Phenol-formaldehyde resins, post

In the development of a reactive non-chrome post-treatment, a variety of phenolic resins were synthesized and commercial phenolic resins evaluated. It was found that phenol-formaldehyde resins, creso1-forma1dehyd e condensates, ortho-novo 1 ak resins, and phenol-formaldehyde emulsions gave positive results when employed as post-treatments over zinc and iron phosphate conversion coatings. The above materials all possessed drawbacks. The materials in general have poor water solubility at low concentrations used in post-treatment applications and had to be dried and baked in place in order to obtain good performance. The best results were obtained with poly-4-vinylphenol and derivatives thereof as shown in the following structure (8,9,10)... 

The foregoing Desmacoll polymers show compatibility with some or all of the following polymers to the extent that they give clear solutions and films phthalic resins (Soft Resin MM, Alkydal BG), xylene-formaldehyde resin, cyclohexanone-formaldehyde resin (Synthetic Resin AFS), highly chlorinated terphenyl (Clo-phen Resin A60), teipene-phenolic resin (Durez 12603), acetyl cellulose (Cellit BL700), nitrocellulose, Desmocolls 12 and 22, nitrile rubber (Perbunan N), post chlorinated PVC (Rheno-flex), vinyl chloride-vinyl acetate copolymer (Vinnol), rosin esters (Pentalin A, Stabelite Ester 10), and coumarone resin. 

The urea usually is added to the finished PF-resin and causes a distinct decrease of the viscosity due to disruption of hydrogen bonds [95] and due to dilution effects. There is obviously no co-condensation of this post-added urea with the phenolic resin. Urea only reacts with the free formaldehyde of the resin forming methylols, which, however, do not react further due to the high pH [19]. Only at the higher temperatures of the hot-press does some phenol-urea co-condensation occur [93,94,96]. 

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