Contact adhesives polyurethane based

In the interior of the vehicle, prefabricated roofs consist of outer decorative layers that are bonded to the layers imparting mechanical rigidity (emulsions, contact adhesives, polyurethane hot-melt adhesives). Contact adhesives, polyurethane adhesives, and high-frequency welding auxiliaries (resin solutions or PVC-based emulsions) are used for attaching textiles or plastic films to the supports made of molded fiberboard or plastics for door inner panels. Emulsions, contact or polyurethane hot-melt adhesives are used for bonding textiles to molded fiberboard or plastics for parcel shelves. 

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]. 

For those products laminated using reactive polyurethane based adhesives, suppliers have been aware for many years of the potential migration of amines formed by the reaction of unreacted isocyanate monomer with water and recommend that laminated products are given time to fully cure before they are used in contact with food. Adhesives have been developed that contain low levels of monomeric aromatic isocyanates, in order to reduce any potential migration of aromatic amines into food in critical applications. Such adhesives are not considered to present any notable amine migration hazard unless used in high-temperature applications. 

To avoid inner tensions through thermal stress, it is recommended to use only adhesives that cure at room temperature. The adhesive selection is limited by the fact that many applications require an invisible glueline. In such cases, adhesives with fillers are excluded, cyanoacrylates and in particular radiationcuring products (Section 9.3.3) are the suitable choice. If the visual appearance of the bonded joint is not important, two-component reactive adhesives based on expoxides, polyurethanes, methacrylates, contact adhesives and, if required, adhesive tapes are recommended. 

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. 

Contact adhesives based on polychlorobutadiene or polyurethane are used for large-area bonds between PVC-U and PVC-C sheets and wood or metal. 

Adhesives for Plastic Floor Covering. Solvent-free adhesives based on acrylic and vinyl acetate - ethylene - acrylic emulsions are used for bonding vinyl, synthetic rubber, and polyolefin flooring. Solvent-containing contact adhesives (rubber- or polychloro-prene-based) still are used for some applications (e.g., stairs). When water resistance is required, reactive polyurethane or epoxy resin adhesives are preferred to waterborne emulsions. 

Prefabricated Construction. Sandwich elements are widely used in prefabricated construction. In this case, bonding must meet stringent requirements with regard to stability and durability, especially in the case of exterior wall elements. Deflections attributable to difierential temperature or moisture-induced expansion or contraction can amount to as much as 5% of the length. The adhesive layer must be permeable to water vapor or act as a water barrier, depending on the structure and function of a given element. The adhesives used are two-component reactive resins, based mainly on epoxy resins, but polyurethane resins are used as well, as are elastomer-based contact adhesives that are applied on both sides. 

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. 

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. 

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. 

Laminating adhesive 2.5 g/m (solvent-based two-part MDI polyester polyurethane), resin solution 1 containing 1-5% 4,4 MDI, solution 2 including 3-aminopropyltriethoxysilane 38 pm polyethylene (food contact surface). 

Polystyrene Although polystyrene is usually bonded by solvent cementing, it can be bonded with vinyl acetate/vinyl chloride solution adhesives, acrylics, polyurethanes, unsaturated polyesters, epoxies, urea-formaldehyde, rubber-base adhesives, polyamide (Versamid-base), polymethylmethacrylate, and cyanoacrylates. The adhesives should be medium-to-heavy viscosity and room-temperature and contact-pressure curing. An excellent source is a Monsanto Company technical information bulletin which recommends particular commercial adhesives for bonding polystyrene to a number of different surfaces. Adhesives are recommended in the fast-, medium-, and slow-setting ranges (10). 

DispercoII. [Bayer Miles] Polychloro-butadiene and polyurethane latexes for formulation of water-based contact cements, laminating and mastic adhesives for the automotive, construction, furniture, footwear, and iricg. industries. 

An advantage of incorporating ECPs into a binder such as epoxy or polyurethane is the good adhesion that such binders provide, and the actual performance of coatings based on formulation may be due to the fact that the adhesion is better than that obtained by electropolymerization. However, this strategy leads to less contact between metal and ECP and, in view of the protection mechanisms described in Section 16.2, this may be to the detriment of the anticorrosion properties. 

PVAc-based commercial wood adhesives are evaluated using standard tests for non-structural applications, as reported in EN 205 [8], and they are classified in agreement with the standard EN-204 [9]. This standard allows to classify wood adhesives in 4 categories from D1 to D4. D1 adhesives show a good resistance only in dry conditions D2 adhesives should withstand a rather low water presence, such as in occasional exposure in kitchens and bathrooms D3 adhesives are suitable to come in contact with cold water, such as for outside windows and doors, kitchen and bathrooms furniture D4 adhesives are suitable to be used in extreme conditions (resistance to hot water). Vinyl acetate homopolymer can be used to formulate D1 or D2 adhesives. Vinyl acetate based adhesives cross-Unked with hardeners and urea-formaldehyde (UF) adhesives belong to class D3. Only the phenol-formaldehyde (PE), resorcinol-formaldehyde (RF) and melamine-formaldehyde (MF) adhesives, some special 2-component polyurethanes (PUs), and cross-linking vinyl adhesives belong to class D4. 

Sealants, while sharing many similarities with adhesives, tend to be made from different materials and include those based on polysulfides (often for uses in contact with fuel), silicones, polyurethanes, acrylics in both solvent-based and latex-based materials, and sealants based on butyl and fluorocarbon polymers. In addition to adhesive and sealant types, this chapter reviews methods for testing and qualifying these materials. 

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