How a thermal inkjet printer puts a code on a pack

In a thermal inkjet, each nozzle contains a tiny heater that warms the ink until a bubble forms and ejects a droplet. The nozzles are part of the ink cartridge, so every new cartridge provides fresh nozzles. The cartridge is positioned 1–2 mm from the surface on the GT-100E and 1–5 mm on the ST-210S models, and the droplets form the text, barcode or logo as the pack moves past.

The code is created as the print head and the surface move relative to each other. On a conveyor, the print head remains stationary while the pack passes at a fixed distance. With the GT-100E in handheld mode, you hold the printer flat against the box, pipe or part and move it across the surface. The print builds up column by column; the GT-100E’s built-in encoder measures the movement, so the speed does not need to be exact, but the printer must stay flat on the surface.

The gap between the cartridge and the surface is important, as the ink droplets travel through the air. If the gap is too wide, the droplets spread and the code edges become blurred. On a line, guide plates keep each pack 1–5 mm from the nozzle. If a box moves away from the guide or the surface is uneven, the code may appear faint or incomplete. In handheld use, the printer must remain flat on the surface throughout the print to maintain the 1–2 mm gap.

Without an encoder, the printer relies on a fixed line speed set on its screen. If the conveyor slows or stops, the code may stretch or compress, making barcodes unreadable. An encoder measures the actual movement of the goods, ensuring the code remains the correct size even if the speed varies. For items moved by hand or lines that stop and start, an encoder is essential to keep every code accurate.

A photo eye is installed before the print head to signal when a pack is approaching. A delay set on the printer determines how far from the leading edge of the pack the code begins. If two packs touch as they pass the photo eye, the printer treats them as one long pack and prints only one code. Each pack must have a clear gap before and after it.

On the ST-210S models, inputs allow you to reverse or invert the print, so the code is readable if the head is mounted on the opposite side of the line or if the line runs in reverse. When printing on film or metal, the fresh code needs a short time to dry, so nothing should touch it immediately after printing.

Choosing a handheld inkjet printer or a fixed model

The GT-100E is a handheld inkjet printer with a battery, suitable for manually marking boxes, pipes or parts. It can also be mounted on a line for automatic operation. The ST-210S-H1 and ST-210S-H2 are fixed to the conveyor, with one or two print heads and a separate controller.

The GT-100E features a 5-inch touchscreen and operates on battery power, while the fixed models have a 7-inch screen, a network port, and additional input and output options. The ST-210S-H2 has two heads, allowing for prints up to 25.4 mm high in one block or marking two sides at once. As a carton printer on a packing line, a fixed model marks every box as it passes, with no need for manual handling.

A handheld printer such as the GT-100E is ideal where goods are not moved on a conveyor. For example, large pipes, metal profiles or panels stored on racks can be marked while stationary. Boxes already stacked on a pallet or stored on the floor can be coded without transferring them to a line. The printer is brought to each item, so there is no need for a conveyor or a fixed coding station.

Handheld use is also suitable for small batches or when many different products are coded in a single day. You enter the text on the screen, print the code on the product, and move to the next. There is no need to set up a line or adjust guides. One printer can serve several work areas, such as goods in and dispatch, by moving it as required.

When using the GT-100E by hand, keep it flat against the surface and move it steadily in one stroke, maintaining a 1–2 mm gap. On a pipe, move the printer along its length to keep the distance constant. If the printer tilts or lifts, the code may become slanted or incomplete.

A fixed printer such as the ST-210S-H1 or ST-210S-H2 is used when every pack passes the same point on a conveyor. The code is applied in the same position on each pack and no manual handling is needed. The ST-210S models can receive data from your system via the network port, so text entry on the screen is not required.

The GT-100E can also be mounted on a line with an external photo eye and encoder, making it suitable for a small line or one under construction. Compared to the ST-210S models, it does not offer 600 DPI, a network port, a 7-inch screen or a second print head. The GT-100E’s removable battery allows you to swap in a charged spare during a shift.

The key considerations are whether your goods are moving on a conveyor or stationary, the number of packs to be coded each day, if the code changes from pack to pack and where its data is sourced, and whether you require the code in one or two locations.

GT-100E, ST-210S-H1 and ST-210S-H2: main distinctions

The table below sets out a comparison of the three thermal inkjet printers: GT-100E, ST-210S-H1 and ST-210S-H2. It details the type and number of print heads, print height, resolution, speed, printing distance, screen, data connections, power supply, cartridge, dimensions and warranty.

When reviewing the comparison table, begin with the printer type and print height. If you require a code taller than 12.7 mm or need to print in two positions on a single pack, only the ST-210S-H2 is suitable. Next, consider the resolution: small barcodes and 2D codes such as DataMatrix need high definition, which the ST-210S models provide with up to 600 × 600 DPI. For data integration, if you need to send data from your own system via a network port, you will need an ST-210S printer. The GT-100E accepts data via USB and RS232, and is also the only model that can operate on battery power.

What a date coder can print on your packaging

All three models print text, time and date, shift indicators, serial numbers and logos, so each can be used as an expiry date printer. Supported barcodes include CODE39, CODE128, EAN13, EAN14 and UPCA; supported 2D codes include QR code, GS1 DataMatrix, MicroQR and PDF417.

Fields can be populated from a database, allowing the inkjet date coder to print batch details or product information that varies from pack to pack.

The date and time on each pack are taken from the printer’s internal clock. This means that the date field updates automatically at midnight, so there is no need to enter the date manually each day. If the clock is set incorrectly, the wrong date will appear on every pack. After installation, always check both the clock and the date format to ensure they match your packaging requirements.

A shift indicator changes with the time of day, so the code shows which shift packed the goods. Counters can be set up to increment with each print, creating a unique serial number for every pack or counting the number of packs in a batch. The ST-210S models can manage more than 20 separate counters, for example one for each product or shift.

EAN13 and UPCA are used on retail packs for scanning at the point of sale, while EAN14 is for outer cartons. CODE128 is widely used in logistics, and NVE18, the German term for SSCC, identifies shipping units such as pallets. A 2D code like a QR code can hold a website address or batch record, and GS1 DataMatrix is used when a single small code must include the product number, batch and expiry date.

Within the 12.7 mm print height of a single head, you can arrange several lines, such as a best-before date, batch number and time, over two or three lines.

How an industrial inkjet printer operates on a conveyor

On a packing line, the print head is mounted on a bracket next to the conveyor, 1–5 mm from the pack. Guide plates keep the packs aligned and prevent them from touching the nozzle. A photoelectric sensor detects each pack, and an encoder monitors the conveyor speed for precise code length.

The print head can mark either the side or the top of each pack. For side printing, the pack travels along a guide rail, keeping it at a fixed distance of 1–5 mm from the print head. For top printing, all packs must be the same height, as a shorter pack will pass too far from the head and the code will be faint.

Guide plates before the print head align each pack and are set 0.5–2.5 mm away, so a bulging or poorly closed box touches the plate rather than the nozzle. The ST-210S print heads can also be fitted with anti-collision devices, useful for lines where pack shapes vary.

At 600 DPI, the ST-210S models print up to 60 m/min, so a packing line running at this speed or slower can use full resolution for clear codes. If your line is faster, a lower resolution must be used: 300 DPI allows up to 120 m/min.

The alarm output can be connected to a warning lamp or used to send a signal to the line control, so any fault is detected immediately and not after a full pallet of uncoded packs. External text selection allows the line control to choose which stored text the printer uses, which is helpful when one line packs several products. The serial number output passes the printed number on to the line control system.

With the ST-210S-H2, the two heads can be stacked to print a single block up to 25.4 mm high, such as a large date and batch line, or set apart so that one head marks the top and the other the side of a pack in a single pass.

Thermal inkjet printer or another coding solution

Thermal inkjet is one of several methods for coding packs. Its sealed cartridges include their own nozzles, so a thermal inkjet printer of this type requires minimal maintenance; its main limitation is the short distance of 1–5 mm between the cartridge and the pack. Continuous inkjet printers use a constant stream of droplets and recirculate unused ink. They can print from further away and on curved surfaces, but require make-up fluid in addition to ink and need more frequent maintenance.

A laser coder marks the pack by burning or removing a thin surface layer, without using ink. A label is preferable when the text is long, when the surface is unsuitable for ink, or when the code must be applied before packing; a labeling machine applies pre-printed labels. The thermal inkjet printers in this category are ideal where you need direct marking on packaging, with codes up to 25.4 mm high and options for handheld or fixed installation.

In daily operation, a thermal inkjet printer does not require the start-up and shut-down procedures of a continuous inkjet printer: there is no ink system to flush, and changing a cartridge takes about a minute. Each new cartridge brings a new nozzle, so print quality remains consistent. By contrast, a continuous inkjet printer circulates ink through pumps and filters that need regular maintenance, including cleaning, filter replacement and managing make-up fluid.

The main limitations of this technology are the print height and the distance to the pack. The print heads here cover 12.7 mm each, so large characters on big outer cartons require two heads or a different solution. The short distance to the pack means that deep recesses or strongly curved surfaces are difficult to mark. Coding inside a deep tray or around a small round bottle is therefore challenging.

Continuous inkjet is typically chosen for very fast lines and for round products such as cans and bottles, as it can print from a greater distance and mark curved surfaces.

A laser code cannot be rubbed off and does not require ink, but the laser must be suitable for the material being marked. Fumes produced by the laser must be extracted from the work area, and the initial investment for a laser coder is generally higher than for a thermal inkjet printer. Laser marking is chosen where a permanent code is needed and the material allows.

Thermal transfer overprinters use a ribbon to print onto flexible film and are usually integrated into bagging or flow wrapping machines. For film packs produced on these machines, they are the standard option. Where the surface is flat, such as on cartons or trays, the code height does not exceed 25.4 mm, and the line speed allows the required resolution, a thermal inkjet printer is a straightforward coder to maintain.

Selecting ink for your packaging surface

The ink for a thermal inkjet printer must be compatible with the surface. Porous materials like carton, paper and untreated wood absorb water-based ink. Sealed surfaces such as plastic film, metal, glass and coated cartons require a solvent-based ink that dries on the surface.

On dark surfaces, a light ink such as white remains legible, and invisible ink is visible only under UV light. If the ink may come into contact with food, a food-grade ink is required, so the cartridge must be chosen for both the product and the surface.

Always test the ink on your own packaging before starting production. Print a code, allow it to dry, and rub it with your thumb. If the code smears or fades, try a different ink type or treat the surface.

Plastic films can differ: some accept ink well, while others have a smooth surface where ink does not adhere. Your film supplier can advise whether the surface has been treated for printing.

Wet, cold or oily surfaces do not take ink well. Condensation on a pack leaving a cold room prevents the ink from sticking, so print before entering the cold room or dry the surface first. Solvent inks dry quickly on film, metal and glass, but also dry rapidly in the nozzles, so remove and seal the cartridge whenever the printer is stopped for an extended period.

Food-grade ink is necessary for codes printed directly onto food, such as eggs, or where the ink may touch the product. A code on a sealed outer carton does not contact the food, so standard ink can be used.

Black ink provides the highest contrast on white or brown carton. Cartridges have a use-by date, so only purchase what you will use within that time and store spare cartridges sealed, in a cool, dry place.

Inks and cartridges for your inkjet coder

These printers use 42 ml cartridges fitted with a contactless RFID chip. The chip informs the printer of the ink type loaded and tracks usage. Inks are available in food-grade, water-based, oily, mild solvent and solvent varieties.

You can select from black, white, red, yellow, blue, green, invisible and UV inks. The manufacturer lists carton, plastic, metal, sheet, pipe, stone, cable, glass, electronic components, automotive parts and industrial or food packaging as suitable surfaces for these printers.

Because the chip tracks ink usage, the operator can replace the cartridge before the code quality declines on the line.

When changing a cartridge, stop printing, remove the old cartridge at an angle, and insert the new one at the same angle. Clean the nozzle plate with a lint-free cloth to remove dust or dried ink, and print a test code to check print quality.

The ST-210S-H2 uses two cartridges, one for each print head. Keep at least one spare cartridge per head at the line, so you can change them without delay. When ordering a printer, specify what you are printing on and whether the ink may contact food, so the correct cartridge is supplied. If your line packs products in different materials, such as carton and film, keep both inks at the line and clearly label which cartridge is for each product.

The role of a code on a pack

A code on a pack serves two purposes. A date and batch code allow you to trace every pack back to its production run, which is essential if a batch needs to be identified. A serial number or QR code goes further and identifies each individual pack.

When a scanner reads the code further along the line, the code must be clear and large enough. Select the resolution and code height with the scanner in mind, and test them on your own packaging before starting the line.

Most prepacked food in the EU must display a best-before or use-by date and a lot mark for traceability. Retailers often require a barcode on outer cartons to support warehouse and store logistics. A missing or unreadable code results in a rejected pack or manual relabelling.

Position the code on a flat, smooth panel, away from folds, flaps, seams and glue lines, and always in the same place on each pack. This helps both staff and scanners to locate the code quickly. A barcode needs strong contrast: a dark code on a light background, a clear margin around it, and bars that are not blurred. Print at a resolution suitable for the required bar width.

Check the code at the point where it will be read: after stretch wrapping, after cold storage, or after transport. A code that appeared clear at the printer may be rubbed off or obscured later.

A batch code is only useful if it is recorded, so link each batch code to the date, the line, the shift and the batches of raw material. This allows a complaint or recall to be limited to the affected packs. Write the date in the format used in your market and keep it consistent for all products. A date that can be read in two ways, such as day and month swapped, is a common source of complaints.

Running costs of a thermal inkjet printer

Ink usage depends on the code height, the amount of text and the print resolution. The cost per print is the cartridge price divided by the number of codes it produces. The GT-100E displays the printing cost on its screen. The ink cartridge records how much ink has been used, so you can monitor usage directly on the printer.

To determine your actual running cost, print your code on your own packaging for a set time, read from the printer how much ink has been used, and count the number of prints. This shows how many of your codes one cartridge provides. Ink usage decreases with lower resolution, fewer characters, smaller text and no logo, so print at the lowest resolution that still gives a readable code and omit fields that are not needed.

With this technology there is no make-up fluid, filter or pump to maintain. Ink is wasted if a cartridge is left open in a printer that is not in use, as the nozzles dry out and then print poorly. Consider the cost of a poor code as well: packs that must be recoded or relabelled by hand, a batch that cannot be traced, or a customer complaint.

What determines the price of a date coder

The price of a date coder depends on whether it is handheld or fixed, the number of print heads, the print resolution and the maximum code height. A network port for data from your own system also increases the price.

The current price of each thermal inkjet printer is shown on its product card above. All models include a 12-month warranty.

A complete coding station on a line requires more than just the printer. You will need a bracket, guide plates, a photo eye and, where the speed varies, an encoder. Use the Get offer button to ask which of these parts are included with the printer and which must be ordered separately. Request the price of spare cartridges with your quote as well, as they determine the running cost over time.

The ST-210S-H2 can print on two areas of a pack using a single controller and screen, so you only need to set up and maintain one machine rather than two. To request a quote for a printer with a supply of cartridges, click the Get offer button on the product card. The Add to inquiry button allows you to gather several products into one enquiry.

Points to consider before ordering

Before purchasing a thermal inkjet printer, check the surface material and the type of ink required, the code height, the speed of your line, and the resolution needed. Decide where the code should be placed on the pack, such as the top, side, or both. Ensure there is a stable location for the bracket and a gap of 1–5 mm to the product. Confirm where the data will be entered, either via the screen or your own system.

A dedicated socket, proper earthing, and ideally a UPS are required. The comparison table above shows which printer matches your code height, speed, data connections, and number of print heads.

Make a note of exactly what the code must include, such as the date and its format, batch number, time or shift, counters, barcode type, and number of lines. Ensure all this information fits within 12.7 mm per head, or 25.4 mm if using two heads.

Measure your line: note the minimum and maximum speed, whether it stops and starts (if so, you will need an encoder), the gap between packs, and whether the packs travel along a rail. Decide which side of the line the code will be printed from. Printing from above requires packs of the same height, while printing from the side needs a rail to keep the distance constant. Record the narrowest and widest packs as the rail must hold both at the correct distance from the print head.

Check the area where the printer will be used: these printers operate at 0–45 °C and 30–70 % relative humidity. Dust, splashes, and condensation from cold rooms require extra care. Decide who will operate the printer, change cartridges, and edit the text. The screen supports over 40 languages, so you can set it up for your team.

Setting up and maintaining a batch coding machine

Install the batch coding machine on its own earthed socket, not shared with other devices. Use a UPS if possible. Mount the bracket securely to prevent vibration, and fit guide plates with 0.5–2.5 mm clearance to stop products from striking the nozzle.

Insert and remove cartridges at an angle; never remove a cartridge while the printer is running, and never connect or disconnect cables while the machine is switched on.

At the start of each shift, clean the nozzle plate with a lint-free cloth, print a test code, and check the first packs for print quality. At the end of the shift, or before any long pause, remove the cartridge and close it. This prevents the nozzles from drying out and helps the next shift start with a clean print.

Always use a lint-free cloth to clean the nozzle plate. Paper tissues leave fibres and fingers leave grease, both of which can block the nozzles. Do not touch the nozzles or the cartridge’s electrical contacts; hold the cartridge by its body.

A faint or broken code is usually caused by dried or dusty nozzles, or the print head being too far from the pack. If the code is too long or too short, check the speed setting or the encoder. If the code appears in the wrong place, check the delay after the photo eye.

Keep the print head and controller away from dust, splashes, and vibration, and route the cable to the head so that products cannot catch it. Keep a brief record of cartridge changes and the number of codes printed by each cartridge. This helps you calculate the actual cost per code and shows if a cartridge is running out sooner than expected.

Frequently asked questions about thermal inkjet printers

What is the maximum code height with these thermal inkjet printers?

The GT-100E and ST-210S-H1 can print up to 12.7 mm high. The ST-210S-H2, with two print heads, can print a single code up to 25.4 mm or mark two areas at once.

What is the maximum speed for these printers on a production line?

At 90 DPI, all three models can print at up to 406 m/min, and at 300 DPI up to 120 m/min. At 600 DPI, available only on the ST-210S printers, the line can run up to 60 m/min.

Can these printers print QR codes and barcodes?

Yes. All three models can print barcodes such as CODE39, CODE128, EAN13, EAN14, and UPCA, as well as 2D codes like QR code, GS1 DataMatrix, MicroQR, and PDF417. Data can be sourced from a counter, the clock, or a database.

What temperature and humidity conditions are suitable for these printers?

The operating environment for all three models is 0–45 °C and 30–70 % relative humidity.