AU2008229810A1 - Injection moulding method and apparatus - Google Patents

Description

AUSTRALIA Patents Act 1990 ORIGINAL COMPLETE SPECIFICATION STANDARD PATENT Invention title: Injection moulding method and apparatus The following statement is a full description of this invention, including the best method of performing it known to us: Injection moulding method and apparatus Field of the Invention The present invention relates to an injection moulding method and apparatus. In particular, the present invention relates to an injection moulding method and 5 apparatus by which an undercut may be applied to the interior wall of an article whilst the article is being injection moulded. Background of the Invention In this specification, where a document, act or item of knowledge is referred to or discussed, this reference or discussion is not an admission that the document, act 10 or item of knowledge or any combination thereof was at the priority date: (i) part of common general knowledge; or (ii) known to be relevant to an attempt to solve any problem with which this specification is concerned. Articles with indentations or grooves in their interior walls - which are known in 15 the art and referred to in this specification as 'undercuts' - are used for a variety of purposes. For example, an undercut may be applied to the interior wall of a food or beverage container to permit engagement between the container and a replaceable closure and to enable use of the replaceable closure to selectively open and close the container. A foil or plastic insert may also be affixed to an 20 undercut in the interior wall of a food, beverage or medicine container as a seal for hygiene purposes and/or to provide tamper-evidency, the seal then being removed by the end consumer of the product after purchase. Traditionally such articles, when made from plastic, have been manufactured by the process of blow moulding, where a cooled, metal mould is closed around a 25 parison of a suitable plastics material and air is blown inside the parison, causing it to inflate and take on the shape of the mould. Undercuts are applied to the interior walls of such articles by forming a corresponding undercut on the inside of the metal mould, into which the inflated plastic is blown. After the inflated plastic has set, the mould is re-opened and the article removed. 30 Such articles have also been manufactured through the process of injection moulding, but to a far lesser extent. As is known to those skilled in the art, 2 injection moulding involves injecting molten plastic at high pressure into a mould which is the inverse of the shape of the article to be formed. The mould is separable into at least two portions, known as the core and the cavity, which are brought together to form the mould into which the molten plastic is injected. For 5 many applications injection moulding is superior to blow moulding, as it produces a controlled wall thickness and less surface imperfections. Better control over wall sections enables a tighter tolerance to be maintained over the moulding process. Applying an undercut to the interior wall of an injection moulded article requires 10 a mould core with a projection or skirt which extends radially outwardly from the core's longitudinal axis and into the mould cavity. The molten plastic which fills the cavity after high pressure injection flows around the projection to thereby apply the undercut to the interior wall of the article. After solidification of the molten plastic in the mould, the projection is typically 15 very snugly nested within the undercut. This can make it very difficult to withdraw the core from the cavity (or vice versa), when removing the article, without damaging the article in the process. The use of 'collapsible' mould cores has been proposed in the past as a potential solution to this problem. One such collapsible core is described in US Patent No. 20 3,843,088, the core comprising three or more separate core members which come together (or expand) to form a moulding surface having an undercutting projection of the kind referred to above. One of the members is movable inwardly, in a direction substantially perpendicular to the longitudinal axis of the core, with the remaining members being movable at an angle to the longitudinal 25 axis of the core. When the core is moved from the expanded position to the retracted position, the moulding surface moves inwardly in a direction substantially perpendicular to the longitudinal axis of the core, thereby causing the projection to move out of the undercut. Another example is US Patent No. 4,524,943, which describes an injection mould 30 with a collapsible core that further incorporates an ejection sleeve and pairs of independently movable followers that act together to remove an article with an undercut in its interior wall from the mould.

3 It will be apparent that these moulds are complex and are therefore very expensive to produce in practice. It would be advantageous to devise an injection moulding method and apparatus for manufacturing articles having undercuts in their internal wall, that does not rely on a movable mould core to remove the 5 article from the mould. Summary of the Invention According to a first aspect of the present invention, there is provided an injection moulding method comprising the steps of: locating an elastically deformable member within a mould; 10 deforming the member; injection moulding an article within the mould such that the deformed member applies an undercut to an interior wall of the article; and allowing the deformable member to return substantially to its original shape to facilitate removal of the article from the mould. 15 The present invention provides in another aspect a method for injection moulding comprising the steps of: forming a mould cavity between a pair of mould parts; bringing a deformable member into the mould cavity; introducing a mouldable material into the mould cavity to form an article, 20 wherein the deformable member is compressed in the mould cavity during the article formation step so as to produce an undercut in an interior wall of the article on contact between the deformable member in its compressed state and the mouldable material; and allowing the deformable member to return substantially to its original 25 shape to facilitate removal of the article when formed from the mould. The deformable member is typically carried by one of the mould parts into the mould cavity during an article formation step. The undercut produced by reason of displacement of mouldable material in a generally outward direction through the action of the deformable member, creates 4 a ledge on an outer surface, typically the rim, of the article, to which a covering such as a closure can be releasably applied. In the method of the present invention, an elastically deformable member acts as a core projection, to apply an undercut to the interior wall of an article to be 5 injection moulded. In contrast to the prior art, the present method does not rely on a movable core to withdraw the projection from the undercut after the article has been produced, but instead utilises the resilient properties of the elastically deformable member. This enables internally undercut articles to be injection moulded using far simpler and less expensive moulds than previously possible. 10 Preferably, the step of deforming the member comprises compressing the member between two parts of the mould so that when compressed, a portion of the member projects into the mould cavity to apply an undercut to the article being injection moulded therein. In some embodiments, the member may be compressed between two parts of the mould core which are movable towards 15 each other as part of the action of locating and securing a mould core within a mould cavity so as to form the mould for the article being injection moulded. In preferred embodiments, the core parts are movable towards each other in a first direction substantially parallel to the direction in which the core or cavity are moved to form the mould, so as to deform the member in a second direction 20 substantially orthogonal to the first direction. The movable core parts between which the deformable member is compressed may be provided at selected locations along the core, so as to apply an undercut to the area of the internal wall adjacent to the deformable member. A plurality of movable core parts may be provided along the mould core, with a 25 deformable member placed within each pair of core parts. This enables a corresponding plurality of undercuts to be applied to the area of the internal wall adjacent each deformable member. In one embodiment the step of locating the elastically deformable member within the mould comprises encircling the mould core with an annular deformable 30 member, to thereby apply an undercut to the internal perimeter of the interior wall of the article.

5 The elastically deformable member may be formed from any suitable material that can withstand the temperatures and pressures found inside an injection moulding machine. Suitably, a synthetic-rubber based material, such as Viton"' may be used. According to a further aspect of the present invention, there is provided an 5 injection moulding apparatus for applying an undercut to the interior wall of an article formed therein, the apparatus including: a mould cavity; a mould core locatable within the mould cavity to define a moulding space; and 10 an elastically deformable member located within the mould, said member being configured to project into the moulding space when deformed to apply an undercut to the article and retract from the undercut when returning substantially to its original shape to facilitate removal of the article from the mould. Preferably, the moulding apparatus includes movable parts, between which the 15 member may be compressed, such that when compressed a portion of the member projects into the moulding space, to thereby apply an undercut to the article. Preferably the movable parts are parts of the mould core, which are movable towards each other as the mould core is located within the mould cavity. 20 Optionally, the movable parts are movable towards each other in a first direction substantially parallel to the direction of movement of the mould core or cavity as the core is located within the cavity, so as to deform the member in a second direction substantially orthogonal to the first direction. The movable core parts may be provided at selected locations along the core, so as 25 to apply an undercut to the area of the internal wall adjacent to the deformable member. A plurality of movable core part may be provided along the mould core, with a deformable member placed within each pair of parts. This enables a corresponding plurality of undercuts to be applied to the area of the internal wall 30 adjacent each deformable member.

6 Optionally, the elastically deformable member is annular and encircles the mould core to thereby apply an undercut to the internal perimeter of the interior wall of the article. The elastically deformable member may be formed from any suitable material that 5 can withstand the temperatures and pressures found inside an injection moulding machine. Suitably, a synthetic-rubber based material may be used such as Viton". In another aspect of the present invention, there is provided an injection moulding apparatus for producing an undercut in an interior wall of an article formed therein, the apparatus including; 10 a pair of mould parts which, when brought together, define a mould cavity for forming an article by injection moulding of a mouldable material into the cavity; and a deformable member capable of being brought into the mould cavity; the arrangement being such that when the mouldable material is introduced into 15 the mould cavity for the formation of an article, the deformable member is compressed during formation of the article in the mould cavity so as to produce an undercut in an interior wall of the article on contact between the deformable member in its compressed state and the mouldable material, the deformable member being capable of returning substantially to its original shape following 20 moulding to facilitate removal of the article when formed from the mould. The deformable member is typically carried by one of the mould parts into the mould cavity. In one preferred embodiment the deformable member is located in a recess in one of the mould parts and deforms outwardly from the recess when compressed on bringing the mould parts together due to the compressible nature 25 of the material of its construction. The article to be formed according to methods and apparatus of the invention may take any suitable form, but will typically be a container requiring a closure or other covering. The container may be of any desired shape. In the case of a food container for containing a product such an ice cream, examples of desirable 30 shapes include substantially circular, substantially square, substantially rectangular, and substantially hexagonal shapes. Other container shapes are 7 envisaged within the scope of the present invention. Methods and apparatus according to the invention have been found to work particularly well if the mould cavity is configured so as to produce an article in the form of a container which is tapered from top to bottom, with the internal undercut and its complementary 5 external ledge being formed in the rim of the container at its largest perimeter. In another aspect the present invention provides an article produced by a method described herein. Typically the article so produced will be a container. In another aspect the present invention provides an article produced by apparatus described herein. Typically the article so produced will be a container. 10 Brief Description of the Drawings The invention will now be further explained and illustrated by reference to the accompanying drawings in which: Figure 1 is a cross-sectional view of a mould for injection moulding articles by performing the method according to one form of the present invention, prior 15 to an injection-moulding operation; Figure 2 is a cross sectional view of the mould illustrated in Figure 1 during an injection-moulding operation; and Figure 3 is a cross-sectional view of the mould illustrated in Figures 1 and 2 after an injection-moulding operation, illustrating removal of an injection 20 moulded article having an undercut applied to its interior wall. Detailed Description of the Drawings Turning to Figure 1, an injection mould 10 is illustrated. The mould 10 is composed of a movable core 12 and a stationary cavity 14. When manufacturing less complex articles, such as single-chambered containers, the core 12 will impart 25 its shape to the interior of the manufactured article. The core 12 is removably attached via connecting elements 16 to a plate 18, which is in turn connected to the machinery (not shown) for moving the core 12 into and out of location within the cavity 14.

8 The connecting element 16 includes a spring 17, that is compressable in a manner described in detail below, to facilitate movement of the core 12 relative to the plate 18. The core 12 is comprised of an attaching portion 13 which is located within a seat 5 in the plate 18, and a moulding portion 15 which extends out of the plate 18, and is the portion of the core 12 that actually imparts its shape to the interior of the article being moulded. The moulding portion 15, being slightly larger in diameter than the attaching portion, defines a circumferential recess 15A around the core 12. 10 Prior to a moulding operation, an elastically deformable member in the form of an o-ring 20 is slipped over the core 12 and into the recess 15A, where it is held in place so as to encircle the core 12. The o-ring 20 must be made from a compressible and resilient material that can nevertheless withstand the high temperatures and pressures present inside an injection moulding machine during 15 a moulding operation. The inventors have found that o-rings made from synthetic-rubber based material such as Viton"' have these necessary properties for both single and anything up to several hundred, uses. The thickness of the o-ring 20 is selected according to the depth of the undercut which is to be applied to the article being manufactured. In the illustrated 20 embodiment, the o-ring 20, in an uncompressed state, is about 4.5mm thick in the 'A' direction shown in Figure 1. Turning now to Figure 2, the mould 10 is shown during a moulding operation, where the core 12 has been moved into the cavity 14 and temporarily sealed in place by the application of a force of a typical magnitude in injection moulding 25 machines, i.e from about 100 tonnes to several thousand tonnes or more. During a moulding operation, a moulding space 19 is defined between the core 12 and cavity 14, into which a predetermined quantity of a suitable material (usually a plastics material) is injected at high pressure through a nozzle 21. The material then rapidly fills the moulding space 19, cools and sets to form the completed 30 article.

9 The core 12 is advanced into the cavity 14 by moving both the moulding portion 15 and plate 18 along a longitudinal axis B until the core 12 is at a suitable location within the cavity 14 to define the moulding space. Once in this location the force applied in direction B compresses the spring 17, causing the plate 18 to 5 move closer to the moulding portion 15 of the core 12. This action compresses the o-ring 20 between the plate 18 and moulding portion 15, causing it to expand into the moulding space 19 in a direction approximately perpendicular to the longitudinal axis B of the core 12. Material injected into the moulding space 19, then flows naturally around a portion 23 of the o-ring 20 that projects into the 10 moulding space, thereby applying an undercut to the interior wall of the article. The material then cools and sets in the usual manner. Finally, turning to Figure 3, as the core 12 is withdrawn from the cavity 14, compression forces acting on the o-ring 20 are released, and upon which, the resilient Viton

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" o-ring 20 returns to its original shape, effectively retreating back 15 into the core 12, and allowing the projecting portion 23 to move easily out of the undercut 25, now formed in the interior wall 27 of the article 29. The finished article 29 is then removed from the mould 10. A ring-shaped member 20 that encircles the core 12 should be used to apply a circular undercut to the interior wall of an injection-moulded article. However, 20 undercuts in other shapes may also be applied to the interior wall of articles, by utilising deformable members of corresponding shapes in the core 12. For example, a series of circumferentially spaced linear members would apply a corresponding plurality of linear, circumferentially extending undercuts to the interior wall of the article 29. 25 Deformable members 20 may also be provided at selected positions along the longitudinal axis B of the core 12, to apply an undercut to the area of the internal wall adjacent to the where the member expands. The vertical cross-sectional shape of the member may also be selected depending on the desired profile of the undercut to be applied. For example, the circular 30 vertical cross-sectional shape of the member illustrated in Figures 1 and 2, applies an undercut with a curved profile, as is illustrated in Figure 3. Similarly, the 10 inventors have found that a member with a square vertical cross-sectional shape, applies an undercut with a wedge-shaped profile. A plurality of movable core part pairs may also be provided on the mould core 12, with a deformable member 20 placed between each pair. This would apply a 5 corresponding plurality of undercuts spaced apart along the longitudinal axis of the article 29. The word 'comprising' and forms of the word 'comprising' as used in this description and in the claims do not limit the invention claimed to exclude any variants or additions. Modifications and improvements to the invention will be 10 readily apparent to those skilled in the art. Such modifications and improvements are intended to be within the scope of this invention.

Claims (24)

1. An injection moulding method comprising the steps of: (a) locating an elastically deformable member within a mould; (b) deforming the member; 5 (c) injection moulding an article within the mould such that the deformed member applies an undercut to an interior wall of the article; and (d) allowing the deformable member to return substantially to its original shape to facilitate removal of the article from the mould. 10

2. An injection moulding method according to claim 1 wherein the mould comprises a core and a cavity and the deformable member is located on the core and is carried into the mould during the injection moulding step.

3. An injection moulding method according to claim 1 or 2, wherein the deforming step comprises compressing the deformable member. 15

4. An injection moulding method according to claim 3 , wherein the deforming step comprises compressing the deformable member between two parts of the mould so that when compressed, a portion of the member projects into the mould cavity to apply an undercut to the article being injection moulded therein. 20

5. An injection moulding method according to claim 4 wherein the deforming step comprises compressing the deformable member between two parts of the core which are movable towards each other as part of the action of locating and securing the core within the cavity during an injection moulding operation. 25

6. An injection moulding method according to claim 5 wherein the core parts are movable towards each other in a first direction substantially parallel to the direction in which the core or cavity are moved to form the mould, so as to deform the member in a second direction substantially orthogonal to the first direction. 12

7. An injection moulding method according to claims 5 or claim 6, further including the step of providing at selected locations along the core, movable core parts between which a deformable member placed within each pair of movable core parts, is compressed, so as to apply an undercut 5 to an area of an internal wall of the article adjacent to the deformable member.

8. An injection moulding method according to any one of claims 2 to 7 wherein the elastically deformable member is annular and encircles the mould core to thereby apply an undercut to the internal perimeter of an 10 interior wall of the article.

9. An injection moulding method according to any one of claims 1 to 8 including the step of selecting the profile of the member in order to apply an undercut having a corresponding profile to the interior wall of the article. 15

10. An injection moulding method according to any one of claims 1 to 9 wherein the elastically deformable member is made of a synthetic-rubber based material, such as Viton".

11. A method for injection moulding comprising the steps of: (a) forming a mould cavity between a pair of mould parts; 20 (b) bringing a deformable member into the mould cavity; (c) introducing a mouldable material into the mould cavity to form an article, wherein the deformable member is compressed in the mould cavity during the article formation step so as to produce an undercut in an interior wall of the article on contact between the deformable 25 member in its compressed state and the mouldable material; and (d) allowing the deformable member to return substantially to its original shape to facilitate removal of the article when formed from the mould.

12. An injection moulding apparatus for applying an undercut to the interior 30 wall of an article formed therein, the apparatus including: (a) a mould cavity; 13 (b) a mould core locatable within the mould cavity to define a moulding space; and (c) an elastically deformable member located within the mould, said member being configured to project into the moulding space when 5 deformed to apply an undercut to the article and retract from the undercut when returning substantially to its original shape to facilitate removal of the article from the mould.

13. An apparatus according to claim 12, wherein the apparatus includes movable parts, between which the member is compressible, such that when 10 compressed a portion of the member projects into the moulding space to thereby apply an undercut to the article.

14. An apparatus according to claim 13 wherein the movable parts are parts of the mould core, which are movable towards each other as the mould core is located within the mould cavity.

15 15. An apparatus according to claim 14 wherein the movable parts are movable towards each other in a first direction substantially parallel to the direction of movement of the mould core or cavity as the core is located within the cavity, so as to deform the member in a second direction substantially orthogonal to the first direction. 20

16. An apparatus according to any one of claims 12 to 15, wherein the movable core parts are provided at selected locations along the core, so as to apply an undercut to an area of the internal wall adjacent to the deformable member.

17. An apparatus according to any one of claims 12 to 16, including a plurality 25 of pairs of movable core parts provided along the mould core and a deformable member located within each pair of parts.

18. An apparatus according to any one of claims 12 to 17, wherein the elastically deformable member is annular and encircles the mould core to thereby apply an undercut to the internal perimeter of the interior wall of 30 the article. 14

19. An apparatus according to any one of claims 11 to 18 wherein the elastically deformable member is made from a synthetic-rubber based material such as Viton".

20. An apparatus according to any one of claims 12 to 19 wherein the profile of 5 the elastically deformable member is selected to apply an undercut having a corresponding profile to the interior wall of the article.

21. An injection moulding apparatus for producing an undercut in an interior wall of an article formed therein, the apparatus including; (a) a pair of mould parts which, when brought together, define a mould 10 cavity for forming an article by injection moulding of a mouldable material into the cavity; and (b) a deformable member capable of being brought into the mould cavity; the arrangement being such that when the mouldable material is 15 introduced into the mould cavity for the formation of an article, the deformable member is compressed during formation of the article in the mould cavity so as to produce an undercut in an interior wall of the article on contact between the deformable member in its compressed state and the mouldable material, the deformable member being capable of returning 20 substantially to its original shape following moulding to facilitate removal of the article when formed from the mould.

22. An article produced by practising the method according to any one of claims I to 11.

23. An injection moulding method substantially as herein described with 25 reference to the drawings.

24. An injection moulding method substantially as herein described with reference to the drawings. 30