CA2869447A1

CA2869447A1 - Injection molded container made of plastic

Info

Publication number: CA2869447A1
Application number: CA2869447A
Authority: CA
Inventors: Guido POEHLS
Original assignee: Knauer Holding GmbH and Co KG
Current assignee: Vva Verpackung Vertriebs- und Absatz AG
Priority date: 2012-04-11
Filing date: 2013-04-11
Publication date: 2013-10-17
Anticipated expiration: 2033-04-11
Also published as: EP2836347B1; PL2836347T3; HUE029251T2; DE102012103082B4; CA2869447C; ES2573836T3; DK2836347T3; WO2013153142A1; DE102012103082A1; US20150060471A1; EP2836347A1

Abstract

The invention relates to an injection molded cup-shaped container (1) made of plastic, comprising a bottom (2) and a container wall (3), which have a uniform thickness, from which bead-like thickenings (4) protrude inward or outward, which thickenings start at a gate location in the bottom (2), have a radial course on the bottom (2), and extend on the container wall (3) at a slant to the top edge (5) of the container (1). The bead-like thickenings (4) on the container wall (3) and on the bottom (2) are designed in such a way that the thickenings do not cross and each have a radius of curvature having a constant sign.

Description

INJECTION MOLDED CONTAINER MADE OF PLASTIC
[0001] The invention relates to an injection-moulded plastics container comprising a bottom and a container wall, the container wall and the bottom each having a uniform thickness, from which ridge-like thickenings protrude inwards or outwards, which thickenings start from a gate mark in the bottom, have a radial course on the bottom and extend obliquely on the container wall towards the top edge of the container.

[0002] Such a container is known from DE 72 27 210 U. Said container is a pot produced by injection moulding. To keep material costs for the pot to a minimum, contours are formed in the pot wall which keep the pot wall, which should have as low a thickness as possible, sufficiently rigid. Various configurations are provided for the contours, such as lines extending straight towards the top edge of the pot, honeycombs, helices, optionally with crossing points.

[0003] Thin-walled pots are known which are produced by the thermoforming method, also known as extrusion or deep-drawing method, in which granular material is processed to form films from which the packaging parts are then drawn. This method is limited in terms of accuracy of shape and wall distribution, and is restricted in terms of possible geometries and functions such as stacking of the products.

[0004] Another type of particularly thin-walled containers is produced by means of injection moulding methods. Generally, in this injection moulding method a plastics granular material is liquefied and injected into a cavity at high pressure in the shortest possible time. The plastics material is cooled in the cavity. The cooling re-hardens the liquid plastics material. When the mould is opened, the finished packaging can be removed or ejected.

[0005] One advantage of the injection moulding method is relatively high accuracy along with a large degree of freedom in terms of shape. A large number of different geometries can be produced. The only requirement is the dennouldability of the parts, i.e. ensuring that it is possible to remove the produced part from the mould.

[0006] Following production of the product, pots and other plastics containers are conventionally printed on, labelled and/or sleeved, in other words enveloped with a heat shrink.

[0007] Nowadays, pots produced by means of injection moulding are no longer normally decorated afterwards. Instead, pre-printed films are inserted into the injection mould. This makes it possible to produce a finished product in one operation.
This approach is referred to as the in-mould labelling method (IML). Attempts are currently being made to also use the IML method in thermoforming methods. With the current state of development, however, this causes significant loss of speed in the thermoforming method, since the packaging that has already been moulded first has to be demoulded before films can be inserted. With injection moulding, on the other hand, the film is inserted into the mould on one side and the completely moulded and decorated part is removed preferably parallel on the other side, which may be the tool side.

[0008] One drawback of the IML method is that the available cross section of the cavity is disadvantageously reduced by the insert. The wall-flow ratio, in other words the ratio of the longest flow path to the average wall cross section, gets worse. As a result, premature hardening of the melt can occur sooner, and this increases the risk of the mould not being completely filled. To compensate for this effect and to obtain form-fitting containers, it is necessary in line with the current state of the art to select a relatively thick wall thickness. This leads to increased material use and heavier pots, the result being higher costs for material and for transport of the produced pots.

[0009] DE 26 14213 A1 discloses a method for improving filling. This method aims to prevent premature hardening by means of pulsating pressure changes. In this case, however, relatively large wall thicknesses would be necessary when using the IML
method. The wall thicknesses of the pots thus produced would not be optimal.

[0010] Pots are known which have various different flow promoters orientated in the flow direction. As a result, the melt flow is facilitated in the flow direction by means of flow promoters. This leads to improved filling, and therefore relatively thin-walled pots can be produced. The flow promoters form ridge-like thickenings leading vertically upwards in the pot. One drawback of these pots, however, is that the flow promoters cause the plastics material to advance at a significantly higher speed during production, and this leads to non-uniform filling of the regions to be filled last. The wall thickness of the pot becomes less uniform.

[0011] The non-uniform filling, in an I ML method, of the regions to be filled last also means that the plastics material flows behind or in front of the insert. This leads to uncontrolled covering of the insert, which is known as back-injection. The advance leads to visual degradation of the overall impression of the pot. In addition, when the wall thickness is reduced, there is the risk of air being entrapped owing to the higher advance speeds in the flow promoters, and this entrapment of air can lead to a lack of a form fit.

[0012] DE 20 46 958 describes a pot which attempts to solve the problem of non-uniform filling, in that the flow promoters, referred to as ribs, form an intersecting lattice.
By defining the rib thicknesses to be closer relative to the wall thickness elsewhere, a container is produced which has uniform filling of the wall surfaces with a likewise uniform rib thickness.

[0013] The rib structure of the pot in this invention is rhomboid. If the rhombi are attached on the outside, in an IML method the labels to be attached will also have a rhomboid structure. This leads to relatively poor legibility of the label and perception of the contents, depicted thereon, of the container. If the ribs are attached on the inside, removal from the moulds is practically impossible. A rhomboid shape on the inside of pots is not desirable either. Smooth inner sides allow the contents that has been filled in to be completely removed. The rhomboid shape, however, impairs removal, since the contents can only be removed with difficulty from the rhombi between the intersecting ribs, and can probably not be removed completely. There is the risk that the contents cannot be completely removed.

[0014] With regard to this prior art, an object of the invention is to provide a container that is thin-walled and sturdy and can be produced in a mechanical production process in a simple and cost-effective manner.

[0015] This object is achieved by a generic container, in which the ridge-like thickenings are formed such that they do not cross on the container wall and on the bottom, and each comprise a radius of curvature of constant sign. The course of said thickenings is thus as diagonals or lines bent in one direction. This allows the containers to be produced having a very thin container wall by means of an injection moulding method.
The ridge-like thickenings are produced along flow promoters which are provided in the injection mould and provided according to the shape of the ridge-like thickenings. Owing to the shape, according to the invention, of the flow promoters, a uniform flow front of the plastics material is ensured during the production process. As a result, entrapped air owing to premature hardening of the plastics material is prevented.

[0016] This course of the ridge-like thickenings deflects the melt flow such that, in the regions at risk of premature hardening or freezing, the melt flow is protected against premature hardening owing to cross-sectional reinforcement and maintenance of the fluid centre. This causes the melt front to flow almost uniformly into all regions to be filled. Uniform filling is thereby ensured. At the same time, molten plastics material is also prevented from advancing too quickly into the regions of the flow promoters and running back down. This saves unnecessary material on the one hand and, in an IML
method, also prevents the insert element from being partly covered by dripping plastics material in the regions in which an insert element has been applied, or prevents the insert element from being back-injected owing to the faster advance of the liquid plastics material, since the plastics material flows behind the insert element in an uncontrolled manner.

[0017] Owing to the course, according to the invention, of the ridge-like thickenings of the pot, simple demoulding of the pot is also ensured. Since the ridge-like thickenings are only curved in one direction, the pot can be removed from the mould simply, by a rotation movement, and without the risk of damage. This means that the method can be carried out in a completely automatic manner to the end, and therefore the method is simplified and costs can be reduced. Complete removal of a material with which the container is filled during use is also facilitated by the shape, according to the invention, of the ridge-like thickenings.

[0018] According to an advantageous development of the invention, the inclination of the ridge-like thickenings on the container wall is selected such that the angle of inclination N relative to the bottom is for example between 30 and 60 . This allows particularly good results to be achieved in terms of a flow front of the plastics melt with a constant speed, so that the container has the desired thin, smooth, resilient and sturdy side wall. It can also be advantageous if the radius of curvature of the ridge-like thickenings increases towards the top edge of the container. As a result, the vertical and thus leading components of the liquid plastics material can be reduced further towards the end of the process, it being possible thereby to achieve an even more uniform and thinner container wall of the container. It is advantageous if the ridge-like thickenings have a constant and at least partly round cross section. The cross section can be half-round, round or even oval. This ensures high stability and simple removal from the mould.

[0019] According to an advantageous development of the invention, branches starting from the ridge-like thickenings are provided, the length and cross section of which branches are smaller than the length and cross section of the ridge-like thickenings, the branches not crossing one another or the thickenings.

[0020] The size and orientation of the ridge-like thickenings produced by the flow promoters are tailored to the desired product and requirements and is determined according to the most favourable wall-flow ratio and the material used for the specific container to be produced. To ensure uniform wall thickness even in products having a relatively large surface area, it is additionally expedient in individual cases to branch the ridge-like thickenings in a similar manner to the vascular system of the human body or to provide smaller branches or branches of the same size that branch from the respective main arm of the respective flow promoter at any given angle according to requirements and size of the product to be injection-moulded. As a result, the container then has a blood-vessel-like system of thickenings, either on the inner wall or the outer wall of the container as desired. The uniform distribution, made possible thereby, of the plastics material over the entire region of the container ensures that the entire wall of the container is filled with plastics material. At the same time, back-injection of potential insert elements is prevented.

[0021] Advantageously, a thickening is provided on the top edge of the container and is formed cohesively with the container wall. This ensures a sturdy region of the container, to which region a lid can be applied.

[0022] According to an advantageous embodiment of the invention, the container wall comprises a first region in which the ridge-like thickenings have a greater cross section than in the second region, whereby the container wall has a greater height in the first region than in the second region. According to another advantageous embodiment of the invention, the container wall comprises a first region in which the ridge-like thickenings are closer together than in a second region, whereby the container wall has a greater height in the first region than in the second region. Owing to the arrangement and configuration, used in this case, of the flow promoters, accelerated flow and later hardening of the melt front is brought about in the first region of the container wall during the production process. As a result, more plastics material is filled into these regions.
The ability of the melt front to flow for a longer period of time allows for a longer pot wall.
A container is produced that has different length walls yet is filled completely. The ridge-like thickenings on the longer container surfaces are designed to be thicker, and those on the shorter container surfaces are correspondingly thinner. This ensures that, apart from the ridge-like thickenings, the wall thickness is as uniform and as thin as possible.

[0023] According to an advantageous embodiment of the invention, an insert element, in particular a paper strip, a plastics strip or a film, is permanently connected to the container in a label region on the outer side of the container wall as a result of the injection moulding method. The container has been produced by means of an IML
method, in which the insert element is inserted into the injection mould before the molten plastics material in injected into the injection mould. In this regard, the uniform course of the melt front as a result of the arrangement, according to the invention, of the flow promoters and the ridge-like thickenings is particularly advantageous, since the insert elements are connected to the container in a simple manner in the production process, without said elements being covered by plastics material or having plastics material run behind them. Completely legible labels can thus be applied to the container in a permanent, smooth, reliable and simple manner.

[0024] Advantageously, containers can be formed having different edge lengths of the insert element, since it is possible, owing to different designs of the flow promoters, to provide the flow front to all ends of the insert at the same time within the mould. This allows for containers having correspondingly variable insert elements while being filled completely.

[0025] According to the invention, the container can also comprise a different material than plastics material, provided that the material is suitable for processing in an injection moulding method. The exact course of the flow promoters, along with their shape, cross section, density, number, and shape and number of the branches, can be optimised according to the invention in that these and similar dimensions can be optimised mathematically for specific product requirements, such as the size of the container, the desired or required wall thickness, the desired thickness and shape of the upper container end or the thickening on the top edge of the container, etc.

[0026] Further details, features and advantages of the present invention can be found in the following description of a preferred embodiment with reference to the drawings, in which:

[0027] Fig. la to Fig. ld are schematic views of the production of an embodiment of a container according to the invention during the production method.

[0028] Fig. la to ld show the production of a container 1. The shaping relevant for the container 1 is shown schematically by an injection mould (not shown in greater detail).
The cavity of the injection mould is designed to shape the container 1 to have a bottom 2 and a container wall 3. Ridge-like thickenings 4 are provided on the bottom 2 and on the container wall 3 in regions provided therefor and protrude out from the bottom 2 and the container wall 3. In the intermediate regions between the ridge-like thickenings 4, the bottom 2 and the container wall 3 of the container 1 to be produced have a uniform thickness. On the bottom 2, the ridge-like thickenings 4 are formed radially.
In the embodiment shown, said thickenings extend in point symmetry with respect to the centre M of the bottom 2 and are slightly curved, the sign of the radius of curvature not changing. The ridge-like thickenings 4 on the container wall 3 extend obliquely from the bottom 2 towards the top edge 5 of the container 1 and are bent in one direction, said thickenings having a radius of curvature, the sign of which does not change. A

thickening is provided on the top edge 5 of the container 1, to which thickening a lid can be applied. The ridge-like thickenings 4 have a constant and round cross section. In the embodiment shown, the arrangement is selected to be axisymmetrical to the perpendicular through the centre M of the bottom 2, so as to produce a symmetrical container 1.

[0029] Fig. la shows a first step of the injection moulding method for producing the container 1. Liquefied plastics material or another material suitable for this method is injected into the cavity of the injection mould at a gate mark located at the centre M of the bottom 2, and spreads out axisymmetrically to the perpendicular through the centre M. In the process, the ridge-like thickenings 4 form flow promoters. Owing to the shape and arrangement of the flow promoters, the flow front of the liquid plastics material spreads out uniformly and at a constant flow speed until the bottom 2 is uniformly covered, as shown in Fig. lb. Owing to the uniform melt flow of the plastics material, the bottom 2 of the pot 1 has a uniform thickness in the regions between the thickenings 4.
As shown in Fig. lc, the liquid plastics material rises upwards, uniformly and at a constant speed, along the flow front by means of the flow promoters on the container wall 3 as far as up to the top edge 5, the container 1 shown in Fig. ld being produced.
In the process, the thickening on the top edge 5 is filled with plastics material. The container wall 3 has a constant uniform thickness in the regions between the ridge-like thickenings 4. The ridge-like thickenings 4 are selected depending on the product requirements. They can also be formed such that the bottom has a different thickness than the container wall.

[0030] In the cavity of the injection mould, an insert element can be inserted in the region of the container wall, which element is rigidly connected to the plastics material and thus to the container wall 3 during production. Owing to the uniform flow of the plastics material, the insert element adheres rigidly to the surface of the container wall 3 and is not covered with plastics material.

[0031] The problem is solved by the present invention by means of specific shaping and orientation of the flow promoters (also termed supply ridges) which are designed as ribs or ridge-like thickenings in the container. During the production process, the faster advance, which begins, of the plastics material is guided over the surfaces to be filled via an optimum course of the flow promoters, so that ridge-like shapes in the form of the flow promoters are produced in a mirror image. The ridge-like shapes are not orientated, or not exclusively orientated, in the flow direction, but rather, according to requirements, are guided around the mould of the container to be produced, in a curved shape or in diagonal positions or, depending on the size and the need to maintain the flowability, in oblique positions relative to the flow direction.

[0032] The supply ridges are introduced in the device, in particular in the injection moulding tools. Here, it is unimportant in terms of the container and the production thereof whether said ridges are attached on the inside or on the outside. In this respect, the present invention differs significantly from the solution described in DE

B2, in which, because of the need to ensure demouldability, it is compulsory for the ribs to be positioned on the outside since shrinkage always has be taken into consideration during production. This shrinkage means that the rhombi effectively attach themselves to the mould. With rhombi on the inside, demoulding is not possible without causing destruction.

[0033] By means of the optimum course of the ridge-like thickenings, which course can be determined according to the product requirements, the melt flow is deflected from the actual flow direction during production, such that the flowable plastics material flows in a targeted manner, through cross sections which have been adapted accordingly in terms of size, until it reaches the desired regions in which premature hardening would occur without appropriate assistance. This technical solution means that the melt flows almost uniformly into all regions, even those to be filled last. Depending on the production requirements in terms of size and desired or required wall thickness and depending on the desired thickness and shape of the upper end region of the pot, the ridge-like thickenings are laid out as paths, so that during production the plastics material is deflected from the actual flow direction in the manner required in each case.
A container is produced that has correspondingly oblique ridge-like thickenings and low wall thickness at the same time. With the exception of the ridge-like thickenings, which are due to the technical requirements within the scope of the production process, said wall thickness is kept as low as possible by the targeted deflection of the plastics material from the flow direction.

[0034] A container that has a particularly thin wall is thus made possible.
The ridge-like thickenings are located on the inside. The ridge-like thickenings do not cross; they are in an oblique position relative to the pot wall. The pot can be demoulded by a rotation movement counter to the oblique direction of the ribs. If demoulding is not possible or not completely possible by a rotation movement either owing to the arrangement of the ridge-like thickenings or the shape of the container, in the event of instantaneous demoulding following production demoulding can be carried out completely or in part by being rapidly slipped over the device owing to the low wall thickness and the flexibility as a result of the residual heat.

[0035] The invention is applicable in particular in the following areas: food containers, in particular pots for holding foodstuffs which are liquid or viscous but which solidify after filling, provided the foodstuffs to be filled into the containers are not corrosive to plastics materials; other containers and pots or products, in particular for holding liquid, viscous or such substances that are not corrosive to plastics material and that solidify after being filled in a liquid or viscous state, or containers for holding solid substances or products.

Claims

1. Injection-moulded plastics container (1) comprising a bottom (2), a container wall (3) and an insert element which is rigidly connected to the container in a label region on the outside of the container wall (3), the container (1) being produced by means of an IML method, and the bottom (2) and the container wall (3) having a uniform thickness, from which ridge-like thickenings (4) protrude inwards or outwards, which ridges start from a gate mark in the bottom (2), have a radial course on the bottom (2) and extend on the container wall (3) obliquely towards the top edge (5) of the container (1), wherein the ridge-like thickenings (4) do not cross on the container wall (3) and on the bottom (2), and are formed such that as flow promoters they ensure a uniform flow front of the plastics material during the production process.

2. Container according to claim 1, characterised in that the ridge-like thickenings (4) are formed such that, during the production process, the flow front of the liquid plastics material spreads out on the bottom (2) and on the container wall (3) at a constant speed in each case.

3. Container according to either of the preceding claims, characterised in that the course and the cross section of the ridge-like thickenings (4) are optimised for specific product requirements.

4. Container according to any of the preceding claims, characterised in that the ridge-like thickenings (4) have a constant and at least partly round cross section.

5. Container according to any of the preceding claims, characterised in that branches starting from the ridge-like thickenings (4) are provided, the length and cross section of which branches are smaller than the length and cross section of the ridge-like thickenings (4), the branches not crossing one another or the thickenings.

6. Container according to any of the preceding claims, characterised in that a thickening is provided on the top edge (5) of the container (1) and is formed cohesively with the container wall (2).

7. Container according to any of the preceding claims, characterised in that the container wall (3) comprises a first region in which the ridge-like thickenings (4) have a greater cross section than in the second region, whereby the container wall (3) has a greater height in the first region than in the second region.

8. Container according to any of the preceding claims, characterised in that the container wall (3) comprises a first region in which the ridge-like thickenings (4) are closer together than in a second region, whereby the container wall (3) has a greater height in the first region than in the second region.

9. Container according to any of the preceding claims, characterised in that the label has different edge lengths and, during production of the ridge-like thickenings, is shaped such that the flow front of the melt is provided to all ends of the label at the same time.