Plastic and nonmetallic article shaping or treating: processes – Utilizing special inert gaseous atmosphere or flushing mold...
Patent
1995-10-17
1997-04-15
Timm, Catherine
Plastic and nonmetallic article shaping or treating: processes
Utilizing special inert gaseous atmosphere or flushing mold...
264504, 264572, B29C 4402
Patent
active
056206399
DESCRIPTION:
BRIEF SUMMARY
THIS INVENTION relates to a new method of manufacturing needles. In particular, the invention relates to needles suitable for use in the irrigation or aspiration of serums or liquids into or from human bodies or any other living bodies or materials. However, it will of course be understood that the invention is not to be limited to needles only usable for these particular uses.
Conventional needles are traditionally formed from more than one component. Typically, these needles comprise a steel cannula and a plastic or metal mounting hub rigidly secured thereto. An adhesive is often utilised as a third component to secure the cannula to the hub.
In these conventional needles there is clearly a manufacturing expense in producing separate components and in subsequently securing those components together. There is thus a need to remove manufacturing difficulties and to be able to more rapidly and more efficiently produce large numbers of needles.
The present invention relates to a method of manufacturing integral one-piece needles so that the difficulties associated with forming needles from more than one component are overcome, or at least partially alleviated. The present invention is characterised by the use of fluid-assisted injection moulding processes.
Fluid-assisted injection moulding comprises a partial injection of a polymer melt to a mould cavity, followed by an injection of a fluid such as compressed gas into the core of the polymer melt. During the gas injection, the gas normally takes the path of least resistance to catch up to the melt front where, if the mould is properly vented, the pressure is lowest. In principle, the gas penetrates and hollows out the network of gas channels, displacing molten polymer at the hot core to fill the entire cavity.
However, this type of process has only been recognised as being capable of producing large parts with thick sections to attain structural rigidity without sacrificing good surface quality (see an article by L S Turng in "Advances in Polymer Technology" from the Journal of the Polymer Processing Institute, titled "Development and Application of CAE Technology for the Gas-Assisted Injection Moulding Process").
The present invention provides a method for manufacturing an integral one-piece needle, the method being characterised by feeding a polymeric resin into a mould cavity and injecting a fluid under pressure into at least a portion of the cavity to eject therefrom the central region of the polymeric resin, creating an annulus of polymeric resin having an orifice therethrough, the annulus of polymeric resin forming the cannula of the needle, the mounting hub being provided by the remaining portion of the cavity.
The fluid injection may be initiated either before or after the cavity is filled. The injection of the fluid before the cavity is filled results in the method of the invention operating similarly in principle to the fluid-assisted injection moulding techniques described above; namely, the fluid assists in pushing the melt through the cavity.
However, the injection of the fluid after the cavity is filled requires the cavity to include an aperture therein (in the form of an exit channel) which allows the expulsion of the displaced molten central region of the polymer.
The moulding process of the present invention preferably utilises conventional moulding machinery, such as injection moulding machinery, to feed the polymeric resin into the mould. In this respect, the mould preferably has a construction such as to allow the passing of fluid under high pressure separate to the means of injecting or feeding the polymeric resin into the mould.
It will also be appreciated that various design guidelines will need to be followed and considered in order to develop moulds and machinery suitable to this application. For example, the fluid and polymer channel networks should be designed to guide the fluid and polymer penetration to the extremities of the moulds and cavities without introducing air-traps and gas permeation. Further, the tool and part designs
REFERENCES:
patent: 4020837 (1977-05-01), Larson
patent: 4058121 (1977-11-01), Choksi et al.
patent: 5225141 (1993-07-01), Hendry
patent: 5454409 (1995-10-01), McAffer et al.
Derwent Abstract Accession No. 75401B/42, Class A32, CH,A, 613399 (Buhler Gebr AG) 28 Sep. 1979 (28.09.79), Abstract.
Derwent Abstract Accession No. 92-214538/26, Class A32, NL,A, 9002483 (Wavin BV) 1 Jun. 1992 (01.06.92), Abstract.
Bartlett Jack H.
Smith Trevor G.
Stevens John F.
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