U.S. patent application number 09/888731 was filed with the patent office on 2001-12-06 for multilayer films having flame retardant layers.
This patent application is currently assigned to 3M Innovative Properties Company. Invention is credited to Devens, Douglas A., Hoisington, Mark A., Kollaja, Richard A., Russell, Patrise M..
Application Number | 20010049025 09/888731 |
Document ID | / |
Family ID | 25527958 |
Filed Date | 2001-12-06 |
United States Patent
Application |
20010049025 |
Kind Code |
A1 |
Kollaja, Richard A. ; et
al. |
December 6, 2001 |
Multilayer films having flame retardant layers
Abstract
The present invention provides unified multilayer films having
at least one layer that includes a flame retardant film layer. In
preferred embodiments the flame retardant film layer is an internal
layer. In particularly preferred embodiments of the present
invention, multilayer films include flame retardant layers
alternating with non flame retardant layers. In other preferred
embodiments, multilayer films include alternating layers of
different flame retardant materials.
Inventors: |
Kollaja, Richard A.;
(Dusseldorf, DE) ; Devens, Douglas A.; (Saint
Paul, MN) ; Russell, Patrise M.; (St. Paul, MN)
; Hoisington, Mark A.; (Austin, TX) |
Correspondence
Address: |
3M Innovative Properties Company
Office of Intellectual Property Counsel
PO Box 33427
St. Paul
MN
55133-3427
US
|
Assignee: |
3M Innovative Properties
Company
|
Family ID: |
25527958 |
Appl. No.: |
09/888731 |
Filed: |
June 25, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09888731 |
Jun 25, 2001 |
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09381844 |
Sep 23, 1999 |
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6280845 |
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09381844 |
Sep 23, 1999 |
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08980920 |
Dec 1, 1997 |
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6045895 |
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Current U.S.
Class: |
428/521 ;
428/343; 428/354; 428/423.1; 428/523; 428/910 |
Current CPC
Class: |
Y10T 428/14 20150115;
Y10T 428/31938 20150401; Y10S 428/921 20130101; Y10T 428/31855
20150401; B32B 7/12 20130101; Y10T 428/31786 20150401; Y10T
428/31931 20150401; Y10T 428/31504 20150401; Y10T 428/24959
20150115; Y10T 428/24967 20150115; B32B 7/027 20190101; Y10S 428/91
20130101; Y10T 428/2495 20150115; Y10T 428/31551 20150401; Y10T
428/2848 20150115; Y10T 428/24975 20150115; Y10T 428/28
20150115 |
Class at
Publication: |
428/521 ;
428/523; 428/343; 428/354; 428/423.1; 428/910 |
International
Class: |
B32B 007/12; B32B
027/00; B32B 015/04; B32B 027/40; B32B 027/32 |
Claims
What is claimed is:
1. A unified multilayer film of at least five continuous film
layers wherein at least one layer comprises a flame retardant film
layer and at least one layer comprises a non-flame retardant film
layer, wherein the flame retardant film comprises organic
phosphorus flame retardants, inorganic flame retardants
incorporated into a melt processible polymer.
2. The multilayer film of claim 1 wherein at least one internal
layer comprises a flame retardant film layer.
3. The multilayer film of claim 1 that comprises flame-retardant
film layers alternating with non flame retardant film layers.
4. The multilayer film of claim 3 wherein the flame retardant of
the flame retardant films layers comprises the same flame
retardant.
5. The multilayer film of claim 3 wherein the flame retardant of
the flame retardant films layers comprises different flame
retardants.
6. The multilayer film of claim 1 wherein the flame retardant
additive comprises a mixture of two or more different flame
retardant additives.
7. The multilayer film of claim 1 wherein the two outermost layers
comprise a non flame retardant film.
8. The multilayer film of claim 1 which is oriented.
9. The multilayer film of claim 1 comprising a flame retardant film
layer, a non flame retardant film layer, and a tie layer
therebetween.
10. The multilayer film of claim 1 comprising at least ten
layers.
11. The multilayer film of claim 1 further comprising at least one
pressure sensitive adhesive layer on at least one surface.
12. The multilayer film of claim 1 wherein the flame retardant
additive comprises from 10 to 90 weight percent of the unified
multilayer film.
13. The multilayer film of claim 1 wherein the flame retardant
additive comprises 40 wt. % or more in each flame retardant
layer.
14. The multilayer article of claim 1, wherein said melt
processible polymer is a thermoplastic, a thermoplastic elastomeric
or elastomeric material.
15. The multilayer article of claim 1, wherein said melt
processible polymer is selected from the group consisting of homo-
and copolymers of ethylene, propylene and butylenes.
16. The multilayer article of claim 14, wherein said a
thermoplastic elastomeric material is selected from the group
consisting of styrene-isoprene block copolymers,
styrene-(ethylene-butylene) block copolymers,
styrene-(ethylene-propylene) block copolymers, styrene-butadiene
block copolymers; polyetheresters; elastomeric ethylene-propylene
copolymers; thermoplastic elastomeric polyurethanes;
polyvinylethers; and poly-.alpha.-olefins.
17. The multilayer article of claim 1 wherein the inorganic flame
retardant additives are selected from the group consisting of
antimony trioxide, antimony pentoxide, and sodium antimonate;
barium metaborate, boric acid, sodium borate, zinc borate; aluminum
tridhydroxide; magnesium hydroxide; molybdic oxide, ammonium
molybdate, zinc molybdate, phosphoric acid; and zinc stannate.
18. The multilayer article of claim 1, wherein said phosphorus
flame retardant additive is selected from the group consisting of
organic phosphonic acids, phosphonates, phosphinates, phosphonites,
phosphinites, phosphine oxides, phosphines, phosphites or
phosphates, phosphonitrilic chloride, phosphorus ester amides,
phosphoric acid amides, phosphonic acid amides or phosphinic acid
amides.
19. The multilayer article of claim 1, wherein said phosophorus
flame retardant additive is of the formula: 2wherein each Q
represents the same or different radicals selected from alkyl,
cycloalkyl, aryl, alkyl substituted aryl, aryl substituted alkyl;
halogen, hydrogen and combinations thereof provided that at least
one of said Q's is aryl.
20. The phosphorus additive of claim 1 selected from the group
consisting of phenylbisdodecyl phosphate, phenylbisneopentyl
phosphate, phenylethylene hydrogen phosphate,
phenyl-bis-3,5,5'-trimethylhexyl phosphate), ethyldiphenyl
phosphate, 2-ethylhexyl di(p-tolyl) phosphate, diphenyl hydrogen
phosphate, bis(2-ethyl-hexyl) p-tolylphosphate, tritolyl phosphate,
bis(2-ethylhexyl)-phenyl phosphate, tri(nonylphenyl) phosphate,
phenylmethyl hydrogen phosphate, di(dodecyl) p-tolyl phosphate,
tricresyl phosphate, triphenyl phosphate, halogenated triphenyl
phosphate, dibutylphenyl phosphate, 2-chloroethyldiphenyl
phsophate, p-tolyl bis(2,5,5'-trimethylhexyl) phosphate,
2-ethylhexyldiphenyl phosphate, and diphenyl hydrogen
phosphate.
21. The multilayer article of claim 1, wherein said inherently
flame retardant polymers incorporated into a melt processible
polymer, comrprise particles of inherently flame retardant polymers
dispersed in said melt processible polymer, or as a blend of
inherently flame retardant polymers in said melt processible
polymer.
22. A process of preparing a multilayer film, the process
comprising melt processing organic polymeric material to form a
unified construction of at least 5 substantially contiguous film
layers of organic polymeric material, wherein at least one layer is
a flame retardant film layer and at least one layer is a non-flame
retardant film layer and wherein the flame retardant film comprises
organic phosphorus flame retardants, inorganic flame
retardants.
23. The process of claim 22 wherein at least one flame retardant
film layer is an internal layer
24. The process of claim 22 wherein all the layers are
substantially simultaneously melt processed.
Description
[0001] This application is a divisional of U.S. Ser. No. 09/381,844
filed Sep. 23, 1999, now allowed, which is a continuation-in-part
of U.S. Ser. No. 08/980,920, filed Dec. 1, 1997, now U.S. Pat. No.
6,045,895.
TECHNICAL FIELD
[0002] This invention relates to flame retardant films, and more
particularly, multilayer films having flame-retardant layers.
BACKGROUND OF THE INVENTION
[0003] Flame retardant films have been used in many applications
where polymeric properties offer unique performance advantages over
properties of other inherently flame retardant materials such as
metal sheets and foils, and ceramics. Typically, the polymeric
articles are either inherently flame retardant or rendered flame
retardant by the addition of flame retardant additives. However,
these approaches are limiting.
[0004] Polymer films made of inherently flame retardant polymers
such as polyvinyl chloride (PVC) and polyimide (PI) usually have a
limited range of properties. For example plasticizers are generally
added to PVC to render it more readily processable, however
plasticizer migration often adversely affects adhesion to
subsequent surfaces. In addition, PVC generally has little
elasticity and low to moderate tensile strength. Similarly, PI is
difficult to process and more expensive than most common
polymers.
[0005] Polymer films made of blends of polymer materials and flame
retardant materials also have limited performance. While the range
of polymer materials is broad, the concentration of flame retardant
material is generally high enough to significantly adversely affect
mechanical properties of the polymer material. In addition, the
flame retardant materials often migrate to the film surfaces and
adversely affect adhesion to subsequent surfaces.
[0006] Thus, there is a need for new flame retardant polymeric
films and articles that have a broader range of mechanical
mechanical properties and reduced surface fouling.
SUMMARY OF THE INVENTION
[0007] The present invention provides flame retardant films that
not only have desirable mechanical properties and reduced surface
fouling, but have improved flame retardant efficiency and/or
reduced cost when compared with conventional flame retardant
polymer films or articles. The present invention provides unified
multilayer films of at least five film layers wherein at least one
layer, preferably an internal layer, comprises a flame retardant
film layer and at least one layer comprises a non-flame retardant
film layer.
[0008] Preferably, multilayer films include layers that include a
flame-retardant film alternating with layers that include a film
that is not a flame retardant. In other preferred embodiments,
multilayer films have layers of different flame retardant films.
For example, the construction can include alternating layers of a
first flame retardant film, a second flame retardant film and a
non-flame retardant film.
[0009] One aspect of the present invention provides a multilayer
film having a unified construction of at least 5, preferably 10,
more preferably at least 13 substantially contiguous film layers
wherein at least one layer (preferably one internal layer)
comprises a flame retardant film layer and at least one layer
comprises a non-flame retardant film layer.
[0010] Another aspect of the present invention provides a
multilayer film having a unified construction; wherein the
construction comprises at least 5, preferably 10, more preferably
at least 13 substantially contiguous layers of organic polymeric
material; the construction comprising layers comprising a flame
retardant film alternating with layers comprising a film that is
not flame retardant.
[0011] The present invention also provides a process of preparing a
flame-retardant multilayer film. The process includes melt
processing organic polymeric material to form a unified
construction of at least 5 substantially contiguous film layers of
organic polymeric material, wherein at least one internal layer of
the organic polymeric material comprises a flame retardant film.
Preferably, all the layers are simultaneously melt processed, and
more preferably, all the layers are simultaneously coextruded.
[0012] A further aspect of the present invention provides a process
of preparing a multilayer film, the process comprising melt
processing organic polymeric material to form a unified
construction of at least 5 substantially contiguous layers of
organic polymeric material, the construction comprises film layers
comprising a flame retardant film layer, alternating with non flame
retardant film layers.
[0013] Herein, the following definitions are used:
[0014] "Unified" means that the layers are not designed to be
separated or delaminated as would a tape in roll form.
[0015] "Flame retardant" means a characteristic of basic
flammability has been reduced by some modification as measured by
one of the accepted test methods such as the Horizontal Burn or
Hanging Strip tests.
[0016] "Flame retardant additive" means a compound or mixture of
compounds that when incorporated (either chemically or
mechanically) into a polymer serves to slow or hinder the ignition
or growth of fire.
[0017] "Flame retardant films" means polymeric films which are
inherently flame retardant, or have been rendered flame retardant
by means of a flame retardant additive.
[0018] "Melt processable" means polymers that are fluid or pumpable
at the temperatures used to melt process the films (e.g., about
50.degree. C. to about 300.degree. C.), and do not significantly
degrade or gel at the temperatures employed during melt
processing.
[0019] "Pressure sensitive adhesive" means an adhesive that
displays permanent and aggressive tackiness to a wide variety of
substrates after applying only light pressure. It has a four-fold
balance of adhesion, cohesion, stretchiness, and elasticity, and is
normally tacky at use temperatures, which is typically room
temperature (i.e., about 20.degree. C. to about 30.degree. C.).
[0020] "Melt viscosity" means the viscosity of molten material at
the processing temperatures and shear rates employed.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0021] The present invention is directed to multilayer products in
the form of films of organic polymeric material, wherein the films
have at least one layer, preferably at least one internal layer
that includes a flame retardant film layer and at least one layer
comprises a non-flame retardant film layer. Each of the other
layers may include a flame retardant film layer, or a film layer
that is not a flame retardant. In certain preferred embodiments
there are flame retardant film layers alternating with film layers
that are not flame retardant. In other preferred embodiments there
are alternating layers of a first flame retardant film layer, a
second flame retardant film layer and a non-flame retardant film
layer. The two outermost film layers may be flame retardant films,
non-flame retardant films, or one of the outermost layers may
include a flame retardant film layer and the other a film layer
that is non flame retardant. Each layer of the construction is
continuous and has a substantially contiguous relationship to the
adjacent layers. Preferably, each layer is substantially uniform in
thickness. The multiple layers in any one construction are
"unified" into a single multilayer film such that the layers do not
readily separate.
[0022] Flame retardant films used in the flame retardant film
layer(s) include films which are inherently flame retardant, or
have been rendered flame retardant by means of a flame retardant
additive. Inherently flame retardant films are prepared from
polymers, which due to their chemical structure either do not
support combustion, or are self-extinguishing. These polymers often
have increased stability at higher temperatures by incorporating
stronger bonds (such as aromatic rings or inorganic bonds) in the
backbone of the polymers or are highly halogenated. Examples of
inherently flame retardant polymers include poly(vinyl chloride),
poly(vinylidine chloride), polyimides, polybenzimidazoles,
polyether ketones, polyphosphazenes, and polycarbonates. Useful
inherently flame retardant films generally have a Limiting Oxygen
Index (LOI) of at least 28% as determined by ASTM D-2863-91.
[0023] Useful flame retardant additives include halogenated organic
compounds, organic phosphorus-containing compounds (such as organic
phosphates), inorganic compounds and inherently flame retardant
polymers. These additives are added to or incorporated into the
polymeric matrix of the polymer film to render an otherwise
flammable polymer flame retardant. The nature of the flame
retardant additive is not critical and a single additive may be
used. Optionally, it may be desirable to use a mixture of two or
more individual flame retardant additives.
[0024] Halogenated organic flame retardant additives are thought to
function by chemical interaction with the flame: the additive
dissociates into radical species that compete with chain
propagating and branching steps in the combustion process. Useful
halogenated additives are described, for example, in the
Kirk-Othmer Encyclopedia of Technology, 4.sup.th Ed., vol. 10, pp
954-76, John Wiley & Sons, N.Y., N.Y., 1993.
[0025] Included within the scope of halogenated organic flame
retardant additives are substituted benzenes exemplified by
tetrabromobenzene, hexachlorobenzene, hexabromobenzene, and
biphenyls such as 2,2'-dichlorobiphenyl, 2,4'-dibromobiphenyl,
2,4'-dichlorobiphenyl, hexabromobiphenyl, octabromobiphenyl,
decabromobiphenyl and halogenated diphenyl ethers, containing 2 to
10 halogen atoms.
[0026] The preferred halogenated organic flame retardant additives
for this invention are aromatic and aliphatic halogen compounds
such as brominated benzene, brominated imides, chlorinated
biphenyl, or a compound comprising two phenyl radicals separated by
a divalent linking group (such as a covlaent bond and having at
least two chlorine or bromine atoms per phenyl nucleus, chlorine
containing aromatic polycarbonates, and mixtures of at least two of
the foregoing. Especially preferred are hexabromobenzene,
decabromodiphenyl oxide and tetrabromobisphenol A.
[0027] Among the useful organic phosphorus additives are organic
phosphorus compounds, phophorus-nitrogen compounds and halogenated
organic phosphorus compounds. Often organic phosphorus compounds
function as flame retardants by forming protective liquid or char
barriers, which minimize transpiration of polymer degradation
products to the flame and/or act as an insulating barrier to
minimize heat transfer.
[0028] In general, the preferred phosphate compounds are selected
from organic phosphonic acids, phosphonates, phosphinates,
phosphonites, phosphinites, phosphine oxides, phosphines,
phosphites or phosphates. Illustrative is triphenyl phosphine
oxide. These can be used alone or mixed with hexabromobenzene or a
chlorinated biphenyl and, optionally, antimony oxide.
Phosphorus-containing flame retardant additives are decribed, for
example, in Kirk-Othmer (supra) pp. 976-98.
[0029] Typical of the preferred phosphorus compounds to be employed
in this invention would be those having the general formula 1
[0030] and nitrogen analogs thereof where each Q represents the
same or different radicals including hydrocarbon radicals such as
alkyl, cycloalkyl, aryl, alkyl substituted aryl and aryl
substituted alkyl; halogen, hydrogen and combinations thereof
provided that at least one of said Q's is aryl. Typical examples of
suitable phosphates include, phenylbisdodecyl phosphate,
phenylbisneopentyl phosphate, phenylethylene hydrogen phosphate,
phenylbis-3,5,5'-trimethylhexyl phosphate), ethyldiphenyl
phosphate, 2-ethylhexyl di(p-tolyl) phosphate, diphenyl hydrogen
phosphate, bis(2-ethyl-hexyl) p-tolylphosphate, tritolyl phosphate,
bis(2-ethylhexyl)-phenyl phosphate, tri(nonylphenyl) phosphate,
phenylmethyl hydrogen phosphate, di(dodecyl) p-tolyl phosphate,
tricresyl phosphate, triphenyl phosphate, halogenated triphenyl
phosphate, dibutylphenyl phosphate, 2-chloroethyldiphenyl
phsophate, p-tolyl bis(2,5,5'-trimethylhexyl) phosphate,
2-ethylhexyldiphenyl phosphate, diphenyl hydrogen phosphate, and
the like. The preferred phosphates are those where each Q is aryl.
The most preferred phosphate is triphenyl phosphate. It is also
preferred to use triphenyl phosphate in combination with
hexabromobenzene and, optionally, antimony oxide.
[0031] Also suitable as flame-retardant additives for this
invention are compounds containing phosphorus-nitrogen bonds, such
as phosphonitrilic chloride, phosphorus ester amides, phosphoric
acid amides, phosphonic acid amides or phosphinic acid amides.
[0032] Among the useful inorganic flame retardant additives include
compounds of antimony, such as antimony trioxide, antimony
pentoxide, and sodium antimonate; boron, such as barium metaborate,
boric acid, sodium borate and zinc borate; aluminum, such as
aluminum trihydroxide; magnesium, such as magnesium hydroxide;
molybdenum, such as molybdic oxide, ammonium molybdate and zinc
molybdate, phosphorus, such as phosphoric acid; and tin, such as
zinc stannate. The mode of action is often varied and may include
inert gas dilution, (by liberating water for example), and thermal
quenching (by endothermic degradation of the additive). Useful
inorganic additives are described for example in Kirk-Othmer
(supra), pp 936-54.
[0033] Especially useful are mixed additives of an antimony
additive and a halogenated organic additive, describes as
"antimony-halogen" additives which produces an especially effective
flame retardant. The two additives react synergistically at flame
temperatures to produce an antimony halide or oxyhalide which
produce radical species (which compete with chain propagating and
branching steps in the combustion process) as well as promoting
char formation.
[0034] Inherently flame retardant polymers may be used in the form
of films, in the form of particles dispersed in a polymer matrix,
or as a blend in a compatible polymer. Examples of inherently flame
retardant polymers include poly(vinyl chloride), poly(vinylidine
chloride), polyimides, polybenzimidazoles, polyether ketones,
polyphosphazenes, polycarbonates and polysiloxanes.
[0035] The additives are generally incorporated into the flame
retardant film layers by addition of the additive(s) to the melt
prior to film formation. The materials may be added neat, as a melt
blend of the additive in a polymer, or with the use of a cosolvent
or comptatibilizer to render the additive and polymer compatible,
which may be subsequently removed prior to film formation. When
using an inherently flame-retardant polymer as an additive, it may
be melt blended if compatible, or a cosolvent or compatibilizer may
be used. Alternatively the inherently flame-retardant polymer
additive may be added as fine particles to the melt. In the case of
halogenated organic additives and organic phosphorus additives,
they may be added neat in the form of liquid or solids to the melt.
Care should be exercised to choose an additive that is stable at
the melt temperature of the polymer.
[0036] The particle size of the inorganic additive (or organic
additives which do not melt) should be less than the thickness of
the flame retardant film layer(s) into which it is incorporated to
ensure uniform thickness of the multilayer film. Preferably the
particle size is less than one-half, more preferably less than
one-third the thickness of the flame retardant film layer(s). In
general, the smaller the particle, or the more surface area the
particle presents, the more effective the flame retardant
properties.
[0037] Generally, when using a low viscosity liquid flame retardant
additive, it is preferable to use a low viscosity polymer, whereby
the best dispersion is obtained when the two viscosities of the
polymer matrix and dispersed phases are closely matched.
Alternatively, when using a solid flame retardant it is preferable
to use a high viscosity polymer as high viscosities are necessary
to generate the stresses necessary to produce a homogenous
dispersion. Viscosities may also be matched by judicious selection
of process temperature conditions. Further information on
multiphase flow in polymer processing may be found in Han,
Multiphase Flow in Polymer Processing, Academic Press, N.Y., 1981,
pp 229-235 and in Elmendorpp, Dispersive Mixing in Liquid Systems,
Mixing in Polymer Processing, C. Rauwendaal, ed., Marcel Dekker,
Inc., N.Y., pp. 17-53.
[0038] Flame retardant additives are added in sufficient amounts to
render the multilayer film flame retardant. Generally the additives
are added in amounts of 40 wt. % or more in each flame retardant
layer. Preferably the additives are added in amounts of at least 50
wt. % in each flame retardant layer or in the amounts of 10 to 90
wt. % of the unified multilayer film.
[0039] Polymeric materials used in the multilayer films of the
present invention include one or more melt-processible organic
polymers, which may include thermoplastic, thermoplastic
elastomeric or elastomeric materials. Thermoplastic materials are
generally materials that flow when heated sufficiently above their
glass transition temperature, or if semicrystalline, above their
melt temperatures, and become solid when cooled. They may be
elastomeric or nonelastomeric.
[0040] Thermoplastic materials useful in the present invention that
are generally considered nonelastomeric include, for example,
polyolefins such as isotactic polypropylene, low density
polyethylene, linear low density polyethylene, very low density
polyethylene, medium density polyethylene, high density
polyethylene, polybutylene, nonelastomeric polyolefin copolymers or
terpolymers such as ethylene/propylene copolymer and blends
thereof; ethylene-vinyl acetate copolymers such as those available
under the trade designation ELVAX from E.I. DuPont de Nemours,
Inc., Wilimington, Del.; ethylene acrylic acid copolymers; ethylene
methacrylic acid copolymers such as those available under the trade
designation SURLYN from E.I. DuPont de Nemours, Inc.;
polymethylmethacrylate; polystyrene; ethylene vinyl alcohol;
polyesters including amorphous polyester; and polyamides.
[0041] Elastomers, as used herein, are distinct from thermoplastic
elastomeric materials in that the elastomers require crosslinking
via chemical reaction or irradiation to provide a crosslinked
network which imparts modulus, tensile strength, and elastic
recovery. Elastomers useful in the present invention include, for
example, natural rubbers such as CV-60, a controlled viscosity
grade of rubber, and SMR-5, a ribbed smoked sheet rubber; butyl
rubbers, such as Exxon Butyl 268 available from Exxon Chemical Co.,
Houston, Tex.; synthetic polyisoprenes such as CARIFLEX, available
from Shell Oil Co., Houston, Tex., and NATSYN, available from
Goodyear Tire and Rubber Co., Akron, Ohio; ethylene-propylenes;
polybutadienes; polybutylenes; polyisobutylenes such as VISTANEX,
available from Exxon Chemical Co.; and styrene-butadiene random
copolymer rubbers such as AMERIPOL SYNPOL available from American
Synpol Co., Port Neches, Tex.
[0042] In the present invention, preferred organic polymers and
homo- and copolymers of polyolefins including polyethylene,
polypropylene and polybutylene homo- and copolymers.
[0043] Thermoplastic materials that have elastomeric properties are
typically called thermoplastic elastomeric materials. Thermoplastic
elastomeric materials are generally defined as materials that act
as though they were covalently crosslinked at ambient temperatures,
exhibiting high resilience and low creep, yet process like
thermoplastic nonelastomers and flow when heated above their
softening point. Thermoplastic elastomeric materials useful in the
multilayer films of the present invention include, for example,
linear, radial, star, and tapered block copolymers (e.g.,
styrene-isoprene block copolymers, styrene-(ethylene-butylene)
block copolymers, styrene-(ethylene-propylene- ) block copolymers,
and styrene-butadiene block copolymers); polyetheresters such as
that available under the trade designation HYTREL from E.I. DuPont
de Nemours, Inc.; elastomeric ethylene-propylene copolymers;
thermoplastic elastomeric polyurethanes such as that available
under the trade designation MORTHANE URETHENE from Morton
International, Inc., Chicago, Ill.; polyvinylethers;
poly-.alpha.-olefin-based thermoplastic elastomeric materials such
as those represented by the formula --(CH.sub.2CHR).sub.x where R
is an alkyl group containing 2 to 10 carbon atoms, and
poly-.alpha.-olefins based on metallocene catalysis such as ENGAGE,
ethylene/poly-.alpha.-olef- in copolymer available from Dow
Plastics Co., Midland, Mich.
[0044] The multilayer films are typically prepared by melt
processing (e.g., extruding). In a preferred method, the flame
retardant and non-flame retardant layers are generally formed at
the same time, joined while in a molten state, and cooled. That is,
preferably, the layers are substantially simultaneously
melt-processed, and more preferably, the layers are, substantially
simultaneously coextruded. Products formed in this way possess a
unified construction and have a wide variety of useful, unique, and
unexpected properties, which provide for a wide variety of useful,
unique, and unexpected applications.
[0045] Preferably, the multilayer films range in thickness from
about 25 to about 750 micrometers (.mu.m) thick (more preferably,
no greater than about 150 .mu.m, and most preferably, no greater
than about 50 .mu.m). The thickness (or volume fraction) of the
multilayer film and the individual film layers depend primarily on
the end-use application and the desired composite mechanical
properties of the multi-layered film. Such multilayer films have a
construction of at least 5 layers, preferably, at least 10 layers,
more preferably, at least 13 layers, and even more preferably, at
least 29 layers. For preferred embodiments, there are generally no
more than about 500 layers, more preferably, no more than about 200
layers, and most preferably, no more than about 100 layers,
although it is envisioned that constructions having many more
layers can be made using the materials and methods described
herein.
[0046] Depending on the polymers and additives chosen, thicknesses
of the layers, and processing parameters used, the multilayer films
will typically have different properties at different numbers of
layers. That is, the same property (e.g., tensile strength,
modulus, fire retardancy) may go through maximum at a different
number of layers for two particular materials when compared to two
other materials.
[0047] In any one construction of the alternating layers of flame
retardant film layers and non flame retardant film layers, each of
the flame retardant layers typically includes the same material
(flame retardant additive in a polymer matrix or in an inherently
flame retardant polymer) or combination of materials, although they
may include different materials or combinations of materials.
Similarly, each of the layers that is not flame retardant typically
includes the same material or combination of materials, although
they may include different materials or combinations of
materials.
[0048] Multilayer films can include an (AB).sub.n construction,
with either A and/or B layers as the outermost layers (e.g.,
(AB).sub.nA, (BA).sub.nB, or (AB).sub.n). In such constructions,
each of the B layers has flame retardant properties as a result of
the incorporation of a flame retardant additive or the use of an
inherently flame retardant polymer, which may be the same or
different in each layer, and each of the A layers does not have
flame retardant properties, which may be the same or different in
each layer. Multilayer films can also include A, A' B, and B' film
layers, with any of the A, A', B or B' layers as the outermost
layers. Preferably the A layers are the outermost layers. In such
constructions, each of the B and B' layers may include a different
flame retardant film layer and each of the B layers may include a
different non-flame retardant film layer. In each of these
constructions, n is preferably at least 2, and more preferably, at
least 5, depending on the materials used and the application
desired.
[0049] In embodiments with alternating different flame retardant
layers (B,B'), the multilayer films can take advantage of the
properties of each of the flame retardant film layers. For example,
a construction with alternating layers of an organic halogenated
flame retardant and an inorganic antimony trioxide flame retardant
has the synergistic effect of reducing the concentration of radical
species and promoting char formation. Similarly the use of organic
halogenated flame retardant and hydrated alumina will retard flames
by reducing radical species and the enthalpy of combustion.
[0050] Preferred embodiments include three or more layers of a
flame-retardant additive in a polymer matrix and three or more
layers of the same polymer matrix that is not a flame retardant
(i.e lacking the flame-retardant additive). More preferred
embodiments include only two types of materials, one inherently
flame retardant polymer and one that is not flame retardant in
alternating layers. Other preferred embodiments include only two
different flame-retardants in alternating layers.
[0051] The two outermost layers of multilayer films of the present
invention can include one or more flame-retardant films, which may
be the same or different in each of the two outermost layers.
Alternatively, the two outermost layers can include one or more
films that are not flame retardant, which may be the same or
different in each of the two outermost layers. Furthermore, the
inventive films include embodiments in which only one of the
outermost layers includes one or more flame-retardant films.
[0052] The individual layers of multilayer films of the present
invention can be of the same or different thicknesses. Preferably,
each internal layer is no greater than about 25 micrometers (.mu.m)
thick, and more preferably, no greater than about 5 .mu.m thick.
Each of the two outermost layers can be significantly thicker than
any of the inner layers, however. Preferably, each of the two
outermost layers is no greater than about 150 .mu.m thick, more
preferably no greater than 50 .mu.m thick. Typically, each layer,
whether it be an internal layer or one of the outermost layers, is
at least about 0.01 .mu.m thick, depending upon the materials used
to from the layer and the desired application.
[0053] Multilayer films wherein one or more of the layers is a
flame retardant can be made that have many significant and
unexpected properties. These can include, for example, good flame
resistance, reduced surface fouling, good weatherability,
relatively low material costs, good flame resistance, and
sufficient tensile strength for handling, relatively high break
elongation and toughness, relatively high yield and break stress,
good drape and softness, good stretch release properties, and
paper-like tensile, elongation and tear properties. Each multilayer
film of the present invention will not necessarily have all of
these advantageous properties. This will depend on the number of
layers, the types of materials, the affinity of the materials for
each other, the modulus of the different materials, and the
like.
[0054] Preferably one or both of the outer layers are not flame
retardant, the multilayer films can be used as single- or
double-sided flame retardant tapes, nonadhesive films for use as
backings for tapes, or flame retardant films for use as adhesive
layers in tapes, for example. This is because they have
advantageous mechanical properties, tensile strength, a relatively
high break elongation (i.e., elongation at break) and toughness,
good yield and break stress, as well as beneficial tear properties,
despite the incorporation of one or more flame retardant film
layers.
[0055] When used as a backing for an adhesive tape, the multilayer
film of the present invention may further comprise a
pressure-sensitive adhesive layer. Pressure sensitive adhesives
useful in the present invention can be self tacky or require the
addition of a tackifier. Such materials include, but are not
limited to, tackified natural rubbers, tackified synthetic rubbers,
tackified styrene block copolymers, self-tacky or tackified
acrylate or methacrylate copolymers, self-tacky or tackified
poly-.alpha.-olefins, and tackified silicones. Examples of suitable
adhesives are described in U.S. Pat. No. Re 24,906 (Ulrich), U.S.
Pat. No. 4,833,179 (Young et al.), U.S. Pat. No. 5,209,971 (Babu et
al.), U.S. Pat. No. 2,736,721 (Dexter), and U.S. Pat. No. 5,461,134
(Leir et al.), for example. Others are described in the
Encyclopedia of Polymer Science and Engineering, vol. 13,
Wiley-Interscience Publishers, New York, 1988, the Encyclopedia of
Polymer Science and Technology, vol. 1, Interscience Publishers,
New York, 1964 and in D. Satas, Handbook of Pressure Sensitive
Adhesives, 2.sup.nd Edition, Van Nostrand Reinhold, New York,
1989.
[0056] A pressure sensitive adhesive useful in the present
invention typically has an open time tack (i.e., period of time
during which the adhesive is tacky at room temperature) on the
order of days and often months or years. An accepted quantitative
description of a pressure sensitive adhesive is given by the
Dahlquist criterion line (as described in Handbook of Pressure
Sensitive Adhesive Technology, Second Edition, D. Satas, ed., Van
Nostrand Reinhold, New York, N.Y., 1989, pages 171-176), which
indicates that materials having a storage modulus (G') of less than
about 3.times.10.sup.5 Pascals (measured at 10 radians/second at a
temperature of about 20.degree. C. to about 22.degree. C.)
typically have pressure sensitive adhesive properties while
materials having a G' in excess of this value typically do not.
[0057] Suitable polymers for use in preparing the films of the
present invention, whether they are inherently flame retardants or
not, are melt processable. That is, they are fluid or pumpable at
the temperatures used to melt process the films (e.g., about
50.degree. C. to about 300.degree. C.), and they are film formers.
Furthermore, suitable polymers do not significantly degrade or gel
at the temperatures employed during melt processing (e.g.,
extruding or compounding). Preferably, such polymers have a melt
viscosity of about 10 poise to about 1,000,000 poise, as measured
by capillary melt rheometry at the processing temperatures and
shear rates employed in extrusion. Typically, suitable polymers
possess a melt viscosity within this range at a temperature of
about 175.degree. C. and a shear rate of about 100
seconds.sup.-1.
[0058] In melt processing multilayer films of the present
invention, the polymers in adjacent layers need not be chemically
or physically compatible or well matched, particularly with respect
to melt viscosities, although they can be if so desired. That is,
although materials in adjacent polymeric flowstreams can have
relative melt viscosities (i.e., ratio of their viscosities) within
a range of about 1:1 to about 1:2, they do not need to have such
closely matched melt viscosities. Rather, the materials in adjacent
polymeric flowstreams can have relative melt viscosities of at
least about 1: 5, and often up to about 1:20. For example, the melt
viscosity of a flowstream of polymer B (or A) can be similar or at
least about 5 times, and even up to about 20 times, greater than
the melt viscosity of an adjacent flowstream of polymer A (or
B).
[0059] In melt processing polymers of different flame retardants
film layers and/or non flame retardant film layers, the differences
in elastic stresses generated at the interface between the layers
of different flame retardants is also important. Preferably, these
elastic differences are minimized to reduce or eliminate flow
instabilities that can lead to layer breakup. With knowledge of a
material's elasticity, as measured by the storage modulus on a
rotational rheometer over a range of frequencies (0.001
rad/sec.<.omega.<100 rad/sec.) at the processing temperature,
along with its viscosity at shear rates less than 0.01
second.sup.-1, and the degree to which the material's viscosity
decreases with shear rate, one of skill in the art can make
judicious choices of the relative thicknesses of the layers, the
die gap, and the flow rate to obtain a film with continuous,
uniform layers. Generally, the elastic stresses at 100 sec.sup.-1
by a more viscous polymer should be greater than the elastic stress
generated by the less viscous polymer. Further, the ratio of the
storage modulus to the viscosity at 0.01 sec.sup.-1 for the more
viscous polymer should be greater than that of the less viscous
polymer.
[0060] Significantly, relatively incompatible materials (i.e.,
those that typically readily delaminate as in conventional two
layer constructions) can be used in the multilayer films of the
present invention. Although they may not be suitable for all
constructions, they are suitable for the constructions having
larger numbers of layers. That is, generally as the number of
layers increases, relatively incompatible materials can be used
without delamination occurring. In addition, film properties such
as elongation at break and toughness often increase as the number
of layers increases, depending on the materials used.
[0061] The flame retardant layer (B or B') can include a single
flame retardant, a mixture (e.g., blend) of several flame
retardants, or a mixture (e.g., blend) of a flame retardant and a
material that is not a flame retardant (e.g., a nontacky
thermoplastic material, which may or may not be elastomeric), as
long as the layer has flame retardant properties. Examples of some
flame retardant blends are described in Kirk-Othmer (supra).
Similarly, the non-flame retardant layer (A or A') can include a
single polymer that is not a flame retardant, a mixture of several
such polymers, , as long as the layer does not have flame retardant
properties.
[0062] The materials of the non-flame retardant layer (A or A') can
be modified with one or more processing aids, such as plasticizers
and lubricants, to modify their properties. Plasticizers and
lubricants useful with the polymeric materials are preferably
miscible at the molecular level, i.e., dispersible or soluble in
the thermoplastic material. External lubricants that are
incompatible with the polymer can also be added that act by
migrating to the surface of the polymer melt and reducing frictions
with the extrusion equipment (the die or extruder barrel for
example). Examples of plasticizers and lubricants include, but are
not limited to, polybutene, paraffinic oils and waxes, fatty acids
including stearic acid and calcium stearate, petrolatum, liquid
rubbers, and certain phthalates with long aliphatic side chains
such as ditridecyl phthalate. When used, a processing aid is
typically present in an amount of about 5 parts to about 300 parts
by weight, and preferably up to about 200 parts by weight, based on
100 parts by weight of the polymeric material in the nonflame
retardant layer.
[0063] Other additives, such as fillers, pigments, crosslinking
agents, antioxidants, ultraviolet stabilizers, and the like, may be
added to modify the properties of either the flame retardant layers
(B or B) or the nonflame retardant layers (A or A'). Each of these
additives is used in an amount to produce the desired result.
[0064] Pigments and fillers can be used to modify cohesive strength
and stiffness, cold flow, and tack, as well as chemical resistance
and gas permeability. For example, aluminum hydrate, lithopone,
whiting, and the coarser carbon blacks such as thermal blacks also
increase tack with moderate increase in cohesivity, whereas clays,
hydrated silicas, calcium silicates, silico-aluminates, and the
fine furnace and thermal blacks increase cohesive strength and
stiffness. Platy pigments and fillers, such as mica, graphite, and
talc, are preferred for acid and chemical resistance and low gas
permeability. Other fillers can include glass or polymeric beads or
bubbles, metal particles, fibers, and the like. Typically, pigments
and fillers are used in amounts of about 0.1% to about 20% by
weight, based on the total weight of the multilayer film.
[0065] Crosslinkers such as benzophenone, derivatives of
benzophenone, and substituted benzophenones such as
acryloyloxybenzophenone may also be added. Such crosslinkers are
preferably not thermally activated, but are activated by a source
of radiation such as ultraviolet or electron-beam radiation
subsequent to forming the films. Typically, crosslinkers are used
in amounts of about 0.1% to about 5.0% by weight, based on the
total weight of the multilayer film.
[0066] Antioxidants and/or ultraviolet stabilizers may be used to
protect against severe environmental aging caused by ultraviolet
light or heat. These include, for example, hindered phenols,
amines, and sulfur and phosphorus hydroxide decomposers. Typically,
antioxidants and/or ultraviolet stabilizes are used in amounts of
about 0.1% to about 5.0% by weight, based on the total weight of
the multilayer film.
[0067] Intermediate layers may be used in a multilayered
construction to adhere different polymeric materials having
insufficient interlayer adhesion. Intermediate layers, or tie
layers, generally have an affinity for both of the principal layers
and typically consist of materials that will not significantly
reduce the overall tensile properties of the multilayer
construction. Some useful tie layers include, for example,
copolymers containing blocks that have an affinity for each of the
principal layers, which flow when melted and cool to a tack-free
state.
[0068] Tie layers, which are typically hot melt adhesive (i.e.,
tacky when in the melt state), can also be used to enhance the
adhesion between each of the layers if so desired. Materials useful
in the tie layers include, ethylene/vinyl acetate copolymer
(preferably containing at least about 10% by weight of vinyl
acetate units), carboxylated ethylene/vinyl acetate copolymer such
as that available under the trade designation CXA, from E.I. DuPont
de Nemours, Inc., copolymers of ethylene and methyl acrylate such
as that commercially available under the trade designation POLY-ETH
EMA, from Gulf Oil and Chemicals Co., ethylene/acrylic acid
copolymer such as that available under the trade designation SURLYN
(a copolymer of ethylene with a methacryic acid) from E.I. DuPont
de Nemours, Inc., maleic anhydride modified polyolefins and
copolymers of polyolefins such as that commercially available under
the trade designation MODIC, from Mitsubishi Chemical Co.,
polyolefins containing homogeneously dispersed vinyl polymers such
as those commercially available under the trade designation VMX
from Mitsubishi Chemical Co. (e.g., FN-70, an ethylene/vinyl
acetate based product having a total vinyl acetate content of 50%
and JN-70, an ethylene/vinyl acetate based product containing
dispersed polymethylmethacrylate and having a vinyl acetate content
of 23% and a methyl methacrylate content of 23%), POLYBOND
(believed to be a polyolefin grafted with acrylic acid) from B.P.
Chemicals Inc., Cleveland, Ohio, PLEXAR (believed to be a
polyolefin grafted with functional groups) from Quantum Chemicals,
Inc., Cincinnati, Ohio, a copolymer of ethylene and acrylic acid
such as that commercially available under the trade designation
PRIMACOR from Dow Chemical Co., Midland, Mich., and a copolymer of
ethylene and methacrylic acid such as that commercially available
under the trade designation NUCREL from E.I. DuPont de Nemours,
Inc.
[0069] The multilayer films of the present invention can be
prepared directly by extrusion, for example, with the outermost
layers being preferably non flame retardant. Frequently,
incorporation of a flame retardant into one or both of the
outermost layers can degrade the surface and/or mechanical
properties of the outermost layer. Halogenated organic flame
retardants, for example, may tend to migrate to the surface of the
film and render the surface non-amenable to further coating, by a
pressure sensitive adhesive for example. Alternatively, the films
can be made with one or both of the outermost layers being flame
retardant layer(s) depending on the application.
[0070] The multilayer films of the present invention can be used as
the backings or substrates for single-sided or double-sided
adhesive products, such as tapes. Preferably the multilayer films
used as backings in tape have a non flame retardant layer as at
least one of the outermost layers. Such films can be prepared using
extrusion techniques, for example, to produce such products
directly (i.e., with one or both outermost layers of the film being
an a pressure sensitive adhesive layer). Alternatively, a
multilayer film can be coated with an adhesive material using
conventional coating techniques. Furthermore, such products can be
coated with a low-adhesion backsize (LAB) material, which restricts
adhesion of various types of surfaces to the film when it is wound
as a coil or is stacked on itself A wide variety of known adhesive
materials (e.g., any of the pressure sensitive materials described
herein) and LAB materials (e.g., polyolefins, urethanes, cured
silicones, fluorochemicals) can be used as well as a wide variety
of known coating techniques, including solvent coating and
extrusion coating techniques.
[0071] Multilayer films of the present invention can be made using
a variety of equipment and a number of melt-processing techniques
(typically, extrusion techniques) well known in the art. Such
equipment and techniques are disclosed, for example, in U.S. Pat.
No. 3,565,985 (Schrenk et al.), U.S. Pat. No. 5,427,842 (Bland et
al.), U.S. Pat. No. 5,589,122 (Leonard et al.), 5,599,602 (Leonard
et al.), and U.S. Pat. No. 5,660,922 (Herridge et al.). For
example, single- or multi-manifold dies, full moon feedblocks (such
as those described in U.S. Pat. No. 5,389,324 to Lewis et al.), or
other types of melt processing equipment can be used, depending on
the number of layers desired and the types of materials
extruded.
[0072] For example, one technique for manufacturing multilayer
films of the present invention can use a coextrusion technique,
such as that described in U.S. Pat. No. 5,660,922 (Herridge et
al.). In a coextrusion technique, various molten streams are
transported to an extrusion die outlet and joined together in
proximity of the outlet. Extruders are in effect the "pumps" for
delivery of the molten streams to the extrusion die. The precise
extruder is generally not critical to the process. A number of
useful extruders are known and include single and twin screw
extruders, batch-off extruders, and the like. Conventional
extruders are commercially available from a variety of vendors such
as Davis-Standard Extruders, Inc. (Pawcatuck, Conn.), Black Clawson
Co. (Fulton, N.Y.), Berstorff Corp. (NC), Farrel Corp. (CT), and
Moriyama Mfr. Works, Ltd. (Osaka, Japan).
[0073] Other pumps may also be used to deliver the molten streams
to the extrusion die. They include drum loaders, bulk melters, gear
pumps, and the like, and are commercially available from a variety
of vendors such as Graco LTI (Monterey, Calif.), Nordson (Westlake,
Calif.), Industrial Machine Manufacturing (Richmond, Va.), and
Zenith Pumps Div., Parker Hannifin Corp. (NC).
[0074] Typically, a feedblock combines the molten streams into a
single flow channel. The distinct layers of each material are
maintained because of the laminar flow characteristics of the
streams. The molten structure then passes through an extrusion die,
where the molten stream is reduced in height and increased in width
so as to provide a relatively thin and wide construction. This type
of coextrusion is typically used to manufacture multilayer film
constructions having about 10 layers or more.
[0075] However, the use of a feedblock is optional, as a variety of
coextrusion die systems are known. For example, multimanifold dies
may also be employed, such as those commercially available from The
Cloeren Company (Orange, Tex.). In multimanifold dies, each
material flows in its own manifold to the point of confluence. In
contrast, when feedblocks are used, the materials flow in contact
through a single manifold after the point of confluence. In
multimanifold die manufacturing, separate streams of material in a
flowable state are each split into a predetermined number of
smaller or sub-streams. These smaller streams are then combined in
a predetermined pattern of layers to form an array of layers of
these materials in a flowable state. The layers are in intimate
contact with adjacent layers in the array. This array generally
comprises a stack of layers which is then compressed to reduce its
height. In the multimanifold die approach, the film width remains
constant during compression of the stack, while the width is
expanded in the feedblock approach. In either case, a comparatively
thin, wide film results. Layer multipliers in which the resulting
film is split into a plurality of individual subfilms which are
then stacked one upon another to increase the number of layers in
the ultimate film may also be used. The multimanifold die approach
is typically used in manufacturing multilayer film constructions
having less than about 10 layers.
[0076] In manufacturing the films, the materials may be fed such
that either a flame retardant layer or the non-flame retardant
layer forms the outermost layers. The two outermost layers are
often formed from the same material. Preferably, although not
necessarily, the materials comprising the various layers are
processable at the same temperature. Significantly, although it has
been generally believed that the melt viscosities of the various
layers should be similar, this is not a necessary requirement of
the methods and products of the present invention. Accordingly,
residence times and processing temperatures may have to be adjusted
independently (i.e., for each type of material) depending on the
characteristics of the materials of each layer.
[0077] The volume fraction of the A and B layers depends primarily
on the ratio of the viscosities of the component polymers or
polymer mixtures (including the addition of the flame retardant
additive). For example, if the outer "A" layer has a higher
viscosity than the "B" layer, process stability considerations
suggest that the "B" layer have a greater volume fraction (i.e
>50%). Conversely, if the A layer has a lower viscosity than the
B layer, process stability should increase if the B layer has a
smaller (i.e. <50%) volume fraction. These considerations are
generally true regardless of the number of layers and the total
flow rate of the process.
[0078] Other manufacturing techniques, such as lamination, coating,
or extrusion coating may be used in assembling multilayer films and
products from such multilayer films according to the present
invention. For example, in lamination, the various layers of the
film are brought together under temperatures and/or pressures
(e.g., using heated laminating rollers or a heated press)
sufficient to adhere adjacent layers to each other.
[0079] In extrusion coating, a first layer is extruded onto a cast
web, a uniaxially oriented film, or a biaxially oriented film, and
subsequent layers are sequentially coated onto the previously
provided layers. Extrusion coating may be preferred over the melt
coextrusion process described above if it is desirable to pretreat
selected layers of the multilayer film or if the materials are not
readily coextrudable.
[0080] Continuous forming methods include drawing the multilayer
film out of a film die and subsequently contacting the extruded
multilayer film with a moving plastic web or other suitable
substrate. After forming, the multilayer films are solidified by
quenching using both direct methods, such as chill rolls or water
baths, and indirect methods, such as air or gas impingement.
[0081] The films of the present invention can be oriented, either
uniaxially (i.e., substantially in one direction) or biaxially
(i.e., substantially in two directions), if so desired. Such
orientation can result in improved strength properties, as
evidenced by higher modulus and tensile strength. Preferably, the
films are prepared by co-extruding the individual polymers to form
a multilayer film and then orienting the film by stretching at a
selected temperature. For example, uniaxial orientation can be
accomplished by stretching a multilayer film construction in the
machine direction at a temperature of about the melting point of
the film, whereas biaxial orientation can be accomplished by
stretching a multilayer film construction in the machine direction
and the cross direction at a temperature of about the melting point
of the film. Optionally heat-setting at a selected temperature may
follow the orienting step.
EXAMPLES
[0082] This invention is further illustrated by the following
examples which are not intended to limit the scope of the
invention. In the examples, all parts, ratios and percentages are
by weight unless otherwise indicated. The following test methods
were used to characterize the flame retardant films in the
examples:
Test Methods
[0083] Horizontal Burn
[0084] Burning characteristics of multilayer films were evaluated
according to ASTM D1000 except the film were first laminated to a
25 micrometer thick layer of pressure-sensitive adhesive (a blend
of 50 parts KRATON.TM. 1107 polystyrene/poluisoprene block
coplolymer available from Shell Chemical, 50 parts NATSYN.TM. 2210
polyisoprene homopolymer available from Goodyear Tire and Rubber,
75 parts WINTACK PLUS.TM. hydrocarbon tackifier available from
Goodyear, 30 parts ENDEX 160.TM. end-block reinforcing resin and 2
parts IRGANOX.TM. 1010 antioxidant available from CIBA-Giegy, as
described in U.S. Pat. No. 5,500,293) as in the vertical burn test)
to permit the film to stick to a brass rod that was used in the
test. The brass rod was wrapped with two overlapping layers of tape
and supported in a horizontal position. A gas burner flame was
applied for 30 seconds and immediately removed. The time required
for the sample to self-extinguish is measured. This test
differentiates among tapes with wide ranges of burning
characteristics but is less precise for tapes of narrow ranges of
burning characteristics.
[0085] Hanging Strip
[0086] Burning characteristics of multilayer films were evaluated
according to ASTM 568-77. A 45 cm.times.25 cm with a 38 cm gauge
length sample was suspended from a clamp inside a protective metal
shield that was located in a fume hood. A gas burner flame of a
given height was applied until film ignited. Flame was removed
immediately and the time needed to burn 38 cm of sample length or
for sample to self-extinguish was measured. This test
differentiates among tapes with wide ranges of burning
characteristics but is less precise for tapes of narrow ranges of
burning characteristics.
[0087] Tensile Testing
[0088] Tensile properties of the multilayer films were evaluated
using a standard tensile/elongation method on an Instron mechanical
testing frame at 12 inches/minute (30.5 cm/minute). Sample were of
0.5 inches width (1.27 cm) and gauge length of 4 inches (10.2 cm).
Thickness of the samples depended on process conditions and were
measured using a Mitutoyo Liner Thickness Gage.
Materials Used
[0089]
1 Material Description Fina .TM. 3374 Isotactic polypropylene
available from Fina Oil & Chem, Dallas, TX. Rexflex .TM. W101
Significantly atactic polypropylene available from Huntsman
Polypropylene Corp., Woodbury, NJ. 1 Nat-2P-W A brominated imide
and antimony trioxide blended into a polyethylene polymer at a
45:55 weight concentration with a 3:1 ratio of brominated imide to
antimony., available as PE Conc. 1 Nat-2P-W from M.A Hannah, Elk
Grove Village, IL. LLDPE 6806 Liner low density polyethylene,
available from Dow Chemical Co., Midland ML. SpaceRite .TM. S11
Alumina trihydroxide, available from Alcoa Chemicals, Charlotte,
NC. Engage .TM. 8100 A metallocene polymerized olefin, containing
24% octane comonomer available from Dow Chemical Co., Midland, MI.
LDPE 1550 Low density polyethylene, available from Eastman Chemical
Products, Inc., Kingsport, TN. ATH FR Alumina trihydroxide
compounded with ethylene vinyl acetate at a 60% by weight
concentration, available from Mach 1 Compounding, Macedonia, Ohio.
Elvax .TM. 410 An ethylene vinyl-acetate copolymer available from
E.I. DuPont de Nemours, Inc., Wilmington DE. 0521-48 FR Magnesium
hydroxide compounded with polypro- pylene at a 50% by weight
concentration, available from Mach 1 Compounding, Macedonia, Ohio.
Escorene .TM. 3445 Isotactic polypropylene available from Exxon
Chemical Co. Environstrand A blend of tetrabromobisphenol A with
antimony oxide in atactic polypropylene, available as Envirostrand
5P280 from Great Lakes Chemical, West Lafayette, IN PPSC 912 An
ethylene-propylene copolymer with a melt index of 65, available as
Profax SC 912 from Montell North America, Wilmington DE
Examples 1-3, Comparative Examples 1-4
[0090] Examples 1-3 were multilayer films having 13 layers of a
construction A(BA).sub.5BA. They were prepared to illustrate the
effect on overall flame retardant properties of using various
amounts of a flame retardant additive in a B layer compared to
using similar amounts in a blended composition.
[0091] In Example 1, the non flame retardant layers were made of
Rexflex.TM. W101 and 35% Fina.TM. 3374, melt mixed in a weight
ratio of 65:35 and conveyed in a BERLYN single screw extruder
(BERLYN, 51 mm, having an L/D of 30/1, commercially available from
Berlyn Corp., Worchester, Mass., operating with zone temperatures
increasing from 149.degree. C. to 238.degree. C.) to A slots of a
feedblock having 13 slots. The feedblock, made as described in U.S.
Pat. No. 4,908,278 (Bland et al.), allowed two flow streams fed
into the 13 slots in an alternating manner to come together in a
multilayer flow stream having layers arranged as A(BA).sub.5BA. The
temperature of both the feedblock and the die were set at
204.degree. C. The flame retardant layers were made from 1
Nat-2P-W, fed by a single screw extruder (KILLION Model KTS-125, 32
mm, having an L/D of 24/1, commercially available from Killion,
Inc., Cedar Grove, N.J.) operating with zone temperatures
increasing from 132.degree. C. to 238.degree. C. into B slots of
the feedblock. The resulting multilayered flow stream was passed
through a single orifice film die and drop cast onto a chill roll
set at a temperature of 15.degree. C. and collected. The line speed
was 4.6 m/min., the individual flowrates of A and B were such that
flame retardant material comprised a calculated 14.3 weight percent
of the overall multilayered film and the overall thickness was
measured at 150 micrometers.
[0092] Examples 2 and 3 were made essentially as in Example 1,
except the flow rates of the materials were adjusted to obtain
flame retardant concentrations of 33.3 and 47 weight percent,
respectively.
[0093] In Comparative Example 1, the same material used in the A
layer of Example 1 was fed into the Berlyn extruder of Example 1,
conveyed through a feedblock and a single layer die and drop cast
onto a chill roll. The temperatures of the extruder increased from
149.degree. C. to 238.degree. C., the feedblock and the die were
set at a temperature of 204.degree. C. and the chill roll was set
at a temperature of 15.degree. C. The overall thickness was 150
micrometers and the flame retardant concentration was 0 weight
percent.
[0094] Comparative Examples 2-4 were made essentially as in
Comparative Example 1 except the flame retardant additive used in
the B layers of Example 1 was melt blended to result in an overall
flame retardant concentration in weight percent of 14.3, 33.3 and
47, respectively.
[0095] Examples 1-3 and Comparative Examples 1-4 were tested for
Hanging Strip Flammability, and Horizontal Burn. The test results,
film layers and flame retardant concentrations are shown in Tables
1 and 2.
2 TABLE 1 FR Hanging Strip Ex. Layers % Flame Comments 1 13 14.3 3
sec, SE Flaming drips 2 13 33.3 3 sec, SE Flaming drips, hard to
ignite 3 13 47.0 <1 sec, SE Very difficult to ignite C1 1 0.0 34
sec, 38 cm Flaming drips C2 1 14.3 17 sec, 38 cm Flaming drips,
easy to ignite, C3 1 33.3 15 sec, SE Flaming drips C4 1 47.0 2 sec,
SE No drips
[0096] As seen, the films of the invention exhibited improved flame
reta4rdant performance as blends having the same overall
concentration of flame retardant material.
3 TABLE 2 FR Horizontal Burn Ex. Layers % Flame Comments 1 13 14.3
18 sec No drips, high char 2 13 33.3 1 sec No drips, high char 3 13
47.0 <1 sec No drips, high char C1 1 0.0 127 sec Flame drips,
all tape burned C2 1 14.3 11 sec Flame drips, low char C3 1 33.3 16
sec No drips, high char C4 1 47.0 4 sec No drips, high char
[0097] As seen, the films of the invention exhibited improved flame
retardant performance over blends having the same overall
concentration of flame retardant material when the flame-retardant
concentration was sufficient.
Example 4 and Comparative Examples 5-6
[0098] Example 4 illustrates the effect of two flame retardant
materials in the flame-retardant layer on overall flame retardant
performance.
[0099] A multilayer film was made essentially as in Example 1,
varying the polymer matrix. Flame retardant additive and process
conditions as noted. The non flame retardant "A" layers were made
of Reflex.TM. W101 and Fina.TM. 3374 in a weight ratio of 75:25
instead of 65:35. The flame retardant "B" layers were made of a
mixture of LLDPE 6806, 1-Nat-2P-W and Alcoa Spacerite.TM. S 11 in a
weight ratio of 25:56:19. The set temperature in the Berlyn
extruder varied from 138.degree. C. up to 193.degree. C. The
temperature in the Killion extruder varied from 132.degree. C. up
to 182.degree. C. Die and feedblock at 193.degree..
[0100] Comparative Example 5 was made essentially as in Comparative
Example 1 except the non flame retardant polymer was made of
Reflex.TM. W101 and Fina.TM. 3374 in a weight ratio of 75:25
instead of 65:35.
[0101] Comparative Example 6 was performed essentially as in
Comparative Example 2 except as follows. The non flame retardant
material was made of Reflex.TM. W101 and Fina.TM. 3374 in a weight
ratio of 75:25 instead of 65:35. The flame retardant mixture used
in the "B" layer of Example 4 was melt blended with the non flame
retardant material to result in an overall flame retardant
concentration of weight percent of 35.
[0102] Examples 1-3 and Comparative Examples 1-4 were tested for
Hanging Strip Flammability and for Tensile Stress. The test
results, film layers and flame retardant concentrations are shown
in Table 3.
4 TABLE 3 Tensile Stress Lay- FR Hanging Strip At 10% strain Ex.
ers % Flame Comments KPa (psi) 4 13 35 <1 sec, SE.sup.1 Drips
but not flaming 535(775) C5 1 0 27 sec, all Flaming drips 635(920)
C6 1 35 4 sec, SE Flaming drips 597(865)
[0103] 1--Self Extinguished Immediately After Burner Removed, Could
Not Be Ignited.
[0104] As seen, a film of the invention exhibited improved flame
retardant performance of a blend having the same overall
concentration of flame retardant. The lower tensile stress value of
Example 4 was attributed to poor mixing.
Examples 5-6
[0105] These examples were prepared to illustrate the use of
halogen-free flame retardant materials with two different non-flame
retardant materials.
[0106] Examples 5 and 6 were made in a manner similar to Example 1
except the materials were different and some process conditions
were changed. In Example 5, the materials used in the not flame
retardant "A" layers were Engage.TM. 8100 and LDPE 1550 melt
blended in a weight ratio of 50:50. In Example 6, the materials
used in the non-flame retardant "A" layers were Reflex.TM. W101 and
Fina.TM. 3374 in a weight ratio of 75:25 instead of 65:35. In both
examples, the materials used in the flame retardant "B" layers were
a mixture of ATH FR and Elvax.TM. 410 in a weight ratio of 90:10. A
KILLION single screw extruder (KILLION Model KTS-125, 32 mm single
screw extruder with L/D of 24/1 and fitted with a mixing screw
containing an Eagan mixing section) was used instead of a BERLYN
single screw extruder to convey the non-flame retardant material to
the "A" slots of the feedblock and a second KILLION single screw
extruder, also fitted with a mixing screw containing an Eagan
mixing section, conveyed the flame retardant material to the "B"
slots. In examples 5 and 6, the first KILLION extruder was operated
at temperatures in the first zone to the last zone ranging from
149.degree. C. to 177.degree. C. and 149.degree. C. to 188.degree.
C., respectively. In both examples the temperatures of the
feedblock, die and chill roll were maintained at 177.degree. C.,
177.degree. C. and 20.degree. C., respectively. The film speeds for
Examples 5 and 6 were 4.9 and 5.5 m/min, respectively. The film
thickness for both was about 130 microns.
[0107] Comparative Example 7 was made as in Example 5 except no
flame retardant material was fed into the "B" slots and the
flowrate was adjusted to result in a one layer film having a
thickness of about 130 micrometers where all seven layers merged
into a single indistinguishable layer.
[0108] Examples 5-6 and Comparative Example 8 were tested for
Horizontal Burn. The test results, film layers and flame retardant
concentrations are shown in Table 4.
5 TABLE 4 FR Horizontal Burn Ex. Layers % Flame Comments 5 13 37 13
sec No/low char, 2-3 drips, flames do not burn down length of rod,
tape does not burn readily, bubbling during burning & no smoke.
6 13 38 16 sec Same as Ex 5 except 1-2 drips. C7 1 0 120 sec No
char, flaming drips, burns entire length of rod and light
smoke.
[0109] As seen, the films of the invention exhibited substantial
flame retardant performance.
Example 7
[0110] These examples were prepared to illustrate the use of an
inorganic flame retardant additive with two different non flame
retardant materials.
[0111] Example 7 was made essentially as in Example 6 except as
follows. The materials used in the non-flame retardant "A" layers
were Rexflex.TM. W101 and Fina.TM. 3374 in a weight ratio of 75:25.
The flame retardant additive in the "B" layer was 0521-48. The
temperatures for the "A" layer extruder and the "B" layer extruder
were set to increase from between 182.degree. C. and 204.degree. C.
and between 171.degree. C. and 227.degree. C., respectively.
[0112] Comparative Example 8 was made essentially as in Example 7
except no flame retardant additive was fed into the "B" slots and
the flow rate was adjusted to result in a one layer film having a
thickness of about 130 micrometers.
[0113] Example 7 and Comparative Example 8 were tested for
Horizontal Burn. The test results, film layers and flame retardant
concentrations are shown in Table 5.
6 TABLE 5 FR Horizontal Burn Ex. Layers % Flame Comments 7 13 42 18
sec High char, no drips, flames do not burn down length of rod,
tape does not burn readily, flakes/ash produced during burning
& no smoke. C8 1 0 127 sec Flaming drips and all tape
burned.
[0114] As seen, the films of the invention exhibited substantial
flame retardant performance.
Examples 8-10
[0115] These examples were prepared to illustrate the effect of
flame retardant materials that melted a processing temperatures on
layer thickness.
[0116] Example 8 was made essentially as in Example 1 except some
equipment, processing conditions and materials were the different.
The not flame retardant "A" layers were made of Escorene.TM. 3445
and the flame retardant "B" layers were made of a mixture of 50%
Great Lakes Environstrand and 50% PPSC 912. The "B" layer material
was conveyed to the "B" slots with a twin screw extruder (LEISTRITZ
Model LSM 34 GL, 34 mm, having 42/1, commercially available from
Leistritz Corp., Sommerville, N.J.). The temperature of the
extruder for the "A" layers varied from 160.degree. C. up to
193.degree. C. The temperature of the extruder for the "B" layers
ranged from 150.degree. C. up to 177.degree. C. The individual
flowrates of A and B were such that flame retardant material
comprised a calculated 25 weight percent of the overall
multilayered film and the overall thickness was measured at 100
micrometers.
[0117] Examples 9 and 10 were made in a similar manner to Example 8
except Example 9 used a 29 layer feedblock and Example 10 used a 91
layer feedblock.
[0118] Examples 8-10 were tested for both Hanging Strip and
Horizontal Burn. The test results, film layers and flame retardant
concentrations are shown in Table 6.
7TABLE 6 FR Ex. Layers % Hanging Strip Horizontal Burn 8 13 25
Melted and dripped <1 sec, low char, low smoke, would not ignite
extinguishes upon removal of flame 9 29 25 Melted and dripped <1
sec, low char, low smoke, would not ignite extinguishes upon
removal of flame 10 91 25 Melted and dripped <1 sec, low char,
low smoke, would not ignite extinguishes upon removal of flame
[0119] As seen, the thickness of the flame retardant layer could be
quite thin without adversely affecting the flame-retardant
performance of the overall film by loss of layer integrity.
[0120] Each of the patents, patent applications, and publications
cited herein is incorporated by reference as if each were
individually incorporated by reference. The various modifications
and alterations of this invention will be apparent to those skilled
in the art without departing from the scope and spirit of this
invention.
* * * * *