Patent Publication Number: US-2015060471-A1

Title: Injection molded container made of plastic

Description:
CROSS-REFERENCE TO PRIOR APPLICATIONS 
     This application is a U.S. National Phase Application under 35 U.S.C. §371 of International Application No. PCT/EP2013/057543, filed on Apr. 11, 2013, and claims benefit to German Patent Application No. DE 10 2012 103 082.0, filed on Apr. 11, 2012. The International Application was published in German on Oct. 17, 2013, as WO 2013/153142 A1 under PCT Article 21(2). 
    
    
     FIELD 
     The invention relates to an injection-molded plastic container. 
     BACKGROUND 
     Such a container is known from DE 72 27 210 U. Said container is a pot produced by injection molding. 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. 
     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. 
     Another type of particularly thin-walled containers is produced by means of injection molding methods. Generally, in this injection molding method a plastic granular material is liquefied and injected into a cavity at high pressure in the shortest possible time. The plastic material is cooled in the cavity. The cooling re-hardens the liquid plastic material. When the mold is opened, the finished packaging can be removed or ejected. 
     One advantage of the injection molding 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 demoldability of the parts, i.e. ensuring that it is possible to remove the produced part from the mold. 
     Following production of the product, pots and other plastic containers are conventionally printed on, labelled and/or sleeved, in other words enveloped with a heat shrink. 
     Nowadays, pots produced by means of injection molding are no longer normally decorated afterwards. Instead, pre-printed films are inserted into the injection mold. This makes it possible to produce a finished product in one operation. This approach is referred to as the in-mold 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 molded first has to be demolded before films can be inserted. With injection molding, on the other hand, the film is inserted into the mold on one side and the completely molded and decorated part is removed preferably parallel on the other side, which may be the tool side. 
     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 mold 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. 
     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. 
     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 plastic 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. 
     The non-uniform filling, in an IML method, of the regions to be filled last also means that the plastic 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. 
     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. 
     SUMMARY 
     An aspect of the invention provides an injection-molded plastic container, comprising: a bottom; a container wall; and an insert element which is rigidly connected to the container in a label region on an outside of the container wall. The container is produced by in-mold labelling process. The bottom and the container wall have a uniform thickness. Ridge-like thickenings protrude inwards or outwards from the bottom and the container wall. The ridge-like thickenings start from a gate mark in the bottom, have a radial course on the bottom, and extend on the container wall obliquely towards a top edge of the container. The ridge-like thickenings do not cross on the container wall and on the bottom. The ridge-like thickenings are formed as flow promoters configured to provide a uniform flow front of the plastic material during the in-mold labeling process. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
       The present invention will be described in even greater detail below based on the exemplary figures. The invention is not limited to the exemplary embodiments. All features described and/or illustrated herein can be used alone or combined in different combinations in embodiments of the invention. The features and advantages of various embodiments of the present invention will become apparent by reading the following detailed description with reference to the attached drawings which illustrate the following: 
         FIG. 1   a  to  FIG. 1   d  are schematic views of the production of an embodiment of a container according to the invention during the production method. 
     
    
    
     DETAILED DESCRIPTION  
     The rib structure of the pot in this invention is preferably a 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 molds is practically impossible. A rhomboid shape on the inside of pots is not desirable either. Smooth inner sides allow the contents that have 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. 
     An aspect of the invention provides a container that is thin-walled and sturdy and can be produced in a mechanical production process in a simple and cost-effective manner. 
     An aspect of the invention provides an injection-molded plastic 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. 
     An aspect of the invention provides a 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 molding method. The ridge-like thickenings are produced along flow promoters which are provided in the injection mold 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 plastic material is ensured during the production process. As a result, entrapped air owing to premature hardening of the plastic material is prevented. 
     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 plastic 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 plastic 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 plastic material, since the plastic material flows behind the insert element in an uncontrolled manner. 
     Owing to the course, according to an aspect of the invention, of the ridge-like thickenings of the pot, simple demolding of the pot is also ensured. Since the ridge-like thickenings are only curved in one direction, the pot can be removed from the mold 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. 
     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 plastic 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 plastic 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 mold. 
     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. 
     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 favorable 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-molded. 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 plastic material over the entire region of the container ensures that the entire wall of the container is filled with plastic material. At the same time, back-injection of potential insert elements is prevented. 
     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. 
     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 plastic 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. 
     According to an advantageous embodiment of the invention, an insert element, in particular a paper strip, a plastic 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 molding method. The container has been produced by means of an IML method, in which the insert element is inserted into the injection mold before the molten plastic material in injected into the injection mold. 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 plastic material or having plastic material run behind them. Completely legible labels can thus be applied to the container in a permanent, smooth, reliable and simple manner. 
     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 mold. This allows for containers having correspondingly variable insert elements while being filled completely. 
     According to the invention, the container can also comprise a different material than plastic material, provided that the material is suitable for processing in an injection molding 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 optimized according to the invention in that these and similar dimensions can be optimized 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. 
       FIG. 1   a  to  1   d  show the production of a container  1 . The shaping relevant for the container  1  is shown schematically by an injection mold. The cavity of the injection mold 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 center 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 center M of the bottom  2 , so as to produce a symmetrical container  1 . 
       FIG. 1   a  shows a first step of the injection molding method for producing the container  1 . Liquefied plastic material or another material suitable for this method is injected into the cavity of the injection mold at a gate mark located at the center M of the bottom  2 , and spreads out axisymmetrically to the perpendicular through the center 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 plastic material spreads out uniformly and at a constant flow speed until the bottom  2  is uniformly covered, as shown in  FIG. 1   b.  Owing to the uniform melt flow of the plastic material, the bottom  2  of the pot  1  has a uniform thickness in the regions between the thickenings  4 . As shown in  FIG. 1   c,  the liquid plastic 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. 1   d  being produced. In the process, the thickening on the top edge  5  is filled with plastic 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. 
     In the cavity of the injection mold, an insert element can be inserted in the region of the container wall, which element is rigidly connected to the plastic material and thus to the container wall  3  during production. Owing to the uniform flow of the plastic material, the insert element adheres rigidly to the surface of the container wall  3  and is not covered with plastic material. 
     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 plastic 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 mold 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. 
     The supply ridges are introduced in the device, in particular in the injection molding 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 20 46 958 B2, in which, because of the need to ensure demoldability, 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 mold. With rhombi on the inside, demolding is not possible without causing destruction. 
     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 plastic 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 plastic 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 plastic material from the flow direction. 
     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 demolded by a rotation movement counter to the oblique direction of the ribs. If demolding 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 demolding following production demolding 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. 
     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 plastic materials; other containers and pots or products, in particular for holding liquid, viscous or such substances that are not corrosive to plastic material and that solidify after being filled in a liquid or viscous state, or containers for holding solid substances or products. 
     While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive. It will be understood that changes and modifications may be made by those of ordinary skill within the scope of the following claims. In particular, the present invention covers further embodiments with any combination of features from different embodiments described above and below. Additionally, statements made herein characterizing the invention refer to an embodiment of the invention and not necessarily all embodiments. 
     The terms used in the claims should be construed to have the broadest reasonable interpretation consistent with the foregoing description. For example, the use of the article “a” or “the” in introducing an element should not be interpreted as being exclusive of a plurality of elements. Likewise, the recitation of “or” should be interpreted as being inclusive, such that the recitation of “A or B” is not exclusive of “A and B,” unless it is clear from the context or the foregoing description that only one of A and B is intended. Further, the recitation of “at least one of A, B, and C” should be interpreted as one or more of a group of elements consisting of A, B, and C, and should not be interpreted as requiring at least one of each of the listed elements A, B, and C, regardless of whether A, B, and C are related as categories or otherwise. Moreover, the recitation of “A, B, and/or C” or “at least one of A, B, or C” should be interpreted as including any singular entity from the listed elements, e.g., A, any subset from the listed elements, e.g., A and B, or the entire list of elements A, B, and C.