FIELD OF THE INVENTION
This invention relates to coextruded laminate structures in which
one of the layers is fluoropolymer.
BACKGROUND OF THE INVENTION
U.S. Patent 5,500,257 discloses the preparation of fluoropolymer
composite tubing useful as automotive fuel line or hose, by first extruding a tubing
of the fluoropolymer, then surface activating the outer surface of the fluoropolymer
tubing by exposure to corona discharge or plasma, followed by extruding an outer
layer of thermoplastic polymer onto the tubing. The fluoropolymer inner layer provides
excellent chemical resistance and impermeability to fluid such as fuel when passed
through the tubing. The outer layer which is preferably polyamide provides strength
and abrasion resistance to the overall composite tubing. Surface activation of
the outer surface of the tubing of fluoropolymer causes the extruded layer of polyamide
to adhere to the inner layer of fluoropolymer to give the tubing integrity. While
this tubing is useful, it has the disadvantage of requiring two extrusion operations
and an intervening surface treatment, and the fluoropolymer tubing has to have
sufficient wall thickness, i.e. at least (0.2 mm) (8 mils), to be self-supporting
until the outer layer of polyamide is applied. This wall thickness is generally
thicker than necessary for providing the chemical resistance and impermeability
required for the composite tubing.
Example 14 of PCT Publication WO 96/03448, published February 8,
1996, (equivalent to U.S. Patent 5,576,106) discloses coextrusion of polyamide,
an adhesive interlayer, and fluoropolymer through a slit die to produce a laminate
in one step. The polyamide and fluoropolymer layers of the laminate are each 0.9
mm (35 mils) thick and the interlayer tying these two layers together is 0.2 mm
(8 mils) thick. This Example also discloses that by using a cylindrical coextrusion
die instead of a slit die, tubular structures can be formed, useful in such applications
as fuel hose and tubing in heat exchangers. The adhesive interlayer is a fluoropolymer
which has an ethylenically unsaturated compound grafted thereon providing polar
functionality to the fluoropolymer of the adhesive interlayer. The fluoropolymer
adhesive starts out as a powder and the grafting reaction is carried out only on
the surface of the powder. Nevertheless, the polar functionality giving the fluoropolymer
its adhesive property survives coextrusion to form the adhesive interlayer tying
the fluoropolymer and polyamide layers together. The teaching in this patent publication
can prepare automotive fuel line or hose which can be used in place of the product
of the '257 patent, but with the advantage of using only one extrusion step. It
has the disadvantage, however, of requiring the expense of the adhesive interlayer
and an additional extruder for the interlayer.
US Patent 5,472,784 discloses a composite material comprising at
least an outer layer based on a polyvinylidene fluoride (PVDF) and a neighbouring
layer made from a composition based on a mixture of 40-90 wt% polyamide and 60-10
wt% polyglutarimide, these layers being adhesively bonded.
US patent 5,500,263 discloses plastic pipes comprising at least one
outer layer, at least one inner layer comprising a PVDF composition and an intermediate
layer comprising a mixture of polyamide and polyalkyl acrylate, these layers adhesively
bonded to one another.
US patent 4,563,393 discloses a laminate consisting essentially of
(A) a layer of thermoplastic resin containing 3-80 wt% of polymerised units of
an ethylenic unsaturated carboxylic acid ester and (B) a layer of a PVDF resin.
The polymerised units of an ethylenic unsaturated carboxylic acid ester in (A)
may exist either as a copolymer constituent of (A) or a polymer blended in (A).
PCT publication WO 96/05965 discloses a method for increasing the
adhesion of a layer of fluoropolymer to a layer of melt-processable, substantially
non-fluorinated polymer. The fluoropolymer comprises interpolymerised units derived
from vinylidene fluoride.
SUMMARY OF THE INVENTION
The present invention relates to a laminate comprising fluoropolymer
and polyamide layers, which laminate can be formed in a single extrusion step,
i.e., by coextrusion, wherein the fluoropolymer layer and the polyamide layer
adhere to one another without the presence of an adhesive tie layer, said fluoropolymer
being a perfluorinated copolymer or a copolymer of ethylene with perhalogenated
monomer, and wherein said layer of fluoropolymer forms a surface of said laminate.
Thus, the present invention provides a coextruded laminate comprising
a layer of fluoropolymer and a layer of polyamide directly adhered to one another,
at least one of said fluoropolymer and said polyamide having been adhesively activated
prior to coextrusion to form said coextruded laminate to provide the adhesion between
said layer of fluoropolymer and said layer of polyamide, said fluoropolymer being
a perfluorinated copolymer or a copolymer of ethylene with perhalogenated monomer,
and wherein said layer of fluoropolymer forms a surface of said laminate.
The laminate can be further characterized by the fluoropolymer layer
being a surface layer of the laminate when the fluoropolymer of this layer is
adhesively activated, i.e. the fluoropolymer layer forms at least one exterior
surface of the laminate. When the laminate is in the form of tubing, the adhesively
activated fluoropolymer layer can form the interior surface or the exterior surface
of the tubing. This characterization of the invention is unnecessary when it is
the polyamide layer that is adhesively activated.
By "directly adhered" is meant that there is no intervening tie layer
present. It is the adhesive activation of at least one of the polymers forming
the layers that causes the adhesion of the layers, one to the other, thereby providing
integrity to the laminate without the use of a tie layer.
In one embodiment, the adhesive activation is obtained by incorporating
a polymeric additive into the polyamide resin which forms the polyamide layer,
the additive having polar functionality and being dispersed as fine particles
within the polyamide resin. The polar functionality of the polymeric additive compatibilizes
the polymeric additive with respect to the polyamide matrix, whereby the polyamide
layer does not lose its strength and/or flexibility. Surprisingly, the additive
dispersion in the polyamide matrix constituting the polyamide layer of the coextruded
laminate also adheres the polyamide layer to the fluoropolymer layer.
In another embodiment, the adhesive activation is obtained by polar-group
functionalizing of the fluoropolymer which forms the fluoropolymer layer.
In still another embodiment, both embodiments of adhesive activation
The laminate of the present invention is made by the process of coextrusion
of the polymers described above, with at least one of the polymers having been
adhesively activated prior to coextrusion as described above. This process is another
aspect of the invention. The polymers are coextruded as layers directly in contact
with one another, so that the resultant adhesion between layers occurs without
a tie layer being present, i.e., the coextrusion is carried out in the absence
of any tie layer. When the fluoropolymer is adhesively activated, it is extruded
as a surface layer for the laminate. In addition to the savings resulting from
the absence of any tie layer, when the coextruded laminate is in the form of tubing,
the thickness of the fluoropolymer layer can be reduced from the conventional minimum
of (0.2 mm) (8 mils) to only the thickness needed for chemical resistance and impermeability
in particular applications such as fuel hose, e.g. to be less than 0.2 mm (8 mils),
such as no greater than (0.18 mm) (7 mils) in thickness. Surprisingly, the polar
functionalizing of the fluoropolymer, when that embodiment is used, does not adversely
affect the permeability of the layer to such fluids as gasoline.
BRIEF DESCRIPTION OF THE DRAWING
The Figure shows a tracing of the interface between the layers of
the tubing made in Example 1 in accordance with the present invention, which tracing
is taken from a photograph of a cross-sectional view of the interface provided
by Transmission Electron Microscopy.
Any polyamide can be used to constitute the polyamide layer of the
coextruded laminate. Such polyamide should of course be melt extrudable, and preferably
has a number average molecular weight of at least 5000. Examples of polyamides
include those made by condensation of equimolar amounts of at least one saturated
carboxylic acid containing 4 to 14 carbon atoms with at least one diamine containing
4 to 14 carbon atoms. Excess diamine, however can be used to provide an excess
of amine end groups over carboxyl end groups in the polyamide. Specific examples
include polyhexamethylene adipamide (66 nylon), polyhexarnethylene azelaamide (69
nylon), polyhexamethylene sebacamide (610 nylon), polyhexamethylene dodecanoamide
(612 nylon) and polycaprolactam (6 nylon). Aromatic polyamides that are melt extrudable
(e.g., aliphatic-aromatic polyamides, as opposed to polyaramids) can also be used
in the melt-mixed blends of the present invention. Examples of such semiaromatic
polyamides include Amodel® A 1000 and copolymers of 2-methylpentamethylenediamineterephthalate
and hexamethyleneterephthalamide such as Zytel® HTN 501 (DuPont). Elastomer-modified
versions of such aliphatic and aromatic polyamides can also be used, e.g., Amodel®
ET 1000 HSNT (Amoco). Polyamides are well-known in the art. See, for example, Kirk-Othmer,
Encyclopedia of Chemical Technology, 4th ed., Vol. 19, p. 454 (1996).
Examples of polymeric additives for the polyamide that adhesively
functionalize it include copolymers of ethylene with (meth)acrylic acid which
have been at least partially neutralized with metal ions, e.g. Li, Na, K, Mg, Ca,
Ba, Sn, Zn, or Al, to form an ionomer as described in U.S. Patent 3,262,272, and
ethylene/acrylate copolymers such as ethylene/n-butyl acrylate/glycidyl methacrylate
copolymer (EBAGMA) and ethylene/n-butyl acrylate/carbon dioxide copolymer (ENBACO).
In the case of these copolymers, the carboxylic acid groups or the salts or esters
thereof provide the polar functionality to the polymeric additive by the copplymerization
process forming the additive.
Additional polymeric additives include those in which the polymer
as made is non-polar but which is then functionalized to become a polar-functionalized
polymeric additive useful in the present invention. Examples of such polymers
include elastomers such as the well-known ethylene(E)/propylene(P)/diene (EPDM)
elastomers, such as E/P/1,4-hexadiene, E/P/dicyclopentadiene, E/P/5-ethylidene-2-norbornene
copolymers. The polymeric additive may also be a non-elastomeric hydrocarbon polymer
such as ethylene polymer, including homopolymer and copolymer. The polymeric additive
can be polar functionalized, for example, by grafting of an ethylenically unsaturated
compound by conventional processes onto the polymer prior to incorporation of the
additive into the polyamide. The compound has polar functionality, whereby the
grafting reaction imparts polar functionality to the polymeric additive.
Another example of polymeric additive that can be used to adhesively
activate the polyamide is functionalized fluoropolymer as described below. When
polyamide is adhesively activated in this way, the amount of functionalized fluoropolymer
is generally in the range of 5-55 wt%, preferably 10-40 wt%, and more preferably
15-30 wt%. Further, when polyamide is adhesively activated in this way, the functionalized
fluoropolymer has the same general composition as the fluoropolymer of the fluoropolymer
layer of the laminate, or is compatible (miscible) with the fluoropolymer of the
Examples of polar functionality whether provided by polymerization
or grafting include acids, including carboxylic, sulfonic and phosphonic acids,
and esters and salts thereof. In the case of compounds for grafting onto and thereby
becoming part of the polymeric additive, diacids and anhydides thereof are preferred.
Examples of grafting compounds include maleic anhydride, phthalic anhydride, diethyl
maleate, itaconic anhydride, citraconic anhydride, and glutaconic anhydride.
The amount of polymeric additive used in the polyamide can vary widely
to provide the strength, flexibility, and/or abrasion resistance desired for the
coextruded laminate. It is only desired that the polyamide be the continuous phase
(matrix) of the polyamide layer. Generally this will require at least 40 wt% of
polyamide based on the combined weight of the polyamide and polymeric additive.
The minimum amount of polymeric additive will usually depend on the amount of polar
functionality present in the additive. The amount of polar functionality will depend
somewhat on whether the polar functionality is obtained by polymerization or by
grafting. In the case of polymerization, e.g., of the ethylene copolymers described
above, the polar-functional monomer will generally constitute from 5 to 35 wt%
of the copolymer forming the polymeric additive. In the case of grafting to form
the functionalized polymer additive, the grafting compound will generally constitute
0.1 to 2 wt% based on the weight of the resultant grafted polymer. Thus the minimum
amount of polymeric additive used in the polyamide will be that which is effective
to provide the direct adhesion of the polyamide layer to the fluoropolymer layer
upon coextrusion. At least 0.5 wt% of the polymer additive will usually be required
to produce this result.
The adhesion of the polyamide layer to the fluoropolymer layer can
be characterized by comparison with the situation when the polyamide and fluoropolymer
resins are coextruded and neither polymer is adhesively activated. The resultant
laminate simply separates into the individual layers upon the slighest touch. When
the coextrusion is in the form of tubing and the fluoropolymer forms the inner
layer, the inner layer practically falls out of the outer layer when the tubing
is cut in half. In contrast, the adhesion between inner and outer layers in coextruded
tubing made in accordance with the present invention is such that the inner layer
is integral with the outer layer, even when the tubing is longitudinally cut in
half. In that case, the cut composite tubing half can be flexed and even bent at
90 degree angle without the remainder of the inner layer of fluoropolymer delaminating
from the remainder of the polyamide outer layer. The same result is obtained when
the fluoropolymer forms the outer layer and the polyamide forms the inner layer
of the tubing and at least one of these layers is adhesively activated in accordance
with the present invention.
The polymeric additive can be incorporated into the polyamide resin
prior to or during the coextrusion operation, but the polyamide composition will
usually be made by melt compounding prior to coextrusion so as to obtain a dispersion
of fine particles sizes of the polymer additive in the polyamide resin. The particles
of the dispersed phase of polymer additive in the polyamide resin matrix can be
seen with a scanning electron microscope, and the particle size in this dispersed
phase will generally be from 0.01 to 10 µm, with smaller sizes, such as 0.1 to
1 µm, within this range being preferred for the grafted polymers.
With respect to the fluoropolymer constituting the fluoropolymer
layer of the coextruded laminate of the present invention, a wide variety of fluoropolymers
can be used which are melt extrudable, such as indicated by a melt viscosity in
the range of 0.5 × 103 to 60 × 103 Pa&peseta;s
as normally measured for the particular fluoropolymer. The fluoropolymer is made
from at least one fluorine-containing monomer, but may incorporate monomer which
contains no fluorine or other halogen. The fluoropolymer, however, preferably
contains at least 35 wt% fluorine. Fluorinated monomers include those which are
fluoroolefins containing 2 to 8 carbon atoms and fluorinated vinyl ether (FVE)
of the formula CY2=CYOR or CY2=CYOR'OR wherein Y is F and
-R- and -R'- are independently completely fluorinated linear or branched alkyl
and alkylene groups containing 1 to 8 carbon atoms. Preferred R groups contain
1 to 4 carbon atoms Preferred R' groups contain 2 to 4 carbon atoms other fluoropolymers
which man be used are the copolymers of ethylene with perhalogenated monomers such
as tetrafluoroethylene (TFE) or chlorotrifluoroethylene (CTFE), such copolymers
being often referred to as ETFE and ECTFE, respectively. In the case of ETFE,
minor amounts of additional monomer are commonly used to improve properties such
as reduced high temperature brittleness. Perfluoro(propyl vinyl ether) (PPVE),
perfluoro(ethyl vinyl ether) (PEVE), perfluorobutyl ethylene (PFBE), and hexafluoroisobutylene
(HFIB) are preferred additional comonomers. ECTFE may also have additional modifying
comonomer. Examples of perfluorinated copolymers include TFE with hexafluoropropylene
HFP and/or PPVE or perfluoro(ethyl vinyl ether). Such fluoropolymers are usually
partially-crystalline as indicated by a non-zero heat of fusion associated with
a melting endotherm as measured by DSC on first melting, and are considered to
be fluoroplastics rather than fluoroelastomers.
The fluoropolymer can be adhesively activated by having a compound
grafted thereto which imparts polar functionality to the fluoropolymer such as
described for the grafted fluoropolymer powder in PCT WO 96/03448. The amount
of grafting compound grafted to the fluoropolymer will vary with the way the polar-grafted
fluoropolymer is used. When polar-grafted fluoropolymer is the adhesively activated
fluoropolymer of the coextruded laminate, or is used to adhesively activate said
fluoropolymer (as in a blend), the amount of grafting compound grafted to the fluoropolymer
is generally in the range of 0.01 wt% to 5 wt% based on the total weight of the
adhesively activated fluoropolymer. Preferably, the amount of grafted polar-functional
compound is 0.02-1 wt%, more preferably 0.04-0.5 wt% based on the total weight
of the adhesively activated fluoropolymer. When the polar-grafted fluoropolymer
is used to adhesively activate the polyamide, the amount of grafting compound grafted
to the fluoropolymer is generally in the range of 0.1 wt% to 5 wt% based on the
total weight of the polar-grafted fluoropolymer. Preferably, the amount of grafted
polar-functional compound is 0.2-3 wt%, more preferably 0.2-2 wt% based on the
total weight of the polar-grafted fluoropolymer. The grafting compounds described
above with respect to the polymer additive for the polyamide resin can also be
used for grafting onto the fluoropolymer. The fluoropolymer can also be functionalized
by copolymerizing polar functional monomer into otherwise non-functional fluoropolymers
as described above. Examples of such functional monomers include fluorovinylethers
such as CF2=CF[OCF2CF(CF3)]m-O-(CF2)nCH2OH
as disclosed in U.S. Patent 4,982,009 and the alcoholic ester CF2=CF[OCF2CF(CF3)]m-O-(CF2)n-(CH2)p-O-COR
as disclosed in U.S. Patent 5,310,838. Additional fluorovinylethers include CF2=CF[OCF2CF(CF3)]mO(CF2)nCOOH
and its carboxylic ester CF2=CF[OCF2CF(CF3)]mO(CF2)nCOOR
disclosed in U.S. Patent 4,138,426. In these formulae, m = 0-3, n = 1-4, p = 1-2
and R is methyl or ethyl. Similar functional monomers are disclosed in European
Patent Application Publication EP 0 626 424. Other functional monomers include
those such as CH2=CFCF2-Z-(CH2)w-X
wherein X is CH2OH, COOR or epoxy, R is H or alkyl having 1-6 carbon
atoms, Z is Rf or ORf', Rf is a fluorine-substituted
alkylene group having 1-40 carbon atoms, Rf' is Rf or a fluorine-substituted
ether group having 3-50 carbon atoms, and w is 0-6 as disclosed in European Patent
Application Publication EP 0 728 776. When, the functionalized fluoropolymer is
perfluoropolymer containing a functional comonomer, the amount of functional comonomer
is generally no more than 10 wt%, usually 1-10 wt% and preferably no more than
5 wt%, based on total weight of functionalized fluoropolymer, i.e., the fluoropolymer
component containing the functional monomer. The fluoropolymer can also be adhesively
activated by blending functionalized fluoropolymer with non-functionalized fluoropolymer,
preferably wherein the fluoropolymers are the same, except for functional units
or groups, so as not to jeopardize the impermeability characteristic.
The adhesively activated fluoropolymer and polyamide are coextruded
by conventional means except that that the extrusion is carried out so that no
appreciable degradation of the lower melting polyamide occurs. This can be accomplished
by having the melt temperature of the polyamide relatively cold, with the highest
temperature exposure of the polyamide occurring for only a short period of time
in the coextrusion crosshead and when the polymers come together as coextruded
layers. The heating of the polyamide in the coextrusion crosshead is caused by
the fluoropolymer being heated to the higher temperature in its particular extruder
feeding the crosshead.
The coextruded laminate in its simplest form consists of two layers,
one of polyamide resin and one of fluoropolymer resin, at least one of which has
been adhesively activated. Such laminate can be used in applications requiring
chemical resistance and/or impermeability to organic compounds in the form of
liquid or gas, with the fluoropolymer layer being the layer contacting such compounds.
The polyamide resin layer provides strength to the overall laminate. When the laminate
is in the form of tubing, the interior surface of the tubing can be the fluoropolymer
layer to resist the gaseous and/or liquid organic compounds passing through the
interior passage of the tubing. The polyamide outer layer provides strength to
the tubing. When the tubing is intended for use in conveying a relatively non-corrosive
compound through a corrosive atmosphere, then the layers can be reversed, i.e.
the polyamide layer constitutes the interior surface and the fluoropolymer layer
constitutes the exterior surface. In another embodiment, the polyamide layer can
be sandwiched between and directly adhered to two fluoropolymer layers, wherein
preferably the polyamide layer is adhesively activated so as to adhere to both
fluoropolymer layers. In this embodiment, both exposed surfaces of the laminate
are chemically resistant and gas impermeable, and the polyamide inner layer is
protected on both sides.
The following Examples demonstrate a variety of ways to carry out
the present invention.
In this Example, the polyamide layer is adhesively activated and this
activation is obtained by incorporation into the polyamide resin of a polymer
additive which is polar-functionalized by grafting.
The polyamide resin is 66-nylon having an inherent viscosity of about
1.25 measured as a solution of 0.5 g of the polymer in 100 ml of m-cresol at 25°C
and having 65-73 eq/106 g of COOH and 47-53 eq/106 g of NH2
end groups. The polymer additive is an ethylene/propylene/1,4-hexadiene elastomer
(62/32/6) having maleic anhydride grafted to it, the amount of the graft being
0.9 wt% based on the weight of the grafted copolymer. The polymer additive is melt
compounded using a twin-screw extruder into the polyamide resin to form a dispersed
phase of the additive, wherein the average particle size of the dispersed phase
is about 0.5 micrometer (0.013 mm). The resultant composition contains 20% additive
based on the weight of the polyamide resin plus the additive. The fluoropolymer
resin is a copolymer of ethylene/tetrafluoroethylene/perfluorobutyl ethylene(PFBE),
having an E/TFE molar ratio of about 0.9, containing 1 mol% PFBE, and having a
melt flow rate of about 7 g/10 min as measured according to ASTM D-3159.
The adhesively activated polyamide composition and the fluoropolymer
resin are coextruded under the following conditions: The fluoropolymer is extruded
using a (2.54-cm) (1.0-in) Davis extruder equipped with a general purpose extrusion
screw and operating at a barrel pressure of 2.93 MPa (410 psig) and at a melt temperature
of (324°) (616°F) entering the coextrusion crosshead to form the inner layer of
coextruded tubing. The polyamide resin composition is extruded using a (3.81-cm)
(1.5-in) Davis extruder equipped with a general purpose screw and operating at
a barrel pressure of (4.24 Mpa) (600 psig) at a melt temperature of (260°C) (500°F)
entering the coextrusion crosshead to form the outer layer of the coextruded tubing.
The crosshead die temperature is 304°C (580°F) and the extrusion rate is (198 cm/min)
The coextruded tubing is (6.86 mm) (0.270 in) in outer diameter and
has a wall thickness of 1.4 mm (0.055 inch) of which the fluoropolymer inner layer
is (0.15 mm) (0.006 inch) thick.
The adhesion of the polyamide layer to the fluoropolymer layer is
demonstrated by cutting a length of the tubing longitudinally in half and then
flexing and bending the remaining half, with the inner layer remaining adhered
to the outer layer.
The experiment is repeated except that no polymer additive is in the
polyamide layer. When the coextruded tubing is cut longitudinally in half, the
inner layer falls out of the outer layer, indicating the absence of adhesion between
these two layers.
The Figure shows that the adhesive activation of the polyamide layer
can also lead to mechanical engagement between the layers of the coextrudate to
supplement the adhesion of the layers together. In the Figure, the adhesively
activated polyamide layer 2 of this tubing of this Example is bonded to the fluoropolymer
layer 4 along an irregular (rough) interface 6 which provides mechanical engagement
between the layers as well as the adhesion provided by the dispersion of polymer
additive particles (not shown) in the polyamide layer. When the polyamide layer
is not adhesively activated as described above, the interlayer between the layers
viewed in the same way (by TEM) is smooth, i.e., the layers are not mechanically
engaged. Thus, the adhesive activation can promote compatibility between layers
to such an extent that the layers tend to merge upon coextrusion. In other experiments,
it has been observed that the adhesive activation achieves adhesion even without
the presence of mechanical engagement between the layers.
This Example is directed at adhering coextruded layers of polyamide
resin and fluoropolymer resin together by having both the polyamide layer and the
fluoropolymer layer functionalized.
In this Example, polyamide used is 6-12 nylon having an inherent
viscosity of 1.4 measured as a solution of 0.5 g of the polymer in 100 ml of m-cresol
at 25°C. The 6-12 nylon contains 6.3 wt% of the maleic anhydride grafted EPDM of
Example 1. The fluoropolymer resin is the same used in Example 1 except that maleic
anydride had been grafted to it to constitute 0.4 wt% of the resultant resin. The
grafting was carried out by exposing a mixture of powdered resin having average
particle size of about 100-120 µm (within the preferred range of 50-500 µm disclosed
in PCT WO 96/03448) and maleic anhydride powder to ionizing radiation in a closed
system to obtain surface-grafted powder, followed by melt extruding the grafted
resin to form molding granules for use in the coextrusion process.
The coextrusion conditions are as follows: The extruders used in
Example 1 are used in the experiment of this Example for the respective resins.
The fluoropolymer melt temperature is (293°C) (560°F) and barrel pressure is (8.38
MPa) (1200 psig), and the polyamide melt temperature is (240°C) (464°F) and barre
pressure is (1.65 MPa) (225 psig). The crosshead die temperature is 304°C (580°F),
and the extrusion rate and dimensions of the coextruded tubing are the same as
in Example 1. When lengths of the coextruded tubing are cut longitudinally in half
and flexed and bent, the inner fluoropolymer layer exhibits adhesion to the polyamide
outer layer by not separating from the polyamide.
This Example shows the adhesive activation of the polyamide layer
by incorporation (dispersion) of a polar functional polymeric additive into the
polyamide, with the polymeric additive being made functional by copolymerization.
The polyamide resin used is the 66-polyamide of Example 1. The polymeric
additive is a copolymer of ethylene/methacrylic acid in which the acid comonomer
units constitute 10 wt% of the copolymer and in which the acid groups are 71% neutralized
with Zn to form an ionomer. The ionomer has a melt index of about 1. The polyamide
resin and the ionomer are melt compounded together to form molding granules having
the composition 80 wt% polyamide and 20 wt% ionomer dispersed in the polyamide.
The fluoropolymer used is the same as in Example 1.
The coextrusion conditions are as follows: The extruder for the polyamide
composition is a (2.5-cm) (1.0-in) Entwhistle extruder and the extruder for the
fluoropolymer is the same extruder as used for the polyamide composition in Example
1. The fluoropolymer melt temperature is (326°C) (619°F) and the barrel pressure
is (1.28 MPa) (170 psig), and the polyamide composition melt temperature is (258°C)
(496°F) and barrel pressure is (2.485 MPa) (350 psig). The crosshead die temperature
is (307°C) (585°F), and the crosshead has a wider annulus (die opening) for extruding
the inner layer of the tubing than used in Example 1. The coextrusion rate is (5.5
ft/min) (168 cm/min), the outer diameter of the coextruded tubing is (6.86 mm)
(0.270 in), and the thickness of the fluoropolymer inner layer is (5.1 mm) (0.020
Adhesion between the inner and outer layers of the coextruded tubing
is demonstrated by cutting lengths of the tubing longitudinally in half and flexing
and bending the resultant half of the tubing. The layers do not separate.
This Example shows the adhesive activation of the polyamide layer
by incorporation (dispersion) of a polar functional fluoropolymer additive into
the polyamide, with the polymeric additive being made functional by grafting.
The polyamide resin used is the 66-polyamide of Example 1. The polar
functional fluoropolymer additive is the fluoropolymer resin having 0.4 wt% of
maleic anydride grafted to it that is used in Example 2. The fluoropolymer additive
is melt compounded into the polyamide resin using a twin-screw extruder to form
a dispersed phase of the additive, wherein the average particle size of the dispersed
phase is about 200 nm. The resultant composition contains 20% additive based on
the weight of the polyamide resin and the polar functional fluoropolymer additive.
The fluoropolymer resin is the E/TFE/PFBE copolymer of Example 1.
In this instance, the extruders of Example 1 are used for the fluoropolymer
resin and the polyamide resin composition, respectively, as in Example 1. The fluoropolymer
melt temperature is (324°C) (615°F), the polyamide resin melt temperature is (260°C)
(500°F), and the crosshead temperature is 304 °C (580°F). The extrusion rate and
dimensions of the coextruded tubing are the same as in Example 1. Adhesion between
the inner and outer layers of the coextruded tubing is demonstrated by cutting
lengths of the tubing longitudinally in half and flexing and bending a resultant
half of the tubing. The layers do not separate, demonstrating the effectiveness
of polar functional fluoropolymer additive in adhesively activating polyamide resin.