CA1071346A - Porous articles from powder blends of polyimides and formaldehyde polymers - Google Patents
Porous articles from powder blends of polyimides and formaldehyde polymersInfo
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- CA1071346A CA1071346A CA218,610A CA218610A CA1071346A CA 1071346 A CA1071346 A CA 1071346A CA 218610 A CA218610 A CA 218610A CA 1071346 A CA1071346 A CA 1071346A
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Abstract
ABSTRACT
A composition of a coalescible polyimide powder and a polymer of formaldehyde is provided, said composition adapted for fabraicating porous polyimide shaped articles by subjecting said composition to a forming pressure of about 100,000 psi to provide a preform, and thereafter sintering said preform by heating said preform to a temperature above about 300°C. to provide a porous polyimide shaped article having interconnecting pores; said porous polyimide shaped articles being useful as, for example, oil-impregnated bearings.
A composition of a coalescible polyimide powder and a polymer of formaldehyde is provided, said composition adapted for fabraicating porous polyimide shaped articles by subjecting said composition to a forming pressure of about 100,000 psi to provide a preform, and thereafter sintering said preform by heating said preform to a temperature above about 300°C. to provide a porous polyimide shaped article having interconnecting pores; said porous polyimide shaped articles being useful as, for example, oil-impregnated bearings.
Description
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
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~
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 .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 _
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~
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 .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 ': ~
- - . . - . - - - : .. . .
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 ., .
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-~
The resulting homogeneous co~positions were u~ed to prepare ~ , ~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
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 ': ~
- - . . - . - - - : .. . .
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 ., .
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-~
The resulting homogeneous co~positions were u~ed to prepare ~ , ~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 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%, 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.
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 ~ 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 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~.
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~.
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~.
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 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 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 .
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.
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.
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~.
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, , ~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.
:
~ .
' , - ,,
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%, 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.
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 ~ 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 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~.
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~.
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~.
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 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 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 .
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.
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.
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~.
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, , ~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.
:
~ .
' , - ,,
Claims (19)
1. A composition comprising a coalescible poly-imide powder and up to about 50% by weight, based upon the total weight of said composition, of a solid, particulate poly-mer of formaldehyde wherein said polyimide is characterized by the following recurring structural unit:
wherein R is a tetravalent radical containing at least one six-carbon atom ring characterized by benzenoid unsaturation and wherein the four carbonyl groups of said recurring structural unit are attached to separate carbon atoms in pairs with the carbonyl groups of each pair being attached to adjacent carbon atoms in said R radical; and wherein R' is a divalent aromatic radical.
wherein R is a tetravalent radical containing at least one six-carbon atom ring characterized by benzenoid unsaturation and wherein the four carbonyl groups of said recurring structural unit are attached to separate carbon atoms in pairs with the carbonyl groups of each pair being attached to adjacent carbon atoms in said R radical; and wherein R' is a divalent aromatic radical.
2. The composition of Claim 1 wherein said solid particulate polymer of formaldehyde is unstabilized polyoxy-methylene.
3. The composition of Claim 1 wherein said polymer of formaldehyde is paraformaldehyde.
4. A method of manufacture for fabricating porous polyimide shaped articles which comprises pressing a preform by subjecting a composition of a coalescible polyimide powder and up to about 50% by weight based upon the total weight of said composition, of a solid, particulate polymer of formalde-hyde to a forming pressure of at least about 10,oo0 psi and heating said preform to a temperature above about 300°C. to sinter said preform and provide a porous polyimide shaped article having interconnecting pores, wherein said polyimide is characterized by the following recurring structural unit:
wherein R is a tetravalent radical containing at least one six-carbon atom ring characterized by benzenoid unsaturation and wherein the four carbonyl groups of said recurring structural unit are attached to separate carbon atoms in pairs with the carbonyl groups of each pair being attached to adjacent carbon atoms in said R radical; and wherein R' is a divalent aromatic radical.
wherein R is a tetravalent radical containing at least one six-carbon atom ring characterized by benzenoid unsaturation and wherein the four carbonyl groups of said recurring structural unit are attached to separate carbon atoms in pairs with the carbonyl groups of each pair being attached to adjacent carbon atoms in said R radical; and wherein R' is a divalent aromatic radical.
5. The method of Claim 4 wherein said solid particulate polymer of formaldehyde is polyoxymethylene.
6. The method of Claim 4 wherein said polymer of formaldehyde is paraformaldehyde.
7. An article of manufacture comprising a self-supporting preform of integral and unitary construction of a coalescible polyimide powder and up to about 50% by weight of said preform of a solid, particulate polymer of formalde-hyde, wherein said polyimide is characterized by the following recurring structural unit:
wherein R is a tetravalent radical containing at least one six-carbon atom ring characterized by benzenoid unsaturatior and wherein the four carbonyl groups of said recurring structural unit are attached to separate carbon atoms in pairs with the carbonyl groups of each pair being attached to adjacent carbon atoms in said R radical; and wherein R' is a divalent aromatic radical.
wherein R is a tetravalent radical containing at least one six-carbon atom ring characterized by benzenoid unsaturatior and wherein the four carbonyl groups of said recurring structural unit are attached to separate carbon atoms in pairs with the carbonyl groups of each pair being attached to adjacent carbon atoms in said R radical; and wherein R' is a divalent aromatic radical.
8. The article of Claim 7 wherein said polyimide is poly-N,N'-(4,4'-oxydiphenylene) pyromellitimide.
9. The article of Claim 8 having present therein graphite.
10. The article of Claim 8 having present therein polytetrafluoroethylene.
11. The article of Claim 9 having present therein polytetrafluoroethylene.
12. The article of Claim 7 wherein said polyimide is a polyimide of 3,3',4,4'-benzophenone tetracarboxylic dianhydride and an organic diamine.
13. The article of Claim 12 having present therein graphite.
14. The article of Claim 12 having present therein polytetrafluoroethylene.
15. The article of Claim 13 having present therein polytetrafluoroethylene.
16. The article of Claim 13 wherein said organic diamine is metaphenylenediamine.
17. The article of Claim 13 wherein said organic diamine is 4,4'-oxydianiline.
18. The article of Claim 14 wherein said organic diamine is methaphenylenediamine.
19. The article of Claim 14 wherein said organic diamine is 4,4'-oxydianiline.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA218,610A CA1071346A (en) | 1975-01-24 | 1975-01-24 | Porous articles from powder blends of polyimides and formaldehyde polymers |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA218,610A CA1071346A (en) | 1975-01-24 | 1975-01-24 | Porous articles from powder blends of polyimides and formaldehyde polymers |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1071346A true CA1071346A (en) | 1980-02-05 |
Family
ID=4102137
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA218,610A Expired CA1071346A (en) | 1975-01-24 | 1975-01-24 | Porous articles from powder blends of polyimides and formaldehyde polymers |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1071346A (en) |
-
1975
- 1975-01-24 CA CA218,610A patent/CA1071346A/en not_active Expired
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