CA1193400A - Formable polyamide compositions - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
A foamable polyamide composition comprising an admixture of an aliphatic polyamide and 0.2 to 10 parts by weight, per 100 parts of polyamide, of a blowing agent is disclosed. The blowing agent is a carbonate or basic carbonate of zinc, iron or copper.
The preferred blowing agent is zinc carbonate. Examples of ali-phatic polyamides are polyhexamethylene adipamide, polycaprolactam, poly-ll-aminoundecanoic acid and copolymers of adipic acid and hexamethylene diamine with caprolactam and/or sebacic acid. A
process for the manufacture of foamed aliphatic polyamide struc-tures is also disclosed. The composition and process of the present invention may be used for the manufacture of foamed poly-amide structures.

Description

The preserlt lnvention relat;es to foamable polyamide ccmpos:Ltlons and ln part:Lcular to f'oamable polyami.de compo~-ition~ in which the blowing agen-t in the compo~itlon is a metal carbonate OI' ba~ic carbonate~
Many i'oamed so-called pla~-l;ic mat~rials are kno~n and some~ for e.xample~ foamed polyst~Treneg are widely used in decoratlve~ container and insulation end u~esO However~
d~pite the reacly availability of polyamides~ especially polyhe~ethylene adlpamide~ the use of foamed polyamide structures has been limited~ It is stated in U~SO Patent 3,728,2g2 of Ho McGrath et al which issued April 179 1973 that one of` the difficultles encountered in producing sa-tisfactory foamed polyamides is the inherent unsuitabllity of the blowing agent~ which are u~ed in the manufacture of foamed structure~
~rom other plastlc materl~lsO The~e blowing agents usually give comparatively poor results when used in the foaming of poly-amides~ It i8 further stated by McGrath et al th~t it is not po$sible to ~elect blowing agents for polyamide~ by reference to the lntrinsic properties of known compounds for some char-~o acteri~tics of the blo~ing agent9 for example, the rate of gasproduction and t:he length o~ any induction period~ are affected by the polyi~mide its~lfo Foamed polyi~mide~ are capable o~ being used in a variety of applirationsO For exampleg foamed polyamides ~re c~pable o~ being ui3ed in the form of trays, pl~te~ i~nd the like and in ~tructura:l applicati~nsO
A ~oam~i~ble polyamid~ composi-tion ln which the blowing agent i~ ~ m~tal carboni~te h~ now been ~oundO
Accord:ingly~ the present inven~ion provides a foa~able 3i~ poly~mide compoi3:ition compri~lng an aliphatic polyamide adrnixed with 002 to lO parts by w~ight3 per lOQ p~rts o~ polyamide~

~3~

of a blowing agent selected from the group consisting of the carbonate~ ~Id basic carbonates of zinc, iron and copper, and mixtures thereofO
In a preferred embodlment of the compo~ition of the present invention the polyamide i~ polyhe~P ?thylene adlpamide.
In another em~odiment the blowing agent is zinc carbonate~
The p:resent in~ention also provides a proceqs ~or the manufacture o~ a ~oamed ~liphatlc polyamide structure, s~id process comprising the steps of (a) a~ ng an aliphatic poly-amide with 0.2 -to 10 parts by weight, per 100 parts o~ polyamide~
of a blowing agent selected ~rom the group consistirlg of the car~
bonates and ba~ic carbonates o~ ~inc, iron and copper~ and m~x-ture~ thereof, at a temperature in the range 210 to 315 C, said temperature belng above the melting point of said polyamide~
(b) :~orming the resultant molten admixture into a ~oa~ed polyamide structure, ~ld (c) cooling the foamed polyamide ~tructureO
In an embodi~ent o~ the proce~. of the present in-ventlon a blend of the pol~mide and blowing agent ~s made andthe bl~nd is sub3equently admixed at a ternperature ln the range of 210 to 315 C~
In another embodiment the blo~ing agent ls added to, ~nd ~ ed ~rith~ molten polyamide9 the temperature o~ the mol-ten polyamide being in the range o~ 210 to 315 C0 In a pr~.~erred embodlm~nt of the process o:~ the present invention the temperature is in the range 250 to 315 C0 In addition the pre~ent invention pro~ideæ an art~cle con~i~ting of f'oamed polyamide derived from an admixture com-30 pri~ing a~iph~tic polyamide and a blowlng agent ~el~cted ~romthe group con~isting o~ the c~rbonate~ and basic carbonates of zinc9 iron and copper~ and mixtures thereof.

The ~.)lowlng aKent~ th~t m~y be u~ed ln the foamable composition~ and ln the p.roces~ Or the pre~nt i.nvention are the carbonat~s and b~,~lc carbona~e~ o~ zlnc3 iron and copperO
Zinc carbonate i.s the pref`erred ~lowlng agent~ ~le blowlng age~t m~ be admlxed by be~ng blendedg e~gO~ physically blended3 with the polya~ide and ~ed to an extruder equipped wlth a sultable m~ ~1 n~ ~crewO ~lterna~ively the blowing agent may be metered lnto an extruder at the de~ired rate and ~m~ed with molten polyamiAe iXl -th~e extruderO
r~e p~olyamldes u~ed in the foamable polyami.~e comp-o~itions o~ the pre~ent ~nvention are aliphatic polyamides~
Examples o~ such polya~mides are polyhe~rpnleth~lene adipamide, poly~
caprs:)lactam poly~ am~oundecanoic acid~ co?olymers o~ adipic ~cid and h~ methylene ~m~ne with caprolactam and/or sebarlc acid and the LLke ~ The pr~ferred polyamide is polyhe~m~thylene adipamideO In a pr~ferred embodiment the polyamide is of a relat:l~e visco$ity in the range 25 to 65 a~d especlally in th~
rang,e 30 to 450 Poly~mides having a relative viscosity of up to at least 250 m~ howeverg be usedO Rela-tlve viscos~ty ls the ratlo of visco~,ity in cen~-Tpoises at 25 C of a 8~4~ by weight solut~on of polyamlde ln 90~ formic acid (90~ formic acid and 10% water~ by weight) to the ~i~coslty ~n centipoises at 25C
of the 90~ ~or~c aci~ aloneO
me f'oamable pol~amide compositions of' the present ~nv~ntion are capable of being u~ed in a variet~ o~ processes for the m~nu~actur~ o~ ~oamed polyamlde structuresO For ex-a~ple, the. ~oa~ble compositions are c~pable o~ being u~ed in ~n~ection moulding proc~es utlli~ing technlques simll~r to thos~ kno~n ln -th~ artO The foam~ble composltions are also capable o~ bein~ ~xtrud~d through ~ d:le 1ll~ fo.r exa~ple~ a continuous melt thermoformin~ proces~p Processes f'or th~
maml~actur~ o~ foamed polyamide strllct~s will generall.y be . 3 .~.

de~cri.bed hereln~te.r with re~erence to the extrus:l.on Or I`oamable polyamide compositions through a die Or a~ extruderO
As stated herei.nabove the blowing agent may be blended with the polyamide and then fed to an e~truder equipped with a suitable mixing screw or the blowing agent may be metered into an e~truder at the desired ra-te and blended wlth molten poly amide ~n the extruderu After the blowing agent is ln the ex-truder there will be a period of time, u~ually known as the induction time~ before the blowing ag~nt begins to decomposeO
For a~y particular blowing ~gent the induction time uill de-pend on a number of inter-related proce~æ variables ~pecially on the temperature and pre~ure at which the extruder is operated3 and in particular on the te~perature ~t which the extruder is operatedu Prior to the end of the induction time the pressure in the extruder should be increa~ed to a level ~uch that there wlli ~ no significant ~ep~ration ~nto two phases of the molten polyamide and the gas formed as a re~ult of decomposition of the blowing agent~ Under the lnfluence of a ~uitable pre~sure the ga~ remains di~olved in the molten polyamide until after the latter is extruded through the die of the extruderu Foaming of the polyamide composition ~o extruded then occursO Normally the decompo~ition of the blowing agent will ~e e~sentially com-pleted prior to extrusion o~ the ~oamable pol~a~de composition~
The importance of the control of pres~ure in the extruder in the e~trusion of ro~n~bl2 mixture~ is ~nownO
The optimum pre~sure at whlch the extruder is operated in the extrusion o~ th~ foamable poly~mlde compositions o~ t.he present invention will be relat~d to other process parameters, ~or ~xample9 t;he appar~tus being used~ the composit:ion being extrud~d~ the temperature o~ the molten polyamideg t,he melt properties Or the polyamide, the rate of extru~iorl and the likeO It haæ3 howeve~:r~ been fo~d th~lt,g a-t least, rmder SOllle 3~
~)rocess cond:L.t:ions~ the l;endency of~ pressure to f:lecrease t,he rate t~:f de~composition of t~le ~lowi.n~; agerlt ~ppears to lncrea,se as ~he pressure :l.s :Lncre~lsed -to about 35 kg/cm ; increases in pressure above about 35 lcfr/cm2 appear -to l~ave rela-tively litt:l.e ad(~i-tional ef`fec t on the rate Or clecompos:Ltion of the bl.ow:Lng agent~ !
After ex-trusion of the fo~lmable polyamide composltion through the die bu-t prior to cooling~ the resultant roarned comp-osition may be thermoformed in a proce~s for the continuous melt therm~forming of thermoplastic polymers. Such a process is described în detail in the copending Canadian patent appli-cation 239 615 of R, A~ Zelonka, filed on the same day as the present application~ In such a continuous melt thermofo~ming process a flat web o~ molten foam~ble polyamide composition is extruded in a downward dlrection over a ~eries of mould cavities movlng a-t a predetermined speed 50 as to sequentially cover the mould cavities. A vacuum i~ applied to the mould cav-ities and the web of molten polyamide, now a web of molten foamed polyamide, is brought into contact with the surface of the ~rlould c~vity. The mould defining the mould cavity is pre~erably sub-stant~lly comprlsed o~ porous metal. me foamed polyamide iscooled and the resultant article ls removed ~rom the mould, The process is controlled so that the article~ thermoformed in the process are o~ sub~tantially uni~orm thicknessO In a pre~erred embodiment the mould cavities are located on the periph~r~ o~ a wheel.
The properties of the ~oam obtained on ~olidification of f'oamed mo:Lten pol~amlde in, :for example ~ a continuous melt ther~o~ormin~ proce~s depend ~n p~r~icular on the amount of gas in the molten polyam1de in the extruder ~eing used~ The amount o~ g~ in -kh~ molten polyamide depends, at least Ln part on the amo~nt of blowing agent in the polyamide composition be:lng extrudetl, In the p:roduct:lorl o~ ~ :f oamed po.ly~mlde struc (/7 tur e having a ~ `orm ~el:l s truc ture an~l a re la-t:LveIy rJmoo th essentl.a:Lly pin-hole :Free surface there will normally be an opti.mwll, ror each partlcul.~r foamabl.e po.ly~mide composition, in the amount of ~as ln the molten polyamide compos.i.tion ln order to obtai.n a st:ruc-ture of m~nimum den3ity~ If there ii3 insu~flc-ient gas the density will be above the mlnlmum attain~ble while if there ii3 excess gas the cells produced may become too large and ru~ture 3 thereby resulting in a structure havlng a roughened surf`ace .
~O The amount of blowing agent in t~le ~oar.~ble pol~amlde composition may be in the range 0,2 to 10 parts by wei~htg es-pecially 0~4 to 300 part~ by weight~ per 100 parts o~ polyamide~
The optimum amount o~ blowing agent will, however ~ depend at least in. part on th.e particul~r process being used for the manu~ac-ture of foamed pol.yamide structures~ In an extrusion process, for example, a continuous melt thermoformlng process, the optimum amount of blowing agent may be in the range O ~ ~ to 1~ 5 parts by weight, per 100 parts o~ polyamide~
In the process o~ the present invention the temperat~e ~0 at which the polyamide and blowing agent are admixed is in the range 210 to 315C provided, however that the temperature is above the melting point ~f the polyamideO Preferably, even for poly-amides o~ rel.atively low melting point~ the temper~ture is in the range 250 to 315~C as ~t such temperatures the rate o~ decomp-ositlon of the blowing agent3 e~g~ zinc c~rbonate, i~ signl~i~
c~ntl~ f~ster than at the lower temperatures~
In the c~tru~ion o~ ~oamable composition the foaming of the cornpo~ition is pre~erably controlled, by rneans Or the process parameter~, i.n such a way tha-t the ~oaming does not occur until the molten composition has exited f`rom the die~
Foalning shoul(l be compl~-ted prlor to ~ol~ lcat;lon o.~ ~the ~) t~

polyamicleO The way to achleve ~3uch con trol w 111 be ~mders tood by tho~e skl lled in t;he art~
A8 stated here:ln~bove th~ foamin~s of' t;he mol~en poly-amide prefer~bly occur~; on e~trusiorl of the multen polyamide throllgh t~e d~ e on ~n extruder or s~lort~y ~ereRfter. The ~;ize of the cells formed ini~lally ls rel.~ively sm~s.ll bu~ the cells terld, e~pecially in pol.ymer~ of l.ow me~t v:lsco~ity9 to combixle an~ there~y ia~cre~se ~n ~ize until 1;he polyamide solidifies~
Thi~ may result in lthe format~ on of relatlvely large cells in ~he foamed mo].ten polyamide pr~ 02 to solldificai tion and such large cells may rupture, ~hereby forming pln~hole~ the sur face of the foamed structure being mar~ufactured and possibly even resultix~g in the cs:~llapse of the ~oam of the s kructure~ Retentior of the size of th~ cells of the fs:~amed polyan~de ~t a size small ~n;:>ugh to prevent ~ignificant pirl~holing of the surface ls de;-sirlble for ma~ly emd-uses~ me retentiorl of the ~ize of the cells below that resulting ln pin-holing m~y be achieveà~ at least in part5 by .~corporating a nucleating agent lnto the polyamide. Examples of suitable nucleatlng agents are sllica 2Q and calcium sllîcate. The effect o~ the llucleatin~; agent is bPlieYeà to be related t~ the proportion and ltyp~ of nuc leatlng agent i~ the polyami~eO The optimum amourlt of a particular nu-cleating agent w:ill depend on the proce~s corldltions used, prop-eI tles, fol ex~mp:lc melt vlscosi ~y, of the polyamide and the like a~ will be understooà by those ski ll~d in the art" Examples o:~
the amo~t oP nucle~tlng agerlt tha t may be use.~ul are up tQ 40,~
~y wei~sh-t of the compositlorl ~nà espec~ lly 10-30~ by wei~ht of the compo~ition. Higher amounts m~y be usef`ul for some nu-cleat~rlg ~ent~ and/or polyamides. However3 as the amou~t o~
nucle~ting agent iIlcreases the ~mount of polymer capable of f`orm:Lng and ma:int~linirlg It,he W~ 9 of' the cell~ ln the :~oam :~, ~33~

decreases and such may have a detrimental e~f'ect on the stability of the ~oam, especially at high amounts o~ nuclea~,lng agent in the polyamideO
The compositions o~ the present invention may contain ~illers especiall~ in amounts o~ up to ~bout 40~ by wei.ghtO
The amount o~ ~iller will depend in part on the particular process in which the ~oamable compositlon is bsing us~d~ For example3 in an extrusion process 10 to 30% by weight of ~iller mlght be used whereas in an ~n~ection moulding process less ~han 10~ by weight, e~g.~ 002 to 200~ might be usedO Examples o~ suitable ~illers are wollastonite, t~lc and micaO Fillers in the ~oamable polyamide composition ma~ assist in the ~ormation o~ cells o~
relatively ~mall size, thereby also acting as nucleatlng agentsO
Fillers and nucleating agents may be used in the æame foamable polyamide compositions although probably in amounJGs less than when used alone~
The compositions of the presen~ invention are capable of being ~ormed into foam~d structures having densities of less than 0090 g/cm ~nd in particular, less th~n 0~70 g/cm3 especialJ.y when the pol~amide is polyh~xP~sthylene adipamideO
The present ln~ention is illustrated by th~ ~ollowin~
e~p~es.
EX~PLE I
Twent~-five parts of pellet~ o~ a poly~e~ thylene adip~mide having a relatlve viscosity o~ 42 were placed in a reaction ve~sel fitted with a stlrrer~ The polyhQ~m~thylene adipamlde waæ then heated to 282C whlle ~nder an atrnosphere o~
ni~rogen~ Some water was removed .~rom ~he reaction ve~sel~ One part o~ blowing agent was added a~d the re~ult~nt mlxture was stirred ~or 2 minut~s~ me mixture was kept in an wn~tirred condition ~o~ a period o~ time and then cooled~ The product waæ
a rigid ~o~med polyamideO

~1~ r~ult~ w~re ~s :follow~o E~Un NoO :1. 2 3 Blowin~ .Ag~n-tZlnc Iron Copper CarbonateGarbo.r: ateCa:r bona te Total Re~,c-tion T.-lm~ ~ (m:inO ) 5 5 10 Produc t Denæi l;y (g~cm3) 0iD20 Ool~ ~34 Produc~ Colour~dhiteChocolate B*GWnDark Red 10 *To~l of' i;i~e stirred ~d time un~tir:r edg before cooling., E~PIE II
Fi*t~ part~ of pslle-t~ of a polyhQ~rf~thylene ad~p ~m~de h~r~ relatlvc vi~cos~ t~ o~ 42 ~d 10 partæ of ~ a filler were placed ~n ~L r~action ves~el :Eitted wlth a stirrer,, The re-~ulta~t mixture wa~ heated to 2829C ~hi~ e u~der ~ atmo$phere oi~ nitrogen ~d stlrred unt~l the mi~{ture appeared to be homo g~l~Leous~, Some water was remov~d f'rom the r~action veæs2l0 TWQ
p~rts of zinc carbonate were added ~d the mixture ~ rred for her 4 minutesO The mlæture was kept in an un~tirred con-20 dit~on ~or 5 ~:nutes ~d then cooled~ ~he prod~ct was a rigid ~o~m~d pol~ide O
me result~ wer~ a~ followsO
Run ~oO 4 5 6~*
F$11~r tælc mica wolla~ton-ite Product Den~ity (,~m3) 0"3~ 0~,42 0,~0 Product Colour Cre~n Gre~ Cre~a *~nly one pa~t o~ z~c carbon~te ~a~ used ~n thi s run~, 9 .

EXAMPLE I :~ I
One p~rt of 2.~nc carbonake o:E 425 rll~3sh (U~SO screen slze) ~ dry ~physlcally) blended with 99 part~ of drled p~llet~
o~ a polyhe~r~nPth;ylene ad-i p~n~de h~ving a relati~e vl~cosity of 65. Th~ mixt;~0 w~ extruded through a ~ingle screw extruder at extruder b~rrel temper~ture~ of ~'55~274~C and th~ough a ~lat ~ilm die havlng a no~nal dle gap oi~ O~ 5 n~. The temperature of th~ I~olt~n polyh~m~thylen~ ad:Lpamide so extruded was 282~Co I~e precsure applied in the extruder wa~ 70 kg/cm2~ The hold~up -time in the extruder wa~ approxi matel~r 2 ~ 5 minute~ ~. Foaming of th~ polyhe~m~thylene adipamide occurred on exit f`romL the di~
~he foame~ polyhf~ ethylerle ad~p~mide was passed to a chill roll., which cau~ed some oriellta~ion of the foamed m~teri~l, and co31ed. A. white rigid partiall~ orlented f'oamed ~heet of a thick ne~ o:~ 1025 mm and a density of: 0~.39 g~cm wa~ obtained~.
EXAMPIE IV
~ he proc~s of ~ r~ e III was repeated u~ing a mixture o~ on~ part of zinc carbona~e ~Li25 me~h) and 99 parts of a dri~d pelletlzed blend o:e 70 parts of polyhe~r~m~th;ylene adip~mide hav~g a r~latî~re vi~co~lty of 42~ 30 parts of ~lla~-ton~te ~d 105 !?~t~3 o:E' iron oxide plgmen~ A red r~gidg part~all~r orlexlted,:fo~d sheet o~ ~ thickne~ of oO91~ mm ~d a density of 00 53 g/cm3 wa~ obtalnedO
EX~IPLE V
The proces~ o~ Example nr ~s r~p~ated except tha-t th~ zinc c~rbonate w~ 200 mesh ~nd 3 p~ts of a tartraz:lne l~Xe/titani~n dlox~de (201 rat~ by w~ight~ mixture was u~ed in place o~ the l o 5 p~rt~ o~ iror:l oxide ,. The po:Lyhexame-th;ylene adlpamld~ extrud~d thro~gh the die was thermo:orm~d u~lng a m~ll; t~r~o:formi.ng proce~s., Th~ rlgld f`oam pol~he:x.~ th~lene ~Ldlpamide tr~y~ æo ~roducecl were pa:le ~el low in ~olou.r ~nd were o:~ ~ k~.c~n~ o~` 0,.~,~1 mlrl ~d ~ d~?n~ t;y ~r ~)~S~ o EX~MPLE VI
The proces~ o~ ~P~e V was repeated using one part o~ copper c~rbonate ~s the blowing agent. me trays so produced were olive green in colour and were o~ a thickness of o~66 mm and a den~ity o~ o~60 g/cm3. When lron-carbo~ate was used as the blowing agent the tr~ys were pa,le brown in colour ~nd o~ a thickness o~ 0,81 mm alld ~ denslt~ of o.69 g/cm39 EXAMPLE VII
A mixture of 70 parts o~ pol~h~ Pthulene adip~mide havlng a rel~tive viscosity o~ 429 30 parts o~ wollastonlteg 105 parts o~ iron oxide p~ t ~nd oOo60 parts of' cupric stearæte ~a~ extruded through a tw~n screw vented extruder h~v~ng three ~ent~ng ports~ A vacuum Or 560 mm Hgg relative to atmo~-pheric pressure~ w~s applied to the ~irst vent o~ the extruder and 1.20 p~rts o~ zinc c~rbonate were metered into the extruder through the third ventO ~he result~t m~xture was extruded at a temperature of 315C ~nd a pre~sure o~ 29 kg/cm through a flat ~ilm die having a nom~lal die gap o~ 1~52 mmO me extruded polymer was thermo~ormed on a cont~nuous melt thermoformer into red trays o~ th~ckness o~ 0.~1 ~ and o~ a density of 0077 g/cm ~
EXAMPLE ~III
The process o~ ~2~rle VII ~a~ repeated except that the zinc carbonate (0~98 parts) was dry blended with the polyh~ t~lene adipamide mi~ture ~ed ~o the extruder and the vacuum w~s ~ppliPd to all thre~ ~ents o~ the e~truder~
me re~ultant xed ~r~y3 were o~ ~ thieknes~ o~ 07~1 mm and a density o~ Oo78 g/cm30 EXAMPLE IX
A mixture o~ 88 par~ o~ pol~h~x~ thylene adipa~de hav~rlg a xel~tive viscoslty o~ 42 ~nd 1~ parts o~ woïlastonite lS e::ct;ru(1e~d t~l:rollg~ win scr~w extrw(3er havi.rlg three verlt l.n~;
port;s., A VaCUl.lm O~ 560 mm ~1~, relat:lve to atmospher.lc ~reC~,su.re7 w~,s ~pplled -to l;he :Eir~-t two vent11lg ]ports of t;he e.xtruder and 1~,1 parts o:~ zinc c~rbon~-te were metered :~nto the extruder through -the t~:r~l vent port.~ The resultant mol-ten ~:~xture w~ e.x-truded at a t~m~?erature o;E 282C and a pressur~ o:f ca 35 kg/cm2 t~ough a die having conv0rging d:ie l:lps and a nominal die gap o r 0O 3 mm. The extruded polyrller was thermo~orrned on aO melt thermo:~ormer into pîe plates o:~ 20.3 cm diameter ~d hav~g a ~mooth pin~hole lree lû surf~ce ~d a uni:Eorm ~ell structure~ me trays had a thlckness o~ o~56 ~ and a density of` Oo58 g/CIll e ~ AMPLE X
Zinc carbonate and a nucleating agent ( CAB O~SIL*
sillcaj were dr~T blended w11;h a polymer and ~xtruded throu~h a 25 cm wide die having convergin~s dle lips ~d a nc:min~1 die gap o~ 0.25 mm using a si~gle screw extruderO ~e extruded poly~er wa~ thermofo~m~d on a melt thermo~ormer into pie plates of 2003 cm di~met~r~
Fur ther experixllental d~ails and the resul1;s obtained ~o w~re a~ f'ollow~
Poly Zinc Car Nucleat~ Melt Temp- Press~re Fo~0m mer~* bona~e ing ~gent erature kg/cm Den~ty (% by wl;o) (~ by ~to~ (C) ~cm3 ~ ~ ~ O O O ~ 305 56 0 0 83 B 2~0 o94. 275 70 o~84 C le~ 0~ 2~0 56 009l' D l o 3 0 ~ 4 27~ 56 0 ~ 51 ~* A ~ polyh~ nRthylene ad:ipamide o~ a rela^tiv~ vl~cos~ty Q~
250.~ obta~ned under the trade mark ZYq~L 42 :~rom Eo I,, du Pon~ de Nemour~ ~;nd Co~parur olyc~prolac tam, obt~ined und~r the trade de~lgnation T~rp~ 212'9 :~rom the F~restone ~ir~ and .P~ubber Comp~
C ~ copol~nner o~ he~ th;ylene adipamlde ~d c~prolactam (90010~, obta~d under the -t:rad~ rk ZYT13L ~1 :Erom E~ Io du Pont d~ ~mouræ ~d Comp~y D -~- poly~ ~no~.d~ca~,o:Lc acid, obta:Lrl~d ~nder t,he tr~cle m~rl~ RILSAN :~rom OrgaAnico~

*d~ cl~

~3~

EXAMPLE XI
A mi~ture o~ calcium silicate (30 parts) and poly-h~methwlene adip~mide (70 part~) was extruded ~hrough a ~lat film die having a nominal die gap o~ 1.65 mm. me extruder used W88 the extruder of ~P~rl~ IX. At an extruder output rate of 86 kg/hour, the pressure at the die was 42 kg/cm2.
When one part o~ zinc carbonate was added to the mixture and the pressure at the die reduced to 29 k~/c~2~ ~owever, the additlon of one part o~ zinc oxide, a therm~l decomposition product of zinc carbonate, did not re~ult in any reductlon in pressure at the die.
mis e~rle dero~rate~ that z~nc carbonate may be used as an extrusion aid.

EXAMPIE XII
A polyhexamethylene ~dipamide o~ a relative ~lscosity o~ 42 was in~ection moulded usi~g a NA~CO* injection mould~ng machlne. The pressure was 385 kg/cm2 and the melt temperature was 282C~ Zinc carbonate and/or nucl ating agent (C~B~O~SIL
silica or c~ n~ s~licate) were dry blended with the polyhexa-methylene adipamide~ The calcLum ~ilicate w~s used in the formo~ a 30% c~lcium ~il1cate/pol~hexamekh~lene adip~mide concen~rate7 Further exper~me~tal deta~ls and the result~ obtained were a3 follows:
Zinc Carbon- Nucleatin~ Agenk In~ect~on Moulded Produc~
ate (%) ~ ~ ei~h~ (g) Den~lt~ (g~cm ) O - O 365 1,1 1.0 CaSiO3 0~5 270 Oo85 loO SiO2 0~5 260 0~81 O CaSi.03 10~0 395 1~28 1.0 CaS103 10.0 280 0~88 *denote3 trade ma~k ~EX~MPLF. X~
A dr:l ed pel:Le tl~ed p.hys:l.ca:l. blend Or 70 par t~3 of a po:lyhex~me thy~.ene adipamlde hav:ing ~ relative vlscos~ t~ o~' 42 and 30 part~ of wollas-toni te was extr~lde~i through a t~ee sec-tion tWin screw ex-truderO Blowing agent was me~,ered into -~he mo].ten ~lend ln the thlrd ~3ectlor of the ex~rude:z and the resultant mixture wa~ r~pidly pres~surlzedO The mi.xture was extruded through a d:ie ha~ring convergirlg die lips and a no~inal die gap of 003 ~0 The ~xtrud~d ~xture was thermoformed irlto pie plates~, F~urther exper ~mental details and -the results obtained w~re a~ ~ollowso Blowin~ :Extrusion Pxess~re Parts B10Win~ n-7 ml~m Densit~
A~ent Tem~erature kg/cm Agent/100 parts Attained (g/cm ) ( C) o~ Blend Zinc Car-296 40 208 0071 bonate Sodium Bi~ 290 45 3~9 Oo91 Carbonate The pie plate~ had a smooth p~n hole free sur~ace and a uni~orm cell structure 9 The use o~ z~nc carbonate resulted in ~lmost twice the reduction i~ the density o~ the thermo~ormed ple plates attained with sod~um bicarbonate as blowlng agent~

Claims (40)

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

1. A foamable polyamide composition comprising an aliphatic polyamide admixed with 0.2 to 10 parts weight, per 100 parts of polyamide, of a blowing agent selected from the group consisting of the carbonates and basic carbonates of zinc, iron and copper, and mixtures thereof.

2. The composition of Claim 1 in which the blowing agent is a carbonate or basic carbonate of zinc.

3. The composition of Claim 1 in which the blowing agent is a carbonate or basic carbonate of iron.

4. The composition of Claim 1 in which the blowing agent is a carbonate or basic carbonate of copper.

5. The composition of Claim 1 or Claim 2 in which the polyamide is selected from the group consisting of polyhex-amethylene adipamide, polycaprolactam, poly-ll-aminoundecanoic acid and copolymers of adipic acid and hexamethylene diamine with caprolactam and/or sebacic acid.

6. The composition of Claim 2 which, in addition, contains a nucleating agent.

7. The composition of Claim 2 which, in addition, contains a filler.

8. The composition of Claim 2 in which the polyamide is polyhexamethylene adipamide.

9. The composition of Claim 8 in which the polyamide has a relative viscosity in the range of about 25 to 250, said composition additionally containing a nucleating agent.

10. The composition of any one of Claim 1, Claim 2 and Claim 8 in which the polyamide is admixed with 0.4 to 3.0 parts by weight, per 100 parts of polyamide, of blowing agent.

11. The composition of any one of Claim 1, Claim 6 and Claim 9 in which the polyamide is capable of being injection moulded.

12. The composition of any one of Claim 1, Claim 6 and Claim 9 in which the polyamide is capable of being extruded in the form of a sheet.

13. A process for the manufacture of a foamed aliphatic polyamide structure, said process comprising the steps of (a) admixing an aliphatic polyamide with 0.2 to 10 parts by weight, per 100 parts of polyamide, of a blowing agent selected from the group consisting of the carbonates and basic carbonates of zinc, iron and copper, and mixtures thereof, at a temperature in the range of 210 to 315°C, said temperature being above the melting point of said polyamide, (b) forming the resultant molten admixture into a foamed polyamide structure, and (c) cooling the foamed polyamide structure.

14. The process of Claim 13 in which the temperature is in the range 250 to 315°C.

15. The process of Claim 14 in which the blowing agent is a carbonate or basic carbonate of zinc.

16. The process of Claim 14 in which the blowing agent is a carbonate or basic carbonate of iron.

17. The process of Claim 14 in which the blowing agent is a carbonate or basic carbonate of copper.

18. The process of Claim 15 in which, in addition, a nucleating agent is admixed with the polyamide and blowing agent.

19. The process of Claim 15 in which, in addition, a filler is admixed with the polyamide and blowing agent.

20. The process of Claim 15 in which the polyamide is polyhexamethylene adipamide.

21. The process of Claim 20 in which the polyamide has a relative viscosity in the range of about 25 to 250, said composition additionally containing a nucleating agent.

22. The process of Claim 13, Claim 15 and Claim 20 in which the polyamide is admixed with 0.4 to 3.0 parts by weight, per 100 parts of polyamide, of blowing agent.

23. The process of any one of Claim 14, Claim 18 and Claim 21 in which a physical blend comprising polyamide and blowing agent is made and the blend is admixed at said tempera-ture.

24. The process of any one of Claim 14, Claim 18 and Claim 21 in which the blowing agent is added to, and admixed with, molten polyamide.

25. The process of any one of Claim 14, Claim 18 and Claim 21 in which the process is an injection moulding process.

26. The process of any one of Claim 14, Claim 18 and Claim 21 in which the process is a sheet-forming process.

27. The process of any one of Claim 13, Claim 14 and Claim 15 in which the polyamide is selected from the group con-sisting of polyhexamethylene adipamide, polycaprolactam, poly-ll-aminoundecanoic acid and copolymers of adipic acid and hexa-methylene diamine with caprolactam and/or sebacic acid.

28. The process of any one of Claim 13, Claim 14 and Claim 15 in which the density of the resultant product is less than 0.70 g/cm3.

29. An article consisting of foamed polyamide derived from an admixture comprising aliphatic polyamide and 0.2 to 10 parts by weight, per 100 parts of polyamide, of a blowing agent selected from the group consisting of the carbonates and basic carbonates of zinc, iron and copper, and mixtures thereof.

30. The article of Claim 29 in which the blowing agent is a carbonate or basic carbonate of zinc.

31. The article of Claim 29 in which the blowing agent is a carbonate or basic carbonate of iron.

32. The article of Claim 29 in which the blowing agent is a carbonate or basic carbonate of copper.

33. The article of any one of Claim 30, Claim 31 and Claim 32 in which the polyamide is selected from the group con-sisting of polyhexamethylene adipamide, polycaprolactam, poly-ll-aminoundecanoic acid and copolymers of adipic acid and hexamethyl-ene diamine wit caprolactam and/or sebacic acid.

34. The article of any one of Claim 30, Claim 31 and Claim 32 on which, in addition, the admixture contains a filler.

35. The article of any one of Claim 30, Claim 31 and Claim 32 in which the polyamide is polyhexamethylene adipamide.

36. The article of any one of Claim 30, Claim 31 and Claim 32 in which the polyamide is a polyhexamethylene adipamide of relative viscosity in the range of about 25 to 250, said admixture additionally containing a nucleating agent.

37. The article of any one of Claim 30, Claim 31 and Claim 32 in which the density of the foamed polyamide is less than 0.90 g/cm3.

38. The article of any on of Claim 30, Claim 31 and Claim 32 in which the density of the foamed polyamide is less than 0.70 g/cm3.

39. A process for expanding a thermoplastic polyamide which comprises heating a composition comprising a thermoplastic polyamide and zinc carbonate as the main blowing agent so as to cause thermal decomposition of the blowing agent.
40. A process as claimed in Claim 39 in which there is also present a nucleating agent.
41. An expandable composition comprising a thermoplastic polyamide and zinc carbonate as the main blowing agent.
42. A composition as claimed in Claim 41 in which there is also present a nucleating agent.
43. An article produced by the process claimed in

Claim 39.
44. An article produced by the process claimed in

Claim 40.