Note: Descriptions are shown in the official language in which they were submitted.
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AN IMPROVED WINDSHIELD WIPER MATERIAL
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This invention relates to an elasto~er
composition suitable foe making windshield wiper blades.
More particularly this invention relates to a composition
comprising a fully saturated backboned elastomer, cucing
agent for the elastomer, reinforcing filler, and a hiyh
loading of graphite particulate.
~ indshield wiper blades may be molded ~com a
wide variety of elastomers including naeural dnd
synthetic rubbers, such as natural or synthe~ic
polyisoprene, butadiene, ethylene-propylene-diene rubbec,
neoprene or blends thereof. Most generally, however,
windshield wipers are made of natural oe synthetic
polyisoprene. In order for a windshield wiper blade ~o
operate propecly, the ~rictional drag of the blade across
the windshield must be low. It is apparent that, i~ the
feictional drag between the cubber and the glass ~an be
reduced, the wiper assembly will require less power to
operate. Likewise, reduclng the frictional drag of the
blades improves the wiping action since, as the drag
increases, there is a tendency toward chatteeing of the
blade as it is pulled over the glass. This is most
commonly a problem when the windshield is only marginally
wet and results in a streaked windshield ducing the
wiping cycle. Thus, the blade must have a low degree o~
frictional drag in order to move over the glass with less
effort and wipe the windshield more uniformly without
streaks. Blades made with some elastomers, e.g.,
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neoprene, possess a coefficient of friction which may be
low enough so that no t~eatmen~ to reduce the surface
friction of the 'olade is required. However, most blade
materials will require some treatment in order to reduce
theic surfa,ce ~riction.
Windshield wiper blades, typically made of
polyisoprene, are generally treated by halogena~ing the
surface of the wiper blade with either chlorine or
bromine. The reaction of the halogen with the elastomer,
by means o~ the ethylenic unsatueation present on the
backbone of the elastomer, hardens the surface o~ the
wipec blade and thus reduces its friction. It is also
possible to reduce the friction of the blades by surface
treatment with an inorganic acid such as nitric acid o~
sulfuric acidO Still another way to reduce the friction
of a wiper blade is to coat the blade with a surface
layec of friction reducing material, e.g., molybdenum
disulfide, as is ~aught in U.S. Patent 3,080,596.
Another attempt to form windshield wiper blades
with improved wipe charac~eristics is described in U.S.
Patent 4,103,385. In that patent, the peocess of formillg
wiper blades comprises first treating the blade to harden
its suLface and then coating the surface hacdened blade
to lower its coefficient o~ friction, as for example, by
~ics~ treating the blade with chlorine, and thereaftec
applying at least one coating comprising materials
selected from elastomeric and plastic materials having a
particular Young's modulus. It is taught therein, that
whe~e halogenation is inaffective ~o increase sureace
hard~ess, as in the case of blades made of
ethylene-propylenediene rubber ~i.e., because it is a
saturated backboned elastomer~, a first coater would
a~ply a hardened layer on the sur~ace of the blade, and
then a second coater would apply the coating comprising
the elastomeric and plastic matecials.
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HoweveL, while such c~atings applied co
windshield wipers may be effective to lowe~ the
Erictional drag of th~ blade, the coatings may be wocn
of~ with use. Additlonally, commonly ernployed windshield
wipers, made o~ unsaturated elastomers such as natucal
rubber, are subject ~o chemical changes caused by
environmental attack of the blade by, e.g., ultraviolet
ligh~, heat, oxygen and ozone during use. The6e ch~3micaL
chang~s in the elas~omer, generally by means of rea~tions
at t~e unsatura~ed sites, change its physical
propertias. Consequently, the blade ~ay stick to the
windshield, losing particles when ~orn loose, and begins
to harden and take a set so ~hat it does not confocm well
to the windshield curvature. This results in a marked
deterioration of the wipe cha~acteristics of the wiper
blades, necessitating their replacemerlt.
This invention is directed to an impro~ed elastomer
composition which may be formed into windshield wiper
blades and cured, which blades have a low coefficient of
friction and excellent environmental durability. The
composition comprises an intimate mixture of (a) 100 parts
by weight fully saturated backboned elastomer, (b) curing
agent for the elastomer in an amount sufficient to cross-
link the elastomer, (c) at least 25 parts by weight par-
ticulate graphite, and (d) reinforcing particulate filler.The composition can optionally include other materials
conventional to windshield wiper compositions.
Preferably, the saturated backbone of the compo-
sition comprises or consists essentially of ethylene-
propylene- diene rubber (EPDM), the curative comprises an
accelerated sulfur curing system, and the composition
contains between about 50 and about 100 parts by weight
particulate graphite (based on 100 parts by weight EPDM).
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Advantageously, windshield wi~ers made from the
composition ~aught in ~his application display excellent
environmental degredation resis~ance while additionally
poss~ssin~ better compression s~t and ~ower f~iction than
that o~ conventional blades made o~ natural rubber. The
environmental stability of the elastomer ~mployed in this
invention results from its not possessing reactive
unsaturated site~ in its backbone, which sites are
susceptible to environmental atSack.
Another advantage of the windshield wiper blades
fo~med from the compo~ition of this invention is ~hat.
since the ~riction modifying graphite is incorporated
into ~he composition as compared to conventionally made
windshield wipers whose surface has only been treated to
eeduce friction. the frictional prope~ties of the blades
of this invention a~e not subject to change a~ the
surface is worn off with use. S~ urther, the
windshield wiper blade made from ~he composition of this
invention aepear to wear uniformly and thus even with
ext~nde~ use, ~he wipérs continue to provide good wipinq
characteristics.
The present invention also includes a method for
making windshield wiper blades, which method comprises (A)
intimately mixing together a composition comprising (a)
100 parts by weight of elastomer having a fully saturated
backbone; (b) curing agent for the elastomer in an amount
sufficient to crosslink the elastomer; (c) at least 25
parts by weight particulate graphite; and (d) reinforcing
particulate filler; (B) forming the composition into the
windshield wiper blades; and (C) curing the composition of
the windshield wiper blades.
ïhe invention is directed to an elastomer compo-
sition suitable for use as windshield wiper material and
to a method of forming windshield wiper blades~ Windshield
wipers made From this composition display improved environ-
mental durability and lower friction than those of conven-
~ ~f~ s~t~tt
tional natural rubber blades. The composition of thisinvention is characterized in that it comprises fully
saturated backbone elastomer material, curative for the
elastomer, particulate graphite and reinforcing particu-
late filler. Each of these components, as well as optionalmaterials which may be included in the composition, will
hereinafter be discussed in detail.
The composition of this invention comprises l00
parts by weight of a fully saturated backboned elastomer,
i.e., an elastomer wherein the backbone contains no
double bonds. Many such elastomers are known to one
skilled in the art. ~xemplary of numerous such
elastomers which may be employed in the composition of
thîs invention are ethylene-propylene-diene rubber
(EPDM), which are commercially available as ~pcar (a
trademark of and available from Polysar Ltd., Sarnia,
Canada); Royalene (a trademark of Uniroyal, ~anugatuck,
CT.); Vistalon (a trademark o~ and available from ~xxon,
Houston, Texas): Nordel (a trademark of an available f com
DuPont, Wilmington, Delaware); and Epsyn (a trademark of
and available from Copolymer, Baton Rouge, La.). Other
suitable sa~urated backboned elastomers include ethylene
propylene rubber, available, e.g., as Epcar (trademark)~
Royalene (trademark~ Vistalon (trademark)~ and ~etsyn
(trademark). Saturated nitrile elastomecs whic~ may
similarly be employed include, but are not limited to
Therban (a trademark of and available from Mobay
Chemical, Pittsburg, Pa.). Still other saturated
backboned elastomers comprises chlorosulfonat~ed
polye~hylene, available commercially as ~1ypalen, (a
tLademark of and available from DuPont~.
The saturated backboned elastomer employed in
the composition of this invention may also be a mix~uLe
of two or more different ~ully saturated backboned
elastomers, such as those described above. The ela6tomec
composition of this application pre~erably compcisest
ethylene-propylenediene rubber, either in total or in
pact. In additlon to the sa~urated backboned elastomec,
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the composition of this invention ma~ include a mi.noc
proportion o~ unsaturated backboned elastomec, e.g.,
polyisoprene as a modifying elastomer. However, in order
to maintain maximum environmental durability of the
bl.~de, it is most p~eferable not to include any such
unsatucated backboned elastomer in the composition.
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The composition of the this application also
includes curative foc ~he elastomer in an amount which is
sufficient to crosslink the elastomer. The selection o~
the particular curative and the optimal amount to be
employed for a particular elastomec composition is
dependan~ upon, e.g., desired physical properties,
compatibility with blade ~orming process, as is known to
those skilled in the art, and thus such selection would
be within the skill of those in the art. Typically, such
curatives include but ace not limited to, sulfur
systems, e.g., conventional sulfur, e~ficien~ and
semi-efficient accelerated sulfur systems, peroxide
curatives, etc. Such systems being well known in ~he
ar~, and are widely dsscribed in literature, e.g.,
"Vulcanization and Vulcanizing Agents", ~. Hof~man,
Maclaren and Son~ Ltd., London, 19670 For the pre-
~erred embodiment EPDN elastomer, an accelerated sulfur
curing ~ystem is pre~erred.
Graphite is incorporated into the elasto~er
composition in order to reduce the fciction of the
composi~ion employed in forming the windshield wiper. Tn
order to sufficiently reduce the fciction to a level
acceptable for wiper blades, at least about 25 parts by
weight particulate gra~hi~e must be incorporated in the
elastomer comeosition (based on lO0 parts by weight of
the fully saturated backboned elastomer). In one
preferred embodimen~ of ths elastomer co~position,
wherein the fully saturated backboned elastomec comprises
EPDM, the elastomer composition preferable comprises
b~tween about 50 and about lO0 parts by weight n~
graphiee particulate, per lO0 parts by weight o~
saturated backboned elastomer in the composition. 'rh~
.
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pacticle size of the graphite employed in the composition
o~ this invention is not limited to any particular
particle size. Mixture of particle sizes may also be
employed. More particularly, the optimal par~icle size
to be employed in the invention composition would be
sugges~ed in p2rt, by the method o~ manufacture o~ t~e
blades. Selection of pre~erred par~icle size would bc
within the skill o~ those in the act. Graphite is
readily comme~cially available as, for example, Dixo~
1176 and Dixon 200-42 (Trademark of and available ~rom
The Joseph Vixon Crucible Co., Je~sey City, New Jersey).
Another component of the composition o~ this
innvention is reinforcing particulate filler, which
comprises organic or inorganic particulate, oc mixtures
~hereof. Examples o~ preferred organic and inorganic
particulate include carbon blacks, zinc oxide, fine
particle calcium carbonates, silicas and silicates.
Pre~ecably, the reinforcing particulates comprises
carbon black. Generally, reinforcing paeticulate levels
in the composition comprise betwel~n about 15 and about
lOd parts by weight, based on 100 parts by weight of the
saturated backboned elastomer.
l'he preferred carbon blacks have an average
particle size of 20-60 nm (nanomete~s) and are employ(?d
in the composition from aboue 50 to 70 parts ~er hundred
parts of rubber. The selection of optimal type and
amounts of reinforcing filler would be within the skill
o~ one in the art.
The elastome~ composition which is employed dS
windshield wiper maeerial may optionally include othl?~
ma~erials commonly employed in such formulations. l'he:;e
optional mate~ials include non-rein~orcing ~illers such
as CaC03, clay, etc.; cure activators such as StO-ILiC
acid and zinc oxide; processing aids includinq napthenic
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oils such as Cieco*light rubber process oil and Circosol*
4240 (both available from Sun Pe~roleum Products, ~kron,
Ohio) and other additives such as de~sicants like CaO.
Antioxidants may be included in the composition. While
5 it is known that, e.g.~ in compounding ethylene-propylene
type rubbers, added antioxidants may not be required,
they may be bene~icial in many cases. Antioxidants
include, e.g., polymerized quinolines, hindered amines,
phenols and ~he like known in the art.
Windshield wipers are genecally made by
exteusion, transfer, or compression moldiny. A mastee
batch of the elastomec composition is first intimately
mixad together, generally in a Banbury type mixer or on
two roll rubber mills, genecally the curative being
15 incorporated last, whereafter the composition is for~ed
into wiper blades and cured. As is known in the act,
when blades are made by extru6ion, teansfer moldinq or
compression moldinq, the blades are made in a tandem
condition, whereafter the product is slit to provide a
20 pair of blades and the slit edges become the wiping edgl~s
of the blade when in use. The method of making the
composition and forming the windshield wiper blades from
the composition o~ this invention is not limited to any
pacticular method. As is well known to one skilled in
25 ~he art, such forming conditions as well as composition
embodiment may be varied (wi~hin those claimed) to obtain
wiper blades with suitable optimal characteeistics.
Industrial AP~licability
It should be appaeent from the foregoing that
30 ~he elastomer composition of this invention finds
application foc use as windshield wipec matHrial.
* - Trademarks
The following examples are presen~ed by way o~
description of the co~posi~ion of this invention and set
forth the best mode contempla~ed by the inventors but are
not to be construed as li~iting. All amounts employed in
the following Examples are in parts by weight.
Exam~e_I
Windshield wiper blades were compression molded
~rom the following compositionl:
Royalene 5021 loo
Statex M_702 119
Circo li~ht R.P.o3. 11
ZnO 5
Stearic acid
Dixon 1176 graphite 100
2-Mercapto benzothiazole thiazole 1.0
Tellurium diethyldithiocarbomate Q.8
Te~ramethylthiuram disulfide 0.~
Vieentamathylene thiuram hexasul~ide 0.8
SulfuL 0.8
This compound has a compression set o~ 14%
compared to 11% for a natural cubber compound. ~'riction,
as measured by moni~oring wiper motor current, is 35%
lower than ~or a NR (natucal rubber) blade. This blade
had a wipe quality o~ 7.5-8.0 on a scale o~ 1-10 (10
25 being excellent).
mark of Uniroyal-
Trademark of Cities Service Co., Columbian Div.,
Akron, Ohio.
Available from Sun Petroleum Peoducts.
30 ~Tra~emark o Joseph Dixon Graphite Co.
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Example II
A series of wiper blades were made from
compounds having varying levels of graphite to study
graphite loading on ~riction and weae. The compounds are:
~ IV
Epcar 585 100 100 100
C-~lack N-650 v~O 70 70
Zn~ 5 5 5
Stearic acid
Circo light R.P.o3 11 11 11
Circosol 42403 49 49 49
Vixon 11764 75 50 25
2-Mercapto benzothiazole 3 3 3
Tetramethylthiuram disulfide .8 .8 .
Tellurium diethyldithio-
carbomate .8 .8 .8
Sulfur .8 .~ .8
Dipentama~hylene thiuram-
hexasulfide .8 .8 .8
It was found that, decreasing the graphite,~
increases f~iction which ~esults in increased wear and
abrasion. At 25 phr friction is comparable to or
slightly greater than for a ~R blade.
.
Tradename of Polysar Ltd.
ASTM designation, carbon black.
3Tradename of Sun Petroleum Products
~Tradename of The Joseph Dixon Gcaphite Co.
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Fix~ e III
~lades were made from two difEerent compounds
which employed dif~erent particle size graphite in order
to study the effect of particle size on Eriction.
V VI
Epcar 585l 100 lo0
N- 3472 70 50
ZnO 5 5
Stearic acid
Circo light R.P.O ll ll
Ci~cosol 42403 ~9 49
Dixon 11164 75 -/s
Dixon 200_424 75
2-Mercapto benzothiazole 2.0 2.0
Tetramethylthiuram disu]fide .8 .8
Tellurium diethyldithio-
carbomate .8 .8
Sulfur .8 .
Dieentamathylene thiuram
hexasulfide .8 .8
Tradename of Polysar Ltd.
2ASTM designation, carbon black.
3Tradename of Sun Petcoleum Products.
4Tradename of The Joseph Dixon Graphite Co.
Windshield wiper blades made from these
materials exhibited comearbale frictional properties.
_xample IV
As evidence of the durability oE these
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materials, a windshield wiper blade of compound VIII
described below was made and subjected to 500,000 cycles
of a durabili~y tes~, during which the blade was exposed
to a cycle o~ water spray comprising 40 seconds on and 20
seconds off. The initial wipe quality of the blade was
'~.0 on a scale of 1-10 (10 being excellent) and after 1
million cycles it still had a wipe quality of 5Ø
VTTI
Epcar 585 100
N-347 .50
ZnO 5
Stearic acid
Circo light R.P.O 11
Circosol 4240~ 49
Dixon 200-424 75
2-Mercapto benzothiazole 20
Tetramethylthiuram disulfide .8
Tellurium diethyldithio-
carbomate .~
Sulfur .8
Dipentamathylene thiuram
hexasulfide . a
Tradename Polysar Ltd.
ASTM desi~nation, carbon black
3Tradename of Sun Petroleum Products.
Tradename of The Dixon Graphite Co.
Example V
The choice of manufacturing method may ofLset
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certain propeeties and suggest the optimal choice oE
elastomer cure system, as one skilled in the art would
know. For example, if one was compression molding
blades, a composition such as IX would produce blades
with compression set of 14% (ASTM D-395 - method B, Z~
hrs. @ 70C). Whereas if one wanted to extrude a blade,
a compound like X might be chosen which cuces faster but
has slightly poorer compression set of 17%. In both
cases, the compression set is better than the 19--20%
observed with natural rubber.
Com~ound IX
Royalene 502 (EPDM)l lOO
Statex M_702 (F~E~ Black Oil) 119
Circo Light Process Oil3 ll
ZnO 5
Stearic Acid
2-MeLcaptobenzothiazide
Tetramethlthiuram disulfide0.8
Tellurium diethyldithiocarbamate 0.8
Dipentameth~lene thiura~ hexasulfide 0.8
Sulfu~ 0.8
Dlxon 11764 graphite lOO
Tradename of Unioyal.
Tradename of CiCes Service Co.
3Trademark of Sun Petroleum Products.
4Tradename of The Dixon Graphite Co.
Com~ound X
P~pcar 585 (EPDM)l loo
ZnO 5
~2~$~5~
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Statex M-70 119
Circo light R.P.0 11
Stearic acid
Dixon 11764 graphite 75
2-Mercapto benzothiazole 3.0
Tetramethylthiuram disulfide 0.8
Tellurium diethyldithiocarbomate 0.8
Dipentama~hylene thiuram hexasulfide 0.8
Sulfur 0.8
Tradename of Polysar Ltd.
Tradename Ci~ies Service Co.
Tradename of Sun Petrolem Produc~s
Tradename of The Dixon Graphite Co.
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In view of the disclosure, many modifications oLthis invention will be apparent to those skilled in the
art. It is intended that all such modifications which
fall within the true scope of this invention be included
within the terms of the appended clai~s.
