Melamine formaldehyde-acrylic copolymers

The crosslinking and degradation chemistry of melamine formaldehyde acrylic copolymer coatings has been a field of renewed Interest recently.(1-4) The Intractability of these highly crossllnked systems makes them difficult to study with conventional physical techniques. We Illustrate here that modern physical methods can give substantially more Information as to both the reaction and degradation chemistry of highly crossllnked systems. 

Sanding is carried out at this stage and, after clean-up, the final colour or top-coat is applied. There is some variation in the resin chemistry used. Alkyds crosslinked with melamine-formaldehyde are widely used for non-metallic pigmentation. Metallics are usually based on acrylics for better durability. The acrylic may be thermoset with melamine-formaldehyde or a thermoplastic lacquer (plasticised copolymer of methyl methacrylate). A thickness of about 50ftm is applied and stoved for 20 min at 130°C (lacquers receive a bake-sand-bake process for a smoother appearance). 

Kinetic Model. All of the coatings used in this study are hydroxy functional acrylic copolymers crosslinked with melamine formaldehyde crosslinkers. The chemistry of crosslinking with melamine formaldehyde crosslinkers has been discussed in detail elsewhere (5.11). The type and rate of the reactions depend primarily on... 

Other NAD microspheres are composed of styrene, MMA, hydroxyethyl acrylate, acrylic acid and acrylonitrile and are blended with acrylic copolymers and melamine/formaldehyde resins [341,342]. Particles of this polymer are used as rheology modifiers to prevent sagging in automotive coatings and for controlling the orientation of metal flake pigments. 

The question whether the intramolecularly crosslinked microparticles of non-aqueous polymer dispersions are really microgels is also justified, considering non-aqueous dispersions prepared from acrylic copolymers and melamine/formaldehyde crosslinker with particle sizes of about 300 nm. [45, 343]. In any case, these crosslinked polymeric microparticles are useful constituents of high-solids coatings, imparting a yield stress to those solutions which probably involves attractive forces between the microparticles. 

Mixtures of rubber latices or elastomer foams were modified with colloidal silica to give improved properties. Typical processes involved drying, gelling, or coagulating the colloidal silica within the elastomer system. Silica sols were used with phenolic, formaldehyde-based, melamine, polyester, acrylic, vinyl or styrene polymer-copolymer, polyamide, and styrene-butadiene rubber systems to provide strength to films and coatings. 

Figure 1. Solid state NMR spectrum of a melamine formaldehyde crossllnked acrylic copolymer coating. The static magnetic field Is 7.0 T and the spinning rage Is S.OKHz Chemical shifts and assignments are given In Table I and features marked with an asterisk are resolved spinning side bands.

Figure 2. Transmission and diffuse reflectance Infrared spectra of a clear melamine formaldehyde crossllnked acrylic copolymer coating.

Figure 3. Elementary crosslinking and hydrolytic degradation reactions Involved In melamine formaldehyde ONCHjOCH.) crosslinking reactions with hydroxy functionalized acrylic copolymers (ROH).

Figure 4. Depth profile of free amine, methoxy methyl, and primary crosslink density of a 50 y thick blue pigmented melamine formaldehyde crossllnked acrylic copolymer coating that was exposed for two years In Florida. Bars on rhs of graph Indicate concentrations expected In the absence of degradation.

Sterotex NF. See Hydrogenated vegetable oil Sterotex . See Hydrogenated cottonseed oil Stetlaprint B-594. See Acrylates copolymer Stetlaprint C-MA. See Melamine-formaldehyde resin... 

Ethylene/butyl acrylate copolymer Melamine-formaldehyde resin, methylated-butylated Polyethylene, low-density coatings, extrusion metal foils Nylon 12... 

Melamine-formaldehyde resin, etherified acrylated Methyltriethoxysilane Silicone glycol copolymer Vinyltriethoxysilane Vinyltrimethoxysilane Vinyltris (2-methoxyethoxy) silane gloss aid, colored cosmetics Octyldodecyl isostearate Polyglyceryl-3 laurate... 

Acrylate Copolymer (AC) A copolymer of eight parts of n-butyl methacrylate, one part of ethyl methacrylate and one part of styrene was prepared. 800 g of n-butyl methacrylate, 100 g of ethyl methacrylate and 100 g of styrene were heated with stirring in a 2000 cc three-necked flask, equipped with a reflux condenser and nitrogen inlet. The reaction was carried out at 80°C until a prepolymer of syrupy consistency was obtained. The polymer was very similar in nature to the polyacrylate used in a previous study (7,8), except that it contained no pendant hydroxyl or carboxyl groups needed for the melamine-formaldehyde cure. 

The binder, therefore, must have the following properties good adhesion to fibre and pigment in the dry state, and in water and solvent a soft, non-tacky handle elasticity lightfastness, clarity and no colour compatibility with, and stability towards, other ingredients in the mix. Some styrene butadiene copolymer rubbers and vinyl latices are used successfully but the most suited are the acrylics. The polymers are usually either self-cross-linking (with heat) or incorporate a cross-linkable resin such as melamine-formaldehyde. 

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