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2003中国聚氨酯行业整体淘汰ODS国际__论文集采用环境友好的变压发泡工艺生产聚氨酯泡沫塑料ChiuY.ChanBeatB.NiederoestWilliamBundy美国FoamexInternational公司摘要变压发泡VPF工艺是具有__生命力的新一代泡沫生产技术,该工艺具有许多优点,首先是在生产低密度泡沫塑料时不需要辅助发泡剂,该工艺中气体在排到大气前通过碳床处理,所以保护环境和操作人员根据配方的优点,可不受配方水用量的约束,制造密度和硬度范围很宽的泡沫塑料可生产超软泡沫,没有火灾和泡沫烧芯的危险另一方面,用于包装的超高承载泡沫已经被制造,缓冲垫材特性优于常规的泡沫工业化实践证明,典型的VPF泡沫塑料具有高度均匀性和优异的产品耐久性VPF独特地将环境友好、优异产品均匀性和优良泡沫性能结合起来VPF技术除了给我们可靠的工艺,以满足日益严格的环境法规,还给我们提供了新产品__平台很明显它是21世纪首选的发泡工艺关键词聚氨酯;软质泡沫塑料;变压发泡;发泡工艺1概述在聚氨酯泡沫塑料生产中,辅助发泡剂通常用于降低泡沫密度在过去30年中,由于生产商经常受到降__品成本和重量的商业压力,泡沫密度一直在稳定地降低尽管CFC发泡剂从20世纪30年代就开始被使用,但在80年代才被确定是主要的臭氧消耗物质ODS1987年签订了蒙特利尔协议书,通过__化学替代物和替代生产工艺,降低ODS生产和消费量特别一提的是,在聚氨酯泡沫塑料生产中,CFC的使用被严格限制,最终在美国被禁止,许多生产商转用非CFC的替代物特别是在90年代,二氯甲烷成为流行的辅助发泡剂在美国,当二氯甲烷被确认是一种可疑致癌物,被美国环保署归类为一种有害的空气污染物HAP之后,它被限制使用在2001年10月,当美国环保署执行有害的空气污染物排放国家标准时,二氯甲烷的使用受到许多详细审查最终,当美国职业安全和健康署OSHA把工作场所二氯甲烷空气浓度水平从500ppm降低到25ppm,泡沫生产商不得不转用替代发泡剂当上述这些__法规开始限制某些辅助发泡剂的使用时,聚氨酯泡沫生产商的压力更大许多泡沫生产商花费大量的精力__新的发泡剂,但是人们发现新的发泡剂本身也存在着环保和操作上的问题回顾历史,我们会发现许多例子在CFC和三氯乙烷被限制时,泡沫生产商匆忙用二氯甲烷取代之;而当人们发现二氯甲烷对人体健康有影响时,丙酮和戊烷发泡剂变得普遍,但是它们的燃烧性和VOC散发问题影响到其__生存能力最近,二氧化碳发泡变得普遍,但人们可能担心是否因为其温室效应,在某一天被限制水是聚氨酯的天然发泡剂,在没有辅助发泡剂存在下,生产者通过提高水的用量来降低泡沫密度高水量导致泡沫的质量和耐久性变差,这将在后文解释采用高水配方,有大量的脲生成,很难制得软质泡沫;并且高水用量导致高放热量,会引起泡沫生产过程中的烧芯甚至引起火灾虽然快速冷却工艺在某种程度上减轻火灾危险性,然而需要过量的TDI,导致TDI蒸汽排放到空气中众所周知,在高海拔地区发泡,由于低大气压力的物理现象,可得到低密度泡沫,同样的产气量得到了更多的泡沫体积下面将用某些原理来设计可变压力发泡工艺本质上,低密度泡沫能够通过在负压下发泡得到,因此充分地降低了水的用量和TDI的用量另外,VPF具有许多独特的优点有几篇论文涉及VPF的工程原理和设计[1~4]但是它们是在获得实质性商业化操作经验之前写的在VPF工艺已经运营了近10年后,我们将作一份较全面的综述,把VPF泡沫耐久性和质量改进、新产品能力和环境友好性等方面的优点介绍给大家2工艺描述VPF体系已在全球范围申请专利
[5]如图1所示,该系统是在一能够控制压力的密闭容器室内生产泡沫塑料在发泡之前,室内的压力是固定的,但在发泡操作期间可调节混合头在发泡室的外面,发泡原料注入该发泡室,先进入溢流槽,再进入发泡设备的降落板上当生产出来的泡沫达到预定位置长度时,自动化的切割锯把泡沫块切下来,切下的泡沫块立即加速进入到压力和发泡室相同的密封过渡室一旦泡沫块进入该压力过渡室中,与发泡室相连的气锁关闭第2室然后与大气相通,泡沫块移出、输送到存放区当泡沫块移出后,第1密闭室内继续重复发泡操作,第2室重新密闭,压力恢复到与第1室相同该步骤自动重复进行,直到浇注操作停止图1VPF工艺图从密闭室排出的挥发物通过活性炭床净化,再排放到大气中图2是活性炭床的照片图2活性炭吸收床图3矩形截面的VPF发泡单元3工程设计为了把整个发泡设备包含进去,封闭室必须足够大因此它具有很大的横截__;根据所需要的泡沫块长度,密闭室的长度从40m到180m不等对于一个典型的真空/压力容器,一般使用圆柱体,这是容易理解的然而,在最初的设计中,生产商担心圆柱体的直径太大,以致于不能作为整体运输,因为这种圆柱体生产室需要分成两半因此在最初少量的商业化装置中,VPF室的截面是矩形的见图3这确实使工程设计复杂化,因为用于圆形剖面的现有设计标准用不上去生产商不得不重新制定钢材的规格,以减少应力对长方体发泡室结构的影响在最近的设计中,生产商已认识到圆形剖面的优势,圆形截面的设计标准已经是确定的发泡部分仍采用一矩形截面,而压力过渡部分采用圆柱体设计这种结合有利于发泡工序得到最大的操作空间,而对于压力过渡工序减少设计和确认时间VPF工艺典型的压力范围是50~150kPa
0.5~
1.5大气压尽管早期的发泡室的压力低限是75kPa,经过改进,已能够在50kPa的压力低限下操作因为发泡室能够在高于大气压力时操作,必须确保没有TDI或其它原料从操作区泄漏出去因此,仓门设计成气密性的,在整个操作期间铰链承受所有的力4商业化装置因为环保法规压力越来越大,美国Foamex公司发现VPF工艺是一种非常好的聚氨酯软泡生产工艺该公司目前已分别在位于美国密西西比州Tupelo、北卡罗来纳州Cornelius、印地安那州Auburn和加利福尼亚州Orange的工厂中__了VPF装置在多个地点采用VPF工艺生产的泡沫产品供应床具、家具、包装和地毯衬垫等主要市场5变压发泡的原理VPF工艺的一个主要优点是它可多样化地生产宽范围的产品首先,我们需要考虑在不同的发泡室压力下制造的泡沫密度在低压力下,泡沫的密度相应地降低atm=P/Patm1式中-在压力P下的密度,atm-在大气压力Patm下的密度,P-发泡室压力,Patm-大气压力例如,在大气压100kPa下制得的泡沫密度为24;同样的配方在压力为70kPa时制得的密度将降低到
16.8kg/m3泡沫的硬度通常通过IFD压陷硬度衡量,它随密度的二次方变化
[6]H/Hatm=2/atm22式中H-在控制压力P下泡沫的压陷硬度;Hatm-在大气压力Patm下泡沫的压陷硬度把1和2式结合,得到下式H/Hatm=P2/Patm23采用上述例子,假设在100kPa1大气压下制造的软泡,其25%压陷硬度IFD25为
124.5N28lb-f;同样的配方在压力为70kPa时制得的泡沫,25%压陷硬度降低到62N6VPF泡沫的耐久性优点聚氨酯泡沫的形成包括了连续反应的复杂过程我们熟知的2个主要反应是凝胶反应和发泡反应凝胶反应产生聚氨基甲酸酯发泡反应产生二氧化碳,导致泡沫膨胀,同时生成聚脲几个反应式如下聚氨酯凝胶反应R-NCO+R-CH2OH──→R-NHCOCH2R异氰酸酯多元醇氨基甲酸酯聚脲发泡反应R-NCO+HOH──→R-NH2+CO2异氰酸酯水胺二氧化碳气体R-NCO+R-NH2──→R-NHCONHR异氰酸酯胺取代脲这2个反应式的动力学是不同的水与异氰酸酯的反应比多元醇与异氰酸酯的反应快反应活性的不等导致两种不同微相畴的形成,最终产生相分离多元醇具有较高的分子量,通常在1000~6000g/mol因此聚氨酯的软段相占泡沫质量的一大半聚氨酯泡沫塑料中聚脲硬段相区分散在聚氨酯软段相区中聚脲的相分离被认为是对泡沫__起关键作用的因素另外,大量__的聚脲相区使得聚氨酯泡沫塑料的承载能力增强,对泡沫的其它物理性能也有影响通过添加某些类型的含微粒多元醇原料,在聚合物中引入其它的增强相人们认为,基于这些增强相相关成分所产生的承载增强的耐久性是不同的本质上,VPF技术提供了一个附加的控制水平现在,泡沫配方__人员对这些独特的增强相的组成和形态学有很大的控制能力例如,通过利用真空发泡,能够生产配方水量比许多常规发泡技术少的泡沫这就导致了有较少的聚脲产生这认为是VPF技术生产的泡沫通常具有比常规工艺生产的泡沫耐久性好的主要原因有实验证明了泡沫的压缩变定和回弹性等性能的改善VPF技术生产的产品与使用辅助发泡剂所生产的泡沫产品相比具有耐久性优点压陷硬度IFD表征硬度或者是耐压缩的能力在本研究中,IFD测试的是泡沫压缩75%5万次循环后的数据这种压缩循环试验用于模拟__垫材使用过程的耐压缩性能实验中测试了3种泡沫的耐疲劳性能其中两种泡沫采用VPF技术生产,密度分别是16kg/m3和
19.2kg/m3,两种样品的初始IFD25相似,分别是133N和142N第3种泡沫采用普通的发泡剂工艺生产,密度为
19.2kg/m3,压陷硬度142N它们在压缩循环5万次后的压缩硬度IFD25保留率分别是
63.4%、
72.1%和
64.9%这说明在相同的密度,VPF产品耐压缩性能比非VPF工艺的泡沫好;较低密度的VPF泡沫的耐压缩性能与较高密度的非VPF泡沫相似这个实验说明在相同密度下VPF技术改善了泡沫的耐久性另一个实验,3种泡沫样品中2种是VPF泡沫,密度分别是
26.4kg/m3和
23.2kg/m3;第3种是非VPF泡沫,密度是
26.4kg/m3,这几种泡沫的IFD25都是196N在5万次压缩循环后的3种泡沫样品的压缩硬度保留率分别是
78.3%、
69.4%和
71.0%这同样和上例一样说明了在相同密度下,VPF泡沫具有更好的耐久性同样有可能通过降低泡沫密度,仍获得和常规高密度泡沫相同的耐久性7VPF工艺的产品创新能力VPF工艺的灵活性使得它制造许多新产品1VPF的最大特点是泡沫的密度和硬度可不受配方中水用量的影响而被控制,这使得配方__者在很广泛的范围__新产品2可用非常规的发泡工艺生产新型的VPF泡沫Foamex公司的新产品牌号有Sensus、Perfor__n__CarpetCushion、Rellltex、Spectrum、Quiltflex和Reflex这些产品具有较宽的应用领域,包括床具、家具、包装和地毯垫材例如,Sensus是一种粘弹性泡沫,是在高于大气压的压力下制造的,密度为80kg/m3,采用VPF工艺除了操作上的优点
[7],可得到微细泡孔结构的慢回弹泡沫3采用低压发泡,无需在配方中加入过多的水就能得到低密度因此,泡沫中的低脲含量使得泡沫具有较好的耐久性和最小的烧芯可能性例如,Reflex高回弹泡沫
26.5kg/m3具有优良的耐久性特点4不用辅助发泡剂就能制备超软泡沫塑料我们生产的令人注目的产品是Quiltflex它替代纤维床垫,密度为
11.2kg/m3,IFD为
35.6N5采用高于大气压的压力,无需接枝多元醇就能生产高硬度的泡沫塑料并且,使用接枝聚醚可以生产超高压陷硬度泡沫,如Foamex公司的Nexol和Spectrum包装泡沫,它们具有与聚乙烯泡沫相近的缓冲性能,而泡沫密度较低6能够制造含微小固体颗粒和功能性填料的泡沫塑料,如阻燃泡沫,能加三聚氰胺是工艺上的优点而用二氧化碳发泡加填料非常困难8VPF工艺的环境友好特点VPF工艺具有多个环保优点1不使用辅助发泡剂2因为聚氨酯化学反应在完全密闭的室内进行,废气通过活性炭床处理后排出,不存在挥发性有机物向周围环境排放的问题在活性炭床的出气口处的检测表明,没有探测到有TDI排向大气
[3]3在车间内工作的泡沫设备操作人员没有暴露在TDI等的挥发气体中4VPF配方中的水量低,降低了TDI的总用量5在发泡室内控制温度,可使泡沫具有较薄的上顶部表皮,减少了泡沫边角废料6在VPF工艺中,因为无需用空气稀释操作场所的气体,流通空气需要量减少因此,不需要处理高流量气体,比较经济,而且活性炭床对废气的吸收效果好9稳定的质量在生产普通块状软泡时,采用VPF方法可具有许多优点,改善了产品的均匀性在常规的发泡条件下,环境压力可在±2kPa范围波动,导致了泡沫密度有±
0.5kg/m3的波动另一方面,在VPF发泡中,通过精确的环境控制,发泡室内的压力可稳定在±200Pa,因此泡沫的密度和硬度的变化不明显在图4列出的数据表明非常好的压力控制水平这使得各批次产品具有一致的质量VPF工艺的发泡室可设置维持在某一温度,因此减少温度的波动图4在发泡室87kPa压力设定值的实时操作压力在真空发泡室制造低密度泡沫,当发泡室压力与压力过渡室的相等时,泡沫可获得优良的“呼吸”性能因为通气性好,所以泡沫的气味很小并且,我们的操作经验表明,与二氧化碳发泡工艺相比,VPF工艺需要较少的胺催化剂,也是泡沫气味小的原因10结束语通过近10年的运转,我们__到了VPF工艺的许多优点它提供了环境友好、优良产品均匀性和优良泡沫性能的独特的结合除了提供我们满足日益严格的环境法规的一个可靠的工艺,它还给我们一个新的产品技术平台它是在21世纪受欢迎的发泡工艺____1TrioloR.VariablePressureFoaming.PFATechnicalMeeting.September19932ClockaertsM.VariablePressureFoaming.__llPolym1994132:873BlackwellJBBuckleyG.__nufacturingFoamVPFPro__ss.__llPolym1995144:3114BlackwellJBBuckleyGBlackwellSW.ComparisonoftheVPFandLiquidCO2FoamingPro__sses.__llPolym1996152:1055PrefoamAG.productbrochureonVariablePressureFoamingTechnologyforPolyurethaneFoams.6GibsonLJAshleyMF.__llularSolids----StructureandProperties.PergamonPress19887NiederoestBChanCYMohrR.Fine__llHighDensityViscoelasticPolyurethaneFoams.USPatentApplicationpending__简介Dr.ChiuY.Chan在Delaware大学获得化学工程__学位涉足聚氨酯行业10多年,在进入Foamex公司之前在Lyondell/ARCO化学公司工作现从事客户技术支持和新产品__工作是5个美国专利的__BeatNiederoest在Cornell大学获得化学工程学士学位1996年进入Foamex公司,参加过包括床具、家具、地毯垫材、汽车和工业产品在内的许多新产品和应用__这些新产品采用VPF技术__拥有2个美国专利WilliamBundy从事泡沫生产30余年,在_____期从Foamex公司退休之前任该公司总裁目前他__包括亚洲__计划在内的Foamex公司特别项目Enviro__entallyFriendlyPolyurethaneFoam__nufacturingUsingVariablePressureFoamingChiuY.ChanBeatB.NiederoestandWilliamBundyFoamexInternational1000Columbia__eLinwoodPA19061USASum__ryVariablePressureFoaminghasbeendemonstratedtobeanewgenerationfoam-__nufacturingtechnologywithlong-termviability.Thispro__ssoffersnumerousadvantagesthefirstofwhichisthatnoauxiliaryblowingagentsarerequiredtoprodu__lowdensityfoams.Withthepro__ssexhausttreatedincarbonbedsbeforereleasetotheatmosphereboththeenviro__entandtheoperatingpersonnelareprotected.Intermsofformulationadvantagesawidespectrumoffoamdensityandhardnesscanbe__deindependentofthewaterlevel.Supersoftfoamscanbe__dewithoutputtingthe__nufacturingfacilityatriskoffirehazardsorscorchingthefoams.Ontheoppositeendofthespectrumsuperhighloadbearingfoamsforpackagingh__ebeen__dethatoffercushioningcharacteristicssuperiortotheconventionalfoams.Forthetypicalfoamsourcommercialexperien__hasdemonstratedhigherlevelofconsistencyandsuperiorproductdurability.OverallVPFoffersauniquecombinationofenviro__entalfriendlinesssuperiorproductconsistencyanduniquefoamproperties.Besidesofferingusareliablepro__sstomeettheincreasinglystringentenviro__entalregulationsitprovidesuswithaplatformfornewproducttechnology.Itisclearlythepreferredfoamingpro__ssforthetwenty-first__ntury.IntroductionInthe__nufacturingofpolyurethanefoamsauxiliaryblowingagentsABAareoftenusedtolowerthefoamdensity.Overthelastthreedecadesthefoamdensityhasbeendroppingsteadilyastheprodu__rsareconstantlyunderthecommercialpressureofcostreductionandweightreduction.AlthoughCFChadbeenusedsin__the1930’stheywereidentifiedas__jorozone-depletingsubstan__sODSinthe1980’s.In1987theMontrealProtocolwassignedandODSproductionandconsumptionweretoberedu__dandeliminatedthroughthedevelopmentofchemicalsubstitutesandalternative__nufacturingpro__sses.Specificallyinthe__nufacturingofpolyurethanefoamstheuseofCFCbecameseverelyrestrictedandulti__telystoppedintheU.S.where__nyprodu__rsswitchedtonon-CFCalternatives.Inparticularinthe1990’smethylenechloridebecameapopularauxiliaryblowingagent.IntheUnitedStateswhenmethylenechloridewasidentifiedasasuspectcarcinogenandclassifiedasanHazardousAirPollutantHAPbyEPAitsusesbecamerestricted.InOctober2001whenEPAimplementedtheNationalEmissionStandardsforHazardousAirPollutantsNESHAPmethylenechlorideusagewasunderalotofscrutiny.FinallywhentheOccupationalSafetyandHealthAdministrationOSHAloweredtheworkerexposurelevelofmethylenechloridefromthepreviouslevelof500ppmto25ppmthefoamprodu__rshadtoscrambleforalternativeblowingagents.Asthesegover__entregulationsbegantorestricttheuseof__rtainauxiliaryblowingagentsitputincreasinglymorepressureonthepolyurethanefoamprodu__rs.__nyfoamprodu__rsh__eexpendedalotofeffortstodevelopanewABAonlytofindthatthenewABAitselfalsohassomecon__rnsenviro__entallyandoperationally.Lookingbackintohistorywefoundnumerousexamples.AstheuseofCFCandtrichloroethanebecamerestrictedfoamprodu__rsrushedtorepla__itwithmethylenechloride.Asthehealtheffectsofmethylenechloridecameintoquestiona__toneandpentanebecamepopularbuttheirflam__bilitycharacteristicsandVOCemissionsraisedcon__rnsontheirlongtermviability.Mostre__ntlycarbondioxidehasbecomeextremelypopularbutonehastowonderifitsuse__yberestrictedonedayduetoitsgreenhouseeffect.Waterisanaturalblowingagent.Intheabsen__ofABAprodu__rsh__etriedtoraisethewaterlevelsubstantially.Howeverasexplainedlaterinmoredetailthehigherwaterlevelresultedininferiorfoamqualityanddurability.Withthehighwaterformulationsthereissomuchureafor__tionthatitisdifficultto__kesoftfoams.Finallythehighexothermassociatedwithhighwaterlevelswouldscorchthefoamandposeafirehazardduringfoam__nufacturing.Althoughtherapidcoolingpro__ssmitigatedthefirehazardssomewhatitrequiredex__ssTDIusageandallowedex__ssTDIvaportobereleasedintotheatmosphere.Itiswellknownthatfoamingathighaltitudesgivesredu__dfoamdensitybasedonthephysicsthatatlowerpressurethesameweightofgashasahighervolume.ThesameunderlyingprincipleisusedinthedesignofthevariablepressurefoamingVPFpro__ss.EssentiallyalowerdensityfoamcanbeachievedbyfoamingundervacuumthussubstantiallyreducingthewaterlevelandthereforetheTDIrequirement.InadditionVPFoffers__nyotheruniqueadvantages.Thereh__ebeenseveralarticlesontheengineeringprinciplesanddesignofVPF[1-4]buttheywerewrittenbeforesubstantialcommercialoperatingexperien__wasgained.Afteralmost10yearsofrunningtheVPFpro__sswearenowinapositiontoofferacomprehensivereviewsheddinglightonthevariousaspectsofdurabilityandqualityenhan__mentnewproductcapabilityandenviro__entalfriendliness.Pro__ssDescriptionTheVPFsystemhasbeenpatentedworldwide
[5].AsshowninFigure1thesysteminvolvesproducingfoaminanenclosedchamberwiththepressurecontrolled.Thepressureinthechamberisfixedpriortofoamingbutcanbeadjustedduringthefoamingoperation.Themixheadisoutsidethechamber;thechemicalsarepumpedintothechamberintoatroughontothefoam__chinefallplates.Whenthepre-setlengthoffoamisprodu__danauto__ticcut-offsawcutsoffthebun.Thisbunisthenac__leratedintoasecondairlockchamberthatisatthesamepressureasthefoamingchamber.On__thecutbunhascompletelyenteredtheairlocksystemtheairlockisclosedfromthefoamingchamber.Thissecondchamberisthenopenedtotheatmosphereandthebunisremovedandtransportedtostorage.Whilethebunsaremovedthefoamingiscontinuinginthefirstchamber.Thesecondchamberisclosedagainandthepressurereturnedtothesamepressureasthefirstchamber.Thepro__ssthenrepeatsitselfuntiltheendofthepouringoperation.Thepro__ssemissionsareexhaustedfromtheenclosuresandarecleanedbyactivatedcarbonbedsbeforereleasingtotheatmosphere.Figure2isapictureofthecarbonbeds.Figure
1.VPFpro__ssdiagramFigure
2.ActivatedcarbonbedabsorbersEngineeringDesignToenclosethecompletefoamequipmentthechamberhastobelargeenough.Assuchthechamberhasalargecrosssectionareaandthelengthvariesfrom130to600ftlongdependingonthedesiredfinishedbunlength.Foratypicalvacuum/pressurevesselitiscusto__rytouseacylindricalcrosssectionwhichisrelativelywellunderstood.Howeverintheoriginaldesignthe__nufacturerwascon__rnedaboutthediameterbeingtoolargetotransportinonepie__thusrequiringthecylindertobecutintotwohalves.ThereforeinthefirstfewcommercialinstallationstheVPFchamberswereallrectangularincrosssectionseeFigure
3.Itdidcomplicatetheengineeringdesignsin__theestablisheddesigncriteriaforcircularsectionscouldnotbeused.The__nufacturerhadtorelyonfiniteelement____ysistospecifythesteelspecificationsandtominimizethestressesonthestructure.Figure
3.RectangularcrosssectionofVPFfoamingsectionInthemorere__ntdesignthe__nufacturerrecognizedthebenefitsofusingcircularsectionsforwhichthedesigncriteriah__ebeenestablished.Whilethefoamingsectionstillusedarectangularcrosssectiontheairlocksectionusedacylindricaldesign.Thiscombinationallowedthe__ximumoperatingspa__forthefoamingsectionbutredu__dtheengineeringand__rtificationtimerequiredfortheairlocksection.ThetypicalpressurerangefortheVPFis
0.5to
1.5bar.Althoughtheearlierchambershadalowerlimitof
0.75bartheyh__ebeenretrofittedtooperatewiththelowerpressurelimitof
0.5bar.Sin__thechambercanoperateataboveatmosphericpressureitwasne__ssarytoensurethatnoTDIorotherchemicalsbeallowedtoleakintotheoperatingarea.Toachievethatthedoorsweredesignedtobeairtightwithhingesdesignedtosustainthefullfor__sduringthewholeoperation.CommercialInstallationsWiththeincreasingpressurefromtheenviro__entalregulationsFoamexhasfoundtheVPFtobeanex__llent__nufacturingpro__ss.StartingwiththeinitialinstallationinTupeloMississippiweh__ebuiltVPFplantsaroundthecountryinOrangeCaliforniafollowedbyCorneliusNorthCarolinaandAuburnIndiana.AsshowninFigure4thesemultiplelocationsallowVPFproductstobe__deandsuppliedtokey__rketssuchasbeddingfurniturepackagingandcarpetcushions.Figure
4.VPFplantlocationsPhysicsofVariablePressureFoamingOne__joradvantageofVPFisitsversatilityto__keawiderangeofproducts.Firstweneedtoconsiderthefoamdensitiesunderdifferentchamberpressures.Atalowchamberpressurethefoamdensitybecomesproportionallylow/atm=p/patm1where=densityatpressurepatm=densityatatmosphericpressurep=chamberpressurepatm=atmosphericpressureAsanexampleatatmosphericpressurepatm=1bardensity=
1.5pcf.Forthesameformulationatp=
0.7barthedensitywilldropto
1.05pcf.ThehardnessofthefoamwhichisusuallymeasuredbytheIFDvariesquadraticallywiththedensity
[6]H/Hatm=2/atm22whereH=IFDatpressurepHatm=IFDatatmosphericpressureCombiningequations1and2givesH/Hatm=p2/patm23Usingtheexampleabovesupposethehardnessasmeasuredbyitsindentationfor__todeflectionat25%compressionIFD25at1baris28lb-f.Atthelowerpressureof
0.7barthehardnesswilldropto14lb-f.DurabilityAdvantageFor__tionofpolyurethanefoaminvolvesacomplexcombinationofsimultaneousreactions.Thetwomostsignificantreactionsarecommonlyreferredtoasthegelandblowreactions.Thegelreactionyieldspolyurethanelinkages.ThealcoholistypicallymultifunctionalcontainingtwoormoreOHgroupsandhen__termedapolyol.Theblowreactionsequen__yieldsCO2whichleadstofoamexpansion.Thissamereactionsequen__alsoleadstopolyureafor__tion.Thesesequen__sareillustratedbelow.PolyurethaneGelReactionPolyureaBlowReactionSequen__Thekineticsofthesetworeactionsequen__saredifferent.Thewater-isocyanatereactionisknowntopro__edmuchfasterthanthepolyol-isocyanatereaction.Thisdisparityinreactivityleadstothefor__tionoftwodistinctdo__insthatulti__telyphaseseparate.Thepolyolmoleculeistypicallyhighinmolecularweightbetween1000and6000g/mol.Asaresultofthisthesoftpolyurethanephasetypicallycomprisesthe__jorityofthefoam__ss.Polyurethanefoamcanthereforebecon__ptualizedasdistinctpolyureahard-segmentdo__insdispersedwithinasoftpolyurethanepolymerphase.Thepolyureaphaseseparationphenomenonisbelievedtobecriticaltofoampro__ssing.Inadditionamore__ssiveanddistinctpolyureado__inisunderstoodtoincreasetheload-bearingabilityofpolyurethanefoamandalsotoimpactotherphysicalproperties.Anadditionalreinforcingphase__ybeintrodu__dintothepolymerviatheadditionof__rtaintypesofpolyol__terialsthatcontainparticulates.Itispostulatedthattherearedifferen__sintheper__nencyofloadenhan__mentbasedupontherelativecompositionsofthesereinforcingphases.EssentiallytheVPFtechnologyprovidesanaddedlevelofcontrol.Thefoamchemistnowhasgreatercontrolofthecompositionandmorphologyofthesedistinctreinforcingdo__ins.Forexamplethroughtheutilizationofvacuumconditionsthefoamchemististypicallyabletoprodu__polyurethanefoamwithlesswaterthanutilizedwithmoreconventionalfoamingtechniques.Thisinturnleadstoaless__ssiveanddistinctpolyureaphase.Itispostulatedthatisthe__jorreasonthatfoamsprodu__dwiththeVPFtechnologyh__eoftenbeenmeasuredtobemoredurablethanfoamsprodu__dwithmoreconventionaltechnologies.Experimentsh__ealsoillustratedimprovementsinotherpropertiessuchascompressionsetsandresiliency.Thefiguresbelowillustratethedurabilityadvantageofproductsprodu__dwithVPFasmeasuredagainstproductsprodu__dusinganauxiliary-blowingagent.TheIFDisameasureofhardnessorresistan__tocompression.Thispropertyistypicallymeasuredinpoundsoffor__lb-f.Inthestudythispropertywasmeasuredbeforeandafter50000cyclesofcompressionby75%.Thiscycletestingisdesignedtosimulatecompressionoverextendedcushionuse.InTable1thefatiguepropertyoftwoseriesoffoamswere____yzed.Infirstseriestwoofthethreefoamswereprodu__dusingVPFtechnologyattwodifferentdensitiesof
1.0and
1.2pcf.TheinitialIFD25ofbothproductswassimilarwiththe
1.0pcfproductmeasuringat30lb-fandthe
1.2pcfproductmeasuringat32lb-f.Thethirdproductwasprodu__dusingconventionalblowingagenttechnology.Ithadadensityof
1.2pcfandanIFD25of32lb-f.AscanbeseenfromthefiguretheVPFproductretainedagreaterper__ntageofitscompressionresistan__thandiditsnon-VPFequivalentatthesamedensity.ItcanalsobeseenthatthelowerdensityVPFproductperformedsimilarlytothehigherdensitynon-VPFproduct.InthisexampletheVPFtechnologyofferstheabilitytoachieveimproveddurabilityatequivalentdensityortoachieveequivalentdurabilityatlowerdensity.ThesecondseriesinTable1alsodisplaysasimilarexample.InthesecondseriesthetwoVPFfoamswere
1.65pcfand
1.45pcf.Thenon-VPFfoamwas
1.65pcf.AllthefoamshadanIFD25of44lb-f.HereagaintherewasadurabilityadvantageatequivalentdensitywithVPF.Therewasalsopotentialtoredu__densitywithVPFandachieveequivalentdurabilitytothehigherdensityconventionalproduct.Table
1.Per__ntIFD25retentionafter50000cycles
1.0-
1.2pcfsampleRetention
1.45-
1.65pcfsampleRetentionP120-
3264.9%P165-
4471.0%VPF120-
3272.1%VPF165-
4478.3%VPF100-
3063.4%VPF145-
4469.4%NewProductCapabilityTheflexibilityoftheVPFallows__nynewproductstobe__de:
1.AgreatfeatureofVPFisthatthedensityandhardnesscanbecontrolledindependentlyofwaterlevel.Thatgivesthefoamchemistanextradimensionincreatingnewproducts.
2.Newtypesoffoamcanbe__dewithVPFthatcannotbe__deusingtheconventionalfoamingpro__sses.TheproductsofFoamexcoverawiderangeofapplicationsinbeddingfurniturepackagingandcarpetcushion.ForexampleSensusisaviscoelasticfoampouredataboveatmosphericpressuretoprovidea5pcfdensity.UsingVPFprovidesfine__llstructureslowrecoveryfoamsinadditiontopro__ssingbenefits
[7].
3.Usinglowchamberpressurelowdensityfoamscanbe__dewithoutex__ssivewaterlevelsintheformulation.Thelowerureacontentresultsinsuperiorfoamdurabilitycharacteristicsandmini__lscorch.AsanexampletheReflexHRfoams
1.65pcfh__eenjoyedthebenefitsofsuperiordurability.
4.Supersoftfoamscanbe__dewithoutABA.Oneoftheexcitingproductsthatweprodu__isQuiltflexwhichisafiberrepla__mentfoamwithadensityof
0.7pcfandanIFDof8lb-f.
5.UsingaboveatmosphericpressurehighIFDfoamscanbe__dewithoutgraftpolyols.InothercasesusinggraftpolyolssuperhighIFDfoamscanbe__desuchastheNexolandSpectrumpackagingfoamswhichoffercushioningperfor__n__closetothatofthepolyethylenefoamsbutatarelativelylowdensity.
6.Foamscontaining__allsolidparticlesandfunctionalfillerscanbe__desuchasFRfoamswheremelamineadditioncouldbeadvantageous.ThisismoredifficultifpossiblewithCO
2.Enviro__entalFriendlinessTherearemultipleenviro__entalbenefitsfromtheVPF:
1.Theuseofauxiliaryblowingagentsiseliminated.
2.Sin__thepolyurethanereactionstakepla__insideatotallyenclosedchamberandtheexhaustisventedthroughcarbonbedstheVOCemissionstothesurroundingenviro__entareeliminated.Indeedmeasurementattheexitofthecarbonbedsshowednon-detectablelevelsofTDIintotheatmosphere
[3].
3.Thefoam__chineoperatorsarenotexposedtothesegaseousemissionsinsidetheplant.
4.ThelowerwaterlevelsintheVPFformulationsredu__theoveralluseofTDI.
5.Temperaturecontrolinsidethechamberresultedinathinnertopskinandthereforelessscrapfromtheproduction.
6.Theventilationairrequirementisredu__dintheVPFpro__sssin__itisnotne__ssarytoh__ea__jordilutionofthepro__ssgaswithair.Consequentlythecarbonbedsarenotrequiredtohandleasuperhighgasflowresultinginamoreeconomicalandefficientabsorption.Figure
5.Plotofoperatingpressureinthechamberforasetpointof870mbarRedu__dCostofQualityEvenfor__kingstandardslabstockfoamtheVPFoffersamultitudeofbenefitsinimprovingtheproductconsistency:
1.Inconventionalfoamingconditionstheambientpressurecouldgothroughfluctuationsofabout+/-20mbar.Asaresultthedensitywillfluctuatewitharangeof
0.03pcf.Ontheotherhandwiththepreciseenviro__entalcontrolthepressureinsidethechambercanbesetand__intainedat2mbarresultingininsignificantvariationsindensityandhardness.IndeedactualoperatingdatashowninFigure5indicatedaneventighterpressurecontrol.Thisprovidesconsistentproductqualityfromruntorun.
2.TheVPFpro__sscanbesetupsuchthatthechamberis__intainedatapresettemperature.Asaresultthetemperaturefluctuationswillbeminimized.
3.In__kingalowdensityfoamundervacuuminthechamberthefoamwasgivenanextraopportunityto“breathe”whenthepressureisequalizedintheairlock.Suchbreathingresultedinalowerodorlevel.Alsoouroperatingexperien__hasindicatedthatcomparedtotheCO2pro__sstheVPFpro__ssrequiresaloweraminecatalystlevelthuscontributingtoastilllowerodor.ConclusionsAfteralmost10yearsofoperationweh__eenjoyedthevariousbenefitsoftheVPFpro__ss.Itoffersauniquecombinationofenviro__entalfriendlinesssuperiorproductconsistencyanduniquefoamproperties.Besidesofferingusareliablepro__sstomeettheincreasingstringentenviro__entalregulationsitprovidesuswithaplatformfornewproducttechnology.Itisclearlythepreferredfoamingpro__ssforthetwenty-first__ntury.Referen__s
1.TrioloR.VariablePressureFoamingPFATechnicalMeetingSeptember
1993.
2.ClockaertsM.VariablePressureFoaming__ll.Polym.13/
2199487.
3.BlackwellJ.B.andG.Buckley__nufacturingFoamVPFPro__ss__ll.Polym.14/
41995311.
4.BlackwellJ.B.G.BuckleyandS.W.BlackwellComparisonoftheVPFandLiquidCO2FoamingPro__sses__ll.Polym.15/
21996105.
5.PrefoamA.G.productbrochureonVariablePressureFoamingTechnologyforPolyurethaneFoams.
6.GibsonL.J.andM.F.Ashley__llularSolids-StructureandPropertiesPergamonPress
1988.
7.NiederoestB.C.Y.ChanandR.MohrFine__llhighdensityviscoelasticpolyurethanefoamsUSPatentApplicationpending.BIOGRAPHIESDr.ChiuY.ChanDr.Chanhasbeeninthepolyurethaneindustryforover10yearsh__ingworkedforLyondell/ARCOChemicalCompanypriortojoiningFoamex.Besideschemicalspecificationandcustomertechnicalsupportheisinvolvedinnewproductdevelopment.Anauthorof5U.S.patentsheholdsaB.S.andaM.S.inChemicalEngineeringfromtheCooperUnionNYandaPh.D.inChemicalEngineeringfromtheUniversityofDelaware.BeatNiederoestMr.NiederoesthasbeenwithFoamexsin__
1996.Hehasbeenengagedinnumerousnewproductandapplicationsdevelopmenteffortscoveringbeddingfurniturepackagingcarpetcushionautomotiveandtechnicalproducts.__nyoftheseproductsweredevelopedontheVPFtechnologyplatform.HeholdstwoU.S.patentsandre__ivedaB.S.inChemicalEngineeringcumlaudefromCornellUniveristy.WilliamBundyMr.Bundyisaveteranofthefoamindustryandhasbeeninvolvedinfoam__nufacturingforover3decades.HewasthePresidentofFoamexintheearly90’spriortoretirement.UponcomingoutofretirementheiscurrentlyleadingspecialprojectsincludingexpansionprojectsinAsia.1157。