Note: Descriptions are shown in the official language in which they were submitted.
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LOW DENSITY CELr,ULRR POT.YVIWYL CHLORIDE
Field of the Invention
The present invention relates to expanded or
foamed vinyl chloride resins and, more particularly, is
directed to foamable blends of polyvinyl chloride resin
and a rubber which is adapted to be expanded to provide
flexible, cellular products having a substantially
closed-cell cellular system~ .
Background of the Invention
Cellular products such as sheets and tubes of
expanded blends of polyvinyl chloride resin and certain
rubbers have achieved wide use as insulating materials,
particularly or pipe insulation.
Expandabl~ blends of polyvinyl chloride resin
and certain rubbers that provide ~oamed prod~lcts having
a closed cell system are described in, for example, U.S.
Patent Nos. 2,849,028~and 4,245,055. In general, the
aforementioned patents disclose a method of incor-
porating a blowing agent into a foamable resin/rubber
blend which can be heated to decompose the blowing agent
and thereby provide an expanded cellular object without
the use of an~ forming molds. For instance, U.S. Patent
No. 2,849,028 discloses blends of polyvinyl chloride
resin and butadiene-acrylonitrile copolymer rubber that
are freely expanded at a temperature of about 300 F. to
provide cell~lar products useful for pipe insulation~
U.S. Patent No. 4,245,055 disc~loses similarly prepared
cellular products prepared from a blend which includes
polymethylmethacrylate.
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Sl~mmary of the Invention
According to the present invention there is
provided a resin blend adapted to be expanded to provide
a cellular product, said blend comprising: (a) between
about 40% and about 80% by weight of a vinyl chloride
resin, e.q., polyvinyl chloride; (b) between abo~t 5%
and about 40% of a rubber, e.g. b~tadiene-acrylonitrile
rubber; and, (c) a polyfunctional monomer, e.g.,
styrene. Preferably, the poly~nctional monomer is
selected from the group consisting of trimethylolpropane
trimethacrylate, diallyl phthalate or styrene, and is
present in an amount between about 5~ and about 40% by
weight, wherein all aforementioned weight percentages
are based upon the total weight of components (a), (b)
and (c).
According to the present invention ti~ere is
further provided a cellular structure comprising between
about 40% and about 80% by weight of a vinyl chloride
resin; between about 5~ and abo~t 40% by weight of a
rubber; and between about 5% and abo~t 40% by weight of
a polyfunctional monomer wherein said we;ght percentages
are based upon the total weight of said resin, rubber
and monomer. The cellular produc~ of the presènt
invention may be either flexible or rigid and of either
a closed cell or open cell cellular structure.
Preferred Embodiment of the Invention
The vinyl chloride resin component of the
blends of the present invention includes homopolymers
such as, for example, polyvinyl chloride (PVC) and copo-
lymers such as, for example, copolymers of vinylchloride-vinyl acetate (VCV~). The PVC and VCVA resins
are standard articles of commerce which are readily
available in the form of a white powder. Suitable PVC
and VCVA resins useul for preparing foamable blends of
the present invention include, for example, the
following: Geon~ 121 resin (B. F. Goodrich Company);
FPC 4301 re-sin (Firestone Company).
The vinyl chloride resin component is present
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in the blc-nds of the present invention in an amount
between about 40% and about 80~ by weight, preferably
about 60% by weight. For instance, mixtures of PVC and
VCVA may be used at the preferred quantity of 60% by
weight wherein the ratio of VCVA:PVC is 301. The
relative amounts of the VCVA and PVC components can be
varied widely to achieve desired prod~ct properties.
For example, increasing the amount of the VCVh copolymer
provides cellular structures having lower softening
temperatures ~hich would be advantageous when
thermoforming the cellular structures. On the other
hand, higher amounts of the PVC homopolymer provide
cellular products having higher softening temperatures.
The rubber component of the foamable blend of
the present invention includes copolymers of b~tadiene
such as, for exa,nple, a butadiene-styrene copolymer and
a butadiene-acrylonitrile copolymer. Suitable hutadiene
rubbers for use in the blends o the present invention
include, for example, the following: Paracril~ B
acrylonitrile-butadiene copolymer (Uniroyal, Inc.);
Hycar 1022 acrylonitrile copolymer tB. F. Goodrich
Chemical Company).
The butadiene rubber component is present in`
the blenas of the invention in an amount between about
5% and 40~ by weight, preferably 25% by weight
Cellular products having greater flexibility and
resilience are obtained when using higher quantities of
the rubber component. Likewise, cellular products
having gr~eater rigidity are obtained when using lower
quantities of the rubber component.
The polyfunctional monomer that constitutes an
essential ~eature of the blends of the present invention
includes monomers such as, for example,
trimethylolpropane trimethacrylate, styrene and diallyl
phthalate. Suitable liquid polyfunctional monomers for
use in the blends of the present invention include, for
example, the following: SR-350 (Sartomer Resins, Inc.);
DAP Monomer (FMC Corporation); and Styrene Monomer, SM
(Monsanto Compahy).
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The polyfunctional monomer is present in the
blends of the invention in an amount between about 5%
and abo~t 40%, preferably 25% by weight. Greater ease
of processability of the resin blend is obtained when
using the higher q~antity of the poly~unctional mono~er.
A significant feat~re and advantage of the
resin blend of the present invention is that the
p~lyfunctional monomer component acts as a plasticizer
which provides for greater ease of processability
mentioned above. Also, the polyfunctional monomer
component results in cellular products of very low
density (e.g., cellular products having a density below
- one pound per cubic foot have been obtained). Thus, the
polyfunctional monomer enables the manufacture of
cellular products that are both rigid and of low
density.
- If desired, any of-the plasticizers normally
used with resin or rubber systems may be incorporated
into the blends of the present invention. The
high-boiling esters, ethers, and ketones, for example,
tricresol phosphate, dibutyl phthalate, di-2-ethylhexyl
phthalate, butyl phthalyl butyl glycolate, dibutyl
sebacate, and the like are suitable. Generally
speaking, the amount of plasticizer is not critical.
The amount of plasticizer normally used to give good
workable compositions will suffice in the present case.
As is well known, too large an amount of plasticizer
will yield a soft product having extremely flexible cell
walls. m e amount of plasticizer will generally range
between 5 and 60 parts by weight per 100 parts by weight
rubber and preferably 30-50 parts by weight per 100
parts by weight rubber. Incorporating additional
plasticizers into the blends of the invention is not
necessary when making rigid cellular products
therefrom.
Lubricants such as stearic acid, including
waxes such as paraffin or ceresin wax or wax mixtures,
may be used in small amounts. Chlorinated paraffins
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which generally contain 38%-70% chlorine can be used as
a combination plasticizer and fire-retardant agent,
particularly where antimony trioxide is ~sed as part o~
the ~iller system. Other chlorinated plasticizers are
suitable.
Various fillers may be incorporated into the
blends of the invention in order to impart desired
properties to the final prod~ct. Exa~ples of s~ch
fillers are limestone, Tio2~ slate flour, clay, silica,
and carbon black. The total amount of filler will
generally run about 5-150 parts by weight per 100 parts
by weight rubber and, preferably, will be between 35-45
parts by weight per 10~ parts by weight rubber.
Mixtures of fillers can be used if desired. It is often
convenient to incorporate antimony trioxide as part or
all of the iller system in order to impart flame
resistance to the final cellular product. The antimony
trioxide is preferably used in an amount of about 10-20
parts by weight per 100 parts by weight rubber,
Pigments may be incorporated in order to impart the
desired color to the ~inal product; products having
di~erent colors are useful in keying a piping system to
aid in the identification of the substances carried by
the individual pipe lines~ Where a black prod~ct is
needed, carbon black may be incorporated to strengthen
the final product, as well as to impart a uniform dead
black color to the final product.
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
incluae dinitroso pentamethylene tetramine, p,p' oxybis
(benzene sulfonyl hydrazide), benzene sulfonyl
; hydraæine, p-toluene sulfonyl semicarbazide, and,
preferably, aæodicarbonamide~
3S Curing agent systems may be any of those
thoroughly understood in the art to produce foamed
products from resin/rubber blends. For instance, sulfur
can be used to cure the rubber component of the resin
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blend of the invention. Al so, conventional accelerator
systems such as benzothiazole disulfide, zinc diethyl
dithiocarbamate and diorthotolyl q~anidine can be used.
Cross-linking agents such as, for example,
benzoyl peroxide, can be utilized to ensure
substantially complete cross-linking of the
polyfunctional monomer. For instance, the benzoyl
peroxide can be added to the resin blend at the same
time that the sulfur curing agent is added.
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
suppressants, and any other conventional ingredients in
these foams would normally be first blended on a mill or
a ~ anbury in accordance with conventional procedures,
The rubber may first be bro~en down, if desired, and any
o~her of these ingredients then added. When the p~rtion
of the inal composition is suitably mixed, the curing
~agent sys~em 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 inished foam product any particular or
special properties normally obtained in such products
having the conventional higher density.
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
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temperature sufficient to decompose the blowing agent
and cure the systemO As is known, these systems expand
linearly in that the finished, foamed dimensions
consistently bear a constant relationship to the
dimensions of the unfoamed composition. Temperature for
expansion and cure will normally be in ~he range of
about 220~-360 F.
The principal advantage of the blends of the
present invention is the ability to form unus~ally low
density products in a reproducible manner. Cellular
products having a density as low as 0.9 pounds per cubic
foot have been obtained.
The thermal conductivity of the low density
cellular products of the invention are lower and thus
improved,when compar,ed to high density cellular
products.
' The following examples illustrate several
emb~diments of the invention.
EXAMPLES I-III
The ~ollowing formulations can be compounded
by conventional procedures well known in the art.
The following ingredients can be placed on a
mill or in a Banbury mixer and blended at a tèmperature
below about 250 F duriny the conventional first process
stage. The master batch product~of Process Stage I is
further processed in Stage II on a mill or in a Banbury
mixer at a temperature below about 200 F.
, ~ Example Example Example
Ingredients I II III
Process Stage I
Butadiene - Acrylonitrile 25 25 25
PVC 25 25 25
VCVA ' , 75 ~75 75
Trimethylol Propane Trimethacrylate 40 - -
35 Styrene Monomer - 40
Diallyl Phthlate Monomer - - 40
Polyethylene Glycol- 2.5- ' 2.5- 2.5~ ~'
Calci-um Carbonate 5 5 5
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Example Example Example
Ingredients I II III
Process Stage II
Azodicarbonamide 31 31 31
5 Sulfur 2 2 2
Zinc Oxide . 2.5 2.5 2.5
Zinc Dimethyl Dithiocarbonate 0.5 0.S 0.5
Dipentamethylene Thierium
Hexa Sulfide 0.5 0.5 0~5
The milled or mixed final batch of Stage II can be
extruded in a conventional manner at a temperature
. between about 125~ F and about 225 F. m e shaped
product can be expanded by heating at a temperature of
between about 200 F and about 360 ~ to provide the
cellular products of the invention.
