Tube shoulder and method for its manufacture

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.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 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. 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 ). 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 . 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 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 . 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 . 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. At the end of a manufacturing cycle the release element 14 additionally serves as an ejection aid for the finished tube shoulder 1 . 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. 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. 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.