3 сентября, 2015 
Pokraskin Contact adhesives are easy to process by casting, spraying, or using a doctor blade. When porous materials are joined, the adherents may be repositioned by briefly lifting them if the solvent has not yet fully evaporated. This property is utilized especially in the textile industry and saddlery, as well as in the manufacture of cars.
Some 70 years of experience have taught us that, depending on the formulation, the age resistance of contact adhesives can be very good. When joining surfaces that are difficult to bond, such as stainless steel, the adhesion properties too are generally good. It is not compatible with conventional adhesion theories (see Chapter 3) that the bond-line generally has a high resistance to water; rather, this is most likely due to the dynamic adhesion properties of contact adhesives (see Section 3.4).
Nowadays, the high solvent content (up to 80%) of contact adhesives is hardly tolerable unless proper ventilation systems are available which provide retrograde condensation ofthe solvents. These systems, in turn, have a high demand for energy, and consequently alternative options such as dispersion contact adhesives are increasingly being used. Nanometric adhesive particles are maintained in a semifluid suspension in water by dispersing agents. A water content of30-40 % necessary to obtain a dispersion in the liquid state which usually contains small amounts (5%) of organic solvents to improve film formation at drying and to enhance diffusion between the particles. Surface-active substances (tensides) are added to maintain the stability of the liquid dispersion, but these may accumulate between the particles and induce inhomogeneities that may adversely affect the resistance to water at a later stage.
As with solvent-based contact adhesives, milky dispersions are applied to both adherent surfaces, and the water is allowed to evaporate from the adhesive layers until they are dry to the touch and tack-free, using the ‘fingerprint method’. The adhesive layers are ready to be joined when the milkiness vanishes, and they become translucent. After the evaporation of water, j oining is carried out using high pressure for a short period of time, as in the case of solvent-containing contact adhesives. If at least one adherent is made from a porous material, the substrates may be joined before the bond is allowed to dry completely. Compared to organic solvents, water has a high boiling temperature and evaporation energy, and therefore the drying process must take place slowly and may only be enhanced by an input of energy.
As mentioned above, when solvent-based contact adhesives change from the liquid into the solid state, a high tack makes it possible briefly to undo the bond for repositioning purposes, the adhesive being already loadable. This is not possible with dispersion adhesives and is considered to be a disadvantage in the textile industry and saddlery. It also causes problems in the car manufacturing industry when bonding insulating pads.
Unless hardeners (crosslinking agents) are added (as in the case of solvent-based systems) in the cured state, all contact adhesives used so far have been thermoplastic
materials with limited resistance to heat and solvents. The primary fields of application of contact adhesives are the bonding of facing materials in car manufacture, the creation of composite panels for furniture and for use as insulating materials, and last — but not least — the textile and leather industries.
At this point it must be noted that it is possible today to create solvent-free and water-free contact adhesives based on modified silane (MS) polymers (e. g. MS polyurethanes). These materials have a high viscosity in the initial state, while tack confers an inherent strength to the bond shortly after compression. The bond-line is cured by the polycondensation reactions of the silane end groups that occur at a later stage, when ambient moisture diffuses into the bond-line.
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