Transcript

POLYSILOXANE COATINGS INNOVATIONS

Norman R. Mowrer
R&D Technical Manager
Ameron International
Performance Coatings & Finishes Group
Brea, CA.


Abstract: Organic modified polysiloxanes
are generally recognized as the newest
generic class of high performance
protective coating. They have gained
commercial acceptance over the last ten
years and are now widely used in new
construction, heavy duty OEM, marine
and industrial maintenance painting.
This paper provides an overview of the
technology, describes the available types
of polysiloxane modified organic coatings
and their properties and briefly discusses
some recent advances in the field.

INTRODUCTION

Inorganic silicon based polymers have
been used as coating binders for more
than 60 years. The first silicon based
coating binders were the waterborne
alkali silicates used in the formulation of
heat-cured zinc rich primers in the
1940’s (1). Ambient-temperature, post-
cure variants of this technology appeared
in the 1950’s. Solvent based, zinc rich
primers based on hydrolyzed ethyl
silicate became available shortly
thereafter.

The development of silicone resins after
World War II resulted in the first major
commercial applications for silicone
coatings; heat-cured, high temperature
resistant paints for exhaust stacks,
boilers, heat exchangers, mufflers,
engines and aircraft components (2).

Coating technologists have long sought to
utilize the properties of inorganic silicon
based polymers to improve the properties
of organic coatings. Early attempts to
combine inorganic silicon materials with
organic resins by cold blending were
limited by incompatibility of the two
materials. The earliest examples of hybrid
organic-inorganic silicone binders are the
silicone alkyd copolymers. First developed
in the 1950’s, these coatings overcame
incompatibility problems by pre-reaction
of silanol functional silicone resin carbinol
functional organic resin. The resulting
silicone alkyd copolymer was used to
formulate industrial maintenance coatings
(3) (4). These coatings are still in use today
for the protection of U.S. Navy vessels,
tanks, process equipment, rail cars and
other steel structures and are the subject
of various specifications including SSPC
Paint 21, SSPC-PS 16.01 and MIL-PRF-
24635C. While these coatings improved
weatherability, they also had all of the
limitations associated with alkyd coatings.
Other early examples of organic –
inorganic silicon based coatings include
silicone polyesters and silicone acrylics
used in heat-cured coil coatings and high
temperature resistant coatings.

For many years, broader use of silicon
based materials as coating binders was
limited to the specialized coatings just
mentioned, primarily because of poor film
flexibility and toughness, incompatibility
with organic polymers, the need for heat-
curing and certain problems associated
with film formation.

A breakthrough was made with the
publication of a patent in 1981 which
described binders based on
interpenetrating polymer networks (IPN)
comprised of a polysiloxane network and
an epoxy-amine network (5). Coatings
based on this chemistry overcame the
need for heat curing and provided good
flexibility with improved solvent and acid
resistance compared to conventional
epoxy coatings. Cost, stability and
intercoat adhesion problems limited
commercial success.

Significant further progress was made in
the mid-1990’s with the
commercialization of a patented epoxy
siloxane hybrid (6). This coating
combined the corrosion resistance of an
epoxy with the weatherability of aliphatic
polyurethane in one coating. When used
in combination with inorganic zinc
silicate primers, it allowed a single coat
of the epoxy siloxane hybrid to replace
one coat of epoxy and one coat of
polyurethane and still provide the same
level of resistance to weathering and
corrosion. The combination of high
performance and lower cost from
elimination of the epoxy intermediate
coat has led to wide spread use of the
two-coat, zinc primer/epoxy siloxane
topcoat system for protection of steel.

Interest in these coatings has continued
to grow and raw material suppliers,
coatings manufacturers and universities
have placed an increased emphasis on
polysiloxane chemistry research over the
last decade. As noted in a recent paper
on the subject, polysiloxanes were the
subject of 70 papers presented at three
conferences during 2001-2003 and
represented about 5% of all coatings
patents issued during a 2-month period
of 2002 (7).

This research has led to rapid
development of a variety of all-polysiloxane
and organic modified polysiloxane hybrids
and an expansion of their use in the
protective coatings industry. With over 10
million square meters applied globally
during the past ten years, polysiloxane
coatings have gained market share
compared to epoxy, polyurethane and
other traditional organic coatings and are
perhaps the fastest growing generic
coating type. Of note, the number of
coating manufacturers that supply
polysiloxane coatings has nearly tripled in
the last four years. The Buying Guide in
the June 2000 JPCL listed nine
manufacturers of polysiloxane coatings.
Twenty-five suppliers are listed in the
September 2004 JPCL Coatings Buyers
Guide.

The reasons for the rapid growth of
polysiloxane coatings are clear. They offer
improved performance properties and cost
effectiveness, lower VOC content and
improved health and safety features
compared to traditional organic coatings.

CHEMISTRY AND PROPERTIES

Epoxy, polyurethane and other organic
coatings degrade by thermal and photo-
induced oxidation and are subject to
chemical attack. This results in
deterioration of coating properties such as
color and gloss retention, flexibility,
adhesion and corrosion resistance, which
in turn reduces overall coating durability
and service life.

Polysiloxane coatings are largely inorganic
in nature and are inherently more
resistant to these degradation
mechanisms for three principal reasons:

1. As shown in Figure 1, polysiloxanes are
characterized by the presence of
repeating Si-O groups in the polymer
backbone. The bond strength of Si-O is
108 kcal/mole. Organic coatings
contain C-C bonds, which have a
bond strength of 83 kcal/mole. The
higher energy required to cleave the
Si-O bonds in polysiloxane coatings
provides greater stability and superior
resistance to weathering and thermal
degradation.
Two additional factors contribute
synergistically to the stability of
polysiloxane. Bulky organic substituents
attached to the Si atom protect the Si-O-R
bonds from hydrolysis through steric
hindrance (9). At the same time, the
positively charged silicon atoms polarize
the organic substituents attached to them,
thereby rendering the organic substituent
less susceptible to attack (10).

Figure 1.Idealized Polysiloxane Structure

R O S i
O
R
O S i
O
O S i R
R R
O
O S i
O R
R
R O S i
O H
R
O
S i O
S i O R
R
S i
R
O S i
R
RO OH
R = Si, H, Methyl, Phenyl, Other Alkyl, Aryl


In addition to their excellent resistance to
ultraviolet light, high temperature,
oxidation and corrosion, polysiloxanes
have a number of other properties that
make them of interest as coating binders.

• Silicone intermediates and silanes used
in polysiloxane coatings have
inherently low viscosities. Coatings
with very high solids and low VOC
(>90% volume solids with < 100 g/l
VOC) can be formulated with the same
application viscosity as much lower
solids coatings. This allows compliance
with current and all known future
emissions regulations.

2. The siloxane bond has about 50%
ionic character and is readily
hydrolyzed, especially when catalyzed
by an acid or base. Coating durability
in weathering is thought to be due to
the reversible nature of siloxane
hydrolysis. Siloxanes in the presence
of moisture are in equilibria that
strongly favor condensation of silanols
to siloxanes (8). The result is that a
photon of absorbed high-energy
radiation in the presence of moisture
will hydrolyze siloxane bonds, but
they reform spontaneously. In this
way no permanent harm is done to
the film.
• Silanes used in formulating
polysiloxane binders are also adhesion
promoters and form tenacious bonds
with both metal and cementitious
substrates.
• Unlike polyurethane, isocyanates are
not used to crosslink polysiloxane
binders. Health hazards associated
with the use of isocyanates are
eliminated.
3. The silicon in the polysiloxane
polymer backbone is already
approximately 50% to 75% oxidized,
i.e., each Si is bonded to 2 to 3 oxygen
atoms. Therefore, oxidative
degradation that affects C-C bonds
present in organic polymers cannot
occur in the already oxidized Si-O
polysiloxane polymer chain (9).
Resistance of the polysiloxane to
attack by atmospheric oxygen and
oxidizing chemicals is improved.
• Inorganic polysiloxanes are not
combustible. Organic modified
polysiloxane hybrids have better fire
ratings and generate considerably less
smoke and toxic fumes than organic
coatings.
• Polysiloxanes have excellent resistance
to radiation. Since they also have good
chemical resistance, nuclear
decontamination properties are
excellent.


CURING REACTIONS

Polysiloxane coatings are based on
alkoxy or silanol functional silicone
intermediates, which cure in the
presence of atmospheric moisture by the
condensation reactions as shown in
Figure 2. Tin and other organometallic
compounds are often used as catalysts to
accelerate cure.

Figure 2
Polysiloxane Hydrolytic Condensation
Reactions
Si OR + H2O
+
Si OH ROH
ROH Si O Si +
+ Si OH RO Si
Si OH
Si HO + Si O Si + H2O


Most commercially available organic –
inorganic polysiloxane hybrids cure by
reaction of an organo-functional
alkoxysilane with both an organic resin
and a silanol or alkoxy functional silicone
intermediate. For example, an amino-
functional alkoxysilane is used to cure
epoxy siloxane and two-component
acrylic siloxane hybrids. In the epoxy
siloxane, the silane amine functionality
reacts with an epoxy resin while the
silanes alkoxysilyl group reacts with
alkoxy or silanol functional silicone
intermediate via hydrolytic
polycondensation. In the acrylic siloxane,
the silane amine functionality reacts with
acrylate functionality via psuedo-Michael
addition while its alkoxysilyl group reacts
as previously described. Representative
reactions are shown in Figure 3 and
Figure 4.

Single-component acrylic siloxane
hybrids are based on pre-reaction of
acrylic resins having hydroxyl, epoxy or
other functionalities with alkoxy,
isocyanate, amine or other organo-
functional silanes. The resulting alkoxy
functional acrylic resin cures in the
presence of moisture via hydrolytic
polycondensation. Figure 5 shows the
representative reactions.

Figure 3.
Epoxy Siloxane Crosslinking Reactions

R1O Si
OR1
OR1
R2 N
H
H + R 3
O O
AMINOSILANE EPOXY
C H 2 C
O H
H
R 3 R2 N
H
R1O Si
OR1
OR1
TOGETHER WITH HYDROLYTIC CONDENSATION REACTIONS SHOWN IN FIG. 2
O


Figure 4
Acrylic Siloxane Crosslinking Reactions
R
1
O SI
OR
1
OR
1
R
2
NH H
R
1
O SI
OR
1
OR
1
R
2
NH CH
2
CH
2
X R
4
+
X R
4
X = ALTERNATIVE NUCLEOPHILES POSSIBLE
TOGETHER WITH HYDROLYTIC CONDENSATION REACTIONS SHOWN IN FIGURE 2


Application temperature and relative
humidity affect the relative rates of both
the organic and inorganic polysiloxane
curing reactions. The multiple reactions
involved in the curing of organic – siloxane
hybrid coatings result in rather complex
polymer networks. Despite these
complexities, polysiloxane coatings are
application tolerant and have proven low
temperature cure capability, even at low
relative humidity.

POLYSILOXANE COATING TYPES

In general, fully crosslinked polysiloxanes
are too brittle and do not have sufficient
strength to be used as the sole binder for
general-purpose coatings. Organic resins
are incorporated to moderate these
properties and tailor coating performance
for specific applications.

Successful coatings must be well
formulated and depend on the selection
of the appropriate type and amount of
organic and inorganic polysiloxane
constituents to achieve a balanced set of
application and performance properties.
Oxysilane and silicone resin precursors
are selected for molecular weight, degree
of crosslinking, reactivity type and
amount as well as their film properties,
cure speed and compatibility with
organic resins. Organic resin precursors
are chosen for their principal
performance feature. For example, an
aliphatic epoxy resin would be chosen for
a coating requiring a combination of
resistance to weathering and corrosion,
an aromatic epoxy resin would be used in
coatings that require excellent chemical
resistance and an acrylic resin would be
selected for use in a weatherable topcoat.

Organic polysiloxane hybrid coatings
vary from about 30 to 80% siloxane
content to give optimum performance in
terms of adhesion, mechanical properties
and chemical, corrosion and weathering
resistance. Lower levels of organic
modification result in coatings the exhibit
undesirable properties, e.g., low impact
resistance and flexibility. Higher levels of
organic modification detract from
important polysiloxane characteristics
like resistance to ultraviolet light and
oxidation.

The most prevalent, commercially
available polysiloxane coatings are the
epoxy siloxane and acrylic siloxane
hybrids listed below. They are discussed
in the sections that follow.

• Weatherable, Corrosion Resistant
Epoxy Siloxane

• Chemical Resistant, Epoxy Siloxane

• One-Component Acrylic Siloxane

• Two-Component Acrylic Siloxane

WEATHERABLE AND CORROSION
RESISTANT EPOXY SILOXANE

Epoxy coatings are the workhorses of the
protective coatings industry because they
are user friendly, have excellent corrosion
resistance and adhesion to steel and
provide good resistance to alkali and
solvents. However, epoxy coatings have a
major deficiency; poor exterior weathering.
Conventional epoxy coatings exhibit
chalking, color fade and lose most of their
gloss after a year of exterior exposure. If
retention of color and gloss is required, an
aliphatic polyurethane topcoat must be
used.

The first epoxy siloxane hybrid was
developed to improve the weathering
resistance of epoxy without compromising
corrosion or chemical resistance.

Table 1 shows the properties of the epoxy
siloxane hybrid coating. It has ultra high
volume solids of 90% with a VOC of 1.0
lb/gal (120g/l). It can be applied by brush,
roll or spray direct to blasted steel,
prepared rusted steel and properly
prepared, previously painted substrates.
As shown in Figure 6, the accelerated
weathering resistance of the epoxy
siloxane hybrid is better than acrylic
urethane.

Table 1.
Properties of Epoxy Siloxane Coating
Volume Solids 90%
VOC 1.0 lbs./gal.
Mix Ratio by Vol 4 to 1
Applied Thickness 3-7 mils/coat
Application Method Brush, Roll, Spray
Substrate Prepared or Primed
Steel, Concrete &
Aged Coatings
Pot Life, 70F 4 hours
Dry to Touch, 70F 3 hours
Dry Through, 70F 6 hours
Recoat, Min. 4.5 hours
Recoat, Max Extended

An important feature of the epoxy
siloxane hybrid is its excellent corrosion
resistance and compatibility with zinc
rich epoxy and inorganic zinc silicate
(IOZ) primers. Table 2 offers a direct
comparison of the following high
performance coating systems:

• 1-coat epoxy siloxane with 2-coat
epoxy/urethane.

• 2-coat IOZ/epoxy siloxane with 3-coat
IOZ/epoxy urethane.

The single coat of epoxy siloxane provides
comparable resistance to corrosion and
better resistance to QUV-B accelerated
weathering than the 2-coat
epoxy/urethane system. The 2-coat
IOZ/epoxy siloxane system has
equivalent or better resistance to
corrosion and better resistance to QUV-B
accelerated weathering than the 3-coat
IOZ/epoxy/urethane system. Similar
performance advantages are seen with
zinc epoxy primer/epoxy siloxane topcoat
systems compared to 2-coat zinc
epoxy/urethane systems.

Further evidence of the durability of
epoxy siloxane is demonstrated by their
excellent performance in various coating
specifications and in tests conducted by
independent laboratories

Norsok Standard M-CR-501
This specification involves 6000 hours
salt spray, 6000 hours condensation
chamber and 4200 hours of cyclic
exposure to salt spray and UV light. This
test program in combination with its
acceptance criteria is among the most
severe performance tests in the protective
coatings industry.

A 2-coat system consisting of 2.5 mils
inorganic zinc silicate primer and 5 mils of
epoxy siloxane topcoat, applied on SA 2
abrasive blasted steel, has been tested
successfully and satisfies the Norsok
Standard Common Requirements as
required by M-CR-501 Rev.2 (11). Further,
a 2-coat system consisting of 3-mils of
inorganic zinc and 5 mils of epoxy siloxane
topcoat applied over UHP water-jet
cleaned steel has also been qualified
under the same specification (12).

ISO 12944
A zinc epoxy primer/epoxy siloxane
topcoat system has been tested in
accordance with the ISO 12944 standard
“Corrosion Protection of Steel by Protective
Paint Systems” and passed the
requirements for the C5M high marine
corrosivity durability class (13).

Cost Efficiency
Epoxy siloxane hybrids have superior
resistance to weathering and significantly
better color and gloss retention compared
to aliphatic acrylic urethanes. Based on
comparative field data collected over the
last 10 years, a 2-coat IOZ/epoxy siloxane
coating system will provide a 30%
improvement in service life compared to a
conventional 3-coat, IOZ/epoxy/urethane
coating system. As previously noted, the
epoxy siloxane hybrid can be applied
directly to inorganic zinc primer without
pinholing, thus eliminating the epoxy tie-
coat used in the traditional 3-coat
IOZ/epoxy/urethane high performance
coating system. Fewer coats minimize
scaffolding, lower labor costs, reduce
waste and result in increased productivity.

The cost savings associated with longer
service life and elimination of the epoxy
mid-coat is significant. Coating system life
projections based on the computer model
described in NACE Paper 477 and
current material, surface preparation
and application labor costs have been
used to calculate the capital expenditure,
maintenance expenditure and total life
costs of 2-coat IOZ/epoxy siloxane and
3-coat IOZ/epoxy/urethane coating
systems. A total life cost savings of 12.9%
was realized with the 2-coat inorganic
zinc/epoxy siloxane coating system.
Significant further cost savings are
apparent when the reduction in man-
hours are considered (14) (15).

CHEMICAL RESISTANT EPOXY
SILOXANE

Epoxy coatings have good resistance to
alkali and solvents but resistance to
certain mineral and organic acids is
limited. Siloxanes, on the other hand,
have excellent resistance to concentrated
mineral and organic acids. A chemical
resistant epoxy siloxane hybrid coating,
first introduced in 1997, combined the
advantages of both polymers and
provided resistance to a broad range of
concentrated mineral and organic acids,
alkali, oxidizing chemicals and aggressive
solvents (16). Overall chemical resistance
was better than methylene dianiline
(MDA) cured epoxy and amine cured
epoxy novolac coatings. Commercial
success was limited by the coatings high
crosslink density and associated
shrinkage on aging, which led to stress
cracking and disbondment from concrete
at high coating thickness.

An improved, elastomer modified epoxy
siloxane hybrid was patented and
commercialized in 2003 (17) (18).
Elastomer modification of the epoxy
siloxane polymer network has reduced
shrinkage stress and eliminated cracking
and concrete disbondment problems
without compromising chemical
resistance.

The elastomer modified epoxy siloxane is a
3-component product consisting of resin,
cure and silica aggregate and is designed
as a self-leveling surfacer for application
on concrete. Important characteristics of
this coating are listed in Table 3.

As shown in Table 4, the elastomer
modified epoxy siloxane has excellent
resistance to a broad range of
concentrated mineral and organic acids,
concentrated alkali, oxidizing chemicals
and aggressive solvents. It is well suited
for use in pulp and paper plants, chemical
process industries, secondary
containment applications and other
industries where outstanding chemical
resistance is required.

Table 3.
Elastomer Modified Epoxy Siloxane
Surfacer
Volume Solids 100%
Applied Thickness 40-60 mils
Application Method Squeegee, Roller
Substrate
Prepared, Primed
Concrete
Work Life @ 70F 2 hours
Initial Setting Time 10 hours
Time to Service
• Light traffic
• Chemical
splash & spill

24 hours
72 hours

ACRYLIC SILOXANE HYBRIDS

Acrylics are the resins of choice to provide
excellent resistance to weathering and are
widely used in high performance acrylic
latex paints and two component aliphatic
polyurethane coatings.

Appropriate acrylic resins can be used to
modify polysiloxane binders to impart
improved flexibility and recoatability while
maintaining the superior weathering
characteristics of the polysiloxane.

The first acrylic siloxane hybrid was
introduced in the late 1990’s (19). This
product is a one-component coating
specifically designed as an isocyanate-
free replacement for two-component
acrylic polyurethane. Advantages of the
acrylic siloxane hybrid include excellent
weathering, chalking and corrosion
resistance combined with the ease of
application of traditional one-component
coatings at significantly lower VOC.

Development of acrylic siloxane hybrid
coatings has continued and a number of
novel binders have been patented (20)
(21) (22). Acrylic siloxane hybrids are
now available from several suppliers. An
epoxy acrylic siloxane hybrid is also
commercially available. The products can
be divided into two categories; 1-
component coatings and 2-component
coatings.

Because the 1-component acrylic
siloxane previously described was
intended to compete with 2-component
acrylic polyurethane at the required
market price, it has low siloxane content
and does not weather as well as the
epoxy siloxane or 2-component acrylic
siloxane hybrids. However, a second
generation, higher solids, 1-component
acrylic siloxane coating has been
developed with higher siloxane content
and improved weatherability. The
versatility of 1-component acrylic
siloxane chemistry also allowed this
coating to be designed with improved
flexibility. Long-term film integrity and
durability should be improved.

The properties of the first and second-
generation, 1-component acrylic siloxane
coatings are compared with commercially
available 2-component acrylic siloxane
and epoxy acrylic siloxane coatings in
Table 5. The first generation, 1-
component acrylic siloxane is not
recommended for application over zinc
rich epoxy but data is presented for
completeness. QUV-B accelerated
weathering of the coatings is shown in
Figure 7.

It is apparent after a review of this data
that the second-generation, 1-component
acrylic siloxane and 2-component acrylic
siloxane have comparable resistance to
corrosion and weathering while the 2-
component epoxy acrylic siloxane has
slightly lower performance. Advantages of
the 1-component acrylic siloxane include
unlimited pot life, better flexibility and the
ease of application of traditional 1-pack
coatings.

The performance characteristics of acrylic
siloxane coatings have been studied
extensively by a number of suppliers.
Based on this data and numerous case
histories, it can be concluded that the
high-solids, low VOC, non-isocyanate
curing mechanism and combination of
excellent corrosion resistance and
superior weatherability of acrylic siloxane
coatings make them an ideal,
toxicologically more acceptable, cost
effective alternative to polyurethane.

It should be noted that acrylic siloxanes
do not provide the same level of corrosion
protection as the epoxy siloxane hybrid.
Table 6 compares the corrosion resistance
of coating systems prepared from a zinc
rich epoxy primer topcoated with epoxy
siloxane, 2-component acrylic siloxane
and a 2-component acrylic urethane. The
zinc epoxy/epoxy siloxane system out-
performs the other coating systems.

NEW ENGINEERED ORGANC-SILOXANE
HYBRIDS

The new siloxane chemistry gives coating
technologists additional tools with which
to design resin binders with improved
properties. Siloxanes have been used
advantageously in combination with
vinyl’s, acetoacetate functional resins,
urethanes, fluoropolymers and phenolics
in coatings, adhesives and composites.

Recent advances include development of
fluorinated organic-siloxane hybrids and
a fast-cure epoxy acrylic siloxane coating.

Fluorinated Acrylic Siloxane and
Fluorinated Epoxy Siloxane Hybrids
The use of fluorinated polymers in highly
weatherable topcoats is well known. For
example, Kynar, one of several
fluorinated polymer coatings on the
market, is used to coat aluminum sheet
metal used in building construction
where the highest level of resistance to
weathering is required. However,
fluorinated polymer coatings generally
have low solids content and high VOC
and often require baking to achieve full
cure.

Fluorinated acrylic siloxane and
fluorinated epoxy siloxane hybrids have
been developed. These coatings combine
improvements in resistance to ultraviolet
light and weathering from proprietary
fluorinated resins with high solids and
low VOC of the acrylic and epoxy
siloxane hybrids. Incorporation of
fluorinated resin has been shown to
improve the weathering resistance of
both acrylic siloxane and epoxy siloxane
hybrids. Comparative QUV-B accelerated
weathering resistance is shown in Figure
8. Further testing of the fluorinated
acrylic siloxane has shown greater than
95% gloss retention after 5-years
exposure in Florida. Of note, weathering
resistance of the fluorinated epoxy
siloxane was improved without
compromising the inherent corrosion
resistance of epoxy siloxane.

Fast-Cure Epoxy Acrylic Siloxane Hybrid
Modification of organic and siloxane
resins and their cure mechanisms has
led to the development of an epoxy
acrylic siloxane hybrid with very fast cure
times. The coating has high solids and
low VOC and exhibits weathering
characteristics similar to the epoxy
siloxane hybrid with 60-90% reduction in
dry times. These properties were achieved
without compromising flexibility. In fact,
the percent elongation and impact
resistance are actually better than the
epoxy siloxane. Properties of the new
coating are shown in Table 7. The fast-
cure epoxy acrylic siloxane coating is ideal
for product finishing, heavy-duty OEM
and as a topcoat in so-called fast
deployment coating systems. The
technology is versatile. Higher solids,
lower VOC versions are being developed
for marine and industrial maintenance
painting.

Table 7. Fast-Cure Epoxy Acrylic Siloxane


Components Resin, Cure
Volume Solids 55%
VOC 420g/l
Application Method Spray
Primers Epoxy, Alkyd, Other
Pot Life, 70F 4 hours
Comparative Properties
Fast-Cure Epoxy Acrylic Siloxane (Epoxy Siloxane)
Dry Times, minutes
- Dust Free
- Tack Free
- Print Free

5 (75)
15 (145)
235 (40)
Conical mandrel elongation 25 (15) %
Impact Resistance
- Direct
- Reverse

6.0 (3.0) Joules
6.5 (2.0) Joules
QUV-B Accelerated Weathering
60
o
Gloss Retention
- 4 weeks
- 8 weeks

78 (75) %
68 (67) %
SUMMARY

In many ways, organic-siloxane hybrids
are the most significant advance in
ambient-cure protective coatings since
polyurethane. The chemistry allows
retention of desirable properties in existing
systems while enhancing those areas
needing improvement. Organic-siloxane
coatings have been formulated with
performance properties, durability and
extended service life not previously
obtainable with conventional organic
coatings.

Acrylic siloxane hybrid coatings have
high solids, low VOC and cure at ambient
temperatures without the use of
isocyanate. Two-component and one
component acrylic siloxane hybrids have
comparable resistance to weathering;
however, the one-component type has
better flexibility, unlimited pot-life and
offers ease of application. The superior
weatherability and good corrosion
resistance of acrylic siloxane hybrid
coatings make them ideal as
toxicologically more acceptable, cost
effective alternatives to aliphatic
polyurethane.

Epoxy siloxane hybrids have ultra high
solids, low VOC and cure at ambient
temperature to provide coatings with an
unsurpassed combination of resistance
to weathering and corrosion. They
provide the corrosion resistance of epoxy
with weatherability better than aliphatic
polyurethane in a single coating.
Improved durability and elimination of
epoxy primer and epoxy mid-coat in
traditional multi-coat, high performance
coating systems provides lower
application and life-cycle costs for the
protection of both small and large
structures.

CONCLUSION

Polysiloxanes are the newest generic
coating type. Recent advances have
resulted in organic-siloxane hybrid
coatings that offer significant
improvements in ultraviolet light, heat,
chemical, oxidation and corrosion
resistance. Commercially available
products offer improved performance
properties and cost effectiveness, lower
VOC content and improved health and
safety features compared to traditional
organic coatings and provide new options
and real value for end users.

References
1. H.H. Kline, “Inorganic Zinc Rich”,
Generic Coating Types, Technology
Publishing Co., p.166 (1996)
2. Hedlund, R.C., “Silicones”, Paint and
Varnish Production, 44, No. 11,
November 1954.
3. R. C. Hedlund, “Reactive Silicone
Resins in Architectural Finishes”’ Paint
Industry, (1959)
4. “Silicone-Organic Copolymer Resists
Rigors of Weather”, Chemical
Processing, November, (1962)
5. Foscante, et al., “Interpenetrating
Polymer Network Comprising and
Epoxy Polymer and Polysiloxane”, US
Patent 4,250,074 (1981).
6. N. R. Mowrer, et al., “Epoxy
Polysiloxane Coating and Flooring
Compositions”, US Patent 5,618,860,
(1997).
7. J.M Keijman, “Inorganic-Organic
Hybrid Coatings in the Protective
Coatings Industry”, Proceedings, SSPC
2002.
8. W.A. Finzel and H.L. Vincent,: Silicones
in Coatongs” FSCT Monograph, p. 21,
(1996)
9. L.H. Brown, “Silicones in Protective
Coatings”, Treatise on Coatings, Vol 1,
Part III, Film Forming Compositions,
Marcel Dekker, p. 530 (1972).
10. W.A. Finzel and H.L Vincent,
“Silicones in Coatings, FSCT
Monograph, p 8, (1996).
11. “Testing of Dimetcote 9HS/PSX-700
in Accordance with Norsok M-CR-
501, System #1”, Corrosion Control
Consultants & Labs, Inc., Report
Number 190619071, November 1999
12. “Cyclic Testing of Amercoat 160HF/
PSX-700 In Accordance With
Norsok M-CR-501, System #1”,
National Institute of Technology,
Norway, Report 27871KA02,
September 1996.
13. “Testing Amercoat 68/PSX-700
System According to ISO/DIS
12944-6”, COT-BV Report Number
LB97-188.RAP, May 1997.
14. G.H. Brevoort, “ A Review and
Update of the Paint and Coatings
Cost Selection Guide”, NACE
Corrosion Conference (1993).
15. J.J. Snedden, “Petrochemical Plant
Project – A Coatings Comparison”,
Ameron UK Engineering Department
Report, Revision 2, March 2000.
16. N.R. Mowrer, “The Use of Novel
Epoxy Siloxane Polymers in
Protective Coatings”, Epoxy Resin
Formulators/ Society of the Plastic
Industry, Proceedings, (1997).
17. H. Sakugawa, “Elastomer Modified
Epoxy Siloxane Compositions”, U.S.
Patent 6,639,025 (2003).
18. H. Sakugawa, “Chemical Resistant
Elastomer Modified Epoxy Siloxane
Surfacer”, Proceedings, SSPC 2003.
19. J.E. McCarthy, “ New Topcoat
Technology For Maintenance Of
Marine And Offshore Structures”,
Proceedings, SSPC 1997.
20. S.A.M Kelly et al., “Coating
Compositions”, PCT W/O 98/23691
(1998)
21. K.Yeats et al., “Ambient Temperature
Coating Composition”, PCT patent
WO 01/51575 (2001)
22. N. Schoonderwoerd et al., ”Coating
Composition Comprising
Polyacetoacetate, Crosslinker and
Organosilane”, US Patent
6,203,607 (2001).




























































Figure 5. One-Component Acrylic Siloxane Reactions
C
H
H
OH HO RO Si
R
R
OR
+
Si
R
O C O Si OR
H
H
R
R
OR
R
O C O Si OH
H
H
R
R
O C O Si OH
H
H
R
R
+
ROH
C O Si
H
H
R
R
O Si OH
R
R
Acrylic Polyol
Alkoxy Functional Silane
Alkoxy Silane Functional Acrylic
Hydrolytic Polycondensation
Crosslinked Acrylic Siloxane
Acid / Base
Water
+
H
2
O
+



Figure 6.
Accelerated QUV-B Weathering of Epoxy Siloxane, Acrylic Siloxane
And Other Generic Coating Types
0
10
20
30
40
50
60
70
80
90
100
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
Exposure Time, Weeks
6
0

D
e
g
r
e
e

G
l
o
s
s
Siloxane
Acrylic Siloxane
Epoxy Siloxane
Acrylic Urethane
Silicone Alkyd
Alkyd
Epoxy







Figure 7. Accelerated QUV-B Weathering Of Acrylic Siloxane Coatings
20
30
40
50
60
70
80
90
100
0 3 6 9
Weeks Exposure
S
i
x
t
y

D
e
g
r
e
e

G
l
o
s
s
12
2nd Gen. 1-Pack Acrylic Siloxane
2-Pack Acrylic Siloxane
2-Pack Epoxy Acrylic Siloxane
1st Gen. 1-Pack Acrylic Siloxane



Figure 8 QUV-B Accelerated Weathering of Fluorinated Siloxane Hybrids
40
50
60
70
80
90
100
0 3 6 9 12 15
Weeks Exposure
S
i
x
t
y

D
e
g
r
e
e

G
l
o
s
s
Fluorinated Acrylic Siloxane
Acrylic Siloxane
Fluorinated Epoxy Siloxane
Epoxy Siloxane



Table 2.
Comparison of Corrosion and Accelerated Weathering Resistance of
Epoxy Siloxane vs. Epoxy/Urethane and IOZ/Epoxy Siloxane vs. IOZ/Epoxy/Urethane

COATING SYSTEM EPS
1.

EPOXY/
URETHANE
IOZ
2.

/EPS
IOZ/EPOXY/
URETHANE
Number of Coats 1 2 2 3
DFT, Mils 7 4 / 3 3 / 7 3 / 4 /3
Salt Spray; ASTM B117, 2000 Hours
Blistering, ASTM D174 10 10 10 10
Rusting, ASTM D1654 10 10 10 10
Scribe Creep 8 7 10 8
Salt Spray, 5000 Hours
Blistering -- -- 10 10
Rusting -- -- 10 10
Scribe Creep -- -- 6 2
Cleveland Humidity, ASTM D2247, 1500 Hours
Blistering 10 10 10 10
Rusting 10 10 10 10
QUV – B Accelerated Weathering, ASTM G53, 60 Degree Gloss
Initial 92 92 -- --
1 week 91 88 -- --
2 weeks 88 84 -- --
4 weeks 78 70 -- --
6 weeks 64 54 -- --
8 weeks 58 46 -- --
10 weeks 54 36 -- --
12 weeks 52 21 -- --
15 weeks 50 3 -- --
1. EPS = Epoxy Polysiloxane 2. IOZ = Inorganic Zinc


















Table 4. Chemical Resistance of Elastomer Modified Epoxy Siloxane Surfacer
Compressive Strength Before Immersion
10,875 psi
Compressive Strength After Seven Day Immersion (psi)
Acetic acid, 70% 10,020 Lime, sat 10,365
Acetic acid, conc. 10,555 Lye, NaOH, 25% 10,775
Acetone 10,855 Methylpyrollidone 10,955
Alum, 15% 10,710 MTBE 10,875
(NH
4
)OH, conc. 10,875 Methanol 10,735
Acetylaldehyde 10,890 Nitric acid, 50% 10,630
Ethanolamine 11,050 Nitric acid, 25% 10,350
Brake fluid 11,005 Potassium silicate 10,575
Citric acid, 25% 10,620 Petroleum ether 10,810
DMSO 10,745 Skydrol 10,530
Ethyl ether 10,715 NaOH, 50% 10,735
Ferric chloride, sat. 10,680 Na hypochlorite, 5% 10,745
Formaldehyde 10,675 Styrene 10,905
Tall oil fatty acid 10,695 Sulfuric acid, 98% 10,835
Gasoline 10,545 Tannic acid, sat. 10,605
Gasohol 10,565 Triethylamine 11,025
Hydrochloric acid, conc. 10,610 Vinyl acetate 11,165
H
2
O
2
, 30% 10,850 Xylene 10,715


Table 6.
Comparative Corrosion Resistance Of Epoxy Siloxane, 2-Component
Acrylic Siloxane and 2-Component Acrylic Urethane Coating Systems
Topcoat Epoxy
Siloxane
2-Component
Acrylic Siloxane
2-Component
Acrylic
Urethane
Primer Zinc Rich Epoxy
Primer/Topcoat DFT,
mils
3/5 3/5 3/5
Salt Fog, 2000 hrs.
(ASTM B-117)
- Unscribed Area, Blister
- Unscribed Area, Rust
- Scribed Area, Blister
- Scribed Area, Creep



10
10
10
10


Few #8
10
Few #4
8


Few #8
9
Few#4
8

Cyclic Prohesion, 2000
hrs.
(ASTM D5894)
- Unscribed Area, Blister
- Unscribed Area, Rust
- Scribed Area, Blister
- Scribed Area, Creep



10
10
10
10



10
10
10
10



10
10
10
10


Table 5. Comparisons of Acrylic Siloxane Coatings
Coating Type 1
st
Generation
1-Component
Acrylic
Siloxane
2
nd
Generation
1-Component
Acrylic Siloxane

2-Component
Acrylic Siloxane

2-Component
Epoxy
Acrylic
Siloxane
Volume Solids,
ISO3233
55% 79% 76% 75%
VOC, EPA Method
24
384g/l 216g/l 172 g/l 216 g/l
DFT/coat 2 mils 5 mils 5 mils 5 mils
Pot Life, 70F Not Applicable Not Applicable 2 hours 8 hours
Dry to Touch, 70F 2 hours 2 hours 3 hours 2 hours
Dry Through, 70F 12 hours 9 hours 10 hours 18 hours
Recoat, Min 6 hours 4 hours 4 hours 6 hours
Recoat, Max Extended Extended Extended Extended
Conical Mandrel Elongation
- After 2 weeks
at 70F
- After 2 weeks
at 70F plus 2
weeks at 140F

14.0%

3.0%

14.0%

9.0%

14.0%

3.0%

14.0%

3.0%
Salt Fog Testing Over Zinc Rich Epoxy Primer – 2700 Hours (ASTM B-117)
Primer/Topcoat
DFT
3/2 mils 3/5 mils 3/5 mils 3/5 mils
Unscribed Area
- Blister
- Rust
Scribed Area
- Blister
- Creep

Few # 2
None

Few # 4
0.5 mm

None
None

Few #4
0.5 mm

None
None

Few #4
0.5 mm

Few #8
None

Med #2
0.8 mm
Cleveland Humidity Testing Over Zinc Rich Epoxy (ASTM D-2247)
1000Hours
- Blister
- Rust
2000 Hours
- Blister
- Rust
Few#2/ Med6,
8
None

Med#2/Den#6
None

Few#2/ Med6, 8
None

Med#2/Den#6
None

Few#2/Med#6,8
None

Med#2/Den#4
None

Med#2/Den#6
None

Med#2/Den#6
None