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Description  |
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BACKGROUND OF THE INVENTION
The present invention relates to a process for producing polyurethane foams
produced using 1,1-dichloro-1-fluoroethane (HCFC-141b) as the primary
blowing agent in which the level of 1-chloro-1-fluoroethylene (HCFC-1131a)
by-product generated is substantially reduced and to the foams produced by
this process.
Rigid polyurethane foams and processes for their production are well known
in the art. Such foams are typically produced by reacting a polyisocyanate
with an isocyanate-reactive material such as a polyol in the presence of a
chlorofluorocarbon blowing agent. It is also known, however, that these
chlorofluorocarbon blowing agents pose environmental problems.
Alternatives to the known chlorofluorocarbon blowing agents are currently
the subject of much research. Hydrogen chlorofluorocarbons (HCFCs) are
among the most promising alternatives. However, one of the problems
encountered with HCFCs is that they tend to degrade under foam-forming
conditions to a greater extent than their chlorofluorocarbon predecessors.
The hydrohalocarbons undergo dehydrohalogenation to form halogenated
alkenes. They may also undergo reduction reactions in which halogen atoms
are replaced with hydrogen.
One solution to the HCFC degradation problem which was suggested by Hammel
et al in their paper entitled, "Decomposition of HCFC-123, HCFC-123a, and
HCFC-141b in Polyurethane Premix and in Foam", was to wait to add the HCFC
to the foam-forming mixture until just before use. This solution is not,
however, practical in commercial foam production processes.
Means for stabilizing hydrohalocarbons under foam-forming conditions have
therefore been sought by those in the art. U.S. Pat. No. 5,137,929, for
example, teaches that inclusion of certain types of stabilizers in a foam
forming mixture reduces the amount of decomposition of hydrohalocarbon
blowing agent during the foaming process. Among the materials taught to be
useful as stabilizers are esters, organic acids, anhydrides, aminoacids,
ammonium salts, bromoalkanes, bromoalcohols, bromoaromatic esters,
chloroalcohols, nitroalkanes, nitroalcohols, triarylmethyl chlorides,
triarylmethyl bromides, 3-sulfolene, zinc dialkyldithiophosphate,
haloalkyl phosphate esters, carbon molecular sieves, powdered activated
carbon, zeolite molecular sieves, sulfonate esters, and haloalkyl
phosphate esters.
In their paper entitled, "Minimization of HCFC-141b Decomposition in Rigid
Polyisocyanurate Foams", Bodnar et al take a different approach. Bodnar et
al recommend that the catalyst employed in the foam forming reaction be
selected so that any compatibilizer present in the polyol will not be able
to solvate the cation of the catalyst and thereby render the anion of the
catalyst more reactive.
U.S. Pat. No. 5,407,596 teaches that use of sucrose-based polyols in which
some of the hydroxyl groups were blocked in the foam forming mixture
reduces or eliminates the degradation of hydrohalocarbon blowing agents.
The use of specially modified polyols, special catalysts and/or stabilizers
necessarily results in increased cost. It would therefore be advantageous
to develop a method for producing foams from HCFC-141b in which
degradation of the blowing agent is diminished without using specially
modified or adapted materials.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a process for the
production of polyurethane foams in which 1,1-dichloro-1-fluoroethane
(HCFC-141b) is used as the primary blowing agent.
It is also an object of the present invention to provide a process for the
production of polyurethane foams with HCFC-141b in which
dehydrohalogenation of the blowing agent is substantially reduced.
It is another object of the present invention to provide polyurethane foams
characterized by outstanding properties in which the amount of
dehydrohalogenation by-product present in the cell walls is substantially
reduced.
These and other objects which will be apparent to those skilled in the art
are accomplished by reacting an organic polyisocyanate with an organic
material having at least two isocyanate reactive hydrogen atoms in the
presence of a blowing agent which is composed of water and
dichloro-fluoroethane (HCFC-141b), The water must be present in an amount
greater than 1.0% by weight of the total foam forming mixture. The
resultant foams are characterized by a thermal conductivity of less than
about 0.160, preferably less than about 0.150, Btu-in./hr.ft.sup.2
.degree. F.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE PRESENT INVENTION
The present invention is directed to a process for the production of
polyurethane foams with dichlorofluoroethane as the primary blowing agent
and to the foams produced with these polyols. In the process of the
present invention, an organic polyisocyanate is reacted with an organic
material having at least two isocyanate-reactive hydrogen atoms in the
presence of a blowing agent which included 1,1-dichloro-1-fluoroethane and
greater than 1% by weight (based on the total weight of the foam-forming
mixture) of water.
HCFC-141b is commercially available and may generally be included in the
reaction mixture in an amount of from about 2 to about 10% by weight,
preferably from about 3 to about 9% by weight, and most preferably about 4
to about 7% by weight, based upon the total weight of the foam forming
mixture.
The water included in the foam forming mixture is generally included in an
amount of greater than 1.0% by weight, preferably from 1.0 to about 4.0%
by weight, and most preferably about 1.5% by weight, based upon the total
weight of the foam forming mixture.
The HCFC-141b and water may be added individually to the foam forming
reaction mixture but it is preferred that the HCFC-141b and water be
combined to form a mixture prior to addition to the foam forming mixture.
It is, of course, possible to use other known blowing agents in addition to
the required HCFC-141b and water. Examples of such optional blowing agents
include other known HCFC's such as monochlorodifluoromethane (HCFC-22);
2-monochloro-2,2-difluoroethane (HCFC-142b); and
1,1,1-trifluoro-2-chloro-2-fluoroethane (HCFC-124).
If used, the optional blowing agent is generally included in the blowing
agent mixture in an amount which is no greater than 70% by weight of the
total weight of the blowing agent mixture, preferably in an amount of 50%
by weight or less, and most preferably in an amount of 30% by weight or
less.
Any of the known organic isocyanates may be used in the process of the
present invention. Isocyanates which may be used include aromatic,
aliphatic, and cycloaliphatic polyisocyanates and combinations thereof.
Examples of suitable isocyanates are: diisocyanates such as m-phenylene
diisocyanate, p-phenylene diisocyanate, 2,4-toluene diisocyanate,
2,6-toluene diisocyanate, 1,6-hexamethylene diisocyanate,
1,4-hexamethylene diisocyanate, 1,4-cyclohexane diisocyanate,
hexahydrotoluene diisocyanate and its isomers, 1,5-naphthylene
diisocyanate, 1-methylphenyl-2,4-phenyl diisocyanate,
4,4'-diphenyl-methane diisocyanate, 2,4'-diphenylmethane diisocyanate,
4,4'-biphenylene diisocyanate, 3,3'-dimethoxy-4,4'-biphenylene
diisocyanate and 3,3'-dimethyl-diphenylpropane-4,4'-diisocyanate;
triisocyanates such as 2,4,6-toluene triisocyanate; and polyisocyanates
such as 4,4'-dimethyl-diphenylmethane-2,2',5,5'-tetraisocyanate and the
polymethylene polyphenylpolyisocyanates.
A crude polyisocyanate may also be used in making polyurethanes by the
process of the present invention. The crude toluene diisocyanate obtained
by phosgenating a mixture of toluene diamines and the crude
diphenylmethane diisocyanate obtained by phosgenating crude
diphenylmethanediamine are examples of suitable crude polyisocyanates.
Suitable undistilled or crude polyisocyanates are disclosed in U.S. Pat.
No. 3,215,652.
Suitable polyisocyanates for the production of rigid polyurethanes will
generally have an isocyanate (i.e., NCO) content of from about 25 toabout
35%. Preferred polyisocyanates are methylene-bridged polyphenyl
polyisocyanates and prepolymers of methylene-bridged polyphenyl
polyisocyanates having an average functionality of from about 1.8 to about
3.5, preferably from about 2.0 to about 3.1 isocyanate moieties per
molecule and an NCO content of from about 28 to about 34% by weight, due
to their ability to cross-link the polyurethane.
The polyisocyanate is generally used in an amount such that the isocyanate
index (i.e., the ratio of equivalents of isocyanate groups to equivalents
of isocyanate-reactive groups) is from about 0.9 to about 1.5, preferably
from about 1.0 to about 1.1.
Any of the known organic compounds but preferably polyols containing at
least two isocyanate-reactive hydrogen atoms and having a hydroxyl (OH)
value of from about 200 to about 650, preferably from about 350 to about
450, may be employed in the process of the present invention.
Suitable high functionality, high molecular weight polyols may be prepared
by reacting a suitable initiator containing active hydrogens with alkylene
oxide. Suitable initiators are those containing at least 4 active
hydrogens or combinations of initiators where the mole average of active
hydrogens is at least 4, preferably from about 4 to about 8, and more
preferably from about 6 to about 8. Active hydrogens are defined as those
hydrogens which are observed In the well-known Zerewitinoff test, see
Kohler, Journal of the American Chemical Society, p. 3181, Vol. 49 (1927).
Representative of such active hydrogen-containing groups include --OH,
--COOH, --SH and --NHR where R is H or alkyl, aryl aromatic group and the
like.
Examples of suitable initiators include pentaerythritol, carbohydrate
compounds such as lactose, .alpha.-methylglucoside,
.alpha.-hydroxyethylglucoside, hexitol, heptitol, sorbitol, dextrose,
manitol, sucrose and the like. Examples of suitable aromatic initiators
containing at least four active hydrogens include aromatic amines such as
toluene diamine, particularly meta-toluene diamine and methane
diphenylamine, the reaction product of a phenol with formaldehyde, and the
reaction product of a phenol with formaldehyde and a dialkanolamine such
as described by U.S. Pat. Nos. 3,297,597; 4,137,265 and 4,383,102
(incorporated herein by reference). Other suitable initiators which may be
used in combination with the initiators containing at least four active
hydrogens include water, glycerine, trimethylolpropane, hexane triol,
aminoethylpiperazine and the like. These initiators may contain less than
four active hydrogens and therefore can only be employed in quantities
such that the total mole average of active hydrogens per molecule remains
at least about 3.5 or more. Particularly preferred initiators for the
preparation of the high functionality, high molecular weight polyols
comprise sucrose, dextrose, sorbitol, .alpha.-methylglucoside,
.alpha.-hydroxyethylglucoside which may be employed separately or in
combination with other initiators such as glycerine or water.
The polyols may be prepared by methods well-known in the art such as taught
by Wurtz, The Encyclopedia of Chemical Technology, Vol. 7, p. 257-266,
lnterscience Publishers Inc. (1951) and U.S. Pat. No. 1,922,459. For
example, polyols can be prepared by reacting, in the presence of an
oxyalkylation catalyst, the initiator with an alkylene oxide. A wide
variety of oxyalkylation catalysts may be employed, if desired, to promote
the reaction between the initiator and the alkylene oxide. Suitable
catalysts include those described in U.S. Pat. Nos. 3,393,243 and
4,595,743, incorporated herein by reference. However, it is preferred to
use as a catalyst a basic compound such as an alkali metal hydroxide,
e.g., sodium or potassium hydroxide, or a tertiary amine such as
trimethylamine.
Polyether polyols are among the preferred polyols. Polyether polyols
prepared by reacting sucrose with an alkylene oxide such as ethylene oxide
and/or propylene oxide in the presence of an alkaline catalyst are most
preferred. U.S. Pat. No. 4,430,490 discloses a suitable process for
producing such polyether polyols.
It is preferred that the sucrose first be reacted with ethylene oxide and
then propylene oxide. The ethylene oxide is generally used in an amount of
from about 10 to about 50%, preferably from about 20 to about 40% by
weight of the total alkylene oxide used. The propylene oxide is generally
used in an amount of from about 50 to about 90% by weight of the total
alkylene oxide employed, preferably from about 60 to about 80% by weight.
The resultant polyol will have a molecular weight (determined by end group
analysis) of from about 400 to about 1200, preferably from about 550 to
about 750.
The acid used to neutralize the alkaline catalyst present in the polyol may
be any acid which reacts with the alkaline catalyst to produce a material
which is soluble in the polyether. Examples of suitable acids include:
sulfuric acid, lactic acid, salicylic acid, substituted salicylic acid
such as 2-hydroxy 3-methyl benzoic acid, 2-hydroxy 4-methyl benzoic acid
and mixtures of such acids.
The sucrose-based polyether polyol is generally included in foam forming
mixtures in an amount of from about 5 to about 35% by weight, based on the
total foam-forming mixture, preferably from about 20 to about 30% by
weight.
The reaction is usually carried out at a temperature of about 60.degree. C.
to about 160.degree. C., and is allowed to proceed using such a proportion
of alkylene oxide to initiator so as to obtain a polyol having a hydroxyl
number ranging from about 200 to about 650, preferably about 300 to about
550, most preferably from about 350 to about 500. The hydroxyl number
range of from about 200 to about 650 corresponds to an equivalent weight
range of about 86 to about 280.
Polyols of higher hydroxyl number than 650 may be used as optional
ingredients in the process of the present invention. Amine-based polyols
having OH values greater than 650, preferably greater than 700 are
particularly useful as optional ingredients.
The alkylene oxides which may be used in the preparation of the polyol
include any compound having a cyclic ether group, preferably an
.alpha.,.beta.-oxirane, and are unsubstituted or alternatively substituted
with inert groups which do not chemically react under the conditions
encountered whilst preparing a polyol. Examples of suitable alkylene
oxides include ethylene oxide, propylene oxide, 1,2- or 2,3-butylene
oxide, the various isomers of hexane oxide, styrene oxide,
epichlorohydrin, epoxychlorohexane, epoxychloropentane and the like. Most
preferred, on the basis of performance, availability and cost are ethylene
oxide, propylene oxide, butylene oxide and mixtures thereof, with ethylene
oxide, propylene oxide, or mixtures thereof being most preferred. When
polyols are prepared with combinations of alkylene oxides, the alkylene
oxides may be reacted as a complete mixture providing a random
distribution of oxyalkylene units within the oxide chain of the polyol or
alternatively they may be reacted in a step-wise manner so as to provide a
block distribution within the oxyalkylene chain of the polyol.
Such polyols include a sucrose-initiated polyol propoxylated to an average
hydroxyl number of from about 400 to about 500, a sorbitol-initiated
polyol propoxylated to an average hydroxyl number of about 250 to about
290, a sorbitol-glycerine initiated polyol having nominally an average of
about 4.0 to about 4.4 active hydrogens and propoxylated to a hydroxyl
number of about 250 to about 290.
The polyol is used in a quantity sufficient to allow the preparation of low
friability, good dimensionally stable and strong foams having a thermal
conductivity of less than about 0.160 Btu-in./hr.ft..sup.2 .degree. F.
Suitable optional polyols include polyether polyols, polyester polyols,
polyhydroxy-terminated acetal resins, hydroxy-terminated amines and
polyamines. Examples of these and other suitable materials are described
more fully in U.S. Pat. No. 4,394,491, particularly in columns 3 to 5
thereof. Most preferred for preparing rigid foams are those having from
about 2 to about 8, preferably from about 3 to about 8 active hydrogens
and having a hydroxyl number from about 50 to about 800, preferably from
about 200 to about 650, and more preferably from about 300 to about 550.
Examples of such polyols include those commercially available under the
product names Terate (available from Cape Industries) and Multranol
(available from Bayer Corporation).
Other components useful in producing the polyurethanes of the present
invention include surfactants, pigments, colorants, fillers, antioxidants,
flame retardants, stabilizers, etc.
When preparing polyisocyanate-based foams, it is generally advantageous to
employ a minor amount of a surfactant to stabilize the foaming reaction
mixture until it obtains rigidity. Such surfactants advantageously
comprise a liquid or solid organosilicon compound. Other, less preferred
surfactants include polyethylene glycol ethers of long chain alcohols,
tertiary amine or alkanolamine salts of long chain alkyl acid sulfate
esters, alkylsulfonic esters, alkylarylsulfonic acids. Such surfactants
are employed in amounts sufficient to stabilize the foaming reaction
mixture against collapse and the formation of large, and uneven cells.
Typically, about 0.2 to about 5.0 parts of the surfactant per 100 parts
per weight polyol composition are sufficient for this purpose.
One or more catalysts for the reaction of the polyol and water with the
polyisocyanate are advantageously used. Any suitable urethane catalyst may
be used including the known tertiary amine compounds and organometallic
compounds.
Examples of suitable tertiary amine catalysts include triethylenediamine,
N-methylmorpholine, pentamethyldiethylenetriamine,
dimethylcyclohexylamine, tetramethyl ethylenediamine,
1-methyl-4-dimethylaminoethyl-piperazine, 3-methoxy-N-dimethyl -propyl
amine, N-ethylmorpholine, diethylethanolamine, N-cocomorpholine,
N,N-dimethyl-N',N'-dimethyl isopropyl-propylene diamine, N,N-diethyl
-3-diethyl aminopropyl amine and dimethyl-benzyl amine. Examples of
suitable organometallic catalysts include organomercury, organolead,
organoferric and organotin catalysts, with organotin catalysts being
preferred. Suitable organotin catalysts include tin salts of carboxylic
acids such as dibutyl tin di-2-ethyl hexanoate and dibutyltin dilaurate.
Metal salts such as stannous chloride can also function as catalysts for
the urethane reaction. A catalyst for the trimerization of
polyisocyanates, such as an alkali metal alkoxide or carboxylate, may also
optionally be employed herein. Such catalysts are used in an amount which
measurably increases the rate of reaction of the polyisocyanate. Typical
amounts are about 0.01 to about 1 part of catalyst per 100 parts by weight
of polyol.
The components described may be employed to produce rigid polyurethane and
polyurethane-modified isocyanurate foam. The isocyanate-reactive compound
having an OH value of from about 200 to about 650 and any other optional
polyol are reacted with an organic polyisocyanate in the presence of
blowing agent, catalyst, surfactant, additives, fillers, etc. The rigid
foams of the present invention may be made in a one-step process by
reacting all of the ingredients together at once, or foams can be made by
the so-called quasi prepolymer method. In the one-shot process where
foaming is carried out in machines, the active hydrogen-containing
compounds, catalyst, surfactants, blowing agents and optional additives
may be introduced separately to the mixing head where they are combined
with the polyisocyanate to give the polyurethane-forming mixture. The
mixture may be poured or injected into a suitable container or molded as
required. For use of machines with a limited number of component lines
into the mixing head, a premix of all the components except the
polyisocyanate can be advantageously employed. This simplifies the
metering and mixing of the reacting components at the time the
polyurethane-forming mixture is prepared.
Alternatively, the foams may be prepared by the so-called "quasi
prepolymer" method. In this method a portion of the polyol component is
reacted in the absence of catalysts with the polyisocyanate component in
proportion so as to provide from about 10 percent to about 30 percent of
free isocyanate groups in the reaction product based on the prepolymer. To
prepare foam, the remaining portion of the polyol is added and the
components are allowed to react together in the presence of catalysts and
other appropriate additives such as blowing agent, surfactant, etc. Other
additives may be added to either the prepolymer or remaining polyol or
both prior to the mixing of the components, whereby at the end of the
reaction a rigid polyurethane foam is provided.
Foams produced in accordance with the present invention are characterized
by reduced levels of the decomposition product HCFC-1131a.
The polyurethane foams of this invention have a thermal conductivity of
less than about 0.160, preferably less than about 0.150
Btu-in./hr.ft.sup.2 .degree. F., are useful in a wide range of
applications. Accordingly, not only can rigid appliance foam be prepared
but spray insulation rigid insulating board stock, laminates and many
other types of rigid foam can easily be prepared with the process of this
invention.
Having thus described my invention, the following Examples are given as
being illustrative thereof. All parts and percentages given in these
Examples are parts by weight and percentages by weight, unless otherwise
indicated.
EXAMPLES
The materials used in the Examples given below were as follows:
POLYOL A: a polyether polyol prepared by reacting sucrose, propylene glycol
and water first with ethylene oxide(30% of total alkylene oxide) and then
with propylene oxide (70% of total alkylene oxide) in the presence of a
base and subsequently neutralizing the reaction mixture with lactic acid.
The salt formed was allowed to remain in the polyol. This polyol had an OH
number of 467.2.
POLYOL B: a polyether polyol prepared by reacting o-toluene diamine with
ethylene oxide and propylene oxide in the presence of a base and
subsequently neutralizing the reaction mixture with lactic acid. The salt
formed was allowed to remain in the polyol. This polyol had an OH number
of 395.
POLYOL C: a polyester polyol which is commercially available under the name
Stepanpol PS-2502A from Stepan Company. This polyol had an OH number of
240.
POLYOL D: a sucrose-initiated polyether polyol prepared by reacting
sucrose, water and propylene glycol with propylene oxide. The OH number of
this polyol was 340.
SURFACTANT A: a polyalkylene oxide dimethyl siloxane copolymer which is
commercially available under the designation DC-5357 from Air Products and
Chemicals, Inc.
SURFACTANT B: a polyalkylene oxide dimethyl siloxane copolymer which is
commercially available under the designation L-1512 from Air Products and
Chemicals, Inc.
CATALYST A: a strongly basic, amber brown liquid having a characteristic
amine odor which is commercially available from Air Products and
Chemicals, Inc. under the name Polycat 41.
CATALYST B: a tertiary amine catalyst which is commercially available from
Air Products and Chemicals, Inc. under the name Polycat 8.
CATALYST C: a tertiary amine catalyst which is commercially available from
Rhein Chemie under the name Desmorapid PV.
HCFC-141b: 1,1-dichloro-1-fluoroethane.
HCFC-1131 a: 1-chloro-1-fluoroethylene.
ISO: a modified polymethylene polyphenyl polyisocyanate prepolymer which is
commercially available from Bayer Corporation under the name Mondur 1451
having an NCO group content of approximately 29.5%.
Polyols A, B, C and D, surfactant, catalyst, blowing agent and ISO were
combined and reacted in the amounts indicated in the Table below. The
properties of the product foams are also reported in the Table.
TABLE
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EXAMPLE 1* 2
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POLYOL A (pbw) 41.79 40.38
POLYOL B (pbw) 20.90 16.07
POLYOL C (pbw) 6.97 8.03
POLYOL D (pbw) -- 15.02
SURFACTANT A (pbw) 2.40 --
SURFACTANT B (pbw) -- 2.44
CATALYST A (pbw) 0.45 --
CATALYST B (pbw) -- 0.86
CATALYST C (pbw) 0.90 0.43
WATER (pbw) 1.50 3.52
HCFC-141b (pbw) 25.09 13.30
ISO (pbw) 123.40 144.50
K-factor (Btu-in./hr.ft..sup.2 .degree.F.)
at 35.degree. F. 0.120 0.130
at 75.degree. F. 0.126 0.145
Overall Density (lbs./ft..sup.3)
2.07 2.18
.mu.g HCFC-1131a/gm of HCFC-141b
1210 .+-. 40
650 .+-. 50
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*Comparative Example
The foam formulation of Example 1 had a water content of 0.67% by weight,
based on the total weight of the foam formulation. The level of HCFC-1131a
by-product generated during foaming of this formulation was 1210
micrograms for each gram of HCFC-141b.
The foam formulation of Example 2 had a water content of 1.44% (based on
the total weight of the foam formulation). The level of HCFC-1131a
by-product generated during foaming of this formulation was only 650
micrograms for each gram of HCFC-141b.
It is readily apparent from the data present in the Table that foams made
with the higher amount of water contained less of the unwanted by-product
HCFC-1131a per gram of HCFC-141b used. This lower relative amount of
HCFC-1131a had not been expected.
Although the invention has been described in detail in the foregoing for
the purpose of illustration, it is to be understood that such detail is
solely for that purpose and that variations can be made therein by those
skilled in the art without departing from the spirit and scope of the
invention except as it may be limited by the claims.
* * * * *
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