BLOW MOLDED CONTAINER AND METHOD OF MAKING

Abstract: A molded polymeric container includes a substantially cylindrical body portion (12) and a bottom portion (20). The bottom portion (20) includes a central pushup area (30) that is substantially symmetrical about the longitudinal axis (18), a plurality of support feet (22) separated by ribs (34). Advantageously, the radius of the pushup area (Rp) is between 10 to 50 % of the radius of the sidewall (RL) of the body portion (12). The longitudinal distance between the central point of the pushup area and the bottom of the support feet (Dp) is no more than 100 % of the radius of the pushup area (Rp). Moreover, the radius of curvature of the ribs (R5) is no less than about 70 % of the radius of the sidewall (RL) of the body portion (12).

Description: BLOW MOLDED CONTAINER AND METHOD OF MAKING BACKGROUND OF THE INVENTION 1 . Field of the Invention This invention relates broadly to the field of container making, and more specifically to blow molded plastic bottles, such as the PET bottles that are in common use today for packaging soft drinks such as soda. 2. Description of the Prior Art and More Recent Technology During the last twenty-five years or so, there has been a dramatic shift in the packaging of carbonated beverages, particularly, soft drinks, away from glass containers and toward plastic containers. The plastic containers initially took the form of a two-piece construction, wherein a plastic bottle having a generally hemispherical bottom was applied a separate base cup, which would permit the bottle to be stood upright . The hemispherical bottom was seen as the most desirable shape for retaining the pressure generated by the carbonation within the container. Pressures in such containers can rise to 100 p.s.i. or more when the bottled beverage is exposed to the sun, stored in a warm room, car trunk, or the like. Such plastic containers represented a significant safety advantage over glass containers when exposed to the same internal pressures. However, the two-piece construction was not economical because it required a post molding assembly step, and, also a separation step prior to reclaiming or recycling the resins forming the bottle and base cup. During this period of development, various attempts were made to construct a one-piece, self-supporting container that would be able to retain the carbonated beverages at the pressures involved. Such a one-piece container requires the design of a base structure which will support the bottle in an upright position and will not bulge outwardly at the bottom. A variety of designs were first attempted, with most following one of two principal lines of thought. One line of designs involved a so-called champagne base having a complete annular peripheral ring. Examples of such bottles are found in U.S. Pat. Nos. 3,722,726; 3,881,621; 4,108,324; 4,247,012; and, 4,249,666. Another variety of designs is that which included a plurality of feet protruding downward from a curved bottom. Examples of this variety are to be found in U.S. Pat. Nos. 3,598,270; 4,294,366; 4,368,825; 4,865,206; and, 4,867,323. In recent years, the latter type of design has achieved primacy in the marketplace. Footed one piece bottles present certain problems, though, which have not yet been worked out to the satisfaction of the packaging industry and its customers. For example, the uneven orientation of the polymer in the footed area of the bottom can contribute to uneven post filling expansion of either one or more feet or the central portion of the bottom, creating what is generally referred to as a "rocker." In addition, the presence of the feet themselves and the need to force the oriented material into the shape of the feet can create stress points in the container bottom that can adversely affect container shape. Container bottom designs that minimize stress and disorientation of the polymer during molding, then are considered preferable. Another concern in the design of container bottoms for one piece containers is the possibility of stress cracking in the base. The amount of stress cracking is related to the geometry of the base. Relatively large radius curves in the base will reduce the stress cracking compared to a base with small radius curves. Yet another factor that is important in the design of such containers is volumetric and structural stability of the container during and after filling and pressurization of the container. Bulging of vulnerable areas in the container bottom, particularly the pushup area in the center, will increase the volume of the container and affect the filling process, as well as permit visible accumulation of gases at the top of the bottle, which will be visible to the consumer. Such deformation is preferably to be avoided. A need exists for an improved bottom design for a polymeric one piece container that will optimize use of material relative to strength, reduce the possibility of stress cracking, reduce deformation during filling and storage, and permit molding with a minimum of stress and disorientation of the polymer material. SUMMARY OF THE INVENTION Accordingly, it is an object of the invention to provide an improved bottom design for a polymeric one piece container that will optimize use of material relative to strength, reduce the possibility of stress cracking, reduce deformation during filling and storage, and permit molding with a minimum of stress and disorientation of the polymer material. In order to achieve the above and other objects of the invention, a molded polymeric container according to a first aspect of the invention is shaped to be easier to mold, have improved rigidity under pressure and improved strength with respect to such containers heretofore known and includes a substantially cylindrical body portion having a longitudinal axis and a circumferential sidewall, the sidewall being separated from the longitudinal axis by a radius R L ; a bottom portion including a central pushup area that is substantially symmetrical about the longitudinal axis; a plurality of support feet surrounding and protruding downwardly from the pushup area, each of the support feet having a bottom support surface that has a radially inner edge, the radially inner edges of the support feet together circumscribing an inner ring having a radius R p that surrounds the pushup area, the support feet extending downwardly from a central point of the pushup area by a longitudinal distance D p ; and a plurality of ribs, each of the ribs being positioned between and helping to define two of the support feet, at least one of the ribs having a radius of curvature R 5 ; and wherein: the radius R p of the pushup area is between 10% to 50% of the radius R L of the sidewall of the body portion, so that the pushup area constitutes a relatively small proportion of the total area of the bottom portion, thus reducing downward deflection of the pushup area when the container is pressurized; the longitudinal distance D p between the central point of the pushup area and the bottom of the support feet is no more than 100% of the radius R p of the pushup area, whereby a transition area defined between the central point and the feet is relatively shallow, thus reducing stresses in the transition area during use of the container and thereby strengthening the container; and the radius of curvature R 5 of the ribs being no less than 70% of the radius R L of the sidewall of the body portion, whereby the bottom portion of the container will be constrained to expand substantially hemispherically during molding, thereby orienting the polymeric material in as relaxed a position as possible during molding, reducing stresses and optimizing the strength of the container bottom. According to a second aspect of the invention, a molded polymeric container that is shaped to be easier to mold, have improved rigidity under pressure and improved strength with respect to such containers heretofore known includes a substantially cylindrical body portion having a longitudinal axis and a circumferential sidewall, the sidewall being separated from the longitudinal axis by a radius R L ; a bottom portion including a central pushup area that is substantially symmetrical about the longitudinal axis; a plurality of support feet surrounding and protruding downwardly from the pushup area, each of the support feet having a bottom support surface that has a radially inner edge, the radially inner edges of the support feet together circumscribing an inner ring having a radius R p that surrounds the pushup area, the support feet extending downwardly from a central point of the pushup area by a longitudinal distance D P ; and a plurality of ribs, each of the ribs being positioned between and helping to define two of the support feet, each of the ribs having a radius of curvature R 5 ; and wherein: the radius R p of the pushup area is between about 25% to about 47% of the radius R L of the sidewall of the body portion, so that the pushup area constitutes a relatively small proportion of the total area of the bottom portion, thus reducing downward deflection of the pushup area when the container is pressurized; the longitudinal distance D p between the central point of the pushup area and the bottom of the support feet is between about 15% to about 50% of the radius R p of the pushup area, whereby a transition area defined between the central point and the feet is relatively shallow, thus reducing stresses in the transition area during use of the container and thereby strengthening the container; and the radius of curvature R 5 of the ribs is no less than about 90% of the radius R L of the sidewall of the body portion, whereby the bottom portion of the container will be constrained to expand substantially hemispherically during molding, thereby orienting the polymeric material in as relaxed a position as possible during molding, reducing stresses and optimizing the strength of the container bottom. According to a third embodiment of the invention, a molded polymeric container that is shaped to be easier to mold, have improved rigidity under pressure and improved strength with respect to such containers heretofore known includes a substantially cylindrical body portion having a longitudinal axis and a circumferential sidewall, the sidewall being separated from the longitudinal axis by a radius R L ; a bottom portion including a central pushup area that is substantially symmetrical about the longitudinal axis; a plurality of support feet surrounding and protruding downwardly from the pushup area, each of the support feet having a bottom support surface that has a radially inner edge, the radially inner edges of the support feet together circumscribing an inner ring having a radius R p that surrounds the pushup area, the support feet extending downwardly from a central point of the pushup area by a longitudinal distance D p ; and a plurality of ribs, each of the ribs being positioned between and helping to define two of the support feet, each of the ribs having a radius of curvature R 5 ; and wherein: the radius R p of the pushup area is between about 25% to about 47% of the radius R L of the sidewall of the body portion, so that the pushup area constitutes a relatively small proportion of the total area of the bottom portion, thus reducing downward deflection of the pushup area when the container is pressurized; the longitudinal distance D P between the central point of the pushup area and the bottom of the support feet is between about 22% to about 28% of the radius R P of the pushup area, whereby a transition area defined between the central point and the feet is relatively shallow, thus reducing stresses in the transition area during use of the container and thereby strengthening the container; and the radius of curvature R 5 of the ribs is no less than about 99% of the radius R L of the sidewall of the body portion, whereby the bottom portion of the container will be constrained to expand substantially hemispherically during molding, thereby orienting the polymeric material in as relaxed a position as possible during molding, reducing stresses and optimizing the strength of the container bottom. These and various other advantages and features of novelty which characterize the invention are pointed out with particularity in the claims annexed hereto and forming a part hereof. However, for a better understanding of the invention, its advantages, and the objects obtained by its use, reference should be made to the drawings which form a further part hereof, and to the accompanying descriptive matter, in which there is illustrated and described a preferred embodiment of the invention. BRIEF DESCRIPTION OF THE DRAWINGS FIGURE 1 is a longitudinal cross-section of an improved polymeric container that is constructed according to a preferred embodiment of the invention; FIGURE 2 is a close-up view of a bottom portion of what is depicted in FIGURE 1; FIGURE 3 is a perspective depiction of the bottom of the container that is shown in FIGURES 1 and 2; FIGURE 4 is a side elevational depiction of the container bottom that is shown in FIGURES 1-2; and FIGURE 5 is a bottom plan view of the container bottom that is shown in FIGURES 1-4. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S) Referring now to the drawings, wherein like reference numerals designate corresponding structure throughout the views, and referring in particular to FIGURES 1 and 2, a molded polymeric container 10 that is shaped to be easier to mold, have improved rigidity under pressure and improved strength with respect to such containers heretofore known, includes, according to a preferred embodiment of the invention, a substantially cylindrical body portion 12 that has a longitudinal axis 18 and a circumferential sidewall 13. Sidewall 13 is separated from the longitudinal axis 18 by a so-called label radius R L . As is typical in such containers, polymeric container 10 includes a neck portion 14 that tapers into a threaded nipple that defines an opening 16. Container 10 further includes a bottom portion 20 including a central pushup area 30 that is substantially symmetrical about the longitudinal axis 18 of the cylindrical body portion 12 of the molded polymeric container 10. Bottom portion 20 further includes a plurality of support feet 22, of which there are five in the preferred embodiment, that surround and protrude downwardly from the pushup area 30. Each of the support feet 22 has a bottom support surface 2 , shown in FIGURE 2, that has radially inner edge 26 and a radially outer edge 28, also shown in FIGURE 2. The radially inner edges 26 of the respective support feet 22 together circumscribe an inner ring 32, that is visible in FIGURE 5 and has a radius R p that surrounds the central pushup area 30. The support feet 22 extend downwardly from a central point of the pushup area 30 by a longitudinal distance D p . The bottom portion 20 of the molded polymeric container 10 further includes a plurality of ribs 34, each of which is positioned between and helps to define two of the support feet 22, as may be best seen in FIGURES 3, 4 and 5. Each of the ribs 34 has a radius of curvature R 5 , as is shown diagrammatically in FIGURES 1 and 2. As may be seen in FIGURE 2, a whole cross section taken longitudinal of the bottom portion 20 of container 10 will reveal that the support foot 22 is preferably formed with a first broad radiused side surface that is curved at a first radius R lf which merges into a second, tighter radiused outer transition surface that has a curvature radius R 2 . The outer transition surface R 2 merges into the flat bottom support surface 24 at the outer edge 28, as may be clearly seen in FIGURE 2. At the inner edge 26 of the bottom support surface 24, the support foot 22 yields to a transition area 36 that is positioned between the center point of the pushup area 30 and the inner edge 26 or inner ring 32 of the support foot 22. This transition area is characterized by a central dome that has a lower concave surface that is curved at a radius R 4 , and a compensating area with a lower convex surface that curves at a radius R 3 , and merges into the bottom of the support feet 22 at the inner edge 26 as shown in FIGURE 2. Preferably, R 4 and R 3 should be no less than about 0.900 inches, and R 2 should be no less than about 0.500 inches. According to one important aspect of the invention, the radius R P of the pushup area 30 is between 10% to 50% of the radius R L of the sidewall 13 of the body portion 12, so that the pushup area 30 constitutes a relatively small proportion of the total area of the bottom portion 20. This reduces downward deflection of the pushup area 30 when the container 10 is pressurized with, for example, a carbonated beverage. More preferably, the radius R p of the pushup area 30 is between about 25% to about 47% of the radius R L of the sidewall 13. Most preferably R p is about 45% of the radius R L . According to another important aspect of the invention, the longitudinal distance D p between the central point of the pushup area 30 and the bottom of the support feet 22 is no more than 100% of the radius R P of the pushup area 30. As a result of this, the transition area 36 that is defined between the central point and the inner ring 32 is relatively shallow, thus reducing stresses in the transition area 36 during use of the container and strengthening the container. More preferably, the distance D p is between about 15% to about 50% of the radius R p , and is most preferably between about 22% to about 28% of the radius R p . Another important feature of the invention is that the radius of curvature R 5 of the ribs 34 is no less than about 70% of the radius R L of the sidewall 13 of the body portion 12, so that the bottom portion 20 of the container 10 will be constrained to expand substantially hemispherically during molding, thereby orienting the polymeric material in as relaxed a position as possible during molding, reducing stresses and optimizing the strength of the container bottom. More preferably, the radius of curvature R 5 of the ribs 34 is no less than about preferably no less than about 99% of the radius R L of the sidewall 13. The longitudinal distance D p between the central point of the pushup area 30 and the bottom of the support feet 22 is preferably no more than about 0.5 inches, and may be as little as 0.15 inches. The radius R p between the longitudinal axis 18 and the inner ring 32 of the container bottom 20 may be as little as about 0.25 inches, and as great as about 1.2 inches. The smaller this dimension, the less deformation or bulging that is likely to occur when the container can is pressurized. Preferably, container 10 is fabricated of PET. Alternatively, it may be fabricated from PEN or a PEN-PET copolymer or physical blend of the two. Container 10 may be molded according to known techniques from a parison in a mold that is contoured according to the dimensions and shape disclosed herein. During such molding, the bottom portion 20 of the container will be kept constrained in a substantially hemispherically shape because of the hemispherically shaped ribs 34 that help define support feet 22. Accordingly, molding will be accomplished with a minimum of disorientation and stress on the polymeric material. It is to be understood, however, that even though numerous characteristics and advantages of the present invention have been set forth in the foregoing description, together with details of the structure and function of the invention, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.

Claims: WHAT IS CLAIMED IS: 1. A molded polymeric container that is shaped to be easier to mold, have improved rigidity under pressure and improved strength with respect to such containers heretofore known, comprising: a substantially cylindrical body portion having a longitudinal axis and a circumferential sidewall, the sidewall being separated from the longitudinal axis by a radius R L ; a bottom portion comprising: a central pushup area that is substantially symmetrical about the longitudinal axis; a plurality of support feet surrounding and protruding downwardly from the pushup area, each of the support feet having a bottom support surface that has a radially inner edge, the radially inner edges of the support feet together circumscribing an inner ring having a radius R p that surrounds the pushup area, the support feet extending downwardly from a central point of the pushup area by a longitudinal distance D p ; and a plurality of ribs, each of the ribs being positioned between and helping to define two of the support feet, at least one of the ribs having a radius of curvature R 5 ; and wherein: the radius R p of the pushup area is between 10% to 50% of the radius R L of the sidewall of the body portion, so that the pushup area constitutes a relatively small proportion of the total area of the bottom portion, thus reducing downward deflection of the pushup area when the container is pressurized; the longitudinal distance D p between the central point of the pushup area and the bottom of the support feet is no more than 100% of the radius R p of the pushup area, whereby a transition area defined between the central point and the feet is relatively shallow, thus reducing stresses in the transition area during use of the container and thereby strengthening the container; and the radius of curvature R 5 of the ribs being no less than 70% of the radius R L of the sidewall of the body portion, whereby the bottom portion of the container will be constrained to expand substantially hemispherically during molding, thereby orienting the polymeric material in as relaxed a position as possible during molding, reducing stresses and optimizing the strength of the container bottom. 2. A container according to claim 1, wherein the container is fabricated from a polymeric material that comprises PET. 3. A container according to claim 1, wherein the radius R p of the pushup area is between about 25% to about 47% of the radius R L of the sidewall of the body portion, so that the pushup area constitutes a relatively small proportion of the total area of the bottom portion, thus reducing downward deflection of the pushup area when the container is pressurized 4. A container according to claim 3, wherein the radius R P of the pushup area is about 45% of the radius R L of the sidewall of the body portion, so that the pushup area constitutes a relatively small proportion of the total area of the bottom portion, thus reducing downward deflection of the pushup area when the container is pressurized 5. A container according to claim 1, wherein the longitudinal distance D p between the central point of the pushup area and the bottom of the support feet is between about 15% to about 50% of the radius R p of the pushup area, whereby a transition area defined between the central point and the feet is relatively shallow, thus reducing stresses in the transition area during use of the container and thereby strengthening the container. 6. A container according to claim 5, wherein the longitudinal distance D p between the central point of the pushup area and the bottom of the support feet is between about 22% to about 28% of the radius R p of the pushup area, whereby a transition area defined between the central point and the feet is relatively shallow, thus reducing stresses in the transition area during use of the container and thereby strengthening the container. 7. A container according to claim 1, wherein the radius of curvature R 5 of the ribs is no less than about 90% of the radius R L of the sidewall of the body portion, whereby the bottom portion of the container will be constrained to expand substantially hemispherically during molding, thereby orienting the polymeric material in as relaxed a position as possible during molding, reducing stresses and optimizing the strength of the container bottom. 8. A container according to claim 7, wherein the radius of curvature R 5 of the ribs is no less than about 99% of the radius R L of the sidewall of the body portion, whereby the bottom portion of the container will be constrained to expand substantially hemispherically during molding, thereby orienting the polymeric material in as relaxed a position as possible during molding, reducing stresses and optimizing the strength of the container bottom. 9. A container according to claim 1, wherein the longitudinal distance D p between the central point of the pushup area and the bottom of the support feet is no more than about 0.5 inches. 10. A container according to claim 5, wherein the longitudinal distance D p between the central point of the pushup area and the bottom of the support feet is no more than about 0.5 inches. 11. A container according to claim 6, wherein the longitudinal distance D P between the central point of the pushup area and the bottom of the support feet is no more than about 0.5 inches. 12. A container according to claim 1, wherein the transition area defined between the central point and the feet includes a central dome with a lower concave surface, and a compensating area with a lower convex surface that merges into the bottom of the support feet. 13. A molded polymeric container that is shaped to be easier to mold, have improved rigidity under pressure and improved strength with respect to such containers heretofore known, comprising: a substantially cylindrical body portion having a longitudinal axis and a circumferential sidewall, the sidewall being separated from the longitudinal axis by a radius R L ; a bottom portion comprising: a central pushup area that is substantially symmetrical about the longitudinal axis; a plurality of support feet surrounding and protruding downwardly from the pushup area, each of the support feet having a bottom support surface that has a radially inner edge, the radially inner edges of the support feet together circumscribing an inner ring having a radius R p that surrounds the pushup area, the support feet extending downwardly from a central point of the pushup area by a longitudinal distance D P ; and a plurality of ribs, each of the ribs being positioned between and helping to define two of the support feet, each of the ribs having a radius of curvature R 5 ; and wherein: the radius R p of the pushup area is between about 25% to about 47% of the radius R L of the sidewall of the body portion, so that the pushup area constitutes a relatively small proportion of the total area of the bottom portion, thus reducing downward deflection of the pushup area when the container is pressurized; the longitudinal distance D p between the central point of the pushup area and the bottom of the support feet is between about 15% to about 50% of the radius R p of the pushup area, whereby a transition area defined between the central point and the feet is relatively shallow, thus reducing stresses in the transition area during use of the container and thereby strengthening the container; and the radius of curvature R 5 of the ribs is no less than about 90% of the radius R L of the sidewall of the body portion, whereby the bottom portion of the container will be constrained to expand substantially hemispherically during molding, thereby orienting the polymeric material in as relaxed a position as possible during molding, reducing stresses and optimizing the strength of the container bottom. 14. A molded polymeric container that is shaped to be easier to mold, have improved rigidity under pressure and improved strength with respect to such containers heretofore known, comprising: a substantially cylindrical body portion having a longitudinal axis and a circumferential sidewall, the sidewall being separated from the longitudinal axis by a radius R L ; a bottom portion comprising: a central pushup area that is substantially symmetrical about the longitudinal axis; a plurality of support feet surrounding and protruding downwardly from the pushup area, each of the support feet having a bottom support surface that has a radially inner edge, the radially inner edges of the support feet together circumscribing an inner ring having a radius R p that surrounds the pushup area, the support feet extending downwardly from a central point of the pushup area by a longitudinal distance D P ; and a plurality of ribs, each of the ribs being positioned between and helping to define two of the support feet, each of the ribs having a radius of curvature R 5 ; and wherein: the radius R P of the pushup area is between about 25% to about 47% of the radius R L of the sidewall of the body portion, so that the pushup area constitutes a relatively small proportion of the total area of the bottom portion, thus reducing downward deflection of the pushup area when the container is pressurized; the longitudinal distance D p between the central point of the pushup area and the bottom of the support feet is between about 22% to about 28% of the radius R p of the pushup area, whereby a transition area defined between the central point and the feet is relatively shallow, thus reducing stresses in the transition area during use of the container and thereby strengthening the container; and the radius of curvature R s of the ribs is no less than about 99% of the radius R L of the sidewall of the body portion, whereby the bottom portion of the container will be constrained to expand substantially hemispherically during molding, thereby orienting the polymeric material in as relaxed a position as possible during molding, reducing stresses and optimizing the strength of the container bottom.

Inventors: ZHANG PETER Q, ZHANG, PETER, Q.
Applicants: CROWN CORK & SEAL CO, CROWN CORK & SEAL COMPANY, INC.
Application year: 1996
Main classification: B65D1
IPC codes: B65D1