Preform of a thermoplastic

© Start of patent period: 1984 03 15 Longest possible duration:

© Published: 1984 10 25 © inventor:

© dependence:

© Pamphlets considered to delineate the prior art:

- 2 - No.376168

The invention relates to a preform of several layers of thermoplastic material for producing a container by blow molding.

It is known to produce containers made of thermoplastics, wherein the containers can withstand increased internal pressure, which occurs, for example, in the storage of carbonated drinks, especially drinks such as sodas and beer. When using, for example, polyethylene terephthalate, hereinafter referred to as PET, it is possible to produce the container with relatively thin walls.

However, such thin-walled PET containers have, to some extent, a gas permeability to, for example, carbon dioxide. Oxygen from the environment, as well as light, can also penetrate the walls. These circumstances adversely affect the taste of the container contents.

In many applications, therefore, there is often the desire that the container has a shielding, which allows only a small amount of passage of gases or light. There are a number of known, various methods of providing containers with such layers. Examples of this are the application of a protective layer to the finished container, the coextrusion of a blank in which a layer contains a visual material, or the application of an inner or outer protective layer to the preform.

The use of a protective layer is necessary in many applications, so that a number of methods have been developed in which a protective layer of required thickness is applied to the preform before forming the preform into the container.

In applications where protective layers have been coated on the outer surfaces of the container, it has been found that carbon dioxide in the storage of carbonated beverages permeates the container wall, the shielding layer having a tendency to dislodge from the outer surface of the container wall. In certain applications, such damage in the layer leads to an undue impairment of the shielding properties of the container. Of course, the layers can also be damaged by external mechanical influences.

In the case of the protective layers arranged on the inner surface of the container, there are difficulties in certain applications in finding shielding materials which comply with official regulations relating to the preservation of food or pharmaceutical products, and which do not influence the taste or other properties of the stored product.

Therefore, solutions have been developed in which the protective layers are enclosed in the container wall, wherein, as stated above, the technique of coextrusion of a pipe or a hose is applied whose walls have a layer of shielding material, surrounded by material of the container walls. The tube or tube are cut in suitable lengths, the respective length is closed in one end and then formed into the container. Hiebei there are difficulties to achieve a closure in which the shielding remains undamaged. Particularly great difficulties arise with thin shielding layers.

There are strong wishes to be able to reuse already used plastics eg for containers for food. In the Wiederweweung of plastics, it is in many ways inconvenient to let the reused plastic come into contact with the stored in the containers on contents, this is especially true for type of food. In order to prevent this direct contact between already used and recovered plastic and the contents stored in the container, attempts have been made to use containers made of a laminated plastic, the recovered material being contacted by a layer of new plastic against contact with the product Container was obstructed. Hiebei above-mentioned coextrusion technique was used. Of course, the difficulties already mentioned with regard to maintaining an intact shielding layer when sealing an extruded tube or tube are also present when closing an extruded tube or tube whose innermost layer is new plastic which forms the protective layer which causes contact between the recovered material and the interior

- 3 - No.376168 of the container prevented. However, Swedish Patent Application No. SE 7705604-2 relates to a preform which consists of a co-extruded tube which has been cut into pieces, after which the pieces have been closed at one end and sealed in such a way that the inner layer is closed Layer remains intact. This is accomplished by the inner layer displacing the outer layer upon closure and extending in the central portions of the closure from the inner surface of the preform to its outer surface.

The invention aims at avoiding these disadvantages and difficulties and consists in that the preform is formed of a number of mutually separate, mating part preforms, each part preform having a mouth part and a closed bottom part, and that optionally the Teilvorformlinge stretched and / or with a Shielding layer are provided.

The invention relates to a preform, are eliminated in the above-mentioned disadvantages, on the one hand intact material layers in all parts of the preform and on the other hand optionally provides an intact shielding. The intact material layers thus allow reuse of the previously used plastic and also ensure that the individual layers of material in the formed from the preform container in all parts of the container, the demands placed on the container with respect to dimensional stability, gas penetration, Liohtpenetration etc. fulfill.

According to the invention, the preform is formed by attaching an inner part preform in an outer part preform, wherein the outer diameter of the inner part preform is less than the inner diameter of the outer part preform.

According to a preferred embodiment of the invention, the preform consists of two partial preforms, wherein the outer part preform is formed of plastic waste material.

In an alternative embodiment of the invention, the preform is composed of more than two partial preforms.

In a further embodiment of the invention, the material is stretched in at least one of the partial preforms in the axial direction, preferably up to a length which corresponds in the main to the length of the profile that the container which is to be formed from the preform in his Axial direction has.

In still another embodiment of the invention, the inner and / or outer surfaces of a number of partial preforms are provided with a shielding layer before the partial preforms are assembled into the preform.

The use of two partial preforms forming a composite preform, with a shielding layer between both partial preforms, provides, inter alia, the advantages that the contents of the filled container can not come into direct contact with the shielding layer of the container and the shielding layer through the enclosure in the container wall has no way to detach from any of the surfaces of the container.

According to a preferred embodiment of the invention, the two partial preforms are provided with a shielding layer, wherein the one layer prevents the penetration of gases and the other the penetration of light, or wherein one prevents the penetration of oxygen and the other the penetration of carbon dioxide. Hiebei the oxygen barrier layer is preferably attached to the outer part preform.

According to a further preferred embodiment of the invention, the one partial preform, and thereby preferably the inner partial preform, is provided with two or more shielding layers on top of each other. The fact that the shielding obtained during heating and subsequent forming of the composite preform in the container good contact against and a secure enclosure between the material layers, the function of the shielding Chi is guaranteed.

It is also possible to provide the outer surface of one of the inner part preforms with a print and / or decor. The execution of the imprint and / or decor is hiebei adapted to the extension of the material, which takes place during the subsequent forming of the preform in the container.

- 4 - No.376168

In a preferred embodiment of the invention, the material in the preform or in the partial preforms in the axial direction and at an initial temperature in or below the range of the glass transition temperature (TG) of the material is stretched. The stretching of the material is preferably carried out by a mechanical method, wherein the preforms pass through one or more draw rings, which reduce the wall thickness in the preforms and thus also the outer diameter of the preforms. Such a stretching method is described in Swedish Patent Application No. SEC. 8004003-3. As a result of the mechanical orientation, it is thus easy to obtain an outer diameter for the inner part preform which can be adapted exactly to the inner diameter of the outer part preform and to the dimensional changes which the application of the shielding layer to the partial preforms entails.

A more detailed description of the invention will be given in connection with a number of figures, wherein FIGS. 1a, b each show a longitudinal section through partial preforms and Fig. 1c shows a longitudinal section through a preform 15 composed of the partial preforms according to FIGS. 1a and 1b. FIGS. 2a, b each illustrate a longitudinal section through axially stretched part preforms. FIG. 2c shows a longitudinal section through a preform composed of the partial preforms according to FIGS. 2a and 2b. 3a, b each show a longitudinal section through provided with a shielding, axially stretched part preforms. FIG. 3c shows a longitudinal section through a preform composed of the partial preforms according to FIGS. 3a and 3b. Fig.3d a²⁰ Enlargement of the area A of Fig.3c.

In Fig.la, b can be seen a part preform --10a - and a part preform --10b-, each with a mouth part --22a, b- and a closed bottom part -25a, b-. The two partial preforms are produced by any desired method, for example by injection molding or by extrusion. In the latter case, as a rule, the closed ground²³ Part produced in a separate molding process.

In Fig.lc is shown how the two partial preforms -10a, b- are assembled into a preform -11-. To enable this, the inner diameter of the partial preform -10b- is slightly larger than the outer diameter of the partial preform -10a-. In the same way, the lengths of the two partial preforms are tuned to one another. The Fig.la³⁰ to c are dimensionally not completely correct in this respect.

In FIGS. 2a, b, one can see an axially stretched partial preform -16a and an axially stretched partial preform -16b-. The partial preform -16a is sized to fit in the partial preform -16b-, and both partial preforms have a mouth portion -21a, b- and a closed bottom portion -24a, b-.

³⁵ The two partial preforms -16a, b- are formed by forming partial preforms, which mainly consist of amorphous material. The two previously discussed partial preforms -10a, b- are examples of such partial preforms. In forming, the cylindrical portion of the partial preform elongates by a stretching process while reducing the wall thickness. This is preferably done in the way that the Teilvorformling, eg

one of the previously discussed partial preforms -10a, b- passes through one or more draw rings whose inner diameter is smaller than the diameter of the partial preform before passing through the draw rings. In order to form the axially stretched part preform according to FIG. 2a, the said stretching process is supplemented by a stretching of the material also in the bottom part of the part preform.

⁴⁵ In Fig.2c is shown how the two partial preforms -16a, b- are assembled into a preform -18-. To enable this, the inner diameter of the partial preform -16b- is slightly larger than the outer diameter of the partial preform -16a-. In the same way, the lengths of the two partial preforms are matched to one another.

In Figures 3a to d an embodiment of the invention is shown in which two Teil50 preforms according to the manner described above carried out axial stretching stretched preforms -13a, b ~ of such dimensions that they fit into each other. After inserting the smaller preform -13a into the larger preform -13b-, the two preforms form a composite preform -15-. The smaller preform -a

No. 376168 is provided in the figures with an outer shielding layer -14a and the larger preform -13b- with an inner shielding layer -14b-. In this way, in the composite preform in the transition between the two partial preforms, a region which consists of the two shielding layers -14a, b-.

Using the part preforms described above to make containers, the composite preform material is heated to the forming temperature, after which the forming takes place in the container. It is of course possible to provide the mouth part of the respective preform with the required closure arrangements for the future container, eg thread, before forming the respective preform into a container. In the same way it is possible according to the invention to start from preforms, which are designed before the axial stretching with such closure arrangements.

As shown above, the axial stretching of the preforms takes place in such a manner that the preforms pass through dies with a gradually decreasing diameter. Of course, the invention can also be applied to those production processes in which the axial stretching of the preforms is carried out by other means. For the embodiment of the invention in which axially stretched part preforms form a composite, axially stretched preform, it goes without saying that there is a requirement that the drawing methods used provide part preforms having the tolerances required for interfitting the part preforms.

By attaching the shielding layers to axially stretched preforms, the shielding foils come to lie on a surface which is substantially larger for preformed containers of the same size than in previously used technology, according to which, unstretched preforms were provided with shielding layers. When using eg PET is aimed at a biaxial orientation of the material in many applications, whereby the material is stretched by at least about 3 times in one of the axial directions. In this way, among other things, the material obtains the mechanical properties required for the respective case. Stretching the material 3 times in both axial directions implies that the surface of the preform is approximately 1: 9 with respect to the surface of the container, which in turn means that the thickness of a shielding layer applied to the preform decreases to the same extent. In certain applications, the required properties are achieved by a monoaxial stretching of about 3 times and a subsequent, smaller stretching in the transverse direction. In the applications in which just mentioned stretch ratios are used, certain embodiments of the invention entail that the shielding layer is reduced by a maximum of 3 times, which again provides the advantage that the shielding layer does not have to be made the same thickness in the preform as in use the technology used so far. Since the application of thick shielding layers represents an aggravating phase in connection with the production of containers, the invention means a substantial simplification of the manufacturing process.

In particular, in the application of a composite preform it is advantageous in certain application examples to allow the final curing of the shielding layer as well as their connection to the material of the partial preform take place after the two partial preforms have been arranged inside each other. Characterized in that the Abschirmschichten only after joining the two Teilvorformlinge and preferably in connection with the heating of the preform to the molding temperature of the material cure, a good concern of the Abschirmschichten is achieved together. Even if only one shielding layer is used, the aforementioned method makes good contact with the material of the partial preform which does not have a shielding layer.

According to the invention, one or more shielding layers are applied to the respective preform by immersion in a solution containing the shielding material. In optional embodiments, the shielding material is sprayed onto the preform. Of course, the idea of ​​the invention also encompasses the application of other contracting procedures.

Even though all the embodiments of the invention taken up in the general part of the description have not been discussed in detail separately following the detailed description

- θ - Nr.376168, it should be clear from the individual description that all embodiments are within the framework of the preform variants (composed of partial preforms), which have been described in connection with FIGS.

Normally, for a polyethylene terephthalate partial preform, crystallization may reach a maximum of about 30% if further forming of the preform is to take place. Preferably, however, the crystallization is allowed to have a value in the range 10 to 25%, wherein the crystallization occurred by the monoaxial orientation is at most about 17%.

The values ​​of crystallization given in the invention refer to the theory shown in the publication The Macromolecular Chemistry 176, 2459 to 2465 [1975].

The above description deals with tubular preforms of circular cross-section. Of course, it is within the scope of the invention to also work with tubular preforms of other cross-sectional shapes.

A large number of materials of the polyester or polyamide type having similar properties to polyethylene terephthalate are known in the art. The invention is fully or partially applicable as such for these materials, the thickness reductions and temperatures are adapted to the specific conditions for the respective material. Examples of materials to which the invention is applicable as above are polyhexamethylene adipamide, polycaprolactam, polyhexamethylene sebacamide, polyethylene 2,6- and 1,5-naphthalate, polytetramethylene-1,2-dioxybenzoate and copolymers of ethylene terephthalate. Ethylene isophthalate and similar polymers.