What is the process flow of plastic bag production?

The process of making plastic bags can be divided into the following core links. There are process differences for different materials (such as PE bags, composite bags, and woven bags). The specific process is as follows:

1. Material preparation

‌Raw material selection and ratio‌

Select polyethylene (PE), polypropylene (PP) or degradable materials (such as PLA) according to the purpose of the plastic bag, and add auxiliary materials such as masterbatch, plasticizer, filler, etc. to optimize performance. For example, food packaging bags need to use food-grade PE, and environmentally friendly bags need to add degradable ingredients‌.

‌Pretreatment‌

The raw material particles need to be pretreated by cleaning, drying, etc. to avoid impurities affecting subsequent processes‌.

2. Film blowing/extrusion molding

‌Melt extrusion‌

The raw material is heated to a molten state by an extruder, and a uniform film is formed by multi-layer co-extrusion technology. The thickness error must be controlled at ≤0.01mm‌.

‌Stretching and shaping‌

The molten material is stretched into a film by a film blowing machine, or made into embryo wire by a flat wire process (woven bag), and then stretched into a flat wire‌.

3. Printing process

‌Plate making and ink blending‌

Design patterns according to customer needs, use gravure or flexographic printing technology, and cooperate with UV curing technology to improve color adhesion and weather resistance‌.

‌Printing implementation‌

The film is printed by a printing press to complete multi-color overprinting, and the ink drying speed and color registration accuracy need to be controlled‌.

4. Bag making and molding

‌Cutting and slitting‌

The printed film is cut according to the preset size. For example, the continuous roll bag uses point-break cutting, and the vest bag needs to hollow out the handle area‌.

‌Heat sealing and sealing‌.

The edge of the bag body is sealed with a heat sealer. Some bag types require additional punching or adding destructive tape‌.

5. Quality inspection and packaging

‌Performance testing‌

The finished product is tested for sealing, tensile strength, thickness uniformity, etc. to ensure compliance with ISO9001 and other standards‌.

‌Packaging and warehousing‌

Qualified products are packaged according to specifications, and marked with production batch, material and other information, and finally put into storage or shipped‌.

Special process differences

Composite bags: After film blowing, different materials (such as aluminum foil and nylon) need to be laminated by glue or hot pressing to enhance the barrier properties.

Woven bags: Flat wire is woven into cloth by circular looms, and then formed by cutting and sewing.

Environmental protection process: Recyclable or biodegradable materials are used to reduce environmental pollution.

The above process needs to be completed with automated equipment (such as film blowing machine, gravure printing machine, heat sealing and slitting machine). The process parameters (temperature, pressure, traction speed) of each link directly affect the quality of the finished product.

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