| 摘要 |
The chips are bound together with a formaldehyde-based resin. The level of free formaldehyde is measured according to Fesyps perforator method to be up to 10 mg of formaldehyde per 100 g of dry board. The chips are dried and sieved to grade them by size. The coarser chips are used for the middle of the board and the finer for the surface. Urea in aqueous solution is added to the middle layer chips. The middle layer chips and surface layer chips are then glued together with a formaldehyde based glue. This includes some formaldehyde and a product which at elevated temperature can react with formaldehyde via a polymerisation reaction to form a plastic. (The formaldehyde is in excess). The glued chips are formed into sheet with heat applied to the surface what the above polymerisation occurs. The excess formaldehyde and steam migrates from the surface layers to the middle. The excess formaldehyde from the glue and that which migrates from the surface react with the urea which was added to the middle layer chips before glueing. |
