Note: Descriptions are shown in the official language in which they were submitted.
~3*6~
I. FIELD OF THE INVENTION
The present invention is directed to a urethane foam
system which utilizes an unhalogenated hydrocarbon propellant.
Specifically, the invention is concerned with a one component
moisture cure system which is suitable for use in an aerosol
or pressurized container.
II. DESCRIPTION OF TEIE PRIOR ART
Polyurethane foam plastics are presently enjoying wide
use as a building insulation material. They demonstrate excep-
tional utili~y as sealants and insulation. This is due to theimperviousness of the foam to the passage of air through its
structure. Urethane foams also show usefulness in the filling
of gaps in structures, holes in walks etc.
Traditionally polyurethane plastics have been prepared
by a multi-component process. Usually they are formed by the
reaction of a hydroxy terminated polyether or polyester or
other active hydrogen compound and a polyisocyanate in the
presence of a blowing agent and a catalyst. In such systems
the reaction materials and conditions must be carefully con-
trolled since they involve a highly exothermic reaction. There-
fore, it has been commercially impractical to produce a foam
dispensing system using a conventional multi-component process
specifically for use by non professionals or that does not re-
quire significant expertise in the preparation of the foam.
The elaborate preparation requirements of multi-component foams
render them especially unsuitable for small job applications.
In recent years one component moisture cure urethane
foams that can be dispensed by aerosol or pressurized con-
tainers have been developed. These products are formed from
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~3~
polyurethane prepolymers which are the reaction products of
organic polyols and organic polyisocyanates and utilize chlo-
rofluorocarbons as propellants. These systems can be used in
many situations that are unsuitable for multi-component pro-
cesses since they are one component and do not involve a per-
ceivable exothermic reaction. They are distinguished from
"one shot" systems which do not utilize a prepolymer and
"quasi-prepolymer" or "prepolymer" process systems which re-
quire rapid mixing of a portion of the components prior to
dispensing and polymerizillg.
A typical method of producing a one component moisture
cure foam product is discussed in U.S. Patent 3,830,760 to
Bengtson. Products produced by this proces suffer dèficien---
cies due to the use of chlorofluorocarbonsl such as dichloro-
difluormethane and trichlorofluoromethane (commonly known as
FREON * 12 and FREON * 11 respectively) as a propellant First,
the use of chlorofluorocarbons is environmentally damaging ~ $e
they are believed to destroy the ozone in the stratosphere.
Second, the products are expensive due to the high cost of
chlorofluorocarbons. And third, the products have only a limited
shelf life of nine to fourteen months.
In order for the foam prepolymer and catalyst of a one
component moisture cure system to be dispersed from an aerosol
container it must have a viscosity of approximately 2,000 centi-
poise. Conventionally, the prepolymers viscosity is appro~i-
mately 60,000 centipoise and therefore is substantially reduced
by the solvent nature of the chlorofluorocarbon propellant.
Chloroflurocarbons have been found to have a very pronounced
solvent effect on these foam L~repol~vmers. Accardingly, other
pneumatogens have been considered unsuitable for use with one
component moisture cure systems.
..~.~,.
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The present invention is advantageous in that it
provides a one-component polyurethane product which is a
moisture curing foam that can be packaged in a pressurized
can or aerosol container both for professional and non-
professional use.
* Trade Mark
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~3736~
T h e foam is ~nvironmental.ly safe since it does not utili.ze
either FREO~ ll or 12 as a propellant, very stable and has a
long sheif life.
~ .~ OF HE IN~ENTIO~
The present inveniion provides a method of producing a
one component moisture cure polyurethane foam utilizing a isocya-
nate terminated prepolymer having a viscosity of from 5,000 to
50,000 centipoise, a catalyst and an unhalogenated hydrocarbon
propellant whose boil.ing point or initial boiling point is no
greater than 10C at atmospheric perssure. The invention also
provides a pressurized container containing a one cornponent
moisture cure foam comprising a isocyanate terminated prepolymer
having a viscosity of from 5,000 to 50,000 centipoise, a cata-
lyst and an unhalogenated hydrocarbon propella.nt whose boiliIIg
pOillt or initial boiling point is no greater than lO~C at atmos-
pheric pressure~
DESC~IPTION OF THE PREFE~ED E~ODIMæNTS
___ __ . _
The pre~ent invention is directed to a method of makin~
a one componellt moisture cure -~olyureth2ne foam that is suitable
for dispensina, from a pressurized or aerosol container. In
particular, the invention is direc-ted to a foam which can be
dispensed from an aerosol container in an environmentally safe
manner. The components for producing the foam comprise a poly~
uxethane prepolymer, a catalyst and an unhalogenated hydrocarbon
propellant whose bolling point or initial boiling point is less
than 10C at atmospheric pressure~
The prepol.ymer is comprised of the reaction product of
an isocyanate and a polyol which produces an isocyanate termin.tted
prepolymer, excess unreacted isocyanate but, no residual hydroxyl.
Surf~ctants and flame retardants are preferably incorporated into
the prepclymer~ It has been found that if the viscosity OI t"le
prepolymer is between 5,000 centipoise and 50,000 centipoise,
preferably between 17,000 and 23,000 centipoise or approximately
~ ~A~ C~ nh~ a~nated h~drocar~on can be used as a
376~8
propellant in a one component moisture cure polyuretnane foam
system.
It is important that the prepolymer be 1,near or sub-
stantially linear. Therefore, it is preferred that the isocya-
nates and polyols be difunctional to trifunctional and that the
specific prepolymers be comprised of isocyanates and polyols that
are inversely related in futlctionality. That is, i~ the polyol
is triunctional (three hydroxy groups per molecule~ the isocya-
nate should be difunctional (two NCO groups per molecule). If
the polyol is difunctional, the isocyanate shouid be trifunctional.
The latter co~blnation of a difunctional polyol and a trifunctional
isocyanate is preferred since the combination has been found to
best prevent foam from becoming brittle and is most suitable for
use in prepaxing prepolymers whose viscosity is between 5~OGO
centipoise and 50,000 centipoise and that when iurther diluted
with unhalogenated h~drocarbon propellarlts are dispersible from
pressurized containers.
Ihe averaye functionality o'~ the polyol and isocyanate
reactants should be bet:ween 2 and 2 :1/2, preferably 2 1/2. For
example: Ifunctionality of the reactants is in parentheses)
~a) isocyanate (3) ~ polyol (2) = 2 1/2 avearae
(b) isocyanate (2) + polyol (3) = 2 1/2 average
(c) isocyanate (2) + polyol t2) = 2 average
Utilizing these reactant combinations allows the formation of
substantially linear prepolymers which permits an increasing
of the free isocyanate levels in the prepolymer without pro-
ducing hrit-tle foams. The increasing of the amount of free
isocyanate reduces the viscosity of the prepolymer resin and
increases the shelf life of the containerized reactants. High
levels of free isocyanate are not feasible in systems containing
unhalogenated hydrocarbon propellants since a prepolymer viscosity
of approximately 60,000 centipoise is necessary for the dispen-
sing of the reactants and to achieve foam stability in such systems.
This is because it has been found that chlorofluorocarbons reduce
the viscosity of the reactants to a far greater extent than lln-
halogenated hydrocarbons.
Isocvanates suitable for the practice of the invention
37G~
are aromatic and aliphatic polyisocyanates having two to -three
reactive isocyanate groups. Examples of suitable polyiso-
cyanates are found in U.S. Patent 3,072,582 to Frost and U.S.
Patent 3,830,760 to sengStOn. Examples of such compositions
are tolylene diisocyanate ~TDI), especially the 2, 4 and 2, 6
isomers and mixtures thereof. The preferred isocyanate which
is safer to handle due to its low vapor pressure is crude poly-
meric diphenylmethane diisocyanate (MDI). r~O achieve the afore-
mentioned advantages of high free NCO levels in the prepolymer,
the free prepolmer NCO should be between 8 and 19% by weight
of the prepolymer, preferably 12 to 15% or optimally 14.~%.
r~his compares to free prepolymer NCO levels of 5 to 7% in
systems using chlorofluorinated prepellants. Mixtures of poly~
isocyanates can be used.
Organic polyols which are normally formatives of urethane
compositions may be utilized to obtain the foams of the inven-
tion. Both polyester and polyether polyols with molecular
weights of from 300 to 2,500 may be used. Discussions of such
pol~ols are found in U.S. Patent 3,830,760 to Bengston. In
particular polyether polyols may be preprepared by the reaction
of an alkylene oxides with compounds containing a plurality of
active hydrogen atoms. The polyols may also be polyesters
which are derived from polycarboxylic acids and polyhydric
alcohols. soth the polyether or polyester polyol may be mi~-
tures. The preferred polyol is a mix-ture of 775 M.W. oxypropy-
lated glycol which is the reaction product of propylene glycol
and propylene oxide, and a 2000 M.W. polyol which is the reaction
product of propylene glycol, propylene oxide, and ethylene
oxide.
The prepolymer may contain the standard polyurethane
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foam additives including flame retardants, stabili~ers,
nucleating agents and cross linking agents. The preferred
flame retardant is tris-2-chloroallyl phosphate which is a
commonly used retardant in urethane foam products. It is
critical that the prepolymer, including the additives, have
a viscosity of between 5,000 and 50,000 centipoise, preferably
between 17,000 and 23,000 centipoise or approximately 20,000
centipoise.
The foam compositions of the invention may also contain
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conventional catalysts and surfactants. The traditional cata-
lysts are tertiary amines. Primary and secondary amlnes are
not useful in moisture cure foam products since they will react
wi~h the isocyanate and cause gellation. It may also be uscful
to employ metal salts, particularly tin catalysts in the prac-
tice of the invention~ The surfactants that are normally used
in one-component moisture cure urethane foam compositions can
be incorporated into the prepolymer. These include organosilicon
polymers, prefexrably siloxane-oxyalkylene copolymer.
The propellant is an unhalogenated hydrocarbon whose boil~
ing point or initial boiling point is no greater than 10C at
atmospheric pressure (76~ ~lmHg). Not only is the propellan~ en-
vironmentally safe bu~ it also produces a oam which has commer-
cially acceptable cell sizel foam stability, bubble uniormity, and
foam properties. The particular unhalogenated hydrocarbon pro-
pellant utilized is not critical, howeverl either propane or a
mixture of isobutane or n-butane with propane is preferable. If
the unhalogenated hydrocarhon propellant is a mixture then the
initial boiling point of the mixture must be less than 10C at
atmospheri- pressure. The choice of propellant is dependent
upon the strenqth of the contain~ em~loyea. For instance, pro--
pane due to its high vapor pressure at room ter;;perature is not
suitable for use in a conventional 2Q (180 psig minimum distor-
tion; 270 psig minimum b~lrst) strength can.
An important characteristic of the propellant is that
i~ does not depend upon exothermic heat of xeaction to expel
it quickly from the prepolymer film rollowing di~pensing of
the prepolymer from the container, unlike t-e higher boiling
blowing agents of the multi-component exothermic systems of
the prior art. A foam will not form if the propellant does not
immediately boil out of the prepolymer to form the foam cells.
Any propellant retained by the prepolymer prevents a foam from
setting up since the retained propellant reduces the viscosity
of the prepolymer too low fox stable foam formation. Therefore
the propellant must have a boiling point or initial b~iling
point lower than 1~C. If the boiling point or initial boi]ing
~3'76
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point of the propellant is greater than 10C in a one-componellt
moisture cure system it will remain as a liquid dissolved in
the prepo1~ner at atmospheric pressure and room temperatl!re an~
thereby prevent ~he formation of a stable foam~
It may be desirable to utilize other gases with unh~lo-
genated hydroca~bon gases to form che propell~nt. For example:
rela~ively small amounts (less than 50~ by volume) of chloro-
carbon or chlorofluorocarbon gases can be used to reduce -the
flamability of the propellant. Significant amounts of
these gases diminish the ad~antages of the invention. In for-
mulating a propellant mixture it is important that the propellant
not be a strong solvent of the prepolymer. If the prvpellant
totally solubilizes the prepolyrner there will be insufficient
nucleating ma-'erial to form a foam when the mixture is dlspensed.
A porl:ion of the prepolymer must be insoluble in the propellant
and present as emulsion droplets. The emulsion droplets act as
a nucleating agent to form the foam cel].s. Sirce the viscosity
of th~ prepol~ner is relatively low, it is easily totally solu-
bilized by strong solvents. Therefore, in formulating a pro-
pellant mi~ture a lo~ overall hydxogen bonding capacity and
Hildebrand solubility parameter is desirable. Unlike multi-
component systems, a one component moisture cure system does
not rely upon a highly exothermic reaction for the formation of
the foam. The foarning of the prepolymer is effectuated by the
release of pressure and not by ~aporization due to the heat of
a reaction as in a multicomponent system. Accordingly, the
higher the vapor pressure or lower the boiling point of the,
propellant the better the foam produced since it evacuates from
the prepolymer more quickly.
The preferable rnethod of producing the foam of the inven-
tion is to mix the isocyanate, polyol, surfactant and fire retar-
dant and heat in the absence of a catalyst to forr~ a prepoly~er.
The prepolymer and catalyst are then introduced into a container
which is pressurized by the propellant. The size of the contair.er
s not critical and both hand-held cans and large cornmercial
n~ L~ ~kP ~r~ition~l method of re~ctin~
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the ingredients of the prepolymer with the catalyst in a batch
process prior to introduction into a pressurized contalner and
gassing can also be utilized. M;xing and reacting all of the
materials within the dispensing container is also feasible. When
this is done, it is important that provision be made for shaking
the container and cooling it to remove the heat of reaction. The
preferred method, of forming an uncatalyzed prepolymer, provides
a stable system which can be stored for long periods prior to
filling.
As previously noted, it is critical that the prepolymer
or resin have a viscosity of 5,000 to 50,000 centipoise, pre-
ferable 17,000 to 23,000 or approximately 20,000 centipoise. It
is also important that the boiling point of the propellant be
less than 10C. The quantity of propellant can also be important
due to the solvent nature of the propellant and is preferably
between 10% and 30% by weight so that the viscosity of the foam
mixture contained within a dispensing container will be between
100 to 2,000 centipoise. This is a similar viscosity as those
one component foams whose prepolymer viscosity is approximately
60,000 centipoise but whose propellant is a chlorofluorocarbon.
An unhalogenated hydrocarbon has been found to reduce tne viscosi-
ty of a prepolymer substantially less than a chlorofluorinated
propellant. Therefore, chlorofluorinated propellants are unsuit-
able for use with the prepolymers of the present invention since
they would reduce the viscosity to levels below which they can
form a foam product~ Also, the foam s~stems of the present in-
vention have shelf lives of approximately two -years, which is
significantly greater than the shelf life of the one component
moisture cure systems of the prior art.
The following table illustrates the principles of the
invention:
~37~
J~ rr~ W rr~ I crZ ~ H ~ZZ ~ ¦ ~J ~ .^Z
Z~Z ~ t.`t O _ O C I rt O Ul ,_. ~ Il~ ~~~ ~ rt -t
C O ~D t~p~ tr pJ r o ~ . o ~,_ o v- H 3 c
r~ X~ 1-- r- ~ 15 :~ U 'a 3 ~ z o o ~ ~D C~
r~- Hl ¦ I t ~ rt tD u) ~D g ~ a ~. X -~ . ~ rt ~D
i- ~t ~ pJ~D rt iD ~ rt ~ i~ ~ ~, I R~ Z a
3 ~D i I_~ C P~ u~ ~ ~ R~ 3 tD :~, . O j_ O
tD tD H) :~, j_Z C~ ~- C ~D rt tD . I ~r ~D 1~
(D i~~ 1_. ~J. ~ r, ~D r~ O l o I ~~ '~,
rt ~ ' rt I H ' r l ~ (D ~ '~ C ¦ t '-- tD
(D I ~Z ~ l l tD I_ ~ c~
S?~ C ¦ ~ ~ ~ x ~ o I ra ¦ Z_ 1 3
(D ~ ~ ~ O ~ tD ~ O ~ ~t ~D
~ W~
~ ~ ~ ~ ¦ _ - ~tt t-- PROPELTZAI~;Z'T E~LE~
tD I x l X o I x tll I tn I ¦ ~ 1 ¦ o ~ 5 0~ 5 0 vol . /vol .
;~ - 1- 1 1 1~P 111~J~ I I ~ 1w 10 10 1~ I ProE)ar~e/isobutane
I I l I I 1'~ 1 1~ 1 ul lo 1~ Iw 1~ 1 ~ I
X X t~ ~ t~ ~t O ~ O ~ ~ i;~ ~C ~ U~ ~ 50~50 vol./vol.
~ 1' ' ~ 1- . 1 1 ~ I I I I ~ W 1 1 1 ~ I Propane/n-bu-tant,
;~ l`q It~ X 13 1 ~ ~ OO~o ProI~al;e
I I I I I I I I I ~ 10 lo
I I I I I I I o 1 l 1 1 I~n lo lo lw
~n ¦ ~ ~ ¦ ~ h~ o
; 10 Il' O I 1~ 1 o I I lo I ~o 1~ IUl 5
~ ~ o ~tD ~ 00% isobutarle
I I l I I I o I 1 1 l IU` I" I IW I'J` I ' ~
1 3 u~ I t~ ~ 0 1
ItD ~ ¦x I I ItD 1~ P' 1~ ¦ IU~ !, 1~ ¦, 1 1 1~ -- IU ¦ 30/70 vol ./vol.
~? ~ It 1- 1 o IU~ w ¦o lo ~ Propa~-le/isobl~tan~
I I I I I I ~ o lo lw ~
Ix o 1~ t~ 13 ¦ O Ul ~ c lo ~0 ~ o~J70 Vc~ vtJl.
~ 1 ' ~ w ¦ ¦ ¦~ ¦ ~ ¦ Prt~pallefiso~utane
Ix tn ILq 1~ t~ 10
O ¦? ¦~ ~ ¦ ~ U' ¦ 40/60 vol./vol.
¦- ¦ ¦~o ¦ I ¦o ¦ I ¦~ ¦o 1o 1 ¦~ ¦ ~ ¦ Propane/isobutane
l~ tn It~ lr~ ~ 3 1 o I 1~
I~ o ¦? ~ ~ I I 1 1 1 1~ 1~ 1~ ¦ U ¦ 40~G0 vc~ ol.
1- ~ 1 1 i- 1~ 1- O 1O 1~ 1~ 11 1~ Iw lo 1O ~ Propane/n-butane
I l I I l I I I 1~ o lo lw ~
I ~ t~ ¦t~ 1~ ¦t~ L~ 13~ ¦ ¦~ ~ ~ ¦ . 1 55~45 vol./vol.
1 1 ~ ~ lo ~ '?ropane/n-~utane
~D I I Ix lo Ix lr, Itn ~ O 1 ¦'' ¦~ 40/60 vol./vol.
In ~ I'J 1~ 10 IU~ 10 10 IW ~ PrOPane/iSObUtane
tn ~ d
I ~ ~x lo 1~- 10 lo 1~ 1 o I lo I I lo lo 1~
l O 1- IO ~ 10 IO ~ 1 . 11 1~ l00~ n-butane
Lo L~ I ~ lo lo 1~ la' I a~ I
9_
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Bubble Size: small-less than a 32nd of an inch
-~edium-bet~Jeen 16th to 1/4 of an inch
large-is between 1/4 to 1 inch
oam Stability: poor-unusable since it is completely flat
fair-unusable since it is substantially flat
good-sags slightly
excellent--does nGt sag after rising
Density: low-less than 25 g/l
medium~between 25 g/l and 5~ g/l
high-greater than 50 g/'
ertical hang up: poor-all of product drips off of ceiling or
wall
fair-mlos-t of p~oduct remains on ceiling or wall
excellent-all of product xemains on ceiling
or wall
Shelf life: air to poor-approximately one year
excellent-approximately two years
Tack free and
cure time: slow-l to 3 hours tack free; 24+ hours cure
medium-20 to 60 minutes tack free, 12 to 24
hours cure
very fast-less than 10 minutes tack free;
2 to 8 hours cure
All percentages are percentage by weight. The components
of the resin were mixed and heated together. They were then
introduced in an aerosol container with a catalyst. The container
was gassed with a propellant. Upon activation of the container's
nozæle a foam product was dispensed which demonstrated the above
characteristics.
The invention may be embodied in other specific forms
without departing from the spirit of essential characteristics
thereof. ~he presen~ embodiments are therefore to be considered
in all respects as illustrative and not restrictive, the scope
of the invention being indicated by the append claims rather
than by the foregoing description, and all charges which come
within the meaning and range of equi~alency of the claims a~e
therefore intended to be embraced therein.
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