A plastic product can be very durable and resist unbelievable pressures. Plastics are used for everything, even rocket and aircraft design. That is a far leap forward from the humble plastic container sitting in your kitchen. If the intimation isn’t obvious, there are many types of plastic.
Naturally that means you have a lot of choice to consider when choosing the resin for your plastic product. Resin designates the types of plastic, which vary tremendously thanks to many breakthroughs in resin sciences. As mentioned earlier, you can use plastic (at least in part) to get to the Moon. Your products may not need to go that far, but the wrong plastic can result in it not going anywhere at all.
So how can you choose the correct resin? Here is a process to follow:
1. Define the Purpose
What will your part need to do? What are the challenges it will face? How long should it be able to do its job? These are some of the questions you should start with, as they will help identify characteristics you will want in your plastic choice.
For example, will your part need to be rigid or flexible? Should it be non-toxic? Are there any standards or regulations you must comply with? Do you need it in certain colours? Will it be exposed to certain chemicals? Will it need to be embossed?
Pay attention to every design requirement, even the texture. Those will guide your resin choice.
2. Know the resin family
There are two types of plastics, generally speaking: thermoset plastics and thermoplastics. Their names identify the difference:
Thermoset plastics are set in heat. They are essentially baked, which makes them incredibly durable but also nearly impossible to recycle. If your product has to endure high amounts of heat, this resin family should be your choice.
But most plastic applications use thermoplastics. These types of resins are melted, then retain a shape once they cool. Plastic injection molding uses this family of resin. It should be mentioned that thermoplastics can resist heat if they are designed to do so. But typically these resins will eventually melt under high-enough temperatures.
3. Understand the resin types
Both thermoplastics and thermoset plastics can be split into three types, which relate a lot to what your parts will do and how much you spend on the quality of resin. Those three types are commodity resins, engineering resins, and specialty or high-performance resins.
Now, commodity resins are not poor or bad resins. They simply just aren’t as resilient as the other two classes. Likewise, engineering resins are tough, but nowhere close to high-performance resins. Remember that trip to the moon? Well, you won’t be doing it using the first two types.
Commodity resins are for high volumes and low costs. Plastic bags, toys, device knobs and such are typical examples. Engineering resins have higher mechanical and thermal properties, and are often used to create resilient housings and industrial parts. High-performance resins are really tough and lightweight, which is why they are most common in the aerospace industry. They are also considerably more expensive.
Derived from the word metamorphosis, to morph is the ability to change. Considering that elasticity is a property of plastics that can be very useful or very disruptive, it’s worth knowing something about resin morphology.
Two classes define how flexible plastics are: amorphous and semi-crystalline. Amorphous resins shrink less when cooled and offer better transparency. But they can be more brittle and less resistant to chemicals. Semi-crystalline shrinks more and are opaque. But they aren’t as brittle and perform much better with chemicals.
Now you know enough to start asking the right questions for your resin. There is one more area to this: additives. The properties of a resin can be altered by adding other materials to it. But additives deserve an entire post, which we will visit soon.
In the meantime, remember that not all plastics are alike! Choosing the best resin is as important as proper design. In fact, resin is part of the design process. So don’t neglect your options, or your entire part might be a total disaster. Pay attention to resin and you will ensure your material quality will last for the ages.