FAQ-2
ANSWERS TO YOUR QUESTIONS
What Thickness Do I need?
The following examples refer to LDPE - Low Density Polyethylene- 25 microns - Magazines sent by post are in 25 micron LDPE bags.
- 36 microns - Minimum for AS 4736-2006 to be allowed as a reusable bag.
- 38 microns - General purpose stationary and light duty bags.
- 50 microns - Same thickness as a Glad Snap lock sandwich bags.
- 65 microns – Express Post and courier satchels.
- 75 microns - 25 L potting mix bag or component bag for mechanical fittings.
- 100 microns - Very heavy Duty Gardening Products.
- 150 microns – Special purpose extra heavy duty.
- 200 microns – Legal minimum thickness for Asbestos bags.
The following examples refer to LDPE - High Density Polyethylene
- 10 microns - Produce Bags on roll in supermarket.
- 15 microns - Typical normal duty carton liner.
- 15 microns - Good Quality singlet bags like supermarkets used to give away.
- 20 - 25 microns - Heavy duty singlet bags.
- 36 microns - Minimum for AS 4736-2006 to be allowed as a reusable bag.
Bottom Seal vs Side Seal
Plastic bags are made by either side sealing or bottom sealing. Side seal bags are slightly cheaper and are usual for small size bags bottom seal bags are typically larger or for heavy duty applications. If you are unsure what type of bag you need call us and we will be sure to be able to help you decide.Side Seal Bags
Side Seal bags are made using center fold film. The bag forming machine simultaneously cuts and seals the sides of the bag. Handles or air holes can be formed prior to the cutting and sealing operation, there are a number of variations on the side seal process.
Side sealing is used to make,
- press seal bags
- trade show bags
- small and medium general purpose bags
- bags with bottom gussets.
Side seal bags are not as strong as bottom seal bags but they are cheaper to produce. Side seal bags are still very strong but they are not suitable for applications such as potting mix, potato bags etc.
Bottom Seal bags
Bottom Seal bags are made using lay flat tube. The bag forming machine seals the bag and cuts the bag just below the seal. Handles or air holes can be formed prior to the cutting and sealing operation. Bottom sealed bags are only stronger than side seal bags when used for carrying materials that flow, IE grain, flour, sand, pebbles, asphalt. For a heavy rigid item (eg a small motor) side seall bags are just as strong.
Bottom seal bags are extremely strong – a 150 micron bag loaded with 25 kg of plastic granules can survive a fall from over 3 meters. This test was forced upon us one day when our forklift broke down.
Bottom seal bags are used for heavy duty applications such as.
- Potting mix and pebbles.
- Onions, potatoes and carrots.
- Food bags that require a water-tight seal.
- Bags with side gussets for increased volume.
We have over a thousand customers, chances are one of them has a similar application to yours - give us a call and we'll help you finalize your requirements.
Biodegradable Bags
Churchill and Coombes is committed to minimising our impact on the environment. We have recently licensed epi technology for producing biodegradable film www.epi-global.com. This technology ensures that when a bag is disposed of in land fill it will quicky degrade leaving no harmful residues.We can make almost any bag using biodegredation technology but minimum quantites apply for some products. If you would like to discuss this further please call or email us or follow the link to the epi website.
How Plastic is Made
What are Plastic Bags made from?
Plastic film is made from polyethylene. Polyethylene is a very simple molecule, a carbon chain forms the "backbone" and each carbon atom has two hydrogen atoms bonded to it.
The picture above shows a chain of 8 carbon atoms forming a polyethylene molecule. In reality polyethylene molecules have carbon backbones that are many thousands of atoms long.
High density polyethylene is comprised simply of long polyethylene molecules. Low density polyethylene has branches from the carbon backbone. These branches improve the toughness and tear-resistance, but reduce the tensile strength.
How is Plastic Made?
Plastics are made from hydrocarbons, as the name implies hydrocarbons are a category of molecules that are made from hydrogen and carbon. Hydrocarbons can be small molecules such as ethane (see picture below) or large molecules with carbon "back bones" or carbon rings. Hydrocarbons are naturally occurring in oil and gas deposits.
In Australia plastic is made from Natural Gas. Natural gas is mainly Methane (one carbon atom), with some ethane (two carbon atoms), a little less propane (three...) and butane (four...) etc.
The natural gas is "cracked" into ethylene by heating it to high temperatures.
Ethylene is converted into long polyethylene molecules by heating it in the presence of a catalyst. The polyethylene is pelletised and bagged.
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