Self-Crosslinking Systems

Numerous possibilities exist for the manufacture of polymers with latent coreactive sites °l The introduction of built in functional groups onto the surface of the polyurethane particle and proprietary reactive groups copolymerised into the backbone of the acrylic and buried deep into the core of the acrylic phase are the usual techniques for crosslinkable copolymer type systems. The crosslinking mechanism is not fully understood, but it is assumed to be made possible via interdiffusion of polymer chains across the former boundaries of adjacent particles. Evidence for the crosslinking can be found in increased solvent resistance, softening temperature and the appearance of a single Tg.. 

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The acrylamide acrylic provides a self-crosslinking system. Cowles dispersion would be used for the resin and pigment. 

Diol Two Component Cure. Amide/blocked aldehyde systems show high reactivity with 1,2 or 1,3 diols and give thermodynamically favored cyclic acetals. As mentioned above, even monomers which self-crosslink poorly because they cannot cycllze to the hemlamidal (I.e., 13, 14) will react efficiently to form crosslinked bis-cycloacetals H In the presence of a tetraol (or, to Impart organic solubility, a blocked tetraol, 15, Scheme 3). 

A system with interesting properties is the poly(ethylene oxide)-Wock-poly[2-(diethylamino) ethyl methacrylalc -.sfa -[3-(trimclhoxysilyl)propyl methacrylate] (PEO-b-P(DEA-sfaf-TMSPMA)) block copolymer. This self-crosslinkable copolymer formed vesicles which demonstrated pH-tunable membrane permeability [223],... 

Uses Binder for wh. and clear interior/exterior can coating systems, stamping enamels, capsule lacquers, foil lacquers, coil-coating primers Features Self-crosslinking exc. resist. good corrosion protection exc. 

Uses Monomer for prod, of thermosetting resins for protective coatings or top coatings for leather, metal, and other substrates crosslinking agent in radiation-cured systems, for photoresists, latex, sol n. coatings Features Bifunctional self-crosslinking Cylink NBMA [Cytec Ind.)... 

Uses Monomer for latex binders used in adhesives, textiles, nonwovens, marine coatings, exterior paints, metal binders, electro-coatings, latex systems, water-resist, coatings Features Self-crosslinking Cymel 245-8 [Cytec Ind.j... 

Uses Surfactant, flow aid, leveling agent, slip agent in solv.-based coatings, amine-neutralized water-reducible coatings such as alkyd/ melamine, hydroxyl/acrylics, self-crosslinking acrylics, polyester/ melamine, nitrocellulose/PU systems Tallicin 5311 [Pfiaumer Bros.]... 

Chem. Descrip. Self-crosslinking elastomeric silicone aq. emulsion Uses Adhesion promoter, flexibilizer, water resist, aid, detergent resist, aid in printing inks water repellent, water resist, aid in industrial coatings, parquet varnishes, facade paints, wood coatings, plastic coatings, leather coatings, aq. systems, esp. acrylic disps. 

As shown in Table 3 in an elevated temperature shear test, acrylic/BKUA-2260 systems perform extremely well, while elevated temperature peel shows some fall off in performance. Since the BKUA-2260 is self-crosslinking at elevated temperature and has the ability to co-cure with certain acrylic and vinyl-acrylic latexes, the elevated temperature performance of bonds depends, to some extent, on the previous thermal history of the bond. The shear test involves a slow heat up to test temperature and allows the bond to cure partially. Mechanical properties of thermally cured films of UCAR Latex 154/BKUA-2260 show 10 fold modulus increases over the uncured films. Vinyl-acrylic latexes that do not have the ability to co-cure with the phenolic do not exhibit the same high elevated temperature shear values. 

Curing Agents. Although SBR latexes often do not require use of curing agents in the normal sense, a number of cure systems are available. For noncarboxylated latex compositions, conventional sulfur systems may be used where external heat can be applied. Otherwise phenolic cures may be used or self crosslinking resins may be blended into the formulation. 

While carboxylated latexes are widely accepted as not needing a cure system, those described above for SBRs are applicable, as are melamine formaldehyde or other formaldehyde condensates. Multivalent metal compounds may also be used with carboxylated systems the most common of these is zinc oxide, but other materials such as zirconium ammonium carbonate may also be used. Some of these types of materials have the advantage that they are effective at room temperature. Some functional SBR latexes have their own cure system built into the polymer and are often referred to as self-crosslinking y or as heat-reactive in instances where heat is involved in the curing process. 

A third example is the ICI patented use of core shell emulsions for use in internal can lacquers. The particles are not as easily deformed during high pressure airless spray applications as are conventional water based systems. The shell could contain a crosslinking comonomer such as n-methylolacrylamide to enable the emulsion to be self crosslinking when stoved. 

Features Highly efficient offers optimum defoaming while utilizing only minimal quantities of incompat. substances preferred binders are epoxies, two-pack polyurethane systems, alkyd/melamine, alkyds, self-crosslinking acrylates, and vinyl resins... 

Chem. Descrip. Polysiloxane sol n. in 2,6-dimethyl4-heptanone Uses Defoamer for org. systems incl. chlorinated rubber, epoxy, two-part polyurethane, alkyd, alkyd/melamine, self-crosslinking acrylates, polyesters used in resinous and polymeric coatings in food pkg. 

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