Note: Descriptions are shown in the official language in which they were submitted.
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.
EXPANDABLE RUBBER/RESIN BLEND AND RESULTING FO.~I
BACKGROUND OF THE INVENTION
The resin/rubber blend of -the present invention is useful f
in making unusually low density foams of a predominantly closed cell
5 structure. In the form of sheets and hollow cylinders, these~ 10W .
density, closea cell foams serve as excellen-t heat insulating material.
~hen appropriately shaped, the foams serve as expansion joint and
sealers generally
In all of these applications, it is the general rule that
10 the lower the density, the better the product, provided strength,
structural integrity, and improved thermal conductivity can be main-
tained during the useful life of the product. Since it is generally
true that the product becomes more flimsy as the density is diminished,
it has been necessary to use higher density foams in order to maintain
15 performance characteristics. Typical products made from resin/rubber
blends in the past have had densities in the range of about 4.5-6
pounds/cu. ft. These products have generally been satisfactory.
- However, by virtue of the resin/rubber blend of the present inven-
tion, densities in the range of 1.8-4 pounds/cu. ft. are readily
obtainable, and commercial products having densities of about 3 pounds/
cu. ft. may be routinely produced reproducibly. These lower density
products have improved thermal conductivity, in addition to the
obvious advantages of cost savings of material and shipping.
Description of the Prior Art
The patent best exemplifying the prior products is U. S.
2,849,028-Clark et al. This patent teaches use of a two-component
resin/rubber blend to form predominantly closed cell products having
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the same utility as the products contemplated by the present inven-
tion. The resin/rubber ratios have changed over the years, and the
actual resins and rubbers have also varied over the years in the
production of these two-component systems. These are the products,
with their densities in the range of about 4.5-6 pounds/cu. ft., that
- have been the standard in the industry.
U. S. 2~788,333-Lewis et al. also shows a two-component
resin/rubber blend for making a foam product.
Other patents disclose various modifications of resin/rubber
blends, including mixtures of polyvinyl chloride, butadiene-acrylo-
nitrile rubbers to form foamed products.
SUMMARY OF THE INVENTION
A resin/rubber blend adapted to form substantially closed
cell, low density foams in the range of about 1.8-4 pounds/cu. ~t. on
being blown at elevated temperature by means of a chemical blowing;
agent, the blend comprising relative portions of 100 parts by weight
of a nitrile-butadiene rubber containing about 20-45 percent by
weight of acrylonitrile; 40-200 parts by weight of a vinyl chloride
resin which may be polyvinyl chloride, a vinyl chloride-vinyl acetate
20 copolymer, or mixtures thereof; and about 25-200 parts by weight
polymethylmethacrylate (PMMA), with the proviso that the PMMA be
present in the blend in an amount of at least 9 percent by weight of
the total blend.
PREFERRED EMBODIMENT OF THE INVENTION
The butadiene-acrylonitrile rubber (NBR) useful in the
present invention is a standard item of commerce. The Mooney viscosity
generally runs between 25 and 90. The NBR will contain between 20
and 45 percent by weight acrylonitrile, with an average of about 30
percent by weight. It is purchased and used in the present invention
in the form of a dry rubber. In describing the resin/rubber blend of
the present invention, it is convenient to base everything on 100
parts by weight of the NBR. The phrase "relative proportions" as
used herein simply means that the amounts of the several ingredients
are adJusted on a basis of 100 parts by weight NBR, no matter what
actual weight of the NBR is actually used. In some instances, as
will be seen in the examples, a 70/30 NBR/resin mixture is used, but
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the critical ingredients will be calculated out as if 100 parts by
, weight NBR were used.
The second ingredient in the resin/rubber blend of the
present invention is a vinyl chloride resin. This term includes the
homopolymer polyvinyl chloride and the copolymer vinyl chloride-vinyl
acetate. The polyvinyl chloride (PVC) are standard items of commerce
made by solution, suspension, or emulsion polymerization and are
generally considered to be low molecular weight with a relative
- viscosity up to about 2.2. The PVC is sold and used in the ~orm of a
white powder.
The vinyl chloride-vinyl acetate copolymer (VCVA) contains
about 1.5-20 percent by weight vinyl acetate, and usually contains
10-15 percent by weight. It, too, is a standard item of commerce and
is sold and used in the present invention in the form of a white
powder. - - ~
To achieve the unusually low density foams of the present
-invention, the PVC or the VCVA must be used in an amount of about 40-
200 parts by weight for each 100 parts by weight of the NBR. This
amount of 40-200 parts by weight of this resin may constitute 100%
PVC or 100% VCVA. Put another way, either of these two vinyl chloride
resins functions adequately in the present invention to allow the
production of these unusual foams. Since either of the two vinyl
chloride resins may be used -to the exclusion of the other, it is
apparent that mixtures of the two can be used in which the mixture
will range from a mere trace of one in almost 100% of the other, all
the way to the exact reverse situation. As a practical matter, it is
usually preferable to use a mixture o~ the two vinyl chloride resins,
and the mixture would usually be about 1:1. This 1:1 ratio will
often be varied according to the existencies of local supplies, local
forming equipment,-the views of the foreman running the line, and
other such intangibles. Most often, the ratio PVC:VCVA will fall in
the range 70:40 to ~0:70.
The final ingredient in the resin/rubber blend of the
present invention, and the one which primarily allows the production
of these unusually low density foams, is the P~A. Again, the PMMA
is an item of commerce sold and used in the form of a free-flowing
white powder. It is sometimes sold and mixed with small amounts of
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copolymers of methylmethacrylate, but these normally have little or
no effect on the presen-t invention. It is preferred that over half
of the PM~LA powder pass through a 200 mesh screen, since the smaller
particle size appears to aid in forming a good blend. The molecular
weight of these Pl~LA~s normally varies around a central point of
about l,000,000; and useful P~A's are sold in a molecular weight
range of` about 700,000 to about 1,250,000. These PMMA's are normally
sold as processing aids for PVC. Their presence in small amounts
aids the physical processing of PVC's when the PMMA is present in an
amount of 1-2 percent by weight of the PVC, up to a maximum 5 percent
by weight. The amount of P~A to be used in the present invention
- will be in the range of about 25-200 parts by weight P~A per lO0
parts by weight ~BR, with the proviso that the resin/rubber blend
- contain at least 9 percent by weight Pk~L~ of the total composition of
NBR, vinyl chloride resin, and P~L~. It is the addition of the P~LA
to the NBR/vinyl chloride resin system, in the amounts defined herein,
that allows the production of the substantially closed cell, unusually
low density foams of the present invention.
The compounding of the resin/rubber blend of the present
invention, as well as -the compounding of the entire foamable system
in which it is used, may proceed in conventional manner. Rubbers,
resins, fillers, plasticizers, waxes, fire retardants, smoke sup-
pressants, and any other conventional ingredients in these foams
would normally be first blended on a mill or a Banbury in accordance
with conventional procedures. The rubber may first be broken down,
if desired, and any other of these ingredients then added. ~1hen that
portion of the final composition is sui-tably mixed, the curing agent
system and the blowing agent may then be added. The point is, nothing
iN the resin/rubber blend of the present invention calls for special
handling beyond that normally used in the art of blending rubbers and
resins to make foamable mixtures.
At the same time, the resin/rubber blend of the present
invention lends itself to compounding to achieve in the finished foam
product any particular or special properties normally obtained in
such products having the conventional higher density. Variations in
plasticizers and in the amounts of plasticizers will produce varia-
tions in the softness or rigidity of the resulting foam according to
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conventional standards. Pigments can be added as desired to achieve
any needed coloring. Flame resistance and smoke suppression can be
taken into account in compounding in the usual ways. The conventional
filler to be used will include the clays, finely ground or precipi-
tated calcium carbonate, silicates, the carbon blacks, hydratedalumina, titanium dioxide, and other suitable fillers.
The blowing agent to be used will be any of the known,
nitrogen-producing, chemical blowing agents to produce a closed cell
structure. Such blowing agents include dinitroso pen-tameth~lene
tetramine, p,p' oxybis (benzene sulfonyl nydrazide), benzene sulfonyl
hydrazine, p-toluene sulfonyl semicarbazide, and, preferably,
azodicarbonamide.
Curing agent systems may be any of those thoroughly under-
stood in the art to produce foamed products from resin/rubber blends.
The plasticizers are conventional and may include tricresyl
phosphate, dibutyl phthalate, di-2-ethylhexyl phthalate, butyl phthalyl
- butyl glycolate, dibutyl sebacate, and the like. Lubricants may be
stearic acid, the paraffins, ceresin wax, or wax mixtures. Fire
retardants include antimony trioxide, chlorinated paraffins, and
other metal oxides.
- Once the completed-composition has been prepared, it may be
shaped as desired. To form pipe insulation, standard extruders may
be used to extrude hollow cylinders in the desired sizes. Sheets may
be formed by extruding, calendering, or molding. Specially shaped
objects may be formed by molding.
Once the finished composition has been shaped into the
desired form, it will be heated to a temperature sufficient to de-
compose the blowing agent and cure the system. As is known, these
systems expand linearly in that the finished, foamed dimensions
consistently bear a constant relationship to the unfoamed composition.
Tempera-ture for expansion and cure will normally be in the range of
about 220-360F., depending to a large extent on the thickness of
the unfoamed composition to be expanded. Depending on the exact
thickness dimension, sheets may be expanded at around 290F. and
tubes can be expanded at around 31~0F., on an average.
As mentioned earlier, the principal advan-tage of the
present invention is the ability to form unusually low density
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products in a reproaucible manner. The present products show a
significant improvement in smoke density on burning by virtue both of
the low density of the product and the presence of the P~A. At the
same time, the thermal conductivity of the products used in heat
insulation improves from a prior value of about 0.27 to a new value
of about 0.25 Btu. in./hr. ft. F.
The following example illustrates several embodiments of
the invention.
- Example I
The following formulation and compounding procedure is con-
ventional and well known in the art.
The following ingredients were placed in a Banbury, blended
to a temperature in the range of 235-290F., and cooled:
Parts by
Ingredients Weight
NBR/PVC blend 70/30 100
stearic acid
magnesium silicate 60
carbon black 10
Kaolin clay 30
dioctyl phthalate 20
octyl diphenyl phosphate 15
wax blend 2
diphenylamine-diisobutylene
reaction product 2
The following ingredients in the amounts stated were then
added and blended to a temperature in the range of 100-200F:
Parts by
Ingredients Weight
zinc oxide 5
surface coated urea 1.5
azodicarbonamide 20
benzothiazole disulfide 0.8
zinc diethyl dithiocarbonate o.8
diorthotolyl guanidine 0.8
sulfur 2.5
.
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The finished composition represents a known and conventiona]
foamable composition for producing, on appropriate hea-ting, closed
cell products having a density in the range of about 4.5-6 pounds/
cu. ft.
Example II
A series of nine compositions was made up, including the
composition of Example I as a control and as a representative of
prior technology. The compositions other than the control were
- varied by the addition of PMMA or vinyl chloride resin or additional
blowing agent to illustrate the parameters of the invention. While
each composition contains lO0 parts by weight of a 70/30 mixture of
~BR/VCVA, the addition of further VCVA change the proportions. The
mixing procedure was the same for all nine compositions, and the
final composition was extruled to form a hollow tube which was then
15 free-blown at a temperature in the range of 250-340F. to form pre-
dominantly closed cell tubes. The following table shows the di~fering
- formulas and the results in each case.
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Following are the commentary on each of the above runs:
Run 1 produced a good tube, conventional of -the prior art,
and having about the lowest reproducible density of the prior art o~
4.5 pounds/cu. ft.
Run 2 produced a product ha~ing longitudinal splits down
the outer surface, and different portions of the same run produced
tubes of differing density and size. This Run 2 illustrates the
point that it is not possible to achieve lower density tubes in prior
resin/blend mixtures simply by increasing the amount of blowing agent
used.
Runs 3 and 4 produced tubes having no improvement in density
and having longitudinal splits rendering the tubes unsatisfactory,
illustrating the effect of insufficient PMMA.
Runs 5, 6, 7, and 8 produced good, reproducible, low density
tubes.
Run 9 produced a good, usable tube and illustrates the
- point that reduced blowing agent did not take the tube out of the
very low density range.
Example III
To illustrate use of a vinyl chloride resin consisting
solely of VCVA, the following resin/blend composition was prepared in
the usual manner:
Parts by
Ingredients Weight
25 NBR 95
polybutadiene (processing aid) 5
VCVA 110
P~A 4
This resin/blend composition was compounded in the usual
way with the usual fillers, plas-ticizers, fire retardants, wax blend,
azodicarbonamide blowing agent, and a curing system. The final
foamable composition was extruded in the form of tubes and heated and
expanded in the usual manner to form a predominantly closed cell
tube. The tubes were excellent in appearance, soft and flexible,
reproducible, and had a density of 3.3 pounds/cu. ft.
