Patent Publication Number: US-11390414-B2

Title: Container with a petaloid base

Description:
The invention concerns the field of containers, in particular bottles or pots, manufactured by blow molding or stretch blow molding from blanks (preforms or intermediate containers) made of plastic material such as polyethylene terephthalate (PET). 
     A container generally comprises an open neck, through which it is filled or emptied, a body, which confers upon the container its volume, and a bottom that closes the body at the end opposite the neck and forms a base for standing the container on a support such as a table. 
     Some contents, typically carbonated drinks, generate in the capped containers high relative pressures that routinely reach or exceed two bar and a half. 
     To receive this type of content it is standard practice to provide the containers with petaloid bottoms that comprise projecting, feet, in the shape of petals, separated by concave wall portions called hollows or valleys that extend radially from a central zone of the bottom. The feet are intended to stabilize the container on a support while the valleys are intended to absorb thermal and/or mechanical forces exerted by the contents. 
     A petaloid bottom, one example of which is proposed in European patent application EP3059175 (Sidel) is by virtue of its construction more resistant to deformation than an ordinary bottom. However, the conditions, in particular of temperature and of relative humidity, to which some containers are subjected sometimes stretches the material beyond its elastic limit, or even to the point of rupture. Such conditions are encountered in particular in some hot countries. 
     Thus storing a container in full sunlight expands the contents and significantly increases the relative pressure inside the container, up to four or even five bar or beyond. 
     Moreover, if subjected to a very hot and humid atmosphere (as encountered in countries in the tropics), PET undergoes a high re-uptake of moisture which reduces its dimensional stability. 
     This explains the appearance of cracks in the bottom, to the point where some containers sometimes begin to leak. 
     A seemingly obvious solution to increase the strength of a petaloid bottom is to increase its thickness, that is to say the quantity of material used to make it. However, two difficulties are encountered. The first difficulty is the necessity, for economic and environmental reasons, to maintain the quantity of material at a reasonable level (manufacturers are even required not to increase the quantity of material or even to reduce it. The second difficulty is that increasing the thickness of the bottom modifies its forming conditions and, to obtain good mold imprint filling, requires a higher pressure for blow molding the container. 
     One objective of the present invention is consequently to propose a container with a petaloid bottom the shape of which improves its mechanical performance and more precisely renders it more resistant to deformation if it is subjected to high temperature and/or relative humidity conditions. 
     To this end there is proposed a container made of plastic material comprising a body and a petaloid bottom that is connected to the body by a periphery, the bottom having a central axis of symmetry and comprising:
         a central dome that projects toward the interior of the container, delimited by a circular external edge at a distance R 1  from the central axis;   a series of feet projecting toward the exterior of the container each of which radiates from the central dome and each of which has a peek radially remote from the central dome and a crest path that extends from the external edge of the central dome to the peak;   a series of valleys each formed as a hollow between two successive feet, each valley radiating from an internal end to the periphery;
 
said container being characterized in that:
   each crest path has:
           an internal section that extends from the external edge of the dome to a junction at a distance R 2  from the central axis, said internal section having in a median radial plane of the foot a first curvature;   an external section that extends from the junction tangentially in line with the internal section to the peak, said external section having in the median radial plane of the foot a second curvature greater than the first curvature;   
           the distances R 1  and R 2  are in a ratio such that:
 
45%≤ R 1 /R 2≤60%
       

     Such a structure confers on the bottom a strength, in particular a thereto-mechanical strength, higher than that of known petaloid bottoms and, for an equivalent quantity of material, renders the bottom more resistant to high temperature and/or relative humidity conditions, as encountered in particular in countries in the tropics. 
     Various supplementary features may, be provided, separately or in combination. Accordingly, for example:
         The ratio R 1 /R 2  may be between 45% and 55% inclusive.   The container having a capacity by volume of 1.5 L, the ratio R 1 /R 2  is approximately 50%.   The peak of each foot is at a distance R 3  from the central axis and the distances R and R 3  are in a ratio such that:
 
25%≤ R 1 /R 3≤35%
   For a container having a capacity by volume of 1.5 L, the distances R 1  and R 3  are advantageously in a ratio R 1 /R 3  of approximately 27%.   The internal end of each valley is spaced from the external edge of the central dome by a distance E.       

     This distance E and the distances R 1  and R 2  are advantageously in a relation such that 45%≤E/(R 2 −R 1 )≤55%, preferably with E/(R 2 −R 1 )≅50%.
         The bottom has a connecting fillet between the internal end of each valley and the external edge of the central dome.   At the junction between the internal section and the external section the crest path has a width L 1  and at a distance R 2  from the central axis the valley has a width L 2  such that 60%≤L 1 /L 2 ≤210%.   For a container having a capacity by volume of 1.5 L the widths L 1  and L 2  are preferably equal or substantially equal.   At the distance R 2  from the central axis, a median point of the crest path and a median point of the valley are spaced, firstly, axially by a distance H and, secondly, in a transverse plane perpendicular to the central axis, by a distance G such that 20%≤H/G≤30%.   For a container having a capacity by volume of 1.5 L the distances H and G are advantageously in a ratio H/G of approximately 25%.   The external section of the crest path is straight and forms with a transverse plane perpendicular to, the central axis an angle between 21° and 24° inclusive, for example approximately 22.5°.       

    
    
     
       Other objects and advantages of the invention will become apparent in the light of the description of one embodiment given hereinafter with reference to the appended drawings, in which: 
         FIG. 1  is a perspective view from below of a container having a petaloid bottom; 
         FIG. 2  is a detail view in perspective showing the bottom to a larger scale; 
         FIG. 3  is a view from above, of the bottom of the container; 
         FIG. 4  is a view in section of the bottom from  FIG. 3  taken along the line IV-IV; 
         FIG. 5  is a detail view to a larger scale of the bottom from  FIG. 3  within the medallion V; 
         FIG. 6  is a detail view in section of the bottom in a median radial plane of a foot; 
         FIG. 7  is a detail view in section of the bottom in a median radial plane of a valley. 
     
    
    
     In  FIG. 1  is represented, in perspective from below, a plastic material container  1  (in this instance this is a bottle). The container is obtained by forming (blow molding or stretch blow molding) a preform made of thermoplastic polymer, for example polyethylene terephthalate (PET). Before forming the preform is heated so that the material reaches a temperature above its glass transition temperature (which is approximately 80° C. in the case of PET). 
     The container  1  extends along a central axis X. It includes a lateral wall called the body  2  and a petaloid bottom  3  that closes the container  1  at a lower end of the body  2 . 
     The bottom  3  has a periphery  4  by which it is connected to the body  2 . The bottom  3  has a central axis of symmetry which in the configuration shown coincides with the central axis X of the container  1 . 
     The bottom  3  includes, firstly, a central dome  5  that projects toward the interior of the container  1 . In the example shown the dome  5  takes the form of a toroidal or hemispherical dome the concavity of which faces toward the exterior of the container  1 . 
     A lump  6  at the center of the dome  5  formed by the injection molding, the material of which has remained substantially amorphous during the forming of the container  1 , projects axially toward the exterior of the container  1 . 
     The dome  5  has in particular the function of stretching the material at the center of the bottom  3  so as to increase the crystallinity and therefore the mechanical strength. 
     The dome  5  is delimited by a circular external edge  7  at a distance R 1  from the central axis X. D 1  denotes the diameter of the circular external edge  7  ( FIG. 4 ). D 1  is such that D 1 =2·R 1 . 
     The bottom  3  includes, secondly, a series of feet  8  projecting toward the exterior of the container  1  that radiate from the central dome  6 . Each foot  8  has a peak  9  that is its farthest projecting part. 
     Each foot  8  is bordered laterally on either side by a pair of flanks  10  of substantially triangular shape. 
     Together, the peaks  9  lie in a common plane P, called the support surface, via which the container  1  is able to rest on a plane surface (for example a table). 
     Each foot  8  has a facet called the crest path  11  that extends radially and slopes from the external edge  7  of the central dome  5  to the peak  9 . 
     Each crest path  11  has from the inside (that is to say the side of the central axis X) to the outside (that is to say the side of the periphery  4 ) two successive sections, namely an internal section  12  and an external section  13  that join at a junction  14 . 
     The junction  14  is at a distance R 2  from the central axis X. D 2  denotes the diameter of the circle joining the junctions  14  ( FIG. 4 ). D 2  is such that D 2 =2·R 2 . 
     The internal section  12  extends from the external edge  7  of the dome  5  to the junction  14  with the external section  13 . The internal section  12  has in a median radial plane of the foot (corresponding to the section plane of  FIG. 4  and of  FIG. 6 ) a first curvature C 1 . If the internal section  12  has a circular contour (when seen in section in the median radial plane) the first curvature C 1  corresponds to the radius of curvature of the internal section  12 . If not, the first curvature C 1  may be considered as being the mean curvature of the internal section  12  measured in the median radial plane. 
     The external section  13  extends from the junction  14  with the internal section  12 , tangentially in line with the latter, to the peak  9  of the foot  8 . 
     The external section  13  has in the median radial plane of the foot  8  (corresponding to the section plane of  FIG. 4  and of  FIG. 6 ) a second tyre C 2  if the internal section  13  has a circular contour (when seen in section in the median radial plane) the second curvature C 2  corresponds to the radius of curvature of the internal section  13 . If not, the second curvature C 2  may be considered as being the mean curvature of the external section  13  measured in the median radial plane. 
     The second curvature C 2  is greater than the first curvature C 1 :C 2 ≥C 1 . 
     In accordance with a preferred embodiment shown in  FIG. 4  and in  FIG. 6  the external section  13  is straight that is to say the second curvature C 2  is infinite. In this case, the external section advantageously forms with any transverse plane perpendicular to the central axis X an angle A between 21° and 24° inclusive and preferably of approximately 22.5° ( FIG. 4 ). 
     The position of the junction  14  between the internal section  12  and the external section  13  depends on the size of the dome  5 . To be more precise, the distances R 1  and R 2  are in a ratio such that:
 
45%≤ R 1 /R 2≤60%
 
     In accordance with a preferred embodiment, the ratio R 1 /R 2  is rather between 45% and 55% inclusive. 
     For a container  1  with a capacity by volume of 1.5 L the ratio R 1 /R 2  is approximately 50%. 
     R 3  denotes the distance from each peak  9  to the central axis X. D 3  denotes the diameter of the circle inscribed in the polygon joining the peaks  9  ( FIG. 4 ). D 3  is such that D 3 =2·R 3 . 
     Note that the peaks  9  are set back in the radial direction relative to the periphery  4  of the bottom  3 . In other words, the diameter D 3  is less than the overall diameter of the bottom  3  (which in the example shown corresponds to the overall diameter of the container  1 ). 
     The distances R 1  and R 3  are advantageously such that 25%≤R 1 /R 3 ≤35%. 
     For a container  1  having a capacity by volume of 1.5 L the distances R 1  and R 3  are preferably in a ratio R 1 /R 3  of approximately 27%. 
     The bottom  3  includes, thirdly, a series of valleys  15  each formed as a hollow between two successive feet  8 . Each valley  15  is connected to each of the flanks  10  that border it by a connecting fillet  16 . 
     Each valley  15  radiates from an internal end  17  to the periphery  4  of the bottom  3 . 
     As shown in  FIG. 5  in particular the internal end  17  of each valley  15  is spaced from the external edge  7  of the central dome  5  by a distance E. In accordance with a preferred embodiment shown in  FIG. 5  the valley  15  appears rounded at its internal end  17  when the bottom is seen from below. 
     The distance E from the internal end  17  of each valley  15  to the external edge  7  of the central dome  5  and the distances R 1  and R 2  are advantageously in a relation such that:
 
45%≤ E /( R 2 −R 1)≤55%
 
     In accordance with a preferred embodiment, the distance E from the internal end  17  of each valley  15  to the external edge  7  of the central dome  5  and the distances R 1  and R 2  are in a relation such that:
 
 E /( R 2 −R 1)≅50%
 
     As can be seen in  FIG. 7  the bottom  3  has a connecting fillet  18  between the internal end  17  of each valley  15  and the external edge  7  of the central dome  5 . This connecting fillet  18  is part of a larger connecting zone  19  of crescent shape when seen from below (that is to say in the plane of  FIG. 5 ), which produces a gentle junction:
         radially, between the valley  15  (at its internal end  17 ) and the external edge  7  of the central dome  5 ;   laterally, between the valley  15  and the internal section  12  of each crest path  11 .       

     Each crest, path  11  as a width L 1  at the junction between the internal section  12  and the external section  13  (that is to say at the distance R 2  from the central axis X). 
     Moreover, at the distance R 2  from the central axis X each valley  5  advantageously has a width  12  such that 60%≤L 1 /L 2 ≤210%. 
     The value of the ratio L 1 /L 2  may in particular depend on the capacity by volume (and therefore the overall diameter) of the container  1 . Accordingly, for a container  1  having a capacity by volume of 1.5 L the widths L 1  and L 2  are advantageously equal (that is to say that the difference between L 1  and L 2  is less than 5%) or substantially equal (that is to say the difference between L 1  and L 2  is between 5% and 10% inclusive). 
     Referring to  FIG. 4  and  FIG. 5 :
         M 1  denotes the (geometrical) median point of the crest path  11  situated at the distance R 2  from the central axis X ((in other words, the point M 1  is the center of the segment forming the junction  14  between the internal section  12  and the external section  13  of the crest path  11 );   M 2  denotes the median point of the valley  15  situated at, the distance R 2  from the central axis X;   H denotes the distance measured axially between the points M 1  and M 2  (and more precisely between the transverse planes perpendicular to the central axis X and respectively passing through the point M 1  and the point M 2 );   G denotes the distance separating M 1  and M 2  in a transverse plane perpendicular to, the axis X (and to be more precise the distance separating the axial projections of M 1  and M 2  on such a plane, which corresponds for example to the plane of  FIG. 5 ).       

     The distances H and are advantageously in a ratio H/G such that 20%≤H/G≤30%. 
     For a container  1  having a capacity by volume of 1.5 L the distances H and G are preferably in a ratio H/G of approximately 25%. 
     Structured in this way, the bottom  3  has a higher thermo-mechanical strength than an ordinary petaloid bottom for an equivalent quantity of material. To be more precise tests have shown that the bottom  3  is more resistant to high temperature and/or relative humidity conditions. 
     This performance stems in particular from the gently curved shape of the bottom  3  which ensure good distribution of forces and minimize the concentration of stresses in one (or more) localized are (s). This gently curved shape results in particular from the location of the junction  14  between the internal section  12  and the external section  13  of the crest path  11  of the feet  8 , characterized by the ratio R 1 /R 2 . 
     Here the presence of the dome  5  is necessary for the structural rigidity of the bottom  3 . If the junction  14  were too close to the external edge  7  of the latter the transition between the internal section  12  of the crest path  11  and the dome would be too brutal and there would then be observed the appearance of a concentration of stresses over the internal section  12 . If on the other hand the junction  14  were too close to the foot  8  the bottom  3  would have too low a height and would provide insufficient mechanical strength. 
     The spacing distance E between the valleys  15  and the dome  5  also enables, via the connecting fillet  18 , a gentle transition between them. Moving closer together the internal end  17  of the valleys  15  of the dome  5  would educe the radius of the connecting fillet  18  and would increase the concentration of stresses over the latter. Taken to the extreme, having the valleys open out onto the central dome would cause a stress peak to appear at the junction between the valleys and the dome. 
     The relatively low ratio H/G and the contrary relatively high ratio L 1 /L 2  also contribute (be it indirectly and in a secondary manner) to the gently curved shape of the bottom  3  and therefore to the distribution of forces over the latter. 
     It is even found that, if the filled and capped container  1  is subjected to high temperature (above 40°) and/or high relative humidity (above 50%) conditions the bottom  3  is deployed slightly (that is to say that the diameter D 3  increases somewhat) in a uniform manner. This results in an improvement in the seating of the container  1  to the benefit of its stability.