{"id":492,"date":"2014-05-09T08:00:17","date_gmt":"2014-05-09T13:00:17","guid":{"rendered":"https:\/\/www.ulprospector.com\/knowledge\/?p=492"},"modified":"2016-04-12T08:58:50","modified_gmt":"2016-04-12T14:58:50","slug":"pc-improving-performance-ambient-cured-latex-paints","status":"publish","type":"post","link":"https:\/\/ulprospector.ul.com\/492\/pc-improving-performance-ambient-cured-latex-paints\/","title":{"rendered":"Improving Performance in Ambient Cured Latex Paints"},"content":{"rendered":"

\"Ambient-Cured-Latex-Paint_0\"Many ambient cured latex paint systems offer deficient properties compared to those of their solvent born counterparts. Issues with water-born, latex-based paints<\/a>\u00a0(EU<\/a>)\u00a0may include poorer chemical resistance, moisture resistance, adhesion, surface hardness, abrasion and block resistance. Latex-based coatings systems where these characteristics are desired include architectural, automotive interior, business machine coatings, general industrial, implement finishes and wood coatings.<\/p>\n

This article will summarize the causes of poorer performance in ambient cured water-born coatings<\/a>\u00a0(EU<\/a>) and provides formulation guidance and the means to improve performance. We will concentrate on aspects involving the use of commercially available latex polymers<\/a>\u00a0(EU<\/a>) and cross-linkers<\/a>\u00a0(EU<\/a>), rather than on improving these properties by varying monomer selection, polymer architecture (e.g. core-shell, dispersion, solution, emulsion or microemulsion etc.) or Tg (the glass transition temperature is the temperature at which a polymer changes from a hard and brittle state to soft and pliable).<\/p>\n

Less than desirable performance properties of traditional thermoplastic latex coatings<\/a>\u00a0(EU<\/a>)<\/strong>\u00a0include water sensitivity attributed to one or more of the following: presence of carboxyl functional groups, water sensitive thickeners, low levels of surfactant remaining at the boundary layer after latex particles coalesce, and residual cosolvent and\/or amine.<\/p>\n

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The addition of a suitable crosslinker<\/strong> or the use of a self-crosslinking latex<\/a>\u00a0(EU<\/a>)<\/strong>\u00a0can dramatically enhance hardness, block resistance and improve moisture and chemical resistance. In addition, cross-linkable resins can offer lower Tg<\/a>\u00a0(EU<\/a>) lattices with the ability to permit improved coalescence with lower levels of cosolvent.<\/p>\n

Crosslinking improves properties by two different mechanisms.<\/strong> The first reduces moisture sensitivity if the reaction occurs with the carboxyl<\/a>\u00a0(EU<\/a>) or other functional groups, and the second occurs as a result of the formation of an increase in the polymeric network as the schematic to the right indicates.<\/p>\n

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The resultant coating of the cross-linked network offers lower solubility in water and solvents, higher Tg and thus a tougher film with higher hardness. Performance properties of thermoplastic emulsions vs. crosslinked emulsions may be summarized as\u00a0the chart at right shows.<\/p>\n

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In addition to the advantages listed in the above table, many crosslinked systems provide higher gloss capability and improved adhesion<\/strong>, as well as better exterior durability. The use of crosslinkers in water-born coatings include polyaziridines, epoxy silanes<\/a>\u00a0(EU<\/a>), carbodiimides<\/a>\u00a0(EU<\/a>) and adipic dihydrazide, as well as suitable isocyanate<\/a>\u00a0(EU<\/a>) functional prepolymers. The table to the right\u00a0illustrates the reactive groups and considerations with the use each of each type of cross-linked system.<\/p>\n

There are two basic types of crosslinkable latex compositions:<\/strong> single component and two component. Incorporation of polyaziridine, carbodiimide and isocyanate functional crosslinkers provide improved performance but will react with functional groups on the latex particle in the package. This creates an unstable system if the formulated coating is not applied within a few days.<\/p>\n

Accordingly, these crosslinkers are normally used to formulate two-component coatings with the latex component in one package and the crosslinker in the second package. Single-component water-born crosslinkable coatings are possible with the use of either a self-crosslinking latex or with the incorporation of a suitable dual functional triethoxy silane crosslinker. In the case of the self-crosslinking latex type, the crosslinker is built into the latex particle and thus the addition of a crosslinker is unnecessary.<\/p>\n

In summary, a crosslinked emulsion coating system<\/strong> can offer a multitude of improved performance properties compared to thermoplastic emulsion coatings. These characteristics also translate to baked systems, and indeed many other crosslinker chemistries and resin functional groups are possible. Choices of crosslinkable resins and crosslinkers offer an array of possibilities to tailor performance properties to meet desired characteristics in ambient cured systems.<\/p>\n

Product Resources – North America<\/strong><\/p>\n