EP0052607A4

EP0052607A4 - Injection moulding machines.

Info

Publication number: EP0052607A4
Application number: EP19810900509
Authority: EP
Inventors: Tad Proske
Original assignee: GARDEN CONTAINERS Pty Ltd
Current assignee: GARDEN CONTAINERS Pty Ltd
Priority date: 1980-02-29
Filing date: 1981-02-27
Publication date: 1983-04-18
Also published as: EP0052607A1; JPS57500277A; WO1981002407A1

Abstract

An injection moulding apparatus for producing injection moulded articles of two or more colours or of two or more synthetic plastic materials has a plunger (31) mounted for axial movement in a barrel (32) to which the two or more different materials, or material of two or more different colours is fed. The plunger (31) is formed with axially extending passageways (33) to convey one of the plastics materials an injection chamber (35), and with additional passageways or grooves (39) to convey a second material to the injection chamber, the arrangement of passageways and/or grooves being such as to provide a predetermined distribution of the plastics materials in the chamber (35) thereby to produce an article having a predetermined colour or material distribution.

Description

FIELD OF THE INVENTION This invention relates to improvements in injection moulding machines used for the injection moulding of synthetic plastic articles. BACKGROUND OF THE INVENTION

Injection moulding, machines are well known for producing moulded plastic articles from synthetic plastic material, for example polypropylene. Because of the nature and operation of the known injection moulding machines, moulded synthetic plastic articles have generally only been produced in a single colour.

BACKGROUND ART Several forms of injection moulding apparatus have been proposed to produce articles of two or more materials of different nature or two or more colours.

French Patent Application No. 72.28131 proposes a form of apparatus which includes a distribution grill to which is fed plastics material of different colours. The grill has grooves or holes through which the different plastics materials pass into a pot in a predetermined manner, and then all are forced through the injection nozzle into a mould. The plastics materials are fed under pressure to the distribution grill by cyclically actuated cam driven pistons which control the timing and amounts of each plastics material fed to the distribution grill.

This apparatus is relatively complex requiring the use of separate piston feed means, piston metering means, cams and cam control means for each of the plastics materials fed to the distribution grill. A method and apparatus for producing composite plastics bodies is disclosed in British Patent No. 1,227,775 in which separate streams of plastics materials are extruded into an annular housing, an inner surface of said housing being rotatable to form layers of the plastics materials.

The method and apparatus disclosed in this British patent enables the production of a laminated or reinforced article but, again, the apparatus is relatively complex and the articles produced are restricted to those of a shape which can be formed around a rotatable mandrel.

A method and apparatus for producing a moulded body with a sandwich structure by injection moulding is disclosed in German Patent Specification No. 2,425,627 in which first and second plastics materials are fed to an injection cylinder having an injection nozzle at one end thereof communicating with a mould cavity, an inner cylinder, which divides the injection cylinder into front and rear chambers, and a conventional injection screw.

The first and second plastics materials are injected as a . single mass into the mould cavity in such a manner that • the second plastics material is enveloped by the firs plastics material to produce the moulded sandwich structure.

It is an object of the present invention to provi injection moulding apparatus which produces an injection moulded plastic article which has a highly decorative surface finish provided by a pattern of two or more colours, or two or more tones of colour.

It is also desirable to be able to mould syntheti plastic articles in an injection moulding machine using various colour or colour tone combinations of the synthet plastic material to produce a decorative moulded article. It is also desirable to provide an injection moulding machine having means for combining various colours or various tones of colours of synthetic plastic ^• material so as to produce a moulded article having a decorative appearance created by the colours, or tones of colours dispersed in a predetermined manner throughout th moulded article.

It is also desirable to provide an injection moulding machine which is able to mould synthetic plastic articles using two or more colours of synthetic plastic material whereby the combination of the colours of materi are consistently reproduced in subsequent moulded article

SUMMARY OF THE INVENTION According to one aspect of the present invention, there is provided, an injection moulding machine having an injection head arranged for at least reciprocal movement in a. barrel, first means feeding plasticized plastics material to be moulded to said injection head, at-least second means feeding further plasticized plastics material to the injection head, said injection head having passage means to distribute said first and second plasticized plastics materials in a predetermined manner for injection into said injection moulding machine, said injection head being reciprocal in said barrel to inject the said plastics materials into the moulding machine die cavity.

The invention also provides an injection moulding machine having a die cavity, a barrel communicating with said die cavity, plasticizing and feed means wherein plastics material to be moulded is heated, plasticized and fed to said barrel to be injected in predetermined quantities into the die cavity, characterized in that an injection plunger is provided in said barrel between said feed means and said die cavity, said plunger being at least reciprocal in said barrel, and possibly also rotatable, said plunger having a predetermined number and array of generally axially extending passageways and/or grooves through which a first plastics material may be fed from said plasticizing and feed means, a second feed and plasticizing means mounted on the barrel and arranged to feed a second plastics material to the barrel, the array of grooves and/or passageways in the plunger providing a predetermined distribution of the first and second plastics material when injected into said die cavity. In one form of this embodiment of the invention, the plunger is mounted coaxially with a rotatable feed screw which operates to plasticize and feed the plasticized plastics material to the die cavity. A second barrel is mounted on the first barrel and a further rotatable screw in the second barrel is selectively operated to feed the second plasticized material to the plunger. The plunger is preferably formed with an annular channel or groove into which the second plasticized material is fed. Axially extending grooves on the surface of the plunger convey t second plasticized material to the front end of the plung the arrangement of the axially extending grooves providin a predetermined distribution of the second plasticized material.

The array of grooves and/or passageways may inclu a passageway extending axially from the rear end of the plunger towards the forward end thereof. The axial passa way communicates with one or more further passageways at the forward end of the plunger which open out on the fron end surface of the plunger to distribute the first plasti material fed to the axial passageway.

The invention also includes a method of producing multi-coloured injection moulded plastic article comprisi the steps of feeding a first plasticized plastics materia to an injection chamber, feeding a second plasticized plastics material of a different colour to that of the fi plastics material to the injection chamber, controlling t feed and distribution of said first and second plastics material to provide a predetermined distribution of the materials in the injection cavity, and injecting the firs and second plastics material into a die cavity.

The invention will be more fully understood by reference to the accompanying drawings. DESCRIPTION OF THE DRAWINGS

Figure 1 is a cross-sectional side elevational view of one form of the apparatus of the invention,

Figure 2 is a cross-sectional side elevational view of the apparatus of Figure 1 but showing the plunger in a rearward position,

Figure 3 is a cross-sectional view taken along t lines 3-3 of Figure 1,

Figure 4 is an enlarged perspective view of a portion of a mould die formed in accordance with a featur of the invention, and

Figure 5 is a perspective view of a container mad in accordance with the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS The apparatus of the embodiment of the invention illustrated comprises a barrel extension 32 which is mounted coaxially on the forward end of the barrel 11 of a conventional injection moulding machine.

Such conventional injection moulding machines incorporating a feed screw 12 are well known in the art and will not be described in detail. In such machines, the feed screw 12 is rotatable and axially movable relative to the barrel 11 so as to plasticize synthetic plastics material supplied to the barrel and to convey the plastic- ized material to the forward end of the barrel 11 whereat a plunger head 13 injects the plasticized material into a die cavity 15. The barrel 11 is normally heated by suitable heating means such as steam, hot water or electrical heating elements (not illustrated) . In accordance with the present invention, the barrel extension 32 is mounted on the barrel 11 and communicates with a die cavity 15 through injection nozzle 36.

A second conventional extruder having a second barrel 14 housing a plasticizing feed screw 16 is mounted to the barrel extension 32 by bolts 22 and communicates with the interior of the barrel extension 3^'2 through a non¬ return valve 18 which permit plastics material to enter the barrel extension 32 through passageway 17, but prevent the material flowing back into the extrusion chamber of the second extruder.

A plunger 31 in the barrel extension 32 extends substantially axially forwardly of the feed screw 12. The plunger 31 is connected to the feed screw 12 by a collar 10 which permits relative rotation of the plunger 31 with respect to the feed screw 12 but causes the plunger 31 to move axially in the barrel extension 32 during reciprocal ' ^■ movement of the feed screw 12.

The plunger 31 is formed with an axial passageway 33 which communicates at its rearward end with the interior of the barrel 11 through passageways 34. The forward end of the axial passageway 33 opens into an injection chamber 35 in the barrel extension 32 through an array of passage¬ wa s 37. The outer surface of the plunger 31 has a substan ially annular channel 38 which communicates with the interior of the second barrel 14 through the passageway 1 to receive second plastics material therefrom. The annul channel 38 also opens into the injection chamber 35 throu a further predetermined arrangement of substantially axially extending grooves or slots 39 in the forward end of the plunger 31. Thus, the first and second plastics material fed from the barrels 11 and 14 are dispersed in the injection chamber 35 in a predetermined manner which is governed by the arrangement of the passageways 37 and grooves or slots 39.

In operation, as the feed screw 12 rotates and moves rearwardly, the plunger 31 is drawn therewith so th first plastics material is forced through the passageway into the injection chamber 35. At the same time, rotatio of the second feed screw 16 causes second plastics materi to be forced from the second extruder through non-return valve 18 into the annular channel 38 and through the grooves or slots 39 to the injection chamber 35. The arrangement of the grooves and slots 39 together with the passageways 37 provides a predetermined distribution of the first and. second plastics material in the injection chamber. During the rearward movement of the feed screw 12 rotation of the plunger 31 may be prevented by the provision of appropriate key and keyway formations 41 and 42 on the plunger 31 and barrel 11, respectively. Alternatively, the plunger may be permitted to rotate wit the feed screw. If desired the rotation may be controlle by guide means on the plunger 31 and the barrel 11, or by external rotating means connected through a wall of the barrel 11 or barrel extension to drivingly engage with th plunger 31. The material in the injection chamber 35 is injec into the die cavity 15 through nozzle 36 by forward movem of the screw 12 and plunger 31 to produce a predetermined dispersion of the first and second plastics material throughout the article which is moulded therefrom. The plastics material in the mould cavity 15 cools and the moulded article is removed from the die, whereupon the moulding cycle is repeated.

The decorative appearance produced in an article by the apparatus of the invention can be varied, as desired, by varying the number, shape and/or location of the grooves and/or passageways in the plunger 31, by varying the degree of rotation (if any) of the plunger, by varying the amount of second plastics material fed into the injection chamber 35 and by varying the time when the second material is introduced into the injection chamber. It has been found that by using two tones of a brown coloured synthetic plastic material a thin walled injection moulded article, i.e. a pot for plants, may be produced having a tortoise shell appearance.

The apparatus of the invention may be used for injection moulding of any suitable mouldable thermoplastic material such as polypropylene, polyethylene, polystyrene, polymethyl methacrylate, and the like. In addition, articles may be produced using two different but compatible thermoplastic materials.

While the present invention enables highly decorative plastic articles to be made by injection moulding, such articles having reproducable, predetermined multi-coloured effects controlled by the feed and distribution of two or more plastics material, the invention may also be utilized for producing more practical effects. Thus, by utilizing the features of the present invention it is possible to provide through a simple moulding operation a moulded thin-walled plastics article such as a container, pot or the like, having an external layer of one plastics material or- a plastics material of one colour and an internal layer of either a different plastics material or a plastics material of a different colour to that of the outer layer.

It is a further feature of the present invention to provide a method of "printing" on an injection moulded plastic article made in accordance with the invention.

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^' Referring to Figures 4 and 5, in accordance with this asp of the invention, one of the dies 46 forming the die cavi 15 is formed with raised, stepped up or embossed letterin 48 or designs, patterns or the like, as shown in Figure 4. For the purposes of this description the formation of lettering 48 will be described although the invention is not so limited. The article 47 to be formed is then produced by injection into the die cavity of a two colour plastics material in the manner previously described with the two colours having a distribution so as to produce tw layers of the plastics material each layer being of a different colour.

The distribution of the two coloured plastics material injected into the die cavity 15 is controlled, a above described, so that layers of the plastics material occur at at least that part of the die cavity 15 adjacent the raised lettering 48.

The thickness of the layer of plastics material adjacent the die 46 having the lettering 48 is arranged t be equal to or less than.the height h of the lettering 48. Therefore the outermost surface 49 of the lettering 48 contacts the other layer of plastic material in the mould.

The finished moulded article 47, therefore, exhibits an outer surface of the layer of plastics materi which was adjacent the embossed die 46 which is dis¬ continuous at the areas produced by the embossed or raise lettering 48 on the die 46 to expose the other plastics material, which is of a second colour. The impression given is one of the outer surface being engraved or cut away to expose the different colour of the underneath plastics layer.

By using this method in accordance with the invention, it is possible to produce injection moulded plastic articles which 'display integrally formed letterin designs or other material, and the use of this technique obviates the need for additional labels or other printing processes.

.In the apparatus of the invention, the plunger 31 may be formed with circumferential shoulders to restri<

C ,.„_ V/ flow of the second plastics material during any predeter¬ mined portion of axial movement of the plunger in the barrel 14.. By this means, the second plastics material may be caused to be fed intermittently to the injection chamber 35 to thereby provide layers, rings, circles or other varying amounts of the second plastics material dispersed throughout the first plastics material.

It will also be appreciated that two or more additional feeds of plasticized plastics material to the injection chamber may be incorporated in the apparatus of the invention.

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Claims

Claims .

1. Injection moulding apparatus having a barrel communicating with a die cavity, plasticizing and feed means wherein plastics material to be moulded is heated, plasticized and fed to said barrel to be injected in predetermined quantities into the die cavity, characterize in that an injection plunger is located in said barrel between said feed means and the die cavity, said plunger being connected to said feed means and being at least reciprocal in said barrel, said plunger having at leas one passageway or groove extending generally axially from one end thereof to the other through which a first plastic material may be fed from said plasticizing and feed means, a second plasticizing and feed means mounted on the barrel and arranged to feed a second plastics material to the barrel, further passageway and/or groove means in the plunger which, with the said at least one passageway or groove, provide a predetermined distribution of the first and second plastics materials when injected into the die cavity.

2. Apparatus according to claim 1 characterized in that the said plasticizing and feed means comprises a rotatable and reciprocal feed screw in said barrel.

3. Apparatus according to claim 1 or claim 2 characterized in that said second plasticizing and feed means comprises a rotatable feed screw mounted on said barrel and communicating with the interior thereof through a passageway and a non-return valve.

4. Apparatus according to claim 3 characterized in that said plunger is connected at its rearward end with the first feed screw for reciprocal movement therewith whilst the feed screw is able to rotate relative to said plunger.

5. Apparatus according to claim 4 characterized in that guide means are provided in the barrel to cooperate with means on the plunger to prevent or restrict rotation of the plunger in the barrel.

6. Apparatus according to any one of claims 1 to 5

OV?I Y.^'IPO ^r characterized in that said plunger is formed with one co¬ axial passageway which divides and diverges into a plurality of passageways adjacent the forward end of the plunger, the coaxial passageway communicating with an outwardly diverging passageway adjacent its rearward end, and an annular recess in its outer surface which communicates with said second plasticizing and feed means, and a plurality of grooves in the outer surface extending between the recess and the forward end of the plunger. 7. Apparatus according to any one of the preceding claims wherein the die cavity is defined by two or more dies at least one of which is formed with upraised formations whereby a moulded article is produced with corresponding recesses, and wherein the moulded article is formed of layers of the first and second plastics materials, the recesses in the article being of a depth to expose one of the plastics materials below a surface of the other plastics material.

8. A method of producing a moulded article of at least two plastic materials_/ or plastics materials of at least two colours by injection moulding into a die cavity defined by two or more die members comprising the steps of feeding a first plastics material through a distribution plunger in an injection barrel to an injection chamber, moving said plunger rearwardly in said barrel, feeding a second plastics material to said injection chamber along or through said plunger, arranging outlet passageways for said first and second plastics materials from said plunger to said injection chamber to provide a predetermined distribution of said first and second plastics material in the injection chamber, moving said plunger forwardly in said barrel to inject the plastics materials in the injection chamber into the die cavity and cooling the material in the die cavity.

9. A method according to claim 8 and including the further steps of forming at least one of the die members with raised formations, and distributing said first and second plastics material such that the material injected into the die cavity forms layers of said first and second

OMPI plastics materials at least adjacent the raised formation 10. An article formed by the apparatus or method of a one of claims 1 to 9.

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