WO1993006983A1

WO1993006983A1 - A method of injection moulding, a mould for use in such a method and a component made by such a method

Info

Publication number: WO1993006983A1
Application number: PCT/GB1992/001750
Authority: WO
Inventors: Gordon Frederick Smith; Ronald Arthur Easterlow
Original assignee: Rover Group Limited
Priority date: 1991-09-28
Filing date: 1992-09-23
Publication date: 1993-04-15
Also published as: GB9120609D0; GB2259883A

Abstract

The method involves providing an injection mould having parts (10, 12) between which is inserted a film-like layer (16). The film-like layer is held between the mould parts and thermoplastics material is injected into the mould against the film. The injection step causes the film to be urged against an adjacent surface (19) of the mould and the film-like layer and the adjacent surface are of different surface texture. The film imparts to the injected plastics material a surface texture (22) which is different from that which would be otherwise imparted by the adjacent surface (19) of the mould. A mould for use in such a method is illustrated.

Description

A METHOD OF INJECTION MOULDING, A MOULD FOR USE IN SUCH A METHOD AND A COMPONENT MADE BY SUCH A METHOD

The invention relates to a method of injection moulding, to a mould for use in such a method and to a component made by such a method.

Injection moulding of thermoplastics components is well known and components formed in that way can have an excellent surface finish. The surface finish itself is dictated by the mould surface against which the thermoplastics material is moulded. Where, for example, a fine surface texture or pattern comprising closely spaced surface irregularities is required, it is necessary for the appropriate surface of the mould to be engraved in order to impart the necessary texture to the surface of the component and such engraving is expensive. Clearly, where many different types of surface texture are required, production of respective moulds can be extremely expensive.

It has been proposed hitherto to provide an injection mould with an insert having a surface formation against which a thermoplastics moulded material will be injected. The formation is different from that which would be imparted by the mould to the injected material if the inserted were omitted. An example of such a mould is described in GB-A-1197727 which is concerned with the manufacture of shoe bottom units. However, the insert is of considerable thickness and is therefore of use only on a mould surface which has no more than a gentle contour.

It has also been proposed, for example in GB-A- 1330281 to provide in a mould a film of thermopl stics material against which the thermoplastics material is injected. However an essential feature of the method described is to achieve a good bond between the injection moulded plastics and the film so that the film itself provides a non-detachable outer surface on the final component. Another injection moulding method utilising film is described in EP-A-0094268 where, again, the film provides a permanent outer cladding of material. In these cases the film imparts to the injection moulded thermoplastics material a surface formation corresponding to that of the adjacent mould surface against which the film is supported during the injection moulded stage.

One object of the present invention is to provide a method of injection moulding which is more versatile than those described above.

According to one aspect of the invention there is provided a method of injection moulding a component comprising providing an injection mould, placing in the mould a layer of material having a surface against which thermoplastics material is injection moulded, the said surface and an adjacent surface of the mould against which the layer of material .is placed being of different surface form, and injecting thermoplastics material into the mould against the layer of material to form the component, the layer of material and the component subsequently being separable and the layer of material being in the form of a film-like layer of plastics material.

By using such a method, a single mould can be used to provide a minimum of two different surface textures to the moulded material, the first being provided by the mould itself and the second being provided by the mould with the film-like layer positioned therein. Also the use of film makes the mould more versatile than the mould described in GB-A-1197727 as it can follow a general mould shape which is more complex than the gentle contour described therein whilst still imparting the desired surface form to the injection moulded thermoplastics material. Moreover by ensuring that the component and film are finally separable, the component surface does not need to be limited to that which can be provided by the film.

In order to minimize or prevent bonding together of the f lm-like layer and the component, the method may include selecting the material of the film-like layer and that of the injected thermoplastics so that the materials are incompatible. To minimise the possibility of bonding even further, and in particular where the material of the film-like layer is also a thermopl stics material, the temperature of the thermoplastics material injected into the mould is preferably below that at which the thermoplastics film material will melt.

Separation of the component from the film may be made easier by applying a release agent to the surface of the film against which the thermoplastics material is injected.

It may be convenient to leave the film-like layer in the mould when removing the moulded component so that the mould is then ready to receive a further quantity of injection moulded material for producing another component.

Alternatively, the component and film-like layer can be removed from the mould so that the film-like layer can subsequently be removed therefrom. That can be useful where the surface of component carrying the film-like layer is to be protected during assembly of the component into, say, a motor vehicle. Up to and during assembly, the film-like layer can be left in place to protect the surface and then easily peeled from the component.

The mould itself will have an overall shape to form a desired component, say a vehicle bumper, and the actual surface form of the moulded bumper, e.g., a grained finish, can be provided by the film-like layer. In such a case, the film-like layer can easily be pre-for ed by, for example, a vacuum forming tool, so that it has the general shape of the mould. In that way, risk of creasing of the film¬ like layer within the mould is minimised.

In order to hold the film-like layer firmly in position, the method may include providing the mould in two parts, introducing the film-like layer into the mould with the two parts separated, and closing the two parts together to clamp the film-like layer in position therebetween prior to injecting the thermoplastics material into the mould.

The surface of the film-like layer against which the thermoplastics material is injected can be given a textured finish such as by embossing the film e.g., to provide a surface simulating woodgrain, leather etc. In such a case, the said adjacent surface of the mould can be flat but need not necessarily be of a very fine highly polished finish as the mould surface itself does not impart its own finish to the component. Therefore it will be appreciated that such a mould will be less expensive to produce than a mould requiring a very fine finish or, indeed, than a mould which requires engraving to produce the textured finish given by the film.

Alternatively, where a non textured finish is required in a mould which is normally intended to apply such a finish, the use of a flat film-like layer can provide the desired finish to the component. Where a shiny film is used, a very smooth surface finish can be imparted to the component in such a mould.

Where the film material is embossed, the embossing may take the cross sectional dimension across the film to around one and a half times the film thickness thus providing an embossing depth of around one half of the film thickness.

Alternatively a very fine surface texture, e.g. a fine leather grain effect, may be suitably impressed or otherwise formed on one surface only of the film leaving the other side substantially flat. According to a second aspect of the invention there is provided a mould for use in a method according to said one aspect of the invention or according to any of the consistory clause statements relating thereto, the mould having said film-1ike layer therein for imparting to the injection moulded thermoplastics material a surface form or texture which is different from that which would otherwise be imparted by said adjacent surface of the mould.

According to a third aspect of the invention there is provided a component, e.g.,' a motor vehicle component, made by a method according to the said one aspect of the invention or according to any of the consistory clause statements relating thereto.

A method of moulding, a mould for use in such a method and a component made therewith in accordance with the method will now be described by way of example with reference to the accompanying drawings in which:-

Fig.1 is a diagrammatic cross section through one form of mould in accordance with the invention shown with two parts of the mould separated,

Fig.2 is a diagrammatic cross section of the mould shown in Fig.1 with the mould parts brought together and plastics material injected into a cavity defined by the mould,

Fig.3 is a view similar to Fig.1 after moulding has taken place,

Fig. is a view similar to Fig.3 but showing the film-like layer left in the mould after removal of the component,

Fig.5 is a view similar to Fig.3 but showing the film-like layer left on the component for subsequent removal after removal of the component from the mould,

Fig.6 is a view to a large scale showing an embossed- film-like layer against a flat adjacent mould surface,

Fig.7 is a view similar to Fig.3 showing a modified mould and flat film-like layer,

Fig.8 is a view similar to Fig.6 but with the adjacent mould surface textured,

Fig.9 is a view showing the way in which the film- like layer can be pre-formed to match the general shape of a mould. Fig.10 is a view similar to Fig.1 drawn to a larger scale showing a different type of film-like layer in a mould, and

Fig.11 is a view similar to Fig.10 showing a film of the Fig.10 type reversed and positioned in a mould having a surface formed with a surface pattern.

In Fig.1, a mould comprises first and second parts 10, 12. In the embodiment illustrated, the first part 10 is movable towards the second part 12.

The first mould part 10 defines a recess 13 and an injection port 14. The mould part 12 defines a recess 15.

A layer of plastics film material 16, such as nylon film, e.g. of around 0.5mm thickness, is embossed to define a surface pattern 17. The embossing may take the cross-sectional dimension D across the film to around one and a half times the film thickness so as to leave the depth of the embossing around one half of the film thickness. In Figs.1 to 3 dimension D and embossing depth are shown exaggerated for clarity. The pattern preferably comprises closely spaced surface irregularities and the zig-zag pattern 17 shown is merely for illustrative purposes. If desired the pattern 17 could be of other form and could even be formed so as to mould a Trade Mark, logo, picture or written matter.

The method of moulding includes placing the film 16 between the mould parts 10, 12 as shown in Fig.1, closing the mould as shown in Fig.2 and then injecting a mouldable thermoplastics material 18 into the mould so as to fill the cavity defined by the recesses 13, 15. When the mould is closed, the film 16 is clamped between surfaces 10a, 12a of the mould parts 10, 12 to hold the film in place. The injection of the thermoplastics material urges the embossed section 17 against the bottom of the recess 15 which has a flat surface 19. The very shallow embossings of embossed section 17 traps tiny pockets of air 11 (see Fig.6) between themselves and the surface 19 which prevent the embossing from flattening against the surface 19 during injection of the thermoplastics material 18. Therefore, the moulded material conforms substantially to the form of embossed film section 17 and when the mould parts are separated as shown in Fig.3, a component 20 formed by the moulding step can be removed from the mould with the desired surface texture 22 formed thereon. When the mould parts 10, 12 are opened, the film 16 may remain in position in the mould as in Fig.4 for a subsequent moulding step or may be left on the component 20 as in Fig.5 and subsequently peeled away from the component 20 and discarded or even placed back in the mould again for subsequent use. For ease of separation of the film 16 from the component 20, the film will be of different material from the material 18 and preferably incompatible therewith and/or may be treated with a release agent. In order further to ensure that the film 16 can be separated from the component 20, the temperature of the injected thermoplastics material 18 will be below that at which the film would melt to form a homogeneous bond therewith.

In Fig.7 mould part 10 is identical to that shown in Figs.1 and 2 but mould part 12 has its recess 15 formed with an engraved bottom surface 119 in place of the flat surface 19. Such a surface would normally produce a component somewhat similar to the component 20 shown in Fig.3. However, by placing a non-embossed film 16 in the mould, air pockets will be trapped during the mould step between the film 16 and the engraved surface 119 and the resulting component 20 will either have a substantially flat right-hand surface or will at least be smoother than the textured surface 119.

If desired the film may have a surface which is formed so as to impart a surface pattern to the component different from that of the engraved surface 119. Such a film 16 is shown in Fig.8 where the embossing 17 on the film is of different form from the texture of adjacent mould surface 19.

The film 16 can be pre-formed, e.g., by vacuum, to fit into a mould of particular shape as shown in Fig.9. That will help to avoid creasing of the film particularly in moulds of complex shape. However the vacuum forming is arranged so as not to cause an embossed film to lose its embossed surface texture. Where the film 16 is to be embossed as in Figs.1 to 3, a vacuum forming step can be used to produce the embossed pattern 17 and a general preforming to match the shape of the mould. Where the film 16 is used as in the Fig.7 mould, the vacuum forming of the film leaves the surface of the film to be positioned adjacent mould surface 119 in a flat form.

Therefore, by using a film 16 in a mould, the mould can be used to produce a variety of components having different textured surfaces in moulds of complex shape. Such surfaces may be of a type which will reproduce a wood-grain, leather-grain or other fine surface texture which, if applied to the surface of an injection moulding tool, would involve engraving.

Although the film surface texture 17 has been described as being formed by embossing, a very fine surface texture 17 could be formed by impression to provide the textured surface on one side of the film 16 only leaving the other side 17a flat as in Figs. 10 and 11. In Figs. 10- and 11 parts corresponding to parts shown in earlier figures carry corresponding reference numerals. The thickness of the film and surface texture of the mould is shown exaggerated for ' clarity.

In Fig.10, the film 16 may again be vacuum formed so as to be of complementary shape to the mould part 12 which has its bottom surface 19 flat as in Figs.1 to 3. With the film 16 in position in the mould, thermoplastics material can be injected into the mould as described with respect to Figs.1 to 3 to form the component. After moulding, the component is removed from the mould and separated from the film 16 or the film is left in the mould as the component is removed. Instead of the surface 19 of the mould part 12 being flat, it could have a surface formation 119 shown in broken lines which is different from that of the embossed surface 17 against which the flat surface 17a will lie and remain substantially flat during the moulding step.

In Fig.11 the film 16 shown in Fig.10 is inverted so that moulding takes place against the flat surface 17a. Such an arrangement is useful where the mould part 12 has an engraved surface 19 as in Fig.4. The flat surface 17a of the film 16 in Fig.11 produces a substantially flat adjacent surface on the moulded component.

The use of the film 16 helps to lengthen the life of the mould as it comes between the injected thermoplastics material 18 and the surface 19, 119. However, if desired, the mould can include a wear liner 22 shown in broken lines in Fig.1. The wear liner can be made from, for example, a moulded material, for location in a recess 23 in mould part 12. The liner then defines the mould surface 19 and the film 16 is then used in the same way as described above. The mould in Fig.4 can similarly be provided with a wear liner 22 defining surface 119. The wear liner can be discarded and replaced should it become worn.

As well as covering the surface 19, 119 of the mould, the film also covers side surfaces 19a (Fig.1) of the mould part 12.

As mentioned above, the film material can be nylon. In such a case examples of suitable non-compatible injection moulded materials 18 are polypropylene and polyethylene. Another suitable thermoplastics material for forming the film is ABS

(acrilonitrilebutadiene styrene). Where a nylon film is used, a suitable temperature for the injection moulded material 18, e.g. polypropylene, is around 210°C to prevent melting of the nylon film.

Claims

1. A method of injection moulding a component comprising providing an injection mould (10, 12) placing in the mould a layer of material (16) having a surface against which thermoplastics material (18) is to be injection moulded, the said surface and an adjacent surface (19, 119) of the mould (10, 12) against which the layer of material (16) is placed being of different surface form or texture, and injecting the thermoplastics material (18) into the mould against the layer of material to form the component whereby the layer of material (16) imparts to the injected thermoplastics material a surface form or texture which is different from that which would otherwise be imparted by the said adjacent surface (19, 119) of the mould, the layer of material (16) and the component (20) subsequently being separable, characterised in that the layer of material is in the form of a film-like layer (16) of plastics material.

2. A method according to Claim 1 characterised by selecting the material of the film-like layer (1β) and the thermoplastics material (18) so that the materials are incompatible to limit or prevent bonding together of the materials.

3. A method according to Claim 1 or 2 characterised in that the film-like layer (16) is a thermoplastics material and the temperature of the thermoplastics material (18) injected into the mould is below that at which the thermoplastics film material will melt to inhibit homogeneous bonding between the film and the injected material.

4. A method according to Claim 1, 2 or 3 characterised by removing the injection moulded component (20) from the mould (10, 12) so as to leave the film-like layer (16) in the mould ready to receive a further quantity of injection moulded material (18).

5. A method according to Claim 1, 2 or 3 characterised by removing the injection moulded component (20) from the mould with the film-like layer (16) thereon for subsequent removal from the component (20) .

6. A method according to any preceding Claim including pre-forming the film-like layer (16) to conform to the general shape of at least part (12) of the mould (10, 12) .

7. A method according to any preceding Claim characterised by providing the mould in two parts -.^, (10, 12), introducing the film-like layer (16) into the mould with the two parts (10, 12) separated, and closing the two parts together to clamp the film¬ like layer (16) in position therebetween prior to injecting the thermoplastics material (18) into the mould.

8. A method according to any preceding Claim characterised by providing the film-like layer (16) with an embossed or impressed surface form or texture (17) which is substantially imparted to the mouldable material (18) and providing the adjacent surface (19) of the mould (10, 12) as a substantially smooth surface or as a surface (119) having a surface form or texture different from that of the film-like layer.

9. A method according to any of Claims 1 to 7 characterised by providing said adjacent surface (19) of the mould (10, 12) with a given surface form or texture (119) and inserting said film-like layer (16) into the mould so as to impart a substantially smooth or flat surface finish to the injected thermoplastics material and not the given surface form or texture which would otherwise be imparted by the said adjacent surface (19) of the mould (10,12).

10. A method according to any preceding Claim-- characterised by forming the mould (10, 12) with a recess (15) having said adjacent surface (19, 119) and a side surface (19a) and causing the film-like layer (16) to cover the adjacent and side surfaces.

11. An injection mould for use in a method according to any preceding Claim characterised in that the mould (10, 12) has said film-like layer (16) therein for imparting to the injection moulded thermopl stics material (18) a surface form or texture (22) which is different from that which would otherwise be imparted by said adjacent surface (19, 119) of the mould (10, 12).

12. A component of thermoplastics material characterised in that the component (20) is made by a method according to any of Claims 1 to 9.