Лако-красочные материалы — производство

A wide array of adhesive raw materials and formulations is available for the purpose of different applications, such as required performance of the adhesive joint, and the chemical and physical properties of the wood-based materials (as described above).

Summer wood — Spring wood — Summer wood —

Summer wood Spring wood Spring wood

Figure 8.19 The dependence of penetration behavior of an adhesive (bright regions) on the wood density.

All of these are required to fulfill the following conditions, however, whenever wood is bonded:

• The adhesive must be compatible with water or water vapor, both when applied and during continuous operation since, in practice, wood always has a residual moisture content of 6-15%; oven-dry wood is only significant for scientific purposes.

• The dimensions of wood change depending on the ambient humidity and climate; this results in the occurrence of high shear stresses at the joint interphases that must either be compensated by the elasticity of the adhesive, or supported by sufficiently high adhesion and cohesion forces.

• Wood adhesives are required to have certain gap-filling characteristics, since even when planed or ground, the wood surfaces are never absolutely flat. Furthermore, wood is generally bonded under pressure that is applied by different means, ranging from clamps or cramps in the case of handicraft applications, to fully automated stack or forming presses in the case of industrial applications.

8.4.6