U.S. patent application number 14/511788 was filed with the patent office on 2015-04-23 for two component polyoxymethylene based systems.
The applicant listed for this patent is Ticona GmbH. Invention is credited to Jos Bastiaens, Oliver Juenger, Qamer Zia.
Application Number | 20150111794 14/511788 |
Document ID | / |
Family ID | 51903962 |
Filed Date | 2015-04-23 |
United States Patent
Application |
20150111794 |
Kind Code |
A1 |
Zia; Qamer ; et al. |
April 23, 2015 |
Two Component Polyoxymethylene Based Systems
Abstract
A two component polyoxymethylene based system is disclosed. The
two component system is comprised of a first polymer layer and a
second polymer layer. The first polymer layer is comprised of a
polyoxymethylene polymer composition comprising a polyoxymethylene
polymer and optionally a tribological modifier. The second polymer
layer is comprised of a second polymer composition comprising a
liquid crystalline polymer, a polyarylene sulfide polymer, or a
combination thereof and at least one tribological modifier. The
compositions provide polymer articles, such as conveyor components,
with improved tribological properties.
Inventors: |
Zia; Qamer; (Frankfurt,
DE) ; Juenger; Oliver; (Mainz, DE) ;
Bastiaens; Jos; (Sulzbach, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Ticona GmbH |
Sulzbach |
|
DE |
|
|
Family ID: |
51903962 |
Appl. No.: |
14/511788 |
Filed: |
October 10, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61893480 |
Oct 21, 2013 |
|
|
|
Current U.S.
Class: |
508/106 |
Current CPC
Class: |
C10M 147/00 20130101;
B32B 2307/746 20130101; B32B 27/42 20130101; B32B 27/286 20130101;
B32B 2371/00 20130101 |
Class at
Publication: |
508/106 |
International
Class: |
C10M 147/00 20060101
C10M147/00 |
Claims
1. A polymer article comprising: a first polymer layer comprising a
polyoxymethylene polymer composition comprising a polyoxymethylene
polymer, and optionally, at least one tribological modifier; a
second polymer layer connected to the first polymer layer, the
second polymer layer comprising a second polymer composition, the
second polymer composition comprising a liquid crystalline polymer,
a polyarylene sulfide polymer, or a combination thereof, and at
least one tribological modifier.
2. The polymer article of claim 1, wherein the tribological
modifier in the second polymer composition comprises a
polytetrafluoroethylene.
3. The polymer article of claim 2, wherein the
polytetrafluoroethylene is present in an amount of from about 1 wt.
% to about 40 wt. %.
4. The polymer article of claim 1, wherein the second polymer
composition further comprises glass fibers.
5. The polymer article of claim 1, wherein the polyoxymethylene
polymer composition comprises a tribological modifier selected from
the group consisting of boron nitride, ultra-high molecular weight
silicone, or a combination thereof
6. The polymer article of claim 1, wherein the polyoxymethylene
polymer composition comprises a tribological modifier selected from
the group consisting of calcium carbonate, ultrahigh-molecular
weight polyethylene, stearyl stearate, silicone oil, polyethylene
wax, amide wax, or a combination thereof.
7. The polymer article of claim 1, wherein the liquid crystalline
polymer contains aromatic ester repeating units.
8. The polymer article of claim 7, wherein the aromatic ester
repeating units comprise aromatic dicarboxylic acid repeating
units, aromatic hydroxycarboxylic acid repeating units, or a
combination thereof.
9. The polymer article of claim 1, wherein the liquid crystalline
polymer repeating units comprise units formed from a
hydroxycarboxylic acid, a dicarboxylic acid, and an aromatic
diol.
10. The polymer article of claim 1, wherein the polyarylene sulfide
polymer is a polyphenylene sulfide polymer.
11. The polymer article of claim 1, wherein the first polymer layer
and the second polymer layer are connected by an interlocking
mechanism.
12. The polymer article of claim 1, wherein the first polymer layer
and the second polymer layer are connected by overmolding.
13. The polymer article of claim 1, wherein the first polymer layer
and the second polymer layer are connected by a fastener.
14. The polymer article of claim 1, wherein the first polymer layer
is in contact with the second polymer layer.
15. The polymer article of claim 1, wherein the second polymer
layer covers at least 85% of the surface area of one surface of the
first polymer layer.
16. The polymer article of claim 1, wherein the second polymer
layer has a thickness of from about 0.01 mm to about 5 mm.
17. The polymer article of claim 1, wherein the polymer article
exhibits a dynamic coefficient of friction against a polyethylene
terephthalate surface of from about 0.01 to about 0.18 as
determined in accordance with VDA 230-206.
18. The polymer article of claim 1, wherein the polymer article
exhibits a dynamic coefficient of friction against a polyacetal
surface, a steel surface, a polyethylene surface, or a
polypropylene surface of from about 0.01 to about 0.18 as
determined in accordance with VDA 230-206.
19. The polymer article of claim 1, wherein the polymer article is
a conveyor component.
20. The polymer article of claim 1, wherein an external lubricant
is not present on a surface of the polymer article.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application claims priority to U.S. Provisional
Application Ser. No. 61/893,480 having a filing date of Oct. 21,
2013, which is incorporated herein by reference in its
entirety.
BACKGROUND
[0002] Polyacetal polymers, which are commonly referred to as
polyoxymethylene polymers, have become established as exceptionally
useful engineering materials in a variety of applications. For
instance, because polyoxymethylene polymers have excellent
mechanical properties, fatigue resistance, abrasion resistance,
chemical resistance, and moldability, they are widely used in
constructing polymer articles, such as articles for use in the
automotive industry and the electrical industry.
[0003] Polyoxymethylene polymers are often provided with additives
to adapt the properties for a specific application, for example by
using reinforcing fibers or tribological modifiers. For instance,
polyoxymethylene polymers have been combined with a tribological
modifier for producing polymer compositions well suited for use in
tribological applications where the polymer article is in moving
contact with other articles, such as metal articles, plastic
articles, and the like. These tribological applications can include
embodiments where the polymer composition is formed into gear
wheels, pulleys, sliding elements, and the like. The addition of a
tribological modifier can provide a composition with a reduced
coefficient of friction, little frictional noise, and low wear.
[0004] In the past, conveyor components such as chain links in
conveying systems for packaging operations have been produced using
various polymers such as polyoxymethylenes and polyamide-imides.
However, in order to convey packages and containers on the conveyor
chain links, lubricants and coatings are often applied to the
conveyor chain links to reduce the coefficient of friction. EP
Patent No. 0831038 to Kasai et al. discloses conveyor chains that
are coated with an external lubricant such as water or soapy water
in order to reduce the coefficient of friction between the conveyor
chain and an opposing surface. In addition, U.S. Pat. Nos.
6,485,794 and 7,067,182 to Li et al. disclose the application of a
thermal or radiation curable coating composition to a plastic
beverage container and a conveying surface in order to reduce the
coefficient of friction. Additionally, U.S. Pat. No. 4,436,200 to
Hodlewsky et al. and U.S. Pat. No. 5,559,180 to Takahashi et al.
disclose the use of polytetrafluoroethylene for modifying the
tribological properties of a polyacetal to reduce the coefficient
of friction.
[0005] Although modified polyoxymethylene compositions have been
found to be well suited in tribological applications, further
improvements are still necessary. For instance, a need exists for
providing a polyoxymethylene based system with improved
tribological properties. In particular, a need exists for providing
a polyoxymethylene based system with a reduced coefficient of
friction when in contact with other moving articles such as metal
articles or plastic articles such as polyethylene terephthalate. In
addition, a need exists for providing a polyoxymethylene based
system with improved tribological properties suitable for conveyor
chain applications.
SUMMARY
[0006] In general, the present disclosure is directed to a polymer
article comprising a first polymer layer and a second polymer
layer. The first polymer layer is comprised of a polyoxymethylene
polymer composition comprising a polyoxymethylene polymer and
optionally, at least one tribological modifier. The second polymer
layer is comprised of a second polymer composition comprising a
liquid crystalline polymer, a polyarylene sulfide polymer, or a
combination thereof. The second polymer composition further
comprises at least one tribological modifier. In one embodiment,
the tribological modifier in the second polymer composition may
comprise a polytetrafluoroethylene. In one embodiment, the second
polymer composition may further comprise a reinforcing fiber.
[0007] The second polymer layer may be connected to the first
polymer layer. In one embodiment, the second polymer layer may be
connected to the first polymer layer via overmolding. In another
embodiment, the second polymer layer may be connected to the first
polymer layer using an interlocking mechanism. In another
embodiment, the second polymer layer may be connected to the first
polymer layer using a fastener.
[0008] Other features and aspects of the present disclosure are
discussed in greater detail below.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] A full and enabling disclosure of the present disclosure is
set forth more particularly in the remainder of the specification,
including reference to the accompanying figures, in which:
[0010] FIG. 1 is a conveyor belt assembly comprising conveyor
components according to one embodiment of the present
disclosure;
[0011] FIG. 2 is a two-component conveyor component according to
one embodiment of the present disclosure;
[0012] FIG. 3a is a two-component conveyor component demonstrating
an interlocking mechanism according to one embodiment of the
present disclosure;
[0013] FIG. 3b is a two-component conveyor component demonstrating
an interlocking mechanism according to another embodiment of the
present disclosure;
[0014] FIG. 4 is a two-component conveyor component demonstrating a
fastening mechanism according to one embodiment of the present
disclosure;
[0015] FIG. 5a is a two-component conveyor component produced using
an overmolding process according to one embodiment of the present
disclosure; and
[0016] FIG. 5b is a two-component conveyor component produced using
an overmolding process according to another embodiment of the
present disclosure.
[0017] Repeat use of the 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
[0018] Reference now will be made in detail to the embodiments of
the invention, one or more examples of which are set forth below.
Each example is provided by way of explanation of the invention,
not limitation of the invention. In fact, it will be apparent to
those skilled in the art that various modifications and variations
can be made in the present invention without departing from the
scope or spirit of the invention. For instance, features
illustrated or described as part of one embodiment, can be used on
another embodiment to yield a still further embodiment. Thus, it is
intended that the present invention cover such modifications and
variations.
[0019] In general, the present disclosure is directed to a
polyoxymethylene based system with improved tribological properties
such as a reduced coefficient of friction. The tribological
properties of the polyoxymethylene based system can be improved by
utilizing tribological modifiers.
[0020] The polyoxymethylene based system may comprise a
two-component system. In general, a two-component system is
comprised of a first polymer layer and a second polymer layer
wherein the second polymer layer may be connected to the first
polymer layer. The first polymer layer is comprised of a
polyoxymethylene polymer composition comprising a polyoxymethylene
polymer and optionally, at least one tribological modifier. The
second polymer layer is comprised of a second polymer composition
comprising a liquid crystalline polymer, a polyarylene sulfide
polymer, or a combination thereof. The second polymer composition
may further comprise at least one tribological modifier, a
reinforcing fiber, or a combination thereof.
[0021] The present inventors have discovered that by utilizing the
polyoxymethylene based system of the present invention, improved
sliding properties and a reduced coefficient of friction against
other surfaces can be obtained. In particular, the system can
exhibit a reduced coefficient of friction against other surfaces,
such as a polyethylene terephthalate surface, while still
exhibiting desirable mechanical properties. In addition, these
systems also generate little frictional noise and experience low
wear.
[0022] Polyoxymethylene Polymer
[0023] According to the present disclosure, the polyoxymethylene
polymer composition of the two-component system is comprised of a
polyoxymethylene polymer.
[0024] The preparation of the polyoxymethylene polymer can be
carried out by polymerization of polyoxymethylene-forming monomers,
such as trioxane or a mixture of trioxane and a cyclic acetal such
as dioxolane in the presence of ethylene glycol as a molecular
weight regulator. The polyoxymethylene polymer used in the polymer
composition may comprise a homopolymer or a copolymer. 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 97 mol. % of
--CH.sub.2O-repeat units.
[0025] In one embodiment, a polyoxymethylene copolymer is used. The
copolymer can contain from about 0.1 mol. % to about 20 mol. % and
in particular from about 0.5 mol. % to about 10 mol. % of repeat
units that comprise a saturated or ethylenically unsaturated
alkylene group having at least 2 carbon atoms, or a cycloalkylene
group, which has sulfur atoms or oxygen atoms in the chain and may
include one or more substituents selected from the group consisting
of alkyl cycloalkyl, aryl, aralkyl, heteroaryl, halogen or alkoxy.
In one embodiment, a cyclic ether or acetal is used that can be
introduced into the copolymer via a ring-opening reaction.
[0026] Preferred cyclic ethers or acetals are those of the
formula:
##STR00001##
in which x is 0 or 1 and R.sup.2 is a C.sub.2-C.sub.4-alkylene
group which, if appropriate, has one or more substituents which are
C.sub.1-C.sub.4-akyl groups, or are C.sub.1-C.sub.4-alkoxy groups,
and/or are halogen atoms, preferably chlorine atoms. Merely by way
of example, mention may be made of ethylene oxide, propylene
1,2-oxide, butylene 1,2-oxide, butylene 1,3-oxide, 1,3-dioxane,
1,3-dioxolane, and 1,3-dioxepan as cyclic ethers, and also of
linear oligo- or polyformals, such as polydioxolane or
polydioxepan, as comonomers.
[0027] It is particularly advantageous to use copolymers composed
of from 99.5 to 95 mol. % of trioxane and of from 0.5 to 5 mol. %
of one of the above-mentioned comonomers.
[0028] 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.
[0029] 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 wt.
%.
[0030] A heteropoly acid refers to polyacids formed by the
condensation of different kinds of oxo acids through dehydration
and contains a mono- or poly-nuclear 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[MmM'nOz].sub.yH.sub.2O
wherein
[0031] 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,
[0032] M' represents an element selected from the group consisting
of W, Mo, V or Nb,
[0033] m is 1 to 10,
[0034] n is 6 to 40,
[0035] z is 10 to 100,
[0036] x is an integer of 1 or above, and
[0037] y is 0 to 50.
[0038] 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.
[0039] 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. 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.
[0040] 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.).
[0041] 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 fulfills the safety aspects and environmental aspects
and, moreover, is inert under the conditions for the manufacturing
of oxymethylene polymers.
[0042] 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)n-(COOR')
wherein
[0043] n is an integer from 2 to 12, preferably 3 to 6 and
[0044] 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.
[0045] In one embodiment, the polybasic carboxylic acid comprises
the dimethyl or diethyl ester of the above-mentioned formula, such
as a dimethyl adipate (DMA).
[0046] The alkyl ester of the polybasic carboxylic acid may also be
represented by the following formula:
(ROOC).sub.2--CH--(CH.sub.2)m-CH--(COOR').sub.2
wherein
[0047] m is an integer from 0 to 10, preferably from 2 to 4 and
[0048] 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.
[0049] 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.
[0050] 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.
[0051] Preferably, the heteropoly acid is dissolved in the alkyl
ester of the polybasic carboxylic acid in an amount lower than 5
wt. %, preferably in an amount ranging from 0.01 to 5 wt. %,
wherein the weight is based on the entire solution.
[0052] 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 at least 80%,
such as at least 90%, oxymethylene units.
[0053] The polyoxymethylene polymer can have any suitable molecular
weight. The molecular weight of the polymer, for instance, can be
from about 4,000 grams per mole to about 20,000 g/mol. In other
embodiments, however, the molecular weight can be well above 20,000
g/mol, such as from about 20,000 g/mol to about 100,000 g/mol.
[0054] The polyoxymethylene polymer present in the composition can
generally melt flow index (MFI) ranging from about 1 to about 50
g/10 min, as determined according to ISO 1133 at 190.degree. C. and
2.16 kg, though polyoxymethylenes having a higher or lower melt
flow index are also encompassed herein. For example, the
polyoxymethylene polymer may be a low or mid-molecular weight
polyoxymethylene that has a melt flow index of greater than about 5
g/10 min, greater than about 10 g/10 min, or greater than about 15
g/10 min. The melt flow index of the polyoxymethylene polymer can
be less than about 25 g/10 min, less than about 20 g/10 min, less
than about 18 g/10 min, less than about 15 g/10 min, less than
about 13 g/10 min, or less than about 12 g/10 min. The
polyoxymethylene polymer may for instance be a high molecular
weight polyoxymethylene that has a melt flow index of less than
about 5 g/10 min, less than about 3 g/10 min, or less than about 2
g/10 min.
[0055] The polyoxymethylene polymer may contain a relatively high
amount of functional 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. It should be understood
that the total number of terminal groups present includes all side
terminal groups. In addition to the terminal hydroxyl groups, the
polyoxymethylene polymer may also have other terminal groups usual
for these polymers such as alkoxy groups, formate groups, acetate
groups or hemiacetal groups.
[0056] The polyoxymethylene polymer may also optionally 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 this
regard, the polyoxymethylene polymer can contain low molecular
weight constituents in an amount less than about 10 wt. %, 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 wt. %,
such as in an amount less than about 3 wt. %, such as even in an
amount less than about 2 wt. %.
[0057] The polyoxymethylene polymer may be present in the
polyoxymethylene polymer composition in an amount of at least 60
wt. %, such as at least 70 wt. %, such as at least 80 wt. %, such
as at least 90 wt. %, such as at least 95 wt. %. In general, the
polyoxymethylene polymer is present in an amount of less than about
100 wt. %, such as less than about 99 wt. %, such as less than
about 97 wt. %, wherein the weight is based on the total weight of
the polyoxymethylene polymer composition.
[0058] Liquid Crystalline Polymer
[0059] According to the present disclosure, the second polymer
composition of the two-component system may comprise a liquid
crystalline polymer.
[0060] Suitable thermotropic liquid crystalline polymers may
include aromatic polyesters, aromatic poly(esteramides), aromatic
poly(estercarbonates), aromatic polyamides, etc., and may likewise
contain repeating units formed from one or more aromatic
hydroxycarboxylic acids, aromatic dicarboxylic acids, aromatic
diols, aromatic aminocarboxylic acids, aromatic amines, aromatic
diamines, etc., as well as combinations thereof.
[0061] Liquid crystalline polymers are generally classified as
"thermotropic" to the extent that they can possess a rod-like
structure and exhibit a crystalline behavior in its molten state
(e.g., thermotropic nematic state). Such polymers may be formed
from one or more types of repeating units as is known in the art.
The liquid crystalline polymer may, for example, contain one or
more aromatic ester repeating units, typically in an amount of from
about 60 mol. % to about 99.9 mol. %, in some embodiments from
about 70 mol. % to about 99.5 mol. %, and in some embodiments, from
about 80 mol. % to about 99 mol. % of the polymer. The aromatic
ester repeating units may be generally represented by the following
Formula (I):
##STR00002##
wherein,
[0062] ring B is a substituted or unsubstituted 6-membered aryl
group (e.g., 1,4-phenylene or 1,3-phenylene), a substituted or
unsubstituted 6-membered aryl group fused to a substituted or
unsubstituted 5- or 6-membered aryl group (e.g., 2,6-naphthalene),
or a substituted or unsubstituted 6-membered aryl group linked to a
substituted or unsubstituted 5- or 6-membered aryl group (e.g.,
4,4-biphenylene); and
[0063] Y.sub.1 and Y.sub.2 are independently O, C(O), NH, C(O)HN,
or NHC(O).
[0064] Typically, at least one of Y.sub.1 and Y.sub.2 are C(O).
Examples of such aromatic ester repeating units may include, for
instance, aromatic dicarboxylic repeating units (Y.sub.1 and
Y.sub.2 in Formula I are C(O)), aromatic hydroxycarboxylic
repeating units (Y.sub.1 is O and Y.sub.2 is C(O) in Formula I), as
well as various combinations thereof.
[0065] Aromatic dicarboxylic repeating units, for instance, may be
employed that are derived from aromatic dicarboxylic acids, such as
terephthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic
acid, diphenyl ether-4,4'-dicarboxylic acid,
1,6-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid,
4,4'-dicarboxybiphenyl, bis(4-carboxyphenyl)ether,
bis(4-carboxyphenyl)butane, bis(4-carboxyphenyl)ethane,
bis(3-carboxyphenyl)ether, bis(3-carboxyphenyl)ethane, etc., as
well as alkyl, alkoxy, aryl and halogen substituents thereof, and
combinations thereof. Particularly suitable aromatic dicarboxylic
acids may include, for instance, terephthalic acid ("TA"),
isophthalic acid ("IA"), and 2,6-naphthalenedicarboxylic acid
("NDA"). When employed, repeating units derived from aromatic
dicarboxylic acids (e.g., IA, TA, and/or NDA) typically constitute
from about 5 mol. % to about 60 mol. %, in some embodiments from
about 10 mol. % to about 55 mol. %, and in some embodiments, from
about 15 mol. % to about 50 mol. % of the polymer.
[0066] Aromatic hydroxycarboxylic repeating units may also be
employed that are derived from aromatic hydroxycarboxylic acids,
such as, 4-hydroxybenzoic acid; 4-hydroxy-4'-biphenylcarboxylic
acid; 2-hydroxy-6-naphthoic acid; 2-hydroxy-5-naphthoic acid;
3-hydroxy-2-naphthoic acid; 2-hydroxy-3-naphthoic acid;
4'-hydroxyphenyl-4-benzoic acid; 3'-hydroxyphenyl-4-benzoic acid;
4'-hydroxyphenyl-3-benzoic acid, etc., as well as alkyl, alkoxy,
aryl and halogen substituents thereof, and combination thereof.
Particularly suitable aromatic hydroxycarboxylic acids are
4-hydroxybenzoic acid ("HBA") and 6-hydroxy-2-naphthoic acid
("HNA"). When employed, repeating units derived from
hydroxycarboxylic acids (e.g., HBA and/or HNA) typically constitute
from about 10 mol. % to about 85 mol. %, in some embodiments from
about 20 mol. % to about 80 mol. %, and in some embodiments, from
about 25 mol. % to about 75 mol. % of the polymer.
[0067] Other repeating units may also be employed in the polymer.
In certain embodiments, for instance, repeating units may be
employed that are derived from aromatic diols, such as
hydroquinone, resorcinol, 2,6-dihydroxynaphthalene,
2,7-dihydroxynaphthalene, 1,6-dihydroxynaphthalene,
4,4'-dihydroxybiphenyl (or 4,4'-biphenol), 3,3'-dihydroxybiphenyl,
3,4'-dihydroxybiphenyl, 4,4'-dihydroxybiphenyl ether,
bis(4-hydroxyphenyl)ethane, etc., as well as alkyl, alkoxy, aryl
and halogen substituents thereof, and combinations thereof.
Particularly suitable aromatic diols may include, for instance,
hydroquinone ("HQ") and 4,4'-biphenol ("BP"). When employed,
repeating units derived from aromatic diols (e.g., HQ and/or BP)
typically constitute from about 1 mol. % to about 30 mol. %, in
some embodiments from about 2 mol. % to about 25 mol. %, and in
some embodiments, from about 5 mol. % to about 20% of the polymer.
Repeating units may also be employed, such as those derived from
aromatic amides (e.g., acetaminophen ("APAP")) and/or aromatic
amines (e.g., 4-aminophenol ("AP"), 3-aminophenol,
1,4-phenylenediamine, 1,3-phenylenediamine, etc.). When employed,
repeating units derived from aromatic amides (e.g., APAP) and/or
aromatic amines (e.g., AP) typically constitute from about 0.1 mol.
% to about 20 mol. %, in some embodiments from about 0.5 mol. % to
about 15 mol. %, and in some embodiments, from about 1 mol. % to
about 10 mol. % of the polymer. It should also be understood that
various other monomeric repeating units may be incorporated into
the polymer. For instance, in certain embodiments, the polymer may
contain one or more repeating units derived from non-aromatic
monomers, such as aliphatic or cycloaliphatic hydroxycarboxylic
acids, dicarboxylic acids, diols, amides, amines, etc. Of course,
in other embodiments, the polymer may be "wholly aromatic" in that
it lacks repeating units derived from non-aromatic (e.g., aliphatic
or cycloaliphatic) monomers.
[0068] Although not necessarily required, the liquid crystalline
polymer may be a "low naphthenic" polymer to the extent that it
contains a minimal content of repeating units derived from
naphthenic hydroxycarboxylic acids and naphthenic dicarboxylic
acids, such as naphthalene-2,6-dicarboxylic acid ("NDA"),
6-hydroxy-2-naphthoic acid ("HNA"), or combinations thereof. That
is, the total amount of repeating units derived from naphthenic
hydroxycarboxylic and/or dicarboxylic acids (e.g., NDA, HNA, or a
combination of HNA and NDA) may typically be no more than 30 mol.
%, in some embodiments no more than about 15 mol. %, in some
embodiments no more than about 10 mol. %, in some embodiments no
more than about 8 mol. %, and in some embodiments, from 0 mol. % to
about 5 mol. % of the polymer (e.g., 0 mol. %). Despite the absence
of a high level of conventional naphthenic acids, it is believed
that the resulting "low naphthenic" polymers are still capable of
exhibiting good thermal and mechanical properties.
[0069] In one particular embodiment, the liquid crystalline polymer
may be formed from repeating units derived from 4-hydroxybenzoic
acid ("HBA") and terephthalic acid ("TA") and/or isophthalic acid
("IA"), as well as various other optional constituents. The
repeating units derived from 4-hydroxybenzoic acid ("HBA") may
constitute from about 10 mol. % to about 80 mol. %, in some
embodiments from about 30 mol. % to about 75 mol. %, and in some
embodiments, from about 45 mol. % to about 70 mol. % of the
polymer. The repeating units derived from terephthalic acid ("TA")
and/or isophthalic acid ("IA") may likewise constitute from about 5
mol. % to about 40 mol. %, in some embodiments from about 10 mol. %
to about 35 mol. %, and in some embodiments, from about 15 mol. %
to about 35 mol. % of the polymer. Repeating units may also be
employed that are derived from 4,4'-biphenol ("BP") and/or
hydroquinone ("HQ") in an amount from about 1 mol. % to about 30
mol. %, in some embodiments from about 2 mol. % to about 25 mol. %,
and in some embodiments, from about 5 mol. % to about 20 mol. % of
the polymer. Other possible repeating units may include those
derived from 6-hydroxy-2-naphthoic acid ("HNA"),
2,6-naphthalenedicarboxylic acid ("NDA"), and/or acetaminophen
("APAP"). In certain embodiments, for example, repeating units
derived from HNA, NDA, and/or APAP may each constitute from about 1
mol. % to about 35 mol. %, in some embodiments from about 2 mol. %
to about 30 mol. %, and in some embodiments, from about 3 mol. % to
about 25 mol. % when employed.
[0070] Regardless of the particular constituents and nature of the
polymer, the liquid crystalline polymer may be prepared by
initially introducing the aromatic monomer(s) used to form ester
repeating units (e.g., aromatic hydroxycarboxylic acid, aromatic
dicarboxylic acid, etc.) and/or other repeating units (e.g.,
aromatic diol, aromatic amide, aromatic amine, etc.) into a reactor
vessel to initiate a polycondensation reaction. The particular
conditions and steps employed in such reactions are well known, and
may be described in more detail in U.S. Pat. No. 4,161,470 to
Calundann; U.S. Pat. No. 5,616,680 to Linstid, III, et al.; U.S.
Pat. No. 6,114,492 to Linstid, III, et al.; U.S. Pat. No. 6,514,611
to Shepherd, et al.; and WO 2004/058851 to Waggoner. The vessel
employed for the reaction is not especially limited, although it is
typically desired to employ one that is commonly used in reactions
of high viscosity fluids. Examples of such a reaction vessel may
include a stirring tank-type apparatus that has an agitator with a
variably-shaped stirring blade, such as an anchor type, multistage
type, spiral-ribbon type, screw shaft type, etc., or a modified
shape thereof. Further examples of such a reaction vessel may
include a mixing apparatus commonly used in resin kneading, such as
a kneader, a roll mill, a Banbury mixer, etc.
[0071] If desired, the reaction may proceed through the acetylation
of the monomers as known the art. This may be accomplished by
adding an acetylating agent (e.g., acetic anhydride) to the
monomers. Acetylation is generally initiated at temperatures of
about 90.degree. C. During the initial stage of the acetylation,
reflux may be employed to maintain vapor phase temperature below
the point at which acetic acid byproduct and anhydride begin to
distill. Temperatures during acetylation typically range from
between 90.degree. C. to 150.degree. C., and in some embodiments,
from about 110.degree. C. to about 150.degree. C. If reflux is
used, the vapor phase temperature typically exceeds the boiling
point of acetic acid, but remains low enough to retain residual
acetic anhydride. For example, acetic anhydride vaporizes at
temperatures of about 140.degree. C. Thus, providing the reactor
with a vapor phase reflux at a temperature of from about
110.degree. C. to about 130.degree. C. is particularly desirable.
To ensure substantially complete reaction, an excess amount of
acetic anhydride may be employed. The amount of excess anhydride
will vary depending upon the particular acetylation conditions
employed, including the presence or absence of reflux. The use of
an excess of from about 1 to about 10 mole percent of acetic
anhydride, based on the total moles of reactant hydroxyl groups
present is not uncommon.
[0072] Acetylation may occur in a separate reactor vessel, or it
may occur in situ within the polymerization reactor vessel. When
separate reactor vessels are employed, one or more of the monomers
may be introduced to the acetylation reactor and subsequently
transferred to the polymerization reactor. Likewise, one or more of
the monomers may also be directly introduced to the reactor vessel
without undergoing pre-acetylation.
[0073] In addition to the monomers and optional acetylating agents,
other components may also be included within the reaction mixture
to help facilitate polymerization. For instance, a catalyst may be
optionally employed, such as metal salt catalysts (e.g., magnesium
acetate, tin(I) acetate, tetrabutyl titanate, lead acetate, sodium
acetate, potassium acetate, etc.) and organic compound catalysts
(e.g., N-methylimidazole). Such catalysts are typically used in
amounts of from about 50 to about 500 parts per million based on
the total weight of the recurring unit precursors. When separate
reactors are employed, it is typically desired to apply the
catalyst to the acetylation reactor rather than the polymerization
reactor, although this is by no means a requirement.
[0074] The reaction mixture is generally heated to an elevated
temperature within the polymerization reactor vessel to initiate
melt polycondensation of the reactants. Polycondensation may occur,
for instance, within a temperature range of from about 250.degree.
C. to about 400.degree. C., in some embodiments from about
280.degree. C. to about 395.degree. C., and in some embodiments,
from about 300.degree. C. to about 380.degree. C. For instance, one
suitable technique for forming the liquid crystalline polymer may
include charging precursor monomers and acetic anhydride into the
reactor, heating the mixture to a temperature of from about
90.degree. C. to about 150.degree. C. to acetylize a hydroxyl group
of the monomers (e.g., forming acetoxy), and then increasing the
temperature to from about 250.degree. C. to about 400.degree. C. to
carry out melt polycondensation. As the final polymerization
temperatures are approached, volatile byproducts of the reaction
(e.g., acetic acid) may also be removed so that the desired
molecular weight may be readily achieved. The reaction mixture is
generally subjected to agitation during polymerization to ensure
good heat and mass transfer, and in turn, good material
homogeneity. The rotational velocity of the agitator may vary
during the course of the reaction, but typically ranges from about
10 to about 100 revolutions per minute ("rpm"), and in some
embodiments, from about 20 to about 80 rpm. To build molecular
weight in the melt, the polymerization reaction may also be
conducted under vacuum, the application of which facilitates the
removal of volatiles formed during the final stages of
polycondensation. The vacuum may be created by the application of a
suctional pressure, such as within the range of from about 5 to
about 30 pounds per square inch ("psi"), and in some embodiments,
from about 10 to about 20 psi.
[0075] Following melt polymerization, the molten polymer may be
discharged from the reactor, typically through an extrusion orifice
fitted with a die of desired configuration, cooled, and collected.
Commonly, the melt is discharged through a perforated die to form
strands that are taken up in a water bath, pelletized and dried. In
some embodiments, the melt polymerized polymer may also be
subjected to a subsequent solid-state polymerization method to
further increase its molecular weight. Solid-state polymerization
may be conducted in the presence of a gas (e.g., air, inert gas,
etc.). Suitable inert gases may include, for instance, include
nitrogen, helium, argon, neon, krypton, xenon, etc., as well as
combinations thereof. The solid-state polymerization reactor vessel
can be of virtually any design that will allow the polymer to be
maintained at the desired solid-state polymerization temperature
for the desired residence time. Examples of such vessels can be
those that have a fixed bed, static bed, moving bed, fluidized bed,
etc. The temperature at which solid-state polymerization is
performed may vary, but is typically within a range of from about
250.degree. C. to about 350.degree. C. The polymerization time will
of course vary based on the temperature and target molecular
weight. In most cases, however, the solid-state polymerization time
will be from about 2 to about 12 hours, and in some embodiments,
from about 4 to about 10 hours.
[0076] The liquid crystalline polymer may be present in the second
polymer composition in an amount of at least 40 wt. %, such as at
least 50 wt. %, such as at least 60 wt. %, such as at least 70 wt.
%, such as at least 80 wt. %, such as at least 90 wt. %. In
general, the liquid crystalline polymer is present in an amount of
less than about 100 wt. %, such as less than about 90 wt. %, such
as less than about 80 wt. %, such as less than about 70 wt. %, such
as less than about 60 wt. %, wherein the weight is based on the
total weight of the second polymer composition.
[0077] Polyarylene Sulfide
[0078] According to the present disclosure, the second polymer
composition of the two-component system may comprise a polyarylene
sulfide polymer.
[0079] Polyarylene sulfide polymers are generally able to withstand
relatively high temperatures without melting. Polyarylene sulfide
polymers generally have repeating units of the formula:
--[(Ar.sup.1).sub.n--X].sub.m--[(Ar.sup.2).sub.i--Y].sub.j--[(Ar.sup.3).-
sub.k--Z].sub.l--[(Ar.sup.4).sub.o--W].sub.p--
wherein,
[0080] Ar.sup.1, Ar.sup.2, Ar.sup.3, and Ar.sup.4 are independently
arylene units of 6 to 18 carbon atoms;
[0081] W, X, Y, and Z are independently bivalent linking groups
selected from
[0082] --SO.sub.2--, --S--, --SO--, --CO--, --O--, --C(O)O-- or
alkylene or alkylidene groups of 1 to 6 carbon atoms, wherein at
least one of the linking groups is --S--; and
[0083] n, m, i, j, k, l, o, and p are independently 0, 1, 2, 3, or
4, subject to the proviso that their sum total is not less than
2.
[0084] The arylene units Ar.sup.1, Ar.sup.2, Ar.sup.3, and Ar.sup.4
may be selectively substituted or unsubstituted. Advantageous
arylene units are phenylene, biphenylene, naphthylene, anthracene
and phenanthrene. The polyarylene sulfide typically includes more
than about 30 mol. %, more than about 50 mol. %, or more than about
70 mol. % arylene sulfide (--S--) units. For example, the
polyarylene sulfide may include at least 85 mol. % sulfide linkages
attached directly to two aromatic rings. In one particular
embodiment, the polyarylene sulfide is a polyphenylene sulfide,
defined herein as containing the phenylene sulfide structure
--(C.sub.6H.sub.4--S).sub.n-- (wherein n is an integer of 1 or
more) as a component thereof.
[0085] Synthesis techniques that may be used in making a
polyarylene sulfide are generally known in the art. By way of
example, a process for producing a polyarylene sulfide can include
reacting a material that provides a hydrosulfide ion (e.g., an
alkali metal sulfide) with a dihaloaromatic compound in an organic
amide solvent. The alkali metal sulfide can be, for example,
lithium sulfide, sodium sulfide, potassium sulfide, rubidium
sulfide, cesium sulfide or a mixture thereof. When the alkali metal
sulfide is a hydrate or an aqueous mixture, the alkali metal
sulfide can be processed according to a dehydrating operation in
advance of the polymerization reaction. An alkali metal sulfide can
also be generated in situ. In addition, a small amount of an alkali
metal hydroxide can be included in the reaction to remove or react
impurities (e.g., to change such impurities to harmless materials)
such as an alkali metal polysulfide or an alkali metal thiosulfate,
which may be present in a very small amount with the alkali metal
sulfide.
[0086] The dihaloaromatic compound can be, without limitation, an
o-dihalobenzene, m-dihalobenzene, p-dihalobenzene, dihalotoluene,
dihalonaphthalene, methoxy-dihalobenzene, dihalobiphenyl,
dihalobenzoic acid, dihalodiphenyl ether, dihalodiphenyl sulfone,
dihalodiphenyl sulfoxide or dihalodiphenyl ketone. Dihaloaromatic
compounds may be used either singly or in any combination thereof.
Specific exemplary dihaloaromatic compounds can include, without
limitation, p-dichlorobenzene; m-dichlorobenzene;
o-dichlorobenzene; 2,5-dichlorotoluene; 1,4-dibromobenzene;
1,4-dichloronaphthalene; 1-methoxy-2,5-dichlorobenzene;
4,4'-dichlorobiphenyl; 3,5-dichlorobenzoic acid;
4,4'-dichlorodiphenyl ether; 4,4'-dichlorodiphenylsulfone;
4,4'-dichlorodiphenylsulfoxide; and 4,4'-dichlorodiphenyl ketone.
The halogen atom can be fluorine, chlorine, bromine or iodine, and
two halogen atoms in the same dihalo-aromatic compound may be the
same or different from each other. In one embodiment,
o-dichlorobenzene, m-dichlorobenzene, p-dichlorobenzene or a
mixture of two or more compounds thereof is used as the
dihalo-aromatic compound. As is known in the art, it is also
possible to use a monohalo compound (not necessarily an aromatic
compound) in combination with the dihaloaromatic compound in order
to form end groups of the polyarylene sulfide or to regulate the
polymerization reaction and/or the molecular weight of the
polyarylene sulfide.
[0087] The polyarylene sulfide(s) may be homopolymers or
copolymers. For instance, selective combination of dihaloaromatic
compounds can result in a polyarylene sulfide copolymer containing
not less than two different units. For instance, when
p-dichlorobenzene is used in combination with m-dichlorobenzene or
4,4'-dichlorodiphenylsulfone, a polyarylene sulfide copolymer can
be formed containing segments having the structure of formula:
##STR00003##
and segments having the structure of formula:
##STR00004##
or segments having the structure of formula:
##STR00005##
[0088] In another embodiment, a polyarylene sulfide copolymer may
be formed that includes a first segment with a number-average molar
mass Mn of from 1000 to 20,000 g/mol. The first segment may include
first units that have been derived from structures of the
formula:
##STR00006##
where the radicals R.sup.1 and R.sup.2, independently of one
another, are a hydrogen, fluorine, chlorine or bromine atom or a
branched or unbranched alkyl or alkoxy radical having from 1 to 6
carbon atoms; and/or second units that are derived from structures
of the formula:
##STR00007##
[0089] The first unit may be p-hydroxybenzoic acid or one of its
derivatives, and the second unit may be composed of
2-hydroxynaphthalene-6-carboxylic acid. The second segment may be
derived from a polyarylene sulfide structure of the formula:
--[Ar--S].sub.q--
[0090] where Ar is an aromatic radical, or more than one condensed
aromatic radical, and q is a number from 2 to 100, in particular
from 5 to 20. The radical Ar may be a phenylene or naphthylene
radical. In one embodiment, the second segment may be derived from
poly(m-thiophenylene), from poly(o-thiophenylene), or from
poly(p-thiophenylene).
[0091] The polyarylene sulfide(s) may be linear, semi-linear,
branched or crosslinked. Linear polyarylene sulfides typically
contain 80 mol. % or more of the repeating unit --(Ar--S)--. Such
linear polymers may also include a small amount of a branching unit
or a cross-linking unit, but the amount of branching or
cross-linking units is typically less than about 1 mol. % of the
total monomer units of the polyarylene sulfide. A linear
polyarylene sulfide polymer may be a random copolymer or a block
copolymer containing the above-mentioned repeating unit.
Semi-linear polyarylene sulfides may likewise have a cross-linking
structure or a branched structure introduced into the polymer a
small amount of one or more monomers having three or more reactive
functional groups. By way of example, monomer components used in
forming a semi-linear polyarylene sulfide can include an amount of
polyhaloaromatic compounds having two or more halogen substituents
per molecule which can be utilized in preparing branched polymers.
Such monomers can be represented by the formula R'X.sub.n, where
each X is selected from chlorine, bromine, and iodine, n is an
integer of 3 to 6, and R' is a polyvalent aromatic radical of
valence n which can have up to about 4 methyl substituents, the
total number of carbon atoms in R' being within the range of 6 to
about 16. Examples of some polyhaloaromatic compounds having more
than two halogens substituted per molecule that can be employed in
forming a semi-linear polyarylene sulfide include
1,2,3-trichlorobenzene, 1,2,4-trichlorobenzene,
1,3-dichloro-5-bromobenzene, 1,2,4-triiodobenzene,
1,2,3,5-tetrabromobenzene, hexachlorobenzene,
1,3,5-trichloro-2,4,6-trimethylbenzene,
2,2',4,4'-tetrachlorobiphenyl, 2,2',5,5'-tetra-iodobiphenyl,
2,2',6,6'-tetrabromo-3,3',5,5'-tetramethylbiphenyl,
1,2,3,4-tetrachloronaphthalene, 1,2,4-tribromo-6-methylnaphthalene,
etc., and mixtures thereof.
[0092] Regardless of the particular structure, the number average
molecular weight of the polyarylene sulfide is typically about
15,000 g/mol or more, and in some embodiments, about 30,000 g/mol
or more. In certain cases, a small amount of chlorine may be
employed during formation of the polyarylene sulfide. Nevertheless,
the polyarylene sulfide will still have a low chlorine content,
such as about 1000 ppm or less, in some embodiments about 900 ppm
or less, in some embodiments from about 1 to about 800 ppm, and in
some embodiments, from about 2 to about 700 ppm. In certain
embodiments, however, the polyarylene sulfide is generally free of
chlorine or other halogens.
[0093] The polyarylene sulfide polymer may be present in the second
polymer composition in an amount of at least 40 wt. %, such as at
least 50 wt. %, such as at least 60 wt. %, such as at least 70 wt.
%, such as at least 80 wt. %, such as at least 90 wt. %. In
general, the polyarylene sulfide polymer is present in an amount of
less than about 100 wt. %, such as less than about 90 wt. %, such
as less than about 80 wt. %, such as less than about 70 wt. %, such
as less than about 60 wt. %, wherein the weight is based on the
total weight of the second polymer composition.
[0094] Tribological Modifiers
[0095] According to the present disclosure, the polyoxymethylene
polymer composition of the two-component system may further
comprise at least one tribological modifier. Additionally,
according to the present disclosure, the second polymer composition
of the two-component system may further comprise at least one
tribological modifier.
[0096] According to the present disclosure, the polyoxymethylene
polymer composition of the two-component system may comprise boron
nitride, ultra-high molecular weight silicone, or a combination
thereof.
[0097] In one embodiment, boron nitride may be used to modify the
polyoxymethylene polymer. Boron nitride can be particularly
beneficial in improving the tribological properties and reducing
the coefficient of friction of polyoxymethylene. Boron nitride
exists in a variety of different crystalline forms (e.g.,
h-BN--hexagonal, c-BN--cubic or spharlerite, and w-BN--wurtzite).
In one embodiment, hexagonal boron nitride may be used in the
composition. Not to be limited by theory, the h-BN may promote
lubricity due to its layered structure and weak secondary forces
between adjacent layers allowing or easy sliding of the layers. The
boron nitride may have an average particle size ranging from about
0.5 .mu.m to about 10 .mu.m, such as from about 1 .mu.m to about 6
.mu.m, such as about 1.5 .mu.m or 5 .mu.m. The boron nitride may be
present in the polyoxymethylene polymer composition in an amount of
at least about 0.1 wt. %, such as at least about 0.5 wt. %, such as
at least about 0.75 wt. %, such as at least about 1 wt. %, such as
at least about 2 wt. % and generally less than about 10 wt. %, such
as less than about 5 wt. %, such as less than about 2.5 wt. %, such
as less than about 2 wt. %, wherein the weight is based on the
total weight of the polyoxymethylene polymer composition. In one
embodiment, the composition may be substantially free of the boron
nitride such that it is present in an amount of 0 wt. %.
[0098] In another embodiment, ultra-high molecular weight silicone
(UHMW-Si) may be used to modify the polyoxymethylene polymer. In
general, the UHMW-Si can have an average molecular weight of
greater than 100,000 g/mol, such as greater than about 200,000
g/mol, such as greater than about 300,000 g/mol, such as greater
than about 500,000 g/mol and less than about 3,000,000 g/mol, such
as less than about 2,000,000 g/mol, such as less than about
1,000,000 g/mol, such as less than about 500,000 g/mol, such as
less than about 300,000 g/mol. Generally, the UHMW-Si can have a
kinematic viscosity at 40.degree. C. measured according to DIN
51562 of greater than 100,000 mm.sup.2s.sup.-1, such as greater
than about 200,000 mm.sup.2s.sup.-1, such as greater than about
1,000,000 mm.sup.2s.sup.-1, such as greater than about 5,000,000
mm.sup.2s.sup.-1, such as greater than about 10,000,000
mm.sup.2s.sup.-1, such as greater than about 15,000,000
mm.sup.2s.sup.-1 and less than about 50,000,000 mm.sup.2s.sup.-1,
such as less than about 25,000,000 mm.sup.2s.sup.-1, such as less
than about 10,000,000 mm.sup.2s.sup.-1, such as less than about
1,000,000 mm.sup.2s.sup.-1, such as less than about 500,000
mm.sup.2s.sup.-1, such as less than about 200,000
mm.sup.2s.sup.-1.
[0099] The UHMW-Si may comprise a siloxane such as a polysiloxane
or polyorganosiloxane. In one embodiment, the UHMW-Si may comprise
a dialkylpolysiloxane such as a dimethylsiloxane, an
alkylarylsiloxane such as a phenylmethylsilaoxane, or a
diarylsiloxane such as a diphenylsiloxane, or a homopolymer thereof
such as a polydimethylsiloxane or a polymethylphenylsiloxane, or a
copolymer thereof with the above molecular weight and/or kinematic
viscosity requirements. The polysiloxane or polyorganosiloxane may
also be modified with a substituent such as an epoxy group, a
hydroxyl group, a carboxyl group, an amino group or a substituted
amino group, an ether group, or a meth(acryloyl) group in the end
or main chain of the molecule. The UHMW-Si compounds may be used
singly or in combination. Any of the above UHMW-Si compounds may be
used with the above molecular weight and/or kinematic viscosity
requirements.
[0100] The UHMW-Si may be added to the polyoxymethylene polymer
composition as a masterbatch wherein the UHMW-Si is dispersed in a
polyoxymethylene polymer and the masterbatch is thereafter added to
another polyoxymethylene polymer. The masterbatch may comprise from
about 10 wt. % to about 50 wt. %, such as from about 25 wt. % to
about 50 wt. %, such as from about 35 wt. % to about 45 wt. % of an
UHMW-Si.
[0101] The UHMW-Si may be present in the polyoxymethylene polymer
composition in an amount of at least about 0.1 wt. %, such as at
least about 0.5 wt. %, such as at least about 0.75 wt. %, such as
at least about 1 wt. %, such as at least about 2 wt. % and
generally less than about 10 wt. %, such as less than about 6 wt.
%, such as less than about 5 wt. %, such as less than about 4 wt.
%, such as less than about 3.5 wt. %, such as less than about 3 wt.
%, wherein the weight is based on the total weight of the
polyoxymethylene polymer composition. In one embodiment, the
composition may be substantially free of the UHMW-Si such that it
is present in an amount of 0 wt. %.
[0102] According to another embodiment, boron nitride, such as
hexagonal-boron nitride, and UHMW-Si may be utilized in combination
to modify the polyoxymethylene polymer. The present inventors have
discovered that when both tribological modifiers are used
simultaneously, the combination provides a synergistic effect with
a resulting polymer composition that exhibits improved tribological
properties while maintaining or even improving the mechanical
properties. In such embodiment, the boron nitride and UHMW-Si may
be utilized in the polyoxymethylene polymer composition in the
amounts disclosed above.
[0103] According to the present disclosure, the second polymer
composition of the two-component system may comprise a
polytetrafluoroethylene (PTFE). In one embodiment, the PTFE may be
in the form of a powder. In another embodiment, the PTFE may be in
the form of a fiber. The PTFE may be present in an amount of at
least 0.1 wt. %, such as at least 1 wt. %, such as at least 5 wt.
%, such as at least 10 wt. %, such as at least 15 wt. % and
generally less than about 50 wt. %, such as less than about 40 wt.
%, such as less than about 30 wt. %, such as less than about 25 wt.
%, such as less than about 15 wt. %.
[0104] In another embodiment, the polyoxymethylene polymer
composition of the two-component system may also comprise PTFE as
described above. In still another embodiment, the second polymer
composition may also comprise boron nitride, UHMW-Si, or a
combination thereof as described above.
[0105] According to the present disclosure, various other
tribological modifiers may be incorporated into the
polyoxymethylene polymer composition or the second polymer
composition. These tribological modifiers may include, for
instance, calcium carbonate particles, ultrahigh-molecular weight
polyethylene (UHMW-PE) particles, stearyl stearate particles,
silicone oil, a polyethylene wax, an amide wax, wax particles
comprising an aliphatic ester wax comprised of a fatty acid and a
monohydric alcohol, a graft copolymer with an olefin polymer as a
graft base, or a combination thereof. These tribological modifiers
include the following:
[0106] (1) From 0.1-50 wt. %, such as from 1-25 wt. %, of a calcium
carbonate particle such as a calcium carbonate (chalk) powder.
[0107] (2) From 0.1-50 wt. %, such as from 1-25 wt. %, such as from
2.5-20 wt. %, such as from 5 to 15 wt. %, of an ultrahigh-molecular
weight polyethylene (UHMW-PE) powder. UHMW-PE can be employed as a
powder, in particular as a micro-powder. The UHMW-PE generally has
a mean particle diameter D.sub.50 (volume based and determined by
light scattering) in the range of 1 to 5000 .mu.m, preferably from
10 to 500 .mu.m, and particularly preferably from 10 to 150 .mu.m
such as from 30 to 130 .mu.m, such as from 80 to 150 .mu.m, such as
from 30 to 90 .mu.m.
[0108] The UHMW-PE can have an average molecular weight of higher
than 1.010.sup.6 g/mol, such as higher than 2.010.sup.6 g/mol, such
as higher than 4.010.sup.6 g/mol, such as ranging from 1.010.sup.6
g/mol to 15.010.sup.6 g/mol, such as from 3.010.sup.6 g/mol to
12.010.sup.6 g/mol, determined by viscosimetry. Preferably, the
viscosity number of the UHMW-PE is higher than 1000 ml/g, such as
higher than 1500 ml/g, such as ranging from 1800 ml/g to 5000 ml/g,
such as ranging from 2000 ml/g to 4300 ml/g (determined according
to ISO 1628, part 3; concentration in decahydronaphthalin: 0.0002
g/ml).
[0109] (3) From 0.1-10 wt. %, such as from 0.1-5 wt. %, such as
from 0.5-3 wt. %, of stearyl stearate.
[0110] (4) From 0.1-10 wt. %, such as from 0.5-5 wt. %, such as
from 0.8-2 wt. %, of a silicone oil. Alternatively, in one
embodiment, the composition may be substantially free of silicone
oil, such as less than about 0.2 wt. %, such as less than about 0.1
wt. %, such as less than about 0.05 wt. %, such as less than about
0.01 wt. %, such as about 0 wt. %. In another embodiment, the
composition may not comprise a combination of silicone oil and
UHMW-Si alone. In such embodiments, the composition may comprise
UHMW-Si, silicone oil, and another tribological modifier, such as
hexagonal boron nitride or PTFE.
[0111] When silicone oil is present in the composition, the
silicone oil can have an average molecular weight of at least about
5,000 g/mol, such as at least about 20,000 g/mol, such as at least
about 50,000 g/mol and generally less than 100,000 g/mol, such as
less than about 75,000 g/mol, such as less than about 50,000 g/mol.
The silicone oil can have a kinematic viscosity at 40.degree. C.
measured according to DIN 51562 of greater than about 100
mm.sup.2s.sup.-1, such as greater than about 5,000
mm.sup.2s.sup.-1, such as greater than about 15,000
mm.sup.2s.sup.-1 and generally less than 100,000 mm.sup.2s.sup.-1,
such as less than about 50,000 mm.sup.2s.sup.-1, such as less than
about 25,000 mm.sup.2s.sup.-1, such as less than about 15,000
mm.sup.2s.sup.-1. The silicone oil may comprise a liquid
polysiloxane such as a polydimethylsiloxane at a room temperature
of 25.degree. C. with the above molecular weight and/or kinematic
viscosity specifications.
[0112] (5) From 0.1-5 wt. %, such as from 0.5-3 wt. %, of a
polyethylene wax, such as an oxidized polyethylene wax.
[0113] (6) From 0.1-5 wt. %, such as from 0.2-2 wt. %, of an amide
wax.
[0114] (7) From 0.1-5 wt. %, such as from 0.5-3 wt. %, of an
aliphatic ester wax composed of a fatty acid and of a monohydric
alcohol.
[0115] (8) From 0.1-50 wt. %, such as from 1-25 wt. %, such as from
2-10 wt. % by weight of a graft copolymer which has an olefin
polymer as a graft base and, grafted on this, at least one vinyl
polymer or one ether polymer, and/or a graft copolymer which has an
elastomeric core based on polydienes and a hard graft envelope
composed of (meth)acrylates and/or of (meth)acrylonitriles. A
suitable graft base can be any olefin homopolymer (e.g.,
polyethylene or polypropylene) or copolymer or copolymers derived
from copolymerizable ethylenically unsaturated monomers (e.g,
ethylenepropylene copolymers, ethylene-1-butene copolymers,
ethylene/glycidyl (meth)acrylate copolymers). Suitable graft
monomers are any of the ethylenically unsaturated monomers having a
polar group or other graftable monomers having polar groups that
modify the polarity of the essentially non-polar graft base (e.g.
ethylenically unsaturated carboxylic acids such as (meth)acrylic
acid and derivatives thereof in combination with acrylonitrile or
styrene/acrylonitrile, if appropriate). In one embodiment, the
graft copolymer may comprise a polyethylene or polypropylene graft
base grafted with acrylonitrile or with styrene/acrylonitrile.
[0116] In general, the tribological modifiers improve the
tribological properties of the polyoxymethylene polymer composition
and second polymer composition of the polyoxymethylene based system
such as by reducing the coefficient of friction and wear when
contacted with another surface, such as a polyethylene
terephthalate surface. In addition, in some instances, the
tribological modifiers may even improve upon the mechanical
properties of the polyoxymethylene polymer composition and/or the
second polymer composition.
[0117] According to the present disclosure, tribological modifiers
improve the tribological properties of the compositions and the
polyoxymethylene based systems without the need for an external
lubricant, such as water-based or PTFE-based external lubricants,
when utilized in tribological applications. An external lubricant
may be a lubricant that is applied to a polymer article or
polyoxymethylene based system of the present disclosure. In one
embodiment, an external lubricant may not be associated with the
polyoxymethylene based system or polymer article such that the
external lubricant is not present on a surface of the
polyoxymethylene based system or polymer article. In another
embodiment, an external lubricant may be utilized with the
polyoxymethylene based system and polymer article of the present
disclosure.
[0118] Fiber Reinforcements
[0119] According to the present disclosure, the polyoxymethylene
polymer composition of the two-component system may further
comprise at least one reinforcing fiber. Additionally, according to
the present disclosure, the second polymer composition of the
two-component system may further comprise at least one reinforcing
fiber.
[0120] The reinforcing fibers which may be used according to the
present invention include mineral fibers, glass fibers, polymer
fibers such as aramid fibers, metal fibers such as steel fibers,
carbon fibers, or natural fibers. These fibers may be unmodified or
modified, e.g. provided with a sizing or chemically treated, in
order to improve adhesion to the polymer.
[0121] According to one embodiment, the reinforcing fibers comprise
glass fibers. Glass fibers may be provided with a sizing to protect
the glass fiber, to smooth the glass fiber, and to improve the
adhesion between the glass fiber and the polymer matrix material. A
sizing usually comprises silanes, film forming agents, lubricants,
wetting agents, adhesives, optionally antistatic agents and
plasticizers, emulsifiers and optionally further additives.
Specific examples of silanes are aminosilanes. Film forming agents
are, for example, polyvinylacetates, polyesters, and polyurethanes.
Particularly suitable glass fibers are E-glass, A-glass, C-glass,
D-glass, AR-glass, R-glass, S1-glass, S2-glass, etc., and mixtures
thereof. In one embodiment, the glass fibers may be chopped glass
fibers or glass fiber rovings (tows).
[0122] The reinforcing fibers may be compounded into the polymer
matrix, for example in an extruder or kneader. However, the
reinforcing fibers may also advantageously take the form of
continuous-filament fibers sheathed or impregnated with the polymer
composition in a process suitable for this purpose, and then
processed or wound up in the form of a continuous strand, or cut to
a desired pellet length so that the fiber lengths and pellet
lengths are identical. An example of a process particularly
suitable for this purpose is the pultrusion process.
[0123] Fiber diameters can vary depending upon the particular fiber
used and whether the fiber is in either a chopped or a continuous
form. The fibers, for instance, can have a diameter of less than
about 100 .mu.m, such as less than about 50 .mu.m. For instance,
the fibers can be chopped or continuous fibers and can have a fiber
diameter of from about 5 .mu.m to about 100 .mu.m, such as from
about 5 .mu.m to about 50 .mu.m, such as from about 5 .mu.m to
about 15 .mu.m. The fibers may also have a relatively high aspect
ratio (average length divided by nominal diameter) to help improve
the mechanical properties of the resulting polymer composition. For
example, the fibers may have an aspect ratio of from about 2 to
about 50, in some embodiments from about 4 to about 40, and in some
embodiments, from about 5 to about 20.
[0124] When employed in the polymer composition, the reinforcing
fibers may also help improve the strength. However, the relative
amount of the reinforcing fiber in the polymer compositions may
also be selectively controlled to help achieve the desired
mechanical properties without adversely impacting other properties
of the composition, such as its flowability. For example, when
present, the respective composition may contain reinforcing fibers
in an amount of at least 1 wt. %, such as at least 5 wt. %, such as
at least 7 wt. %, such as at least 10 wt. %, such as at least 15
wt. % and generally less than about 50 wt. %, such as less than
about 45 wt. %, such as less than about 40 wt. %, such as less than
about 30 wt. %, such as less than about 20 wt. %, wherein the
weight is based on the total weight of the respective
polyoxymethylene or second polymer composition.
[0125] Other Additives
[0126] The polymer compositions of the present disclosure may also
contain other known additives such as, for example, antioxidants,
formaldehyde scavengers, acid scavengers, UV stabilizers or heat
stabilizers. In addition, the compositions can contain processing
auxiliaries, for example adhesion promoters, lubricants, nucleants,
demolding agents, fillers, or antistatic agents and additives which
impart a desired property to the compositions and articles or parts
produced therefrom.
[0127] In one embodiment, an ultraviolet light stabilizer may be
present. The ultraviolet light stabilizer may comprise a
benzophenone, a benzotriazole, or a benzoate. The UV light
absorber, when present, may be present in the polymer composition
in an amount of at least about 0.01 wt. %, such as at least about
0.05 wt. %, such as at least about 0.075 wt. % and less than about
1 wt. %, such as less than about 0.75 wt. %, such as less than
about 0.5 wt. %, wherein the weight is based on the total weight of
the respective polymer composition.
[0128] In one embodiment, a formaldehyde scavenger, such as a
nitrogen-containing compound, may be present. Mainly, of these are
heterocyclic compounds having at least one nitrogen atom as hetero
atom which is either adjacent to an amino-substituted carbon atom
or to a carbonyl group, for example pyridine, pyrimidine, pyrazine,
pyrrolidone, aminopyridine and compounds derived therefrom. Other
particularly advantageous compounds are triamino-1,3,5-triazine
(melamine) and its derivatives, such as melamine-formaldehyde
condensates and methylol melamine. Oligomeric polyamides are also
suitable in principle for use as formaldehyde scavengers. The
formaldehyde scavenger may be used individually or in
combination.
[0129] Further, the formaldehyde scavenger can be a guanamine
compound which can include an aliphatic guanamine-based compound,
an alicyclic guanamine-based compound, an aromatic guanamine-based
compound, a hetero atom-containing guanamine-based compound, or the
like. The formaldehyde scavenger may be present in the polymer
composition in an amount of at least about 0.01 wt. %, such as at
least about 0.05 wt. %, such as at least about 0.075 wt. % and less
than about 1 wt. %, such as less than about 0.75 wt. %, such as
less than about 0.5 wt. %, wherein the weight is based on the total
weight of the respective polymer composition.
[0130] In one embodiment, an acid scavenger may be present. The
acid scavenger may comprise, for instance, an alkaline earth metal
salt. For instance, the acid scavenger may comprise a calcium salt,
such as a calcium citrate. The acid scavenger may be present in an
amount of at least about 0.001 wt. %, such as at least about 0.005
wt. %, such as at least about 0.0075 wt. % and less than about 1
wt. %, such as less than about 0.75 wt. %, such as less than about
0.5 wt. %, wherein the weight is based on the total weight of the
respective polymer composition.
[0131] In one embodiment, a nucleant may be present. The nucleant
may increase crystallinity and may comprise an oxymethylene
terpolymer. In one particular embodiment, for instance, the
nucleant may comprise a terpolymer of butanediol diglycidyl ether,
ethylene oxide, and trioxane. The nucleant may be present in the
composition in an amount of at least about 0.01 wt. %, such as at
least about 0.05 wt. %, such as at least about 0.1 wt. % and less
than about 2 wt. %, such as less than about 1.5 wt. %, such as less
than about 1 wt. %, wherein the weight is based on the total weight
of the respective polymer composition.
[0132] In one embodiment, an antioxidant, such as a sterically
hindered phenol, may be present. Examples which are available
commercially, are pentaerythrityl
tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate],
triethylene glycol
bis[3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionate],
3,3'-bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionohydrazide],
and hexamethylene glycol
bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]. The
antioxidant may be present in the polymer composition in an amount
of at least about 0.01 wt. %, such as at least about 0.05 wt. %,
such as at least about 0.075 wt. % and less than about 1 wt. %,
such as less than about 0.75 wt. %, such as less than about 0.5 wt.
%, wherein the weight is based on the total weight of the
respective polymer composition.
[0133] In one embodiment, a light stabilizer, such as a sterically
hindered amine, may be present in addition to the ultraviolet light
stabilizer. Hindered amine light stabilizers that may be used
include oligomeric hindered amine compounds that are N-methylated.
For instance, hindered amine light stabilizer may comprise a high
molecular weight hindered amine stabilizer. The light stabilizers,
when present, may be present in the polymer composition in an
amount of at least about 0.01 wt. %, such as at least about 0.05
wt. %, such as at least about 0.075 wt. % and less than about 1 wt.
%, such as less than about 0.75 wt. %, such as less than about 0.5
wt. %, wherein the weight is based on the total weight of the
respective polymer composition.
[0134] In one embodiment, a lubricant, not including the
tribological modifiers mentioned above, may be present. The
lubricant may comprise a polymer wax composition. Further, in one
embodiment, a polyethylene glycol polymer (processing aid) may be
present in the composition. The polyethylene glycol, for instance,
may have a molecular weight of from about 1000 to about 5000, such
as from about 3000 to about 4000. In one embodiment, for instance,
PEG-75 may be present. Lubricants may generally be present in the
polymer composition in an amount of at least about 0.01 wt. %, such
as at least about 0.05 wt. %, such as at least about 0.075 wt. %
and less than about 1 wt. %, such as less than about 0.75 wt. %,
such as less than about 0.5 wt. %, wherein the weight is based on
the total weight of the respective polymer composition.
[0135] In one embodiment, a compatibilizer, such as a phenoxy
resin, may be present. Generally, the phenoxy resin may be present
in the composition in an amount of at least about 0.01 wt. %, such
as at least about 0.05 wt. %, such as at least about 0.075 wt. %
and less than about 1 wt. %, such as less than about 0.75 wt. %,
such as less than about 0.5 wt. %, wherein the weight is based on
the total weight of the respective polymer composition.
[0136] In one embodiment, a colorant may be present. Colorants that
may be used include any desired inorganic pigments, such as
titanium dioxide, ultramarine blue, cobalt blue, and other organic
pigments and dyes, such as phthalocyanines, anthraquinnones, and
the like. Other colorants include carbon black or various other
polymer-soluble dyes. The colorant may be present in the
composition in an amount of at least about 0.01 wt. %, such as at
least about 0.05 wt. %, such as at least about 0.1 wt. % and less
than about 5 wt. %, such as less than about 2.5 wt. %, such as less
than about 1 wt. %, wherein the weight is based on the total weight
of the respective polymer composition.
[0137] Polymer Articles
[0138] The compositions of the present disclosure can be compounded
and formed into a polymer article using any technique known in the
art. For instance, the respective composition can be intensively
mixed to form a substantially homogeneous blend. The blend can be
melt kneaded at an elevated temperature, such as a temperature that
is higher than the melting point of the polymer utilized in the
polymer composition but lower than the degradation temperature.
Alternatively, the respective composition can be melted and mixed
together in a conventional single or twin screw extruder.
Preferably, the melt mixing is carried out at a temperature ranging
from 100 to 280.degree. C., such as from 120 to 260.degree. C.,
such as from 140 to 240.degree. C. or 180 to 220.degree. C.
However, such processing should be conducted for each respective
composition at a desired temperature to minimize any polymer
degradation.
[0139] After extrusion, the compositions may be formed into
pellets. The pellets can be molded into polymer articles by
techniques known in the art such as injection molding,
thermoforming, blow molding, rotational molding and the like.
According to the present disclosure, the polymer articles
demonstrate excellent tribological behavior and mechanical
properties. Consequently, the polymer articles can be used for
several applications where low wear and excellent gliding
properties are desired.
[0140] Polymer articles include any moving articles or moldings
that are in contact with another surface and may require high
tribological requirements. For instance, polymer articles include
articles for the automotive industry, especially housings, latches
such as rotary latches, window winding systems, wiper systems,
pulleys, sun roof systems, seat adjustments, levers, bushes, gears,
gear boxes, claws, pivot housings, wiper arms, brackets or seat
rail bearings, zippers, switches, cams, rollers or rolling guides,
sliding elements or glides such as sliding plates, conveyor belt
parts such as chain elements and links, castors, fasteners, levers,
conveyor system wear strips and guard rails. An almost limitless
variety of polymer articles may be formed from the polymer
compositions of the present disclosure.
[0141] According to the present disclosure, the polyoxymethylene
based system can be used to produce a polymer article comprising
two layers to provide at least a two-component system. In such
system, the second polymer layer is connected to the first polymer
layer.
[0142] The first polymer layer is comprised of a polyoxymethylene
polymer composition comprising a polyoxymethylene polymer and
optionally at least one tribological modifier. In general, the
first polymer layer provides a support or base for the second
polymer layer. The second polymer layer is comprised of a second
polymer composition comprising a liquid crystalline polymer, a
polyarylene sulfide polymer, or a combination thereof and at least
one tribological modifier. In general, the second polymer layer
provides a surface for contacting and/or conveying against another
body to provide a tribological effect. The second polymer layer may
contact a sliding body such as a bottle or a container.
[0143] The first polymer layer and/or the second polymer layer may
contain engaging mechanisms allowing one article to be connected to
an adjacent article. Such mechanisms include but are not limited to
a pin or the like. It should be noted that any engaging mechanisms
in the art may be utilized to engage adjacent articles.
[0144] Further, the first polymer layer can be connected to the
second polymer layer using any method known in the art. For
instance, the polymer layers may be connected to one another such
that they are directly or indirectly connected or linked. The
layers may be fixedly or removably attached to one another and/or
an intermediate layer. The layers may be connected using any method
known in the art. The polymer layers may be connected by
interlocking mechanisms, fasteners, co-molding, overmolding,
intermediate layers, adhesives, etc.
[0145] The interlocking mechanism may include a male member and a
female member for accepting the male member, such as grooves and
plugs. The male member or groove and/or female member or plug may
be located on either the first or second polymer layer. It should
also be understood that the these members may be of any shape or
configuration as long as they provide an interlocking mechanism. It
should also be understood that more than one interlocking mechanism
may be utilized. The members may be formed into the respective
layers and subsequently combined to form the polymer article. On
the other hand, a member may be created in one layer and the other
layer may be injection molded to provide the corresponding
interlocking part comprising a member. For instance, in one
embodiment, the first polymer layer can be connected to the second
polymer layer during a two-component injection molding process.
[0146] In another embodiment, the first polymer layer may be
connected to the second polymer layer using a fastener, such as a
mechanical fastener. Fasteners include screws, nails, rivets,
snaps, and the like and others generally known in the art. The
fastener can be inserted through either the first polymer layer or
the second polymer layer in order to attach or connect the polymer
layers together. It should also be understood that any number of
fasteners may be utilized for connecting the polymer layers.
[0147] In one embodiment, the first polymer layer is in direct
contact and connected to the second polymer layer. In another
embodiment, the first polymer layer is in indirect contact and
connected to the second polymer layer. For instance, an
intermediate layer may also be utilized to connect the polymer
layers. For instance, an intermediate layer may be utilized
individually or in conjunction with an interlocking mechanism or a
fastener as described above.
[0148] In another embodiment, the second polymer layer may be
overmolded onto the first polymer layer. The second polymer layer
may entirely overmold or partially overmold the first polymer
layer. However, it should be understood that any overmolding
configuration may be utilized as long as the second polymer layer
generally provides a surface for contacting and conveying against
another body to provide a tribological effect. In addition, when
overmolding, it should be understood that either the first polymer
layer or second polymer layer may employ engaging mechanisms. It
should be understood that any method of overmolding known in the
art may be utilized to connect the second polymer layer with the
first polymer layer.
[0149] In one embodiment, the second polymer layer overlays or
covers at least 50%, such as at least 75%, such as least 85%, such
as at least 90%, such as at least 95% of at least one surface of
the first polymer layer. In one embodiment, the second polymer
overlays or covers 100% of at least one surface of the first
polymer layer.
[0150] In general, the second polymer may have a thickness of at
least about 0.01 mm, such as at least about 0.02 mm, such as at
least about 0.1 mm, such as at least about 0.5 mm, such as at least
about 0.75 mm, such as at least about 1 mm and generally less than
about 10 mm, such as less than about 7.5 mm, such as less than
about 5 mm, such as less than about 3 mm.
[0151] According to one embodiment of the present disclosure, the
polymer article can be a conveyor component, such as a conveyor
chain component. Generally, conveyor chains are made from a series
of links having generally flat surfaces wherein the links may be
connected to each other by pins. General examples of such conveyor
components are disclosed in U.S. Pat. No. 5,309,705 to Takahashi et
al., U.S. Pat. No. 6,161,685 to Stebnicki, and U.S. Pat. No.
4,436,200 to Hodlewsky et al., which are all incorporated herein by
reference in their entirety.
[0152] In one embodiment, the conveyor component may be a conveyor
chain link. As shown in FIG. 1, a conveying system 10 is comprised
of a conveyor belt 12. The conveyor belt 12 is comprised of
conveyor components 14. The conveyor belt 12 and conveyor
components 14 are used to transport items 16 such as packages,
containers, and the like. According to the present disclosure, the
conveyor components 14 may exist as a two-component system.
[0153] For instance, as shown in FIG. 2, the polymer article may be
a conveyor component 14 that exists as a two-component system 34.
FIG. 2 exhibits a general characterization of a two-component
system. According to the two-component system, the second polymer
layer 22 is connected to the first polymer layer 24. In FIG. 2, a
second polymer layer 22 overlays a first polymer layer 24 such that
the second polymer layer 22 covers an entire surface of the first
polymer layer 24. However, the second polymer layer 22 may
partially overlay the first polymer layer 24 such that the second
polymer layer 22 only partially covers a surface of the first
polymer layer 24.
[0154] The first polymer layer 24 is comprised of a
polyoxymethylene polymer composition comprising a polyoxymethylene
polymer and optionally at least one tribological modifier. In
general, the first polymer layer 24 provides a support or base for
the second polymer layer 22. The second polymer layer 22 is
comprised of a second polymer composition comprising a liquid
crystalline polymer or a polyarylene sulfide polymer and at least
one tribological modifier. In general, the second polymer layer 22
provides a surface for contacting and conveying a sliding body or
container such as a plastic or glass bottle.
[0155] According to FIG. 2, the engaging mechanisms 18 and 20 are
located on the first polymer layer 24. However, it should be
understood that engaging mechanisms 18 and 20 may be located on
second polymer layer 22 or on both polymer layers 22 and 24.
Engaging mechanisms 18 and 20 of adjacent components 14 can be
connected using a pin (not shown) or the like to create a conveyor
belt as shown in FIG. 1. It should be understood that any engaging
mechanisms 18 and 20 known in the art can be utilized to engage
adjacent conveyor components 14.
[0156] According to FIGS. 3a and 3b, first polymer layer 24 can be
connected to the second polymer layer 22 using an interlocking
mechanism 26 such as a male member 28 or a groove 28 and a female
member 30 or a plug 30. As shown in FIG. 3a, the first polymer
layer 24 may comprise a male member/groove 28 while the second
polymer layer comprises a female member 30. However, as shown in
FIG. 3b, the first polymer layer 24 may comprise a female member 30
while the second polymer layer 22 comprises a male member 28. It
should also be understood that the male member and female member
may be of any shape or configuration as long as they provide an
interlocking mechanism 26. It should also be understood that more
than one interlocking mechanism may be utilized.
[0157] When an interlocking mechanism 26 is used to connect the
first polymer layer 24 with second polymer layer 22, the male
member 28 or female member 30 may be formed into the respective
layers and subsequently combined to form a conveyor component 14.
On the other hand, a male member 28 or female member 30 may be
created in one layer and the other layer may be injection molded to
provide the corresponding interlocking part comprising a male
member 28 or female member 30. For instance, in one embodiment, the
first polymer layer 24 can be connected to the second polymer layer
22 during a two-component injection molding process.
[0158] In another embodiment, as shown in FIG. 4, the first polymer
layer 24 may be connected to the second polymer layer 22 using a
fastener 36. Fasteners include screws, nails, snaps, and the like.
According to FIG. 4, the fastener 36 is inserted through the second
polymer layer 22 and into the first polymer layer 24. However, the
fastener 36 may also be inserted through the first polymer layer 24
and into the second polymer layer 22. It should also be understood
that any number of fasteners 36 may be utilized for connecting the
polymer layers.
[0159] In another embodiment, as shown in FIGS. 5a and 5b, the
second polymer layer 22 may be overmolded onto the first polymer
layer 24. As shown in FIG. 5a, the second polymer layer 22 entirely
overmolds the first polymer layer 24. As shown in FIG. 5b, the
second polymer layer 22 partially overmolds the first polymer layer
24. However, it should be understood that any overmolding
configuration may be utilized as long as the second polymer layer
24 generally provides a surface for contacting and conveying a
sliding body or container such as a plastic or glass bottle. In
addition, when overmolding, it should be understood that either the
first polymer layer 24 or second polymer layer 22 may employ
engaging mechanisms 18 and 20. It should be understood that any
method of overmolding known in the art may be utilized to connect
the second polymer layer 22 with the first polymer layer 24.
[0160] Properties
[0161] Utilizing the polyoxymethylene based system according to the
present disclosure provides compositions and articles with improved
tribological properties. According to the present disclosure, the
tribological properties are generally measured by the coefficient
of friction.
[0162] In general, static friction is the friction between two or
more surfaces that are not moving relative to each other (ie., both
objects are stationary). In general, dynamic friction occurs when
two objects are moving relative to each other (ie., at least one
object is in motion). In addition, stick-slip is generally known as
a phenomenon caused by continuous alternating between static and
dynamic friction.
[0163] According to the present disclosure, the polymer article of
the two-component system may exhibit a static coefficient of
friction against another surface, as determined according to VDA
230-206, of greater than about 0.01, such as greater than about
0.03, such as greater than about 0.05, such as greater than about
0.08, such as greater than about 0.1 but generally less than about
0.18, such as less than about 0.15, such as less than about 0.12,
such as less than about 0.1. In one embodiment in particular, the
second polymer layer of the polymer article may exhibit the
aforementioned static coefficient of friction.
[0164] According to the present disclosure, the polymer article of
the two-component system may exhibit a dynamic coefficient of
friction against another surface, as determined according to VDA
230-206, of greater than about 0.01, such as greater than about
0.03, such as greater than about 0.05, such as greater than about
0.08, such as greater than about 0.1 but generally less than about
0.18, such as less than about 0.15, such as less than about 0.12,
such as less than about 0.1. In one embodiment in particular, the
second polymer layer of the polymer article may exhibit the
aforementioned dynamic coefficient of friction.
[0165] In one embodiment, the above static coefficient of friction
and dynamic coefficient of friction values are exhibited between
the polymer article, such as the second polymer layer, of the
two-component system and various counter-materials. For instance,
the above values can be exhibited between the polymer article, such
as the second polymer layer, of the two-component system and a
polyester surface such as a polyethylene terephthalate surface. In
another embodiment, the above values are exhibited between the
polymer article, such as the second polymer layer, of the
two-component system and a polyacetal surface, a metal surface such
as a steel surface, or a polyolefin surface such as a polypropylene
surface or a polyethylene surface such as an ultra-high molecular
weight polyethylene surface.
[0166] The present disclosure may be better understood with
reference to the following example.
Examples
[0167] The examples of the invention are given below by way of
illustration and not by way of limitation. The following
experiments were conducted in order to show some of the benefits
and advantages of the present invention.
[0168] The compositions comprise either a liquid crystalline
polymer or a polyphenylene sulfide polymer and at least one
tribological modifier such as polytetrafluoroethylene. In addition,
glass fibers were also utilized in the compositions. The
formulations are disclosed in the table below.
[0169] The components of each respective polymer composition were
substantially and homogeneously blended and compounded using a
co-rotating intermeshing twin screw extruder. When glass fibers
were utilized, they were added to the twin-screw extruder at a
suitable downstream feeding position. The respective compositions
were extruded, pelletized, and then molded using an injection
molding machine.
[0170] The molded compositions were then tested to determine the
tribological properties against a polyethylene terephthalate
surface. Stick-slip tests were conducted to determine the dynamic
coefficient of friction and the static coefficient of friction.
Stick-slip tests were conducted according to VDA 230-206. A
ball-on-plate configuration was utilized with a load of 10 N,
sliding speed of 8 mm/s, and a test duration of 8-45 minutes.
[0171] New polymer layers or molds were tested after injection
molding. Used polymer layers or molds were produced by abrading a
new polymer mold with sand paper in order to simulate a used mold
or article.
TABLE-US-00001 Comparative Sample 1 Sample 2 Sample 3 Sample 1 POM
(wt. %) 0 0 0 100 (HF C9021) LCP (wt. %) 75 65 0 PPS (wt. %) 0 0
52.5 0 PTFE (wt. %) 25 20 7.5 0 Gass fibers (wt. %) 0 15 40 0 Used
Mold Dynamic 0.070 0.067 0.082 0.107 CoF Static CoF 0.076 0.079
0.094 0.116 New Mold Dynamic 0.075 0.088 0.094 0.134 CoF Static CoF
0.098 0.101 0.112 0.145
[0172] 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.
[0173] 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.
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