August 17, 2021 

Digital Printing on Flexible Film: Choosing the Best Variable Data Printer

Colorful film is often used for digital printing on flexible film.

Flexible film is the key component of the rapidly growing flexible packaging market. Particularly popular in food production, flexible film is used to provide tamper resistance, protect the product against harmful environmental factors (e.g. light, moisture, air, etc.), and better preserve freshness. The most common flexible film applications include:

  • Prepared food items such as baked goods and other snacks.
  • Poultry, beef, and other meats.
  • Microwavable frozen food bags.
  • Cosmetic products.
  • Medical instruments.
  • Pharmaceuticals.

In each one of these applications, the manufacturer is responsible for marking their flexible film with a variety of codes at the behest of either supply chain partners, the government, or both. Food producers, for example, must mark their goods with expiration dates, lot numbers, barcodes, and more to align with traceability standards to protect the consumer and avoid fines. The medical industry as well requires that all instruments and drugs carry similar markings for quality assurance and reporting purposes. 

Given that required markings like expiration dates and lot numbers are constantly changing on a batch-by-batch basis, companies need to use marking equipment that:

  1. Enables users to easily update labels to reflect accurate dates and lot numbers.
  2. Is compatible with the flexible film substrate.
  3. Can maintain a marking speed that meets operational needs.

Fortunately, digital printing technologies like continuous inkjet (CIJ) printers, thermal inkjet (TIJ) printers, and thermal transfer overprinters (TTO) can fulfill each of these duties. However, the coding market is filled with countless printers, leading many companies to wonder how they can find equipment that’s right for them. 

For those new to digital printing on flexible film, here's what to ask yourself when looking for hardware.

What Marks Need to Be Made?

Flexible film is used across a variety of industries for different purposes. Accordingly, businesses that use flexible film do not all have the same marking needs. For example, a meat producer that uses flexible film to package its poultry products may need to use digital printing to place an expiration date and lot number on each unit. Meanwhile, in the consumer goods sector, manufacturers don’t often have to place expiration dates on their products. However, they are often required to place barcodes on their packaging. 

For text codes like expiration dates and lot codes to work as intended, they simply must be legible to the human eye. However, more companies, especially those in the life sciences, are employing machine vision in their operations to validate lot and date codes, so this may require higher resolution marks. In all cases, markings like barcodes and data matrices must be clear and sharp enough for a scanner to read them. This requires a higher level of contrast than simple text codes. If the codes are not machine-scannable, it can lead to major supply chain problems and possibly result in fines for the manufacturer. 

Consequently, users must understand which codes they are going to be digital printing on flexible film to determine what code resolution they require. Generally speaking, experts suggest that barcodes be printed at 200 DPI to ensure scannability—any lower than that and companies risk having scannability issues. 

Here is a breakdown of the maximum DPI resolutions that CIJ, TIJ, and TTO machines are capable of:

  • Continuous inkjet printers: 60-180 DPI
  • Thermal inkjet printers: 300-600 DPI
  • Thermal transfer overprinters: 300 DPI

Accordingly, CIJ printers are great for text coding, whereas TIJ and TTO are better suited for applying high-resolution barcodes and other images.

What Material Is the Flexible Film Made Of?

Although flexible film is almost always made of plastic, there are many different types of plastic used to make flexible films. These plastics all feature slightly different material properties that affect how well ink adheres to their surfaces. The most common plastics used to make flexible films include:

  • Polyolefin (POF)
  • Polyethylene (PET)
  • Linear Low-Density Polyethylene (LLDPE)
  • Low-Density Polyethylene (LDPE)
  • High-Density Polyethylene (HDPE)
  • Polypropylene (PP)
  • Polyvinyl Chloride (PVC)

For thermal transfer overprinters, this substrate variation requires the flexible substrate to be tested with various ribbons to ensure compatibility, as thermal ribbons are compatible with plastics at large. For CIJ and TIJ printers, it’s also important to use ink formulas that are explicitly compatible with the films that you will be printing on. TIJ users in particular need to be diligent about this, as not all TIJ printers are compatible with solvent-based inks (i.e. the type of ink most commonly used for plastic applications to meet dry time requirements).

What Speed Will You Be Digital Printing on Flexible Film?

Just as different printer types have distinct resolution capabilities, they also widely differ in maximum coding speed. CIJ printers offer the fastest speeds, as most models can print above 300 meters per minute, with certain machines (e.g. the Koening & Bauer alphaJET 5 HS-M) reaching levels around 700 meters per minute. TIJ printers have lower maximum speeds, with most models capable of coding materials moving at around 120 meters per minute. Thermal transfer overprinters are the slowest option, as their operating mechanism restricts them to coding substrates at speeds around 60-80 meters per minute. 

To make the most of your uptime and meet output requirements, it’s essential to have a comprehensive understanding of your line speeds and find a printer that meets them.

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C&M Digest Team

The C&M Digest Team is composed of experts from across the coding and marking world. Comprised of ink developers, hardware veterans, and engineers, our News Team delivers informed coverage that is always free from brand bias.

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