PRESSURE RESISTANT BOTTLE-SHAPED CONTAINER

Abstract: A pressure resistant bottle-shaped container (1) having a body (2) including panels (3) surrounded by outer sheaths (5), characterized in that each panel (3) has stress absorbing strips comprising vertexes (6, 23) recessed from the outer surface of the panel toward the interior of the container (1) and bending lines (7, 24) formed in V shape and inverted V shape from the vertexes (6, 23) toward the outer sheaths (5). Thus, the container does not retain in permanent deformation by the deformations corresponding to pressure changes at the time of filling high temperature liquid content.

Description: This invention relates to a blow-molded bottle-shaped container of biaxially oriented polyethylene terephthalate resin and, more particularly, to a bottle-shaped container in which large durable strength is created against an increase in the pressure in the bottle-shaped container but which is easily and uniformly deformed under reduced pressure in the container. It is known that a blow-molded bottle-shaped container of biaxially oriented polyethylene terephthalate resin (hereinafter referred merely to a "PET") is improved in the heat resistance of the container body itself by heat setting the resin after the biaxial-orientation blow-molding to provide a heat resistance bottle-shaped container for filling with a content liquid necessary to be filled at high temperature, such as juice drink. However, the bottle-shaped container of PET of this type does not have high rigidity like a glass or metal bottle-shaped container but is flexible. Thus, the body of the bottle-shaped container is improperly deformed under reduced pressure generated in the container due to a volumetric contraction of content liquid or a decrease in the vapor pressure of a head space when filling the content liquid at high temperature to cause the container to be remarkably defected in its external appearance. The bottle-shaped container of the PET of this type is prevented from being deformed in the configuration of the body by recessing and aligning flat longitudinal reduced pressure absorbing panels on its body to absorb the reduced pressure in the container by means of the panels. Such a container is shown, for example, in EP-A-198 587. Pressure and stress are acted on the panels of the heat resistant bottle-shaped container of the PET as below. Hydraulic pressure produced due to the difference in height of the surface of the content liquid filled in the container from the content liquid in a tank disposed at its upper position at the time of pressing to seal the neck of the container and filling the liquid content in the container by a filling machine in case of filling the content liquid at high temperature acts on the panels of the container. The hydraulic pressure is opened with the atmospheric pressure immediately after filling the content liquid in the container. A rise in the internal pressure in the container due to vapor pressure in the head space of the container takes place at the time of capping the neck of the container (e.g., the internal pressure in the container is raised to approx. 1.7149 kg/cm² when the content liquid of 90°C is, for example, filled in the container.). The vapor pressure in the container is reduced gradually from the state at capping time to the atmospheric pressure at sterilization time, and the pressure in the container is decreased in the deforming stress in response to the pressure change caused by the content from being reduced in volume at cooling time and to the reduction in the vapor pressure in the head space of the container. The deforming stresses are generated at the panels in response to the pressure change. As described above, the panels are effected by the heat from the content liquid in the container and also subjected to the pressure change at pressurizing time (at the time of filling the content or capping the neck of the container), to the ambient pressure (immediately after filling the content liquid in the container) or to the pressure reduction (at the time of cooling the container). Therefore, the panels are heated to high temperature and pressurized to high pressure at the time of filling the content in the container, capping the neck of the container due to the vapor pressure and the heat of the content liquid immediately thereafter, and thus extrusion-deformed in a raised shape at the outside of the container as compared with that at the time of vacant container. According to a number of experiments, generated vapor pressure is relatively low when the temperature of the content liquid to be filled is 80°C or lower, so that the temperature rising degree of the container is less. Thus, the allowable stress to the container itself is still large, a trend that the panels are deformed in a raised shape is relatively small, and the influence of the raised deformation of the panel is not almost presented after cooling the container. However, when the temperature of the content liquid is 85°C or higher and particularly 90°C or higher, generated vapor pressure in the container is raised, and the raised deformation of the panel after capping the neck of the container is much increased. Since the raised deformation of the panel of the container is affected by the influences of the temperature of the content liquid and the vapor pressure of the container, a permanent strain remains in the material of the container due to a decrease in the strength of the material and the remaining strain. The panels provided on the bottle-shaped container of this type are heretofore composed, in order to obtain uniform deformation, of (1) flat surfaces as large as possible on the entire area of the panels, (2) external projections of the entire panel in advance, (3) external protrusion of partial panel in advance, (4) inclined surfaces of the panels to reduce the raised deformation, (5) recess grooves surrounded on the panels to scarcely cause the panels to be deformed in a raised shape, and (6) lateral and longitudinal rib strips formed on the panels. However, when the temperature of the content liquid filled in the container is actually raised to 85°C or higher, raised deformations indispensably generated on the panels are increased due to the influences of the heat and vapor pressure of the liquid content in the container, and permanent deformations remain at the panel as remaining strains at the time of cooling the container. The panels which have once been subjected to the raised permanent deformations cannot function as ordinary panels to loose its reduced pressure absorbing action. Thus, the entire body of the container is improperly deformed to triangular or elliptical shape, or the panels cannot absorb the normal pressure reduction, thereby causing the external appearance of the container to be deteriorated. As described above, it is also known that panels which cause less raised deformation against an increased pressure at the time of capping the neck of the container and also cause easy deformation due to recessed deformation under reduced pressure in the container at the time of cooling the container are formed in flat structure in the whole inside of the stepped portion of the panels surrounded by bent stepped portions on the periphery. However, mere flat structure of the entire panel causes the stepped portions to be subjected to permanent deformations as will be described so that the panels cannot absorb deformations due to normal reduced pressure. Even if the panels may absorb the reduced pressure deformation, the available state of the stress acting on the panels due to the reduced pressure cannot be specified to be uniformized. Thus, predetermined stable deformations cannot be proceeded at the panels. In this manner, the degrees of absorbing the deformation due to reduced pressure in the panels become different, so that the external appearance of the bottle-shaped container is abnormally deteriorated. The most simple means which do not retain permanent deformations in the raised strains of the panels is to raise the heat setting effect of the container. The heat setting includes biaxial-orientation blow-molding a preformed piece by injection molding, then cooling the piece, then heating again the piece to remove its remaining stress, and thereafter further blowing the piece to complete a product. However, in order to raise the heat setting effect of the bottle-shaped container, it is necessary to raise the heat setting temperature and to increase the setting time. Thus, the heat setting remarkably reduces the productivity. Therefore, a method of raising the heat setting is not practical. Even if the container is sufficiently heat set in this manner, the deformation for the reduced pressure absorbing effects of the panels cannot be always uniformly generated, but a decrease in the external appearance of the container due to irregular deformation still remains unsolved. Since blow-molded bottle-shaped container of biaxially oriented synthetic resin is removed from a metal mold in the state the container is yet soft after blow-molding, the container is feasibly deformed due to small remaining distortion. This distortion of the container is understood to be largely affected by the structure of the panels. The bottle-shaped container having conventional panels as described above has remarkable drawbacks to be readily deformed in its structure after blow-molding. The causes of the permanent deformation of the panel in the bottle-shaped container have been observed in detail. It is discovered that one of the causes resides in the fact that the bending angles of two bent portions of the stepped portions bent at the periphery of the panels are varied in opposite directions each other to be different from the angle at the time of molding. The variations in the bending angles of the two bent parts of the stepped portions was understood from the fact that permanent deformations occurred due to the excess of allowable range of the deformations varied in opposite directions at the two bent parts by the temperature and the vapor pressure of the liquid content to be filled. When the stepped portions are thus deformed, the entire panels remain deformed in raised shape, so that the panels results in impossibility of smoothly recessed distortion for absorbing reduced pressure in the container. In a cylindrical bottle-shaped container, the body is located at equal distances from the center line at any portion. Thus, the container is easily uniformly oriented. However, in a polygonal bottle-shaped container, the body is not located at equal distances from the center line according to the positions, the container is subjected to irregular orientations. Therefore, the amounts of orientations are different at the positions on the container. Thus, internal remaining stresses generated by blow-molding are different at positions on the body. The differences in the blow-molding cause the panels to be subjected to permanent deformations at the time of heat setting or completing the container. This is also remarkable particularly at the bottom of the container at the portions which are most feasibly affected by the orientations. Accordingly, it is an aim of this invention to provide a blow-molded bottle-shaped container of biaxially oriented synthetic resin which can eliminate the drawbacks and inconvenience of the conventional bottle-shaped container described above and does not retain in permanent deformation by the deformations corresponding to pressure changes at the time of filling high temperature liquid content. In order to achieve the above aim, the present invention is directed to a pressure-resistant bottle-shaped container having the features set forth in claim 1. The characteristic features of the invention will become more fully apparent and more readily understandable by the following description and the appended claims when read in conjunction with the accompanying drawings, in which : Fig. 1 is an entire external view of a large-sized blow-molded bottle-shaped container of biaxially oriented polyethylene terephthalate resin used in embodiments of the present invention; Fig. 2 is a front view of a panel of a bottle-shaped container according to a first embodiment of the present invention; Fig. 3 is a sectional view taken along the line I-I in Fig. 2; Fig. 4 is a front view of a panel for a second embodiment of a bottle-shaped container; and Fig. 5 is a sectional view taken along the line II-II of Fig. 4. A bottle-shaped container 1 used in the present invention comprises a body 2. The body 2 has a plurality of panels 3 disposed in parallel longitudinally of the body 2, and a plurality of ribs 4 provided between the panels 3. In the container 1 used in first and second embodiments, outer sheaths 5 of the panels 3 have stepped portions. Each panel 3 is formed with a plurality of stress-absorbing zones. Each stress-absorbing zone has vertexes 6 recessed from the outer surface of the panel 3 toward the interior of the container 1, and bending lines 7 formed in V shape and inverted V shape from the vertexes 6 toward the outer sheaths 5. In the first embodiment of the bottle-shaped container of the invention, each vertex 6 is formed on the center line M of the panel 3 along an imaginary line located along the longitudinal direction of the panel 3. Reference numeral 8 designates a flat portion recessed from the outer surface of the body toward the interior of the container 1 from the panel surface between the bending lines 7 and 7 to be formed flat. The flat portion 8 is disposed at the longitudinal center of the panel 3. The step of the bending line 7 is defined to be 1.0 mm or less. A portion 9 except the flat portion 8 of the panel 3 is defined in a deforming portion. Since the bending lines 7 are formed through the vertexes 6 along the center line M, the stress, when reduced pressure is acted on the panel 3 so that a stress for the deformation is generated, is concentrated at the vertexes 6 along the bending lines 7. Thus, the panel 3 is deformed so as to absorb the reduced pressure from the position disposed at the vertex 6. Since the flat portion 8 is disposed between a pair of bending lines 7 and 7, the flat portion 8 is affected by the deforming forces at both upper and lower ends of the lateral center when the stress is concentrated at the vertexes 6 due to the reduced pressure deformation. Thus, the reduced pressure deformation is smoothly and reliably absorbed at the flat portion 8 to be always in constant degree. Since the flat portion 8 is disposed at the longitudinal center of the panel 3, the reduced pressure deformation is absorbed at the center of the panel 3. Thus, the deformation caused due to the reduced pressure absorption of the panel 3 is not irregular, but is generated entirely in order. Since the step distance of the bending lines 7 is set to 1.0 mm or less, the interval of the two bending portions for forming the bending lines 7 is narrowed in a wall sectional structure. Thus, the wall sectional structure of the bending lines is hardly deformed irrespective of the pressure increase or decrease and the temperature of the content liquid contained in the container 1. Therefore, even if the pressure increase at the time of capping the neck of the container 1 and the temperature of the content liquid in the container 1 at the time of filling the liquid in the container 1 are acted at the bending lines 7, the bending lines 7 are not permanently deformed nor permanently raised to be deformed at the panel 3. The flat portion 8 is scarcely affected by the remaining stresses from the deforming portion 9 and the rib 4 at the periphery of the container 1 at the time of biaxial-orientation blow-molding the container 1. Therefore, the dimensional accuracy of the flatness of the panel 3 is increased at the time of heat setting the container to suppress the increase in the irregularity due to the filling of high temperature liquid content in the container 1 thus blow-molded, thus manufacturing the bottle-shaped container 1 of high quality. Thus, even if the pressure increase at the time of capping the neck of the container 1 and the high temperature of the liquid content to be filled in the container 1 are effected at the bending lines 7, the bending lines 7 are not permanently deformed, nor the panel 3 is permanently deformed in a raised shape. The flat portion 8 of the container 1 is scarcely affected by the remaining stresses from the deforming portion 9 and the rib 4 at the periphery at the time of biaxial-orientation blow-molding the container 1 due to the presence of the bending lines 7. Therefore, the dimensional accuracy of the flatness of the panel 3 is raised at the time of heat setting the container 1 to suppress the increase in the irregularity of the liquid content at high temperature in the blow-molded container 1, thus manufacturing the container 1 of high quality. Examples A bottle-shaped container 1 was made of PET of standard of biaxial-orientation blow-molding having 0.33 to 0.35 mm of thickness at a body 2. The relationship between the steps of the bending lines 7 and the deformation of the panel 3 was observed by variably altering the steps of the bending lies 7 in the panel 3 of the container 1 in case of filling specified amount of hot water at 90°C, overturning the container 1 for 30 seconds after capping the neck of the container 1, allowing the container 1 to stand for 5 minutes and 30 seconds in an erected attitude, then cooling it to room temperature with cold water, and the following results were obtained. 2.0 mm of step of bending lines 7 The swelling deformation of the panel 3 after capping the neck of the container was large, the deformations of the bending lines 7 due to the deformation of the panel became permanent, and reduced pressure absorbing deformation of the panel 3 became improper at the time of cooling. 1.2 mm of step of bending lines 7 The swelling deformation of the panel 3 after capping the neck of the container was ordinary, the deformations of the bending lines 7 due to the deformation of the panel became permanent, and reduced pressure absorbing deformation of the panel 3 did not smoothly occur at the time of cooling. 1.0 mm of step of bending lines 7 The swelling deformation of the panel 3 after capping the neck of the container was relatively small, the deformations of the bending lines 7 due to the deformation of the panel became less permanent, and reduced pressure absorbing deformation of the panel 3 did not become irregular to cause the external appearance of the container 1 to be defected at the time of cooling. 0.7 mm of step of bending lines 7 The swelling deformation of the panel 3 after capping the neck of the container was small, the deformations of the bending lines 7 due to the deformation of the panel did not almost occur, and reduced pressure absorbing deformation of the panel 3 became very smooth and uniform at the time of cooling. 0.5 mm of step of bending lines 7 The swelling deformation of the panel 3 after capping the neck of the container was substantially the same as the case of 0.7 mm of the step of the bending lines 7, the deformations of the bending lines 7 due to the deformation of the panel also became not permanent, and reduced pressure absorbing deformation of the panel 3 became extremely smooth and uniform at the time of cooling. From the experiments, it is confirmed that the step of the bending lines 7 formed on the panel 3 necessary to be deformed for absorbing the reduced pressure in the container 1 must be 1.0 mm or shorter. The flat portion 8 formed on the panel 3 is a main portion for stabilizing the deforming state of the panel 3. According to various experiments, the area of the flat portion 8 is preferably approx. 1/4 of the area of the entire panel 3. Further, the bending lines 7 for concentrating the stress generated by the external pressure acting on the panel 3 at the vertexes 6 are preferably necessarily disposed obliquely with respect to the center line M. In other words, the bending lines 7 must be formed in V shape or in inverted V shape with respect to the center line M as a center. The angle of the V-shaped bending lines 7 is preferably approx. 30 to 140°. If the angle is smaller than 30°, the concentrating degree of the stress generated to the vertex 6 is excessively strengthened to cause the deformation of the flat portion 8 to become near the bending deformation, thus causing a trend of concentrating the deformation on the flat portion 8. On the contrary, if the V-shaped angle is larger than 140°, the concentration of the generated stress at the vertex 6 is deteriorated to cause the uniform deformation of the panel 3 to be deteriorated. In the first embodiment of the invention in Figs. 2 and 3, the vertexes 6 are disposed at the trisections of the longitudinal sides of the panel 3, and the V-shaped angle of the vertexes 6 is set to approx. 80°, and the step of the bending lines 7 is set to 0.7 mm. In this first embodiment, the raised deformation due to the increased pressure at the time of capping the neck of the container was performed mainly at the deforming portion 9, and the raised deformation of the flat portion 8 was small. In case of reduced pressure absorbing deformation, the flat portion 8 was largely recessed to be deformed, the deforming portion 9 was largely bent in the state pulled by the recessed deformation of the flat portion 8, and the entire panel 3 was deformed constantly. In the second embodiment in Figs. 4 and 5, the flat portion 8 of the first embodiment in Figs. 2 and 3 is completely surrounded by the bending lines 7. Further, bending lines 11 at second vertexes 10 as bending points ar formed at both deforming portions 9, the deforming portions 9 are partly obliquely raised toward the outer sheaths 5 to form an auxiliary deformation 12 of a bending wall structure. In this second embodiment, the swelling deformation of the deforming portions 9 with respect to the increased pressure at the time of capping is suppressed. Thus, the swelling deformation of the entire panel 3 at the time of capping is reduced, and no permanent deformation is generated at the step 5 for forming the boundary between the panel 3 and the rib 4. Since the stresses are concentrated to some degree to the vertexes 6 at both ends of the flat portion 8 and the second vertexes 10 of the deforming portions 9 at the time of reduced pressure absorbing deformation, the deforming states of the deforming portions 9 can be uniformized, thus obtaining more stable reduced pressure absorbing deformations of the panel 3. Since the pressure resistance bottle-shape container according to the present invention is constructed as described above, the deformations of the panels are suppressed when the pressure in the bottle-shaped container is increased, and the panels are smoothly, uniformly and reliably recessed to be deformed when the pressure in the container is reduced. Since the bending lines are formed on the panels, the dimensional stability of the flat panels can be enhance at the time of heat setting the container. Further, when removing the bottle-shaped container from the metal mold after blow-molding the container, no deformation occurs at the panels. Since the surfaces of the body of the container is formed in a polygonal shape of the integer number times of the number of the side surfaces of the body in the cross sectional shape of the bottom of the container as the peripheral end of the bottom wall, orientations of the bottom walls are uniformized, resulting in no permanent deformation occurring at the time of heat setting or completing the container. Further, excellent external appearance of the bottle-shaped container may be provided by the features of the invention described heretofore.

Claims: A pressure-resistant bottle-shaped container (1) having a body (2) including panels (3) surrounded by outer sheaths (5), each panel (3) having stress-absorbing strips comprising vertexes (6) recessed from the outer surface of the panel (3) towards the interior of the container (1) and bending lines (7) formed in a V-shape and in an inverted V-shape from the vertexes (6) towards the outer sheaths (5), the vertexes (6) being formed on the centre line (M) of the panel (3) along the longitudinal direction of the panel (3), characterised in that : (a) a flat recessed portion (8) of the panel (3) is formed between the bending lines (7), the flat portion (8) being disposed at the centre in the longitudinal direction of the panel (3); and (b) a step between the surface of the panel and the flat portion (8) is no greater than 1.0 mm. A pressure-resistant bottle-shaped container according to claim 1, characterised in that the area of the flat portion (8) is ¼ of the area of the panel (3). A pressure-resistant bottle-shaped container according to claim 1, characterised in that the angle of the V-shape of the bending lines (7) is between 30° and 140°. A pressure-resistant bottle-shaped container according to claim 1, characterised in that the vertexes (6) are disposed at tri-sections of the length of the longitudinal side of the panel (3), the angle of the V-shape of the bending lines (7) is 80°, and the step is substantially 0.7 mm. A pressure-resistant bottle-shaped container according to claim 1, characterised in that the flat portion (8) is formed in the state surrounded by the bending lines (7); second vertexes (10) are formed on the centre line (M) out of the flat portion (8); and bending lines (11) are formed in a V-shape and in an inverted V-shape from the second vertex towards the sheath (5) on a deforming portion (9).

Inventors: HAYASHI, YOSHIAKI, ITAKURA, TAKESHI, KATO, TOYOJI, KOSHIDAKA, YUKIO
Applicants: YOSHINO KOGYOSHO CO., LTD.
Application year: 1988
Main classification: B65D1
IPC codes: B65D79, B65D1