Abstract: The plastic container according to the present disclosure is an aesthetically pleasing plastic container suitable for premium hot fill beverages, such as teas and fruit juices. The plastic container defines a body and includes an upper portion having a finish. Integrally formed with the finish and extending downward therefrom is a shoulder region. The shoulder region merges into and provides a transition between the finish and a first vacuum absorbing region. The first vacuum absorbing region merges into a waist region. The waist region merges into a second vacuum absorbing region. The second vacuum absorbing region transitions into a base portion having a base.

Abstract: A hot fill type plastic container includes a bottom portion and a main body having a vacuum uptake portion that is bounded by upper and lower horizontal grooves. The vacuum uptake portion has four side panel portions, and each of the side panel portions has at least one vertical groove defined therein. The vertical grooves are substantially centered with respect to the side panel portions. No surface features other than the vertical grooves are included on the side panel portions. The main body further includes upper and lower round portions that are respectively positioned above and below the vacuum uptake portion.

Abstract: Method and system for handling a plurality of hot-filled and capped containers having temporary deformations or distortions caused by vacuums induced in the containers. For each container, temporary deformations are confined or directed to a particular portion of the container. Annular hoop rings can be provided to confine the temporary deformations to a smooth sidewall portion of the container between the annular hoop rings. Alternatively, one or more supplemental vacuum panels can be provided to confine or direct the temporary deformation thereto. The annular hoop rings and the one or more supplemental vacuum panels can provide for substantially stable touch points for the container. The containers are conveyed with temporary deformations such that substantially stable contact points of each container are in contact with corresponding substantially stable contact points of other containers.

Abstract: A round, hot fillable plastic container includes an upper portion defining an opening; a bottom portion; and a main body portion having a plastic sidewall that has a plurality of vacuum panels defined therein. The main body portion has a generally hourglass shape with a central portion that is narrower than upper and lower portions thereof. The hourglass shape optimizes grippability of the container. Grippability is optimized further by the presence of indentations that are formed between columns that define the hourglass shape and pillow portions that are provided for finger support. The indentations permit a consumer to gain finger traction and purchase with respect to the container body, even when a label is positioned between the container body and the user's fingers. The main body portion further has a first groove defined in the upper portion thereof, a second groove defined in the lower portion thereof and a third groove that is defined in the central portion thereof.

Abstract: The object of this invention is to provide a container having a reduced area of vacuum-absorbing panels and thus acquiring improved appearance and having strength against a pressure drop, i.e., the strength enough to retain the shape of the container even when there is a pressure drop inside the container. A shoulder portion or a bottom portion of a resin-made storage container is molded by aligning one or two groups of three corners and one or two groups of three pillars vertically and in parallel to the central axis of the container. Each group of three corners is a part of the corners forming a cross-section of a regular enneagon and being connected to either the shoulder portion or the bottom portion, and the lines connecting these three corners form a regular triangle. Each group of three pillars is a part of the pillars belonging to the body and forming a cross-section of a hexagon, and the lines connecting these three pillars form a regular triangle.

Abstract: A hot-fill PET container or bottle (10) for filling with a liquid at an elevated temperature has a side wall (9) extending to a lower portion including a pressure panel (11) and a base (2) in its unfolded or pre fill position. The panel (11) is transversely oriented and has a decoupling or hinge structure (13), an initiator portion (1) and control portion (5) of a steeply angled inverting conical section between 30 and 45 degrees. The control portion enables the inversion of the panel (11) into the container (10) to compensate for vacuum or reduced pressure induced within the container as the liquid cools down. The base (2) can also have a plurality of reinforcing ribs (3).

Abstract: A bottle. The bottle may include a cup with a number of first conical sections, a lid with a number of second conical sections, and a closure positioned on the lid. The upper conical sections mate with the lower conical sections.

Abstract: A blow molded container has a neck portion defining a mouth. The neck portion leads into a shoulder portion and a bottom portion forms a container base. A sidewall portion connects the shoulder portion and the bottom portion and employs a first pair of opposing convex vacuum panels and a second pair of opposing convex vacuum panels. The first pair of opposing convex vacuum panels is larger in surface area than the second pair of opposing convex vacuum panels. A vertical column at each corner of the container joins the first pair of opposing vacuum panels to the second pair of opposing vacuum panels. A structural convex arch resides above and below each convex vacuum panel. Each of the vertical columns are molded into the structural convex arches. Vacuum initiator grooves may be molded into the first and second pair of opposing vacuum panels to control vacuum panel movement.

Abstract: A container structure for a hot fill liquid may employ an upper portion defining a mouth, a shoulder portion integrally formed with and extending downward from the upper portion, a bottom portion defining a base, and a body and sidewall extending between and joining the shoulder and bottom portions. The sidewall may employ a pair of opposing columns oriented diagonally relative to the base and concave inward relative to a container central vertical axis before the container is filled. The columns become concave inward to a lesser extent when the bottle is under an interior vacuum. The sidewall may also employ a pair of opposing, compound angle vacuum panels oriented diagonally relative to the base. A vacuum initiator groove is formed in each of the vacuum panels to initiate panel movement during liquid content cooling. The vacuum initiator groove is generally coincident with a vacuum panel longitudinal centerline.

Abstract: A synthetic resin bottle is provided with a shape that improves rigidity and strength in a lateral direction, without increasing the cost of material to thicken the bottle wall. The synthetic resin bottle is provided at a low cost in such a way that the bottles can be used smoothly on the carrier line, in vending machines, and in storage in stacks with no deformation. The bottles are capable of performing a vacuum-absorbing function enough to be used in hot filling. Multiple pillar sections in a projected strip-like shape are disposed on the body of a synthetic resin bottle, the pillar sections being inclined spirally at a uniform angle of gradient (?) relative to a central axis of the bottle and disposed in parallel to one another, so that the cylindrical body wall is prevented from being deformed by a pressure force acting in a lateral direction.

Abstract: A plastic container that particularly adapted for hot-fill applications includes a bottom portion; and a sidewall portion that is unitary with the bottom portion. The sidewall portion has a maximum outer diameter, and includes first and second pairs of opposing first and second vacuum panels, respectively. At least one of the second vacuum panels includes gripping structure. The first and second vacuum panels respectively have first and second substantially constant radii of curvature as measured in a horizontal plane that are substantially constant from upper to lower ends of the vacuum panels. At least one of the second vacuum panels may be asymmetric about a central vertical axis as viewed in side elevation.

Abstract: There is provided a synthetic resin bottle having high commercial value, which prevents plastic deformation accompanied with buckling. The invention provides a PET bottle comprising a body portion connected to a mouth portion via a shoulder portion, and a constricted portion provided on the body portion and looping along the circumferential direction. The body portion comprises a front wall and a back wall which face to each other, a left sidewall and a right sidewall which face to each other, and connecting portion which respectively join the walls. The cross section of the body portion along the circumferential direction a generally polygonal outer profile.

Abstract: A container adapted to increase volume contraction and reduce pressure having four panels that are adapted to contract inwardly from vacuum forces created by contraction of container contents. The container has a sidewall including four panels. The four panels are vacuum panels, including vertical transitional walls disposed between and joining the panels and the body is adapted to increase volume contraction and reduce pressure. The panels are adapted to contract inwardly in response to internal negative pressure created during hot-fill processing and subsequent cooling of a hot liquid in the container.

Abstract: A bottle includes a top portion and a bottom portion. The top portion includes a shoulder that extends away from a neck of the bottle, and a grip portion. The grip portion is recessed within the top portion of the bottle. The top portion of the bottle includes at least one strengthening element, preferably in the form of a rib or column that may be provided between the upper and lower bell portions, or between the upper bell or shoulder portion and the grip portion. The bottle can be used for hot or cold fill applications.

Abstract: Formation of an “organically”-shaped feature on an otherwise abstract-shaped package. In particular, an organic or human anatomical feature is provided on an otherwise inanimate shape. More particularly, a package, such as a bottle, having a non-representational form (in other words, a package not shaped to resemble any particular form existing in nature) is provided with a feature specifically designed to resemble a form in nature or “organic” form. In an exemplary embodiment, the form in nature (or “organic” feature) is a “baby fat crease.” In particular, a crease is provided on the package to mimic the look of a baby fat crease. The geometry of the crease as well as the geometry of the package are optimized to achieve the desired organic look or effect.

Abstract: A heat resistant plastic container containing hot-filled liquid contents, comprising: a spout for filling the container with liquid contents; a closure configured to seal the spout; a base including a bottom portion that is bent toward the spout, the base including a structural reinforcement; and a sidewall extending upwardly from the base toward the spout, the sidewall including a zone of deformation, wherein the zone of deformation in the sidewall is configured to accommodate an initial deformation due to the cooling of the contents and to substantially regain its initial shape upon the relieving of immobilized stresses.

Abstract: A plastic container includes an upper portion having a mouth defining an opening into the container. A shoulder region extends from the upper portion. A sidewall portion extends between the shoulder region and a base portion. The base portion closes off an end of the container. A vacuum panel region defined in part by at least two vacuum panels. Each of the vacuum panels are movable to accommodate vacuum forces generated within the container resulting from heating and cooling of its contents. The vacuum panel region occupies an area outboard of the sidewall portion.

Abstract: A semi-rigid collapsible container (10) has a side-wall with an upper portion (5), a central portion (6), a lower portion (7) and a base (8). The central portion (6) includes a vacuum panel portion having a control portion (2) and an initiator portion 1. The control portion (2) is inclined more steeply in a vertical direction, i.e. has a more acute angle relative to the longitudinal axis of the container (10), than the initiator portion 1. On low vacuum force being present within the container panel following the cooling of a hot liquid in the container 10 the initiator portion (1) will flex inwardly to cause the control portion (2) to invert and flex further inwardly into the container (10) and the central portion (6) to collapse. In the collapsed state upper and lower portions of the central portion (6) may be in substantial contact so as to contain the top-loading capacity of the container (10). Raised ribs (3) made an additional support for the container in its collapsed state.

Abstract: A container may employ an upper portion defining a mouth, a shoulder portion formed with the upper portion and extending away from the upper portion, a bottom portion forming a base, a sidewall extending between and joining the shoulder portion and the bottom portion, and a plurality of smooth surfaced vacuum panels formed in the sidewall, which may be separated by one or more strengthening grooves. The vacuum panels and/or the container in a profile view may form an hourglass shape. The container may also employ a sidewall utilizing three smooth, grooveless, vacuum panels, which may form a triangle in cross-section. The vacuum panels may be concave inward toward a central vertical axis of the container and have an hourglass shape when the container is viewed in a side view.

Abstract: A heat set container comprising a base portion, a shoulder portion, and a sidewall portion extending from the shoulder portion to the base portion. The shoulder portion, the sidewall portion and the base portion cooperate to define a receptacle chamber within the container into which product can be filled. A plurality of vacuum panels are equidistantly disposed about the sidewall portion. A plurality of transition lands are disposed between adjacent ones of the plurality of vacuum panels and spaced outwardly relative thereto. The plurality of vacuum panels and the plurality of transition lands cooperate to be inwardly collapsible from a first outside diameter to a second outside diameter in response to at least internal vacuum forces.

Abstract: The plastic container includes a hollow body of plastic material having a lower supporting base, a sidewall extending upwardly from the lower base and an upper neck portion extending upwardly from the sidewall with an opening therein. The sidewall includes at least one panel having a central region and an outer boundary, with the outer boundary being depressed with respect to the central region.

Abstract: A container made of plastic material, such as PET, that is adapted to be hot-fillable. The container has flex panels located on its sides. The flex panels are surrounded by frames. The frames and the flex panels have medallions located on them to prevent creasing from occurring during the hot-fill process.

Abstract: A plastic container that is adapted for adjustment to internal volumetric changes such as those that occur during the hot-fill process includes a container body defining an internal space and having a sidewall. The container body has a maximum lateral dimension and a plurality of flexible panels and posts defined in the sidewall. The posts are respectively interposed between the flexible panels around the outer circumference of the sidewall. Each of the plurality of posts has a minimum width and a maximum width, and a ratio of the minimum width to maximum width is preferably within a range of about 0.3 to about 0.7. A ratio of the minimum width to the maximum lateral dimension is preferably within a range of about 0.05 to about 0.30. In addition, a ratio of the maximum width to the maximum lateral dimension is preferably within a range of about 0.15 to about 0.45.

Abstract: Method and system for handling a plurality of hot-filled and capped containers having temporary deformations or distortions caused by vacuums induced in the containers. For each container, temporary deformations are confined or directed to a particular portion of the container. Annular hoop rings can be provided to confine the temporary deformations to a smooth sidewall portion of the container between the annular hoop rings. Alternatively, one or more supplemental vacuum panels can be provided to confine or direct the temporary deformation thereto. The annular hoop rings and the one or more supplemental vacuum panels can provide for substantially stable touch points for the container. The containers are conveyed with temporary deformations such that substantially stable contact points of each container are in contact with corresponding substantially stable contact points of other containers.

Abstract: A plastic container that is adapted for adjustment to internal volumetric changes such as those that typically occur during the hot fill process includes a container body defining an internal space. The container body has a sidewall that is shaped to define at least one flexible panel. The flexible panel has a central longitudinal axis, an upper portion, a lower portion and a central portion. The central portion of the flexible panel has a width that is greater than a respective width of at least one of the upper and lower portions. The flexible panel is substantially flat as viewed in a longitudinal cross-section taken along the central longitudinal axis. Additionally, the central portion has a transverse radius of curvature that is greater than a transverse radius of curvature of at least one of the upper portion and said lower portion.

Abstract: A plastic container that is adapted for adjustment to internal volumetric changes such as those that occur during the hot-fill process includes a container body defining an internal space. The container body includes a main body portion having a plurality of vacuum panels disposed about an outer circumference thereof and a corresponding plurality of columns interposed between the vacuum panels. A label covers at least a portion of the vacuum panels and the columns. The label has a first portion having a first surface area that is in contact with the container and a second portion having a second surface area that is not in contact with the container. A ratio of said first surface area to said second surface area is at least 1.0, thereby ensuring superior label support. The main body portion further has a maximum outer radius and a maximum depth that is defined with respect to the maximum outer radius. A ratio of the maximum depth to the maximum outer radius is preferably no greater than about 0.

Abstract: Systems and methods for vacuum compensation in hot-filled and cooled containers. Each container reduces, via one or more vacuum panels, a first portion of a vacuum created in the container. Each container also has a repositionable portion to reduce a second portion of the vacuum. During hot-filling, no portion of the repositionable portion extends below a standing or bearing surface of the container.

Abstract: A thin-walled, non-round plastic container having a body portion with generally rectangular sidewalls and a base. The body portion having a label mounting area extending between an upper label bumper and a lower label bumper on at least two of the adjacent sidewalls. The label mounting area includes a vacuum panel on a first sidewall, and a plurality of ribs, which may be on a second sidewall.

Abstract: A beverage container that is prevented from tipping is provided. The beverage container includes a main unit configured to contain liquid therein, the main unit having a front surface, a bottom end, and a fall-stopping surface formed on the front surface of the main unit, the fall-stopping surface being located at a predetermined position in a range of 20 mm to 70 mm from the bottom end, the fall-stopping surface being located at a position in a front-to-back direction the same as or in front of a surface below the fall-stopping surface.

Abstract: A plastic container that is adapted for adjustment to internal volumetric changes includes a container body defining an internal space and having a main body portion that defines a longitudinal axis and an outer diameter. The main body portion is substantially cylindrical at its outer diameter, and includes first and second recessed flexible vacuum uptake panels, each of which is constructed and arranged to flex inwardly to provide vacuum uptake when a sufficient underpressure exists in the internal space relative to ambient external pressure. The main body portion further includes a front side defining a first curved sidewall portion between the first and second recessed panels and a rear side defining a second curved sidewall portion between the first and second recessed panels. The first curved sidewall portion has a length L1 as viewed in horizontal cross-section that is less than a length L2 of the second curved sidewall portion.

Abstract: A container body and base being lightweight structures designed to accommodate vacuum forces either simultaneously or in sequence. The container body and base each absorb a significant percentage of the vacuum. By utilizing a lightweight base design to absorb a portion of the vacuum forces enables an overall light-weighting, design flexibility, and effective utilization of alternative vacuum absorbing capabilities on the container body.

Abstract: A plastic aerosol container comprising a neck, a support ring, a shoulder, a cylindrical body, a base, a dispensing valve and a cap. The neck further includes a lip and a lip cavity. The support ring protrudes below the lip cavity and above the shoulder. The shoulder supports the neck and aides in preventing deformation of the container. The base further includes legs. The dispensing valve is placed atop the neck and sealed thereto. The cap is placed atop the valve and functions as an actuator to release the contents of the can.

Abstract: A plastic container that is adapted for adjustment to internal volumetric changes such as those that occur as a result of internal pressure and temperature changes during the hot-fill process includes a container body defining an internal space. The container body has at least one flexible panel defined therein, which includes an outer flexible panel portion and an inner flexible panel portion. The outer flexible panel portion has a shape when a pressure equilibrium exists between the internal space and ambient external pressure, and is further constructed and arranged to assume a shape of increased concavity when a sufficient underpressure exists in the internal space. The inner flexible panel portion is constructed and arranged to flex relative to the outer flexible panel portion in order to accommodate internal pressure changes within the container body. The inner and outer flexible panel portions accordingly work in tandem to permit efficient vacuum uptake in a hot-fill type container.

Abstract: A container exhibiting superior resistance to unwanted or uncontrolled sidewall deformation has plurality of vacuum responsive panels, generally uniformly spaced around the sidewall periphery, including a panel surface portion radially inset from the sidewall. A post or land is provided between each nearest neighbor pair of vacuum panels, the posts having upper and lower ends joined together upper and lower sidewall edge portions. A margin is located at least at the upper and lower edges of each vacuum panel and extending between the panel surface and the sidewall. At least one of the upper and lower margins of each vacuum responsive panel includes an axially offset portion, which in response to decreasing pressure focuses any initial deflection of the panel surface to that portion of the panel contiguous to the axial offset portion.

Abstract: A plastic container having a shoulder region adapted for vacuum pressure absorption, a sidewall portion having a rigid support ledge and a tapered base structure having a geometrical shaped footprint. The base having an oriented standing surface to urge the container into a predetermined orientation during processing. The shoulder region including vacuum panels being movable to accommodate vacuum related forces generated within the container.

Abstract: A plastic bottle that can easily be collapsed after used is provided. The plastic bottle has a body portion that is depressed internally by applying external force, and a depressible portion formed on a circumferential wall of the body portion to protrude externally. The depressible portion is depressed internally by applying external force. Plural depressible portions and plural depression-resistant portions may be formed alternately on the circumferential wall of the body portion in the circumferential direction of the body portion.

Abstract: A lightweight, thin-walled heat resistant plastic container containing hot-filled liquid contents, comprising: a spout for filling the container with liquid contents; a closure configured to seal the spout; a base including a bottom portion that is bent toward the spout, the base including a structural reinforcement configured to withstand hydrostatic pressure from the hot-filling of liquid and configured to prevent significant deformation in the base upon the cooling of the hot liquid; and a sidewall extending upwardly from the base toward the spout, the sidewall including a zone of deformation, wherein the zone of deformation in the sidewall is configured to accommodate an initial deformation due to the cooling of the contents and to substantially regain its initial shape upon the relieving of immobilized stresses.

Abstract: A thermoplastic container (1) having a body (2) provided with at least one groove (6) that forms a closed loop and that extends perpendicularly to the axis of the body; the groove having a depth (p) that lies in the range 3 mm to 6 mm; in right section, the groove comprises: an bottom (8) that is rounded, having a small radius of curvature (R1) in the range 0.2 mm to 1.5 mm; two faces (9) that are plane and that flare apart from each other on either side of the bottom (8) at an angle (?) in the range 50° to 90°; and two faces (10) that are curvilinear, and that extend away from the respective plane faces (9) at an angle (?) that is less than 180°, and that are connected thereto by respective rounded walls (11) of small radius of curvature (R2) that does not exceed 1.5 mm, and that are connected tangentially to the wall (12) of the body (2). Such a groove (6) is deformable with a capacity to pinch axially in the presence of an axial force applied to the container.

Abstract: The plastic container has a heel portion having an enclosed base; a body portion transitioning into the heel portion; a bell portion transitioning into the body portion; and a finish attached to the bell portion and defining an opening. The body portion is formed into a generally tubular structure by a plurality generally flat panels. Each of the panels is connected to an adjacent panel with a chamfered post, and the body portion includes at least one vertically oriented rib at each of the chamfered posts.

Abstract: A plastic container comprises an upper portion including a finish, a lower portion including a base, a sidewall extending between the upper portion and the lower portion, the sidewall defining a central longitudinal axis of the container, and at least two vacuum panels located in the sidewall and separated by a substantially longitudinal rib having a wavy longitudinal profile. Each vacuum panel comprises a first portion having a first cross-section in a plane substantially transverse to the longitudinal axis, and a second portion having a second cross-section in a plane substantially transverse to the longitudinal axis, the second cross-section being arced to a greater extent than the first cross-section.

Abstract: The present invention relates to a plastic container comprising two substantially smooth opposing squeezable panels, separated by a vacuum panel and having at least one arcuate indentation adapted to allow flexure of the respective panel without permanent distortion or creasing when a force is applied to the panel toward the container interior.

Abstract: The bottle has accordion-like collapsible bellows ridges (1) with upper and lower arched shape surfaces (1?,1?), always only one of the surfaces (1?,1?) is provided with a system of ridge embossed or stamped stiffenings (2) without horizontal continuity. System of vertical stamped stiffenings (3) is present as well, creating recesses (4) of the bellows ridges (1) with angle greater than 90°, having arched shape haunches (5) at the top and bottom. Stacking depression (6) is created in the bottom of the bottle, the bottle is preferably provided with removable label leaving no residue and it has completely detachable cap (7).

Abstract: The present invention relates to a plastic container comprising two substantially smooth opposing squeezable panels, separated by a vacuum panel and having at least one arcuate indentation adapted to allow flexure of the respective panel without permanent distortion or creasing when a force is applied to the panel toward the container interior.

Abstract: The invention relates to a container (1?) made of a thermoplastic material, especially PET, having a body (2?) which, for at least a part of its height, is substantially prismatic in shape with a substantially triangular cross section and with three faces (6) joined by three edges (7), each of which is shaped in the form of a groove (8) which opens outwards and which has a rear wall (9) having a reversed curvature with its convexity being directed outwards.

Abstract: A base including an inwardly and upwardly projecting flexible surface within a continuous seating ring supports a generally cylindrical wall extending upward from the base. A plurality of annular inwardly projecting, and vertically flexible rings interrupting the cylindrical wall. At least one of rings projects inwardly more than some others of the rings to achieve an improved sidewall crush resistance A shoulder portion, includes a plurality of vertical ribs separating a plurality of vacuum responsive panels. The vertical flexibility of the bottle sidewall reduces the amount of flexing required in the shoulder panels and base to accommodate the same vacuum development, and enhances the total amount of post capping vacuum development that can be accommodated by the bottle as a whole.

Abstract: A lightweight container includes an enclosed base, an upper portion that extends upwardly to a finish; and a body located between the base and the upper portion. The sidewall includes vacuum compensation elements having a series of arches that are arranged to resemble water ripples formed by a water droplet.

Abstract: A lightweight container includes an enclosed base, an upper portion that extends upwardly to a finish; and a body located between the base and the upper portion. The sidewall includes vacuum compensation elements that have an open end and an opposing closed end, and that form a V-shape. Each element has nested fields.

Abstract: A one-piece plastic hot-fill container may employ a shoulder portion, a base portion and a sidewall portion, which may be integrally formed with and extend from the shoulder portion to the base portion. The container may further employ a plurality of compression ribs molded into the sidewall portion—a first of the plurality of compression ribs intersecting a second of the plurality of compression ribs to form a rib interface, at least the first and the second of the plurality of compression ribs changing from a first shape to a second shape in response to cooling of the liquid.

Abstract: A lightweight, thin-walled heat resistant plastic container containing hot-filled liquid contents, comprising: a spout for filling the container with liquid contents; a closure configured to seal the spout; a base including a bottom portion that is bent toward the spout, the base including a structural reinforcement configured to withstand hydrostatic pressure from the hot-filling of liquid and configured to prevent significant deformation in the base upon the cooling of the hot liquid; and a sidewall extending upwardly from the base toward the spout, the sidewall including a zone of deformation, wherein the zone of deformation in the sidewall is configured to accommodate an initial deformation due to the cooling of the contents and to substantially regain its initial shape upon the relieving of immobilized stresses.

Abstract: A blow-molded bottle has a flexible concave perimeter surface extending between an upper peripheral margin projecting outward from the bottle neck and an outwardly protruding ring located above the sidewall upper margin. The flexible concave perimeter surface is specially dimensioned to respond to the presence of a vacuum within the bottle by forming linear segments between the upper peripheral margin and the outwardly protruding ring. The average radius of the vertical mid-point of the concave perimeter surface is generally greater than (3/?) (sin ?/3) (R1+R2), and less than (6/?) (sin ?/6) (R1+R2), where R1 is the outermost radius of the upper peripheral margin, and R2 is the radius of the outwardly protruding ring. The vertical midpoint radius of the flexible concave perimeter surface measured from the vertical axis can be made to vary by between one and five percent at between three and five positions around the perimeter.