Note: Descriptions are shown in the official language in which they were submitted.
~ 163~74
SUM~lARY OF THE INVENTION
The invention is directed to providing a gasket having
a sealant coating that is compressible, resilient, and foamed.
Thus, according to the present invention, there is
provided a process for preparing a gasket having a compressible,
resilient sealant coating, comprising: (a) comminuting to a
particulate form a partially cured dry resin selected from the
group consisting of epoxy, polyester, and polyurethane thermoset-
ting resins, said resin being sufficiently cured to be solid and
dry at room temperatures but capable of further cure at a tem-
perature within an elevated, predetermined temperature range, (b)
admixing a blowing amount of a dry blowing agent with said resin
particles to form a substantially dry admixture, said blowing
agent having a temperature of activation within said elevated,
predetermined temperature range, (c) electrostatically directing
said sub~tantially dry admixture of resin particles and blowing
agents toward and onto a base sheet, (d) heating the base sheet
and applied admixture to a temperature within said predetermined
temperature range to further cure the resin of said particles,
(e) activating substantially all of the blowing agent during
said heating step within said predetermined temperature range
to foam the resin and form a compressible, resilient, foamed
sealant coating on said base sheet, and (f) adhering the seal-
ant coating to said base sheet to prepare said gasket, said
8ealant coating being adapted to effect a fluid-type seal for
said gasket without resort to permanent deformation of the
sealant coating by excessive pressure or by plastic flow.
In another aspect the present invention provides a
gasket including a base sheet having a sealant coating thereon,
said coating comprising a compressible, resilient, foamed, cured
resin.
~`
'C.,
1~3&74
The compressible and resilient character of the seal-
ant enables it to effect a fluid-type seal between mating parts
without resort to permanently deforming the seal, either by
excessive pressure or by frictionally heating the seal to cause
plastic flow.
The compressible, resilient seal is formed by foamed
resins. Resins useful in the invention are thermosetting, cross-
linked resins and preferably include epoxy, polyester, and poly-
urethane thermosetting, cross-linked resins.
In one form of the invention, the resin is partially
cured to a solid state at room temperatures and then ground or
comminuted to a finely divided particle form. A blowing agent
suitable for use with the resin chosen is admixed with the
comminuted regin, and the admixture applied to a base sheet of
the gasket, preferably electrostatically as by an electrostatic
gun. The resin is then finally cured while the blowing agent is
activated to form a sealant coating over the base sheet which
hag the desired compressible, resilient, and foamed properties.
These properties provide a fluid-type seal for the resulting
gasket and eliminate the need for permanent deformation or
plastic flow of the sealant coating to obtain such a seal.
- 3a -
f~,
I, ~.
~ ~3S~il
DESCRIPTION OF THE P~EFERRED EMBODIMENT
In general, a gasket is prepared by forming as a
sealant coating on a base sheet a compressible, resilient,
foamed, cured resin. The resin is thermosetting in which
the thermoset character is preferably achieved by cross-
linking. It is important that the resin reach the base
sheet in a state short of complete polymerization or
cure. Accordingly, the reactants which form the resin
can themselves be applied to a base sheet, and cure of
the ultimate resin commence and continue to a final state
while the reactants are on the sheet. Preferably, however,
reactants are first polymerized physically apart from the
base sheet to form a polymer or prepolymer that is sufficiently
polymerized to be solid at room temperatures but still
capable of further polymerization or cure. In this form,
the resin is comminuted to a dry powder and admixed with
a blowing agent suitable for that resin, the agent also
preferably being dry. The admixture is then applied to a
base sheet. Finally, the cure of the dry resin powder is
advanced to a final stage, usually by heat, which activates
as well the blowing agent. This forms the compressible,
resilient, foamed sealant coating on the base sheet and
results in forming the gasket.
More particularly, the resin is preferably selected
from the group consisting of epoxy, polyesters, and
polyurethane thermosetting, cross-linked resins. The
preparation and curing of these resins involving curing
i 1~3&7a~
agents and catalysts are weIl known in the art. In the
preferred pracrice, the resin is polymerized or cured to
a stage where it is sufficiently solid at room temperatures
to be ground to a powder and yet capable of further
polymerization or cure to a final stage. The resin can
be suitably comminuted by any known means, such as a ball
mill, to finely divided particles which, for example, may
have an average particle size of about 5 microns to about
150 microns.
The comminuted particulate resin is next admixed
with a blowing agent, preferably from about 01.% to about
6.0% by weight of the admixture. In a preferred practice,
the blowing agent is also dry at room temperatures or
substantially so, and a substantial amount of the resin
particles contain the agent as an integral part, rather
than having a simple mixture of resin and blow agent
particles.
More particularly, epoxy resins are preferred,
including the three prominent types, namely, the diglycidyl
ethers of bisphenol-A resins, novolac epoxy resins, and
cycloaliphatic epoxy resins. Of these the first mentioned
epoxy resins are preferred. Curing systems for these
resins are also known in the art. The resins, for example,
can be cured by catalyst-initiated homopolymerization or
by copolymerization which includes reacting a hardener
with the base resin. The hardener becomes part of the
molecule. Curing agents which may be used include aliphatic
amines, aromatic amines, Lewis acids like boron trifluoride,
and carboxylic acids and their anhydrides.
-- 5 --
~ 163~7~
A curing or hardening agent that is chosen should
preferably maintain the dry or substantially dry character
of the resin powder to assist in its application in a dry
state. Specific curing or hardening agents that may be
used include dicyandiamide, pryridine, 2,6 diamino-
pyridine, 2-ethylhexyl amine, piperidine, ethylamine,
methylenedianiline, phthalic anhydride, chlorendic
anhydride, maleic anhydride, trimellitic anhydride,
azelic acid, sebacic acid, dodecanedioic acid, and the
like.
It is understood that conventional fillers, extenders
and/or pigments may also be present in the resinous
systems, such as silica, alumina, carbon black, mica,
clay, and the like. Merely as examples, partially cured
epoxy resins may begin to melt and flow at temperatures
within the range of about 48C to about 66C. Final cure
temperatures may be of the order of about 150C to about
180C and higher for about 0.5 minute to about lO minutes.
Polyester resins useful in the invention include
those thermosetting, cross-linked polyesters formed by
reacting polycarboxlic acids of about 2 carbon atoms to
about 6 carbon atom8 with diols, such as alkylene diols,
having about 2 carbon atoms to about 5 carbon atoms, or
with triols. It is possible for saturated linear polyester
chains to cross-link, but usually the cross-linking takes
place between unsaturated polyester chains in the presence
of a cross-linking agent such as styrene, vinyl toluene,
methyl,acrylate, methyl methacrylate, diallyl phthalate,
diacetone acrylamide, divinyl phthalate, and the like.
~ ~6~&7'1
Specific alkylene glycols that may be used include
ethylene glycol, propylene glycol, butylene glycol.
diethylene glycol, and hexylene glycol. Optionally, a
triol like glycerine can be used at least as part of the
reacting alcohol. Specific dicarboxylic acids that may
be used include phthalic acid, isophthalic acid, terephthalic
acid, succinic acia, sebacic acid, maleic acid, ethylmaleic
acid, including anhydrides and mixtures thereof. The
proportions and temperatures of reacting the glycol and
acid reactants are well known in the art.
In general, a urethane may be considered an ester of
carbamic acid, and a polyurethane may be regarded as a
polymer of the ester in which the repeating unit is a
urethane linkage. One method employed method for the
production of the urethane linkage is the reaction of an
isocyanate radical with a compound or radical having an
active or labile hydrogen atom, such as the hydroxyl and
amino radicals. Thus, polyeurethane resins may be generally
defined as polymers produced by the addition reaction
between organo isocyanates and active hydrogen-containing
compounds.
When in such a reaction, an organic diisocyante is
used together with a reactant having bi-functional
groups, each group having an active hydrogen atom, a
polymer is produced having a relatively large molecule.
The polymer of these reactants is substantially linear or
straight-chained and normally exhibits thermoplasticity
or heat sensitivity. These properties are thought to
-- 7 --
1 1~3~7~
result from a linear polyeurethane, because each of such
relatively large straight-chained molecules is not chemically
bonded with companion macro-molecules, and therefore the
physical relationship of the molecules with respect to
each other is not fixed. Freedom of these molecules to
move r~latively to each other provides the thermoplasticity.
Further, when in such a reaction the organic isocyanate
or labile hydrogen containing reactant has more than two
functional groups, such as, respectively, in a tri-
isocyanate or in glycerol; or if a third bi-functional
reactant is included having an active hydrogen atom which
has become known in the art as a cross-linker or cross-
linking agent; a substantially rigid, apparen$1y thermo-
set or cured polymer is formed having a three dimensional
spatial configuration. Often such a polymer is subjected
to a "post-cure" operation which completely reacts all
isocyanate groups, although there may be some active
hydrogen atoms remaining. These polyurethanes, because
of their three dimensional structure and lack of free
isocyanate groups (or nearly so) are tougher, more resistant
to wear and heat, are less active chemically and have a
greater mechanical strength. Such polyurethane resins
are those contemplated by the present invention.
Thus, a polyurethane resin useful in the present
invention includes those reaction products of an organic
polyisocyanate with a variety of other multifunctional
compounds that contain a free or labile hydrogen atom.
The latter compounds may also be further described as
:~ 163~7~
those providing a positive Zerewitinoff test, that is,
any compound which, when added to a Grignard solution of
methyl iodide, liberates methane by decomposition of the
Grignard reagent. Examples of compounds meeting the
Zerewitinoff test include those compounds having hydroxyl,
carboxyl, amino, and amido groups.
In general, the organic polyisocyanate which may be
used in preparing the present polyurethane resins includes
diphenylmethane-4 4'-diisocyanate; 3, 3' dimethyldiphenylmethane-
4, 4'-diisocyanate; ethylene diisocyanate; ethylidene
diisocyanate; propylene-l, 2-diisocyanate; butylene-l, 4-
diisocyanate; hexylene-l, 6-diisocyanate; cyclohexylene-
l, 2-diisocyanate; m-phenylene diisocyanate, p-phenylene
diisocyanate; 2, 4-toluylene diisocyanate; 1, 6-toluylene
diisocyanate; 3, 3'-dimethyl-4, 4' biphenylene diisocyanate;
3, 3'-dimethoxy-4 4'-diphenylene diisocyanate; 3, 3'-
diphenyl-4, 4'-biphenylene diisocyanate; 4, 4'-biphenylene
diisocyanate, 3, 3'-dichloro-4, 4'-biphenylene diisocyanate;
triphenylmethane triisocyanate; l, 5-naphthalene diisocyanate;
hexamethylene diisocyanate; and the like.
The compounds most usually reacted with an organic
polyisocyanate are the polyesters, such as linear or
branched chain polyesters, and/or polyesteramides which
contain free hydroxyl groups, and/or polyethers, and/or
other groups containing reactive hydrogen atoms such as
amino and/or amido groups. Acrylic-modified polyurethane
resins may also be used.
1 1~3S7~ .
Thus, useful polyesters and/or polyesteramides may
include those obtained by condensing any polybasic (preferably
dibasic carboxylic) organic acid, such as adipic, sebacic,
phthalic, isophthalic, terphthalic, oxalic, malonic,
succinic, maleic, cyclohexane-l, 2-dicarboxylic, cyclohexane-
l, 4-dicarboxylic, polyacrylic, naphthalene-l, 2-dicarboxylic,
fumaric, itaconic, glutaric, pimelic, suberic, azelaic,
etc., with polyalcohols such as ethylene glycol, diethylene
glycol, pentaglycol, glycerol, sorbitol, di(beta-hydroxyethyl)
ether, etc.~ and/or amino-alchols such as ethanolamine,
triethanolamine, 3-aminopropanol, 4-amino-propanol, 5-
aminopentanol, 6-aminohexanol, 10-aminodecanol, 6-amino-
5-methylhexanol,p-hydroxy methylbenzylamine, etc. In the
esterification, the acid itself may be used for condensation
or the acid halide or anhydride may be used.
~he alkylene glycols and polyoxyalkylene glycols
useful in the preparation of polyurethane resins useful
in the invention may comprise ethylene glycol, propylene
glycol, butylene glycol, 2-methylpentanediol, 2-ethylhexanediol,
hexamethylene glycol, styrene glycol, decamethylene
glycol, diethylene glycol, triethylene glycol, tetraethylene
glycol, polyethylene glycols, dipropylene glycol, tripropylene
glycol polypropylene glycols, and the like.
Where a cross-linker is used, as in preparing a
three-dimensional cross-link, cured polyurethane resin,
this reactant glycol, glycerol, trimethylol propane, and
the like. Aromatic cross-linkers such as l, 4-di-(hydroxyethyl)
benzene and hydroquinone may also be used. Nontertiary
-- 10 --
3i~3~7~
amines because of their active hydrogen atoms can also
serve as cross-liners. The polyurethane reaction may be
promoted by accelerators or catalysts known in the art,
although polyurethanes have been formed without the use
of any accelerator.
The manner of preparing a polyurethane as by polyaddition
is known in the art. Reference is made, for example, to
U. S. Patents No. 2,577,279; No. 2,620,516; No. 2,621,166;
No. 2,729,618; and No. 2,764,565.
Considering next the blowing or foaming agent, many
such agents may be employed in the practice of the invention.
Agents can be chosen which chemically react with the
resinous 6ystem in use to produce a blowing, effluent gas
as a by-product. More usually, however, the action of
the blowing agent is separate from that of the chemical
reaction or further polymerization of the resin, and the
flowing agent is present only to convert the resin into a
blown, foamed, or cellular state as it finally cures.
Accordingly, the blowing agent can be selected primarily
for its temperature of activation which generally corresponds
to or falls within the temperature range of final cure
for the resin.
In this manner, a number of known blowing agents can
be used as a source of gas which foams the selected
resinous system in place on a base sheet to form the
gasket. While materials which volatalize under the heat
of resin-cure can be used, it is preferred to employ
chemical blowing agents which decompose to yield an
~ 1~3&7~
expanding volume of gas when heated to within a specific
temperature range. Decomposable organic compounds, and
especially those which are solid or nearly solid at room
temperatures, are'preferred for this role. A leading
characteristic of a blowing agent is its decomposition
temperature which determines the required processing
temperature range and the resins with which it can most
efficiently be used.
Among the blowing agents useful in the present
invention are:
Blowl~Aqent Appro~m~te Operating Te~ature Range-C
4,4' oxybis
~benzenesulfonylhydrazide) 127 - 419
p-toluene sulfony~razide 105 - 132
l,l'azobisformamide 160 - 232
azodicarb ~ mide 160 - 232
p-toluenesulfonyl
semicarbazide 193 - 235
5-phenyltetrazole 232 - 288
trihydrazinatriazine 265 - 290
dinitrosopent~methylene- 190 - 200
tetramine
For example, the first mentioned blowing agent is a white
powder and releases mainly nitrogen gas on activation.
The agent, p-toluene sulfonylhydrazide, is often used
with epoxy resins.
The blowing agent may be incorporated into a selected
resinous system by any convenient technique. Dry tumbling
is often used. The blowing agent, preferably in dry
- 12 -
~ ~63~74
powder form, is added to the comminuted, partially cured
resin and admixed as in drum tumblers. A standard wetting
agent in an amount of about 0.05% to about 0.1% by weight
of the admixture may be included to coat the resinous
particles and cause better adhesion thereto of the blowing
agent. Or, as previously indicated, a substantial portion
of the resin particles may contain the blowing agent as
an integral part. Liquid dispersiGns can also be used
for adding a blowing agent to a resinous system, but in
this case the liquid level should be sufficiently low to
avoid interference with the manner of applying the resin-
blowing agent admixture to a base sheet.
The base sheet may comprise compositions presently
used in the art for that purpose. It may comprise, for
example, any one of a number of relatively dense sheet
materials having a substantially uniform thickne~s which
is deformable so as to conform to the contour of the
surfaces over which the sheet is applied. Sheet materials
which have been found useful include various fibrous
compositions usually containing a fibrous reinforcing or
bonding agent. Such fibers may include organic fibers,
such as cellulose, or inorganic fibers, such as asbestos,
as well as mixtures of the two. The fibrous network can
be bonded into an integral sheet by employing a suitable
binding agent which can be naturally occurring resinous
substances or various synthetic resins and elastomeric
materials, such as natural or synthetic rubbers including
polysulfide, acrylonitrile-butadiene, polychloroprene,
1 1~3&74
and the like. Small proportions of metallic fibers can
also be included in the base sheet. The base sheet may
also comprise such structures as a semi-porous fiberboard
reinforced with a thermosetting resin, such as a sheet of
mineral fibers bonded with cured nitrile rubber or phonolic
resin. In gaskets designed for high temperature applications,
the base sheet preferably is a metal sheet such as a
sheet of steel, aluminum, zinc, alloys of the same, and
the like. The base sheet may range in thickness from
about 0.002 inch up to about 0.250 inch and preferably
from about 0.005 inch to about 0.065 inch, although sizes
outside of these ranges can be used.
The resin may be comminuted by any convenient means
such as by ball milling. The comminuted resinous particles
may be applied to a base sheet by any suitable means,
such as dusting, but are preferably applied electrostatically.
Electrostatic application of the admixed resin particles
and blowing agent may be from an eIectrostatic fluidizing
bed or from an electrostatic gun. A gun is especially
used if relatively thin sealant coatings are desired on
the base sheet. Electrostatic guns, voltage and current
condition~, and related techniques kn~wn in the art for
this type of application can be used. The electrostatic
gun disperses the charged resinous powder as a cloud of
particles which are directed by virtue of their charge
and the output air pressure of the electrostatic gun
toward a grounded substrate. The substrate on which the
deposition takes place may be electroconducting such as
- 14 -
~ 163S'Y4
when the base sheet is a sheet of metal. But the substrate
need not be electroconducting~ For example, a grounded,
electroconducting plate can be placed behind a non-
electroconducting substrate so as to attract the charge
particles toward and onto such a substrate. Fluidized
bed application of comminuted resin particles provides a
thicker coating.
After application of the resinous powder-blowing
agent admixture to a base sheet, the final cure of the
resin and activation of the blowing agent are carried
out. This is usually accomplished by heat such as by
passing the assembly through an oven. The resin actually
passes from a solid to a liquid back to a solid when it
thereafter becomes infusible. When the resin particles
have fused and become liquid or semi-liquid or otherwise
brought to a proper melt viscosity, the blowing agent
activates and foams the resin into a compressible, resilient
sealant coat on the base sheet. When the resin is finally
cured, it is in a foamed or cellular state which it
thereafter maintains. The foam is self-adhering to the
base sheet and can comprise either a closed-cell or open-
cell construction. The thickness of the foam sealant
coating on the base sheet may vary depending on the
intended use of the gasket. Normally, thickness ranges
from about 0.001 inch to about 0.015 inch. An average
thickness is about 0,005 inch.
The following examples are intended only to illustrate
the invention and should not be construed as imposing
1 163&7~
limitations on the claims. Percentages are by weight
unless otherwise indicated.
`EXAMPLE 1
An epoxy powder coating was prepared using the following
formulation:
Compound Percent
Diglycidyl ether of bisphenol A epoxy
resin having epoxide equivalent
weight of 750 61.00
Accelerated amine curing agent having
amine nitrogen content of 56% (Shell-
Epon curing agentl 3~35
Flow control agent 2.21
Colloidal silica 0,30
Titanium Dioxide 31.0
Phthaloblue Pigment (DuPont BT-297-D)2.14
10~;~
The flow control agent may be omitted if desired.
When used, it may be any of those available on the market
for epoxy resin systems, such as those sold under the
trademark "Modaflow" by Monsanto or the trade designation
"Hoechst Mowital 30-F". Such agents may also be used in
combination.
An amount of eight hundred grams of the above components
was charged into a 1.5 gallon jar mill containing 5500 grams
of cylindrical high density porcelain grinding media and
pulverized to 100 mesh or finer.
A mixture of the above epoxy powder coating and 0.5% of
4,4' oxybis (benzene-sulfonylhydrazide) as a blowing agent
was then prepared by blending the mixture 10 to 15 minutes in
a Patterson-Kelly twin shell blender.
- 16 -
1 1~3~74
A Nordson ModeI Gl-12 electrostatic powder gun applied
the mix onto a steel sheet defining a base sheet for the
gasket, after which the sheet was heated at about 170C for
about 20 to 8 minutes. The blowing agent decomposed and
foamed the epoxy resin as it cured. This provided a compressible,
resilient sealant coat on the resulting gasket.
EXAMPLE 2
An amount of one thousand grams of diglycidyl ether of
bisphenol. A resin powder coating, sold uhder trademark
"Polyset 202", and 10 grams of azodicarbonamide blowing
agent, sold under the trademark ~Kempore 60/40", were blended
for 10 to 15 minutes in a Patterson Kelly twin shell blender.
After spraying the assembly the epoxy powder coating -
blowing agent mix onto a metal sheet, the assembly was
heated between 190C and 200C for about 5 to 10 minutes.
The blowing agent decomposed and foamed an epoxy coating as
it cured.
While the examples illustrate the use of epoxy resins,
it is understood that polyester and polyurethane resins as
~0 described can be similarly used with blowing agents. Sur-
factants, fillers, extenders, pigments and the like may also
be included in the resin-blowing agent mix.
Although the foregoing describes several embodiments of
the present invention, it is understood that the invention
may be practiced in still other forms within the scope of the
following claims.
- 17 -
