Specifically designed Urea-Formaldehyde (UF) adhesives for veneer splicing.
Outstanding durability of the spliced joints, good flexibility and excellent staining and varnishing properties are some of the advantages of these products. Suitable for veneer joining in the furniture, doors and panel industry as well as for caravan-, car- and boat interior.
Carbamide glue is intended for hot pressing on the basis of carbamide resins. This type of glue is used in large quantities in the timber industry, in the manufacture of plywood, furniture, etc. It is also used for bonding metal. Hot consolidation powdered adhesive is easy to prepare and has a particularly strong adhesive qualities.
Carbamide resins may be used as adhesives. To speed up the process of tightening, fixtures is used. Carbamide resins with fixtures are called carbamide glue. This type of glue is based on the base of urea and formaldehyde or melamine and formaldehyde, or on their mixtures. This type of glue is used in large quantities in the timber industry, in the manufacture of plywood, furniture, etc. It is also used for bonding metals.
Often it also contains various impurities which alter its consistency. The period of usage for mixed carbamide glue depends on the type of glue used, but it is usually between 0.5 and 48 hours. The period of usage for unmixed glue depends on the temperature at which it is stored, as the lower the temperature, the longer it retains its adhesive properties. The addition of ammonia water, urea and melamine may extend the usage period. Carbamide glue freezes at high temperatures, as well as at room temperature, if it contains a curing agent. Glued surfaces do not require special preparation. The glue is used in thin formulae, which can be applied with a brush or sprayed. This glue is characterised by extremely high durability and resistant to moisture.
If it is necessary to increase the viscosity or other properties of this type of glue, it can be mixed with organic and inorganic solvents. White clay is the most commonly used mineral for this. It is advisable to use compounds which are also characterised by adhesive properties. Carbamide glue tightening takes place due to two processes, i. e. physical process, when the solvent is eliminated from the glue and chemical process, when the resin hardens. Both these processes take place simultaneously and can be synchronised. The speed of the hardening process primarily depends on the amount of solvent and its type.
The fixtures used in carbamide glue can be divided into the following three groups: hot, warm and cold. The first group includes ammonium salt. Its operation is based on the ability of these materials to respond to formaldehyde resin, which results in the excretion of acid causing tightening of the glue. The second group consists of weak organic acid ammonium salt. The glue containing this salt hardens at room temperature, but this process happens faster if heat is applied. The third group consists of weak and mineral acids. The process of the glue tightening can be adjusted by adding “buffer supplements”. The supplements increase the viscosity of the glue, preventing it from penetrating to the surface rapidly and helping to reduce costs. Good fillers can combat the disadvantages of carbamide glue, as it become less brittle and shrinks less. Wood powder and lithopone is often used. By gluing together plywood and wooden details, the fillers can reduce glue consumption.
Carbamide glue is water-resistant but not resistant to heat. Studies have proved that the glue does not lose its properties for 4-5 years, even if it is exposed to temperatures up to 50 degrees Celsius. But if the temperature is higher than 60 degrees Celsius, the properties of carbamide glue gradually decrease. This glue is a popular material for wood, plywood and other wood-based items. It is transparent, durable and environmentally friendly. Seams reinforced by this type of glue are not very strong, so this type of glue is not the best option for objects which have to support varying loads. In order to make it more elastic, the glue is mixed with polyvinyl acetate glue.