Glue (adhesives)

Adhesives are mixtures and solutions of substances of organic and inorganic nature, which, after technological processing form seams-layer, firmly linking the various materials. By type of feedstock adhesives are divided into two groups: those based on synthetic materials based on natural materials. The main components of the first group of adhesives, synthetic resins, which are derived from simple substances in chemical reactions. The basis of the second group of adhesives are substances of plant and animal origin. Adhesives vegetable protein derived from legume seeds, starch, resins, and sap of plants. Glues of animal origin (glyutinovye, albumin, casein) are derived from proteins contained in the tissues, bones, blood and milk of animals. In furniture manufacture are the most common adhesives based on synthetic resins. The characteristics of resin adhesives are divided into thermoset, thermoplastic and rubber. Thermoset adhesives are cured by chemical reactions in the polycondensation or polymerization. During this process irreversible adhesive joint with increased teplovodostoykostyu. Thermoplastic adhesives are cured by physical means the removal of solvents, thinners. They form reversible elastic adhesive joint which softens under the influence of heat. Adhesive joint in thermoplastic adhesive has a slightly lower teplovlagostoikost than thermosetting adhesives. Rubber adhesives cure physical and chemical means for removal of solvents, thinners, vulcanization of rubber mixtures. Adhesives based on synthetic materials are often prepared in the form of mixtures of adhesive materials of different characteristics (thermosets, thermoplastics, rubber). In this case, adhesives belong to the type of adhesive material content in the mixture above. Adhesives based on natural materials used is limited. Used adhesives based on natural rubber produced from the sap of plants, and some types of protein glues. Protein adhesives are used more frequently for repairs. Adhesive protein adhesives - glues the collagen - derived from raw materials of animal origin: mezdrovy - from the skins, bone - from bones and horns of animals. Adhesive casein glue made from milk products. Depending on the physical state in which the glue is transported and stored, they may be liquid, gel, powder, as granules, rods and films. The glue is different. It may include adhesives, solvents, thinners, hardeners, fillers, additives. Some adhesives used several types of adhesives. In liquid adhesives adhesive substance is in solution or in dispersion. In powdered adhesives, rods and granules film adhesives are solid. Dispersion - aqueous solution with uniformly distributed therein small particles (globules) of adhesive. To achieve the desired viscosity liquid adhesive dissolving solvents and diluents. Solvents used to prepare solutions, thinners - dispersions. The solvents and diluents using water, organic solvents, etc. The fillers are introduced into the adhesive is mainly to reduce costs and increase the viscosity of the adhesive composition. Some of the fillers themselves have an adhesive ability. Used as a wood flour filler, waste flour production, kaolin, sodium alginate, gypsum binder, phosphogypsum, etc. hardeners used in the composition of reactive adhesives. Hardeners are selected according to the type of adhesive and processing technology of glue. Additives are introduced into the adhesive for different purposes: stabilization of the composition, increasing the period of viability, binding of harmful emissions, plasticization, etc. The composition of the adhesive is given by the technical documentation on the glue and its mode of application. Adhesive properties derived from the technological and operational performance. On technological performance depends on the quality of bonding and the duration of this process. The quality of the glue in the initial state is characterized by the appearance of the components of the adhesive. Mass fraction of solids shows how many from the adhesive used to form the adhesive joint. The higher proportion of solids, the more economical than the adhesive. The viscosity of the adhesive depends on its nature and content of dry matter - the concentration (mass fraction of solids). The viscosity of the adhesive depends on the method of its application. It is important that the viscosity of the adhesive during the operation remained stable. This affects the uniformity of flow and deposition on the bonding surfaces, ie, the quality of bonding and economy of the process. The duration of solvent evaporation effect, on the one hand, the duration of open time after application of glue, on the other - to change the viscosity of the working solution in the process. The viscosity of the adhesive during storage should not change more than the permissible value. The concentration of hydrogen ions (pH) shows acidity (alkalinity) adhesive solution. It affects the shelf life and stability of indicators of glue. Time zhelanizatsii glue in the presence of curing agent describes the ability to cure under standard test methods. Term cure depends on the properties of the adhesive and curing conditions. Curing conditions may be different: the use of short-term or long-term pressure, the use of conventional or high temperature, etc. on time and curing conditions depend on the choice of equipment and devices for gluing. Miscibility with water - an important indicator of water-soluble adhesives. When adding water should not precipitate. Shelf life means the time during which obveivaetsya stability performance adhesive. It also determines the amount of glue, which should prepare or store. Viability of the working solution ensures the stability of the finished adhesive composition and determines the extent of his workplace. The longer viable, tesch less waste glue. Adhesion is the ability to stick to the glue bonded. From this property depends on the uniformity of application of glue and adhesive joint strength. The rise time determines the strength of adhesive bonded materials duration of exposure to subsequent processing. Abrasive properties (the ability to blunting of the cutting tool in post-processing) in the adhesive joint should be minimal. Of performance indicators depends on the strength and durability of bonded assemblies, the appearance of the product. Color of the adhesive joint and the adjacent material (wood, etc.) in locations where they are available for review, should not stand out sharply. Shrinkage of the adhesive joint during drying should be minimal, otherwise it will lead to tensions within it. Due to stress may have warped parts, or the destruction of the adhesive joint. The strength of the adhesive joint - one of the most important indicators - depends on the type of adhesive and bonding is provided by the regime. Durability of glue joints should be appropriate for the duration of the product, which is determined by the properties of the main structural materials. Affect the longevity of water-resistance and biological resistance of the adhesive. Performance indicators are defined for the conditions of product use (indoors, outdoors, under tropical conditions, etc.). By the technological and operating properties are safe and benign starting materials of adhesives and adhesive joints. During storage, preparation, bonding, machining and maintenance of adhesive should not release toxic and flammable substances, so as not to create conditions for the fire danger, destruction of the body of people and pollution. The main requirements to the mix glue parts, parts, products, strength and stealth place bonding. Especially in the works of fine and applied arts, these places should not differ from the rest of the material nor the strength nor the color. The choice of adhesive depends on the requirements for bonding pieces of sculpture or artistic production and arts. The quality of the glue for them is only as strong adhesive bonding, water resistance, light resistance, vitality and biological stability. Water resistant glues determine the level of weakening glue joints in the process of boiling or soaking them in water: 50% or more - nevodostoyky glue, no more than 20% - vysokovodostoyky. Assess the viability of the adhesive for a period of his zhidkotekuchego state in which it is suitable for bonding. About lightfastness glue is judged by its darkening the light. Biological resistance by the absence of lesions adhesive bacteria or fungi.