U.S. patent application number 09/435514 was filed with the patent office on 2002-01-03 for flame retardant insulation compositions having improved high temperature performance.
Invention is credited to LEE, LESTER Y..
Application Number | 20020002221 09/435514 |
Document ID | / |
Family ID | 23728710 |
Filed Date | 2002-01-03 |
United States Patent
Application |
20020002221 |
Kind Code |
A1 |
LEE, LESTER Y. |
January 3, 2002 |
FLAME RETARDANT INSULATION COMPOSITIONS HAVING IMPROVED HIGH
TEMPERATURE PERFORMANCE
Abstract
Flame retardant compositions useful as insulation for
150.degree. C.-rated wire and cable applications are provided. The
compositions of the invention utilize an ethylene-alkyl acrylate
copolymer base resin with a two-component stabilizer package
consisting of a zinc salt of a mercaptobenzimidazole and an
aromatic secondary amine compound. Also, included to achieve the
requisite flame retardance, crosslinkability and physical
properties are a brominated flame retardant, antimony trioxide, a
hydrated inorganic filler and a chemical crosslinking agent.
Inventors: |
LEE, LESTER Y.; (HAMILTON,
OH) |
Correspondence
Address: |
GERALD A BARACKA
EQUISTAR CHEMICALS LP
11530 NORTHLAKE DRIVE
CINCINNATI
OH
45249
|
Family ID: |
23728710 |
Appl. No.: |
09/435514 |
Filed: |
November 8, 1999 |
Current U.S.
Class: |
524/93 ; 524/225;
524/229; 524/255; 524/258; 524/281; 524/305; 524/387; 524/411;
524/412; 524/436; 524/562; 524/94 |
Current CPC
Class: |
C09K 21/14 20130101;
H01B 7/295 20130101 |
Class at
Publication: |
524/93 ; 524/94;
524/225; 524/229; 524/255; 524/258; 524/411; 524/412; 524/436;
524/562; 524/281; 524/305; 524/387 |
International
Class: |
C08L 001/00 |
Claims
I claim:
1. A crosslinkable, flame retardant composition useful for high
temperature service wire and cable insulation comprising: (1) 30 to
65 weight percent of a base resin which is a copolymer of ethylene
and 3 to 40 weight percent alkyl acrylate having the formula 7
wherein R' is C.sub.1-4 alkyl and R" is hydrogen or methyl having a
melt index of 0.1 to 15 g/10 mins; (2) 1 to 10 weight percent of a
stabilizer consisting of a mixture of a zinc salt of a
mercaptobenzimidazole of the formula 8 where R is a C.sub.1-4 alkyl
group and n is 0 to 4 with a secondary aromatic amine, the ratio of
the zinc mercaptobenzimidazole compound to the secondary aromatic
amine ranging from 0.2:1 to 20:1; (3) 5 to 40 weight percent
brominated aromatic flame retardant compound; (4) 1.5 to 20 weight
percent antimony trioxide; (5) 5 to 50 weight percent hydrated
inorganic filler; and (6) 0.1 to 4 weight percent chemical
crosslinking agent.
2. The composition of claim 1 which additionally contains a
crosslinking coagent selected from the group consisting of
triallylcyanurate and trimethylolpropane trimethacrylate.
3. The composition of claim 1 which additionally contains an
alkoxysilane binding agent having 2 or 3 C.sub.1-3 alkoxy
substituents.
4. The composition of claim 1 wherein the base resin is an
ethylene-n-butyl acrylate copolymer; the aromatic secondary amine
has the formula 9where R.sub.1 is an aryl group of the formula
10wherein R* is alkylene, alkylidene, --O--, --NH-- or --SO.sub.2--
and R** is hydrogen or C.sub.1-4 alkyl and R.sub.2 is hydrogen,
alkyl, aryl, alkaryl, aralkyl or R.sub.1; and the chemical
crosslinking agent is a tertiary organic peroxide.
5. The composition of claim 4 wherein the zinc
mercaptobenzimidazole is selected from the group consisting of zinc
2-mercaptobenzimidazole and zinc 2-mercaptotolylimidazole.
6. The composition of claim 5 wherein the ratio of zinc
mercaptobenzimidazole to aromatic secondary amine is 0.5:1 to
10:1.
7. The composition of claim 4 wherein the hydrated inorganic filler
is magnesium hydroxide.
8. The composition of claim 4 wherein the tertiary organic peroxide
is selected from the group consisting of dicumyl peroxide and
.alpha.,.alpha.'-bis(t-butylperoxy)diisopropylbenzene.
9. The composition of claim 4 containing 42 to 52 weight percent
base resin, 2.5 to 9 weight percent stabilizer, 10 to 15 weight
percent brominated aromatic flame retardant, 3 to 6 weight percent
antimony trioxide, 20 to 35 weight percent magnesium hydroxide and
1 to 2 weight percent tertiary organic peroxide.
10. The composition of claim 9 wherein the base resin has a melt
index of 0.3 to 10 g/10 min and contains 10 to 30 weight percent
n-butyl acrylate; the zinc mercaptobenzimidazole is selected from
the group consisting of zinc 2-mercaptobenzimidizole and zinc
2-mercaptotolylimidazole; R* is --CH.sub.2--, --CH.sub.2CH.sub.2--,
--C(CH.sub.3).sub.2--, --NH-- and --NH--SO.sub.2-- and R** is
hydrogen or methyl; the brominated aromatic flame retardant is
ethylene bistetrabromophthalimide; the hydrated inorganic filler is
magnesium hydroxide; and the tertiary organic peroxide is selected
from the group consisting of dicumyl peroxide and
.alpha.,.alpha.'-bis(t-butylperoxy)diisopropylbenzene.
11. The composition of claim 10 wherein the zinc
mercaptobenzimidazole is zinc 2-mercaptotolylimidazole, the
aromatic secondary amine is BDBDA and the ratio of zinc
2-mercaptotolylimidazole to 4,4'-bis(.alpha.,.alpha.-di-
methylbenzyl)diphenyl amine is 1:1 to 6:1.
12. An insulated conductor coated to a wall thickness of 2 to 100
mils with the flame retardant insulation composition of claim
1.
13. The insulated conductor of claim 12 wherein the conductor is 1
to 30 AWG copper or aluminum wire.
14. The insulated conductor of claim 13 wherein the flame retardant
insulation composition is crosslinked.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates to improved crosslinked polymeric
compositions used as insulation for wire and cable products. More
particularly, the invention relates to flame-retardant
ethylene-alkyl acrylate copolymer formulations used as wire and
cable insulation for applications where high service temperatures
are required.
[0003] 2. Description of the Prior Art
[0004] Fire resistant polyolefin compositions are widely used for
wire and cable insulation. In electrical environments both
insulating and fire resistant properties are considered to be
essential. Additionally, the compositions must be readily
processable and should not deteriorate under the service
conditions.
[0005] A widely used fire retarding insulation for wire and cable
is comprised of a crosslinkable polymer, such as polyethylene or
ethylene-vinyl acetate copolymer, one or more stabilizers or
antioxidants, one or more hydrated inorganic fillers, and a
crosslinking agent. Other additives such as pigments, processing
oils, lubricants and coupling agents can also be included in these
formulations. Compositions of this type which find use as single
layer insulation and jacketing for copper wire are disclosed in
U.S. Pat. Nos. 3,832,326 and 3,922,442 to North et al., and U.S.
Pat. Nos. 4,349,605 and 4,381,362 to Biggs, et al.
[0006] For applications involving high service temperatures, such
as 150.degree. C. rated wires for use in ovens, water heaters,
dryers, toasters, cookers and "under-the-hood" automobile uses,
numerous compositions based on crosslinked polyethylene were
developed capable of meeting the tensile strength and percent
elongation retention requirements under the initial test criteria
which specified aging at 158.degree. C. for 90 days. However, as
test conditions became more stringent in recent years, extending
the aging period of 150 days in UL Standard 1581 (Style 3321), few
of these original formulations were capable of meeting the more
rigorous test conditions--particularly when copper wire was being
insulated. Copper has been reported to catalyze the auto-oxidation
of polymers (see Z. Osawa, Polym. Deg. And Stab., 20, 203-236
(1988)) and, at the elevated temperatures encountered in severe
service applications, it is believed copper I and II ions further
accelerate the decomposition of polymer hydroperoxides to chain
propagating radical species.
[0007] Accordingly, there is a need for effectively stabilized
flame retardant insulation compositions which are readily
processable yet capable of retaining tensile and elongation
properties upon long term aging at elevated temperatures,
particularly in the presence of copper.
[0008] The use of benzimidazoles to stabilize polyolefin
compositions, particularly polyethylene and polypropylene, is
known. U.S. Pat. No. 3,218,276 discloses the use of alkyl
benzimidazole to stabilize fiber-forming polyolefins. Polypropylene
fiber-forming compositions containing 0.2 to 2.0 percent
benzimidazole with other conventional additives are disclosed. U.S.
Pat. No. 2,997,456 teaches the use of metallic
mercaptobenzimidazole compounds as stabilizers for polymers of
1-olefins, primarily polypropylene, to protect against molecular
degradation under conditions of elevated temperature and/or
mechanical working and zinc mercaptobenzimidazole is specifically
mentioned.
[0009] The use of combinations of and hindered phenols with various
zinc salts of mercapto compounds to provide stabilization of cured
and crosslinked polyolefins utilized as insulation for electrical
conductors is disclosed in U.S. Pat. Nos. 4,260,661, 4,693,937,
4,797,323 and 4,824,883. For example, combinations of IRGANOX 1010
with the zinc salt of 2-mercaptobenzimidazole (ZMB), the zinc salt
of 2-mercaptotolylimidazole (ZMTI) and the zinc salt of
2-mercaptobenzothiazole (ZMBT) are all illustrated. U.S. Pat. No.
4,459,380 discloses combining a sterically hindered phenol with a
zinc salt of a mercaptoimidazole to stabilize crosslinkable curable
ethylene-propylene rubber compositions. All of the references
provide for the inclusion of other conventional additives, such as
Sb.sub.2O.sub.3, halogenated compounds, fillers, silanes and
crosslinking agents in the formulations. It is mentioned that
ethylene copolymers, including ethylene-acrylate copolymers, can be
stabilized using these zinc salt/hindered phenol combinations. U.S.
Pat. No. 5,196,462 also shows the use of these combinations to
stabilize thermoplastic elastomers and indicates that other
antioxidants, such as phenols, thiodipropionates and quinolines may
also be present.
[0010] Rubber/silicone compositions containing a metal
benzimidazole, an aromatic secondary amine, an organopolysiloxane
oil and organic peroxide are disclosed in U.S. Pat. No.
4,808,643.
SUMMARY OF THE INVENTION
[0011] It is an object of the present invention to provide improved
crosslinkable, flame retardant polymeric compositions based on
ethylene-alkyl acrylate copolymers which have good processing
characteristics and are resistant to oxidative degradation. It is a
further objective to provide compositions useful as insulation for
wire and cable, particularly applications involving exposure to
high service temperatures. The compositions of the invention meet
UL Standard 1581 and, more specifically, UL Subject 758, Style
3321.
[0012] In accordance with this invention, the above objectives are
realized utilizing an ethylene-alkyl acrylate base resin with a
stabilizer consisting of a mixture of a zinc salt of a
mercaptobenzimidazole and secondary aromatic amine compound at
prescribed ratios, a brominated flame retardant, antimony trioxide,
a hydrated inorganic filler and a chemical crosslinking agent. More
specifically, the formulations comprise (1) 30 to 65 weight percent
of a copolymer of ethylene and 3 to 40 weight percent alkyl
acrylate having the formula 1
[0013] wherein R' is C.sub.1-4 alkyl and R" is hydrogen or methyl
having a melt index of 0. 1 to 15 g/10 mins; (2) 1 to 10 weight
percent of a stabilizer consisting of a mixture of a zinc salt of a
mercaptobenzimidazole of the formula 2
[0014] where R is a C.sub.1-4 alkyl group and n is 0 to 4 with a
secondary aromatic amine, the ratio of the zinc
mercaptobenzimidazole compound to the secondary aromatic amine
compound ranging from 0.2:1 to 20:1; (3) 5 to 40 weight percent
brominated aromatic flame retardant compound; (4) 1.5 to 20 weight
percent antimony trioxide; (5) 5 to 50 weight percent hydrated
inorganic filler; and (6) 0.1 to 4 weight percent chemical
crosslinking agent.
[0015] Ethylene-n-butyl acrylate copolymer formulations stabilized
using a combination of ZMTI or ZMB with
4,4.sup.1-bis(.alpha.,.alpha.-dimethylben- zyl)diphenyl amine are
highly useful for the invention. Compositions of the above type
containing 42 to 52 weight percent base resin, 2.5 to 9 weight
percent of the stabilizer combination, 10 to 15 weight percent
brominated aromatic flame retardant, 3 to 6 weight percent antimony
trioxide, 20 to 35 weight percent magnesium hydroxide and 1 to 2
weight percent tertiary organic peroxide are an even more preferred
embodiment. Most preferred and highly useful for 150.degree.
C.-rated appliance wire applications are compositions wherein the
copolymer base resin has a melt index of 0.3 to 10 g/10 min and
contains 10 to 30 weight percent n-butyl acrylate; the brominated
aromatic flame retardant is ethylene bistetrabromophthalimide; the
hydrated inorganic filler is magnesium hydroxide; and the tertiary
organic peroxide is selected from the group consisting of dicumyl
peroxide and .alpha.,.alpha.'-bis(t-butylperoxide)d-
iisopropylbenzene.
DETAILED DESCRIPTION
[0016] The present invention relates to wire and cable insulation
compositions which exhibit significantly improved performance under
high temperature service conditions. The compositions of the
invention are comprised of the ethylene-alkyl acrylate base
polymer, a stabilizer package consisting of a zinc salt of a
mercaptobenzimidazole combined with an aromatic secondary amine
compound, a brominated flame retardant compound, antimony trioxide,
a hydrated inorganic filler and a chemical crosslinking agent.
Optionally, other additives commonly used for the formation of
insulation compounds such as processing aids, coupling agents and
the like can also be included. The compositions of the invention
are readily processable and crosslinkable using conventional
techniques. When extruded onto a wire or cable and crosslinked they
provide a tough, flame retardant insulation useful for high
temperature service applications.
[0017] As employed herein, the terms "crosslink" and "cure" are
used interchangeably and denote the formation of primary valence
bonds between polymer molecules. Also, all parts, percentages and
ratings referred to in the specification and claims which follow
are on a weight basis unless otherwise indicated and weight
percentages of the components of the formulation are based on the
weight basis based on the weight of the total composition.
[0018] The ethylene-alkyl acrylate copolymer, also referred to
herein as the base resin, used for the composition is a copolymer
of ethylene and an alkyl acrylate of the formula 3
[0019] wherein R" is hydrogen or methyl and R' is a C.sub.1-4 alkyl
group. The alkyl acrylate comonomer will typically constitute from
3 to 40 weight percent and, more preferably, from 10 to 30 weight
percent of the copolymer. Copolymers of this type are known and
commercially available.
[0020] In one highly useful embodiment of the invention, the base
resin is an ethylene-n-butyl acrylate (EnBA) copolymer obtained by
copolymerizing ethylene and n-butyl acrylate (nBA). Formulations
obtained using EnBA resins containing 15 to 25 weight percent nBA
have been shown to have particularly desirable properties.
[0021] The ethylene-alkyl acrylate base resin will have a melt
index ranging from 0.1 to 15 g/10 min and, more preferably, in the
range 0.3 to 10 g/10 min. Melt index values are determined in
accordance with ASTM D1238.
[0022] It is also possible to include minor proportions of other
crosslinkable polymers or copolymers in the composition; however,
the ethylene-alkyl acrylate copolymer should comprise at least 60
percent of the total polymers present. Representative of such minor
polymeric components which can be used in such embodiments include
polyethylene, polypropylene, ethylene-propylene copolymers and
terpolymers. Low density polyethylene and linear low density
polyethylene having melt indexes from 0.5 to 5 can be particularly
beneficial.
[0023] A stabilizer consisting of a zinc salt of a
mercaptobenzimidazole having the formula 4
[0024] where R is a C.sub.1-4 alkyl group and n is 0 to 4 and an
aromatic secondary amine compound is employed with the
ethylene-alkyl acrylate base resin. This combination affords
superior stabilization at the high temperatures encountered in
severe service applications where 150.degree. C.-rated wire and
cable insulations are required.
[0025] Mercaptobenzimidazoles where n is 0 or 1 and particularly
those wherein R is methyl are especially useful for the invention.
Zinc 2-mercaptobenzimidizole (ZMB) and zinc
2-mercaptotolylimidazole (ZMTI) are particularly advantageous and
are available from commercial suppliers.
[0026] Aromatic secondary amine compounds which are employed with
the mercaptobenzimidazole have the formula 5
[0027] where R.sub.1 is an aryl group of the formula 6
[0028] where R* is alkylene. alkylidene, --O--, --NH-- or
--SO.sub.2-- and R** is hydrogen or C.sub.1-4 alkyl and R.sub.2 is
hydrogen, alkyl, aryl, alkaryl, aralkyl or R.sub.1. Secondary
aromatic amine compounds wherein R* is --CH.sub.2--,
--CH.sub.2CH.sub.2--, --C(CH.sub.3).sub.2--, --NH-- and
--NH--SO.sub.2-- and R** is hydrogen or methyl are especially
useful. Compounds within this latter group which are advantageously
employed in view of their commercial availablility are
4,4'-bis(.alpha.,.alpha.-dimet- hylbenzyl)diphenyl amine (BDBDA)
and N-phenyl-N'-(p-toluenesulfonyl)-p-phe- nylenediamine.
[0029] The weight ratio of the zinc mercaptobenzimidazole salt to
aromatic secondary amine can range from 0.2:1 to 20:1 but, more
preferably, will be from 0.5:1 to 10:1. In a particularly useful
embodiment of the invention where the zinc mercaptobenzimidazole is
ZMTI and the aromatic secondary amine is BDBDA, the ratio of ZMTI
to BDBDA is 1:1 to 6:1.
[0030] A brominated aromatic flame retardant and antimony trioxide
are included in the formulations in order to achieve the required
flame retardancy for the compositions of the invention. Any of the
commonly used brominated aromatic compounds can be used of which
the following are representative: hexabromobenzene,
pentabromoethylbenzene, tribromophenyl allyl ether,
octabromodiphenyl, pentabromodiphenyl ether, octabromodiphenyl
ether, decabromodiphenyl ether, tetrabromobisphenol A,
bis(dibromopropyl)ether of tetrabromobisphenol A,
tetrabromophthalic anhydride, ethylene bistetrabromophthalimide,
hexabromocyclododecane and the like. Ethylene
bistetrabromophthalimide has been found to be a particularly
effective flame retardant for the ethylene-alkyl acrylate
insulation compositions of the invention.
[0031] Antimony trioxide (Sb.sub.2O.sub.3) is included with the
brominated aromatic compound Sb.sub.2O.sub.3 is known to function
as a synergist with halogenated compounds and while it is possible
to obtain useful formulations without a synergist, flame retardance
is increased when Sb.sub.2O.sub.3 is included and it is possible to
use lower levels of the brominated compound. This is advantageous
from an economic standpoint and also from the standpoint of
maximizing physical properties and processability. While antimony
trioxide is the synergist of choice, other known synergists such as
antimony pentoxide, antimony silicates, boron compounds, tin oxide,
zinc oxide, zinc borate, aluminum trihydroxide may be used. In
general, the weight ratio of brominated compound to synergist
typically ranges from about 2:1 up to about 5:1 and, more
preferably, from about 2.5:1 to 4:1.
[0032] A hydrated inorganic filler, such as hydrated aluminum
oxides (Al.sub.2O.sub.3.3H.sub.2O or Al(OH).sub.3), hydrated
magnesia, hydrated calcium silicate, hydrated magnesium carbonates,
or the like are also included in the formulations of the invention.
It is known that these types of fillers can enhance physical
properties and the water of hydration chemically bound to these
inorganic fillers is released endothermically upon combustion or
ignition of the base resin to assist in flame retardance. The
filler size should be in accordance with those sizes used by the
prior art. Magnesium hydroxide (Mg(OH).sub.2), also known as
magnesium hydrate or hydrated magnesia, is most advantageously used
in formulating the present compositions.
[0033] To achieve useful wire and cable insulation compositions
having the necessary balance of physical properties and thermal and
chemical resistance, it is necessary that the compositions be
crosslinked. While crosslinking can be accomplished chemically or
by using high energy radiation, it is more customary to use
chemical crosslinking agents. Organic peroxides are the most
commonly employed chemical crosslinking agents since they are
capable of developing high levels of cure and uniform results. The
organic peroxides are incorporated into the formulation at a
temperature below their decomposition temperature and later
activated to effect cure. Known crosslinking coagents, such as
triallylcyanurate, trimethylolpropane trimethacrylate and the like,
may be included with the organic peroxide to enhance cure.
[0034] Conventional organic peroxides known to the art which do not
appreciably decompose at the temperatures employed during
mixing/processing, typically 90.degree. C. to 120.degree. C., can
be used for the invention. In an especially useful embodiment
organic peroxides which undergo rapid decomposition in the range
130.degree. C. to 205.degree. C. are employed. Temperatures in this
range are typically used in wire curing operations, such as when
the coated wire is passed through a steam tube, a widely practiced
procedure used in commercial operations. Cure time is a function of
temperature and the heat transfer properties of the insulation.
Accordingly, cure times will vary depending on the thickness of the
insulation, the size of the conductor and, when continuous steam
vulcanization is used, the steam pressure.
[0035] Tertiary organic peroxides are particularly useful chemical
crosslinking agents. Dicumyl peroxide and
.alpha.,.alpha.'-bis(t-butylper- oxy)diisopropylbenzene are
especially advantageous tertiary organic peroxides. The
above-describe ingredients may be combined and processed using
conventional procedures. Typically mixing is accomplished using a
high shear internal mixer such as a Banbury mixer, Farrel
continuous mixer, Bolling Mixtrumat TM or Werner & Pfleiderer
mixer at a temperature below which significant decomposition of the
chemical crosslinking agent occurs. In addition to the previously
mentioned mixers, other processing devices known to the art capable
of intimately mixing the essential components may be used.
[0036] The formulations of the invention will typically contain 30
to 65 weight percent base resin, 1 to 10 weight percent of the
stabilizer pacakage, 5 to 40 weight percent brominated aromatic
flame retardant, 1.5 to 20 weight percent Sb.sub.2O.sub.3, 5 to 50
weight percent hydrated inorganic filler and 0.1 to 4 weight
percent chemical crosslinking agent. More preferably, the base
resin will comprise 42 to 52 weight percent of the total
composition which will also include 2.5 to 9 weight percent
stabilizer package, 10 to 15 weight percent brominated aromatic
flame retardant, 3 to 6 weight percent Sb.sub.2O.sub.3, 20 to 35
weight percent hydrated inorganic filler and 1 to 2 weight percent
organic peroxide.
[0037] The compositions may also contain other conventional
additives such as carbon black, pigments, lubricants, processing
aids, cure coagents and the like, provided they do not interfere
with crosslinking or detract from the physical properties of the
composition. Processing aids which can advantageously be employed
include fatty acids or fatty acid derivatives, polymeric processing
resins and hydrocarbon oils, or combinations thereof. The fatty
acid derivatives can include metal soaps, esters, ester-soaps,
amides and the like. The total amount of any additional ingredients
will generally not exceed about 10 weight percent and, most
typically, will constitute less than 5 weight percent of the total
composition.
[0038] Alkoxysilane additives may also be included in the
formulation to facilitate binding the polymer and inorganic filler.
Any conventional alkoxysilane known to the art can be used so long
as it does not combust or degrade during polymer processing or
interfere with crosslinking. Alkoxysilanes having 2 or 3 C.sub.1-3
alkoxy substituents, e.g., methoxy, ethoxy, propoxy or combinations
thereof, are particularly advantageous. Illustrative silanes
include methyl triethoxysilane, methyltris (2-methoxyethoxy)
silane, dimethyldiethoxysilane, ethyltrimethoxysilane, vinyltris
(2-methoxyethoxy)silane, phenyltris (2-methoxyethoxy)silane,
vinyltrimethoxysilane and vinyltriethoxysilane and
gamma-methacryloxypropyltrimethoxysilane.
[0039] In a particularly useful aspect of the invention, the bases
resin is an ethylene-n-butyl acrylate copolymer comprising 45 to 50
weight percent of the total composition with 4 to 8 weight percent
of a stabilizer package consisting of ZMTI and BDBDA, 10 to 15
weight percent ethylenebistetrabromophthalimide, 3 to 6 weight
percent Sb.sub.2O.sub.3, 25 to 30 weight percent Mg(OH).sub.2 and 1
to 2 weight percent tertiary organic peroxide. Notably, wire
constructions insulated with the improved compositions of the
invention meet the requirements set forth in Underwriters
Laboratories Inc., Subject 758 (Appliance Wiring Material Section
General Guide) and significantly surpass the 158.degree. C. oven
aging requirements of Style 3321 for retention of 50 percent of the
original elongation.
[0040] The present flame retardant compositions of the invention
are therefore highly useful as insulating coatings for metal
conductors--especially 1 to 30 AWG copper and aluminum, single or
multi-strand wire or cable. The compositions are typically applied
by extruding a substantially uniform 2 to 100 mil thick layer onto
the metal conductor. More typically, insulation thicknesses will
range from 10 to 60 mils. The compositions are especially useful to
insulate wires for appliances, motor leads, etc., and have a
superior balance of processability and physical properties and,
when properly formulated, do not significantly discolor or tarnish
the surface of the metal conductor. Furthermore, they are readily
strippable from the conductor and leave a clean, shiny surface.
[0041] As previously pointed out, the compositions of the invention
are readily processable and, after extrusion and cure, the
resulting insulation meets the requirements for 150.degree.
C.-rated applications specified for 600 V appliance wire in UL
Style 3321.
[0042] The polymer compositions may also be used for other
applications. For example, they can be extruded onto pipes and
conduits for electrical and other applications. They can also be
coextruded with one or more other thermoplastic materials to
produce useful laminated constructions. Powders of these resins may
be applied as coatings to either interior or exterior surfaces
utilizing conventional powder coating procedures.
[0043] The following specific examples are provided to illustrate
the flame retardant compositions of the invention and the manner in
which the invention may be carried out. The examples are not
intended to limit the invention and numerous variations within the
scope of the invention will be apparent to those skilled in the
art. In the examples, all parts and percentages are on a weight
basis unless otherwise indicated.
EXAMPLE 1
[0044] To demonstrate the superior heat stability of the
crosslinkable, flame retardant compositions of the invention upon
aging at elevated temperatures, the following formulation was
prepared and evaluated in an accelerated heat aging test.
1 Ethylene-n-butyl acrylate copolymer.sup.1 49.3% Stabilizer.sup.2
4% Ethylenebistetrabromophthalimide 8% Antimony trioxide 2.4%
Magnesium hydroxide 35% .alpha.,
.alpha.'-bis(t-butylperoxy)diisopropylbenzene 1.3% .sup.119%
n-butyl acrylate; MI 0.3 g/10 mm .sup.2a mixture of ZMTI and BDBDA
at a ratio of 1.5:1.
[0045] The formulation was prepared by combining all of the
ingredients and blending in a 240 cc Brabender mixer at 105.degree.
C. A small amount (100 ppm) copper powder was also included in the
composition as an oxidation promoter for the accelerated heat aging
test. Test specimens were prepared in accordance with ASTM D638 and
cured at 176.degree. C., 5000 psi for 20 minutes. The
dumbbell-shaped samples were then hung in a convection oven and
heated at 180.degree. C. Samples were examined daily and
brittleness determined by flexing the sample five times and then
bending the sample back on itself until the ends touched. After
releasing the bent specimen, it was visually examined in the area
of stress for the formation of cracks. Specimens were determined to
have failed at the first appearance of any cracks. The values
reported are the average obtained for three samples.
[0046] The formulation of the invention withstood 19 days before
failure. Two samples, idenitically prepared except that in one
instance, the ZMTI was omitted (Comparative Sample 1A) and in the
second instance (Comparative Sample 1B) the ethylene
bistetrabromophthalimide, were also tested. Comparative Sample 1A
failed after only five days and Comparative Sample 1B failed after
seven days. The improvement in stability obtained using the mixed
stabilizer system, i.e., the combination of ZMTI and BDBDA, is
nearly 60 percent greater than the additive results obtained for
the two comparative formulations.
[0047] To further illustrate the unobviousness of the improved heat
aging results, a third comparative composition (Comparative Sample
1C) was identically prepared except that a hindered phenol was
combined with the ZMTI at a weight ratio of 1.5:1. The hindered
phenol used was 2,2'-oxamido-bis-[ethyl
3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate] a commercial
antioxidant sold under the tradename NAUGARD XL-1. When evaluated
in the accelerated heat aging test, Comparative Sample 1C only
withstood 12 days testing before failure.
[0048] Whereas all of the above formulations, inventive and
comparative, exhibited comparable flame retardance, only the
composition of the invention utilizing aromatic secondary amine in
combination with a zinc mercaptobenzimiidazole for stabilization
had the requisite thermal stability when subjected to the rigorous
conditions of the accelerated heat aging test.
EXAMPLES 2 and 3
[0049] To demonstate the ability to vary the amount of the
brominated flame retardant and hydrated inorganic filler, two
formulations were prepared in accordance with the following
recipes. Except for the addition of a silane coupling agent, all
the ingredients used were the same as employed for Example 1.
2 Example 2 Example 3 Ethylene-n-butyl acrylate copolymer 51.6 47.7
Stabilizer 4 4 Ethylene bistetrabromophthalimide 2 5 Antimony
Trioxide 0.6 1.5 Magnesium hydroxide 40 40 Vinyltrimethoxysilane
0.5 0.5 .alpha., .alpha.'-bis(t-butylperoxy)diisopropyl benzene 1.3
1.3
[0050] Results of the accelerated heat aging test performed on both
of these products were favorable. The formulation of Example 2 ran
for 16 days before failure and the product of Example 3 withstood
18 days aging before onset of brittleness and failure.
EXAMPLES 4 and 5
[0051] Flame retardant insulation compositions were prepared
identical to the recipes of Examples 2 and 3 except that a
different brominated aromatic flame retardant was used. For these
products the ethylene bistetrabromophthalimide was replaced with
SAYTEX 8010, a proprietary non-diphenyl oxide based flame retardant
compound containing a high level of aromatic bromine manufactured
by Albermarle Corporation. Upon accelerated heat aging, these
formulations ran for 16 and 17 days, respectively, before
failure.
EXAMPLE 6
[0052] A flame retardant insulation compositions similar to that of
Example 1 was prepared and evaluated for heat stability. The
formulation was as follows:
3 Ethylene-n-butyl acrylate copolymer.sup.1 47.3 Stabilizer.sup.2
6.2 Ethylene bistetrabromophthalimide 12.5 Antimony Trioxide 4.5
Magnesium hydroxide 27.0 .alpha.,
.alpha.'-bis(t-butylperoxy)diisopropyl benzene 1.5 crosslinking
coagent.sup.3 1.0 .sup.120% n-butyl acrylate; MI 6 g/10 mm .sup.2a
mixture of ZMTI and BDBDA at a ratio of 4.2:1
.sup.3trimethylolpropane trimethacrylate
[0053] Heat aging was conducted at 180.degree. C. as in Example 1;
however, for this test physical properties (tensile and elongation)
were determined on the aged specimens in accordance with ASTM D638.
For the purpose of comparison and to demonstrate the selectivity of
the mixed stabilizer of the invention for ethylene-alkyl acrylate
copolymers, a formulation (identified as Comparative 6A) was also
prepared. The comparative composition was identical in all respects
to the above recipe except that an ethylene-vinyl acetate copolymer
(19% vinyl acetate; MI 2.5 g/10 min) was substituted for the EnBA
copolymer.
[0054] Test results obtained for the inventive and comparative
insulation compositions are tabulated below for the tensile
strength (psi), elongation (%) and percent retention of original
elongation. Values for the comparative composition are in
parenthesis.
4 Percent Tensile Elongation Elongation Retained Original (0 days)
1730/(2313) 343/(353) 100/(100) 7 days 1879/(2627) 247/(280)
72/(79) 14 days 2051/(2513) 233/(230) 68/(65) 21 days 2107/(2599)
227/(172) 66/(49) 28 days 2095/(2212) 213/(63) 62/(18) 35 days
2236/(1606) 155/(25) 45/(7)
[0055] The ability of the zinc mercaptobenzimidazole/aromatic
secondary amine combinations to provide enhanced high temperature
stabilization for the formulations of the invention which use an
ethylene-alkyl acrylate copolymer as the base resin is apparent
from the above data. While it was possible to retain greater than
50 percent of the original elongation for over 28 days with the
composition of the invention, the same stabilizer used with a
structurally similar ethylene-ester copolymer widely used in wire
and cable formulations had more than 50 percent loss in elongation
before 21 days.
EXAMPLE 7
[0056] An identical formulation to that of Example 6 was prepared
except that the copper powder was omitted. Mixing was carried out
by combining all of the ingredients in a Banbury mixer and mixing
at 120.degree. C. for 4 minutes. The resulting homogeneous blend
having a density of 1.3 g/cm.sup.3 was evaluated for electrical
properties in accordance with ASTM D150. The compound had a
dielectric constant of 3.48 and dissipation factor of 0.004, both
determined at 60 Hz. The composition was extruded onto 20 AWG
tinned copper wire at a wall thickness of 30 mil using a single
screw extruder (L/D 20 to 1; 14 rpm; heating zones at
225-235.degree. C.; head temperature 240.degree. C.). The line
speed was 400 ft/min. Vulcanization was accomplished by passing the
insulated wire through a steam tube maintained at 260 psi. The
crosslinked insulated wire was then evaluated by methods described
for UL Subject 758, Style 3321 and met all of the test criteria.
The insulated wire passed the horizontal flame test and no cracks
were observed in the cold bend (1 hour at -10.degree. C.) and
flexibility (150 days at 158.degree. C.) tests. There was no
conductor corrosion after oven aging. Percent retention of tensile
strength and elongation after testing 7 days at 180.degree. C. was
122 percent and 80 percent, respectively. Even after testing 150
days at 158.degree. C., 72 percent retention of the elongation was
achieved.
[0057] Oven aging results at 158.degree. C. (UL 1581, Style 3321)
obtained with 20 AWG tin coated solid copper conductor insulated
(30 mil wall thickness) with the above formulation were as
follows:
5 Percent Elongation Tensile (psi) Elongation (%) (Retained)
Original (0 days) 1554 323 100 30 days 2017 257 80 60 days 2142 247
76 90 days 2441 225 70 120 days 2582 248 77 150 days 2454 232
72
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