Q - Why do boards delaminate?
A - All boxboards are a multiply construction. Each ply is bonded to the adjacent ply during manufacture. If the board is subjected to a force greater than the strength of the plybond, the plies will separate and the board will delaminate. It is possible to create these forces in a number of ways, for example:

• during manufacture if the board is dried unevenly
• during sheeting if excessive decurl is applied
• during printing if the ink tack is too high

If a board is delaminating it is important to bear in mind the potential causes and look for evidence, which may prove or disprove each cause, for example:

• If the board is delaminating during a print run, check if the delamination is occurring on all colours or if it is confined to one colour.
• Check the viscosity of the ink.
• If the board is delaminating during sheeting, is the board being run through a tight bend? Typically rolls of 100 mm diameter or less will be able to delaminate any board if enough tension is applied.

Q - Why does board curl?
A - The main ingredient in boxboard is wood pulp fibres, which are made of a chemical called cellulose. Cellulose contains some water at room temperature and humidity. If the temperature or humidity changes then the cellulose will gain or lose water. This has the side effect of causing the cellulose to shrink or grow, which in turn causes the pulp fibres to shrink or grow. Unfortunately the fibres change more in one direction which causes the board to grow or shrink more in one direction than another. This causes the sheet to curl. When board is made it is manufactured at a given water content which is likely to be found in a normal press room. Storing board correctly in its mill wrapping and at the press room temperature will minimise curl problems.

Q - Why does the backliner shade of packaging boards vary?
A - The backliner of packaging boards is made from unbleached Kraft pulp. The Kraft cooking process has a number of variables, which affect the final colour of the pulp. These are:

• the type of wood
• cooking conditions
• efficiency of the washing stage after cooking.

Key variables which affect pulp strength are monitored and controlled to ensure that the pulp strength, and hence board strength, is consistent.