Contact adhesives polychloroprene based

Plate 23 Insulated roof panels are prepared from the shaped steel profile shown and polystyrene board. Both are sprayed with a solvent-borne polychloroprene-based contact adhesive. By balancing the rate of solvent evaporation carefully it is possible to apply the adhesive without damaging the polystyrene - which dissolves readily in many organic solvents, Some 5-10 minutes after being sprayed the two parts are assembled and passed through rollers which press them firmly together. This process is very quick and a stationary press is not required. Material SPRAYLOCK 901 manufactured by National Adhesives Resins Ltd. 

Table 3.5 Polychloroprene based contact adhesive for EPDM membrane installation (phr) ...

Historically, solvent-based contact adhesives such as polychloroprene were used, but have been phased out for environmental reasons. 

Water-based dispersion adhesives consist of oligomers dispersed in water with surfactants as dispersing agents and stabilizers. Before dispersions, natural rubber latex and casein were used to manufacture such adhesives. Currently, polyvinyl acetate (PVAc) and polyacrylate serve as synthetic base polymers for water-based PSA, while polychloroprene and thermoplastic polyurethane serve the same purpose for water-based contact adhesives. 

Natural rubber adhesives were traditionally used as contact adhesives. However, synthetic polymers are more generally used today. Polychloroprene adhesives are the most common contact adhesives based on synthetic rubber, although recently some have been displaced by polyurethane and acrylic polymers [2]. 

Polymeric materials are commonly used for bonding materials. Impact or contact adhesives are mainly based on highly crystalline polychloroprene (Neoprene), NR latex is used as a flexible adhesive very suitable for use with fabrics. Rigid adhesives based on materials such as polystyrene cement, epoxy resin or cyanoacrylates are suitable for bonding of rigid materials. The bond is provided by intramolecular forces between the adhesive and the adherend. Adiabatic... 

Since it is not possible to commercially produce a polymer that is based on the cis 1,4 form, commercial polymers are based on the Irons 1,4 form which has a crystalline melting point, Tm, of +75 °C and a Tg of -45 °C. Pure 1,4 trans polychloroprene thus crystallises readily and would normally be considered to be of limited use for a rubber. Such a polymer, however, does not crystallise when dissolved in a solvent, but will do so when the solvent evaporates. This feature is used to good effect in the production of contact adhesives. 

A bodied, or more viscous, solvent may be required by certain joint designs and for producing airtight or watertight seals. These are made by dissolving usually 5%-15% of polystyrene by weight in a solvent. Solvent-based contact cements provide the strongest bond between polystyrene and wood. These adhesives all have a neoprene (polychloroprene) base and a ketonic-aromatic solvent system. 

A special type of organic solvent-based adhesive is the so-called contact adhesive. This makes use of the fact that certain elastomeric or rubbery solids (e.g., polychloroprene) have the property of autohesion, i.e., they can stick readily to themselves, especially if compounded with resins and containing small amounts of solvents. The bonding takes place by a diffusion process, the adhesive being applied to both surfaces to be bonded. Thus substrates may be coated with a contact adhesive, the adhesives can be allowed to dry till most of the solvent has evaporated (the dry adhesive film at this point will contain... 

Polychloroprene has been used as a polymer in contact adhesives for many years. Its use in pressure-sensitive adhesives is not as widespread however, the availability and properties of this polymer make it another attractive alternative for water-based PSA s. Polychloroprene is available in both conventional uncarboxylated or carboxylated forms. 

Water-borne contact adhesives are growing in importance because of environmental regulations, occupation health and the flammability of solvents. The solids content in the water-borne polychloroprene adhesives varies between 40 and 60 wt%, and viscosities between 15 and 500 mPa can be obtained. Although polychloroprene Unices are water based, they are generally inflammable as the resin is dissolved in organic solvents before emulsifying. All polychloroprene latices are susceptible to coagulation by mechanical, thermal and chemical means. 

Contact cements based on nitrile rubber and polyurethane are more resistant to oils and plasticizers than polychloroprene adhesives. To improve adhesion and to increase thermal stability, contact adhesives may be applied together with isocyanate hardeners. Today solvent-free contact adhesives based on aqueous polychloroprene latexes are also available. 

Most contact adhesives contain a solvent and have a formulation tiiat combines a base of synthetic rubber such as polychloroprene or polystyrene-butadiene with reactive phenolic resins and metal oxides. In addition, there are also transparent types based on polyurethane which provide excellent bonding results for soft plastics such as plasticized PVC (used in many household articles). Recently, a solvent-fi-ee generation of contact adhesives, e.g, based on acrylate, has entered the market. This type can be used to bond solvent-sensitive materials such as polystyrene foam. 

Solvent cements encompass a wide range of performance properties, from the simple natural rubber based cements which are widely used for low performance applications in homes and schools to the structural applications of contact adhesives based on polychloroprene and reactive phenolic resins. 

Contact adhesives appUed on both substrates Complete drying followed by immediate bond by contact under pressure - Same as solvent based - - - Minimum pressure 5 bar - Polychloroprene adhesives... 

Contact adhesives based in one- and two-component polychloroprene (neoprene) and mainly polyurethane adhesives are the most commonly used in shoe industry to bond upper to sole (see O Chap. 14). These adhesives are bonded by autoadhesion which implies the application of adhesive to both surfaces to be joined diffusion of polymer chains must be achieved across the interface between the two films to produce intimate adhesion at molecular level. To achieve optimum diffusion of polymer chains both high wettability and adequate viscosity and rheology of the adhesive should be achieved. 

The atomization is controlled by the air pressure, the air inlet (controlled by button G), and the air holes on the sides of the head. The air coming out of these air holes also flattens the adhesive stream so that the adhesive stream becomes a narrow strip, instead of being in a conical shape. For instance, with a fluid polychloroprene solvent based adhesive, this strip on contact with the substrate located at a distance of 40 cm, will give a trace of 4 cm width and 50 cm length (Fig. 20). 

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