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Description  |
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BACKGROUND OF THE INVENTION
Polyurethane foams are conventionally prepared by reacting polyols with
polyfunctional isocyanates with the use of a chlorofluoroalkane as a
blowing agent. It is often desirable to prepare large quantities of the
reaction mixture, known as master batches, for the preparation of foamed
materials. Certain chlorofluoroalkanes conventionally used as blowing
agents, including trichlorofluoromethane, trichlorotrifluoroethanes, and
tetrafluorodifluoroethanes, appear to react in part with the primary and
secondary polyols to form hydrogen chloride, aldehydes, ketones and other
reaction products. These products formed by the reaction of the
chlorofluoroalkanes with the polyols adversely effect the properties of
the polyurethane foams. Accordingly, it has previously been found
desirable to incorporate stabilizers in such mixtures to prevent the
reaction of blowing agent and polyurethane precursors. Typical of those
stabilizers previously used are those shown in Bauer, U.S. Pat. No.
3,183,192.
While the stabilizers previously used to inhibit undesirable reactions in
polyurethane foam precursors have been effective in their intended use,
the stabilizers often result in an objectionable odor that persists in the
completed foam when rigid foams are prepared.
SUMMARY OF THE INVENTION
The present invention provides an improved process for the preparation of
polyurethane foams which eliminates the need for stabilizers previously
used in the preparation of such foams.
Specifically, there is provided, in the process for preparing polyurethane
foams by reaction of at least one polyol with at least one polyfunctional
isocyanate in the presence of a chlorofluoroalkane blowing agent, the
improvement wherein the chlorofluoroalkane consists essentially of
CHCl.sub.2 CF.sub.3.
DETAILED DESCRIPTION OF THE INVENTION
The blowing agent used in the instant invention is a known
chlorofluorocarbon material, 1,1-dichloro-2,2,2-trifluoroethane. This
chlorofluorocarbon is known in the nomenclature conventional to the field
as fluorocarbon 123. It can be prepared by known reaction techniques, for
example, those shown in McBee et al., Ind. Eng. Chem. 39 409 (1947).
The present process is applicable to the preparation of a wide variety of
polyurethane foams, including both rigid and flexible foams. These foams
are conventionally prepared by the reaction of organic diisocyanates with
polyols. The rigidity of the foam products is generally regulated by the
selection of the polyol material. Typical of the foams that can be used in
the invention are those shown in U.S. Pat. Nos. 3,072,582, 3,159,591 and
3,298,974.
In many cases, a small amount of water may be added to the polymerizing
mixture. The water reacts with isocyanate groups to produce an urea group
and a mole of carbon dioxide per mole of water. The carbon dioxide forms a
large number of gas cells, thus foaming the polymerizing mass. Blowing
agents, such as those of the instant invention, are usually present in
liquid form. Under the influence of the heat of polymerization, these
blowing agents volatize to gases. Water is generally not used in the
preparation of rigid insulating foams.
Catalysts are often used in the preparation of polyurethane foams,
including tertiary amines such as triethylene diamine and tin catalysts
such as stannous octanoate. Such catalysts are often used in combination
to provide a balance of properties and to insure adequate curing of the
foam. In addition, silicone surfactants are often added to the mixture of
foam components to regulate the cell size in the final foam product.
The blowing agents of the instant invention are used in quantities of about
from 1 to 30 parts per 100 parts of polyol when a flexible foam is being
prepared, and quantities of about from 15 to 40 parts per 100 parts of
polyol when rigid foams are prepared. In general, the present blowing
agents are used in substantially the same manner as
trichlorofluoromethane, fluorocarbon 11, most typically used in the past.
However, the quantity of the present blowing agents used in generally
about 11% more than the quantity of fluorocarbon 11 used to give
comparable density in the final foam product. In general, the blowing
agent is mixed with the reactants in the required proportions, and the
mixture poured into a mold of the desired configuration for the formation
of the foam. In the preparation of master batches, the blowing agent and
other components are usually combined with one of the two basic reactants,
and admixed with the second reactant just prior to the preparation of the
foam.
The instant invention provides an excellent method of preparing
polyurethane foams that exhibits unexpected advantages over previous
processes using trichlorofluoromethane. Specifically, the present blowing
agents permit the preparation of master batches of polyol and blowing
agent having excellent storage stability without the need for the
stabilizers previously considered necessary. Thus, the inconvenience and
expense of adding the stabilizers to the master mixture is eliminated, as
well as the undesirable residual odor often resulting from the stabilizers
previously incorporated.
The invention is further illustrated by the following specific examples, in
which parts and percentages are by weight unless otherwise indicated.
EXAMPLE 1
A flexible polyurethane foam was prepared using
1,1-dichloro-2,2,2-trifluoroethane as a blowing agent. The following
ingredients in the stated porportions were mixed rapidly in a high-speed
mixer for 15 seconds:
##STR1##
The mixture was quickly poured into an open-top container and allowed to
expand.
The foam obtained had a density of 0.022 g cm.sup.-3 ; indent load
deflection at 65% deflection, according to ASTM Method D1564 (1971) was
227 Newtons per 3.2 dm.sup.2.
EXAMPLES 2-3
In Examples 2 and 3, 1,1-dichloro-2,2,2-trifluoroethane was used in the
preparation of rigid polyurethane foams employing a polyvinyl polymeric
toluene diisocyanate and a polymeric methylene phenylisocyanate,
respectively.
A master batch was prepared by mixing the following ingredients in the
proportions shown:
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Proportion (Wt. %)
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Polyoxypropylene octol.sup.(1)
73.1
Silicone fluid.sup.(2)
1.1
Triethylenediamine.sup.(3)
1.0
1,1-dichloro-2,2,2-Trifluoroethane
24.9
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.sup.(1) Condensation product of propylene oxide and sucrose obtained
from Pittsburgh Plate Glass Corp. under the trade name of
"Selectrofoam" 6402 and having the properties:
Hydroxyl number mg KOH/g
450
Equivalent Weight 125
Viscosity, Brookfield, 25.degree. C, cps
30,000
Water content, percent 0.15
Specific Gravity 1.15
.sup.(2) Cell size regulator obtained from Dow-Corning Co. under the
trade name Silicone Fluid DC-193, a silicone-glycol copolymer
having the properties:
Viscosity at 25.degree. C, centistokes
465
Specific Gravity at 25.degree. C
1.07
Refraction Index, 25.degree. C
1.4515
Color, Gardner Scale 2.
.sup.(3) Catalyst.
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In Example 2, one part by weight of the master batch was admixed with 0.75
parts of polyvinyl polymeric toluene diisocyanate.* The mixture was poured
into a rectangular open-top aluminum panel mold preheated to 50.degree. C.
The foam completed its rise in 90 seconds. The finished rigid foam panel
had a core density of 0.039 g cm.sup.-3.
*Obtained from E. I. du Pont de Nemours and Co., Inc. as "Hylene" TRF
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Physical Form clear, dark
brown liquid
NCO content 34.4 .+-. 0.5
Amine equivalent 122.2 + 1.8
Viscosity, 25.degree. C, cps
300-1100
Total Acidity, max. % 0.04
Specific Gravity 25/4.degree. C
1.27 .+-. 0.02.
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In Example 3, one part by weight of the master batch was vigorously mixed
for 11 seconds with 0.78 parts of a polymeric methylene phenylisocyanate**
and molded as in Example 2. The foam completed its expansion in 80
seconds. The core density of the rigid foam was 0.034 g cm.sup.-3.
**Prepared by phosgenation of aniline-formaldehyde condensation product
and obtained from the Mobay Corp. as "Mondur" MR.
EXAMPLE 4 AND COMPARATIVE EXAMPLE A
Simultaing commercial practice, 70 parts by weight of a basic polyether
polyol.sup.(1) was mixed with 30 parts by weight of
1,1-dichloro-2,2,2-trifluoroethane and the mixture was placed in a closed
tin-plated can. After accelerated 10-week storage at 55.degree. C, a
representative sample of the mixture was titrated with standard aqueous
potassium hydroxide to phenolphthalein endpoint. Per gram of mixture 0.95
mg of KOH was consumed. The mixture performed normally in the preparation
of foamed polyurethane foam therefrom.
.sup.(1) Obtained from Jefferson Chemical Co. under the trademark "Thanol"
R-350X.
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Hydroxy number, mg KOH/g
520-540
Equivalent weight 106
Viscosity, 25.degree. C, cps
12,000-17,000
Water content, percent 0.1
Specific Gravity, 20.degree./20.degree.
1.116.
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In Comparative Example A, the procedure of Example 4 was repeated, except
that trichlorofluoromethane was used instead of CHCl.sub.2 CF.sub.3. After
storage, the trichlorofluoromethane underwent decomposition requiring 7.5
mg of KOH per gram of mixture. The mixture was black and polyurethane foam
could not be prepared therefrom.
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