Start with the surface, not the artwork
Most container print problems are not about artwork. They are about the surface. PP, the material of most food containers, has a low surface energy: ink does not wet it or bond to it well without help. Before printing, PP parts are usually given a surface treatment, typically by flame or corona, which raises the surface energy for a short time so the ink can anchor. PET bonds more readily but still needs inks matched to it. If treatment is skipped, too weak or done too long before printing, the print looks fine at the line and rubs off in a delivery bag or a dishwasher.
That is why print adhesion and rub resistance belong on the test plan for any printed container, checked on production parts, not only on the approved sample. They sit alongside the other checks listed on testing and inspection.
The main print methods
| Method | Best on | Colors and detail | Watch points |
|---|---|---|---|
| Dry offset | Round cups, tubs and bowls | Several colors in one pass, line and solid art; no photo images | Round shapes only; colors cannot overlap precisely |
| Screen print | Flat lids, flat panels on boxes | Strong opaque color, one color per pass | Slower; registration across colors |
| Pad print | Small logos on curved or recessed areas | Small areas, fine detail | Small print area; slower for volume |
| Hot stamping | Metallic logos on lids and organizers | Foil, one color per pass | Retail look; foil wear on handled parts |
| In-mold label | Retail tubs, lids, storage containers | Full surface, photo quality | IML-ready mold and robot; label stock per design |
| Sleeve, band or label | Any container, including stock molds | Full color on paper or film | Separate part; removed before use |
In-mold labeling has its own note: in-mold labeling explained.
Dry offset for round containers
Dry offset is the standard method for round cups and tubs. Each color is inked onto a plate, all colors are transferred to a single rubber blanket, and the blanket rolls the image onto the rotating container in one pass. It is fast and suits large runs of cups, soup containers and round lids. The limits come from the method: because the colors are laid side by side on the blanket, they cannot be printed one on top of another with fine overlap, so photographic images and gradients are not practical. Designs work best as clean line art and solid areas with small gaps between colors. Export soup cups from the partner cluster in Guangdong, which run from 350 ml at 116x99x45 mm to 950 ml at 117x82x141 mm, are typical candidates.
Screen, pad and hot stamping for lids and boxes
Flat lids and the panels of rectangular boxes are usually screen printed. Ink is pressed through a fine mesh, one color per pass, which gives strong opaque color and works well for a logo and a short line of text on a takeout lid. Pad printing lifts the image from an etched plate on a soft silicone pad and presses it onto curved, small or recessed areas, which suits small logos on handles, organizer fronts or a recessed lid panel. Hot stamping transfers a metallic or colored foil with heat and pressure, used mainly on cosmetic organizers and retail storage items for a premium look. Each of these is slower per piece than dry offset, so they suit smaller print areas and moderate runs.
Sleeves, bands and labels: print without touching the mold
A paper sleeve or band around a container or a set is the most flexible route. It works on stock molds, so a brand can launch with partner plant stock containers and its own print from the first order, and it allows photographic images and full-color design. Paper sleeves come from paper packaging plants, including the printing cluster around Longgang near Wenzhou. Pressure-sensitive labels on the lid are another low-entry route, but can lift in the freezer or dishwasher. Shrink sleeves in film cover the full body of tubs and cups for retail. The printing and labeling page and the private label guide cover these routes.
Embossed and molded-in branding
A logo can also be cut into the mold itself, so it appears raised or recessed in the base or lid of every part. It needs no ink and cannot rub off, but it needs either a custom mold or a changeable insert in an existing mold, and it is monochrome by nature. Resin identification codes and microwave or freezer symbols are applied the same way; soup cups from a partner thermoforming plant carry the PP code 5 and a microwave marking in the base, as the supplier states.
Inks and food contact
Print goes on the outside of the container, but containers nest and stack, so the printed outside of one part touches the inside of the next. Ink can transfer in this way, called set-off, which is why inks for food packaging are chosen for low migration and dried fully before packing. The food contact file for a printed container should cover the printed article, not only the plain resin: a supplier declaration for PP against FDA 21 CFR 177.1520 for the US, and for Europe a declaration to Regulation 1935/2004 and Regulation (EU) 10/2011 with migration testing on the printed part where required. Documents are issued to partner plants or brands per project and verified by the desk. See food contact safety.
Checks and order quantities
- Approve a print proof with Pantone references and position on the part.
- Approve a printed sample from production tooling.
- Agree adhesion and rub checks, plus freezer, dishwasher or microwave checks where the use requires them.
- Check color, position and adhesion on every lot at inspection.
Printed lids, cups or sleeves typically start at 10,000-50,000 pieces per item, and printed paper boxes at 5,000-10,000 per design, confirmed in writing per program. Printed samples take about 7-15 working days. See MOQ and lead time and send the artwork and container through the quote form.