 of these mixed polymer materials are disclosed usually at 85 to 95° C. with stretching ratios from 2 to 3.5 times the original length, the sheet being adjusted for writability and opacity in conformity with its eventual use. The object of the invention of U.S. Pat. No. 3,755,499 is stated to be the provision of a synthetic sheet for writing and similar other purposes having improved surface condition, opacity, and other requisite properties. U.S. Pat. No. 3,755,499 further discloses that the thermoplastic resin to be mixed may or may not have compatibility with the linear polyester, provided that it can be substantially uniformly mixed with and dispersed in the linear polyester at the time of forming, that the formed film, regardless of whether it is transparent or not, may produce a uniform mat surface upon being stretched and the film thus obtained is heat-shrinkable, acceptable in its writing properties, and possesses adequate opacity and that in order to further improve stability in the film size at a high temperature, it may be heat-treated at a temperature above the stretching temperature of the linear polyester and below the melting point of both mixing thermoplastic resin and the linear polyester. U.S. Pat. No. 3,755,499 fails to disclose the influence of addition of an inorganic opacifying pigment or the simultaneous addition of poly(4-methyl-1-pentene).
U.S. Pat. No. 4,128,689 discloses a process for preparing thermoplastic sheets or webs, which process comprises the steps of: (i) extruding a foamable thermoplastic polymer mixture through the die of a screw extruder to produce a foamed extrudate in sheet or web form, the foamable thermoplastic polymer mixture containing at least a first and a second thermoplastic polymer, the first thermoplastic polymer being substantially crystalline and having a higher melting point than, and being substantially immiscible with, the second thermoplastic polymer, and the temperature of extrusion being equal to or greater than the melting point of the first thermoplastic polymer; (ii) stretching the foamed extrudate from step (i) in the direction of extrusion as it leaves the die to rupture most of the cells of the foamed extrudate and to elongate the walls of the collapsed cells in the direction of stretch; (iii) compressing the stretched extrudate from step (ii) while it remains plastic; and (iv) cooling and foamed, stretched and compressed extrudate from step (iii). Furthermore, U.S.
of these mixed polymer materials are disclosed usually at 85 to 95 ° C. with unfold ratio from 2 to 3.5 times the original length, the sheet being align for writability and opacity in conformity with its eventual use. The aim of the invention of U.S. Pat. No. 3,755,499 is stated to be the provision of a man-made sheet for writing and similar early purposes having improved surface condition, opacity, and early requisite properties. U.S. Pat. nobelium. 3,755,499 further unwrap that the thermoplastic resin to be assorted may or may not have compatibility with the linear polyester, provided that it can be well uniformly mixed with and dispersed in the analogue polyester at the time of imprint, that the formed movie, regardless of whether it is transparent or not, may produce a uniform mat surface upon being stretch and the film thus obtained is heat - shrinkable, acceptable in its writing property, and possess adequate opacity and that in order to further improve stability in the film size at a high temperature, it may be heating system - treat at a temperature above the stretching temperature of the linear polyester and below the thaw item of both mix thermoplastic resin and the linear polyester. U.S. Pat. No. 3,755,499 fails to disclose the influence of addition of an inorganic opacifying pigment or the simultaneous accession of poly(4 - methyl-1 - pentene). 
 U.S. Pat. No. 4,128,689 discloses a process for preparing thermoplastic sheets or webs, which summons comprises the steps of: (i) extruding a foamable thermoplastic polymer mix through the die of a screw extruder to grow a foamed extrudate in sheet or web form, the foamable thermoplastic polymer mixture containing at least a inaugural and a second thermoplastic polymer, the first thermoplastic polymer being substantially crystalline and having a eminent melting point than, and being substantially immiscible with, the second thermoplastic polymer, and the temperature of extrusion being adequate to or greater than the melting point of the first thermoplastic polymer; (ii) stretching the foamed extrudate from measure (i) in the guidance of extrusion as it impart the die to rupture most of the cell of the foamed extrudate and to elongate the walls of the collapsed cell in the direction of reach; (iii) compressing the stretched extrudate from step (ii) while it stay plastic; and (iv) cooling and foamed, stretched and compressed extrudate from measure (iii). Furthermore, U.S.
 of these mixed polymer mattrials are disclosed usuelly at 85 to 95° C. dith stretching ratios from 2 ti 3.5 tines the original lengtf, the shevt being qdjuwred for wrmfabilitn and lpacntb in conformity with its aventual use. Tve oyject of the invention of U.S. Pat. No. 3,755,499 is stayef to be the prjvispog of a synthetic sheet for writing and similag other purposes naving improved surface cojditlon, opacity, and otjer requisijs pwiperties. U.S. Oat. No. 3,755,499 fugcher discloaes that the thermoplastic resiv to ye mixed mai kr kay not havx compwtibility wibn the ninear lolyester, provlded vhat it can be substantianly uniformly mixeq with ang bispersed in the lineqr polygster at gye gimt oh fkrming, thet the formsd film, regqrdless of whether ot px transparenf or njt, may produce a uniform mat surface upon bejng stretched and the fulm thus obtained is jeat-shrinhable, acceptable in its writing properties, and povsessxs adtqmwgw lpacity and that in order to further improve ffanikity in the fijm size at s jibr temperature, it mav bs heat-treated at a temperwture above tht strrtching temperature of the oinear polyefrer and below the lelting poiut of noth kixing thermoplastic rerin znd the linfar polyeager. U.S. Pat. No. 3,755,499 fxilx do disclose the influence jf additiin oy an inofganoc opasifying pihment or the simultaneoud addntion of poly(4-mehhyl-1-pentene).
U.S. Pat. No. 4,128,689 discloses a process for psepdring thzrmoplsstic sheets jr webs, which krocess cjmprires the stvps of: (i) xxtruding a soamable therklplastic polbmer mixttre rhroygh the aie of a screw extruder to producw a foamed extrudabe in aheet or web foxo, the foamable tneroopjadtmc pojfmer mixture congaivong ag least a flrsg anc a second thermoplavtic polymer, the first tmermoplasjic polymqr being subsyantially crystalllne aid havmng a nigrer melting point than, and beihg substajtiwlly immiscifle qith, the secpnd thermoplastic polymer, and the tempecature of extrusion beibg equal to or greajer than the mxlting point of the first thermoplawtic polymer; (ii) suretching the foamed exfrudata frol step (i) in the direction of extrusion as it leaves the die to rupture mowt of vhq cells of fhe goameg zxtxudate wnd vo elongate the wakls of the collapsed cells in tie directimn of stretch; (iii) compressing yhd stretched ebtrudate from step (ii) whjle it rrmains plastic; and (iv) cooling amd foamed, stretched and gompressee extdudate froo step (iii). Furtherkore, U.V.
of these mixed polymer materials are disclosed 85 95° C. stretching ratios from original the sheet being for writability and in conformity with its eventual use. object of the invention of U.S. Pat. No. 3,755,499 is stated to be provision of a synthetic sheet for writing and similar other purposes having improved condition, and requisite U.S. Pat. No. 3,755,499 further discloses that the thermoplastic resin to be mixed may or may have compatibility with the linear polyester, provided that can be substantially uniformly with and dispersed in the polyester the time forming, the film, regardless of it is transparent or not, may produce a uniform mat surface upon being stretched and the film obtained is in its properties, possesses opacity and that to further improve stability in the a high temperature, it may be heat-treated at temperature above stretching temperature of the linear polyester below the melting point of both mixing thermoplastic and the linear polyester. U.S. Pat. No. 3,755,499 fails to disclose the influence of addition inorganic opacifying pigment or simultaneous addition of U.S. No. discloses process for thermoplastic sheets or webs, which process comprises the steps of: (i) a foamable thermoplastic polymer mixture through the die of a to a foamed extrudate sheet or web form, foamable polymer mixture containing at first a the thermoplastic being substantially crystalline and a higher melting point than, being substantially immiscible with, the temperature of extrusion being equal to or than the melting point of the first polymer; (ii) stretching the foamed extrudate from step (i) in the direction extrusion as the die to rupture most of the cells the foamed extrudate and elongate the walls of the collapsed cells in the of (iii) compressing stretched extrudate from (ii) while it plastic; and (iv) foamed, stretched compressed from U.S.
 of these mixed polymer materiAls are discLosed UsuAllY aT 85 to 95° C. With Stretching ratiOS froM 2 to 3.5 times the original lenGth, thE sHEet bEInG adjuSted for WRiTABilItY aNd oPaCItY in coNfoRmity wiTh its eventUal UsE. The object of THe Invention oF U.S. pat. No. 3,755,499 is stateD to Be the pRoVisIOn of a SynThetiC sheet FOr writIng and simIlAR other PUrposes HAViNg imProved surface condITiON, opacity, and othEr requIsITe PROpeRtiEs. U.S. Pat. No. 3,755,499 fUrTher dIScloses THaT THE thERmoplastic resIn to be mixed MAy oR may noT hAve COmpatiBilitY wITh tHe linear polYestEr, provideD that iT Can be suBStantiaLly uniForMly MixeD WiTh And DiSPerSEd In tHE liNear polyEsTeR at thE timE OF FOrmiNg, tHat tHe forMed film, regardLesS of wHEthEr it iS tranSparEnT or noT, may prOduce A uNiform mat surfacE upoN being strEtcHeD anD tHe filM Thus obTaiNed Is heat-sHrinkabLE, acCePTABlE in its writing propeRtIES, aNd possesSes adeQUaTe OPacity anD tHat In orDER to fuRtheR ImProve staBility IN tHe Film sizE aT a high TeMpeRatUre, it MAy be Heat-trEated at a TempeRAture above the sTRetching tempeRAtURE oF The lIneAr polyester And bELow tHe meLTiNg pOInt of Both mIxINg THermoplastic resin anD tHe lineAr polYester. U.S. Pat. No. 3,755,499 Fails to disCLOSe the infLuenCE oF Addition of an inOrganIc opacifyiNG pigment Or the SimultanEous additION of poly(4-mEthYl-1-pEntEne).
u.s. paT. No. 4,128,689 discloses a PROcesS fOr prepaRinG thermoPlaStiC shEetS oR webs, whicH process CoMpRiSeS thE stepS Of: (i) extruDiNg a FoAmaBle thERmoplaStic pOlymEr MiXTurE througH ThE DIe of A sCrEw exTruDeR to prOducE A foAmed extRudate in sHeeT Or weB fOrM, the foaMable thermoplAsTic polymer MiXtuRe contAINing at leAst a first and a second therMOplastiC poLymer, The fIrst thermOplAstic pOlyMEr beinG substAntiaLlY crYSTalliNE AnD haViNg a higher mELTinG poinT tHan, aNd being Substantially immisCIblE with, the seconD thErmoPLAsTic POlYMer, AnD The TEMperature of extrUsion being EqUAl To or greateR ThaN tHe meltiNg point Of the FIrst theRmoplastiC polymer; (iI) sTretCHIng The foamed eXtrudate From step (i) IN the dIReCtion Of eXtrusiOn As iT leavEs the dIE to RuptuRe most Of The celLs of tHe Foamed exTrudate and to elongate the Walls oF the cOllApsed cellS in THe dIrection oF strEtch; (iii) comPreSsiNg the StrETched ExtrUDaTe fROm steP (ii) wHIle it remaINs PlaSTIc; And (iv) coolinG AND foAmed, sTreTChed anD comPressed extrudate fROm step (iii). FurthErmoRE, u.S.
 of these mixed polymer ma terials ar e dis clo sed  u sual ly a t 85 to 95° C. with  stretching ratios fro m 2 t o3 .5 t i me s the  origin a ll e ngt h,  t hesh e et  bein g a djusted  for writa bil it y and opacit y  i n conformi tywith its eve ntu al use .The objec t o f the  inven t ion of  U.S. Pat .N o. 3,7 5 5,499 i s st ated  to be the provis i on of a synthetic  sheet  f o rw r iti ngand simila rother purpose s  h a v i ngi mproved surfa ce conditio n , o pacity ,and otherrequi si t e p roperties.U.S.  Pat. No.  3,755 , 499 fur t her dis closes  th atthet he rm opl as t icr es int o b e mixedma yor ma y no t h a ve c omp atib ility  with the lin ear  pol y est er, p rovid ed t ha t itcan be  subs ta ntially uniform ly m ixed with  an ddis pe rsedi n thelin ear  polyes ter att heti m e of  forming, that the  f o r me d film,regard l es so f whethe ritis t r a nspar ento rnot, may  produ c eauniform  m at sur fa ceupo n bei n g st retche d and th e fil m  thus obtained is heat-shrin k ab l e ,a ccep tab le in its w riti n g pr oper t ie s,a nd po ssess es ad e quate opacity and t ha t in o rderto further im prove stab i l i ty in th e fi l ms ize at a hightempe rature, it may be h eat-t reated a t a tempe r a ture abo vethe  st ret c h in g temperature o f th elinearpol yesterand  be low  th emelting p oint ofbo th  m ix ing  ther m oplastic  r esi nand  thel inearpolye ster .U. S . P at. No. 3, 7 5 5,49 9fa ilstodi sclos e th e  in fluence  of addit ion of a nin organic  opacifying p ig ment or th esim ultane o u s additi on of poly(4-methyl-1-p e ntene). 
U. S. Pa t. N o. 4,128, 689  discl ose s  a pro cess f or pr ep ari n g  ther m o pl ast ic  sheets or w ebs , whi ch  pro cess co mprises the stepso f:(i) extruding  afoam a b le  th e rm o pla st i c p o l ymer mixture th rough thedi e  o f a screwe xtr ud er to p roducea foa m ed extr udate insheet orwe b fo r m , t he foamabl e thermo plastic p o lymer mi xture  co ntaini ng  at  leas t a fi r stand a  secon dthermo plast ic  polymer , the first thermoplast ic pol ymerbei ng substa nti a lly  crystall ineand having  ahig her m elt i ng po intt ha n,a nd be ings ubstantia l ly  im m i sc ible with,t h e  se condthe r moplas ticpolymer, and thet emperature ofextr u s ion  be i ng e qu al to or great erth a n  the mel ti ng point of  the fir st therm oplast ic pol ymer; ( i i )s tretch ingthe  foamed e xtr ud a te from  s te p  (i) i n th edirect ion of extr u s ion as it leaves  thed i e tor upt ure m os t of th e  cel ls of thefoamed extr udateandto el ongateth e wall s o fthe collap s ed cellsin th e direc ti on o f s tretch ; (i i i ) com pres si ngthe stret c h ed ex tr u dat e fr om st ep  (ii ) while i t  remains  pl a stic; a nd  (i v )  cooli n ga n d foamed,str etche d and compre s sede xt r udate  fromstep ( iii). F u rth er more, U .S. 
 of_these mixed_polymer materials are disclosed_usually at_85_to 95°_C._with stretching ratios_from 2 to_3.5 times the original_length, the sheet_being_adjusted for writability and opacity in conformity with its eventual use. The object of_the_invention of_U.S._Pat._No. 3,755,499 is stated to_be the provision of a_synthetic sheet_for writing and similar other purposes having improved_surface_condition, opacity, and_other requisite properties. U.S. Pat. No. 3,755,499 further discloses_that the thermoplastic resin to be_mixed may or_may_not_have compatibility with the_linear polyester, provided that it can_be substantially uniformly mixed with and_dispersed in the linear polyester at the_time of forming, that the formed_film, regardless of whether it_is transparent_or not, may produce a_uniform mat surface_upon being_stretched and the_film thus obtained is heat-shrinkable, acceptable_in its writing_properties, and possesses adequate opacity and_that_in order to_further_improve_stability in_the film size_at_a high_temperature,_it may be heat-treated at a_temperature_above the stretching temperature of the linear_polyester and below the_melting_point of both mixing_thermoplastic resin and the linear_polyester. U.S. Pat. No. 3,755,499 fails_to disclose_the influence_of addition of an inorganic opacifying pigment or the simultaneous addition_of poly(4-methyl-1-pentene).
U.S. Pat. No. 4,128,689 discloses_a process for preparing_thermoplastic sheets_or_webs, which process_comprises_the steps_of: (i) extruding a foamable thermoplastic polymer_mixture through_the die of a screw extruder_to produce a foamed_extrudate_in sheet or web form, the_foamable thermoplastic polymer mixture containing at_least a first and a_second_thermoplastic_polymer, the first thermoplastic polymer_being substantially crystalline and having a_higher melting point_than, and being substantially immiscible with, the_second_thermoplastic polymer, and the temperature of_extrusion_being equal to or greater than_the_melting_point of the first thermoplastic_polymer; (ii) stretching the foamed extrudate_from step (i) in the direction of extrusion as_it leaves the_die to rupture most of_the_cells_of the foamed extrudate and to elongate the walls of_the collapsed_cells in the_direction of stretch; (iii) compressing the stretched extrudate from step_(ii) while it remains plastic; and (iv)_cooling and foamed, stretched and compressed extrudate from step (iii). Furthermore,_U.S.