WO1999036242A1

WO1999036242A1 - Methods of producing coated articles, particularly injection moulding tools and press tools

Info

Publication number: WO1999036242A1
Application number: PCT/GB1999/000043
Authority: WO
Inventors: Leo Giano Bonassera
Original assignee: Leo Giano Bonassera
Priority date: 1998-01-20
Filing date: 1999-01-20
Publication date: 1999-07-22
Also published as: AU2286299A; GB9801031D0

Abstract

Instead of machining tool surfaces from hard metals, the tools are moulded from a resin and metallic particle mix which is then metal-plated on the operative surfaces of the mould. The inventive method comprises forming an article body from a resin mix (5) which contains metallic particles, at least in the surface region of the formed article body, arranging that the metallic particles in the surface of the article body are exposed, and then coating the surface of the article body with a metallic coating (4) which is bonded to the exposed particles by a metal to metal bond. Press tools or injection moulding tools produced by the method are of high durability and provide cost savings in manufacturing such tools. In a modification the volume of resin in the mix is reduced whereby a foraminous structure is produced, and the passages in the moulded article can be used for air or liquid cooling of the moulded article. The moulded article can be used as a vacuum moulding tool.

Description

METHODS OF PRODUCING COATED ARTICLES,

PARTICULARLY INJECTION MOULDING TOOLS

AND PRESS TOOLS

This invention relates to methods of producing coated articles, particularly, but not exclusively, tools such as press tools, plastics injection moulding tools, thermo-moulding tools, rubber moulding tools and the like. The invention is concerned with providing a hard surface coating on a forming surface of such tools.

Press tooling used in the pressing of sheet metal in a power press generally comprises a hard metal body which is machined to the desired shape by special machining processes. Spark erosion is commonly used to create the finished surface shape of the tool, under the control of a CAD output. The creation of tooling using CAD - controlled spark erosion requires an expensive investment in machines, skilled labour and the electricity cost associated with the removal of large quantities of metal by spark erosion is substantial.

Similarly the production of injection moulding tools for plastics, or press-moulds for rubber moulding, is an expensive and time-consuming activity using conventional techniques to shape the forming surfaces of the tools.

An object of the present invention is to provide a less expensive method of producing tooling.

According to one aspect of the invention a method of producing a tool comprises forming a tool body from a resin mix which contains metallic particles, at least in a surface region of the moulded article body that provides a forming surface of the tool, arranging that the metallic particles in the surface of the body are exposed, and then coating the body surface with a metallic coating which is bonded to the exposed particles by a metal to metal bond.

By a 'forming surface' of the tool we mean a surface of the tool that defines the shape of the product to be produced using the tool. Thus, in the case of an injection moulding tool, the forming surface will bound at least part of the mould cavity.

By employing suitable resins, such as epoxy, polyester, or polyurethane resins, for the matrix of the tool body, the tool is provided with body strength, and a suitable choice of the metallic coating can provide a high surface hardness.

The tool body is preferably formed by moulding, and since relatively cheap moulds can be utilised in moulding of resin articles, the cost of moulding the tool body will not generally be expensive. For example, a mould for injection moulding of a resin-matrix tool body would typically cost only 35% (estimated) of the cost of a metal mould.

The metallic particles employed in the tool body are those which are capable of forming the metal to metal bond with the applied metallic coating .

The method of applying the metallic coating to the tool body is preferably by an electro-less chemical coating method but, in appropriate cases, electro-plating may be employed. It will be appreciated that the metallic particles in the surface layer of the tool body are held firmly in place by the adhesive bonding between the resin matrix and the metallic particles, and the metal to metal bonds between the surface particles and the applied coating anchor the applied coating firmly in place.

The surface of the body is preferably abraded, either mechanically, chemically or in some other way prior to application of the metallic coating in order to facilitate a secure metal to metal bond between the applied metallic coating and the outer surfaces of the metallic particles in the surface region of the tool body. The metallic particles at the surface of the body may, during forming of the body, become covered by a thin film of the resin which can be removed by such an abrasive step.

When the metallic coating is applied by electro-less or electro-plating, then the exposure of the outer surfaces of the metallic particles is desirable so as to provide a large number of local sites for initiating electro-deposition of the coating, thereby assisting in producing a coating of relatively uniform thickness.

It will be appreciated that a relatively high content of metallic particles in the surface of the uncoated tool body will thereby help to promote the formation of a coating of relatively uniform thickness due to the provision of closer initiation sites, and will help to ensure that substantially all of the surfaces particles are electrically connected together by contact between adjacent particles, so as to complete the electrical circuit required for the electro-plating process. Care must be taken, however, against overloading with metallic particles. The metallic particles can advantageously provide the resin mixture with torsional and flexural strength.

A coating of substantially uniform thickness helps to minimise the need for any surface polishing required to achieve the desired surface smoothness of the forming surface of the tool, since the surface finish achieved during forming of the uncoated tool body can be substantially retained in the coated tool.

The feature of achieving a desired surface finish is particularly advantageous for quality tooling, for example, injection moulds.

The texture of the coated tool can be determined to a large extent, by selecting a particular size of metallic particle used in the resin mix. If sufficiently fine metallic particles are employed then moulds suitable for injection moulding of optical components can be produced.

The weight percentage of metallic particles in the surface region of the article body is preferably at least 50% and is most preferably greater than 60%, and can depend on the type of plating to be used.

The metallic particles are preferably aluminium particles. These have a high electrical conductivity which facilitates plating. Copper or any conductive metal particles could also be used when the coating is to be electro-deposited.

An electro-deposited coating could be of silver, gold, cadmium or chromium for example, or any other suitable plating metal. Should the metallic coating wear after extensive use then the coating can be removed and the article can then be re-plated. If nickel is used as the coating then the coating can be removed with nitric acid.

According to a second aspect of the invention a tool is produced by the method in accordance with the first aspect of the invention.

The invention, according to a third aspect, also comprises a method of moulding a plastics or rubber article in which at least a portion of the mould tool has been formed by a method in accordance with the first aspect of the invention.

According to a fourth aspect of the invention I provide a method of moulding a vehicle tyre in which at least a portion of the mould tool has been produced by a method in accordance with the first aspect of the invention.

Vehicle tyres are generally press-moulded, and the invention is applicable to the press mould.

A fifth aspect of the invention is based upon our finding that it is possible to produce a tool body, or other article body, by resin-bonding together metallic particles as a foraminous structure, to provide interconnecting voids between the bonded-together particles. The particles in a surface of the body can then be used, as previously described, for initiating the production of a metallic coating anchored to those surface particles.

According to the fifth aspect of the invention, a method of producing a coated article comprises moulding an article body from a mixture of metallic particles and resin, the volume of the resin being so chosen that the moulded article body contains voids between the metallic particles bonded together by the resin, removing resin from the particles that are present at a surface of the article body, and then coating that surface of the article body with a metallic coating which is bonded to the surface particles by a metal to metal bond.

The porosity of the resulting article body may then be employed to allow air or liquid coolant to be passed through it.

The moulding process preferably comprise tamping the mixture of metallic particles and resin into the mould to help with subsequent bonding during curing of the resin which by then has substantially coated the individual metallic particles.

The removal of resin from the surface of the article body is preferably carried out by bead blasting with glass beads.

When relatively large metallic particles are employed, the metallic coating will not bridge the voids defined between the surface particles, and accordingly the coated surface is porous. This feature can be useful for some applications.

For example, a tool produced by the method of the fifth aspect of the invention, and which has a porous coating, may be used in vacuum forming of plastics. The air passages through the coating provide air connection to the porous body of the tool which can be connected to a vacuum 'source¹. A coated article produced by the method in accordance with the fifth aspect of the invention, and which has a porous coating, may be used as a filter body, the coated surface of the article providing mechanical strengthening for resistance against knocks.

The porosity of the article body produced by the method of the fifth aspect of the invention can be varied by varying the size of the metallic particles and/or the volume of resin employed depending on the viscosity of the resin used.

The invention will now be further described, by way of example only, with reference to the accompanying drawings in which:

Figure 1 is a cross-sectional view of a first injection mould formed by the method of the invention; and

Figure 2 is a cross-sectional view of a second injection mould formed by the method of the invention.

Example 1

In the production of a press tool, 62% by weight of aluminium powder of 200 mesh was intimately mixed by stirring of epoxy resin and cured at room temperature. The mix was de-gassed by placing in a vacuum chamber) and the mix was pour- or fill-moulded into a mould constructed of a silicone material. The mould was then de-gassed by placing the mould in a vacuum chamber, for 1 to 3 minutes, in order to remove air and maximise density. Once cured the moulded tool body was removed from the mould. In order to remove films of resin from the outer surfaces of the aluminium particles in the surface layer of the body, the body was then subjected on one side, that side which is to provide the operative or forming face of the press tool, to a high pressure blast of compressed air and aluminium filings.

In order to produce an electro-deposited coating an electrode was cast into the reverse side of the body and the body was subjected to a standard electro-plating procedure in order to deposit a coating of metal of approximately 4 thousandths of an inch on the body.

The operative side of the body was then polished.

The resulting tool was then used in a power press to form shaped articles from pressed metal sheets of varying thicknesses.

The surface hardness of the tool was approximately 700 Vickers when a coating of nickel was used.

In the foregoing example a coating of thickness 4 thou was deposited, but it is believed that a coating of 2 thou would suffice for many tools.

A polyurethane or polyester resin could also have been used. It should be noted that some resins are heat cured, the method of curing depending on the type of resin used. Example 2

Figure 1 shows an injection mould 1 comprising two mould halves 2 and 3. Each mould half 2 and 3 comprises in section two layers 4 and 5, and 8 and 9 respectively. The composition of each layer is given in the following table:

The mould half 2 also comprises an aluminium insert 13. The mould halves 2 and 3 together define a void or mould cavity 12 which when filled with plastics material via the mould inlet, as indicated by arrow A, forms a moulded product.

As is shown in Figure 1 the aluminium insert 13 is plated with nickel and partially defines the shape of the moulded product. The purpose of the aluminium insert is to define a fine rib on the forming surface of upper mould half 2 which would otherwise be difficult to create.

The mould halves 2 and 3 further comprise lost wax passages 6 and 10.

The lost wax passages 6 and 10 allow heat to be dissipated from the mould 1 and are produced by the addition of wax rods into the uncured resin mixture during the manufacture of the mould halves 2 and 3. When the layers 5 and 9 are cured the wax rods melt and are drained away to leave the passages 6 and 10. The wax rods are shaped so that they are close enough to the mould cavity 12 to ensure sufficient cooling of the cavity 12. The feature of being able to shape the cooling passages 6 and 10 is particularly advantageous since it is necessary to negotiate ejector pin holes (not shown) and sprue holes (not shown) .

Example 3

Figure 2 shows a second injection mould 16 which comprises two mould halves 14 and 15, and the mould half 14 comprises an aluminium insert 23. The mould halves 14 and 15 comprise layers 17, 18, 19 and 22, 23, 24 respectively. The composition of each of the layers making up each mould half is shown in the following table:

The aluminium needles are 0.3-1.2 mm in diameter and approximately 7 mm long. Advantageously, the aluminium needles provide flexural strength to the mould.

The aluminium granules are of 20/60 mesh.

The mould halves 14 and 15 also comprise lost wax passages 20 and 25 respectively. Layers 19 and 24 may, alternatively, comprise a resin mixture containing glass flake, for example in the following proportions:

The resin system used in the table above is LY5210 Resin and HY2954 Hardener produced by Ciba-Geigy™. The Aluminium fillers used in the above examples are available from the Aluminium Powder Company Limited, Forge Lane, Minworth, Sutton Coldfield, West Midlands, England, and the glass flake used in example 3 is Microglas^® glass flake (RCF) and is available from NGF Europe Limited, Lea Green, St Helens, England.

Example 4

In order to produce a coated article which comprises a porous body the following mix of materials was prepared using CIBA™ resin system:

LY5210 Resin 5.12% by weight HY2954 Hardener 2.71% by weight

Aluminium Granules 20/60 mesh 99.5% 0.2/0.75 mm 92.16% by weight

The mixture was fed into a resin mould and then tamped down. After curing of the article, one side of the article was bead blasted with glass beads. That surface was then subjected to an electro-less plating process to apply a 0.003 inch coating of nickel to that surface. The relatively large size of the aluminium granules results in relatively large voids between the granules. The nickel deposited on the exposed granules to the specified thickness does not completely bridge the surface voids, and accordingly the surface coating is porous, the passages in the surface coating communicating with the voids in the article body.

Claims

1. A method of producing a tool (1) comprising forming a tool body from a resin mix (5) which contains metallic particles, at least in a surface region of the tool body that provides a forming surface, as hereinbefore defined, of the tool, arranging that the metallic particles in the surface of the body are exposed, and then coating the body surface with a metallic coating (4) which is bonded to the exposed particles by a metal to metal bond.

2. A method of producing a tool as claimed in claim 1 wherein the tool body (1) is formed by moulding.

3. A method of producing a tool (1) as claimed in claim 2 wherein the tool body is formed by injection moulding.

4. A method of producing a tool (1) as claimed in any one of the preceding claims wherein the method of coating the surface of the tool body with a metallic coating (4) is by an electro-less chemical coating method.

5. A method of producing a tool (1) as claimed in any one of claims 1 , 2 or 3 wherein the method of coating (4) the surface of the tool body with a metallic coating is by an electro-plating coating method.

6. A method of producing a tool as claimed in any one of the preceding claims wherein the surface of the tool body is abraded prior to application of the metallic coating.

7. A tool produced by a method as claimed in any one of the preceding claims.

8. A tool as claimed in claim 7 and which is a press tool.

9. A tool as claimed in claim 7 and which is an injection moulding tool.

10. A plastics or rubber moulding tool comprising a tool body formed from a resin mix which contains metallic particles, and an outer metallic layer bonded to the tool body.

11. A tool as claimed in claim 10 wherein an interface region of the outer metallic layer and the tool body comprises metallic particles bonded to the outer metallic layer by a metal to metal bond.

12. A tool as claimed in claim 10 or 11 wherein the resin mix comprises at least 50% weight percentage of metallic particles.

13. A tool as claimed in claim 10 or 11 wherein the resin mix comprises greater than 60% weight percentage of metallic particles.

14. A tool as claimed in any one of claims 10 to 13 wherein the tool is an injection moulding tool.

15. A method of moulding a plastics or rubber article in which at least a portion of the mould tool has been formed by the method of any of claims 1 to 6.

16. A method of moulding a vehicle tyre in which at least a portion of the mould tool has been formed by the method of any of claims 1 to 6.

17. A method of producing a coated article comprising moulding an article body from a mixture of metallic particles and resin, the volume of the resin being so chosen that the moulded article body contains voids between the metallic particles bonded together by the resin, removing resin from the particles that are present at a surface of the article body, and then coating that surface of the article body with a metallic coating which is bonded to the surface particles by a metal to metal bond.

18. The method of claim 17 in which the metallic coating is applied such that voids between the particles at the surface are not fully bridged by the coating material, whereby the coated surface is porous.