Omar Khalid
Markings on plastic products can serve a variety of purposes, from identifying the type of plastic and its recyclability to indicating the manufacturing process and date. The interpretation of these marks depends on their format, which can vary from symbols and numbers to dials and diagrams. Standardized marking systems, such as ISO 11469:2016, have been established to ensure uniform labelling of plastic products by their material components. These markings are crucial for responsible waste management, influencing decisions regarding handling, waste recovery, and disposal. Additionally, markings can aid in product traceability, deterring tampering and counterfeiting by providing unique identifiers like barcodes or serial numbers. Understanding the meaning of marks on plastic products is essential for proper recycling, sustainability, and consumer confidence.
| Characteristics | Values |
|---|---|
| Purpose of marks on plastic | Identification and traceability |
| Permanent marking methods | Scribing, laser marking |
| Laser marking types | Green Laser (532 nm), Ultraviolet laser (375 nm), Vanadate lasers (1064 nm) |
| Laser marking advantages | Environmentally friendly, reduces production waste, no-contact (suitable for medical and food industries) |
| Burn marks | Defects in injection molding caused by machine, mold, or resin issues |
| Marking standards | ISO 11469:2016, Plastics – Generic identification and marking of plastics products |
| Marking symbols | Mobius Symbol with a number (1-7), PET or PETE (polyethylene terephthalate) |
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What You'll Learn
Plastic marking methods
Marking plastic materials can be challenging, especially when manufacturers use sticky paper labels, which can tear off, get dirty, or become unreadable. Permanent marking is the most desired option for manufacturers that plan to track or record information about a part.
One way to achieve permanent marking is to scribe the mark into the plastic. This mechanical process involves driving a scribing pin across the surface to engrave the mark without puncturing the plastic. The pressure applied by the pin determines the depth of the mark, and even very lightly scratched characters can be achieved. This method can work on various plastic applications, including ABS, Delrin, polypropylene, PVC, HDPE, and others.
Another permanent marking method is laser marking, which offers numerous benefits. Laser marking provides a durable and high-quality solution for product information, logos, or serial numbers. It is a cost-effective, precise, and versatile technique that can create high-contrast markings without damaging the material. Different types of lasers work better with different materials. For example, the Green Laser (532 nm) is suitable for PVC, ABS, and polystyrene, while the Ultraviolet laser (375 nm) is perfect for marking HDPE material commonly used in pill bottles and health and beauty containers.
Other printing methods for marking plastics include digital inkjet printing, UV Litho printing, and pad printing. Digital inkjet printing ensures high-quality images on various plastics but can be expensive due to the ink's evaporation. UV Litho printing produces high-definition and high-quality images in a wide range of colours but may be costly for short production runs due to the time-intensive setup. Pad printing, the simplest and most widely used method, involves etching an image onto a silicone plate, flooding it with ink, and then pressing it onto the plastic, leaving a 2D image.
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Tracking and identification
Marks on plastics can also help consumers confirm a product's authenticity, ensuring they are not purchasing a counterfeit. To achieve this level of security, the marking must be done directly onto the plastic material. Laser marking is an environmentally friendly option that produces high-quality, permanent marks.
Dial markings are another type of mark found on plastic products. These dials are built into the mould and can be rotated with a screwdriver. They typically indicate the month or year of production. By using a dial system, manufacturers can easily reset the date without replacing the mould, reducing expenses. Additionally, the dials can indicate the type of plastic used, such as "5" for polypropylene.
Standardization plays a crucial role in tracking and identification. ISO 11469:2016 provides a uniform system for labelling plastic products by their material components. This standard includes the marking of recyclates, with the abbreviation "(RECx)" indicating the specific amount of recyclate. The symbols and abbreviated terms for plastics and related materials are detailed in international standards.
The Universal Recycling Symbol, a triangle made of three arrows surrounding a number from 1 to 7, is commonly used for plastic identification. This symbol indicates the packaging material and whether it can be recycled to create new products. Different types of recycling processes exist, such as mechanical recycling, chemical recycling, and energy recovery, each with its own identification codes. These codes are essential for responsible waste management and disposal.
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Burn marks
To fix the issue of burn marks, it is crucial to identify the root cause, which can be tricky as there are many factors in the injection moulding process that can contribute to the problem. Common causes include issues with the machine hardware, such as gate sizing and nozzle size, or the moulding conditions, such as high injection speed or pressure. It is important to lower the pressure or speed and ensure proper gate and nozzle sizing to prevent burn marks.
If burn marks do occur, there are a few methods to remove or reduce their appearance. Firstly, it is important to determine the extent of the damage. If the burn mark is superficial, it may be possible to remove it by scrubbing the area with a soft cloth, liquid soap, and water. This can help remove any discolouration caused by the burn. If the burn mark is more severe, you may need to use sandpaper to carefully sand away the burnt plastic. In some cases, it may be necessary to cut out the burnt area with a razor if the burn is very deep. After removing the burnt plastic, the area may need to be filled with epoxy or another filler and then painted to match the surrounding surface.
To summarise, burn marks on plastic are typically caused by issues in the injection moulding process, resulting in degraded material and discolouration. While there are methods to remove or reduce the appearance of burn marks, it is essential to address the root cause and prevent them from occurring in the first place. Partnering with an experienced injection moulding company can help ensure the quality of the mould design and prevent defects.
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Plastic recycling symbols
The recycling symbol, known as the "chasing arrows" symbol, does not always indicate that the product is recyclable. Instead, the number inside the triangle helps identify the type of plastic used, which then helps determine the proper disposal or recycling method. These numbers are known as Resin Identification Codes.
- Symbol 1 (PETE/PETG): This stands for polyethylene terephthalate, which is easily recyclable and commonly used for soft drink bottles, water containers, and cooking oil containers.
- Symbol 2 (HDPE): This stands for high-density polyethylene, a commonly used plastic that is widely recycled. It is often used for containers like milk cartons and detergent bottles.
- Symbol 3 (PVC): This represents polyvinyl chloride, which is rarely recycled. It is often found in bubble foil and trays for sweets and fruit.
- Symbol 4 (LDPE): This stands for low-density polyethylene, which is also not commonly recycled. It is used for items like plastic bags, shopping bags, and wrapping.
- Symbol 5 (PP): This type of plastic is widely recycled and used for tubs and trays.
- Symbol 6 (PS): Plastic with this symbol is used for takeaway boxes and disposable cutlery and is not easily recyclable.
- Symbol 7 (Other plastics): This category includes plastics like acrylic and polycarbonate, which are not always recyclable but can be repurposed due to their thermoplastic properties.
It is important to note that not all packaging will have a recycling label, but that does not mean it cannot be recycled. Additionally, some packaging components need to be separated before disposal, as different parts may have different recyclability.
Apart from recycling symbols, other marks on plastic can include permanent markings for traceability and identification. These may include deterrence features, traceable identifiers like barcodes, and authentication identifiers to prevent tampering and counterfeiting. Laser marking is an environmentally friendly option for creating permanent marks on plastic.
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Injection moulding defects
Injection moulding is a common manufacturing process used to make components from metals, polymers, glasses, confections, and other materials. It is an efficient production method when high volumes of identical parts are needed. However, it requires a high degree of technical expertise to master. Injection moulding defects can reduce the cosmetic appeal and structural integrity of moulded parts. These defects can range from minor surface issues to more serious problems that affect safety, performance, and function.
Some of the most common injection moulding defects include flow lines, sink marks, weld lines or knit lines, jetting, and warping. Flow lines are off-color lines, streaks, or patterns on the surface of a part caused by the molten plastic moving at different speeds and solidifying at different rates. They can also occur when the mould has sections with different wall thicknesses. Sink marks appear as depressions or dents in thick sections of a part, indicating that the plastic needs more time to cool and cure. Weld lines or knit lines occur when two flows of molten resin meet and fail to properly bond, resulting in visible marks and reduced strength. Jetting happens when resin enters the mould too quickly and begins to cool before the cavity is filled, creating thin, squiggly lines on the surface. Warping is caused by rapid cooling or non-uniform mould design, leading to uneven stresses on the material.
To prevent these defects, manufacturers can adjust the moulding process by changing the flow rate, temperature, or pressure. For example, increasing the temperature of the molten resin and raising the injection speed and pressure can help prevent weld lines. Optimizing the gate's design and choosing lower-viscosity plastics can also reduce defects. Additionally, maintaining consistent wall thickness and ensuring proper rib thickness can minimize sink marks.
It is important to take a proactive approach to risk mitigation during product development to reduce the occurrence of injection moulding defects and maintain product quality.
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Frequently asked questions
Markings on plastic can refer to a few different things. Firstly, they could be related to the manufacturing process, indicating things like the date and time of production, the specific cavity within a mould that the part came from, or the type of plastic used. Secondly, markings on plastic products may be related to recycling. The Universal Recycling Symbol, for example, is a triangle made of three arrows surrounding a number from 1 to 7, indicating the type of plastic and its recyclability. Finally, some markings may be related to permanent marking methods used by manufacturers to track or record information, deter tampering, and prevent counterfeiting.
Different types of markings on plastic serve different purposes. For example, manufacturing markings help identify when and how a product was made, while recycling markings indicate the type of plastic and its recyclability. Permanent markings, on the other hand, are used for traceability, authentication, and deterring tampering and counterfeiting.
There are various methods for applying markings to plastic products. Traditional methods include using sticky paper labels, but these may not be durable or practical for certain applications. More permanent marking methods include laser marking, which is environmentally friendly and suitable for industries where avoiding contamination is crucial, such as the medical sector or food and beverage production.
