Лако-красочные материалы — производство

One of the more common difficulties in bonding pine veneers and chips is adhesive dry­out. Dry-out is associated with the high liquid absorbancy of pine sapwood and it appears especially during long assembly times. This problem can be overcome by using resins modified through reaction with alkylated phenols, especially 3,4-xylenol [52]. Another technique used to achieve similar results is the manipulation of synthesis procedures used in preparing a standard PF resin [52]. The dry-out resistance imparted by alkylated phenols is due to an initial semithermoplastic character in the resin. This is derived from their monomer bifunctionality and the linear polymer that is consequently formed.

If a linear and essentially non-cross-linking prepolymer is prepared from phenol and formaldehyde, it can be coreacted with a nonlinear and cross-linking prepolymer to form a resin. The latter resin will have some initially semithermoplastic or dry flow character but will be primarily thermosetting. The product is an alkaline novolak-resol copolymer.

Evaluation of this copolymer concept has shown that many resins possess a controlled initial semithermoplastic character which improves resistance to dry-out. Good dry-out resistance is achieved without loss of press-time efficiency or broad-range bonding ability. Such resins perform noticeably better than other types of resins that are resistant to dry-out.

Such a resin of the alkaline novolak-resol type can be prepared by coreacting a prepolymer, prepared by reacting formaldehyde and phenol in the molar ratio of 2.6:1.0, and a prepolymer obtained by reacting formaldehyde and phenol in the molar ratio of 1:1. The two prepolymers are then mixed in 50:50 proportions by mass and coreacted.