Polychloroprene adhesion

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]. 

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... 

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. 

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]). 

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. 

Metal oxides. Magnesium oxide is used to cure polychloroprene by converting its few active allylic chloride from 1,2 addition into ether cross-links. There is a synergistic effect when magnesium oxide is used in combination with t-butyl phenolic resins in solvent-borne polychloroprene adhesives. When solvent is removed, the phenolic group in the resin reacts with the magnesium oxide to cross-link [49]. 

There are several excellent reviews on polychloroprene adhesives (for specific aspects see [2,14,70]). 

Metal oxides. Metal oxides provide several functions in solvent-borne polychloroprene adhesives. 

Acid acceptor. This is the main function of metal oxides in CR adhesive formulations. Upon age, small amounts of hydrochloric acid are released which may cause discolouration and substrate degradation. Magnesium oxide (4 phr) and zinc oxide (5 phr) act synergistically in the stabilization of solvent-borne polychloroprene adhesives against dehydrochlorination. 

Scorch retarder. Magnesium oxide retards scorch during mill processing of polychloroprene adhesives. 

Solutions of polychloroprene adhesives containing metal oxides and r-butyl phenolic resin may show phasing (e.g. clear upper layer and flocculated lower layer of metal oxides) on standing for days or months. To recover the full utility... 

Chlorinated rubber is also used to promote the adhesion of solvent-borne CR adhesives to metals and plasticized PVC. Addition of a low molecular weight chlorinated rubber (containing about 65 wt% chlorine) improves the shear strength and creep resistance of polychloroprene adhesives [75] but a reduction in open time is also produced. A heat reactivation (process in which the surface of the adhesive film is raised to 90-100°C to destroy the crystallinity of the film and allowing diffusion to produce polymer chain interlocking more rapidly) restores tack to the polychloroprene adhesives. 

Properties of solvents commonly used in polychloroprene adhesives formulations [77]... 

The properties of the solvent-bome CR adhesives depend on the molecular weight, degree of branching and rate of crystallization of the polymer. The ability of polychloroprene adhesives to crystallize is unique as compared to other elastomers. The higher the crystallization rate, the faster the adhesive strength development. 

The crystallization is responsible for the quick grab of polychloroprene adhesives. This rapid bond strength development allows the formation of immediate dry bonds without the need of clamping or pressing. 

High-pressure lamination constitutes a large market for water-borne polychloroprene adhesives. The choice of the polymer has a high impact on end-use properties. 

Solvent-borne polychloroprene adhesives are unsuitable for bonding low-energy substrates, such as PVC. However, water-borne polychloroprene adhesives display good peel adhesion to vinyl substrates. Addition of an accelerator such as zinc oxide is essential for improved hot bond strength. 

Information provided by Mr. Juan Jose Hemandez-Gonzalez from Adhesivos Heman (Leon, Mexico) on water-borne polychloroprene adhesives is greatly acknowledged. The financial support for research in rubber adhesives from the Spanish Research Agency (MCYT) and the University of Alicante is greatly appreciated. Finally, my deep recognition and acknowledgement to my wife and children for the time I took from them to write this chapter. 

This certificate relates to Climatube extruded foam PE pipe insulation. It is used in the thermal insulation of water supply pipes and heating pipework. The insulation is semisplit for ease of fitting, and polychloroprene adhesive and climatape adhesive tape are supplied for sealing cut ends and joints. Thermal conductivity data are tabulated. EUROPEAN COMMUNITY UK WESTERN EUROPE... 

Polychloroprene adhesives offer good resistance to acids, alkalis, oils and water, and are used widely for bonding rigid thermoplastics such as ABS and... 

Polychloroprene. Polychloroprene dispersions have a range of qualities similar to those of solvent-based polychloroprene adhesives and a similar range of uses. As an example, the bonding of vinyl materials with phenolic resin/paper decorative laminates often is carried out with these products. It is necessary to incorporate acid-acceptor dispersions of metallic oxides, and the dispersions in general do not provide such long open times as solvent-based polychloroprene adhesives. 

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