CA2054267A1 - Electroviscous fluid - Google Patents

Abstract

ELECTROVISCOUS FLUID

ABSTRACT

The electroviscous fluid according to the present invention comprises a dispersion of wet-method particles having an average particle diameter of 10 to 500 micrometers and having a pH of not greater that 6.5 in an electrically insulating fluid. The fluid of this invention are characterized by a substantial increase in yield value at low voltages and excellent shear stability.

Description

SE~T BY~ P~T~ EFrr. ;10-~-91 :11:21AM: ~C PAlEN~ DEFYr.~O~LIYCST~ATfN~;#
L~

TllO~ISCOU~ l~LUID

The pr~n~ ~ention xelates to ~n eloo~rovi~ou~ Xluid which cc-mp~i~e~ a d~per~lon o~
we~-metho~ ~ilica particle~ in ~n el~ctrically insulating ~luid .
Fl~its who~e vi~co~ity can be v~ried b~r the ~ppli~atit~n of an external volta~e h~v~ receivet at~ent~on in the la~ s~eral year~ beca~s~ they may be u~ed ~or applic~ion~ ~uch a~ drive power trans~isgion, irapa~t ab~o~ption, val~re- like behavi~r, and ~o forth.
811C~ flu~ whos~ Vi8~:0~ity i~ incre~ed by means of ~n el4ct~1c f~eld ~re ~enerally called "elec~craviEcou~ flui~l~". H~weve~, in a~der t~ be abl~ to ~th~tand th~ ~eYere ~e~ic~ in, :Eo:r example, a clutch~
~n~Sine ~ount ~ or shoc1c absorb~r ~ a fl~id i~ rsquired which und~rgs3es ~ ~ub~t~nt~al increa~e ln yield v~lue at low volt~;e~ .
Varlou~ typ~ o~ th~se ~luid~ ha~e al~eady been pr4posed, and they are typi~ied by, Por ex~nple~
di~p~r~ianc of por~u~ inor~sanic partiel~s ~e. ~. ~ sili~a, alu~na, ~alc) in an ele~t~ all~ in~ulatin~ flu~d. In ~a~h ca~e, through the f~Jrma~ion o~ electric~$ do-sble lsyer by m~ans of w~t~r ~dsorbed s~ he part~le surac~s, the pa~icle~ becom~ ~r~ent~s~ in re!!spon$~ to an external ~lectric ~ield and th~ ~vi ~o~ity increa~ re ~pecifically, ~che fluld i~ convert~d into ~ Bin~ham fluid, which exh~bit~ a yi~ld ~alu~). Th~ Eeci~ is c~lled ~h~ "~1in~10w e~e~t"~ Tlle ~ollowitlg di~ad~ant~g~s have been ~3sociated with ~ a- ~a~d gL~ctro~ ~cou~
~lui~: they 1~ave limlte~ ~pplicatt o~ te~peratu~es (~pproxim~t~ly l~C t~ 8~)C), they a~3r~to ~h~ surrountinf3 machlnery, ~nd l:he particl~ f~ s~diment. Still, SENT EIY:DCC PATE~T DE~. ;10-'74-91 ;11:21.4~ C PAl~ DEYr.~X)NLll'lKiSTl~ATHY~E~ 3 2 ~O~?,g7 ainc~ sllica i~ ea~ily ~bta~ned ~n an indus~rial ba~i~
and 1~ hi~ly ~u~ceptibl~ to improvament and rnanipulation, it ha~ b~en o~n~idered pvtentiA~ly llse~ul fox cert~in secto~s of ~pplication~ ~or exaDple, ~achinery whi~h would be u~ed in ~ room temp~rature ~nvironment and ~h~h ~oul~ unde~go littls ab~adin~
motion. Silica-~ased ele~trovisco~ ~luid3 ar~ closed in Unit~d Skate~ Patent ~umber 3,047,507 and in Japanese Patent Appli~a~ion ~aid Open tK~kai o~ Unexamined~ Num~r 61-44g~8 ~44,~98/86}, bLlt in ~ach cas~ the9~ e~hibit an lmpractically weak Win~low effe~t.
The pre~ent i~v~ntor ~arried o~t ex~en3i~e inv~tigations with a view to Yolv~n~ ~he ~fo~e~entioned problem~, ~nd discoYere~ a re~ult that the afore~en~ioned problem~ are ~stanti~.ly reduced ~y the use o~ ~ parti~ular type oi~ wet-met~od ~ili&a in ~uch ele~ctro~ cr:~u~ flui~s. The pretl*nt ln~ention was d~velope~ ba3ed on thia di~covery.
It ~ sn ob.~ect of the p~:e~nt inven~ion to intxod~ce ~n ~lectrovi~ou~ f~lid which e~hibitB
e~ccelle~t prop~rties, Por ex~ple, whi~h unteT~oe~ a sub~t~n~cial lncre~se in yield v21-le at low ~rolt~ge~.
~ he obje:~t ~f thi~ inver~ti~n i~ al~ to provide an elect~oYiscous fluid which co~prises dixper~ion of Wet- meth~d 8ilica particle~ in an electrically insulatinE~ id 1 ~ut whi~h i~ . urtheI~
characterized by wet-met~od ~ilica ~ ticles ha~rin~ an averaee p~rtic~e dia~tQr ~f 10 to 5(~0 micrD~er~ an~
having a pH not ex~:~edln~ 6 . $ wheh tested ~ a 4 percent aque~lJs ~u~pen~
Fi~,ure 1 reporc~ the rele,tion~hip betw~en the ~h~r rate ~nd ~he~r ~tres~ ft>r th~ elect~viæc~u8 ~luid prepared ;n lçxçlmple l~ ~nd Fip~ur~3 2 rep~rt~ t~o l~elation~hip b~tw~sn th~ ~hs:qr ~at~ and ehear ~tr~ for SEI~iT BY:~CC PATENT DEFYr, ;1~-2~-91 ;11:7~4~: DCC PATENT ~EYr.~i~LINGST~ATHJ~ 4 3 2~5~2~

the elect~viscous fluid prepar~d in Comparis~n E~c~mple .
The pr~nt ~n~e.s)t:lon ut~lizels wet-method silic!a pa~tic!le~ which ~Pmpri~e th~ sential component or ithparti~ trong Win~luw ef~ect:. Theae wet-methot 9illca particle~ a~ prepared by the pxoduc~l on oP ~ilica by ~he add~iorl of a~id undeI~ wet cc~nditions ~o Wate~
glas~ starting r~a~erial. ~he~ w~t-method ~i~ica particle~ ar~ ~n ideal flisper~:e pba5e fo~ el~ctr~vi~cou8 fluid~ becauæe thei~r ~urfaces pos~es~ a la~er Gi~ a~l~orbed wa~er, which i~ ldoal for the dev~lopm~nt of t~e Winslnw ef~ec~, and ~cau~;~ they have optimal par~icle SizeB.
'rho a~er~e pa~ticle ~ize sh~ul~l ~all within the rang~ of LO to SOO microme~ex~ and pre~erably fall~ within the range o~ 50 to 2~0 micrt~m~ter~. When elle pa~ ize is 1~5 than lO ~icr~met~r~, the part~cle~ exhi~it a la~ge orientabili~y~ ~ut the interparticle ~orce~ a~e ~mall and a ~atl~Pactory ~visco~ity will no~ be achieve.d. On the other hand, at parti~ ize~ in e~es3 o~ 500 micra~e~er~, the orientability i8 diminiYh~d and the thickening af ~ect is ~duced . tlareover ~ ~ SlUCh dimen~ion~, ~he p~tic:le size it~elP b~ins ~o po~e ~i~niicant proble~s. The particle ~hap~ should be a~
clo~e to truly ~pherical as po~si~le, When ~e particle~
~ubstantiall~ de~iate fr~m sph~rical ~ ~he ~ffecti~
int~ r~lcle ~:ontact ar~a declin~38 and the coh~iYe o~ceo ~ th~n wesk. With reg~r~ to the p2~ticle ~ize d~tribu~lo~, th~ ~rro~e~ the l~ett~, The p~rticle orientabili~y bec~ cre~singly ~ o~ a~ the particla dl~t~ibutioll ~ecome~ narro~e~ ~hic:h provit~ or a m~re efPicient viscosity ri~. V~iot~ m~thod~ can be devi~d ~or t1~ ptoduc:tion o ~i~ica p~rticlex which have narrow p~tiol~ dlst~ibu~i~n and a~e a~ clo~e t~
sph~ric~l as po~ible, but su~h particles are ob~aine~

SENT BY Dcr PATE~T DEF~ 24-91 ;11:22.4~ PATE~r D~.~GOnLIN~;STP~

2 ~ 2 ~ ~

mainly b~r ~e~ ing a ~uitsbl~ dry~ng proc~s. For example, ~pray dry~ g m~thod~ ~e id~al.
In ~diti4n to l:lhR p~oEI~rtie~ cl$scu~ed al~ove, the quantit~ o ion in ~et-method silic~ particles i~ alsc) a cxucial ieactor in ~ rmining th~ ma~itude of the Winsl~w effect. ~ile not limi~ing the present inven~ion witll ~ny particular ~heory, the inYen~O~
b~llev~ th~t the prin~ipal ioll p~ nt in ~he silica i~
'ch~ ~odi1lm iun, and this 1~ mainly th~ ces~ f~om the sodium ion u~ed or neut~alizstion o~ the sc~l~d acid p~e~nt a~ an ir~purity in '~ha water gla~s s~ca~tin~
~at~rial. Accordingly~ the 1uidity o ~he 3ilica i~
g~ve~n~d b~ th~ raagnitude ox~ thi~ q~ tity o sodiu~n 7on.
~c~ording to ~xper~ment~ by ~he ln~entor, t~e pre~en~e ~r~e lon in the~ silic~ brin~s abos~t a .reta~dation in partiole ~rienta~iotl. A cle~r ~c~nple o~ th~ 9 ph~no~enon is the insltabllity in ~hear ~t~e~ at a con~tan~ or variab~ shear rate that i~ obs~rved when an e1ectric field is applied to an e1a~trovi~co!ls f~llid prepared by the di~per~ion of fre~ i~n c~ntai;lin~ w~t-methnd ~ c~.
In the ~a~e of free i~n- contaill:Lnl;; particle~, this ia thought ~o be due to ~ cr~a~o in the tim~3 r0quired for ~;rientatiorl o~ ~he randoolly distrib~ d particle~ d~e to 'ch~ rel~4ti~ely lon~ a ~oclat~d wi~h io~ m~remen~.
The roslllt 18 the appe~rance o~ inatabili~y under dynamlc c~nclitic~ns. I~ 19 f~r tlli~ re~nn ~ha~ w~ methoci ai1ica :partic1~ deplated o~ Pre~ i~3tl ~e. 13., ~odi-lm lon~ etc.
ar~ ~pti~al ;EQ3r the de~Je1~pm~3nt o~ a usefu1 Wi~low effec~. Purl! weé-metho~ si1ica pa~ticle~ genera11y e~h1b1t ~luidity 1n the aoid ~giorl, i. e., acldic 3il~ca i~ id~al~ The fluidity index a~ccrdinE to the pr~nt 1n~rention is ~h~rac~cerized by the ~llowing: th~ pH of the 4 weight per~nt aqueou~ pen~ion o~ ~h~ si1ica pax~ s m~ not exceed 6 . ~, a~d more p~eferably ~oæs SENT ~Y:~ P~T~`~IT DEYr. ;10-24-91 ;11:22A~; ~CC PATE~T DEE~,~CO~ ~Sl~hTHY~lE;Y~;~ ~

2 ~ ~
.

nc~ ceed ~.S. A use~ul Win~l~w ef:Eect doe~ not appear at pH v~l~b~ in exc~8~ ~f 6 . 5 . In order to obtain we!t-method 9ilica psl~ticleg which h~ s~ch Çl fluidil~y inde~, tb~ exce8~ sodillm ion ~u~t be ~em~ d to the maximllm po~sible extent, orI alternatively, a pure water ~S:Ia~ w~ich ~ontain~ o~l~r trace~ o ~olid ac~d mu~ be employaA a~ the ~tarting ~a~rial. T~e pH of the wf~t-m~thod ~ilica p~rticle~ ~re te~ted in a 4 weight peI~cen~C ~llql~U8 8u~pen~ion prior to addition af lche p~ticle~ tn th~ electrically in~ulatin~ ~luid.
No ~peci~ic le~triction~ are plac~d on ~he wet-method silica partlcles ~mlployed b7 the praaent irnrenticn a~ loslf; as they ~ati~ the condition~
di~cu~se~l æbove. Th~y ~ ,r be ~elected ~Otll among commercial wet-method ~ particle~ r example, Nipsil A~-S fr~M Nippo~ Silica Ro~o K~bu~hiki i~ai~ha and itc ecluivalents.
The olec~rovis~ou~ ~lu~d accordin~S to th~
pre~ent invell~ioA con~pri~ea ~he disper~ion of wet-methot cilic~ parti~le~ ~ de~cribed hereinb~i~ole in an eJ.ectrlcally in~ tinp, fluid. Howeve~, t~e ele~tric~lly insul~tin~ ~luld it~el~ i9 no~ p~rticularly ~estrict~d as long ns i~ is ~ liq~i~ a~ roo~n te~per~ture ~lld i~
electric~lly inaulat:inE. ~uch alectrically insulatin~
fluitls ~re ~Ice~plified by miner~l o~ dibutyl ~bacate, ~hlorinated pa~f~in~, fl~t>rine oils, ~nd ~ ne oil9.
Amon~ th~ preceding, $ilic4rLe ~ are pr~ferre~ ~or the~r ~tron~ ~lectric~l in~ulatio~9 lo~
te~per~ture-dep~ndent ~i~cos~ t~r v~iatio~, and s~ ~ort~.
~h~ ~ilic~ne oil~ are e~;e~pliiEi~tl h~ ~he fluid diorgah~poly~ilox~nea with the ollow~ng ~herQical stru~ur~:

SENT BY:~C PATE~T DEpr~ 24-91 ;ll 2aAN; DCC PATENT DEE~.~O~LIhY~ST~4TflY&HE~E;~ 7 2 ~ 7 R R R
R~ O~--~SiC)~n~

wh~rein e~ah R denotes A ~unovalent hyd~Rcar~s~n group a~
e~mp~ .ed by ~lkyl ~roup~ ~uch a~ thyl, ethyl, a~d propyl ~ an~ axyl ~Srs~ups ~uch a~ phenyl. It i~ pref~rred that ~t least 3~ aP ~he }~ ~ro~p~ are ~thyl ~roups.
M~reov~r, whil~ tlle de8~ee of polym~ri~tion c-~ n is not pa~tlc~la~l~ speci~ied, lt i~ preerabl~ that n to~ not exce~d l,O~Q it~ order t~ a~hie~r~ a pr~L~tical visco~it~
ran~e. Value~ not escceedin~ 100 ~re cyen more pr~ferred.
Sllicone oil6 wi'ch thi8 fl~ctur~ a~e a.railable in the fo~n oP ~ l~rge ~umb~r cf comme~cial prod~cts, or example, SHZ~O ~rom To~ay 130w Co rnin~ Silicone Company 9 Li~it ed .
Fu~thermore, among the æili~on~ oils ~lur~o~lkyl- ~on'caininE~ diorg~nopaly~iloxane~ a~
particularly pre~err~d bec~u~ they enhance t~e Win~low ef~ect and i~hibit the pasticl~ ~edi~ntation ~au~ed by speci~ic g~avl~y di:~fer~nce~. The~e ara concretely ~pre~ed by th~ ~ollowis~E~ 3tr~Jctural f~mula:

~ o~m~ }p~

whe~eiII R i~ ds~ined a~ above, ~c2 i~ a f!l~broa~ group ha~in~ 10 o~ ~ewer carbone, and ~ and p are i nteger~ with Yalues not e~cceedin~ 1, 000 .
The ~t:t~uctu~ o~ tlhe a~o~r~m~nti~necl l::clO
r~luor~alkyl group i~ not particula~ p~3cified, but the 3,3,3- tri~ orop;rc~pyl 13roup iu pref~rsed from ~he ~tandpoint ~ ~a~e oi~ ~ynth~ . In ~sder to obtain a ~ub~t~ntial enh~nc~ment o~ th~ Win$10w e~ec~c, it will be : :.

, SE~;~ BY~ PATE.~T DE~. ;10-24-91 ;11:23A,~ PA~T DEYr.~;O~llLINCSTRhTHY&lENDE,# ~

2 ~ ~

preferable or e~ch molec~le to contain at l~as~ 30 mole percent ~ oroal~yl ~roup. Purthermore, methyl should ~omp~i~a at l~ast 30% of th~ R group~ frotn the st~ndpoints o m~terial ~cguisition ant ~conomics. While the d~gree of p~lyme~rizatl~n m is a~ain no~ particularly ~pecified, it pref~r~bly doe~ no~c e~ceed 1,000 in o~de~
to Dchie~e a practical v~co~ity rango. V~lues not exc:eetlin~ 100 a~f~ even moxe prei~erred. The mech~nissn by wh~h the ~luc~ro~lkyl gro~lp enh~nce~ the Win~low e~ect is n~t cle~r. ~ile not limiti.nE~ the pr~ent invention w~th any pa~cula~ th~ry, ~]~e inYentOr bolleve~ that 13 3tronl3 intr~nolecl~laa~ dipola is eenerated ~y the ~imu~taLneou8 p~once in ~he ~o~l ecule oP ehe electxon~gative ~luorine a~om a~d electropositive ~ilicon atom separated by a ~uit~ di~tanoo. eOlariz~tiOn ~f the double ~ayer i~ then p~omoted hy conthct betwe~n thi~
dipole ~nd the ~lect~ical ~ouble laye~ on ~che w~t-me~hod ~ilic~ particl~. Oth~rwise, fluorine-contair~ing ~luicl~
tend to have la~gex speci~ic g~a~iti~s, ~hiah results in 8 concc~si~ant 1nh~b~tloll of ~ilica particle~
sedilnent&tion. The~e fluoroalkyl-containin~
dior~an~p~ly~iloxan~ are commerclally sv~ilable, for e:l~ample, a~ FS126S rom ~or~r Oow Corl~inE~ Silicone Gool~aIIg Limited .
The ~l~ctro~i~cou~ fluid ac~ording to th~
present inven~cicm campri~es th~ di~peroion of w~t-method ~lllca pa~tîcl~ as ds3c~1bed hereinbeore in ~n el~3ct~ a:1 ly ins~ lng ~luid a~ de~cri~e,d he~ein~e~ore.
The qu~Ltl~ity di~persed ~hould Iall within the ~ane~ v~
0.1 to 50 w~igh~ pe~cent ~nd p~e~ lbly is in the ran O:e 10 t~ 40 weiE~ht percent. A ~atisf~ctory thickes~in~
e:~ect l~ not ~btained ~t 1~5 than 0.1 wei~ t percent.
At value~ e:cce~din~ 50 w~ight p~rcent~ the viscu~ity o~
the el~ctroviscou~ 1uid i~ ~o ~ub~tan~cial~ lncres~ed a~
~ be impr~ ctical .

âENT BY:~C PAT~iT DEFYr. ;10-~4-91 ;;i:2~.4M; D~C PAT~T D~.~ STRATHY&HE~

2 ~ 3 ~ 2 The ~lectrovi~otls ~luid according to the prexent ln~ention a~ ~e~c~ibed ahove i~ u~eful a~ the wo~king oll or function~l oil ~n par~icular typen o ~chinery, ~n~ ~xampl~, machinery whiah will be emplo~ed in ~h~ v~cini~y o~ ro~m tq~mperatur~ ~nd wl~ere there will be little abra~inB m~ ion~
Th~ pr~s~nt lnventlon w~ll be ~plalned in ~reate~ de~ail bolow throu~h the use o~ illu~trative and ~o~p~rison e~le~ he e:~ample~, part~ = welght p~rt~, c~ = cen~i~toka~, ;nt th~ si~ the va~e at 25~.
~ rha el~tro~i~c~ behavi~r ~88 la~a~ur4d as foll~ws. The te~t f~ d w~ placed in an aluminum cup (intarior diam~te~ ~ 4~ milliDl~ter~ into whi~h an ~lu~nin~n~ rotor tdielmeter = 40 mm, length ~ ~0 mm3 was ~tlb~Aquently in~erted. Th~ resultin~ ~ylindrical cell w~9 ~ek up ~re~ all~, ~d the cup wa~ lin~arly acc~lerated ~rom a ~hca~ Iate (D) o~ 2ero to 330 ~ 1 oYer 40 3e~:0t~5. Durin~s ~hi~ period, th~ torqu~ applied to the rotor wa~ m~a~r~d wi'ch a torque ~en~or, ~nd thiY wa~
converted into th ~hea~ ~tr~ S) ~nd l:h~ D-ve~ s-S
cur~re was draw~ on ~n X-Y reco~d~r~ I~ s,d~lition, the rotor ~qa~ tri~ally ~3,round~d and ~-vo~u~-~ cur~e~
we2~e ~ recorded while appl~i~g ~ dire~t-curr¢nt ~olt~g~ to th~ cup. The inter~acti~n ~ th~ ext~apolation o~ ~he linsar sa~ment with th~ 5- a~ wa~ te~ignat~d the ylald val-le ~t the psrtic~lax ~ld ~tr~ngth. Ths s~cabi~i~y oi the oheas~ ~tres~ a~t th~ ~Qdi~ntab~lity of th~ wot-method ~ilica particle~ were fll~o ~amin~d.
In ~hQ ~ llowing e~ar~ples all amoun~ ~parts Qnd percentagæ~ ) al~e by weigh~ unles~ 2tho~
in~icat~d .

, SE~T BY:~C PATE~rr DE~ 2~ 24.4~ C PATE~r DEfYr.~O~LI.~K;5rR~l~E~;#l~

2 ~

Exanllp~~e 1 15 ~art~ w~-method ~ilica partic~es (Nip~il AQ-S ~cm Nippon Silica RoE;y4 Ka~u~hiki Rai~) wi.th an ~v~ra~ q~ pa~ticle siz~ o~ LOO micrometers and a pH of 5 .
to ~.5 tpH wa~ te~ted in a 4 woiE~ht pe~ent ~queou~
~It~p~nsio~ w~ acld~d with ~ti~rinf~, to 8g parta alipha~c hyd~ocarbon oil with a vioco~ity o$ 100 C9 ~ubb~r Swclling Oil lat). 3 ~or~ Nippon Sekiyu Kabu~hiki Kai~h~) 'c~ af~ord s,n electrc7Yiscoll~ f~uid in ~he f~rm o~ a ~u~pens~.on ~n which the w~ m~thod ~ilica p~icle~ w~re di~p~rs~d in th~ aliphati~ hydroca~bo~ ~il.
1~he ~l~c~rovl~cou~ bQhavior of thiY flui~ wa~
than n~ ured, and the mea~gure~ent ~ ult~ are rep~t~d in Table I and P~gure 1 be10w. Tho three line~ ln Fi~5ure 1 repre~ent the~ yi~ld ~allle~ te~ted at 0, ~, and 2 ~/nn~.
I:xa~le 2 1~ E!a~ts w~t-met~d ~illca pa~ticlec ~Nip~il A.Q-~ ~ronll Nippon Sllic~ Kogyc Kabu~hiki Kai~ha) wi~h an aY~rage pirticle siz~ of lOO oaicrometQ~ and pH ~ 5.S to 6 . 5 tpH wa~ in ~es~d in a 4~ wei~ p~rcent aque~u~
~u~pen~ion) wa~ Added with ~ti~r~n~ to 85 part~
trim~thyl~i10~y-t~rminated polyc~imeehylsilw~ane (vi~co~ity ~ l()O C8) to give an elQccroviscou~ ;~luld ln which the we~ thos~ 8i~ wa~ unifonnl r di~p~rsed in 'ch~ polydimethyl~iloxane.
The ~l~ct~oYi~ceu~ b~h~ior of thi~ fluid w~
'chen mea~ed, ~d th~ ~eaa~rem~res~llt~ ar~ repo~ted in Tabl~ I be~ow.
xampl~ 3 ~n ~lectrovi~c~u~wa9 pr~pared ~L~ in E~caople 2, bu~ hi~ u~ing ~rimeth~ 03ly-termlnated poly(~ethrl-3., 3, ~-tr;~luo~opropy1)~ ;all~ (vi~oo~ity -300 c~ ln plac~ of the p~ly~im~tl~yls~lo~tane tvi~co~t~ ~

SENT BY:~C PA~ENT DEM. ;10-24-91 ;11 24h~ CC PATEt~T DE~.~WLINGS1R41HY~DE;~11 2~42~
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1~0 cs~ u~d in Exa~pl~ 2. Th~ properti~ of thi~ fluid e n~asu~ed a~ in Exa~ple 2, Qnd ~he~q measur~eht r~lt~ ~r~a repor~ed in Tabl~ I be~w, Com~a~n E~
An elect~ovi~cous l!lu~d wa~ prepared ns in E:~campl~ 2, ~ut ln th~ ca~ u~ wQt-l~ethtsd ~ilica particle~ (Nipsil L- ~00 rom Nipp~n ~ilica P~og~o Kab~hiki ~a;~l~a) with an ~IVQ~ pa:rticl~ ~ize of 4 ~aicr~e~ers ~nd pE~ - S.S to ~.3 (pH ~Rain wa~ ted in a 4 w~i~ht percent aqueou~ ~u~p~si~n) in p7~e o~ the we~-~ethod oilica particle~ with ~v~x~ga parti~le s~e =
lW mic~om~r~ u~ed in Exampl0 2. ~e prop~rt~e3 of this 1u~d we~e measured a~ in E~ample 2.
m~as~lre~eslt re~It~ ar~ also reportf~d in Ta~le I.
CoDIparison lE::~ampIe 2 ~ n el~ctro~iscoua ~luid~ wa~ prod~ced a~ in Exampl~ ~, but ln thi~ ~:a~Q using w~t-~thod ~illca part1cle~ (Xip~il NA-R ~rom NippQn Silica ~E~ l~abu~;hiki ~aisha) with an ~Yeraee part~cle 8iZ~ of~ 8~ microDl~sers and pH ~ 10 . O to 11. 0 ~tested 1~ a 4 weight pe~rcont ~q~l~ou~ pensio~ in pl~ce of the ~t-~th~d ~ilic~
~ith avera~e psrti~ isse - lOQ mic~o~e~ers ~od in E;~nple~ ~. The ~l~ctr~Yi~cous bel~rio~ of thi~ ~luid wa~
then measured, and the result3 r~po~ted b210w in T~
~nd Figure 2 were ~ained. A~ain, th~ ~h:~ee lines in FigUrQ 2 rep~es~nt the yield value~ t~ at 09 1~ and 2 KV/~

.

SEh~ RY:DOC; PAl~ UE~. ;10-24-~1 ;11:24~7~ C PATI~T ~I~.~O~LINGSTRATHY&}IE~ 12 .
, 11 2~2,~ 1 Tabl~ I
_. . .. " , .. _ _........ . _ __.
yleld v~luo ~P~ llhe~r str~ particle 1 KVfnu~ n ~tability ~iment-~blllty _ ........ ~__ ~.. _ __ Bxanple ~ 170 280 highmoderat~

~xan plo 2 220 460 highmoder~te ~xampl~ 3 ~ao ~so h~ gh low .
~anlp~rison 110 ZOO h i gh rnoderate ex~mpie 1 co~p~rison 160 230 low modera'ce ~x~ 2 .
.. _._..... ,. . .~ . _ .........
The ~ca~le~ delin~ated he:~einabove ~how t~e ~lect~u~riscou~ $1uid ac~ordil)g to the p~resent ~ tion which ~mplo~s wot-method ~ a p~ticlQs with an ~rer~g~
p~rti<~le eize o~ 10 tn 500 ~lr~on~eter~ ~nd a p}~ (~ytsog~n ion ~oncentrati~nj n~ e~c~ing 6 . 5, wherein the pH of the ~ot- mothud ~ilical. particles wa~ ~teste~ ~n a 4 welght perc~nt aque~ls ~u~p2~0n p~ior to addit~on of ~he :~
p~rticle3 ~o ~h2 the ~le~trically insulating 1~ . Th~
~luid2~ of the~: in~v~nt~h di~pl~y exc~llent elet::~xov:l~cous b~h~io~ i.e., ~ b3tankial iLnc:r~a~e i~ ~i~ld ~valu~
lo~ vol~ge~ ~nd an ~ n~ ~h-~r ~tabillty.

,' :

:

Claims

CLAIMS:

1. In an electroviscous fluid comprising a dispersion of silica particles in an electrically insulating fluid, the improvement comprising using wet-method silica particles having an average particle diameter of 10 to 500 micrometers and having a pH of not greater than 6.5.