Plastic and nonmetallic article shaping or treating: processes – With measuring – testing – or inspecting
Reexamination Certificate
1999-05-25
2001-09-11
Kuhns, Allan R. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
With measuring, testing, or inspecting
C264S045500, C264S241000, C264S328180, C425S145000, C425S461000, C425S580000
Reexamination Certificate
active
06287491
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a method of and apparatus for moulding plastics articles.
BACKGROUND OF THE INVENTION
In plastics injection moulding, molten plastics material forms layers as it fills the mould cavity. The first material entering the cavity forms the outer skin of the article being moulded and the rest of the material entering after this continues to form the core layers of the article. This phenomenon has been exploited by using two barrel injection moulding machines and injecting in sequence materials to form articles in which the skin is formed of a different material from the core, for example incorporating colour in the skin and then filling with cheaper uncoloured material, or by filling the skin with a plastics material containing fillers which would otherwise give an unsatisfactory surface finish.
In JP-A-5084733 there is disclosed an arrangement in which two separate materials are injected sequentially by two separate injectors into an accumulator, and then the sequence is expelled from the accumulator by a piston into the mould cavity to produce moulded articles with layers of the different materials. It will be seen that in this arrangement the materials are only formed into a sequence after being separately melted and plasticised in separate injectors. The necessary apparatus is costly and complex.
A disadvantage of such techniques is that the machinery required is costly and complicated.
SUMMARY OF THE INVENTION
The invention provides a method of moulding plastics articles wherein at least one predetermined part of each moulded article is of different composition from the remainder of the article, comprising propelling a solid plastics feed material (
1
,
2
) by screw feed means through a melting zone (
5
a
), the screw feed means (
3
,
10
) propelling the resultant molten plastics material to shaping means, shaping the molten plastics material in the shaping means and allowing the material to solidify to retain the shape, wherein the composition of the material entering the shaping means is varied cyclically, characterized by varying the composition of the plastics material cyclically before or along the length of the screw feed means.
Preferably the method comprises providing in the plastics material entering the screw feed means sequential layers of materials of different composition, the size and spacing of the layers being chosen such that a predetermined part of each moulded article is of a different composition from the remainder of the article.
Alternatively, the method may comprise providing in the plastics material at a predetermined position along the length of the screw sequential layers of materials of different compositions, the size and spacing of the layers being chosen such that a predetermined part of each moulded article is of a different composition from the remainder of the article.
Preferably, one of the materials is a first plastics material and the other material is a combination of the first material and at least one additive material which can alter a physical characteristic or property of the first material. Thus, for example, a part of the surface of the article could be made softer than the remainder of the article by introducing insufficient of the softer material to coat the whole of the mould surface on initial injection into the mould.
In one method in accordance with the invention, the additive material, or at least one of the additive materials (since more than one additive may be introduced, either simultaneously or in such a manner as to produce additional sequential layers of different characteristics) is a blowing agent and the timing of the dose is such that the blowing agent is delivered to the interior of the article in the mould after the formation of a surface layer free from the blowing agent, thereby producing a moulded article whose core is of expanded plastics material (and thus of relatively low cost).
Alternatively, injection blow moulding may be carried out, with a first mould being used as an injection mould, and the resultant article being removed to a blow mould while the plastics material is still capable of stretching, to be inflated into contact with the blow mould to form the final article, for example, a plastics bottle. In this manner, the resultant hollow article may be formed with, for example, an overall surface layer of a different material or characteristic than the inner core of the moulding. The surface layer can thus form a barrier layer which will not affect, or be affected by, the contents of the bottle, while the core, which may not be suitable for contact with the bottle's contents, provides the strength of the bottle.
Another aspect of the invention provides a method of forming an extruded plastics article, comprising passing a solid plastics feed material through a melting zone, extruding the resultant molten material through a die, and allowing the extruded plastics material to solidify, characterised by providing in the feed material entering the melting zone sequential layers of first and second materials, the size and spacing of the layers being chosen such that the first and second materials appear sequentially along the length of the extruded article.
The or each material may be delivered to the feed hopper of a plasticising screw device, or to a point along the plasticising screw device.
Where an additive material is used, it may be selected from such materials as colorants, ultra violet protective materials, reinforcing materials, for example glass powder or fibres, and other fillers, as well as materials affecting the hardness, resilience or surface finish of the plastics material. The additive may be in the form of a powder, granules, a masterbatch, a paste or a liquid.
Since some blending of the materials will take place in the plasticising device, the layers produced will not have sharply-defined boundaries. This will have the beneficial effect of improving adhesion between the layers, avoiding the risk of desalination, for example. Where a small dose of an additive such as a colorant is added to a basic plastics material, the boundaries between the coloured and non-coloured regions of the final moulded article will be even less sharp, and may give rise to a continuous variation between maximum and minimum concentration of colorant. In this case, the timing of the additive may be arranged to give a maximum concentration in the surface region of an injection moulded article, with some residual coloration of the interior of the article. While it may be argued that such coloration represents a wastage of colorant, the costs benefits over moulding in continuous colour will be substantial, and the cost of adapting the injection moulding apparatus to provide skin coloration in accordance with the present invention will be relatively small, far outweighing the possible slightly greater usage of colorant as compared with twin injection techniques.
In the case of sequences of two or more materials being used, the materials may be different grades of plastics material, for example softer and harder materials, or of different chemical composition. Alternatively one or both materials may comprise a basic plastics material with additives of the type mentioned hereinbefore blended therewith.
The plastics material may be thermoplastic or thermosetting. Synthetic and natural rubbers may be moulded in accordance with the method of the invention, permitting such articles as shoe soles to be formed with, for example, a wear resistant skin and a soft core.
It has been found that, in some plasticising machines, a sharper boundary may be produced between two different materials in a sequence if the first material is introduced into the screw, and the next material is not introduced until the first has been conveyed by the screw to a point adjacent to the front end of the screw. The second material is then conveyed into contact with the first before it is propelled to the shaping process (injection or extrusion).
The invention also provides apparatus for moulding
Kilim Rafael Zvi Karl
Kilim Simcha Izkhak
Jackson Walker L.L.P.
Kuhns Allan R.
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