Supporting a Circular Economy by Facilitating Sorting Operations Through New Technology
Raman Spectroscopy Technology for Sorting Black Plastic Pieces
Black-colored plastic is used in many items around us including home electronics and automobile upholstery. Unfortunately, however, it has been difficult to identify the material type of black plastic at recycling centers. To address this issue, Canon has developed an accurate plastic sorting technology that can handle black plastic pieces and those in other colors simultaneously. The new technology will help to maximize the volume of recycled plastic by making sorting more efficient.
“Raman” is an unfamiliar word to many. About 100 years ago, Sir Chandrasekhar Raman, an Indian physicist, discovered that when he shone light on a substance, the type of light bouncing back from the substance was different from the original. This discovery won him the 1930 Nobel Prize in physics. The phenomenon was named “Raman scattering” in his honor, and has since become an essential method for material composition analysis in both the research and manufacturing fields.
Plastics Require Advanced Sorting Methods
Currently, only a small part of the plastic waste in our daily lives is recycled as materials. The rest is simply incinerated and only used as a thermal energy source. In order to obtain plastics with the purity required for material recycling, plastic waste must be sorted by material type, such as ABS* and polypropylene (PP).
The existing dominant method for sorting plastic applies near-infrared spectroscopy, which involves shining an infrared ray invisible to human eyes—the same as that used in television remote controls—on the plastics and sorting them depending on how much light they absorb. While this method can identify and differentiate light-colored plastic pieces, it cannot identify black plastic pieces. Black plastics often used in home electronics and automobile upholstery and other items do not reflect incoming light, absorbing most of it instead. Therefore, that method cannot be easily applied to black plastic.
* A plastic made from acrylonitrile (A), butadiene (B), and styrene (S). It is notable for high heat and impact tolerance.
Technology that Supports a Circular Economy
Canon focused its attention on these un-recycled black plastic pieces. It explored the idea of sorting them by shining a strong laser light onto the plastic pieces to detect two different types of light: Raman scattering and another form of scattered light. Canon thought that detecting Raman scattering through this method might enable the sorting of black plastic pieces.
However, Raman scattering takes certain amount of time to measure accurately as it is emitted in extremely small amounts. Canon found the solution for this problem by combining Raman spectroscopy, which captures and analyzes Raman scattering, with its proprietary measurement and control devices.
The interior of a plastic sorter that uses Tracking Raman spectroscopy
The plastic sorting technology that Canon developed uses Tracking Raman spectroscopy, and sorts plastics in three steps: detection, identification, and sorting.
Step 1: Detection
Mixture of plastic pieces of different types are fed into the sorter. A camera captures the color and position of each plastic piece traveling through the machine on the conveyor belt.
Canon’s Non-Contact Displacement Sensor (①) takes a highly precise measurement of the distance each plastic piece travels on the conveyor belt. These measurements/information on the position of each plastic piece is used to determine the exact positions for emitting the laser light onto the plastic pieces. An image recognition system (②) is then used to determine the position, color, and size of each plastic piece.
Non-Contact Displacement Sensor (PD series) that measures conveyor belt speed
Step 2: Identification
A laser light is emitted onto each plastic piece on the conveyor belt based on its position, color, and size. Each plastic piece transported on the rapidly moving conveyor belt is tracked by one of the 10 units* of Canon’s galvano scanner motors arranged in a line across the conveyor belt to emit laser light onto a target position (➂).
* Equipped to plastic sorter TR-S1510
A Canon galvano scanner motor ("GM Series")
Light-colored plastic pieces require a shorter laser exposure time for measurement, whereas black plastic pieces require longer time due to the weaker Raman scattering from them. Both black and light-colored plastics are analyzed at the same time, with the duration of laser emission adjusted according to the color of the plastic.
Exposure to the laser light causes Raman scattering to be emitted from the surface of the plastic piece. The Raman scattered light indicates the properties of each type of plastic, which are then measured by Canon’s proprietary light spectrum unit (④). The data is analyzed by a special recognition software developed by Canon which identifies types of plastic in an instant.
Diagram of light spectrum unit
Step 3: Sorting
The identified plastics are separated by air jets, and the pieces that can be recycled are collected separately from the rest.
Advanced sorting of plastics is performed in these three processes, thereby helping to maximize the volume of reusable plastics.
Resolving a Demand-Supply Mismatch
One complaint from product and parts manufacturers is that the supply of recycled plastics with sufficient quality falls short of what they need. At the same time, recycling plants have their own issues. Many of the collected plastics are dark, including black pieces, and the proportion of light-colored plastics, which are easy to sort, is small, making it difficult to secure sufficient quantities. Furthermore, increasing the sorting accuracy in order to improve the quality of the plastics raises the cost.
The Raman Plastic sorter "TR-S1510" operated by Re-Tem Corporation, a resource recycling company.
Canon’s Raman spectroscopy-based plastic sorting technology resolves this mismatch. Canon started taking orders for the machines in June 2024. These machines enable recyclable black and light-colored plastic pieces to be sorted for collection at the same time, reducing recycling costs and eliminating the demand-supply gap between plastic users and plastic recycling businesses.
Canon will continue to contribute to building a circular economy through activities that reduce the burden on the environment and provide products and services that enrich people’s lives.
