CA1244582A - Windshield wiper material - Google Patents

Abstract

Abstract of the Disclosure This invention relates to an elastomer composition which is suitable for use as windshield wiper material. The composition comprises fully saturated backboned elastomer, curitive for the elastomer in amounts sufficient to crosslink the elastomer, and at least 25 weight percent particulate graphite, based on the weight of the saturated backboned elastomer. The particulate graphite modifies the frictional properties of the fully saturated backboned elastomer. The composition has excellent weatherability and low friction and thus is ideally suitable for making windshield wiper blades.

Description

:~'2~'~5~

AN IMPROVED WINDSHIELD WIPER MATERIAL
-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., .

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, t - 5a -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.

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 5~

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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-- 10 -- .

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 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 8~

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 ~2~5~

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~

- ~4 -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.
-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.

Claims (11)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. An elastomer composition which may be formed into windshield wiper blades and cured, characterized in that said composition comprises an intimate mixture of:
(a) 100 parts by weight fully saturated back-boned elastomer;
(b) curing agent for said elastomer in an amount sufficient to crosslink said elastomer, and (c) at least 25 parts by weight particulate graphite; and (d) reinforcing particulate filler.

2. An elastomer composition according to claim 1, wherein said fully saturated backboned elastomer comprises ethylene-propylenediene rubber.

3. An elastomer composition according to claim 2, wherein said curative for said elastomer comprise an accelerated sulfur curing system.

4. An elastomer composition according to claim 2, wherein said composition comprises between about 50 and about 100 parts by weight of said particulate graphite.

5. An elastomer composition according to claim 1, wherein said reinforcing particulate comprises carbon black.

6. Windshield wiper blades made from the composition of claim 1.

7. A method for making windshield wiper blades, which method comprises:
(A) intimately mixing together a composition compri-sing:
(a) 100 parts by weight of elastomer having a fully saturated backbone;
(b) curing agent for said elastomer in an amount sufficient to crosslink said elastomer;
(c) at least 25 parts by weight particulate graphite; and (d) reinforcing particulate filler;

(B) forming said composition into said windshield wiper blades; and (C) curing said composition of said windshield wiper blades.

8. A method for making windshield wiper blades according to claim 7, wherein said elastomer having a fully saturated backbone comprises ethylene-propylenediene rubber.

9. A method for making windshield wiper blades according to claim 8, wherein said curing agent for said elastomer comprises an accelerated sulfur curing system.

10. A method for making windshield wiper blades according to claim 8, wherein said composition comprises between about 50 and about 100 parts by weight of said particulate graphite.

11. A method for making windshield wiper blades according to claim 7, wherein said reinforcing particulate comprises carbon black.