CA1273763A

CA1273763A - Preparation of polyester hollow formed body

Info

Publication number: CA1273763A
Application number: CA000545612A
Authority: CA
Inventors: Setsuko Iida; Yoshitsugu Maruhashi; Takashi Sugisaki; Yohji Mizutani; Nobuhiro Kishida
Original assignee: Toyo Seikan Kaisha Ltd
Current assignee: Toyo Seikan Group Holdings Ltd
Priority date: 1986-08-30
Filing date: 1987-08-28
Publication date: 1990-09-11
Anticipated expiration: 2007-09-11
Also published as: EP0280742A4; KR880701628A; DE3776891D1; KR910005156B1; EP0280742A1; US4803036A; US4913945A; AU7858687A; WO1988001563A1; AU587912B2; JPH0453695B2; EP0280742B1; JPS6359513A

Abstract

Abstract of the Disclosure Disclosed is a process for the preparation of a heat-resistant polyester hollow formed body, which comprises mounting a preform of a thermoplastic polyester composed mainly of ethylene terephthalate units, which is maintained at a temperature where high-speed drawing is possible but whitening can be prevented, especially at a temperature represented by the following formula:
T = k(100?IV - 8?DEG + 42) (1) wherein IV stands for the intrinsic viscosity (d?/g) of the thermoplastic polyester, DEG stands for the content (% by weight) of diethylene glycol units in the thermoplastic polyester, k is a number of from 0.95 to 1.05, and T stands for the temperature ( C) of the preform, in a hollow forming mold maintained at a temperature as high as possible within the range where a final hollow formed body can be withdrawn without deformation substantially wider non-cooling, blowing air maintained at a temperature higher than the preform temperature into the preform to effect stretch drawing and expansion drawing so that the drawing speed in the axial direction is at least 250%/sec and the drawing speed in the circumferential direction is at least 450%/sec, and effecting heat setting while the preform is being draw-formed.
According to this process, a polyester hollow formed vessel excellent in the resistance to thermal contraction can be prepared at a very high manufacturing speed.

Description

~X~3763 PREPARATION OF POLYESTER ~IOLLOW FORMED BODY
Back~rouJId of the I~velltio (1) Field Or the Illventioll The presellt illvelltiorl relates to a process f'or the preparatioll Or a po]yester hollow rormed body alld also to a vessel prepared accordiJIg to this process. More particularly, the presellt il-vel~tioll relates to a process iJI which simultall~ously with draw-blow-formillg of a polyester preform to a hollow forrned body, heat settil-g Or -the molecular orielltatioll call be perf~ormed erf`icielltly. Purtherrnore, the presellt illvelltioll relates to a polyester vessel havillg llovel orielltat:ioll charac-teristics alld beillg exce'ilellt ill the resis-tallce to colltraction.

(2) Descriptio~l of the Prior Art A biaxially draw-blow-rormed vessel Or a thermoplastic polyester such as polyethy]elle terephthalate has llot ollly exccllellt trallsparellcy a~ld surrace gloss but also impact resistallce, rigidity alld gas-barrier properties required ror bottles, and therefore, this vessel has beell used ror bottlillg various liquids.
Ilowever, polyester vessels are generally defective ill that the heat resistarlce is poor, alld whell colltellts are hot-rilled, thernlal def'ormatioll or coll-tractioll Or the volurne is readily caused. Accordillgly, mally methods for heat-settillg biaxially draw-blow-rormed vessels af'ter the formillg operatioil have beell proposed as mealls for elimil~atillg this disadvalltage.
As the heat-settillg method, there are kllowll a method ill which a rormed body obtailled by draw-blow-rormillg is takell out f`rom a draw-blowillg mold and thell held in a heat-set-tillg mold and -the rormed body is heat-set, as disclosed ill Japanese Patent Publicatioll No.
35 56606/85, alld a method ill which heat set-tillg is carried ~,~

12~376~

out simultalleously with draw-blow-rorrning in a blow-forming mold, as disclosed in Japanese Patent Publication No. 6216/84. Furthermore, Japanese Patent Applicatioll Laid-Open No. 53326/82 teaches a met~,od in ; 5 which a heat treatment is carried out simultaneously with draw-blow-f'orming in a primary mold and the f'ormed body is taken out f'~rom the primary mold and blow-f~orrned ill a secolldary mold directly without coolillg.
or the roregoing knowll methods, the method in which heat settillg is carried out simultaneously with draw-blow-f`orming ill a blow-rorrning mold is industria11y excellent because the llurnber Or steps is small alld the apparatus cost is low. However, the method is still insurriciellt in that the manufacturillg speed is low because a relatively long residence time in the mold is necessary ror heat settillg arter the draw-blowing operation and cooling ror withdrawal Or a hollow rormed body.
As means ror overcoming this disadvarltage, there has been proposed a method in which the hollow-rorming mold is ma:intailled at a tempera-ture as high as possible within a rallge where the fillal hollow rormed body can be taken out without derormation substantially ullder llOII-cooling, ror example, at lOO C, and a polyester preform is biaxially drawn simul-taneously with bLowing Or high-temperature high-pressure air in the polyester prerorm (see Japanese Patent Application Laid-Open No.
95666/79 ). According to this method, it becomes unrlecessary to elevate and drop the temperature Or -the mold, but in case Or conductioll of' heat rrom the high-temperature gas, because Or the presence Or the heat transrer boundary rilm, a relatively long time is still necessary ror completion Or heat setting and the resistarlce to thermal contractioll is not satisractory.
Ill the process ror the preparation Or a hollow ~3 formed body ill which draw-blow-formillg alld heat setting of' the molecular or:ientatioll are sirnultaaeously carried out, it is expected that ir a pref'orm beiag draw-formed is maintailled at a temperature as high as possible, heat setting will be possible while the preform is being draw-f'ormed and the residence tirne of the hollow f'ormed body in the mold will be drastically shortelled.
However, preheating of an amorphous preform at a high temperature results ill occurrence of troubles such as thermal deformatioll of' the pref'orm and thickness ullevenlless at the draw-forming step. Moreover, whitellillg and reduction of' the drawability are caused by therrnal crystallizatioll of the polyester. Therefore, this means canllot be practically adopted.
Summary of the Invell-tioll It is therefore a primary object of the present invelltioll to solve the above-mentioned problems in the process for the preparation of a polyester hollow formed body in which heat setting is carr-ied out simultaneously with draw-blow-formillg and provide a process ill which by maintaillillg a polyester in a mold at a high temperature, heat settillg is advanced simultaneously with draw-forming and -therefore, a polyester hollow formed body excellent ill the resistance -to thermal colltraction can be prepared at a high manufacturillg speed.
This process is f'urther advantageous ill that the contractioll of the formed body with the lapse of time durillg the storage in a warehouse or -the like call be reduced.
We foulld that by maintaillillg a hollow-f'ormillg mold, a polyester preform and air to be blown into the pref'orm at predetermined levels, respectively, and adoptillg a certain high speed for drawillg the preform, the temperature of the preform being draw-formed becomes higher than the tempera-ture of heat by interllal friction 1~73'763 or the temperature Or heat by crystallizatioll, aJId draw-f'ormillg alld heat se~tillg are simultalleously advallced a~ld a hollow formed body excellellt in the resistarlce to contrac-tioll is obtained at a high manufacturillg speed.
It also was fou[ld that a vessel obtai~led accordillg to this process has llovel oriellta-tio~l characteris-tics il~
the shoulder port:ion where the colltractioll tendellcy is largest and the vessel is especially excell~llt i~- -the resistallce to contractiorl.
More specifically, in accordallce with the ~resellt illventioll, there is provided a process ~or the preparatioll of' a heat-resistant polyester hollow f'ormed body, which comprises mounting a prerorm of a thermoplastic polyester composed maillly of ethylene terephthalate UllitS, which is maintailled at a temperature where high-speed drawillg is possible but whitenillg call be prevented, especially at a temperature represellted by the following formula:

T = k(l00 IV - 8~DEG + 42) (l) whereill IV stands for the intrillsic viscosity (d/g) of the thermoplastic polyester, DEG stands for the contellt (~ by weight) of' diethylene glycol units in the thermoplastic polyes-ter, k is a number of from 0.95 to 1.05, and T stands for the temperature ( C) Or the preform, in a hollow formillg mold maintairled at a temperature as high as possible within the range where a fillal hollow formed body can be withdrawn without deformation substantially under no~l-coolillg, blowing air mailltained at a temperature higher than the preform temperature illtO the preforrn to effect stretch drawing and expansio drawing so that the drawing speed in the axial directio is at least 250~/sec and the drawing speed in the 1;~73~3 circumferential direction is at leas t 450%/sec, and effecting heat setting while the preform is being draw-rormed .
Furthermore, in accordance with the present invelltioll, there is provided a vessel comprisillg a neck, a shoulder, a barrel alld a closed bottom, which is obtained by draw-blow-f orming a preform of a thermoplastic polyes ter composed maillly of` ethylelle -terephthalate units alld heat-setting the orielltatioll, wherei n the cellter of' the shoulder of' -the vessel has a crystalli~at:ioll degree of at least 2~% as measured by the dellsi-ty method, -the refractive index (IIXO) il~ the thicklless directioll of the outer face side of the cel~ter of shoulder, measured by USillg NaD rays, is larger thall the rerractive index (llXi ) ill the thicklless direction Or the inller face side Or the cen-ter of the shoulder, measured by using NaD rays, and there is formed such a molecule orientatiorl distribution that the orientatio degree ratio ( Ro ) defined by the rollowing formula:

l~o = (lla - llxo)/(lla - IIXi) (2) whereill na is a refractive index of the unoriellted polyester, which is equal to l . 5760 according to Polymer Handbook, the second edi tion, is less thall 0 . 95 .
Brief Description of the Drawings Fig. l illustrates the relation between the highest arrival sheet temperature and the drawing speed when a 3û polyethylene terephthalate sheet having a thicklless of 2 mm is simultaneously biaxially drawn.
Fig. 2 is a sectional view of a bottle, which illustrates the change Or the shape by therrnal contractioll.
Fig. 3 illustrates the relation between the orientatiol- degree ratio (Ro) in the vicinity of the center of the bottle and the thermal contractioll ratio in the axial direction of the bottle.
~ igs. 4 and 5 show thermal contrac-tioll ratios at various pOSitiOllS Or the bottle.
Detailed Descriptioll of -the Pref'erred Embodiments In the process where draw-blow-formillg and heat setting are performed simultaneously (at one stage), i~
view of the resistance to conductioll, it is pref'erred that the ternperature of -the hollow formillg mold be as high as possible, and in view of the productivity or the withdrawal Or a hollow f'ormed body, it is preferred that the temperature of the hollow formillg mold be low. In the present invelltioll, by maintailliilg the hollow forming mold at a temperature as high as possible within the rallge where a final hollow f'ormed body can be withdrawn without deformatioll substantially under non-coolillg, no substantial coolillg time becomes necessary in the formillg cycle and the preparation of a hollow formed body can be performed at a high manuracturillg speed.
This tempera-ture dirfers according to the kind of' the polyester and the degrees of the molecular orientatioll and heat setting, but the temperature is generally 100 to 120 C and pref'erably 106 to 115 C. The conditioll Or "substantially under llon-coolillg" referred to in the installt specification is advantageously accomplished by substitu-ting interllal hot air with open air in withdrawing the hollow formed body from the mold. In this case, unilltellded cooling is caused to some extent, but this ullilltended cooling is included in this conditioll .
In the present invelltioll, the preform is prelimillarily heated at a temperature as high as possible within the range where thermal deformatioll Or the preform and occurrence of thickness unevelllless at the draw-formillg step call be prevellted. This temperature is given by the above-mentiolled forrnula (l).
This formula is an empirical formula obtained based on the fact that this thermal deformation temperature 5 becomes high as the illtril-sic viscosi-ty (IV) of the polyester is illcr eased alld the thermal def'ormation temperature becornes low as the contellt ( DE~ ) Or diet}lylelle glycol u~ ts in the polyester is increased.
The coeff'icient of the right side Or the formula ~ l ) 10 definillg the preform temperature (T) defines the allowable range. If' this coef'f'icient k is larger than l . 05, occurrellce of thickness unevelllless ill tile preforrn canllot be prevented at the draw-blow-formillg step alld the preparatioll Or a good hollow formed body becomes 15 difficult. Furthermore, the preform is whitened by crystallization and the transparellcy of the formed body is degraded, resultillg in reduction of the commercial value. On the other hand, ir the coefficiellt k is smaller thall 0 . 95, although draw-blow-forming is 20 possible, the strain at the draw-blow-forming step is left ill the formed body, and the resistance to contractioll canllot be improved unless heat settillg is conducted for a relatively lorlg time.
In the present inventiol-, by blowing hot air 25 maintailled at a temperature higher than the preforrn temperature into the preform, expansioll drawing in the circumferential direction is accomplished simultaneously with stretch drawing in the axial direction by a drawillg rod. The present invelltioll is promillelltly characterized 30 in that at this draw-blow-formillg step, the drawing speed ill the axial direction is at leas t 250%/sec, especially at least 300%/sec, and the drawing speed in the circumferential direction is at least 450%/sec, especially 500%/sec, that is, drawillg is performed at a 35 very high speed.

12~763 Ullder the preparatiol) conditiolls of the preselltinvelltioll, the pref'orm temperature is relatively high alld hot air mailltailled at a temperature higher than the pref'orm temperature is compressed ill the interior of the preform. Even under such high -temperature conditiolls, by drawing the pref'orm at a high speed, ef`f'ective molecular orientatioll is produced. What is most importallt is that spolltalleous heat gelleratioll, which is deemed to be due to interllal friction of -the polyester alld crystallization, is caused at the above-melltiolled high-speed draw-blowillg, and the temperature of the preform being draw-blow-formed is further elevated alld relaxation of the strain and crystallization are promoted.
In Fig. l of the accompanyillg drawings, the relation between the drawing speed alld the elevation of the temperature by generatioll of heat which is deemed to be due to the interllal friction and crysta11izatioll is plotted while the temperature of polyethylene terephthalate is chal~ged. From the results shown in Fig. 1, it is understood that with increase of'-the drawing speed, the degree of' elevation of the temperature is increased, and as the original temperature is low, the degree of elevation of the temperature is large.
In order to increase the absolute value of -the temperature at which the preform arrives, it is preferred tha-t the preheating temperature of the preform be maintailled at an allowable high temperature defined by the formula (l) and the drawing speed be increased -to further elevate the temperature. From this viewpoint, in the present inventioll, it is specified that the drawing speed in the axial direction is at least 250%/sec and the drawing speed in the circumferential direction is at least 450%/sec. This drawing speed is g much higher thall the drawi~lg speed adopted ill the collvelltiol~al method, that is, tlle drawillg speed of abou-t 150%/sec ill the axial directioll al~d the drawillg speed of about 200%/sec ill the circumferel~tial directioll.
Ill the presellt illvelltioll, by utilizillg elevatioll of the temperature, which is deemed to be due to iaterllal frictioll or crystal1izatioll, for relaxatioll of' the straill alld promotioll of' the crystallizatioll, draw-blow-formillg alld heat settillg are sirnultalleously advallced alld f'urthermore, drawillg is perrormed at a high speed.
Accordillg1y, the blowil~g time call be greatly shortelled as compared with the blowillg time ill the collvell-tiollal method.
A draw-blowll heat-set polyester vessel obtailled accordillg to the above-melltiolled preparatioll process was foulld to have a llovel molecule orielltatioll distributioll.
Referrillg to Fig. 2 illustratillg the sectiollal structure of all ordillary draw-blowll heat-set polyester vessel, this vessel 1 comprises all ulloriellted thick lleck 2, a highly oriented alld crystallized thinllest barrel 3, all oriellted alld crystallized shoulder 4 collnectillg the lleck to the barrel alld a closed bottom 5.
Whell a colltellt is hot-filled ill the vessel 1 or the vessel 1 is stored ill all empty state for a lollg time, the portioll where contractioll is most easily caused is the shoulder 4, alld a colltracted shoulder 4' showll by chaill lilles ill Fig. 2 is formed as the resul-t of colltractioll of the shoulder 4 ill the circumf'erelltial directioll. The llovel characteristic feature of' the bi-axially draw-blowll heat-set polyester vessel accordillg to the presellt invelltioll is that although the vessel is oriellted alld crystallized so that the cellter 4a of -the shoulder 4 has a crystallizatioll degree of at least 28%, especially at least 30%, as measured by the dellsity method, there is formed such a molecule orielltatioll 1~73763 -- ],o distributioll that the refractive index (nxo, NaD rays) i.n the thicl;lless direction of' the outer face side of the center Or the shoulder is large than the refractive illdCX (llXi, NaD r~ys) in the thickness direction of' the illller face side of the center of the shoulder.
The ref'ractive index ref'erred to in the installt specif'ication is one measured by using NaD rays as the light source, an Abbe refractometer as the refractometer and a polarizing plate al~d makillg light inc:ident in parallel to the sample surface while regardillg -the polarizatio~ directioll of the polarizing plate as the thicklless direction. This method is advantageo-ls in that the refractive illdex on the side f'alling in contact with a main prism can be selectively measured.
Furthermore, refractive indexes of the sample in various directions can be measured by changillg the polarization direction.
The refractive index (IIZ) ill the height direction, the refractive index (ny) in the circumf'erelltial direction and the ref'ractive index (IIX) ill the thickness direction, measured in the above-mentiolled manller with respect to each plane of the polyester vessel wall, have certain relations, described below, to the molecular orielltation. More specifically, supposing that the ref'ractive index of the unoriellted polyester is lla, the orientatioll degree in the height direction is proportional to the value (nz - na) and the orientatio degree in the circumferential direction is proportional to the value of' (ny - na), while the in-plane orientatioll degree is proportional to the value of ( na - nx ) .
At the step of draw-blow-formillg the polyester preform, the inller face side of the vessel wall undergoes a higher molecular orienta-tioll thall the outer face side. In the convelltiollal heat-setting method, trallsfer of' heat frorn the outer face side Or the vessel wall, that is, -trallsfer of heat from the mold, is preferentially caused, alld oriell-tatioll alld crystalli~atioll by heat settillg are caused from the outer f'ace side. Accordingly, the orientatiol degree on the outer face side is substantially the same as the orientatiol- degree on the inller f'ace side. Practically, when the ref'ractive illdex (~IXO) on the outer face side alld the refractive index (llXi ) 011 the illller f'ace side are measured with respect to the cen-ter of the shoulder of' a kllowa heat-set vessel, it is collf'irmed tha-t there is no substalltial differellce between both the values.
~'urtherrnore, ill this heat-set vessel, colltractioll of the shoulder as illdica-ted by chain lines in Fig. 2 is caused.
Accordillg to the present illventioll, by perf'ormillg draw-blow-f'orming alld heat-settillg ullder the above-mentiolled strict temperature control ullder conditiolls causing spontalleous heat gelleratioll in the polyester pref'orm beillg formed, at -the cellter of the shoulder of the vessel there is formed such a molecule orientatio distributioll that the conditioll of the f'ollowillg inequality:
IIXO ~ IlXi ( 3) is satisfied alld the orientation degree ratio (Ro) defilled by the formula (2) is less thall 0.95, especially ill the range Or from 0.75 to 0.93, whereby contractio of the shoulder is prominelltly controlled.
I:t was f'ound that when a polyester vessel is allowed to stand still for olle day in an atmosphere rnaintailled at a temperature of 30 C and a relative humidity of 80% and is then subjected to the hot filling operatioll, the vessel has a much larger thermal colltractiol~ than the vessel which is IIOt subjected to this hygroscopic treatment. It is deemed that the iZ737~,3 - l2 -re,lsoll -is that water absorbed ill the polyester shows a plastici~ g ef't'ect ill the hot sta-te alld the orie~-tatio is rclaxed.
~ig. , of' the accornpallyi;lg drawillgs illustrates the relatioll betwee~l the orielltatio~l degree ratio (~o) alld the thernlal colltract:ioll af'ter the above-melltiolled hydroscol~ic treatmellt a~ld fillillg of' hot watcr at 8~ C, which is plotted with respect to draw-blow~ eat-set vessels obtailled ullder various heat-settillg collditiolls while mailltaillillg the crys-talli~atioll clegree of' the cellter of the shoulder at a collstallt level of' 32%. It is seel~ that ill order to reduce the thermal colltractiOIl, it is cri-tical that the oriel~-tatioll degree ratio (Ro) should be less -thall 0.95.
In the presellt illvelltioll, a thermoplastic polyester composed maillly of ethylelle terephthalate UllitS is used as the thermoplastic polyes-ter. For example, there ca be melltiolled polyethylene terephthalate (PET) and so-called modif'ied PET obtailled by incorporatillg a small amoullt of other glycol such as hexahydroxylylelle glycol as the glycol compollellt or a small amoullt Or other dibasic acid such as isophthalic acid or hexahydrophthalic acid as the dibasic acid cornpollellt.
The polyester rnay be used sillgly or in the f'orm of` a blelld with other resill such as a llyloll, a polycarbonate or a polyacrylate.
It is preferred that the illtrillsic viscosity of the thermoplastic resil- used be at least 0.67 d~/g a~ld the colltellt of diethylelle glycol ullits be lower thall 2.0% by weight.
The bot-tomed preform used f'or draw-blow-formillg ca be prepared according to a kllowll optiollal method, for example, the injectiorl moldillg method or the pipe extrusioll moldillg method. Accordillg to the former

3~ method, a moltell polyester is illjected aad a bot-tomed lZ73763 preform having a mouth-neck portion, which corresponds to a final vessel, is prepared in the amorphous state.
The latter rneth-,d is advantageous f'or preparing a bottomed pref'orm having an intermediate layer of' a gas-barrier resil1 such as an e-thylene/villyl alcohol copolymer, and according to this lat-ter method, an extruded amorphous pipe is cut, a~1d a mouth-neck portiol-is formed Oll one end of the cut pipe by the compressio molding while the other end is closed, whereby a bottomed pref'orm is formed. In order to attain good engagernellt with a lid at a high temperature and rnaintaill a good sealing state, only the portion to be formed in-to a rnouth-nec~ portion can be heat-crystalli%ed. or course, this heat crystallization can be performed at any optional subsequent step.
Draw-blow-formil1g and heat setting of the prer'orrn can be perf'ormed under knowl1 conditions except the above-mentiol1ed limitations. It is preferred that -the temperature of hot air to be blown into the pref`orm be higher by at least l0 C than the preform temperature (T), and that the draw ratio in the axial direction be l.3 to 3.5, especially l.5 to 3, and the draw ratio in the circumferential direction be 2 to 5.5, especially 3 to 5, in the barrel.
After draw-blow-formil1g, hot air compressed into the formed body is substituted with air under atmospheric pressure, and the formed body is withdrawn from the mold. According to the present invel1tiol1, the time necessary for draw-blow-forming is only l to 4 seconds and the time necessary for. gas substitution is only l to 4 seconds,.a11d the residence time of the formed body in the mold can be prominel1-tly shortened and the manufacturing speed can be highly increased.
According to the present invel1tiol1, there is attained an advantage that a draw-blow-formed heat-set ~Z73763 lL~

hollow formcd body in which the thermal contractioll af'ter absorption of the rnoisture is controlled to a low level can be prepared at a very high manllracturil~g speed.
The present invelltioll will IIOW be described in detail with the following examples that by no rnealls limit the scope of the invelltioll. Incidelltally, in the examples and comparative examples given hereillaf'ter, the characteris-tics of' vessels were de-termined and evaluated according to the f'ollowing methods.
(a) Intrillsic viscosity 200 mg of a sample collected from a pref'orm or bottle was dissolved ill 20 mQ of a phenol/tetrachloro-ethalle mixed solvent (1/1 weight ratio) at 105 C f'or 20 minutes with stirring. The solution viscosity of the obtained solution was measured in a thermostat water tank maintailled at 30 C by a Ubbellohde viscometer and the intrillsic viscosity was calculated from the solu~tion viscosity.
Relative viscosity nrel = t/to t: dropping time (sec) of solution to: dropping time (sec) of solvent Specific viscosity nsp = nrel - 1 Intrillsic viscosity (n) = 2k'C

k': Haggins' constall-t (0.33) C: solution concentratiorl (g/100 m~) (1000) (b) Diethylene glycol contellt 3 About 2 g of a sample collected from a preform or a bottle was precisely measured, and 10 m~ of' hydrazine containillg an interllal standard (0.02 g of 1,6-hexane-diol) was added to the sample and the mixture was heated at 100 C f'or 30 minutes. The obtained decomposition liquid was subjected to centrifugal separation and the i273~63 liquid layer sample was analyzed by the gas chromatography to determine -the diethylelle glycol contellt. The filler used f'or the gas chrornatography was PEG-2OM.
(c) Pref'orm temperature Just before entrallce of' a heated pref'orm illtO a hollow formillg mold, -the outer surface temperature of' the central portion of the pref`orm was detected by a il~frared radiatioll thermometer.
(d) Temperature of' blown air The ternperature of blowll air was measured by a ternperature sellsor attached ill the ViCilli ty of a blow air outlet of' a pipe of high-pressure air to be blown.
~e) Drawing speed in circumferential directio~l by blowing A temperature sensor was attached in the ViCillity of the central portion of the bottle barrel on the inller face of the mold arld the time required for elevation of the temperature from the initiatioll of blowing was measured. The drawing speed was calculated by the f'ollowing formula:
R /~ t whereia ~ t stands for the above-mentiolled time, r stands for the average radius of the preform and R
stands f'or the distance between the central line of the bottle and the attachment position of the temperature sensor.
(f) Drawing speed in axial direction by drawing rod The time ~t' required f'or drawing in the axial direction of' the preform was measured by using a proximity switch and the drawing speed in the axial direction was calculated according to the followillg f'ormula:

12737~3 h /~t' whereill ~t' stands for the above-melltiolled time, ~l stands for the average height o f the drawn portion of the bottle and h stands for the average height of the drawn portioll of the preform.
(g) Crystallization degree By USi.llg all ll-heptalle/tetraChlOrOCarbOII dellSity gradieilt tube (supplied by Ikeda Rika), the density of a sample was measured at 20 C. From this dellsity, the crystallization degree was calculated accordillg to the followirlg f'ormula:
Crystallization degree Xc = ~ ~ ¦~c ~am)) x 100 wherei~ stallds for the measured density (g/cm3), Pam stands for the amorphous densi-ty (1.335 g/cm3) and ~c stands for the crystalline density (l.L~55 g/cm3).
(h) Refractive index ~y using NaD rays as the light source, an Abbe refractometer as the refractometer and a polarizing plate, the refractive indexes IIZ, lly alld IIX ill the axial, circumferential and thickness directions of a sample cut out from a bottle were measured according to the method of R. J. Samuels (Journal of Applied Polymer Science, Vol. 26, 1383 (1981)).
Inciderltally, according to this method, the refractive index of the side falling in contact with the main prism can be selectively measured. The results of the measuremellt made on polyethylene terephthalate bottles according to this method are reported by M.
Cakmak et al (ANTEC '84, p. 920).
(i) Thermal contraction A strain gauge (supplied by Kyowa Dengyo) was 5 attached to a measurement pOSitiOII either in the ~27~763 circumferential direction of the bottle or in the axial direction of the bottle, and the bottle was filled with hot water mailltailled at 88 C. Arter llatural coolillg, the contractio~l was measured by a static s-trai rneasuring device.
Incidelltally, the formed bottle was allowed to stand still ror 1 day ill an atmosphere maintailled at a temperature of 30 C alld a relative humidity of 80% a~ld was thell subjected to the measuremellt.
Example 1 All injectioll-molded polyethylelle tereph-thalate preform (havillg a weight of 66 g) was heated by a f'ar illfrared heater alld was then biaxially draw-blowll to prepare a bottle havillg an inller capacity of' l.5 Q and a shape showll in Fig. 2 (the average thickness of the barrel was 300 ~). Whell a sample collected from the preform was measured accordillg to the methods described above, it was found that the intrinsic viscosity was 0.74 and the diethylene glycol contellt was 1.3~ by weight.
Bottles obtained at various drawillg speeds under conditiolls cr a preform temperature of 106 C, a blown air temperature of 130 C, a blowillg time of' 3 secollds, a hot air substitution time of 3 secollds and a mold temperature Or 106 C were evaluated. The ob-tained results are shown in Table 1 and Figs. 4 and 5.

3o ~73763 C: * .

~h o O O O .' O ~ ~ b~
iL
h ~:

O ~

N ^ ~) t\l CO ~ 3 h O h oi C C~
rO ¦ O h E~ ~ S

X.C'~ ~ ~ O ~ 3 _ ~ h Q ti1 C

a ~ o ~ ~ ~ ~ ~ ~, s~
ssV
~ o ol lZ73763 In the sample D, deformation and shrinkage were large, and theref'ore, the contraction could not be measured.
From the foregoing results, it is seen that the higher is the drawing speed, the smaller is the thermal contrac tiOII . In case of a bottle having an inller capacity of 1.5 Q, i-t is preferred that the contractio of' the inner volume be smaller than lO cc. ~'or this purpose, it is necessary that the thermal contractio 10 should be lower thall 0.7%. 'l~his volume col~ditioll is satisf~ied in sample C, but the contractioll in the ViCillity of the shoulder Or the bottle is large alld the shaE)e is as shown by a broken line ill ~ig. 2. Ill order to maintaill the shape of' the vessel even after hot filling, high-speed drawing as adopted for sample A is ecessary.
Ill case of sample C, ill order to adjust the crystallization degree of 32% for reducing the thermal contractioll, a blowing time of 30 seconds was necessary. In this case, the orientation degree ratio in the vicinity of the center Or the shoulder was 0.98.
A time Or 25 seconds was necessary for adjusting the crystallization degree Or 32% in blow-formed bottle C by substitution with air maintailled at 200 C in the mold.
In this case, the orientatioll degree ratio in the ViCillity of the center Or the shoulder was 0.99.
F,xample 2 Bottles were prepared under the same conditiolls as adopted for sample A in Example 1 excep-t that the temperature of the preform was changed as indicated in Table 2. The obtained results are shown in Table 2.

1~73763 ,~
r1 a.) h aJ (~ ~ ~ 0 o o,~
~ ~ ~ O O O ~ O Lf\
m ~ C~ O c c r-t J

r ~ ~ ~ ~ O Lr~ ~o ,~0 ~/ ~IJ U~ ~ ~ O O r1 ~ .~.~ 6R~ O
~ ~ ~ ~ O ~Sa m E '~
E , ~ ~ co ~ ~
~ ~ ~ ~ C~ C O O o ~:
.C ~ I O ~ O U~
E-~ ~a~ 6~ C) '''I c~; o ~ ¦ o ~ a~ ~o r~ ~o a~
C~ O O O O ~:
r~

O r1 N ~` r r1 ~S5 t~l N ('\J ~ ~C
~ ~ t~ ~1 1~^1 t~ ~
h r1 E

i ~~ a~ a~ ~ o v E _ E
C
a~ I . .

E ~ ~ (~ ¢ ~ ¦
u~ ~1 1273'763 It is seen that the higher is the preform temperature, the smaller is the thermal colltrac tion .
~lowever, ill sample C, the preform was crystallized at the time of heating and the preform was sornewhat whitened, al~d also the bottle was whitened.
F'urthermore, sillce blow-formillg was carried out in the state where the preform was sof'-telled by a higl-l temperature, thic~l~ess ullevenlless was readily caused (the axis of' the bottle deviated f'rom the axis of the 10 prerorm). Accordillgly, the thlll portiol~ of' the barrel was readily def'ormed at the hot water f'illing step.
Example 3 Bottles A and D obtained in Example l were stored for l month in an atmosphere maintailled at a temperature f 3 C aild a relative humidity of 80%, and the thermal contractioll with the lapse of time was determilled in the following manller.
The amount (W) of water sufficiently filled in the bottle just after the formation and the amount (W') of water sufficiently filled in the bottle after the storage were measured. The temperature of filled water was 20 C. The contractioll with the lapse of time was determined according to the following formula:
Contraction (%) with lapse of time = ( WwW ) x lO0 The obtained results are shown in Table 3.
Table 3 Sample Contractioll (%) with Lapse of Time A0.8 3 D6.5 From the foregoing results, it is seen that bottle A obtained according to the present invelltioll is excellent in the resistance to contractioll with the lapse of time during the storage.

Claims

1. A process for the preparation of a heat-resistant polyester hollow formed body, which comprises mounting a preform of a thermoplastic polyester composed mainly of ethylene terephthalate units, which is maintained at a temperature where high-speed drawing is possible but whitening can be prevented, in a hollow forming mold maintained at a temperature as high as possible within the range where a final hollow formed body can be withdrawn without deformation substantially under non-cooling, blowing air maintained at a temperature higher than the preform temperature into the preform to effect stretch drawing and expansion drawing so that the drawing speed in the axial direction is at least 250%/sec and the drawing speed in the circumferential direction is at least 450%/sec, and effecting heat setting after the preform is being draw-formed.

2. A process according to claim 1, wherein the temperature of the preform mounted in the mould is a temperature represented by the following formula:
T = k(100?IV - 8?DEG + 42) wherein IV stands for the intrinsic viscosity (d?/g) of the thermoplastic polyester, DEG stands for the content (% by weight) of diethylene glycol units in the thermoplastic polyester, k is a number of from 0.95 to 1.05, and T stands for the temperature (°C) of the preform.

3. A process according to claim 1, wherein the hollow forming mold is maintained at a temperature of 100 to 120°C.

4. A process according to claim 1, wherein the intrinsic viscosity of the thermoplastic polyester used is at least 0.67 d?/g and the content of diethylene glycol units is lower than 2.0% by weight.

5. A process according to claim 1, wherein the temperature of hot air blown into the preform is higher by at least 10°C than the preform temperature (T).

6. A vessel comprising a neck, a shoulder, a barrel and a closed bottom, which is obtained by draw-blow-forming a preform of a thermoplastic polyester composed mainly or ethylene terephthalate units and heat-setting the orientation, wherein the center of the shoulder of the vessel is transparent and has a crystallization degree of at least 28% as measured by the density method, the refractive index (nxo) in the thickness direction of the outer race side of the center of shoulder, measured by using NaD rays, is larger than the refractive index (nxi) in the thickness direction of the inner face side of the center of the shoulder, measured by using NaD rays, and there is formed such a molecule orientation distribution that the orientation degree ratio (Ro) donned by the following formula:
Ro = (na - nxo)/(na- nxi) wherein na is a refractive index of the unoriented polyester, which is equal to 1.5760, is less than 0.95.