Characteristics of the Various Types of Plastics
written by: Rolf Hansen
Consumers have a way of identifying the type of plastic used to make numerous products, especially containers for food storage and packaging. Most of such plastic products, but not all of them, have a number molded, imprinted or formed on the container known as the resin identification code.
This coding system was developed by the Society of the Plastics Industry based in the United States back in 1988 to enable recycling of post-consumer plastics. For plastics companies, it is voluntary but is now relatively standard on particular products sold across the world. By having knowledge of a particular product’s code, a consumer can find out characteristics of the plastic and the risks of using it. Below is a brief description of some of the plastic resin codes.
Abbreviated as PETE or PET, this type of plastic is used in juice, soft drink, water, mouthwash, beer, peanut butter, detergent, salad dressing, cleaner and detergent contained. It is capable of leaching antimony trioxide, and the longer a liquid is left inside such a container, the greater the risk of the antimony being released into the liquid. However, it is considered a comparatively safe plastic.
High Density Polyethylene
This plastic is abbreviated as HDPE and is used opaque water, milk and juice containers as well as detergent, bleach, and shampoo bottles, together with garbage bags, margarine and yogurt tubs, and also cereal box liners. It is considered a safer plastic.
Low Density Polyethylene
Abbreviated as LDPE, it is used in dry cleaning, grocery store, frozen food and bread bags, as well as most squeezable bottles such as mustard and honey, and plastic wraps. It is also one of the plastics considered safe.
The plastic is used in egg cartons, Styrofoam containers, disposable bowls and cups, as well as plastic cutlery, take-away food containers and compact disc cases.
Know your plastics.
We have added five new 300 ton electric injection molding presses.
SE280HDZ — 308 US tons, injection weight (GPPS) range 17-42.4 oz (481-1200 grams)
Electric presses are quiet and very efficient.
SE-HDZ benefit is increased injection capacity for
large parts. On the SE280HDZ, for example, the injection
capacity ranges up to 76.1 in
Plastic Rapid Prototyping
Rapid prototyping has come a long way from its inception in the 1980s. Once limited to scale models and prototype parts, this technology is now utilized to manufacture production quality components and by artists for complex shapes. The process involves slicing an intricate three dimensional CAD model STL file into thin virtual horizontal cross sections, which are then “printed” in real space using a liquid, powder, or sheet material. This method of adding layers one on top of the other is additive fabrication – obviously advantageous for producing any shape or contour. Some of the freeform techniques actually employ two materials: the part material and a support material that is used to prop any overhanging features. The secondary material can then be removed via heating or dissolution.
The popularity of rapid prototyping for producing small quantities of production parts has led to the growth of multiple competing technologies. All of them are additive fabrication, but they differ in the materials used and methods for building layers. The most common methods are melted material layers, laying liquid layers to be cured, or lamination processes.
Rapid Prototyping Plastic Parts
|Selective laser sintering (SLS)||Thermoplastics, metal powders|
|Fused deposition modeling (FDM)||Thermoplastics, eutectic metals|
|Laminated object manufacturing (LOM)||Paper|
|Electron beam melting (EBM)||Titanium alloys|
|3D Printing (3DP)||Various materials
Since the 1930s, savvy manufacturers and designers have been driving a technical explosion in plastics, and today there are over 30 product families and literally thousands of individual grades, from the familiar to the exotic. Much of this growth has come with the large-scale switch from metal to plastics, and with good reason.
Almost unlimited design freedom
Welcoming, user-friendly colors and surfaces
Inherent rust and corrosion resistance
Electrical and thermal insulation at no extra cost
Functional additives such as biocides, odorants, and lubricants are easily “built in”
Electrical and thermal conductivity can be precisely tailored to the application
Many products can be manufactured in a single step
Easy, low-cost assembly and fabrication
But switching from metal to plastic should be done with care. With all its advantages, plastic may not be the best choice.
Metal is stiffer at equivalent thickness
Metal is naturally conductive, both electrically and thermally
Metal provides inherent radio and magnetic shielding
- Metal provides low-cost resistance to high temperatures
What this all means is that switching from metal to plastic should start with an in-depth analysis of what the product is designed to do. Simply replacing a metal part with an identical plastic part fails to take advantage of plastic’s enormous versatility. Think in terms of possibilities. Ask the right questions. Measure the costs and benefits. Chances are, you’ll make the switch.
Demand for Pittsfield Plastics’ custom molding services, particularly for its large press capabilities (500 ton and 700 ton), is growing. President/CEO Tom Walker said improvements in the residential and commercial building markets (for products such as electrical and communications wire and cable) and for the medical device market (custom plastic parts) account for some of the increase.
Pittsfield Plastics underwent a major plant upgrade recently. A shiny new floor, which involved grinding the old floor down until they got to the base level, then adding a glossy new protective coating, contributed to a cleaner, more efficient and even safer plant. The walls also got a new coat of paint.
Pittsfield Plastics added a robot to pick “runners” out of the production line on a 300-ton injection molding press. The robot picks parts out of the line, supporting manufacturing employees as they meet customer demand and ship product out on time every time. The company eventually plans to add larger robots that will pull parts off the press and stack them on pallets and will steadily add more robots to its production process to help employees and facilitate continued sales growth.
Pittsfield Plastics’ slicer got an upgrade so it can cut larger barrel sizes many customers want: it can now cut up to an 8″ inside diameter barrel. Call to learn more — 413-442-0067.
A Plastics Technology editor recently visited the company’s headquarters to learn more about us. Now, we are grateful to be on the cover of Plastics Technology magazine. The article discusses our history and foray into extrusion. There are also quite a few great photos.