Plastic container

Abstract: A plastic container, especially a bottle for thermally treatable liquid, has a body (1) with a cylindrical part (2) and a conical part (3). The body (1) has elongate grooves (9) adapted to take up deformations.

Description: Field of the Invention The present invention relates to a plastic container for thermally treatable liquid, relevant background art being reflected by EP-A-1 009 615 (WO 98/36891) and WO 97/03885. The invention is specifically directed to a plastic beverage bottle. Background Art In recent years, plastic bottles have been a great success in storing many different kinds of liquids. Above all, the market for plastic beverage bottles has expanded significantly. For example, PET bottles are used to store carbonated and non-carbonated beverages, juices and juice concentrates, mineral water, beer etc. Especially PET bottles for carbonated beverages have reached large sales volumes on the European market, particularly in the 90's. Bottles of this type are manufactured by heating a tubular PET blank (preform) and blow moulding it to the final shape of the bottle. Such manufacture is disclosed in, for example, applicant's EP-A-521,841. It is well known that PET bottles can also be used for beverages and other liquids that are pasteurised in the bottle. In pasteurisation, the beverage is bottled at a temperature of e.g. about 8-12°C, whereupon the bottles are sealed. Subsequently the bottles are supplied to the actual pasteurising process, in which gradual heating occurs to a temperature of about 60-75°C. This temperature is maintained for about 15 min and is then gradually lowered to room temperature. When heating the bottle and the liquid, the volume of the liquid increases while the bottle strives to contract and return to the shape of the preform from which the bottle was made (owing to the memory effect of plastic). These two factors generate an internal pressure in the bottle. At this stage, the bottle is slightly expanded. In the subsequent cooling at the end of the pasteurisation, the bottle is cooled before the liquid has become cool and reduced its specific volume. During this cooling, the bottle "solidifies" in a slightly expanded state. This causes an undesirable subatmospheric pressure in the bottle which is dependent on the size of the volume increase, and there is a risk of the bottle being unsymmetrically deformed. With a view to decreasing the effect of the cooling on the volume increase of the bottle, it is possible to decrease the cooling speed and interrupt the cooling at a temperature of, for instance, about 35-40°C. This implies, however, that the beverage ages much more rapidly, which causes a shortening of its shelf-life. Plastic bottles are available on the market, which are intended to master the counteracting movements that arise in the above-mentioned heating. These bottles are provided with so-called panels which serve to expand/contract to take up the differences in volume between liquid and bottle. A bottle of this type was put on the market by the applicant in the early summer of 1997. The bottle is the subject matter of Swedish Design Registration No. 62 341. Applicant's bottle provided with panels functions in an essentially satisfactory manner, but during expansion, the relatively wide panels must be able to take up largely the entire relative change in volume between bottle and liquid. Otherwise there would be a risk of the bottom of the bottle bulging, thus causing aesthetic inconvenience as well as handling difficulties. Moreover, the volume of the bottle would increase drastically. After expansion, the bottle must be able to contract sufficiently so that the relative change in volume between bottle and beverage is as small as possible. With the bottles provided with panels that are available today, the final result of the expansion and contraction that arise during pasteurisation is that the volume of the bottle increases somewhat (for instance about 7 ml for a 0.5 l bottle). The volume increase of the bottle results in the internal pressure during storage being below the ambient pressure. As a consequence, the bottle tends to collapse inwardly. This inconvenience is accentuated by the fact that the bottles are frequently stored in refrigerating rooms where the cooling effect further increases the internal subatmospheric pressure. This also takes place with the consumer who puts the bottles in the refrigerator. Furthermore, beverages containing a large amount of vitamin C tend to consume the oxygen of the air enclosed in the upper part of the bottle, which also increases the subatmospheric pressure. In respect of prior-art technique, a few more known bottle models will be discussed below. US-A-3,871,541 discloses a plastic bottle whose body is formed with elongate grooves which primarily are of an aestethic nature and have no technical function. WO 97/10998 discloses a similar bottle with wide vertical panels which are adapted to be pressed out by the internal pressure caused by the carbonated beverage to form a circular surface, on which the label of the bottle is to be placed. WO 95/06593 discloses a hot-fill plastic bottle, in which problems arise similar to those in pasteurisation. An important difference, however, is that the bottle is not sealed before the beverage is heated, which means that the bottle need not be able to take up any expansion. The wall of the bottle has inclined grooves, which are intended to combine two properties, viz. that circumferential recesses permit a great elastic deformation capability and that vertical recesses impart mechanical stability to the bottle. According to WO 95/06593, the bottle must have circumferentially extending grooves for taking up the changes in volume. Moreover, the grooves must have a vertical component for the bottle to be stable in handling. The inclined grooves, however, increase the cost of manufacturing the bottle since the moulds are expensive. One more prior-art plastic bottle is disclosed in US-A-5,279,433, which has wide panels serving to prevent that part of the bottle on which the label is to be fixed from bulging. A further prior-art plastic bottle provided with panels is disclosed in EP-A-628 482, in which the purpose of the panels is to provide a bottle which is stable when being handled. The two latter bottles have panels which have a very complicated cross-section, thus making the manufacture of these bottles complicated and expensive. Over the years, a number of different designs of plastic bottles have thus been tested with a view to trying to manage the inconvenience of the bottle collapsing, but up to now, no one has succeeded in fully solving the problem. In particular, it has not been possible to provide a bottle which first allows expansion and which then can still contract enough to prevent the internal pressure from making the bottle collapse. Summary of the Invention An object of the present invention is to find a solution to the above problems and to provide a plastic container which withstands the expansion and contraction that are required in thermal treatment of the liquid with which the container is filled. A further object of the invention is that the plastic container should be light, without decreasing its strength. One more object of the invention is that the plastic container should be easy to manufacture. According to the invention, these and other objects that will appear from the following description are now achieved by a plastic container as defined in appended claim 1. Preferred embodiments are stated in the appended subclaims. A particularly distinguishing feature is that the plastic container according to the invention has areas which take up deformations and which can be said to have a controllable flexibility. These areas which comprise elongate grooves make it possible for the container, in thermal treatment, to expand with the liquid and then contract during cooling. The inwardly bulging grooves formed in the body of the container make the container essentially retain its shape even if its dimensions change. This makes it possible for the container to smoothly and easily expand and then contract to the desired dimensions. The deformation-absorbing capability of the grooves is promoted by their being directed in such manner that their projections on a plane, in which the centre axis of the container is positioned, extend in the same direction as does said centre axis, wherein said grooves make the container essentially retain its shape even if its dimensions change. Moreover, the grooves have a generally stabilising effect on the container against deformation, such as in the handling of the container. According to a preferred embodiment of the invention, each groove has a cross-sectional shape comprising three radii, of which two outer radii are directed so as to define convex surfaces on the exterior of the container while an intermediate third radius defines the bottom of the groove. This design additionally promotes the deformation-absorbing function of the groove while at the same time sharp edges are avoided, which could cause stress concentration. Plastic containers designed in accordance with the invention are in no way limited to applications involving pasteurisation, and their combination of flexibility and stability is usable in many other cases where plastic containers are used. By thermal treatment is here meant all forms of treatment of liquid in the container (bottle), in which the temperature of the liquid is changed after filling of the container, such as pasteurisation, in which the container is filled with hot liquid and sealed. All such applications require that the shape of the container be flexible in a controllable manner. Brief Description of the Drawings A currently preferred embodiment of the invention will now be described with reference to the accompanying schematic drawings, in which Fig. 1 shows how pasteurising temperature and pressure in a plastic bottle vary over the time of pasteurisation (prior-art bottle and inventive bottle, respectively), Fig. 2 is a partial cross-section showing how an expansion-absorbing panel of a prior-art plastic bottle behaves during pasteurisation of the content (liquid) of the bottle, Fig. 3 is a cross-sectional view corresponding to Fig. 2, showing how a deformation-absorbing groove of a plastic bottle according to the preferred embodiment of the invention behaves during pasteurisation, Fig. 4 is a side view of a plastic bottle according to the preferred embodiment, Fig. 5 is a cross-sectional view of the bottle taken along line V-V in Fig. 4, and Fig. 6 illustrates on a larger scale part of a groove in the wall of the bottle. Description of Preferred Embodiments Fig. 4 shows a plastic container in the form of a bottle, which is intended to be filled with a thermally treatable liquid and which comprises a body 1, whose side wall has a cylindrical part 2 and a conical part 3, which is referred to as shoulder portion. The lower portion of the cylindrical part 2 is connected with the bottom portion 4 of the bottle, and the upper portion passes into the conical part 3 via a waist portion 5 of the bottle. The upper portion of the conical part 3 passes into a neck portion 6 provided with an annular flange 7 and a threaded top 8. The bottom portion 4 is a champagne bottle bottom. According to the embodiment illustrated, elongate grooves or flutes 9 are formed in the cylindrical part 2, which extend vertically and in parallel with the centre axis C of the bottle. The grooves 9 are thus directed in such manner that their projections on a plane, in which the centre axis C of the bottle is positioned, extend in the same direction as this centre axis C. In an alternative embodiment (not shown), the grooves extend also on the conical part, the above-mentioned projection conditions still applying. In this case, the grooves can be discontinued in the transition or waist portion between the cylindrical and the conical part of the body of the bottle (not shown). The grooves 9 can have one or more discontinuities (not shown) having a total length below 25% of the extent of the groove 9, preferably below 15%. Each groove 9 has a cross-section the bottom 10 of which is formed as a radius R2 with its concave side on the exterior of the bottle (see Fig. 6). The transitions between the bottom 10 of the groove 9 and the wall of the bottle are radius-shaped R1 with their convex sides on the exterior of the bottle. According to a preferred embodiment of a bottle having a volume of 0.5 l, the bottle is formed with ten grooves 9 symmetrically distributed along the circumference of the body 1. Each groove 9 is defined by the radii R1 = R2 = 3 mm (see Fig. 6). The relatively narrow grooves 9 extend essentially over the entire cylindrical part 2 and, in the shown embodiment, take up about 35% of the circumferential surface thereof. This parameter relationship has been found to give the bottle excellent performance while at the same time its shape is aestethically attractive. Practical experiments have produced good results when the grooves have a share of the circumferential surface of the cylindrical part 2 in the range of 10-60%, preferably 25-45%. The grooves 9 serve to take up or compensate for such deformations (expansion and contraction) as arise in thermal treatment (e.g. pasteurisation) of the liquid contained in the bottle. The deformation-absorbing capability provided by the grooves 9 can be compared to the effect of an accordion. Furthermore, the grooves 9 have a stiffening and reinforcing effect on the bottle. It should be pointed out that other liquids may require quite different degrees of deformation capability, in which case a different number and a different shape of the grooves 9 may be necessary. The Tables below describe the variation of the different parameters in respect of the grooves 9 in the bottles. The top line indicates within which limits it is today-considered reasonable to vary the parameters. The intermediate line is a preferred range within which the parameters are selected to obtain an improved functional and more aesthetically attractive appearance of the bottle. The bottom line indicates the choice of parameters for the currently most preferred embodiment of the bottle. (D = diameter of the bottle body, see Fig. 6). For bottles in the range of 0.2-0.6 l (D=45-70 mm) R1 [mm] R2 [mm] Number of grooves 1.5-5 1.5-5 6-20 2-4 2-4 8-16 3 3 10-12 For bottles in the range of 0.5-1.5 l (D=60-95 mm) R1 [mm] R2 [mm] Number of grooves 2-7 2-7 6-20 3-6 3-6 8-16 4-5 4-5 10-12 This can also be described as the desired ratio of diameter D to R1 and R2 respectively, according to the Table below. D/R1 D/R2 Number of grooves 9-45 9-45 6-20 15-30 15-30 8-16 20-24 20-24 10-12 The volume of liquid can be reduced somewhat so as to obtain a greater resilient effect of the easily compressible air that is contained in the bottle. However, this necessitates a larger volume of the bottle for the same desired volume of liquid. When testing different methods of manufacture and preforms for blow moulding to form the desired bottles, it has been found that blow moulds which result in the bottle returning to its original volume are advantageous. It is even possible to manufacture plastic bottles having a slight pressure above atmospheric. The manufacture can be carried out according to conventional methods, the bottles being blow moulded in a cavity which on its mould surface has elongate ridges (not shown) forming the grooves 9. When comparing a bottle provided with grooves 9 according to the invention with a prior-art bottle provided with panels, an important difference has been discovered. The panels of the prior-art bottle tend to increase their width during expansion (see Fig. 2). When the bottle then is to contract, this extra width must buckle in the opposite direction and snap through the smallest panel width for the bottle to contract sufficiently. This buckling snap action results in additional resistance which means an increased risk of the volume of the bottle increasing during the thermal treatment (see Fig. 2). When using the inventive bottle, this phenomenon does not occur at all, which makes the bottle contract much more easily during cooling (see Fig. 3). To achieve an aesthetically attractive appearance of the bottle as well as easy manufacture, the grooves 9 are advantageously arranged symmetrically along the circumference of the bottle. The symmetry also implies that any loads acting on the bottle are taken up symmetrically, which results in a stronger bottle. All the grooves 9 need not, however, follow the same symmetry pattern, but they can be relatively offset in the circumferential and axial directions. In consideration of factors as to strength and design, the grooves 9 are advantageously formed in the bottle in such manner that the transitions between the radii R1, R2 are such that their derivatives coincide (so-called tangential transition, see Fig. 6). By varying the size and relationship between the radii R1, R2 as well as the angle of arc of the different radii, it is possible to obtain different shape, width and depth of the grooves 9. In this manner, it is possible to vary the grooves 9 so that their function is essentially directed to optimising a property which is particularly important for a specific thermal treatment of the liquid to be contained in the bottle. According to the preferred embodiment, the depth of the groove 9 is approximately half the radii R1, R2. For example, the depth is preferably about 1 mm for bottles having R1 = R2 = 3 mm and the volume 0.2-0.6 l. For corresponding bottles having the volume of 0.5-1.5 l, the depth is 1.5 mm and R1 = R2 = 4 mm. It should be mentioned here that in the illustrated embodiment, the side wall of the bottle preferably has a thickness in the range of 0.35-0.55 mm, in actual practice usually 0.4-0.5 mm. The share of grooves 9 in relation to the total circumference of the bottle also influences the expansion and detraction capability of the bottle. The greater share of grooves 9 the greater deformation capability of the bottle. The bottle is made of a plastic material suited for blow moulding starting from a preform, conceivable materials being PET, PEN or mixtures thereof. The blow moulding operation can be carried out, for instance, according to the technique described in applicant's Patent Publication EP-A-521 841 mentioned by way of introduction. Finally it should be pointed out that the invention is not limited to the embodiments described above, and modifications are feasible within the scope of the appended claims. For example, the shape of the plastic container can be different from what is shown here, and in some cases also the cross-sectional shape of the grooves can be different.

Claims: A plastic container for thermally treatable liquid, comprising a body (1) whose side wall is formed with areas which are adapted to take up deformations as the volume of the container changes, wherein said areas for taking up deformations comprise elongate, expansion/contraction-compensating grooves (9) which are formed in the body (1) and which are directed in such manner that their projections on a plane, in which the centre axis (C) of the container is positioned, extend in the same direction as does said centre axis (C); wherein said grooves (9) make the container essentially retain its shape even if its dimensions change. A plastic container as claimed in claim 1, wherein each groove (9) has a bottom (10) defined by a radius (R2). A plastic container as claimed in claim 1 or 2, wherein each groove (9) has a cross-sectional shape comprising three radii (R1, R2), of which two outer radii (R1) are directed so as to define convex surfaces on the exterior of the body (1) while an intermediate third radius (R2) defines the bottom (10) of the groove (9). A plastic container as claimed in claim 3, wherein the transition between the radii (R1, R2) of each groove (9) is arranged such that their derivatives coincide. A plastic container as claimed in claim 3, wherein the radii (R1, R2) of each groove (9) are equal. A plastic container as claimed in any one of claims 2-5, wherein the bottom-defining radius (R2) of each groove (9) is directed in such manner that the bottom (10) of the groove (9) defines a concave surface in the body (1). A plastic container as claimed in any one of the preceding claims, wherein the body (1) comprises a cylindrical part (2) and a conical part (3), and the grooves (9) are arranged at least in the cylindrical part (2). A plastic container as claimed in any one of the preceding claims, wherein the body (1) comprises a cylindrical part (2) and a conical part (3), and the grooves are arranged in the cylindrical part (2) only. A plastic container as claimed in any one of the preceding claims, wherein the grooves (9) are symmetrically arranged along the circumference of the body (1). A plastic container as claimed in any one of claims 7-9, wherein the grooves (9) have a share of the circumferential surface of the cylindrical part (2) between 10% and 60%, preferably between 25% and 45%. A plastic container as claimed in any one of the preceding claims, which is a beverage bottle.

Inventors: LANDBERG JOHAN, LANDBERG, JOHAN
Applicants: REXAM AB
Application year: 1999
Main classification: B65D1
IPC codes: B65D1, B65D79