Paper Bag Machine Product

Overview

Paper bag machines are specialized converters that form disposable shopping and kraft bags from continuous rolls of kraft paper. They are found in supermarkets, bakeries, print shops, and packaging facilities worldwide, producing millions of bags daily.

The complete automated process wraps continuous paper into a tube, glues the sidewall seam, folds the bottom, and applies twisted-paper or twine handles. A single operator can produce 2,400-4,800 finished bags per hour with minimal intervention.

Paper bags are gaining renewed interest as retailers move away from single-use plastic. Modern bag machines are designed for speed and reliability, handling specialty papers (compostable kraft, print-decorated blanks) as well as standard kraft.

How it works

An operator threads a continuous roll of kraft paper (typically 20-40 lbs basis weight, 50-100 cm wide) onto the Roll Unwind Section reel. The Unwind Motor is a servo motor that maintains constant paper tension (10-20 N/mm) via a Dancer Roller feedback control.

The paper web advances through the Tube Former, where a rotating Folder Plate wraps the paper around a Tube Former Mandrel (a cylindrical steel core). The paper overlaps itself by 20-40 mm on each wrap. This overlap zone is where the seam will be glued.

The wrapped tube exits the folder and enters the Tube Gluer. A Adhesive Pump delivers water-based starch adhesive (or hot-melt) at 1-3 L/min to a Glue Roller. The roller applies adhesive to the paper overlap. A Glue Press Roller presses the overlap together, bonding the seam. The adhesive cures within 2-5 seconds.

The continuous tube of glued paper then enters the Bottom Folder station. A rotating Tube Cutter Blade blade cuts the tube to bag length (typically 250-350 mm for grocery bags). Immediately after cutting, the tube falls onto a forming block where Left Folder Blade, Right Folder Blade, and Center Folder Blade blades fold the bottom flaps inward in a sequence.

The folded bottom enters the Bottom Sealer station. A Bottom Glue Applicator spray-applies adhesive to the bottom folds. A Bottom Press Roller presses them together, sealing the bottom envelope-style.

Next, the Handle Applicator applies pre-twisted paper or twine handles to the bag sides. A Handle Supply Reel supplies handles, and a small Handle Application Motor positions each handle. Adhesive is applied to the handle base, and a Handle Press (pneumatic) presses the handle onto the bag.

The finished bag drops onto the Delivery Conveyor Belt and is conveyed to a collection area. A Bag Counter counts bags and signals a Stacking Arm to bundle completed bags into a collection bin or bale.

Tube Formation Precision

The tube former is the heart of the machine. Paper wrapping around the mandrel must be uniform and concentric, or the bag walls will be uneven. A rotating Folder Plate guides the paper as it wraps. Typically, 1.5-2 full rotations of the mandrel occur per bag length, meaning each bag overlaps 20-40 mm of the previous bag's seam region.

Timing synchronization between the tube former rotation and the bottom folder/cutter is critical. If timing drifts, the bag length becomes inconsistent or the bottom fold doesn't align with the cut point.

Adhesive Application

Water-activated starch adhesive is the traditional choice because it is inexpensive, non-toxic, and works well on kraft paper. However, it requires careful tank maintenance—starch can mold and degrade if left standing. The Adhesive Heater warms adhesive to 40-50 C for optimal flow.

Hot-melt adhesive (polyethylene-based) is faster-setting (< 1 second) and requires less maintenance, but is more expensive and requires heated tanks (150-160 C).

The adhesive quantity and pressure both affect seam strength. Too little adhesive or low pressure results in weak seams that split. Too much adhesive causes bleeding and soiling of the bag exterior.

Handle Options

Traditional paper handles are twisted kraft paper rope, 3-5 mm diameter, pre-made into U-shaped loops. The loop is fed from a Handle Supply Reel reel and positioned on the bag sides via the Handle Application Motor.

Modern machines also support twine handles (jute, cotton, polypropylene) for specialty bags. Some machines can apply printed paper handles for branded bags.

Handle attachment adhesive is critical—weak bonding causes handles to tear off in use, resulting in product liability and customer complaints.

Bottom Folding Sequence

Bag bottoms are typically formed using one of two methods:

1. Inward-folding bottom (IF): Side flaps fold inward, then the top flap folds down over them, creating an envelope-style seal. This is the most common.

2. Pasted bottom (PB): Side and back flaps are all glued to the main bag body. This method is slower but creates stronger bottoms for heavy items.

The Bottom Folder and Bottom Sealer are optimized for the inward-fold method because it is faster.

Speed and Capacity

Speed depends on bag size and complexity. Small grocery bags (250 mm long, light handles) run 60-80 bags/minute (3600-4800/hour). Larger or specialty bags (gusseted sides, reinforced bottoms) run 40-60 bags/minute.

Paper web consumption is significant. A roll of kraft paper 100 cm wide contains approximately 1000-2000 meters. At 60 bags/minute, a single roll supplies ~3-6 hours of production (depending on bag width).

Quality and Defects

Common defects in paper bag production:

• Weak seams: Adhesive under-application or low pressure. Check glue pump flow and press roller pressure.
• Misaligned bottom: Bottom fold not centered on the cut. Adjust folder blade timing or cutter position.
• Wrinkled sides: Paper tension too low or tube former misaligned. Increase unwind tension and check folder geometry.
• Handle pull-off: Weak handle adhesive or poor surface prep. Test adhesive cure and verify surface cleanliness.

Specialty Bags

Modern machines handle compostable kraft (PHA or PLA coated), recycled kraft, and printed decorator papers. Some specialty bags have gusseted sides (folded flaps on the sides for extra capacity) requiring additional forming stations.

Machines can also be configured for different handle types: no handles (open-top bags), single handle (beverage bags), or dual handles (shopping bags).

Maintenance

Daily: Verify paper tension and alignment, check adhesive level and temperature, inspect for adhesive buildup on rollers.

Weekly: Deep-clean adhesive applicator and press rollers (adhesive hardens and reduces effectiveness), verify tube former concentricity, check handle feed for tangles or wear.

Monthly: Bearing lubrication and inspection, blade sharpness verification (dull cutter produces torn edges), motor amperage check for mechanical stress.

Yearly: Professional service of main motor and gearbox, bearing replacement, tube former remachining if eccentricity develops.

Typical component lifespans:

• Tube cutter blade: 2-6 months depending on paper abrasiveness
• Bottom fold blades: 6-12 months
• Folder plate (tube former): 18-24 months before remachining needed
• Handle unwind mechanism: 12-18 months

Modern paper bag machines are highly reliable when properly maintained, often running 15-20 years before major rebuild.