Millboard is the generic term for any solid paperboard, which, unlike corrugated board, contains no cavities. Couching may finish the surfaces, i.e. applying an outer layer made from higher grade raw materials onto the web while it is still wet (to give "lined paperboard"). The properties of millboard may also be improved by adhesive lamination, lining, impregnating or coating. Millboard is made as machine-made board or wet machine board.
Millboard is a flat packaging material, which is preferably made from chemical pulp and/or mechanical pulp. Its basis weight is > 600 g/m2, i.e. greater than that of paper and cardboard.
Accordingly a distinction is drawn between the following types of paperboard depending upon the raw material used or the intended use:
- Wood board: made from wood pulp;
- Grayboard: made from waste paper.
- Auto panel board: bulky, bituminized paperboard, made from waste paper.
- Fine board (hard board): stiff, non-splitting paperboard with a hard surface, generally made from higher grades of waste paper, chemical pulp and textile waste. Types of fine board include bookbinding board, fireboard, jacquard board, gasket board, suitcase board, shoe board, pressboard and punching board.
- Roofing felt: paperboard impregnated with tar, bitumen and/or natural asphalt
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