How to Print on Plastic Boxes: Tips and Advice

Durable, versatile, and affordable to produce, plastics have been a ubiquitous part of human life since gaining widespread use in the twentieth century. Now, everything from cups to bags to shoes is made with plastic, with product packaging being the most common use for this material. In fact, of the 82,000,000 tons of plastic produced in the U.S. in 2018, 14,500,000 tons were used to produce containers and packaging for long-term use. This designation excludes single-service containers (e.g., trash bags or grocery bags, which are considered to be “nondurable goods”) and focuses on product packaging like plastic storage containers, Tupperware, and plastic enclosures for things like internet modems, desktop computers, and outlet casings.

For personal care products or electrical components utilizing plastic containers, manufacturers are often required to print compliance codes with respect to federal regulations and industry/retailer standards. Common code requirements include expiration dates, lot codes/batch numbers, and barcodes. 

To ensure product traceability and to meet mandatory requirements, operations that handle these materials must have a complete understanding of how to print on plastic boxes and utilize the correct machines for the process. If your company falls into this category, here are some tips and advice for you. 

How to Print on Plastic Boxes with Opaque Surfaces

It’s important to note that there are many different types of plastics used for packaging. Depending on the type of plastic that you are planning to code, you need to use an ink/printer combination that will accommodate its specific needs. For instance, while the majority of plastics are considered non-porous substrates, some non-rigid plastics can absorb a certain amount of ink, leading to unclear markings and non-scannable barcodes. Accordingly, it’s essential to be well-informed on what plastics you are using so that you can use the right ink to code them. 

Some of the most common plastic varieties used for long-term packaging include:
 

• High-Density Polyethylene (HDPE): HDPE is the most widely used type of plastic in the world. It offers excellent resistance to strong solvents and smells, which is why it is frequently used to package personal cosmetics and cleaning products.
   
• Polypropylene (PP): Strong, chemical resistant, and offering a high melting point, this plastic is used to make products as diverse as automotive parts and bottle caps.
   
• High-Impact Polystyrene (HIPS): HIPS is produced by combining rubber with polystyrene (a general-purpose plastic often used in the foodservice industry). This mixture increases the durability of the polystyrene, making it one of the go-to materials for computer and television construction.
   
• Polyvinyl Chloride (PVC): Used to make pipes, electrical outlets, and countless household items, PVC is prized for its stable electrical properties, chemical resistance, and high durability. 

For these plastics and others, a continuous inkjet (CIJ) printer is the recommended coding option. Plastic substrates generally need to be coded with pigment-based or solvent-based inks to ensure long-lasting readability, and other inkjet printers are often incompatible with these ink varieties. By consulting with an ink expert, you can find a formula that will successfully code your plastic boxes and account for any additional elements, such as temperature. 

If you are wondering how to print on plastic boxes that are clear, you must also outfit your CIJ printer with the right product sensor/print trigger (photo eye) to recognize the container, which is what we will look at next. 

How to Print on Plastic Boxes with Transparent Surfaces

To be able to code transparent surfaces, CIJ printers need to be equipped with a product sensor that automatically detects when an item is passing by on the production line. As the product triggers the sensor, the CIJ prints the desired code on the product being detected. However, when attempting to code a transparent surface, not all product sensors will prove 100% effective. A good quality sensor that has a sensitivity adjustment can help get a reliable print signal such as a smart eye can be tuned to sense different color ranges.

For coding completely clear plastics, we recommend using photoelectric sensors, also known as photo-eyes. Photo-eyes detect a material’s distance, presence, or absence by emitting light to a receiver. When this light is interrupted, the printer knows to encode the substrate. 

Photo-eyes come in two varieties that work with clear containers:
 

• Through-Beam Sensor: The most widely used photo-eye, through-beam models emit light to a separate physical receiver. When any disruptions occur, printing is initiated.
   
• Retro-Reflective Sensors: Operating off the same idea as the through-beam sensor, retro-reflective sensors differ from through-beams in that the emitter and receiver are built into the sensor’s housing. Retro-reflective sensors emit the light to a reflector on the other side of the production line, which reflects the light back into the sensor’s receiver. When the beam is broken, printing is initiated. Compared to through-beam sensors, retro-reflective models are easier to install and are less critical of physical position. They can prove to be challenging with reflective substrates, but for many clear plastics, this will not be an issue. 

 For more information on which photo-eye will best meet your needs, contact our expert team. 

Need Guidance on Which Printer/Ink Combinations Will Work For You? 

Plastics are one of the most commonly used packaging materials today for good reason. Different varieties of plastic offer varying amounts of temperature-resistance, durability, and lightweight properties that make them perfect for specific purposes. However, this same variety requires that manufacturers be vigilant when coding their plastic products. The wrong ink can cause codes to become illegible over time, creating issues with traceability and retail operations. 

To ensure that your company is well-suited to code its product line, consult with the experts at InkJet, Inc. about what printer/ink combination is right for you. At InkJet, Inc., we have been involved with ink chemistry for nearly thirty years, and we’re ready to share our knowledge with you.

For more information on how to print on plastic boxes, or for any other questions related to printers or ink, contact InkJet, Inc. online or by phone at 1-(800) 280-3245. Our expert team is ready with answers.