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Introduction
Over the last few years, the surface caotings industry has sean
a rapid increase in the use of radiation curing. [1] The most
commonly used materials in conjunction with radiation curing are
acrylates. These materials are polymerised by afree radical
chain process which in uv. curing is triggered by the use of a
photoinitiator and in the case of e.b. curing, by the radiation
inducing ionisation of themedium which leads.to radical
prodcution. [2]. In order to attain the required coating
properties eg. toughness, adhesion etc., itis necessary to have
available acrylates possessing a variety ofbackbones eg.
alkanes, aromatic residue's, urethanes, esters etc. and ones
where the degree of functionality can be varied. To produce a
formulation which will give a coating with the desired
characteristics requires skill ,and inevitably the formulator has
to resort to blending a mixture of acrylates with various
additives. In many, cases the wéatherability of a coating may
not be of great importance eg., coating compact discs,
but in some eg. wood and steel coating it is of paramount importance.
This paper addresses some of the factors affecting weatherability of acrylatecoatings.
What factors may influence the weatherability of a coating? The
following list isnotexhaustive but gives some idea as to the complexity of
the problem.
(a) Residual unpolynierised acrylate groups which may participate in further
crosslinking reactions. [3]
(b) Groups in the backbone which are thernselves photoactive eg.
esters of phenols which undergo the photo—Fries rearrangement.
(c) Groups in the backbone which are susceptible to free
radical attack eg. C—H bonds adjacent to oxygen or nitrogen,
tertiary C—H bonds.
(d) Presence of extraneous light absorbing species eg. unused
photoinitiator, low molecular weight photoinitiator reaction
products, amines used as synergists to aid the rate of uv.
curing. [4]
