What are the production processes of a bag-making machine? This article details the complete manufacturing process from raw materials to finished product.

In the modern packaging industry, bag-making machines, as core production equipment, are widely used in the manufacture of flexible packaging for food, pharmaceuticals, daily chemicals, and electronics. The rationality and technical level of their production process directly affect bag quality, production efficiency, and cost control. This article will provide an in-depth analysis of the complete production process of bag-making machines, from raw material preparation to finished product output, breaking down the technical points and operating procedures of each step to help readers gain a comprehensive understanding of this professional field.

I. Overview of Bag Manufacturing

A bag-making machine is an automated device that processes roll-shaped film material into various bag shapes through multiple steps. Depending on the bag type, bag-making machines can be categorized into three-side sealing machines, center-sealing machines, back-sealing machines, stand-up pouch machines, zipper bag machines, and others. Although the equipment configurations differ, the basic production process is similar, mainly including raw material preparation, printing, lamination, curing, slitting, bag making, inspection, and packaging. We will explain each step in detail below.

II. Raw Material Preparation and Pretreatment

The first step in bag production is the selection and preparation of raw materials. Commonly used materials include polyethylene (PE), polypropylene (PP), polyester (PET), nylon (PA), aluminum foil, and biodegradable materials. Depending on the intended use of the bag, the materials must possess corresponding physical properties (such as strength and toughness) and chemical properties (such as acid and alkali resistance and barrier properties).

Raw materials typically arrive at the workshop in roll film form and undergo visual inspection first to check for defects such as impurities, crystal points, and holes. Simultaneously, the thickness, width, and surface tension of the roll film must be measured to ensure it meets production requirements. For certain materials, pretreatment, such as corona treatment, is also necessary to improve surface wettability and adhesion, facilitating subsequent printing and lamination.

III. Printing Process

Printing is a crucial step in bag production, not only giving packaging its appearance but also conveying product information. Common printing methods include gravure printing, flexographic printing, and digital printing.

Gravure printing produces exquisite results with high color saturation, making it suitable for mass production. The process includes plate mounting, ink mixing, material loading, printing, and drying. Strict control of ink viscosity, drying temperature, and printing speed is crucial during printing to avoid issues such as color difference and ghosting.

Flexographic printing is relatively environmentally friendly and is often used in food packaging. After printing, the ink must be thoroughly dried using a drying system to prevent sticking.

After printing, the roll film needs to be left to stand for a period of time to allow the ink to fully cure before proceeding to the next step.

IV. Composite Process

Lamination is the process of combining two or more materials into one using adhesives to improve the barrier properties, strength, and aesthetics of packaging. Common lamination methods include dry lamination, solvent-free lamination, and extrusion lamination.

Dry lamination is the most widely used method, and the process is as follows: First, an adhesive is applied to the substrate, and then the solvent is removed by heating in an oven. Next, it is bonded to another layer of material under the action of hot rollers. This process requires control of the coating amount, oven temperature, and lamination pressure to ensure that the peel strength meets the requirements.

Solvent-free lamination is environmentally friendly and efficient, but requires sophisticated equipment. Extrusion lamination, on the other hand, bonds materials together using molten resin and is suitable for thick materials.

The laminated film needs to proceed to the next stage – curing.

V. Maturation Process

Curing (also known as hardening) is the process of allowing the adhesive to fully cross-link and react, thereby increasing the bond strength of the composite layer. The roll of film is placed in a curing chamber and kept at a specific temperature (typically 40-60°C) and humidity for 24-72 hours. The curing time depends on the type of adhesive and the material structure.

Insufficient curing will result in poor peel strength, while excessive curing may cause the material to become brittle. Therefore, it is necessary to strictly follow the process parameters and regularly check the curing effect.

VI. Slitting and Rolling

After curing, the film roll needs to be cut to the required width using a slitting machine. The slitting process includes unwinding, alignment, cutting, and rewinding. The slitting blades must be kept sharp to avoid burrs or uneven cuts. The rewinding tension must be uniform to prevent wrinkling or deformation of the roll.

The slit narrow rolls can then be machine-made into bags.

VII. Bag Making Process

Bag making is the core step, and the entire process is automated by a bag-making machine. Taking a common three-side seal flat bottom bag as an example, the process is as follows:

1. Feeding and correction : The slit film rolls enter the machine through the feeding rack, and the photoelectric correction device ensures that the material is in the correct position.
2. Fixed-length feeding : The servo system controls the feeding rollers to precisely deliver the film and determine the bag length.
3. Bottom folding and sealing : For flat-bottom bags, the bottom of the bag must be folded first, and then sealed with a heat sealer.
4. Side sealing : After the material is folded in half, both sides are sealed by a heat sealing device. The heat sealing temperature, pressure, and time are key parameters that directly affect the sealing strength.
5. Cooling and shaping : After sealing, cooling and shaping are required to prevent deformation of the seal.
6. Punching and tear-off processing : If handle holes or tear-offs are required, they are punched out using a die.
7. Bag cutting and counting : A rotating knife cuts continuous bags into individual bags, and a counter controls the output quantity.

For complex bag types such as stand-up pouches and zipper bags, additional steps such as forming the stand-up bottom and installing the zipper are required. The entire bag-making process necessitates frequent checks on sealing quality, dimensional accuracy, and appearance defects.

VIII. Quality Inspection and Packaging

Finished bags must undergo rigorous inspection, including size measurement, seal strength testing, airtightness testing (such as the bubble test), and visual inspection. Defective products must be rejected.

After passing inspection, the bags are packaged and stored in the warehouse according to quantity. Usually, a certain number are bundled together, wrapped in packaging film, and the outer box is labeled with information such as specifications, quantity, and production date.

IX. Process Optimization and Handling of Common Problems

Common problems in bag manufacturing include loose sealing, uneven bag cutting, and misaligned patterns. The causes need to be analyzed from three aspects: materials, equipment, and processes. For example, issues such as poor heat-sealing properties of materials, uneven heat-sealing knife temperature, and insufficient feeding accuracy may arise. Regular equipment maintenance and optimization of process parameters are key to ensuring quality.

With the development of technology, intelligent bag making machines are becoming increasingly popular. Through the PLC and touch screen control system, precise parameter adjustment and fault diagnosis can be achieved, greatly improving production efficiency and stability.

The production process of a bag-making machine is a complex system engineering project involving multiple stages and technologies. From raw material selection to finished product output, each step requires strict quality control. Only by deeply understanding the process principles and continuously optimizing operational details can high-quality packaging bags be produced to meet market demands. In the future, with the advancement of environmentally friendly materials and intelligent manufacturing, bag-making technology will continue to evolve, injecting new vitality into the packaging industry.

Through the detailed introduction above, readers should now have a comprehensive understanding of the production process of bag-making machines. In actual production, it is also necessary to flexibly adjust the process according to the equipment model and product requirements to achieve the best production results.