GB2138736A

GB2138736A - Making Multilayer Hollow Plastics Bodies

Info

Publication number: GB2138736A
Application number: GB08410185A
Authority: GB
Inventors: Theo Rydmann
Original assignee: Spiess & Sohn Kunststoffwerk G
Current assignee: Spiess & Sohn Kunststoffwerk G
Priority date: 1983-04-19
Filing date: 1984-04-19
Publication date: 1984-10-31
Also published as: GB8410185D0; FR2544657B3; DE3314108A1; FR2544657A1

Abstract

Multilayer hollow plastics bodies are made by coating a hollow plastics preform 12, and reshaping the coated preform, e.g. by blow moulding. Coating may be effected by injection moulding or spraying. The process may be carried out continuously on turntable 2, Fig. 3. <IMAGE>

Description

SPECIFICATION A Method and Apparatus for Manufacturing a Hollow Body Having a Wall with at Least Two Layers The invention relates to a method and an apparatus for the manufacture of hollow bodies each having a wall which has at least two layers in at least a predetermined region thereof, particularly but not exclusively a wall layer having a blocking effect or barrier property, wherein laminated semi-finished products corresponding to the desired layered structure of the hollow body wall are manufactured first, the hollow bodies then being formed from these products.

It is known that particularly the mass-produced plastics materials, such as PE, PP, and PETP, vary in their permeability to different media, and an adequate barrier effect against almost all media can be achieved by combinations or different plastics materials having permeability values which are occasionally contrary to one another, the differing barrier qualities of these materials also being exploited in this case.

There are already known methods of manufacturing containers according to which a special extruder die, with the aid of a plurality of extruders, produces a tube-like or web-shaped laminate in the form of semi-finished product which can be shaped to form each container in accordance with conventional thermoforming processes.

In addition, there are known methods which are intended to give the finished hollow body a greater barrier effect by subsequent coating with an appropriate coating material which may be a lacquer.

Moreover, it is known practice, at least in the case of containers having rotational symmetry, to provide at least a partially impermeable surface by applying thereto a barrier material, for example aluminium foil, but it is impossible from a practical stand point to cover the entire surface.

All these known methods have considerable drawbacks and disadvantages, particularly in connection with mass production.

The object of the invention is, in contrast, to provide a simple method, which is not susceptible to trouble and is particularly suited to mass production for the manufacture of hollow bodies having a wall which has at least two layers.

According to the present invention there is provided a method for the manufacture of a hollow body having a wall which has at least two layers in at least a predetermined region thereof wherein a single-layered parison in the form of a hollow body is manufactured in the form of a semi-finished product, the parison then being coated with one or a plurality of layers and the parison which is thus provided with a laminated wall structure is then formed into a finished hollow body.

In accordance with the invention the hollow body is thus manufactured in two stages, it being possible for various suitable materials to be processed in the lamination of the parison depending on the intended use and on the type of material with which the hollow body is to be filled.

It is preferable for the hollow body-shaped parisons to be coated on their outer faces.

A great variety of methods can be used for coating the parisons, for example, coating in the manner of an injection moulding operation, spraying with coating material, immersing the parisons in coating material, brushing, in particular painting, the parisons with coating material, coating by vapour deposition in a high vacuum or by coating sputtering, or even coating by applying a foil-like coating material in the deep-drawing process.

First, a single-layered parison can be manufactured in a first step in accordance with known methods, for example injection moulding, the parison already having substantially the final dimensions preferably in a neck area, but not yet being fully formed in the remaining lower neck area or body.

The single-layered parison forms, as it were, the base for the hollow body which is subsequently to be fabricated, whilst the layer which has been applied or layers which have been applied to this parison can be made up of materials, for example PA, PVDC, EVAL, or other materials, which are to be selected according to the desired properties, such as blocking or barrier properties.

The coated parisons may be stored in any desired manner and reheated by known means and expanded, partly by mechanical means and partly by blow moulding, in a forming station and thus formed into the final hollow body shape.

An apparatus for coating hollow body-shaped parisons which is particularly suitable for carrying out the method includes a conveying device for receiving a parison and moving the parison stepwise past a receiving station, at least one coating station and an ejecting station, the conveying device having receiving fingers adapted to engage inside the parison.

This apparatus makes it possible for the parison to be coated in a practically continuous operation and at a rate of throughout which is particularly advantageous for the mass production of articles. An apparatus of this type is distinguished by particularly high operational reliability, simple mode of operation and great adaptability which can be quickly effected.

In a preferred embodiment of the apparatus according to the invention there is provided, at least between the receiving station and the first coating station, an indexing station which includes means for activating the surface of the parisons to be coated by a mechanical, thermal, electric or radiation effect or by the application of a chemical activator or bonding agent. This indexing station for activating the surface which is to be coated not only ensures reliable adhesion of the coating, but also makes it possible to apply durable coatings to parisons which have been stored for a relatively long time after manufacture.

For coating the parisons an injection moulding apparatus may be provided in the apparatus according to the invention, the injection mould of this moulding apparatus having cavities, each of which receives a parison and is larger than the outer dimension of the parison by the thickness of the layer to be applied. In this connection the layer thickness may be designed to be variable and can thus be better adapted to the subsequent degree of deformation in relation to strength. The apparatus according to the invention may also include a spraying device for coating the parisons, this spraying device being equipped with a nozzle arrrangement which extends over the axial length of each parison and means for rotating the parison about its longitudinal axis or for guiding the nozzle arrangement around the stationary parison.

Accordingly, many other types of coating equipment may be used. In this case it is quite possible for the apparatus according to the invention to be equipped with different types of coating apparatus; for example, a spraying device for applying a first coating and an injection moulding apparatus for applying a second coating.

The conveying device is preferably in the form of a rotary indexing table around which the receiving station, preferably a plurality of coating stations, and the ejecting and forming station are arranged.

Embodiments of the invention will now be described by way of example, with reference to the accompanying drawings, in which: Fig. 1 shows, in side view, a parison which has been coated in accordance with the invention, Fig. 2 shows an enlarged sectional view of the wall section II in Fig. 1, Fig. 3 shows, in a diagrammatic plan view, a coating apparatus and a rotary indexing table, Fig. 4 shows, in axial section, an injection moulding apparatus (which is included in an apparatus according to Fig. 3) for coating the parisons, and Fig. 5 shows a spraying device-which can be used in an apparatus according to Fig. 3~for coating the parison.

Figure 1 shows a parison 1 after being coated, the contour of the untreated parison being indicated by broken lines in the area of the parison wall 11 which is subsequently to be formed. As shown in Figure 1, the parison 1 is designed with an opening 12 which is already substantially identical to the opening of the finished hollow body to be manufactured. The drawing also shows that the parison 1 has been coated only in the area of its parison wall 11 which is to be shaped into the final article and not in the area of its opening 12.

Figure 2 shows an example of the layered of laminated structure of a treated parison and illustrated to a larger scale the section II at the parison shown in Figure 1. In this example, the parison has been manufactured by injection moulding and coated on its outer face.

Accordingly, the inner layer 13 represents the wall which has been produced during injection moulding of the parison and made, for example, of polyethylene (PE) or polypropylene (PP) and which is also subsequently to form the supporting wall layer for the hollow body. After activation, a thin first coating 14, which can be made for example, of polyvinylidene chloride (PVDC), which has good barrier properties, is applied to the outer face of the wall layer 13 by spraying. To this coating 14 there is applied an outer layer 15 which can be made of polyester plastic material or polyamide to achieve good surface qualities on the hollow body to be manufactured.

Figure 3 shows a diagram of a coating machine in which the parisons 1 are provided with the various layers at one or a plurality of stations. The coating machine includes, as a conveying device, a rotary indexing table or plate 2 with radially extending receiving fingers 21 arranged on its circumference. These receiving fingers 21 can be rotatably mounted about their longitudinal axis and can be used to rotate in one position or another of the rotary indexing table 2, as described in connection with Figure 5.

The various stations for coating the parisons 1 are arranged around the rotary indexing table 2.

The receiving station 3 is followed, in the direction of rotation of the indexing table 2, by an indexing station 4 in which the outer surface of each parison 1 is activated. This activation can be effected, for example by means of radiant heaters 22 which are guided about the parison in the direction of arrow 23. However, as stated above, the parison 1 can also be rotated by causing the receiving finger 21 which supports it to rotate.

After further pivoting of the rotary indexing table 2 (a double indexing step in the example shown), the parison which has been activated on its surface passes into the first coating station 5.

According to Figure 3 this first coating station 5 is occupied by an injection moulding apparatus, that is an injection mould 24 which is to be guided over the parison 1, and an extruding press 25. The essential parts of this injection moulding apparatus are reproduced in Figure 4. According to this Figure the injection mould 24 has a cavity 26, 26a which is to be larger by the thickness of the layer which is to be applied. The coating material is pressed into the formed gap by the moulding nozzle of the extruding press 25, the preformed opening 12 in this case being omitted from the coating operation.

In place of the injection moulding apparatus, a spraying device 27 (shown in Figure 5) could also be provided in the first coating station in order that, for example in keeping with Figure 2, a barrier layer made of PVDC may first be sprayed on the parison 1 in the area of its wall 11 which is subsequently to be formed. In this case also, the preformed opening 12 remains uncoated. As shown in Figure 5, the parison 1 in this example is caused to rotate by rotating the receiving finger 21 supporting it, whilst the spraying device 27 is designed in the form of a fixed arm on which a series of spray jets 28 is mounted.

Figure 3 shows that the first coating station 5 can also be followed by a second coating station 6 and a third coating station 7. As shown in Figure 3 these other coating stations 6 and 7 are equipped with injection moulding apparatus, i.e.

injection moulds 24 and extruding presses 25.

From the last coating station 7 the coated parison moves in the final forming and ejecting station 8 in order to be packed for transportation or stored.

The forming and ejecting station 8 can include blow-moulding apparatus of a known type.

Instead of coating by injection moulding or spraying any other method of coating may be considered for use. For example, the vacuum deposition of layers in a high vacuum or immersion of the parison. The parison can be coated with foil in the deep-drawing process. The coating can also be applied by brushing the coating material on or applying lacquer to the parison. All the coating methods mentioned can be used individually or even in combination with one another. For this purpose the apparatus according to Figure 3 would provide the various coating stations 5, 6 and 7 with the equipment which is suitable in each case for the desired coating method. It is also easily possible for the apparatus according to Figure 3 to be equipped with more or less than three coating stations.

Claims

1. A method for the manufacture of a hollow body having a wall which has is at least two layers in at least a predetermined region thereof wherein a single-layered parison in the form of a hollow body, is manufactured in the form of a semi-finished product, the parison then being coated with one or a plurality of layers and the parison which is thus provided with a laminated wall structure is then formed into a finished hollow body.

2. A method according to claim 1, wherein the hollow body-shaped parison is coated on its outer face.

3. A method according to claim 1 or 2, wherein the parison is coated in the manner of an injection moulding operation, for which purpose the parison is introduced individually into a corresponding injection mould.

4. A method according to any one of claims 1 to 3, wherein the parison is sprayed with a coating material.

5. A method according to any one of claims 1 to 4, wherein the parison is coated by immersion in a coating material.

6. A method according to any one of claims 1 to 5, wherein the parison is coated by brushing with a coating material.

7. A method according to any one of claims 1 to 6, wherein the parison is coated by vapour deposition in a high vacuum or by the cathode sputtering process.

8. A method according to any one of claims 1 to 7, wherein the parison is coated by the application of foil-shaped coating material.

9. A method according to any one of claims 1 to 8, wherein the parison has an opening which, in form and dimensions, is substantially indentical to the opening of the finished hollow body, and the opening is omitted from the coating process.

10. A method according to any one of claims 1 to 9, wherein the parison is manufactured by injection moulding and the main wall layer of the hollow body is performed during the course of this manufacture.

11. Apparatus for coating hollow-body shaped parisons by carrying out the method according to any one of claims 1 to 10, including a conveying device for receiving a parison and moving the parison stepwise past a receiving station, at least one coating station and an ejecting station, the conveying device having receiving fingers adapted to engage inside the parison.

12. Apparatus according to claim 11, wherein at least between the receiving station and the first coating station there is provided an indexing station which includes means for activating the surface of the parison to be coated by a mechanical, thermal, electric or radiation effect or by the application of a chemical activator or bonding agent.

13. Apparatus according to claim 11 or 12, including an injection moulding apparatus for coating parison, the injection mould of which moulding apparatus has cavities each of which receives a parison and is larger than the outer dimensions of the parison by the thickness of the layer which is to be applied.

14. Apparatus according to any one of claims 11 to 13, including a spraying device for coating the parisons comprising a nozzle arrangement, which extends over the axial length of each parison, and means for rotating the parison about its longitudinal axis or for guiding the nozzle arrangement about the stationary parison.

15. Apparatus according to any one of claims 11 to 14, wherein the conveying device is in the form of a rotary indexing plate or table around which are arranged the receiving station, at least one coating station and an ejecting station.

16. Apparatus according to claim 15 including a plurality of coating stations.

17. A method of manufacturing hollow bodies having a wall which has at least two layers substantially as described herein with reference to and as illustrated in, the accompanying drawings.

18. Apparatus adapted to carry out the method claimed in any one of claims 1 to 10 or 17, and substantially as described herein with reference to and as illustrated in the accompanying drawings.