GB2324496A

GB2324496A - Two component plastics article and method for its manufacture

Info

Publication number: GB2324496A
Application number: GB9805722A
Authority: GB
Inventors: Sumeth Kongpatanakul
Original assignee: Individual
Current assignee: Individual
Priority date: 1997-04-26
Filing date: 1998-03-19
Publication date: 1998-10-28
Also published as: GB9805722D0; GB9708419D0

Abstract

An article comprises a first portion 10 of plastics material having at least one aperture extending from one side thereof and a second portion 30 of plastics material placed against that one side such that material of the second portion extends into the aperture(s) 16,18 thereby forming a zone of different resilience. The method of manufacture comprises providing a first portion of resilient plastics material having an aperture therein and forming a second portion of plastics material against that first portion, for example by injection, such that the material of the second portion enters the aperture(s) in the first portion. The second portion may be formed by injection of a liquid plastics foam and the aperture(s) may extend through the first portion or be blind apertures.

Description

Title - Plastics Article The present invention relates to plastics articles and methods for manufacturing the same.

The present invention is particularly but not exclusively relevant to the field of footwear.

Modern footwear is commonly provided with a sole of plastics material. Plastics material is utilised because a sole can be built up from several layers to provide a finished product with required strength and resilience characteristics. It is known to provide air pockets within a sole to provide particular regions where cushioning is required. An air pocket is usually defined within a sole by means of a bladder of plastics material inserted between two layers of the sole. Accordingly, construction of a sole with an air pocket can be complicated and therefore costly.

It is an object of the present invention to provide a plastics article and a method of producing the same which can be implemented to provide a sole of a shoe which ameliorate the above problems.

According to one aspect of the present invention there is provided a method of forming a plastics article, the method comprising the steps of providing a first portion of resilient plastics material having an aperture therein, and forming a second portion ofplastics material against said first portion such that material of said second portion enters said aperture and thereby forms a zone of different resilience.

In a preferred embodiment of the invention, the step of forming said second portion comprises the steps of placing the first portion in an injection mould and injecting a quantity of liquid plastics material thereagainst.

Preferably, the liquid plastics material is foaming. In that way, the material will expand into the aperture.

According to a second aspect of the invention there is provided a plastics article comprising a first portion of plastics material, said first portion having an aperture extending from one side thereof, and a second portion ofplastics material against said one side wherein material ofthe second portion extends into the aperture, thereby forming a zone of different resilience.

According to one embodiment ofthe invention, the aperture is blind. The blind aperture may have a cavity at its blind end. The cavity is preferably substantially spherical. In a preferred embodiment, the cavity has a larger width than the width of the aperture.

In that way, an air pocket can be defined in the cavity and sealed by the entry of material of the second sheet into the aperture.

The aperture preferably has a substantially uniform entry portion. Preferably, the entry portion extends into a progressively widening portion. That portion is advantageous as it stalls the advance of liquid plastics material entering the aperture.

According to another embodiment of the invention, the aperture is a through hole extending through the first portion. In that way, a pillar of material of the second portion can be formed in the aperture.

The material of the second portion is preferably a foam. In that way, during formation of the article the material will be foaming and will expand into the aperture with ease. Furthermore, the gases associated with foaming will be released into the cavity of a blind hole provided in accordance with the invention, and can define a pocket of pressurised gases within said cavity.

In a preferred embodiment of the invention, the material of the first portion is a foam, and is preferably a foam less dense than the foam ofthe second portion. In a preferred embodiment of the invention, the foam of the second portion is twice the density of the foams or the first portion.

The first portion and the second portion may each be polyurethane foams.

Preferably, an article is formed in accordance with the invention and comprises a plurality of apertures as described above, at least one of which is blind as described above and at least one of which is a through hole as described above.

Further features and advantages of the present invention will become apparent from the following description of a specific and preferred embodiment of the invention with reference to the accompanying drawings in which: Figure 1 is a cross-section through a first sheet of material forming an article of a specific embodiment of the invention; Figure 2 shows a cross-section similar to that of Figure 1 illustrating the formation of a second sheet of material against the first sheet illustrated in Figure 1; Figure 3 shows a cross-section similar to those of Figures 1 and 2 of a finished article formed in accordance with the specific embodiment ofthe present invention; and Figure 4 shows a plan view of a sole of a shoe incorporating the specific embodiment of the present invention as illustrated in Figures 1-3.

Referring firstly to Figure 1, a first sheet 10 of polyurethane material is formed by means of the usual pouring techniques. The first sheet has an upper face 12 and a lower face 14.

Extending through the thickness ofthe first sheet 10 is a circular through hole 16. Extending from the lower face 14 is a blind hole 18 comprising a first tubular entry portion 20, an expansion portion 22 having a progressively wider diameter, and a spherical cavity 24. The cavity 24 has a diarneter substantially larger than that of the entry portion 20.

Figure 2 shows a second sheet 30 of plastics material being applied against the lower face 14 of the first sheet 10. As before, the second sheet is made of a polyurethane, but in this case the polyurethane is injection moulded onto the first sheet 10. The polyurethane is injection moulded while it is foaming. Foaming takes place because polyurethane can be made of isocyanate and polyol which together form carbon dioxide gas. This gas expands the liquid in plastics to form a light, cellular material that becomes a solid after approximately 20 seconds. It has been found that the mixture will release carbon dioxide after about 5 seconds from initial mixing, prior to that the liquid is very searching and so is highly suitable for injection moulding. On formation of the gas the liquid starts to solidify. From Figure 2, it is clear that the liquid plastics is sufficiently searching to extend through the through hole 16, and also to enter the entry portion 20 of the blind hole 18. Expansion due to foaming also assists in the extension of the liquid plastics through the holes 16, 18.

Figure 3 illustrates the end state of the injection moulding process. Liquid plastics has extended through the through hole 16 to the upper face 12. The solid plastics pillar 32 is particularly useful for supporting at a particular point on the article formed by the combination ofthe first and second sheets 10, 30. That is the case when the second sheet is more dense than the first sheet. In this case the second sheet is twice as dense as the first sheet.

In the blind hole 18, liquid plastics material has entered the entry portion 20 but the increased diameter of the expansion portion 22 limits the progress of liquid plastics material along the blind hole before solidification occurs. Therefore, an air pocket is defined in the cavity 24.

It can be seen that an air pocket has been formed without the need for introduction of bladders into the manufacturing process.

Figure 4 illustrates how the features of the previous drawings can be implemented in a sole of a shoe. In that case the first sheet 10 is constructed as the mid-sole of a shoe, and the second sheet 30 is constructed as the out-sole of a shoe. Air pockets are placed in positions where the foot requires cushioning, i.e. the heel, ball and toe of the foot, whereas the sole is provided with pillars 32 where additional support is required, such as at the bridge.

The method described above of producing a sole of a shoe is particularly useful in that it removes the need for specific bladders to be introduced between layers of a sole. In that way, the manufacturing process can be greatly simplified.

Claims

1. A method of forming a plastics article, the method comprising the steps of providing a first portion ofresilient plastics material having an aperture therein, and forming a second portion of plastics material against said first portion such that material of said second portion enters said aperture and thereby forms a zone of different resilience.

2. A method in accordance with claim 1 wherein the step of forming said second portion comprises the steps of placing the first portion in an injection mould and injecting a quantity of liquid plastics material there against.

3. A method in accordance with claim 2 wherein the liquid plastics material is foaming.

4. A plastics article comprising a first portion of plastics material, said first portion having an aperture extending from one side thereof, and a second portion of plastics material against said one side wherein material of the second portion extends into the aperture, thereby forming a zone of different resilience.

5. A plastics article in accordance with claim 4 wherein the aperture is blind.

6. A plastics article in accordance with claim 5 wherein the blind aperture has a cavity at its blind end.

7. A plastics article in accordance with claim 6 wherein the cavity is substantially spherical.

8. A plastics article in accordance with claim 6 or claim 7 wherein the cavity has a larger width than the width of the aperture.

9. A plastics article in accordance with claim 4 wherein the aperture is a through hole extending through the first portion.

10. A plastics article in accordance with any one of claims 4 to 9 wherein the aperture has a substantially uniform entry portion.

11. A plastics article in accordance with claim 10 wherein the entry portion extends into a progressively widening portion.

12. A plastics article in accordance with any one of claims 4 to 11 wherein the material ofthe second portion is a foam.

13. A plastics article in accordance with claim 12 wherein the material ofthe first portion is a foam.

14. A plastics article in accordance with claim 13 wherein the foam ofthe first portion is less dense than the foam of the second portion.

15. A plastics article in accordance with claim 14 wherein the foam of the second portion is twice the density of the foam of the first portion.

16. A plastics article in accordance with any one of claims 12 to 15 wherein the first portion and the second portion are of polyurethane foams.

17. A plastics article comprising a first portion of plastics material, said first portion having at least one blind aperture and at least one through aperture extending from one side thereof, and a second portion ofplastics material against said one side wherein material ofthe second portion extends into the apertures, thereby forming zones of different resilience.

18. A plastics article substantially as described herein, with reference to the drawings appended hereto.

19. A method of forming a plastics article substantially as described herein, with reference to the drawings appended hereto.