Curing of Adhesives

Curing of adhesives and polymer systems depends on the characteristics of the particular material. A few of the more common curing modes are presented as follows  

Thermoplastic materials are typically cured by evaporation of solvent or by cooling below their melt temperature. 

Thermosets are cured by chemical cross-linking, which is enhanced by temperature or catalysts. 

In situ polymerization occurs with monomeric materials, where the monomer polymerizes in the presence of some catalyst (e.g., cyanoacrylate in the presence of water). 

For a thermoset adhesive there are at least four regimes of phases of final cure state. The four regimes are as follows  

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Panels then move into a cooling device, normally a wheel or rack, where they are held individually and air is circulated between them to remove the majority of heat remaining in the boards after pressing. It is desirable to reduce the average board surface temperature to about 55°C. This temperature is sufficient to complete the cure of adhesive in the core of the board. The heat also helps to redistribute moisture uniformly within the boards, because the board surfaces are drier than the core when the boards come out of the press. Warm boards are normally stacked for several hours to a day to allow for resin cure and moisture equalization. 

Polymeric films, metallic foils. Curing of adhesives, coatings. Low energy processing in... 

No-wear high-performance floors for high-traffic areas Heat-shrink films and tubing Curing of adhesives, coatings and inks... 

The yields of radiation-induced polymerizations can be very high. No additives are required, which makes it possible to synthesize very pure polymers. The initiation step is temperature independent giving rise to an easily controlled process at any desired temperature. These features account for the commercial interest in radiation polymerization. The very high speeds attainable within the layers of monomers subjected to powerful electron beams explain the wide use of this technique in radiation curing of adhesives, inks and coatings. The corresponding formulations are "solvent-free" and involve pre-polymers and monomers as reactive diluents. 

Inhomogeneities [137] and traveling waves of the initiator [138] have been investigated during the formation of PMMA, and the spatial variation and the dynamics of a photo-induced polymerization have been followed in another example [139]. The curing of adhesives [112], and the influence of embedded fibers on the loeal polymerization rates of epoxy resins [140, 141], have been investigated in a similar way. A related subjeet is the vulcanization process of elastomers (cf. Section 5.2.2). 

Cold curing Curing of adhesives without heat supply. Temperatures below room temperature delay reaction, while those above room temperature accelerate reaction. 

In the manufacture of amino resins every effort is made to recover and recycle the raw materials. However, there may be some loss of formaldehyde, methanol, or other solvent as tanks and reactors are vented. Some formaldehyde, solvents, and alcohols are also evolved in the curing of paint films and the curing of adhesives and resins appUed to textiles and paper. The amounts of material evolved in curing the resins may be small so that it may be difficult to justify the installation of complex recovery equipment. However, in the development of new resins for coatings and for treating textiles and paper, emphasis is being placed on those compositions that evolve a niinimum of by-products on curing. 

INSTITUTE OF PACKAGING PROFESSIONALS 481 Carlisle Drive, Herndon VA 22070, (703) 318-8970. A variety of topics covering adhesives, cure of adhesives, hot melt tackifying Resins, labels, packaging, and more. 

Analysis of interfaces between materials, especially for failure analysis after aging and testing of adhesively bonded systems Study of the cure of adhesives. 

Uses Free radical initiator for UV curing of adhesives, coatings, inks Trade Names Containing Esacure KIP100F Esacure KT37... 

Heat heatment can also reduce the pH of the wood to a value of 3.5 [10], which might retard or accelerate the curing of adhesives, depending on the type of adhesive used for bonding. For instance, the acetic and formic acids which are present in wood after heat treatment might neutralize the alkaUne hardeners used for phenolic resins and hinder the adhesive hardening. On the other hand, a low pH of the wood surface could accelerate the chemical reactions of the acid catalyzed amino resins [31]. 

The contributions of physics to adhesion are further manifested by the extension of uv- and electron-beam curing of adhesives to low temperatures. Radiation-curable adhesives were originally intended to eliminate solvents in the systems. However, the use of certain toxic acrylate monomers presented some problems. So far, radiation-curable systems have become technologically challenging, but economically less attractive than most thermally cured systems. Since one of the earliest papers on photoadhesives by Nakano (35) many patents have been issued on this subject. Two reviews have been published by Stueben (36). ... 

A second aspect is that some adhesives/sealants cure by the diffusion of water vapour. This causes a sequence of chemical reactions, which leads to chain extension and possibly cross-linking by step copolymerization. Examples are some silicone and isocyanate materials, where the depth of cure is often proportional to the square root of RH, and to the square root of time" (Moisture cure of adhesives, Silicone adhesion). 

A stoichiometric mixture of an oligomeric diol and diisocyanate will react to give a polyurethane. However, if there is double the quantity of diisocyanate, the reaction product will be an ohgomer with isocyanate end groups. Such adhesives cure by the ingress of moisture by the following sequence of reactions. (Moisture cure of adhesives). 

Moisture cure of adhesives J COMYN Cyanoacrylates and isocyanates... 

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