CA2186262A1 - Thermoforming of thin polystyrene foam sheet - Google Patents
Thermoforming of thin polystyrene foam sheetInfo
- Publication number
- CA2186262A1 CA2186262A1 CA002186262A CA2186262A CA2186262A1 CA 2186262 A1 CA2186262 A1 CA 2186262A1 CA 002186262 A CA002186262 A CA 002186262A CA 2186262 A CA2186262 A CA 2186262A CA 2186262 A1 CA2186262 A1 CA 2186262A1
- Authority
- CA
- Canada
- Prior art keywords
- webs
- sheet
- foam
- thermoforming
- thermoformed
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B37/00—Methods or apparatus for laminating, e.g. by curing or by ultrasonic bonding
- B32B37/04—Methods or apparatus for laminating, e.g. by curing or by ultrasonic bonding characterised by the partial melting of at least one layer
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C51/00—Shaping by thermoforming, i.e. shaping sheets or sheet like preforms after heating, e.g. shaping sheets in matched moulds or by deep-drawing; Apparatus therefor
- B29C51/02—Combined thermoforming and manufacture of the preform
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C51/00—Shaping by thermoforming, i.e. shaping sheets or sheet like preforms after heating, e.g. shaping sheets in matched moulds or by deep-drawing; Apparatus therefor
- B29C51/14—Shaping by thermoforming, i.e. shaping sheets or sheet like preforms after heating, e.g. shaping sheets in matched moulds or by deep-drawing; Apparatus therefor using multilayered preforms or sheets
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J9/00—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof
- C08J9/22—After-treatment of expandable particles; Forming foamed products
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C2793/00—Shaping techniques involving a cutting or machining operation
- B29C2793/009—Shaping techniques involving a cutting or machining operation after shaping
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C51/00—Shaping by thermoforming, i.e. shaping sheets or sheet like preforms after heating, e.g. shaping sheets in matched moulds or by deep-drawing; Apparatus therefor
- B29C51/08—Deep drawing or matched-mould forming, i.e. using mechanical means only
- B29C51/082—Deep drawing or matched-mould forming, i.e. using mechanical means only by shaping between complementary mould parts
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29K—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES B29B, B29C OR B29D, RELATING TO MOULDING MATERIALS OR TO MATERIALS FOR MOULDS, REINFORCEMENTS, FILLERS OR PREFORMED PARTS, e.g. INSERTS
- B29K2105/00—Condition, form or state of moulded material or of the material to be shaped
- B29K2105/04—Condition, form or state of moulded material or of the material to be shaped cellular or porous
- B29K2105/043—Skinned foam
Landscapes
- Engineering & Computer Science (AREA)
- Chemical & Material Sciences (AREA)
- Mechanical Engineering (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Materials Engineering (AREA)
- Health & Medical Sciences (AREA)
- Manufacturing & Machinery (AREA)
- Medicinal Chemistry (AREA)
- Polymers & Plastics (AREA)
- Organic Chemistry (AREA)
- Blow-Moulding Or Thermoforming Of Plastics Or The Like (AREA)
- Laminated Bodies (AREA)
- Manufacture Of Porous Articles, And Recovery And Treatment Of Waste Products (AREA)
- Extrusion Moulding Of Plastics Or The Like (AREA)
Abstract
A co-thermoforming process for forming thermoplastic foam sheet of low density and small cell size. The sheet is formed from multiple webs of thinner gauge polystyrene foam which permits improved control of cell size and resultant functionality of product thermoformed from the sheet. Adhesion of the webs is achieved in the thermoforming process. The co-thermoformed products have improved ductility and surface characteristics.
Description
wog5125625 21 86262 1~1" ~
.
THERMOFORMING OF THIN POLYSTYRENE FOAM SHEET
This i nventi on rel ates to a process for provi di ng i m proved ~ - " ,v i v., - le~ parts made from thin polystyrene foam sheet prepared with a blowing agentwhich preferably 5 comprisesonlyor~.,e.lùn~;n~ carbondioxide(CO2). Theinventionisparticularlysuitedfor makingsuchpolystyrenefoamsheethavingathicknessoflessthanabout1t2inch(12.7mm) whichistobeL~,e,-"vru".l~;iintoproductslikecontainerssuchastrays,cups,tubsandthelike.
It has become increasingly important to provide polystyrene foam sheetwith blowing agents otherthanha~9ellaL~cloraliphaticllJJlu~alLlull~forell.:~vlllll~ alreasonsandtobein 10 compliancewithregulations. Onesolution istoproducesuchfoam usingablowingagentwhich is comprised essentially of carbon dioxide as described in U .S. Patent S 250,577 of which one of the inYentors hereof is the inYentor.
It has been found when extruding poiystyrene foam with C2 as the sole blowing agentitbecomesil,.,ec,i,,yl~difficulttocontrolgaugevariationathighergauges~suchas greaterthanaboutO.16inches(4.1mm),andlowdensity,thatislessthanabout4poundsper cubicfoot(64.1kgtcu.meter),duetothehigherlevelsofC02.o,).~,.L,a~ionandthesubsequent increase in the foaming rate. Such gauge variation is sometimes referred to as corrugations whichnotonlyadYerselyaffectscellsize,surfacecharacteristics,andoveralltrayFu~.~;u"ali~y m easu red i n terms of brittleness and .v, . ~,uul Id i, ,u, contai ner ~ y, but fi nal pa rt 20 aesthetics as well. It is therefore desirable to manufacture high gauge, low density d polystyrene foam sheet products which have preferred cell size adec~uate surface characteristics and physical ~_. fv, Illâ(l~e.
This invention takes advantage of the easier processing window associated with lower gauge C2 blown polystyrene foam sheet to manufacture a superior high gauge low 25 density~ lllu~ullller~polystyrenefoamsheetproductwithbetterphysicalandaesthetic characteristics than heretofore possible. As the gauge levels increase the difficulty in extruding increases. ThepresentinYentiontakesadvantageofthefactthatitiseaslertoextrudealower gaugeproductwithminimalgaugevariationandsmallercells~ze Theimprovedresultis achievedbyextrudingtwoormorewebsoflowergaugethanthefindidesiredgaugeand 30 joiningthesethinnerwebsintoasinglesheetofdesiredgaugeprlorto~l,e-,,,vrv-,,~ing The lurullll;llgprovidesaslight~ulllule~iollandordinariiysufficientheattorhefoamwebstonotonlypermitthewebsheetformedfromthemateriaitobeLI,-:.,,,uiu,..,aLl~ina conventional manner but also to obtain good adhesion between the adjoining component webinsidesurfaces. TheprocessconcludesbytheLl,el,l.ufu.l..~Jpar~sbeingtrimmedfromthe 35 sheet in a conventional manner.
Figure 1 isaschematic-ev,e,~-,La~ionofa ~I,e,.llvrul,,,ingprocessforforming products in accordance with the present invention; and W09512562v 2 ~ 86262 P~ c Figure 2 is an exploded broken away section of the process of Figure ~, indicated assection2-2thereof,showingmultiplewebsbeingbroughttogetherforformingintosheet duringthe ~ .,,.v'u.l.,;.,gprocess.
Polymersusefu~inthepresentinventionaswellasblowingagentsintheprocess for forming thin polystyrene foam sheet are described in U.S. Patent 5,520 577. For purposes of illustration the foam sheet described herein will be that of a polystyrene foam made with carbondioxideasthesoleblowingagent. Althoughthisinventionmaybeapplicabletoother resins and blowing agents it has been found to be of particular benefit with such foam sheet.
A preferred ellluOdillle"~ of the process of this invention is illustrated 1û schematicallyinFigure1. Howevervariationsintheprocessmaybeemployedandstillobtain thebeneficialeffectsofthisinvention. Figurelillustratesrolls10and12conbiningwebsl4 and 16 of thin extruded polystyrene foam sheet of about half the gauge thickness of the resultingfoamsheetdesiredtobe~ .vrv~ éd. Forpurposesofillustration thewebs14 and 16aremadeofpolystyreneresinfoamedwithco2asessentiallythesoleblowingagent~
Whilewebs14and16havebeenpre-extrudedandinventoriedasrolls10andl2, itisconceivablethatinafullycontinuousprocesswebs14and16couldlnsteadbedirectly extruded from two extruders. Whether sourced from rolls 10 and 12 or directly from extruders, the webs 14 and 16 thereafter meet but are not necessarily joined at a junction 18. When the webs 14 and 16 are combined in an unheated condition, an inside surface heater 20 may be 20 emp~oyed if a high degree of adhesion between thewebs is desired. Howeverthe use of an insidesurfaceheater20isoptional inthatithasbeendiscoveredthatsufficientheatand pressure may be obtained in the Lll_. ,~u'.., ~ y process itself to provide adequate heat substantially to achieve mutual adhesion of the webs in the final product.
Idlerollers22helpbringthewebs 14and 16generallytogetherat juncture 18 25 thei r respective interfaces 26 and 28 being in close proximity to form the elements of sheet 24.
Thewebsformingsheet24thereafterpassthroughaconvenl1onal Lll l"uru".._. heattunnel 30 comprised of heating elements 32 and 34 with chain rails 36 2nd pin chains 38 (like bicycle chainswithprotrudingpins)grippingedgesofsheet24tomovethesheet24toaformlng station 40.
Formingstation40iscomprlsedofconventional Ll, .,llu~o"(ullgmatchmolds42 and44havingamaleplug46andafemalecavity480faconfiguralloncon~ormingtoa containerpartdesiredtobeformed. The.u.,,u,e,,iu,,pressureancresiduaiheatoccasloned bythematchmoldsc~osingalsoservetoordinarilycausetheinterfaces26and280fthewebsto securelyadheretooneanother,ifnotear~ieradequatelyjoinedintheprocess. Thusthe 35 thermoformi ng station simu Itaneously provides the dual function of causing web adhesion and shapinginthisprocessasillustrated. Whenmolds42and44close ina.u"._.,.iu"~lwayand engagesheet24,acontainerofthedesiredconfigurationisformedinthesheetasillustratedatsection SOofthesheet. Sheet24thenadvancesloa,~ .iul1al trlmstation S2 inciuding WO 95125625 2 1 8 6 ~ ~ ~ PCTIUS9510134~
trimming knives 54 on mold part 56 and receptacles 58 in matching mold 60 adapted to receive thetrimknivesS4totrimthedesiredpart62fromthesheettoformafinishedpart62. A
pluralityoffinishedpartsQarethereafterdischargedandmaybestackedatstackingstation640rremoved inany~u..._."iol~al mannerwellknownintheart.
Theprocessofformingasinglesheetfrommultiplethinnerwebsishereinafter referredtoas"co-LI,_.,..urL",l.;.,g"or"co-LI,_., r.,.."~;l"sheetbytheprocessofco-Ll,_,l".,~u-,-l;n~. Aspreviouslyalludedto,thecurrentinventiontakesadvantageofthefact thatalowergaugeproductatalowdensitywithminimalgaugevariationismorereadily extrudable than is the same density product at higher gauge, when extruding polystyrene lO foammadewithCO2asthesoleorprimaryblowingagent. Byextrudingthinnergaugesone has the advantage of being able to use higher nucleation levels and obtain smaller cell sizes resulting in a smoother foam surface without excessive gauge variations due to corrugations.
A part formed from highly corrugated sheet can result in u, I,dLi,ra.tory wastage due to a high scrap ratewhen wrapping food traystoo brittle, forexample. Large cell sizes induce brittleness ~5 whilesmallseilsizesinduceductilityandtraytoughnessinproductsll.e,l-",fullll r~from polystyrene foam sheet.
EXAMPLE I
A specific example of co-forming by practice of the present invention was practicedbycombiningtwowebs,suchaswebs14an 16,ofaboutO.l inch(2.55mm)gaugeto 20 formapolystyrenefoamsheetofO.2inch(5.1mm)gaugeforll,...l,.,ru,~ .Table1discloses the detailsof the conditionsand results using the process generally illustrated in Figure l (Col.
B) as compared with the prior practice (Col. A~.
TABLE l Col. A Col . B
Standard Co-100% C2 thermoforming Polystyrene 100% C2 Foam Sheet Polystyrene Foam SheetGauge,in.(mm) 0.200 (5.1) 0.098 (2.5) Sheet Density, cu. ft/lb. 3.0 2.9 ~kg/cu.meter) (48.1) (46.5) Tray Cell Size, mm, MD, CD, VD~ 0.54, 0.54, 0.54 0.33, 0.27, 0.18 Tray Bottom Gauge, in. (mm) 0.220(5.7) 0.220 (5.6) Tray Stiffness good good Tray Surface Appearance average excellent WO 9S/25625 2 1 8 6 ~ ~ 2 ~ 40 ~MD = Machinedirection,CD = Crossdirection, VD = Vertical direction AscanbeenseeninTable l,insteadofproducingapolystyrenesheetproductmadeWithco2 5 blowing agent of 3 pounds per cubic foot (48.1 kglcu. meter) density and about û.2 inch (S. l mm) gauge ~Col. A), C2 blown poiystyrene foam sheet webs were produced (Coi. B), with a similar density, that is about 3 pounds per cubic foot (48.1 kg/cu. meter) but with about half the gaugethickness,ofaboutû.l inch(2.54mm),û.û98inch(2.49mm). Twowebsofthethinner ga uge sheet were unwou nd from rol l s l O and 12 and brought together at j u nctu re l 8 to looselyformsheet24whichwasthenfedintothechainrails36. Oncethepinchains38have grippedthesheetedges,thesheet24wasthenpulledforwardthroughthethermoformerheat tunnel 40 where the outside surfaces of web 24 were heated . The sheet 24 comprised of the websl4and 16wasthenindexedtoformingstationS2wherethematchedmoldsclosedtoa speciFied mold gap to form parts 62 which can be trays having defined walls. This slight 5 ~v~ e~iol) of the heated foam sheet caused the webs forming sheet 24 to not only be formed buttoalsoprovideexcellentadhesionbetweenthetwoinsidesurfaces26and280fwebsl4 and 16,respectively,formingsheet24. Thefinal Ll,~""~,ful~ ;ipartswerethentrimmedfrom thesheet24attrimmingstationS2inaconventional manner.
TheresultsshowninTable1illustratethatthedesiredsmallercellsizecanbe 20 achievedbythisinventionforimprovedproductp~,tul,,,~,,.eandappearance. Byemploying the~ .l,.utu.,l,;,.yprocessofthepresentinventionsmallcellsizesoflessthanabouto~4mm (aboutO.3mm)wereobtainedintheco-Ll.t:,,,,urv,ll.~;iproduct. Thisishighlypreferabletocell si2es greater than about 0.4mm, such as the 0.5mm, common with standard polystyrene foam products~ ,"lurv""J~iina,~".~ iù,l~lmanner. Whilebothproductstestedasillustratedin 25 Table 1 showed satisfactory or good tray stiffness it should be appreciated that the fai I u re rate wouldbeexpectedtobehigherintraywrappingasthestandardsheet(Col.A)wouldbemore brittlethanthesmallercellsizedco ~ll~,,l,_Çu,,,.~dsheet(Col.B)produced. Byproducinga foamsheetwithoutexcessivegaugevariationandsmallercellsizesasmoothermorefunct~onai '~3nddesirablefinishisobtainedandagenerallyperceivedaswellasactually~L~llyLll~ d30 product due to the lack of gauge varialions throughout the formed product is provided .
Additionally, it shouid be evident that the webs forming sheet 24 can be extruoed al a higher rate because less residence time is required for cooling.
Althoughtheco-Ll,~.",urv",.;.~gprocessofthisinventionhasbeenparticuiarly describedwithrespecttothe~ l",ur~"""~gofpolystyrenefoamsheetwhereCO2isthe 35 primary or sole biowing a_ent, it is conceivable that this invention would also provide advantageswithotherresinmaterialsandblowingagents Theresultingproductscanbe contalnerssuchasforfoodproductsanathelike,butmayhaveapplicaoilitytoproouctsother than conlainers.
.
THERMOFORMING OF THIN POLYSTYRENE FOAM SHEET
This i nventi on rel ates to a process for provi di ng i m proved ~ - " ,v i v., - le~ parts made from thin polystyrene foam sheet prepared with a blowing agentwhich preferably 5 comprisesonlyor~.,e.lùn~;n~ carbondioxide(CO2). Theinventionisparticularlysuitedfor makingsuchpolystyrenefoamsheethavingathicknessoflessthanabout1t2inch(12.7mm) whichistobeL~,e,-"vru".l~;iintoproductslikecontainerssuchastrays,cups,tubsandthelike.
It has become increasingly important to provide polystyrene foam sheetwith blowing agents otherthanha~9ellaL~cloraliphaticllJJlu~alLlull~forell.:~vlllll~ alreasonsandtobein 10 compliancewithregulations. Onesolution istoproducesuchfoam usingablowingagentwhich is comprised essentially of carbon dioxide as described in U .S. Patent S 250,577 of which one of the inYentors hereof is the inYentor.
It has been found when extruding poiystyrene foam with C2 as the sole blowing agentitbecomesil,.,ec,i,,yl~difficulttocontrolgaugevariationathighergauges~suchas greaterthanaboutO.16inches(4.1mm),andlowdensity,thatislessthanabout4poundsper cubicfoot(64.1kgtcu.meter),duetothehigherlevelsofC02.o,).~,.L,a~ionandthesubsequent increase in the foaming rate. Such gauge variation is sometimes referred to as corrugations whichnotonlyadYerselyaffectscellsize,surfacecharacteristics,andoveralltrayFu~.~;u"ali~y m easu red i n terms of brittleness and .v, . ~,uul Id i, ,u, contai ner ~ y, but fi nal pa rt 20 aesthetics as well. It is therefore desirable to manufacture high gauge, low density d polystyrene foam sheet products which have preferred cell size adec~uate surface characteristics and physical ~_. fv, Illâ(l~e.
This invention takes advantage of the easier processing window associated with lower gauge C2 blown polystyrene foam sheet to manufacture a superior high gauge low 25 density~ lllu~ullller~polystyrenefoamsheetproductwithbetterphysicalandaesthetic characteristics than heretofore possible. As the gauge levels increase the difficulty in extruding increases. ThepresentinYentiontakesadvantageofthefactthatitiseaslertoextrudealower gaugeproductwithminimalgaugevariationandsmallercells~ze Theimprovedresultis achievedbyextrudingtwoormorewebsoflowergaugethanthefindidesiredgaugeand 30 joiningthesethinnerwebsintoasinglesheetofdesiredgaugeprlorto~l,e-,,,vrv-,,~ing The lurullll;llgprovidesaslight~ulllule~iollandordinariiysufficientheattorhefoamwebstonotonlypermitthewebsheetformedfromthemateriaitobeLI,-:.,,,uiu,..,aLl~ina conventional manner but also to obtain good adhesion between the adjoining component webinsidesurfaces. TheprocessconcludesbytheLl,el,l.ufu.l..~Jpar~sbeingtrimmedfromthe 35 sheet in a conventional manner.
Figure 1 isaschematic-ev,e,~-,La~ionofa ~I,e,.llvrul,,,ingprocessforforming products in accordance with the present invention; and W09512562v 2 ~ 86262 P~ c Figure 2 is an exploded broken away section of the process of Figure ~, indicated assection2-2thereof,showingmultiplewebsbeingbroughttogetherforformingintosheet duringthe ~ .,,.v'u.l.,;.,gprocess.
Polymersusefu~inthepresentinventionaswellasblowingagentsintheprocess for forming thin polystyrene foam sheet are described in U.S. Patent 5,520 577. For purposes of illustration the foam sheet described herein will be that of a polystyrene foam made with carbondioxideasthesoleblowingagent. Althoughthisinventionmaybeapplicabletoother resins and blowing agents it has been found to be of particular benefit with such foam sheet.
A preferred ellluOdillle"~ of the process of this invention is illustrated 1û schematicallyinFigure1. Howevervariationsintheprocessmaybeemployedandstillobtain thebeneficialeffectsofthisinvention. Figurelillustratesrolls10and12conbiningwebsl4 and 16 of thin extruded polystyrene foam sheet of about half the gauge thickness of the resultingfoamsheetdesiredtobe~ .vrv~ éd. Forpurposesofillustration thewebs14 and 16aremadeofpolystyreneresinfoamedwithco2asessentiallythesoleblowingagent~
Whilewebs14and16havebeenpre-extrudedandinventoriedasrolls10andl2, itisconceivablethatinafullycontinuousprocesswebs14and16couldlnsteadbedirectly extruded from two extruders. Whether sourced from rolls 10 and 12 or directly from extruders, the webs 14 and 16 thereafter meet but are not necessarily joined at a junction 18. When the webs 14 and 16 are combined in an unheated condition, an inside surface heater 20 may be 20 emp~oyed if a high degree of adhesion between thewebs is desired. Howeverthe use of an insidesurfaceheater20isoptional inthatithasbeendiscoveredthatsufficientheatand pressure may be obtained in the Lll_. ,~u'.., ~ y process itself to provide adequate heat substantially to achieve mutual adhesion of the webs in the final product.
Idlerollers22helpbringthewebs 14and 16generallytogetherat juncture 18 25 thei r respective interfaces 26 and 28 being in close proximity to form the elements of sheet 24.
Thewebsformingsheet24thereafterpassthroughaconvenl1onal Lll l"uru".._. heattunnel 30 comprised of heating elements 32 and 34 with chain rails 36 2nd pin chains 38 (like bicycle chainswithprotrudingpins)grippingedgesofsheet24tomovethesheet24toaformlng station 40.
Formingstation40iscomprlsedofconventional Ll, .,llu~o"(ullgmatchmolds42 and44havingamaleplug46andafemalecavity480faconfiguralloncon~ormingtoa containerpartdesiredtobeformed. The.u.,,u,e,,iu,,pressureancresiduaiheatoccasloned bythematchmoldsc~osingalsoservetoordinarilycausetheinterfaces26and280fthewebsto securelyadheretooneanother,ifnotear~ieradequatelyjoinedintheprocess. Thusthe 35 thermoformi ng station simu Itaneously provides the dual function of causing web adhesion and shapinginthisprocessasillustrated. Whenmolds42and44close ina.u"._.,.iu"~lwayand engagesheet24,acontainerofthedesiredconfigurationisformedinthesheetasillustratedatsection SOofthesheet. Sheet24thenadvancesloa,~ .iul1al trlmstation S2 inciuding WO 95125625 2 1 8 6 ~ ~ ~ PCTIUS9510134~
trimming knives 54 on mold part 56 and receptacles 58 in matching mold 60 adapted to receive thetrimknivesS4totrimthedesiredpart62fromthesheettoformafinishedpart62. A
pluralityoffinishedpartsQarethereafterdischargedandmaybestackedatstackingstation640rremoved inany~u..._."iol~al mannerwellknownintheart.
Theprocessofformingasinglesheetfrommultiplethinnerwebsishereinafter referredtoas"co-LI,_.,..urL",l.;.,g"or"co-LI,_., r.,.."~;l"sheetbytheprocessofco-Ll,_,l".,~u-,-l;n~. Aspreviouslyalludedto,thecurrentinventiontakesadvantageofthefact thatalowergaugeproductatalowdensitywithminimalgaugevariationismorereadily extrudable than is the same density product at higher gauge, when extruding polystyrene lO foammadewithCO2asthesoleorprimaryblowingagent. Byextrudingthinnergaugesone has the advantage of being able to use higher nucleation levels and obtain smaller cell sizes resulting in a smoother foam surface without excessive gauge variations due to corrugations.
A part formed from highly corrugated sheet can result in u, I,dLi,ra.tory wastage due to a high scrap ratewhen wrapping food traystoo brittle, forexample. Large cell sizes induce brittleness ~5 whilesmallseilsizesinduceductilityandtraytoughnessinproductsll.e,l-",fullll r~from polystyrene foam sheet.
EXAMPLE I
A specific example of co-forming by practice of the present invention was practicedbycombiningtwowebs,suchaswebs14an 16,ofaboutO.l inch(2.55mm)gaugeto 20 formapolystyrenefoamsheetofO.2inch(5.1mm)gaugeforll,...l,.,ru,~ .Table1discloses the detailsof the conditionsand results using the process generally illustrated in Figure l (Col.
B) as compared with the prior practice (Col. A~.
TABLE l Col. A Col . B
Standard Co-100% C2 thermoforming Polystyrene 100% C2 Foam Sheet Polystyrene Foam SheetGauge,in.(mm) 0.200 (5.1) 0.098 (2.5) Sheet Density, cu. ft/lb. 3.0 2.9 ~kg/cu.meter) (48.1) (46.5) Tray Cell Size, mm, MD, CD, VD~ 0.54, 0.54, 0.54 0.33, 0.27, 0.18 Tray Bottom Gauge, in. (mm) 0.220(5.7) 0.220 (5.6) Tray Stiffness good good Tray Surface Appearance average excellent WO 9S/25625 2 1 8 6 ~ ~ 2 ~ 40 ~MD = Machinedirection,CD = Crossdirection, VD = Vertical direction AscanbeenseeninTable l,insteadofproducingapolystyrenesheetproductmadeWithco2 5 blowing agent of 3 pounds per cubic foot (48.1 kglcu. meter) density and about û.2 inch (S. l mm) gauge ~Col. A), C2 blown poiystyrene foam sheet webs were produced (Coi. B), with a similar density, that is about 3 pounds per cubic foot (48.1 kg/cu. meter) but with about half the gaugethickness,ofaboutû.l inch(2.54mm),û.û98inch(2.49mm). Twowebsofthethinner ga uge sheet were unwou nd from rol l s l O and 12 and brought together at j u nctu re l 8 to looselyformsheet24whichwasthenfedintothechainrails36. Oncethepinchains38have grippedthesheetedges,thesheet24wasthenpulledforwardthroughthethermoformerheat tunnel 40 where the outside surfaces of web 24 were heated . The sheet 24 comprised of the websl4and 16wasthenindexedtoformingstationS2wherethematchedmoldsclosedtoa speciFied mold gap to form parts 62 which can be trays having defined walls. This slight 5 ~v~ e~iol) of the heated foam sheet caused the webs forming sheet 24 to not only be formed buttoalsoprovideexcellentadhesionbetweenthetwoinsidesurfaces26and280fwebsl4 and 16,respectively,formingsheet24. Thefinal Ll,~""~,ful~ ;ipartswerethentrimmedfrom thesheet24attrimmingstationS2inaconventional manner.
TheresultsshowninTable1illustratethatthedesiredsmallercellsizecanbe 20 achievedbythisinventionforimprovedproductp~,tul,,,~,,.eandappearance. Byemploying the~ .l,.utu.,l,;,.yprocessofthepresentinventionsmallcellsizesoflessthanabouto~4mm (aboutO.3mm)wereobtainedintheco-Ll.t:,,,,urv,ll.~;iproduct. Thisishighlypreferabletocell si2es greater than about 0.4mm, such as the 0.5mm, common with standard polystyrene foam products~ ,"lurv""J~iina,~".~ iù,l~lmanner. Whilebothproductstestedasillustratedin 25 Table 1 showed satisfactory or good tray stiffness it should be appreciated that the fai I u re rate wouldbeexpectedtobehigherintraywrappingasthestandardsheet(Col.A)wouldbemore brittlethanthesmallercellsizedco ~ll~,,l,_Çu,,,.~dsheet(Col.B)produced. Byproducinga foamsheetwithoutexcessivegaugevariationandsmallercellsizesasmoothermorefunct~onai '~3nddesirablefinishisobtainedandagenerallyperceivedaswellasactually~L~llyLll~ d30 product due to the lack of gauge varialions throughout the formed product is provided .
Additionally, it shouid be evident that the webs forming sheet 24 can be extruoed al a higher rate because less residence time is required for cooling.
Althoughtheco-Ll,~.",urv",.;.~gprocessofthisinventionhasbeenparticuiarly describedwithrespecttothe~ l",ur~"""~gofpolystyrenefoamsheetwhereCO2isthe 35 primary or sole biowing a_ent, it is conceivable that this invention would also provide advantageswithotherresinmaterialsandblowingagents Theresultingproductscanbe contalnerssuchasforfoodproductsanathelike,butmayhaveapplicaoilitytoproouctsother than conlainers.
Claims (9)
1, A co-thermoforming process for producing a thermoformable thermoplastic foam sheet with a carbon dioxide blowing agent comprising the follow steps:
a. producing a plurality of thin webs of polystyrene foam the total thickness of which substantially equals the total thickness of the sheet to be thermoforming into a product each of said webs presenting an interface to the other, b. bringing said thin foam webs into close proximity at their interfaces to form said sheet, c. heating said sheet interfaces to a thermoforming temperature, d. thermoforming the sheet into products of a desired configuration with said webs adhered to one another, and e. trimming and collecting said thermoformed products.
a. producing a plurality of thin webs of polystyrene foam the total thickness of which substantially equals the total thickness of the sheet to be thermoforming into a product each of said webs presenting an interface to the other, b. bringing said thin foam webs into close proximity at their interfaces to form said sheet, c. heating said sheet interfaces to a thermoforming temperature, d. thermoforming the sheet into products of a desired configuration with said webs adhered to one another, and e. trimming and collecting said thermoformed products.
2. The process of Claim 1, wherein the interfaces of the thin webs are preheated prior to being joined to form the sheet.
3. (Cancelled).
3. (Cancelled).
3. The process of Claim 1, wherein the carbon dioxide blowing agent is the sole blowing agent used in forming the thermoplastic webs.
4. The process of Claim 1, wherein the co-thermoformed product has a cell size of less than about 0.4mm.
5. The process of Claim 1, wherein the webs have a density of less than about 4 pounds per cubic foot (64.1kg/cu. meter).
6. The process of Claim 1, wherein the thickness of each of thermoformed webs is less than about 0.16 inches (4.1mm) and the gauge thickness of the sheet formed from combining the webs is greater than about 0.16 inches(4.1mm).
7. Products formed from the foam sheet made by the process of Claim 1.
8. A co-thermoformed product having foam walls comprised of two or more foam webs joined together, wherein said walls are of a low density and small cell size.
9. The co-thermoformed product of claim 8, wherein the walls are composed of polystyrene foam having cell sizes of less than about 0.4mm.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US21726294A | 1994-03-24 | 1994-03-24 | |
| US08/217,262 | 1994-03-24 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2186262A1 true CA2186262A1 (en) | 1995-09-28 |
Family
ID=22810314
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002186262A Abandoned CA2186262A1 (en) | 1994-03-24 | 1995-02-02 | Thermoforming of thin polystyrene foam sheet |
Country Status (9)
| Country | Link |
|---|---|
| EP (1) | EP0751859A1 (en) |
| JP (1) | JPH09510413A (en) |
| KR (1) | KR970701623A (en) |
| CN (1) | CN1146745A (en) |
| AU (1) | AU1869595A (en) |
| BR (1) | BR9507434A (en) |
| CA (1) | CA2186262A1 (en) |
| CO (1) | CO4410359A1 (en) |
| WO (1) | WO1995025625A1 (en) |
Families Citing this family (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| IT1281635B1 (en) * | 1995-09-14 | 1998-02-20 | Antonio Riglietti | METHOD OF CREATION OF DISPOSABLE MULTI-LAYER CONTAINERS, PARTICULARLY FOR PERISHABLE AND/OR AGGRESSIVE SUBSTANCES, AS WELL AS |
| GB2372478B (en) | 2001-01-26 | 2003-04-16 | Reckitt Benckiser | Process for preparing a laminated,thermoformed film |
| JP5684582B2 (en) * | 2011-01-19 | 2015-03-11 | 株式会社積水技研 | Manufacturing method of resin foam molded product and resin foam molded product manufacturing equipment |
| CA2874498A1 (en) | 2012-05-22 | 2013-11-28 | Owens Corning Intellectual Capital, Llc | Laminated foam product and methods for making laminated foam products |
| CN103350512A (en) * | 2013-06-21 | 2013-10-16 | 英特普制品有限公司 | Device for forming thermoformed pad |
| KR101724956B1 (en) * | 2015-12-02 | 2017-04-10 | 현대자동차주식회사 | Manufacturing method for vehicle side step |
| CN106696299B (en) * | 2017-01-17 | 2023-10-27 | 罗松 | Modeling processing process flow of packaging container made of foamed polyethylene |
| CN106903904B (en) * | 2017-04-07 | 2023-03-28 | 罗松 | Mechanical equipment for molding and processing foamed polyethylene product and using method |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3589592A (en) * | 1967-03-01 | 1971-06-29 | Dow Chemical Co | Foam receptacle |
| US4411849A (en) * | 1981-08-03 | 1983-10-25 | James River-Dixie/Northern, Inc. | Method for forming a plurality of objects from a plurality of superimposed sheets |
| US4476183A (en) * | 1983-11-21 | 1984-10-09 | Monsanto Company | Thermoformable laminate structure with improved acoustical absorption |
| US4595551A (en) * | 1984-09-21 | 1986-06-17 | Monsanto Company | Thermoforming of styrenic foam laminates |
| US5250577A (en) * | 1989-08-02 | 1993-10-05 | The Dow Chemical Company | Polystyrene foam made with only carbon dioxide as a blowing agent and a process for making the same |
-
1995
- 1995-02-02 BR BR9507434A patent/BR9507434A/en not_active Application Discontinuation
- 1995-02-02 AU AU18695/95A patent/AU1869595A/en not_active Abandoned
- 1995-02-02 JP JP7524628A patent/JPH09510413A/en active Pending
- 1995-02-02 WO PCT/US1995/001340 patent/WO1995025625A1/en not_active Application Discontinuation
- 1995-02-02 CA CA002186262A patent/CA2186262A1/en not_active Abandoned
- 1995-02-02 KR KR1019960705297A patent/KR970701623A/en not_active Application Discontinuation
- 1995-02-02 EP EP95910905A patent/EP0751859A1/en not_active Withdrawn
- 1995-02-02 CN CN95192737A patent/CN1146745A/en active Pending
- 1995-03-22 CO CO95011567A patent/CO4410359A1/en unknown
Also Published As
| Publication number | Publication date |
|---|---|
| WO1995025625A1 (en) | 1995-09-28 |
| JPH09510413A (en) | 1997-10-21 |
| CO4410359A1 (en) | 1997-01-09 |
| CN1146745A (en) | 1997-04-02 |
| KR970701623A (en) | 1997-04-12 |
| BR9507434A (en) | 1997-09-16 |
| EP0751859A1 (en) | 1997-01-08 |
| AU1869595A (en) | 1995-10-09 |
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