RFL dips

Cord Resorcinol Formaldehyde Latex (RFL) Dipping/Drying Lines.170... 

RFL dip is known to possess the required properties resorcin is precondensed in an alkaline medium, whereby monomethylol, dimethylol and trimethylol resorcins are formed. 

The standard aqueous treatment for textile adhesion is based on resorcinol/formaldehyde resin/latex (RFL) dip systems. A typical formulation for such an adhesive dip is given in Table 9.1. 

The rayon textile is then dipped through the RFL dip and the impregnated fabric dried and baked, to cure the deposited dip solids. With these fabrics, exposures of 1 - 2 minutes at between 130 °C and 150 °C are sufficient to achieve good adhesion levels, the time and temperatures being to some extent controlled by the weight of the fabric. 

This system requires just a single pass through this modified RFL dip, again with the need for high temperature curing, around 215 °C. 

The use of a solvent solution of an isocyanate as the predip for polyester textiles, followed by an aqueous RFL dip has already been described. The main solvent systems employed today involve the use of rubber cements or solutions, generally including adhesion promoters such as isocyanates, to give the required levels of adhesion between the applied... 

Rayon and nylon are the main fibers with which RFL dips func-tion well directly. For polyester and glass, the textiles require a special treatment, usually involving a polyisocyanate and a reactive silane respectively, to afford appropriate levels of RFL adhesion. In the glass-silane case, the mechanistic contribution is almost surely one of strong adsorption and attachment through the silane s organofunctional end with reactive R-F species. 

Additional evidence for sulfur s role was provided by a paper two years ago by K-D Albrecht of Bayer. With both nylon and rayon, RFL dips furnished markedly improved adhesion as the level of sulfur was increased in the carcass compound over the range from one part to three parts. This is shown in Figure 9. 

In the applications of SRH additives for typical industrial molded or extruded elastomers, there has been considerable study of formulating variables which has thrown some light on the mechanism. Chemisorption or methylol reaction with the non-elastomer substrate is, of course, probably similar to that of RFL dips, assuming that a significant level of resorcinol-formaldehyde condensate can find its way into the interface. 

The final data of interest for the proprietary bonding agent were in regard to peel strength development as a rate process. Here we compared the solvent based adhesive again with a typical RFL dip for laminating nylon strips to SBR (Figure 22). 

Before synthetic textile cord was developed, the rubber industry was using casein or animal blood to promote adhesion between cotton cords and rubber. However, when rayon started to be used in the manufacture of tires in 1931, a new adhesive system was needed to promote a good rubber-to-rayon bond. In 1938, W.H. Charch and D.B. Maney of DuPont developed a new adhesive system that involved dipping rayon cord into what is today referred to as an RFL dip. This RFL dip has changed and been modified for the newer synthetic cords discussed earlier however, basically it is still very similar to what was originally developed seven decades earlier. 

An RFL dip consists of an aqueous resorcinol formaldehyde resin liquid with a ruhher latex. The RF resin is used to achieve good adhesion to the organic fiber substrate whether it be rayon, nylon, or polyester. The rubber latex portion can be a natural rubber latex or a styrene butadiene vinylpyridine (terpolymer) latex or even a neoprene latex. This rubber latex is present to achieve good adhesion with the rubber matrix itself. So the RFL allows good adhesion between the rubber and the textile cord reinforcement whether it is used in the manufacture of passenger tires, truck tires, off-the-road tires, power transmission belts, V-belts, timing belts, or various hose products. 

The textile cord or fabric is first immersed in the RFL dip suspension and then passed through a vertical oven under tension at a predetermined elevated temperature and time. This process is called heat setting, where the adhesive dries and coats the cord or fabric while under tension. 

Resorcinol formaldehyde resin is a vital ingredient in preparing the RFL dips. Without the RF resin, it would be most difficult to achieve acceptable adhesion with the textile cord substrate. 

Resorcinol formaldehyde resins used to prepare RFL dips are the product of a chemical reaction between resorcinol and formaldehyde (or formalin) as shown in Figure 5.21. 

An aqueous solution of RF resin is used with different rubber latexes to make the RFL dip needed to treat the textile cord to allow it to achieve rubber-to-cord adhesion during the curing process. It is the RF resin portion of the RFL dip that is responsible for the good adhesion with the textile cord. 

Styrene butadiene vinylpyridine latex (SBVPL) is the most popular rubber latex used to make RFL dips to achieve good rubber-to-fabric adhesion. Usually SBVPL is used for good adhesion between textile cord and rubber compounds based on general-purpose elastomers (NR, SBR, and BR). Occasionally other latexes besides SBVPL are used as well. For example, sometimes natural rubber latex is used for an RFL dip. Then again, neoprene latex can also be used, especially if the rubber compound is based on neoprene. The purpose of the rubber latex component of the RFL is to promote adhesion with the rubber matrix of the product. 

Sometimes natural rubber latex can be substituted in the RFL dip. This may result in a loss in adhesion. Neoprene latex has also been used in RFL dips, but usually it has more of a specific use, such as with a neoprene compound. 

Certain textile cords, such as polyester, do not have sufficient surface activity to properly react with the RFL dip. Therefore, these special textile cords require a predip in a proprietary blocked polyisocyanate and/or an epoxy dip, after which they are heat treated and dried before the RFL dipping procedure. 

Benzene reacts with ethylene to produce ethylbenzene, a feedstock for styrene, the monomer used to produce SBR (the largest volume synthetic rubber), as well as SBVP for RFL dips, and the block polymers SIS, SBS, SEES, and SEPS, which are used as thermoplastic elastomers (TPEs). 

Benzene is used as a feedstock to produce resorcinol, a very important chemical that is used to manufacture resorcinol formaldehyde (RE) resin for RFL dips for tire cord adhesion, as well as RF resin for HRH adhesion systems for rubber-to-metal adhesion, and for the production of TIER for curing polyurethane rubber. 

Ethylene reacts with benzene to form ethyl benzene to make styrene to produce SBR rubber and SBVP latex for RFL dips for cord adhesion. 

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