CA2030646A1

CA2030646A1 - Process for producing expandable termoplastic microparticles

Info

Publication number: CA2030646A1
Application number: CA 2030646
Authority: CA
Inventors: Richard Brian Allen; Wayne Paul Bobal; Richard Charles Bopp; Frederick Lyle Sanford; George Fredrick Willard, Jr.
Original assignee: Individual
Current assignee: General Electric Co
Priority date: 1989-12-27
Filing date: 1990-11-22
Publication date: 1991-06-28

Abstract

(8CN-8429) ABSTRACT
A process for producing expandable thermoplastic microparticles by melt compounding micropellets of a thermoplastic resin and then impregnating the micropellets with a blowing agent is disclosed.

Description

203~6~6 -1- (8CN-8429) PROCESS FOR PRODUCING EXPA~DA~LE
T~R~O~ASTIC MICROPAR$ICL~S
The present invention relates to the production of expandable thermoplastic microparticle~.
More particulariy it relates to a process for melt compounding micropellets of a thermoplastic resin and impregnating the micropellets with a blowing agent to form expandable microparticles. As used hereinafter the term microparticles is intended to comprise both substantially cylindrical micropellets and substantially spherical microbeads.
8AC~GROUND OF T~E INVENTION
:et.^^_s for the production of exoandable thermoplasti_ ~esin beads for use in the manufacture of foam moiaea _rt-cles are well known in the art. For instance, traditional expanded polystyrene tecnnology has existed since the early 1~5~'s.
The production of expandable beads can include the incorporation of a blowlng agent by one of three methods. ~ne method, known as the "one-step" ?rocess, is to suspend styrene monomer, initiators ana nyarocarbon blowing agent in water and polymerize at Aigh temperature.
This metnod is taught by Japanese Patent ?ublication No.
32623/70.
In a second process, called the "l~ step"
process, t~.e polymerization is brougnt to ~0 percent completion before the blowing agent is introauced into the system. ~e "two-step" process incorporates the blowing agent into suspension polymerized beads (100%
converted) or melt compounaed pellets. llhe two-step process is used in Japanese Patent Publication No.
36097/72 wAicn discloses neat-melting a polymer, pelletizing the melt and incorporating t.~e formed pellets wlth a blowinq agent.
Incorporation of the blowing agent into the -2- (8C~-8429) extruder has been disclosed in Collins, United States ~atent ~io. 3,250,~34. ~ollins compressed the heated polystyrene prior to introduction of the blowing agent and cooled the mixture thereafter extruding the mixture into stranas wnich are later cut into pellets. The problem in Collins is the cooling necessary to prevent expansion of the mixture prlor to extrusion. Further, the strands produced by the Collins process are taught to have a diameter of about 0.06 inches.
~he ?roDlem of temperature control wnile cooling the extrudate passing through the die, as causing -locKa~e of t..e die, is dealt with in United ~ingdom 2~te~.r ~.o. 348,200 (Platz et al.) and Canadian ?atent o. ~o~,i64 (acnroeaer et al.). Platz et al.
make use o~ a -ie either made from or lined with polytetrafluoroe~hylene having openings of ~ to 8 mm in aiameter. Schroeder et al., on the other hana, deal with this DroDlem by regulating the temperature of the composition entering the die to assure free flow and cooling t-e composition almost immediately as it exits the die. achroeder e~ al. make no mention of a minimum diameter of extrudate leaving the die.
~ther -rocesses for the productlon of expandable resin compositions are disclosea in ~1nited States Patent ~o. 3,026,273 (Engles), United States Patent ~o. 3,026,272 (~ubens et al.), United States Patent No. 3,121,132 (Bene) and United States Patent No.

3,u26,274 (~lactiillan et al.). These disclosures aeal with the pre-expansion of the composition. The size of the pellets proauced in these disclosures are limited, in their minimum dimensions, to normal diameters, as no mention of small or microdiameter particles is made.
The process of underwater pelletizin~ of polymers wltn an adjustable blade for varying ^eilet size is disclosed in Smith, United States Patent ~o.

20306~

_3_ (8CN-8~29) ~,500,271. Size restrictions of the extrusion die due to flow of the polymer are limltea to a minimum of about 0.035 inches to proauce uniform beaa size distribution.
Sucn techniques are good for resins which process at low temperatures, such as polyolefins, but not for engineered thermoplastics. Allen et al., in commonly assigned United States Patent Application, Serial ~o.
093,317, filed September 4, 19~7, attorney's docket 335-2051 (8C~-8335) discloses a one-step process for the ?roduction of small spnerical expandable beads employing a heated die and unàerwater ?elletizer. Allen et al.
claim small expanàaDle Deaas naving aiameters ranging from aoout ~.ûlC to aDout 0.~50 incnes and more referaDiy -om aDout 0.ul~ ~o about 0.025 incnes.
1~ ~urrently, expandable polystyrene beaas are generally ?roduced from so-called raw polystyrene Deads which are made Dy a relatively inexpensive batch emulsion polymerlzation process. As a consequence, modification of the expandable polystyrene beads through either coooli~,erlzation or Dlending is ,~ade airficult ~ecause of deleterious effects of additives on both the ?olymerization ~inetics and emulsion sta~ility.
It would therefore be a notable advance in the state or the art i~ expanaable t-.ermoplastic resin ~eads could be made from a resin produced througn a continuous method of ~olymerization other tnan oatch emulslon polymerization and/or modified with a variety of additives sucn as plasticizers, lubricants, -lame retardants, anti-static agents, ?igments and the like ~or improved ?roperties.
Allen et al., United States Patent No.
~,72/,093 teacn producing oolypnenylene etherJpOly-styrene beads rangin~ in size from 0.0212 to 0.0661 inches (10 - 30 mesn, J.S. stanaard sieve size) :n diameter and then imbibing tO produce expandable beads.

20306~6 _~_ (8CN-8429) It has now unexpectedly been discovered that ?roducing micropellets, less than 0.02 inches in diameter, facilitates ~he imbibing of a blowing agent into the resin and that such microparticles suDse~uently expand and fuse Detter when placed in a mold.
Surprisingly, tnese micropellets are also nighly amenable to tne addition of a wide variety of additives and copolymerizations thus enabling the producer to obtain a resin with a wide variety of desired improved properties.
This is especially significant in the instances -~nere ~he resins sougnt tO be micropeiletized ~re Drl..ie, _ucn as .or principally atactic polystyrene ana styrene-~aieic anhyaride copolymers. ?rocesses employing stranas of tnese Drittle materials having very small iiameters suffer from poor productivity aue to strand breakage. Consequently, micropelletization is not currently used in the production of expandable polystyrene beaas.
~0 It has now been found, however, that microparticles of these brittle resins ;nay be produced accordin~ to the present invention by the addition of a auctiii~y ennancing resin such as polypnenyiene ether~
; SUMMARY OF T~ PR~SENT INVENTION
Accorain~ to the present invention there is providea a process for the production of expandable microparticles of a thermoplastic resln, comprlsing the following steps: (a) plasticating a substantially nomo~eneous thermoplastic resin or a blena of at l~ast two substantially miscible thermoplastic resins capable of becomins substantiaily homogençous after said plastication (b) extruding the plasticated material formed in step (a) throush a multi-strana ;icrodie tO
form strands having an average diameter of less t~an about 0.02 inches; (c) cooling the strands; (a) 20306~6 _5_ (8CN-0429) comminuting the cooled strands to form substantially cylindrical micropellets having a length to diameter ratio of about 1:1; and either (e)(i) impregnating the substantially c lindrical expandable micropellets with S an effective amount of a blowing agent to form substantially cylindrical expandable microparticles or (e)(ii) impregnating the substantially cylindrical micropellets with an effective amount of a blowing agent at a temperature above the glass transition temperature of the thermoplastic resin to form substantially sphericai exDandable microparticles.
:-~efsraDly, the suDstantially homoaeneous ther~opl-at - -esin ;s selected from the group consistlng o, ~ ?oiypnenylene etner, a polyester, a polystyrene, -n amorphous polyamide, a polycar~onate, a polyether sul~one, a polyetherimide and substantially nomogeneous mixtures and copolymers thereof. The preferrea polyphenylene ethers are poly(2,~-dimethyl-1,4-phenylene)ether and poly(2,6-dimethyl-co-2,3,6-tri-methyl~ -pnenylene)ether. ~he preferred polystyrenes are prlnci?aily atactic polystyrene, ooly(alpha-methyl-styrene~, poly(nuclear-methylstyrene), poly(para-methyl-styrene)~ poly(para-tert-butyl styrene), ..alogenated poly-styrene, a styrene-maleic anhydride copolymer, styrene-butadiene co?olymer, atyrene-acrylonitrlle copolymer, styrene-acrylonitrile-butadiene terpolymer, styrene-di-vinyl ~enzene copolymer and high i.mpact poiystyrene.
Also preferrea is a polyphenylene ether/polystyrene blend.
,he preferred blowing agents are selected from tne grouD consisting of n-pentane, isopentane, neopentane, _yclopentane, butane, sobutane, ~en~ene, hexane, heptane, octane, propane, methylene chlorlde, cnloroform, CarDOn tetracnloride, tric~lororluoromethane, dichlorodifluoromethane, chlorodifluoromethane, CClF2-CClF2, dichlorotrifluoroethane (CHCl~C~3), 203064~

-6- (8CN-a429) dichlorotr1fluoroethane (CHFClCClF2), chlorotetrafluoro-ethane, tetrafluoroethane, dichlorofluoroethane, chloro-difluoroethane, difluoroethane, acetone, alcohols having from 1 to 5 car~on atoms, halogenated alcohols such as i fluoroisopropanol, carbon dioxide, nitrogen, water, methylethyl ketone, ethyl acetate and mixtures or any of the foregoing.
DETAIL~D D~SCRIPTION O~ T~ INVENTION
As used hereinabove and throughout the application, the term plasticating is defined as a process of heatlng and shearing a thermoplastic resin at a temperature of at least the glass transition ~emper~tur~ --e case or amorpnous resins ana of at least ~ne ~el~ temperature in the case of crystalline resins. ~::.e -erm nomogeneous is aefinea as a resin or blend of resins uniformly dispersed in each other having a single onase tnermodynamically. The term "suostantially miscible" is defined a~ substantially soluble or substantially tnermoaynamlcally compatible, i.e. the materials exist primarily as a single phase. However, those of orainary skill in the art will understand that such polymer systems may include minor amounts of phase separatea or icropnase separated materials wnich exist without detracting from the overall performance or the oolymer system.
.Ae present invention relates to a process for the proauction of expanaaDle thermoplastic microparticles.
~he invention may be practiced with the use of a wide variety of materials encompassed within tne broader description given above. In the typical case nowever, use is maae or certain preferrea materials whic" are described below.
.he oolyphenylene ether (PPE) is normaily a nomo- or coDolymer inaving units of tne rcrmuia 20306~6 - ,- ( 8CN-8429 ) ~ O ~ O ~

Q Q

. - . . .
wherein Q, ~ , 2 , Q are independently selected from the group consisting of hydrogen, halogen, hydrocarbon, halohydrocar~on, hydrocarDonoxy, and halohydrocarbonoxy;
and n represents the total ~umber of monomer units and is an integer of at least about 20, and more usuaily at leas t _ O .
The ?oiypnenylene ether can be prepareà in ~ccordance ;ilt.. ~nown ?rocedures such as those aescribed in Hay, Unitea States Patent Nos. 3,306,874 and 3,306,875;
ana ~tamatoff, ~nlted States ~atent Nos. 3,2S7,357 and O,257,35a, from the reaction of phenols including but not limited to: 2,6-dimethylphenol; 2,6-diethylphenol;
2,6-dibutylphenol; 2,6-dilaurylphenol; 2,6-dipropylphenol;
2,6-diphenyi?henol; .-methyl-6-tolylphenol; 2-.~ethyl-6-~ethoxyphenol; 2,3,6-trimetnylphenol; 2,3,5,6-tetramethyl-?nenol; and 2~o-aietnyoxyphenol.
Eacn of tnese may be reacted alone to produce the corresponaing homopolymer, or in palrs or ~ltn still other ?nenols to produce the corresponaing copolymer.
Examples of the homopolymer include poly(2,6-dimethyl-l, 4-phenylene)ether, poly(2,6-diethyl-l,4-pnenylene~ether, ?oly('~,~-aibutyi-i,~-pnenylene)ether, poly(2~6-dilauryl-i~
~-phenylene)ether, ?oly(2,6-dipropyl-l,4-phenylene3ether, ?oly(2,6-aiphenyl-l,4-phenylene)ether, poly(2-.~ethyl-6-outyl-l,~-phenylene)ether, poly(2,6-dimethoxy-l,'-Dneny-lene)ether, ~oly(2,~,6-trimethyl-l,s-pnenylene)ether, ?oly(2,3,5,6-tetramethyl-l,4-pnenylene)ether, and poly (2,6-diethyoxy-l,4-pnenylene)ether. Examples of ~he copolymer include, especially those of 2,6-dimetnylphenol -a- ( scN-a~2s ~ith other phenols, such as poly(2,6-~imethyl-co-2,3,6-trimethyl-1,4-onenylene~et~er ana poly(2,6-dimethyl-co-2-methyl-6-butyl-1,4-phenylene)ether.
For purposes of the present inven~ion, an especially preferred family of polyphenylene ethers include those naving alkyl substitution in the two positions ortho to the oxygen ether atom, i.e., those of the above formula wherein Q and Q are alkyl, most preferaDly having from 1 to 4 carbon atoms. Illustrative members of this class are: poly(2,6-dimethyl-1,4-pheny-lene~ether: ~olv(2,6-diethyl-1,4-ohenylene)ether: poly (2-methyl-6-etnvl-1,4-phenylene)echer poly(2-methyl-6-~ropyl~ onenviene~ether: ?oly(2~6-dipropy~ -ohen lene)etr.er; _oly(2-ethyl-6-propyl-1,4-pnenylene) ether;
anà t~.e l~e.
The most preferred polyphenylene ether resin for purposes or the present invention is poly(2,6-ai-methyl-l,~-phenylene)ether.
The term "alkenyl aromatic polymer" as it is employed in t.his disclosure is intended to encompass homopolymers, as well as rubber modified high impact Jarieties, and also copolymers ana terpoiymers of alkenyl aroma~ic compounds with one or more other materials. ?refera~ly, the alkenyl aromatic polymer is based at least in part on units of the formula R5 CRl = CHR2 R6 ~ R3 wherein Rl and R2 are selected from the group consisting of lower a!kyl or alkenyl ~roups of from 1 to 6 carDOn 203~646 _9_ (8CN-8429) atoms and hydrogen R3 and R4 are selected from the group consisting of chloro, bromo, hydrogen and low-r alkyl of from 1 to 6 c~rbon atoms; R5 and R6 are selected from the ~roup consisting of hydrogen and lower alkyl and alkenyl groups of from 1 to 6 carbon atomnS or R5 and R6 may be concatenated together with hydrocarbyl groups to form a naphthyl group.
The aDove will encompass styrene, as well as homologs and analogs of styrene. Specific example~
include in addition to styrene, chlorostyrene, dichloro-styrene, ~romostyrene, dibromostyrene, alpha-methyl styrene, auciear-metnyl styrene, para-methyl stvrene, ?ara--er--e~t l styrene, vinyl styrene, divinyi ~enzene and vinyl napnthalene. Styrene is especlally preferred.
Ry way of illustration, the polystyrene (PS) component can se a homopolystyrene ~principally atactic) or other alkenyl aromatic homopolymer which has been modifiea by admixture or interreaction with a natural or synthetic rubDer, for example, polybutadiene, polyiso-2U prene, EPDM rubber or silicone rubber: or it can be a copolymer or terpolymer of styrene or other alkenyl aromatic compound with an elastomeric or other material, such as ~lock copolymers of styrene ana Dutadiene (for example, AB, ABA, A~AB or ABABA type), including hydro-genated forms of t~e foregoin~, a raaial teleblockcopolymer of styrene, butadiene ana a coupling agent, inclualng nyarogenated forms, ter?olymers of acrylonitrile, styrene and butadiene (ABS~, styrene-acrylonitrile copolymers (SA;~), and a copolymer of styrene and maleic anhydride (SMA); or it can also be an alkenvl aromatic copolymer or teroolymer ~nich has been modified with rubber, for example, rubber modified styrene-maleic anhydride copolymer. ~any of these are described in the patent literature, such as Cizek, United States Patent No. 3,383,435.

20306~6 -10- ( scN-a42s ) The polyphenylene ether (PPE) and polystyrene resins may be comolneà in a conventional manner. PPE
resin will typically be in powder or pellet form and the polystyrene will typicaily be in pellet form. The resins may De combined by dry blending in a blender which proviaes a relatively uniform mixture of the resins or by other conventional means. This mixture is typically airectea to a thermoplastic extruder, usually of the single or twin screw type, wnere in the case of a blend the resin is compounded with sufficient temperature and shear tO ?rovlde an intimate PPE/PS blend.
Ihe product of the conventional extruder is an extruaare :. -e ~orm of stranas wnicn may oe quenched with a coolant âuch as cooling water. The cooled ,tranas are _ rected .o a pelletizer aevice whicn provides the PPE/PS resin pellets in a conventional form for use ln tne present invention.
Durlng the blending step it is contemplated that convent.onal additives may be incorporated in the resin mixture if desired. These lnclude rubbery impact modifiers, Clame retarding agents, stabilizers ror thermal and color stability, antioxidants, ?rocessing aids, plasticizers, reinforcing and extenaing fillers, pigments, antistatic agents, lubricants, mixtures of any o~ ~he roregoing ana the like. Eacn of tnese may be utilized to a greater or lesser degree depending on the final requlrea proDerties desired in the foamea ?roauct.
Conventional surfactants and nucleants used in expanaed polystyrene foams may also be utilized.
Examples of these include zinc or tin stearates, ,~aleates, fumarates, .alc, a citric acid and sodium oicarbonate mixture (Hydrocerol-) and the like.
~ ther vrererred resins contemplatea for use in the present invention are polyamides, e.~. nylon-6 and nylon-6,6; ana oreferably amorpnous nylons, e.~.

2~3~6~6 -ll- (8CN-8429) Selar- PA (DuPont), 3exloy- C (DuPont), Zytel- 330 (DuPont), Trogamid- ~ (Dynamit Nobel), Grilamid T~55 (Emerson Industries) and MXD6 (Mitsubishi Gas Chemical);
Dolycarbonates such as poly(bisphenol-A) carbonate; poly-ethersulfones and polyetherimides. These are available commercially and are described in the literature.
The substantially homogeneous thermoplastic resin is generally plasticated in a melt compounder.
This typically comprises an extruder although any melt compounding apparati ~nown to those skilled in the art ~ may be employed. (See Modern Plastics Encyclopedia '89, ~cGraw Hill, ctooer 1988, ~ol. 65, ~o. ll, Dage 345 -346). ; wlde iariety of extruders may ~e e.mploved, sucn as those aescribed in Modern Plastics Encyclopeaia '89, 15 .~cGraw ~ill, ~ctoDer 1988, ~ol. 65, ~o. ll, ?P. 242 - 244.
~ he plasticated resins are then extrlded through a multi-strand microdie. The microdie is construc~ed to comprise a olurality of holes having a diameter of up to about 0.02 inches. The strands exiting ~ne ~icrodie have an average diameter of less than about 0.02 inches.
It is also contemplatea herein that tne olasticated tnermoplastic resin is directed through a spinning aoparatus c~ntaining a multi-fiber s?innerette die to form fibers having an average diameter of less than about O.C2 inches. Any spinning appa ~tus known to those skilled in the art is contemplatea.
The strands or fibers are then cooled. It is contemplated to effect the cooling by quenching the stranas or fibers with a coolant. Typical coolants may comprise water, air, aitrogen, helium, alcohols, polyols, glycols or mixtures of any of them. Preferred is a waterbath or air coolins.
The cooled strands or fibers are then directed to a comminuting device, typically a high speed chopper 20306~6 -12- (8CN-8429) or an impeller. See Modern Plastics Encyclopedia '89, .~cGraw ~ill, Octobe l9a8, Yol. 65, No. 11, pp. 352 -353. The strands or fibers are co~minuted to form ~
substantially cylindrical micropellets having an average diameter of less than about 0.02 inches. Preferably the micropellets have a length to diameter ratio of about 1:1.
The micropellets are then impregnated with a blowing agent. Preferably the blowing agent comprises a volatile liquid or gas capable of being absorbed by the thermoplastic resin and which will vaporize at or below ~he glass transition temperature of the thermoplastic resin.
The clowing agents may include conventional hydrocarbon or 'luorocarbon blowing agents. The ?referred h~drocarbon blowing agents will include aliphatic hvdrocarbons. Examples include propane, butane, isobutane, n-pentane, isopentane, neopentane, pentene, cyclopentane, cyclohexane, hexane, heptane, octane, .~ixtures thereof and the like. FluorocarDon blowing agents incluae trichlorofluoromethane (CC13F), dichlorodifluoromethane (CC12F2) ana CClF -_ClF_. These are commercially available as FREON- 11, FREON- 12, and FREON- 114. ~ther halogenated hyarocarbon ~lowing 2S agents include methylene chloride, chloroform, carbon tetrachloride (CC14), HCFC's such as difluorochloro-~ethane (CHClF~) (HCFC-22) (FCRCMACEL- S), dichlorotri-fluoroethane (HCFC-123) (CHCl~CF3), dichlorotrifluoro-ethane (HCFC-123A) (CHFClCClF2), chlorotetrafluoroethane (HCFC-124) (CHClFCF3), tetrafluoroethane (HFC-134A) (CH2FCF3), dicnlorofluoroethane (~CFC-141B) (CCl~cCH3), chlorodifluoroethane (HCFC-142B) (CH3CClF2), difluoro-ethane (HFC-152A) (CH3CHF2) the like. Other blowing agents contemplated for use in the present invention are: acetone, alcohols having ~rom 1 to 5 carbon atoms 20306~6 -13- (8CN-a~29) such as isopropanol, halogenated alcohols such as fluoro- isoproDanol, carbon dioxide, nitrogen, water, mathy~ethyl ketone, ethy~ acetate or mixtures of any of the foregoing.
The blowing agent may be impregnated into the microparticles in any manner known to those skilled in the art.
In one preferred embodiment the substantially cylindrical thermoplastic resin micropellets and desired amount of blowing agent are placed in a vessel, the - mixture is agitated until tne blowing agent and thermoDiastic resin micropellets are thoroughly mixed.
,e 1xture is then allowed to age at or near ambient conaitlons for a period of time sufficient to - 15 impregnate t.~e thermoplastic resin micropellets with the blowing agent. Substantially cylindrical expandable microparticles are produced by this method.
In another preferred embodiment the substantlally cylinarical thermoplastic resin micropellets are impregnated with an effective amount of blowing agent at a temperature above the glass transition temperature o~ the _olymer and blowing agent composition.
.ypicall~ the tnermopiastic resin micropellets are supported in a wire mesh screen and placed in an autoclave. The micropellets are dispersed on the screen support in order to expose a maximum surface area to the blowing agent vapors.
The autoclave is sealed and evacuated. Once ; tne autoclave is evacuated, a quantity o~ blowing agent is drawn into tne autoclave. The amount of blowing agent charged is aetermined by the amount of absorption -~ desired and the amount of blowing agent required to m~intaln a saturated atmosphere.
The autoclave is slowly heated to about a temperature at or sligntly above the glass transition -14- (8CN-~q29) temperature (Tg) of the polymer and blowing agent composition and maintained thereat for an extended period of time. Higher temperature~ would result in ~icropellets that nave fused together. The temperature and time is determlned by the Tg of the composition and the rate at which the blowing agent is absorbed by the pellets.
The autoclave is allowea to cool to room temperature, opened and substantially spherical expandable microparticles are removed.
Alternatively, the blowing agent may be absorDed into tne micropellets through exposure of a water/^eile- _uspenslon to the blowing agent as follows.
Substantially cylindrical micropellets, e.g.
125 9, ~re _~spended in an aqueous solution of polyvinylalcohol (about l percent PVA by weight). Other suspending agents or surfactants may be employed, e.g.
tricalcium pnosphate. ~his suspension is charged to an autoclave (~0 ml) and is sufficient to fill this size autoclave to 75 percent of capacity.
A quantity of blowing agent is cnargea to the autoclave. .he autoclave is sealed, agitation is initiate~, and the temperature is slowly increasea.
Agitat1on is required in order to prevent clumping of the mlcropellets and to improve contact of the mlCrO-pellets with the blowing agent. This is especially useful for systems whicn consist of more than one liquid phase.
The system is heated to a temperature of about the Tg of the blend and maintained thereat for a period of .ime.
The elevatea temperature increases the rate at wnich the blowing agent evenly disperses through the micropellets and determines the necessary absorption ~ime.
lhe system is then all^wea to cool ~nd ;he micropellets are removed from the autoclave. ~he micropeLlets are separated from the suspension solution ;

203064~
-15- (8CN-8~29) with a sieve, rinsea with water and allowed to dry at ambient conditions. Substantially spherical expandable microparticles are thus produced.
DBSCRiPTIO~ OF Tn~ PR8PERReD E~BODIN~TS
The following spec~fic examples illustrate the present invention. However, they are not to be construed to limit the claims in any manner whatsoever.
ESA~PLE 1 A mixture of 10 weight percent of poly(2,6-di-methyl-1,4-phenylene)ether and 90 weight percent of principally atactic polystyrene are fed into a 30 mm ~erner Pfleiderer extruder equipped with a multiple strand microaie. ~ultiple strands having a diameter of less tnan 0.~2 inches are then cooled in a water bath and fed tO a nigh speed chopper to produce micropellets having a length to diameter ratio of about l:l. The micropellets are then exposed to a saturated atmosphere of blowing agent at a temperature of about 100C in an autoclave for about 4 hours. The autoclave is allowed to cool ana expanaable micropartlcles are produced in accordance with the present invention.
EXA~PLES 2 - 5 The proceaure of Example 1 is followed except blenas containing 20, 30, 40 and 50 weight percent of polyphenylene ether are employed. The tempereature is accordingly increased about 1C aoove 90C for each adaitionai 1 weight percent of polyphenylene ether in the composition. Expandable microparticles are produced in accordance with the present invention.

The proceaure of Example 1 is followed except a Dlena of 10 welght percent of Drominatea polys~yrene, ;0 weight percent polyphenylene ether and 40 weight pPrcent of prlncipally atactic po~ystyrene is employea.
Expandable flame retardant microparticles are produced 2030~46 -16- (8CN-~429) in accordance with the present invention~
~LB 7 The procedure of Example 1 is followed e~cept 3 weight percent of carbon black pigment is added to the resin blend. Black expandable microparticles are produced in accordance with the present invention.
E~a~PLeS 8 - 21 The procedure of Example 1 is followed except that poly(alpha-methylstyrene), poly(nuclear-methyl-styrene~, poly(para-methylstyrene~, poly(para-tert-butyl-styrene~, polymonochlorostyrene, polydichlorostyrene, polybromostyrene, polydibromostyrene, styrene-maleic annydride copolymer, styrene-butadiene copolymer, styrene-acrylonitrile copolymer, styrene-acrylonitrile-butadiene terpolymer, styrene-divinylbenzene copolymer and rubber modified high impact polystyrene are substituted for the principally atactic polystyrene.
ExpanaaDle ~icroparticles are produced in accordance with the present invention.
EXAffPL~S 22 - 3~
lhe procedure of ~xample 1 is followed except that instead of the polyphenylene ether~polystyrene resin ~lend an amorphous polyamiae, a polycarDonate, a polyphenylene ether~polyethylene blend, a polycarbonate/
polyetr,erimlde Dlend, a polycarDonate/amorphous polya~ide blend, a polystyrene, a polysulphone, a polyphenylene ether, a functionalized polyphenylene ether/amorphouS
polyamide blend, a polycarbonate/polyester blend, a polyester/amorphous polyamide blend, a polyester~poly-3~ etherimide blend, a polyetherimide/amorphous polyamideblend and a polyetherimide/polycarDonate/poiyester blend are employed as the substan~ially homogeneous thermoplastic resin. Expancable microparticles are prod~ced in accordance with the present invention.

203~6~6 -17- (8CN-a~29) ESA~PLeS 35 - 73 The procedure of Example 1 is followed exceet ~tXat inQtead of n-pentane, isopentane, neopentane, - -cyclopentane, butane, isobutane, pentane, hexane, S cyclohexane, heptane, octane, propane, methylene chloride, chloroform, carbon tetrachloride, trichloro-fluoromethane, dichlorodifluoromethane, difluorochloro-methane, CClF2 - CClF2, HCFC - 123, HCFC - 123A, ~CFC -124, HFC - 134A, HCFC - 141B, HCFC - 142B, HFC - 152A, acetone, butanol, isopropanol, methanol, ethanol, ~ propanol, fluoroisopropanol, carbon dioxide, nitrogen, air, methyl ethyl ketone, ethyl acetate and water are employed as the blowing agent. Expandable microparticles are producea in accordance with the present invention~
E~A~PLES 7~ - 8~
The procedure of Example 1 is followed except that a plasticizer, a flame retardant, a thermal stabilizer, a U-V stabilizer, a lubricant, an antistatic agent, a nucleating agent, a pigment, a reinforcing filler, a non-reinforcing filler and a mixture of the~e are added to the extruder with the resin blend.
Fxpandable microparticles are produced in accoraance with the present invention.

lhe procedure of Example 1 is followed except that the resin blend is fed to a spinning apparatus equipped with a multi-fiber spinnerette aie to rorm multiple fibers having an average diameter of less than 0.02 incnes, air cooling the fibers and directing the fibers to a high speed chopper to form substantially cylindrical micropellets having a length to diameter ratio of 1:1. The micropellets are then imbibed with n-pentane. Expandable microparticles are produced in accordance with the appended claims.
The above-mentioned patents, patent applications 203064~

-}8- t8CN-8429) and publications are incorporated herein by reference.
^- Many variatio~ of the present invention will ~uggest themselves to those skilled in the art in light of the above-detailed description. For example instead of poly(2,6-dimethyl-1,4-phenylene)ether, a poly(2,6-dimethyl-co-2,3,6-trimethyl-1,4-phenylene)ether resin may be employed. It is also contemplated to use any type of melt compounding apparatus instead of an extruder, and an impeller or other comminuting device may be used to form the substantially cylindrical micropellets. Further, any imbibing process known to those sKilled in the art is contemplated to impregnate the microp~llets with blowing agents. All such obvious modificatlons are with the full intended scope of the appended claims.

Claims

1. A process for the production of expandable microparticles of a thermoplastic resin comprising the following steps:
(a) plasticating a substantially homogeneous thermoplastic resin or a blend of at least two substantially miscible thermoplastic resins capable of becoming substantially homogeneous after said plastication;
(b) extruding the plasticated material in step (a) through a multi-strand microdie to form strands having an average diameter of less than about 0.02 inches;
(c) cooling said strands;
(d) comminuting said cooled strands to form substantially cylindrical micropellets having a length to diameter ratio or about 1:1; and either (e)(i) impregnating said substantially cylindrical micropellets with an effective amount of a blowing agent to form substantially cylindrical expandable microparticles; or (e) (ii) impregnating said substantially cylindrical micropellets with an effective amount of a blowing agent at a temperature above the glass transition temperature of said thermoplastic resin to form substantially spherical expandable microparticles.

2. A process as defined in Claim 1 wherein said plasticated material is selected from the group consisting of a polypnenylene ether, an alkenyl aromatic polymer, an amorphous polyamide, a polycarbonate, a polyether sulfone, a polyester, a polyetherimide and substantially homogeneous mixtures and copolymers thereof.

-20- (8CN-8429

3. A process as defined in Claim 2 wherein said polyphenylene ether is selected from the group consisting of poly(2,6-dimethyl-1,4-phenylene)ether, poly(2,6-dimethyl-co-2,3,6-trimethyl-1,4-phenylene)ether and a mixture thereof.

4. A process as defined in Claim 3 wherein said polyphenylene ether resin comprises poly(2,6-di-methyl-1,4-phenylene)ether.

5. A process as defined in Claim 2 wherein said alkenyl aromatic polymer is selected from the group consisting of principally atactic polystyrene, poly(alpha-methylstyrene), poly(nuclear-methylstyrene), poly(para-methylstyrene), poly(para-tert-butylstyrene), polymonocnlorostyrene, polydichlorostyrene, polyoromo-styrene, polydibromostyrene, styrene-maleic anhydride copolymer, styrene-butadiene copolymer, styrene-acryloni-trile copolymer, styrene-acrylonitrile-butadiene terpolymer, styrene-divinylbenzene copolymer, high impact polystyrene, copolymers and mixtures of any of the foregoing.

6. A process as defined in Claim 5 wherein said alkenyl aromatic polymer comprises a principally atactic polystyrene.

7. A process as defined in Claim 5 wherein saia alkenyl aromatic polymer comprises a hign impact polystyrene.

8. A process as defined in Claim 5 wherein said alkenyl aromatic polymer comprises polybromostyrene, polydibromostyrene or copolymers and mixtures thereof with other styrenic resins.

9. A process as defined in Claim 2 wherein said substantially homogeneous thermoplastic resin comprises a blend of a polyphenylene ether resin and a polystyrene resin.

-21- (8CN-8429)

10. A process as defined in Claim 9 wherein said blend comprises from about 98 to about 2 parts by weight of a polyphenylene ether and from about 2 to about 98 parts by weight of a polystyrene resin based on 100 parts by weight of the two resins combined.

11. A process as defined in Claim 11 wherein said blend comprises from about 20 to about 80 part by weight of a polyphenylene ether and from about 80 to about 20 parts by weight of a polystyrene resin based on the weight of the two resins combined.

12. A process as defined in Claim 1 wherein said substantially homogeneous thermoplastic resin comprises a polyamide selected from the group consisting of nylon-6, nylon-6,6 and mixtures thereof.

13. A process as defined in Claim 1 wherein said substantially homogeneous thermoplastic resin comprises an amorphous polyamide.

14. A process as defined in Claim 1 wherein said substantially homogeneous thermoplastic resin comprises a polycarbonate.

15. A process as defined in Claim 1 wherein said substantially homogeneous thermoplastic resin comprises a polyetherimide.

16. A process as defined in Claim 1 wherein said substantially homogeneous thermoplastic resin comprises a polyester.

17. A process as defined in Claim 1 wherein said step (a) is carried out in is an extruder.

18. A process as defined in Claim 1 wherein said cooling step (c) is effected by a water bath.

19. A process as defined in Claim 1 wherein said cooling step (c) is effected by air cooling.

20. A process as defined in Claim 1 wherein said comminuting step (d) is carried out in a high speed chopper.

-22- (8CN-8429)

21. A process as defined in Claim 1 wherein said blowing agent comprises a volatile liquid or gas capable of being absorbed by the thermoplastic resin and which will vaporize at or below the glass transition temperature of the thermoplastic resin.

22. A process as defined in Claim 21 wherein said blowing agent is selected from the group consisting of n-pentane, isopentane, neopentane, cyclopentane, butane, isobutane, pentene, hexane, cyclohexane, heptane, octane, propane, methylene chloride, chloroform, carbon tetrachloride, trichlorofluoromethane, dichlorodifluoromethane, difluorochloromethane, CClF2-CClF2, HCFC-123, HCFC-123A, HCFC-124, HFC-134A, HCFC-141B, HCFC-142B, HFC-152A, acetone, alcohols having from 1 to 5 carbon atoms, halogenated alcohols, carbon dioxide, nitrogen, methylethyl ketone, ethyl acetate, water, air and mixtures of any of the foregoing.

23. A process as defined in Claim 22 wherein said blowing agent comprises an HCFC.

24. A process as defined in Claim 23 wherein said HCFC is selected from the group consisting of HCFC-22, HCFC-123, HCFC-123A, HCFC-124, HFC-134A, HCFC-141B, HCFC-142B, HFC-152A and mixtures of any of the foregoing.

25. A process as defined in Claim 1 wherein said effective amounts of a blowing agent comprises from about 3 to about 15 weight percent of a blowing agent based on the weight of said thermoplastic resin.

-23- (8CN-8429)

26. A process as defined in Claim 1 wherein said steps (b), (c) and (d) comprise:
(b) extruding and spinning the plasticated material formed in step (a) through a multi-fiber spinnerette die to form fibers having an average diameter of less than about 0.02 inches;
(c) cooling said fibers;
(d) comminuting said cooled fibers to form substantially cylindrical micropellets having a length to diameter ratio of about 1:1.

27. A process as defined in Claim 1 which also comprises adding plasticizers, flame retardants, thermal stabilizers, U-V stabilizers, lubricants, antistatic agents, nucleating agents, pigments, reinforcing or non-reinforcing fillers or mixtures of any of the foregoing during said melt compounding step (b).

28. The invention as defined in any of the preceding claims including any further features of novelty disclosed.