Bottles, cups and pens: UV printing on round objects
are explained briefly when you hover over or tap them.
A flatbed printer prints on flat things. For bottles, cups and pens you need a device that rotates the object during printing. This works well but has its own limits: diameter, shape and the point where the start and end of the design meet.
The rotary attachment
A rotary attachment holds the object horizontally under the print head. While the head prints in one direction, the attachment turns the object a little at a time. Instead of moving the plate, the surface is rolled off.
There are two designs:
- Rollers: The object rests on two driven rollers and turns through friction. Simple and flexible, but light or slippery objects can slip.
- Chuck: The object is clamped at one or both ends and turned directly. More precise, but not suitable for every shape.
For pens and small parts there are also jigs in which many pens lie side by side. These print only the top line, without rotation.
Which diameters work?
That depends heavily on the device. A few examples from manufacturer specifications:
| Device and attachment | Diameter | Further details |
|---|---|---|
| eufyMake E1 with rotary attachment | 40 to 100 mm | length 80 to 245 mm, up to 1 kg, taper up to about 13 to 15° (retailer specifications) |
| Mimaki Kebab (UJF series) | 10 to 110 mm | for industrial machines |
| Procolored TX800 with cup attachment | up to about 100 mm | retailer specification, limited by the height under the print head |
These values change with new models. Check the current data sheet of your device. You will find an overview under UV printers.
The limits are set not only by the attachment but also by the printer’s build height. A thick mug with a handle may fit under the head, but the handle collides as it turns.
Conical shapes
Many cups and bottles are not cylindrical but get narrower towards the bottom. This causes two problems:
- Gap: The gap between the print head and the surface is smaller at the wide end than at the narrow end. Large differences cause blur and overspray.
- Distortion: At the narrow end the circumference is smaller. A rectangular design is visually compressed there.
Some attachments can be tilted so that the top of the cone lies level under the head. For the eufyMake attachment, retailers give about 13 to 15°; eufyMake itself gives no value. For the distortion, many programs have a function that pre-distorts the design to suit the cone. Without this function, it helps to keep the design narrow and print only part of the circumference.
Alignment
Round objects lack the fixed corner that you use to orient yourself on a flat plate.
- Mark the centre: Use a wipeable pen to draw a fine line where the design should start.
- Handle and seam: Insert mugs with a handle so that the handle is not in the print area. On bottles with a moulding seam, put the seam at the back.
- Level: Use a spirit level to check that the object lies straight. Even a slight tilt makes the design crooked.
- Height: Measure the highest point of the object and set the print height accordingly.
More on jigs and camera positioning in Positioning.
The seam
If a design is meant to go all the way round, the start and end meet somewhere. This seam is the weak point of wrap-around printing. Even half a millimetre of deviation in the circumference results in a gap or an overlap.
How to avoid trouble:
- Measure the circumference exactly or calculate it from the diameter (circumference = diameter × 3.14).
- Choose designs where a seam is not noticeable, for example with a gap in the design.
- For full-surface designs, do a test print on the same cup.
- With roller attachments, watch for slip: light or smooth objects slide and the seam becomes uneven.
Durability on drinks bottles and cups
Customers’ expectations are high, especially for cups and drinks bottles. To be honest: a directly printed cup is not a dishwasher-safe product.
- Primer: Stainless steel, glass and many powder-coated cups need primer. Details in Printing on metal.
- Dishwasher: Heat, detergent and knocks loosen UV ink after a while. Recommend hand washing only.
- Food contact: UV ink is not intended for contact with food. Print only the outside and leave a margin from the rim where the lips touch the vessel.
- Curing: Give the print time before you use or package it.
For products you sell, legal requirements for items in contact with food apply. If in doubt, get advice rather than making promises.
Alternative: UV DTF
If your printer has no rotary attachment, the object is strongly conical or has an irregular shape, UV DTF is often the simpler solution. You print the design flat onto a film and then stick it on like a sticker. This also works on shapes that an attachment cannot handle. Here too: hand wash rather than dishwasher. More in UV DTF.
For business use
Personalised cups and bottles sell well but carry the highest risk of complaints. Include a care note with every parcel: “Hand wash only, do not soak, do not put in the dishwasher.” Write the same in the product description. And factor in rejects at the seam, especially at the beginning.
Continue with: Printing on metal, UV DTF and the materials overview.