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BACKGROUND OF THE INVENTION
This invention relates to a closed-cell rigid polymer foam prepared in the
presence of a physical blowing agent comprising a C.sub.2-6
polyfluorocarbon compound containing no chlorine or bromine atoms.
The usefulness of foamed plastic materials in a variety of applications is
well-known. Rigid closed-cell polymer foams such as, for example,
polyurethanes and polyisocyanurate foams are widely used as insulating
structural members.
The good insulative properties of such foams are provided for by firstly
the fact that they are fine closed-celled foams and secondly the
closed-cell contains within a gas mixture which has a high thermal
resistance or in the alternative a low thermal conductivity.
Generally, polyurethane and polyisocyanurate foams are prepared by reacting
an organic polyisocyanate with an active hydrogen-containing compound in
the presence of a blowing agent or agents. Generally, such blowing agents
are inert organic compounds which do not decompose or react during the
polymerization reaction and which as a result of the exothermic reaction
if not already in the gaseous phase become converted to a gaseous phase.
The gas becomes encapsulated in the liquid phase of the polymerizing
reaction mixture resulting in the formation of cells, causing the reaction
mixture to expand and form a foam which subsequently cures to become a
rigid closed-cell foam.
Frequently used blowing agents, until recently, have been the fully
halogenated chlorofluorocarbons, especially trichlorofluoromethane
(Refrigerant, R-11). However, the continued use of such chlorofluorocarbon
blowing agents is undesirable in view of the current opinion that their
presence in earth's upper atmosphere may be a contributory factor in the
recently observed reduction of the ozone concentrations.
The current commercial trend for the production of such closed-cell polymer
foam is to replace the fully halogenated chlorofluorocarbons with
hydrogen-containing chlorofluorocarbon compounds. These alternative
blowing agents are selected as they have been identified as having
significantly lower ozone depletion potentials relative to R-11. Such
alternative hydrogen-containing blowing agents include
dichlorotrifluoroethane (R-123), dichlorofluoroethane (R-141b),
chlorodifluoromethane (R-22) and difluorochloroethane (R-142b), the use of
which in the preparation of polyurethane foam has been described: see, for
example, U.S. Pat. Nos. 4,076,644: 4,264,970: and 4,636,529.
However, a significant disadvantage of replacing the R-11 gas contained
within the cells of the foam by such alternative compounds is a frequent
loss in the initial and aged thermal insulation performance of the foam.
Such loss occurs due to the generally higher gas thermal conductivities of
the replacement blowing agents.
If insulative foam, especially polyurethane foam is to remain commercially
attractive and be able to comply with various national standards relating
to energy consumption, it is important that the foam is able to retain a
good thermal insulation performance with time. This is especially critical
where, because of other factors dictating the selection of blowing agents,
the initial thermal conductivities of the foam may already be relatively
high.
The thermal insulation properties of closed-cell foam, especially
polyurethane and polyisocyanurate foam are known to become inferior with
time. The loss of thermal insulation properties of a foam generally
results from diffusion into the closed cells of high thermal conductivity
gases, particularly nitrogen and oxygen or alternatively loss of cell gas
having lower thermal conductivities. It is therefore desirable to provide
for a means of limiting such loss.
One possible means to prevent loss of thermal insulation properties would
be to use, for example, a gas impermeable barrier surrounding the foam.
However, in most foam applications this is not a practical solution.
Alternatively, the foam could be modified to minimize or prevent loss of
thermal insulating efficiency with time. With respect to this latter
approach, the open literature contains relatively few teachings as to how
rigid, closed-cell polymer foams might be modified to give products
exhibiting an enhanced retention, or minimized loss, of thermal insulation
performance with time.
U.S. Pat. No. 4,795,763 discloses carbon black-filled polyurethane foam
exhibiting improved aged-thermal insulation properties. Japanese Patent
Application No. 57-147510 discloses the use of carbon black to provide for
lower initial thermal conductivities of the foam. The selection of
graphite over carbon black for the preparation of foam from a
thermoplastic resin having increased initial thermal insulation properties
is disclosed by Japanese Patent Application No. 63-183941.
However, the use of fillers such as, for example, carbon black and graphite
for enhancement of foam thermal insulation properties is not always
possible as other physical properties of the resulting foam and
processibility leading to the foam may suffer. Particularly, a high filler
content can lead to highly friable and open-celled foams. Open-celled
foams do not provide the desirable thermal insulation performance normally
offered by closed-cell foams.
It is therefore desirable to consider the use of alternative blowing agents
which provide for closed-cell foam having improved thermal insulation
properties whilst additionally maintaining the overall desirable foam
physical properties and processibility.
In the art, the term "thermal insulation" may be interchanged with the term
"K-factor" or "thermal resistance" when discussing thermal physical
properties of foams and gases.
SUMMARY OF THE INVENTION
It has now been discovered that rigid closed-cell polymer foams having
improved aged thermal insulation properties may be prepared in the
presence of blowing agents or compositions comprising a polyfluorocarbon
compound.
In one aspect, this invention is a closed-cell rigid polymer foam prepared
from a foam-forming composition containing a physical blowing agent
present in up to about 20 weight percent, based on the total weight of the
composition, and characterized in that the physical blowing agent
comprises a C.sub.2-6 polyfluorocarbon compound containing no chlorine or
bromine atoms, and in that the cells of the foam contain the
polyfluorocarbon compound as a gas in an amount which reduces the thermal
insulation loss of the foam relative to the thermal insulation loss, with
time, of the same foam having the same density and prepared from the same
foam-forming composition in the presence of an equivalent molar quantity
of blowing agent in which a C.sub.2-6 polyfluorocarbon compound,
containing no chlorine or bromine atoms, is absent.
In a second aspect, this invention is a process for producing a closed-cell
rigid polyurethane or polyisocyanurate polymer foam containing within its
cells a gas mixture comprising a C.sub.2-6 polyfluorocarbon compound
containing no chlorine or bromine atoms and characterized in that
(a) an isocyanate-containing compound is mixed and allowed to react with an
active hydrogen-containing compound in the presence of up to about 20
weight percent, based on combined weight of isocyanate-containing compound
and active hydrogen-containing compound, of a physical blowing agent
comprising the polyfluorocarbon compound, and
(b) wherein the cells of the resulting foam comprise the polyfluorocarbon
compound in an amount which reduces the thermal insulation loss of the
foam relative to the thermal insulation loss, with time, of the same foam
having the same density and prepared from the same foam-forming
composition in the presence of an equivalent molar quantity of blowing
agent in which a C.sub.2-6 polyfluorocarbon compound, containing no
chlorine or bromine atoms, is absent.
In a third aspect, this invention is an active hydrogen-containing
composition suitable for reacting with an isocyanate-containing compound
in the preparation of a closed-cell rigid polyurethane or polyisocyanurate
foam characterized in that the composition comprises
(a) an hydrogen-containing compound having at least 2 active hydrogen atoms
per molecule and having an equivalent weight of from about 50 to about
700, and
(b) from about 1 to about 20 weight percent, based on a combined weight of
(a) and (b) present, of a physical blowing agent comprising a C.sub.2-6
polyfluorocarbon compound containing no chlorine or bromine atoms,
which provides for a foam wherein the thermal insulation loss of the foam
relative to the thermal insulation loss, with time, of the same foam
having the same density and prepared from the same active
hydrogen-containing composition in the presence of an equivalent molar
quantity of blowing agent in which a C.sub.2-6 polyfluorocarbon compound,
containing no chorine or bromine atoms, is absent.
In a fourth aspect, this invention is a laminate comprising at least one
facing sheet adhered to the polymer foam as described in the first aspect.
In a fifth aspect, this invention is a process for preparing a laminate as
described in the fourth aspect.
These findings are surprising in view of the fact that substituting fully
halogenated or hydrogen-containing chlorofluorocarbons with
polyfluorocarbons having significantly higher gas thermal conductivities
would not be expected to reduce relative thermal insulation losses and in
some instances actually provide foam exhibiting superior insulation
properties on aging. The findings are especially significant when
considered in combination with the desire to use foaming systems having
minimized ozone depletion potentials.
DETAILED DESCRIPTION OF THE INVENTION
As described hereinabove, in one aspect this invention is a closed-cell
rigid polymer foam prepared from a foam-forming composition containing a
physical blowing agent.
The foam-forming composition used to prepare the foam of this invention may
be a thermoplastic composition comprising, for example, a thermoplastic
polyethylene or a polystyrene polymer or the like. However, preferred
foam-forming compositions are those which lead to the preparation of
thermoset polymers, especially polyurethane and polyisocyanurate polymers.
Such thermoset foam-forming compositions are preferred because of the
ability to prepare fine-celled polymers by foam-in-place procedures. To
provide for the optimum physical foam properties including thermal
insulation advantageously, the average cell size of the foam is less than
about 0.5, preferably less than about 0.45, and more preferably less than
about 0.4 mm.
The composition contains the physical blowing agent in a quantity
sufficient to provide a foam having an overall density of from about 10 to
about 200, preferably from about 10 to about 100, more preferably from
about 15 to about 80 and most preferably from about 18 to about 60
kg/m.sup.3.
To provide for such foam densities, the physical blowing agent
advantageously is present in quantities up to and including 20 weight
percent based on the total weight of the foam-forming composition,
including physical blowing agent present. Foams having the higher
densities are prepared in the presence of lower quantities of the physical
blowing agent. When blowing agent precursor compounds are present in the
composition the total quantity of physical blowing agent required to
produce foams of the desired densities will be reduced.
The physical blowing agent used to prepare the foam of this invention is
characterized in that it comprises at least one component which is a
C.sub.2-6 polyfluorocarbon compound containing no chlorine or bromine
atoms. Preferably the blowing agent comprises at least one
polyfluorocarbon compound which is a C.sub.2-3 compound.
The polyfluorocarbon compound component of the physical blowing agent is
present in an amount which provides for reduced thermal insulation losses
of the foam. Advantageously, the polyfluorocarbon compound component of
the physical blowing agent is present in from about 0.5 to about 15,
preferably from about 1.0 to about 10 and more preferably from about 1.5
to about 8.0 weight percent based on total weight of the foam-forming
composition and physical blowing agent present. When used in combination
with a blowing agent precursor compound these quantities of
polyfluorocarbon compound may account for the physical blowing agent
requirement in its entirety.
The absence of chlorine or bromine atoms is desirable as such compounds
generally have very low or zero ozone depletion potentials relative to
trichlorofluoromethane (R-11). Advantageously, the compounds used as
physical blowing agents including the polyfluorocarbon compounds used in
this present invention exhibit relative ozone depletion potentials, as
currently recognized, of less than about 0.15, preferably less than about
0.05, more preferably less than 0.01 and most preferably zero.
The polyfluorocarbon compound is further characterized by advantageously
having a boiling point at standard atmospheric pressure of less than about
65.degree. C., preferably less than about 45.degree. C., more preferably
less than about 25.degree. C. and most preferably less than about
0.degree. C. Use of polyfluorocarbon compounds having a boiling point
above 65.degree. C. may not be desirable if resulting foams are to exhibit
good low temperature dimensional stability. To allow for convenient
handling and foaming of the composition advantageously, the
polyfluorocarbon compound has a boiling point of at least -60.degree. C.,
preferably at least -40.degree. C. and more preferably at least
-30.degree. C.
To provide for desirable initial thermal insulation properties of the foam
of this present invention it is further advantageous if the
polyfluorocarbon compound when in a gaseous phase exhibits a gas thermal
conductivity of less than about 20, preferably less than about 18 and more
preferably less than about 16 mW/MK at 25.degree. C.
Polyfluorocarbon compounds are preferred over monofluorocarbon compounds as
they generally have a reduced flammability which may be of importance for
some foam applications.
Exemplary of C.sub.2-6 polyfluorocarbon compounds suitable for use as
physical blowing agents when preparing the foams of this invention are the
polyfluoroethanes including 1,1-difluoroethane (R-152a),
1,2-difluoroethane (R-152), 1,1,1-trifluoroethane (R-143a),
1,1,2-trifluoroethane (R-143), 1,1,1,2-tetrafluoroethane (R-134a),
1,1,2,2-tetrafluoroethane (R-134), pentafluoroethane (R-125)and
hexafluoroethane (R-116): and the polyfluoroethylenes including
1,2-difluoroethylene (R-1132).
Other polyfluorocarbon compounds suitable for use in this present invention
also include the perfluorinated C.sub.2-6 compounds such as, for example,
perfluoropropane, perfluorobutane, perfluoro-n-pentane and isomers
thereof, perfluoro-n-hexane, perfluoroacetone, mixtures thereof and the
like.
Equally suitable for this present invention are cyclic polyfluorocarbon
compounds including perfluorocyclopropane (C-216), perfluorocyclobutane
(C-318), 1,1,2,2-tetrafluorocyclobutane (C-354) and
1,2,3,3,4,4-hexafluorocyclobut-1,2-ene (C-1316).
The above listed polyfluorocarbon compounds may also be used in admixture
or in admixture with additional secondary blowing agents providing for the
complete blowing requirement to give foams of a desired density. Suitable
secondary blowing agents are listed later.
The preferred polyfluorocarbon compounds for this present invention are the
polyfluoroethanes, especially 1,1,1,2-tetrafluoroethane (R-134a): and the
perfluorocarbon compounds, especially perfluoro-n-hexane. These compounds
are preferred due to their ready availability and currently recognized low
ozone depletion potentials.
As already mentioned, the foam of this present invention is characterized
in that it exhibits a reduced thermal insulation loss in comparison to the
same foams having effectively the same overall density and being prepared
from the same foam-forming composition but in the absence of a C.sub.2-6
polyfluorocarbon physical blowing agent containing no chlorine or bromine
atoms. The same density is obtained by use of alternative blowing agent(s)
in a quantity which provides for an equivalent molar quantity, volume, of
gas.
To obtain such reduction in thermal insulation loss the initial gas
composition within the closed cells of the foam advantageously comprises
up to about 60 mole percent, based on molar quantities of all gases
present within the cell, of the C.sub.2-6 polyfluorocarbon compound.
Preferably, the initial gas composition of the closed cells comprises from
about 5 to about 55, more preferably from about 10 to about 55 and most
preferably from about 15 to about 50 mole percent of the polyfluorocarbon
compound, the remaining part of the cell gas composition being obtained
from secondary physical blowing agents and/or blowing agent precursor
compounds.
In a preferred embodiment of this invention when the rigid polymer foam is
a polyurethane or polyisocyanurate polymer, especially prepared in the
presence of a blowing agent precursor such as, for example, water
providing carbon dioxide gas: the initial gas composition within the
closed cells of the foam comprises
(a) from about 1 to about 60 mole percent, based on the combined mole
quantities of (a) and (b) present, of a C.sub.2-6 polyfluorocarbon
compound containing no chlorine or bromine atoms, and
(b) from about 40 to about 99 mole percent, based on the combined
quantities of (a) and (b) present, carbon dioxide.
Preferably, the initial cell gas composition comprises the polyfluorocarbon
compound in from about 5 to about 55, more preferably from about 10 to
about 55 and most preferably from about 15 to about 50 mole percent,
whilst the same mixture comprises the carbon dioxide in preferably from
about 45 to about 95, more preferably in from about 45 to about 90, and
most preferably in from about 50 to about 85 mole percent.
Although foams having initial cell gas compositions comprising mole
quantities of polyfluorocarbon compound(s) and carbon dioxide outside
these given ranges may be prepared, such foams may not exhibit the
advantageous thermal insulation aging characteristics as the foams of this
present invention.
Reference is made to "initial" gas compositions, as with time the
composition of such cell gas mixtures may change due to diffusion in and
out of environmental gases and cell gases respectively.
In the second aspect of this invention, a process for the preparation of a
rigid, closed-cell polymer foam is disclosed. Particularly, the disclosed
process relates to the preparation of a thermoset polymer which is a
polyurethane or polyisocyanurate foam containing within its cells a gas
mixture comprising a C.sub.2-6 polyfluorocarbon compound containing no
chlorine or bromine atoms.
The process is characterized in that an isocyanate-containing compound is
mixed and allowed to react with an active hydrogen-containing compound in
the presence of up to about 20 weight percent, based on total combined
weights of isocyanate-containing and active hydrogen-containing compound
present, of a physical blowing agent comprising a C.sub.2-6
polyfluorocarbon compound containing no chlorine or bromine atoms.
In the process of the invention, advantageously the polyfluorocarbon
compound component of the physical blowing agent is present in from about
0.5 to about 17, preferably from about 1.0 to about 10, and more
preferably in from about 1.5 to about 8.0 weight percent based on the
combined weights of isocyanate-containing material and active
hydrogen-containing compound present. Suitable and preferred
polyfluorocarbon compounds for use in the process are as already
described.
Isocyanate-containing compounds suitable for use in the process of this
invention are organic polyisocyanate compounds having an average
isocyanate content of from about 20 to about 50, and preferably from about
25 to about 35 weight percent.
Polyisocyanates suitable for use in the process of this invention include
aromatic, aliphatic and cycloaliphatic polyisocyanates and combinations
thereof. Representative of these types are diisocyanates such as m- or
p-phenylene diisocyanate, toluene-2,4-diisocyanate,
toluene-2,6-diisocyanate, hexamethylene-1,6-diisocyanate,
tetramethylene-1,4-diisocyanate, cyclohexane-1,4-diisocyanate,
hexahydrotoluene diisocyanate (and isomers), naphthylene-1,5-diisocyanate,
1-methylphenyl- -2,4-phenyldiisocyanate,
diphenylmethane-4,4'-diisocyanate, diphenylmethane-2,4'-diisocyanate,
4,4'-biphenylene diisocyanate, 3,3'-dimethoxy-4,4'-diphenylenediisocyanate
and 3,3'-dimethyldiphenylpropane-4,4'-diisocyanate: triisocyanates such as
toluene-2,4,6-triisocyanate and polyisocyanates such as
4,4'-dimethyldiphenylmeth- ane-2,2',5',5'-tetraisocyanate and the diverse
polymethylene polyphenyl polyisocyanates.
A crude polyisocyanate may also be used in the practice of this invention,
such as the crude toluene diisocyanate obtained by the phosgenation of a
mixture of toluene diamines or the crude diphenylmethane diisocyanate
obtained by the phosgenation of crude methylene diphenylamine. The
preferred undistilled or crude polyisocyanates are disclosed in U.S. Pat.
No. 3,215,652, incorporated herein b reference.
Especially preferred are methylene-bridged polyphenyl polyisocyanates, due
to their ability to cross-link the polyurethane.
The isocyanate is used in a quantity sufficient to provide for a well
cross-linked rigid, closed-cell foam. Advantageously the isocyanate index,
ratio of isocyanate moieties to active hydrogen atoms present in the
foam-forming composition, is from about 0.9 to about 5.0, preferably about
0.9 to about 3.0, more preferably about 1.0 to about 2.0 and most
preferably from about 1.0 to about 1.6.
Active hydrogen-containing compounds which are useful in this present
invention include those materials having two or more groups which contain
an active hydrogen atom that will react with an isocyanate, such as is
described in U.S. Pat. No. 4,394,491 and incorporated herein by reference.
Preferred among such compounds are materials having hydroxyl, primary or
secondary amine, carboxylic acid, or thiol groups. Polyols, i.e.,
compounds having at least two hydroxyl groups per molecule, are especially
preferred due to their desirable reactivity with polyisocyanates.
Suitable active hydrogen-containing compounds for preparing rigid
polyisocyanate-based foams include those having an equivalent weight of
about 50 to about 700, preferably from about 70 to about 300, more
preferably from about 90 to about 200. Such active hydrogen-containing
compounds advantageously have at least 2, preferably from about 3, and
advantageously up to about 16 and preferably up to about 8 active hydrogen
atoms per molecule. The number of active hydrogen atoms may also be
referred to as "functionality". Active hydrogen-containing compounds which
have functionalities and equivalent weights outside these limits may also
be used, but the resulting foam properties may not be desirable for a
rigid application.
Suitable additional isocyanate-reactive materials include polyether
polyols, polyester polyols, polyhydroxyl-terminated acetal resins,
hydroxyl-terminated amines and polyamines, and the like. Examples of these
and other suitable isocyanate-reactive materials are described more fully
in U.S. Pat. No. 4,394,491, particularly in columns 3-5 thereof. Most
preferred for preparing rigid foams, on the basis of performance,
availability and cost, is a polyol prepared by adding an alkylene oxide to
an initiator having from about 2 to about 8, preferably from about 3 to
about 8 active hydrogen atoms. Exemplary of such polyether polyols include
those commercially available under the trademark, VORANOL and include
VORANOL 202, VORANOL 360, VORANOL 370, VORANOL 446, VORANOL 490, VORANOL
575, VORANOL 800, all sold by The Dow Chemical Company, and Pluracol* 824,
sold by BASF Wyandotte.
Other most preferred polyols include alkylene oxide derivatives of Mannich
condensate as taught in, for example, U.S. Pat. Nos. 3,297,597: 4,137,265
and 4,383,102 and incorporated herein by reference, and
amino-alkylpiperazine-initiated polyether polyols as described in U.S.
Pat. Nos. 4,704,410 and 4,704,411 also incorporated herein by reference.
In addition to the foregoing critical components, it is optional but often
desirable to employ certain other ingredients in preparing
polyisocyanate-based foams. Among these additional ingredients are
secondary physical blowing agents and blowing agent precursor compounds,
catalysts, surfactants, flame retardants, preservatives, colorants,
antioxidants, reinforcing agents, fillers, antistatic agents and the like.
Secondary blowing agents suitable for use in admixture with the
polyfluorocarbon compound(s) providing for the complete blowing
requirement when preparing the foam include physical blowing agents
containing chlorine and/or bromine atoms. Preferably, such secondary
blowing agents are the hydrogen-containing chlorofluorocarbon compounds
exemplary of which are Refrigerant 21, Refrigerant 22, Refrigerant 123,
Refrigerant 123a, Refrigerant 124, Refrigerant 124a, Refrigerant 133 (all
isomers), Refrigerant 141b, Refrigerant 142, Refrigerant 151. Among these,
Refrigerant 123 (all isomers), Refrigerant 141b and Refrigerant 142 (all
isomers) are most preferred, as these are more readily commercially
available in addition to being recognized as having low ozone depletion
potentials.
In addition to the chlorofluorocarbon compounds, other low boiling
compounds are also useful herein, including, for example, carbon dioxide,
nitrogen, argon, pentane, and the like.
Blowing agent precursor compounds are compounds which during the
preparation of the foam react with one or more components contained within
the foam-forming composition generating a gas which then functions as a
blowing agent. Alternative precursor compounds may generate a gas as a
result of decomposition by the reaction exotherm. Exemplary of, and a
preferred, blowing agent precursor compound is water which reacts with
isocyanate leading to the generation of carbon dioxide gas. Other carbon
dioxide generating blowing agent precursor compounds include the
amine/carbon dioxide complexes such as taught in U.S. Pat. NOs. 4,735,970
and 4,500,656: incorporated herein by reference.
When water is contained in the foam-forming composition advantageously it
is present in from about 0.5 to about 10.0, preferably from about 1.0 to
about 7.0 and more preferably from about 2.0 to about 6.0 weight percent
based on total weight of active hydrogen-containing compounds within the
composition.
One or more catalysts for the reaction of the active hydrogen-containing
compound with the polyisocyanate are advantageously present. Any suitable
urethane catalyst may be used, including tertiary amine compounds and
organometallic compounds. Exemplary tertiary amine compounds include
triethylenediamine, N-methylmorpholine, pentamethyldiethylenetriamine,
tetramethylethylenediamine, 1-methyl-4-dimethylaminoethylpiperazine,
3-methoxy-N-dimethylpropylamine, N-ethylmorpholine, diethylethanolamine,
N-cocomorpholine, N,N-dimethyl- -N',N'-dimethyl isopropylpropylenediamine,
N,N-diethyl- -3-diethylaminopropylamine, dimethylbenzylamine and the like.
Exemplary organometallic catalysts include organomercury, organolead,
organoferric and organotin catalysts, with organotin catalysts being
preferred among these. Suitable tin catalysts include stannous chloride,
tin salts of carboxylic acids such as dibutyltin di-2-ethyl hexanoate, as
well as other organometallic compounds such as are disclosed in U.S. Pat.
No. 2,846,408. A catalyst for the trimerization of polyisocyanates and
formation of polyisocyanurate polymers, such as an alkali metal alkoxide,
alkali metal carboxylate, or quaternary amine compound, may also
optionally be employed herein.
When employed, the quantity of catalyst used is sufficient to increase the
rate of polymerization reaction. Precise quantities must be determined
experimentally, but generally will range from about 0.001 to about 3.0
parts by weight per 100 parts active hydrogen-containing compound
depending on the type and activity of the catalyst.
It is generally highly preferred to employ a minor amount of a surfactant
to stabilize the foaming reaction mixture until it cures. Such surfactants
advantageously comprise a liquid or solid organosilicone surfactant.
Other, less preferred surfactants, include polyethylene glycol ethers of
long chain alcohols, tertiary amine or alkanolamine salts of long chain
alkyl acid sulfate esters, alkyl sulfonate esters and alkyl arylsulfonic
acids. Such surfactants are employed in amounts sufficient to stabilize
the foaming reaction mixture against collapse and the formation of large,
uneven cells. Typically, about 0.2 to about 5 parts of the surfactant per
100 parts by weight polyol are sufficient for this purpose.
In the process of making a polyisocyanate-based foam, the polyol(s),
polyisocyanate and other components are contacted, thoroughly mixed and
permitted to expand and cure into a cellular polymer. The particulate
mixing apparatus is not critical, and various types of mixing head and
spray apparatus are conveniently used. It is often convenient, but not
necessary, to preblend certain of the raw materials prior to reacting the
polyisocyanate and active hydrogen-containing components. For example, it
is often useful to blend the polyol(s), blowing agent, surfactants,
catalysts and other components except for polyisocyanates, and then
contact this mixture with the polyisocyanate. Alternatively, all
components can be introduced individually to the mixing zone where the
polyisocyanate and polyol(s) are contacted. It is also possible to
pre-react all or a portion of the polyol(s) with the polyisocyanate to
form a prepolymer.
In the third aspect of this invention, an active hydrogen-containing
composition suitable for reaction with an isocyanate-containing compound
in the preparation of a rigid, closed-cell polyurethane or
polyisocyanurate foam is disclosed.
The active hydrogen-containing composition is characterized in that it
contains at least one active hydrogen-containing compound as already
described and additionally, based on the combined weight of active
hydrogen-containing compound(s) and physical blowing agent present up to
about 20 weight percent of a physical blowing agent comprising a C.sub.2-6
polyfluorocarbon compound containing no chlorine or bromine atoms.
Advantageously, the polyfluorocarbon compound component of the physical
blowing agent is present in the composition in from about 0.5 to about 20,
preferably from about 1.0 to about 10 and more preferably from about 1.5
to about 8 weight percent.
In the fourth aspect of this invention, laminate comprising at least one
facing sheet adhered to the closed-cell rigid polymer foam is disclosed.
Preferably, the facing sheet which may be paper, metal, wood or a
thermoplastic or thermoset polymer is adhered to a polyurethane or
polyisocyanurate foam which has been prepared in the presence of a
physical blowing agent comprising a C.sub.2-6 polyfluorocarbon compound
containing no chlorine or bromine atoms.
Suitable processes for preparing such a laminate are disclosed in, for
example, U.S. Pat. Nos. 4,707,401 and 4,795,763; incorporated herein by
reference.
The rigid closed-cell polymer foams of this invention are of value in a
number of applications such as, for example, spray insulation,
foam-in-place appliance foam rigid insulating board stock and laminates.
ILLUSTRATIVE EMBODIMENTS
The following examples are given to illustrate the invention and should not
be interpreted as limiting it in any way. Unless stated otherwise, all
parts and percentages are given by weight.
Foams are prepared using a low pressure foaming machine. Properties of the
resulting foams are determined on samples taken from 20.times.20.times.20
box foams having the stated molded density.
Post-demold expansion is measured in millimeters in the parallel-to-rise
direction on a molded 20.times.20.times.20 cm foam. The expansion is
observed after a curing time of 10 minutes with an appropriate face of the
mold having been opened after 3 or 4 minutes into the curing period. The
observed expansion is that of the foam out of the plane of the opened
face. Lower value of expansion indicates improved demold performance.
The thermal insulation, K-factor, is measured with an Anacon Model 88
Thermal Conductivity Analyzer having cold and hot plate temperatures of
10.2.degree. C. and 37.8.degree. C., respectively. The foam samples used
to determine the aged K-factor are stored at ambient temperature, pressure
and humidity conditions. Lower values (mW/MK) indicate better thermal
insulative properties.
Foam compressive strengths are observed in the parallel-to-rise and
perpendicular-to-rise direction using individual 5.times.5.times.5 cm
samples taken from the core of a molded 20.times.20.times.20 foam.
Compressive strengths are observed at 10 percent compression.
The average foam cell diameter is determined from a thin section of foam
using a polarized-light optical microscope together with a Quantimet 520
Image Analysis system to study the cells.
The reported, calculated thermal conductivity of the gas mixture within the
closed cells of the foam is according to the Lindsay-Bromley procedure,
Industrial and Engineering Chemistry, Vol. 42, p. 1508 (1950) using
temperature-dependent Sutherland Constant approximations as discussed.
The composition of the gas mixture considered for the calculation is that
which can be anticipated if there is a full retention of all blowing
agents and gases within the initial foam based on components of the
reacting mixture.
The physical properties of the various blowing agents used in the following
examples are summarized:
______________________________________
gas ther-
b.p. mal con- Relative
(.degree.C.)
ductivity ozone
760 (mW/MK) depletion
Blowing Agent
mm/Hg (25.degree. C.)
potential.sup. .circle.1
______________________________________
R-134a: C.sub.2 H.sub.2 F.sub.4
-26 15,5 0.0
R-11: CCl.sub.3 F
+24 7.9 1.0
R-142b*: C.sub.2 H.sub.3 ClF.sub.2
-9 11.7 0.06
R-22*: CHClF.sub.2
-41 10.6 0.05
______________________________________
*comparative blowing agent for the purpose of this invention
.sup. .circle.1 potentials are relative to Refrigerant R11
EXAMPLE 1
This example illustrates the aged thermal insulation performance of a
polyurethane foam containing a cell gas mixture of about 50 mole percent
carbon dioxide and about 50 mole percent physical blowing agent (based on
components present in the foam-forming composition).
Sample 1 indicates the advantageous use of a C.sub.2-6 polyfluorocarbon
compound, Refrigerant 134a. Comparative samples A and B illustrate foams
prepared with comparative blowing agents, Refrigerant 11 and Refrigerant
142b.
Foam properties are presented in Table I and thermal insulation properties
in Table II.
The data presented in Table I indicates foams prepared with Refrigerant
134a exhibit equivalent or better mechanical physical properties than
foams prepared with comparative blowing agents.
In Table II, the thermal insulation properties show that the thermal
insulation loss on aging is reduced for foam comprising Refrigerant 134a
in the cell gas mixture.
The higher initial foam thermal conductivity values of the example is not
unexpected when considering the relative thermal conductivities of the
gases. However, what is very surprising is the significantly reduced
thermal insulation loss relative to the calculated cell gas conductivity
of the initial gas mixture contained within the cells of the foam.
The cells of the foams initially contain 50 mole percent carbon dioxide
which is able to diffuse out relatively quickly, leaving the cells with a
gas mixture containing highly enriched levels of the physical blowing
agent. It would therefore normally be anticipated that foams containing
within their cells enriched concentrations of higher thermal conductivity
gas would show significantly greater thermal insulation losses with time,
but this is not observed.
Considering the difference between the calculated thermal conductivity of
the initial cell gas mixture and that initially observed for the foam is
indicative of heat transfer by radiation and solid conduction mechanisms
as opposed to gas conduction. Once the foam structure is established, the
quantity of heat transfer through the foam by solid conduction and
radiation mechanisms does not change on aging and therefore any change in
thermal insulation properties of a foam with time can be related
specifically to the cell gas composition.
It is interesting to note that the foam prepared in the presence of
Refrigerant 134a exhibits significantly lower heat transfer by the solid
conduction and radiation mechanisms than the comparative foams.
TABLE I
______________________________________
Physical blowing agent (B.A.)
1 A* B*
(R-134a)
(R-11) (R-142b)
______________________________________
Polyol.sup. .circle.1
100 100 100
Isocyanate.sup. .circle.2
157 157 157
Isocyanate Index 1.05 1.95 1.05
BA wt % on polyol 16.3 22 16
BA wt % composition
6.0 7.9 5.9
Molded foam density (kg/m.sup.3)
32.5 30 30
Post-expansion (mm)
3 min. (10 min. cure)
5.1 7.2 8.1
4 min. (10 min. cure)
2.0 6.4 6.3
Compressive strengths
164/193 125/72 119/82
10% compression (KPa)
II/l to rise
Average foam cell diameter
0.44 0.58 0.60
(mm)
Standard deviation
0.22 0.37 0.40
______________________________________
*Comparative example, not an example of this invention
.sup. .circle.1 A fully formulated polyol system comprising a
sucroseglycerine initiated polyether polyol and about 3 wt % water
.sup. .circle.2 A crude polymeric methylene diphenylisocyanate, average
functionality 2.7, NCO wt percentage 31 | | |
