NZ248584A

NZ248584A - Preform for blow moulding a refillable container

Info

Publication number: NZ248584A
Application number: NZ248584A
Authority: NZ
Inventors: Suppayan M Krishnakumar; Wayne N Collette; Thomas E Nahill
Original assignee: Continental Pet Technologies
Priority date: 1990-03-05
Filing date: 1991-01-04
Publication date: 1994-08-26
Also published as: NZ248585A

Description

<div class="application article clearfix" id="description"> Utidsr ic.tiC'' ~ Spocir.wo^c:^ "v.-; ■■.•:•• '• " to k... .M. Initials 2 4 8 5 8 4 \ J\.. ria ^ Uf\$ are: Ai^anlnf,. N.z.PAT£NTOFfl&E__J • -6 SEP 1993 REcevvso_ 2 6 AUG 1994 '' . I3.8i Patents Form No. 5 This is a divisional out of application number 236672 dated 4 January 1991. NEW ZEALAND PATENTS ACT 1953 COMPLETE SPECIFICATION PREFORM FOR FORMING REFILLABLE POLYESTER CONTAINER WE, CONTINENTAL PET TECHNOLOGIES, INC, a corporation organized and existing under the laws of the State of Delaware, USA, of 800 Connecticut Avenue, Norwalk, Connecticut 06856, United States of America hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: - 1 - 2 4 8 5 PREFORM FOR FORMING REFILLABLE POLYESTER CONTAINER This application is a divisional application of New Zealand patent application no. 236,672. The parent application relates to a refillable polyester container and a method of producing such a container. The present application relates to a new preform design suitable for producing such containers by blow molding. An economically and commercially viable, refillable plastic bottle reduces the existing land fill and recycle problems associated with disposable plastic containers, and more particularly with plastic containers formed of PET. In addition, a refillable container will permit the entry of the safer, lighter weight plastic containers into those markets currently dominated by glass, where legislation prohibits use of non-returnable packages. The desirability of a refillable container formed of a polyester is specifically discussed, for example, in U.S. Patent No. 4,334,627 granted June 15, 1982. The disclosure of that patent is incorporated herein by reference. At the present, it is to be understood that several polyester candidates provide the desired clarity and physical properties deemed necessary to produce refillable plastic containers. These polymers include polyethylene terephthalate (PET) acrylonitrile, polyarylate, polycarbonate, etc. Of the polymers commercially available, PET, at the present, offers the best balance of properties and cost/performance ratios. The container specifically disclosed in U.S. Patent No. 4,334,627 has been improved and is specifically disclosed in U.S. Patent No. 4,725,464, granted February 16, 1988. This patent makes specific reference to U.S. Patent No. 4,334,627. This invention relates to a preform suitable for blow molding a container which is an improvement over the container specifically disclosed in U.S. Patent No. 4,725,464. A refillable container must go through a loop each WC - 2 - time it is reused. The loop is comprised of (1) an empty caustic wash followed by (2) contaminant inspection and distribution to wholesale and retail locations, and (5) purchase, use and empty storage by the consumer followed by eventual return to the bottler. It is the hot caustic wash which is most determinental to the reuse of a blow molded polyester container. It has been found that failure (via crack initiation and propogation) of biaxially oriented blow molded polyester containers exposed to the caustic wash baths occurs primarily in the base area and most particularly in the central part of the base area which has little or no orientation. It is to the provision of a preform which can be used in the production of a container having improved resistance to crack failure in the base that this invention relates. In accordance with this invention there is provided a preform for use in blow molding a container suitable for refilling, the preform being an injection molded member formed of polyester and having; a closed bottom end and an open top end, a neck finish at the open top end, a body-forming portion which on blow molding will form a body of the container, a shoulder-forming portion disposed between the neck finish and the body-forming portion and which on blow molding will form a shoulder of the container, and a base-forming portion which on blow molding will form a base of the container, the base-forming portion having generally hemispherical inner and outer surfaces at the closed bottom end and a thickened portion between the bottom end and the body-forming portion, the thickened portion having an increased wall thickness as compared to the wall thickness of the body-forming portion, characterized in that the thickened portion has an upper cylindrical portion of the increased wall thickness and a lower tapered portion which gradually reduces in wall thickness towards the bottom end. With the above and other objects in view that wi: product filling/capping, (3) warehouse storage, (4) WC 3 hereinafter appear, the nature of the invention will be more clearly understood by reference to the following detailed description, the appended claims and the several views illustrated in the accompanying drawings. FIG. 1 is a schematic.diagram showing the typical cycle or loop to which a refillable container usually passes. FIG. 2 is a vertical sectional view taken through a container formed from a preferred preform of the invention. FIG. 3 is an enlarged fragmentary vertical sectional view taken through the base construction of the container of FIG. 2. FIG. 4 is a vertical sectional view taken through a preferred preform of the invention suitable for forming the container of FIG. 2. FIG. 5 is a horizontal sectional view taken generally along the line 5-5 of FIG. 4 and shows the specific cross section of the body portion of the preform. FIG. 6 is a transverse horizontal sectional view taken generally along the line 6-6 of FIG. 4 and shows specifically the increase in thickness of the container base forming portion of the preform. FIG. 7 is an enlarged fragmentary vertical sectional view taken through the base portion of the preform and shows the specific configuration of the improved preform construction. FIG. 8 is a fragmentary vertical sectional view showing generally the base construction of FIG. 7 with the bottom central part of the base being engaged by a stretch blow centering rod. FIG. 9 is a fragmentary vertical sectional view taken through a base portion of a blow mold in which the preform of FIG. 4 is blow molded to form the container of With reference to Figure 1, each container formed from a preform of the invention can be tested for its acceptability as a reusable container by being subjected to a typical commercial caustic wash solution which is prepared 3.5 sodium hydroxide by weight with tap water. The wash solution is maintained at 140°F and the// FIG. 2 WC 4 \ 2 4 8 5 containers are submerged uncapped in the wash for 15 minutes in accordance with a commercial bottle wash system. After removal from the wash solution, the containers are rinsed in tap water and then filled with a desired liquid product which may be in the form of a carbonated drink which is packaged at 4.0 + 0.2 atmospheres and capped. Such a filled container should withstand a temperature of 100°F at 50% RH for 24 hours. The general loop through which a container passes in a single use of the container is shown in FIG. 1. Generally, the degree of molecular orientation in the upper shoulder section and in the base section of a stretch blow molded container is lower than that in the body or panel section of such container. In a refillable container, all features such as flutes, grooves and steps, which are potential stress risers, are avoided in the upper shoulder region and in the base section. Any decorative embossing, flutes, grooves, etc. should be restricted to sections having higher degrees of orientation. To achieve a good balance between creep-volume growth and thermal shrinkage in the hot caustic wash, the preform segment, which forms the panel section of the container, is configurated to give a total thickness reduction ratio of 7.5 to 10.5, with a stretch ratio of 3.2 to 3.5 in the hoop direction and 2.3 to 2.9 in the axial direction. The lower body and base forming portion of the preform (see FIG. 7) is configurated to have sections PQ, QR, RS and ST. These form the segments pq, qr, rs and st, respectively, of the container shown in FIG. 3. Referring now to the drawings in detail, reference is first made to FIG. 4 wherein there is illustrated the vertical cross section of a preform formed in accordance with this invention, the preform being generally identified by the numeral 10. The upper part of the preform 10 is of the same configuration as the preform of U.S. Patent No. 4,725,464 and includes a threaded neck finish 12 which terminates at its lower end in a capping WC - 5 - M flange 14. Below the capping flange 14, there is a generally cylindrical section 16 which terminates in a section 18 of gradually increasing external diameter so as to provide for an increasing wall thickness. Below the section 18, there is an elongated body section 20, the extreme lower part of which forms an upper part of a container base forming portion generally identified by the numeral 22. The base forming portion 22 includes at least the section QR (FIG. 7) at the top thereof. As is best shown in FIG. 7, in the section QR, the internal diameter of the preform 10 gradually decreases as at 24 wherein the section RS is of increased wall thickness. It will also be seen from FIG. 7 that the diameter of the section ST gradually reduces so as to reduce the wall thickness of the section ST. Additionally, the lower part of the section ST is generally of a hemispherical configuration as at 26. Furthermore, the inner surface of the section ST as at 28 is also of a generally hemispherical configuration, but with the surfaces 26 and 28 having different centres so that there is a continued gradual decrease in wall thickness. At the centre T of the section ST, there is a smoothly rounded upstanding projection 30 which is to be received in the lower end of a stretch blow centering rod, as shown in FIG. 8 and to be described in more detail hereinafter. Further, at the bottom of the centre T, there is a downwardly directed axial projection 32 which is in the form of an elongated gate. The outer surface 26 of the preform 10 smoothly turns to form the outer surface of the projection 32. Reference is now made to FIG. 9 wherein there is illustrated the configuration of the base portion of a blow mold cavity 34 defined by a customary type of blow mold 36. The blow mold cavity 34 in the base of the blow mold 36 has a lower outer generally hemispherical surface 38 which terminates in a base contact radius C which is centered a distance B which is 50 to 75% of the general overall radius A of the blow molded container. The radius C is 5 to 15% of the radius A. WC - 6 - r' } o / ' -J Lk It will be seen that the blow mold 36 is of a configuration so as to have a central dome 40 which is of a height D having a dimension which is 20 to 40% of the radius A. It will also be seen that the dome 40 is provided with a central recess 42 of a size and shape to receive the projection 32. Further, the domed surface of the cavity 34 also includes a surface portion 44 which gradually slopes into the recess 42. At this time it is also pointed out that the wall thickness of the preform at the cross section U in FIG. 7 is about 50 to 70% of the cross section of the preform in the segment RS. The preform 10 is reheated to the required glass transition temperature, placed within the blow mold 36 in the conventional manner, engaged by a stretch blow centering rod 50, as is shown in FIG. 8, inflated by internal pressurization so as to be stretched in both the axial and hoop direction to match the configuration of the cavity 34 and form a container such as the container of FIG. 2 which is identified by the reference numeral 52. At this time, it is to be noted that the rod 50 has a recess 54 in the bottom thereof so as to clear the projection 30. At the same time, the projection 32 is received in the recess 42. As a result, when the container 52 is blow molded within the blow mold 36, both the inside surface and the outside surface of the base, generally identified by the numeral 56 of the container 52, will be free of stress concentrations. The container 52 will include the threaded neck 12 and the capping or support flange 14 in their original configurations. Immediately below the flange 14, the container 52 will have a generally unoriented thick wall portion 58 which terminates in a thin wall shoulder 60 which is formed from the preform section 18. Beneath the shoulder 60, there is the container body 62. In the illustrated form of container, the container body 62 is provided with an elongated panel section 64 which is of a reduced cross section and is intended to receive a WC - 7 - 9 I f r-r • M suitable label (not shown). The body 62 continues below the panel section 64 as at 66 and terminates in the base 56, which, as previously described is of the domed type. The wall thicknesses of the various portions of the container 52 above the base construction 56 are clearly shown in FIG. 2. At this time it is pointed out that the container 52 is a 1.5 liter bottle and the preform 10 is configurated to form the container 52. Reference is now made to the enlarged showing of the base construction 56 found in FIG. 3. It is to be noted that the various lines P,Q,R,S and T find their equivalent lines in the container 52 as lines p,q,r,s and t, respectively. The base construction 56 starts generally at the line p and includes an axially extending and radially inwardly directed outer surface 68 which is generally hemispherical. It will be seen that there is a very slight increase in wall thickness between lines p and q while the section qr has a gradual increase in wall thickness with the base construction terminating in a chime c which forms the support radius. In the section rs, the wall thickness continues to increase with the base construction 56 being domed as at 72 and the wall thickness continuing to gradually increase until it reaches the point 70 which corresponds to the outer edge of the sloping surface 44. Thereafter, the base construction 56 continues to smoothly increase but at a slightly greater rate until the outer surface terminates in the projection 32 and the inner surface terminates to the projection 30. To achieve the required wall thickness at chime c of the base construction 56, FIG. 3, the wall thickness of segment RS is about 1.10 to 1.30 x that of the segment PQ. The transition from thin to thick wall section is gradual and smooth as described above. This elminates any abrupt wall thickness change in the segment qr. A higher degree of orientation in the dome segment st of the base 56 is achieved by optimizing the base configuration and by the gradual decrease of the preform wall thickness in the segment ST. WC - 8 - The projections 30, 32 at t insures that a crystalline region, if any, in this area does not weaken the section. As pointed out above, the elongated gate 32 is not crushed during blow molding. Inasmuch as the base construction gradually increases in wall thickness as the orientation decreases, it will be seen that the desired strength requirement is obtained for the base construction 56 by way of smoothly curved surfaces which greatly reduce the possibility of stress cracking. It is believed that 28-30% crystallinity is an optimum level for a refillable PET container which is preferably in the form of a bottle having an injection molded threaded neck finish. Further, it is to be understood that the preform, and thus the container, may be formed of a multilayer construction including internal barrier layers so as to extend shelf life. The application of such multilayer preforms may be utilized to reduce contaminate absorbtion, if filled with non-food products, and subsequent product contamination after washing and filling. Although only a preferred embodiment of the preform has been specifically set forth herein, it is to be understood that minor variations may be made in the preform to form a desired container without departing from the scope of the invention as defined by the appended claims. WC 9 </div>

Claims

<div class="application article clearfix printTableText" id="claims"> WHAT WE CLAIM IS: 248 58

1. A preform for "use in blow molding a container suitable for refilling, the preform being an injection molded member formed of polyester and having; a closed bottom end and an open top end, a neck finish at the open top end, a body-forming portion which on blow molding will form a body of the container, a shoulder-forming portion disposed between the neck finish and the body-forming portion and which on blow molding will form a shoulder of the container, and a base-forming portion which on blow molding will form a base of the container, the base-forming portion having generally hemispherical inner and outer surfaces at the closed bottom end and a thickened portion between the bottom end and the body-forming portion, the thickened portion having an increased wall thickness as compared to the wall thickness of the body-forming portion, characterized in that the thickened portion has an upper cylindrical portion of the increased wall thickness and a lower tapered portion which gradually reduces in wall thickness towards the bottom end.

2. A preform according to claim 1, wherein the generally hemispherical outer and inner surfaces of the bottom end have different centres so that there is a continuing gradual reduction in wall ' thickness in the bottom end.

3. A preform according to any of claims 1 and 2, wherein the bottom end has a centrally-located thickened gate region joined to the inner and outer surfaces in a smooth connection free of sharp corners.

4. A preform according to claim 3, wherein the bottom end adjacent the thickened gate region has a wall thickness which is 50% to 70% of the thickness of the upper cylindrical portion.

5. A preform according to any foregoing claim, wherein the polyester is selected from the group consisting of polyethylene terephthalate (PET), a WC polyacrylate, and polycarbonate. 10 24 85 8

6. A preform according to claim 5, wherein the polyester is PET.

7. A preform according to any foregoing claim, wherein the thickness of the upper cylindrical portion is about 10 to 30% greater than the thickness of the body-forming portion.

8. A preform according to any foregoing claim, wherein the upper cylindrical portion is joined to the body-forming portion by a tapered portion which gradually reduces in thickness from the upper cylindrical portion to the body-forming portion.

9. A preform according to any foregoing claim, wherein the shoulder-forming portion is tapering in increasing wall thickness from the neck finish to the body-forming portion.

10. A preform according to any foregoing claim, wherein the bottom end of the preform has a centrally-located outer projection.

11. A preform according to claim 10, wherein the outer projection is joined to the outer surface in a smoothly tapering connection free of sharp corners.

12. A preform according to claim 11, wherein the outer projection is an axially elongated gate for engagement by a recess in the blow mold.

13. A preform according to any foregoing claim, wherein the bottom end of the preform has a centrally-located inner projection.

14. A preform according to claim 13, wherein the inner projection is joined to the inner surface in a smoothly tapering connection free of sharp corners.

15. A preform according to claim 14, wherein the inner projection is adapted for engagement by a centering rod during blow molding of the preform.

16. A preform according to any foregoing claim, wherein the ratio of the length of the upper cylindrical portion to the length of the lower tapered portion is about 1:1.

17. A preform substantially as hereinbefore described with reference to what is shown in Figures 4, 5, 6, 7 and A I _____ , COKjTCNE^TAL, PET TECHNOLOGIES ,• INC wcf |77p&tewtopf'Ce_ By thjfeir Attorneys ■6 SEP 1993 JP' I BALDEN, SON & CAREY T" "r-CffVHD, -11- </div>