CA1139248A - Forming molecularly oriented containers from reheated preforms - Google Patents

Abstract

402 APPLICATION FOR LETTERS PATENT FOR IMPROVEMENTS IN FORMING MOLECULARLY ORIENTED CONTAINERS FROM REHEATED PREFORMS ABSTRACT OF THE DISCLOSURE In forming containers from injection molded preforms of thermo-plastic material such as nitrile-based polymers by a process which includes heating the preforms to orientation temperature followed by distension to container form in a mold, the improvement providing re-duced thickness variability in lower portions of the containers which in-volves controlling preform shrinkage during such heating to between about 4 to 15% of the initial length for nitrile materials by maintaining the ratio of average thickness to inside preform surface area within de-fined limits and then axially and radially stretching such preforms during distension to predetermined levels. Nitrile preforms convertible to such improved quality containers have values of between about 0.005 to 0.011 inch-1 for the aforementioned ratio. Inventors: Purushottam D. Agrawal John E. Griesing

Description

T 0 2 1~l 39 24~3 IMPROVEM_N~S IN :FORMING ~O:LECULARLY ORl~N~-FD
CONTAII~ERS FROM ~EHF~ --D PREFOR~S

This application is a divisional of copending A~plication Serial Number 314,070, filed October 24, 1978.
'rhis invention relates to Lorming molecnlarly Grienled cc,ntainers oL theTr;~op1astic ~nate~ial, and rnore particula ly to i~r,proverr,ents in a 5 preiorrn reheat pIocess ior lorrning containers especially ol nitrile thelmo~iastic rnaterial where strength is cieveloped and wall thicicness variation rninirnized especially in the lo~eI coD.ziner body portions.
Systems lor iorming cortainers Irorn ?relorms reheated to molding temperature and then eY~--~znded in 2 r~oId are k~.ov~n. I~ the preIorm at the tirre or re~orming is at moleculc- orier.tation 'er~perature which is usually just above the glass transition terr.?eratuIe zone Ior the rnaterial, the resulting stressed containers r.zve improved i~pact and burst strength which rnd};es it possible to dchi2ve a signiLicant reduc'ion in weight ior a given perIormance over that reouired when IGrming at higher rnolding temperatures. As also '~own ,~er~r.o?le-s.ic .n.zte.i~ls containing a rnajor proportion of poly-nerized ni.rile-c roup-ccntainir~g rnonomeI can be abricated into oriented ccntaine. s in this nnanner and, though llsable ior packdging a wide v~riety oI pro(`ucts ~uch d5 Ioc~cls, pkarmaceuticals, personal care, household and industrial corn?ositions and tbe like, in view oL the;r eY.ceptio~dl st en~th znd be rier prope ties they are es?ecially desirable Lor packaging pressuri~ed con'ents s~ch zs ca-`ro-.Gted lic!uids in tke Lorrn of ~oft crin~; beve-,ges ~nd beer.
?reIor~s of these dnC, 5ir-.ilCr ~-cte ials, ho~eve, "~ecent ?roble~s ;n a reheat procecs iri ~hc~ the terr- e ature rcnge ~ulhin wr.!ch ,~ ~

' 02 ~39248 orientation can be developed is quite narrow, as typically exemplified by the modulus-temperature plot of Fig. 6 of U. S. No. 3, 814, 784, and accordingly reheat process parameters for such materials must be tightly controlled. Consequently, though possible to form oriented high nitrile containers via a prelorm reheat process, it is important in obtaining high yields with minimum usage of material to precisely control variables such as preform wall thickness and the temperature pattern in the walls at the time of blowing. In this last respect, heat programm-ing is usually employed to locally influence the extent of stretch during container formation. Also, though desirable for control it is difficult and most likely impossible to accurately measure temperature through the thickness of the preform wall after reaching orientation temperature since surface deformation will occur if a probe is used and radiation techniques are only effective to provide surface measurements.
Regarding the manner of forming preforms for such a reheat process, injection molding is preferred to minimize excess wall thick-ness variation since the plastic is molded in a cavity delimited by two surfaces defining the inside and the outside of the molded part vis-a-vis blowing where the inside surface of the part is not formed to a cavity wall. However, in pumping relatively stiff high nitrile thermoplastic material into an injection mold, frozen strains will inherently develop on cooling. Such strains relieve during reheat resulting in shrinkage along the preform length which has to be dealt with since no way has yet been found to entirely avoid developing such strains in an elongated preform. More specifically, a system employing temperature programm-ing during reheat typically results in a region of the preform exposed to a heat source at one temperature gradually approaching the desired level for such region and then, because of strain relaxation, retracting to a T~ A 02 il3~

position where the same plastic which had been-exposed to the ii~st source is now beiore a source set at a different t~Inperature. Whe~
pre~orms subject to such overlapping exposu,e are expanded in the mold substantial thickn~ss variability results which ~n tuTn can lead tb ~xces-5 si~ely th~n or thick a~eas ~nd the appar~nt n~ed for more Ir.aterial in theoontailler tban is ~eally necessary fo~ the int~n~ed end use.

Now, however, improvements have been develop~:d which sub-stantially minimize or overcome such prior art di~ficulties in a p~e~orm reheat ~rocess for ~o~ming molecula-ly oriented c~>ntainers of thermo-10 plastic ~naterial.

Accordingly, this invention provides improvements in sucha reheat process which result in im~roved control of material thickness distribution without sacrifice in strength or increase in material usage in lower portions of the resulting molecularly oriented containers. Preform shrink in such a reheat process is recognized as a controllable parameter influencing material thick-ness distribution in the containers and is used instead of direct temperature measurement as a hot preform quality con~rol pararneter in a reheat system for forming molecularly oriented conta;ners.
Shrink and dimensional characteristlcs of an injection molded preform and are related and the relationship is cGntrolled within defined limits in producing high yields of finished, moie-cularly oriented containers of optimum quality Tubular preforms having predetermined dimensional character-istics within defined limits are provided, which when heated and stretched axially and laterally will yield containers of improved quality in terms of material thickness variability.

' -- ~
. ~2 ~39Z48 High nitrile polymers are utilized as the thermo~lastic material in carrying out the process of ~he invention.

-In broad terms the invention isproviding a method of forming containers from injection molded prefor~s of thermoplastic material which comprises providing preIorms having ?redetelmined dimensional characteristics such that shrinkage during 5 heating to or!entation temperature is maintainable withir) predetermined lirnits, heating such preforms to such temperature by temperature programming while r~aintaining shrin}cage within such limits and then axially and radially stretching such heated preforms beyond predetermined minimum levels but within predetermined total stretch levels to 10 form the containers, whereby strength is developed and t~ickness-variability minir,nized.
Ill more specific terms, there is provided in the method of forming containers from injection molded preforms comprising a major proportion of a polymerized nitrile-group-containing monorner, which 15 method includes heating the preIorms to molecular orientation tempera-ture followed by a~cial and radial stretching to container form in a mold, the improvement therein providing reduced thickness variability in lower portions of the containers which comprises, in combination, the steps of controlling shrinkage of the preforms during such heating to 20 between about 4 to 15% of the total initial preform length and then con-trolling the e~tent of such stretching according to the relation:

I ~ 02 ~ 139Z48 % axial stretch (A) =(container length minus preforTn length~(loO) - preform length min!ls preform neck inish length (maximum container diameter min~s ~reform outside diameter~(100) % radial stretch (B) =
preform outside diameter wherein:
A is at least about 30;
B is at least about 100; and A plus B is between about 130 and 280.
From a product standpoint a tu~ular, injection molded preform comprising a major proportion of a polymerized nitrile-group-containing - mcnomer is provided for forming into container shape which has a value of between about 0. 005 to 0. 011 inch~l (0. 012 to 0.028 cm.) for the ratio averag e thickne s s body inside surface~ area In describing the overall invention, reference will be Inade to the accompanying drawings wherein:
Fig. 1 is a graphical repre5entation in accordance with an embodiment of the invention of the relationship between shrink of a nitrile preform and certain of its dimensional characteristics;
Fig. 2 is a partial, sectional perspective view of a preform co~iguration flmctional in the process of the invention;
F-ig. 3 is a schematic view of the preform heating step in a re-heat pro c e s s .
Fig. 4 is a schematic elevational view of a stretch-blow assembly converting the preform of Fig. 2 into container form; and Fig. 5 is a graphical representation of the levels of stretch to 25 be used with a nitrile polymer version of the preform of Fig. 2 in forr~ing L~ 02 li39248 containers according to Fig. 4.

Referring now to the drawings, an elongated, tubular, injection molded preform 10 of thermoplastic material is shown in Fig. 2, which can be distended into col~tainer shape in accordance with the invention.
Preform 10 is circula~ in cross section and includes body portion 12 havi~g closed end 22 which i5 shown curved in the shape of ahemisphere but could be of alternate configuration such as substantially flat, pointed, conca~e or the like. Annular finish portion lA preferably surrounds an opposite open end, is formed to final shape in the preform injection mold-ing step and is not intended for remolding with body lZ during formation of the container. Alternatively, such finish may be formed during the final molding step and in such case the preform during injection molding will be provided with a length increment corresponding to 14 from which such finish is formed in the blow molcl.. The wall of body 12 may be substan-tially constant or progressively gradually variable in thickness depending on the nature of the thermoplastic material. Body 12 extends from finish 14 at substantially the same crosswise dimensions and cross sectional shape as that of portion 1~' and though such body may vary fr~m this con-figuration it should not be appreciably greater in such dimensions or dif-fereslt in shape thar~ finish 14. With nitrile polymers body 12 preerably smoothly increases i4 thiclcness along its length from a minimum imrnediately adjacent the finish to a maximum at the junction of the side-wall with hemispherical end 22. ~he sidewall of body 12 also preierably tapers inwardly at a slight angle a1 on the order of about 1/4 to 3/4 degrees to facilitate extraction from the injection mold. Preforms 10 have predetermined dimensioral characteristics such that shrinkage during heating in a manner to be described is maintainable within predeter-~139~48 mined limits. ~Iore specifically, the ratio of average preform thicl~ess to the inside surface area of body 12 lies within a predetermined range to be further described, such average thickness being the arithmetical mean of a. ) the thickness at 16 in the vicinity of the junc+ion of the body with finish 14 and b. ) the thickness of the ~all at 20 at the confluence of the sidewall with closed end 22.
Containers formable according to the invention from preforms 10 may vary widely in size and shape and can be characterized in terms of weight and volume as ranging from between about 0. 03 to 0. 13 glns. /
cc. of internal volume. The preferred configuration is a bottle shown as 34 in Fig. 4 which is circular in cross section, has a volume of be-tween about 170 to 3780 cubic centimeters, has a maximuDn diameter D
somewhere along its iength and a lower body region where wall thic};ness control for optimum functional preformance is important. Such area in Fig. 4 is shown as heel or chime 45 in the region of the confluence of the bottle sidewall and base.
Referring to Fig. 3, during temperature prograrnn~ed heating to molecular orientation temperature each preform 10 while supported on a suitable carrier, not shown, is interposed between opposing banks Z4, 26 of heating assemblies, each of which comprises a pluraLity of imlnediately adjacent, vertically arranged emitt er strips typically shown as 28, 30, with refLectors 29 interposed therebetween, each pair of opposing strips being in heat transfer proximity opposite a preform zone, with eight zones shown for the particular preform illustrated. The heating assemblies affecting each zone are set and adjusted to a predeter;nined temperature to accommodate the particular plastic of the preform via conventional control instrurnentation. Such settings are arranged to ~:~ 3C~Z48 provide the specifically desired temperature within the overall molecular orientation temperature range for the portiona preform body 12 in such zone, yet while controlling the amount of shrink via such settings which occurs in raising preform 10 to orientation ternperature from sub'stantial-ly room temperature, Though a single preform between oppositely arranged heating assemblies is shown and preferred to provide optimum zone temperature control,it is possible to interpose plural rows betweer opposing assembly pairs when the nature of the thermoplastic material in terms of modulus change with temperature within the orientation range does not dictate a need for unusually precise temperature control. In the illustrated embodiment, finish portion 14 is vertically below and outside the influence of the heating assemblies and therefore no increase in temperature to any substantial extent occurs in such finish during heating since reshaping in the containing forming step is not contemplated.
If reshaping is contemplated, the portion to form the finish should be within the influence of the heat transfer assembLiesO
With respect to Fig. 4, a stretch blow assembly 32 is exemplarily shown for converting a preform lO into molecularly oriented container 34. This is accomplished by first enclosing each preform 10 while within the molecular orientation temperature range for the parti-cular thermoplastic material within partible sections 36, 38 of conven-tional blow mold 40. Next, stretching mechanism 42 is moved over the open end of blow mold 40 whereupon telescopic rod 44 is caused to move to extended position by a suitable mechanisrn, not shown, in order to draw hemispherical end Z2 against base portion 46 of blow mold 40 there-by axially stretching body portion 12 in the manner illustrated in phantom at 48 in Fig. 4. Simultaneously therewith or preferably ~02 1~392~8 immediately thereafter, blowing medium such as compressed air is admitted to the interior of the preform through openings 50, 52 in rod 44 to stretch it radially outwardly against the cavity walls to the shape of bottle 34. Under certain circumstances, for exarnple those contemplating non-pressure applications for the finished container, it may not be neces-sary to provide a separate stretch rod in that the pressure of the blowing medium and the reduced length of the preform versus the container may be adequate to provide the axial stretch desired.
The amount of axial and radial stretch is defined by the con-figuration of the blow mold cavity in comparison with that of the preform and will vary with the nature of the material involved. In general, if stretch is too great in one direction there will be significant imbalance of orientat.on in that direction which results in substantially reduced strength in the opposite direction,whereas if stretch is too low the reverse is true. For example, with excessive axial stretch good columnar strength is achieve at the expense of hoop strength such that arL unwanted hole my develop in the preform during blowing. Such stretch amounts during formation of the container must be greater than predetermined minimums but within predetermined total levels The area within the cross hatched portion of the graph of Fig. 5 represents the axial and radial stretch amounts for preforms comprising a 70/30 weight percent acrylonitrile/styrene polymer which may be successfully empolyed in orming containers according to the invention. The percentage axial and radial stretches as used in Fig. 5 are defined by the formulas:

o~
:~3~2~ `

% axial stretch (A) =(container length minus preform length preform length minus preform neck finish length (maximum container diameter minus preform outside diameter)(100) % rad~al stretch (B) =
preform outside diameter In accordance with the process of this invention, injection molded preforms 10 to be subject to the described heating step are pro-vided which have the ratio of average preform thickness to inside body surface area within predetermined limits such that when program heated to within the orientation temperature of the polymer, measurable shrink-age which is neither excessive nor inconsiderable will occur, the range within which it should b,e controlled by the heat input from the programmed heaters being established from yields of good quality containers 34 having minimum thickness variability and the necessary levels of thickness in the lower body portions formed by axially and radially stretching in amounts which do not substantially imbalance the resulting orientation in eit~er the axial or radial direction. In arriving at values for such variables as heater temperature settings, oven residence time, prelorm thickness levels and the extent of stretching in the mold for any particular therrmoplastic material, tracking just where the material of a particular part of the preform ends up during stretching may be faciliated by initially physically marking the preforms with a grid pattern and then visually examining such markings and the distribution of plastic thereat in the finished container. As exemplified in Figs. l and 5, when the above considerations are applied to nitrile-based materials, i. e. polymers comprising a major proportion of nitrile-group-containing rnonomer, the ratio of preform average thickness to preform body inside surface area should be between 0. 005 to 0.011 inch~l which should be controlled on ~02 ~i39248 heating to provide between about 4 to 15% and preferably 6 to 15% shrink-age. The stretch parameters as above defined should provide A plus B
values of between about 130 to 280 but with the proviso that A be at least about 30 and B be at Least about 100. At these stretch levels for such nitrile-based materials, substantial imbalance in the resulting levels of orientation in one direction versus the other is avoided.
Nitrile-based preforms according to the invention, and as shown in ~ig. 1 (the arrowed numbers correspond to various preform weights) satisfy the equation:
y = 0. 247 x 10-3 (X) 2. 068 where:
y = % shrink of the preform during heating to orientation tem-perature and is between 4 to 15 and X= average preform thickness/inside preform body surface area.
The preforTns of this invention may be formed by conventional injection molding techniques from any molecularly orientable thermo-plastic material. Typical of such materials are polymers and copolymers of styrene, vinyl haiides, olefins of at least one aliphatic mono-l-ole~in having a maximum of 8 carbon atoms per molecule, and polyesters such as polyethylene terepthalate. The invention has been folmd particularly applicable to nitrile polymers containing a rnajor proportion of a poly-merized nitrile-group-containing monomer, such materials generally comprising from about 50 to about 90% by weight of nitrile monorner units, based on the total polymer weight, wherein the weight percent of nitrile is calculated as acrylonitrile. More particularly, the nitrile polymers used in this invention will comprise at least one nitrile monomer having the formula:

oz ~139248 CH2 = C-CN

wherein R is hydrogen, an alkyl group having 1 to 4 carbon atoms or a halogen. Such compounds include acrylonitri!e, methacrylonitrile, ethacrylonitrile, propacrylonitrile, alpha chloronitrile, etc. as well as mixtures thereof. The most preferred nitriles are acrylonitrile and methacrylonitrile and mixtures thereof.
The nitrile compositions generally will contain one or more comonomers copolymerizable with the nitrile monomers including monovinylidene aromatic hydrocarbon monomers of the formula:

H2C = C~

wherein R is hydrogen, chlorine or methyL and R2 is an aryl group of 6 to 10 carbon atoms and may also contain substituents such as halogen as well as alkyl groups attached to the aromatic nucleus, e. g. styrene, alpha methylstyrene, vinyl toluene, alpha chlorostyrene, ortho chloro-styrene, meta chlorostyrene, para chlorostyrene, ortho methylstyrene, para methylstyrene, ethyl styrene, isoproyl styrene, dichloro styrene, vinyl naphthalene, etc.
Additional useful comonomers include the lower alpha olefins of from 2 to 8 carbon atoms, e. g. ethylene, propylene, isobutylene, butent-l, pentene-l and their halogen and aliphatic substituted deriva-times, e. g. vinyl chloride, vinylidene chloride, etc; acrylic acid and methacrylic acid and the corresponding acrylate and methacrylate alkyl esters wherein the alkyl group contains from 1 to 4 carbon atoms, e. g.
methyl acrylate, ethyl acrylate, propyl acrylate, methyl methacrylate, etc. Other comonomers which may be used include vinyl esters such as ~139~:48 ~02 vinyl acetate; ~nd alkyl vinyl ethers wherein the alkyl group contains from 1 to 4 carbon atoms such as methyl vinyl ether, ethyl vinyl ether etc. and mixtures of the foregoing, AdditionaL comonomers useful in the ?ractice of this invent on are those comonomers which contain a mono- or di-nitrile function.
EY.amples of these include methylene glutaronitrile, Z, 4-dicyanobutene-1, vinylidene cyanide, crotonitrile, fumaronitrile, maleonitrile. The pre-ferred comonorrlers are the monovinylidene aromatic hydrocarbons, lower alpha olefins and acrylic and methacrylic acid and the correspond-ing acrylate and methacrylate esters with the monovinylidene arGmatic hydrocarbons being more particularly preferred. More specifically preferred are styrene and alpha methylstyrene. Another preferred composition is that wherein a terpolymer of nitrile, styrene and vinyl ether is used such as disclosed in U. S. Patent No. 3, 863, 014.
Optionally, the high nitrile materials may contain from 0 to about 25% by weight of a synthetic or natural rubber component such as polybutadiene, isoprene, neoprene, nitrile rubbers, acrylate rubbers, natural rubbers, acrylonitrile-butadiene copolymers, ethylene-propylene copolymers, chlorinated rubbers, etc., which is used to strengthen or toughen the high nitrile packaging materials. This rubbery colnponent may be incorporated into the polymeric packaging material by any of the methods which are well known to those s~i]led in the art, Æ. g., direct polymerization of monomers, grafting the nitrile monomer onto the rubbery backbone, polybend of a rubber graft polymer with a rnatrix polymer, etc.
The preferred nitrile polymers for container packaging applica-tions requiring excellent oxygen and water vapor barrier properties are 1~

~39~8 those containing from about 55 to about 85% by weight, based on the total polymer weight, of an acrylonitrile and/or methacrylonitrile monomer (wherein the weight percent of mel:hacrylonitrile is calculated as acrylonitrile). When acrylonitrile is used as the sole nitrile moriomer the preferred range is from about 60 to 83% by weight ~vhereas with methacrylonitrile the preferred range is from about 70 to about 98~o by weight of methacrylonitrile which correspon~s to about 55 to about 78%
by weight of nitrile monomer calculated as acrylonitrile.
The following examples are given to illustrate the principLes and practice of this invention and should not be const~ued as limitations the r eof .
EXAMPLE I
It was decided to form containers in the form of bottles 34 in Fig. 4 from reheated injection molded preforms. Such containers, intended for multiple use applications were to have 950 cc. nominal capacity, a weight of 85 gms., a maximum outside dian~eter (D in Fig. A) of 8. 3 cms., a total length of 27. 9 cms. and a finish length (33 in Fig. 4 of l. 68 cms.
Thermoplastic material in the form of a polymer comprising a 70/30 percent mi~ture by weight of polymeri~ed acrylonitrile/styrene monomer was injection molded in conventiollal equ3 p~nent into preforrns configured as in Fig. 2 having the following dimensional characteristics:
total length = lS. 6 cms.; finish iength = l. 6~ cms.
outside diameter (at 20 i~ Fig. 2) = 3. 20 cms.
z5 average thickness = 0. 399 cms.
l/4 taper along preformd body (~ in Fig. 2) inside body surface area (i. e. exlcuding that of finish 14 in Fig. 2) = 123 sq. cms. 15 ` ` 02 1139Z48 average thickness = 0. 0198 c~ 1 or 0. 0078 inch~
body i~side surface area With cavity dimensions of a blow mold set to pro~ide the above bottle configuration, the percentages of axial and radial 5tretch were calculated 5 at 47% aDd 159 respectively as ollows:
% axial stretch (A) = bottle len~th minus preforrn len~thl_oo) preform length minus preform neck finish length A = 27- 9-19- 6 (100), 19. 6-1. 68 A = 47%
,. . . =
~maximum container outside diameter minus preform outside diameter (at 20 in Fig. 4) ]
% radial stretch (B)= ---- (I ~ ~ ---------, preform outside diameter B = (8- 3 2 )( 100) B = 159%
A plus B = 47 + 159 = 206 These individual levels of A and B are within the cross hatched area of Fig. 5 with the total being within the previously deter~nined acceptable range of 130 to 280, While rotating about their iengthwise axes, the body portions of such preforms (12 in Fig. 2) were heated from substantially room temper-ature to within about 132 138C. which is the molecular orientation temperature of the polymel composition of the preforms, in accordance with a heating arrangement as shown in ~ig 3 wherein the te.nperature of the emitters for the various zones within an enclosing oven were set as follows:

'~ 02 1139248 . . .
Zorle 1 2 3 4 5 6 7 8 . ~
Tempera~ure 422 383 390 413 409 418 408 327 C . ) . ~
Res-dence time before he heaters was approximately 196 seconds iollowed by a conditioning tin~e in air at about 82C. of 98 seconds to permit the tempesature through the preform walls to equilibrate. Re-preser~t~ti~re preform ~;ample6 on exiting the oven were checked for re-duction in length from shrinkage due to strain relaxation and found after appropriate i~itial manipulation of the controls on the electrical power ~ to the emitter strips to be about 6. 65% of the total initial preform length.
The remaining preforn~s after conditioning were introduced to a stretch-blow assemb,ly as illustrated in Fig. 4 which included a mold cavity having a surface corresponding in shape and extent to that of the desired end bottle configuration. The preforms were then stretched a~ciall-r against the base of such cavity and expa~ded radially agairlst the side walls to form the bottle shape.
Bc~ttles thus formed were presented to a thickness m,easuring instrument manufactured by American Glass Research, Inc., of :~3utler, Penn., Model 2697-9-0062. This instrument was preset to reject bottles having a thickness in chime area 45 in r ig. 4 either below or above or which varied circu~;~erentially beyond certain limits. These setting6 were 38 mils (965 microns) for minimum thickness and 70 mils (L778 microns) for maximum thickness. Thickness variability was in-corporated as a range based on the minimum thickness se~-ting and was allowed to vary between 15% at the minimum setting ~f 38 mils to 30% at maximum setting value. These instrument se~ting values were obtained by measuring the performance of calibraLion bottles not made according to the present Example but which were de-! 17 3 139;~:48 `~02 termined by the values of a. ) fill level drop, b. ) lean from the vertical, c. ) internal pressure strength and d. ) impact resistance to be acceptable as within established specifications for these properties, whereupon settings of the thickness rnonitroing instrument were determined which would discriminate in terms of chirne thickness and variability levels between bottles equivalent to the caLibration bottles al~d those which were not.
Such tests were as follows:
a. ) F;ll Level Drop - Bottles were filled with a carbonated coLa beverage at 3. 9 volumes CO2 to a level of 3. 5 crns, below the topmost sur-face of the finish, then capped and placed in an oven at 37. 8C. for 24 hours whereupon they were removed and allowed to return ~o room temperature.
.
The unopened bottles were placed on a flat surface and the new fill level measured with the difference from the initial level being the actual fill level drop. The specification on maxium fill level drop was 3. 8 cms. after exposure to the conditions noted.
b. ) Lean - Each bottle was filled with a carbonated cola beverage at 3. 9 voluInes CO2, capped and placed in an oven at 37. 8C. for 24 hours, removed and allowed to return to room temperature. The unopened bottles were placed on a flat, level surface and a diaL gauge positioned adjacent each one, such gauge having a feeler resting against the bottle surface irnmediately beneath the finish designed to deflect with any deviation of such surface from vertical, and to indicate the magnitude of such de-flection via a pointer on a face calibrated in crns. Each bottle was then rotated 360 and the total difference between minimum and maximum pointer readings measure, the specification being no greater than 1. 14 cms .
c. ) Impact Resistance ~ Filled and capped bottles at room temp-erature were dropped once from a height of 1. 0 meter at a 30 degree . 02 ~392~8 angle to the vertical onto a flat steel plate and the number passing noted, the specification being at least 50% of those dropped surviving without rupture.
d. ) Burst Pressure - 3Ott1es filled with tap water were clamped in place in an Americal Glass Research Incremental ~ressure Tester and the internal psessure gradually increased uDtil each bottle failed.
Pressure at failure was noted, the specification on minimu~r~ pres6ure retention be~ng 10. 6 kg. /cm. 2 When bottles made according to this Exarnple were examined by the thickness instrument with the aforementioned settings, it was found that 97. 8% of those tested were passed as acceptable.
EXAMPLE II
.
The procedure of Example I was repeated in forming the same bottle configuration and size from preforms having the same length, diameter and taper dimensions except that preform weight was reduced to 58 gms, which resulted in values for average thickness of 0. 298 c.-n.
and for the ratio of average thickness to body inside surface area of 0. 0056 inch~l or 0. 0132 cm. -1 The heaters in the reheat oven were set as follows:
Z0 Zone 1 2 3 4 5 6 7 8 .
Temperature 416. 7 417 433 452 438 421 457 458 (C. ) Residence time before the heaters was 120 secoDds with con-ditioning time being about 60 seconds. On exiting the oven, shrink of the prefo~ms was measured at about 13%.
Minimurn ~nd maximum values on the thickness measuring instrument were the same as for Example I but si~ce the bottles of this Exar~ple were intended for single trip use in compa~ison with those c~

1~39248 Example I, the maximum percentage variation was preset at 45%.
Of the bottles fabricated and presented to the thickness measur-ing instrument preset as stated, 94. 5% were passed as acceptable.
EXAMPLE III
The procedure of Example I was repeated except that bottle size was proportionately reduced from 950 cc. to 475 cc. with the over-all configuration being otherwise the same. This resulted in a bottle with a maximum diameter of 6. 70 cms., a height of 21. 6 cms., a weight of 39. 5 gms., and a finish length of 1.42 cms. The dimensions of the preforms selected to be formed into such containers were as follows: total length 16. 0 cms.; finish length 1.42 cms.; outside diameter (at location 20) 2. 53 cms.; average thickness 0.333 cms;
inside surface area 85. 0 sq. cms.; average thickness/surface area 0. 0099 inch~l or 0. û039 cm. -1; axial stretch 38. 3%; radial stretch 164. 5Vo, total stretch 202. 8%. The heaters in the oven were set as follows:
Zone 1 Z 3 4 5 6 7 8 Temperature 765 617 645 748 670 705 620 555 (C. ) Residence time before the heaters was about 104 seconds with conditioning time of 52 seconds. On exiting the oven preform shrink was measured at 9%.
Whenbottles made from the preforms just described were examined to determine if they were within the thickness specifications of Example I it was found that 95% of those examined were acceptable.
The following Examples IV and V are provided for comparison purposes to illustrate the poor yield of acceptable bottles obtained when not operating in accordance with the invention.

T 4 02 113g248 E XA MP LE IV
The bottles had the same overall configuration as those in Example I except tbat maximum outside diameter D was 8. 1 cms., the height was 26. 7 cms., the weight was 49 gms,, and the finish length 5 was 1. 68 cms. The preform selected weigbed 49 gms.; the total length befc,re heatislg was 19. 6 crns.; outside diameter (at 20) was 2. 90 cms.;
average thickness was 0.243 cms.; inside surface area was 138 sq. cm6.;
average thickuess/body surface was 0. 0045 inch 1 orO. 0114 cm. -1;
axial stretch was 49%, radial stretch waS 172%; and total axial plus radial stretch was 212%. Heater settings in the reheat ovenwere:
Z one 1 2 3 4 5 6 7 8 _ Temperature~ 394 347 363 365 329 329 333 338 C ) .. ... ~
- Residence time before the ~ aters as preset above was 112 seconds with 56 seconds conditioning time. On exiting the oven preform shrinkage was determined to be 21%. On presentation of the resulting bottles to the thickDess measuring instrument, set as in Fxample II, a yield of 56% of accpetable bottles ~as obtained. Such poor yield is be-lieved due to excessive shrinkage dusing reheat which resulted in cross-over of material from one preLorm zone intended or treatment by heaters of one teInperature into adjacent heater zones set at different temperatures. Such poor temperature distribution at the time of re-molding resulted in poor thickness distribution in the lower body portions of the resulting containers and low yields.
_~rA ~P LE V

The procedure of Example I is repeated except that preform dimensions are as follows: weight 65 gms, length 15. 8 cms., outside diarneter (at 20) 2. 5'1 cm.s., average thickness 0. 42Z c~ns., body ~9248 inside surface area 87. 8 sq. crns. average thiel~ess/inside body surface area 0. OlZ2 inch~l, or 0 0309 cm. -1, axial stretch 77. 6%, radial stretch 219% and total stretch stretch 296. 6%.
When these preforms are heated via temperature ?rogramming with heater settings generally in accordance with those in Examplè I and with somewhat longer residence time to allow absorption of more heat by the relati~ely thick preform wall as reflected by the relatively high 0~0122 inch value, it is believed the percent shrin~cage on exiting the oven will be about 3. 8% which is an indication oL a low stIess le~el but because such prefo~ns are relatively thick and short, the percent axial and radial stretch a~nounts to form the bottle are excessive such that the quality control limits on thickness in the lower body portions will be e~ceeded. Bottles formed by axially stretchLng and blovi~i ng the preforn~s of this Example in the amounts indicated herein on presentation to the 1~ thickness measuring instrument set as in Example I are be!ieved to p~ovide yields on the order of 40% acceptable bottles.
VariGus modifications and alterations will be readily suggested to persons skilled in the art. It is intended, therefore, that the following be considered as exemplary only and that the scope o the invention be ascertained frorn the following claims.

Claims (8)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A tubular, injection molded preform of thermoplastic material for distending into a container shape, said preform comprising a body having a closed end and a finish portion at the opposite end, said preform having a value of between about 0.005 to 0.011 inch-1 for the ratio of average thickness to inside body surface area, wherein average thickness is the arithmetical mean of:
(a) the thickness in the vicinity of the junction of the body with the finish portion and (b) the thickness at the confluence of the side wall with the closed end, said body exhibiting between about 4 to 15 percent shrinkage on reheating to within the orientation temperature range of the thermoplastic material.

2. The preform of claim 1 wherein the preform comprises from about 50 to about 90 weight percent of a polymerized monomer selected from the group consisting of acrylonitrile, methacrylonitrile and mixtures thereof.

3. The preform of claim 2 wherein the polymerized monomer is acrylonitrile.

4. The preform of claim 1 wherein the thermoplastic material comprises a major proportion of a polymerized nitrile-group-containing monomer.

5. A tubular, injection molded preform for blowing into a circular, molecularly oriented container, said preform comprising a thermoplastic material containing from about 50 to 90 weight percent of a polymerized monomer selected from the group consisting of acrylonitrile, methacrylonitrile and mixtures thereof, said preform satisfying the relation:

y = 0.297 x 10-3(x)-2.068 where:
y = percent shrink of the preform during heating to orientation temperature of the thermoplastic material and is between 4 to 15; and (x) = average preform thickness/inside preform body surface area in reciprocal inches.

6. The preform of claim 5 wherein the thermoplastic material is a 70/30 weight percent mixture of polymerized acrylonitrile/styrene.

7. An injection molded preform comprising a body having closed and open ends which is free of excessive strains as evidenced by a shrinkage of between about 6 to 15 percent during reheat to molecular orientation temperature, said preform being formed of a polymerized nitrile-group-containing monomer and having a value of between about 0.005 to about 0.011 inch-1 for the ratio of average thickness to inside body surface area wherein average thickness is the arithmetical mean of the thickness adjacent the open and closed ends.

8. The preform of claim 7 wherein the polymerized nitrile-group-containing monomer comprises a major proportion of polymerized acrylonitrile.