CA2299011A1

CA2299011A1 - Plastic article consisting of several materials as well as method for the manufacture thereof

Info

Publication number: CA2299011A1
Application number: CA002299011A
Authority: CA
Inventors: Karl Hehl
Original assignee: Individual
Current assignee: Individual
Priority date: 1999-02-20
Filing date: 2000-02-21
Publication date: 2000-08-20
Also published as: DE19907387A1; EP1029645A1

Abstract

A hollow plastic article consisting of several materials has a wall in which the materials are joined together via their contact surface. At the closed lower end (10b) of the plastic article (10) there are sprues (51, 52, 53). Because the lower end (10b) is amorphous inside the wall thickness x in spite of the sprues, a homogeneous structure of the plastic article is achieved.
This can be realized by injection moulding in several steps in mould cavities in which case the injection preferably is carried out with open shut-off nozzle, or when the first material is injected a long sprue stalk is produced in order to keep the closed lower end (10b) amorphous, or to keep any crystalline areas outside the wall thickness (Fig. 2).

Description

PLASTIC ARTICLE CONSISTING OF SEVERAL MATERIALS AS WELL AS METHOD
FOR THE MANUFACTURE THEREOF
Field of the Invention The invention relates to a hollow plastic article, consisting of several materials for the manufacture of hollow plastic bodies by means of stretching according to the description of claim 1, which preferably is manufactured on an injection moulding machine for the processing of plastics and other plasticisable substances as well as method for the manufacture thereof according to the description of claims 6 and 12.
Prior Art Various materials with different properties are preferably used for the manufacture of such hollow plastic articles which usually are called preforms and later can be biaxially oriented into hollow plastic bodies. These materials can be various PET types, but also other materials such as PEN, polycarbonates or barrier materials such as, for example, nylon MXD6, PAN, LCP, PEN, EVAL
(EVOH) , etc. which in a multicomponent technique are joined into preforms in such a way that their particular advantages come to fruition. The various materials have, for example, different barrier properties, thermal stability, tendency to crack formation due to aging (stress cracking) or can and partly also have to be made by the use of virgin and recycled material. In this respect, the various load ranges both in the manufacture and in the utilization as well as official regulations determine the use of the respective materials. While the multiway thread does not experience any improvement of its properties in the subsequent stretching since it remains amorphous, the properties of the bottle body are improved by the stretching. The barrier properties present a limit of applicability. Moreover, in the beverage sector the recycled materials at present are not allowed to come into contact with the contents. A minimum layer thickness of virgin material is required between recycled material and contents.
In blow moulding, the bottle bottom likewise remains to a large extent amorphous so that here the same applies as for the thread.
Furthermore, this area is especially subject to stress cracking.
Under pressure and acid or alkaline influence, a rapid aging occurs here which is increased further by UV light. However, especially in the gate area, which usually is at the bottom of the bottle, crystalline material can occur at the end of the gate.
The gate area therefore must be designed in such a way that this crystalline material does not cause any problems during the stretching since when bottles are under pressure, it can trigger the bursting of the bottles. The barrier material, which likewise is injected in the same gate area, must not come onto the exterior of the plastic article. The barrier material therefore has to be completely enclosed by the material of the other injection operations. Otherwise moisture can penetrate and delaminate the layers.
To solve the problem with the combination of amorphous sections with crystalline sections of the preform due to its manufacture, it was proposed already in WO-A 98/46410 to heat or to cool, in the manufacture of such a plastic article, different sections in the mould wall of a multilayer plastic article in order to generate in this way specific crystalline or amorphous areas in the preform. Apart from the cost required therefor, the proposals there had no effect on the gate area which in this regard was neglected.
From the older German Patent Application 198 56 356.6 it is known to build up the various layers in a mould in exactly defined mould cavities layer by layer.
Abstract of the Invention Starting from this prior art, the object of the present invention is to form a homogeneous sprue area.
This problem is solved by means of a plastic article with the features of claim 1 which can be manufactured with the method with the features of claim 6 or 12.
The gate area is designed in such a way that no crystalline material will be in the wall of the plastic article itself.
Because of that, there is a homogeneous material in the remaining area so that under pressure and during the stretching, this results in fewer rejects since the crystalline area - if present at all - does not have any effect anymore on the to-be-stretched area. Through an adept selection of geometry, the crystalline area thus is shifted outwards from the wall area of the bottom of the plastic article.
According to claims 2 and 3, care is at the same time taken in the selection of geometry so that the gate point is not significantly bigger than the sprues known up till now since one has to continue to work with the same blow moulding machines and blow moulds. In this case, for example, it is according to claim 3 also possible not to bring the barrier material universally over the sprue since sufficient material is present there which offers the required permeability resistance. But, above all, the background here is that the barrier material cannot come on the outside of the plastic article in order to avoid penetration of moisture between the layers.

The methods according to claims 6 and 12 permit in connection with the manufacture of the plastic article in clearly defined mould cavities of a plastic injection moulding machine that either no crystalline area is formed, or the crystalline material will be specifically outside the wall, in which case solutions are proposed which allow one to produce injection points without crystallinity in the wall area. Thus in the injection moulding, a smaller sprue is produced which remains amorphous due to the more rapid cooling either by producing the individual layers without shut-off needle, or by working with a long sprue stalk. In this case, the closed contour in the mould cavity makes possible an exact positioning in contrast to the previously known sandwich method, in which the various materials still are brought into the warm centre of the previously injected material.
Brief Description of the Figures In the following the invention is elucidated by means of the attached figures of exemplified embodiments. Here, Fig. 1 shows a section through a plastic article manufactured according to the method, Figs. show the schematic manufacture of a plastic article according to Fig. 1 by means of injection moulding, Figs. show sections area of plastic 5,6 through a the bottom article, Figs. show the schematic manufacture of a plastic article according to Fig. 6 by means of an injection moulding being carr ied out in several steps, Fig. 10 shows a presentation according Fig. 1 of plastic re to a article another embodiment.
in Description of preferred exemplified embodiments Fig. 1 shows a hollow plastic article 10 consisting of several materials. These plastic articles are also described as preforms and are usually used for the manufacture of hollow plastic bodies by means of biaxial orienting of this preform. The plastic article 10 has a wall lOc in which the materials are joined together via their contact surfaces. In the exemplified embodi-ment, the materials in the wall are built up layer by layer in which case, for example, the layer 61 is virgin material, layer 62 is a barrier layer and the layer 63 can be formed, for example, by recycled material since this layer does not come into contact with the contents.
The plastic article has an open upper end lOd on which a thread area l0a and a neck ring lOh are provided. The neck ring has in the transition to the intermediate area lOf a recess lOg in which the barrier layer 62 definitely ends with regard to its upwards extension. This can be determined unequivocally through injection into clearly defined mould cavities. There, with sufficient outwards distance, it is covered by the outermost layer 63.
The plastic article 10 has moreover a closed lower end lOb which in the stretched hollow plastic body forms the bottom with the wall thickness x. This lower end lOb is connected with the upper end lOd via the intermediate area lOf. In the lower end area there are several sprues for the various materials. Inside its wall thickness x, the lower end lOb is amorphous so that the sprues are without influence on the plastic article when it is stretched. Through an appropriate geometry selection of the mould cavities, all sprues 51, 52, 53 are made in such a way that either no crystalline area is formed in the manufacture without shut-off needle (Figs. 2-4), or the areas of crystalline material are outside the wall thickness x (Figs. 7-9).

By means of injection with open shut-off nozzle or without shut-off needle, the sprue area can be kept amorphous since this area cools more rapidly in which case the sprue at the same time becomes narrower. Admittedly according to Fig. 5, a longer sprue 51 can also be produced through an appropriate selection of geometry of the mould cavity. In the injection of the following materials in the exemplified embodiment for making the layers 62 and 63, this long sprue is sprayed over according to the geometry of the following mould cavities by the sprues 52 and 53.
According to Fig. 6, it is not absolutely necessary that the barrier layer is brought over the sprue 51 of the previous layers.
This is then in particular of importance if the entire gate point is not to be larger than common up till now in the prior art.
The exact mould geometry allows also the manufacture of a plastic article according to Fig. 10 in which the bottom area of the bottle is reinforced. For this purpose, material can be amassed in the bottom area lOb in the plastic article. Through the increase in the wall thickness in this area, the flow resistances become lower during the injection of the material into the mould cavity. In order to minimize the flow paths and the flow resistances, the entire bottom area can be designed in such a way that the thickness of the layers 61, 62, 63 increasingly is reduced from the respective sprues 51, 52, 53 up to the transition to the intermediate area lOf. This has the advantage that there, where more material is required in the stretching due to the semicircular shape, more material is available than in the rectilinear areas of the intermediate area lOf.
Figs. 2 to 4 and 7 to 9 show schematically a method for the manufacture of such a hollow plastic article 10 consisting of several materials. Shown is a mould 13 with a core or core insert 25. Between mould 13 and core insert 25, mould cavities are formed which are filled with plasticised material via the injection nozzles 64, 65 or 45, 48 and 49. The method is carried out in such a way that a plasticised first material is injected into the first mould cavity 14 of Fig. 2 or 7. This mould cavity determines the portion of the first material of the total form of the hollow plastic article 10. In this case an intermediate moulding 21 is made. This intermediate moulding is placed together with the core insert 25 in the other cavity 23 in which case the intermediate moulding 21 is located on the core insert 25. In this way, the other mould cavity 15 is formed in the cavity 23. After injection of the second material, another moulding 22 is formed which subsequently can be placed together with core insert 25 in the cavity 24 of Fig. 4 or 9, and there form the other mould cavity 16. Into this mould cavity 16 a third material can be injected. If required, these steps can be repeated to build up other layers until the last material is injected in the manufacture of the final plastic article 10.
Based on this basic principle, which also was elucidated in the older Patent Application 198 56 356.6 and to which moreover reference is hereby made, at least one of the first materials to form the first parts of the plastic article is injected, according to Figs. 2-4, without needle shut-off of the injection nozzle. In the exemplified embodiment (Figs. 2,3), the layers 61, 62 are both injected with open nozzle 64 without shut-off needle. In this way, the sprue can be made very small and to a large extent amorphous. According to Fig. 4, the further injection operations then can be carried out with an injection nozzle 65 with shut-off needle 47. However, there is also the possibility to carry out the following injection operations likewise with open nozzle.
Alternatively, according to Fig. 7, the sprue can also be made so long that the crystalline area comes outside the wall thickness x of the lower end lOb. Thus the crystalline area of the barrier material also is outside this wall thickness x. In Fig. 8, the sprue stalk formed by the superposition of the sprues is kept as small as possible. How this is realized with respect to the mould is shown in Fig. 8. In the introduction of the injected second layer 62 of the barrier material, a shut-off needle 46 is placed against the sprue 51 of the previously made part (layer 61). In this way, a positive sealing is achieved in which case the shut-off needle possibly can be spring-mounted. The shut-off needle itself is enclosed by a sleeve which represents the actual injection opening for the injection of the following layer 62 or of the following material. Thus, after the barrier layer was injected via the injection nozzle 48, the third layer 63 then can be produced according to Fig. 9, as known from the prior art, with another shut-off nozzle 49 with shut-off needle 47. It is obvious that also plastic articles with additional layers can be manufactured by means of this method.

Claims

1. Hollow plastic article (10) consisting of several materials for the manufacture of hollow plastic bodies by means of stretching with - a wall (10c) in which the materials are joined together via their contact surface, - an open upper end (10d), - a closed lower end (10b) with a wall thickness (x), - an intermediate area (10f) connecting the upper and lower end, - several sprues (51,52,53) for the various materials which will be in the lower end area (10b), characterized in that the lower end (10b) is amorphous in spite of the sprues inside the wall thickness (x).

2. Plastic article according to claim 1, characterized in that the sprue (51, 52, 53) of all materials is arranged outside the wall thickness (x).

3. Plastic article according to claim 1 or 2, characterized in that the plastic article (10) has at least three layers (61, 62, 63) of which one of the middle layers (62) is a barrier layer, and that the barrier layer does not cover the sprue stalk of the sprue (51) of at least one of the first layers (61).

4. Plastic article according to one of the claims 1-3, characterized in that the thickness of the layers (61, 62, 63) and thus preferably of the wall (10c) increasingly is reduced from the respective sprue (51, 52, 53) up to the transition to the intermediate area (10f).

5. Plastic article according to one of the claims 1-4, characterized in that all layers (61, 62, 63) of a plastic article (10) forming a preform are produced by means of injection moulding.

6. Method for the manufacture of a hollow plastic article (10) consisting of several materials according to one of the claims 1-5, characterized by several injection mould operations in mould cavities (14, 15, 16) with the steps:
a) Injection of a plasticised first material in a first mould cavity (14) which corresponds to the portion of the first material of the total form of the hollow plastic article (10) for the forming of an intermediate moulding (21), making a first part of the plastic article (10), b) introduction of the intermediate moulding (21) into at least another cavity (23) for the formation of another mould cavity (15) which to some extent is limited by the intermediate moulding (21) and corresponds to the portion of another material of the total form of the plastic article (10), c) injection of at least another plasticised material into the other mould cavity (15) for the formation of another moulding (22) forming a part of the plastic article (10), d) if required, repetition of the previous steps b) and c) using the other moulding (22) as intermediate moulding (21) until the manufacture of the complete plastic article (10), e) in which case at least one of the first parts is injected without needle shut-off of the injection nozzle (45) so that the lower end (10b) is amorphous inside its wall thickness (x).

7. Method according to claim 6, characterized in that the mould cavity (14) of the first part is built up in such a way that it results in a longer stalk of the sprue (51).

8. Method according to claim 6 or 7, characterized in that the plastic article (10) is built up layer by layer.

9. Method according to one of the claims 6-8, characterized in that the first part (layer 61) is injected without needle shut-off of the injection nozzle.

10. Method according to one of the claims 6-8, characterized in that the first two parts (layer 61, 62) are injected without needle shut-off of the injection nozzle.

11. Method according to one of the claims 6-8, characterized in that all parts (layer 61, 62, 63) are injected with open injection nozzle (45).

12. Method for the manufacture of a hollow plastic article (10) consisting of several materials according to one of the claims 1-5, characterized by several injection operations in the mould cavities (14, 15, 16) with the steps:
a) Injection of a plasticised first material into a first mould cavity (14) which corresponds to the portion of the first material of the total form of the hollow plastic article (10) for the forming of an intermediate moulding (21) forming a first part of the plastic article (10), b) introduction of the intermediate moulding (21) into at least another cavity (23) for the forming of another mould cavity (15) which to some extent is limited by the intermediate moulding (21) and corresponds to the portion of another material of the total form of the plastic article (10), c) injection of at least one other plasticised material into the other mould cavity (15) for the forming of another moulding (22) making a part of the plastic article (10), d) if required, repetition of the previous steps b) and c) using the other moulding (22) as intermediate moulding (21) up to the manufacture of the complete plastic article (10), e) in which case the mould cavity (14) of the first part is built up in such a way that it results in a long stalk of the sprue (51) so that an area of crystalline material of the sprue (51) is arranged outside the wall thickness (x) of the lower end (10b), in which case the injection of at least one of the first parts of the plastic article (10) is carried out using a shut-off needle (44) in the injection nozzle (55).

13. Method according to claim 12, characterized in that the following part forms a barrier layer (layer 62) in which case in the injection of the material required therefor, the shut-off needle (46) positively seals the sprue (51) of the previous parts of the plastic article (10) while the sprue (52) of the barrier layer follows around the injector needle (46).

14. Method according to claim 13, characterized in that the sprue (53) of the last layer (63) follows using a shut-off needle (47).