WO1992001546A1

WO1992001546A1 - Injection-moulded thermoplastic container and methods for producing the same

Info

Publication number: WO1992001546A1
Application number: PCT/SE1991/000314
Authority: WO
Inventors: Hans Linner
Original assignee: Norden Pac Development AB
Current assignee: Norden Pac Development AB
Priority date: 1990-07-16
Filing date: 1991-05-02
Publication date: 1992-02-06
Anticipated expiration: 1993-01-16
Also published as: SE9002442D0; JPH0473121A; AU7996591A

Abstract

A thermoplastic, injection-moulded container (1) comprising an end wall (3), a substantially tubular body portion (2) and a threaded portion (5) remote from the end wall (3) for receiving a cap (4) with mutually-cooperating threads, wherein the threads (6) are rounded, whereby the threaded portion (5) for receiving the cap (4) is located on the tubular body portion (2) and the tubular body portion's wall thickness, its inner diameter and its axial length are selected such that the threaded portion (5) is able to flex sufficiently to permit axial withdrawal of the container (1) from a mould of an injection-moulded machine with no torque being applied to the container and without the need for the mould to split. The invention also disclose methods for the production of such a container.

Description

Title: Injection-moulded thermoplastic container and methods for producing the same

Technical Field;

The present invention relates to an injection-moulded thermoplastic container according to the preamble of claim 1 and to methods for its production according to the preambles of claims 6 and 8 respectively.

Background and Problem:

Containers of this type are typically assembled from at least two parts, that is, a substantially tubular body portion and a head-piece upon which screw threads are located for cooperation with a closure cap.

To manufacture these containers the pre-moulded tubular body portion is introduced into a mould wherein the head¬ piece is injection-moulded onto the body portion. The head¬ piece is typically of thicker material than the body and comprises a threaded portion for locating a closure cap. Usually the threads of the threaded portion have a pointed profile and may be angled towards the base of the container.

In order to remove the assembled container from the mould, the mould is split or the container is screwed out. These measures are necessary since the thread profile is such that substantial resistance to any axial movement is present. Such a method of manufacture is disclosed in, for example, FR-A-2 596 699.

That the prior art methods of manufacturing containers require firstly that the container be made in two stages, i.e. formation of the body portion followed by the moulding

of the head-piece thereto, and secondly that the assembled container is removed from the mould by either screwing or splitting the mould results in a complex and expensive manufacturing process. Another type of prior art container is disclosed in FR-A- 1 345 603. In this document, a container body portion is moulded simutaneously with a threaded head-piece in a separate split-mould. The split-mould is then opened and the united body portion and head-piecer is extruded by the introduction of a new batch of material into the apparatus.

Whilst such a process is more efficient that those mentioned previously, a relatively expensive mould arrangement is still needed.

A combined body portion and head-piece which can be axially withdrawn from the head-piece mould is described in CA-A- 691 156. In the process according to this document, the head-piece of the container is first formed in a head-piece mould and the tubular body portion is then formed threon through extrusion. Once the desired length of the body portion has been reached, the extrusion process ceases and the head-piece end of the container is pushed from its mould. The threaded portion of the head-piece is given a frustro-conical shape so as to aid the deformation of the head-piece to facilitate the axial ejection of the container from the head-piece mould.

A major disadvantage with the above-described process is the need for complex machinery. Furthermore, the axial force required to eject the container from the head-piece mould is high since the threads are shaped such that they cause deformation of the wall of the head-piece to allow its withdrawal. The object of the invention is thus to provide a container and methods for its production which overcome the problems mentioned above.

Solution and advantages:

This object is achieved by a container according to claim 1 and methods according to claims 6 and 8 respectively.

The claimed characteristics of the container allow it to be moulded in one piece and axially withdrawn after moulding, without the need for screwing or split-moulds. Furthermore, the provision of a rounded thread profile reduces the frictional force tending to retain the threaded portion in its mould, thereby allowing a lower axial withdrawal force to be used. Clearly, this reduces the danger of damaging the threads during withdrawal.

It is envisaged that a container according to the invention may also have a head-piece moulded onto the body portion with the threaded portion being on the head-piece. The dimensions of the head-piece and body portion are likewise chosen such that this thus formed container may similarly be axially withdrawn from the mould.

In a preferred embodiment of the present invention, the theaded portion is provided on the tubular body portion itself. Thus, a container having a wide opening can be produced in which the end wall remote from the threaded portion is moulded simultaneously with the tubular body portion. The provision of a simultaneously moulded end wall means that there is absolutely no danger of leakage from, or into, the container at the junction between the end wall and the tubular body portion, a problem which has affected prior art containers in which an end wall is later heat- sealed to the tubular body portion. A further advantage of this type of container is that its wall thickness i substantially uniform about the entire container.

Further embodiments of a container and methods according to the invention are given in the respective dependent claims.

Brief description of the drawings:

Further advantages and characteristics of the invention will be described in more detail in the following, with reference to the attached drawings in which

Fig. 1 is a sectional view through a container according to the invention with a cooperating cap; Fig. 2 is a sectional view through a container according to the invention in which the cap portion -is externally threaded; Fig. 3 is a schematic sectional view of a mould assembly for the production of a container according to the invention, and Fig. 4 is a perspective view of a container according to a further embodiment of the present invention.

Best mode of carrying out the invention:

With reference to Figs. 1 and 2, reference numeral 1 denotes a thermoplastic container according to the invention. The container comprises a substantially tubular body portion 2 with an end wall 3 and a cap portion 4. As shown in Fig. 1, upper region 5 of the body portion 2 is provided with integrally moulded screw-threads 6.

The wall thickness, length and diameter of the body portion 2 are chosen to allow a certain degree of flexing of the body portion 2 to permit its axial withdrawal from an injection-moulding machine. The axial withdrawal is greatly facilitated by the provision of a rounded thread profile, as clearly seen from the figures. By way of example a container according to the invention can have a body length of 50 mm, a diameter of 25 mm and a wall thickness of less than 1 mm. A cap for use of such a container naturally has the same diameter of 25 mm and may have a length of 25 mm. Clearly these dimensions depend on the type of material used.

In the embodiment of the invention shown in Fig. 4, the tubular body portion 2 is provided with a head-piece 13 which is moulded onto the preformed body portion. The head¬ piece 13 is of smaller diameter than the body portion at a region in which an outlet for the contents of the container is situated. The threaded portion 5, instead of being located on the tubular body portion 2, is in this case located on the head-piece 13. In accordance with the invention, the threads have a rounded profile and the length, diameter and wall thickness parameters relating to the head-piece 13 are chosen such that the container can still be axially withdrawn from its mould assembly. When producing such a container it is clear that the end wall 3 must be added after the body portion and head-piece have been moulded. This can be achieved by using a premoulded end-pice which is subsequently affixed to the body portion/head-piece by for example hot gas welding.

Fig. 3 shows a schematic view of a mould assembly for producing a container according to the present invention. Reference numeral 7 denotes a mould having a rounded thread profile formed at a region 8 thereof. Said mould 7 is provided with a passageway 10 for the introduction of molten thermoplastic material. Reference numeral 9 denotes a mandrel which is introduced into the mould 7 to a position in which a gap of substantially constant thickness is left between it and the mould wall. This gap corresponds to the container to be moulded. The open end of the mould is sealed by a plate 11 or similar so that injection of molten material can take place. After injection, the moulded container is cooled by not shown cooling means, for example with the aid of cooling passages in the mould, to a desired temperature. During cooling the moulded container shrinks somewhat. Said desired temperature is chosen such that a predetermined amount of shrinkage of the container is achieved whilst the container also possesses sufficient flexibility to be axially removed from the mould. So that the threads on the container will not be damaged by the mould assembly during axial removal, the container material must have solidified sufficiently. The desired temperature is naturally dependent on the choice of material, the dimensions of the container and the size of the thread profile. The fact that the thread profile is rounded means that a greatly reduced frictional force results during the axial withdrawal.

To achieve withdrawal of the moulded container, the mandrel 9 and sealing plate 11 are moved away from the mould 7 and the container is ejected from the mould 7 by ejection means 12. Although a mechanical pusher is shown in Fig. 3, it is clear that any suitable type of ejecting means, such as pneumatic means, may be used.

Because the container is withdrawn from the mould 7 at a temperature at which it is sufficiently flexible and because it has a thread profile which least resists axial displacement, the container can be removed from the mould by the exertion of solely an axial force, i.e. without the need for complicated screwing machinery or split moulds.

Obviously, if it is desired to provide a container and cap assembly as shown in Fig. 2 where the container 2 is threaded on its inner surface, then the mould assembly consists of a smooth-walled mould and a mandrel with the desired thread profile therein. Likewise, the corresponding cap-portion 4 can be produced in a similar mould assembly so that a cooperating threaded portion is achieved.

Whilst the above description relates to a container with a cap, the axial withdrawal method may be applied to any substanially tubular elongated object having a threaded portion. Examples of such objects include low pressure pipes and flexible tubing.

Claims

1. A thermoplastic, injection-moulded container (1) comprising an end wall (3), a substantially tubular body portion (2) and a threaded portion (5) remote from the end wall (3) for receiving a cap (4) with mutually-cooperating threads, c h a r a c t e r i z e d in that the threads (6) of the threaded portion (5) for receiving the cap (4) are rounded and that the container's wall thickness, its inner diameter and its axial length are selected such that the threaded portion (5) is able to flex sufficiently to permit axial withdrawal of the container (1) from a mould of an injection-moulding machine with no torque being applied to the container and without the need for the mould to split.

2. Container according to claim 1, c h a r a c t e r i z e d i n that the tubular body portion (1) has a head-piece (13) moulded thereon at the end remote from the end wall (3), said head piece having an outlet for the contents of the container and the diameter of the head-piece (13) at the outlet is smaller than that of the tubular body portion (2), and in that said threaded portion (5) is located on the head-piece (13) and is dimensioned so as to permit said axial withdrawal of the container.

3. Container according to claim 1, c h a r a c t e r i z e d in that the threaded portion (5) is located on the tubular body portion (2) and that the tubular body portion's wall thickness, its inner diameter and its axial length are selected such that the threaded portion (5) is able to flex sufficiently to permit axial withdrawal of the container (1) from a mould of an injection-moulding machine with no torque being applied to the container and without the need for the mould to split.

4. Container according to claim 3, c h a r a c t e r i z e d in that the threads (6) are located on the outer surface of the body portion (2).

5. Container according to claim 3, c h a r a c t e r i z e d in that the threads (6) are located on the inner surface of the body portion (2).

6. Method of producing a thermoplastic container (1), having a threaded portion (5) for receiving a cap (4) in a mould assembly comprising a mould (7) and a mandrel (9), comprising the following steps:

a) introducing the mandrel (9) into the mould (7), the mould (7) having the desired thread profile therein, b) leaving a space between the mandrel (9) and the mould (7) which determines the wall thickness of the container's tubular wall, c) injecting hot molten thermoplastic material into the said space, d) allowing the themoplastic material to solidify, e) removing the thus-formed thermoplastic container, from the mould (7), c h a r a c t e r i z e d in that the mould is provided with a rounded thread profile, and in that the thus-formed thermoplastic container is cooled to a temperature at which a predetermined degree of shrinkage of the container is achieved whilst the container also possesses sufficient flexibility to allow its axial withdrawal from the mould assembly with no torque being applied to the container and without the need for the mould to split, and at which temperature the threads (6) have solidified sufficiently so as not to incur damage from the mould assembly during withdrawal therefrom.

7. Method according to claim 6, c h a r a c t e r i z e d i n that the mould (7) and mandrel (9) are so shaped that a head-piece is formed on the tubular body portion (2) and in that the threaded portion (5) is moulded onto said head-piece.

8. Method of producing a thermoplastic container (1) having a threaded portion (5) for receiving a cap in a mould assembly comprising a mould (7) and a mandrel (9), comprising the following steps:

a) introducing the mandrel (9) into the mould (7), the mandrel (7) having the desired thread profile therein, b) leaving a space between the mandrel (9) and the mould (7) which determines the wall thickness of the container's tubular wall, c) injecting hot molten thermoplastic material into the said space, d) allowing the themoplastic material to solidify, e) removing the thus-formed thermoplastic container, from the mould (7), c h a r a c t e r i z e d in that the mandrel is provided with a rounded thread profile, and in that the thus-formed thermoplastic container is cooled to a temperature at which a predetermined degree of shrinkage of the container is achieved whilst the container also possesses sufficient flexibility to allow its axial withdrawal from the mould assembly with no torque being applied to the container and without the need for the mould to split, and at which temperature the threads (6) have solidified sufficiently so as not to incur damage from the mould assembly during withdrawal therefrom.

9. A method according to any of claims 5 to 7, c h a r a c t e r i z e d i n that an end wall (3) is formed simultaneously with the body portion (2) , which ύ wall (3) is located at the end of the body portion remote from said threaded portion (5).