Note: Descriptions are shown in the official language in which they were submitted.
73~
Background of the Invention
Fluorocarbon polymer coatings on surfaces or
substrates for diverse applications are known. Most
familiar is the polytetrafluoroethylene ~hereinafter,
PTFE) coating applied to pots and pans to provide
non-stick suxfaces for cooking applications. Such
surfaces are generally coa~ed by first etching the
substrate and then coating the substrate with the
fluorocarbon followed by coalescing (sintering) the
polymer in situ on the substrate~
In addition to the non-stick characteristics
o~ 1uorocarbon polymer coatings, such coatings offer
high heat resistance, stability at cryogenic
temperatures, non-wettable surface characteristics,
exceptional dielectric properties, exceptional weather
resistance, and provide one of the most chemically
inert coating subs-tances presently known.
Methods of spray coating PTFE finishes and
enamels onto various substrates are also known. These
PTFE finishes and enamels are applied over a primer to
obtain satisfactory adhesion. These enamels can be
applied in multiple coats, each coating being baked
above the melt temp~rature of PTFE to coalesce the
polymer. The maximum film thickness which can be
applied by this technique is limited by a mud-crackir:c;
phenomenon. Mud-cracking is a common problem associated
with coating fluorocarbon polymers on substrates and
refers to the~
73~
surface effect which resembles the mud-cracks which
form in sun-parched grownd. Mud-cracks are generally
undesirable in fluorocarbon coatings, and represent
defects in the coating.
Mud-cracks occur when a film is sprayed too
thickly onto a surface and cracks form upon drying.
Most PTFE finishes and enamels can be applied in single
coating thicknesses up to about 0.001 inch without
mud-cracking. All PTFE finishes will crack if a
critical thickness is exceeded in a single coat. These
cracks will not heal upon sintering. For example, the
maximu~ one-coat dry film thickness without
mud-cracking for duPont's 851-214 and 852-201* PTFE
enamels is 0.001 inch, and for the so-called "high
build" enamels, the maximum thickness per coat is 0.003
inch.**
Sprayable polyfluorocarbon powders are also
known. Poly~:erized perfluoroalkoxy resin (hereinaft,er,
the term PFA is used to designate the polymerized
perfluoroalkoxy resin) in powder form can be applied to
hot or cold substrate surfaces using conventional
electrostatic spray equipment. Perfluoroalkoxy resin is
a copolymer obtained through the copolymerization of
perfluoroalkyl perfluorovinyl ethers and
tetrafluoroethylene monomers.
**Teflon Finishes Product and Application Techniques'l,
Bulletin No. 1, 14th Edition, published by E.I. duPont
de Nemours and Co., Inc. See also "Teflon PTFE Coatings
~,51-Line", ~ulletin No. E-05440, Revision 3, published
by duPont.
* denotes trade mark 3
73-~
Using electrostatic powder spray techniques, "TEFLON-P"
PFA resin*, commerclally available from E. I. duPont de Nemours &
Co., Inc., under product designation 532~5010, can be used to
provide a continuous film up to 0.002 inch thick without mud-crack-
ing. Thick films of PAF of 0.005 inch or more have been achievedthrough the application of multiple coats of PFA sprayable powder.
Application techniques for coatlngs of TEFLON-P PFA powder are
contained in the bulletin "TEE'LON coatings Fact Sheet - TEFLON-P
PFA POWDER COATING 532-5010" published by duPont in bulletin
number E-054409 dated June, 1977.
Regarding end-use applications, the PAF powders may be
used wherever a coating is desired having one or more of the basic
properties inherent to fluorocarbon polymers. The sprayable
powders are useful in applications where mechanical, electrical,
thermal and chemical properties approaching those of PTFE fluoro-
carbon resin are required~
Summary of the Invention
The present invention relates fo a new composi-
tion comprising sheared particles of polytetrafluoroethylene
(PTFE) dispersion powder and perfluoroalkoxy (PFA) powder in a
carrier liquid, wherein PTFE is contained in an amount between
about 5% and 100% by weight and PFA is contained in an amount
between about 95% and 0% by weight, based upon the total weight
of said PTFE and PFA polymers, said composition being sprayable
using conventional paint spraying apparatus to produce a coating
substantially free of mud-cracks or blisters on a substrate, the
shearing of said particles being sufficiently high to enable
spraying to a thickness exceeding 0.003 inch per layer. The
sprayable composition according to this invention comprises pre-
ferably particles of PTFE and PFA dispersed in a liquid carrierof water.
* TEFLON is a registered trademark of duPont
--4--
1/' . i
73~
The inven~ion relates also to a method for coating a
substrate with a fluorocarbon polymer composition, said method
comprising essentially the following steps:
ta) applyin~ to said substxate at least one coating of a composition
in a carrier liquid the composition comprising sheared particles
of polytetrafluoroethylene (PTFE) dispersion powder and
perfluoroalkoxy (PFA) powder in a carrier liquid, wherein PTFE
is contained in an amount between about 5% and 100% by weight
and PFA is contained in an amount between about 95% and 0~
by weight, based upon the total weight of said PTFE and PFA
pol~mers, said composition being sprayable using conventional
paint spray.ing apparatus to produce a coating substantially
free of mud-cracks or blisters on a substrate, the shearing
of said particles being sufficiently high ~o enable spraying
to a thickness exceeding 0.003 inch per layer, and
-4a-
'73~L
(b) heating the resulting coated substrate to evaporate said
liquid from the coating and to coalesce the polytetrafluoro~
ethylene and th~ perfluoroalkoxY resins thereofO
As used herein, the tPrm PTFE is intended to designate
homopolymers; also the expression "PT~E ~ispersion p~w~er" is
intended to designate the extrusion grade PTFE powders used in
paste extruslon.
The preferred method oE applying the coating to the
substrate is by spraying and the preferred carrier liquid is water.
Substantially nonporous coatings free of mud-cracks can
he obtained by applying a force, either a shear force or a
compressive force, to the top surface of the coating prior to
heating according to step (b) above, in order to densify the
coating.
Also provided is a substrate coated with the composition
oE this .invention.
The thickness o each layer of the coating of this inven
kion exceeds 0.003 inch and can exceed 0.009 inch.
~ method o molding a shaped article and a molded shaped
article comprised of the above fluorocarbon compositions, option-
ally Eilled and reinforced, are also provided.
Both porous and substantially nonporous compositions,
coatings and shaped articles are provided, as well as filled and
reinforced products.
Detailed Description of the Invention
and Preferred Embodiments
According to the present invention, a new sprayable
composition is provided comprising be~ween about 5% and about lO0
by weight ofa polytetrafluoroethylene resin and between about 0~
and about 9S% by weight of a perfluoroalkoxy resin, wherein said
percentages are based upon the total weight of the polytetrafluoroethylene and the perfluoroalkoxy resins. As used herein, all
percentages denote weight percentages unless otherwise indicated.
It has been found that a suspension comprising PTFE
dispersion powder and PFA powder in the above proportions, when
mixed vigorously with about two (2) to about six (6) volumes of
73~
conventional sprayin~ equipment such as that employed in the
spraying of paint. Other carrier liquids which may be employed
include mineral spirits, oils, kerosene and the like. However,
water is preferred because it is readily available, simple to use
5 and is free of fire or pollution hazards.
3~
The PTFE/PFA composition of this invention can
be sprayed onto the substrate desired to be coated, the
coating can be heated to remove the liquid carrier, and
the coated substrate can then be raised to a
temperature above the melt temperature* of the polymer
particles resulting in coalescing of the particles into
a cc,ntinuous coating of perfluorocarbon polymer on the
substrate, the coating having a thickness greater than
has heretofore been achieved using aqueous spray
coating compositions.
Such coatings may be applied several times to
a single substrate in order to increase the thickness
of the overall coating. By the process of this
invention, no noxious fumes or dust ar~ produced. The
cost of the coating composition of this invention is
much less than prior conventional coatings utilizing
PFA powder, since PTFE is presently less expensive
t~,~n PE'A. Also, the cost. of applying the coating of
this invention is significantly reduced over prior
methods. Simple spraying devices are used to prc.d~ce
thick coatings herein, as compared to costly
electrostatic spray guns or fluidized beds needed to
apply PFA powder. A much larger number of coatinss
using prior PTFE spray methods are needed to produce
thicknesses (where possible) of PTFE coatings
comparable to the coatings of this invention.
_ _ _ _ _ _ _ _ _ _
* The melt temperature for virgin PTFE is about 342C
and about 327C :Eor previously melted polymer. The melt
temperature for PFA is about 307C.
~8~3~
The coatings achievable by the method of this
invention can be modified if desired. If reinforcement
is required to improve the physical properties of the
coating or to reduce its thermal expansion, glass
flakes, carbon black, the "granul2r" type of PTFE or
other fillers can be mixed with the PTFE/PFA powder to
provide such reinforcement. Also, a layer of glass
cloth or mat, or like reinforcing material, can be
placed wi-thin the coating. This may be accomplished by
spraying a coating of the PTFE/PEA mixture of this
invention onto the substrate desired to be coated,
allowing the coating to dry slightly, and applying the
cloth or mat to the coating and forcing it into the
coating. The mat rnay easily be forced into the coating
by using a simple roller device such as a paper
hanger's roller. Following installation of the cloth or
mat, more coats of the PTFE/PFA mixture may be applied,
dried and rolled, followed by sintering in place, to
achieve a continuous, essentially nonporous reinforced
coating substantially free of mud-cracks.
The sprayable composition and spraying method
of this invention have great advantages over the known
PTFE enarnel spraying prccess. Thick single coatings may
now be applied, having thicknesses exceeding 0.003 inch
and being substantially free of mud-cracks, as compared
to the maximum Frior art single coating thickness of
0.003 inch. Single layer coa-tings, substantially free
of rnud-cracks, can now --
X 8
73~
be applied having a thickness exceeding 0.009 inch. Multiplelayer coatings can now be applied having thickness grea-ter than
0.100 inch. The surlaces of very large vessels and -tanks can now
be coated economically to pr~vide thick, corrosion resis~ant coat-
ings. Reinforced coatings are now possible, as discussed above,whereas heretofore such reinforced coatings were not available.
In a preferred embodiment of preparing and applying the
coating of this invention, the following procedures are employed.
Fifty grams of PFA resin such as duPont's #532-5010 and
0 50 grams of PTFE fine powder resin such as ~CI's "FLUON"* CD 1,
~L
duPont's "I~EF~ON" 6A or Ugine Kuhlmann's "Soxeflon"** S620 or S630
are added to 175 ml water to which has first been added 2 grams
~ 4c
Triton X100 wetting agent and a few drops of Dow Corning antifoaming
agent. This fluorocarbon/water mixture is blended vigorously for
about 1 to 5 minutes using, for example, a Waring blender. The
speciEied quantities and proportions are not precisely re~uired
and ~ne skilled in the art can readily alter these quantities
and specific proportions to suit particular applications.
The high speed agita-tion of the polymer/water mixture
~ ,,c~
in the Waring blender is an important process step in preparing
the coating composition of this invention. Such high speed
agitation vigorously mixes the polymer/water suspension at a
rapid rate, and the use of such rapid mixing in preparation of
sprayable compositions is contrary to prior art teachings. High
speed stirring or violent agitation was known to cause irreversible
coagulation of PTEE aqueous dispersions, and such rapid agitation
was to be avoided.*** Forpurposes of this invention, the mixing
of the aqueous polymer suspension must be high enough to break
up the agglomerates present in PTFE dispersion powder and permit
spraying of the suspension withou-t clogging of the spray gun.
* Registered trademark of Imperial Chemical Industries
** Registered trademark o Uyine Kuhlmann
*** See "Teflon 30 TFE-Fluorocarbon Resin", Bulletin No. A-46473,
Published by E. I. duPont de Nemours & Co. and Bulletin No.
E-05440, Revision 3, referred to hereinabove.
o ~ .~ / ~
~5~3~
The surface of the substrate to be coated should be prepared
prior to coating to thoroughly clean it and remove all contarni-
nants which may affect the continuity and bonding of the coating
to be applied. If the surface to be coated is metallic such as
steel, it may be prepared prior -to coating by conventional sand-
blasting and applying a surface primer such as duPont's ~850-201
prlmer .
The PFA/PTFEjwater suspension or dispersion is then
sprayed onto the surface to be coated using conventional paint
spraying or similar apparatus. A Model 18 paint spray gun manu-
' factured by the Binks Manufacturing Company or a DeVilbls EGA 502
spray gun is suitable.
~ o~/~s
i73~
After spraying the coating onto - th~
substratel the coating should be thoroughly dried in
any convenient mannerO For ~xample, air from a hot air
gun may be directed to the coating to evaporate the
liquids. The coated substrate is then placed in an oven
maintained at a temperature above the melt temperature
of the polymers for a time sufficient to effect
coalescing of the polymers into a continuous film
bonded to the substrate. The preferred temperature
range is 700 to 750F. Alternatively, the coated
article may be su~jected to a heating cycle comprising
several stages wherein the first heating stage is
conducted at lower temperature levels to effect removal
o the liquid carrier and a second heating stage is
conducted at higher temperature levels to effect
coalescing of the polymer particles to provi~e a
continuous coating on the substrate.
Additional coats may be applied by repeating
the above procedures as many times as desired.
To obtain nonporous coatings it is necessary
to denslfy the applied coating. This may be
accomplished by rolling the coati~g prior to heating
the coating to coalesce it. For this purpose, a roller
such as a paper hanger's roller may be used. If the
polymer tends to Ctick to the ro~ler, a film or coating
of thin plastic such as polyethylene may be applied to
the surface of the roller to prevent such sticking.
If multiple cocts are required, it is
desirable to spray a light coat of the polymer
suspension on the prior coat after rolling and kefore
heating to coalesce r in order to obtain good adhesion
of subsequent coats to the previous coat.
X
11
~5~3~
The compostion and procedures descriked abc~e
have been found useful in the spray coating of a
variety of substrates. They are particularly useful in
the coating of large irregular shapes such as the
interior of large chemical reactox vessels. These
coatings are especially suited for the repair of
glass-lined chemical equipment such as Pfaudler lined
vessels and glass-lined metallic piping. Virtually any
substrate which can withstand the temperatures required
to coalesce the polymers may be coated by the
techniques of this invention.
It has also been found that shaped articles
can be molded from the composition of this invention,
including simple flat sheets as well as very highly
irregular shaped articles. In particular, flasks such
ag Erlenmeyer flasks and the like can be molded using
this composition. This is accomplished by sprairing the
composition on the outside of a mold, such as a
conventional glass Erlenmeyer flask using the cleaning
and coating techniques described above. Preferably
several coats are applied until a desired thickness is
obtained. Following application of the coating
composition, the glass mold is broken and xemoved
leaving a flask in the shape of the mold made of the
PFA/EqFE coating composition of this invention.
Examples of the invention are given below. The
preceding description and the examples are intended to
be ful]y illustrative of the invention, but not to
limit its scope in any way. Minor modifications or
~ 12
73~
changes from the description can be made by one skilled
in the art, and such modifications or changes are
deemed to fall within the scope of the claims
hereinbelow.
In the examples below, reference is made to a
spark test. This test utilizes an electrical holiday
detector to locate areas or points on a coated metal
surface where there is a great difference in electrical
resistance between an exploring electrode passed over
the coating and the underlying metal. The holiday
detector consists of an electrical energy source such
as a batt~ry or high voltage coil, an exploring
eleckrode and a connection from the energy source to
the coated metal. The device is usually equipped with a
vlsual or audible alarm which signals current flow
through the apparatus.
In using such spark detector, a high vcltage
is applied to the surface oE the coating, ranging
usually from 1,000 to 30,000 volts. The exploring
electrode can be a wire brush, electrica~ly conductive
silicone or a coil spring. When a very thin section of
coating is passed over by the electrode, a spark will
jump from the electrode through the air gap to the
metal, indicating a defect in the coating.
Example 1
A sheet of steel plate was sand-blasted and
primed with duPont 850-201* primer.
* denotes trade mark
Fifty (50) grams of PFA powder (duPont product
designation 532-S010), fifty (50) grams of PTFE
dispersion powder (Imperial Chemical Industries product
designation CD-l*), 2 grams Triton X100* surfactant and
a drop of anti-foaming agent (Dow Corning Antifoam A)
were added to 175 ml water and blended in a Waring
blender for about 2 minutes. This mixture was sprayed
onto the surface of the primed plate using a DeVilbis
EGA 502 spray gun. The coating on the plate was dried
using a hot air gun and then the coated plate was baked
in an oven at 700F (385~C) for 15 minutes.
A second coating of the above mixture was then
sprayed onto the top of the first coating and dried as
above. This second coating, after drying, was rolled
using a 1.5 inch wide, 1.5 inch diameter wall paper
roller -to increase the density of the coating. The
coated plate was then baked at 700F for 15 minutes.
A third coat was applied using the same
procedures employed for the second coat.
A fourth coat was applied, dried but not
baked, followed by a fifth coat which was applied,
dried and baked using the same procedures followed in
applying the second coat. The thickness of the coating
(five layers) was approximately 0.040 inch (0.101 cm).
The average thickness per coating layer was thus 0.008
inch (0.020 cm).
* denotes trade marks
73~
The coated steel plate passed a 10,000 volt
spark test over its entire surface, had a good
appearance and was free of mud-cracks.
Following these procedures, the mixture was
found to be easily sprayable and single coating
thicknesses were produced which are greater than the
thickness of any prior fluorocarbon coating produced by
known spraying techniques.
Example 2
A sheet of steel plate having dimensions of 8
inch x 8 inch x 1/4 inch was sandblasted and primed
with duPont 850-201 primer.
A mixture of 50 grams of PFA (duPont 532-50101
and 50 grams of PTFE (ICI CD~l) in 175 ml water was
prepared, to which 2 grams Triton X100 surfact~nt had
been added. To this mixture, one-fourth teaspoon of
carbon black pigment was added and the mixture was
blended in a Waring blender for about A minutes~
This mixture was then sprayed on the primed
steel plate and hot air dried~ A second coating was
sprayed on top of the first coating, dried and baked in
an oven at 725F until the resin turned black in color.
A third coat was sprayed onto the plate~ hot
air dried and rolled using a sheet of plastic to cover
the roller to prevent the resin from sticking to the
roll. A futher coat was then applied, dried and baked
at 725F for ]5 minutes.
i73~
A fifth and sixth coat were applied by the
same technique as the first and second coats,
respectively.
A seventh and eighth coat were applied by the
same technique as the third and fourth coats,
respec-tively.
A ninth coat was applied, dried and a layer o
fiberglas veil was pressed into the coating using the
plastic covered roller.
A tenth coat was applied over the fiberglas,
dried and rolled very hard and an eleventh and twelfth
coats were applied using the same techniques as for the
Eirst and second coats, respectively.
A thirteenth and fourteenth coat were applied
using the same techniques as the third and fourth coats
respectively.
Upon rernoval from the sintering oven the
coating was firmly bonded to the substrate and had a
thickness of about 0.055 inch. The average thickness
per coat was thus 0~004 inch. The coating passed a
10,000 volt spark test over its entire surface, was
bonded well to the substrate and had no mud-cracks. The
black color from the pigment yielded an aesthetically
pleasing appearance.
Example 3
Seventy (70) grams of PFA (duPont 532-5010)
and thirty (30) grams of PTFE (ICI CD-l) ancl thirty
(30) grams of 1/64 inch diameter glass flake were
blended in a Waring blender for 5 minutes with 175 ml
water to which had been added 2 grams Triton X100
surfactant.
~ 16
73~
This mixture was sprayed onto a sandblasted
and primed steel plate as described in Example 2. The
coating was dried and then baked at 700F (385C) for
15 minutes.
Three additional coatings were applied,
repeating each of the above steps, with the exception
that just prior to baking, each coating was rolled with
the small roller previously described.
A further top coating was applied by spraying
a mixture of seventy ( 70) grams of PFA (532-5010) and
thirty (30) grams of PTFE (CD-13 in 175 ml water
containing 2 grams Triton X100 but containing no glass
flake. This top coating was rolled as above, dried and
baked at 700F (385C) for 15 minutes. Upon removal
from the oven, the coated plate passed a 10,000 volt
spark test and appeared to be a continuous, well-bonded
coa-ting.
Ninety-five (95) grams dispersion grade PTFE
(ICI CD-1), five (5) grams PFA (duPont 532-5010), 2
grams Triton X100 surfactant and 2 drops Dow Corning
antifoaming agent were added to 175 ml water and
blended in a Waring blender for about 2 to 3 minutes.
The mixture was then sprayed onto a steel plate which
had been sandblasted and primed as described in Exampl~
2. The coated plate was dried to remove the water and
additives and then baked in an oven at 725F. The plate
was removed from the oven and water-quenched, and then
~S7~
a second coat of the above mixture was sprayed onto the
first coat. This second coat was then dried, rclled
with the paper hanger's roller to increase the density
of the coating, and baked at 725F.
The thickness of the coating produced was
0.010 inch (0.025 cm) to 0.012 inch (0.027 cm). The
average thickness per coat was thus 0.005 inch (0.0125
cm) to 0.006 inch (0~0145 cm). The coating was substantially
nonporous and free of mud-cracks.
5uch coating is especially suitable as a thick
release coating.
Example 5
Nine-ty~five (95) grams PFA (duPont 532-5010),
five (5) grams dispersion grade PTFE (ICI CD-l), 2
grams Triton X100 and 2 drops antifoaming agent were
added to 100 ml water and blended in a Waring blender
for 2 to 3 minutes. This mixture was then sprayed onto
a steel plate which had been sandblasted and primed as
in Example 2~ The coated plate was then dried and baked
at 700F until the coating gelled. This procedure of
spraying, drying and baking was repeated four (4) times
to produce a total of five (5) coats on the surface of
the plate. No rolling was employed in this example.
The resulting coating had a good physical
appearance and passed a 10,000 volt spark test over
approximately~
18
i73~
95% of the surface area of the plate. Such mixture can be applied
to surfaces which are very irregular and thus difficult to roll,
i.e. in corners, to achieve a thick, acceptable fluorocarbon
coating. The thickness of the coating was 0.025 inch. The average
thickness per coate was thus 0.005 inch.
Example 6
Fifty (50~ grams of PTFE (ICI CD-l), fifty (50) grams of
PFA (duPont 532-5010), 2 grams Triton X100 and 2 grams of carbon
black pigment were blended in a Waring blender for 1 to 2 minutes.
This mixture was then sprayed as before onto a 14 inch by 18 inch
steel manway cover that had Eirst been sandblasted and primed with
duPont primer 850-201. The coating was dried and then baked at
725F until -the coating turned black. The coated cover was then
quenched in water. A second coating was applied as above and
dried in an oven until the coating turned a whitish color and all
the water was evaporated.
The coating on the cover was then rolled with a 1.5
~nch diameter roller until the coating turnéd grayish in color.
~hird coating oE the above mixture was then sprayed onto the
~0 second coat as above and the coated cover was dried and then baked
at 725F until the coa-ting turned black. Upon removal from the
oven, the coated cover was quenched in water.
~357~3~
The above coating, drying, rolliny and baking
procedure was then repeated to provide a total of six
(6) coats on the surface of the cover.
The coated cover passed a 10,000 volt spark
test over its entire surface. The thickness of the
coating was approximately 0.050 inch to 0.060 inch. The
average thickness per coat was thus 0.008 to 0.010
inch. The coating was free of mud-cracks and had an
aes-thetically pleasing appearance.
Example 7
One hundred (100) grams of PTFE (ICI CD 014)*,
two (2) drops of Triton X100 and 225 ml water were
blended in a Waring blender for 2 to 3 minutes. This
mixture was then sprayed onto a steel plate which had
been sandblasted and baked in an oven at 750F until
the po]ymer coalesced.
A second coating of this mixture was sprayed
onto the first coat to a thickness of about 0.015 inch.
This coating was dried in an oven and, upon removal
from the oven, mud-cracks had formed. This top coating
was then rolled as in Example 6 until substantially all
of the mud-cracks disappeared. The coating was baked in
an oven at 750F until the polymer coalesced.
The resultant second coating was substantially
nonporous, had a smooth appearance and was
approximately 0.012 inch thick.
* denotes trade mark
3~
Example 8
Fifty (50~ grams of PTFE (ICI CD-l), fifty
(50) grams of PFA (duPont 532-5010), 2 grams Triton
X100 and one-quarter teaspoon carbon black pigment were
added to 175 ml water and blended for 1 to 2 minutes in
a Waring blender. This mixture was sprayed onto the
outside surface o~ a glass, 125 ml, Ehrlenmeyer flask~
The coating was dried and the coated flask was baked in
an oven at 725F until the coating turned black.
Seven (7) additional coats were then applied
by repeating the above procedure.
The glass f:lask (mold) was then broken and the
broken glass removed leaving a flask in the shape oE
the mold comprised of the 50% PTFE/50~ PFA polymeric
composition.
By this technique, shaped fluorocarbon
articles, including highly complex shapes, can be
molded using inexpensive glass or similar molds.
Exampl
One hundred (100) grams of PTFE (ICI CD 014)
and two ~2) drops of Triton X100 were added to 225 ml
water and vigorously blended for 2 to 3 minutes in a
Waring blender.
The above mixture was sprayed onto the outside
surface of a glass beaker which had been previ~usly
sandblasted. The coating was dried and then baked in an
oven at 700-750F.
~1
5~
Six (6) additional coatings were applied,
dried and baked as above, to provide a total of seven
~7) coats on the beaker. The glass mold was then broken
and removed. The molded PTFE beaker so produced had a
wall thickness of 0.045 inch (i.e. 0.006 inch per
layer) and the surface of the PTFF did not have
visually a~parent mud-cracks.
The PTFE beaker was then filled with water.
Under pressure, the water penetrated the walls of the
beaker indicating that the beaker was porous.
Example 10
-
A glass-lined steel pipe spool was
sand-blasted and primed with duPont 850-201 primer,
then placed in an oven at 700F for 10 minutes, and
~hen air cooled. The glass coating had a chip in it,
and steel was exposed at the chip location.
Fifty (S0) grams of PTFE (ICI CD-l), fifty
(S0) grams of PFA (duPont 532 5010), 2 grams Triton
X100 and one-quarter teaspoon ferous black pigment were
added to 175 ml water and blended for one to twc
minutes in a Waring blender.
This mixture was then sprayed onto the
glass-coated steel in the vicinity of the chip and
baked in an oven at 750F until the mixture turned
black. A second coating was applied and dried in an
oven. This seccnd coating was then rolled to densify
it, and a third coating was applied, dried and rolled.
22
73~
A total of six coats were similarly applied and then
the coated spool was baked in an oven at 750F until the
coating materials coalesced.
The resultant coating was firmly honded to the
spool and passed a 10,000 volt spark test over its
entire surface at the location of the chip in the
glass.
The total thickness of the coating on the
substrate was about 0.050 inch. The average thickness
per coat was thus 0.007 inch.
According to this technique, defects in
glass-lined equipment may be repaired by application of
the polymer composition of this invention.
Comparative Example 11
Eighty (80) grams of PFA (duPont 532-5010) and
twenty (20) grams of PTFE (ICI CD-l) were blended with
175 ml water containing 2 grams Triton X100 surfactant
and, while mixing, a drop of Dow Corning Antifoam A
antifoaming agent was added.
This mixture was sprayed on a sand-bla~ted and
primed steel plate at room temperature. The Water was
evaporated using a hot air gun and the dried, coated
plate was baked for 15 minutes at 700F.
A mixture of 95 grams of PFA (duPont 532-5010)
in 175 ml water to which 2 grams of surfactant had been
added was blended for 5 rninutes and this mixture was
sprayed on top of the first coat using the technique of
X
S~3~
Example 1, and the water evaporated using a hot air
gun. The coated, dried plate was then baked at 700~F
for 15 minutes.
The PFA top coat was found to have small
bubbles over approximately 60% of the surface and had
little or no adhesion to the first coat. This
comparative example illustrates that a pure PFA coating
is unsui-table and failed to provide a uniform,
nonporous coating.
X 24
