Note: Descriptions are shown in the official language in which they were submitted.
1~7~34G
FIELD OF ~ INVENTION
me pre~ent inventlon relates to composltions of
polyimide po:Lymeric material and to a process ~or preparing
porous pol~imlde tructures from such cOmpo31tionB~
BACKGROUND OF THE INVENTION
Polyimides are known polymeric material6 and are
described in, ~or example~ U.S. Pa~ent Nos. 3,179~631 lssued
on Aprll 20, 1965 to A. L. Endrey;3,179,634 is~ued on April
20~ 1965 to E. M. Edwards and 3,249,588 issued on May 3, 1966
to W. G. Gall~ As descrlbed in the a~orementioned patents,
the polyimides are obtained by reacting speci~ied tetracarboxy-
li~ acid dianhydrides with specl~ied diprlmary diamines to
obtain intermediate polyamide-acids which may be converted by
any one o~ several suitable methods, such as chemical or hea~
treatment, to the corresponding polyimlde. Shaped structures
may be prepared from coalescible polyimide powderæ by hot-
forming or molding technique~ as de~cribed ln U.S. Patent Nos.
3,179,631 and 3,249,588 or by dlrect-~orming, ~ree-slntering
techniques described in U.S~ Patent No. 3~413,394 issued on
November 26, 1968 to T. F. Jordan. ~or instance, U.S~ Patent
~o. 3,179,631 de~cribe~ ~inely-dlvided polyimide powders having
a sur~acs area o~ greater than 0.1 ~quare meter per gram that
are coalesced into solid homogeneous object~ at pre~sures above
3000 psl and at temperatures in the range o~ 200C. to 500C.
Hereto~ore, porous structures o.~ coalesced polyimide resin
powder have been provided, ~or.e~ample, by compacting a poly~mlde : -
powder at a pressure level lower than the pressure u~ilized
normally for preparing shaped polyim~de structures by the
direct-form~ng technique thereby to provide a preform which
30 has sufficient structural integrity to be handled ~hysically~ -
and ~herea:fter sub~ectin~ sald preform to a heatinG sequence
at temperature~ abo~e 400C. in the absence o~ applied
2 `
r ~ .
.
pressure thereb~r to sinter the preform and provide a molding
or shaped structure having a density o~ le~ than 92~ o~ the
density of a no~mally, ~ully coalesced polyimide ~haped
struc~ure prepared by hot-foxming or molding techniquPs
5 (Prodllct l;icenslng Index3 Nc>ve~iber, 1970~. A si~i~i~ant
disadvantage and drawback o:E ~he above~scribed proces~ ~or
preparing porous polyimide shaped ~tructures i8 the in~bility
to prepar~ ~truc~ures havir~g adequate pore structure as3 for
ex~ple, in ~leeve or journal b~arings~ For exan~ , p~rous
10 sleeve bearings o~ polyim~de polyme~c material are ~abrica-
ted by compactlng a polyimide powder in a cored ~e assembly,
and in tha course o:~ such manu~actlAre, the sleeve bearing
sur~aces parallel to the pre~sin~ direction of the die assem-
bly are sub~ected to high frictional ro~ce~ along the walls
~ the die (inclu~ing the die core rod~ during the compactlon
and e~ection sequence of the molding operation with the con-
sequent re~ult o~ provlding ~leeve bearings h~ving sub~tan-
tially ~mooth surface~ and onl~ ~ew ~urface p~res o~ gener-
ally sma~ler s~ze than desired3 l.e.~ inade~ua~e pore st~uct-
ure; sueh sleeve bearings ha~e inadequate ~il capacity andoil ~low (~or l~lbrication.purposes) because ~ the inadequate
pore structure ~hereof. Accordinglyg lt is ~he principal
ob~ect of the pre~ent in~ren~ion to provide a co~posl~ion o~
coalesci~le polyimide polymeric mate~al and a process for
25 pr~paring por~us pol~imide sh~ped ~tructures fr~m such com-
poeitione ~h~t 0~2rcome and obv:iat~ the ~bove-descri~ed
drawbacke and limita~ion~
TE3 INVEIITION
A.cco~in~ to the present i~venti~n, there is provided
30 a compo~it~o~ co~ri~in~ a eoalesci~le polyimid~ powder and a
.
9713~
solld particulate polymer o~ ~ormaldehyde. The composition
of the invention comprise~ preferably a coalescible polyimide
pow~er and up to about 50~ by weightg based upon the total
compositlon weight, o~ a ~olid par~iculate pol~mer o~ ~ormal-
dehyde. In a pre~erred embodiment, the co~position o~ theinvention comprises a coalescible po~ylmide powder~ ~aid poly-
imide having the ~ollowing recurring structura~ unlt:
O O ~
" 11
- N / R / N- R'- _
\~ /
_ O O _ I .'
15 wherein R ls a tetrav~lent :rad~cal containing at least one
si~-carbon atom ring characterlzed by ben~e~oid unsaturation
and wherein the four carbonyl groups o~ ~aid recurring ~truc-
tural unit are attached to separate carbon atoms in pairs with
the carbonyl groups o~ each pair being attache~ to adj~cent
carbon atoms in said R ~d~cal3 and ~rhere~n Rl is a divalen~
aromatlc radical, and a solid part~culate polymer o~ ~ormal-
dehyde. In anothe~ preferred embod~me~t~ the composition of
the invention comprises a coalescible pol~Timide powder, said
polyimide having t~he recurring s~uctural ~ormula described
2~ :imme~iately hereinabove, and a solid particulate polymer of
uns~abilized poly~x~nneth~lene.
Accor~lng to the pres~nt invention3 th~re is further
pr~vided a method o~ manufac~ure f~r fabricatl~g porous poly-
imide shaped articles such as sleeve bearings or ~ournal
.~ 30 beari~gs which con~prises pressing a pre~ m b~ s~bJecting a
c~ position of a coalescible polyimide powder arld a solid
pa~ticul~e polymer o~ formaldehyd~ to a :~o~ming pres~ure of
~7~346
at least about 10,000 psi, and heating said preform to a tem~
peratur~ above 300C. to sin~er said preform a~d provide a
porous polyirnide sh~ped article having interconnecting
pores. In a preferred embodimen~ the method of the in~en-
5 tion comprises pressing a preform by subjectin~ a com~osi-
tion o~ a coalescible polyimide powder3 sald polyimide
having the recurring structural uni~:
O O
" "
lo t N / \ ~ Rl t
~t tl
O O
1~ wher~in R 1~ a tetrav~lent~radical con~ainig at least one
six-carbon atom ring characterized by benzenoid unsaturatlon
and wherein the ~our carbonyl groups o~ said recurring struc-
tural unit are attached ~o separate carbon ato~s in pairs
with the carbonyl groups of each pair being att~ched to
adjacent carbon atom~ in said R ~a~i~al; and wher~in R' is a
div~lent aromati~ radieal~ and a sol~d particulate polymer
o~ ~ormaldehyde to a forming pressure of at le~s~ about
10~000 psi, ~nd heating said pre~o~m to a temperature above
about 300C. to sin~er said pre~or~ and provide a porous
25 polyimide sh~ped arkicl~ havlng interc~3nnecting pores~ In
another pre~erred embodiment, th~ method o~ the inventlon
cvm~rises pres~ing ~ pre*orm by subjec~ing a co~po~ition o~
a coalescible polgimide powd~r, said polyimide ha~ng the
recurring structu~al unlt de~cribed immediately hereinabo~e,
30 and ~ solid particul~te polymer of un~tabilized polyoxy-
methyl~ne to a formin~ pressure o~ at leas~ abou~ 10,000 psi,
and hea~ing said pre*o~m to a temper~ture aboYe about 300C.3
- 5 -
.3~
to sinter said pre~orm and provide a porous polyimide shaped
a~ticle having interconnecting pores.
D: ZTAIIED DESCRIPTION
The nature and advantage~ of ~he con~position and
5 method o~ the present inven~ion w~ll be more clearly Imder-
stood ~rom the :ollowing more detailed description thereoP.
me composition o~ the pres~n~ inventiorl compri~es
a~ least two esser~ial con~onents, r~nely, a coale~cible
polyimide powder ~nd a 301id par~iculate polymer o~ ~o~
10 dehyde. The poly~mide polymeric m~tex~al o~ the col~position
o~ the invention is character~ed by the following recurring
structural unit:
O O ~
~I It
+ \XC/ ~ ~ ~
O O _
20 whéreirl R is a t~ravalent arvraatic radical contain~ng at
lea.st one ring ~ six carbon atoms charac~eri~ed by benzenoid
unæatura1;ion, the îour carbonyl groups o* said recurring
stxructural unit b~:ing attached to separa~e carbon ~om~ in
pairs w~th the carbonyl groups o~ each pair being attached
25 to ad~acent car~on atom~ in sald R radical3 and wherein R'
is a divalen~ aro~tic ra~cal~
The polyimides are prepared b~r reac~ing at least
one org~nic di~nine h~bviIlg the ~tru~tural ~ormula:
( ~2N ~R ~ NH2 )
30 wherein R' is a~ a~e de~ned and the ~wQ amino groups o~
said d~a~ine are each attachea to separate carborl a~o:ns o~
s~id aromatic ra~ical, w:ith ~ le~st one tetracar~x~lic ~c~d
dia}~ydrid~ ring the ~trllctural ~ormula:
:- , .
6 - :
~ o
\C/ \C/
Il 11
O O
whe~ein R is as above de~ined, ln an organic ~olven~ ~sr at
leas~ one o~ the reactarl~, the ~ol~ren~ being in~r~ to th~
reactant~, pxefe:rably u~der an~yd:~us condition~" ~or ~ t~me
and at a ter~p~rature below 175aO su~icien~ ~o ~oxm a poly- :
amide acld ~ich is then c~on~rerted by suita~le mean~ ~uch aæ
. . . .
by heati~ ~o the above polyimideO Sultable po~imideæ
~o~ the methsd o~ the prese~t lnY~ ar~ ~ho~e ba~ed upon~ :
~or e~leJ pyromellitic dla~ lride and 4,4~-o~yd~anilin~
or based ~pon 3,3',4,4l-benzophenone tetracarboxyllc dianhy-
dr:Lde and 4,~1~x~dia~1ine or ~etaphe~yle~edia~ne. Suitable
poly~;~des and powders ther~o~ ~re ~ore e~ens~vely de~eribed
in U.S. Pætent No~. 3,179,631 and 392~,5880 The f~ore~i~g
polgimide~ may be util~zed e~ther ~ gly or ir~ mi~rtures th~re-
o~ 1~ th~ C~o~it:~O~ t~i~ lrwbn~ion. T~18 pol~ lde pow~er
COII~priE3e9 ~4t lea~t 50% by ~l~h~ o~ th~ c~po3ition Q:~ the
in~re~kion when l;he eo~po~itio~ ls~ o:~ un~illed polyimi~e
and a p~lymer of formal~leh~rde.
The other essen~ on~ e~rt o~ ~he co~posit~on o~
the lnve~tic~ a ~ol~d ~ ula~e ~polymer o~ *~aldehy~e,
I
Polymers o~ }dehyd~ are more gerlerally denomin~ed p~ly-
acetal~ and include or are charactexized by a l~n~ar poly~ner
Chal~l coI~t;a~ g r~currix~ Ullit~ or g~l~5- me
. 1 30 pr~ erre~ polymer o~ ~ldehyde i~ the es~lt~Gn o:E the
i~vent~on 18 poly~Yymeth~rle~3 ~h:Lch hs~ ~ot bee~ ~tab~lized :.
a~i~t thermal aegr~da~lo~ as, ~or e~l~, by end-ca?pi~g
: _ 7 _
:, .
:
~7~3l~
the ends o~ the llnear polymer chaln with stabilizing end-
groups. m us, the pre~erred polymer of formaldehyde is para-
~ormaldehyde, whlch 1~ a lower molecular weight l~near polymer
avallable commercially as a fine p~wder. Polymers Q~ formal-
dehyde are described more ~ully in U.S. Patent No. 2,768,994
i~sued on October 30, 1956 to R4 N. MacDonald and are sold
under the trademark DELRI ~ by E. I. du Pont de N~mours and
Company, Inc. D~LRI ~ polymers usually have been stabilized
against thermal degradation but th~se polymer~ may be utilized
a3 is illu~trated in Example 2 herebelow. Suitable polymers
o~ ~ormaldehyde also include, for ex~ple) trioxane~ The
polymer o~ ~ormaldehyde compri~es up to about 50~ by wei~t
of the compo~it~on of the invention.
The composi tion o~ the inventlon may include~ in
addition to the coalescib~e polyimide powder and the solid
particulat,e polymer of formaldehyde J other additives and
materials adapted to be fabricated into shaped articles.
Suitable additives and materials ~or combining with the
coalescible polyimlde powder and the polymer o~ formaldehyde
include ~inely divided particulate materlals such as other
particulate polymers, e.g., polytetra~luoroethylene, and
finely dlvlded metals, metal oxides, minerals, carbon, graph-
ite, asbe~tosJ glassg mica, vermicullteJ kaolin and abrasive
partlcles such as 9ilicon carbide, boron nitride and diamorld~,
also including mixtures o~ any o~ the foregoing material~.
Addltive materials may comprise up to about 70~ by weight9
based upon the total weight o~ the polyimide and the addi-
tive materials in the compo~ition of the invention.
The compo~ition of the invention may be formed into
porous polyimide shaped ar~lcles by a direct-forming and free-
slntering method which comprisss sub~ect~ng the compo~ition
o~ a coalescible polyimid~ p~wder and a sol~d particula~e
j" ~
~ ~ ~
.. . . . ....
polymer of ~o~ldehyde to a compressive force o~ at l~ast
about 10,000 p~l, pre:Eerably 100,000 pei, at a te~?er~ture
pre~erably about room te~perature ~25C.) t,hereb~r to provide
a pre~orm and thereaf~ter heatirlg ~he pre~o~n to a te~perature
5 above about 300C~ to sint~r s~ld pre*o~n and prov~de a
porous pol~imide shaped a~ic;Le having i~terconnec~ing pore~.
~he h~ g step ln th~ method of the in~entlon both ~oal~ces
th~ pol~n~d~ po~der ln ~he pre~or~ an~ the~lly d~gr~deg
and ~epolymeriæss the solid pa~iculate polymer o:~ fo~al-
10 dehyde which is e~rolved in ga~eous fo:~m thereby leaving void~in the pre~o:~m to provide a porou~ polyimide ~haped article
ha~ in~rconnecting por~ Chus" the solid par~iculate
pol~rmer of fo~qnaldehyde in the co~positio~ of the invention
acts or ~unctions as a ~ugltive or translent fill~r which iæ
15 evol~red during th~ ltial hea~ing st~p of the method of
the inven~ion.
The he~ting se~uerlce o~ the method o:~ the inven~ion
may preferably be conducted in a step-wise marmer as ~ v~
iYlg the he~ing rate of the pre~orm în and throu~h more than
20 one heat~ng cycle. Speci~icall~g it is prefe:rable to he~
the pre:Eorm at ~ subæ~ant:lally u~fo:~m rat~ from room ten~pera
ture to about Bo~. by rai~ing the temperature o~ the pre~o~n
in increment~ o~ 5C. at thiF~y m:lnute interval~, and there-
a:Eter to c~ntinue heating the pre~oIm to & te~perature of
25 about 150C. a;t an incremen~al h~at~ng ~ate o~ 7C. per
hour, and therea:f~er to cor~inue heating the pre:fo~m at a
~aster ~e, e.g., 1-1/2C. E~er m:}~ute~ to ~ te~p~r~:l;ure oî
aboul; 400~. ~d the~ t~ intain the pre~o~ ~ the ~tter
te~erature fQr a ~uitable perlod QI time such a~, :Eor exa~ple,
30 t~ee hour~. q~e ~oregoing ~eating cycl~ precludes :inad~er-
te~ a~l/or unaesired c~acking OI the pre~orm structure. To
_ g _
3~
illustr~te, the solid pa~t.iculate polymer OI fo~naldehyde
deco~poses ~s by depolymerization to g~se~us fo~ldehyde
during the initial heating sequence of the method, and
release or escape o~ the ~ormaldehyde gas w~thout contain-
5 ment of the gaseous ~o~naldehyde in th~ preform is desirablesince, otherwise~ ~ormaldehyde gas trapped within the pre~orm
may develop- suffic:Len~ pressure dur:ing the he~tlng se~uence to
crack the pre~orm. For this reason, the concentration o~ the
solid particul~te polymer o~ ~o~maldehyde in the composition
10 and preform of the in~ntion should be su~icient t~ pro~lde
intercsnnected pores in the preform which provlde ~uita~le
pathwa~s ~or allowing release o~ ~he gaseou~ ~ormaldehyde.
The concentration o~ the ~olid particul~te polymer o~ ~ormal-
dehyde in the composition and preform o~ the in~ention should
15 be at least about 5% by wel~t, based upon the total weight oP
the con~position c)r pre~o~m, and prefer~bly ~etwe~n about 12%
and 30% by weight. Therea*ter, the pre*o~n is p~e~erabl~
heated to a tel~pe:~ture above a~out 300C. to coale~ce
the polyimide pa~ic~s and obt~n ~ porou~ polyim:ide shaped
20 a~ticle. ~he f`oregoing he~ting sequerlce has been ~und to be
~atis~actor~T :Eor prep~ring porous polyimide cylinders having
a dlameter of 1-1/8 inches and a height o~ 1-1/4 inches.
A sal~ent feature o~ the present inven~ion i8 tha~ :
the solid particula~e polymer o~ fo:~ldehyde pyroly~es cleanly
25 to Po~maldehyde ~;as ~na is evolved ~rom the prePo~ without
leavlng a ~ormaldehyde residue therein and w:itho~ e~ectlng
a ch~nge i~ the density o~ the polyimi~e phase o:E the pre-
~orm which coalesc~s si~ ltaneousl~ ~o provide a porvus poly-
imide shaped article. Thu~. the pore structure Q:P the pol~-
30 imide ~h~ped ar~icle corre~ponds s~ibs~an~ially identic~lly
: . . . : , . . . , : .
3~7
to the pa~icle size and d:istributlon of the ~olld p~rticul~t~
polymer o~ formald~hyde present originall~ in the pre:form.
me pore si~e o~ the porous polyimide sha~ed a:~icle may be
regulated as desired by util~zlng solid pa~icula~e pol~nners
o~ ~o~ldehy~e having varying and/or speci~ic pa~icle size.
For exa~le~ pa~ticulate polyme~s o~ ~o~ldehyde o~ ur~fo~
particle size may be u~ed) ~r mi~,ures of pa~lcul~e polym~r~
o~ ~ox~lde~urde o~ different pa le ~iæe m~y be util;lzed to
provide the porous polyimide shaped a~ticle~. Pa.ra~o~nal-
dehyde :in the ~orm o~ con~erciall~r available powder consls~s
o~ solid h~rd par~icles h~ving a ra~ge o~ pax~icle ~i3es
wi~h a typical avera~;e size o~ about 2~ 2S dete~qnined u~ing
a connnercial micromerograph. This analytical me~hod inYolves
a sedimenta~ion process using a gas as the sedimentation îluid.
The particleæ settl~ do~ the sedlmenta~ioll tube on~o a
balance pan and a graph of weigh~ ver~us time ~s obtained.
mrough proper calibral;ion, a continuous particle siæe d:1 s-
tribu~ion cu~ve is obt~ined for par~icles in the 1 to 250
size rarlge. ~e~e~ence: T~. Allan, "Pa:r~icle Si~ Measuremen~
2Q C~apm~n and Xa.ll, Iitdo.~ don 1968~, pg. 99.
I he paYrticles of par~:Eo~aldehyde are ha rd and non -
po:rous. ~nu~, ~he pores left in ~he porous polyimide mold-
ings ha~e the size and distxikution o~ the ~3riginal para-
fo~nald~hyde pax~icles in the pre~o~m~. The size and d:Lstri~
~5 bu~lo~ of pore~ an~ pore volume are thu~ ~ub,~ect to delibera~e
control~ If larger or smaller pores are desired, the para-
~o:~maldehyde po~der may be screened to obtain a l~rger or
small~r pa:~icle size i~raction~, Al~e~nately, the smaller
particles ma~r be remo~r~d ~y ga~ ~lutriation. ~3he~ larger
part~cl~s are desired ~han can be obt~ined ~rom the parafor-
maldehyde powder3 ~ e para~o~ldehyde m~y b~ gr~u~d arld
': ~
- 11 -
- - . . - . - - - : .. . .
3~
screened to the desired size. Pore vol~une is ~ontrolled
si~ly by the quantity o~ para~ormaldehyde used in ~he ini-
tial conposition.
The abo~e~e~cribed method o:~ ~he invention may be
5 used to make standard shapes o~ porous polyimide ar~ticles
such as rods, tubes and discs which may subsequently be
machined into a variety of ar~icles, or to fo~n directly
such articles as bush~ngs, electric insulators, gears and
bearings. An i~orta~t utility of porou~ polyimide shaped
10 a~ticles includes use as oil-~illed bearings which will be
illustrated in some o~ the ex~n~les herebelow.
The prin~ipal and practice o~ the present imrention
will now be illustr~ted ~y the ~ollowin~ exan~ples whlch are
exem~lary only and it is not in~ended that the invention be
15 llmited thereto since modifications in technique and oper~-
tlon will be apparent to anyone skilled in the axt. All parts
and percentages specified herein are by weight unle~s other- ~ -
wiee indicated,
The te~t specimens prepared in the following : .
20 Examples were evaluated ~n accordance with the follo~lng
proce~ures:
OIL IMPR~GNATION - The porous polyimide specimens were im-
pregnated with oil (a~ specl~iea in the Examples) by sub-
merging the porous specimen below the s~r~ace of the oil in
a clo~ed container at a temperature o~ nominall~ 150C. and
an absolu~e pressure o~ about 0.5 mm. Hg. The residence time
. . ~ .
under vacuum wa~ cont$nued un~il al7 evidence o~ air bubble~
emerging from the specimen ceased. ~ypic~lly~ the time
requlred was about 4 hours. At thls time, the vacuum was
broken, the heat to the oil was turned o~, and a~mo~pheric
- ..',:
~ ~ -12_
~ ~ 7
pressure was established over the oil v~a ~ nitrog2n blanket~
After a time interval o~ nomi~ally 16 hours J the specimen
was removed ~rom the oil, allowed to drai.n, and wa~ then
wiped clean o~ all traces o~ excess sur~ace oil. The aver-
age weight gain o~ the test specimen r~sulting ~rom oil
impregnation was used to calculate the precen~ of the total
porosity of the specimen th~t had been ~iled with oil.
W~AR TEST - The wear charact,eristics ~nd the coe~icient o~
friction of the porous polyimid~s w~r~ evaluated by mach~ning
standard thrus~ bearing te~t specimens using the wear testing
apparatu~ ~nd procedure descr~bed by R. B. Lewls in "Predicting
the Wear o~ Sliding Plastic 5urface~"~ Mach. Eng.~ 86, 32
(1964). The standard thrus~ bearing test ~peci~en each con-
sisted of a cylindrical di~c having (1~ a cylindr~cal body
1~ member of a diameter o~ 0.980 ~ O.OOZ inch ~nd a height
(thickness) o~ 0.10 inch~ and (2) a rai~ed annular ring on
one end of the cylindrical body member (the ba~ of the raised
annular ring was integral with the cylindrical body member)
h~ving an outer diameter equal to the diameter of ~he cylin-
drical bod~ member and an internal diameter o~ o,.840 ~ 0.002
inchg ~nd a height o~ 0~10 inch (measured from the end sur~ace
of the body member~. In this te~t, the wear test specimen w~s
secured in a ~el~-aligning mount und~rneath a revolvin~ ~teel
di~c. The steel d:Lsc wa~ loaded ~o a force of 50 lbeO which
produced a 250 psi loading on the 0,20 in,2 running surf~ce o~
th~ wear teæt specimen. The angular veloc~tg of t~e re~rolving
steel disc was controlled to provide 100 ft./min. velocity
on the ~ng sur~ce o~ the wear te~t specimen, thus providing
a PV (pressure x veloci~ ~ 25~000. The wear test was con- ;
;~ 30 ducted fo~ the indicated time periods, a:fter ~Jhich a~ ave:rage
., .
- 13 -
3~
coe~icient o~ frictlon and the wear factor were calculated
from the change in thickness o~ the test specimen~ The sel~-
aligning mount for the test specimen was ~upported ~n a nearly
frictionles~ bearlng assembly and the mount wa~ provided wlth
a lower arm e~tending horizontally outwardly there~rom adapted
to contact a mechanical stop member for preventing rotation
o~ the mount and the test specimen secured thereln~ me
coefficient of friction, ~ was calculated from thP equation:
~X
,u ~ ,,,
wherein F i~ the ~orce (lbs.) applied at a distance on the
lever arm X (in.~ ~rom the center o~ the te~t specimen su~ff -
cient to move the lever arm from the stop member, and N is the
force (lb~.) normal to the test ~pecimen, and R is the average
radius (in.) of the te~t specimen obtained by divlding the ~um
of the outer diameter and the inner diameter o~ the ralsed
annular ring o~ the test specimen by four (4).
: . '
I~XAMPhE
; The blends li&ted below of po~y-NtN'-(4,4'-oxy-
diphenylene~ pyromellitimide resin and para~ormaldehyde pow-
der were prepared by dry blendlng in a jar on rolls for about
5 minutes followed by dry blending in a blender, obtainable
under the trade mark "Osterizer", ~or approximately 1 ~inute.
Resin (g-)~ar~Sormaldel4~ (g-~
A 45 5
C 35 15
D 30 20
The resulting homogeneous co~positions were u~ed to prepare
- 14 -
~ ,
~B
..
disc pre~orms of 1 inch di~meter by 0.25 inch thickness by
compaction in a cylindrical mold at room temperature and at
a pressure o~ 1009000 psi. The prefo~ms were then thermally
cycled in a nitrogen atmosphere by slowly preheating the pre-
~orms to 80C. and therea~t~r heati~g the ~pecimens to 150C.by increasing the tempera~ure con~inuously at a r~te o~ 7C.
per hour (this stage o~ the he~ting cycle ef~eets remo~al of
the paraformaldehyde filler)g and thereafter heating the
specimens to ~00C. by increas~ng the temperatu~e con~inu-
ously at a rate o~ 1.5C. per minute3 and main~aining thespecimens at 400C. for three hours ~this ~t&ge o~ the
heating cycle e~ects sln~ring o~ the specimens)J The void
content o~ each disc specimen was determined ~rom the actual
density o~ the disc, as calculated ~rom its dlmensions and
weigh~, and th~ fully compacted density of 1.43 g.Jcc. The
disc specime~s were impregnated with Sunvis 31 hydrocarbon ;
oil as described above, From the weight of oil absorbed and
its density ~o.86 g~/cc.~ the volume o~ oil a~sorbed was cal-
culated and used to determi~e the percent VQidS filled. The
results are zumm~rlzed ln the table below.
, .'
. .
- 1~
~7~L3fl~6
~,
~n
CO ~ "~
O rl Or~co r~
OC c
~ ~ ~O~
S ~ ~ ~D ~ O~
d ~~
rl O ~ ~00 3r--
;~ OO O O
~ ~ J ~
3 ~O
O~ O u~ ~ : ' "' ' '
O rl C~ Jt~
~~
OO O r-l
r_
D
U~
~ . .
r~ rl 0
O
t~J r~
rl tU(~) 3
t~ O
~ ~1 c~r~ 3 0 ~
r~ U~ c) t~ C) J al
r~ O a~ 00 0
bD .. . . O
~d r~ r-l O O r-( ~
. .
. C) X rl
~~ O ~ ': ~
~ O ~ ~ ~i "'.,
S ~` ~ :1 r-~ .
J b~ bl c 3 0.1 r~ ~1 O ...
, ~ o oo ~ o i~ ~
:~ ~ ~ ~ ~ ~ ., .
.' ~ ~ ~o '. '':'
~:i ~ O ~ ~ r~
rt ~ >
t~J ~ N
:~ rl ~ t~ 00 C~ C~ ~ C ~
O ~ ~\1 N N N I r-l O : . -
r~
CO ~ S: O
C ~~ r-l rl(X:) 3 ~ r-l
Nfr~ t~l 3
rl r~ ~J N N N r-l
_ . . . . r~l 11
O O O O ~i .,
r-l
h N O C~ O N 1I r~
E~ r/ a~
' O O O O 11 ~ ~, '
t9~
~ ~ .
¢f:4 C~ D C)
- 1 6 ~ .
. :
':
7~3~6
EXAMPLE 2_
60 grams of solid particulate end-c~pped poly~ormal-
dehyde (DELRI ~ 500) were added to 900 millll~Tters of N,N7
dimethyl~ormamide in a round bottom ~lask of two liter capa~
city having a ~tirrer, reflux conden~er and a gas inlet tube
connected thereto~ A bubbler~ obtai~able under the trade mark
l'Primol" D, was connected to the top o* the conden~er and
nltrogen was pa~sed throu~h the s~tem for 45 minute~ to purge
the air therein. The stirred 31urry was then heated using a
heating mantle until the bolllng polnt of the solvent was
reached and the polymer dis~olved. me heating mantle wa~
turned o~ and the solution wa~ st~rred during cooling. A
~luffy polymer pr0cipitated to produce a thick slurry requir-
ing an increase in the RPM of the stirrer. The polymer was
recovered by filtration uslng a medium frit Buchner funnel,
re~lurrying with acetone, filtration~ and drylng overnight
in a vacuum oven with nitrogen bleed at 80~C.
A blend of 17.5 grams poly-N,~'-(4~4'-oxydiphenylene)
pyromellitimide and 7~5 gram~ ~lu~y polyformaldehyde obtained
by precipitation a~ above deRcribed was prepared by ml~ing
dry in an Oeterizer blender ~or 1 mlnute at high speed ~ollow-
ed by wet mixing for 10 minutes with enough acetone (about 65-
70 ml~.) to make a smooth mix. The mixture wa~ filtered
and dried in a vacuum oven with nitrogen bleed at 90CO for
4 hours. The mi~ture contained 30~ by weight poly:formalde-
hyde was compacted in a 1/2~' diameter cylindrical mold at a
pressure of 100,000 psi to produce disc pre:~orms. The pre-
~orms were heated ~n a nitrogen atmosphere at a rate o~ about
1-1/2C.jmin. to 150C., then at a ~low rate to 200C. over a
640 minute period and ~nal~y at 200C. ~or 3 hours. The
- 17 -
l3~
avera~e weigh~ loss of the preforms was 30.48~. The porous
preforms were then free ~intered by heating ln a nitrogen
atmosphere at a rate of l-l/2C./min. to 400C. and then
maintained at this temperature for 3 hours. The porous discs
were removed ~rom the oven and they had lost an average of
32.43~ of the original w~ight, corresponding to an approxi~
mate void volume o~ 32%,
EXAMPIE 3
A blend ~as prepared by dry mix~ng 40 grams of' the
polyimide resin o~ E~amp3~e 2 and 10 ~rams o~ p~a~ormaldehyd~
powder in a blenaer de~ice operat~d at high shear ~or 1 min-
u~e. Disc pre~orms 1/2" in diam~ter were prepared by compact-
ing samples of the m~xture at 1009000 psi and the pre~orms
were subj~c~ed to a thermal cycle consisting of a gradual
heating to 150C. in ~n atmosphere o~ nltrogen over a period
. .
o~ 13-14 hours ~ollowed by heating a~ a rate o~ 1/2C./m~n.
to 400C~ and then maintaining the preform at 400C~ for 3
hours. The average we~gh~ loss of the pre~orms was 2}o 11
correspondlng to an approximate vold ~olume of 21~.
'
~XAMPLE
Example 3 was repeated except ~hat the pre~orm~
were compacted using a pressure of 509000 pæi. ~uring the
overall thermal cycleg an avera~ total weight loss of 20.85
occurred.
EXAMPLE 5
A mix~ure o~ 4.60 gram~ o~ the polyimide resin of
Example 2 a~d 0.40 gram para~orm~ldehyde powder was dry
blended in ~ 2 ~z. wide mou~h jar o~ rotating roll~ for 2
hours. The blend wa~ pre~ormed ~nto 1/2i' disc~ uslng a
pressure o~ 100,000 psi. me di~cs were con~erted to porous
- 18 -
~ 3 ~ ~
moldings uslng the thermal cycle of Example 3. The a~e~age
overall weight loss was 9~76%o
EX~MPLE 6
A blend was prepared by dry mixing in a blender
device 38 grams o~ the polyimide re~in o~ Exam~le 2 an~ 12
grams o~ Pluf:P~T polyfo~maldehyde precipitated from a 6.6,Q~ by
weight solution. Porous discs were prepared as in Exa~ple 3
with an ov~rall weight los~ o~ about 24.2~. A porou~ cylinder
1/2" in diameter and 1-1/4" long was also made. Weight loss
10 w~s 24~2~ The dlmensions o~ the cylinder were m~asured and
the density wa~ calculated to 2how a void volume o~ 29~. Por-
ous ~ensile bars made uslng the same ~abrication technique
had a tensile strength of 3400 psi and elongation of 2a~ as
measured usirlg the procedure og~ ASIM-E80
EXAMPLE 7
Flu~y polyformaldehyde precipitated ~rom a 6.6
by w~ight solu~ion was screened through a 140 mesh sieve
(U.. S. Bureau of S~andards ) wl~h openings o~ 105~. A blend
wa~ then prepared ~m 7~ grams o~ the poly~ormaldehyde
wh~ch passed through the si~ve~ 7.5 grams o~ paraformaldehyde
powder and 40 grams of the polyimide resin o~ Example 2 by
dry blending in a mixer ~or 20 seconds. A total o~ lO disc~
approximately 1/2" in diamete~ and 0.2~1 thick were pre~o~med
at 100.,000 psi pressur~ A~ter a the~ï cycle of 16 hour~
in a vacuum oven wlth nitrogen bleed at 86C. and 20 hours
at 150C,, the average weight loss was 1301~. One disc had
- ~mall cracks on the ed~e. me pre~orms w~re sintered b~
heating at a rate o~ l-l/2C. per minute ln a ~itro~n atmos-
phere ~o 400C. and maintaining ~his tem~erature ~or 3 hours~ :
The edge cra~k n~ted pre~iously did not enlarge and no ~ddit~onal
~-
~ 3
crackin~ was observed. The average weight lo~æ for the en~ire
cycle was 27.25~. The dimensions of the dis~s were measured
and the a~rage density was calculated to be 1.016 ~rams/cc.
corresponding to a void volum8 0~ 29~.
EXAMPIE 8
A blend was prepared by dry mixing in a blender
40.O grams o~ the polyim~de re~in o~ Example 2 and 10 . O gram~
of the fluffy poly~ormaldehyde o~' Exampl~ 7. The blend waæ
used to prepare 10 preform discs o~ 1/2 inch diameter by
compact~on at 100~000 psi. The ~hermal cycle of ælow heating
to 200C. (19.2~ average weight lo~s) ~ollowed by free sin-
tering at 400C. as in Ex~mple 7 yielded po~ous discs ha~ing
an average over~ll w.e~ght loss o~ 20.31~ The dimensions
of the discs were me~sured and thè average density was calcu-
lated to be 1.086 grams/cc., corresponding to a void volume
o~ 24.1~.
EXAMPLE 9
A blend was prepared by dry mixing in a blender
43.0 gramæ o~ the po~ de re~in of Exa~ple 2 and 7.0 gra~ns
of fluX:~y polyf`o~ldehyde which w~s precipitated f`rom ~
6.6~ solution by weight and screened throu~h a 200 mesh sieve
(U.S. Standard~ hav:lng 74~1 openings. Pref'o~m discs 1/2 inch
in diameter were con~pacted at 100,000 psi and put through the . .
the~mal cycl~ o~ Example 2. The calcul~ted ~roid voluDle o~
the porous disc~, based on dimensions and weights was 18~.
. .
EX~PLE 10 . .
A blend was pr~d by dry mixing in ~ blender ~or ~-
3~) seconds 20.0 grams of poly N,N'-(4,~'~xydlphenylene~ pyro-
mellitimide containing 20.0% by weight of graphi~e and 5.tO ~.
- 30 grams o~ the flu~fg polyfo~aldehyde used in Eacample 9. Discs
,
::
2~ -
~7~3~6
1/2 inch in diameter were preformed using a pressure o~100,000 psi and heated using the thermal cycle of ~xample 2.
Based on calculations of volume us~ng dimensions of the pQrous
discs, void volumes of about 25.1~ were calculated. Discs were
impregnated with a perfluorinated polyether oil, (obtainable
under the trade mark ~Krytox" 143 AD (~peci~ic gravity o~ 1.91)),
by submerging the dlscs below the sur~ace of the oil wh-Lle main-
taining a temperature o~ 150C. and a pressure within the con-
tainer o~ about 0.5 mm. EIg ab~olute. When bubbles ceased
emerging ~rom the disc, a~ter about 4 hours, the vacuum wa~
broken with nitrogen and atmospheric pressure was establiæhed
over the o~l surface~ After about 16 hour~ the discs were
removed from the oil, allowed to drain and were wiped clean of
traces o~ excess sur~ace oll. The weight gain resulting from
the impregnation indicated 80.4~ of the voids present had been
filled with oi~.
EXAMPLE 11
A blend of 80 grams of poly-N~N'-(4,4'-oxydiphenylene)
pyromellitimide resin p~wder and 20 grams of uncapped poly-
~ormaldehyae powder was prepared by dr~ blending for 30 secondsat low ~peed in a blender~ The resultlng homogeneous compo
sition was used to prepare disc pre~orms o~ 1 inch diameter
by 0.25 inch thickness by compaction in a cylindrical mold
at room temperature and at a pressure of 100~000 pæi. The
disc preformæ were then converted into porous moldings by a
thermal treatment o~ 16 hours at 80C. under a vacuum of
25 inches ~g to remove the pvly~ormaldehyde filler followed
by heating at l l/2C./min~ to 400Co which was ma~ntained
for 3 hours. The density o~ the re~ultin~ moldings showed
~5.5 percent porosity. A porous molding was subsequently
machined to the dlmensions of a standard thrust washer wear
21 ~ ~ -
~L~7~
specimen which was then impregnated with "Krytoxl1 AD ~43 oil,
81.8~ o~ the available porosity was ~illed with the oil. The
oil-~illed specimen was ~ub~ec~ed to the wear test for 775
hour~; the average coe~icien~ o~ ~riction o~ the te~t speci--
men was 0.174 and the wear ~ctor ~as 2~73 ~ 10 10 (in.3-min~/
ft.-lb.-hr.).
F,XA~LE 1_
Example 11 was repeated except para~ormaldeh~de
po~der w~ used in place of uncap~ed poly~ormaldehyde to
generate porosity~ The wear test specimen h~d a porosity
o~ 22.7~ ~d 2~.6~ of the a~ailable pores were filled with
"Krytox" AD 143 oil du~ing lmpregnation. After 930 hour~ o~
test t~me the specime~ showed an average coe~icient o~
~riction o~ 0.171 and an averaga wear factor o~ 1.20 x 10 10
1~ (in.3-min./~t,-lb~hr.).
EXAMPLE 13
Example 11 was repea~ed except that rela~i~ely
large p~rticles o~ uncapp~d polyfo~m~ld~hyde ~100-200~) were
employe~ ~o gen0rate porosity. The wear t~st ~pecimen showed
a porosity lev&l of 23.8% and 7~2~ o~ the available porosity
wa5 oil-filled during im~regnation with "Krytox" ~D 143 oil.
A~ter 320 hours of testing, the wear specimen showed an
ave~age coef~icien~ of ~riction o~ 0~185 ~nd an a~rage wear
~actor o~ 6~.~ x 10-1 (in.3-min /ft lb hr )
. :
EXAMPLE 14
Example 12 was r~p~a~ed ~xcept that the polyimide :
r~sin used als3 con~ained graphite a~d p~lytetr~f'luQroeth~lene
at ~ominal levels of 13~ and 10~ by~weight, r~specti~ely. The
~; wear test 3pecimen had a porosity of 27.9% and 9098~ o~ the
a~ail~ble porosity was oil-~illed duXi~ lmpreg~ation with
.
- 22 -
37~L3~
"Krytox" AD 143 oil. A~ter 5820 hours o~ run time, the speci-
men showed an average coe~ficient o~ fYiction o~ 0.11 and an
average wear ~actor of 002 x 10 10 (in.3~ . -hrO ).
E~
Exan~ple 14 was repeated with a specimen having a
porosity of 2803~ ~nd 89.,3~ o~ the available porosity o~ the
spscimen was filled with Sunvis 319 a hydrocarbon oil. A~t~r
4248 hours o:~ wear testing, the ~pecimen sho~ed an ave:rag
coef~icien~ of ~riction o~ 0005 and an average wear ~actor
of` 0.1 x 10 10 (in~3-min~/~. -lb. -hr. ) .
EXA~IE 16
Exar[~ple 12 was repeated except that 30% by weight
of para~o~naldehyde ~Tas used instead of 20%. The wear test
specimen had a po~osity o~ 31.~% and 86.1S~ oi~ the available
porosity wa~ oil-~llled du~ng in~pregnatlo~ w~th "Krytox"
AD 143 oil. Af~er 774 hour~ o~ oper~tion the specimen showed
an aver~ge coe~iciPnt o~ ~riction o~ 0.198 and an average :-
wear ~actor o~ 3.76 x 10 10 ~n.3-min./~t.-lb.-hr.).
An o~1 impregnated porcu~ bronze thru~t washer
~machined to size ~rom br~nze3 oil-~illed washer available
commerclally from Boston Gear Division3 Norkh American
Rockwell, Quincy, Massachusetts~ we~r tes~ specimen was
e~aluated under identical conditlons o~ testing ~æ described
~or E~ample~ 16~ A~ter 1~2 houxs of operation this
specimen ~howed an a~erage coe*~icien~ o~ ~rict~on o~ 0.054 : .
and an average wear *~ctor of 0.5 x ~0 (in~3-~in~/~t.-lb.-
hr.). Several hours later the test specimen ~ailed catas-
trophically. ~our other oil impregnated porous brvnze bear~
lngs were tested under th~ same conditions described before
and all ~ai-ed catastrophically wlt~in 2~ to 250 hour~ of
te~ting.
- 23 -
3~6
The procedure o~ ~ample 10 w~s repeated using 20.0
grams o~ the polyimide resin obtained ~rom metaphenylene-
diamine and 3,3~4,4~benzophenone tetracarboxylic dianhydrlde
and ~.0 grams o~ the flu*~y poly~Qrmaldehyde used in Exampl~
9. The pOrQUS discs contained void volumes o~ about 21~6~o
with essen~ially all of` the voids being ~illed by oil durlng
i~pregnation.
EXAMPLE 18
lo m~ procedure o:f Exan~ple 10 was repe~ted using
; 20.0 grams o~ the polyimide resin obtained ~ro~ 4~4l-3xydi-
aniline and 393~4,4~-benzophenone tetracarboxylic dianhy-
drlde and 5.0 grams o~ the ~lu~ pol~f'Qrmaldahyde used in
Exa~æle 9. ~he porouæ discs contalned void volumes of about
1~ 23.8~ wi~h about 87.2~ of the void~ ~eing ~illed by oil
during in~pregnation.
ExA~rpIE 19
~ ca~le 18 w~s repeated u~ing a low molecular weight
version of the ~ame polyimide resln. Void volume o~ abo~
20 26.~ was measured with about 87~ being filled by oil
d~ring impregnation.
EX~IE 20
50 G~n~ o~ gra~ular trioxane wa~ cu~ in a labora-
tory blender at high speed :for 2 minu~es to reduce pa:~ticle
25 s~ze ~o less than 100 mi~ron~. Ten grsuns o~ the cut trioxane
~s then blended wlth 40 grams of poly N,N~-(4,4~ ~xydlpheny-
lene) pyromellitimide in the same ~lender for 1 minute. The
re~ulti~g compo~tion wa~ compacted in a cylind~ical mold at
30,Q00 psi and at 50~000 psi ~o pr~duce disc prefo~ms o~ 1-1/8
inch ~iameter. Te~sile bar pre~o~s were co~acte~ at 100,000
psi. Much o~ the trloxane ~olatillzed on ~anding at room
tempe~ature. me preform~ were then given a thermal ~reat-
men~ in the usual way to produce porous discs and tensile
bars. Measuremen~ of the discs co~pacted at 50,000 psi
showed 16.3~ voids present. These voids were 75.5~ filled
by oil using the usual methodO Tensile strength o~ the ten-
sile bar pre~o~m~ ~s found to ~e 3900 psi, an~ elongation
of the tensile bar pre~orms wa~ 2.3~.
EXAMPLE 21
An un.c~pped polyfo~maldehyde of granular form was
ground in a laboratory pulverizing mill and screened to pro-
duce a ~raction pa~sing a No~ 60 sieve and being r~tained on
a No. 11~ sieve (Tyler Sieve Series)~ rorresponding to parti-
cles having a particle size in the range o* 124-246~. A
blend of 74.7g of this poly~ormaldehyde wi~h 86.2g of poly-
N, N ' -( 4, ~ l -oxydiph~nylene ) pyromellitimide cor~taining nomin -
ally 40~ by w~ight of graphite was prepared by dry bl~nding
on rotating rolls. The polyfoxmaldehyds ~ugitive ~iller was
présent at a 50~ by volume level. A disc 4 incheæ ln dia-
meter and 1~2 lnch thick was pre~ormed by co~pact:io~ at
50,000 p~i and put through the ~ollowing thermal cycle (in a
n~.t~ogen atmosphere): :
a) rapld heat-up to 150C.;
b) slow heat-up to 175C. at a rate o~
5C.~hr.;
c) i~othermal heating at 175a. ~or 16 hours;
d) rapid hea~-up to 200~.; -
e~ ~sothermal heat~ng at 200C. for 30
min~tes; ~-
f) cooling to room te~pera~ure5
g) heating to ~00C. at a rate ~f l-l/?~Co
per minu~e,
,
- 25 -
~7~3~6
h) isothermal heating at 400 C~ for 3
hour~, and
i) coo:ling to ros)m temperature.
A pcrou~ machlna~le d:lsc was obtalned.
:
~ .
'
,
- 26 -
- ,,
