systems Engineering from Materials to Finished Products

Abstract: Soft packaging, as an indispensable component in the modern commodity circulation system, involves a manufacturing process that is a comprehensive technology integrating polymer materials science, precision mechanical engineering, printing technology, and chemical treatment. This article aims to systematically deconstruct the complete process flow of soft packaging from design to finished product, delving into its core stages and technical key points, with the goal of providing a comprehensive and professional cognitive framework for industry practitioners and those interested.

I. Overview of Soft Packaging and Process Summary

Soft packaging broadly refers to all flexible packaging products, common forms include bags, pouches, films, etc. Its core advantages lie in being lightweight, space-saving, adjustable barrier properties, and high design freedom. A complete soft packaging manufacturing process is not a simple application of a single technology but an interlinked precision chain, mainly including the following core steps:

Pre-design and Material Selection → Base Film Preparation → Printing → Lamination → Curing → Slitting and Bag Making

The precision and control of each step directly determine the performance, appearance, and cost of the final product.

II. In-Depth Analysis of Core Process Stages

1.Pre-design and Material Selection

This is the starting point of the process and a key factor determining the success of the product. This stage requires comprehensive consideration based on the characteristics of the packaged contents (e.g., food, pharmaceuticals, chemicals), storage conditions, shelf-life requirements, transportation methods, and end-market positioning.

Functional Design: Determine the core performance indicators required for the packaging, such as:

Barrier Properties: Barrier capabilities against oxygen, water vapor, aroma, and light. For example, puffed snacks require high oxygen barrier to prevent fat oxidation, while desiccants require high moisture barrier.

Mechanical Properties: Tensile strength, tear strength, puncture resistance, flexibility.

Chemical Properties: Oil resistance, resistance to content corrosion.

Hygiene and Safety: Compliance with relevant regulations for food or pharmaceutical contact materials (e.g., FDA, EU 10/2011).

Material Selection and Structure Design: Based on functional requirements, choose single-layer or multi-layer composite materials. Common base materials include:

Printing/Support Layer: BOPP (Biaxially Oriented Polypropylene), BOPET (Biaxially Oriented Polyethylene Terephthalate), PA (Nylon), paper, etc. This layer primarily provides mechanical strength and printability.

Barrier Layer: VMPET (Vacuum Metallized PET), AL (Aluminum Foil), EVOH (Ethylene-Vinyl Alcohol Copolymer, high oxygen barrier), PVDC (Polyvinylidene Chloride). This layer is the core of functionality.

Heat-Seal Layer: LDPE (Low-Density Polyethylene), LLDPE (Linear Low-Density Polyethylene), CPP (Cast Polypropylene), mPE (Metallocene Polyethylene). This layer is responsible for achieving good, strong seals during bag making.

A typical three-layer structure might be: BOPP (printing/appearance) / AL (barrier) / CPP (heat seal).

2.Base Film Preparation

This step provides qualified raw materials for subsequent processing. Main processes include:

Casting: Extruding molten plastic through a long, narrow die and rapidly cooling it on a cooling roll to form films like CPP, CPE, etc. Characteristics include softness and good heat-sealing properties.

Biaxial Orientation: Stretching a thick sheet (cast sheet) above its glass transition temperature intensely in both longitudinal and transverse directions, followed by heat setting, to produce films like BOPP, BOPET, etc. This process significantly enhances the film's strength, rigidity, transparency, and barrier properties.

3. Printing

Soft packaging printing aims to reproduce exquisite patterns while ensuring the print is suitable for subsequent processing (e.g., lamination strength). The mainstream process is gravure printing.

Principle: Ink is carried by the cells on an engraved cylinder and transferred to the printing substrate.

Process Flow: Unwinding → Tension Control → Multi-color Unit Printing (each unit corresponds to one color) → Drying (hot air drying) → Rewinding.

Technical Key Points:

Tension Control: The lifeline for ensuring registration accuracy, requiring precise control throughout the process.

Ink System: Primarily uses solvent-based inks or environmentally friendly water-based inks, solvent-free inks. Key indicators include ink adhesion, rub resistance, and solvent residue.

Post-Printing Inspection: Uses automatic online inspection systems to monitor defects like registration, color deviation, streaks, and spots in real-time.

4. Lamination

Lamination is the core process of firmly combining two or more different performance base materials (e.g., printed film, aluminum foil, other plastic films) using adhesives to form a multi-functional composite material. Mainly includes three techniques:

Dry Lamination:

Process: Evenly coat adhesive (solvent-based or solvent-free) onto the first substrate → Thoroughly dry the solvent in an oven → Combine with the second substrate under heat and pressure at the laminating roller → Rewind.

Characteristics: Most widely used, broad material applicability, high bond strength. But risks solvent residue and environmental pollution.

Solvent-Free Lamination:

Process: Use 100% solid content adhesives, coated at room temperature through metering and mixing devices, directly combined with the second substrate.

Characteristics: No solvent emissions, energy-saving, safe and hygienic, high production efficiency, currently the mainstream development trend. But requires extremely high equipment precision, operational skills, and environmental temperature/humidity control.

Extrusion Lamination:

Process: Use molten polyethylene (PE) or polypropylene (PP) resin as the adhesive layer, extruded from the die, directly coated onto the first substrate, and immediately combined with the second substrate and cooled.

Characteristics: Combines lamination and coating functions, lower cost, but relatively poorer product transparency and flatness.

5. Curing

Curing, also known as aging, is a crucial chemical reaction process following lamination.

Purpose: To allow full cross-linking reaction between the main agent and curing agent of the laminating adhesive (mainly polyurethane type), thereby achieving the designed bond strength, heat resistance, and media resistance.

Process Conditions: Place the laminated semi-finished roll material in a curing room at a specific temperature (usually 50-55°C) for a certain duration (usually 24-72 hours).

Importance: Insufficient curing leads to inadequate bond strength and delamination; over-curing may embrittle the material. This process is key to 'awakening' the material's performance.

6. Slitting and Bag Making

This is the final step converting large rolls of cured material into the final product form.

Slitting: Cut the wide material roll into narrow rolls of specific widths according to customer requirements using a slitting machine.

Bag Making: Completed by automatic bag-making machines. Processes include:

Back Seal Bags: Sealed at the back of the bag, the most common bag type.

Three-Side Seal Bags: Three sides of the bag are sealed.

Stand-up Pouches: Special structure at the bottom allows the bag to stand upright.

Zipper Installation: Heat-sealing a resealable zipper at the bag mouth.

Punching: Precise punching for easy-tear notches or hang holes.

Technical Core: Precise matching of heat seal temperature, pressure, and time to ensure strong, flat, leak-free seal lines. Online inspection is the final checkpoint for ensuring outgoing quality.

III. Future Process Development Trends

Green and Environmental Protection: Solvent-free lamination technology and water-based ink applications will become more widespread; R&D and process optimization for mono-material recyclable packaging (e.g., all-PE structures) become an industry focus.

Intelligentization and Digitalization: Implement full-process data monitoring and process parameter optimization through MES (Manufacturing Execution Systems); use AI visual inspection to replace manual labor, improving defect detection rates and consistency.

Functionalization and Personalization: Process integration for functional packaging like high-barrier, antimicrobial, smart labels (e.g., RFID); digital printing technology enables small-batch, personalized customization.

Conclusion

The manufacturing process of soft packaging is a rigorous and complex systems engineering. From initial functional definition and materials science application, through midstream precision mechanical processing and chemical reaction control, to downstream finishing and quality assurance, each stage contains profound technological accumulation. A deep understanding and continuous innovation of this process system are the fundamental driving forces propelling the soft packaging industry towards greater efficiency, environmental friendliness, and higher performance.