What it is
A board for folding cartons is not a single sheet: it is a layered structure. At the centre sits the fibre that gives bulk and stiffness, on the outside the finer fibres and the coating that receives the print. The code the supplier uses describes that sandwich exactly. GC1 and GC2 are virgin fibre boards with a bulky middle layer: high stiffness for a given grammage and a white coated printing surface; what changes is the reverse, white in GC1, cream or manila in GC2. GD and GT are recycled fibre boards: in GD the reverse stays grey, in GT it is white. Board made of pure bleached chemical pulp, what the market calls SBB or SBS, is white right through the thickness, has the most uniform surface and the most closely controlled fibre.
The choice is almost always a compromise between four things: stiffness for grammage, purity of the fibre, print result and cost. Bulky virgin fibre gives the best stiffness for weight, and it is what is needed when the carton has to stand up on its own without being heavy. Recycled costs less and is the natural choice for secondary packaging and for products not in direct contact, but for a given grammage it is less stiff, its shade is less stable between batches and it brings with it a contaminant issue to manage. Bleached chemical pulp is the most neutral and the most printable, and it stands up to the strictest food-contact checks. Through-dyed boards are a separate matter: the colour runs through the whole thickness, so the die cut and the split along the crease stay the same colour. That is why they are chosen, and it is also why printing on top of them behaves differently.
How to prepare the file
- Grain direction is decided together with the imposition: the main fold of the carton has to run with the grain, otherwise the crease tends to crack exactly where it shows most.
- The cutting die is designed on the actual thickness of the board, not on the grammage. Matrix channel, crease rule height and compensations change with the caliper: changing substrate once the die is made is an expensive problem.
- Ask prepress for the profile suited to the substrate and a proof on similar stock. A bright white coated board and a slightly grey recycled board do not give the same black, and above all they do not give the same skin tones.
- Where blacks and solids fall on the folds, ask for a creasing trial before the print run: cracking shows on the folded piece, never on the flat sheet.
- Check the actual availability of the chosen board and of at least one alternative before freezing the project. The second supplier does not have exactly the same white.
What can go wrong
- Swapping one board for an "equivalent" of the same grammage is not painless: thickness, stiffness and whiteness change, and with them the cutting die, the colour result and the behaviour on the folder-gluer.
- The grey reverse of recycled board is visible inside the carton, and the customer discovers it on the finished product. It has to be agreed beforehand, with a sample in hand.
- Recycled board is not automatically suitable for direct contact with food. Without a functional barrier and without a declaration of compliance covering that precise use, it cannot be taken for granted.
Frequently asked questions
- What is the difference between GC1 and GC2?
- The reverse: white in GC1, cream or manila in GC2. The printable face and the bulky structure belong to the same family. GC1 is chosen when the inside of the carton is visible.
- Can I use recycled board for food?
- For secondary packaging, yes. For direct contact you need a functional barrier and a declaration of compliance referring to that food and that type of contact: it is not enough for the board to be generically "for food use".
- Is a heavier board always stiffer?
- No. Stiffness depends on thickness and on the layered structure, not on weight. A bulky virgin fibre board can be stiffer than a heavier recycled one.