Note: Descriptions are shown in the official language in which they were submitted.
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Docket No. 664.00002
Field of the Tnventi~"
This invention relates to tubing, such as that
used to convey beverages, and, more particularly, to
multi-layer tubing.
Background o the Th~~pntion
Tubing used in the beverage industry has several
special performance criteria that must be met. Unfortu-
nataly, oftentimes these criteria are competing in that
the fulfillment of one of the criterion necessarily leads
l0 to a failure in another. Likewise, while the use of
thermoplastic materials in the manufacture of beverage
tubing can afford a performance advantage, it can likewise
create special problems specific to the thermoplastic
material used.
For example, tubing used to transfer syrups and
carbonated beverages can be designed with thermoplastic
materials that~will not impart taste or odor to the bever- .
age but will then be susceptible to stress cracking.
Other thermoplastic materials have inherent stress crack
resistance, butltend to impart a taste to the beverage.
Thus, thermoplastic beverage tubing is often made to
compromise between low taste transmission and stress crack
resistance.
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In addition, due to the relatively high perme-
ability of these thermoplastic materials, beverages can
- become contaminated by the ingression of vapors and/or
liquids. Cleaners, pesticides, and disinfectants can come
in contact with the tubing. When installed in under-the
floor conduits, water can collect around the tubing,
become stagnant and effect contamination thereof. When
held in relatively close proximity, aggressive liquids,
such as root beer, can permeate out through one tube and
into an adjacent tube thereby affecting the flavor of the
beverage in that tube.
Similarly, these thermoplastic materials can
have inherently low resistance to permeation by carbon
dioxide gas so that carbonated drinks tend to lose their
carbonation.
The use of a gas barrier layer can offer excel-
lent resistance to permeation by oxygen, carbon dioxide
gas, and organic hydrocarbons, thus keeping the proper
flavor and carbonation in the beverage within the tubing
and the unwanted flavors outside the tubing. However, the
tubing with a gas barrier layer in the outermost layer in
a thermoplastic beverage tube may not perform well when
carbonated beverages are used. The carbon dio~Cide gas
from the carbonated beverage, while being impeded by the
barrier layer, can cause a build-up in pressure sufficient
to blister the 'outer gas barrier layer. Hence, the need
to compromise between low taste transmission and control
of gas permeation and tube blistering (in carbonated
applications) has existed.
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Finally, to prevent leakage of beverage between
beverage tubing and a metal fitting thereon, it is impor-
taut that there be close, sealing contact between the
thermoplastic tube material and the metal. Generally, a
narrow', metal band clamp forces the tubing onto barbs on
the fitting. If the thermoplastic material used is one
that will not impart taste or odor to the beverage, then
the stresses exerted by the clamp can lead to stress
cracking in the vicinity of the clamp. If a stiff gas
barrier layer is used at the inner surface of a beverage
tube, it can be difficult to maintain close, sealing
contact with the metal fitting since the stiff material
tends not to conform to the barbs on the fitting without
the use of excessive force exerted through the clamp. The
need for excessive force on the clamp can lead to cutting
or cracking of the outer layer of the tubing.
Thus, there is a need for beverage tubing that
effectively avoids taste transmission, and resists stress
cracking, vapor and/or liquid permeation, loss of carbon
ation, and tube blistering.
Summary of the Inven -i ~.,
The, present invention is specifically directed
to overcoming the above-enumerated problems in a novel and
simple manner.
According to the invention, a multi-layer tubing
for beverages is provided, with the tubing including a
beverage contact layer formed from a first thermoplastic
material, a second layer formed from a second thermoplas-
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tic material wherein the second thermoplastic material is
coextruded with the first thermoplastic material, a gas
barrier layer bonded to the second thermoplastic material
and formed from a material resistant to gas diffusion, and
an outer layer bonded to the material resistant to gas
diffusion and formed from a third thermoplastic material.
Through use of a multi-layer construction, the
tubing can obtain the benefit of the performance advantag
es afforded by a specific thermoplastic material used to
form a layer while compensating far its deficiencies
through the use of another thermoplastic material in a
different layer. The manner and order in which the layers
are put together also contributes to the benefits to be
achieved through a multi-layer construction.
Preferably, the first thermoplastic material
imparts low taste and resists odor transgression to the
beverage, the second thermoplastic material is coextruded
with the first thermoplastic material so that the forma-
tion of stress cracks in the beverage contact layer is
minimized, the material resistant to gas diffusion is
bonded to the coextruded second thermoplastic material by
a first layer of adhesive material therebetween, and the
third thermoplastic material is bonded to the material
resistant to gas diffusion by a second layer of adhesive
material therebetween with the outer layer being of suffi-
cient thicknesslto prevent blistering of the gas barrier
layer in use.
In a preferred form, the first thermoplastic
material is low density polyethylene or polypropylene.
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Preferably, the second thermoplastic material is linear
low density polyethylene, ethylene vinyl acetate, or a
-' thermoplastic elastomer. Even more preferably, the ther
moplastic elastomer is a polypropylene-based thermoplastic
elastomer. In another preferred form, the third thermo
plastic material is linear low density polyethylene,
ethylene vinyl acetate, a thermoplastic elastomer, or
polyvinyl chloride. Even more preferably, the thermoplas-
tic elastomer is a polypropylene-based thermoplastic
elastomer. In yet another preferred form, the material
resistant to gas diffusion is ethylene vinyl alcohol.
In one exemplary embodiment, the first and
second layers of adhesive materials are the same material.
In another exemplary embodiment, the second and third
thermoplastic materials are the same material. In yet
another exemplary embodiment, the second and third same
thermoplastic materials are one of either linear low
density polyethylene, ethylene vinyl acetate, or a thermo-
plastic elastomer. In yet another exemplary embodiment,
the thermoplastic elastomer is a polypropylene-based
thermoplastic elastomer.
brief Descr i nt i nn Of the Dratoi nrr
Fig. 1 is a cross-sectional view of a multi-
layer beverage tubing.
Vita>>ed Description of thA n,.~~°"~
Fig. 1 shows a cross-sectional view of a multi-
layer tubing l0 for transporting beverages 12
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therethrough. With the introduction of beverage bundles,
several tubes are disposed in close proximity carrying
different beverages and syrups to the dispenser.
The beverages 12 to be transported by the tubing
10 will normally be carbonated beverages but can also be
noncarbonated beverages or beverage syrups. Carbonated
beverages include three chief ingredients: syrup, water,
and carbon dioxide. The syrup provides the flavor and
generally contains sugar and some flavoring material,
which may be from natural fruit or, more often, synthetic
flavors. Fruit acids, such as citric acid, are commonly
used as an important constituent of syrups to accentuate
the other flavoring used. The carbon dioxide is usually
pressurized and is combined with water by cooling the
water to near freezing to increase the solubility of the
carbon dioxide in the water.
Referring to Fig. 1, an innermost layer or
beverage contact layer 14 is formed from a first thermo-
plastic material 16 that imparts low taste and odor to
the beverage 12 as it flows through the tube 10. The
first thermoplastic material is highly stable and inert.
Preferably, the first thermoplastic material 16 is low
density polyethylene or polypropylene.
Because the first thermoplastic material 16
generally will not have good environmental stress cracking
resistance, a second layer 18, formed from a second ther
moplastic material 20, is coextruded therewith so that the
formation of stress cracks in the beverage contact layer
vis minimized. The second thermoplastic material 20 exhib
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,its excellent inherent environmental stress crack resis-
tance but will generally have a decreased stability to
- oxidation during the extrusion process and is therefore
more likely to impart a taste or odor to the beverage 12
than the first thermoplastic material 16. Preferably, the
second thermoplastic material 20 is one of either linear
low density polyethylene, ethylene vinyl acetate, or a
thermoplastic elastomer. Even more preferably, the ther
moplastic elastomer is a polypropylene-based thermoplastic
elastomer.
Die lines from the extrusion process lower the
environmental stress crack resistance along those lines.
Coextruding the thermoplastic beverage contact layer 16
with a surrounding, concentric second thermoplastic layer
20 allows the two thermoplastic resins 16 and 20 to come
together in the molten state so that the outer surface of
the thermoplastic beverage contact layer 14 can not cool
with die lines and can not come in contact with any envi-
ronmental stress cracking agents. Since stress cracks are
propagated at the outer surface of the tube, the use of
the second thermoplastic layer 18 protects the thermoplas-
tic beverage contact layer 14 and affords the tube 10
improved environmental stress crack resistance'while the
use of an inner thermoplastic beverage contact layer 14
provides low taste and odor properties.
Because the thermoplastic beverage contact layer
14 and the second thermoplastic layer 18 have relatively
high permeability, a gas barrier layer 22 can be bonded to
the second thermoplastic layer 18. The gas barrier layer
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22 is concentric with and circumscribes the second layer
18 and coextruded beverage contact layer 14. The gas
barrier layer 22 is formed from a material resistant to
gas diffusion 24. Preferably, the gas resistant material
24 is a seamless, coextruded layer of ethylene vinyl
alcohol. The ethylene vinyl alcohol provides excellent
resistance to permeation by oxygen or organic hydrocar-
bons, thus isolating the flavor of the beverage 12 in the
tube 10 from external contaminating agents. When several
different beverages 12 are used in different beverage
tubes 10 in close proximity to one another and one of the
beverages 12 is root beer, the gas barrier layer 22 is of
particular importance since gas chromatography mass spec-
troscopy evidence exists showing that the root beer fla-
vor, notorious for permeating through conventional tubes
not employing such a layer, does not permeate through
applicants tubing 10 incorporating the gas barrier layer
22.
A relatively thick outer layer 26 formed from a
third thermoplastic material 28 can be bonded to the gas
barrier layer 22. The third thermoplastic material 28
exhibits excellent stress crack resistance, provides the
tube 10 with improved kink resistance, and holds the
barrier layer 22 down, eliminating blistering in
applications involving carbon dioxide or carbonated beWer-
ages. furthermore, by having the barrier layer 22
sandwiched between the second and third thermoplastic
layers 18, 2C, the barrier layer 22 is protected, which is
especially important under the clamp at the fitting, and
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allows the thermoplastic beverage contact layer 14 to
conform more readily to the barbed fitting providing
better sealing performance. Preferably, the third thermo-
plastic material 28 is one of either linear low density
polyethylene, ethylene vinyl acetate, a thermoplastic
elastomer, or polyvinyl chloride. Even more preferably,
the thermoplastic elastomer is a polypropylene-based
thermoplastic elastomer.
To bond the gas barrier layer 22 to the second
to thermoplastic layer 20, a first adhesive layer 3o can be
used. The adhesive resin employed must be compatible with
both the second thermoplastic material 20 and the gas
resistant material 24. Likewise, to bond the gas barrier
layer 22 to the third thermoplastic layer 26, a second
adhesive layer 32 is used. Both adhesive layers 30 and 32
provide the barrier layer 22 with improved resistance to
blistering in carbonated applications and resistance to
separation of the layers during flexing.
While the thicknesses of the layers can vary,
generally the thermoplastic beverage contact layer 14 and
the second thermoplastic layer 18 are approximately the
same thickness, while the third thermoplastic outer layer
26 is approximately 1.5 times as thick as either one of
the beverage contact layer 14 or second thermoplastic
layer 18. The barrier layer 22 and the,adhesive layers 30
and 32, by comparison, are relatively thin with their
thicknesses being anywhere from 5 to 15 times thinner than
the thickness of either one of the beverage contact layer
14 or second thermoplastic layer 18. In an exemplary
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embodiment where the tube wall is .06 inches thick, the
thicknesses are as follows: beverage contact layer 14 and
- second thermoplastic layer 18 - .015 inches; first adhe
sive layer 30 - .003 inches; gas barrier layer 22 - .001
inches; second adhesive layer 32 - .002 inches; and outer
thermoplastic layer - .024 inches.
To manufacture the tube 10, a three-stage con-
tinuous extrusion process is employed. In stage one, the
beverage contact layer 14 and second thermoplastic layer
18 are coextruded. A dual walled tube is formed in one
extrusion die and cooled in water. In stage two, three
layers are simultaneously extruded from one extrusion die
coating the dual-layered tubing. The three layers are:
the first adhesive layer 30 which fuses to the second
thermoplastic layer 18, the barrier layer 22 which is
fusion compatible with the adhesive layers 30 and 32, and
the second adhesive layer 32 which is fusion compatible
with the barrier layer 22 and the outer thermoplastic
layer 26. A relatively thick outer layer 26 is then
applied to the five-layer tube, fusing to the second
adhesive layer 32 in the final stage. This is a conven-
tional, single component extrusion coating operation,
thereby creating the complete multi-layer tube 10 with
each layer fused to the adjacent layer.
To convert the tube 10 for use in high pressure
environments, yarn reinforcement can be used (not shown)
between the thick outer layer 26 and the second adhesive
layer 32. To produce the reinforced hose or tube 10, the
reinforcement is a pair of spirally opposed textile yarn
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layers applied to the five-layer tube immediately prior to
the application of the outer layer 26. Fusiori between the
second adhesive layer 32 and the outer layer 26 occurs
through the interstices of the reinforcement layer.
Examtile 1
A tube formed using low density polyethylene as
the beverage contact layer offers flexibility and low
taste properties but does not have good resistance to
environmental stress cracking. Therefore, a second layer
l0 of linear low density polyethylene with excellent inherent
environmental stress crack resistance is coextruded with
the low density polyethylene.
An ethylene vinyl alcohol layer is used to
provide excellent barrier resistance to oxygen, carbon
15 dioxide, and organic hydrocarbons, thereby protecting the
fluid inside the tube from contamination by the exterior
environment, flavor transfer from other nearby tubes, and
oxidation. The excellent resistance to permeation by
carbon dioxide preserves the carbonation in carbonated
20 fluids.
The relatively thick outer layer of linear low
density, polyethylene provides further stress crack resis-
tance as well as physical protection. The similarity in
the physical properties of the various polyethylene layers
25 enables the multi-layer composite tube to be coupled to
the fitting in the same fashion as single component poly-
ethylene tubing.
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Examtile 2
For added flexibility, the thick outer layer can
be formed from ethylene vinyl acetate instead of linear
low density polyethylene, which will stall be fusion
compatible with the second adhesive layer used with the
linear low density polyethylene.
ESA
For even greater flexibility, both the thick
outer layer and the second layer can be formed from ethyl
ene vinyl acetate. Due to the improved resilience of the
ethylene vinyl acetate, stress crack resistance is still
preserved.
Example 4
The structures of Examples 1 or 3 can be modi
Pied so that polyvinyl chloride is used in the outer
layer. Although it does have a low coefficient of fric
tion, the abrasion resistance of linear low density poly
ethylene is not exceptional. Ethylene vinyl acetate has a
high coefficient of friction but relatively low abrasion
resistance and low resistance to thermal softening.
Flexible polyvinyl chloride is an excellent
choice for flexibility, abrasion resistance, and resis-
tance to thermal softening. The use of. polyvinyl chloride
allows for a much thicker outer layer to greatly improve
the kink resistance.
When polyvinyl chloride is used for the thick
4outer layer, the second adhesive layer has to be modified
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to provide fusion to the ethylene vinyl alcohol barrier
layer as well as the polyvinyl chloride outer layer.
Ex~ple 5
In some cases, it may be important to reduce
ingression into the tube by the fluid or certain organic
components of the fluids generally associated with the
flavor itself. A different choice for the beverage con
tact layer may be used, such as polypropylene.
Polypropylene provides a more inert surface to reduce the
absorption of flavor-carrying chemicals into the beverage
contact layer. This is particularly important in applica-
tions where it is desired to change the beverage being
carried by the tube without flavor carry-over to the next
beverage to be used in the tube.
While polypropylene provides low taste proper-
ties and resistance to environmental stress cracking, it
sacrifices flexibility. Using thermoplastic elastomer
blends based on polypropylene in the second layer and
outer layer affords the multi-layer composite tube good
flexibility and kink resistance. When using a thermoplas-
tic elastomer, care, should be taken to make the proper
choice of adhesive for the first and second 'adhesive '
layers, so that they fuse to both the thermoplastic elas-
tomer and the ethylene vinyl alcohol barrier layer.
The foregoing disclosure of specific embodiments
is intended to be illustrative of the broad concepts
comprehended by the invention.
