CA2029164A1 - One step process for simultaneous extrusion and impregnation of blowing agent in the production of expandable thermoplastic resin particles - Google Patents

Abstract

(8CN-8428) ONE STEP PROCESS FOR SIMULTANEOUS EXTRUSION AND
IMPREGNATION OF BLOWING AGENT IN THE PRODUCTION OF
EXPANDABLE THERMOPLASTIC RESIN PARTICLES

ABSTRACT
A one-step process for simultaneous extrusion and impregnation of blowing agent in the production of expandable thermoplastic resin microparticles employing a microdie or a granulator is disclosed.

Description

~2~
-1- (scN-a42s) 0~ STEP PROCESS ~OR SI~ULTANEO~S E~RUSIOD AND
I~PR~GN~TIO~ OF BLO~ING AGE~T IN T~ P~OD~C~ION OF
EXPANDABLE T~ER~OPLASTIC R~SIN PARTlCL~S
The present invention relates to expandable thermoplastic resin particles. More particularly it relates to a process for simultaneously extruding and-impregnating a thermoplastic resin with a blowing agen~
to produce expandable thermoplastic resin particles.
BAC~GR~ND OF T~ INVENTION
Methods for ~he proauction o~ expanaaDle thermoplasti_ resin beads for use in the manufacture of foam molded ,r..~les are well known in tne art.
Lraditional expanded polystyrene technology has existed slnce t',e earl~ 1950's.
~he production of expandable Deads can include the incorporation of a blowing agent by one of tnree methods. One ,metnoà, known as the "one-step" process, is to suspenà st~rene monomer, initiators and hycrocarbon blowing agent ln water and polymerize at high temperature.
This method is taught by Japanese ~atent Publication No.
32623/70.
In a second processt callea the "l~ step"
process, the polymerization is brought to ~0 ?ercent completion before the blowing agent is introduced into the system. ~he "~wo-step" process incorporates the blowing agent into suspension polymerized beads (100%
converted) or ~elt compounded pellets. ~he two-step process is used in Japanese Patent Publication ~o.
36097/7~ which discloses-heat melting a polymer, pelletizing ~he melt and incorporatin~ the formed pellets wi~h a blowing agent.
Canadian Patent No. 1,023,521 and ~.S. Patent " 003,193 disclose processes for pellet production wherein the resin is passed through a die and intermittently ex~ruded. Canadian Patent l,023,52l -2~ (8CN-a428) discloses intermittently extruding the resin in a heat plastified form under continuously applied pressure through a plurality of constricted passage~ays into a plurality of outlets into a zone of lower pressure to provide a plurality of closely adjacent extruded globules which then expand and adhere together to form strands which are then mecnanically agitated to separate the strands into individual particles. U.S. Patent ~o.

3,003,193 teaches intermittent extrusion of the resin through a die with non-reactive fluid between the intermittent resln particles as an ejection fluid.
'~eltner the Canadian Patent 1,C23,521 nor the ~nited States ~,003,193 patent disclose the produc~ion o~ micropellets oy continuously extruding tne resin througn a die and immersing the resulting stranas in a coolant ana tnen cutting the strands into pellet snapea particles wherein either the die is a microdie or the process includes a granulating step.
Incorporation of the blowing agent into the extruder has Deen disclosed in Collins, ~nited States Patent No. 3,250,834. Collins compressed the heated polystyrene prior to introauction of the blowing agent and coolea the mixture thereafter extrudiny the mixture lnto strands which are later cut into pellets. The problem in Collins is the cooling necessary to prevent expansion of the mixture prior to extrusion. Furt~er, the stranas produced by the Collins process are taught to have a diameter of about 0.06.
The problem of temperature control wnile cooling tne extrudate passln~ through the die, as causing blockage of the die, i~ dealt with in ~nited ~in~aom Patent ~o. 948,200 ~latz et al.) ana ~anadian Fatent No. 682,464 ~Scnroeder et al.). Platz et al.
ma~e use of a die eitner ~ade from or iined with polytetrafluorce~hylene having openings of 2 to 8 mm in 2û29164 -3- (8CN-8428) diameter. Schroeder et al., on the other hand, deal with this problem by regulating the temperature of the composition entering the die ~o assure free flow and cooling the composition almost immediately as it exits the die. Schroeder et al. makes no mention of a minimum diameter of extrusion leaving the die.
Other processes for the production of expandable resin compositions are disclosed in United States Patent No. 3,026,273 (Engles), United States Patent No. 3,026,272 (Rubens et al.), United States Patent No. 3,121,132 (Bene) and United States Patent No.
3,026,274 (MacMillan et al.). These disclosures deal with the pre-expansion of the composition. The size of the pellets produced in these disclosures are limited, in their minimum dimensions, to normal diameters, as no mention of small or microdiameter pellets is made.
The process of underwater pelletizing of polymars with an adjustable blade for varying pellet size is disclosed in Smith, United States Patent No.

4,500,271. Size restrictions of the extrusion die due to flow of the polymer are limited to a minimum of about 0.035 inches to produce uniform bead size distribution.
Such techniques are good for resins which process at low temperatures, such as polyolefins, but not for engineered thermoplastics. Allen et al. in commonly assigned Canadian Applicatlon Serial No. 598,071 filed April 27, 1989 discloses a one-step process for the production of small spherical expandable beads employing a heated die and underwater pelletizer. Allen et al.
claim small expandable beads having a diameter ranging from about 0.010 to about 0.050 inches and more preferably from about 0.015 to about 0.025 inches.
Allen et al., United States Patent No.
4,727,093 also teaches a two-step process for producing - 2~916~
_4_ (8CN-~428) expandable resin particles wherein extrudate in the form of strands is quenched in cooling water. The cooled strands are directed to a pelletizer device to pro~ide pellets of the thermoplastic resin. The blowing aqent is then imbibed into the pellets. This imbibing step generally requires large, capital intensive pressure vessels ana several hours to complete adding substantially to the final cost of the product.
It has now been surprisingly discovered that the imDibing step in the beaa manufacturing process can be effectively eliminated by injecting the blowing agent airectly into tne extruder during the plasticat1ng step.
~hus, in one-step the polymer b~end is compounded together wlth a blowing agent to form a homogeneous mixture wnicn is subsequently cooled and extruaed into stranas Defore substa~tial foaming occurs. These strands can tnen be pelletized without the need for an un~erwater pelletizer. The desired microparticle slze can be attained either by extruding through a microdie or granulating larger size pellets.
3RIEF D~SCRIPTIO~ OF T~ DRAWI~G
FIG. 1 illustrates schematically an extruaer useful in the practice of the present invention.
SU~ARY OF T~ INVE~TIQN
Accor~ing to the present invention there is provided an improved process for the production of expanaable tnermoplastic resin microparticles comprisin~:
(a) feedin~ the thermoplastic resin into an extruaer;
(b) injecting~an effective amount of a blowing agent into the extruaer;
(c~ mixing the thermopiastic resin and the blowing agent in-the extruaer;
(d) cooling the mixture, optionally in a second extruder;

~29~
,_ ( scN-a42s ) (e) extruding the mixture through a die to form at least one strand of the thermoplastic resin containing the blowing agent (f) immersing the resulting strand or strands in a coolant to solidify the strand or strands;
(g) air drying the strand or strands; and (h) cutting the strand or strands into pellet shaped expandable thermoplastic resin particles; the improvements comprislng either (1) providing a microdie in step (e); or (2) providing a normal aie in s.ep (e) and including a granulating step in (h).
rref~raDly, .~e thermoplastic resin is selectea from the group consisting of a polyphenylene ether, an al~enyl aromatic polymer or copoiy~er, a polycarbonate, a polyamide, a polysulfone, a polyethersulfone, a polyester, a poly(etheri~iae~, a poly(e~herimide ester), a polyarylate and mixtures of any of t~e foregoing. ~he preferred polyphenylene ethers are poly(2,6-dimethyl-1,4~phenylene)ether, poly~2,3,6-trimethyl-1,4-phenylene)ether and poly(2,6-dimethyl-co-2,3,6-trimethyl-1,4-phenylene) ether. ~he preferred alkenyl aromatic polymers are selectea from the group consisting of principally atactic ?olystyrene, poly(alpha-methylstyrene), poly(nuclear-methylstyrene), poly(para-methylstyrene), poly(para-tert-butyl styrene), halogenated polystyrenes, a styrene-maleic anhydride copolymer, a polyphenylene eeherfpolystyrene blend and mixtures of any of the foregoing.
The preferred blowing agents are selected from tne group consistin~ or n-pentane, isopentane, neopentane, cyclopentane, butane, isobutane, pentene, nexane, neptane, octane, propane, metnylene chloride, chloroform, carbon tetrachloride, trichlorofluoromethane, -6- (8CN-a428) dichlorodifluoromethane, chlorodifluoromethane, CClF2-CClF2, dichlorotrifluoroethane (C~C12F3), dichlorotri-fluoroethane (CHFClCClF2), chlorotetrafluoroethane, tetrafluoroethane, dichlorofluoroethane, chlorodifluor ethane, cifluoroethane, acetone, alcohols having from 1 to 5 carbon atoms, halogenated alcohols such as fluoro-isopropanol, carbon dioxide, nitrogen, water, methyl-ethyl ketone, ethyl acetate and mixtures of any o~ the roregoing.
Also, according to the present invention there are provided micropartic~es producea by the process as defined above wnerein the microparticles possess an average ~iameter rangin~ from about 0.10 to about 0.005 inches, preferaDly from about 0.05 to about 0.01 inches.

~ he present invention relates to a process for tne production of expandable thermoplastic microparticles.
In reference to the drawing, FIG. 1, a polymer resin or mixed polymer resin is fed into an extruder 2 through hopper 4 wherein it is melted ano mixed. At a point on the extruder 2 downstream from hopper 4 and before die i~ and preferably about ~/3 of the way from hopper 4 to die 10 is locateà a blowing agent injector 6. The blowing a~ent injector 6 introauces a Dlowing agent to the melt, under pressure, to form a mixture of the polymeric composition and the blowing agent. Lhe strand or strands of extrudate exiting out die 10 is immediately immersed in a coolant to solidify the strand or strands. Although water is the preferred coolant, other suitaDle coolants ~all within the scope and spirit of the present invention including coolants which are non-reacting and ~enerally immiscible with the plastic, e.g. air, nitrogen, helium, alcohols, polyols and ~lycols.
The invention may be practiced with the use of ~202~16~
_7_ (8CN-a428) a wide variety of materials encompassed within the broader description given above. In the typical ca~e however use is made of certain preferred materials which are described below.
The polyphenylene ether (PPE) is normally a homo- or copolymer having units o~ the formula , . . .
~~ ' Q Q
.
wherein Q, 2 , Q , Q are independently selected from ehe qroup consisting of hydrogen, halogen, nydrocarbon, halonydrOcarDon, hydrocarbonoxy, and halohydrocarbonoxy;
and n repcesents the total number of monomer units and is an integer of at least about 20, and more usually at least 50.
The polyphenylene ether can be prepared in accordance with known procedures such as those described in Hay, ~nited States Patent Nos. 3,306~R74 and 3,3~6,675; and Stamatoff, United States Patent ~os.
3,257,357 and 3,257,3;8, from ~he reaction of pnenols including but not limited to: 2,6-aimethylphenol; 2,6-diethylphenyl; 2,6-dibutylphenol; 2,6-diaurylphenol;
2,6-dipropylphenol; 2,6-diphenylphenol; 2-metnyl-6-tolylphenol; 2-methyl-6-methoxyphenol; 2,3,6-trimethyl-phenol; 2,3,5,6-tetramethylphenol; and 2,6-diethyoxy-phenol.
Each of these may be reacted alone to produce the corresponding homopolymer, or in pairs or with still other phenols to produce the corresponding copolymer.
Examples of the nomopolymer include poly(2,6-aimethyl-1, 4-phenylene)ether, poly(2,6-diethyl-1,4-phenylene)ether, 2~16 -a- ( scN-a42s poly~2,6-aibutyl-1,4-phenylene)e~her, polyt2,6-diauryl-1, 4-phenylene)ether, poly(2,~-dipropyl-1,4-phenylene~ether, poly(2,6-diphenyl-1,4-phenylene~ether, poly(2-methyl-6-butyl-1,4-phenylene)ether, poly(2,6-dimethoxy-1,4-phenylene)ether, poly~2,3,6-trimethyl-1,4-phenylene~ether, poly(2,3 ",~-tetramethyl-1,4-phenylene~ether, and poly (2,6-diethyoxy-1,4-phenylene~ether. Examples of the copolymer include, espe~ially those of 2,6-dimethylphenol with other phenols, such as poly(2,6-dime~hyl-co-2,3,6-trimethyl-1,4-phenylene~ether and polyt2,6-dimethyl-co-2-methyl-6-butyl-1,4-phenylene)ether.
.-r ?ur?oses of ~he present lnvention, an especially preferred family of polyphenylene ethers include those having alkyl substitution in the two positions o~tno to the oxygen ether atom, i.e., those of the above formula wherein Q and Q are alkyl, most preferably having from 1 to 4 carDon atoms. Illustrative members or this class are: poly(2,6-dimetnyl-1,4-pheny-lene)ether; poly(2,6-dieehyl-1,4-phenylene)etner; poly (2-methyl-6-ethyl-1,4-phenylene)ether; poly(2-methyl-6-pro?yl-l,~-pnenylene)etner; ?oly(2,~-dipropyl-1,4-pneny-lene)ether; poly(2-ethyl-6-propyl-1,4-phenylene) ether;
and the like.
The most preferred polyphenylene ether resln 2S for purposes of the present invention is poly(2,6-di-methyl-1,4-pnenylene~ether.
The term "alkenyl aromatic polymer" as it is employed in this disclo~ure is intenaed to encomDass nomopolymers, as well as rubber modified high impact ~0 varieties, and also copolymers and terpoiymers of alkenyl aromatic compounds with one or more other materials. Preferably, the alkenyl aromatic polymer is based at least in part on units of the formula - 2~29164 -9- (~c~-a4~8 CR = CaR2 R ~

~ 3 R~ R

wherein Rl and R2 are selected from the group consisting of lower alkyl or alkenyl groups of from 1 to 6 carbon atoms and hydrogen; R3 and R4 are selected from the group consistin~ or cnlcro, bromo, hydrogen ano lower alkyl o~ from 1 .o 6 carbon atoms, R5 and R6 are selectea tro;r, tne ~roup cGnsisting of hyarogen ana lower alkyl and alkenyl groups of from 1 to 6 carbon atoms; or R5 and R6 may be conc~tena~ea together with hydrocarbyl 4roups to ~orm a naphehyl ~roup.
The above will encompass styrene, as well as homologs ana analojs of styrene. Specific examples inalude, in addition to styrene, chlorostyrene, bromostyrene, alpha-methyl styrene, para-methyl s~yrene, vinyl styrene, divinyl benzene and vinyl naphthalene.
Styrene is es~ecially preferred.
By way of illustration, the polystyrene (P ) component can oe a homopolystyrene (principally ?tactic) or other alkenyl aromatic homopolymer which has Deen ~O modifiea by admixture or interreaction with a n~turaL or synthetic rubber, for example, polybutadiene, polyisoprene, EPDM rubber or silicone rubber; or it can be a copolymer or terpolymer of styrene or other alkenyl aromatic compound witn an elastomeric or o~her material, such as block copolymers of styrene and butadiene (for example, AB, ABA, AB~B or ABA~A type~, including hydrogenated forms of the foregoing, a radial teleblock copolymer of seyrene, butadiene and a coupling agent, includinq hydrogenated forms, terpolymers of -10~ (8CN-~428) acrylonitrile, styrene and butadiene (A8S~, styrene-acrylonitrile copoiymers (SAN), and a copolymer of styrene and maleic anhydride (SMA); or it can also be an alk~nyl aromatic copolymer or terpolymer which has been modified with rubber, for example, rubber modified styrene-maleic anhydride copolymer. Many of these are described in the patent literature, such as Cizek, United States Patent ~lo. 3,383,435.
The polyphenylene ether (PPE) and polystyrene resins may be combinea in a conventional manner. PPE
resin will typically be in powder or pellet form and the polystyrene will typlcaily be in pellet form. .he resins ~ay be comDined by dry blending in a blender whicn provlaes a relatively uniform mixture or tne resins or by other conventional means. This mixture is typically directea to a thermoplastic extruoer, ~sually of the single or twin screw type, where in the case of a ~lend the resin is compoundea witn sufficient temperature and shear to provide an intimate PPE/PS blena.
Tne ?roàuct of tne conventional extruoer is an extrudate in the form of strands which may be quenched with a coolant such as cooling water. ~he cooled strands are directed to a pelletizer device which proviaes the FP~/PS resin pellets in a conventlonal form for use in tne present invention.
During the blenaing step it is contemplated that conventional additives may be incorporated in the resin mixture if desired. These include rubbery impact modifiers, flame retarding agents, stabilizers for thermal and color stability, antioxidants, processlng aids, plasticizers, reinforcing and extending fillers, pigments, antis~atic agents, lubricants, mixtures of any of the foregoing and the like. Each of these may be utllizea to a greater or lesser degree depenalng on the ~5 final required properties desired in the foamed product.

2~916 ~ -~ (8CN-8428) Conventional surfactants and nucleants used in expanded polystyrene foams may also be utilized. Examples o these includ~ zinc or tin stearates, maleates, fumarates, talc~ a citric acid ana sodium bicarbonate mixture (~ydrocerol-) and the like.
The resin pellets may then be fea into an extruder wherein the blowing agent is injected through injection port 6.
The blowing agents which may be utilized in the practice of this invention are volatile liquids or gases which can be absorbed into the polymer mixture and which wlll vaporize at a temperature below the ~ of the resin matrix. PPE/PS blends typically have a Tg in excess of 100C. The T~ of such blenas increases roughly 10C for each 10 weight percent PPE in the resin blend, up to tne ~9 of PPE (approximately 210C). Thus a 30:70 mixture of PPE~PS has a Tg of approximately 125C and the Tg of a 50:50 Dlena is approximately 145 -155C. Note that these temperatures are for blends prior to the aaditlon of the blowing agent.
The blowing agents may include conven~ional nydrocarDon or fluorocarbon blowing agents. mhe ~referred hydrocarbon blowing agents will include alipha~ic hyàrocarbons. Examples incluae 2ropane, butane, isobutane, n-pentane, isopentane, neopentane, pentene, cyclopentane, hexane, heptane, octane, mixtures thereof and the like. Fluorocarbon blowing a~ents include trichlorofluoromethane (CC13F), dichlorodifluoro-methane (CC12F2), difluorDchloromethane (HCFC-22) (CHClF2) and CClF2-CClF2. These are commercially available as FREON- 11, FREON- 12, FORMACEL~S and FREON-114. Other halogenated hydrocarbon blowing agents include methylene chloride, chlorofor~ carbon tetracnlorioe ~CC14~, HCFC's such as dichlorotrifluoro-ethane (HCFC-123) (C~C12CF3), dichlorotrifluoroethane -12- (8CN-8428) (HCFC-123A) (CHFClCClF2), chlorotetrafluoroethane (HCFC-124) (CHClFCF3), tetrafluoroethane (HFC-134A) (CH2FCF3), dichlorofluoroethane (HCFC-141B) (CC12FCH3), 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 from 1 to 5 carbon atoms such as isopropanol, halogenated alcohols such as fluoroisopropanol, oarbon dioxide, nitrogen, water, methylethyl ketone, ethyl acetate or mixtures of any of the foregoing.
The resin and blowing agent are intimately mixed in the extruder 2. The mixture is then cooled, either in a downstream portion of extruder 2 or in a second extruder (not shown) if tandem extruders are employed. The extrudate is transported down the extruder by screw 8 through the die 10 and exits the extruder in at least one strand through at least one exit opening in die 10.
The invention contemplates two types of extruder dies 10. In the first instance the extruder die 10 comprises a microdie. The microdie is constructed to comprise one or a plurality of holes having a diameter of from about 0.02 to about 0.10 inches, more preferably the diameter ranges from about 0.05 to about 0.10 inches. The extrudate strands exiting the microdie are then quenched in a coolant, air dried and directed to a pelletizer to produce microparticles possessing an average diameter ranging from about 0.005 to about 0.10 inches and more preferably from about 0.01 to about 0.05 inches.
In the second instance, the extruder die 10 comprises a conventional size die, the extrudate strand or strands are quenched, air dried and directed to a pelletizer. The strand or strands are cut into pellet -13- 21)29~ (8CN-~428) shaped particles which ar~ then granulated to produce microp~rticles possessing an average diameter ranging ~rom abou~ 0.005 to about 0.10 i~ches and more p~eferably from about 0.01 to about 0.05 inches.
S In either case any conventional pelletizing d~vlce such as a high speed chopper or an impeller m~y be employed. Suitable conventlonal pelletizers are those such as described in Modern Plastics Encyclopedia '89, McGraw-~ill, October 1988, Vol. 65, No. 11, pps 352 - 353.
Any suitable conventional granulator is contemplated for use in the second case of the present invention. T~pical granulators are described in Modern Plastics Encyclopedia '89, McGraw Hill, October 19~8, Vol. 65, No. 11, pp. 336 - 338.
DESCRIPTION O~ T~E PREFERRED EHBODIM~NTS
~he followlng specific examples illustrate the present invention. They are not to be construed to limit the cla ims in any manner whatsoever.
2 0 ~XA~LES 1 AND 2 25 parts by weight poly(2,~-dimethyl-1,4-phen~lene)ether and 75 parts by weight principally atactic polystyrene and 0.75 parts by weight or talc are added to a 34 mm Leistritz twin screw extruder. To this is adde~ 5 parts by weight or either dichloroaifluoro-methane or trichlorofluoromethane, and the mixture is compoundea in the extruder until essentially homogeneous.
The homogeneous mixture of resin and blowing agent is then transferred to a 1.5 inch diameter (38:1 L/D) Sterling single screw extTuder through a heated pipe and coolea to a ~emperature of about 330~. ~he extruaate is then pumped through a stranding microdie, immersed in water, air dried and pelletized. T~e exit die pressure is maintained bet~een 2500 and 4000 psi. Expandable - 35 microparticles are produced in accoraance with the - 202~
-14- (8CN-~428) appended claims. The microparticles are then expanded ~o 70 percent density reauction by heating at 170C for aboue 7 minutes.
~XaXPLBS 3 - 20 The procedure o~ Example 1 is repeatea, except the thermoplastic resin employed is poly(2,6-dimethyl-1, 4-phenylene)ether alone, poly(2,3,6-trimethyl-1,4-phe~y-lene ether3, principally atactic polystyrene, poly(alpha-methylstyrene), poly(nuclear-methylstyrene), poly(para-methylstyrene), poly(para-tert-butylstyrene), polybromo-styrene, polychlorostyrene, styrene-maleic anhydride copolymer, poly(bisphenol-A carbonate), a polyamide, a polyarylate, a ~olysulfone, a polyethersulfone, a poly(l,4-butylene terephthalate), a poly(etherimiae) and a poly(etherimide ester). Expandable thermoplastlc mircoparticles are produced in accordance with the scope of the appendea claims.
EXA~PLES 21 - 53 The procedure of Example 1 is repeated except that the following are employed as blowing agents:
n pentane, isopentane, neopentane, cyclopentane, butane, isobutane, pentene, hexane, heptane, octane, propane, ,~ethylene chloride, chloroform, carbon tetrachloriae, chlorodifluoromethane, CClF2-CClF2, acetone, HCFC-123, HCFC-123A, HFC-134A, HCFC-141B, HCFC-142B, HFC-152A, HCFC-124, methanol, butanol, isopropanol, fluoroiso-propanol, carbon dioxide, nitrogen, methylethyl ketone, ethyl acetate and water. Expanaable microparticles are produced in accordance wi-th the scope of the appended claims.

~ he ~rocedure of Example 1 is repeated except a normal die is employed on the second extruder and the particles proauced in the pelle~izer are subjected to a granulation step. Expandable microparticles are - 2~916~ (8C~-84~8) produced in accordance with the scope o~ the appende~
claim3.
T~e above-mentioned patents, patent applic~tion~
and publications are incorporated herein by reference.
S Many variations of the present invention will suggest thermselv~s to tho~e skilled in the art in light of the above detailed description. For example, in~tead of poly(2,6-dime hyl-1,4-phenylene~ether, a poly~2,6-dimethyl-co-2,3,6-trimethyl-1~4-phenylene)ether could be 10 employed as the thermoplastic resin. It is also contemplated to US@ an effective amount of any of the above-mentioned blowing agents in an amount ranging between from about 2 to about 20 parts by weight instead of 5 parts by weight. Effective amounts of impac~
modifiers, flame retaraants, stabilizers for thermal and color staDility, antioxidants, pigments, process aids, plastici~ers, antistatic agents, reinforci~g and exten~ing fillers, lubricants or mixtures of any of the foregoing may be added to the thermoplastic resin particles during mixing. All sucn obvious modifications are within the full intended scope of ~he appended claims.

Claims (31)

1. In a process for the production of expandable thermoplastic resin microparticles comprising:
(a) feeding said thermoplastic resin into an extruder;
(b) injecting an effective amount of a blowing agent into said extruder;
(c) mixing said thermoplastic resin and said blowing agent in said extruder;
(d) cooling the mixture; optionally in a second extruder;
(e) extruding said mixture through a die to form at least one strand of said thermoplastic resin containing said blowing agent;
(f) immersing the resulting strand or strands in a coolant to solidify said strand or strands;
(g) air drying said strand or strands; and (h) cutting said strand or strands into pellet shaped expandable thermoplastic resin particles, the improvements comprising either (1) providing a microdie die in step (e) or (2) providing a normal die in step (e) and including a granulating step in (h).

2. A process as defined in Claim 1 wherein said thermoplastic resin is selected from the group consisting of a polyphenylene ether, an alkenyl aromatic polymer or copolymer, a polycarbonate, a polyamide, a polysulfone, a polyethersulfone, a polyester, a poly(etherimide), a poly(etherimide ester), a polyarylate and mixtures of any of the foregoing.

3. A process as defined in Claim 2 wherein said thermoplastic resin comprises a polyphenylene ether.

-17- (8CN-8428)

4. A process a defined in Claim 3 wherein said polyphenylene ether comprises poly(2,6-dimethyl-1, 4-phenylene)ether, poly(2,3,6-trimethyl-1,4-phenylene) ether, poly(2,6-dimethyl-co-2,3,6-trimethyl-1,4-phenylene) ether or a mixture thereof.

5. A process as defined in Claim 2 wherein said thermoplastic resin comprises an alkenyl aromatic polymer.

6. A process as defined in Claim 5 wherein said alkenyl aromatic polymer comprises principally atactic polystyrene, high impact polystyrene, poly (alpha-methylstyrene), poly(nuclear-methylstyrene), poly (para-methylstyrene), poly(para-tert-butylstyrene), a halogenated polystyrene, a styrene-maleic anhydride copolymer, a polyphenylene ether/polystyrene blend or a mixture of any of the foregoing.

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

8. A process as defined in Claim 6 wherein said alkenyl aromatic polymer comprises a styrene-maleic anhydride copolymer.

9. A process as defined in Claim 6 wherein said alkenyl aromatic polymer comprises a halogenated polystyrene.

10. A process as defined in Claim 9 wherein said halogenated polystyrene comprises a polybromo-styrene.

11. A process as defined in Claim 9 wherein said halogenated polystyrene comprises a bromostyrene copolymer.

12. A process as defined in Claim 6 wherein said alkenyl aromatic polymer resin comprises a polyphenylene ether/polystyrene blend.

-18- (8CN-8428)

13. A procecs as def ined in Claim 12 wherein said polyphenylene etherJpolystyrene blend comprisen from about 20 to about 80 parts by weight of polyphenylene ether resin and from about 80 to about 20 parts by weight of polystyrene resin based on 100 parts by weight of the combined resins.

14. A proce s 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.

15. A process as defined in Claim 14 wherein said blowing agent is selected from the group consisting of n-pentane, isopentane, neopentane, cyclopentane butane, isobutane, pentene, hexane, heptane, octane, propane, methylene chloriae, chloroform, carbon tetrachloride, trichlorofluorom2thane, dichlorodifluoro-methane, aifluorochloromethane, 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 alconols, carbon dioxide, nitrogen, methylethyl ketone, ethyl acetate, water and a mixture of any of the foregoing.

16. A process as defined in Claim 15 wherein saia blowing agent comprises n-pentane, isopentane, neopentane, cyclopentane of mixtures thereof.

17. A process as defined in Claim 15 wherein said blowing agent comprises dichlorodifluoromethane, trichlorofluormoethane or a mixture thereof.

18. A process as defined in Claim 15 wherein said blowing agent comprises an HCFC.

-19- (8CN-8428)

19. A process as def ined in Claim 18 wherein said HCFC is selected from the group consisting of HCFC-22, HCFC-123, HCFC-123A, HCFC-124, HPC-134A, HCFC-141B, HCFC-142B, HFC-152A and mixtures of any of the foregoing.

20. A process as defined in Claim 15 wherein said blowing agent comprises isopropanol, fluoro-isopropanol or a mixture thereof.

21. A process as defined in Claim 1 wherein said effective amount of a blowing agent comprises from about 2 to about 20 parts by weight based on 100 parts by weight of the thermoplastic resin.

22. A process as defind in Claim 21 wnerein said effective amount of a blowing agent comprises from about 5 to about 10 parts by weight based on 100 parts by weight of the thermoplastic resin.

23. A process as defined in Claim 1 wherein effective amounts of impact modifiers, flame retardants, stabilizers for thermal and color stability, antioxidants pigments, process aids, plasticizers, reinforcing and extending fillers, antistatic agents, lubricants or mixtures of any of the foregoing are added to the thermoplastic resin particles.

24. A process as defined in Claim 1 wherein said coolant is selected from the group consisting of water, air, nitrogen, helium, alcohols, polyols, glycols and mixtures of any of the foregoing.

25. A process as defined in Claim 24 whereln said coolant comprises water.

26. A process as defined in Claim 1 wherein said step (h) comprises feeding said strand or strands into a high speed chopper or an impeller.

27. A process as defined in Claim 1 wherein said microdie comprises a plurality of holes having a diameter of from about 0.010 to about 0.02 inches.

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28. A process as defined in Claim 27 wherein said microdie comprises a plurality of holes having a diameter of from about 0.010 to about 0.05 inches.

29. Microparticles produced by the process as defined in Claim 1 wherein said microparticles possess an average diameter ranging from abut 0.010 to about 0.005 inches.

30. Microparticles as defined in Claim 29 wherein said microparticles possess an average diameter ranging from about 0.001 to about 0.005 inches.

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