PET Article
Please see extrusion process notes below. (Taken from Visipak Website)
“Extrusion is the process of pushing hot material through a form or die creating a continuous profile such as a tube. The hollow section of a tube is usually extruded by placing a pin or mandrel inside of the die and in most cases positive pressure is applied to the internal cavities through the pin. The new product requires cooling and this is achieved using a water bath. The water bath is in a vacuumed controlled environment to keep the tube from collapsing. Common tube shapes are round, square and triangular, but can be almost any shape as long as it is continuous. Various materials can be extruded. Raw material used to produce our clear tubes are typically PETG, PET, or propionate.”
Main problem is the temp difference that the PET material has to run at. Approx. 500°F (260°C) Up from to 400 to 425°F (205 to 218°C)
Doesn’t sound a lot but when you have to balance 6 or 7 heat exchangers and the head temperatures each with they own adjustable temp.
The speed of the injection screw is also tricky to balance along with the temps. Resulting in a tendency to easily overheat!
Then you add the water flow and vacuum chamber to the the mix and have yourself a challenging time of it!
The notes below are taken from info found on various websites, I would suggest not using the info word for word!!
- What is PET?
Polyethylene Terephthalate is durable and strong material that becomes ideal for packaging applications, especially bottles. When we mention Pet, we complete the word “bottles” automatically.
As a material, it is known for its transparency, chemical resistance, and high strength.
These unique properties make “PET” the most common plastic material in the world.
Usages
- Plastic Bottles
- Mineral water
- Carbonated soft drinks
- Tape applications
- Thermoforming sheets
- Food packaging
- Cosmetic applications
- Electronics
2- What is PETG?
Have you ever wondered about this extra letter “G”? How can this letter be a factor to choose from the two options?
This “G” stands for “GLYCOL.” It becomes a different material with different usage. It becomes a thermoplastic polyester that provides high chemical resistance and formability during manufacturing processes.
Glycol prevents most PET problems such as cloudiness, fragility, and overheating. The chemical resistance and the absence of odours makes PETG the best for 3D printers.
This amazing copolymer combines the properties of glycol and PET. This will reduce the overheating issues that face manufacturers with PET.
Usages
- Medical applications packaging
- Beverage containers for cooking oils, drinking water and soda
- Mall Displays and stands because of its easy colouring
- Machines protection covers
Both materials are transparent. PETG is slightly opaque while PET is more transparent. This makes PET perfect for packaging as transparency is necessary.
Recycling PET vs PETG
Even though PETG and PET are chemically very similar, PETG is excluded from being recycled by most programs.
In fact, PETG is a pesky contaminant during the recycling of PET because their chemical similarity makes them difficult to distinguish and separate
Sustainability is the fundamental difference between these products. Whilst PETG can be said to be “almost unbreakable, affordable and durable”, it actually falls into resin identification code 07 (mixed/other recycling) due to the processing requiring much higher temperatures than standard PET (PETE). This means that although it is recyclable, it is not widely recycled, therefore it is likely to end up at incineration or landfill.
Contrary to this, PET (resin identification code 01) is widely recycled in the UK through household recycling streams.
