 |
Description  |
|
|
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to foam insulating products, particularly
polyurethane and polyisocyanurate foams, containing carbon black as a
filler and to a process for providing the insulating products.
2. Description of the Prior Art
The usefulness of foamed plastic materials in a variety of applications is
well known. Rigid polyurethane and polyisocyanurate foams, for instance,
are widely used as insulating structural members. It would be highly
desirable to reduce the polymer content and concomitantly the cost of
these members by the addition of fillers. The incorporation of fillers in
the foam-forming reaction mixture has been repeatedly proposed in a
general fashion in the prior art but little concrete evidence of such
filler utilization has been described; see, for example, U.S. Pat. Nos.
3,644,168, 4,092,276, 4,110,270, 4,165,414, 4,248,975, 4,366,204,
4,467,014 and 4,649,162, and Canadian Pat. No. 853,771. This failure to
broadly utilize fillers in rigid insulating foams is explainable because
the advantages of adding the fillers have been perceived to be outweighed
by the problems involved in incorporating them in the foam, maintaining
the overall good foam quality, etc.
Japanese patent application, laid open as No. 57-147510, describes the use
of carbon black in rigid foam plastics but reports k-factor reductions of
less than 4% achieved with maximum carbon black levels under 0.7 weight
percent. Nothing is disclosed in the application regarding the effect of
aging on the k-factor of the filled foams. Although the degree of success
reported in this Japanese application justifies little interest in carbon
black as a filler for foams, it would be a considerable advance in the art
to provide a filled, rigid foam characterized by reduced cost and a
significantly improved insulating value.
OBJECTS OF THE INVENTION
It is therefore an object of the present invention to provide an improved
method for the production of a filled, rigid, highly insulating foam
plastic in a simple and economical manner.
It is another object of the present invention to produce a filled, rigid
foam plastic which exhibits overall good properties, including excellent
thermal insulative properties, good dimensional stability, thermal
resistance, and compressive strength and acceptable friability.
It is a further object of the present invention to produce filled, closed
cell foam materials which can be used in building panels having superior
insulating and fire resistant properties.
These and other objects and advantages of the present invention will become
more apparent by reference to the following detailed description and
drawings wherein:
FIG. 1 is a schematic elevation of an apparatus suitable for practicing the
process of the invention in a free-rise mode; and
FIGS. 2 to 8 are a series of graphs showing the relationships between the
k-factor of various filled foams and the content of the material used as
filler in these foams.
SUMMARY OF THE INVENTION
The above objects have been achieved through the development of a rigid
plastic foam which contains carbon black as a filler material to improve
the insulating qualities of the foam. The carbon black is uniformly
dispersed throughout the foam product and is employed in an amount
sufficient to increase both the initial and aged insulation value, i.e.,
R-value, of the product to above the respective insulation values it would
have with the carbon black omitted. Any carbon black which can be
uniformly dispersed in the foam at levels of about 1-20, preferably 2 to
10, weight %, based on the weight of the polymer in the foam, can be used
for improvement of insulation value.
In the broadest aspects of the present invention, the rigid foamed plastic
materials may be any such materials described in the prior art. Examples
of these materials are polyurethane, polyisocyanurate, polyurea,
polyolefin, polystyrene, phenol-formaldehyde, epoxy and other polymeric
foams. The invention finds greatest utility when the foamed plastics are
of the rigid type used to provide high efficiency insulation, especially
rigid polyurethane and polyisocyanurate foams.
More particularly, the invention relates to the production of a closed
cell, rigid, polymer foam prepared from a polymer foam-forming composition
containing a foaming agent, the foam containing as filler at least about 2
percent by weight of carbon black, based on the weight of the polymer in
the foam, the carbon black being uniformly dispersed throughout the foam
so that there is present in the cell walls of the foam an amount of carbon
black which reduces the aged k-factor of the foam to below the aged
k-factor of the corresponding unfilled foam having approximately the same
density and prepared from the same foam-forming composition as the filled
foam except that the carbon black is omitted and the amount of foaming
agent is decreased to equalize the densities of the filled and unfilled
foams.
DETAILED DESCRIPTION OF THE INVENTION
The rigid foam plastics of the present invention have improved insulating
properties because of the presence of the carbon black filler. It has been
discovered that a uniform dispersion of a sufficient amount of carbon
black in a rigid foam brings about a significant reduction in both the
initial and long-term aged k factors of the foam. For example, the
preferred carbon black filled polyurethane and polyisocyanurate rigid
foams of the invention exhibit k-factor reductions of as much as 14%, as
compared to the unfilled foams of comparable density. This represents a
substantial improvement in the insulation value or R-value of the foam,
which is attained despite a reduction in product cost. The higher the
R-value of a foam the greater is its resistance to heat flow, whereas the
higher the k-factor the greater is the thermal conductivity or ease of
heat flow through the foam.
While it is desirable to reduce the polymer content of foams by adding
fillers for cost reduction, it has proven difficult to provide rigid
foams, such as the polyurethanes and polyisocyanurates, which contain more
than a minor proportion of the fillers. Furthermore, too much filler is
known to rupture the cells of the foam, which dramatically reduces its
insulative capacitive, and to cause the foam to be very friable. The
disposition to use little filler in foams is revealed in Japanese patent
application, laid open as No. 57-147510, which exemplifies carbon black
levels of less than 0.7 weight percent, based on the weight of the
reactive polymer-forming components (isocyanate and polyol components).
No significant benefit is realized from the small amount of filler used in
producing the foams illustrated in the Japanese patent application. At
this low level, carbon black performs much like various other conventional
fillers in imparting to the foam an initially somewhat improved insulation
value which unfortunately is not retained with aging. The present
invention involves the surprising discovery that a substantial long-term
improvement in insulation value results from the use of higher levels of
carbon black than those exemplified in the Japanese application, whereas
other conventional fillers, when used at the higher levels, contribute to
a loss of the foam's insulation value with aging.
The amount of carbon black in the foam should be sufficient to obtain the
desired level of improved insulative properties, such as a k-factor
reduction of at least about 5%, which persists with aging of the foam.
Typically, the amount ranges from about 1% to 10% by weight of the solid
foam polymer, such as 4% to 9%, particularly 7% to 8%. The particle size
of the carbon black particles to be employed may vary, but generally the
carbon black has a mean particle diameter of from about 10 to 150,
preferably from 50 to 100, and more preferably from 70 to 95, nm.
The carbon black may be any of the different kinds available, such as
lampblack, channel black, gas furnace black, oil furnace black and thermal
black. Although both fluffy and pelleted types of carbon black may be
used, the pelleted carbon blacks have been found especially suitable for
large-scale processing. A preferred pelleted carbon black having a mean
particle diameter of 75 nanometers is available from Cabot Corporation
under the trade name Sterling-NS.
Particularly suitable carbon blacks for use in the insulating foams of the
present invention are non-electroconductive. The electroconductive carbon
blacks are used in electroconductive foams and are generally characterized
by a relatively small average particle size and large specific surface
area, as compared to the non-electroconductive type. While the
electroconductive carbon blacks may be used in accordance with the present
invention, especially good insulating foam products contain a substantial
amount of carbon black particles whose average particle diameter is larger
and specific surface area smaller than the respective dimensions
characterizing the carbon blacks conventionally used in electroconductive
foams. The carbon black material of these highly desirable foam products
of the present invention has an average particle diameter which is
preferably greater than about 40, and more preferably greater than about
50, nm. This carbon black material has a specific surface area which is
preferably less than about 200, more preferably less than about 142 and
most preferably less than about 100, m.sup.2 /g.
A uniform carbon black dispersion in the finished foam product is essential
for the significant improvement of insulation value in accordance with the
present invention. To produce the requisite homogeneously filled foam, the
carbon black is first uniformly distributed in at least one of the
foam-forming ingredients by any conventional dispersing means. There must
be a sufficient amount of the ingredient or ingredients which is to serve
as the dispersion medium to totally disperse the carbon black and prevent
its agglomeration.
The carbon black is uniformly dispersed throughout the closed cell, rigid,
polymeric foams of the invention so that a sufficient amount of the carbon
black becomes located in the cell walls of the foam to reduce the aged
k-factor of the carbon black-filled foam to below the aged k-factor the
foam would have with the carbon black omitted. The content of carbon black
for optimum long-term preservation of insulation value has been found to
be at least about 2, more preferably at least about 5, weight percent, and
preferably is in the range from about 5 to 9, more preferably from about 5
to 8, weight percent, based on the weight of the polymer-forming reactants
in the foam system. The carbon black will advantageously reduce the aged
k-factor of the foam at 90 days by at least about 4, more preferably at
least about 5 and most preferably at least about 6 percent, as compared to
the unfilled foam having substantially the same density and prepared from
the same foam-forming ingredients except for the carbon black.
The use of fine dispersions of carbon black can result in excessively high
foam system viscosities which lead to incomplete chemical mixing and
physical defects in the core foam, e.g., a wide variation in k-factor
throughout the product. This problem can be overcome in various ways, such
as through the introduction of viscosity-reducing diluents. The
foam-forming ingredients themselves may function as diluents. For example,
in the formation of polyurethane and polyisocyanurate foams, low viscosity
isocyanates or polyols can be employed. Also, chlorofluorocarbons like
dichlorotrifluoroethane, besides their role as foaming agent, can be used
to reduce system viscosity, improve dispersibility of the carbon black
particles, and bring about uniform physical properties throughout the foam
product.
The large-scale production of carbon black-filled foam advantageously
begins with the preparation of a dispersion of the carbon black filler in
the foam-forming ingredient(s) which constitutes the best medium for
providing the highest loading of finely divided and well-dispersed filler
particles and also a workable viscosity. This pre-blended mixture is next
thoroughly mixed with the remainder of the foam-forming material, and the
resultant total mixture is foamed and cured. Dispersion of the carbon
black is conducted to provide the finest grind of particles economically
attainable for easier processing and extending the life of the process
equipment.
It is common practice in the manufacture of the preferred rigid cellular
polyurethanes and polyisocyanurates to utilize two preformulated
components, commonly called the A-component and the B-component.
Typically, the A-component contains the isocyanate compound that must be
reacted with the polyol of the B-component to form the foam, and the
balance of the foam-forming ingredients are distributed in these two
components or in yet another component or components. In general, the
carbon black may be dispersed in either the polyisocyanate or the polyol
or both. Isocyanurate foams of superior insulating value have been
produced by dispersing high levels of carbon black in the isocyanate
component. These carbon black/isocyanate dispersions have shown excellent
age stability with no settling or agglomeration of carbon black particles.
Carbon black containing A-components exhibit the same stability and show
no signs of particle agglomeration on addition of chlorofluorocarbon (CFC)
blowing agents.
Among the numerous organic polymers which may be foamed in accordance with
this invention, the following may be mentioned as examples: polystyrene,
polyvinyl chloride, polyethylene, polypropylene, polyacrylonitrile,
polybutadiene, polyisoprene, polytetrafluoroethylene, polyesters,
melamine, urea, phenol resins, silicate resins, polyacetal resins,
polyepoxides, polyhydantoins, polyureas, polyethers, polyurethanes,
polyisocyanurates, polyimides, polyamides, polysulphones, polycarbonates,
and copolymers and mixtures thereof.
Preferred carbon black-filled foams of this invention are rigid
polyurethane and polyisocyanurate foams. In the broadest aspects of the
present invention, any organic polyisocyanate can be employed in the
preparation of these foams. The organic polyisocyanates which can be used
include aromatic, aliphatic and cycloaliphatic polyisocyanates and
combinations thereof. Such polyisocyanates are described, for example, in
U.S. Pat. Nos. 4,065,410, 3,401,180, 3,454,606, 3,152,162, 3,492,330,
3,001,973, 3,394,164 and 3,124,605, all incorporated herein by reference.
Representative of the polyisocyanates are the diisocyanates such as
m-phenylene diisocyanate, toluene-2,4-diisocyanate,
toluene-2,6-diisocyanate, mixtures of 2,4- and 2,6-toluene diisocyanate,
hexamethylene-1,6-diisocyanate, tetramethylene-1,4-diisocyanate,
cyclohexane-1,4-diisocyanate, hexahydrotoluene 2,4- and 2,6-diisocyanate,
naphthalene-1,5-diisocyanate, diphenyl methane-4,4'-diisocyanate,
4,4'-diphenylenediisocyanate, 3,3'-dimethoxy-4,4'-biphenyldiisocyanate,
3,3'-dimethyl-4,4'-biphenyldiisocyanate, and
3,3'-dimethyldiphenylmethane-4,4'-diisocyanate; the triisocyanates such as
4,4',4"-triphenylmethanetriisocyanate, polymethylenepolyphenyl isocyanate,
toluene-2,4,6-triisocyanate; and the tetraisocyanates such as
4,4'-dimethyldiphenylmethane-2,2',5,5'-tetraisocyanate. Especially useful
are polymethylene polyphenyl polyisocyanates. These isocyanates are
prepared by conventional methods known in the art such as the phosgenation
of the corresponding organic amine.
Prepolymers may also be employed in the preparation of the foams of the
present invention. These prepolymers are prepared by reacting an excess of
organic polyisocyanate or mixtures thereof with a minor amount of an
active hydrogen-containing compound as determined by the well-known
Zerewitinoff test, as described by Kohler in "Journal of the American
Chemical Society," 49, 3181 (1927). These compounds and their methods of
preparation are well known in the art. The use of any one specific active
hydrogen compound is not critical hereto, rather any such compound can be
employed herein.
The preferred polymethylene polyphenylisocyanates desirably have a
functionality of at least 2.1 and preferably 2.5 to 3.2. These preferred
polymethylene polyphenylisocyanates generally have an equivalent weight
between 120 and 180 and preferably have an equivalent weight between 130
and 145.
A preferred subclass of polymethylene polyphenylisocyanates especially
useful in the present invention is a mixture of those of the following
formula:
##STR1##
wherein n is an integer from 0 to 8 and wherein the mixture has the
above-described functionality and equivalent weight. This mixture should
have a viscosity between 100 and 4,000 and preferably 250 to 2500
centipoises measured at 25.degree. C. in order to be practical for use in
the present invention.
Examples of suitable polymethylene polyphenylisocyanates useful in the
present invention include those of the above formula, wherein n is 1 as
well as mixtures wherein n can have any value from 0 to 8 as long as the
mixture has the specified equivalent weight. One such mixture has 40
weight percent of n=0, 22 weight percent of n=1, 12 weight percent of n=2,
and 26 weight percent of n=3 to about 8. The preferred polymethylene
polyphenyl isocyanates are described in U.S. application Ser. No. 322,843,
filed Jan. 11, 1973, now abandoned. The synthesis of polymethylene
polyphenylisocyanates is described in Seeger et al., U.S. Pat. No.
2,683,730 and in Powers U.S. Pat. No. 3,526,652 at column 3, lines 6-21.
It should, therefore, be understood that the polymethylene
polyphenylisocyanates available on the market under the trade names of
CODE 047 or PAPI-20 (Dow) and MR 200 (Mobay/Bayer) can successfully be
employed within the spirit and scope of the present invention.
In addition to the polyisocyanate, the foam-forming formulation also
contains an organic compound containing at least 1.8 or more
isocyanate-reactive groups per molecule (hereinafter called
"isocyanate-reactive compounds"). Suitable such compounds include polyols,
polyamines, polyacids, polymercaptans and like compounds. Preferred
isocyanate-reactive compounds are the polyester and polyether polyols.
Particularly preferred are polyester polyols or mixtures of polyester and
polyether polyols.
The polyester polyols useful in the invention can be prepared by known
procedures from a polycarboxylic acid or acid derivative, such as an
anhydride or ester of the polycarboxylic acid, and a polyhydric alcohol.
The acids and/or the alcohols may, of course, be used as mixtures of two
or more compounds in the preparation of the polyester polyols.
Particularly suitable polyester polyols of the invention are aromatic
polyester polyols containing phthalic acid residues.
The polycarboxylic acid component, which is preferably dibasic, may be
aliphatic, cycloaliphatic, aromatic and/or heterocyclic and may optionally
be substituted, for example, by halogen atoms, and/or may be unsaturated.
Examples of suitable carboxylic acids and derivatives thereof for the
preparation of the polyester polyols include: oxalic acid; malonic acid;
succinic acid; glutaric acid; adipic acid; pimelic acid; suberic acid;
azelaic acid; sebacic acid; phthalic acid; isophthalic acid; trimellitic
acid; terephthalic acid; phthalic acid anhydride; tetrahydrophthalic acid
anhydride; pyromellitic dianhydride; hexahydrophthalic acid anhydride;
tetrachlorophthalic acid anhydride; endomethylene tetrahydrophthalic acid
anhydride; glutaric acid anhydride; maleic acid; maleic acid anhydride;
fumaric acid; dibasic and tribasic unsaturated fatty acids optionally
mixed with monobasic unsaturated fatty acids, such as oleic acid;
terephthalic acid dimethyl ester and terephthalic acid-bis-glycol ester.
Any suitable polyhydric alcohol may be used in preparing the polyester
polyols. The polyols can be aliphatic, cycloaliphatic, aromatic and/or
heterocyclic, and are preferably selected from the group consisting of
diols, triols and tetrols. Aliphatic dihydric alcohols having no more than
about 20 carbon atoms are highly satisfactory. The polyols optionally may
include substituents which are inert in the reaction, for example,
chlorine and bromine substituents, and/or may be unsaturated. Suitable
amino alcohols, such as, for example, monoethanolamine, diethanolamine,
triethanolamine, or the like may also be used. Moreover, the
polycarboxylic acid(s) may be condensed with a mixture of polyhydric
alcohols and amino alcohols.
Examples of suitable polyhydric alcohols include: ethylene glycol;
propylene glycol-(1,2) and -(1,3); butylene glycol-(1,4) and -(2,3);
hexane diol-(1,6); octane diol-(1,8); neopentyl glycol;
1,4-bishydroxymethyl cyclohexane; 2-methyl-1,3-propane diol; glycerin;
trimethylolpropane; trimethylolethane; hexane triol-(1,2,6); butane
triol-(1,2,4); pentaerythritol; quinitol; mannitol; sorbitol; formitol;
.alpha.-methyl-glucoside; diethylene glycol; triethylene glycol;
tetraethylene glycol and higher polyethylene glycols; dipropylene glycol
and higher polypropylene glycols as well as dibutylene glycol and higher
polybutylene glycols. Especially suitable polyols are oxyalkylene glycols,
such as diethylene glycol, dipropylene glycol, triethylene glycol,
tripropylene glycol, tetraethylene glycol, tetrapropylene glycol,
trimethylene glycol and tetramethylene glycol.
The term "polyester polyol" as used in this specification and claims
includes any minor amounts of unreacted polyol remaining after the
preparation of the polyester polyol and/or unesterified polyol added after
the preparation.
The polyester polyols of the invention advantageously contain at least 1.8
hydroxyl groups and generally have an average equivalent weight of from
about 75 to 500. Preferably, the polyesters contain from about 1.8 to 8
hydroxyl groups had have an average equivalent weight of from about 100 to
300, more preferably from about 120 to 250. Highly desirable aromatic
polyester polyols of the invention have an average functionality of about
1.8 to 5, preferably about 2 to 2.5. Polyesters whose acid component
advantageously comprises at least about 30% by weight of phthalic acid
residues are particularly useful. By phthalic acid residue is meant the
group
##STR2##
Particularly suitable compositions containing phthalic acid residues for
use in the invention are (a) ester-containing by-products from the
manufacture of dimethyl terephthalate, (b) scrap polyalkylene
terephthalates, (c) phthalic anhydride, (d) residues from the manufacture
of phthalic anhydride, (e) terephthalic acid, (f) residues from the
manufacture of terephthalic acid, (g) isophthalic acid and (h) trimellitic
anhydride. These compositions may be converted to polyester polyols
through conventional transesterification or esterification procedures.
While the polyester polyols can be prepared from substantially pure
reactant materials, more complex ingredients are advantageously used, such
as side-stream, waste or scrap residues from the manufacture of phthalic
acid, terephthalic acid, dimethyl terephthalate, polyethylene
terephthalate, adipic acid and the like. Suitable polyol side-stream
sources include ethylene glycol, diethylene glycol, triethylene glycol and
higher homologs or mixtures thereof. The similar homologous series of
propylene glycols can also be used. Glycols can also be generated in situ
during preparation of the polyester polyols of the invention by
depolymerization of polyalkylene terephthalates. For example, polyethylene
terephthalate yields ethylene glycol. Polyester polyols derived from raw
materials containing compounds having the above defined phthalic acid
residues constitute a preferred embodiment of the invention.
Preferred residues containing phthalic acid groups for reaction with the
polyol mixture in accordance with the invention are DMT process residues,
which are waste or scrap residues from the manufacture of dimethyl
terephthalate (DMT). The term "DMT process residue" refers to the purged
residue which is obtained during the manufacture of DMT in which p-xylene
is converted through oxidation and esterification with methanol to the
desired product in a reaction mixture along with a complex mixture of
by-products. The desired DMT and the volatile methyl p-toluate by-product
are removed from the reaction mixture by distillation leaving a residue.
the DMT and methyl p-toluate are separated, the DMT is recovered and
methyl p-toluate is recycled for oxidation. The residue which remains can
be directly purged from the process or a portion of the residue can be
recycled for oxidation and the remainder diverted from the process, or, if
desired, the residue can be processed further, as, for example, by
distillation, heat treatment and/or methanolysis to recover useful
constituents which might otherwise be lost, prior to purging the residue
from the system. The residue which is finally purged from the process,
either with or without additional processing, is herein called DMT process
residue.
These DMT process residues may contain DMT, substituted benzenes,
polycarbomethoxy diphenyls, benzyl esters of the toluate family,
dicarbomethoxy fluorenone, carbomethoxy benzocoumarins and carbomethoxy
polyphenols. Dimethyl terephthalate may be present in amounts ranging from
about 6 to 65% of the DMT process residue. Hercules, Inc., Wilmington,
Del., sells DMT process residues under the trademark Terate.RTM.101.
Similar DMT process residues having a different composition but still
containing the aromatic esters and acids are also sold by DuPont and
others. The DMT process residues to be transesterified preferably have a
functionality at least slightly greater than 2.
A suitable DMT residue is disclosed in U.S. Pat. No. 3,647,759, and
suitable transesterified polyol mixtures are described in U.S. Pat. No.
4,237,238. Another suitable DMT residue and suitable transesterified
polyol mixtures made therefrom are described in U.S. Pat. No. 4,411,949.
Other preferred aromatic polyester polyols are those produced by digesting
polyalkylene terephthalate, especially polyethylene terephthalate (PET),
residues or scraps with organic polyols, such as the digestion products
disclosed in U.S. Pat. Nos. 4,233,068, 4,417,001, 4,469,824, 4,529,744,
4,539,341 and 4,604,410, U.S. patent application Ser. No. 756,107, and
European patent application Nos. 83102510.1 and 84304687.1. Still other
especially useful aromatic polyester polyols are the aromatic Chardol
polyols of Chardonol Corporation, and the aromatic Stepanpol polyols of
Stepan Company.
The polyols which can be employed alone or in combination with polyester
polyols in the preparation of the carbon black-filled polyurethane and
polyisocyanurate foam compositons of the invention include monomeric
polyols and polyether polyols. The polyether polyols are found
particularly useful in preparing rigid polyurethane foams. Polyether
polyols of this type are the reaction products of a polyfunctional active
hydrogen initiator and a monomeric unit such as ethylene oxide, propylene
oxide, butylene oxide and mixtures thereof, preferably propylene oxide,
ethylene oxide or mixed propylene oxide and ethylene oxide. The
polyfunctional active hydrogen initiator preferably has a functionality of
2-8, and more preferably has a functionality of 3 or greater (e.g., 4-8).
A wide variety of initiators may be alkoxylated to form useful polyether
polyols. Thus, for example, polyfunctional amines and alcohols of the
following type may be alkoxylated: monoethanolamine, diethanolamine,
triethanolamine, ethylene glycol, polyethylene glycol, propylene glycol,
hexanetriol, polypropylene glycol, glycerine, sorbitol,
trimethylolpropane, pentaerythritol, sucrose and other carbohydrates. Such
amines or alcohols may be reacted with the alkylene oxide(s) using
techniques known to those skilled in the art. The hydroxyl number which is
desired for the finished polyol would determine the amount of alkylene
oxide used to react with the initiator. The polyether polyol may be
prepared by reacting the initiator with a single alkylene oxide, or with
two or more alkylene oxides added sequentially to give a block polymer
chain or at once to achieve a random distribution of such alkylene oxides.
Polyol blends such as a mixture of high molecular weight polyether polyols
with lower molecular weight polyether polyols can also be employed.
The polyurethane foams can be prepared by reacting the polyol and
polyisocyanate on a 0.7:1 to 1.1:1 equivalent basis. In an advantageous
embodiment of the invention wherein the polyester polyols are combined
with another polyol(s) to produce polyurethane foams, the polyester
polyols can comprise about 5 to 100, preferably about 5 to 75, and more
preferably about 20 to 50, weight percent of the total polyol content in
the foam preparations. The polyisocyanurate foams of the invention are
advantageously prepared by reacting the polyisocyanate with a minor amount
of polyol, such as sufficient polyol to provide about 0.10 to 0.70
hydroxyl equivalents of polyol per equivalent of said polyisocyanate,
wherein the polyester polyol comprises about 5 to 100, and preferably
about 50 to 100, weight percent of the total polyol content in the foam
preparations.
Any suitable blowing agent can be employed in the foam compositions of the
present invention. In general, these blowing agents are liquids having a
boiling point between minus 50.degree. C. and plus 100.degree. C. and
preferably between 0.degree. C. and 50.degree. C. The preferred liquids
are hydrocarbons or halohydrocarbons. Examples of suitable blowing agents
include, among others, chlorinated and fluorinated hydrocarbons such as
trichlorofluoromethane, CCl.sub.2 FCClF.sub.2, CCl.sub.2 FCF.sub.2,
trifluorochloropropane, difluorochloromethane,
1-fluoro-1,1-dichloroethane, 1,1-trifluoro-2,2-dichloroethane,
1,1-difluoro-1-chloroethane, methylene chloride, diethylether, isopropyl
ether, n-pentane, cyclopentane, 2-methylbutane, methyl formate, carbon
dioxide and mixtures thereof. Trichlorofluoromethane is a preferred
blowing agent.
The foams also can be produced using a froth-foaming method, such as the
one disclosed in U.S. Pat. No. 4,572,865. In this method, the frothing
agent can be any material which is inert to the reactive ingredients and
is easily vaporized at atmospheric pressure. The frothing agent
advantageously has an atmospheric boiling point of -50.degree. to
10.degree. C., and includes carbon dioxide, dichlorodifluoromethane,
monochlorodifluoromethane, trifluoromethane, monochlorotrifluoromethane,
monochloropentafluoroethane, vinylfluoride, vinylidene-fluoride,
1,1-difluoroethane, 1,1,1-trichlorodifluoroethane, and the like.
Particularly preferred is dichlorodifluoromethane. A higher boiling
blowing agent is desirably used in conjunction with the frothing agent.
The blowing agent is a gaseous material at the reaction temperature and
advantageously has an atmospheric boiling point ranging from about
10.degree. to 80.degree. C. Suitable blowing agents include
trichloromonofluoromethane, 1,1,2-trichloro-1,2,2-trifluoroethane,
acetone, pentane, and the like, preferably trichloromonofluoromethane.
The foaming agents, e.g., trichlorofluoromethane blowing agent or combined
trichlorofluoromethane blowing agent and dichlorodifluoromethane frothing
agent, are employed in an amount sufficient to give the resultant foam the
desired bulk density which is generally between 0.5 and 10, preferably
between 1 and 5, and most preferably between 1.5 and 2.5, pounds per cubic
foot. The foaming agents generally comprise from 1 to 30, and preferably
comprise from 5 to 20 weight percent of the composition. When a foaming
agent has a boiling point at or below ambient, it is maintained under
pressure until mixed with the other components. Alternatively, it can be
maintained at subambient temperatures until mixed with the other
components. Mixtures of foaming agents can be employed.
Any suitable surfactant can be employed in the foams of this invention.
Successful results have been obtained with silicone/ethylene
oxide/propylene oxide copolymers as surfactants. Examples of surfactants
useful in the present invention include, among others,
polydimethylsiloxane-polyoxyalkylene block copolymers available from the
Union Carbide Corporation under the trade names "L-5420" and "L-5340" and
from the Dow Corning Corporation under the trade name "DC-193". Other
suitable surfactants are those described in U.S. Pat. Nos. 4,365,024 and
4,529,745 and supplied by Sloss Industries Corporation under the
trademarks Foamstab 100 and 200. Generally, the surfactant comprises from
about 0.05 to 10, and preferably from 0.1 to 6, weight percen | | |
