In the world of digital printing, the term rotary printing – also known as cylindrical printing, digital cylinder printing, or direct-to-object printing – is often used to describe the method of printing directly onto cylindrical items such as drinkware, glassware, candles, and plastic tubing, using a cylindrical inkjet printer. In the past, sublimation and screen-printing were the most popular decorating options for these applications. Once digital technology evolved from printing on just flat items, digital became a top contender for rotary printing.
Although sublimation and screen-printing are commonly used techniques, the limitations of these print methods are design capabilities, sustainability, and speed. The first digital technology for cylindrical printing was rotary attachments for flatbed printers, rather than a dedicated rotary UV printer. Now, with new innovations in digital technologies, this method has similar limitations to traditional methods.
Sublimation is the process in which a graphic is printed onto a plastic sleeve. This plastic sleeve is then placed on a drinkware item and heated until it has fully adhered to the substrate. Although this enables companies to get full-color graphics, achieving seamless artwork is almost impossible. For every piece sublimated, there will be inconsistencies in where both sides of the artwork meet. Next, sublimation requires an excess of plastic. This is typically thrown away and contributes to the modern plastic waste issue. Finally, this process limits operators from quickly switching from one part to another. Inventory management becomes crucial at this point because if one piece is missing or sublimated incorrectly, it could potentially result in long lead times and cost a company an order.
Although screen printing cannot achieve the same photographic design capabilities as digital printing or sublimation, it is still widely used to print logos and graphics on drinkware pieces. Screen printing enables operators to print 360-degree graphics, but again, the results are not seamless. There will always be a registration mark on the finished product. This process also uses a great amount of excess ink (which cannot be reused) and other consumables that can be harmful to the environment. Finally, screen printing can be a fast process for one color graphics, but it does require drying between every color, which can be time consuming for those looking to print multi-color designs or large orders in a short amount of time.
A rotary attachment can be configured to a flatbed printer in order to enhance the capabilities of a standard flatbed. Some of these attachments require extra tooling fixtures, while others magnetically attach to a flatbed printer. The rotary movement is driven by the operation of the bed. Flatbed rotary attachments typically only enable printing on straight-walled cylinders, not tapers, which hinders the capabilities of the system. In addition, these types of attachments cannot be used to print on items with handles, such as mugs. Narrow swaths are imaged with each pass of the flatbed inkjet carriage resulting in very slow imaging times, especially with small height artworks. The printing process requires digital ink and does not produce waste. The inks are typically constituted from environmentally friendly materials.
This leads us to digital printing on machines that were built specifically for imaging objects with round cross sections. Digital printing is a process in which digital ink is applied directly onto the substrate without the need of transfer paper, a heat press, or screens. The artwork is created, prepped for print, and loaded onto the computer. Once the operator hits print, a beautiful, full-color graphic is printed directly onto the object. As noted earlier, rotary printing in its infancy was accomplished by adding a rotary fixture to a flatbed inkjet printer. This rotary attachment would incrementally rotate the drinkware as the flatbed inkjet printer printed the graphic directly to the item. Although this worked for some time, innovations in rotary printing advanced and provided users with faster, more high-resolution printing technology. Different types of rotary printing machines offer 3 main printing approaches: multi pass, single pass, and helical printing. Below, we compare the speed, print quality, automation, and cost of each technology.
Multi Pass: Multi pass printing is when the print heads or printed object move axially in steps down the part like a flatbed printer. The move time is inefficient and can lead to stitching artifacts between moves.
Single Pass: Single pass involves using an array of print heads to print the full image length with a single revolution of the printed object. Different colors are usually printed at different stations leading to high cost, complexity, and sensitivity to nozzle drop-outs. While capable of high imaging rates, these systems are very expensive and maintenance intensive.
Helical Printing: Helical printing is the ideal hybrid between the single pass and multi pass approaches. Image data is mapped to allow continuous imaging in a helical pattern with a limited number of print heads. Users can optimize the print resolution, speed, and curing controls to realize the best image quality possible or choose higher speed when the utmost quality isn’t critical. Tapers can be imaged at high speed and curved vessels can be managed through the range of controls offered.
A number of factors influence the print speed including:
– The size of the image.
– The number of nozzles in the ink jet head array.
– The firing frequency that can be realized by the head used.
– The coverage requirements and drop size.
– The number of colors imaged.
– Whether a finishing coat or varnish is desired on the final product.
Helical Printing: Helical printing is the most efficient as all head nozzles are used for each image size, high speeds can be achieved when good quality is enough, and higher pass counts and resolutions can be opted for when the best image quality available is needed.
Single Pass: If the single pass array is tall enough for all images and enough heads are used to deliver more than 600 dpi in a single pass, single pass imaging is the best choice for very high production rates. These machines often cost more than $1 million and high production levels are usually fully dependent on the reliability of a single system. High speed automation and achieving registration between colors are key challenges.
Multi Pass: Multi pass imaging is the slowest architecture as rotation time is wasted as the head moves from the position associated with the previous print swath.
Compared to single pass printers, helical printing gives you several significant benefits including multiple and higher resolution images, image-dependent ink coverage, and the ability to optimize the output for the application. Helical printing enables continuous printing of long images in a single motion, unlike multi pass printing which requires stitching for any image over the size of the print head (typically 30-60mm). Stitching refers to a second pass, which can leave a line in the print where one print swath ended and the other one started. With single pass and multi pass printing, you rely on the print head for resolution and image height. For example, if you are trying to print an image 220mm in height, the company will have to invest in another print head to print the additional piece.
Helical printing can achieve much higher resolution images than single pass printing. Helical printing is ultimately the more efficient and flexible printing technology. With this method, the resolution can be increased to 12-pass or 24-pass to maximize image quality. Helical technology prints in both horizontal and vertical (X and Y) directions, unlike single pass printing, which is limited by the low print head native resolution in the Y direction.
In addition, helical printing interlaces the inkjet drops, smoothing out band lines and ensuring uniform coverage. With single pass and multi pass printing, if you are missing just one nozzle, a visible line of missing ink will appear running through the image, resulting in poor image quality. Helical printers utilize RIP software and a helical print engine, which provide you with greater control over printing your graphics. The RIP software turns a vector image into a bitmap, providing a digital representation of each color plane, organized into color layers, (typically cyan, magenta, yellow, black, white, and varnish, if desired). The helical engine maps the RIPPED image into a pattern which provides a seamless mapping onto vessels of various shapes and sizes. On the other hand, single pass means that the print heads jet every color individually in single lines. As the product moves through the machine, cyan is jetted, then magenta, then yellow and finally black.
Although the operator can “trick” the machine into printing more dots horizontally (by printing slower at a higher resolution), the vertical resolution is limited to the maximum resolution of the print head. With helical printing, all colors are jetted at once in a gradual, angled motion to get the best resolution possible. CMYK printed all at the same station yields consistent, highly accurate dot placement and excellent print quality and color reproduction.
Helical Printing: The print quality is superior to single pass and multi pass printing, resulting in seamless images and uniform coverage.
Single Pass: The resolution of the images is limited by the resolution of the print heads. For images larger than the print head, stitching is required, which will leave a visible line in the print, decreasing the overall print quality.
Multi Pass: The resolution of the images is limited by the resolution of the print heads. This technology results in the worst image quality compared to helical and single pass printing.
For high-speed operations and large production runs, automation is required. The cost of traditional methods of printing such as sublimation and screen-printing is largely affected by economies of scale. The set-up and tooling costs associated with traditional printing methods mean short runs are very expensive and personalization is not possible. With a digital printer, the cost per unit is roughly the same whether you are printing 10 cups or 10,000 cups. This makes digital printing ideal for the personalization industry, which commonly requires one-off printing. A rotary printer is a perfect machine to use for the drinkware industries, as well as for promotional products and personalization. Overall, helical printing provides the best productivity as a function of the cost of equipment.
Helical Printing: Helical printing provides the best price/performance ratio. It was built for continuous printing and is best suited for the promotional and industrial markets.
Single Pass: Single pass printing is the fastest and can produce high volumes of output. Yet, quality is sacrificed for speed.
Multi pass: Multi-pass printing is the slowest technology, resulting in lower volumes of output compared to single pass and helical printing.
When it comes to the different methods of digital printing, the main driver of cost is the print heads and associated electrical hardware and ink circuitry. Driver boards and complex ink fluid circuits are required for each to support the additional heads needed for single pass machines. With single pass printing, multiple print heads must be stacked to exceed the native resolution of the print head (typically 300-600 dpi). Print heads are costly and require regular maintenance; more print heads result in more problems.
Helical Printing: Lowest cost as with multi pass.
Single Pass: Single pass is the most complex and expensive method. Image size, resolution, and speed dictate precision alignment, thermal stability, and a large number of print heads.
Multi Pass: No benefit over helical printing.
When choosing which type of printing is best for your business, consider the internal design goals and production requirements. The desired speed, print quality, production cost, and financial budget will influence whether helical printing, single pass printing, or multi pass printing is right for you.