Building panels, especially laminated floor panels are shown, which are provided with a locking system and several core grooves at the rear side in order to save material and decrease weight.
1. Building panels, each having a surface layer on a front side, a backing layer on a rear side and an intermediate core, wherein the intermediate core and the surface and the backing layer all comprise wood fibres and thermosetting resins, said building panels are provided with a locking system for vertical and horizontal locking of a first edge of a first building panel to an adjacent second edge of a second building panel, wherein upper parts of the first and the second edge in a locked position together define a vertical plane perpendicular to a horizontal plane, which is parallel to the surface layer, said locking system comprises a tongue and a tongue groove configured to cooperate for vertical locking, and at the first edge a strip provided with a locking element, which is configured to cooperate for horizontal locking with a downwardly open locking groove formed in the second edge,
wherein the backing layer and the intermediate core comprise at least two vertically extending core grooves with an opening towards the rear side, and
wherein the area of the backing layer is less than about 90% of the area of the surface layer.
2. The building panels as claimed in claim 1 , wherein the backing layer comprises at least three core grooves spaced horizontally and inwardly from the locking system at one pair of opposite edges.
3. The building panels as claimed in claim 1 , wherein the area of the backing layer is less than 80% of the area of the surface layer.
4. The building panels as claimed in claim 1 , wherein the entire parts of at least one core groove is arranged inside the vertical plane VP at all edges.
5. The building panels as claimed in claim 1 , wherein the building panels are rectangular with long edges and short edges and wherein the core grooves are essentially parallel with the long edges.
6. The building panels as claimed in claim 1 , wherein the core groove depth is at least 0.3 times the floor thickness.
7. The building panels as claimed in claim 1 , wherein the core grooves comprises an opening with a groove width that is larger than an inner part of said groove.
8. The building panels as claimed in claim 1 , wherein the backing layer comprises essentially the same types of fibres as the core.