Wednesday, February 19, 2014

Acrylamide Acrylic Resin


Acrylamide acrylics contain the same reactive groups as Amino resins, namely amide, methylolamide and butylated methylol groups.

                       NH2                                                  CH2OH
                 Amine group                                     Methylol group

Can self polymerise.  Acrylamide acrylics cured by any resin which will cure amino resins.  React with resins containing –OH groups such as Epoxy, Alkyd and Polyesters.  As with amino resins the proportions of these reactive groups determine their reactivity and compatibility with other resin systems.

As with amino resins, the presence of acid speeds the curing rate.  Self cured films are not brittle and they don’t need the addition of other resins just to make them more flexible.  This gives the formulator more tolerance in ratio of hydroxyl polymer and acrylamide acrylic which he blends.

Acrylamide acrylic / Epoxy systems have excellent chemical resistance and flexibility.  These are pale coloured and have good enough colour retention.  These are commonly stoved for 30 minutes at 160°C or 20 minutes at 170°C but can be stoved for 12 minutes at 180°C if necessary.  Widely used as white appliance finishes where excellent detergent and stain resistance is important.  These are also used on aluminium sheeting for caravan exteriors although here they will suffer from chalking.  Both these applications can utilize pre-painted coil strip.  In this case flexibility and adhesion which these blends have become important.  Acrylamide acrylic / Epoxy blends also used on roller-coated strip.  An example here is white exteriors for cans.  The white surface is usually overprinted and so the ability to remain flexible and not to yellow on double stoving is important.

As acrylamide acrylics are self polymerized,  if formulated correctly, produce excellent films.  Acrylamide acrylics are expensive, so they are often blended with alkyds or polyesters.  These blends are used for factory applied car finishes, usually for the solid or non-metallic colours where a water white colour is not necessary.  Darker shades tend to use alkyds, where any yellowing tendency is less noticeable, whereas for whites and pale shades, the acrylic is usually blended with polyester.  In both cases a clear coat can be applied over the colour coat, as with metallics, for better durability and gloss.