Patent Publication Number: US-2005140056-A1

Title: Plastics moulding

Description:
This invention relates to a method of and apparatus for moulding a plastics article, at least a part of which has a ‘soft-feel’ finish.  
      It is known to be desirable to incorporate a ‘soft-feel’, in other words a yieldable surface to parts which have surfaces in the passenger compartment of a motor vehicle. This gives improved aesthetic/tactile comfort for the vehicle occupants and can help to minimise injury in the event of an impact of the vehicle with another object.  
      Most such parts, for example the instrument panel, the console and the door trims are moulded in a shape which has three dimensions. The manufacture of such parts calls for a moulding technique, which is more often than not a plastics moulding technique. The part needs to have sufficient ‘solid’ plastics to support the shape and to support any loads which will, in use, be imposed on the part.  
      The ‘soft-feel’ is usually produced by applying a layer of soft material, typically a foamed material, to the part surface. This layer of material can be attached to a moulded part by adhesive after the part itself has been moulded. This is time consuming, difficult to do and expensive.  
      It is also known to place the layer of soft material in the mould tool and then to use an injection moulding process to mould plastic behind the material. However, with this technique it is difficult to make a tidy edge where the soft material meets the relatively rigid part.  
      According to the present invention, there is provided a method of manufacturing a plastics moulded part with a soft-feel surface, the method comprising the steps of preparing a sheet of soft material of a desired shape and form, preparing a mould tool to mould the part with a rib on the moulded part extending generally parallel to the surface which will be covered by the soft material, placing the soft material in the mould tool with the edges of the material in register with the rib, injecting molten plastics into the mould tool to fill the tool and to compress the soft material, allowing the mould tool and its contents to cool and removing the moulded part from the tool to allow the soft material to expand to fill the space behind the rib.  
      Soft material means any sheet-like material which can be compressed in thickness and can subsequently recover to its original thickness. Rubbers and elastomers are examples of such materials, but preferably the material is or includes a foamed plastic. More specifically the material may be a laminate made up of an outer skin (which may be a continuous sheet material or a fabric, eg a woven or knitted cloth), a foam middle layer and an inner skin. After moulding, the inner skin will bond to the injected plastics so that a unitary product is produced.  
      It is an advantage of the present invention that a moulded part can be produced, with an outer surface which, in part has a soft feel and in part is hard, with the soft surface being substantially flush with the hard surface and there being substantially no gap where the soft feel surface meets the hard surface.  
      The invention also provides a mould tool for manufacturing a part which has one surface portion having a soft feel finish and another surface portion having a hard finish, wherein the tool half which will form the outer surface of the part has, in the region where the soft feel surface is to meet the hard surface, a cavity region extending substantially parallel to and outboard of the adjacent tool wall such that the moulded part has a rib which extends along the region where the soft-feel surface meets the hard surface. 
    
    
      The invention will now be further described, by way of example, with reference to the accompanying drawings, in which:  
       FIG. 1  is a perspective view of a console armrest for a motor vehicle, constructed using the method of the present invention;  
      FIGS.  2  to  4  show a cross-section through a set of mould tools, at a position corresponding to the position of the line A-A, at three sequential steps in the method; and  
       FIG. 5  shows a section on the line A-A through part of a completed armrest. 
    
    
       FIG. 1  shows a typical component  10  which can be manufactured using the process of this invention. The component is a motor vehicle armrest which also forms a top cover to a storage box in a vehicle console between the vehicle front seats.  
      The armrest  10  has an injection moulded plastic body which has a major surface  12  covered in a soft-feel material and an edge region  14  where hard plastic is exposed. This invention is concerned with the region where the soft and hard surfaces meet, ie the detail at the junction line  16 .  
      The armrest is to be manufactured by injection moulding in a moulding tool  18 .  FIG. 2  shows a section through a part of the tool, the section being taken on the lines A-A from  FIG. 1 . The tool has a core side  20  and a cavity side  22  which define a cavity  24  between them. The core side  20  and cavity side  24  are shown in the relative positions they take up when the tool is closed.  
      The first stage in manufacturing this armrest is to prepare the material which will form the soft-feel surface. In this example, the material is a three-layer laminate with an outer skin  26 , a foam layer  28  and an inner skin  30 . This can be seen in  FIG. 3 . A blank  31  of appropriate size is cut from a sheet, and is then vacuum formed into the approximate three-dimensional shape required to form a the armrest surface.  
      The tool cavity  24  has an upper region  34  in which the upper part  12  of the armrest will be moulded, and a lower region  36  in which the edge region  14  of the armrest will be moulded. Between these two regions of the tool, there is a transition region. In the transition region, there is a step  32  on the core side of the tool. This step provides an edge against which the soft-feel material can be placed in the mould. On the cavity side of the tool, there is a downwardly-extending fin  38  and, outboard of that fin, a narrow recess  40 . All of these features, ie the step, the fin and the recess extend all the way around the tool where the junction line  16  runs.  
      The next stage in manufacturing is to place the blank  31  in the tool, which at this stage will be open. As can be seen in  FIG. 3 , the edges of the blank fit against the step  32  in the mould cavity  24 . At this stage, the foam is uncompressed and the soft-feel material blank  31  substantially fills the cavity  24 .  
      Next, the tool is closed ( FIG. 3 ) and molten plastic  33  is injected into the tool, using standard injection moulding technology. Details of the injection equipment and of the tool features required to enable injection to take place are not shown, as they will be well known to the skilled man and form no part of this invention. The injection takes place from the core side  20  of the tool, and the pressure generated in the molten plastic by the injection equipment, as well as forcing the molten plastic to flow throughout the tool cavity, also acts against the inner layer  30  of the soft-feel blank  31  to compress the foam  28 . This can be seen in  FIG. 4 . It will also be seen from  FIG. 4  that once the foam has been compressed, a passage opens up between the upper and lower regions of the tool cavity at the step  32 . The moulding conditions, the composition of the inner laminate layer  30  and the injected plastics will be chosen so that a bond is formed during the injection process between the laminate and the injected plastic.  
      Suitable materials are: polypropylene for the base moulding, extruded polypropylene for the inner layer  30 , polypropylene foam for the core  28  and TPO (thermoplastic olefins) for the outer layer  26 . The outer layer can if desired be printed with a grain pattern, carry a flocked surface or have some other decorative finish. Many other different materials and combinations of materials can however be used, and the invention is not restricted to any particular material or materials. Alternatively, the outer skin  26  can be a fabric, for example a woven or knitted fabric.  
      Once injection has been completed, and the plastic has set, the tool is opened. Once the constraint provided by the cavity tool wall is removed, the foam expands again (this time expanding from the inner laminate layer  30  outwards) so that the soft-feel characteristic is restored and so that the outer layer  26  of the laminate lies flush with the outer surface of the hard plastic edge region  14 . The edges of the blank  31  are hidden in a channel  42  formed in the moulded part by the fin  38 , and are thus concealed.  
      The dimensions of the blank and of the tools are deigned so that, when the foam in the blanks expands after removal from the mould tool, the outer surface  12  and  14  are substantially flush with one another. This provides a neat finish to the part, and no major finishing operations are required after the part has been removed from the mould.