U.S. patent application number 13/879360 was filed with the patent office on 2013-12-12 for voc or compressed gas containment device made from a polyoxymethylene polymer.
This patent application is currently assigned to Ticona LLC. The applicant listed for this patent is Lowell Larson, Christopher McGrady, Ursula Ziegler. Invention is credited to Lowell Larson, Christopher McGrady, Ursula Ziegler.
Application Number | 20130330491 13/879360 |
Document ID | / |
Family ID | 44908104 |
Filed Date | 2013-12-12 |
United States Patent
Application |
20130330491 |
Kind Code |
A1 |
Larson; Lowell ; et
al. |
December 12, 2013 |
VOC or Compressed Gas Containment Device Made From a
Polyoxymethylene Polymer
Abstract
VOC or compressed gas containment devices, such as polymer fuel
tanks, are made from a polyoxymethylene polymer composition. The
polymer composition contains a polyoxymethylene polymer that is
directly or indirectly chemically attached to an impact modifier.
In one embodiment, for instance, a coupling agent bonds the impact
modifier to the polyoxymethylene polymer. In order to preserve the
permeability of the polymer material when combined with the impact
modifier, a polyoxymethylene polymer is used that contains a low
level of low molecular weight constituents.
Inventors: |
Larson; Lowell;
(Independence, KY) ; Ziegler; Ursula;
(Mainz-Kostheim, DE) ; McGrady; Christopher;
(Wilder, KY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Larson; Lowell
Ziegler; Ursula
McGrady; Christopher |
Independence
Mainz-Kostheim
Wilder |
KY
KY |
US
DE
US |
|
|
Assignee: |
Ticona LLC
Florence
KY
|
Family ID: |
44908104 |
Appl. No.: |
13/879360 |
Filed: |
October 14, 2011 |
PCT Filed: |
October 14, 2011 |
PCT NO: |
PCT/US2011/056252 |
371 Date: |
August 29, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12904575 |
Oct 14, 2010 |
|
|
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13879360 |
|
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Current U.S.
Class: |
428/36.92 ;
264/523 |
Current CPC
Class: |
B29C 2948/92228
20190201; B60K 15/03006 20130101; C08G 18/7671 20130101; B29C
49/0005 20130101; B29C 48/832 20190201; Y10T 428/1397 20150115;
B29C 48/05 20190201; Y10T 428/1352 20150115; C08G 18/56 20130101;
B29C 48/395 20190201; C08L 59/00 20130101; C08L 75/04 20130101 |
Class at
Publication: |
428/36.92 ;
264/523 |
International
Class: |
B60K 15/03 20060101
B60K015/03; B29C 49/00 20060101 B29C049/00 |
Claims
1.-20. (canceled)
21. A containment device having a hollow volume surrounded by a
wall, the wall being made from a polymer composition comprising: a)
a polyoxymethylene polymer having terminal groups and wherein at
least 50% of the terminal groups are hydroxyl groups, the
polyoxymethylene polymer having a melt index of from about 5
cm.sup.3/10 min to about 20 cm.sup.3/10 min measured at 190.degree.
C. and at an applied weight of 2.16 kg; b) an impact modifier
comprising a thermoplastic elastomer, the impact modifier being
present in an amount of at least about 5% by weight, the impact
modifier being chemically attached to the polyoxymethylene polymer;
c) a coupling agent present in an amount of from about 1.5% by
weight to about 10% by weight, the coupling agent comprising an
isocyanate; and wherein the polymer composition has a permeation of
less than 5 g mm/m.sup.2 per day at 40.degree. C. according to SAE
Test J2665 and has a multi axial impact strength at -40.degree. C.
of greater than about 15 ftlb-f according to ASTM Test D3763.
22. A containment device as defined in claim 21, wherein at least
about 70% of the terminal groups on the polyoxymethylene polymer
are hydroxyl groups and wherein the polyoxymethylene polymer has a
melt index of from about 7 cm.sup.3/10 min to about 12 cm.sup.3/10
min measured at 190.degree. C. and at an applied weight of 2.16
kg.
23. A containment device as defined in claim 21, wherein the
polymer composition has a multi axial impact strength at
-40.degree. C. of greater than about 18 ftlb-f according to ASTM
Test D3763.
24. A containment device as defined in claim 21, wherein the
polymer composition has a multi axial impact strength at
-40.degree. C. of greater than about 20 ftlb-f according to ASTM
Test D3763.
25. A containment device as defined in claim 21, wherein the
containment device has been blow molded.
26. A containment device as defined in claim 25, wherein the
containment device comprises a fuel tank that has a volumetric
capacity of up to 5 gallons.
27. A containment device as defined in claim 25, wherein the
polymer composition has a shear viscosity of from about 8000 Pa-s
to about 30,000 Pa-s at a shear rate of 0.1 rad/sec and at a
temperature of 190.degree. C.
28. A containment device as defined in claim 21, wherein the wall
comprises only a monolayer of the polymer composition.
29. A containment device as defined in claim 21, wherein the
coupling agent comprises methylenediphenyl 4,4''-diisocyanate.
30. A method for blow molding hollow articles comprising: combining
a polyoxymethylene polymer with an impact modifier to produce a
polymer composition, the polyoxymethylene polymer including
terminal groups wherein at least about 50% of the terminal groups
are hydroxyl groups, the polyoxymethylene polymer having a melt
index of from about 5 cm.sup.3/10 min to about 20 cm.sup.3/10 min
measured at 190.degree. C. and at an applied weight of 2.16 kg, the
impact modifier comprising a thermoplastic elastomer, the impact
modifier being present in the polymer composition in an amount of
at least about 5% by weight; adding a coupling agent to the polymer
composition, the coupling agent comprising an isocyanate that
couples the impact modifier to the polyoxymethylene polymer, the
coupling agent being added to the polymer composition in an amount
sufficient for the polymer composition to have a shear viscosity of
at least about 8000 Pa-s at a shear rate of 0.1 rad/sec and at a
temperature of 190.degree. C., and wherein greater amounts of the
coupling agent are added to the polymer composition as the melt
index of the polyoxymethylene polymer increases; and blow molding a
hollow article from the polymer composition.
31. A method as defined in claim 30, wherein at least about 70% of
the terminal groups on the polyoxymethylene polymer are hydroxyl
groups and wherein the polyoxymethylene polymer has a melt index of
from about 7 cm.sup.3/10 min to about 12 cm.sup.3/10 min measured
at 190.degree. C. and at an applied weight of 2.16 kg.
32. A method as defined in claim 30, wherein the polyoxymethylene
polymer has a melt index of from about 10 cm.sup.3/10 min to about
11 cm.sup.3/10 min measured at 190.degree. C. and at an applied
weight of 216 kg.
33. A method as defined in claim 30, wherein the coupling agent is
added to the polymer composition in an amount from about 1.5% to
about 10% by weight.
34. A method as defined in claim 30, wherein the coupling agent is
added to the polymer composition in an amount from about 1.5% to
about 5% by weight.
35. A method as defined in claim 30, wherein the polymer
composition has a multi-axial impact strength at -40.degree. C. of
greater than about 15 ftlb-f according to ASTM Test D3763.
36. A method as defined in claim 30, wherein the polymer
composition has a multi-axial impact strength at -40.degree. C. of
greater than about 18 ftlb-f according to ASTM Test D3763.
37. A method as defined in claim 30, wherein the coupling agent is
added to the polymer composition such that there is from about 0.5
to about 4 mol of the coupling agent per mol of hydroxyl groups on
the polyoxymethylene polymer.
Description
RELATED APPLICATIONS
[0001] The present application is a continuation-in-part
application of U.S. patent application Ser. No. 12/904,575, filed
on Oct. 14, 2010, which is incorporated herein by reference.
BACKGROUND
[0002] Fuel tanks for use in vehicles or other mobile devices
should generally possess various characteristics and properties.
For instance, the fuel tanks should be capable of holding a fuel
without significant amounts of fuel vapor escaping. The tanks
should also be chemically resistant to the fuel that is contained
in the tanks. The fuel tanks should also have good impact
resistance properties. In the past, conventional fuel tanks were
generally made from a metal.
[0003] In the relatively recent past, those skilled in the art have
attempted to design fuel tanks made from polymers. For instance,
many small fuel tanks, such as those used by small off-road
vehicles and devices, are currently made from high density
polyethylene. High density polyethylene has good impact strength
resistance properties. The above polymer, however, has a tendency
to release fuel vapors over time. Consequently, fuel tanks made
from high density polyethylene are typically fluorinated which not
only adds significant cost to the product but is also shown to
produce inconsistent results. Thus, those skilled in the art have
been seeking to produce polymer fuel tanks from other types of
polymers.
[0004] In this regard, those skilled in the art have proposed using
polyester polymers to produce fuel tanks, particularly small fuel
tanks. For instance, in U.S. Patent Application Publication No.
2006/0175325, which is incorporated herein by reference, an impact
modified polyester is disclosed which comprises a polyester
combined with an olefin-vinyl alcohol component and an impact
modifier component.
[0005] Another type of polymer that has good permeability
resistance properties are polyoxymethylene polymers. Although
standard polyoxymethylene polymers have good permeability
resistance, the polymers tend to have insufficient impact strength
for fuel tank applications due to the high crystallinity of the
material. The impact strength of polyoxymethylene polymers can be
improved by incorporating an impact modifier into the material. It
is known, however, that incorporating an impact modifier into a
polyoxymethylene polymer can significantly increase the
permeability properties of the polymer. Thus, problems have been
encountered in being able to develop a polymer material containing
a polyoxymethylene polymer for use in producing fuel tanks.
[0006] In U.S. Patent Application Publication No. 2009/0220719,
which is incorporated herein by reference, a low fuel-permeable
thermoplastic vessel is described made from a polyoxymethylene
polymer in combination with an impact modifier. The '719
application teaches using an "uncompatibilized" blend of a
polyoxymethylene, a thermoplastic polyurethane, and a copolyester.
The term "uncompatibilized" as used in the '719 application means
that the compositions do not contain polymer compatibilizers.
[0007] Although the teachings of the '719 application have provided
great advancements in the art, further improvements are still
needed.
SUMMARY
[0008] The present disclosure is generally directed to volatile
organic compound ("VOC") and compressed gas containment devices
made from a composition containing a polyoxymethylene polymer. The
polyoxymethylene polymer composition is formulated to have a unique
combination of properties making it well suited for use in
constructing various hollow vessels, especially fuel tanks. For
instance, the polymer composition not only has very good impact
strength resistance properties, but is also well suited to
preventing fuel vapors and gases from escaping the containment
device over time. In particular, the polymer composition can be
formulated so as to reduce or prevent VOC vapor emissions while
still providing a fuel tank that is capable of not rupturing, even
when subjected to relatively high impact forces at colder
temperatures.
[0009] In this regard, in one embodiment, the present disclosure is
directed to a containment device, such as a container, comprising
an opening configured to receive a VOC or a compressed gas, such as
a fuel. The containment device may also include a discharge for
feeding the fuel to a combustion engine or other similar device.
The containment device includes a volume surrounded by a wall.
[0010] In accordance with the present disclosure, the wall is made
from a polymer composition comprising a polyoxymethylene polymer.
More particularly, the polyoxymethylene polymer for use in the
composition comprises a polyoxymethylene in which at least 50% of
the terminal groups are hydroxyl groups. For instance, at least
about 70% of the terminal groups can be hydroxyl groups, such as at
least about 80% of the terminal groups can be hydroxyl groups, such
as even greater than about 85% of the terminal groups can be
hydroxyl groups. In addition, the polyoxymethylene polymer may
contain little or no low molecular weight constituents having a
molecular weight below 10,000 dalton. For instance, the
polyoxymethylene polymer can contain low molecular weight
constituents in an amount less than about 10% by weight, such as in
an amount less than about 5% by weight, such as in an amount less
than about 3% by weight, based on the total mass of
polyoxymethylene.
[0011] In general, the molecular weight of the polyoxymethylene
polymer may vary depending upon the particular application. For
instance, the polyoxymethylene polymer may have a melt index of
from about 1 cm.sup.3/10 min to about 50 cm.sup.3/10 min. As used
herein, the melt index of the polymer is measured at 190.degree. C.
at an applied weight of 2.16 kg according to ISO Test 1133. As will
be described in greater detail below, in one embodiment, a
polyoxymethylene polymer is used that has a relatively low
molecular weight (higher melt index) to create molded articles,
particularly blow molded articles, that have excellent multi axial
impact strength at low temperatures, such as at -40.degree. C.
[0012] In addition to a polyoxymethylene polymer, the composition
further includes an impact modifier that is attached to the
polyoxymethylene polymer. The impact modifier may comprise, for
instance, a thermoplastic elastomer, such as a thermoplastic
polyurethane elastomer. A coupling agent may be used to couple the
impact modifier to the polyoxymethylene polymer. The coupling
agent, for instance, may comprise an isocyanate. For example, in
one embodiment, the coupling agent may comprise methylenediphenyl
4,4'-diisocyanate.
[0013] In one embodiment, the amount of low molecular weight
constituents contained in the polyoxymethylene polymer, the amount
of impact modifier, and the amount of the coupling agent are
carefully controlled so that the resulting composition produces a
polymer having good impact strength resistance in combination with
low permeability properties. For instance, in one embodiment, the
polymer composition can have a multi axial impact strength
resistance at -30.degree. C. of greater than about 4 ftlb-f, such
as greater than about 10 ftlb-f, such as greater than about 15
ftlb-f, when tested according to ASTM Test D3763.
[0014] In an alternative embodiment, the molecular weight of the
polyoxymethylene polymer is relatively low and is used in
combination with greater amounts of a coupling agent so as to
produce a polymer composition not only amenable to blow molding,
but also has excellent multi axial impact strength when measured at
very low temperatures and according to stringent tests. For
instance, in one embodiment, the polyoxymethylene polymer not only
has a significant number of hydroxyl terminal groups, but also has
a melt index of from about 5 cm.sup.3/10 min to about 20
cm.sup.3/10 min. The polyoxymethylene polymer is combined with an
impact modifier and a coupling agent in an amount greater than
about 1.5% by weight, such as in an amount from about 1.5% to about
10% by weight. It has been discovered that the low molecular weight
polyoxymethylene polymer in combination with greater amounts of
coupling agent produces a polymer composition having a multi axial
impact strength at -40.degree. C. of greater than about 15 ftlb-f,
such as greater than about 18 ftlb-f, such as greater than about 20
ftlb-f when tested according to ASTM Test D3763.
[0015] The permeation of polymer compositions made according to the
present disclosure can be less than about 5 g mm/m.sup.2 day at
40.degree. C. when tested according to SAE Test J2665. For
instance, the permeation can be less than about 4 g mm/m.sup.2 day,
such as less than about 3 g mm/m.sup.2 day, such as even less than
about 2.5 g mm/m.sup.2 day. When tested with a 2 mm wall thickness,
for instance, the permeation can be less than about 2.5 g/m.sup.2
day, such as less than 2 g/m.sup.2 day, such as even less than 1.5
g/m.sup.2 day.
[0016] As described above, in one embodiment, the polyoxymethylene
polymer may contain relatively low amounts of low molecular weight
constituents. In one embodiment, the polyoxymethylene polymer can
be produced with relatively low amounts of low molecular weight
constituents by using a heteropoly acid catalyst. The amount of
polyoxymethylene polymer contained in the composition can generally
be from about 50% to about 95% by weight, such as greater than
about 65% by weight, such as greater than about 70% by weight. The
impact modifier, on the other hand, can generally be present in an
amount from about 5% by weight to about 30% by weight, such as from
about 10% by weight to about 25% by weight. The coupling agent, on
the other hand, can generally be present in an amount less than
about 5% by weight, such as in an amount from about 0.2% to about
3% by weight.
[0017] Another aspect of the present disclosure is directed to a
method for blow molding hollow articles. The method includes the
steps of combining a polyoxymethylene polymer with an impact
modifier to produce a polymer composition. The polyoxymethylene
polymer includes terminal groups wherein at least about 50% of the
terminal groups are hydroxyl groups. The polyoxymethylene polymer
has a melt index of from about 5 cm.sup.3/10 min to about 20
cm.sup.3/10 min. The impact modifier comprises a thermoplastic
elastomer and is present in the polymer composition in an amount of
at least 5% by weight.
[0018] According to the present disclosure, a coupling agent is
added to the polymer composition in an amount sufficient for the
polymer composition to have a shear viscosity of at least about
8000 Pas at a shear rate of 0.1 rad/sec and at a temperature of
190.degree. C. The coupling agent may comprise, for instance, an
isocyanate that couples the impact modifier to the polyoxymethylene
polymer. The method further includes the step of blow molding a
hollow article from the polymer composition.
[0019] Although the polymer composition is suitable for producing
all types of containment devices for VOC's and compressed gases, in
one embodiment, a fuel tank is constructed having a fuel capacity
of generally less than about five gallons. Of particular advantage,
the fuel tank can be comprised of only a monolayer of the polymer
composition. The container wall can generally have a thickness of
from about 0.5 mm to about 10 mm, such as from about 1.5 mm to
about 5 mm.
[0020] Any suitable molding process may be used to produce the
containment device. For instance, in one embodiment, the
containment device is blow molded. In an alternative embodiment,
however, the containment device is injection molded. For instance,
two different portions of the containment device may be injection
molded and then later welded together.
[0021] Other features and aspects of the present disclosure are
discussed in greater detail below.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] A full and enabling disclosure of the present invention,
including the best mode thereof to one skilled in the art, is set
forth more particularly in the remainder of the specification,
including reference to the accompanying figures, in which:
[0023] FIG. 1 is a perspective view of one embodiment of a fuel
tank made in accordance with the present disclosure;
[0024] FIG. 2 is a cross sectional view of the fuel tank
illustrated in FIG. 1; and
[0025] FIGS. 3 through 7 are graphical representations of the
results obtained in the example below.
[0026] Repeat use of reference characters in the present
specification and drawings is intended to represent the same or
analogous features or elements of the present invention.
DETAILED DESCRIPTION
[0027] It is to be understood by one of ordinary skill in the art
that the present discussion is a description of exemplary
embodiments only, and is not intended as limiting the broader
aspects of the present disclosure.
[0028] In general, the present disclosure is directed to polymer
compositions containing a polyoxymethylene polymer that are
particularly well suited to molding articles, such as VOC and
compressed gas containment devices. As will be described in greater
detail below, the polyoxymethylene polymer composition is
formulated in a manner that produces molded articles with very good
impact resistance properties in combination with very good
permeability properties. In particular, the polymer compositions
are capable of producing molded articles that are relatively
impermeable to gas vapors, such as fuel vapors and other volatile
organic compounds, and impermeable to compressed gases, such as
natural gas, propane, and other hydrocarbon gases.
[0029] In the past, various problems were encountered in producing
fuel tanks from polyoxymethylene polymers. Although
polyoxymethylene polymers have good natural permeability
properties, the materials tend not to have acceptable impact
strength when used in fuel tank applications due to the high
crystallinity of the material. Increasing the impact strength with
compatibilized impact modifiers was found to adversely affect the
permeability properties of the material. It was unexpectedly
discovered, however, that by using a polyoxymethylene polymer with
a high concentration of hydroxyl end groups and optionally with a
low concentration of low molecular weight fractions in combination
with an impact modifier that can be chemically reacted with or
otherwise attached to the polyoxymethylene polymer, a polymeric
material can be produced that has the desired balance of properties
with respect to impact strength and permeability.
[0030] Although the polymer composition of the present disclosure
can be used to produce any suitable type of VOC or compressed gas
containment device, the polymer composition is particularly well
suited to producing fuel tanks for a category of engines referred
to as small off-road engines. Such engines typically have a power
rating of up to 25 horsepower and are used in various vehicles and
mobile devices. For instance, small off-road engines are typically
used in small utility equipment, lawn mowers, weed trimmers, chain
saws, motorcycles, lawn tractors, blowers, and the like. Such fuel
tanks typically have a fuel capacity of less than 20 gallons, and
particularly less than 5 gallons.
[0031] It should be understood, however, that other products and
articles in addition to fuel tanks may be made in accordance with
the present disclosure. In particular, any type of VOC or
compressed gas containment device may be made in accordance with
the present disclosure. As used herein, a "containment device"
refers to any hollow article that is designed to contain or in any
way come in contact with VOCs and/or compressed gases. In addition
to tanks, for instance, a containment device may comprise a tube, a
hose, or any other similar device. The containment device, for
instance, may be designed to contact or contain hydrocarbon fluids,
pesticides, herbacides, brake fluid, paint thinners, and various
compressed hydrocarbon gases, such as natural gas, propane, and the
like. When used as a fuel tank, the containment device may contact
or contain any suitable hydrocarbon fluid, whether liquid or
gas.
[0032] Referring to FIGS. 1 and 2, for instance, one embodiment of
a fuel tank 10 that may be made in accordance with the present
disclosure is shown. The fuel tank 10 includes an opening or inlet
12 for receiving a fuel. The opening 12 can be defined by a
threaded fixture 14. The threaded fixture 14 is adapted for
receiving a fuel and for receiving a cap (not shown). A cap can be
placed over the threaded fixture 14, for instance, in order to
prevent fuel and vapors from leaving the fuel tank 10.
[0033] The fuel tank 10 further includes at least one outlet 16 for
feeding a fuel to a combustion device, such as an engine.
[0034] The fuel tank 10 defines a container volume 18 for receiving
a fuel. The container volume 18 is surrounded by a container wall
20. The container wall 20 can include multiple sides. For instance,
the container wall can include a top panel, a bottom panel, and
four side panels. Alternatively, the fuel tank 10 can have a
spherical shape, a cylindrical shape, or any other suitable shape.
In accordance with the present disclosure, the fuel tank 10 is made
from a polymer composition containing a polyoxymethylene polymer.
Of particular advantage, the polymer composition is capable of
forming a monolayer tank without having to apply any further
coatings or layers to the container wall for increasing either
impact resistance or permeability resistance.
[0035] For instance, polyoxymethylene polymer compositions made in
accordance with the present disclosure can have a permeation of
less than 5 g mm/m.sup.2 per day at 40.degree. C. when tested
according to SAE Test J2665. SAE Test J2665 tests the permeability
of the material with a test fuel comprising 10% ethanol, 45%
toluene, and 45% iso-octane. Determination of the steady-state flux
reported in gmm/m.sup.2 per day is carried out per SAE Test J2665,
Section 10. In certain embodiments, the polymer composition is
capable of producing a polymer material having a permeation of less
than 4 g mm/m.sup.2 per day, such as less than 3 g mm/m.sup.2 per
day, such as even less than 2.5 g mm/m.sup.2 per day.
[0036] When tested according to a 2 mm wall thickness, such as
according to SAE Test J2665, Section 11, the polymer composition of
the present disclosure may have a permeation of less than about 2.5
g/m.sup.2 per day, such as less than 2 g/m.sup.2 per day, such as
even less than 1.5 g/m.sup.2 per day.
[0037] In addition to having excellent permeability properties, as
described above, the polymer composition formulated according to
the present disclosure also displays excellent impact strength
resistance. For instance, the polymer composition may have a multi
axial impact strength at -30.degree. C. according to ASTM Test
D3763 of greater than 4 ftlb-f, such as greater than 10 ftlb-f,
such as greater than 15 ftlb-f. The multi axial impact strength is
generally less than 60 ftlb-f, such as from about 5 ftlb-f to about
25 ftlb-f.
[0038] Since the polyoxymethylene polymer is a thermoplastic
polymer, the fuel tank 10 as shown in FIGS. 1 and 2 can be made
according to different processes. For instance, in one embodiment,
the fuel tank 10 can be formed through a blow molding process.
Alternatively, rotational molding or injection molding may be used
to produce the tank.
[0039] In one particular embodiment, different portions of the fuel
tank 10 can be made using injection molding. For instance, as shown
in FIGS. 1 and 2, the fuel tank 10 may be formed from a first
portion or half 22 and a second portion or half 24. The first
portion 22 can then be attached to the second portion 24 using any
suitable welding process. Such welding processes include hot-plate
welding, vibration welding, laser welding, or ultrasonic
welding.
[0040] The polymer composition of the present disclosure generally
contains a polyoxymethylene polymer that is chemically reacted with
or attached to an impact modifier. For example, in one embodiment,
a coupling agent may be present in the composition that couples the
impact modifier to the polyoxymethylene polymer. More particularly,
the coupling agent may react with first reactive groups on the
polyoxymethylene polymer and with second reactive groups present on
the impact modifier. In one embodiment, for instance, the coupling
agent may comprise an isocyanate that chemically attaches the
impact modifier to the polyoxymethylene polymer.
[0041] The polyoxymethylene polymer used in the polymer composition
may comprise a homopolymer or a copolymer, The polyoxymethylene
polymer, however, generally contains a relatively high amount of
reactive groups, such as hydroxyl groups in the terminal positions.
More particularly, the polyoxymethylene polymer can have terminal
hydroxyl groups, for example hydroxyethylene groups and/or hydroxyl
side groups, in at least more than about 50% of all the terminal
sites on the polymer. For instance, the polyoxymethylene polymer
may have at least about 70%, such as at least about 80%, such as at
least about 85% of its terminal groups be hydroxyl groups, based on
the total number of terminal groups present. It should be
understood that the total number of terminal groups present
includes all side terminal groups.
[0042] In one embodiment, the polyoxymethylene polymer has a
content of terminal hydroxyl groups of at least 5 mmol/kg, such as
at least 10 mmol/kg, such as at least 15 mmol/kg. In one
embodiment, the terminal hydroxyl group content ranges from 18 to
500 mmol/kg, such as from about 50 mmol/kg to about 400 mmol/kg. In
one particular embodiment, for instance, the terminal hydroxyl
group content may be from about 100 mmol/kg to about 400
mmol/kg.
[0043] In addition to the terminal hydroxyl groups, the
polyoxymethylene polymer may also have other terminal groups usual
for these polymers. Examples of these are alkoxy groups, formate
groups, acetate groups or aldehyde groups. According to one
embodiment, the polyoxymethylene is a homo- or copolymer which
comprises at least 50 mol-%, such as at least 75 mol-%, such as at
least 90 mol-% and such as even at least 95 mol-% of
--CH.sub.2O-repeat units.
[0044] In addition to having a relatively high terminal hydroxyl
group content, the polyoxymethylene polymer according to the
present disclosure can also have a relatively low amount of low
molecular weight constituents. As used herein, low molecular weight
constituents (or fractions) refer to constituents having molecular
weights below 10,000 dalton. In order to produce a polymer having
the desired permeability requirements, the present inventors
unexpectedly discovered that reducing the proportion of low
molecular weight constituents can dramatically improve the
permeability properties of the resulting material, when attached to
an impact modifier. In this regard, the polyoxymethylene polymer
contains low molecular weight constituents in an amount less than
about 10% by weight, based on the total weight of the
polyoxymethylene. In certain embodiments, for instance, the
polyoxymethylene polymer may contain low molecular weight
constituents in an amount less than about 5% by weight, such as in
an amount less than about 3% by weight, such as even in an amount
less than about 2% by weight.
[0045] The preparation of the polyoxymethylene can be carried out
by polymerization of polyoxymethylene-forming monomers, such as
trioxane or a mixture of trioxane and dioxolane, in the presence of
ethylene glycol as a molecular weight regulator. The polymerization
can be effected as precipitation polymerization or in the melt. By
a suitable choice of the polymerization parameters, such as
duration of polymerization or amount of molecular weight regulator,
the molecular weight and hence the MVR value of the resulting
polymer can be adjusted. The above-described procedure for the
polymerization can lead to polymers having comparatively small
proportions of low molecular weight constituents. If a further
reduction in the content of low molecular weight constituents were
to be desired, this can be effected by separating off the low
molecular weight fractions of the polymer after the deactivation
and the degradation of the unstable fractions after treatment with
a basic protic solvent. This may be a fractional precipitation from
a solution of the stabilized polymer; polymer fractions of
different molecular weight distribution being obtained.
[0046] In one embodiment, a polyoxymethylene polymer with hydroxyl
terminal groups can be produced using a cationic polymerization
process followed by solution hydrolysis to remove any unstable end
groups. During cationic polymerization, a glycol, such as ethylene
glycol can be used as a chain terminating agent. The cationic
polymerization results in a bimodal molecular weight distribution
containing low molecular weight constituents. In one particular
embodiment, the low molecular weight constituents can be
significantly reduced by conducting the polymerization using a
heteropoly acid such as phosphotungstic acid as the catalyst. When
using a heteropoly acid as the catalyst, for instance, the amount
of low molecular weight constituents can be less than about 2% by
weight.
[0047] A heteropoly acid refers to polyacids formed by the
condensation of different kinds of oxo acids through dehydration
and contains a mono- or polynuclear complex ion wherein a hetero
element is present in the center and the oxo acid residues are
condensed through oxygen atoms. Such a heteropoly acid is
represented by the formula:
H.sub.x[M.sub.mM'.sub.nO.sub.z]yH.sub.2O
wherein [0048] M represents an element selected from the group
consisting of P, Si, Ge, Sn, As, Sb, U, Mn, Re, Cu, Ni, Ti, Co, Fe,
Cr, Th or Ce, [0049] M' represents an element selected from the
group consisting of W, Mo, V or Nb, [0050] m is 1 to 10, [0051] n
is 6 to 40, [0052] z is 10 to 100, [0053] x is an integer of 1 or
above, and [0054] y is 0 to 50.
[0055] The central element (M) in the formula described above may
be composed of one or more kinds of elements selected from P and Si
and the coordinate element (M') is composed of at least one element
selected from W, Mo and V, particularly W or Mo.
[0056] Specific examples of heteropoly acids are phosphomolybdic
acid, phosphotungstic acid, phosphomolybdotungstic acid,
phosphomolybdovanadic acid, phosphomolybdotungstovanadic acid,
phosphotungstovanadic acid, silicotungstic acid, silicomolybdic
acid, silicomolybdotungstic acid, silicomolybdotungstovanadic acid
and acid salts thereof.
[0057] Excellent results have been achieved with heteropoly acids
selected from 12-molybdophosphoric acid (H.sub.3PMo.sub.12O.sub.40)
and 12-tungstophosphoric acid (H.sub.3PW.sub.12O.sub.40) and
mixtures thereof.
[0058] The heteropoly acid may be dissolved in an alkyl ester of a
polybasic carboxylic acid. It has been found that alkyl esters of
polybasic carboxylic acid are effective to dissolve the heteropoly
acids or salts thereof at room temperature (25.degree. C.).
[0059] The alkyl ester of the polybasic carboxylic acid can easily
be separated from the production stream since no azeotropic
mixtures are formed. Additionally, the alkyl ester of the polybasic
carboxylic acid used to dissolve the heteropoly acid or an acid
salt thereof fulfils the safety aspects and environmental aspects
and, moreover, is inert under the conditions for the manufacturing
of oxymethylene polymers.
[0060] Preferably the alkyl ester of a polybasic carboxylic acid is
an alkyl ester of an aliphatic dicarboxylic acid of the
formula:
(ROOC)--(CH.sub.2).sub.n-(COOR')
wherein [0061] n is an integer from 2 to 12, preferably 3 to 6 and
[0062] R and R' represent independently from each other an alkyl
group having 1 to 4 carbon atoms, preferably selected from the
group consisting of methyl, ethyl, n-propyl, iso-propyl, n-butyl,
iso-butyl and tert.-butyl.
[0063] In one embodiment, the polybasic carboxylic acid comprises
the dimethyl or diethyl ester of the above-mentioned formula, such
as a dimethyl adipate (DMA).
[0064] The alkyl ester of the polybasic carboxylic acid may also be
represented by the following formula:
(ROOC).sub.2--CH--(CH.sub.2).sub.m--CH--(COOR').sub.2
wherein [0065] m is an integer from 0 to 10, preferably from 2 to 4
and [0066] R and R' are independently from each other alkyl groups
having 1 to 4 carbon atoms, preferably selected from the group
consisting of methyl, ethyl, n-propyl, iso-propyl, n-butyl,
iso-butyl and tert.-butyl.
[0067] Particularly preferred components which can be used to
dissolve the heteropoly acid according to the above formula are
butantetracarboxylic acid tetratethyl ester or butantetracarboxylic
acid tetramethyl ester.
[0068] Specific examples of the alkyl ester of a polybasic
carboxylic acid are dimethyl glutaric acid, dimethyl adipic acid,
dimethyl pimelic acid, dimethyl suberic acid, diethyl glutaric
acid, diethyl adipic acid, diethyl pimelic acid, diethyl suberic
acid, diemethyl phthalic acid, dimethyl isophthalic acid, dimethyl
terephthalic acid, diethyl phthalic acid, diethyl isophthalic acid,
diethyl terephthalic acid, butantetracarboxylic acid
tetramethylester and butantetracarboxylic acid tetraethylester as
well as mixtures thereof. Other examples include
dimethylisophthalate, diethylisophthalate, dimethylterephthalate or
diethylterephthalate.
[0069] Preferably, the heteropoly acid is dissolved in the alkyl
ester of the polybasic carboxylic acid in an amount lower than 5
weight percent, preferably in an amount ranging from 0.01 to 5
weight percent, wherein the weight is based on the entire
solution.
[0070] In some embodiments, the polymer composition of the present
disclosure may contain other polyoxymethylene homopolymers and/or
polyoxymethylene copolymers. Such polymers, for instance, are
generally unbranched linear polymers which contain as a rule at
least 80%, such as at least 90%, oxymethylene units. Such
conventional polyoxymethylenes may be present in the composition as
long as the resulting mixture maintains the above amounts of
hydroxyl terminated groups and the above amounts of low molecular
weight constituents.
[0071] The polyoxymethylene polymer present in the composition can
generally have a melt volume rate (MVR) or melt index of less than
50 cm.sup.3/10 min, such as from about 1 to about 40 cm.sup.3/10
min, determined according to ISO 1133 at 190.degree. C. and 2.16
kg. In general, the molecular weight of the polyoxymethylene
polymer is related to the melt index. In particular, a higher melt
index refers to a lower molecular weight. In one embodiment of the
present disclosure, a polyoxymethylene polymer is incorporated into
the polymer composition having a relatively low molecular weight.
The amount of coupling agent, however, is increased based upon the
molecular weight and the number of terminal hydroxyl groups. It has
been discovered that lowering the molecular weight of the polymer
while increasing the amount of coupling agent produces a polymer
composition capable of being blow molded and that has significantly
improved multi axial impact properties, especially when measured at
extremely low temperatures. For example, in one embodiment, the
present disclosure is directed to a polyoxymethylene polymer having
an increased number of hydroxyl terminal groups and that has a melt
index of from about 5 cm.sup.3/10 min to about 20 cm.sup.3/10 min,
such as from about 7 cm.sup.3/10 min to about 12 cm.sup.3/10 min,
such as from about 8 cm.sup.3/10 min to about 10 cm.sup.3/10 min.
In this embodiment, the polyoxymethylene polymer may optionally
have lower amounts of low molecular weight constituents. In the
past, polyoxymethylene polymers having a melt index within the
above range have been found unsuitable for use in some blow molding
applications since the polymers do not have sufficient shear
viscosity. The present inventors discovered, however, that using
lower molecular weight polymers as described above in combination
with greater amounts of coupling agent produces polymer
compositions that not only have increased shear viscosity, but also
have excellent multi axial impact properties.
[0072] The amount of polyoxymethylene polymer present in the
polymer composition of the present disclosure can vary depending
upon the particular application. In one embodiment, for instance,
the composition contains polyoxymethylene polymer in an amount of
at least 50% by weight, such as in an amount greater than about 60%
by weight, such as in an amount greater than about 65% by weight,
such as in an amount greater than about 70% by weight. In general,
the polyoxymethylene polymer is present in an amount less than
about 95% by weight, such as in an amount less than about 90% by
weight, such as in an amount less than about 85% by weight.
[0073] As described above, in addition to a polyoxymethylene
polymer, the composition also contains an impact modifier and a
coupling agent if needed for an attachment to occur. The impact
modifier may comprise a thermoplastic elastomer. In general, any
suitable thermoplastic elastomer may be used according to the
present disclosure as long as the thermoplastic elastomer can
attach to the polyoxymethylene polymer whether through the use of a
coupling agent or otherwise. In one embodiment, for instance, the
thermoplastic elastomer may include reactive groups that directly
or indirectly attach to reactive groups contained on the
polyoxymethylene polymer. For instance, in one particular
embodiment, the thermoplastic elastomer has active hydrogen atoms
which allow for covalent bonds to form with the hydroxyl groups on
the polyoxymethylene using the coupling agent.
[0074] Thermoplastic elastomers are materials with both
thermoplastic and elastomeric properties. Thermoplastic elastomers
include styrenic block copolymers, polyolefin blends referred to as
thermoplastic olefin elastomers, elastomeric alloys, thermoplastic
polyurethanes, thermoplastic copolyesters, and thermoplastic
polyamides.
[0075] Thermoplastic elastomers well suited for use in the present
disclosure are polyester elastomers (TPE-E), thermoplastic
polyamide elastomers (TPE-A) and in particular thermoplastic
polyurethane elastomers (TPE-U). The above thermoplastic elastomers
have active hydrogen atoms which can be reacted with the coupling
reagents and/or the polyoxymethylene polymer. Examples of such
groups are urethane groups, amido groups, amino groups or hydroxyl
groups. For instance, terminal polyester diol flexible segments of
thermoplastic polyurethane elastomers have hydrogen atoms which can
react, for example, with isocyanate groups.
[0076] In one particular embodiment, a thermoplastic polyurethane
elastomer is used as the impact modifier either alone or in
combination with other impact modifiers. The thermoplastic
polyurethane elastomer, for instance, may have a soft segment of a
long-chain diol and a hard segment derived from a diisocyanate and
a chain extender. In one embodiment, the polyurethane elastomer is
a polyester type prepared by reacting a long-chain diol with a
diisocyanate to produce a polyurethane prepolymer having isocyanate
end groups, followed by chain extension of the prepolymer with a
diol chain extender. Representative long-chain diols are polyester
diols such as poly(butylene adipate)diol, poly(ethylene
adipate)diol and poly(.epsilon.-caprolactone)diol; and polyether
diols such as poly(tetramethylene ether)glycol, poly(propylene
oxide)glycol and poly(ethylene oxide)glycol. Suitable diisocyanates
include 4,4'-methylenebis(phenyl isocyanate), 2,4-toluene
diisocyanate, 1,6-hexamethylene diisocyanate and
4,4'-methylenebis-(cycloxylisocyanate). Suitable chain extenders
are C.sub.2-C.sub.6 aliphatic diols such as ethylene glycol,
1,4-butanediol, 1,6-hexanediol and neopentyl glycol. One example of
a thermoplastic polyurethane is characterized as essentially
poly(adipic acid-co-butyleneglycol-co-diphenylmethane
diisocyanate).
[0077] The amount of impact modifier contained in the polymer
composition used to form the containment device can vary depending
on many factors. The amount of impact modifier present in the
composition may depend, for instance, on the desired permeability
of the resulting material and/or on the amount of coupling agent
present and the amount of terminal hydroxyl groups present on the
polyoxymethylene polymer. In general, one or more impact modifiers
may be present in the composition in an amount greater than about
5% by weight, such as in an amount greater than about 10% by
weight. The impact modifier is generally present in an amount less
than 30% by weight, such as in an amount less than about 25% by
weight, such as in an amount up to about 18% by weight in order to
provide sufficient impact strength resistance while preserving the
permeability properties of the material.
[0078] The coupling agent present in the polymer composition
comprises a coupling agent capable of coupling the impact modifier
to the polyoxymethylene polymer. In order to form bridging groups
between the polyoxymethylene polymer and the impact modifier, a
wide range of polyfunctional, such as trifunctional or bifunctional
coupling agents, may be used. The coupling agent may be capable of
forming covalent bonds with the terminal hydroxyl groups on the
polyoxymethylene polymer and with active hydrogen atoms on the
impact modifier. In this manner, the impact modifier becomes
coupled to the polyoxymethylene through covalent bonds.
[0079] In one embodiment, the coupling agent comprises a
diisocyanate, such as an aliphatic, cycloaliphatic and/or aromatic
diisocyanate. The coupling agent may be in the form of an oligomer,
such as a trimer or a dimer.
[0080] In one embodiment, the coupling agent comprises a
diisocyanate or a triisocyanate which is selected from 2,2'-,
2,4'-, and 4,4'-diphenylmethane diisocyanate (MDI);
3,3'-dimethyl-4,4'-biphenylene diisocyanate (TODD; toluene
diisocyanate (TDI); polymeric MDI; carbodiimide-modified liquid
4,4'-diphenylmethane diisocyanate; para-phenylene diisocyanate
(PPDI); meta-phenylene diisocyanate (MPDI); triphenyl methane-4,4'-
and triphenyl methane-4,4''-triisocyanate;
naphthylene-1,5-diisocyanate; 2,4'-, 4,4'-, and 2,2-biphenyl
diisocyanate; polyphenylene polymethylene polyisocyanate (PMDI)
(also known as polymeric PMDI); mixtures of MDI and PMDI; mixtures
of PMDI and TDI; ethylene diisocyanate; propylene-1,2-diisocyanate;
trimethylene diisocyanate; butylenes diisocyanate; bitolylene
diisocyanate; tolidine diisocyanate;
tetramethylene-1,2-diisocyanate; tetramethylene-1,3-diisocyanate;
tetramethylene-1,4-diisocyanate; pentamethylene diisocyanate;
1,6-hexamethylene diisocyanate (HDI); octamethylene diisocyanate;
decamethylene diisocyanate; 2,2,4-trimethylhexamethylene
diisocyanate; 2,4,4-trimethylhexamethylene diisocyanate;
dodecane-1,12-diisocyanate; dicyclohexylmethane diisocyanate;
cyclobutane-1,3-diisocyanate; cyclohexane-1,2-diisocyanate;
cyclohexane-1,3-diisocyanate; cyclohexane-1,4-diisocyanate;
diethylidene diisocyanate; methylcyclohexylene diisocyanate (HTDI);
2,4-methylcyclohexane diisocyanate; 2,6-methylcyclohexane
diisocyanate; 4,4'-dicyclohexyl diisocyanate; 2,4'-dicyclohexyl
diisocyanate; 1,3,5-cyclohexane triisocyanate;
isocyanatomethylcyclohexane isocyanate;
1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane;
isocyanatoethylcyclohexane isocyanate;
bis(isocyanatomethyl-cyclohexane diisocyanate;
4,4'-bis(isocyanatomethyl) dicyclohexane;
2,4'-bis(isocyanatomethyl) dicyclohexane; isophorone diisocyanate
(IPDI); dimeryl diisocyanate, dodecane-1,12-diisocyanate,
1,10-decamethylene diisocyanate, cyclohexylene-1,2-diisocyanate,
1,10-decamethylene diisocyanate, 1-chlorobenzene-2,4-diisocyanate,
furfurylidene diisocyanate, 2,4,4-trimethyl hexamethylene
diisocyanate, 2,2,4-trimethyl hexamethylene diisocyanate,
dodecamethylene diisocyanate, 1,3-cyclopentane diisocyanate,
1,3-cyclohexane diisocyanate, 1,3-cyclobutane diisocyanate,
1,4-cyclohexane diisocyanate, 4,4'-methylenebis(cyclohexyl
isocyanate), 4,4'-methylenebis(phenyl isocyanate),
1-methyl-2,4-cyclohexane diisocyanate, 1-methyl-2,6-cyclohexane
diisocyanate, 1,3-bis (isocyanato-methyl)cyclohexane,
1,6-diisocyanato-2,2,4,4-tetra-methylhexane,
1,6-diisocyanato-2,4,4-tetra-trimethylhexane,
trans-cyclohexane-1,4-diisocyanate,
3-isocyanato-methyl-3,5,5-trimethylcyclo-hexyl isocyanate,
1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane,
cyclo-hexyl isocyanate, dicyclohexylmethane 4,4'-diisocyanate,
1,4-bis(isocyanatomethyl)cyclohexane, m-phenylene diisocyanate,
m-xylylene diisocyanate, m-tetramethylxylylene diisocyanate,
p-phenylene diisocyanate, p,p'-biphenyl diisocyanate,
3,3'-dimethyl-4,4'-biphenylene diisocyanate,
3,3'-dimethoxy-4,4'-biphenylene diisocyanate,
3,3'-diphenyl-4,4'-biphenylene diisocyanate, 4,4'-biphenylene
diisocyanate, 3,3'-dichloro-4,4'-biphenylene diisocyanate,
1,5-naphthalene diisocyanate, 4-chloro-1,3-phenylene diisocyanate,
1,5-tetrahydronaphthalene diisocyanate, metaxylene diisocyanate,
2,4-toluene diisocyanate, 2,4'-diphenylmethane diisocyanate,
2,4-chlorophenylene diisocyanate, 4,4'-diphenylmethane
diisocyanate, p,p'-diphenylmethane diisocyanate, 2,4-tolylene
diisocyanate, 2,6-tolylene diisocyanate,
2,2-diphenylpropane-4,4'-diisocyanate, 4,4'-toluidine diisocyanate,
dianidine diisocyanate, 4,4'-diphenyl ether diisocyanate,
1,3-xylylene diisocyanate, 1,4-naphthylene diisocyanate,
azobenzene-4,4'-diisocyanate, diphenyl sulfone-4,4'-diisocyanate,
or mixtures thereof.
[0081] In one embodiment, an aromatic polyisocyanate is used, such
as 4,4'-diphenylmethane diisocyanate (MDI).
[0082] The polymer composition generally contains the coupling
agent in an amount from about 0.1% to about 10% by weight. In one
embodiment, for instance, the coupling agent is present in an
amount greater than about 1% by weight, such as in an amount
greater than 2% by weight. In one particular embodiment, the
coupling agent is present in an amount from about 0.2% to about 5%
by weight. To ensure that the impact modifier has been completely
coupled to the polyoxymethylene polymer, in one embodiment, the
coupling agent can be added to the polymer composition in molar
excess amounts when comparing the reactive groups on the coupling
agent with the amount of terminal hydroxyl groups on the
polyoxymethylene polymer.
[0083] As described above, in one embodiment, greater amounts of
the coupling agent are combined with the polyoxymethylene polymer
when the polyoxymethylene polymer has a relatively low molecular
weight. For instance, in one embodiment, the polyoxymethylene
polymer can have a melt index of greater than about 5 cm.sup.3/10
min, such as greater than about 7 cm.sup.3/10 min. For instance,
the polyoxymethylene polymer can have a melt index of from about 5
cm.sup.3/10 min to about 20 cm.sup.3/10 min, such as from about 7
cm.sup.3/10 min to about 12 cm.sup.3/10 min, such as from about 8
cm.sup.3/10 min to about 10 cm.sup.3/10 min. In this embodiment,
the coupling agent may be added in an amount such that there is
from about 0.8 to about 2 mol of the coupling agent per mol of
hydroxyl groups on the polyoxymethylene polymer. For instance, in
one embodiment, the coupling agent can be added in an amount
greater than 1.5% by weight, such as in an amount greater than
about 3% by weight, such as from about 1.5% by weight to about 10%
by weight, such as from about 1.5% by weight to about 5% by
weight.
[0084] Combining a relatively low molecular weight polyoxymethylene
polymer with greater amounts of coupling agent may produce hollow
articles having increased multi axial impact strengths, especially
at relatively low temperatures. For instance, the polymer
composition may have a multi axial impact strength when tested
according to ASTM D3763 and when measured at -40.degree. C. of
greater than about 15 ftlb-f, such as greater than about 18 ftlb-f,
such as greater than about 20 ftlb-f. In general, the impact
strength will be less than about 50 ftlb-f. Articles produced from
the composition can thus pass SAE Test J288.
[0085] In one embodiment, a relatively low molecular weight
polyoxymethylene polymer may be used and sufficient amounts of
coupling agent may be combined with the polymer in conjunction with
an impact modifier so as to produce a polymer composition that not
only has excellent multi axial impact strength characteristics, but
also is capable of being used in a blow molding process. In this
regard, in one embodiment, the coupling agent can be added to the
polymer composition in an amount sufficient for the polymer
composition to have a shear viscosity of at least about 8000 Pa-s
at a shear rate of 0.1 rad/sec and at a temperature of 190.degree.
C. For instance, the coupling agent may be added such that the
polymer composition has a shear viscosity of from about 8000 Pa-s
at the above conditions to about 30,000 Pa-s, such as from about
8000 Pa-s to about 15,000 Pa-s, such as from about 8000 Pa-s to
about 12,000 Pa-s.
[0086] The above polymer composition is particularly well suited to
producing small off-road engine fuel tanks that may require very
high impact strength at cold temperatures, such as temperatures
even as low as -40.degree. C. The above results can be obtained
using a polyoxymethylene polymer having a relatively high number of
terminal hydroxyl groups that may also optionally have a relatively
low amount of low molecular weight constituents.
[0087] In one embodiment, a formaldehyde scavenger may also be
included in the composition. The formaldehyde scavenger, for
instance, may be amine-based and may be present in an amount less
than about 1% by weight.
[0088] The polymer composition of the present disclosure can
optionally contain a stabilizer and/or various other known
additives. Such additives can include, for example, antioxidants,
acid scavengers, UV stabilizers or heat stabilizers. In addition,
the molding material or the molding may contain processing
auxiliaries, for example adhesion promoters, lubricants, nucleating
agents, demolding agents, fillers, reinforcing materials or
antistatic agents and additives which impart a desired property to
the molding material or to the molding, such as dyes and/or
pigments.
[0089] In general, other additives can be present in the polymer
composition in an amount up to about 10% by weight, such as from
about 0.1% to about 5% by weight, such as from about 0.1 to about
2% by weight.
[0090] When forming containment devices in accordance with the
present disclosure, the above described components can be melt
blended together, which automatically causes the reaction to occur
between the coupling agent, the polyoxymethylene polymer, and the
impact modifier. As described above, the coupling agent reacts with
the reactive end groups on the polyoxymethylene polymer and the
reactive groups on the impact modifier. The reaction between the
components can occur simultaneously or in sequential steps. In one
particular embodiment, the components in the composition are mixed
together and then melt blended in an extruder.
[0091] The reaction of the components is typically effected at
temperatures of from 100 to 240.degree. C., such as from 150 to
220.degree. C., and the duration of mixing is typically from 0.5 to
60 minutes.
[0092] The proportion of coupling agent in relation to the other
components can be chosen within wide limits. For instance, the
coupling agent may be used in an amount such that there are from
0.2 to 5 mol, preferably from 0.5 to 4 mol, of the coupling agent
per mole of active hydrogen atoms, for example in the form of
hydroxyl groups, of the polyoxymethylene containing active hydrogen
atoms. When using a polyoxymethylene polymer having a relatively
low molecular weight, for instance, the coupling agent may be
present in the composition such that there is at least 0.6 mol of
coupling agent, such as from about 0.6 mol of coupling agent to
about 4 mol, such as from about 0.6 mol of coupling agent to about
2 mol of coupling agent per mol of hydroxyl groups on the
polyoxymethylene polymer.
[0093] In one embodiment, the molding composition of the present
disclosure is reacted together and compounded prior to being used
in a molding process. For instance, in one embodiment, the
different components can be melted and mixed together in a
conventional single or twin screw extruder at a temperature
described above. Extruded strands may be produced by the extruder
which are then pelletized. Prior to compounding, the polymer
components may be dried to a moisture content of about 0.05 weight
percent or less. If desired, the pelletized compound can be ground
to any suitable particle size, such as in the range of from about
100 microns to about 500 microns.
[0094] As described above, the formation of VOC and compressed gas
containment devices in accordance with the present disclosure can
be done using any suitable molding process, such as blow molding,
rotational molding, or injection molding. In one particular
embodiment, injection molding is used to form the containment
devices. For instance, a plurality of portions of the containment
devices can be first produced and then welded together.
[0095] When injection molding, the pre-compounded composition or
the individual components can be fed to a heated barrel, mixed and
forced into a mold cavity. The heated barrel may comprise a single
screw extruder or a twin screw extruder. While in the barrel, the
composition is heated to a temperature sufficient to form a molten
mixture that flows. Once forced into a mold cavity, the polymer
composition cools and hardens producing the desired part. In one
embodiment, injection molding can be gas assisted. For instance,
non-reactive gases, such as nitrogen or supercritical gases can be
used to place pressure on the molten material for forcing the
material against the walls of the mold. In other embodiments,
however, no such gas is needed to obtain the pressures necessary
during injection into the mold.
[0096] After the portions or parts of the containment device are
molded, the different portions are then attached together. In one
embodiment, for instance, any suitable welding process may be used
to attach the portions together. For example, the portions may be
attached together using laser welding, ultrasonic welding, linear
vibration, orbital vibration, hot plate welding, or spin
welding.
[0097] During laser welding, the components are subjected to
electromagnetic radiation at wavelengths that causes absorption.
The absorption of the electromagnetic radiation results in heating
and melting at the interface of the components causing the
different parts to join together.
[0098] During linear vibration, heat is generated by moving one
part against another under pressure through a linear displacement
in the plane of the joint. When a molten state is reached at the
joint interface, vibration is stopped and clamping pressure is
maintained until a bond is formed between the parts. Orbital
vibration is similar to linear vibration only an electromagnetic
drive is used to create relative motion between the two
thermoplastic portions. This constant velocity motion generates
heat and causes the two parts to bond together.
[0099] During hot plate welding, a heated platen assembly is
introduced between the two portions to be joined together. Once the
interface polymer on each part is melted or softened, the heated
platen is withdrawn and the parts are clamped together.
[0100] Spin welding is a process that joins circular thermoplastic
parts by bringing the part interfaces together under pressure with
a circular spinning motion. One of the portions is typically held
stationary in a fixture while the other is rotated against it under
pressure. The frictional heat that is generated causes the part
interfaces to melt and fuse together.
[0101] In one particular embodiment, the different parts or
portions of the containment device are bonded together using
ultrasonic welding. During ultrasonic welding, an ultrasonic tool
called a horn transfers vibratory energy through one or both parts
at the interface. The vibratory energy is converted into heat
through friction which causes the parts to bond together when
pressure is applied. More particularly, during ultrasonic welding,
one or more of the parts can be held between an anvil and the horn,
which is connected to a transducer. Typically, a low-amplitude
acoustic vibration is emitted. The frequency used during ultrasonic
welding can generally be from about 10 kHz to about 100 kHz.
[0102] The present disclosure may be better understood with
reference to the following example.
EXAMPLE NO. 1
[0103] The following experiments were conducted in order to show
some of the benefits and advantages of compositions made according
to the present disclosure.
[0104] First, polyoxymethylene polymers were prepared using
cationic polymerization with ethylene glycol as the chain
terminating agent, followed by solution hydrolysis. One of the
polyoxymethylene polymers (Sample No. 1) was made using a
conventional catalyst, namely boron trifluoride (BF.sub.3). For
purposes of comparison, a polyoxymethylene polymer (Sample No. 2)
was produced using a heteropoly acid (HPA) as a catalyst.
[0105] The polymer feed composition for Sample Nos. 1 and 2 are
included in the following table.
TABLE-US-00001 TABLE 1 Ethylene HPA BF3 Sample Trioxane Dioxolane
Glycol Catalyst Catalyst No. wt % wt % ppm ppm ppm 1 96.4 3.5 700 0
21 2 96.4 3.5 700 2 0
[0106] The molecular weight distribution of the polyoxymethylene
samples was determined by GPC. Each sample was dissolved (.about.30
minutes at 40.degree. C., under N.sub.2 (g)) in distilled
hexafluoroisopropanol (HFIP) buffered with potassium
trifluroacetate. The samples were closely monitored and removed
from heating as soon as the material was dissolved. The solution
was filtered through a 0.45 uM PTFE filter.
[0107] The analysis was performed at 40.degree. C. using HFIP
w/TEAN as the mobile phase on a Waters 2695 separations unit
coupled with a Waters 2410 refractive index (RI) detector. Two
PL-HFIP gel columns fitted with an HFIP-gel guard column were used
for the separation. The data was acquired and processed with
EMPOWER PRO software. The sampling conditions were as follows:
Conditions
[0108] 1. Flow rate: 1.0 ml/min
[0109] 2. 100 uL injection volume
[0110] 3. Collection time 30 mins
[0111] 4. Multiple injections
[0112] 5. Calibrated vs. well known PMMA standards
[0113] The end group analysis for the polyoxymethylene samples was
determined by NMR. The samples were prepared by silylation prior to
being tested. A solution of 0.84 mL BSTFA and 63 .mu.L pyridine
(anhydrous) was added under nitrogen to a 10 mL vial fitted with
TEFLON septum.
[0114] The solution was heated to 45.degree. C. in a sample
preparation unit with agitation. A second solution containing 30 mg
acetal and 0.6 mL 60% CHCl.sub.3/40% HFIP was prepared at
45.degree. C. The acetal solution was transferred to the BSTFA
solution via a glass syringe with metal tip that was preheated in
an oven to 50.degree. C. The mixture was agitated at 45.degree. C.
for 1 hour after which time the solvent was evaporated under a
stream of dry nitrogen. The white residue was re-dissolved and
evaporated with dry HFIP an additional 3 times in the same
manner.
[0115] The residue was dissolved at 45.degree. C. in a HFIP-d.sub.2
solution (w/0.1% pyridine). The H NMR spectrum for each sample was
collected on a Bruker DMX300 spectrometer (Dual 5 mm probe,
30.degree. pulse, D1=6 s, 256 transients, 40.degree. C.). Peak
deconvolution was performed with the Bruker TopSpin v.1.3
software.
[0116] The following results were obtained:
TABLE-US-00002 TABLE 2 Molecular Weight (wt %) End Group Analysis
Product Main Peak LMWF Peak --C.sub.2OH --OCH.sub.3 Sample No. 1
89.9 10.1 85 15 Sample No. 2 98.1 1.9 86 14 LMWF--"low molecular
weight fractions"
[0117] The molecular weight distribution for the polyoxymethylene
polymers are also shown in FIGS. 3 and 4. A comparison of the GPC
curve in FIGS. 3 and 4 demonstrates the reduction in the low
molecular weight constituents that is achieved through the use of
the heteropoly acid catalysts.
[0118] As shown above, the polyoxymethylene polymer made with the
heteropoly acid contained less than 2% by weight low molecular
weight constituents. Both polymers contained significant amounts of
hydroxyl terminal groups.
[0119] The above polyoxymethylene polymers were then melt blended
with an impact modifier, a coupling agent, and a stabilizer package
including an antioxidant and a lubricant. The lubricant used
contained a combination of ethylene bis stearamide and ethylene bis
palmitamide. The antioxidant used was
tetrakis-(methylene-(3,5-di-(tert)-butyl-4-hydrocinnamate))metha-
ne. The formulated compositions were melt blended using a 92 mm
twin screw extruder. The extrusion conditions were as follows:
TABLE-US-00003 TABLE 3 Extruder Temperatures .degree. C. Extruder
Extruder Barrel Zone Number Feed Rate Screw Spe 1 2 3 4 5 6 7 DIE
(kg/hr) (rpm) 177 177 177 177 177 177 177 188 817 210 indicates
data missing or illegible when filed
[0120] The polymers were blended with a thermoplastic polyurethane
elastomer impact modifier. In particular, the impact modifier was
obtained from BASF under the trade name ELASTOLLAN. The coupling
agent used was 4,4'-diphenylmethane diisocyanate. As described
above, the compositions also contained a stabilizer package
including an antioxidant and a lubricant.
[0121] The samples were molded for multi axial impact testing using
a Roboshot 165 SiB molding machine. The test specimen was a 4''
diameter disc 1/8'' of an inch thick. The molding conditions are
included in the following table.
TABLE-US-00004 TABLE 4 Barrel Zone 1 (.degree. C.) 177 Barrel Zone
2 (.degree. C.) 182 Barrel Zone 3 (.degree. C.) 188 Nozzle
(.degree. C.) 193 Melt (.degree. C.) 205 Mold Movable (.degree. C.)
80 Mold Stationary (.degree. C.) 80 Back Pressure (psi) 50 Hold
Pressure (psi) 11600 Hold Pressure (psi) 35 Cooling Time (sec) 15
Cycle Time (sec) 50 Melt Cushion (mm) 5 Injection Velocity (mm/s)
200 Injection Time (sec) 2 Screw Retraction Time (sec) 10
[0122] The molded discs were tested for multi axial impact at
-30.degree. C. using ASTM method D3763. The instrument was a
Dynatup 8250. The test speed was 11 ft/sec. The samples were
conditioned for 24 hours at 23.degree. C. and 50% RH prior to
testing.
[0123] The permeation testing was conducted using molded discs. The
discs were molded using the same molding machine (Roboshot 165 SiB)
and molding conditions as the multi axial samples.
[0124] Material sample plaques were made by injection molding four
inch diameter discs with an average thickness between 1/32 and 1/8
of an inch. The plaques were die cut into three inch circles in
order to fit the permeation cup. The thickness of the material was
measured at a minimum of five points, and the average thickness was
determined from these measurements. Permeation cup test fixtures
were assembled with the desired material plaque per SAE J2665,
Sections 8.3 through 8.11.
[0125] Permeation values of the material were determined
gravimetrically using a modified version of SAE J2665 "Cup Weight
Loss Method" (Issued October 2006). Vapometer Model 68 permeation
cups, commercially available from Thwing-Albert, were used as the
test fixture. The cups were modified per SAE J2665 in the following
manner: 1) Neoprene gaskets were replaced with FKM gaskets and 2)
the six supplied knurled head screws were replaced to allow for
torque wrench tightening.
[0126] Fuel CE10 was used as the test fuel (10% ethanol, 45%
toluene, and 45% iso-octane). The cups were placed right-side up
into a controlled thermal environment (T=40.degree. C..+-.2.degree.
C.) so that the test material was in contact with only the vapor
phase of the fuel. The weight of the test fixtures were measured
twice a week. Weight-loss versus time was plotted using the method
described in SAE J2665, Section 9. Determination of the
steady-state flux, reported as [grams/(m.sup.2-day)], was carried
out per SAE J2665, Section 10. Determination of the vapor
transmission rate (VTR), or "permeation constant," reported as
[grams-mm/(m.sup.2-day)], was carried out per SAE J2665, Section
11.
[0127] In the first set of experiments using the above procedures,
permeation was tested on compositions where the impact modifier
levels were varied. More particularly, a first set of compositions
were formulated that are indicated below as "Sample No. 3". The
Sample No. 3 compositions contained the polyoxymethylene polymer
described above that contained low molecular weight constituents in
an amount of greater than 10% by weight. Identical compositions
were also formulated and are indicated in the table below as
"Sample No. 4". The Sample No. 4 compositions contained the
polyoxymethylene polymer described above that contained low
molecular weight constituents in an amount less than 2% by
weight.
[0128] Each of the Sample No. 3 compositions and the Sample No. 4
compositions contained the stabilizer package in an amount of 0.4%
by weight and the impact modifier in the amounts listed below in
Table 6. For compositions containing 18% by weight impact modifier
or less, the compositions contained the coupling agent in an amount
of 0.5% by weight. For the compositions containing the impact
modifier in an amount of 30% by weight or more, the compositions
contained the coupling agent in an amount of 0.8% by weight. The
remainder of each composition was made up of the appropriate
polyoxymethylene polymer. The following results were obtained:
TABLE-US-00005 TABLE 5 Impact Modifier Permeation (g mm/m.sup.2) %
Concentration (wt %) Sample 3 Sample 4 Decrease 0 1.09 -- -- 5 3.24
-- -- 7 3.73 -- -- 9 4.95 2.57 48.1% 12 -- 3.45 -- 14 6.36 4.64
27.0% 18 8.46 5.73 32.3% 30 34.53 27.25 21.1% 38 42.02 27.44 34.7%
-- Not analyzed. Compositions indicated as "Sample 3" above
contained polyoxymethylene polymer that included low molecular
weight constituents in an amount greater than 10% by weight.
Compositions indicated as "Sample 4" above contained
polyoxymethylene polymer that included low molecular weight
constituents in an amount less than 2% by weight.
[0129] The above results are also graphically shown in FIG. 5.
[0130] The data above illustrates the dramatic and unexpected
reduction in permeability for the Sample 4 compositions containing
the polyoxymethylene polymer having low levels of low molecular
weight constituents. For instance, permeation decreased by greater
than 30% on average when using the polyoxymethylene polymer
containing low amounts of low molecular weight constituents.
[0131] It is believed that the lower permeability of the
polyoxymethylene polymer containing low amounts of low molecular
weight constituents allows the impact modifier concentration to be
increased, while still maintaining the permeability performance of
the material. The permeation data at a 2 mm wall thickness for
compositions made according to Sample No. 3 and compositions made
according to Sample No. 4 are shown below.
TABLE-US-00006 TABLE 6 Permeation @ 2 mm Wall Impact Modifier
Thickness (g/m.sup.2 day) (wt %) Sample 3 Sample 4 0 0.55 -- 9 2.48
1.29 18 4.23 2.87 -- Not analyzed
[0132] Currently, most fuel tanks require that the material used to
form the tank have a permeation of no greater than 2.5 g/m.sup.2
day. The above results are also graphically illustrated in FIG.
7.
[0133] The following experiments were conducted to show how multi
axial impact strength changes based on the amount of coupling agent
present in the composition. Multi axial impact strength is measured
at -30.degree. C.
[0134] The following compositions were formulated:
TABLE-US-00007 TABLE 7 Sample Sample 1 Sample 2 Impact Coupling No.
POM POM Modifier Agent Stabilizer 5 90.7 0.0 9.0 0.0 0.4 5 90.2 0.0
9.0 0.5 0.4 5 89.9 0.0 9.0 0.8 0.4 5 89.7 0.0 9.0 1.0 0.4 6 81.7
0.0 18.0 0.0 0.4 6 81.2 0.0 18.0 0.5 0.4 6 80.9 0.0 18.0 0.8 0.4 6
80.7 0.0 18.0 1.0 0.4 6 79.7 0.0 18.0 2.0 0.4
[0135] As shown above, all of the "Sample No. 5" compositions and
all of the "Sample No. 6" compositions were formulated using the
polyoxymethylene polymer that contained the low molecular weight
constituents in an amount greater than 10% by weight. The
compositions made according to Sample No. 5 contained an impact
modifier in an amount of 9% by weight, while the compositions
formulated according to Sample No. 6 contained the impact modifier
in an amount of 18% by weight.
[0136] The following results were obtained:
TABLE-US-00008 TABLE 8 Coupling Agent Multi Axial Impact
Concentration Strength @ -30.degree. C. (ftlb-f) (wt %) Sample 5
Sample 6 0.0 2.3 2.0 0.5 4.7 14.0 0.8 8.3 31.2 1.0 29.6 43.2 2.0 --
50.3 -- Not analyzed
[0137] As shown above, the cold temperature multi axial impact
strength increases significantly as the coupling agent
concentration increases and as the impact modifier amount
increases. The above shows that the impact strength of the material
can be increased by increasing the concentration of the coupling
agent.
EXAMPLE NO. 2
[0138] The following experiments were conducted in order to
demonstrate the advantages to using a lower molecular weight
polyoxymethylene polymer in combination with higher amounts of a
coupling agent. It is believed that the lower molecular weight
polyoxymethylene polymer may contribute to better multi axial
impact strength characteristics, while the higher amounts of
coupling agent may increase the shear viscosity of the composition
sufficient so the composition can be used in blow molding
processes.
[0139] Impact modified polyoxymethylene polymer samples were
prepared by melt blending a polyoxymethylene polymer with an impact
modifier, a coupling agent, and a stabilizer package. The
stabilizer package included an antioxidant and a lubricant. The
extrusion conditions that were used to produce Sample Nos. 1-8 are
provided in the following table.
TABLE-US-00009 TABLE 9 Extruder Extruder Extruder Temperatures
.degree. C. Feed Screw Sample Barrel Zone Number Rate Speed No.
Extruder 1 2 3 4 5 6 7 8 9 DIE (kg/hr) (rpm) 1 92 mm 177 177 177
177 177 177 177 NA NA 188 817 210 2 92 mm 177 177 177 177 177 177
177 NA NA 188 817 210 3 40 mm 190 190 190 185 175 165 165 165 NA
190 56.7 125 4 32 mm 190 190 190 185 175 175 165 165 165 175 29.5
150 5 32 mm 190 190 190 185 175 175 165 165 165 175 29.5 150 6 32
mm 190 190 190 185 175 175 165 165 165 175 29.5 150 7 32 mm 190 190
190 185 175 175 165 165 165 175 29.5 150 8 32 mm 190 190 190 185
175 175 165 165 165 175 29.5 150
[0140] Sample Nos. 1-3 above were prepared using a higher molecular
weight polyoxymethylene polymer having a melt index of 2.5
cm.sup.3/10 min. Samples 4-8, on the other hand, were prepared
using a lower molecular weight polyoxymethylene polymer having a
melt index of about 9 cm.sup.3/10 min. The polyoxymethylene
polymers used in Samples 4-8 also contained less than 10% by weight
low molecular weight constituents. The polyoxymethylene polymer
used in Samples 1-3, however, contained greater amounts of the low
molecular weight constituents than Samples 4-8. The coupling agent
used was 4,4'-diphenylmethane diisocyanate. The amount of each
component (weight percent) is included in the following table.
TABLE-US-00010 TABLE 10 Poly- Sample oxymethylene Polymer Impact
Coupling No. Polymer MI Modifier Agent Stabilizer 1 81.2 2.5 18.0
0.5 0.4 2 81.2 2.5 18.0 0.5 0.4 3 81.2 2.5 18.0 0.5 0.4 4 79.7 9.0
18.0 2 0.4 5 79.7 9.0 18.0 2 0.4 6 79.7 9.0 18.0 2 0.4 7 79.7 9.0
18.0 2.0 0.4 8 79.7 9.0 18.0 2 0.4
[0141] The above polymer compositions were molded into discs. The
discs were molded using a Roboshot 165 SiB molding machine. Each
test specimen had a 4'' diameter and each disc was 1/8'' thick. The
molding conditions were as follows:
TABLE-US-00011 TABLE 11 Barrel Zone 1 (.degree. C.) 177 Barrel Zone
2 (.degree. C.) 182 Barrel Zone 3 (.degree. C.) 188 Nozzle
(.degree. C.) 193 Melt (.degree. C.) 205 Mold Movable (.degree. C.)
80 Mold Stationary (.degree. C.) 80 Back Pressure (psi) 50 Hold
Pressure (psi) 11600 Hold Pressure (psi) 35 Cooling Time (sec) 15
Cycle Time (sec) 50 Melt Cushion (mm) 5 Injection Velocity (mm/s)
200 Injection Time (sec) 2 Screw Retraction Time (sec) 10
[0142] The sample discs were tested for multi axial impact strength
at 23.degree. C., at -30.degree. C., and at -40.degree. C.
according to ASTM Method D3763. The testing speed was 11
ft/sec.
[0143] Various physical properties of the polymer compositions were
also tested using ISO tensile bars. The tensile bars were molded on
a Roboshot 110 SiB molding machine. The tensile properties were
measured according to ISO Test Method 527. Charpy impact properties
were also measured according to ISO Method 179. The following
results were obtained:
TABLE-US-00012 TABLE 12 Complex Shear Tensile Aven Viscosity .eta.*
Stress Tensile Total Total Total Mu @ 0.1 rad/ Tensile @ Stress @
Strain @ Strain @ Charpy Charpy Energy Energy Energy Ax Sample MI
sec-1 Modulus Yield Break Break Yield 23 C. -30 C. 23 C. -30 C. -40
C. Imp No. (g/10 min) and 190 C. (MPa) (MPa) (MPa) (%) (%) (kJ/m2)
(kJ/m2) (ftlb-f) (ftlb-f) (ftlb-f) Stre 1 1.4 NA NA NA NA NA NA NA
NA 18.7 NA 1.2 N 2 1.6 8168 NA NA NA NA NA NA NA 40.7 5.5 10.1 N 3
1.5 12190 1543 43.1 35.3 131.3 17.3 20.7 16.2 19.5 1.6 2.2 4. 4 1.3
10437 1814 47.4 38.1 55.0 13.9 22.4 12.4 35.7 23.8 17.1 N 5 1.4 NA
1559 43.2 35.3 72.9 14.4 23.7 10.0 39.9 24.2 11.7 N 6 0.8 NA 1648
45.7 36.3 57.3 15.9 21.8 NA 38.9 40.7 16.3 N 7 0.5 18168 1673 46.2
37.3 56.0 16.4 23.2 NA 39.2 14.0 24.6 N 8 1.3 NA 1649 46.0 37.4
70.7 16.7 20.8 NA 42.9 31.9 34.6 20. indicates data missing or
illegible when filed
[0144] As shown above, polymer compositions made from the lower
molecular weight polyoxymethylene polymers had better multi axial
impact strength, especially at lower temperatures. Sample Nos. 4
and 7 also demonstrated a shear viscosity of greater than 8000
Pa-s, indicating that the low molecular weight polyoxymethylene
polymer compositions were also amenable to blow molding
processes.
[0145] These and other modifications and variations to the present
invention may be practiced by those of ordinary skill in the art,
without departing from the spirit and scope of the present
invention, which is more particularly set forth in the appended
claims. In addition, it should be understood that aspects of the
various embodiments may be interchanged both in whole or in part.
Furthermore, those of ordinary skill in the art will appreciate
that the foregoing description is by way of example only, and is
not intended to limit the invention so further described in such
appended claims.
* * * * *