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Plastic Extrusion and Manufacturing Process

These are the three steps involved in making any plastic bag:

  1. Raw Materials
  2. Extruding Plastic Film
  3. Printing Bags
  4. Bag Making or “converting”

Blending and Mixing Resins

Clear LDPE (low density polyethylene) plastic resin in pellet form is vacuum fed from storage silos and blended with various additives as required for specific product applications. These mixes transform the plastic polymer to improve their basic mechanical, physical and chemical properties into a commercial product.

Additives combine to create the desired proprietary blends of clarity, strength, stretch ability, seal ability, scuff and tear resistance, UV protection, bacterial protection, surface appearance, slip resistance and other properties required for the finished product. If colored film is to be made, colored pellets (called “Master Batch”) are added in blends from 1% to 25% to achieve different opacities and virtually any color imaginable. Numerous resins, both LDPE, and Linear LDPE, are kept in stock to allow for the many diverse applications that are manufactured daily.

1. Raw Material

Oil and natural gas are the major raw materials used to manufacture plastics. The plastics production process often begins by treating components of crude oil or natural gas in a “cracking process.” This process results in the conversion of these components into hydrocarbon monomers such as ethylene and propylene. Further processing leads to a wider range of monomers such as styrene, vinyl chloride, ethylene glycol, terephthalic acid and many others. These monomers are then chemically bonded into chains called polymers. The different combinations of monomers yield plastics with a wide range of properties and characteristics.

2. Extruding Plastic Film

The blended resins are then fed into extruders and melted at 380F. Screw drives, force the molten mixture through a precision die where air is introduced and a ‘bubble is formed’ This process is known as “blown film extrusion”.

Adjustments to wall thickness and diameter are made in this continuous bubble or tube. As it rises some 20 feet, it cools and is flattened and wound under tension into 50 – 200 lb. rolls. Our line-up of extruders gives us the flexibility to regularly produce custom film orders. This allows also for quick order fulfillment where tubing may be available in as little as 2 or 3 days.

3. Printing Bags

From the extruders, the rolls of film are delivered to our print department. Flexographic stacked presses produce printed film in up to 6 colors with matte to gloss to metallic finishes. A smaller press does the less complex jobs such as produce roll bag printing and other I or 2 color jobs.

This versatility allows us to print small quantities of bags and also to handle huge press runs of a week or more. We can consistently meet deadlines while achieving consistent, quality results.

4. Bag Making or ``Converting``

Either plain rolls from the extruder line or printed rolls form our presses are delivered to the bag making area of our plant. A myriad of sizes and options are available in essentially 3 types of bag conversion: single bags, bags on rolls (perforated tear-off) or bags on wire wickets.

Roll stock is loaded onto bag making machines where repetitive bottom seal or side seal converting takes place to produce individual bags from the large rolls Holes, vents, slits, perforations, handle punching, header sealing arc some of the many options available in each production run.