Abstract:
A multilayer tube shoulder and method for manufacture wherein a first material component is injected into a cavity ( 22 ) and then removed from the cavity on a support ( 12 ) while in a partly-plastic state. Thereafter, following insertion of the first material component into a second cavity ( 23 ), a second material component is injected around the first material component, and thereby leads to a positive connection between the first and second material components.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to a multilayer tube shoulder for a tube and to a method for the manufacture of such tube shoulders according to the preambles of the independent claims.  
           [0002]    The prior art discloses numerous tube shoulders for tubes. Currently, such tube shoulders are almost exclusively made from thermoplastic material by injection molding and are then welded to the tubular tube body in a further operation.  
           [0003]    Certain plastics, such as polyethylene (PE), have a considerable permeability for oxygen, carbon dioxide and odorous/aromatizing substances. In the case of tube shoulders made from these materials, undesired substances diffuse or pass out of the tube into the environment or pass from the environment into the tube, which is prejudicial to the substance introduced into the tube. In order to prevent this harmful permeability, tube shoulders generally have a two-layer structure, comprising an outer, shaping layer and an inner barrier layer.  
           [0004]    The material generally used for the shaping layer is polyethylene (PE), while the barrier layer material is polyethylene rerephthalate (PET). The fact that these materials do not adhere to one another constitutes one of the main problems in the rational, economic manufacture of tube shoulders.  
           [0005]    The use of multilayer tube shoulders of PE and PET has been adopted. Thus, the prior art discloses numerous attempts to rationally and economically manufacture known, multilayer tube shoulders. U.S. Pat. No. 4,185,757 discloses one such attempt. However, none of the known solutions is completely satisfactory. Since tube shoulders are mass produced articles, the price is mainly determined by two factors: cost/material consumption and cycle time for manufacture. The tube shoulders known from the prior art on the one hand have an excessive material consumption, which has a negative effect on the consumption of resources, and therefore costs and environmental compatibility. On the other hand they cannot be manufactured rationally, because they require long cycle times. In fact, certain tube shoulders even require several injection molds and several operations, which amounts to a poor utilization of the machines and molds.  
           [0006]    The problem of non-mutually adhering materials has in the prior art led to inefficient or even impracticable solutions. As e.g. in U.S. Pat. No. 4,185,757, these are based on filigree undercuts and keys or wedges, which are intended to bring about a positive connection between the inner barrier layer and the outer, shaping layer of a tube shoulder. These undercuts and keys e.g. comprise mutually corresponding grooves and ribs, which are generally made at right angles to the symmetry axis of the tube shoulder and are so constructed that they must be forcibly demolded.  
           [0007]    Another multilayer tube shoulder is described in European patent application EP-130 239. This application teaches a multilayer tube shoulder having an inner barrier layer adhering by friction to an outer, shaping layer. This arrangement is unsatisfactory for various reasons. Firstly, the two layers must be combined in a separate operation. Secondly, there is no reliable hold between the two parts. Thirdly, the parts require increased manufacturing precision, which, inter alia, takes into account the differing shrinkage behavior of the materials.  
           [0008]    The parts of the above-described tube shoulders can generally only be further processed after complete cooling. It is also necessary to manually join the individual parts in a separate operation. Thus, the prior art arrangements lead to the manufacturing process for the corresponding tube shoulders being directly and completely decelerated.  
         SUMMARY OF THE INVENTION  
         [0009]    The present invention is directed toward a tube shoulder and method for making a tube shoulder that avoids the disadvantages discussed in conjunction with the aforementioned prior art. On the one hand, by means of the present invention, drastic material reductions are possible and, on the other hand, the manufacturing time is greatly reduced and optimized, leading to a better utilization of the invested resources.  
           [0010]    Unlike in the prior art, which is generally based on a forced demolding (removal from the mold) of cooled parts, in the present invention there is no need to wait until the material of the first component has cooled. Instead, further processing takes place when the first part is in the uncured state. Accordingly, the present method provides considerable time saving while greatly reducing material consumption because the layers of the tube shoulder disclosed here, unlike with the conventional tube shoulders, are made significantly thinner.  
           [0011]    In further accordance with the present invention, further processing the first component of the tube shoulder can be done before the material has completely cured. Therefore, the present production-optimized design of the tube shoulder does not, unlike the known designs, constrain the production cycles. Undercuts or filigree keys, which are difficult to remove from the mold or which must even be forcibly de-molded, are not needed in the present ivnetion. Rather, the inventive design utilizes generously dimensioned contact faces between the individual parts of the tube shoulder that are arranged so that no forced de-molding is necessary and, therefore, leads to a very simple construction of the injection mold. The design is also optimized such that material shrinkage has no negative effect on manufacturing precision.  
           [0012]    The present invention makes it possible, for the first time, for a first material component to be injected in a first cavity of an injection mold and to remove said first material component, before the material has cured or completely hardened, from the first cavity. Then, after release, a second component of another material is injected around the first material, either in a second cavity of the first injection mold or a second injection mold, so as to obtain a strong mechanical connection between the first and second material components.  
           [0013]    The first material component in the first cavity is injected on a support, which is designed to transport or convey partly plastic material. Following injection of the first phase, the support with the partly plastic material of the first component is removed from the first cavity and introduced into the second cavity. The material of the second component is injected and positively joined to the first component. Prior to the injection of the material of the second component, there is a release of the material of the first component. This is a mechanical process wherein, by means of a slider or a functionally equivalent element, a certain area or surface of the first material component is freed, so that the material of the second component in this area engages in undercutting manner around the material of the first component following the second injection process. As a result of the thus formed mechanical stop, a positive connection is obtained between the first material component and the second material component. This release preferably takes place in a very large-area manner.  
           [0014]    Compared with the prior art the invention has two vital advantages. On the one hand the material consumption of a two-layer tube shoulder is massively reduced and, on the other hand, the cycle time during manufacture is drastically decreased.  
           [0015]    The present invention is also suitable for integrally joining a tube body to the tube shoulder in a first step. This tube body can be supplied as an extraneous part from the outside to the processing operation. This additional step advantageously takes place in a further cavity or is combined with one of the steps in which the first or second material component is produced. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]    The invention is described in greater detail hereinafter relative to a preferred embodiment and the attached drawings, wherein show:  
         [0017]    [0017]FIG. 1 diagrammatically shows a preferred embodiment of a tube shoulder in a perspective sectional view.  
         [0018]    [0018]FIG. 2 diagrammatically shows a sequence of a tube shoulder manufacturing process. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0019]    [0019]FIG. 1 shows a preferred embodiment of a tube shoulder  1  in a perspective sectional view. The tube shoulder  1  comprises an outer layer  2  and an inner barrier layer  3 . Preferably the outer layer  2  is of polyethylene (PE) and the barrier layer  3  of polyethylene terephthalate (PET). The outer layer  2  is primarily used for shaping the tube shoulder  1  and the barrier layer  3  serves to seal the tube shoulder  1 . The two materials of the outer layer  2  and barrier layer  3  will typically not melt, fuse, or bond with one another. In order, despite this, to bring about a mechanical connection, the outer layer  2  engages, or extends around, the barrier layer  3 , here at a lower face  4  and an upper face  5 , so that a large-area, positive connection is formed between the outer layer  2  and the barrier layer  3 . The inner layer is essentially captured by the outer layer. The use of the method described relative to FIG. 2 is made possible by the represented embodiment of the tube shoulder  1  as a result of the inventive construction, which deliberately avoids small undercuts and the like.  
         [0020]    As a result of the inventive construction of the tube shoulder  1 , in which all the mechanical connections between the outer layer  2  and barrier layer  3  are in large-area form, it is possible to release the barrier layer in a mold  10  while the material of said barrier layer  3  is still partly plastic. With filigree or difficultly demoldable undercuts (e.g. undercuts which must be forcibly demolded) this is not possible. The presently disclosed invention is therefore based on a design of tube shoulders permitting an optimum, large-area and unforced demolding, without undercuts. The individual steps of the manufacturing process are diagrammatically represented in FIGS. 2 a ) and  2   b ).  
         [0021]    [0021]FIG. 2 a ) diagrammatically shows a sectional representation through an injection mold  10  for the manufacture of the tube shoulder  1  shown in FIG. 1. The injection mold  10  here comprises a base body  11 , which has two openings  20  and  21 . Two, here identical, rotationally symmetrical cores  12 . 1  and  12 . 2  and two identical, annular release elements  14 . 1  and  14 . 2  engage from below and in sealing manner in the openings  20  and  21 , so as to form a first cavity  22  and a second cavity  23 . The first cavity  22  corresponds to the negative of a barrier layer  3  according to FIG. 1. The second cavity  23  corresponds to the negative of a barrier layer  3  and an outer layer  2 .  
         [0022]    By means of a first runner or port  25  molten plastic of a first material component, preferably PET, is injected into the first cavity  22 , so as to form a barrier layer  3  according to  
         [0023]    [0023]FIG. 1. Before the plastic material of the barrier layer  3  has cured, the core  12 , release element  14  and partly plastic barrier layer  3  are drawn out of the opening  20 . This process is illustrated by an arrow  30 .  
         [0024]    As shown in FIG. 2 b ), subsequently the release element  14  is so displaced (arrow  37 ), that there is a release of a lower surface  4  of the barrier layer  3 . The core  12 , release element  14  and barrier layer  3  are subsequently sealingly inserted into the second opening  21  of the injection mold  10  (FIG. 2 a ). This is diagrammatically represented by an arrow  31 . By means of a second runner or port  26 , a second material component is injected around the released barrier layer  3  formed by the first material component that a strong, mechanical connection is formed. At least one face, preferably an annular face  4 ,  5  (cf. FIG. 1), serves as a mechanical stop. The second material component forms an outer layer  2  according to FIG. 1.  
         [0025]    The entire sequence is represented here in a highly diagrammatic manner and is, in practice, advantageously incorporated into a reversing mold with typically two cavities  20  and two cores  14 . 1  and  14 . 2 . The two cores  14 . 1  and  14 . 2  are simultaneously used. As a result of the tube shoulder design according to the invention and the resulting unforced release of the first material component in a partly plastic state, compared with conventional tube shoulders, it is possible to achieve a massive reduction of cycle times and material consumption. Also, the barrier layer can be made very thin, because the core  14  acts as a shaping support, thereby saving material costs.  
         [0026]    At the end of a manufacturing cycle the release element  14  additionally serves as an ejection aid for the finished tube shoulder  1 .  
         [0027]    To achieve a better sealing of the cavities  22  and  23 , the faces of the release elements  14 . 1 ,  14 . 2  and the cavities  22 ,  23 , which are in functional combination with one another, are advantageously conically constructed.  
         [0028]    Optionally, the core  14  and mold  1  may be cooled to further control and speed the manufacturing process. Advantageously gas or liquid cooling systems are used.  
         [0029]    For aesthetic reasons it is possible to use differently colored or transparent plastics, in order to achieve special optical effects. This can, for example, be advantageous if the barrier layer  3  is so positioned in the vicinity of an outlet port  6  (cf. FIG. 1) that it is visible from the outside for the user. The outlet port  6  can also have a non-circular cross-section, so that a pattern can be impressed on the filled material passing out.