Acrylic latex film formation

Dobler F, Holl Y. Mechanism of latex film formation. Trends Polym Sci 1996 4 145-151. Eckersley ST, Rudin A. Fihn formation of acrylic copolymer latices a model of state II film formation. In Provder T, Winnik MA, Urban MW, eds. Film Formation in Waterborne Coatings ACS Symposium Series No. 648. Washington, DC American Chemical Society, 1996 1-21. 

A combination of methacrylates and acrylates is used on occasion to achieve needed film properties. While poly(methyl methacrylate) is commonly used for film strength and hardness, poly(methyl acrylate) will improve film flexibility. A plasticizing monomer, such as ethyl acrylate or ethylhexyl acrylate is therefore sometimes added with the methyl methacrylate monomer by the polymer manufacturer in an addition-polymerization process to produce a copolymer for use in coating formulations. The softer and more flexible polymer facilitates latex film formation. 

Formation of solubilized surfactant-latex complexes can influence the properties and performance of vinyl acrylic latexes prepared with NaLS and other penetrating type anionic surfactants. Such complexes seem to affect glass transition temperature and film coalescence process (12). 

The polarity and adsorption data discussed above reveal some interesting aspects of the surface chemistry of vinyl acrylic latex surfaces. It is quite likely that the polarity of the latex films, expecially of the two co-polymers, determined by contact angle measurements may not correspond exactly with their respective latex surfaces in the dispersed state due to reorientation of polymer chains during film formation. But the surfactant adsorption data shows clearly that the three latex surfaces in their dispersed state do exhibit varying polarity paralleling the trend found from contact angle measurements. The result also shows that the surface of the co-polymer latex surface is a mixture of vinyl acetate and acrylate units. This result is somewhat unexpected in a vinyl acrylic latex, prepared by a batch... 

The "onion skin" growth mechanism is supported by filming experiments in which film formation is greatly effected by the nature of the monomer composition added last in the polymerization. In power feed examples, as well as in staged feeds, hard and hydrophobic compositions hinder film formation while softer and more hydrophilic compositions aid film formation. Curiously, in this respect, it was found that the filming characteristics of all-acrylic latexes responded to non-uniform polymerization techniques much more dramatically than did their styrene-acrylic counterparts. 

Inaba et al. prepared a series of model styrene/butyl acrylate copolymer latexes with glass transition temperatures at room temperature. The functional monomer 2-(3-isopropenylphenyl)-2-methylethylisocyanate (TMI) was used as monomer/crosslinking agent for further film formation. A small amount of methacrylic acid was introduced in some formulations in order to enhance the crosslinking reaction. A redox initiation system was used to reduce premature crosslinking during the polymerization [82]. 

Butoxyethanol acetate is primarily used as a high-boiling, retarder solvent (i.e., an active, slow-evaporating solvent which ensures smooth film formation) for nitrocellulose lacquers, acrylic enamels, epoxy resins, and multicolor lacquers (Leaf 1985 as cited in NIOSH 1990 Lewis 1993). 2-Butoxyethanol acetate is also a film-coalescing aid for polyvinyl acetate latex and is used in some ink and spot remover... 

A series of latex copolymers were prepared using a typical emulsion polymerization recipe and procedure only the monomer composition was varied. The control composition (80/20 vinyl acetate/butyl acrylate) is similar to that used for interior latex paint. Table V lists the compositions and properties of the latexes. Percent solids, pH, and particle size are similar for all the latexes. Viscosity varies somewhat, but is within limits for this type of latex. The only unreacted monomer detected was the vinyl acetate. Thus, the incorporation of VEC into the emulsion polymerization via the monomer mixture did not affect the latex synthesis. The Tg and minimum film formation temperature (MFFT) of the latexes increase with increasing VEC content, which is expected based on the previous results. 

A latex used for coating applications and made from an acrylic phase and an alkyd phase contains surfactant particles that stabilize the phases after the film-forming process. Using STEM, the imaging of these surfactant molecules was carried out in order to understand the influence of the surfactant-polymer affinity on the surfactant location after film formation [59]. 

In acrylic latices, the hard monomer is methyl methacrylate and the plasticizing monomer an acrylate, such as butyl acrylate or one of the acrylate comonomers mentioned above. Acrylic latices usually contain copolymers of acrylic or methacrylic acid as colloids and thickeners, these being solubilized by neutralization with base. Whatever the type of latex, coalescing solvents are also normally added to improve film formation. These may or may not be water miscible and include alcohols, glycols, ether-alcohols, ether-alcohol esters and even hydrocarbons, all of high boiled point. 

It is well-known that viscosity, self-diffusion coefficient and glass transition temperature are a strong function of molecular weight (MW). The film formation characteristics of an acrylic (BM A/MM A/M AA) latex as a function of its average MW is reported. The latex with the high MW is compared to an identical formulation with a low MW. The latex dispersions are prepared by standard techniques of emulsion polymerisation using an anionic surfactant, ammonium dodecyl benzene sulphonic add, and ammonium persulphate... 

The effect of the Tg of the latex on the film-formation behaviour of a series of 2-ethylhexyl acrylate/methyl methacrylate emulsion copolymers was studied. Stage 1 of fihn formation was examined using a combination of DMA and conductivity measurements. Stages 2 and 3 were investigated using calorimehic compensation, DSC, dielectric spectroscopy and atomic force microscopy. Comparison of the results from the different methods employed led to a detailed model of the film-formation process in which the temp, used relative to the minimum film-formation temp, determined the effectiveness of the processes. The relative usefulness of the techniques used in their ability to characterise the various stages in the film-formation process was assessed for these copolymer systans. 23 refs. 

No.6,23rd March 1999, p. 1715-21 LATEX BLENDS OF FLUORINATED AND FLUORINE-FREE ACRYLATES EMULSION POLYMERIZATION AND TAPPING MODE ATOMIC FORCE MICROSCOPY OF FILM FORMATION... 

The influence of particle size distribution in the use of latex dispersions is shown to be of great practical importance. The practical consequences are examined of bimodal particle size distribution with respect to coatings applications. The introduction of polydispersity in acrylic dispersions is examined as a way of obtaining a lower dispersion volume loading at an equivalent viscosity as for monodisperse spheres. Aspects such as film formation, rheology, and drying behaviour are discussed. 39 refs. 

Keddie JL, Meredith P, Jones RAL, Donald AM. Film formation of acrylic latices with varying concentrations of non-film-forming latex particles. Langmuir 1996 12 3793-3801. Winnik MA, Feng J. Latex blends an approach to zero VOC coatings. J Coat Tech 1996 68 39-50. 

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