How PP Lined Paper Bags Is Made?

In this article we will walk through the production process of poly-propylene (PP) lined paper bags, exploring raw materials, production steps, quality controls and application advantages. We also highlight how suppliers such as YINGTONG can offer suitable bag solutions for various industrial packaging needs.

Raw Materials and Bag Structure

PP-lined paper bags combine the strength of kraft or multi-wall paper with internal PP or PE film or liner layers to provide moisture resistance, dust barrier and improved durability. Typical components:

The standard process for multi-wall paper bag production follows a series of steps: printing, tubing, bottom forming and palletising. When a liner is included, additional steps of film lamination or insertion are required.

Production Steps of PP-Lined Paper Bags

Here is a detailed walk-through of how the bag is made, step by step.

1. Paper ply preparation

First, the kraft or sack paper rolls are sourced, typically in multiple plies. The paper may have been produced via the kraft process to yield high strength and tear resistance. The rolls are checked for grammage, tensile strength and moisture content.

2. Liner (PP film) preparation

The inner liner – typically a polypropylene film or tape – is prepared. This PP film may be extruded and slit to width, or supplied as rolls ready for lamination or insertion. The liner provides the barrier function. A common method is extrusion coating/lamination of resin onto paper or film substrate.

3. Lamination / Bonding of Liner to Paper

To create a bag wall with liner, the PP film is bonded to the inner face of the paper plies, or inserted as a separate liner layer within the tube structure. The bonding process uses adhesives or heat-lamination to ensure the liner remains fixed during filling and transport.

4. Printing & Bag Face Finishing

Next the external surfaces of the bag are printed with brand logo, product information, batch codes, handling instructions, etc. Modern flexographic or gravure printing methods are used. Quality control ensures ink adhesion, registration and clarity.

5. Tubing / Forming the Bag Body

The coated/laminated paper (with liner) is then converted into a continuous tube by a tuber machine. The process joins multiple plies and bonds the liner as needed to form a flat or gusseted tube.

6. Bottom Formation & Sealing

The bottom of the bag is formed and sealed. For valve bags or open-mouth bags, this may involve folding, gluing or stitching. With liner bags, additional care is given to ensure the liner is properly sealed to prevent leakage. According to case studies of paper bag manufacturing the bottom forming is critical and often automated to high speed.

7. Cutting, Sewing (if applicable) and Finishing

The continuous tube is then cut to length, and if the bag requires sewing (for example a multi-ply valve bag with liner), the seams are stitched or reinforced. For heavy duty applications, double stitching or reinforcement patches may be applied to the seam area.

8. Quality Inspection

Finished bags undergo inspection for correct dimensions, seam integrity, liner bonding, print quality and cleanliness of valve or filling openings. Any defective units are rejected or reworked. Quality assurance ensures the bag meets strength, barrier, and appearance specifications.

9. Packaging & Palletising

After approval the bags are stacked, bundled and palletised ready for shipment. This step often includes applying moisture-protective wrap and labelling for logistics. Proper storage protects the bags from moisture, UV and other damage prior to filling.

Advantages of PP-Lined Paper Bags

When compared to plain paper bags or single-material bags, PP-lined paper bags provide several benefits:

• Strong barrier against moisture and fine dust, useful for powders and hygroscopic materials.

• Good bulk strength from multi-wall paper combined with flexibility of liner.

• Better print-ability and premium appearance on outer paper surface.

• Cost-effective for heavy-duty packaging compared to full plastic sacks.

• Customisable with liner thickness, paper plies, printing and valve options to match application needs.

Application Fields

PP-lined paper bags are widely used in sectors such as:

• Cement and building materials: For powders that need dust barrier and strength in transit.

• Food grade powders: Where hygiene, moisture protection and strong outer packaging are required.

• Chemical granules: For dry flowable bulk products requiring sturdy packaging with barrier liner.

• Animal feed & fertilizer: To provide cost-sensitive yet robust packaging that resists moisture ingress.

Choosing a Reliable Supplier

When sourcing PP-lined paper bags it is essential to select a manufacturer who offers:

• Good material sourcing and consistent quality of paper and liner.

• Precision in lamination and sealing processes to prevent delamination or leaks.

• Printing and finishing capabilities to support branding and information requirements.

• Reliable logistics and packaging to protect bags during transport and storage.

An example is YINGTONG, an established building-material packaging enterprise in South China, offering kraft paper bags with plastic liners and multi-ply valve bag solutions for industrial materials. Their experience and production capacity make them a partner worth considering.

Summary

The production of PP-lined paper bags integrates multi-wall paper technologies with internal liner lamination to yield high-performance packaging solutions. From raw material selection through lamination, printing, forming, sealing and inspection, each step must be carefully controlled. When correctly manufactured, these bags deliver the required strength, barrier performance and appearance demanded by industrial applications. By partnering with a professional supplier, businesses can secure packaging that protects their product, reinforces brand image and supports efficient logistics.

Whether you require bags for cement, food powders, chemicals or other dry bulk materials, understanding the manufacturing process helps you specify the right structure, liner thickness and finishing details to match your needs.