Adhesive is a process material, which is used for sticking.

According to DIN EN 923 an adhesive becomes as "non-metallic material, the jointing parts by surface adhesion (see adhesion) and internal firmness (see coherence) to connect can "defined.

Although there are also adhesives on basis of inorganic compounds, as for example water glass (sodium and/or Kaliumsilikat) or the products on basis of cement, the predominant majority of the adhesives used today is to be assigned to the organic compounds.

History

Already before 6000 years the Mesopotamier used bitumen for building purposes. 3000 v.Chr knew the Sumerer manufacturing glue from animal skins and about 1500 v.Chr used the Egyptians animal glues for Furnierarbeiten.Das "sticking" is thus both one of the oldest techniques, and one of the most modern joining processes.

Organization of the adhesives

In the bio and a large number of different kinds of adhesive is used. The different kinds of adhesive can be divided on the one hand according to the chemical basis and on the other hand according to the solidification mechanism.

after the chemical basis

after the solidification mechanism

The organization into Duromere, thermoplastics and elastomers, how it is usual with plastics, is a little meaningful with adhesives. There are adhesives (particularly with the PU), which harden as Duromere, elastomers and thermoplastics. A better order criterion is solidified the way like itself the adhesive - like it thus the necessary coherence develops.

Physically tying adhesives

By this one understands such adhesives, with which already the finished adhesive, i.e. the polymer are brought actually, into the bonding slit. In addition a physical procedure is used, which brings the adhesive first into a processable form, in order to let it solidify later in the sticking gap again.

of wet adhesives

With wet adhesives the polymer is present solved in organic solvents and is in such a way appliziert. Adding takes place at one time, at which still sufficient solvent is present in the layer of adhesive, in order to ensure a wetting of the second jointing part surface. By evaporating the solvents the adhesive ties, i.e. it first tougher and finally solidifies itself by the training of physical reciprocal effects between the polymer chains.

of wet adhesives can be used also for the diffusion sticking (cold shuts) of thermoplastic plastics. Both sticking surfaces are coated with the adhesive, which contains a solvent, which is capable, the surface of the jointing parts After short impact time the two jointing parts are added under pressure, whereby the polymer chains of the surface - similar as the bristles of two brushes, which are into one another pressed -, opened by the solvent, to penetrate itself and with one another loops. After escaping the solvent in such a way a connection after some time, which is based purely on develops.

Application risks:

• of wet adhesives cannot being e.g. inserted on shatter crack-sensitive materials like polycarbonate, since by the existing solvents the shatter cracks are indicated.

• With wide gluings at least one substrate should be solvent permeable, since otherwise complete hardening of the gluing for a very long time (up to some days/weeks) can last.

Emulsion bonding adhesives

Emulsion bonding adhesives usually use water as mobile phase (dispersing agent), in which the adhesive components are present as dispersion. After applying on the surface which can be stuck together the dispersion breaks by escaping the dispersing agent into the jointing parts or by its evaporation into the environment and/or by change of the pH value. The adhesive components approach thereby on and form a film, which can connect the two jointing parts.

Aqueous emulsion bonding adhesives are used variously today as substitution of the solvent adhesives, since they are not as these fire and explosion dangerous and also no health-impairing solvents set free. Disadvantage is however that water-based adhesives need longer time or more energy for tying. In addition emulsion bonding adhesives are frost sensitive.

Application risks:

• At least one substrate must be water permeable (similar to the solvent adhesives), since otherwise the hardening by precipitation of the adhesive can last for a very long time.

• With substrates which bend under influence of water to the corrosion, should Dispersiosnklebstoffe are not used.

• Gluings with emulsion bonding adhesives are sensitively to high humidity/water, it perhaps come to a complete failure of the gluing.

Fusion adhesives

Fusion adhesives - often also called "Hotmelts" - are at ambient temperature and become through melt opens processable. The hot adhesive melt is applied on the part which can be stuck together and added immediately with the second part within the Offenzeit. Immediately after the cooling and solidifying the adhesive the connection is fixed and functional. This made possible in production processes very fast cycle times and direct processing.

For the hobby and small user fusion adhesives come in the form of sticking candles (sticking sticks) into the trade, which can be processed with fusion sticking pistols. With technical applications they are processed also in the form of foils, granulates or blocks by fusion devices and order headers downstream.

Fusion adhesives are solvent-free, however their employment is limited because of the high processing temperatures to temperature-resistant materials. On the other hand the adhesive behaves reversibly, i.e. during rise in temperature it becomes again soft and possesses therefore only a reduced heat resistance (see also reactive fusion adhesives).

Contact contacts

Contact contacts can be both solvent adhesives and emulsion bonding adhesives, which are processed in the contact sticking procedure.

In addition first both adhesive surfaces are coated evenly with adhesive. Then one lets the adhesive ventilate so long, until the adhesive film feels drying, i.e. with the Fingerprobe pulls no more threads and exhibits only a small Soforthaftung. In the next step the adhesive surfaces must be joined within the open working time accurately. A correction is not possible. In order to obtain a good gluing, it is necessary to press the adhesive surfaces together briefly under as high a pressure as possible. If a substrate is flexible, one avails oneself best of a role, with which a high line pressure can be obtained. Sticking is immediately loadable after adding. The ultimate strength is reached after some days, if the remainder solvents escaped from the bonding slit are. One of the most well-known Kontaktkleber for the domestic purposes is the solvent adhesive "Pattex" manufactured by handle.

Application risks:

• As is the case for the solvent adhesives at least one substrate must be solvent permeable also here, since otherwise the hardening by precipitation of the adhesive can last up to reaching the ultimate strength for a very long time.

• Gluings with contact contacts are not warm stable. Particularly under peeling load at temperature increased at the same time leads to a failure of the gluing

Articles in category "Adhesive"

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