CH719139A1 - Extrusion blown plastic container. - Google Patents

Abstract

The invention relates to an extrusion-blown plastic container, comprising a container body which is closed with a container base and a container neck (17) which delimits a pouring opening (19). At the open end (37) of the container neck (17), a step (39) extending in the circumferential direction and having a calibrated sealing surface (41) is embossed on the outside thereof.

Description

field of invention

The invention relates to an extrusion-blown plastic container according to the preamble of claim 1, a sealing system according to the preamble of claim 7 and a method for ensuring the dimensional accuracy of the open end of a plastic container neck according to the preamble of claim 16.

State of the art

Containers which are produced using the extrusion blow molding process have the advantage, among other things, that the production speed is high and handles can be formed. Due to the process, the dimensional accuracy of the pouring opening is lower compared to injection molding. This makes it difficult to close the pouring opening in a liquid-tight manner with a closure cap alone. In order to ensure reliable sealing of the pouring opening, extrusion blow-moulded containers are used for filling goods such as milk, juices and the like. usually closed with a sealing film. The sealing film also fulfills the function of a first opening guarantee. The sealing foil increases the production costs considerably due to the additional material requirement and the additional work step of sealing the pouring opening.

object of the invention

The disadvantages of the prior art described result in the task of creating a container closure through which a reliable seal between the closure cap and the extrusion blow molded container is achieved without a sealing film being necessary.

Description

The solution to the problem is achieved with an extrusion-blown plastic container by the features listed in the characterizing section of claim 1. Further developments and/or advantageous embodiment variants are the subject matter of the dependent patent claims.

The invention is preferably characterized in that at the open end of the container neck on the outside of a circumferentially extending step is embossed with a calibrated sealing surface. The embossing gives the sealing surface a high degree of dimensional accuracy and can be used together with a screw cap to seal the pouring opening of an extrusion-blown plastic container reliably and at least in a liquid-tight manner. This has the great advantage that there is no need for a sealing foil attached to the open end of the container neck for sealing purposes. In particular, if the sealing foil is made of aluminum, the manufacturing costs can be significantly reduced. In addition, the sealing film is not present when the container is disposed of or recycled.

In a particularly preferred embodiment of the invention, a sealing ring with an outer wall, an inner wall and a head surface extending between the outer wall and the inner wall is formed at the open end of the container neck, the calibrated sealing surface corresponding to the outer wall. The sealing ring can provide 3 sealing surfaces for sealing the pouring opening when it interacts with a corresponding closure, thereby optimizing the sealing effect between the container neck and the screw cap.

The invention is also preferably characterized in that the sealing ring is free of burrs. Burrs, which occur when the neck of the container is deflashed, contribute to a sealing surface that is not dimensionally accurate and therefore unreliable. In contrast to this, the sealing ring is sufficiently dimensionally accurate for reliable sealing of the pouring opening. Vertical burrs, which are caused by the forming tool, are also removed by the special cutting ring geometry.

In a further particularly preferred embodiment of the invention, the step is embossed with a cutting ring, which cutting ring serves to separate a slug formed on the container neck during extrusion blow molding. No further process step is required to form the step, which is stamped at the same time as the slug is removed. As a result, the stage is produced without any additional expenditure of time.

A retaining ring is expediently formed on the outside of the container neck below the step to interact with a plastic screw cap and below the external thread. As a result, the container neck can interact with a standardized plastic screw cap to seal the pouring opening and to attach a guarantee ring.

It has proven to be useful if the extrusion-blown plastic container is made of HDPE or PP. These polymers are very suitable for extrusion blow molding. The calibrated sealing surface also enables the pouring opening of relatively thin-walled container necks to be sealed with a screw cap.

A further aspect of the invention relates to a sealing system with the above-described extrusion-blown plastic body and a plastic screw cap with which the pouring opening can be closed in a sealing manner. As described above, the sealing system does not require an additional sealing foil.

An outer sealing jacket and an inner sealing jacket expediently protrude from the top plate on the inside of the head plate and a groove running in the circumferential direction is formed between the sealing jackets. The sealing ring is accommodated in this groove in the screwed-on or pressed-on position of the screw cap and is surrounded by the groove, as a result of which the largest possible sealing surface is produced.

It is preferred if the inner sealing jacket is higher than the outer sealing jacket. As a result, the sealing ring is automatically centered in the groove during the vertical movement of the screw cap.

In a further preferred embodiment of the invention, the inner sealing jacket exerts pressure in the radial direction on the sealing ring in the unwound position. This strengthens the sealing function. In addition, the radial pressure is transferred from the sealing ring to the outer sealing jacket, as a result of which the sealing effect can be improved even further. In addition, the radial pressure causes the sealing ring to stabilize in the groove, which means that leaks due to relaxation (reduction of material stress in the container neck) can be prevented.

The invention is also preferably characterized in that a first sealing surface is realized between the outer sealing jacket and the outer wall of the sealing ring, a second sealing surface is realized between the base of the groove and the top surface, and between the inner sealing jacket and the inner wall of the Sealing ring, a third sealing surface is realized.

In addition, a fourth sealing surface can preferably be realized between a first horizontal surface of the step and a second horizontal surface of the outer sealing jacket. Due to the burr-free and dimensionally accurate design of the sealing ring, up to 4 sealing surfaces can be used, which on the one hand increases the sealing surface as such (multiple or labyrinth seal) and on the other hand "freezes" the applied stresses and can thus prevent leaks through relaxation.

Advantageously, a guarantee ring with predetermined breaking webs is held on the jacket on the underside of the jacket and the guarantee ring engages under the retaining ring with inwardly projecting retaining projections. As a result, the tamper evidence can be guaranteed even without the presence of a sealing film.

Another aspect of the invention relates to a method for ensuring the dimensional accuracy of the open end of a container neck on a plastic container produced in an extrusion blow molding process. The dimensional stability or accuracy is achieved in that the cutting ring has a stamping extension with which a step extending in the circumferential direction with a calibrated sealing surface is stamped on the outside of the open end of the container neck when the cutting ring is axially inserted into the slug at the open end of the container neck. The embossing extension does not form burrs like prior art cutting rings do. In addition, the embossing extension smooths out burrs that occur in the blow molding tool on the container neck. Another advantage of the embossing extension is that no further process step and no further tool is required to emboss the step.

Further advantages and features emerge from the following description of an embodiment of the invention with reference to the schematic representations. In a representation that is not true to scale: FIG. 1 shows a side view of an extrusion-blown container; FIG. 2: an enlarged side view of the container neck; FIG. 3: a side view of a plastic screw cap; FIG. 4: a sectional illustration of the closure from FIG. 3; FIG. 5: a perspective sectional view of the container neck and the screwed-on screw cap; Figure 6 is a side view showing the prior art severing of a slug in the neck area; FIG. 7: a detailed view of a container neck and a screw cap according to the prior art; FIG. 8: a side view showing the separation of a slug in the neck area with an adapted cutting ring; and FIG. 9: a detailed view of the container neck and the screw cap according to the present sealing system.

An extrusion-blown plastic container is shown in FIG. The container 11 has a container body 13 which is closed by a container bottom 15 . The container body 13 transitions into a container neck 17 which encloses or delimits a pouring opening 19 .

On the outside of the container neck 17 an external thread 21 and below the external thread 21 a retaining ring 23 is formed. A handle 25 may be formed on the container body 13 . The plastic container 11 can be extrusion-blown from HDPE (high density polyethylene) or PP (polypropylene).

A plastic screw cap 27 can be screwed onto the container neck 17 in order to seal the pouring opening 19 . The closure 27 has a cylindrical casing 29 and a head plate 31 in the shape of a circular disk. The jacket 29 protrudes from the head plate 31 and has an internal thread 33 formed on its inside. Preferably, the closure 27 is injection molded.

The container 11 and the closure 27 form a sealing system 35 which enables the closure 27 to close the pouring opening tightly and in particular in a liquid-tight manner. This is done without an additional sealing film being necessary to close the pouring opening and even though the container neck 17 is extrusion blow molded.

To realize the sealing system 35, the container neck 17 requires improved dimensional accuracy, which cannot be achieved by extrusion blow molding alone. Only improved dimensional accuracy leads to reliable sealing surfaces between the container neck 17 and the screw cap 27.

At the open end 37 of the container neck 17 a step 39 is stamped. The step 39 is located on the outside of the container neck 17 and extends in the circumferential direction. The step 39 has a calibrated sealing surface 41 and a first horizontal surface 43. The step 39 is embossed with a cutting ring 45b, which cutting ring 45b serves to sever a slug 46 formed on the container neck 17 during extrusion blow molding (FIG. 8). The embossing of the step 39 creates a sealing ring 47 on the neck end 37. The outer wall of the sealing ring 47 corresponds to the sealing surface 41. The sealing ring 47 also has an inner wall 49 and a head surface 51 which extends between the walls 41,49. The embossing means that the sealing ring 47 is free of burrs, which significantly improves its dimensional accuracy and sealing ability.

On the inside of the top plate 31 protrudes from an outer and an inner sealing jacket 53.55. A groove 57 is formed between the sealing jackets 53, 55 and runs in the circumferential direction. The sealing ring 47 is accommodated in the groove 57 when the closure 27 is pressed on or screwed on for the first time. The inner sealing jacket 55 is higher than the outer sealing jacket 53, which makes it easier to receive and center the sealing ring 47 in the groove 57.

A first sealing surface 59 is realized between the outer sealing jacket 53 and the outer wall 41 of the sealing ring 47 . A second sealing surface 63 is implemented between the base 61 of the groove 57 and the top surface 51 . A third sealing surface 65 is realized between the inner sealing casing 55 and the inner wall 49 of the sealing ring 47 . A sealing system in the form of a labyrinth seal is implemented by the three sealing surfaces 59,63,65. The inner sealing jacket 55 can be designed in the shape of a cone. As a result, when the closure 27 is applied, the inner sealing jacket 55 generates a compressive force on the sealing ring 47 which is also transmitted to the outer sealing jacket 53 . As a result, the sealing effect between the sealing ring 47 and the groove 57 is further improved. In addition, a change in the dimensions or tension of the sealing ring 47 over time (“relaxation”) is prevented by being fixed on both sides.

The total sealing surface can be increased even further if a fourth sealing surface 69 is realized between the first horizontal surface 43 of the step 39 and a second horizontal surface 67 of the outer sealing jacket 53 . Accordingly, leaks in the sealing system 35 are reliably prevented on the one hand by maximizing the dimensionally accurate sealing surfaces and on the other hand by stabilizing the material stresses (avoiding relaxation) in the sealing ring 47 .

The present sealing system 35 also allows the use of a first-opening guarantee with a guarantee ring 71, as is known from stretch-blown PET bottles. Accordingly, the guarantee ring 71 is held on the underside of the casing 29 with predetermined breaking webs 73 on the casing. The guarantee ring 71 engages under the retaining ring 23 with inwardly projecting retaining projections 74. When the closure 27 is rotated for the first time, the predetermined breaking points 73 break, as a result of which the initial opening can be recognized by the broken predetermined breaking points 73 and the increased turning resistance when opening.

The step 39 is stamped by the cutting ring 45 during the separation of a slug 46 from the container neck 17 . FIG. 6 shows the separation of the slug 46 according to the prior art. First, a section of a plastic hose extruded in one or more layers through an extrusion die is placed in a mold cavity of a blow molding tool. The section of the hose is inflated according to the enclosed mold cavity by means of a blowing mandrel. The finished inflated plastic container is demoulded. Then the slug 46 that inevitably forms on the container neck 17 is severed between a neck knife 75 and a cutting ring 45a that moves into the slug 46 in the axial direction. A calibration sleeve 76 is retracted within the neck 17 . According to the prior art, a burr 77 develops at the open end 37 of the container finish, which reduces the dimensional accuracy of the container finish. Accordingly, such a container neck is unsuitable for sealing by cone sealing systems.

An embossing extension 79 is present on the cutting ring 45b according to FIG. When the cutting ring 45b is moved axially into the slug 46 at the open end 37 of the container neck, this is used to stamp the step 39 with the calibrated sealing surface 41 extending in the circumferential direction on the outside thereof. The sealing system 35 described above can be used because the open end is now burr-free and a calibrated, precisely dimensioned sealing surface 41 is present. Thin-walled container necks can also be sealed with the present sealing system. This sealing system is preferred for non-carbonated juices and milk products.

Because the present sealing system does not require a sealing film, it has significantly lower packaging costs than prior art sealing systems for extrusion blown containers. In addition, the recyclability increases and the sealing system 35 is compatible with future regulations that require the plastic screw cap to be held captive on plastic containers after opening for the first time.

Legend:

11 Extrusion-blown plastic container 13 Container body 15 Container bottom 17 Container neck 19 Pouring opening 21 External thread 23 Retaining ring 25 Handle 27 Plastic screw cap 29 Cylindrical jacket 31 Circular disc-shaped top plate 33 Internal thread 35 Sealing system 37 Open end of the container neck 39 Embossed step 41 Calibrated sealing surface 43 First horizontal surface 45 a,45b cutting ring 46 slug 47 sealing ring 49 inner wall 51 head surface 53 outer sealing jacket 55 inner sealing jacket 57 groove 59 first sealing surface 61 base of the groove 63 second sealing surface 65 third sealing surface 67 second horizontal surface 69 fourth sealing surface 71 guarantee ring 73 predetermined breaking bars 74 retaining projections 75 neck knife 76 calibration sleeve 77 burr 79 embossing extension

Claims (16)

Claims 1. Extrusion blown plastic container (11). - a container body (13) which is closed with a container bottom (15), and - a container neck (17) delimiting a pouring opening (19), characterized in that that at the open end (37) of the container neck (17) on the outside thereof a circumferentially extending step (39) with a calibrated sealing surface (41) is embossed. 2. Container according to claim 1, characterized in that at the open end of the container neck (17) there is a sealing ring (47) with an outer wall (41), an inner wall (49) and between the outer wall (41) and the inner wall (49) extending head surface (51), wherein the calibrated sealing surface corresponds to the outer wall (41). 3. Container according to claim 2, characterized in that the sealing ring (47) is free of burrs. 4. Container according to one of the preceding claims, characterized in that the step (39) is embossed with a cutting ring (45b), which cutting ring (45b) serves to separate a slug (46) formed on the container neck (17) during extrusion blow molding . 5. Container according to one of the preceding claims, characterized in that on the outside of the container neck (17) below the step (39) an external thread (21) for cooperation with a plastic screw cap (27) and below the external thread (21) a retaining ring ( 23) is formed. 6. Container according to one of the preceding claims, characterized in that the extrusion-blown plastic container (11) is made of HDPE or PP. 7. Sealing system (35) with - A container (11) having a container body (13) which is closed with a container bottom (15) and a container neck (17) which delimits a pouring opening (19), and - Having a plastic screw cap (27) with which the pouring opening (19) can be closed in a sealing manner a cylindrical jacket (29) which protrudes from a circular disc-shaped top plate (31), characterized, in that the container is an extrusion-blown plastics container (11) according to any one of the preceding claims. 8. Sealing system according to Claim 7, characterized in that on the inside of the head plate (31) an outer sealing jacket (53) and an inner sealing jacket (55) protrude from the head plate (31) and between the sealing jackets (53, 55) there is an in Circumferentially extending groove (57) is formed. 9. Sealing system according to claim 8, characterized in that the sealing ring (47) is accommodated in the groove (57) in the unscrewed position of the screw cap (27). 10. Sealing system according to claim 8 or 9, characterized in that the inner sealing jacket (55) is higher than the outer sealing jacket (53). 11. Sealing system according to one of claims 8 to 10, characterized in that the inner sealing jacket (55) is conical. 12. Sealing system according to one of claims 8 to 11, characterized in that the inner sealing jacket (55) exerts a pressure in the radial direction on the sealing ring (47) in the unwound position. 13. Sealing system according to one of claims 8 to 12, characterized in that a first sealing surface (59) is realized between the outer sealing jacket (53) and the outer wall of the sealing ring (47), between the base (61) of the groove (57) and the top surface (51) has a second sealing surface (63) and a third sealing surface (65) is formed between the inner sealing jacket (55) and the inner wall of the sealing ring (47). 14. Sealing system according to one of claims 8 to 13, characterized in that a fourth sealing surface (69) is realized between a first horizontal surface (43) of the step (39) and a second horizontal surface (67) of the outer sealing jacket (53). 15. Sealing system according to one of claims 7 to 14, characterized in that a guarantee ring (71) with predetermined breaking webs (73) is held on the jacket (29) on the underside of the casing (29) and the guarantee ring (71) has the retaining ring ( 23) with inwardly projecting retaining projections (74). 16. Method for ensuring the dimensional accuracy of the open end (37) of a container neck (17) on a plastic container (11) produced in an extrusion blow molding process, in which a section of a plastic hose extruded through an extrusion nozzle in one or more layers is placed in a mold cavity of a blow molding tool and a blow mandrel is inflated according to the enclosed mold cavity, the completely inflated plastic container (11) is removed from the mold and the slug (46) produced on the container neck (17) is placed between a neck knife (75) and a cutting ring ( 45a, 45b) is separated characterized in that that on the cutting ring (45b) there is an embossed extension (79) with which, when the cutting ring (45b) is moved axially into the slug (46) at the open end of the container neck (17), a step (39 ) is stamped with a calibrated sealing surface (41).