Patent Application
20060251754
The invention relates to a method and apparatus for forming a moulding, more particularly an injection moulding, and an article formed by injection moulding.
Injection moulding is a technique in which a moulding material is injected into a mould such that it coats the mould surfaces. The moulded component may then be allowed to harden prior to removal from the mould.
However, a significant disadvantage of injection moulding is that the flow of the moulding material within the mould, and hence the finished appearance of the moulding, is highly dependent upon the shape of the mould. Moulds having simple, continuous surfaces generally produce mouldings having a surface of a reasonably consistent appearance. However, moulds having irregularly shaped or discontinuous surfaces distort the flow of the moulding material within the mould and hence result in the product having a surface appearance which is non-uniform or distorted. For example, a mould formed with regions for producing a moulding having holes or protrusions therein may cause non-uniform flow lines in the moulding about these regions. This typically results in the moulding having a distorted appearance. The surface appearance of the moulding is further distorted by weld lines produced about the interface between the components of the mould.
Furthermore, because the moulding material is injected into the mould it is not possible to produce an image on the moulding surface or vary the appearance over the surface.
Dual injection moulding is a specific type of injection moulding in which a first material is injected into a mould followed by a second material. The first material coats the mould surfaces, while the second material forms a substrate for the first material. The composite moulded component may harden in the mould prior to removal from the mould.
Dual injection moulding processes may be used to provide a paint coating on a moulded plastics body. In such a process paint is injected as the first material and the base plastic as the second material. Such a process has the advantage that the moulding is co-formed with a paint coating and thus does not need subsequent painting.
An example of a dual injection moulding process which produces a pre-painted moulding is disclosed in GB 2280401. This document discloses a method of forming a painted moulding wherein a powdered or granulated plastics paint material is heated and injected into a mould, followed by the injection of a substrate plastic. The use of powdered or granulated plastics enables a more controllable flow to be obtained in the mould resulting in a paint coating thickness which is more uniform.
However, as with the injection moulding techniques discussed above, wherein a single material is injected into the mould, the surface appearance of a product produced by dual injection moulding is also affected by weld lines and is highly dependent upon the profile of the inner surface of the mould. Moulds having irregular or discontinuous inner surfaces cause the flow of the first coating (i.e. paint coating) across the surface of the mould to be distorted. This results in the first outer coating of the moulding having a distorted appearance.
This is particularly visible when the moulding requires a metallic paint finish, because the reflective, metallic flakes used in the first coating material align with the flow lines of the coating material. Furthermore, because the paint layer is injected into the mould it is not possible to produce an image on the moulding surface or control the surface appearance of the moulding.
Accordingly, it is an object of the present invention to provide an improved method and apparatus for forming a moulding by an injection moulding process, wherein the moulding has an appearance which is not distorted by weld lines or by the flow lines of the coating material.
A further object of the present invention is to provide a method and apparatus for forming a moulding by injection moulding wherein the moulding has a predetermined image, pattern or texture thereon.
From a first aspect there is provided a method of forming a moulding by injection moulding. The method comprises injecting a moulding material into a mould, the moulding material comprising magnetic particles. The method further comprises applying a magnetic field to at least a portion of the moulding material so as to change the orientation and/or distribution of magnetic particles in the moulding material.
From a second aspect there is provided a moulding apparatus comprising a mould and means for injecting a moulding material into the mould, wherein the moulding material comprises magnetic particles. The apparatus further comprises means for applying a magnetic field in the mould so as to change the orientation and/or distribution of magnetic particles in the moulding material.
From a third aspect there is provided a method of forming a moulding by multiple injection moulding. The method comprises injecting a first material into a mould, injecting at least a second material into the mould behind the first material so that the first material covers a surface of the mould, wherein at least one of the materials includes magnetic particles. The method further comprises applying a magnetic field to at least a portion of at least one of the materials so as to change the orientation and/or distribution of magnetic particles in at least one of the materials.
From a fourth aspect there is provided a moulding apparatus comprising a mould, means for injecting a first material into the mould and means for injecting at least a second material into the mould, wherein at least one of the materials comprises magnetic particles. The apparatus further comprises a means for applying a magnetic field in the mould so as to change the orientation and/or distribution of magnetic particles in at least one of the materials.
In a preferred embodiment, the first material comprises a coating material which coats the moulding and the second material comprises a substrate material. Preferably, the coating material comprises the magnetic particles.
In another preferred embodiment, at least a third material is injected into the mould after the second material is injected. In this embodiment, preferably the first material forms a coating layer, the second material comprises magnetic particles and the third material forms a substrate layer.
It is further contemplated that fourth, fifth, sixth, seventh or a higher number of materials may also be injected into the mould, each of which may or may not comprise magnetic particles.
The term magnetic particles as used herein encompasses any particles which are able to be manipulated by a magnetic field so that their orientation and/or distribution is altered. The magnetic particles themselves preferably do not generate magnetic fields.
Thus in accordance with the invention, at least one material is used which contains magnetic particles, and a magnetic field is applied to the material(s) in the mould so as to cause a desired orientation and/or distribution of the magnetic particles in the material(s) to give a desired visual effect. By choice of appropriate magnetic fields it is possible to compensate for the irregular surface appearance which may be caused by weld lines or non-uniform flow lines within the moulding. Furthermore, the magnetic field(s) may also be such as to form a desired image, pattern or texture in the material(s) comprising magnetic particles.
More particularly, the concentration and/or orientation of the magnetic particles within a given region of the moulding will determine the appearance of the moulding surface. These properties may be manipulated and controlled by the magnetic field(s) so as to produce any desired surface appearance. The magnetic particles align along the magnetic field(s) which are applied to the coating. Thus, in a preferred embodiment, for example, the level of light reflection and/or absorption by the magnetic particles in a particular region may be altered by changing the orientation and/or concentration of the particles in that region. For example, the magnetic fields may be arranged to move the magnetic particles into or from a particular region of the moulding or may change the orientation of the magnetic particles such that light is incident on a larger area of the particles to increase the reflectivity or absorption of that region of the moulding.
In moulds having irregular or discontinuous surfaces such as holes, protrusions or the interfaces between the multiple mould components the present invention can be employed to compensate for the distorted appearance created at these regions. The magnetic fields may be arranged such that the magnetic particles are drawn to give a substantially uniform coating and/or be orientated in the required direction. Any desired image may also be formed on the moulding surface, or substrate surface in multiple injection moulding, by arranging the magnetic fields to draw or push relatively reflective or absorptive magnetic particles to or from regions of the moulding. In this manner two-dimensional, three-dimensional and/or textured appearances may be created in regions of the moulding during the moulding process.
In the preferred embodiment the mould surface may be heated electrically, or by any other means, in order to prevent the moulding surface from curing or “skinning” before the magnetic particles have been manipulated as desired.
The magnetic particles which are included in the moulding or coating and/or substrate material may consist of a magnetic core which may be spherical, elongated or any other shape. Preferably, the magnetic core is elongated and coated with an outer layer consisting of a material which reflects or absorbs light relatively well.
In a preferred embodiment the magnetic particles are nickel. In some embodiments the particles may comprise a nickel core which may be coated in, for example, aluminium or alternatively coated with, for example, magnesium fluoride and aluminium or another metal. The magnetic particles may also have coloured coatings.
In a preferred embodiment the magnetic particles comprise leafing grade nickel flakes such as those manufactured by Novamet Speciality Products Corporation. Such flakes may be used in a coated or uncoated state. More preferably, extra fine pigment grade nickel flakes are used in the moulding or coating and/or substrate materials. The magnetic particles can be added to the moulding or coating and/or substrate materials as a dry powder or pigment slurry.
In certain embodiments, for example when a single moulding material is injected into the mould, the magnetic particles may make up 2-15% of the weight of the material(s) comprising magnetic particles. More preferably, the magnetic particles comprise 3-10% of the material(s) by weight. Even more preferably, the magnetic particles make up 5% of the material(s) by weight.
In a preferred embodiment the method is used to produce a relatively thin moulding such as, for example, a credit card. In this embodiment the moulding may be substantially translucent or transparent and preferably the magnetic particles make up between 0.1% and 0.5% of the weight of the moulding. In other embodiments in which the moulding is relatively thick the magnetic particles preferably make up about 4% of the weight of the moulding.
In other embodiments, for example when more than one material is injected into the mould, the magnetic particles may make up 0.1-15% of the weight of the material(s) comprising magnetic particles. More preferably, the magnetic particles comprise 0.5-10% of the material(s) by weight. More preferably, the magnetic particles comprise 0.1-3% of the material(s) by weight. Even more preferably, the magnetic particles make up 2% of the material(s) by weight. However, it is also contemplated that the magnetic particles can be added to the material(s) in any desired proportion and the magnetic particles may make up more than 15% or less than 0.1% of the weight of the material(s). In a preferred embodiment, the substrate and coating materials of the moulding comprise different weight percentages of magnetic particles.
Where the particles are being added to a moulding material, rather than a coating, it is preferred that the moulding material is transparent. Pigment may be added to the material for decorative effect.
The magnetic fields which manipulate the magnetic particles may be generated by one or more permanent magnet and/or electromagnets provided in or adjacent the mould.
The poles of the magnets may be arranged such that the magnetic fields are substantially parallel, perpendicular or oblique to the surface of the region of the mould comprising the magnetic particles which are to be manipulated.
These magnets may be recessed into or formed integrally with the inner or outer surfaces of the mould, or disposed between the inner and outer surfaces. Alternatively, the magnets may be arranged adjacent to the surfaces of the mould.
In some embodiments an electromagnet is used, particularly when it is desired that the magnetic field is applied only selectively during the moulding process.
Any number of magnets having any shape or size may be used in the apparatus depending upon the desired pattern or effect to be achieved. The strength of the magnetic field and the duration that it is applied may also be varied depending upon the effect to be achieved, the distance and material between the magnet and material comprising magnetic particles and the level of curing of the material comprising magnetic particles.
In order to vary the strength or position of the magnetic fields the magnetic field generating means may be movable relative to the mould. In such an embodiment magnets may be positioned, for example, within bores in the mould casing and may move perpendicularly or parallel to the coating. Alternatively, if electromagnets are employed, the power delivered to them may be varied.
In the preferred embodiment, the mould is made from metal, preferably steel. Magnets may be provided in regions of the mould by drilling a bore part way or completely through the mould. The bore may then be plugged with a non-magnetic material. Once the bore has been plugged with the non-magnetic material it may then be drilled itself to provide a bore for inserting a magnetic material. After the magnetic material has been inserted into the bore the edges of the mould, non-magnetic and magnetic materials are preferably peened over and the whole region polished smooth.
From a further broad aspect the invention provides a mould for injection moulding plastics, the mould having one or more openings receiving a copper insert, the copper insert comprising a magnetic insert.
In a preferred embodiment, the bore drilled into the mould is cylindrical and may have a diameter of approximately 5 mm. This bore may then be filled with non-magnetic copper which is then preferably bored into to provide a cylindrical bore of diameter 2 mm for receiving the magnetic material. Preferably, the magnetic material is a sintered ferrite magnet. In the preferred embodiment, the non-magnetic material is provided between the magnetic material and the mould inner surface in order to substantially prevent the inner surface of the mould from becoming magnetised as this may adversely affect the orientation and/or distribution of the magnetic particles in the moulding. In a less preferred embodiment the mould itself may be manufactured from a non-magnetic material, such as non-magnetic steel, which may be bored into in order to insert the magnetic material directly.
In the preferred embodiment liquid, powdered or granulated material may be used as the moulding, coating and/or substrate material which includes the magnetic 3b particles.
Where the magnetic particles are being added to a moulding material (rather than to a coating), it is preferred that the moulding material is transparent or translucent. Tints may be added to the plastics material to give a desired colour.
The moulding, coating and/or substrate material is preferably heated to a plastic condition and injected into the mould. It is particularly preferred to use a powdered or granulated plastics material of a thermosetting kind which has a thermoplastic phase, with the magnetic pigment mixed therewith. In such a case the powdered or granulated plastics material can be heated sufficiently to bring it to a plastic condition (typically a putty-like conditions) in its thermoplastic phase to enable it to be injected at high pressure into the mould (e.g. in excess of 1000 bar). For example, heating a powdered or granulated plastics material to a temperature in the range 80° C. to 260° C. will normally bring it to a plastic condition for injection into the mould. With such a material, the heat absorbed to bring it to the plastic phase may ideally be utilised to cause the material to begin thermosetting, e.g. as it coats the mould or, in multiple injection moulding, following the introduction of the substrate material. In that way reasonably rapid curing of the mould can be achieved. However, if desired, the coating can be cured or curing can be completed after removal of the moulding from the mould, i.e. post-cured.
Post curing enables the curing temperature and curing time to be particularly carefully controlled. This is particularly advantageous in multiple injection moulding with regard to creating a strong bond between the coating and substrate materials.
In dual or multiple injection moulding the coating and substrate materials are preferably selected so as to have an affinity for one another. Cross-linking between the moulded coating and substrate materials may be effected during moulding or curing of the material.
The method and apparatus provided in accordance with the present invention are particularly suited to the production of credit cards, casings for electronic equipment such as mobile phones and various body components of a motor vehicle.
Various embodiments of the present invention will now be described, by way of example only, and with reference to the following drawings in which:
With reference to
The extruder 17 may be associated with a heater 17a and is operated to deliver the moulding material 23 comprising magnetic particles. The moulding material 23 may consist of liquid paint although is preferably formed by heating thermosetting granulated plastics paint material 23a, including the magnetic particles, into a thermoplastic phase in which it takes on a putty-like plastic condition. A suitable granulated plastics material has been found to be one which will have a plastic condition at a temperature of around 170° C. with a putty-like viscosity. Preferably, the moulding material 23 comprises a substantially transparent or translucent plastic such as polycarbonate provided in the form of granules. The plastic may be mixed with magnetic particles comprising nickel flake pigment at a ratio of 3% by weight before being heated and injected into the mould 10 at a temperature of approximately 280° C. In a preferred embodiment the plastic material may be tinted with any colour, for example, by use of plastic tints. In this embodiment the cycle time between shots may be approximately 20 seconds.
The magnets 21 produce a magnetic field within the mould 10. The magnets 21 are arranged such that the fields manipulate the magnetic particles in the moulding material 23 before it has cured. The magnetic fields may be arranged to distribute and/or re-orientate the magnetic particles such that the moulding has a uniform appearance, or alternatively, to produce a moulding of which at least a portion is created having a 2-D, 3-D or textured image or appearance.
The moulding material 23 is preferably injected into the cavity 14 whilst the mould 10 is at an elevated temperature. The temperature of the mould may be in a range of, for example, 20° C. to 150° C., preferably around 100° C. The valve 20 may then rotated to shut off the feed of moulding material 23.
The heat applied to the thermosetting moulding material 23 while it is temporarily in the extruder 17 is absorbed by the material 23 and, once in the mould 10, the heat will begin the curing process of the material 23. That process may begin as the material 23 is being spread over the mould 10 surfaces or may begin after the injection steps are complete. However, the magnetic fields are applied to manipulate the magnetic particles in the moulding material 23 before the curing process is completed. Preferably, the inner surface of the mould 10 is maintained at an elevated temperature of, for example, 100° C. in order to prevent the outer surface of the moulding from completely curing or “skinning” before the magnetic particles have been manipulated as required.
Referring to
The first extruder 17 is associated with a heater 17a and is operated to deliver a coating material 23′ which may comprise magnetic particles. The coating material may consist of liquid paint or may be formed by heating thermosetting granulated plastics paint material 23a′ including magnetic particles into a thermoplastic phase in which it takes on a putty-like plastic condition. A suitable granulated plastics paint material has been found to be one which will have a plastic condition at a temperature of around 170° C. with a putty-like viscosity.
An initial quantity of the coating material 23′ is injected into the cavity 14, the mould 10 being at a temperature in a range of, for example, 20° C. to 100° C. The valve 20 is then rotated to shut off feed of coating material 23′.
The magnets 21 produce a magnetic field within the mould 10. The magnets 21 are arranged such that the fields manipulate the magnetic particles in the fluid coating material 23′ and/or substrate material 24 before it has cured. The magnetic fields may be arranged to distribute and/or re-orientate the magnetic particles such that the moulding has a uniform appearance, or alternatively, to produce a moulding of which at least a portion is created having a 2-D, 3-D or textured image or appearance.
In
The heat applied to the thermosetting coating material 23′ while it is temporarily in the extruder 17 is absorbed by the coating material 23′ and, once in the mould 10, the heat will begin the curing process of the material 23′ and substrate material 24. The curing process may begin as the coating material 23′ is being spread over the mould 10 surfaces by the incoming substrate material 24 or may begin after the injection steps are complete. However, the magnetic fields are applied to manipulate the desired magnetic particles in the coating 23′ and/or substrate 24 material before curing of the respective material(s) is completed.
Preferably, the curing of the thermosetting coating material 23′ and substrate material 24 will also allow sufficient time to enable cross-linking to take place between the two materials 23′,24 thereby ensuring an extremely good bond between them. Instead of a cross-linking occurring between the coating 23′ and substrate 24 materials, a good bond alone may be achieved between them due to their intimate contact during injection.
Referring to
The substrate material 24 is preferably selected so that it will have an affinity to the coating material 23′ and materials such as ABS and nylon constitute suitable substrate materials 24 for such a coating material 23′.
Referring to
Moreover, by producing a moulding 11 having a predetermined appearance in an injection moulding process, the finished moulding will be free from contamination by air-borne dust as well as being uniform and consistent. Also, the method of the preferred embodiment is cleaner and more environmentally friendly than producing a moulding having a finish using a conventional paint facility because the preferred process does not involve extracting contaminated air or effluent from a paint facility and emitting it into the atmosphere.
If desired, the substrate material 24 can be a thermosetting material instead of a thermoplastics material. The injection steps will be the same as that described above with reference to the drawings except that the mould 10 will be hotter, for example, at a temperature in a range 100° C. to 180° C. As before, the heat applied to the coating material 23′ will lead to the onset of curing and the hot mould 10 will speed up curing of the coating formed by coating material 23′. The heat from the mould 10 may also at least partially cure the substrate material 24. If desired the moulding 11 can be left to cure completely in the mould 10 or can be removed for post curing outside the mould, for example, in an oven 30. In the latter case heat applied to the thermosetting substrate material 24 preferably does not present any distortion problems to the thermosetting material.
The substrate material 24 may be injected as a foamed thermoplastic/thermosetting material.
In another embodiment one or more further materials may be injected into the cavity 14.
In this embodiment the first material is preferably a coating material 23″ and the third material 25 may be a substrate layer. The coating material 23″ may be relatively hard or resilient and/or translucent or transparent. The coating material 23″ may serve to protect the second material 24′ which contains the magnetic particles. Further, as the layer 24′ containing the magnetic particles is provided between the coating 23″ and substrate 25 materials it need not provide any structural function and therefore may have a relatively small volume. This relatively small volume is advantageous as it enables the quantity of magnetic particles required to achieve the desired visual effect.
Although various types of magnetic particles have been discussed above it is contemplated that the magnetic particles used in the present invention may comprise pigment flakes such as those disclosed in WO 03/000801 and US 20030143400, the entire contents of which are incorporated herein by reference.
Although the present invention has been described with reference to the preferred embodiments, it will be understood by those skilled in the art that various changes in form and detail may be made without departing from the scope of the invention as set forth in the accompanying claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 0317508.0 | Jul 2003 | GB | national |
| 0404202.4 | Feb 2004 | GB | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/GB04/03224 | 7/26/2004 | WO | 1/24/2006 |
