Primer coating composition of a fluorocarbon polymer and an amino alkyl alkoxy silane

A primer composition for fluorocarbon polymer coatings which cures at ambient temperatures and contains a fluorocarbon polymer of vinylidene fluoride and hexafluoropropylene and has a weight average molecular weight of about 50,000-300,000; PA0 a metallic oxide such as magnesium oxide which is an acid acceptor and PA0 an amino alkyl alkoxy silane; preferably, the primer contains a reinforcing pigment such as titanium dioxide; The primer is used in combination with fluorocarbon polymer coatings to provide corrosion and abrasion resistant coatings for equipment used in chemical plants, oil refineries, oil drilling platforms, and for the interior of smoke stacks of large utility companies.

BACKGROUND OF THE INVENTION 
This invention is related to a coating composition and in particular to a 
fluorocarbon primer coating composition. 
Fluorocarbon polymers are inert to strong acids such as sulfuric acid, 
nitric acid, hydrochloric acid and strong bases such as sodium hydroxide 
and are resistant to weathering and salt water corrosion and are tough and 
abrasion resistant. Coatings of these polymers can be used in chemical 
plants and oil refineries to coat pipes, vessels and other equipment, on 
off shore oil well platforms, on ships and as protective coatings for the 
interior of smoke stacks of utility companies. Metal smoke stack interiors 
are subjected to abrasion from fly ash and corrosion by acids resulting 
from combustion products such as SO.sub.x and NO.sub.x and halogen ions. 
To obtain adequate adhesion of a fluoropolymer coating to the substrate, a 
primer coating is required. 
The composition of this invention is directed to a primer that cures at 
ambient temperature, has excellent adhesion to a variety of substrates and 
provides a surface to which a fluorocarbon polymer coating composition 
will adhere. 
SUMMARY OF THE INVENTION 
A primer composition containing about 10-50% by weight binder and 50-90% by 
weight of an organic solvent, wherein the binder is 
a fluorocarbon polymer of vinylidene fluoride and hexafluoropropylene and 
has a weight average molecular weight of about 50,000-300,000; 
a metallic oxide such as magnesium oxide which is an acid acceptor and 
an amino alkyl alkoxy silane; 
preferably, the primer contains a reinforcing pigment such as titanium 
dioxide. 
DETAILED DESCRIPTION OF THE INVENTION 
The composition contains about 10-50% by weight binder and about 50-90% by 
weight organic solvent. The binder is a blend of a fluorocarbon polymer, a 
metallic oxide which is an acid acceptor and an amino alkyl alkoxy silane. 
One of the advantages of the composition is that it cures at ambient 
temperatures and baking is not required. Therefore, the composition can be 
used on large structures such as the interior of smoke stacks or large 
chemical tanks which could not be subjected to baking temperatures using 
conventional techniques. 
The fluorocarbon polymer is of polymerized monomers of vinylidene fluoride 
and hexafluoropropylene. Preferably, the polymer contains about 50-70% by 
weight of vinylidene fluoride and 30-50% by weight of hexafluoropropylene. 
The polymer can contain up to 40% by weight of other monomers such as 
tetrafluoroethylene. One useful polymer contains about 20-30% by weight of 
tetrafluoroethylene. 
The fluorocarbon polymer has a weight average molecular weight of about 
50,000-300,000. Preferably, fluorocarbon polymers are used that have a 
weight average molecular weight of about 75,000-250,000. Two particularly 
useful fluorocarbon polymers have a weight average molecular weight of 
about 75,000-125,000 and 150,000-250,000. Polymers in the lower end of the 
molecular weight range are preferred for forming compositions with higher 
binder content. 
Molecular weight, as used herein, is determined by gel permeation 
chromatography using polymethylmethacrylate as a standard. 
A metallic oxide which is an acid acceptor is used in the composition to 
react with the hydrofluoric acid which is generated during curing or 
crosslinking reaction. Typical metallic oxides are magnesium oxide, lead 
oxide, calcium oxide, lead hydrogen phosphite and a mixture of calcium 
oxide and magnesium oxide. Magnesium oxide is preferred. 
The composition contains an aminoalkyl alkoxy silane. A variety of these 
silanes can be used but preferred are gamma-aminopropyl trimethoxy silane 
and gamma-aminopropyl triethoxy silane and the like. 
Generally, the binder contains about 55-90% by weight, of the fluorocarbon 
polymer, 5-25% by weight of the above silane and 5-20% by weight of a 
metallic oxide which is an acid acceptor such as magnesium oxide. 
Preferably, the composition contains a reinforcing agent such as titanium 
dioxide pigment usually in a pigment to binder weight ratio of about 
20:100 to 200:100. Other inert pigments can be used such as barytes, 
barium sulfate, fibrous calcium silicate and the like. Carbon black, bone 
black or lamp black can also be used as a reinforcing pigment in a pigment 
to binder weight ratio of about 20:100 to 50:100. 
Typical organic solvents that are used in the composition are acetone, 
tetrahydrofuran, methyl ethyl ketone, ethyl acetate, propyl acetate, butyl 
acetate, isobutyl acetate, methyl isobutyl ketone, methyl amyl acetate, 
diisobutyl ketone, ethylene glycol monomethyl ether acetate, ethylene 
glycol monoethyl ether and mixtures of the above. The solvents are used to 
make the composition and can be used to reduce the composition to an 
application viscosity. 
Generally, the composition is sold in two components. The solvents, 
fluorocarbon polymer, pigments such as titanium dioxide and metallic oxide 
acid acceptor are the first component and the amino alkyl alkoxy silane is 
the second component which is blended by the user with the first component 
to form the primer composition. The primer is then reduced with one of the 
aforementioned solvents to an application viscosity and then applied to a 
substrate. 
To decrease curing time and increase toughness of finishes of the 
composition about 0.01-3% by weight, based on the weight of the binder, of 
a bicyclic amidine can be added. One preferred bicyclyic amidine is 
1,8-diaza-bicyclo(5,4,0)undecene-7. 
The composition can be applied over a wide variety of substrates and 
provides a primer to which a fluorocarbon polymer coating composition can 
be applied. Typical substrates are untreated steel, phosphatized steel, 
grit blasted steel, galvanized steel, aluminum, copper, brass, cement and 
cementitious surfaces such as fire brick, mortar used for fire brick and 
the like. 
Generally, the primer composition is applied to the substrate and the 
solvent is allowed to flash off and then a fluorocarbon polymer coating is 
applied and the resulting composite is cured at ambient temperatures. The 
primer can be cured in about 15 minutes to 48 hours or longer and can be 
heated to 80.degree. C. to 120.degree. C. for 0.5 to 2 hours for rapid 
curing. The thickness of the primer is about 75-250 microns depending on 
the end use. The thicker primer coatings provide additional corrosion 
resistance. 
The ambient temperature curing characteristic of the composition allows for 
its application on large vessels and reactors, chemical plant and oil 
refineries, large metal structures and equipment and pipes, off shore oil 
well platforms, heat risers, i.e., pipes which are used in an oil well to 
transport the oil from underground to the surface and interior of smoke 
stacks used by large utility companys. Conventional compositions that do 
not cure at ambient temperatures but require elevated temperatures are not 
practical to use for the above applications.

The following examples illustrate the invention. All parts and percentages 
are on a weight basis unless otherwise indicated. 
EXAMPLE I 
Primer A was prepared as follows: 
______________________________________ 
Parts by 
weight 
______________________________________ 
Portion I 
Titanium dioxide pigment 
100 
Magnesium oxide 15 
Fluorocarbon polymer solution 
303 
(33% solids solution in ethyl 
acetate of a copolymer of 60% 
vinyldene fluoride and 40% 
hexafluoropropylene having 
a weight average molecular 
weight of about 100,000) 
Portion 2 
gamma-aminopropyltrimethoxy 
18 
silane 
Total 436 
______________________________________ 
The constituents of portion 1 were charged into a mixing vessel and 
thoroughly blended and then portion 2 was added and blended. The resulting 
composition was reduced to a spray viscosity with methyl ethyl ketone and 
sprayed onto untreated steel panels and solvent was allowed to flash from 
the primer at ambient temperatures. The resulting primer coat has a 
thickness of about 125 microns. 
A fluorocarbon polymer coating composition was prepared using the same 
above constituents in the same amounts as for the primer except portion 2 
was replaced with 5.5 parts by weight of a 55% solids solution in 
isopropanol of an amine curing agent which is the reaction product of 3 
moles isophorone diamine and 1 mole of dimethylmaleate. The coating 
composition was reduced to a spray viscosity with methyl ethyl ketone and 
sprayed onto the above prepared primed panels. In each case, thick films 
were applied by allowing flash drying between each application and the 
coatings were dried at ambient temperatures and gave a 200 micron thick 
dry coating. On each panel, the coating had excellent adhesion to the 
primer and could not be separated from the primer. After 7 days of curing, 
each coating was fully cured and was resistant to sulfuric acid, sodium 
hydroxide and solvents such as methyl ethyl ketone and ethyl acetate. 
The above primer A was reduced to a spray viscosity with methyl ethyl 
ketone and sprayed onto untreated steel panels and aluminum panels and 
dried and cured at ambient temperatures for 7 days. The resulting dry 
films were about 125 microns thick and had excellent adhesion to the metal 
substrates and were white and smooth in appearance. 
Primer B was prepared using identical constituents in the same amounts as 
in the above primer A except magnesium oxide was omitted. The primer was 
reduced to a spray viscosity with methyl ethyl ketone and sprayed onto 
steel panels and aluminum panels and dried and cured for 7 days at ambient 
temperatures. The resulting film on each of the panels was about 125 
microns thick. The films were relatively soft in comparison to Primer A 
and were not resistant to methyl ethyl ketone which indicated a lack of 
cure. 
Primer C was prepared using identical constituants in the same amounts as 
used in the above primer A except the titanium dioxide and magnesium oxide 
were omitted. The primer was reduced to a spray viscosity with methyl 
ethyl ketone and sprayed onto steel and aluminum panels and dried and 
cured for 7 days at ambient temperatures. The resulting film on each of 
the panels was about 125 mils thick. The films were relatively soft in 
comparison to Primer A and were not resistant to methyl ethyl ketone 
indicating a lack of cure. 
EXAMPLE 2 
Primer D was prepared using the same constituents and amounts as in Example 
1 except gamma-amino propyltriethoxy silane was substituted in the same 
amount for the gamma-aminopropyltrimethoxyl silane. The primer was reduced 
to a spray viscosity as in Example 1 and sprayed onto aluminum and steel 
panels and flash dried as in Example 1 to provide a primer coating about 
125 microns thick. 
The fluorocarbon polymer coating composition of Example 1 was applied to 
each of the above primed metal substrates and dried and cured at ambient 
temperatures and gave a 200 micron thick dry coating. In each case, the 
coating had excellent adhesion to the primed metal substrate and was 
resistant to sulfuric acid, sodium hydroxide and solvents such as methyl 
ethyl ketone and ethyl acetate. 
EXAMPLE 3 
To each of the above prepared Primers A and D about 0.17% by weight, based 
on the weight of the fluorocarbon polymer binder, of an additive of 
1,8-diaza-bicyclo(5,4,0)undecene-7 was added. Each of the primers were 
reduced to a spray viscosity as in Example 1 and sprayed onto aluminum and 
steel panels and dried at ambient temperatures. Each of the primer 
coatings cured in several minutes to a solvent resistant coating which was 
more rapid than the curing of the primers without the additive. Also, a 
harder finish was formed. The primer is expected to be useful in 
automotive and truck applications where finishes are exposed to greases 
and synthetic fluids and lubricants.