METHOD OF PRODUCING A MOULDED ARTICLE HAVING A HOLLOW RIM

Abstract: A method of producing an injection moulded article (1) made of a polymeric material and having a hollow rim (2) being an integrated part thereof. The rim (2) is produced using a gas injection procedure. At least one moulding impression (4) producing a circumambient rim (2) of a moulding tool (3) is provided with at least one gate (6) for injection of a molten polymeric material (10), at least one gas duct (8) for gas injection, at least one gate (7) for discharge of excess of molten polymeric material (10) and/or at least one moving part (11) for controlled expansion of the moulding impression (4) to a pre-determined volume and at least one cavity (12) being coupled to and/or surrounding a gas duct (8). The cavity (12) constitutes a material reservoir for levelling of the discharge of the excess of molten polymeric material (10) and/or for levelling of the expansion of the moulding impression (4).

Description: METHOD OF PRODUCING A MOULDED ARTICLE HAVING A HOLLOW RIM The present invention relates to an improved method of producing an injection moulded article having a hollow blown rim being an integrated part of the article. The article is preferably manu¬ factured in one piece and the rim is produced using a gas injec¬ tion procedure. The article is preferably a transport and/or a storage container, a bottle crate,, a waste container, a pallet or a pallet container and is made of a polymeric material as for instance a thermoplastic material such as polyethylene and poly¬ propylene. In a further aspect the invention refers to an artic¬ le produced by using said improved method. Injection moulded containers, crates, pallets and the like have most often one or more upper and/or outer rims, whereby the rim provides strength and stability as well as it works as stacking and/or gripping mean. A commonly used concept for a rim consists of at least one U-shaped and downward open profile being circum¬ ambient or located on at least two opposite sides of a container etc. In order to obtain a satisfactory strength, rims of such a type require reinforcing and other structural means, such as ribs, girders, webs, edgings, rippings and the like, which means are placed inside the rim and/or connecting the rim with a side wall of a container, a loading area of a pallet etc. A manufac¬ turing of injection moulded articles having such a rim concept, furthermore incur a complex build-up of the moulding impressions included in used moulding tool, an excessive material usage and an increased cycle time resulting in an unnecessary high product weight and unnecessary high costs. Open rims also causes and effects accumulation of various contamination, which is a major problem especially in food processing and food transporting. There is a certain and increasing need for containers, crates, pallets etc. having a rim providing a high degree of strength, a low weight and a facilitated build-up, excluding reinforcing means as above and giving an article of a substantially uniform surface quality, of the moulding tool as well as of the article per se. Hollow blown profiles, produced by using a gas injection procedure, can to a certain extent overcome or reduce discussed problems. Hollow profiles can be produced using a number of well known and in detail disclosed gas injection procedures. Some of the most important and commonly used procedures and companies of origin include AIRMOLD - Battenfeld AIRPRESS - Klδckner Ferromatik CINPRES (Controlled Internal Pressure Moulding) - Pearless Cinpress ENCORE (Engineered Nitrogen Coresystem) - Encore Systems GAIN (Gas-assisted Injection Molding) - Detroid Plastic Molding GASMELT - Engel GID (Gasinnendruckverfahren) - Dynamit-Nobel GIP (Gasinnendruckprozeβ) - Demag GIT (Gasinjektiontechnik) - Schade Common features of gas injection procedures are that a mould impression of a moulding tool is filled with a molten polymeric material followed by injection of a pressurised gas. The molten polymeric material is thereby displaced with the gas by dischar¬ ge of excess material or expansion of the mould impression re¬ sulting in a hollow substantially closed moulded article or a part of such an article. The pressurised gas is normally injec¬ ted into the core of the molten polymeric material. Gas injection procedures are in conjunction with injection moul¬ ding of containers, crates, pallets and the like, used for the manufacture of i.a. pallet skids, various gripping and reinfor¬ cing means, partial rims etc. Circumambient hollow blown rims of a function similar to the circumambient U-shaped rims, have due to limitations in the adaptation of gas injection procedures not been possible to satisfactorily produce. The limitations consti¬ tuting a number of problems and drawbacks mainly refer to the discharge of excess of molten polymeric material and/or the ex¬ pansion of the mould cavity. The migration of the gas through the volume of the mould impression will with increasing dimen¬ sions of the moulded article be increasingly obstructed. Such obstructions may or will result in inferior quality, such as undercut, uneven material thickness and/or contorted parts. If the increased obstructions are compensated for by an increased gas pressure, the risk for ruptures or blow outs of the material is obvious and very high. In the international patent applica¬ tion WO 90/00466 is a method allowing articles of relatively larger dimensions to be produced using a gas injection proce¬ dure. The method comprises a moulding tool provided with a spill cavity. A charge of pressurised gas is injected into the mould impression to displace a portion of the molten material. Displa¬ ced material flows through a passage into a connected spill cavity or reservoir alternatively serving as an appendage of the article, a separate article or a cavity to receive spilled mate¬ rial for regrinding. Such cavities necessitate a certain amount of subsequent treatment, such as removal of separate articles, spill material and strings, bars and the like connecting the finished moulded article with the material or article in a spill cavity. The present invention provides a method of producing an injec¬ tion moulded article having a circumambient substantially closed hollow rim. The rim is produced using a gas injection procedure. The provides a rim giving adequate strength without reinforcing means as well as a substantially uniform surface structure. Problems and drawbacks, as disclosed above, due to obstructions related to the gas injection and caused by the relatively large volume and length of a circumambient rim are overcome without using spill cavities resulting in appendages, separate articles etc. and pendant subsequent treatment. The method of the present invention comprises a moulding tool having one or more moulding impressions producing at least one circumambient rim. The rim has a substantially closed circumam¬ bient hollow internal channel. The moulding impression is pro¬ vided with - at least one gate for injection of a molten polymeric material, - at least one gas duct for gas injection into the core of the molten polymeric material thus giving an internal gas pressure resulting in a hollow channel, - at least one gate for discharge of excess of molten polymeric material and/or at least one moving part for controlled expan¬ sion of the moulding impression to a pre-determined volume and - at least one cavity having a pre-determined volume and being coupled to and/or surrounding a gas duct. The cavity constitutes a material reservoir for levelling of the pressure inside the channel resulting from the gas injection, whereby the discharge of the excess of molten polymeric material and/or the expansion of the moulding impression is levelled. The cavity produces an abscess in rim. Such an abscess further in¬ creases the strength and can be designed to work as a stacking, piling or guiding mean, a stopper, a gripper, a lid attachment and the like. The fact that the abscess in an integrated part of the rim makes a subsequent treatment as discussed above unnecessary. In various embodiments of the present invention can the volume of a cavity coupled to and/or surrounding a gas duct be adjusted by the gas pressure and/or by a regulating device. The moving part for controlled expansion of the moulding impression is also and suitably controlled by the gas pressure and/or by a regula¬ ting device. The moulding impression is in a further embodiment provided with at least one cavity coupled to or surrounding a gate for discharge of excess of molten polymeric material. Such a cavity is similar to a cavity coupled to and/or surrounding a gas duct. The volume of the cavity can preferably be adjusted by the gas pressure and/or by a regulating device. In case a gas duct and/or a gate for injection or discharge of the molten polymeric material give rise to apertures or other openings in the circumambient rim, these are suitably sealed by applying a molten polymeric material or by means of loosely at¬ tached, glued or ultrasonically welded plugs, plates and/or the like. Plugs, plates etc. are suitably made of the same material as the article per se or of a material compatible therewith. In a further aspect the present invention refers to a moulded article produced by using above disclosed method. The article is preferably selected from the group consisting of transport and/or storage containers, bottle crates, waste containers, pallets, pallet containers or similar storage and/or transport appliances. These and other objects and the present invention will be more fully understood from the following detailed description, taken in conjunction with appended drawings, wherein like reference numerals have been applied to like parts throughout the various Figures and wherein Figures 1 - 4 are schematical cross-sections of moulding impressions 4 equipped for a gas injection procedure. A moulding impression 4 is a part of a moulding tool 3 used in various embodiments of the present invention and is shown before and after gas injection. Figure 5 is an injection moulded artic¬ le 1 having a circumambient rim 2 being an integrated part of the article 1. The article 1 is a transport and storage contai¬ ner. Figure 6 is a planar cross-section of an injection moulded article 1 being a pallet. The pallet is provided with a circum¬ ambient rim 2 similar to that in Figure 5. The container of Fig. 5 the pallet of Fig. 6 are both produced using embodiments of the method according to the present invention. Figures 1 and 2 show schematically cross-sections of a part of a moulding tool 3 comprising a moulding impression 4 having a gate 7 for discharge of excess of polymeric material 10, which moul¬ ding impression 4 produces a substantially closed hollow circum¬ ambient rim 2 (see Fig. 5 and 6). Only a part of said rim 2 is for reason of simplicity shown and from a long side. The moul¬ ding impression 4 includes a gate 6 for injection of molten polymeric material 10, a duct 8 for injection of gas into the core of the molten polymeric material 10, a cavity 12 coupled to and surrounding the duct 8 and said gate 7 for discharge of ex¬ cess of molten polymeric material 10. Figure 1 shows the moul¬ ding impression 4 after filling of molten polymeric material 10 but before gas injection through the duct 8. Figure 2 shows the same moulding impression as Figure 1 but after the gas injection through the duct 8, whereby excess of molten polymeric material is discharged through the gate 7 and a hollow channel 5 is for¬ med within the molten polymeric material 10 and thus within the rim 2 (see Fig. 5 and 6). The cavity 12 works as a material re¬ servoir levelling the discharge of the molten polymeric material 10. Molten polymeric material 10 is injected through the gate 6 as indicated by arrow A and discharged through gate 7 as indi¬ cated by arrow B. Gas is injected through the duct 8 as indica¬ ted by arrow C. Figures 3 and 4 show schematically cross-sections of a part of a moulding tool 3 comprising a moulding impression 4, having a moving part 11 for controlled expansion of the moulding impres¬ sion 4, said moulding impression 4 producing a substantially closed hollow circumambient rim 2 (see Fig. 5 and 6). Only a part of said rim 2 is for reason of simplicity shown and from a short side. The moulding impression 4 includes a gate 6 for injection of molten polymeric material 10, a duct 8 for injec¬ tion of gas into the core of the molten polymeric material 10, a cavity 12 coupled to and surrounding the duct 8 and said moving part 11 which is provided with a regulating device 9. Figure 3 shows the moulding impression 4 after filling of molten polymeric material 10 but before gas injection through the duct 8. Figure 4 shows the same moulding impression as Figure 3 but after gas injection through the duct 8, whereby the moulding im¬ pression 4 is expanded when the moving part 11 moves as indica¬ ted by arrow D and a hollow channel 5 is formed within the mol¬ ten polymeric material 10 and thus within the rim 2 (see Fig. 5 and 6). The cavity 12 works as a material reservoir levelling the expansion of the moulding impression 4. Molten polymeric ma¬ terial 10 is injected through the gate 6 as indicated by arrow A and gas is injected through the duct 8 as indicated by arrow C. The moving part is controlled, giving desired expansion of the moulding cavity, by the regulating device 9. Figure 5 shows in a perspective view seen from above an injec¬ tion moulded article 1 being an transport and storage container having a substantially closed hollow circumambient upper rim 2. The article is produced using the method according to the pre¬ sent invention and said hollow rim 2 is an integrated part of the article 1. The rim 2 has abscesses 13 resulting from cavi¬ ties 12 (see Fig. 1-4) in the moulding impression 4 (see Fig. 1-4). Apertures in the abscess 13 resulting from a gas duct 8 (see Fig. 1-4) are sealed by ultrasonically welded plates 14. The abscesses 13 and hence cavities 12 and gas ducts 8 (see Fig. 1-4) are placed in pairs on the long sides of the rim 2 and of the moulding impression 4 (see Fig. 1-4), respectively. Figure 6 shows from a long side a planar view a cross-section of an injection moulded article 1 being an pallet having a substan¬ tially closed hollow circumambient upper rim 2. The pallet is produced using the method according to the present invention and said hollow rim 2 is an integrated part thereof. The rim 2 has a hollow circumambient channel 5 and has, furthermore, abscesses 13 resulting from cavities 12 (see Fig. 1-4) in the moulding im¬ pression 4 of used moulding tool 3 (see Fig. 1-4). While particular embodiments of the invention have been shown, it will be understood, of course, that the invention is not limited thereto since many modifications may be made, and it is, therefore, contemplated to cover by the appended claims any such modifications as fall within the true spirit and scope of the invention.

Claims: CLAIMS 1. A method of producing an injection moulded article (1), such as a storage, a transport or a waste container, a pallet, a pallet container or the like made of a polymeric material, and having a hollow rim (2) being an integrated part of said article (1), whereby the rim (2) is produced using a gas in¬ jection procedure involving a moulding tool (3) having one or more moulding impressions (4) of which at least one produces a rim (2) or part of a rim (2) having at least one hollow channel (5) c h a r a c t e r i s e d i n, that a moul¬ ding tool (3) has one or more moulding impressions (4) produ¬ cing at least one circumambient rim (2), which rim (2) has a substantially closed circumambient hollow internal channel (5), the moulding impression (4) being provided with at least one gate (6) for injection of a molten polymeric material (10), at least one gas duct (8) for gas injection into the core of the molten polymeric material (10) thus giving an in¬ ternal gas pressure resulting in a hollow channel (5), at least one gate (7) for discharge of excess of the molten polymeric material (10) and/or at least one moving part (11) for controlled expansion of the moulding impression (4) to a pre-determined volume and at least one cavity (12) having a pre-determined volume and being coupled to and/or surrounding a gas duct (8), which cavity (12) constitutes a material re¬ servoir for levelling of the pressure inside the channel (5), which pressure resultes from the gas injection, whereby the discharge of the excess of molten polymeric material (10) and/or the expansion of the moulding impression 4) is level¬ led and a to the cavity (12) corresponding abscess (13) is formed in the rim (2) . 2 . A method according to claim 1 c h a r a c t e r i s e d i n, that the volume of the cavity (12) can be adjusted by the gas pressure and/or by a regulating device. 3. A method according to claim 1 or 2 c h a r a c t e r i s e d i n, that the moving part (11) for controlled expansion of the moulding impression (4) is controlled by the gas pressure and/or by a regulating device (9). 4. A method according to any of the claims 1 - 3 c h a r a c ¬ t e r i s e d i n, that at least one cavity similar to a cavity (12) is coupled to and/or surrounding a gate (7) for discharge of excess of molten polymeric material (10). 5. A method according to claim 4 c h a r a c t e r i s e d i n, that a volume of a cavity coupled to and/or surrounding a gate (7) for discharge of excess of molten polymeric mate¬ rial (10) can be adjusted by the gas pressure and/or by a re¬ gulating device. 6. A method according to any of the claims 1 - 5 c h a r a c ¬ t e r i s e d i n, that any aperture in the circumambient rim (2) resulting from a gas duct (8) and/or a gate (6, 7) for injection or discharge of molten polymeric material is sealed. 7. A method according to claim 6 c h a r a c t e r i s e d i n, that a sealing is performed by applying a molten poly¬ meric material (10). 8. A method according to claim 6 c h a r a c t e r i s e d i n, that a sealing is performed by means of a loosly at¬ tached, a glued or an ultrasonically welded plug, plate or the like (14) . 9. An injection moulded article (1) produced by using the method of claims 1 - 8 c h a r a c t e r i s e d i n, that the article (1) is a transport and/or storage container, a bottle crate, a waste container, a pallet or a pallet container.

Inventors: BRAUNER MANFRED, BRAUNER, MANFRED
Applicants: BRAUNER MANFRED, PERSTORP AB, BRAUNER, MANFRED
Application year: 1995
Main classification: B29C45
IPC codes: B29C45, B65D1