Polychloroprene adhesive

Adhesive bonds, 1 501-502 breaking, 1 513-517 practical strength of, 1 517-521 Adhesive compositions, 1 524-525 Adhesive joints, 1 501-502 Adhesive polychloroprene grades, 19 852 Adhesive resins, amino acid resins,... 

Further information on rubber-based adhesives is to be found in specialized articles Natural Rubber-Based Adhesives, Nitrile Rubber Adhesives, Polychloroprene Rubber Adhesives Applications and Properties and Polychloroprene Rubber Adhesives Modifiers and Additives. 

In summary, like Nitrile rubber adhesives polychloroprene adhesives use a polar mb-ber and their properties complement one another. 

Contact adhesives (polychloroprene, nitrile, or polyurethane rubber) are used for fitting vinyl roofs, roof linings, sound-deadening mats (where they are not already incorporated in the primer-coated body), and carpets. More recent prefabricated roof constructions are designed for bonding with special emulsions. 

An adhesive may be defined as a material which when applied to surfaces of materials can join them together and resist separation. Adhesive is the general term and includes cement, glue, paste, etc. and these terms are all used essentially interchangeably. Various descriptive adjectives are often applied to indicate certain characteristics. For example, to indicate the physical form of the adhesive, e.g. liquid adhesive, liquid two-part adhesive, film adhesive its chemical form, e.g. epoxy adhesive, cyanoacrylate adhesive, polychloroprene adhesive to indicate the type of materials bonded, e.g. metahto-metal adhesive, paper adhesive, wood adhesive or to show the conditions of use, e.g. solvent based adhesive, cold-hardening, or -curing, adhesive, hot-melt adhesive. 

Non-structural adhesives Polychloroprene Di-acrylic esters Cyanoacrylate... 

The synthesis in 1928 of polychloroprene or Neoprene, which has found much use in high strength elastomeric adhesives. 

The tendency of polychloroprene to crystallize enhances its value as an adhesive (97). The cured or uncured polymer can crystallize on stretching thereby increasing the strength of gum vulcaniza tes. Elastomers that caimot crystallize have poor gum vulcaniza te properties (98). 

Gel polymers such as AG are used as part or all of the polychloroprene component ia an adhesive. Its principal value is ia providing relatively high... 

Latex Adhesive Applications. Polychloroprene latex adhesives have a long history of use in foil laminating adhesives, facing adhesives, and constmction mastics. Increasingly stringent restrictions on the emission of photoreactive solvents has heightened interest in latex compounds for broader apphcations, particularly contact bond adhesives. Table 10 makes a general comparison of solvent and latex contact bond adhesives (158). 

The use of polychloroprene in solvent and latex adhesives has been the subject of a recent review (155). 

Other polymers used in the PSA industry include synthetic polyisoprenes and polybutadienes, styrene-butadiene rubbers, butadiene-acrylonitrile rubbers, polychloroprenes, and some polyisobutylenes. With the exception of pure polyisobutylenes, these polymer backbones retain some unsaturation, which makes them susceptible to oxidation and UV degradation. The rubbers require compounding with tackifiers and, if desired, plasticizers or oils to make them tacky. To improve performance and to make them more processible, diene-based polymers are typically compounded with additional stabilizers, chemical crosslinkers, and solvents for coating. Emulsion polymerized styrene butadiene rubbers (SBRs) are a common basis for PSA formulation [121]. The tackified SBR PSAs show improved cohesive strength as the Mooney viscosity and percent bound styrene in the rubber increases. The peel performance typically is best with 24—40% bound styrene in the rubber. To increase adhesion to polar surfaces, carboxylated SBRs have been used for PSA formulation. Blends of SBR and natural rubber are commonly used to improve long-term stability of the adhesives. 

During World War II, several new synthetic elastomers were produced and new types of adhesives (mainly styrene-butadiene and acrylonitrile copolymers) were manufactured to produce adequate performance in joints produced with new difficult-to-bond substrates. Furthermore, formulations to work under extreme environmental conditions (high temperature, resistance to chemicals, improved resistance to ageing) were obtained using polychloroprene (Neoprene) adhesives. Most of those adhesives need vulcanization to perform properly. 

Structural applications of rubber base adhesives were also obtained using rubber-thermosetting resin blends, which provided high strength and low creep. The most common formulations contain phenolic resins and polychloroprene or nitrile rubber, and always need vulcanization. 

The diffusion process in natural and polychloroprene rubber adhesives can be explained by Campion s approach [1] which considers the concept of molecular free volume. This free volume is mainly affected by the solvent mixture of the adhesive (which will determine the degree of uncoiling of rubber chains) and by the ingredients in the formulation (mainly the amount and type of tackifier). 

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]. 

The elastomers considered in this section have been selected considering the most commonly used in rubber base adhesives natural rubber butyl nibber and polyisobutylenes styrene-butadiene rubber nitrile rubber polychloroprene rubber (neoprene). Typical properties of these rubbers are shown in Table 2. 

Polychloroprene rubber (CR) is the most popular and versatile of the elastomers used in adhesives. In the early 1920s, Dr. Nieuwland of the University of Notre Dame synthesized divinyl acetylene from acetylene using copper(l) chloride as catalyst. A few years later, Du Pont scientists joined Dr. Nieuwland s research and prepared monovinyl acetylene, from which, by controlled reaction with hydrochloric acid, the chloroprene monomer (2-chloro-l, 3-butadiene) was obtained. Upon polymerization of chloroprene a rubber-like polymer was obtained. In 1932 it was commercialized under the tradename DuPrene which was changed to Neoprene by DuPont de Nemours in 1936. 

During World War II, polychloroprene was chosen as a replacement for natural rubber because of its availability. Two copolymers of chloroprene and sulphur which contain thiuram disulphide were available (Neoprene GN and CG). One of the first successful applications of these polychloroprene adhesives was for temporary and permanent sole attachment in the shoe industry. However, these polychloroprene cements show a decrease in viscosity on ageing and a black discolouration appears during storage in steel drums. Discolouration was produced by trace amounts of hydrochloric acid produced by oxidation of polychloroprene... 

Several types of polychloroprene elastomers have been commercialized. The most important polymers used in solvent-borne adhesives are the following. 

Neoprene AF ( 963). It is a polychloroprene modified with methacrylic acid. Although it is a slow-crystallizing elastomer, the cohesive strength develops very rapidly and it has improved creep resistance at high temperature compared with Neoprene AC or AD. The improved properties of Neoprene AF are derived from the interaction between the carboxyl functionality with the metal oxides added in the solvent-borne polychloroprene adhesives. 

About one dozen polychloroprene latices have been developed for adhesive... 

Influence of solvent on viscosity and tack of polychloroprene adhesives... 

Butyl phenolic resin is a typical tackifier for solvent-borne polychloroprene adhesives. For these adhesives, rosin esters and coumarone-indene resins can also be used. For nitrile rubber adhesives, hydrogenated rosins and coumarone-indene resins can be used. For particular applications of both polychloroprene and nitrile rubber adhesives, chlorinated rubber can be added. Styrene-butadiene rubber adhesives use rosins, coumarone-indene, pinene-based resins and other aromatic resins. 

Rosins and rosin derivatives. The resins more commonly used in rubber base adhesives are rosin esters, particularly glycerol and pentaerythritol esters, as well as rosins modified by disproportionation and hydrogenation. The glycerol ester of hydrogenated rosin has been reported to be an excellent tackifier for polychloroprene adhesives (see pp. 344-357 in [17]). 

The chemical nature of the tackifier also affects the compatibility of resin-elastomer blends. For polychloroprene (a polar elastomer) higher tack is obtained with a polar resin (PF blend in Fig. 27) than with a non-polar resin (PA blend in Fig. 27). Further, the adhesion of resin-elastomer blends also decreases by increasing the aromatic content of the resin [29]. Fig. 28 shows a decrease in T-peel strength of styrene-butadiene rubber/polychloroprene-hydrocarbon resin blends by increasing the MMAP cloud point. Because the higher the MMAP... 

Resistance to weathering. Zinc oxide and magnesium oxide stabilize poly-chloroprene against dehydrochlorination. Further, zinc oxide helps vulcanize the rubber, and magnesium oxide reacts with /-butyl phenolic resin to produce a resinate which improves heat resistance of solvent-borne polychloroprene adhesives. 

Fumed silicas (Si02). Fumed silicas are common fillers in polychloroprene [40], natural rubber and styrene-butadiene rubber base adhesives. Fumed silicas are widely used as filler in several polymeric systems to which it confers thixotropy, sag resistance, particle suspension, reinforcement, gloss reduction and flow enhancement. Fumed silica is obtained by gas reaction between metallic silicon and dry HCl to rend silica tetrachloride (SiCU). SiC is mixed with hydrogen and air in a burner (1800°C) where fumed silica is formed ... 

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