CN1241961A - Process for obtaining blow molded plastic containers - Google Patents

Abstract

The present invention relates to a blow molded plastic container and a manufacturing method thereof. The container has a support element in the container cavity, the support element fully traverses the cavity and is integrated with the inner wall surface of the container main body at two separated positions to support the inner wall surface. The shape of the container is variable in stress centralizing area in order to reduce the stress function, thereby avoid the excessive distortion in the area.

Description

Method for making blow molded plastic containers

Background of the invention

The present invention relates to plastic containers and methods of manufacture thereof, in particular to such plastic containers capable of containing fluids under pressure, such as carbonated drinks or the like. Such plastic containers are usually manufactured from preforms which can be produced by injection molding or extrusion and then blow molded using a blow mold having the desired shape. Make a container of suitable shape. Commonly used thermoplastic materials are polyethylene terephthalate (PET), polyolefins, etc., but other materials may also be used.

The shape of the container generally includes a neck, a shoulder extending downwardly from the neck, a side wall or body portion extending downwardly from the shoulder, and a The bottom of the side wall extends downwards, and the neck has a means for fixing the cover.

Convenience and economy often require large sized containers such as the two liter PET bottle widely used for carbonated beverages and the gallon of milk bottle. In fact, there is a need for larger containers. However, when utilizing such containers for carbonated beverages, the carbonated beverage may lose significant amounts of carbon dioxide which is well soluble in the beverage. When a container has a volume greater than the amount of beverage that can be consumed in one opening, loss of carbon dioxide occurs when the container is opened multiple times. The loss of carbon dioxide is known as head space loss, "head space" refers to the volume of the container that does not contain the beverage, the space that carbon dioxide that may escape from said beverage can enter, when consumed multiple times in the same container When drinking, the head space will increase as the amount of beverage in the container decreases.

Because of said loss of head space, the size of bottles for carbonated beverages is usually limited to two liters, and three-liter bottles for carbonated beverages are usually used when the beverage is consumed very quickly, for example during group outings.

Also, when pouring drinks, larger containers (such as those holding 1.5 liters or more) can be difficult for people with small hands (especially children) to hold and thus require more work than having to grab the bottle with both hands. A device for carrying and holding said container for convenience.

The above-mentioned disadvantages of this type of bottle can be solved by providing an integral inner wall in such a large container. For larger bottles, it is possible to divide it into several compartments by means of such an inner wall, thus having a structure in which one compartment is opened at a time in order to consume only the drink in said compartment at a time. Of course, in order to be able to effectively consume the beverage step by step, the bottle must be provided with an openable and closable closure. An example of the above-mentioned container divided into several chambers is disclosed in US Patent No. 5,232,108 to Y. Nakamura.

In order to improve the maneuverability of larger bottles, as described in U.S. Patent No. 5,398,828, a reinforced handle can be formed integrally with the container by having an inner wall member in the recess forming the handle engages the inside of the container wall to prevent the recess from everting due to internal pressure in the container.

Thus, the use of an integral inner wall has two purposes, one is to subdivide the container into several chambers, and the other is to prevent eversion of the recess in the outer wall of said container.

It is an object of the present invention to provide an economical and aesthetically pleasing bottle made of PET or other plastic materials with similar molding properties, such as polycarbonate, polystyrene, etc., which can have Compartments and/or a handhold as part of the side wall of the bottle which deforms in a predetermined manner under the pressure inside the bottle but which, when in use, Will not evert.

This has been achieved in the past, for example as described in US Patent No. 5,232,108, by providing a preform and blow molding said preform in a mold with a cavity dimension corresponding to the final desired container dimension. A disadvantage of this approach is that the blow molded container exhibits a deformation pattern due to the internal pressure generated by the carbonated beverage, whereas the container cannot deform in a similar geometrical manner due to the constraints imposed by the inner walls. If the deformation is too large, the shape of the bottle filled with beverage and under pressure is unacceptable to the consumer who wants to buy the beverage. In the case of a bottle having the aforementioned handle, the handle may be deformed so as to prevent its use.

The above-mentioned problems can be substantially solved by increasing the rigidity of the container when molding the container. This can be achieved, if desired, by increasing the thickness of the walls of the container, but this increases the amount of plastic material used to manufacture the container, which increases costs. In the case of crystalline plastics, such as polyethylene terephthalate (PET), polycarbonate (PC) and nylon, increasing the container wall thickness can lead to undesired structural morphology.

Therefore, a fundamental purpose of the present invention is to provide a blow-molded plastic container for containing pressurized contents and a manufacturing method thereof, especially to provide a container for containing carbonated beverages and having the present Plastic containers with improved shape and/or dimensions based on the containers used and methods for their manufacture.

A further object of the present invention is to provide a container and a method for its manufacture which do not result in undesired structural configurations and which do not unduly increase the cost of the plastic materials required to manufacture the container.

Another object of the present invention is to provide a container and its manufacturing method, if the container has a hand-held part, when filling the container under a certain pressure, for example, when filling carbonated beverages, the hand-held part can be kept. potency.

A further object of the present invention is to provide a method of manufacturing a container with internal compartments created by supporting walls, capable of ensuring a predetermined final shape of said container under a certain internal pressure.

Other objects and advantages of the invention will appear from the following description. Summary of invention

The above objects and advantages of the present invention will be obtained from the following description of the present invention.

The present invention provides a method of molding a blow-molded plastic container for a pressurized liquid, the container having an inner member and an outer wall, the outer wall having an inner surface and an outer surface, the inner member in The intersecting region is connected to the inner surface of said outer wall, the shape of the molded container is different from that of said container for pressurized liquid, and the molded container, once pressurized, can be converted in a predetermined manner to hold pressurized liquid as described above. The shape of the container for the liquid.

The present invention also provides an improved method of making a blow molded plastic container for carbonated beverages, the method comprising: providing a first blow molded container precursor comprising an outer wall and an inner member , the outer wall has an inner surface and an outer surface, the inner element is connected to the inner surface of the outer wall; determining the stress-strain characteristic of the precursor and thereby determining the shape of the precursor under compression; according to said characteristics and determining the shape of a similar container precursor capable of deforming under pressure into the desired shape of said pressurized liquid container; preparing said similar precursor; and imposing a certain internal pressure on said similar precursor pressure to produce a second container having a predetermined shape.

The container of the present invention has many advantages. The container is a blow-molded plastic container having a compartment, the container has at least one inner wall, and the inner wall may further include a handle portion with a support, which is held when the container is filled with a liquid under pressure. The part can achieve the intended effect and get the desired final shape. The container of the present invention is convenient and easy to manufacture and solves the problem of undesired deformation without unduly increasing the weight of the container.

The present invention provides a method of making a blow molded plastic container for carbonated beverages, the method comprising: providing a blow molded plastic precursor having a shape and wall thickness and including an outer wall and an inner an element, the outer wall has an inner surface and an outer surface, the inner element is connected to the inner surface of the outer wall; at several selected locations the mechanical properties of the precursor are determined and when the precursor is subjected to internal pressure Stress distribution around said location under action; preparing a modified precursor by changing at least one of wall thickness and shape of said precursor so as to obtain a desired deformation due to stresses generated by applied internal pressure form; thereby providing the desired blow molded plastic container.

Preferably, the step of modifying the precursor can also reduce the stress concentration so that the stress concentration is limited within a specific range.

Other advantages of the invention will appear from the following description. Description of drawings

For ease of description, the present invention will be described below in conjunction with accompanying drawing, wherein:

Figure 1 is a side sectional view of a preform for making a container of the present invention;

Fig. 1A is a sectional view along line 1A-1A in Fig. 1;

Figure 2A is a partial perspective view of a core used to form the preform of Figure 1;

Figure 2B is a cross-sectional view of a core injection molding system used to form the preform of Figure 1;

Figure 3 is a partial sectional view of a blow mold for forming a container of the present invention using a preform similar to that of Figure 1;

Fig. 4 is the front view of container of the present invention;

Figure 5 is a cross-sectional view of the container shown in Figure 4 along the line 5-5 in Figure 4, wherein the container precursor in the non-filled liquid state and the container filled with carbonated beverage are shown;

Fig. 6 is a partial cross-sectional view of the intersecting part of the inner wall and the outer wall of the container under a certain internal pressure;

Fig. 7 is a partially enlarged cross-sectional view similar to Fig. 6;

Fig. 8 is a partially enlarged sectional view similar to Figs. 6 and 7, showing a modification of the present invention.

preferred embodiment

According to the invention, the inventive container has inner walls capable of forming compartments, and/or recesses and, between said recesses, projections which facilitate handling of the container.

A preform for forming the container may be produced by pressure molding, the preform comprising at least one inner wall at a location corresponding to an inner support element in the final blow molded and pressurized container completely traverses the interior of the preform.

Referring to Figure 1, a plastic parison or preform 10 is formed by compression molding from a synthetic resin, preferably biaxially oriented, such as polyethylene terephthalate. Said preform 10 has a neck 11 defining an opening 12, said preform 10 may be provided with an external thread 13 which may be compatible with the final obtained blow molded plastic container. A cap or closure engages, eg, an optional closure. The preform 10 has a main body portion 14 extending downwardly from the neck 11 and a bottom portion 15 extending downwardly from the main body portion 14 , the bottom portion 15 being integral with the main body portion 14 . The body portion in Figure 1 is generally tubular, but the body portion may also take other configurations than tubular. The neck 11 has an inner wall surface 11A and an outer wall surface 11B, the tubular body portion 14 has an inner wall surface 14A and an outer wall surface 14B, and the bottom 15 has an inner wall surface 15A and an outer wall surface 15B. The body portion 14 defines a cavity 16 within the preform 10 , the cavity 16 being closed at the bottom 15 and open at the neck opening 12 . The bottom 15 can take some desired or conventional shape depending on the desired final container properties, for example the bottom 15 can be a complete semicircle as shown in Figure 1, a flat or slightly inward bottom shape or a A few legs.

The preform 10 has at least one inner wall 17 , possibly two or more inner walls 17 , for example the preform 10 shown in FIG. 1A has two inner walls 17 . Said inner wall 17 completely traverses cavity 16 and extends from said bottom 15 into said tubular body portion 14, said inner wall 17 preferably terminating in said body portion 14, but said inner wall 17 also Can extend into the neck or extend to the edge. As shown in FIG. 1A , the inner wall 17 forms four chambers 17A, 17B, 17C and 17D spaced apart from each other, but these chambers may also communicate with each other above the inner wall 17 . Alternatively, the inner wall 17 may also be limited to an area of the preform 10 which will subsequently form a handhold as described in US Patent No. 5,398,828. As apparent from Figures 1 and 1A, the inner wall 17 engages the inner wall surface 14A. The preform can be made of transparent PET so that the inner wall 17 can be easily seen.

Figures 2A and 2B illustrate a method of making a preform 10 by injection molding, wherein an injection core 20 includes a generally cylindrical outer wall 21 and grooves corresponding to the partitioned inner walls required in the preform twenty two. The core 20 is placed in the injection mold 23 in a conventional manner, and the injection nozzle 24 is placed in the injection mold 23 at a position adjacent to the bottom 25 of the injection core 20 in a manner centered on the injection core 20 . The core 20 is positioned in the injection mold 23 to form a cavity 26 between the core 20 and the injection mold 23 , and the molten plastic 27 is injected into the cavity 26 through the injection nozzle 24 and filled with the molten plastic 27 . Molten plastic 27 will also flow into the groove 22 in the core 20 to form the inner wall 17 . Alternatively, if desired, the inner walls 17 can also be formed separately and then glued to the preform or precursor. Next, the system consisting of the injection mold and core is opened and the preform 10 is removed in a conventional manner.

When the preform is at a temperature suitable for blow molding, as shown in FIG. 3, the hot preform 10 is placed in a blow mold 30, from which A hollow part is formed which serves as a precursor for the container according to the invention, the example shown here being a bottle with a handle.

The hot preform is placed in a blow mold having the shape of the desired container precursor, such as the blow mold 30 shown in Figure 3, and compressed air is blown to cause the preform to move along the axis. extending radially and circumferentially so that the preform expands into a shape 31 corresponding to the precursor, said shape 31 being shown in dashed lines in FIG. 3 . This process can be carried out with or without a tension rod or mandrel for axially extending the preform. If such a rod is used, it should have as many prongs as there are preform chambers, each of which bears in each chamber on the preform bottom. Said wall 17 will extend as far as the blow mold 30 allows. The inside of the blow mold shown in Figure 3 is capable of forming a hollow plastic part which is the precursor of the container 40 shown in Figure 4, the dotted line in Figure 5 showing the protruding part of said precursor section. The blow mold 30 comprises at least two adjacent protrusions connected together by the recesses, the protrusions not shown in the section shown in FIG. 3 . , but the bulge is clearly shown in FIG. 5 .

According to a conventional process, the blow mold is separated along the direction indicated by the arrow in Fig. 3 to remove the blow molded container precursor.

As can be seen from Figure 5, the circumference of the precursor is larger than the circumference of its circumscribed circle. The wall 14 of the preform 10 shown in FIG. 1 is stretched to a greater extent in the region of the recess forming the handle than in other regions. In a preferred embodiment, as shown in Figure 1A, the preform wall may be provided with a thickened portion 19 where the walls 17 and 14 meet. During blow molding, the thickened portion and the recess are juxtaposed so as to minimize stress concentrations that would occur without the thickened portion. The thickened area may also be juxtaposed with an area of the blow mold where the recess can be formed to prevent this area from being too thin.

Like this, the plastic container 40 that utilizes blow molding method to form has a neck 41, a bottom 43 and a body portion 44, wherein said neck 41 defines an opening 42, and said body portion 44 defines said neck 41 and bottom 43 are interconnected. The neck 41 is provided with an external thread 45 corresponding to the thread 13 on the preform 10 for the attachment of a closure device. The bottom 43 may have a base 46 tapered axially inwardly. Said container 40 also comprises a shoulder 47 for connecting said neck 41 and tubular body portion 44 .

The container 40 is provided with at least one inner wall 50 corresponding to the inner wall 17 of the preform 10, said inner wall 50 completely traversing the cavity 51 in the container 40 and extending from the bottom 43 to the body part 44, or It extends from the bottom 43 to the neck to form a container with compartments. The one or more inner walls may also be limited to the handle portion.

It can be seen from Fig. 3 and Fig. 5 that the inner wall is integrally formed with the container. The one or more inner walls may extend all the way to the bottom of the container (as shown in FIG. 3 ), may also start and end within the body portion (as shown in FIG. 4 ), or extend all the way to the neck or opening.

Referring to Figure 5, the body portion 44 has adjacent arcuate projections 60 connected together by a recessed area or recess 61 which is particularly suitable for In the hand-held part as a container of a larger size. Of course, other shapes of hand-held parts can also be provided. Support elements 50 in cavities 51 are associated with the recesses so that the recesses are spaced apart and are able to support the recesses so as to prevent them from everting. As can be seen in Figure 4, the inner wall may terminate at an end within the body portion proximate to the hand-holding portion. In another embodiment shown in FIG. 4 , the container 40 has separate handle portions formed by the concave portion 61 and the protruding portion 60 . Arranged adjacent to them is a support element 50 which can extend as far as the bottom or into the shoulder and supports the recess in the manner described above.

Figures 4 and 5 show another embodiment of a container 40 of the present invention, preferably having a hand-held portion. Figure 5 shows the bulge precursor 52 formed in the blow mould, the dashed line in Figure 5 indicating the boundary between the bulge precursor 52 and the inner support element 50, which The element 50 joins two adjacent recessed areas or recesses 61 at its bottom to prevent said protrusion from expanding at the junction between the support element 51 and the recessed area 61 . In the precursor of the container 40, the protruding portion precursor 52 has an inner wall and a segmented portion 53, the inner wall may be a straight wall or have a little outward taper, as shown by the dotted line in the figure, the inner wall and Segments 53 are joined together by arcuate portions 54, so that when said container precursor is subjected to pressure, for example filled with a carbonated drink, said segmented portions 53 are deformed into arcuate portions 55, said arcuate portions 55 The boundaries of the smaller raised portion 60 may be defined. A similar problem exists for bottles with compartments without handle projections, that is, in said bottle with compartments under pressure, the segmented portion 53 is located between the inner walls. The restrained deformation is a bulge between the inner walls, rather than deformation into a generally circular cross-section, as exhibited by the bottle under pressure.

A main object of the present invention is to design a precursor of the final container so that the precursor is transformed into the desired final container using the above step of applying pressure, the pressure required for the transformation should reach a pressure capable of forming the container. The final shape and achieve the effect of the final container performance.

Therefore, according to the present invention, it is determined by performing static tests and creep tests at different positions on several parts of a precursor sample which are very close in size and shape to the desired precursor at several different ambient temperatures. The mechanical properties of materials used in containers, such as polyethylene terephthalate (PET), especially the need to determine the relationship between tensile stress and deformation under the conditions of changing time, temperature and other factors related to the external environment relation.

The average properties obtained from the tests are not sufficient for the purposes of the present invention. Many properties of a blow molded container will change due to changes in shape and size. These properties depend on the preform structure being fabricated as well as the temperature profile of the preform and other variables during processing of the preform. Thus, during the transformation of the precursor into a container due to internal pressure, the stress and corresponding deformation at critical locations depends on the corresponding stress-strain relationship at a particular location.

In particular, the stress-strain relationship must be determined under static (transient) and creep conditions, taking into account the environmental factors to which the final container may be exposed.

Using a reasonably predicted precursor geometry as a starting point, deformation patterns are measured in a precursor sample under internal pressure. Assuming that the stress-strain information has been determined as described above, the resulting data are used in computerized sample analysis techniques, such as known finite element analysis (FEA), to derive the desired the final container. When FEA is used to obtain the shape of the desired final container and obtain its desired final dimensions, the corresponding stress distribution can also be obtained. For these data to be obtained, the predicted dimensional data of the precursor and the sample of the desired container are provided to the FEA program taking into account the precursor properties and the stress-strain relationship at different locations. For example, while the properties of the inner wall 50 are substantially different from the properties of the outer wall 44, the properties at the intersections of these walls are also substantially different than the properties away from those intersections.

The same applies to the intersection between wall 50 and the bottom wall shown in Figure 4 and other locations where significant variations in wall thickness occur, resulting in the geometry of the precursor and desired final container.

Computer programs such as known as FEA have been used in the design of stressed structural parts, including containers and bottles subject to internal pressure, mainly for predicting the service life of said structural parts performance, including failure analysis. In fact, FEA uses the modulus characteristics of the material used in the structural member to express the linear relationship between the deformation and the stress in a specific structural member, such as Young’s modulus, Poisson’s ratio, characteristics such as creep rate. The FEA generally depends on the modulus eigenvalues as constants in the corresponding equations, but regardless of the structure of the desired final structure and is manufactured under similar circumstances, the modulus eigenvalues are based on a fixed determined experimentally, e.g. by tensile tests using specimens made of the same material. In the case of a complex geometry, where differences in modulus characteristics lead to different implementations, FEA must be employed and is an integral part of the product described here and the manufacturing process for that product.

The FEA can reveal, as part of the stress distribution, areas of stress concentration that can deform beyond the allowable deformation limits of the desired final container, even to the point of causing the container to fail. Such stress concentrations occur, for example, at abrupt changes in wall thickness between one wall thickness and another. It is therefore an object of the present invention, in addition to determining the shape relationship between the precursor and the final container, to detect areas of possible stress concentrations, such as at transition radii and where there are large variations in wall thickness, in order to reduce the The stresses acting on these locations are minimized, thereby avoiding excessive strains in said container when the desired container is subjected to internal stresses.

Figures 6-8 show examples of specific locations where stress concentrations may exist, with morphological features that may provide excessive stress concentrations.

FIG. 6 is a partial cross-sectional view showing the intersection of the inner wall 50 and the outer wall 44 of the container 40 under internal pressure. An extended force F1 acts on the inner wall and a tangential force F2 acts on the outer wall. These forces produce corresponding average tensile stresses at locations other than the intersection points on the cross-sectional area. At the intersection, the stress is several times the above average stress, the magnitude of which depends on several factors, one important factor being the transition radius between the two walls and the microstructure at the intersection. The choice of said transition radius also depends on the necessary design of the preform injection mold.

FEA predicts the maximum stress as a function of the structure and the transition radius, and then makes choices to employ preform and molded bottle conditions that produce allowable stresses, taking into account the material morphology at different locations.

Figure 7 shows an example of the stress concentration produced by the morphology of the precursor. It should be noted that stresses are superimposed, so stresses due to transition radii will be superimposed on stresses due to other factors, such as stresses due to inhomogeneous morphology. Figure 7 shows the same cross-section as Figure 6, which is part of a precursor sample. It can be seen that the web section and resulting material accumulation at intersection location 70 is greater than the web section and material accumulation at locations 71 and 72 . Therefore, the crystal structure 70A in the regular circular area in FIG. 7 is coarse-grained spherical along the length direction of the intersection point, and the crystal structure 70A can be used as an effective gap in other fine-grain sections, thereby forming a stress concentration . Additionally, the orientation of region 70 differs due to its volume and subsequent response to heating. It can be overstretched to a point of dehiscence, and/or have mostly spherical crystallinity and thus act as a notch.

Differences in stretch ratios can result in different levels and types of crystallinity. In this embodiment, a significant difference in deformation temperature in blow molding between the two walls increases. The properties of crystalline plastics such as PET depend primarily on their crystalline orientation. When there is a significant difference in crystallographic orientation in the same structure, the structure is stressed, with an effect similar to that which occurs in the case of a structural break, such as a notch.

Particular attention is paid to position 70 in FIG. 7 where material build-up of the preform, precursor and final container can result in a significant difference in the conditions required to heat the preform prior to blow molding. Therefore, it is desirable that the region near region 70 reach a higher temperature than the central or core portion of region 70 in the same amount of time. This is valid for variants of preforms and precursors where there are significant differences between corresponding parts of the precursor and/or final container. Again, there is a notch effect.

FEA can be used to justify dimensional corrections to avoid these gaps only if it is based on a detailed analysis of stress-strain data at these critical locations.

Generally, for a good precursor, there must be a sufficient transition radius and the same wall thickness at the intersection between the walls, and when using PET material, the difference in crystal morphology of the precursor must also be judged.

FIG. 8 is a cross-sectional view similar to FIGS. 6 and 7 showing an embodiment of the invention for adjusting the cross-section of the precursor at the intersection, wherein on the outer surface 75 of the outer wall 74 adjacent to the An outer groove 73 is provided at the intersection of the inner element 76 and said outer wall 74 .

It should be understood that the present invention is not limited to the content shown in the above description and accompanying drawings, which are only descriptions of the preferred embodiments of the present invention, and details of the shape, size and arrangement of various parts and operations can be modified. Make improvements. Various improvements made to the present invention within the protection scope defined by the claims will fall within the protection scope of the present invention.

Claims (7)

1. a manufacturing is used for the method for the blow molding plastic containers (40) of splendid attire soda, this method comprises: a blow molding precursor (31) is provided, described precursor has definite shape and wall thickness and comprises an outer wall and an inner wall element (50,76), described outer wall has inner surface and outer surface, and described inner wall element links to each other with the inner surface of described outer wall; Measure mechanical performance in the several selected position of described precursor and be subjected near the stress distribution definite described position under the internal pressure effect at described precursor; Wall thickness by changing described precursor and at least one in the shape provide an improved precursor so that obtain desirable because of applying the form of distortion that stress that internal pressure produces causes; Thereby provide desirable blow molding plastic containers (40).

2. the method for claim 1 is characterized in that, the described step that precursor is changed reduces that stress is concentrated so that stress is concentrated is limited in the specific scope.

3. the method for claim 1 is characterized in that, determines that the stress distribution of described precursor under the internal pressure effect is to design a kind of desirable blow molding plastic containers.

4. method as claimed in claim 3 is characterized in that, described method comprises makes one and the very similar precursor (31) of described desirable blow molding plastic containers (40); Described precursor (31) is pressurizeed and determines stress distribution and distortion in the described precursor.

5. method as claimed in claim 4 is characterized in that, utilizes the finite element analysis method to determine described stress and deformation behaviour according to the performance profile of described precursor.

6. the method for claim 1 is characterized in that, described method is included in that the intersection point place near described inner wall element (76) and described outer wall is provided with a groove (73) on the outer surface of described outer wall (74).

7. method as claimed in claim 6 is characterized in that, described groove is designed so that at the structural form at described intersection location place even substantially.

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