The production process and structure of kraft paper bags vary depending on the intended use (e.g., food packaging, shopping bags, industrial packaging bags, etc.), but the overall process and structure are generally as follows:
1. Kraft Paper Bag Production Process
Material Selection and Pulping: The raw material is primarily wood pulp or recycled pulp. It undergoes beating, bleaching (or retaining the original color), pressing, and drying to form a kraft paper roll.
Printing: Flexographic, gravure, or offset printing techniques are used to print brand logos, designs, and text on the paper.
Food packaging bags are often printed with environmentally friendly soy ink.
Lamination (Optional): The kraft paper is laminated with a film (such as PE film, aluminum foil, or PLA film) to enhance its waterproof, moisture-proof, and oil-proof properties.
Food, coffee, and tea products often use a paper + PE/CPP/aluminum film composite structure.
Slitting and Bag Making: Large rolls of paper are slit into smaller rolls of the desired width. Automatic bag-making machines perform hemming, bottom folding, gluing, and bottom gluing to form the bag.
2. Molding Structure Processing
Flat Bags: Simply glue the bottom.
Square Bottom Bags: Fold the bottom into a square shape and crimp to secure the shape.
Handbags: Reinforce the bag opening and thread a paper or cotton string.
Ziplock Bags: Add a zipper or ribbed strip to the bag opening.
3. Inspection and Packaging
Inspect load-bearing capacity, adhesive strength, printing quality, and water resistance.
Qualified products are packaged and boxed for easy transportation.
4. Kraft Paper Bag Structure
Different types of kraft paper bags may have the following components:
Bag Body: Made of kraft paper, it can be single-layer or multi-layer.
Industrial bags often have three or more layers (kraft paper + interlayer PE/PP/aluminum film).
Bag Opening: Flat: Simple opening for easy loading and unloading.
Valve: Commonly used in industrial bags, allowing for automatic filling and self-sealing.
Ziplock: Commonly used in ziplock bags and food bags.
Bag Bottom: Flat: Suitable for flat packaging. Square bottom: Stands upright, commonly found in shopping bags, bread bags, and takeout bags.
Folded bottom: Increases weight-bearing capacity.
Folding sides: Expands capacity and gives the bag a more three-dimensional look.
Handles (optional): Flat rope, paper rope, cotton rope, or plastic handles.
Layering (optional): PE film: Waterproof and oil-resistant.
Aluminum foil: Light-proof and moisture-resistant.
PLA film: Environmentally friendly and biodegradable.
5. Typical Structure Examples
Food bags (coffee bags/nut bags):
Kraft paper + aluminum foil/PE/CPP (moisture-proof, anti-oxidation, and aroma-preserving).
Shopping bags/tote bags:
Single-layer kraft paper + reinforced bottom + handles.
Industrial bags (fertilizer and cement bags):
Multi-layer kraft paper + PE film inner layer, valve design, wear-resistant and moisture-proof.
