Omar Khalid
Plastic products often have cryptic symbols and dials on them, which can be confusing to consumers. These dials are called indicators or inserts and are used in injection moulding plastics to help manufacturers identify when and how a finished part was manufactured. The dials can also indicate the type of plastic, with recycling symbols and numbers in the centre of the symbol to help consumers identify how to recycle their plastic waste. These dials can also be mould numbers, which help the quality department at the factory to quickly identify which mould may need maintenance.
| Characteristics | Values |
|---|---|
| Purpose | To help the manufacturer identify how a finished part was manufactured |
| Clock-like symbols | Could indicate the mold used to form the part |
| Mold number | Could be the last dial or the bottom dial |
| Date-related information | Could indicate the year, month, and week of manufacture |
| Material source identifier | Could indicate the manufacturer of the injection molding pellets |
| Recycling symbol | Indicates the type of plastic and its recyclability |
| Resin identification code | Developed by the Society of the Plastics Industry to identify the materials/chemicals in each plastic item, its biodegradability, and potential toxicity |
| Example resin codes | PETE or PET (1), HDPE (2), PVC (3), LDPE (4), PP (5) |
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What You'll Learn
Date and time stamps
The dials on plastic items are date stamps, which indicate when the item was manufactured. The dials are usually marked with numbers and arranged in a circular pattern, resembling a clock.
The date stamps are used for traceability and quality control. The upper dial typically represents the year, the middle dial the month, and the bottom dial could be a mould identifier, shift indicator, or lot number. These dials allow manufacturers to identify and address any issues with specific batches.
Date stamps are commonly found on plastic items, including food storage containers, toys, automotive parts, and plastic cups. They help manufacturers track down defects and ensure product safety and freshness, especially for items like grocery products with expiration dates.
The dials can also indicate the type of plastic material used, which is important for recycling purposes. Additionally, they can be used to identify the mould or machine that was used to make the item, aiding in maintenance and quality control.
The specific format of the date and time stamps may vary depending on the manufacturer and the type of plastic item. Some dials may use a combination of numbers and arrows to indicate the date, while others might have different clock positions to represent the manufacturing date, lot number, or shift information.
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Lot numbers
The dials on plastics with arrows and numbers are called "indicators" or "inserts". They are used in injection moulding to help the manufacturer identify how a finished part was manufactured. These dials are usually found on plastic toys and containers.
The dials can be rotated with a screwdriver and usually have clear month or year numbers. They are part of the mould and are used to track down defects, understand how much inventory needs extra screening, and identify the mould or machine the piece was made on.
The upper dial typically indicates the year, the middle one the month, and the bottom one could be a mould identifier or a shift indicator. The bottom dial could also indicate the time and/or date that the item was manufactured.
In some cases, the last dial is a material source identifier, indicating which company's resin was used, allowing for the tracing of quality issues to a specific date and material source.
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Resin identification codes
The Resin Identification Code (RIC) is a technical standard that uses a set of symbols to identify the type of plastic resin used in a product. The code was developed in 1988 by the Society of the Plastics Industry (SPI) (now the Plastics Industry Association) in the United States. The SPI introduced the system as the "Voluntary Plastic Container Coding System", with the purpose of providing "a consistent national system to facilitate recycling of post-consumer plastics". Since 2008, the RIC system has been administered by ASTM International, an international standards organisation.
The RIC consists of an equilateral triangle, a Resin Identification Number, and an Abbreviated Term for polymeric material. The numbers 1-7 indicate the different types of plastic resins:
- Poly(ethylene terephthalate)
- High-density polyethylene
- Poly(vinyl chloride)
- Low-density polyethylene
- Polypropylene
- Polystyrene
- Other resins
The RIC is often mistaken for a recycling symbol due to their resemblance, and this has led to consumer confusion about which plastic products can be recycled. It is important to note that Resin Identification Codes are not 'recycle codes' and do not imply that an article is recycled or that systems are in place to process it for reclamation or reuse. Instead, they are used solely to identify the plastic resin used in a manufactured article.
The RIC has undergone revisions, and the current standard, as per ASTM D7611, features an equilateral triangle instead of the previous "chasing arrows" to distinguish it from the recycling symbol.
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Material source identifiers
Plastic products often have cryptic symbols on them, such as dials with arrows, which can be used to identify the type of plastic and how it can be recycled. These dials are known as indicators or inserts and are used in injection moulding to help manufacturers trace quality issues back to the date and material source. The last dial on a plastic product is often the material source identifier.
The dials indicate the type of plastic, with each plastic type having a unique number or code. For example, PETE or PET (coded as 1) is used in the production of plastic water and soft drink bottles, salad dressing containers, and plastic peanut butter jars. This type of plastic can be recycled into fibre fill for sleeping bags, carpet fibres, and rope.
HDPE (coded as 2) is a slightly denser plastic used in milk and juice bottles, shampoo, and shopping bags. When recycled, these products are often turned into laundry detergent bottles, pens, drainage pipes, benches, and fences.
PVC (coded as 3) is used in sewage pipes and synthetic window frames. While some PVC products like raincoats and aprons can be recycled, other single-use products like food wrap and plastic utensils are notoriously difficult to recycle.
LDPE (coded as 4) is used in soft plastics such as cling film, plastic dry cleaner covers, and carry bags.
PP (coded as 5) is used in plastic furniture, jerry cans, car parts, and bottle tops.
Polystyrene (coded as 6) and polyurethane and polycarbonate (both falling under code 7) are mentioned as the most problematic plastics to recycle.
These dials and codes allow consumers to identify the type of plastic they are dealing with and determine how it can be recycled or disposed of responsibly.
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Mould numbers
Additionally, the last dial may indicate the material source identifier. Different manufacturers of comparable quality are assigned numbers, so it is possible to trace quality issues to a specific date and material source.
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Frequently asked questions
The dials on plastic containers indicate the type of plastic and can be used to identify how to recycle the product. The numbers refer to resin identification codes, which show what materials/chemicals are in each plastic item, how biodegradable it is, and the level of toxicity.
Clock-like symbols on plastic containers indicate the date and month of manufacture. The dials with arrows, known as indicators or inserts, are used in injection moulding plastics to help manufacturers identify how a finished part was manufactured.
The recycling symbol with an encircled number in the centre indicates the resin identification code. For example, PETE or PET (number 1) is used in the production of plastic water and soft drink bottles, salad dressing containers, and plastic peanut butter jars.
