GB2529865A

GB2529865A - A method of manufacture of injection moulded articles

Info

Publication number: GB2529865A
Application number: GB1415678.0A
Authority: GB
Inventors: Raymond Foad; Kenneth Crow
Original assignee: R & K PARTNERS LLP
Current assignee: R & K PARTNERS LLP
Priority date: 2014-09-04
Filing date: 2014-09-04
Publication date: 2016-03-09
Also published as: GB201415678D0

Abstract

A method of manufacture of an injection moulded article comprising the steps of: providing a mould tool 4 having at least one cavity 12 located therein; bringing the temperature of at least a portion of the mould tool to a first temperature; injecting a polymeric material comprising at least one aesthetic additive into the or each cavity; bringing the temperature of at least a portion of the mould tool to a second lower temperature; wherein said polymeric material further comprises a disrupting agent. The polymeric material may be an amorphous or crystalline, semi-crystalline polymer wherein the first temperature is equal to or higher than the glass transition or melting temperatures respectively of the polymer. The aesthetic additive may be pigments or metallic flakes / spangle. The disrupting agent may comprise a number of different agents including glass, carbon or ceramic fibres; a chemical or physical blowing agent. An article formed by the method is further disclosed. An injection moulded article comprising a polymeric material and an aesthetic agent, wherein the article comprises substantially no visible weld, meld, flow or fold lines is disclosed. The use of a disrupting agent to prevent or reduce visible anomalies in an injection moulded article comprising a polymeric material and an aesthetic agent is also provided.

Description

A method of manufacture of injectioll moulded articles

Technical Field of the Invention

The present invention relates to a method of manufacture of injection moulded articles, and in particular, to injection moulded articles formed from thermoplastic materials having aesthetic additives located therein.

Baqjçgjupd to the Invention Injection moulding is a well4cnown technique used to manufacture articles which comprises injecting molten material into a mould and allowing for the material to cool, The technique provides a way to manufacture a plurality of articles which are of consistent size and shape.

Perhaps the most common form of injection moulding uses molten polymeric materials such as thermopla.stics, for example. One of the many benefits of using polymeric materials is that the manufactured articles require no additional finishing (eg. painting) after the moulding process given that the colour of the material used can be chosen.

One particular variant of the above technique is to add aesthetic additives, such as metallic flakes or spangle' into the molten material prior to injection. This produces a metallic paint' like finish on the fonned articles.

A significant drawback of using aesthetic additives such as metallic flakes in the molten material is that the formed article generally comprises weld and/or flow lines within the surface finish of the article. Weld lines (or meld or flow lines) are formed when two or more flows of material meet during the injection moulding process, such as when the flow of the material splits to go around an obstruction, This is exaggerated when metallic flakes are included in the molten material as the metallic flakes do not tend to travel as quickly as the molten material, resulting in a greatly increased concentration of flakes at the point where the flow fronts meet. Furthermore, it is S believed that a higher proportion of the flakes at the edges of the flow are orientated such that only the dark edges of the flakes are seen, rather than the metallic faces of the flakes, when compared with the main body of the flow. In addition, flow lines can occur where the design of the mould is such that it causes abrupt changes to the flow path of the material during injection. These changes in the flow of the material change the orientation of the flakes at the edge of the material flow such that some may he orientated as described above.

It is known that by adjusting the temperature of the mould during the injection process, the presence of the weld. meld, flow and/or fold lines can be reduced.

However, heating of the mould can lead to extended cycle times. In addition, current IS tecimiques only allow for the heating of the entire mould, which is not energy efficient.

Furthermore, even when adjusting the temperature of the mould during injection, the appearance weld/fold/meld!flow lines is only marginally reduced, It is therefore an aim of embodiments of the invention to provide a method of manufacture of an injection moulded article in which the appearance of weld lines and/or how lines in the surface finish of the manufactured article is substantially reduced or eliminated.

It is also an aim of embodiments of the invention to provide a method of manufacture of an injection moulded article which utilises temperature control of the mould in a time and energy efficient manner.

It is a further aim of embodiments of the invention to ovcrcomc or mitigate at least one problem of the prior art disclosed herein.

Summary of tile Invention

According to a first aspect of the present invention there is provided a method of manufacture of an injection inoulded article comprising the steps of: a) providing a mould tool having at least one cavity located therein; b) bringing the temperature of at least a portion of the mould toM to a first temperature; c) injecting a polymeric material comprising at least. one aesthetic additive into the or each cavity; and d) bringing the temperature of at least a portion of the mould tool to a second temperature, said second temperature being lower than said lirsi temperature.

wherein said polymeric material tltrther comprises a disrupting agent.

The term disrupting agent is intended to cover any agent operable to create turbulence within the polymeric material during injection to disrupt the orientation of the additive in order to prevent unwanted alignment ofthe additive in the formed article.

The use of a disrupting agent having this properly is of particular importance in embodiments wherein the aesthetic additive has a tendency to align and fomi wcldlflow/meld/fold lines within the bulk material and on the surface of the manufactured article.

In sonic embodiments the polymeric material is a plastics material. The plastics material may be an amorphous polymer such as acrylonitrile hutadienc styrene, polycarbonate or polystyrene, or any combination thereof, for example. In other embodiments the plastics material comprises a crystalline or semi-crystalline polymer such as polypropylene, polyacrylarnide, polyphenylene oxide or polybutylene tcrephthalatc, or any combination thereof, for example.

The plastics material may comprise a blend of any one or more of the above amorphous polymers and any one or more of the above crystalline or semicrystallinc polymers.

In embodiments wherein the polymeric material comprises an amorphous polymer, the first temperature of the mould tool may comprise a temperature equal to, or in excess of, the glass transition (Tg) temperature of the amorphous polymer being used.

In embodiments wherein the polymeric material comprises a crystalline or semi-crystalline polymer, the first temperature of the mould tool may comprise a temperature near to, equal to, or in excess of the melting temperature (I m) of the crystalline or semierystalline polymer being used.

The polymeric material maybe in a flowahle state before being injected into the or each cavity of the mould tool. In such embodiments, the method may further comprise preparing the polymeric material into a flowable state prior to injecting the material into the mould tool.

In some embodiments the flowable polymeric material is formed by heating and mixing solid forms of the material, In such embodiments, the flowable material may be formed using an injection moulding machine, The injection moulding machine may comprise a heating barrel for the heating and mixing of the polymeric material. The injection moulding machine may further comprise a ran or screw type plunger within the barrel, operable to move the material along the machine and inject the material, once in a flowahie state, into the mould tool.

The first temperature may he chosen depending on the type of polymeric material used, and may be at least 60°C, or may hc at least 80°C, or may he at Least 100°C. for example. In sonic embodiments the first temperature ma.y be at least 120°C, 140°C, 160°C, 180°C, 200°C, 220°C, 240°C, 260°C, 280°C, 300°C,320°C 340°C, 360°C, 380°C or 400°C Preferably, the first temperature comprises a temperature at which the polymeric material is in a fiowable state.

The sccond temperature may also be chosen depending on the type of polymeric material used and may be no more than 200°C, 180°C, 160°C 140°C, 120°C, 100°C or 80°C, or may be no more than 70°C or may be no more than 60°C, for example. In some embodiments the second temperature may be no more than 50°C. Preferably, the second temperature comprises a temperature at which the polymeric material is se1f supporting, and more preferably comprises a temperature at which the polymeric material is rigid.

The first temperature may be at least 120°C and the second temperature may be no more than 80°C, or may be no more than 70°C, or may be no more than 60°C. In some embodiments the first temperature may be at least 100°C and the second (3 temperature may be no more than 80°C, or may he no more than 70°C, or may be no more than 60°C. In other embodiments the first temperature may be at least 80°C and the second temperature may be no more than 70°C, or may he no more than 60°C. or may be no more than 50°C.

In embodiments wherein the polymeric material comprises acrylonitrile butadienestyrene (ABS), the first temperature may be at least 90°C -120°C and the second temperature may he no more than 40°C -60°C.

In embodimenl.s wherein the polymeric material comprises aerylonitrile hutadiene styrene/polycarbonate (ABS/PC) Blend, the first temperature may he at least 90°C 150°C and the second temperature may be no more than 60 100°C.

In embodiments wherein the polymeric material comprises polycarbonate (PC), the first temperature may be at least 140°C. 170°C and the second temperature may be no more than 70°C 100°C.

In embodiments wherein the polymeric material comprises polypropylene (PP), the first temperature may be at least 80°C -130°C and the second temperature may be no more than 20°C -80°C.

In embodiments wherein the polymeric material comprises polyacrylarnide (PA), the first temperature may he at east 1(30°C -1 70°C and the second temperature maybe no more than 60°C 120°C.

The term "aesthetie additive" refers to any additive which is intended to impart a visual difference to the polymeric material, and may comprise an additive intended to provide a homogenous visual difference, such as a hornogenous spread of a coloured or metallic inclusion.

In some embodiments the aesthetic additive may comprise metallic flakes, for example. The metallic flakes may be formed from aluminium, however, metallic flakes formed of other materials may be used.

In other embodiments the aesthetic additive may comprise one or more pigments, which may independently comprise a natural or synthetic pigment.

The aesthetic additive may comprise a combination of different additives, such as metallic flakes and one or more pigments, for example.

In some embodiments the disrupting agent comprises fibres added to the polymeric material, which may comprise glass or carbon or ceramic fibres, or any combination thereof for example. In other embodiments the disrupting agent comprises a blowing agent, which may be a chemical or physical blowing agent, for example.

In some embodiments the polymeric material may comprise a blowing agent in the form of a foaming agent The foaming agent may comprise pressurised gas, such as nitrogen or carbon dioxide, for example or may form the pressurised gas during the inventive method, such as through heating. In other embodiments the foaming agent comprises pressurised water.

Such blowing agents include azodicarbonamide (evolved gas is nitrogen -N2) and hydrocerol (evolved gas is carbon dioxide C02) The disrupting agent may comprise a combination of different agents, such as a combination of glass, carbon, or ceramic fibres and a chemical blowing agent, or a combination of fibres and a foaming agent, for example.

The disrupting agent may be added to the polymeric material prior to, or during the injection of the polymeric material into the mould tool.

The polymeric material may comprise the disrupting agent at a proportion olat least 1% by weight, or at least 1.5% by weight, or at least 2% by weight, or at least 3%by weight. In some embodiments the polymeric material comprises the disrupting agent at a proportion of no more than 30% by weight, or no more than 275% by weight, or no more than 25% by weight, or no more than 22.5% by weight, or no more than 20% by weight, or no more ihan 17.5% by weight, or no more than 15% by weight, or no more than 10% by weight. In preferred embochments the polymeric material may comprise a disrupting agent at a proportion of between 3% and 10% by weight, or may bc between 5% and 15% by weight.

In some embodiments the at least one portion of the mould tool is brought to a first temperature by supplying a fluid to the or each portion. The fluid may be pressurised hot water or hot oil, for example. In some embodiments pressurised steam may be used to bring the temperature of the mould tool to the first temperature. The mould tool may comprise one or more flow channels through which the fluid may be passed, said flow channel/s being in close proximity to the at least one portion of the mould tool to be brought to the first temperature.

In other embodiments the at least one portion of the mould tool is brought to the first temperature using an induction coil. The induction coil may be separate to the mould tool (external induction coil) and may be positioned in close proximity to the or each portion of the mould tool and subsequently removed before injection. In other embodiments the induction coil may be embedded in the mould tool itself, and may be located in close proximity to the or each portion of the mould tool to be brought to the first temperature, (internal induction coil).

in yet further embodiments, the or each portion oF the mould tool may he brought to the first temperature using at least one electrical cartridge heater, radiant heater (infra red heater) or contact heater, for example. The or each heater may he embedded within the mould tool, or may be a separate component.

The temperature of the or each portion of the mould tool maybe brought to the second temperature from the first temperature by supplying a fluid to the or each portion. In embodiments wherein the mould tool comprises one or more flow channels, the fluid may be passed through the flow channel/s to bring the or each portion of the mould tool to the second temperature. The fluid may be water, for example, or may be oil in embodiments wherein oil is used to bring the or each portion of the mould tool to the first temperature, The oil may be passed through the or each flow channel located within the mould tool. In another embodiment, chilled gas (nitrogen or carbon dioxide) may be passed through the cooling channels to move to the second temperature from the first temperature.

In some embodiments the method may further comprise removing the formed article from the mould after the temperature of the mould tool has been lowered to the second temperature. In such embodiments the temperature of the or each portion of the mould tool may be brought to the first temperature subsequent to the formed article being removed from the mould tool. In this way the method comprises a cyclic process which maybe repeated to form a plurality oF injection moulded articles.

In some embodiments the cooling of the or each portion of the mould tool to the second temperature is initiated after the polymeric material has been injected into the mould tool. However, in other embodiments cooling is before the polymeric material has been injected into the mould tool. Such embodiments make use of the fact that there will be a time lag between the initiation of the cooling of the or each portion of the mould tool, and the actual temperature change in the or each portion of the mould tool.

Similarly, in embodiments wherein the method further comprises raising the or each portion of the mould tool to the first temperature after cooling to the second temperature to restart the process, the heating may lie initiated before or after the formed article is removed from the mould tool.

By initiating Lhe heating and cooling of the or each portion of the mould tool before the completion of the previous method step, cycle times can he significantly reduced which is advantageous from a energy and time efficiency point of view.

1 5 The or each portion of the mould tool being brought to the first and second temperatures may comprise a surface or surfaces in contact with the injected polymeric material when within the mould tool, In such embodiments, the surface or surfaces may comprise a surface/s defining the at least one cavity within the mould tool.

The method may comprise providing a mould tool comprising a plurality of plates defining the cavity. The plurality of plates may comprise a pair of opposing plates. In some embodiments the or each portion of the mould tool being brought to die first and second temperatures may comprise at least one plate defining the cavity.

In some embodiments the temperature of each plate may he controlled.

I I

The method may comprise measuring the temperature of the or each portion of the mould tool being brought to the first and second temperatures. The temperature of the or each portion may be measured using at least one sensor located within, or on a surface of the mould tool. The at least one sensor may comprise a thermocouple sensor, a thermometer, or a thermistor, for example.

In embodiments wherein the temperature of the or each portion of the mould tool is measured, the measurements may be used to monitor and control the heating and/or cooling of the mould tool. lhe injection of the polymeric material into the mould tool may be controlled based on thc measured temperature of the or each portion of the I 0 mould tool, and in such embodiments, the polymeric material may he injected into the or each cavity within the mould l.ool upon instruction from the or each sensor. In some embodiments the initiation of injection of the physical material into the mould tool may he based on the amount of time that the mould tool has been heated and/or cooled (such as the amount of time that the heating and/or cooling medium has circulated through the mould tool). Injection of the physical material may only be initiated on reaching a certain time threshold for example.

The method may further comprise external gas moulding (EUM) of the polymeric material. In such embodiments, pressurised gas may be introduced into the mould tool to aid in the reduction of sink marks by increasing the pressure inside the or each cavity, In preferred embodiments the pressurised gas may be introduced after the surface of the polymeric material has begun to so1idi'. In this way, none of the introduced gas skill penetrate into the polymeric material.

According to a second aspect of the present invention there is provided an article formed using a method in accordance with the first aspect of the present invention.

According to a third aspect of the present invention there is provided an injection moulded article comprising a polymeric material and an aesthetic agent, wherein the article comprises substantially no visible weld lines, meld lines, flow lines or fold lines.

The polymeric material may comprise a plastics material, which may be an amorphous polymer, a crystalline polymer, or a semi-crystalline polymer. for example.

The aesthetic agent may comprise metallic flakes. In other embodiments the aesthetic agent comprises on or more pigmcnts, which may independently comprise a natural or synthetic pigment According to a fourth aspect of the present invention there is provided the use of a disrupting agent to prevent or reduce visible anomalies in an injection moulded article comprising a polymeric material and an aesthetic agent The disrupting agent may comprise fibres, such as glass, carbon or ceramic fibres, for example. In some embodiments the disrupting agent comprises a blowing agent, such as a chemical blowing agent. In other embodiments the disrupting agent comprises a physical foaming agent. The disrupting agent may comprise a combination of different agents.

The visible anomalies may comprise weld lines, meld lines, flow lines or fold lines within the injection moulded article.

In some embodiments the polymeric material comprises a plastics material, which may be an amorphous polymer, a crystalline polymer, or a semi-crystalline polymer, for example.

Detailed Dcscripfign of the Invent In order that the invention may be more dearly understood an embodiment/embodiments thereof will now he descrihcd by way of example only, with reference to the accompanying drawings, of which: Figure 1 is a schematic diagram of an apparatus used to pcrfbrm a mcthod in accordance with a first crnbodimcnt the present invention.

1 0 Figure 2 is a schematic diagram of the mould tooi of the apparatus illustrated in Figure 1.

Figure 3 is a schematic diagram of the mould tool shown in Figure 2 illustrating its operationai use.

Figure 4 is a schematic diagram of a mould tool used to perform a method iii accordance with a second embodiment of the present invention.

Figure 5 is a schematic overview of action of the disrupting agent on the aesthetic additive in accordance with the present invention.

Figures 1 to 3 illustrate an apparatus for use to perform the method in accordance with the present invention. The apparatus 2 comprises a mould tool 4 in fluid connection with an injection moulding machine 6.

The mould tool 4 includes a first section 8 and a second section 10, said first and second sections 8, 10 being operable to move between a connected configuration and a separated configuration. In the connected configuration, as shown in Figures 1 and 2, adjacent surfaces of the first and second sections 8, 10 are connected forming a cavity 12 within the mould tool 4, the cavity 12 being of the size and shape of the article to he manufactured. The adjacent surfaces of the first and second 8, 10 sections comprise corresponding first and second mould plates 14, 16 connected around their perimeter to form the cavity 12. The mould tool 4 additionally includes a. fluid inlet 1 8 within its first section 8. The inlet 18 is configured such that fiowable polymeric material may be injected into the cavity 12 through the first section 8. The first and second plates 14, 16 also include fluid channels 20 located adjacent to the surface of the plates 14, 16 defining the cavity 12. In addition, the mould tool 4 also includes a gas inlet 21 through die second mould plate 16. This inlet 21 may be used to perform external gas moulding of the introduced polymeric material.

The injection moulding machine 6 includes a hopper 22 for locating the polymeric material into the injection moulding machine 6, a heating barrel 24 [or heating and mixing the polymeric material, and a find outlet 26 at an opposing end of the machine 6 to the hopper 22. The heating barrel 24 also includes a screw-plunger 28 for both the mixing the polymeric material and also to move the material between the hopper 24 and the fluid outlet 26. The injection moulding machine 6 ftirther includes a control mechanism 30, operable to control the position andlor operation of the screwplunger 28 to control the outflow of polymeric material from the machine 6, A method of manufacture of an injection moulded article in accordance with the present invention using the apparatus illustrated in Figures Ito 3 will now be described.

Initially, the polymeric material to be moulded is inserted into the injection moulding machine 6 through the hopper 22. The material may be in a solid form and subsequently be heated into a flowable form under the operation of the heating barrel 24, or may already he in a flowable state prior to insertion through the hopper 22. In addition, the aesthetic additives and/or the disrupting agent may also be added into the machine 6 at this stage.

The heating barrel 24, in combination with the screw plunger 28 act to heat and mix the polymeric material/additive/disrupting agent medium to form a polymeric material mixture, The plates 14, 16 of mould tool 4 are heated to a pre-set first temperature by passing a fluid through the fluid channels 20. The first temperature is chosen to comprise a temperature at which the polymeric material mixture is in a flowable state.

In the present embodiment, the fluid comprises pressurised steam, however, it should be appreciated that any suitable fluid may he used such as pressurised water, or hot oil, for example. Once the temperature of the plates 14, 16 reach the preset first temperature, the polymeric material nuxture is expelled from the fluid outlet 26 of the machine 6, and into the fluid inlet 18 of the mould tool 4. In this way, the cavity 12 is filled with the polymeric material mixture.

Once the cavity 12 is filled with the polymeric material mixture, the control mechanism 30 acts to prevent any further mixture from being expelled from within the heating barrel 24. In addition, the first and second mould plates 14, 16 are cooled to a second pre-set temperature lower than the first temperature. The second temperature is chosen to comprise a temperature at which the polymeric material mixture is self supporting, and in preferred embodiments is a temperature at which the mixture is rigid.

The plates 14, 16 are cooled by again passing a fluid through the fluid channels 20. In the present embodiment the cooling fluid is cold water however other fluids may be used. In another embodiment chilled gas (nitrogen or carbon dioxide) may he used as S the cooling medium.

After the plates 14, 16 have been cooled sufficiently, and the polymeric material mixture is in the desired state, the plates 14, 16 are separated and the formed article 32 is removed (as shown in Figure 3). Subsequently, the plates 14, 16 may be returned to the configuration shown in Figure 2 and their temperatures raised back to the first temperature. In this way, the apparatus 2 is returned to its initial configuration and thc method may be rcpcatcd. The method may be repeated any number of times to form a plurality of injection moulded articles, Figure 5 illustrates the operational use ol disrupting agents in the form of glass fibres 204 and a blowing agent 206 when introduced into a polymeric material 200.

1 5 The polymeric material 200 includes an aesthetic additive in the form of metallic flakes 202 in addition to the disrupting agents 204, 206.

In the absence of the disrupting agents 204, 206, the metallic flakes 202 tend to align in the same orientaiion when passing around an obstruction 208 within the flow path of the polymeric material 200. The alignment of the metailie flakes 202 results in weld/flow/meld/fold lines in the surface finish of the formed article 32.

By using a disrupting agent in the form of fibres, such as glass fibres 204, the presence of weld lines in the fonned article 32 can he reduced. The fibres 204 act to disrupt the orientation ofthe metallic flakes 202 within the polymeric material 200 such that the particles or flakes at the flow fronts do not tend to align in the same direction.

This reduces the presence of weld lines, meld lines, fold lines and Ilow lines in the formed article.

By using a blowing agent 206 as the disrupting agent, the increased tcmperature of the polymeric material 200 in conjunction with the pressure drop that occurs as the polymeric material flows into the mould cavity, causes the blowing agent to react, forming a. gas which suhscquently comes out of solution and which in turn acts to foam the polymcric material 200. This foaming effect causes the disruption of the orientation of thc metallic flakes 202 leading to a reduction of weld lines in the formed article 32 as described above. A downside to the use of a blowing agent 206 on its own for this purpose is that the formed article 32 may have an unsatisfactory surface finish.

Specifically, the formed article 32 may not comprise the metallic like surface finish you would expect as a result of introducing the metallic flakes 202, but rather has a matt-like surface finish or a surface finish containing swirls or streaks. In some applications, I 5 a matt-like surface fInish may he preferred, however.

By introducing both glass fibres 204 (or ceramic or carbon fibres) and a blowing agent 206 into the polymeric material 200, the formed article 32 may comprise the desired metallic surface finish and the effectiveness of the removal of the weld lines, meld lines and flow lines is increased thither. Tn addition, by combining the action of the disrupting agents with temperature control of the moulding apparatus, alternating the temperature between the first temperature and the second temperature, it is possible to prevent the normal surface finish achievable with such disrupting agents (swirl marks, sp]ay marks, silver streaking) and achieve a high gloss or matt metallic surface finish (dependant upon the surface polish of the mould) whilst at the same time further increasing the effectiveness of weld line, meld line and flow line reduction.

Referring now to Figure 4, other methods of heating the plates 14, 16 may he employed. The apparatus 102 shown in Figure 4 is substantially identical to the S apparatus 2 as shown in Figures 1 to 3. However, the apparatus 102 includes the additional Feature of an induction coil 134 located proximal to the first plate I 4.

In the illustrated embodiment the induction coil 134 is an external coil and may be located next to the first and/or second plates 14, 16 when the plates are separated (as shown in Figure 4). The coil 134 acts to heat the plates 14, 16 by inducing a magnetic field upon the application of an alternating current through the coil. The magnetic field induces eddy currents within the surfaces of the plates 14, 16 causing their temperatures to increase. When thc tcmperatures of die plates 14, 16 have been raised sufficiently, the coil 134 is then removed and the plates 14, 16 are brought back together to form the cavity 12. The process is then substantially identical to the mcii od described with refercnce to Figures 1 and 2.

Although illustrated as being an external induction coil 132, it is envisaged that the coil may be an internal coil and maybe fixed within the apparatus 102.

The apparatus 2, 102 may additionally include a temperature sensor to monitor the temperature of the first and second mould plates 1 4, 16. The temperature sensor may be a thermocouple sensor, a thermometer or a thermistor, for example. The temperature sensor may he operable to communicate with the control mechanism 30 to control the operation of the injection moulding machine 6 based on the temperaturc of the plates 14, 16. For example, the temperature sensor may instruct the control mechanism 30 to initiate the injection of the polymeric material into the mould tool 4 at the point where the temperature of the plates 14, 16 reaches the pre-set first temperature. Ihe temperature sensor may also he operable to only allow the plates 14, 16 to be separated when they are at the pre-set second (emperature.

The apparatus 2, 1 02 may ffirther include a timing unit operable in use to optimise the length of the production cycle to maximise the energy'ti me effideney of the process.

In embodiments utilising the gas inlet 21 to perform external gas moulding of the introduced polymeric material, this may be done whilst the plates 14, 16 are being cooled to If e pre-set second temperature.

Although the illustrated apparatus 2, 102 include two mould plates 14, 16 which may be heated or cooled, it is envisaged that any number ol'plates may be employed to form the cavity 12 (e.g. stack mould) The choice of the number and configuration of the mould plates is entirely dependent on the configuration of the article to be manufactured.

Purthermore, it is also envisaged that not all of the plates need to he heated or cooled, rather only some of the plates may change temperature during the manufacturing process.

The above embodiments are described by way of example only Many variations are possible without departing from the scope of the invention as defined in the appended claims.

Claims

CLAIMSA method of manufacture of an injection moulded article comprising the steps of: a) providing a mould tool having at least one cavity located therein; b) bringing the temperature of at least a portion of thc mould tool to a first temperature; e) injecting a polymeric material comprising at least one aesthetic additive into the or each cavity; and d) bringing the emperat.ure of at least a portion of the mould tool to a second temperature, said second temperature being lower than said first temperature; wherein said polymeric material further comprises a disrupting agent.
2. A method as claimed in claim I wherein the polymeric material comprises an amorphous polymer.
3. A method as claimed in claim 2 wherein the first temperature is equal to, or is excess of the glass transition temperature of the amorphous polymer.
4. A method as claimed in claim I wherein the polymeric material comprises a crystalline or a semicrystalline polymer.
5. A method as claimed in claim 4 wherein the first temperature is near to, substantially equal to, or is in excess of the melting temperature of the crystalline or semi-crystalline polymer.
6. A method as claimed in any preceding claim wherein the polymeric material is in a flowable state before being injected into the or each cavity of the mould tool.
7. A method as claimed in ally preceding claim wherein the aesthetic additive comprises one or more pigments.
8. A method as claimed in any one of claims ito 7 wherein the aesthetic addilive comprises metallic flakes.
9. A method as claimed in any preceding claim wherein the disrupting agent comprises a combination of different agents.
10. A method of any preceding claim wherein the disrupting agent comprises fibres.
11. A method as claimed in claim 10 wherein the fibres comprise glass, carbon or ceramic fibres.
1 2. A method of any prcccding claim wherein the disrupting agent comprises a.chemical or physicai blowing agent.
13. A method as claimed in claim 12 wherein the chemical blowing agent comprises a compound capable of releasing a gas upon chemical or physical stimulus.
14. A method as claimed in claim 12 wherein the physical blowing agent comprises a gas.
15. A method of any one of claims I to 14 wherein the or each portion of the mould tool is brought to the first and/or second temperature by supplying a fluid to the or each portion.
16. A method as claimed in claim 15 wherein the fluid is passed through one or more flow channels within the mould tool to heat or cool the or each portion.
17. A method according to any preceding claim further comprising measuring the temperature of the or each portion of the mould tool being brought to the first and second temperatures.
18. A method as claimed in claim 17 wherein the injection of the polymeric material into the mould tool is controlled based on the measured temperature of the or each portion of the mould tool.
19. A method as claimed in 17 wherein the injection of the polymeric material into the mould tool is controlled based on the amount of time the heating and/or cooling fluid has flowed around the mould.
20. An article fonned using a method as claimed in any onc of claims ito 19.
21 An injection moulded article comprising a polymeric material and m aesthetic agent, wherein the article comprises substantially no visible weld lines, meld lines, flow lines and/or fold lines.
22. An article as claimed in claim 21 wherein the polymeric material comprises a plastics material.
23. An article as claimed in claim 21 or claim 2}4 wherein the aesthetic agent comprises metallic flakes.
24. The use of a disrupting agent to prcvcnt or reduce visible anomalies in an injection mouldcd article comprising a polymeric material and an aesthetic agent.23. A method, article or use substantially as described herein with reference to the accompanying drawings.