Лако-красочные материалы — производство

The purposes of the addition of tannins are to accelerate the hardening reaction [110,116,176-178] and to replace phenol or a part of the PF resin [179-185]. 2. Addition of Lignins Lignins can be added to phenolic resins (i) as an extender, e. g., in order to increase the cold tack or to reduce costs, or […]

A real concondensation between phenol and urea can be performed in three ways: Reaction of methylolphenols with urea [166-169]. Acidic reaction of urea-formaldehyde concentrate (UFC) with phenol followed by an alkaline reaction [170,171]. Reaction exclusively under alkaline conditions of urea and phenol in competition with each other leading to reaction of methylol ureas with phenol […]

1. Post-Addition of Urea The addition of urea to a phenolic resin causes several effects: decrease of the content of free formaldehyde decrease of the viscosity of the adhesive resin acceleration of the hardening reaction via the possible higher degree of condensation of the resin reduction of the costs of the resin. The urea can […]

Phenol-formaldehyde core layer resins usually have the highest molar masses and hence show a high reactivity and quick gelation. They contain higher amounts of alkali than face layer resins in order to keep the resin soluble even at higher degrees of condensation. The higher the degree of condensation during the production process (the higher the […]

Table 9 summarizes some resin glue mixes for different applications in the production of particleboard and MDF. Table 10 summarizes various resin glue mixes for different applications in the production of plywood, parquet flooring, and furniture. II. PHENOLIC RESINS Phenolic resins [phenol-formaldehyde (PF) resins] show complete resistance to hydrolysis of the C-C bond between the […]

Not much work has been done up to now concerning the prediction of bond strengths and other board properties based on the results of the analysis of the adhesive resin in its liquid state. What has been investigated and derived up to now are correlation equations that correlate the chemical structures in various UF resins […]

Table 8 describes an example of the use of an accelerator which distinctly increases the gelling rate of a core layer glue mix, hence enabling a significant shortening of the neces­sary press time. The quick reaction of the accelerator with the hardener salt generates the acid for the acid-induced hardening reaction of the resin. The […]

During the curing process a three-dimensional network is built up. This leads to an insoluble resin which is no longer thermoformable. The hardening reaction is the conti­nuation of the acid condensation process during resin production. The acid hardening conditions can be adjusted (i) by the addition of a hardener (usually ammonium salts such as ammonium […]

The resin used has a crucial influence on the properties of wood-based panels. Depending on the requirements, different resin types are selected for use. Whereas UF resins are mainly used for interior boards (for use in dry conditions, e. g., in furniture manufactur­ing), a higher water resistance can be achieved by incoroporating melamine and also […]

Cold tack means that the particle mat has attained some strength already after the pre­press at ambient temperature, without any hardening reaction having occurred. This ‘‘green’’ strength is necessary for better handling of the particle mat during transfer on the production line. This can well be the case in multiopening presses, in special forming presses, […]