Abstract:
A method and an injection mold for carrying out the method. The method according to this invention allows for a collar made of plastic to be injected molded onto an insert part having a circumferential edge. According to this invention, the insert part is inserted into a receptacle cavity of an injection mold. In a first step, plastic webs directed radially outward are formed and then mobility or means of the injection mold are lowered, the bottom part of the collar is completely formed and finally, in a third injection step, a top plastic layer of the collar is formed at the top on the edge.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    This invention relates to a method for producing an insert part with an edge running perpendicular to a central axis of the insert part, at which edge a collar made of plastic can be provided by an injection mold, including at least one upper and one lower plate with mobility or mobile ability. 
         [0003]    2. Discussion of Related Art 
         [0004]    In the case of disposable containers, such as cups or bowls, attempts are made for economic and ecological reasons to design these containers as thin-walled as possible. If these containers are designed particularly thin-walled, they exhibit only a very small dimensional stability. This dimensional stability is usually achieved by the fact that, especially in the case of cups or bowls made of plastic, the upper edge is formed thickened or flanged. If such containers are produced deep-drawn from a film material, such flanging or thickening is virtually impossible to produce. 
         [0005]    If a hot drink is poured into a disposable plastic cup, it is difficult for the user to hold it without burning fingers of the user. Also, the dimensional stability of the cup is again or further reduced by the raised temperature. 
         [0006]    Accordingly, disposable cups are also produced from foamed plastic, in particular from foamed polystyrene, which has a relatively high insulating effect. With these cups, on the other hand, there is one problem that these foamed cups are perceived as inconvenient by many users and in addition the edge of the cup is not extremely dimensionally stable and so small parts of the foamed material break away and are also drunk or consumed by the user. The holding strength of a lid made of another material pushed onto such a cup is also insufficient. 
         [0007]    In the foodstuffs industry, various products are filled into bowls made of plastic. Because these products often have a tendency towards oxidation, it is not sufficient simply to push on a lid. Instead, an aluminium foil is usually pressed onto the product and a lid is then placed over the latter. Because the aluminium foil is placed slightly oversized precisely onto the food that is filling the bowl, this is not a complete seal. The plastic lid pushed onto the bowl likewise does not represent an airtight closure. Such an airtight closure could be produced with a suitably selected foil that is welded on or sealed with the cup or the bowl. However, since such bowls are very thin-walled, they are not suitable for a weld joint and other thermal seals usually cannot be produced either, because the bowls are made from a specially selected plastic with a UV radiation-blocking layer and are not thus suitable for a welded or sealing joint. 
         [0008]    One problem as such has been known for a very long time, and suggestions have already frequently been put forward to provide such containers subsequently with a special collar, which is produced from another plastic which has a much greater strength than the material from which such disposable cups or bowls are produced. Most solutions proceed on the basis that the cup is regarded as an end product and a separate plastic part fixable on the edge of this bowl is produced, after which the two parts are then jointed together mechanically and possibly also welded or glued. A corresponding solution is known for example from French Patent Reference FR-2175094 A. Furthermore, U.S. Patent Reference US 2012/0318858 shows a paper cup, which can be pushed in a form-fit manner into a plastic part which comprises a plastic collar with a cup-shaped portion open at the lower side, wherein the cup wall comprises a plurality of grooves running approximately up to the collar in order thereby to form a holding region not lying directly adjacent to the paper cup. 
         [0009]    Similarly, European Patent Reference EP 0453754 A2 discloses a container, in particular a drinks cup, with a container body preferably made of plastic, paper or the like, which comprises an upper circumferential edge for forming an opening, wherein a circumferential collar made of a compact material is assigned to this upper edge. 
       SUMMARY OF THE INVENTION 
       [0010]    There is believed to be no container known from the prior art that has a circumferential edge that is inserted as an insert part in an injection mold and on which a circumferential plastic collar is directly injection molded. 
         [0011]    For technical reasons, this is relatively complex because insert parts are relatively unstable and very light due to their thin-wall nature. It is thus extremely complex to hold such an insert part in an injection mold in such a way that the edge of the container can be overmolded from all three sides. 
         [0012]    One problem is solved by a method of the type mentioned at the outset with steps described in this specification and in the claims. This method is based on the knowledge that, during the injection process, webs are first injected at the lower part of the edge of the insert part while the cup is pressed against the upper injection molding plate, and these still plastic webs have sufficient load-bearing capacity to hold the extremely light insert part in position, even if a corresponding part of such an injection mold no longer supports the circumferential edge, and the collar can then be overmolded all round. The individual injection steps can correspondingly take place with a time overlap. It is also one object of this invention to provide an injection mold which is suitable for performing the method according to this invention. Such an injection mold is disclosed in this specification and in the claims. 
         [0013]    When, in the present case, mention is made of an insert part, it relates to a thin-walled unstable container with a circumferential edge running at least approximately perpendicular to the central axis of this container. The insert part can be made of paper, aluminium foil, or paper or plastic, wherein it can be both a deep-drawn container made of the plastic film, as well as a container made from a correspondingly formed aluminium foil. The edges of such insert parts are typically unstable and usually relatively imprecise in terms of shape. It is one advantage of this invention that such insert parts can be formed into a precise container, which then acquires a stable edge and overall becomes a relatively stable container. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    The appended drawing represents in cross-section one preferred embodiment of an injection mold suitable for performing the method, as well as a symbolic representation to explain the method according to the invention, wherein: 
           [0015]      FIG. 1  shows a partial cross-section through a lower plate of an injection mold in the position before the insert part is inserted; 
           [0016]      FIG. 2  shows the same view as  FIG. 1  but with an inserted insert part; 
           [0017]      FIG. 3  shows a situation after a first injection has been carried out; 
           [0018]      FIG. 4  shows a mold after retraction of the supporting sleeve with the omission of the insert part; 
           [0019]      FIG. 5  shows the situation according to  FIG. 4  but with the insert part and after the second injection is carried out; 
           [0020]      FIG. 6  shows the same view as in the preceding Figures, but after the third injection has been carried out; 
           [0021]      FIG. 7  shows a simplified representation of the injection mold, the position during the first injection being represented here; and 
           [0022]      FIG. 8  shows the situation in which the third injection has been carried out. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0023]    The structure of an injection mold suitable for performing the method according to this invention is first described by reference to  FIGS. 7 and 8 .  FIGS. 7 and 8  show a simplified representation of an injection mold as a partial cross-section in the region in which an insert part is produced with a collar made of plastic. The injection mold is referred to as a whole by element reference numeral  1 . It usually comprises two plates, such as a lower plate  2  and an upper plate  3 . A slide  4  can be seen in upper plate  3 . A slide  5  is also represented in cross-section in lower plate  2 . At least one receptacle cavity  7  is present in lower plate  2 , an insert part  20  being received therein. This insert part can be inserted into receptacle cavity  7  when upper plate  3  with slide  4  is raised sufficiently far. In the case of an injection mold with a single receptacle cavity, insert part  20  is inserted manually for cost reasons. In the case of larger injection molds  1  with a plurality of receptacle cavities  7 , insert part  20  is inserted by a handling robot. Such devices or handling robots, with which insert parts are introduced into injection molds, are sufficiently well known, and their representation and description can accordingly be dispensed with. In this case, all the cooling channels, heating channels and injection units are also omitted, just like the various mechanical parts in order to operate the slide, or to move upper and lower plate  3 ,  2 . In any case, only the upper plate is usually moved, while the lower plate remains stationary. 
         [0024]    Reference is made to  FIG. 1  for the explanation of the method according to this invention.  FIG. 1  represents lower plate  2  on a smaller scale than in  FIGS. 7 and 8 , once again in a partial cross-section. Slide  5  can be seen in this cross-section, which preferably comprises a cylindrical sleeve, which is denoted by element reference numeral  8  and upper end  9  of which comprises slots, so that cylindrical sleeve  8  forms pins  10  running in an axial direction above closed end  9 , the upper ends of said pins being able to be pushed out of lower plate  2 . In the situation represented here, slide  5  is in its upper position in which support platelets  11 , which are the upper ends of pins  10 , extend out of the lower plate upwards into the receptacle cavity. Lower plate  2  of the injection mold comprises corresponding channels, in which these pins  10  can be moved in a sliding manner. Plate  2  is continuous between individual pins  10 . 
         [0025]    In the position as represented in  FIG. 1 , slide  5  is in an upper position. Pins  10  project with their upper ends, which form support platelets  11 , out of lower plate  2 , but beneath parting plane T. Parting plane T denotes the plane which forms the closing surface of injection mold  1  when lower plate  2  and upper plate  3  lie one upon the other in a sealing manner in the injection position. In this position, there remains, apart from receptacle cavity  7 , a cavity  12  in which material finds space for the first injection to be carried out for the collar that is to be formed on the insert part. This cavity can clearly be seen in  FIG. 1  and in.  FIG. 7 . Cavity  12  extends from an edge region between support platelets  11  approximately up to the inner edge of receptacle cavity  7 . 
         [0026]      FIG. 2  shows the same partial view of injection mold  1  as in  FIG. 1 , with insert part  20  however already lying in receptacle cavity  7  here. Peripherally outwardly formed edge  21  of insert part  20  rests, as represented here, on the edge of cavity  12  for the collar that is to be formed. When cylindrical sleeve  8  of slide  5  is in the lower position, edge  21  of insert part  20  lies on lower plate  2 , if slide  5  or cylindrical sleeve  8  is located in the upper position, on support platelets  11 . As soon as insert part  20  is inserted into receptacle cavity  7 , injection mold  1  closes and upper and lower plate  2 ,  3  lie directly upon one another in parting plane T. Edge  21  is held in a clamped manner between the two slides  4 ,  5 . Thus, slide  4  in upper plate  3  presses on edge  21 , while slide  5  or support platelets  11  press edge  21  towards upper slide  4 . 
         [0027]    The first injection of plastic takes place in this position. A first part of the peripheral region of the circumferential collar and the webs of plastic are hereby formed, which extend from this peripheral region of collar  22  beneath edge  21  almost up to the side wall of insert part  20 . This is most clearly shown in.  FIG. 3 , in which it can be seen that, after this first injection has been carried out, peripheral cavity  12  is already filled, as is concentric edge region  13  of cavity  12 . The filled region of the webs between adjacent support platelets  11  cannot be seen in this representation, because in this view the cross-section runs through a pin  10  of the cylindrical sleeve of slide  5 . 
         [0028]    Once this first injection has been completed, slide  5  in the lower plate  2  is lowered and support platelets  11 , which are in principle the upper end faces of pins  10 , lie flat and flush with the upper face of lower plate  2  in the region of cavity  12 . In this position represented in  FIG. 4 , insert part  20  is not represented for the sake of clarity and the view is correspondingly free onto receptacle cavity  7  in which insert part  20  itself would rest. 
         [0029]      FIG. 5  represents a situation whereby the second injection is completed. As a result of the lowering of slide  5  or cylindrical sleeve  8  with pins  10 , an additional space is freed that can be filled during the second injection. During this time, insert part  20 , which is again represented in this  FIG. 5 , initially rests only on the webs formed after the first injection, whereas in the second injection the intermediate spaces between the webs, which have become free by the lowering of support platelets  11 , are filled. Collar  22  that is to be formed on insert part  20  comprises, after this second injection, a completely covering area beneath edge  21  of insert part  20  and the peripheral part of collar  22 , which adjoins in an adhering manner the peripheral end face of edge  21  of the insert part. 
         [0030]    In a further step, which can be seen most clearly in  FIG. 8 , upper slide  4  in the upper plate  3  is also raised and peripheral collar  22  is completed with a third injection. A plastic layer  23  of collar  22  is formed in the third injection. This upper plastic layer  23  can, as represented in  FIG. 6 , only be a flat top layer, which covers the peripheral region of collar  22  and the part lying towards the center, and thus also edge  21  of insert part  20 . 
         [0031]    The plastic will be selected depending on the conditions that the insert part has to meet in the finished state. There is a wide variety of possible variations here. In the simplest case, the first, second and third injection will all be carried out with the same plastic. However, the first and second injection can perfectly well be carried out with the same plastic, while the third injection is carried out with a plastic differing from the latter, which for example is particularly well suited for applying a weld thereon, or a plastic can be used that has particularly elastic properties in order to achieve a form-fit connection as elastic as possible for the seal with a lid to be placed thereon. In principle, however, all three injections can be carried out with different plastics. Thus, in certain circumstances it may be advisable to carry out the second injection with a plastic which has a higher strength in the cooled and hardened state than the plastic that has been used in the first injection. This is particularly advisable if the insert part is an insert part made of particularly unstable material, such as for example paper or paperboard. The injection molded collar then endows the insert part with a much greater strength through its rigid collar, which can be produced according to the method of this invention. 
         [0032]    Even though, for the sake of clarification, the method is described here in such a way that the individual injection steps are each completed in themselves, and then the next injection procedure takes place, these injection steps can in actual fact virtually merge into one another. This is particularly the case when two such injection steps following one another and take place with the same plastic. In particular, the second injection can already take place towards the end of the first injection. In other words, the webs between support platelets  11  are filled very quickly during the injection of the first step and very quickly achieve, thanks to suitable cooling of the injection mold, sufficient load-bearing capacity to hold the very light insert part in place. Even before the end of the first injection, support platelets  11  can already be lowered and these intermediate spaces can thus also be filled by the virtually interruption-free first and second injection. 
         [0033]    If the third injection is carried out with the same plastic as the first and second injection, slide  4  in the upper plate can already be pulled upwards towards the end of the second injection and the third injection can be started. 
         [0034]    If the three injections all take place with the same plastic where these injections will also be carried out by the same injection nozzles, the individual injections in this case also virtually merge into one another interruption-free. The individual steps will in this case take place primarily through the movement sequence of the two slides  4  and  5 . 
         [0035]    If the method is considered, for example, with regard to the movement sequence of the two slides  4 ,  5 , the mold is closed after the insertion of insert part  20  into receptacle cavity  7 , the two slides  4  and  5  are moved towards one another and insert part  20  is clamped in the region of its edge  21 . This is followed immediately by the first injection and, after cavity  12  is partially filled, lower slide  5  is lowered and injection is continued, this now being the second injection. As soon as this second injection is for the most part completed, slide  4  in the upper plate is raised and the second injection transforms directly into the third injection. 
         [0036]    As already mentioned, these injections merging into one another are only possible to a limited extent depending on which plastic combinations are used, or the individual steps actually have to be completed in themselves. 
       LIST OF REFERENCE NUMBERS 
       [0000]    
       
           1  injection mold 
           2  lower plate 
           3  upper plate 
           4  slide in upper plate 
           5  slide in lower plate (cylindrical sleeve) 
           7  receptacle cavity for insert part 
           8  cylindrical sleeve 
           9  upper end of the sleeve 
           10  pins 
           11  support platelets 
           12  cavity for collar to be formed 
           13  concentric edge region of the cavity 
           20  insert part 
           21  edge of the insert part 
           22  collar on the insert part 
           23  upper plastic layer of the collar