Past, Present, and Future Options for Preservatives in Coatings
March 2017 www.coatingsworld.com Coatings World | 77
are evaluating formaldehyde-mechanism
preservatives. Regulatory reviews of this
type seldom lead to an outright ban on the
use of a compound; however, outcomes
involving restrictions on use patterns or
dosage levels are commonplace.
The second headwind faced by
formaldehyde-mechanism preservatives
stems from the less obvious impact from
changes to hazard communication requirements. Broadly speaking, paint ingredients represent a low hazard group
of chemicals. Therefore, formulators of
water-based coatings often begin with the
assumption that they can achieve their
formulation quality and performance
goals without triggering the requirement
for problematic hazard communication
phrases (or alarming symbols) on the
paint container label. By the same token,
consumers of water-based coatings start
with the assumption that paint represents
a non-hazardous chemical and, therefore, the presence of hazard phrases on a
paint container label can undermine the
consumer’s perception of the safe nature
of the product. In other words, hazard
phrases can be problematic because they
may alarm consumers and alter their
buying behaviors. The relevance of this
situation, in the context of formaldehyde-mechanism preservatives, is that a coatings formulator may choose to avoid
using a particular preservative if the addition of that preservative would trigger
a hazard communication requirement on
a coating formulation that would otherwise be classified as non-hazardous. This
could be described as an indirect regulatory headwind, since the preservative
would still be legally available.
Lastly, there is a headwind faced by
formaldehyde-mechanism preservatives
from market forces. Various non-govern-
mental organizations (NGOs) offer green-
label branding for coatings products that
comply with their restrictions on specific
ingredients. As an example, Green Seal
publishes a standard (GS- 11) for paints,
coatings, stains, and sealers that specifi-
cally lists formaldehyde donors as one of
the prohibited ingredients. Other NGOs
do not necessarily restrict formaldehyde-
mechanism preservatives as specific ingre-
dients, but they specify an upper limit for
the formaldehyde content of the coating.
As an example, the Blue Angel publishes
an environmental label criterion for low-
emission interior wall paints which states
that the free-formaldehyde content of
such coatings shall not exceed 100 ppm.
These restrictions from NGOs represent
another indirect headwind, in that, while
the NGOs do not have the authority to
change the regulatory status of preserva-
tives, they can nevertheless cause certain
preservatives to fall out of favor.
In summary, in the days since the ban
on mercurial biocides, formaldehyde-mechanism preservatives have encountered both direct and indirect barriers to
their use. While members of this class of
compounds are still available in the marketplace, the coatings formulator of today
has a narrower range of formaldehyde-mechanism preservatives to choose from.
This makes it less likely that the selected
active agent will be a good fit with the
needs of a particular coatings application.
Preservation – Present
Members of the isothiazolinone class of
preservatives have long been available
as alternatives to organo-mercurials and
formaldehyde-mechanism preservatives.
However, the more recent decline in the variety of formaldehyde-mechanism preservatives has provided an additional incentive
for formulators to evaluate isothiazolinone
preservatives as alternative options.
Members of the isothiazolinone
chemical family contain an isothiazoli-
none ring with an activated N-S bond
which can react with nucleophilic cell
entities and thus exert antimicrobial ac-
tivity. Beginning in the 1960s and 70s,
one of these isothiazolinone derivatives
(1,2-benzisothiazolin-3-one, BIT) be-
came available as a non-formaldehyde-
mechanism alternative preservative for
industrial products. Since that time
other isothiazolinone derivatives have
become available, and usage of isothia-
zolinone biocides has grown to the point
where today they represent one of the
major types of biocides used for mate-
rial protection. Derivatives of isothia-
zolinone are used as both anti-bacterial,
in-can preservatives and as anti-fungal,
dry-film preservatives. Other examples
of isothiazolinone biocides include; MIT
(2-Methylisothiazol- 3(2H)-one), CMIT/
MIT (5-Chloro-2-methyl-4-isothiazolin-
3-one/2-Methylisothiazol- 3(2H)-one),
OIT (2-Octyl-2H-isothiazol-3-one),
BBIT (2-Butyl-1,2-benzisothiazolin-3-
one), and DCOIT ( 4,5-Dichloro-2-n-
octyl- 3(2H)-isothiazolone).
Isothiazolinone biocides represent a
step away from the broadly toxic and
highly persistent first-generation group of
biocides and, unlike formaldehyde-condensate biocides, they are not associated
with a carcinogen. Nevertheless, in some
regions, isothiazolinone biocides have
begun to experience the sort of indirect
headwinds associated with changes to
hazard communication requirements. In
developing an understanding of the current situation it is helpful to first review
some background.
All of the commonly used isothiazolinone biocide active agents are either
known or potential skin sensitizers. As a
consequence of this fact, hazard communication regulations can impact the labeling required for materials protected with
isothiazolinone biocides. This is particularly true in Europe.
In Europe in the 1990s the Biocidal
Products Directive (BPD) was implemented across the European Union. The major
intention of this directive was to ensure
that biocidal products covering in-scope
applications demonstrated an acceptable
human health and environmental use profile in a consistent process across the EU.
Throughout the active substances evaluation phase of the BPD, many actives have
disappeared from the market in part due
to the high costs associated with supporting active substances and the requirement
for compliance with ever-stricter risk assessments. In 2012, the Biocidal Products
Regulation (BPR) replaced the BPD. This
legislation, now a regulation, corrected
and strengthened the previous BPD to further regulate the use of biocidal products
within the EU marketplace.
The Classification, Labeling and
Packaging (CLP) Regulation (1272/2008/
EC), the EU implementation of the
United Nation’s Global Harmonized
System (GHS), replaced both the
Dangerous Substances Directive 67/548/
