WOOD PROCESSING GLUES
Vinyl acetate adhesives have long been used in the wood and joinery production, mainly because of the high adhesion to wood and the penetration into wood. Compared to other types of adhesives, they have several important properties which are particularly relevant to this area of application. The first is the immediate readiness of the adhesive to be used without any special treatment. The adhesive is softer and more elastic after hardening than other wood adhesives, and therefore does not cause dulling of tools when machining the glued parts. Working with glue is harmless in terms of health because the adhesive does not contain any harmful solvents. Its versatility of use is unmatched and therefore a small variety of adhesives is used for many different types of joints, woods and materials.
Vinyl acetate adhesives are white liquids with a low fluidity and characteristic aroma. They are non-explosive, non-flammable and non-toxic. The film formed by drying the adhesive is transparent or matte with white ink. It is a continuous, relatively hard, slightly elastic and non-sticky substance.
From a chemical point of view, these are aqueous homopolymeric polyvinyl acetate dispersions, treated with a plasticizer and other components (standard adhesives) or aqueous copolymer dispersions of vinyl acetate with other comonomers, which may be treated with various additives, e.g. a hardener, a plasticizer, etc. (expressive and water resistant adhesives). Adhesives do not contain any organic solvents.
There is no chemical reaction or change in the bonding process when in action. This is the physical process in which wood removes water gradually from the dispersion adhesive, forming a continuous film on its surface. No hardener (except waterproof adhesives) is added to the glue, it is not necessary to dilute or to heat it.
Resistance to climatic stress
Articles made of wood or from other pulp-based material, are often placed in places which may be exposed to high humidity, water, high or low temperatures, etc. in order to withstand such a stress, the bond must also meet certain criteria. Specific conditions are defined in STN EN 204. According to this standard, wood adhesives are divided into four classes of resistance:
|Group of resistance||Examples of requirements on surroundings1) and area of use|
|D1||Interior, where temperature is only rarely or for a short period of time higher than 50 oC and dampness of wood is 15 % at most.|
|D2||Interior with rare short-term influence of water or condensate of air humidity and/or short-term high humidity of air, which results in increase of wood dampness up to 18 %.|
|D3||Exterior protected from climatic stress or interior with regular short-term influence of water or condensate of air humidity or long-term influence of high air humidity.|
|D4||Exterior exposed to climatic stress, but with adequate protection of surface, or interior with regular intense influence of water or condensate of air humidity.|
Surface of glued parts must be clean, with no dust and greasy and oily stains. Generally, it is required, that the sawn wood was dried on air for 8 - 12 months and subsequently artificially dried till final dampness is 8 - 12 %. Sawn wood should be stored in places with air conditioning to balance eventual differences of dampness. Second seasoning should follow gross dimension goods. Planning, milling or, respectively, sawing, storing and sticking together should be carried out in one day because thus it is possible to prevent prolonged hardening time and reducing of joint rigidity. It is important to keep precision in glued gaps and possibly in minimum thickness differences of individual boards for it is the only way how to achieve the shortest possible time of press working and the highest possible rigidity.
Duvilaxes can be applied in practically by all manner of use, e.g. brushes, rollers, spreading machines and spray guns.They can be applied on one or both sides depending on type of application.
Work tool cleaning
Cleaning the tool is simple. While the adhesive is still damp, it is cleaned with lukewarm water. After drying, it is best to leave the tool for several hours in water and, after swelling, the adhesive layer is mechanically removed.
D1 acc. EN 204
D2 acc. EN 204