U.S. patent application number 10/991452 was filed with the patent office on 2005-05-05 for thermoplastic jacket belt.
Invention is credited to Dunlap, Paul N., Martin, Dieter, Visser, Harry D..
Application Number | 20050093205 10/991452 |
Document ID | / |
Family ID | 23087601 |
Filed Date | 2005-05-05 |
United States Patent
Application |
20050093205 |
Kind Code |
A1 |
Martin, Dieter ; et
al. |
May 5, 2005 |
Thermoplastic jacket belt
Abstract
A belt having a body, a tensile member and an outer surface. The
body comprises an elastomer. An outer surface of the belt having a
profile, foe example teeth. A layer of Ultra high molecular weight
polyethylene thermoplastic (UHMWPE) is bonded to the profile
surface. The layer bonded to the profile surface having a low
softening point allowing it to conform to a mold shape prior to
cure of the rubber body material. The layer having a molecular
weight in the range of 3-7 million grams per mole. The layer causes
the belt to exhibit superior abrasion resistance and flexibility
while reducing the cost per belt as compared to fabric jacket
belts. The UHMWPE jacket belt has significantly reduced dust and
debris production during operation.
Inventors: |
Martin, Dieter; (Lakewood,
CO) ; Visser, Harry D.; (Lakewood, CO) ;
Dunlap, Paul N.; (Centennial, CO) |
Correspondence
Address: |
Jeffrey Thurnau
The Gates Corporation
Mail Stop 31-4-1-A1
900 S. Broadway
Denver
CO
80209
US
|
Family ID: |
23087601 |
Appl. No.: |
10/991452 |
Filed: |
November 18, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10991452 |
Nov 18, 2004 |
|
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10121556 |
Apr 12, 2002 |
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60283801 |
Apr 12, 2001 |
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Current U.S.
Class: |
264/326 ;
156/137 |
Current CPC
Class: |
B29K 2223/0683 20130101;
F16G 5/20 20130101; F16G 1/28 20130101; B29K 2023/0683 20130101;
B29D 29/08 20130101 |
Class at
Publication: |
264/326 ;
156/137 |
International
Class: |
B29C 035/00 |
Claims
We claim:
1. A method of making a belt comprising the steps of: applying a
layer of ultra high molecular weight polyethylene thermoplastic
film having a thickness to an outer surface of a mandrel; applying
a layer of elastomeric material over the ultra high molecular
weight polyethylene thermoplastic film; applying a tensile member
over the layer of elastomeric material; applying a layer of
elastomeric material over the tensile member; curing the belt;
quenching the mandrel in a cool fluid; and removing the cured belt
from the mandrel.
2. The method as in claim 1 further comprising the step of: using
an ultra high molecular weight polyethylene having a molecular
weight in the range of approximately 3,000,000 to approximately
7,000,000 grams/mole.
3. The method as in claim 1 wherein a peak melt temperature for the
ultra high molecular weight polyethylene layer is approximately
128.degree. to approximately 132.degree. C.
4. The method as in claim 1, wherein the thickness of the ultra
high molecular weight polyethylene is in the range of 0.025 to
approximately 3.0 mm.
Description
REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of U.S. non-provisional
application Ser. No. 10/121,556 filed Apr. 12, 2002.
FIELD OF THE INVENTION
[0002] The invention relates to power transmission belts, more
particularly, the invention relates to belts having a jacket
comprising an ultra high molecular weight polyethylene
thermoplastic layer.
BACKGROUND OF THE INVENTION
[0003] Toothed power transmission belts have a polymeric body such
as a rubber, thermoplastic, or urethane, with a plurality of teeth
or cogs formed along at least one side or both sides of such belts.
A tensile member is typically embedded in the body as a tensile
load-carrying member.
[0004] It is preferred to have the belt teeth reinforced with a
material to enhance their shear strength and wear-resistance, or to
alter their coefficient of friction for engagement with a toothed
pulley. The material generally comprises fabrics of a woven type
such as a canvas, a crimped stretchable nylon, and a leno-weave,
etc., and may be of a knit fabric such as a 1.times.1 rib knit.
Such fabrics are disposed in the belt at a peripheral surface that
includes the belt teeth and may be in the form of a single layer
fabric, multiple layers of woven fabrics, or bonded layers of
fabrics.
[0005] During operation, the fabric reinforcement wears creating
dust and debris particles. The dust and debris is detrimental to
the operation of adjacent components and may interfere with
operation of certain types of equipment over time. For example,
printers, copiers and cameras to name a few. Further, the dust and
debris particles from the prior art belts may be electrically
conductive, depending upon the belt materials. Depending upon the
application, it is not desirable to have electrically conductive
materials coating components in electrical equipment.
[0006] Belts are also taught with fabric jackets having an outer
layering of impervious thermoplastic film. The film is used during
the fabrication process to contain the belt body material with
respect to an outer fabric reinforcement layer. The outer film
layer has very poor abrasion resistance. Once in use, the film
wears off exposing the fabric layer below.
[0007] Particularly relevant prior art is found in U.S. Pat. No.
3,964,328 (Redmond) which discloses a fabric in the preferable form
of a stretchable nylon with a thermoplastic layer such as
polyethylene bonded to an exterior surface thereof. The fabric is
disposed at a peripheral surface of a belt including belt teeth as
a wear-resistant fabric and friction modifying reinforcement. The
thermoplastic surface has low abrasion resistance and wears away
during operation.
[0008] What is needed is a belt having a film jacket comprising
UHMWPE thermoplastic film. What is needed is a belt having a film
jacket comprising UHMWPE thermoplastic film on a pulley engaging
surface. What is needed is a belt having a film jacket comprising
UHMWPE thermoplastic film and having high abrasion resistance. The
present invention meets these needs.
SUMMARY OF THE INVENTION
[0009] The primary aspect of the invention is to provide a belt
having a film jacket comprising an ultra high molecular weight
polyethylene thermoplastic film.
[0010] Another aspect of the invention is to provide a belt having
a film jacket comprising an ultra high molecular weight
polyethylene thermoplastic film on a pulley engaging surface.
[0011] Another aspect of the present invention is to provide a belt
having an ultra high molecular weight polyethylene thermoplastic
film jacket having high abrasion resistance.
[0012] This and other aspects and advantages of the invention will
be apparent after reviewing the drawings and detailed description
thereof.
[0013] The invention comprises a belt having a body, a tensile
member and an outer surface. The outer surface having belt teeth.
Ultra high molecular weight polyethylene thermoplastic film
(UHMWPE) is bonded to an outer load bearing surface. The outer
surface comprises teeth in the preferred embodiment. The
thermoplastic film bonded to the outer surface has a low softening
point allowing it to comply with a mold shape prior to cure of the
rubber body material. The UHMWPE film has a molecular weight in the
range of 3-6 million grams per mole, although the range may be
extended down to 250,000 grams per mole. The film exhibits superior
abrasion resistance while reducing the cost per belt as compared to
fabric jacket belts. The film jacket belt has significantly reduced
dust and debris production during operation.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] Preferred aspects of this invention will be described with
reference to the accompanying drawings, in which like numerals
designate like parts in the several figures.
[0015] FIG. 1 is a perspective view of a film reinforced belt.
[0016] FIG. 2 is an enlarged cross section of film taken along the
line 2-2 of FIG. 1.
[0017] FIG. 3 is a chart depicting relative test lives for
inventive belts compared to prior art fabric jacket belts.
[0018] FIG. 4 is a chart depicting wear for the inventive belts
compared to prior art fabric jacket belts.
[0019] FIG. 5 is a cross-sectional view of wrapped plies of
film.
DESCRIPTION OF PREFERRED EMBODIMENT
[0020] FIG. 1 is a perspective view of a thermoplastic jacket power
transmission belt. The belt includes a body 10 having a top rubber
12. Top rubber 12 comprises a rubber stock or other elastomeric
material as described herein. In the preferred embodiment the belt
elastomeric comprises EPDM. Cogs or teeth 15 are arranged
transversely along a longitudinal axis L of the belt 10. A land
portion 17 is located between each set of adjacent cogs 15. Cogs 15
comprise an elastomeric or thermoplastic material compatible with
or identical to the body 10 elastomeric material.
[0021] Tensile members 20, which run in the longitudinal direction
of the belt, are loaded into the top rubber 12. Tensile members 20
bear a tensile load imposed upon the belt during operation.
Elastomeric layer 21 extends between tensile members 20 and
thermoplastic jacket 30. Layer 21 prevents the tensile members from
chafing against jacket 30 during operation, thereby significantly
extending the life of the belt.
[0022] Thermoplastic jacket 30 is bonded to the belt body on an
outer surface 35 of the teeth 15 as described herein. Unlike the
prior art, the jacket construction disclosed herein does not
require an outer fabric layer on the tooth surface to reinforce the
belt. Elimination of the fabric layer reduces the material and
production cost per belt. The thermoplastic jacket belt
construction disclosed herein is in the range of 18% to 24% less
costly than a comparable belt having a fabric jacket, such as
cotton, polyester, polyamide, hemp, jute, fiberglass, aramid or
other natural and synthetic fibers known in the art.
[0023] In the preferred embodiment, jacket 30 comprises an ultra
high molecular weight polyethylene (UHMWPE) thermoplastic film, for
example, D/W 402.TM. by DeWal Industries, Inc. The UHMWPE film has
a molecular weight in the range of 3 to 7 million grams per mole
and an elongation percentage in the range of up to 375% of an
original length. The density range for suitable polyethylene jacket
materials is in the range of 0.93 to 0.95 grams/cc. The
thermoplastic material for the jacket 30 may comprise a material
that has a softening point temperature below the cure temperature
of the rubber stock used for the belt body. The jacket may also
comprise other polyethylene films known in the art, for example,
BFI 2287 by Blueridge Films, Inc. The molecular weight of BFI 2287
is approximately 250,000 grams per mole with an elongation at break
in the range of up to 500% of the original length. The jacket may
also comprise blends and mixtures of other polyethylenes. An
example of such a blend is a combination of UHMWPE particles in
HDPE. An example of suitable UHMWPE particles is GUR 4150 from
Ticona. GUR 4150 has a molecular weight in the range of 3 to 7
million grams per mole and a particle size of approximately 125
microns. It was found that a loading of as little as 30% by weight
GUR4150 in BFI 2287 showed suitability as a jacket material. The
use of UHMWPE significantly reduces the stiffness of the belt as
compared to other thermoplastics in the same application.
[0024] The polyethylene films also comprise a low softening point
generally less than a vulcanization temperature of the belt. The
low softening point allows the thermoplastic film to soften and
flow to conform to a mold shape before cross-linking of the rubber
with the film is initiated during curing.
[0025] The polyethylene material may also have a softening
temperature that is greater than a body cure temperature. In this
embodiment the film is molded into a preformed shape, for example a
toothed shape, before being incorporated into the belt build are
described later herein.
[0026] Some rubber stocks have high adhesion values without the use
of additional adhesive materials when bonded to certain
thermoplastic films used for the jacket. For example, peroxide
cured EPDM (ethylene-propylene-diene terpolymer) and peroxide cured
nitrile have particularly good adhesion to untreated UHMWPE. This
high adhesion is attributable to molecular entanglement of the very
long chains of the UHMWPE within the crosslinked rubber chains that
occurs during the rubber cure process.
[0027] Other rubber stocks, such as SBR, polychloroprene, natural
rubber and isobutene isoprene rubbers are also known to have good
adhesion to UHMWPE, and are acceptable materials for the rubber
stock used with UHMWPE jackets. Rubber stocks are formulated to
achieve a balance among various factors, including low cost, good
processibility in mixing and calendaring, building tack, long
scorch times and low modulus.
[0028] In the preferred embodiment no adhesives or primers are be
needed to achieve good bonds between the thermoplastic films and
the rubber stocks. In an alternate embodiment, an adhesive can be
used to bond the UHMWPE to the rubber stocks. Adhesives for bonding
the UHMW polyethylene jacket to the rubber body of the belt include
those suitable for bonding of polyolefins. The preferred adhesives
are solvent based adhesives made from modified polyolefin
elastomers, such as chlorosulfonated polyethylene. An example of
such an adhesive is Master Bond Polymer System X17.TM.. Other lower
performance, but also suitable, adhesives are solvent based
elastomeric adhesives formulated from rubbers and certain resins,
such as EPDM or nitrile rubber and alkylated phenol resins. An
example of such an adhesive is Master Bond Polymer System X5198 .
Suitable solvents for the solvent based adhesives include acetone,
xylene and methyl ethyl ketone. Bonding of the polyethylene jacket
to the rubber body of the belt can also improved by oxidative
treatments of the polyethylene surface, as well as other
polyethylene pretreatments known in the art, such as solvent
washing or vapor degreasing. Examples of oxidative treatments
include exposure to corona discharge, flame oxidation, and plasma
etching in an oxygen atmosphere.
[0029] The use of thermoplastic jackets does not limit the choice
of belt tooth profiles. For example, standard trapezoidal, square
and the many types of curvilinear shaped teeth known in the art are
all compatible with a thermoplastic film jacket. Tooth pitch sizes
may be in the range of 1 mm to 32 mm.
[0030] The jacket material may also be compounded with friction
modifiers or conductive agents, for example graphite, waxes, oils,
molybdenum disulfide, PTFE, mica talc, carbon black, and various
blends of the above, to address uses for specific applications. The
additives are used to modify the coefficient of friction or to
achieve a desired conductivity. The applications may comprise uses
where frictional characteristics impact system operation or where
it is desirable for the belt to be conductive to dissipate static
electrical charge.
[0031] The use of a thermoplastic jacket does not limit the
selection of tensile members. All known tensile member materials
are suitable. These comprise fiberglass, aramid, nylon, polyester,
polyolefin, PBO, PEN, carbon, metal wire/cable, cotton, rayon, as
well as other known tensile member materials. Nor does the use of a
thermoplastic film jacket limit the construction, geometry and/or
shape of the tensile member; single yarns, plied yarns, cabled
cords, twisted cords, woven cords, woven fabrics, round &
multilobal monofilaments, tapes, films and ribbons are all
suitable.
[0032] Example belts were produced using peroxide cured EPDM. EPDM
was selected for its good adhesion to the materials used as
jackets.
[0033] FIG. 2 is an enlarged cross section of belt along the line
2-2 of FIG. 1. Tensile members 20 may or may not bear upon jacket
30 as required by a user.
[0034] FIG. 3 is a chart depicting relative test lives for
inventive belts compared to prior art, nylon fabric jacket
belts.
[0035] The flex test apparatus comprises a set of pulleys over
which the belt is trained. Each belt is run at 3600 RPM on the
two-point drive with 1201 Newtons (270 pounds) total tension at
22.degree. C. Each sprocket has 22 grooves; each test belt has 120
teeth. The flex test is used to evaluate jacket wear. No torque is
transmitted during the test.
[0036] For the load test the belt is run at 2500 RPM on a two-point
drive with 1716 Newtons (385 pounds) total tension and a tension
ratio of 3.5 (this is approximately 12 horsepower) at a temperature
of 22.degree. C. Each sprocket has 28 grooves; test belt has 120
teeth. Torque is transmitted during this test.
[0037] In particular, the UHMWPE belt shows an approximately 452%
increase in flex life, from approximately 133 hours for the prior
art nylon fabric jacket to approximately 735 hours for the
inventive belt. Load life increased from 304 hours to 771 hours
representing a 154% increase.
[0038] FIG. 4 is a chart depicting mass loss for the inventive
belts compared to prior art nylon fabric jacket belts. In
particular, the UHMWPE belts shows mass loss equal to approximately
1/4 of the mass loss for the prior art fabric belts for 100 hours
on the flex tester. This illustrates the advantage of the inventive
belts, particularly with respect to low wear rates and low mass
loss during operation.
[0039] Method of Manufacture:
[0040] The belts are produced using the ply-up method using rolled
sheets of thermoplastic material and calendered rubber. Curing the
belt is accomplished in a steam vulcanizer. The mold has two main
parts--an inside mandrel, which has the desired tooth profiles cut
into its surface, and an outer shell, which contains a flexible
bladder (cure bag) to transmit the pressure to the belt without
allowing steam to contact the belt material.
[0041] The jacket is the first layer applied around the building
mandrel. The jacket can be applied as several plies, or as one ply.
More particularly, it may be applied in a single sheet or in a
series of film layers built upon each other. Further, a preformed
jacket already molded into a tooth profile may also be applied in
lieu of the unmolded plies.
[0042] FIG. 5 is a cross-sectional view of wrapped plies of film.
In the case of several plies, the material is wrapped around the
mandrel until the desired number of plies or thickness is achieved.
The end of the wrap 100 can be held in place with a spot tack or
adhesive. In the preferred embodiment, the end of the ply wrap is
substantially aligned A-A with the leading edge 200 of the ply on
the mandrel to avoid a thick spot in the layer once the belt is
vulcanized. If one ply, the UHMWPE film can be butt spliced into a
tube of the appropriate circumference and this tube is placed on
the building mandrel before winding the cord. The splice may be
accomplished using methods of thermoplastic welding such as use of
a hot knife or hot plate, each known in the art.
[0043] The tensile members are next applied over the jacket
material, followed by one or more plies of elastomeric or rubber
stock. In order to improve belt flex and load life, a thin layer 21
of rubber is applied between the jacket film and the tensile cord.
Layer 21 increases belt life by preventing chafing of the tensile
member on jacket 30. The tensile member and rubber are applied
using known methods used for production belts using fabric jackets.
The mandrel, with the uncured belt build, is then placed inside the
outer shell for curing.
[0044] As noted, the jacket 30 may be laid up in a single layer or
ply, or as a laminate comprising a plurality of layers. The
thickness of each layer is only limited by the availability of
suitable thermoplastic film(s), but generally is in the range of
0.025 to 1.27 mm per layer. The total thickness of the jacket 30
may be in the range of 0.025 to 2.8 mm, depending upon the design
and operational requirements placed upon the belt. This represents
a jacket thickness to belt thickness ratio in the range of 25% to
35%. Operational requirements may include high MTBF (mean time
between failures), or reduced dusting or debris production. The
ranges are offered by way of example and not of limitation.
Further, the laminating process may use any number of layers, in
any thickness combination, to achieve the desired jacket
thickness.
[0045] Once the belt is laid up on a mandrel and the mandrel is
placed in the mold, a typical fabrication process comprises:
[0046] 1) evacuating the air from inside the mold and holding for 1
to 5 minutes;
[0047] 2) increasing the steam pressure on the outside shell to a
range of 175 to 235 psig;
[0048] 3) after 2 to 10 minutes, increasing the steam pressure on
the inside of the mold to a range of 85 to 210 psig;
[0049] 4) curing for 10 to 20 minutes;
[0050] 5) decreasing the steam pressure inside the mold to
atmospheric pressure;
[0051] 6) decreasing the steam pressure outside the mold to
atmospheric pressure;
[0052] 7) quenching the mandrel in a cool fluid, such as water;
[0053] 8) removing the cured belt blank from the mandrel.
[0054] The optimum tooth shapes are achieved with process pressures
on the high end of the range.
[0055] Hydraulics or other methods known in the art (pneumatic,
electrical) can also be used to apply pressure the belt, in
conjunction with concurrently applied electric heat for curing in
lieu of steam cure. The pressure range for a hydraulic cure is 85
to 500 psig. The temperature range is 250 to 500.degree. F. This
method of curing broadens the choice of films and rubber
stocks.
[0056] Typical elastomeric formulations and film types for the
belts are;
[0057] Belt Elastomeric EPDM formulations
1 Parts PHR General Preferred EPDM 100-70 Vistalon .TM. 606 70 EP
Copolymer 0-30 Trilene .TM. CP80 30 Silica 30-70 HiSil .TM. 190G 50
TiO.sub.2 2-10 TiO.sub.2 4 Antioxidant 0.5-5.0 ZMTI 1 Lubricant 1-5
Navgard 455 1 Cure Activator 2-10 Ethanox 702 0.5 Peroxide 2-10
Zinc Stearate 1.5 Co-Agent 0-20 Zinc Oxide 5 Vulcup 4 Saret .TM.
708 15
[0058] Belt Film
2 Material Tradename Elongation Molecular Weight Range UHMWPE
D/W402 300% 3 million-7 million g/mole HMW-HDPE BFI 2287 500%
250,000 g/mole GUR 4150 + 2287 (Blend) 300-500% 250,000 to 3
million g/mole BFI
[0059] The peak melt temperature for each is approximately:
132.degree. C. for the D/W 402 and 128.degree. C. for the BFI 2287.
One skilled in the art can appreciate that polyethylene sheets or
films having molecular weights in the range of 500,001 g/mole up to
and including 2,999,999 g/mole also are applicable to the instant
inventive belt.
[0060] Other alternate elastomeric formulations useful for the
instant invention are disclosed in U.S. Pat. No. 5,610,217 to
Yarnell et al. To form the elastomer composition of the present
invention the ethylene-alpha-olefin elastomer may optionally be
blended with less than 50% by weight, more preferably up to about
25%, and most preferably from about 5% to about 10% based on the
total elastomeric content of the composition of a second
elastomeric material including but not limited to silicone rubber,
polychloroprene, epichlorohydrin, hydrogenated nitrile butadiene
rubber, natural rubber, ethylene-vinyl-acetate copolymer, ethylene
methacrylate copolymers and terpolymers, styrene butadiene rubber,
nitrile rubber, chlorinated polyethylene, chlorosulfonated
polyethylene, alkylated chlorosulfonated polyethylene,
transpolyoctenamer, polyacrylic rubbers, butadiene rubber, and
mixtures thereof, to fine-tune certain mechanical properties such
as high temperature performance and tack.
[0061] The incorporation of metal salts of alpha-beta-unsaturated
organic acids in the elastomeric compositions of the present
invention may also be included. The metal salts of
alpha-beta-unsaturated organic acids useful in the present
invention are metal salts of acids such as, for example, acrylic,
methacrylic, maleic, fumaric, ethacrylic, vinyl-acrylic, itaconic,
methyl itaconic, aconitic, methyl aconitic, crotonic,
alpha-methylcrotonic, cinnamic, and 2,4-dihydroxy cinnamic acids.
These salts may be of zinc, cadmium, calcium, magnesium, sodium or
aluminum, and are preferably those of zinc. The preferred metal
salts of alpha-beta-unsaturated organic acids are zinc diacrylate
and zinc dimethacrylate. Other co-agents may comprise, but are not
limited to 1,4-butanediol diacrylate, 1,4-butanediol
dimethylacrylate, tetraethylene glycol diacrylate, ethoxylated
Bisphenol-A diacrylate, ethoxylated Bisphenol-A dimethacrylate,
trimethyl propane triacrylate, timethyl propane trimethacrylate,
glycerol triacrylate, glycerol trimethacrylate, trimethyl ethane
triacrylate, propoxylated glycerol triacrylate, ethoxylated
trimethylpropane triacrylate, pentaerythreltol tetraacrylate,
pentaerythritol tetramethacrylate, di-trimethylolpropane
tetraacrylate, ethoxylated pentaerythritol tetraacrylate,
dipentaerythritol pentaacrylate, pentaacrylate ester,
1,2-polybutadiene, N,N'-m-phenylenebismaleimide.
[0062] The most preferred metal salt of unsaturated organic acid is
zinc dimethacrylate. Amounts of the metal salt useful in the
present invention may range from about 1 to about 30 phr, and are
preferably from about 5 to about 20 phr. The metal salt is zinc
dimethacrylate used in an amount of about 5 phr when used in
conjunction with EPDM mixed with up to about 10% of silicone
rubber, and from about 10 to about 20 phr and more preferably about
15 phr when used in conjunction with the other
ethylene-alpha-olefin elastomers useful in the present
invention.
[0063] The ethylene-alpha-olefin elastomeric compositions useful in
the endless belts of the present invention further comprise from
about 40 to 150 phr of a reinforcing filler such as carbon black,
calcium carbonate, talc, clay or hydrated silica, or mixtures of
the foregoing. The incorporation of from 1 to 30 phr of a metal
salt of an unsaturated organic acid and from about 25 to about 250
phr and preferably about 25 to about 100 phr of reinforcing filler
in the peroxide-cured ethylene-alpha-olefin elastomeric composition
preserves the heat stability of conventional peroxide-cured
elastomers, while providing the tear strength and dynamic
properties usually associated with sulfur cured elastomers.
[0064] The free-radical producing curatives useful in the present
invention are those suitable for curing ethylene-alpha-olefin
elastomers and include for example, organic peroxides and ionizing
radiation. The preferred curative is an organic peroxide, including
but not limited to dicumyl peroxide, bis-(t-butyl
peroxy-diisopropyl benzene, t-butyl perbenzoate, di-t-butyl
peroxide, 2,5-dimethyl-2,5-di-t-butylperoxyhexane- ,
alpha-alpha-bis (t-butylperoxy) diisopropylbenzene. The preferred
organic peroxide curative is alpha-alpha-bis(t-butylperoxy)
diisopropylbenzene. Cure-effective amounts of organic peroxide for
purposes of the present invention are typically from about 2 to
about 10 phr. Preferred levels of organic peroxide are from about 2
to about 10 phr. Sulfur may optionally be added to the organic
peroxide curative as part of a mixed cure system in an amount of
from about 0.01 to about 1.0 phr, to improve the cured elastomer's
Young's modulus without negatively affecting its tear
resistance.
[0065] Other conventional ethylene-alpha-olefin elastomer
additives, process and extender oils, antioxidants, waxes,
pigments, plasticizers, softeners and the like may be added
according to common rubber processing practice without departing
from the present invention. For example, in a preferred embodiment
of the present invention, the elastomeric composition also contains
from about 0.5 to about 5.0 phr of an antiozonant or antioxidant
and from about 10 to about 50 phr of a paraffinic petroleum oil
plasticizer/softener.
[0066] The ethylene-alpha-olefin elastomeric compositions useful in
the present invention may be prepared by any conventional procedure
such as for example, by mixing the ingredients in an internal mixer
or on a mill.
[0067] In yet an alternate embodiment, the tensile members 20 are
omitted from the belt 10. The jacket 30 is used to carry the
tensile load experienced by the belt during operation. The method
of construction is as described above, with the exception that the
step including the tensile member is deleted. This alternate
embodiment can produce belts for low power applications, such as
printers.
[0068] During operation, although the inventive belt exhibits high
abrasion resistance and low wear rates, a very slight amount of
dust and debris particles may be created over time. If so, the dust
and debris may settle on adjacent components, forming a thin layer
of belt material. Further, it may not be possible or feasible to
remove the dust layer due to physical or operational constraints,
causing the dust layer to accumulate over time. Thermoplastic film
has a relative dielectric constant or permittivity, .epsilon., in
the range of approximately 2 to 3, which is appropriate to
insulating solids. Since the film is a dielectric, any film dust
created during operation is not electrically conductive, as
compared to polysulfide belts that produce greater quantities of
more conductive dust. Although the behavior of an insulator is time
and frequency dependent, on balance, dielectric dust significantly
diminishes or eliminates the potential for dust to interfere with
or affect the operation of electronic components otherwise
adversely affected by belt dust.
[0069] In yet another embodiment, jacket 30 comprises a polyamide
or polyester thermoplastic film. The other belt components are as
described in FIG. 1. Jacket 30 is connected to an outer surface 35
of body 10. Surface 35 extends in an endless direction on the belt.
Teeth 15 are arranged transverse to an endless direction.
[0070] Various types of polyamide may be used for jacket 30.
Examples include, but are not limited to, polyamide 6,6 exemplified
by Dartek EN560.TM. by Enhance Packaging Technologies, polyamide 6
exemplified by Capran 100.TM. by Allied Signal, or polyamide 12
exemplified by Grilamid L25FVS10.TM. by EMS Chemie. Others include
various copolymers such as polyether block amide exemplified by
Pebax grades with peak melt temperatures ranging from 138.degree.
C. to 205.degree. C. by Elf Atochem, or polyamide 46 exemplified by
Stanyl.TM. by DSM. The jacket film material may also be compounded
with friction modifiers, crystallinity modifiers, or conductive
agents such as molybdenum disulfide, PTFE, graphite, and their
equivalents.
[0071] The polyamide film must be flexible for the particular
thickness used in the belt. Many grades of polyamide, being highly
crystalline, must be used as very thin films, in the range of
approximately 0.025 mm to 0.1 mm. Other less crystalline grades,
being more flexible can be applied at greater thicknesses, up to
approximately 3 mm. Greater thickness is desirable for greater wear
resistance and load capability. Ultimately, the thickness used will
depend on the design and operational requirements of the belt.
[0072] If a flow-through process is used, the grade of polyamide
chosen should also have a softening point in substantially the same
temperature range as the cure temperature of the elastomeric body
of the belt. If the softening point is too high, the body will cure
before the film is soft enough to flow and form the belt teeth. If
the softening point is too low, an operational temperature of the
belt will be reduced below a desirable level, for example, blow a
temperature required for a satisfactory vehicle application.
Polyamide films with melting temperatures up to 260.degree. C. are
successfully used in the flow through process. For some polyamide
films melting in the 260 to 300.degree. C. range, including
polyamide 4,6, a preform process is preferable, wherein a jacket
layer is preformed into a tooth shape prior to curing the belt. A
flow-through process is one in which the rubber flows through the
tensile cords and into the teeth during the cure process.
[0073] Consequently, the polyamide film embodiment comprises a
higher softening point than that of the UHMWPE film described
elsewhere in this specification. The elastomeric compounds
described herein that are suitable for use with UHMWPE have been
slightly modified for use with polyamide. The cure temperature and
scorch time are raised to match the higher polyamide softening
temperatures, as exemplified by the following. The following
examples are offered by way of description and not of limitation.
Other combinations, configurations utilizing the foregoing are
possible. Each of the belts in the following examples exhibited
excellent tooth formation, jacket adhesion and flexibility.
EXAMPLE 1
[0074] Nine layers of 3-mil (1.1 mm total thickness) Dartek EN560
polyamide 6,6 thermoplastic film layered together. The peak melt
temperature is approximately 220.degree. C. On top of the film
layers is placed a 3 mm thick layer of EPDM, formulated as above
except for 3.1 phr of Vanderbilt's Varox 130XL
(2,5-dimethyl-2,5-di(t-butylperoxy)-3-hexyne) being substituted for
the 4 phr of Vulcup. The peroxide raises the cure temperature of
the belt body approximately 20.degree. C., making it more suitable
for use with the polyamide film. The materials and mold are placed
in a mold under a pressure of 250 psi. The mold is brought to a
temperature of approximately 210.degree. C. to soften the film,
form the teeth, and cure the body. Then the mold is cooled to
175.degree. C. while maintaining pressure of 250 psi before
removal. Cooling is performed to resolidify the thermoplastic film
for better tooth shape retention. This is necessary with
crystalline thermoplastic materials that have very sharp melting
points and low melt viscosity.
EXAMPLE 2
[0075] Eleven layers of 2.1-mil (0.9 mm total thickness) Dartek
SF502 polyamide 6,6 thermoplastic film, having a peak melt
temperature of 260.degree. C., are placed in a mold with the
modified EPDM body rubber as in Example 1. The materials and mold
are placed in a bag mold under a pressure of 200 psi. The mold is
brought to a temperature of approximately 240.degree. C. as quickly
as possible (about 8 minutes) to soften the film, form the teeth,
and cure the body. Rapid heating is required to obtain good tooth
formation before the body cures. Then the mold is cooled to
200.degree. C. under pressure before the belt is removed. The
resulting belt exhibits excellent tooth formation and adhesion, but
with limited flexibility because of the brittleness of this
polyamide film. It is expected that a total film thickness of 0.1
to 0.2 mm for this polyamide film would make a sufficiently
flexible belt.
EXAMPLE 3
[0076] Twenty layers of 1-mil (1.2 mm total thickness) Capran 100
polyamide 6 thermoplastic film, having a peak melt temperature of
220.degree. C., were placed in the mold with the body rubber as in
Example 1 and 2. The materials and mold are placed in a bag mold
under a pressure of 250 psi. The mold is brought to a temperature
of approximately 210.degree. C. to soften the film, form the teeth,
and cure the body. Then the mold is cooled to 175.degree. C. under
pressure (250 psi) before removal.
EXAMPLE 4
[0077] Three layers of 10-mil (1.2 mm total thickness) Grilamid
L25FVS10 polyamide 1,2 thermoplastic film, having a peak melt
temperature of 174.degree. C., were placed in the mold as in
Examples 1, 2 and 3, but with a body rubber based on HNBR. The
rubber in this Example uses the same peroxide cure system as the
EPDM in Examples 1 and 2. The materials are molded in a bag mold
under a pressure of 250 psi. The mold is brought to a temperature
of approximately 180.degree. C. to soften the film, form the teeth,
and cure the body. The mold is then cooled to 150.degree. C. under
full pressure (250 psi) before removal.
EXAMPLE 5
[0078] Five layers of 5-mil (1 mm total thickness) Pebax 7033.TM.
polyether block amide thermoplastic film, having a peak melt
temperature of 170.degree. C., are molded with the body rubber as
in Example 4. The materials and mold are placed in a bag mold under
a pressure of 250 psi. The mold was brought to a temperature of
approximately 181.degree. C. to soften the film, form the teeth,
and cure the body. The mold is then cooled to 140.degree. C. under
full pressure (250 psi) before the belt is removed.
[0079] In yet another embodiment, jacket 30 comprises a polyester
thermoplastic film. Various types of polyester may be used.
Examples include, but are not limited to, the polyester copolymers
Hytrel.TM. by DuPont and Arnitel.TM. by DSM. Polyester
thermoplastic films are available in a range of grades with peak
melt temperatures ranging from approximately 148.degree. C. to
219.degree. C. Polyester films make very flexible and durable belt
jackets.
EXAMPLE 6
[0080] Six layers of 5-mil (1.2 mm total thickness) Hytrel.TM. 4056
copolyester thermoplastic film, having a peak melt temperature of
approximately 150.degree. C., are molded with the HNBR body rubber
as in Examples 4 and 5, but modified by substituting Vulcup for
Varox 130XL for curing at a lower temperature. The materials and
mold are placed in a bag mold under a pressure of 250 psi. The mold
is brought to a temperature of approximately 156.degree. C. to
soften the film, form the teeth, and cure the body. Then the mold
is cooled to 100.degree. C. under full pressure (250 psi) before
the belt is removed.
[0081] The HNBR formulation used in Examples 4-6 is as follows:
3 Therban C3467 100 (Bayer) Carbon Black 5 Zinc Oxide 10 Stearic
Acid 2 Plasticizer 5 Zinc Diacrylate 39 (Sartomer) Antioxidants 4
sulfur and 2.25 accelerators Varox 130XL 9 (Vanderbilt)
[0082] It should be understood that the invention is capable of a
variety of modifications and variations that will become apparent
to those skilled in the art upon a reading of this specification.
Such modifications and variations and equivalents are intended to
be a part of the scope of the invention as defined by the appended
claims.
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