~ 59 8
E~ACKGROUND QF THE INVENTION:
Plastic ma~erials have been commonly employed in
the packaging industry for containing food, household and
pharmecutical products. Plastic containers have the
advantage of light weight and generally good chemical re-
: 5 ~i~tance and toughness~ Further plastic containers are
- available in a wide range of shapes, colors, and rigiditie~
: a~d can be formed by a variety of automatic apparatus.
` One of the main limitations of plast~cs in packaglng
:~ appli~atio~s ~s their permeability to ga~es and molsture~
which in many instances, can lead t~ product ~poilage or
deterioratLon ~ Effort~ to resolve this problem have lead
to the development of high-nitrile barrier type plastics ;~
- ~ which are said to minimize permeability but have yet to
achieve significant commerci2l1 usage.
Another approach has been the use of plastic/metal
laminates. Aluminum foil is most widely employed for this ~ .
- . appliaation and plastic/aluminum laminate material~ providean çffective gas/moisture barrier. Plastic/aluminum composite
i materials have very limited formability and, in mo~t instances,
aluminum laminated containers are fabricated by folding over
and heat ~ealing seams. In the deformation processes, aluminum
and aluminum alloys behave as conventional metals with ambient
temperature ~ensile elongation capabilities of about 30%O
As the working temperature i3 increased to an optimum of about
- 2 -
.
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:' ., '
- ~5~1~8~
~25C, uniform elongation increases to a maximum of about
60~. Most plastics start to deteriorate at temperatures
above 200C~ ~hus plastic containing lamina~es can be
worked at ~emperatures generally no higher than 200C and
at this low tempera~ure the limited ductility of aluminum
limits the forma~iiity of the laminate to shallow cup type
parts, that is, where the height to diameter of the cup is
not greater than 1~ This lack of formability of aluminum
laminated materials prevents their use in many packaging
applications.
.
Lead foil has also been considered for barrier type
plastic/metal laminates in that the resulting laminate
; would have improved formability. However, extensive post-
laminating processing is necessary to achieve sufficient
workability with plastic/lead laminates, and this require--
. men~ materially increases production cost. Other factors
limiting significant commercial use of plastic/lead laminate
materials are the low strength, high density and toxicity
of the lead.
THE PRESENT INVENTION: \~
; The family of alloys based on zinc-aluminumlsystems
have unique properties ~nd characteristics. These blloys,
under proper working conditions are superplastic, ~hat is
they possess the ability to withstand large, uniform deforma-
tion sustained by low applied pressure. For example, at
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~s9~
temperatures between 150C and 260~C sup~rplastic zinc-
22% by weight aluminum alloys have maximum elongation
capabilities of over 1,000% and minimal resistance to
deformation with flow stre~es of approximately 200 to
2,000 PSI. Within this temperature range thermoplastic
p~lym~rs are normally vacuum or gas pressure formed.
The eutectoid superplastic zinc alloys, that is
aIloys comprising zinc with ?2~ by weight of aluminum hav~
elongation capabilities of approximately 100% at ambient
temperature, and thus are uniqualy suited for cold forming
operation~ 9 Furthermore at room temperature, such binary
alloy system displays minimal strain hardening, a characteristic
which allows repeated flexure without appreciable hardening
o~ fracture of ~he alloy she~t.
~ 15 Table I set3 forth typical elongation as a function
of temperature for the zi~c- 22% by weight aluminum alloy
in ~he as-worked condition.
~ABLE I
TYPICAL ELONGATION AS A FUNCTION OF TEMPERATURE
FOR T~E ZINC-22% BY WEIGHT AL ALLOY
(as-worked condition) - :
20 1~0
- 65 ~0
25 260 425-~
)
~)5~ 8
With minor alloying additons, as to be more fully
discussed hereinafter, to the basic zinc-aluminum eutectoid
system, that is, zinc and 22% by weight aluminum, signifi-
cant increases in mechanical properties can be achieved while
5 still maintaining superplastic forming characteristics. For
example, a wrouyht quinary alloy consisting of zinc, 22
by weight aluminum, 1~ by weight copper, .04~ by weight
magnesium and .02% by weight calcium has particularly use~ul
properties in the present invention.
Typical mechanical strength properties of this wrought ~: '
quinary alloy as compared with the binary zinc-22~ by weight
aluminum alloy are ~et forth in Table IIo
TABLE II
Typical Room Temperature Mechanical Properties
of the Binary Zn-22~ by Weight Al Alloy and the
Quinary Zn-22% by Weigh~ 1% by Weight Cu-.04%
by Weight Mg~.02% by Weight Ca Alloy
(as-worked condition)
.
~ Binary Quinary
ao Tensile Streng~h, psi 25,000 60,000
Yield Strength, psi 20,000 50,000
Table III sets forth typical elongation as a function
o~ temperature for the zinc - 22% by weight a7uminum, 1% by
weight copper,.04% by weight magnesium, .02% by weight calcium
alloy.
`
g~
- - TABLE III
TYPICAL ELON~ATION AS A FUNCTION OF TEMPERATURE
FOR THE Zn-22% BY WEIGHT AL ~ 1% BY WEIGHT Cu - .04% BY
WEIGHT Mg - .02% BY WEIGHT Ca ALLOY
(as-worked condition)
.
T~y~, C % Elongation
200
260 425~
The family of alloys based on the ~inc-aluminum system
havi~g superplastic properties suitable for use in the present
.inventio~ comprises aluminum in the range of from-about 1 to ~ ~:
S0~-by weight; copper in a range of from about 0 to 10% by
~ ~ . weight with the balance being~zinc with or without traces of
:~ 15 magnesium, calcium, sodium and potassium from about 0 to about
O3% by weight.
: '
The copper and the trace element~ improve corrosion
resistance and strength~
, -- .
ParticularIy useful examples within the family of
~0 alloys based on the zinc~aluminum system are set forth in
the following tabl~:
TABL~ IV
Al Cu Zn Traces
_
5~ 0.1 to 5~ Bal. Mg. and Ca.
22~ 0 to lG~ Bal. Mg~ and Ca.
Percentages are by weigh~.
~ 59 ~ ~ 8
It is ~herefore an object of the present invention to
provide a unique family of plastic/metal laminate materials.
In particular, the combination of ~inc-aluminum alloys with or
without alloying additions and thermoplastic polymers provide
new and novel materials which (1) can withstand large amounts
of deformation at both ambient and low elevated temperatures;
(2) are impermeable to gas and moisture thus providing ~arrier
type protection; (3) can be tailored to achieve a wide range
of service properties; (4) can be readily fabricated or
laminated by existing technology; (5) and require no special
post-laminating processing.
The unique forming characteristics of the plastic/
- metal laminate of the present invention are achieved by
utilizing a member of the superplastic zinc system for th~
-: 15 at least one metal layer so that the optimum elevated temp-
erature range for working the indivîdual layers overlap with
one another and a nominal working temperature of 150C can
. .
; be used for the laminated material. Furthermore, at 150C
; ~ alloys of ~le zinc-aluminum system display superplasticity
and thus thermoforming processes typically utilized for
thermoplastic polymers can be employed with the thermoplastic
polymer/superplastic zinc laminate material.
Similarly, the excellent cold formability of the
binary zinc - 22~ by weight aluminum alloy permits the forma-
tivn of a plastic/metal laminate material with excellentcold forming characteristics. Thermoplastic polymers with
good cold formability with the binary zinc-aluminum alloy
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; ~
~ ~Q~ 388
~uch as acrylonitrile-butadiene-styrene or polyvinylchloride
are to be preferred in the cold forming application of the
new laminate material.
- The above and other objects and advanta~es are
S provided by a laminated sheet structure comprising.a layer
of thermoplastic polymeric material adherently associated
with a surface of a layer of zinc-aluminum alloy having
superplastic properties at a temperature below the tempera-
.
ture at which substantial deterioration of the polymeric
-- 10 material occurs and by a method of making a laminated
- sheet structure which comprises adhering at least one layer
. ~ .
of thermoplastic polymeric material to a surface o a layer
of zinc-aluminum alloy having superplastic properties at
a temperature below the temperature at which substantial
.~ . . .
deterioration of the polymeric material occurs.
~, The invention will be more particularly described
'~J . ' in reference to the accompanying drawings, wherein:
.. ~
. ~ FIGURES 1, 2 and 3 are greatly enlarged rapresenta-
tions of several useful forms of the laminated sheet structure.
.. ~ .
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~` 20 The plastic film employed in the laminate must have
sufficient ductility to withstand large deformation; there-
after the selection of the plastic material will to a sub-
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/ stantial extent depend on the environmental and service
.' requirements of the application in which the laminate is
.,
::- 25 to be used.
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In general the laminate material may be fabricated
with the plastic layers of the same or different composition
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5~81~3
on each side of the zinc-aluminum alloy layer and multiple
layers of zinc-aluminum alloy and plastic may be employed.
With plastic layers on each side of the zinc-aluminum alloy
the metal is protected from the environment and the plastic
layers facili~ate joining, labeling, etc. of the product to
be formed from the laminate~ While in general it is anticipated
that plastic layers of the same or different composition will
be on each side of the zinc aluminum alloy in some applications
it may be desirable to use only a single plastic layer and to
then plate or anodize the exposed metal surface for special
effects. It is as hereinbefore set forth possible in following
the teachings of the present invention to provide multi-layered
plastic/metal laminates. -~
. , .
Throughout the specificat:ion and claims the word
I'layers" is intended to include sheets, foils, bars, wire,
tubes and the like.
- Where, for example, the improved laminate is to be
- used for interior panels of automotive vehicles a single
exposed layer of plastic and a strength producing layer of
the zinc-aluminum alloy would be sufficientO However, where
the new laminate material is to be used in the construction
of an automotive gas tank the interior plastic layer would
be one particularly inert to liquid hydrocarbons and the
outside plastic layer would be selected for its weathering
and abrasion resistance characteristicsO
Thermoplastic polymers, that is plastics capable of
heing repeatedly softened by increase of temperature and
hardened by decrease of temperature and wherein the change
_9_
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l~S9i~8~ .
upon heating is substantially physical rather than chemical
in nature which are suitable for use in the improved laminate
- material of ~he invention include:
Rolyolefins:
polyethylene (high and low density)
- RlYpropylene
polybutene (polybutylene)
Vinyl polymers:
polyvinylchloride and copolymers
polyvinylidenechloride
polystyrene and copolymers
poly (co-acrylonitrile-butadiene-styrene~ (ABS)
polyvinylfluoride
Acrylic polymers: polymethylmethacrylate and
copolymers
Polyesters: polyethylene terephthalata ~Mylar)
Polyamides:
- poly (hexamethyleneadipamide) (nylon 6, 6)
poly (~ -caprolactam~ (nylon 6)
Po~yacetals: polyoxymethylene and copvlymers
Cellulose esters: cellulose acetate
. ~ .
As hereinbefore set forth~ the metal layer, of the
- plastic metal laminate in ths present invention provides an
, effective gas-moisture barrier. A key factor in selecting the
, .
composition of the metal layer is that its forming capabilities
be compatible with the plastic layer or layers. A large
number of the thermoplastic polymers have an optimum forming
te~perature of about 150C such as polyethylene, cellulose
acetate, et~. and it is in the vicinity of this temperature
that the metal layers display good forming characteristics.
, . . .
; Alloys of zinc - 22% by weight aluminum display superpIastic
forming characteristics within the temperature range of 150C
and 260C as illustrated in Tables I and III and these alloys
have a favorable density of about 0.187 pound per cubic inch
and are generally non toxic, a very imporkant consideration
-~ ~ in packaging applications.
--10--
. .
~s~
The binary zinc - 22% by weight aluminum alloy as
illustrated in Table I displays good cold formabilit~ and a
plastic/metal laminate using this alloy for the metal layer
may be employed in cold fo~ming operations in which the limits
of formability will usually be defined by the plastic layer
or layers.
While the zinc - ~2% by weight aluminum alloys appear
- to be best suited for use in the present invention æinc
based alloys containing from 1 - 50% by weight aluminum
display superplastic characteristics at temperatures
compatible with plastics and are within the ~cope of the
pxesent invention.
The plastic/metal laminate material can be laminated
by methods commonly employed for o her plastic/metal
laminates. With respect to sheet or foil, techniques
1 employed for plastic/aluminum laminates are suitable including
` ~ continuous and non-continuous processes with or without the
use of adhesives~ The bond between plastic and the metal
layers should be of sufficient integrity to withstand large
deformation and the desired ser~ice condition including
thermal cycling required for thermoforming of the laminates.
In general mechanical bonding of the plastic to the
zinc-aluminum alloy in a continuous process is preferred on
both a product reliability and economic basis. In general the
metal suxface should be thoroughly cleaned to remove oil and
grease prior to bonding and surface treatment of the metal
such as the conventional phosphate or chromate conversion
coating may be used to aid bonding.
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~59~388
Where an adhesive is required to bond the plastic-
metal interface it should have sufficient flexability to
withstand the large deformation and epoxy or nitrile rubber
based adhesive are suitable for this purpose.
Table V sets forth examples of plastic/superplastic
zinc laminate materials which were fabricated under the tabl~d
conditions; the materials laminated as set forth in Table
V were subjected to me~hanical testing to assess ~heir
properties and the materials were tensile tested in a con-
ventional manner at room temperature and elevated temperatures
of 150C, 200C and 260C~ In addition room temperature Olsen
ductility tests were run on the composites and typical results
- of the tests are presented in Tables VI, VII and VIII.
Re~erring specifically to Table VI it will be noted
that the table presents the room temperature tensile properties
of a number of laminates and of t:he binary foil consisting of
zinc and 22~ by weight aluminum. It will be noted that all
of the laminates have modest strength and excellent elongations.
. I .
Further, the results indicate that the laminates can be
subjected to extensive cold deformation without failure of
the laminate.
,
The results of the room temperature Olsen ductility test-
; ing are presented in Table VII. The higher the height to
*ailure value, the greater the ductility of the material. The
results of these tests show that the improved laminate materials
of the invention have almost the same degree of ductility as
the unlaminated superplastic zinc aluminum foil. The
-12-
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,' ' -' ' : '
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~ s9~
inclusion of the tests on the cartridge brass foil and sh~et
consisting of 70~ copper, 30% zinc are presented for
ComparisQn purposes since this particular brass is considered
a ~'standard" for cold forming metals.
. The elevated temperature tensile strength data pre-
sented in Table VIII indicate that the laminate materials of
the invention have low tensile strength and very high elongation
factors even at 150C.
Suitable methods of utilization of the new laminated
material includes techniques commonly employed for metals
an~ plastics. For example, in sheet form, these include
; stamping and deep drawing as co~nonly done with metals, as
` ~ well as plastic forming techniques such as compression molding,
matchplate forming, and pressure vacuum thermoforming. The
excellent forming characteristic~; of the new laminate
materials are consistent with fo:nming a deep "cup" having
a large height to diameter ratio that is greater than one.
Blow molding cups and bulge forming hollow sections are also :~
within the realm of suitable forming techniques.
The structural strength of the laminate material may
to a large extent be controlled by varyin~ the composition
and/or the thickness of the plastic and/or the metal layer.
With respect to the metal layer(s) use of the binary zinc -
22~ by weight aluminum alloy optimizes formability both at
ambient and low elevated temperatures and such binary alloy
could be desirable in applications where strength and rigidity
-13-
,
~5~9~3133 3
are not critical or where the properties of plastic material
are close to the required laminate properties. Also, the binary
alloy, zinc - ~2% by weight aluminum, is probably the most
suitable for application where repeated flexing is important as
the binary alloy has minimal strain hardeniny characteristics.
Use of the higher strength zinc aluminum alloys, that is for
example zinc - 2~% aluminum by weight - 1% by weight copper -
oO4% by weight magnesium and .02% by weight calcium permits
the thickness of the laminate material to be minimized while
still providing a relatively high strength structureO
In applications, such as packaging where the metal
layer is present essentially to provide barrier protection
economics dictate that the metal layer be as thin as possible.
It has been found that by employing superplastic zinc alloys
~ 15 in the laminate the thickness of the metal layer can be
; reduced to less than 0.025 mm while still maintaining a
continuous pinhole free layer. TID achieve a greater rigidity
and strength, a thicker metal layler can be utilized. Such
- laminates have been found to have good formability where the
superplastic zinc sheet has thickness greater than for
- example 3 mm.
The structural strength of the laminate is also
influenced by the plastic component ox components thereof.
As previously set forth, in most instances, the selec~ion of
-14-
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~L~59~38~3
the plastic or plastics employed for the laminate material
will be dictated by service requirements, of which structural
streng h may be secondary. However t the use of reinforcing
fi~lers t which is a common and effective method of increasing
~trengths of plastic~, may also be employed in the plastics
used in use with the plastic~metal laminates of the inventlonO
The plastic/zinc-aluminum alloy laminate may contain layers
~f other materials to achieve special propexties or characteris-
tics. For example, a layer of fiber glass fabric or rubber
can be included in the laminate o~ ~his invention. The prime
consideration in adding layers of other materials is that the
~ ductility of the additional layers be compatible with the
- deformation to be experienced by the laminate as a whole.
Referring to figures 3, 4 and 5 which are greatly
enlarged representations of se.veral useful forms of the
laminated sheet structure of the invention in each of which
(1~ indicates a layer of zinc-aluminum alloy having ~uperplasti~
: properties and (2) indicates a thermoplastic polymeric material.
In addition to the particular suitable use of the
laminates of the invention in the packaging industry the
new materials have a wide variety of other applications
~uch as for example gasket material, gas tanks, automobile
interior panels, static electricity shielding materials,
etc. It is apparent that in view of the extreme versatility
of the plastic/superplastic zinc laminate material ~he ma~erial
may ~ind application in thin or thick sheet fo~m as well as
- 15 -
.
"
~ S~ 8 8 ~
: ~ar, wire, fibre and tubular products and wo~en material.
From ~he oregoing description of the present
invention it will be recognized by those skllled in the art
that the object and advantages hereinbefore set forth and
S others are fully accomplished.
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