Q & A
General Information

The extruded film tubing can be processed further in subsequent steps. Large film rolls, often containing several kilometers of material, are placed in converting machines, also known as bag-making or sealing machines.
The film is unrolled, cut with heated blades, and sealed with welding beams into desired bag or sack sizes—using technology similar to that of household heat sealers commonly used to seal items like frozen food. In a single step, depending on the bag size, not only one but often four, five, or even six bags are produced. Modern converting machines can perform over 200 seals (cycles) per minute, resulting in more than 1,000 bags per minute.
Since the bag size is predetermined, the film width and thickness must be adjusted during extrusion. If the required dimensions are not met, the film cannot be converted into the desired bag format and would need to be recycled.
If printed bags are to be produced, the film undergoes printing in a separate step. The roll of film is unspooled through a printing machine where it passes multiple rotating printing cylinders. Each cylinder applies a different color, creating the final image step-by-step. The printing machine ensures each color aligns precisely to form the desired design.
The printed film is then rewound on the other side of the machine and subsequently sent to the converting machine, where it is set to ensure the design appears centered on each bag. This avoids having a bag with an incomplete image split between edges, which would not meet customer expectations.
HDPE (High-Density Polyethylene) or LDPE (Low-Density Polyethylene) is supplied as granulate. This granulate is melted in extruders, which function similarly to a large meat grinder but with heating elements. The melted material is then pushed through a blowing head and inflated like a "bubble gum" bubble, cooled, and formed into a film tube through rollers.
The film tube is wound onto large rolls, which are then either sold or further processed.
The different properties of HDPE and LDPE can be distinguished by sight, touch, and sound. Due to its less branched molecular chains, HDPE is sturdier and more rigid than LDPE. This is why it was once referred to as "Hard-PE" and "Soft-PE."
An HDPE film feels sturdier and sounds crinkly, similar to paper, while an LDPE film feels softer, thicker, and doesn’t make a crinkling sound.
Thanks to its greater strength, HDPE films can be made as thin as about 5 µ (micrometers), where one µ equals a thousandth of a millimeter. In contrast, LDPE films are rarely produced at less than 12 µ. A 200 µ LDPE film remains relatively flexible, while a 200 µ HDPE film feels as rigid as a board.
Whether HDPE or LDPE films are used depends on the product being packaged and the customer’s preference. Consumers can identify the type of polyethylene by looking at the recycling symbol:
- 04 = LDPE
- 02 = HDPE
Both types are, and will always remain, polyethylene.
Yes, polyethylene film can be recycled, meaning that used film can be processed into "new" film. The used or "old" film is shredded into small pieces in a machine similar to an industrial shredder.
These particles are melted in an extruder (see the "From Polyethylene to Film" chapter) and produced into film once again. However, the molecular chains of the film (see "From Crude Oil to Polyethylene") get partially broken during the recycling process. As a result, recycled film has slightly lower strength properties compared to film made from pure, virgin material.
Before recycling, the used film is thoroughly washed, although some impurities (such as inks from printed materials) often remain. Since film production requires very high temperatures, bacteria or germs are eliminated, but the recycled film typically appears cloudier than film made from new material. Therefore, recycled film is often dyed and repurposed, commonly into blue or black trash bags, or used as covering or construction film.
The type of film—whether made from recycled or virgin materials—can also be identified by its smell. Film or bags made from new material have a faint odor reminiscent of an extinguished stearin candle, while film with recycled content has a scent similar to burnt rubber.
PE Foil
Question:
As you know, we use PE flat foil sheets as a separator layer for paving stone packages. Occasionally, less frequently sold items remain on our grounds for 1-2 years, exposed to weather. We’ve noticed that the film eventually disintegrates, quite literally blowing away and becoming an environmental burden. Can anything be done to prevent this?
Answer:
Polyethylene, along with other thermoplastics like polypropylene, belongs to the group of polyolefins. The basic unit of polyethylene, ethylene, is the simplest form of olefin:
H H
| |
C = C
| |
H H
During polymerization, ethylene molecules link up, forming long, chain-like macromolecules. The polyethylene molecules are branched, and the degree of branching and chain length significantly affect the properties of polyethylene.
Under exposure to oxygen and light, these molecular chains break down; the polyethylene decomposes back into its basic elements—water and carbon. While this process starts immediately, it usually takes about a year for visible degradation, depending on sunlight exposure. This characteristic is why polyethylene is considered environmentally friendly, as it leaves no residues, gases, or other harmful byproducts.
However, in your case, this degradation is undesirable. The situation is further complicated if recycled film is used. During recycling, the film is shredded, melted down, and re-extruded, which significantly shortens the molecular chains and reduces branching. Consequently, recycled film typically has lower mechanical strength.
Here are some potential improvement suggestions:
- Use transparent virgin material. Since the film is positioned between stones, it stays relatively dry and shaded, slowing down the degradation process. Only film sections that protrude from the stones or are exposed as cover sheets would be prone to disintegration.
- Use virgin material with UV protection. This option is pricier (a quote is attached) and would be applied uniformly across all products, including those with higher turnover.
- Cover less frequently sold items with a black protective cover. Black provides the best protection against light and UV exposure, though it comes with the drawback of obscuring the contents unless labeled.
Please discuss these suggestions with your team, and don’t hesitate to reach out if you have further questions.
Question:
We are looking for a clear, transparent polypropylene film, double-sided with "anti-fog" treatment, for manufacturing frozen food bags. Thickness 20-25 µ, roll length 2000-4000 meters, approximately 20-40 tons/month. Do you have a solution?
Answer:
The "anti-fog" coating is achieved by applying an antistatic agent. However, this additive may not fully comply with food safety regulations and is therefore controversial for use with food products. While the coating would be completely safe for packaging textiles (e.g., shirts), in this particular case, we must refrain from submitting a quote. We appreciate your understanding.
Question:
Dear Sirs/Madams, we are an event and outdoor agency currently designing a large maze made of wood and film. We are searching for a film that is highly tear-resistant, weatherproof, non-transparent, and approximately 250 cm wide. The length is still being calculated but will likely be around 2000 - 3000 meters. Could you assist us with this?
Answer:
We exclusively process environmentally friendly polyethylene (PE), which naturally degrades under exposure to light and oxygen, breaking down into its basic components, carbon and hydrogen.
However, by adding UV stabilizers during production, this degradation process can be delayed. Additionally, using a black-colored film further slows down decomposition and provides an opaque finish—though, of course, this depends on whether that fits your aesthetic requirements.
A thicker film will degrade more slowly and offer greater strength. We recommend a black-colored film (potentially also UV-stabilized) with a thickness of 250 - 300 µ (0.250 - 0.300 mm) for optimal durability and resistance.
Question:
Could you please send me all information on your aluminum composite bags (sizes, thickness, order quantities, specifications, and pricing)? Additionally, I need details on the material's water vapor permeability and whether it can be sealed with a heat sealer. Thank you in advance.
Answer:
Aluminum composite bags are produced from aluminum composite foil, available with or without a tear notch for easier opening.
An aluminum composite foil is constructed by laminating an aluminum layer with other types of film. Various layer structures and combinations are possible, and the aluminum layer ensures the film is water and water vapor-resistant.
These bags offer protection against corrosion, color changes, UV radiation, acids and bases, odors, and mechanical damage, making them suitable for long-term preservation.
The aluminum composite bags are heat-sealable and can also be closed with clips.
Additionally, they are solvent-free, providing an environmentally friendly option.
Question:
Is polyethylene environmentally hazardous during production, use, or disposal?
Answer:
Polyethylene is considered one of the most environmentally friendly materials from an ecological perspective:
- Efficient Resource Usage: Polyethylene production worldwide consumes less than 1% of the global oil and gas output annually.
- Clean and Efficient Production: The production process for polyethylene emits minimal pollutants and generates almost no waste.
- Highly Recyclable: As a thermoplastic, polyethylene can be melted down and reprocessed almost indefinitely. Today, recycled polyethylene is commonly used to make items like carrier bags and garbage bags.
- Energy Recovery: When collected post-use and not suitable for recycling, polyethylene can serve as a high-quality fuel source for energy generation.
Question:
A safety officer from a customer who uses shrink hoods called with a question from employees: "Is the inherent odor of the shrink hood or the smell that occurs when shrinking the pallet potentially harmful to health?"
Answer:
Dear Mr. S.,
Following our conversation earlier today, we would like to clarify the details regarding your query.
Polyethylene, like other thermoplastics such as polypropylene, is classified among the polyolefins. The building block of polyethylene is ethylene, the simplest olefin:
H H
| |
C = C
| |
H H
In the polymerization process, the ethylene molecules bond to form long, chain-like macromolecules with identical units. Think of polymerization as a sort of "cooking process" in a high-pressure cooker, where the C=C double bond is broken with heat and pressure, allowing the molecule to link with others. This process results in branched polyethylene molecules, with chain branching and length affecting polyethylene’s characteristics.
Under the influence of oxygen and light, these molecular chains can eventually degrade, breaking down into carbon and water molecules. This natural process is one reason polyethylene is considered environmentally friendly, as it leaves no residual gases or pollutants after decomposition, which typically becomes noticeable within about a year, depending on sun exposure.
Polyethylene is available as HDPE and LDPE (high and low-density variants), distinguishable by the recycling codes 2 and 4, respectively. The polyethylene granulate used for films is sourced from major chemical companies like BASF or Degussa-Hüls. This granulate is melted down in extruders (which function similarly to a large, heated meat grinder), then blown into film through a "bubble gum" technique, cooled, and rolled up for further processing into products like shrink hoods.
During the melting and blowing process, a faint smell reminiscent of a burning stearin candle may develop. You can replicate this by carefully igniting a small piece of the film and noting the smoke scent (exercise caution as melted polyethylene can cause severe burns). This odor disperses quickly and is entirely harmless to health.
The shrink hoods you use are packed immediately after production, so the odor does not have time to dissipate, explaining the scent upon unfolding or applying the hood. However, the odor fades rapidly and does not transfer to your packaged goods.
We trust this information meets your needs. Should you have further questions, please don’t hesitate to contact us. We are here to provide any additional information or assistance you may require.
Question:
As part of a project with a client, we are looking for a breathable film that also allows nitrogen diffusion. Could you please let us know the thickness of your films?
Answer:
Low-Density Polyethylene (LDPE) is, like all plastics, permeable to gases and vapors, a property that is particularly relevant for packaging materials. Instead of using the permeation coefficient PPP, the permeability qqq is generally given for films, without reducing the values to specific thickness units. Below is the permeability of a 100-micron thick LDPE film (density 0.918 g/cm³) for various gases and vapors at 23°C:
Gas or Vapor | Permeability (cm³/m² x day x bar, DIN 53 380) |
Nitrogen | 700 |
Oxygen | 2.000 |
Helium | 5.000 |
Hydrogen | 8.000 |
Carbon Dioxide | 10.000 |
Sulfur Dioxide | 40.000 |
Ethylene Oxide | 100.000 |
Methyl Bromide | 300.000 |
Water Vapor | 1g/m² x d (DIN 53122) |
The permeability depends on both the density and thickness of the film. We produce LDPE films starting from approximately 20 microns up to nearly 500 microns, and HDPE (density ~0.95 g/cm³) in thicknesses from 7 microns up to about 150 microns.
In addition to film thickness and density, factors such as the chemical nature of the contents, storage temperature, and storage duration also influence permeability.
Water-Soluble Foil
Question:
We are planning to use water-soluble films. How can these be sealed?
Answer:
Water-soluble films can be sealed using standard thermal sealing equipment. However, for certain types, it may be necessary to increase the sealing time and temperature. These settings often need to be determined and adjusted based on on-site testing and experience.
Question:
Dear Sir/Madam,
I work for a consulting firm in the Netherlands, and I've encountered an issue during a project. While laying a concrete floor, we found pieces of plastic film embedded in the concrete. It seems that the (water-soluble) bags used for the added color pigments did not fully dissolve. Have you come across this issue before, and if so, what could be the cause? According to the concrete supplier, the mixture was in the mixer for two hours. We suspect that the knots in the film bands used to tie the bags may not have dissolved...
Answer:
Dear Mr. ...,
The issue may have a few possible causes:
- As you correctly suspect, the knot may be too thick, causing the film to require more time to dissolve.
- It could be a compatibility issue; the product (concrete pigment) may have reacted chemically with the film, preventing it from dissolving fully or making hot water necessary for dissolution.
Please feel free to reach out if you have further questions.
Question:
Dear Sir/Madam,
We request your assistance in resolving a packaging issue. For a solid development product of our company, we are seeking a soluble film packaging solution. However, the dissolution should occur in an aqueous solution rather than pure water.
Thank you for your efforts.
Question:
Good day, Dr. ...,
Thank you for your inquiry. I will send you documents and samples of our water-soluble film by separate mail.
Please note that when using a water-soluble film (PVOH material), a preliminary product compatibility test is essential. There may be a reaction between the film and the product, which could prevent the film from dissolving. Additionally, the filling product should contain a maximum of 5% water; otherwise, the film will dissolve immediately.
We can arrange compatibility tests for you, and I will need a safety data sheet beforehand. This will help us select the appropriate film type from our extensive range.
We can produce both blown film and cast film. The production method influences the appearance and behavior of the film. It would be ideal to know beforehand which packaging machine will be used for processing the film, as this may affect the choice of material for optimal performance.
Please don’t hesitate to contact us with further details or questions.