IMPROVEMENTS IN MOULDED SYNTHETIC CLOSURE MANUFACTURE

Abstract: A mould apparatus (1) for producing a moulded synthetic closure for a container, such as a synthetic cork for a wine bottle, the apparatus including one or more mould cavities (14), the capacity of which is infinitely variable during charging or filling of the or each cavity (14) by means of a piston (16) slidably engaged within the or each cavity (14), and wherein the distal end of the piston (16) constitutes a movable end wall of its associated mould cavity, and wherein each piston (16) acts as an ejector for removing the moulded product from the or each mould cavity (14). A method of manufacturing moulded synthetic closures using the mould apparatus (1) is also disclosed, as are moulded synthetic closures produced thereby.

Description: IMPROVEMENTS IN MOULDED SYNTHETIC CLOSURE MANUFACTURE TECHNICAL FIELD The present invention relates to moulded synthetic closures and to methods and apparatus for making the same More particularlv, the invention relates to closures for liquid product containers, and particularly concerns closures for containers of wine or wine-based products, other beverages, and other comestibles More specifically , the present invention relates to moulded synthetic plastic closures which constitute an alternative to or substitute for natural cork BACKGROUND ART Synthetic plastic closures for wine or other liquid product containers are known However, such closures ha\e hitherto had little or no commercial success largeh because of their tendency to noticeably taint the product and/or because of the relatively resistance which they present to oxygen permeation into the container It is known heretofore to manufacture articles from foamed thermoplastic mateπal by injection or extrusion of polyurethane. polystyrene or polyolefms In these cases, the thermoplastic mateπals may be expanded from a granular form to assume a porous, solidified foam-like structure b\ the action of various propellants or agents for expanding or blowing the mateπals The blowing agents, in accordance with normal practice, are usually gases or gas generating substances that have been dissolved or otherwise intimately incorporated within the thermoplastic resinous mateπal while it is in an unexpanded granular form The application of heat to such a mixture causes the blowing agent to be released or thermally expanded or both, while the thermoplastic mateπal is attaining a foaming temperature at which it is sufficiently softened and yieldable to permit the pressure of the expanding blowing agent to expand it into the desired foam structure In a special case of extrusion forming of foamed thermoplastic mateπal, it is also known to decorate the surface of articles so produced to resemble natural wood or cork by imparting to the surface a parallel gram structure Such decoration is accomplished by extruding the mateπal through a die having, in particular, a multiple number of apertures to form a corresponding number of strands of expanding res . collecting these strands m parallel relationship, and then coalescing them into a body of any desired length Contacting surfaces of the strands create parallel gram lines which remain clearh visible m the surface of the finished articles and resemble natural wood grain In a special case of injection mouldmg of foam thermoplastics, it is known to mould articles by injecting into an enclosed cavity a measured amount of expandable thermoplastic resm so that the cavity is not completely filled by the unexpanded mateπal but becomes filled as the mateπal expands As expansion occurs, the softened rεsm is forced by a gaseous blowing agent into contact with the relatively cool walls of the mould cavity where the portion of the resm in direct contact with the walls is solidified and forms a dense outer layer or skm conforming to the shape of the cavity and ύmctiomng as a barπer, thereby preventing the escape of the gaseous blowing agent from the article and causing gas bubbles to be entrapped m the article ' s mteπor region Thus, articles moulded in this manner are characteπsed by a porous, foam-like mteπor and a dense outer shell or sk having the same general size and shape as the mould cavity and which are essentially impermeable to most substances By employing certain highly flexible thermoplastic mateπals, for example polyolefm ethylene-vmylacetate, in the previoush descπbed injection mouldmg process, the resulting foamed articles will exhibit elastic properties closely resembling similar products manufactured from other natural and synthetic elastomers This flexibility and resiliency plus the presence of an essentially impermeable skm allows these same articles if moulded into the proper size and shape, to function as closures for liquid product containers by being compressed and fitted into the container opening, then being allowed to expand, filling the opemng and creating a continuous seal about its perimeter Therefore, such articles would theoretically be useful as replacements for similar closure devices manufactured of more familiar mateπals, such as natural cork used m containers of medic c, wine and spiπts In reality, efforts at replacing natural cork closures in liquid product containers, especially containers for wine products, by manufactuπng and utilising closures from injection moulded foamed thermoplastics have not been very successful This has been due pπmaπly, it is believed, to the lack of aesthetically created consumer appeal for such closures, and the relationship of the dense outer skm to the porous inner core which dense outer skm. while necessary to make the closure essentially impermeable, can be a detriment to the scaling function of these articles, particularly when leakage channels are formed on the dense outer skm dunng the sealing of these articles Since such pπor art closures must be compressed to be fitted into liquid product containers there is a tendency for the dense outer layer of the closures to wnnkle and form longitudinal channels m the outer surface of the foamed articles Such channels could form leakage paths for the container contents or allow the ingress of substances harmful to the product being contained, such as ambient air m the case of the medicine or food products Tests have shown that these channels are caused pnmaπly by the presence of relatively large void spaces between the dense outer skins and the porous inner core of the foamed articles, their presence being the result of a previously unrecognised phenomena occurπng duπng the moulding of the articles Since the dense outer skm has a much higher resistance to compression than the porous inner core, it tends to deflect into any available void space, creating a channel on the outer surface of the closure that could result m a disruption of the otherwise continuous perimeter seal In addition to the foregoing problems, pπor art moulded closures have not been uniform and consistent m design and performance Thus, such pπor art closures have not been found readily acceptable as a replacement for similar closure devices, such as natural cork used m containers of medicine, wine and spiπts It is well known that natural cork contains vaπous holes and crooks and many times will crumble and break when inserted or withdrawn from the product container U S Patent 4,363,849 discloses a method for making closures resembling natural cork for sealing liquid product containers, wherein a strand of expandable plastic mateπal is injected into each mould cavity and is permitted to collect in that cavity in randomly oriented grounds of coils which expand to fill the cavity and coalesce to create randomly oriented grain lines on the surface of the closure resembling the appearance of natural cork. Also described are methods of moulding the closures which are said to preclude the formation of leakage channels on the closure surface and preferred blends of plastic resins and pigment particulars used to achieve the cork-like appearance. U.S. Patent 4,499,141 is a divisional of U.S. Patent 4,363,849 and relates to moulded synthetic closure of this type and having a particular composition. However, a major deficiency of the prior art is the apparatus is complex and therefore expensive, and the products produced are less than satisfactory because they allow air or oxygen permeation into the container. DISCLOSURE OF THE INVENTION It is a primary object of the invention to provide a moulded synthetic closure and methods and apparatus for making the same which go at least some way towards overcoming or at least minimising the prior art problems or limitations outlined above, or at the very least provide a clear alternative choice for consumers or manufacturers. It is another object of this invention to provide a moulded synthetic closure for liquid product containers which have a relatively uniform cellular or amorphous structure, such that when fitted to the container it presents a high resistance to oxygen permeation and/or product leakage through or around the closure to ensure a long shelf life for the product and yet produces little or no noticeable product tainting. It is a further object of the present invention to provide a moulding method, and apparatus therefor, wherein the capacity of the mould cavity is variable during the moulding process through use of an ejector piston the leading or distal end of which comprises a movable end wall of the mould cavity. It is yet another object of the present invention to provide a synthetic cork article and a means of making same which approaches many of the physical properties of natural cork when employed as a closure for a liquid product container. It is another object of the present invention to provide a synthetic cork article and a means of making same that may be employed as a bottle stopper and is removable using an ordinary corkscrew. It is another object of the present invention to provide a synthetic cork article and a means of making same which may be used as a cork substitute in existing bottling equipment without malfunction of said equipment. It is another object of the present invention to provide a synthetic cork article that can be manufactured with uniformity and will not break or crumble when inserted or withdrawn from the product container. Thus, the combined objectives of the present invention are to provide a synthetic cork article and a means of making same which will perform satisfactorily as a substitute for natural cork in a closure, or portion of a closure, for a liquid product container without fear of leakage into or out of said container and will satisfy the aesthetic requirement for a natural cork closure in such containers as those for wine and liquor products. These and other objects of the invention will become more apparent from the following description and the drawings. According to one aspect of the present invention, there is provided a mould apparatus for producing a moulded synthetic closure for liquid product containers, said mould apparatus including one or more mould cavities, the capacity of which is infinitely variable during charging or filing of said one or more cavities by means of a piston slidably engaged within each of said one or more cavities wherein the distal end of said piston constitutes a movable end wall of its associated mould cavity, and wherein said piston acts as an ejector for removing the moulded product from the mould cavity According to another aspect of the invention, there is provided a method for making a closure made of a thermoplastic resinous mateπal, which compπses providing a mould cavity of predetermined dimensions having a movable end wall opposite an entrance oπfice for injection of thermoplastic resinous mateπal into said cavity, injection at high speed of an expandable thermoplastic mateπal m an amount less than required to fill the mould cavity and allowing expansion thereof against the end face of the distal end of an ejector piston slidably mounted m said mould cavity whereby the capacity of the mould cavity increases as required to accommodate the expanding thermoplastic mateπal with mimmal entramment of air or other gaseous mateπal According to a further aspect of the invention, there is provided a moulded synthetic closure for liquid product containers produced by the method or process of the invention, the product being a substitute for natural cork closures but having a regular relatively umform cellular or amorphous structure throughout the core, and a liquid impervious outer skm contiguous with the inner core BRIEF DESCRIPTION OF THE DRAWINGS The objects of the present invention and the attendant advantages thereof will become more readily apparent by reference to the following drawings relating to a non-hmiting embodiment of the invention In the drawings - FIG 1 is a cross-sectional view of a typical mould which could be used according to the present invention to manufacture closures for liquid product containers as a substitute or alternative for natural cork The mould is depicted in the closed position and in the first stage of a product being moulded in situ FIG 2 is a further cross-sectional view of the mould of Fig 1 a further stage of filling of the mould cavity FIG 3 is another cross-sectional view of the same mould in the final stage of filling FIG 4 is an exploded or open view of the mould of Fig 1, for ejection of the finished product BEST MODE OF CARRYING OUT THE INVENTION Refernng to the drawings, Fig 1 depicts the first stage the operation of the mould 1 For the sake of claπty, only one of a possible plurality of mould cavities 14 is depicted, m a titree-plate injection mouldmg tool or apparatus having a sprue/runner system whereoy the thermoplastic mateπal is injected into the mould cavities via the galleπes of tne sprue/runner system 13 The injection moulding tool or apparatus 1 compnses m combination a top plate 2 and a back plate 3. a runner plate 4, a gasket plate 5, an intermediate plate 6. a cavity plate 7. a cavity insert retaining plate 8. an ejector plate 9 and an ejector retaining plate 10 A cavity insert 11 with external cooling water chambers 12 defines a vaπable cavity space 14 between the lower end of the runner plate 4 and the top end of slidably mounted ejector cavity pin 16 which is attached to the ejector plate 9 and ejector retaining plate 10 In operation, the moulding apparatus 1 closes the upper and lower potions of the mould (20 and 21 in Fig 4) at the parting line 15 about the guide post 19 When the apparatus has achieved the fully closed position (Fig 1) the injector umts injects unfoamed thermoplastic mateπal into the runner system 13 at high speed The plastic mateπal is forced through channels 13 past the filling adjustment pm 22, which may be moved in or out to reduce or increase the amount of plastic mateπal that flows past the filling adjustment p 22 and through a reduced diameter gate 23 The filling ad j ustment pm 22 at each ca ity 14 may be moved in or out as necessar to ensure that a uniform amount or weight of plastic mateπal flows through the gate 23 into each cavity 14. enabling each cavity to produce corks of the same uniform physical characteπstics The raw mateπal is further heated by shear as it passes through the small gate diameter 23 The increase in temperature causes the blowing agent to be activated and starts to expand the plastic raw mateπal As the raw mateπal expands (Fig 2) the ejector system is forced back by two hydraulic cylinders mounted on the side of the mould The hydraulic cylinders force the ejector plate 9 (slidably moulded on guide post 18 in the cavity space between ejector guide rails 17) back which retracts the cavity ejector pm 16 The rate of retraction of the cavity ejector pm matches the expansion of the plastic raw mateπal Referπng to Fig 3. the hydraulic cylinders continue to move back until the ejector plate 2 comes into contact with the mould back plate 3 This determines the length of the synthetic cork, which can be vaπed as may be required The plastic mateπal cools to ejection temperature Water 12 flowing m the cavity insert 11 cools the plastic raw mateπal and solidifies the mouldmg When the plastic mateπal reaches ejection temperature the mould opens along the parting line 15 and about the guide post 19 Fig 4 shows the tool m the open position with the synthetic cork in the cavity insert The machine ejector pm 16 moves forward (upwards) and ejects the cork out of the mould cavity 14 m the cavity insert 11 When the signal is given that the ejector has achieved its full forward stroke the injection mouldmg machine closes the mould as per Fig 1 and the cycle is repeated In an alternative method for manufactuπng moulded synthetic closures according to the invention, the or each mould cavity is disposed in a sprueless (hot runner) mould tool which includes means to seal the or each cavity at the entrance orifice immediately after the predetermined amount of thermoplastic mateπal has been injected therein, to stop any further flow of thermoplastic feed mateπal into the or each cavity and keeping the entrance oπfice sealed until the mateπal has expanded in the mould cavity to form the synthetic closure having a liquid impervious outer skm and a foamed core with no appreciable void spaces or separations between the outer skm and the core To provide a synthetic cork closure which can function satisfactoπly as a replacement for natural cork for use in closures for containers of medicine and food products such as wine and spiπts. vaπous factors need to be taken into account, including the type of thermoplastic resms and blends thereof, processing temperatures, injection pressures, injection speed, mould design and mould temperatures In producing synthetic cork closures, suitable amounts of each of the mateπals are mixed thoroughly pπor to moulding By way of example onl> , the closure for a container of wme or wine based product, compπses (or at least that part of the closure intended to contact the product) a moulded stopper of a flexible thermoplastic mateπal, such as ethylene vinyl acetate and polypropylene copolymer having a foamed core within a liquid impervious sk , wherein the foamed core has been produced by blowing the thermoplastic mateπal with a blowing agent including a thermally decomposable mateπal which evolves carbon dioxide In addition to the resins and chemical blowing agent, pigments may be added to the raw mateπal blend to give a cork-like colour or any other desired colour By selecting the additives and the processing conditions as required, it is possible to fabπcate a synthetic closure which reproduces the desirable properties of natural cork The fπctional characteπstics of the synthetic closure are such that the stopper firmly gπps the internal surfaces of the neck of the bottle and is not liable to accidental displacement, but can be drawn out when required by use of a conventional corkscrew or the like The gas barπcr charactcπstics of the closure are such that a synthetic closure of conventional size (e.g. length about 44 mm and an uncompressed diameter of about 22 mm) will restrict the ingress of oxygen into the bottle. Although an exemplary embodiment of the present invention has been shown and described, it will be apparent to those having ordinary skill in the art that a number of changes, modifications or alterations to the invention described herein may be made, none of which depart from the spirit of the present invention. All such changes, modifications, and alterations should therefore be seen as being within the scope of the present invention. It should be appreciated that the present invention provides a substantial advance in the moulding of synthetic closures and to methods and apparatus for making same, providing all of the herein-described advantages without incurring any relative disadvantages.

Claims: CLAIMS 1. A mould apparatus for producing a moulded synthetic closure for a container, said mould apparatus including one or more mould cavities, the capacity of which is infinitely variable during charging or filling of said one or more cavities by means of a piston slidably engaged within each of said one or more cavities, wherein the distal end of said piston constitutes a movable end wall of its associated mould cavity, and wherein said piston acts as an ejector for removing the moulded product from the mould cavity. 2. A mould apparatus as claimed in claim 1, further comprising means to adjust the rate of filling of said one or more cavities. 3. A mould apparatus as claimed in claim 2, wherein the means to adjust the rate of filling of said one or more cavities comprises an entrance gate or orifice and a pin or valve slidably engaged therein to adjust the circumferential space between the outer diameter of the pin valve and the periphery of the gate inlet. 4. A method for manufacturing a moulded synthetic closure for a container, comprising providing a mould cavity of predetermined dimensions having a movable end wall opposite an entrance orifice to said mould cavity for injection of thermoplastic resinous material into said cavity, injection at high speed of an expendable thermoplastic material in an amount less than required to fill the mould cavity and allowing expansion thereof against the end face of the distal end of an ejector piston slidably mounted in said mould cavity whereby the capacity of the mould cavity increases as required to accommodate the expanding thermoplastic material with minimal entrainment of air or other gaseous material. 5. A method as claimed in claim 4 wherein the ejector piston is moved in the direction opposite to the direction of travel to accommodate expansion of the thermoplastic material to eject the moulded synthetic closure from the mould cavity. 6. A moulded synthetic closure for a container when produced by a method as claimed in claim 4 or claim

Inventors: HIGGINS CHRISTOPHER LYNDON, IRWIN LIAM STEPHEN, HIGGINS, CHRISTOPHER, LYNDON, IRWIN, LIAM, STEPHEN
Applicants: C T E B EQUIPMENT PTY LTD, HIGGINS CHRISTOPHER LYNDON, IRWIN LIAM STEPHEN, C.T.E.B. EQUIPMENT PTY. LTD., HIGGINS, CHRISTOPHER, LYNDON, IRWIN, LIAM, STEPHEN
Application year: 2000
Main classification: B29C45
IPC codes: B29C44, B29C45