FIELD OF THE INVENTION The invention relates to a process and composition for binding of a powder substrate, in particular metal-bearing powder such as for example occurring in ferro and non-ferro metallurgy, metal processing & metal recycling, sand blasting residue and blasting slag, residue powder of plasma-/laser cutting, machine borings, machine turnings, steel making, metal smelting processes, steel powder dust from airfilters in cyclones from any kind.

The present invention is based on the finding that the presence of a thermoplastic material as solidifying agent in a binder composition for binding of a metal-bearing substrate, results in a composite material with previously unknown characteristics.

Using a binder according to the present invention, the resulting material has a very homogenous structure, a high mechanical strength, an improved sustainability profile, an improved water resistance, and a dimensional stability even temperatures up to 900°C.

It is accordingly an object of the present invention to provide, a binder for binding of a metal-bearing substrate, in particular metal-bearing powder, said binder comprising a water borne binder and a thermoplastic material. The invention further relates to a process and composition for binding of a powder substrate, including composite materials thus obtained.

SUMMARY OF THE INVENTION Numbered statements of the invention are as follows:

1 . A binder for binding of a metal-bearing substrate, in particular metal-bearing powder, said binder comprising a water borne binder and a thermoplastic material, wherein the weight ratio between the binder and the metal-bearing substrate amounts between 1 : 200 to 1 : 5. 2. The binder according to statement 1 , characterized in that the thermoplastic material consists of solid thermoplastic particles whereby 90% wt of the particles have a particle size below 500 micrometer, in particular between and about 0.5 to 500 micrometer.

3. The binder according to statement 2 whereby 90% of the particles have a particle size below 200 micrometer, in particular between and about 1 .0 to 200 micrometer.

4. The binder according to statement 1 , wherein the thermoplastic material has a melting point or a glass transition temperature of between and about 40°C and 250°C.

5. The binder according to statement 1 whereby the thermoplastic material comprises a polymer selected from the group consisting of polyesters, polyamides, polyolefins, polyvinyls, polyacrylates, polyvinylacetates, polyurethanes, and combinations/ copolymers thereof.

6. The binder according to statement 5 whereby the thermoplastic material comprises an ester-containing polymer, such as a polyester, polyvinylacetate or a polyacrylate.

7. The binder according to statement 5, wherein the thermoplastic material further contains one or more other materials such as fillers, pigments, opacifiers, UV- stabilizers, cross-linkers and catalysts.

8. The binder according to any one of statements 2 to 7, wherein the thermoplastic material is present as a water borne dispersion of the thermoplastic particles.

9. The binder according to any one of statements 1-7 whereby the water borne binder is a binder such as water glass, starch polyvinylalcohol, styrene- butadiene, or polyvinylacetate; that is water borne by solution, emulsion, dispersion or combinations thereof; in particular the water borne binder is the combination of a water soluble binder and a water borne emulsion; more in particular the water borne binder is a water soluble binder; even more particular the water borne binder is water glass.

10. The binder according to statement 9, wherein the water borne binder is water glass having a ratio of Si0 ₂ to Na ₂ 0 ranging from about 1 to about 3.5; in particular from about 2.5 to about 3.5.

1 1. The binder according to statement 1 whereby the ratio between the water borne binder and the thermoplastic material amounts to between about 1 : 3 and 40 : 1. 12. A composition comprising a binder as defined in any one of statements 1 to 1 1 and a metal-bearing substrate, in particular a metal-bearing powder such as for example in ferro and non-ferro metallurgy, metal processing & metal recycling, sand blasting residue and blasting slag, residue powder of plasma-/laser cutting, machine borings, machine turnings, steelmaking, metal smelting processes, steel powder dust from air filters in cyclones from any kind.

13. The composition according to statement 12, wherein the metal-bearing powder is ferrous metal powder.

14. The composition according to statement 12, wherein the metal-bearing powder has a particle size below 2000 micrometer; in particular at least and about 40% wt of the metal-bearing powder has a particle size below 500 micrometer; more in particular at least and about 20% wt of the metal-bearing powder has a particle size below 100 micrometer.

15. The composition according to any one of statements 12 to 14, further contains additives such as fillers, dyes, crosslinkers, pigments, UV-stabilizers, waxes.

16. Substrates (composite materials) made by heating the composition according to any one of statements 12 to 15 at a temperature above the melting point or glass transition temperature of the thermoplastic material.

17. Substrates made according to statement 16 whereby a pressure of at least 2 bar is used during the curing process.

BACKGROUND OF THE INVENTION

In each of the aforementioned metal treatment processes, scrap metal waste and metal-bearing powders are produced. In as far this waste material contains a high quantity of pure metal, making it an interesting resource of metal stock, the lose material has major handling disadvantages. Metal powder is prone to scattering and ferrous metal powder is even prone to ignition, rendering the handling thereof quiet problematic. Especially, the use of the iron dust for the foundry industry is problematic as the dust will be blown away when added to the hot furnace. Consequently, a lot of this metal waste is committed to landfill disposal as industrial waste.

In view of the foregoing, it is accordingly not surprisingly that there have been attempts to recover this material in a bound form, simplifying handling of this material, but also enabling reuse of this waste as for example in the foundry industry or as a steelmaking material. In US patent US 3,316,083, the metal-bearing waste is converted into a solid pellet by compressing a mixture of the metal borings and turning with aqueous sodium silicate, water-soluble starch, and water in a mold. In this method the pellets are dried by exposure to ambient air conditions. In European Patent EP 1 323 838, the metal-bearing waste further comprises cottonlike aggregates and is impregnated with a solidification assistant prior to the pressure molding step, including colloidal silica, silicate of soda and aluminum phosphate. In analogy with US 3,316,083, also in this method the pellets are dried by exposure to ambient air conditions. In European Patent EP 1 482 061 , the metal-bearing waste in the composition is characterized in that 30-50 wt% of the material consists of unquenched ferrous metal, and in that an oil containing aqueous solution is added to the mixture prior to the compression molding.

In European Patent EP 1 734 138, the dry briquettes for use as metal stock are simply made by solidifying metal-bearing powder dust using a solidification agent such as sodium silicate.

Japanese Patent JP 1 1 130515, discloses a process for binding aluminium residual ash and solves particular problems related thereto, requiring high binder loadings.

US554207 and BE1009228, disclose the use of thermoplastic resins as binders for metallurgical waste, however both relate to a water-free system, and neither of them discloses, nor hints to the use of a water-borne binder, let it be in combination with a thermoplastic material.

Where each of the aforementioned cases does indeed result in a bound material comprising the metal waste, certain problems still reside. For example, when using aqueous sodium silicate as a solidification agent, the resulting material is hygroscopic. The compressed metal substrate will disintegrate when moisture is present in the atmosphere. Further, organic binders like starch, will lose their binding power at higher temperatures rendering the material unsuitable in the foundry industry as the compressed substrate will rapidly fall apart into the metal particles that can be blown away out of the hot furnace. It is accordingly an object of the present invention to provide a further and improved method and composition for binding of a powder substrate, in particular metal-bearing powder. DESCRIPTION OF THE INVENTION

The present invention is based on the finding that the presence of a thermoplastic material as solidifying agent in a binder composition for binding of a metal-bearing substrate, results in a composite material with previously unknown characteristics. As will be evident from the examples hereinafter, using a binder according to the present invention, the resulting material has a very homogenous structure, a high mechanical strength, an improved sustainability profile, an improved water resistance, and a dimensional stability even at temperatures up to 900°C.

It is accordingly a first aspect of the present invention to provide a binder for binding of a metal-bearing substrate, in particular metal-bearing powder, said binder comprising a water borne binder and a thermoplastic material, wherein the weight ratio between the binder and the metal-bearing substrate amounts between 1 : 200 to 1 : 5.

Whenever, in the present invention, reference is made to an amount, ratio or % of a substance (such as water glass binder, thermoplastic material, or metal-bearing substrate), it is meant to represent the dry matter weight, dry matter ratio or weight % of said substance, unless indicated otherwise. Within a first embodiment the thermoplastic material is characterized in that it consists of a thermoplastic material that is solid at room temperature and hence its melting point (m.p.) or its glass transition temperature (Tg) should preferably be above 40°C. A m.p or Tg higher than 250°C makes hardly sense because a too high temperature will be needed to let the thermoplastic material flow during the compression step. Consequently in a further embodiment the present invention provides the aforementioned binder, further characterized in that the thermoplastic material consists of thermoplastic particles that are solid at room temperature; more in particular wherein the thermoplastic material has a melting point or a glass transition temperature of between and about 40°C and 250°C.

In as far there are no particular requirements regarding the dimensions of said solid thermoplastic particles, best results are obtained when the thermoplastic material is evenly distributed over the metal-bearing substrate to be solidified. Consequently, in a further aspect of the present invention, the thermoplastic particles have a small particle size. In one embodiment 90% wt of the particles have a particle size below 500 micrometer, in particular between and about 0.5 to 500 micrometer; in a further embodiment the thermoplastic material is characterized in that it consists of solid thermoplastic particles whereby 90% of the particles have a particle size below 200 micrometer, in particular between and about 1 .0 to 200 micrometer.

Examples of suitable thermoplastic materials are polyesters, polyamides, polyolefins such as polyethylene and polypropylene, polyvinylchloride, polyvinylacetates, polyacrylates. A preferred thermoplastic binder is one that contains ester groups such as a polyester, a polyvinylacetate or a polyacrylate. Thus in another aspect the thermoplastic material comprises a polymer selected from the group consisting of polyesters, polyamides, polyolefins, polyvinyls, polyvinylacetate, polyacrylates, polyurethanes, and combinations/ copolymers thereof. More in particular the thermoplastic material comprises an ester-containing polymer, such as a polyester, a polyvinylacetate or a polyacrylate.

In a preferred embodiment of this invention the thermoplastic material stems from a waste stream. Such a waste stream is for instance the powder coming from the production and the use of powder paints. Usually, such a powder is contaminated with other products and can not longer be used as a powder paint. This waste stream is usually burnt and the generated energy can be used for other purposes. By using the waste stream as a binder to make new substrates it gets a higher added value.

This thermoplastic material may contain other materials such as fillers, pigments, opacifiers, UV-stabilizers, crosslinkers and catalysts. Thus in another embodiment of the present invention, the thermoplastic material further contains one or more other materials such as fillers, pigments, opacifiers, UV-stabilizers, cross-linkers and catalysts.

The water borne binder and the thermoplastic material can be added together before it is added to the particles. It is also possible to add the two binders separately. In a preferred form the water borne binder is added first to the fibers or the particles, subsequently followed by the addition of the thermoplastic binder. The water borne binder will as a liquid be well distributed over the fiber or particles. Due to the presence of the water borne binder the thermoplastic binder will as well be better distributed over the particles. Evidently from the foregoing, and given the presence of a water borne binder, depending on the ratio of water borne binder to thermoplastic material, the consistency of binder according to the present invention will change, from a more liquid (higher amount of water borne binder) to a more solid state (higher amount of thermoplastic particles). Within the context of the present invention, the ratio between the water borne binder and the thermoplastic material typically amounts to between about 1 : 3 and 40 : 1 ; in particular to between about 1 : 2 and 30 : 1 .

Irrespective of the aforementioned ratio, a proper distribution of the thermoplastic material in the binder is clearly enhanced when present as a water borne dispersion. Consequently, in a further aspect the thermoplastic material is present as a water borne dispersion of the thermoplastic particles.

The water borne binder can be a binder that is water borne by solution, emulsion or dispersion. A solution of a water borne binder can be starch, polyvinylalcohol, water glass. A water borne emulsion can be a styrene butadiene latex, polyvinylacetate or alkyd emulsion.

Accordingly, in an embodiment of the present invention, the water borne binder is a binder such as water glass, starch polyvinylalcohol, styrene-butadiene, or polyvinylacetate; that is water borne by solution, emulsion, dispersion or combinations thereof; in particular the water borne binder is the combination of a water soluble binder and a water borne emulsion (in particular water glass and polyvinylacetate); more in particular the water borne binder is a water soluble binder; even more particular the water borne binder is water glass.

Preferably, the binder is water glass. Water glass is derived from sand and sodium hydroxide and as such does not contain products derived from fossil fuel. The type of water glass is described by its ratio Si0 ₂ to Na ₂ 0. A higher ratio results in a product with lower water sensitivity. Principally, all types of water glass can be used in this application, ranging from a ratio of 1 to 3.5, but preference is given to a ratio of 2.5 to 3.5. As already explained hereinbefore, the binder of the present invention is of particular interest to bind dust to make larger entities. More in particular to bind metal-bearing substrate, in particular a metal-bearing powder such as for example occurring in machine borings, machine turnings, steelmaking, metal smelting processes or the like.

Thus, in a second embodiment, the present invention provides a composition comprising a binder as defined herein and a metal-bearing substrate, in particular a metal-bearing powder such as for example occurring in machine borings, machine turnings, steelmaking, metal smelting processes or the like. In a preferred embodiment the metal-bearing powder is ferrous metal powder, including iron, iron oxides and the like.

In the solidification of the metal-bearing substrate using the binder according to the present invention, it is important that the binder and the metal-bearing substrate are good admixed with one another and that there is an evenly distribution of either component in the compositions thus obtained. Especially, when the amount of binder is below 10% of the total mass a very well mixing is crucial. Within the context of the present invention the weight ratio between the binder and the metal-bearing substrate typically amounts between 1 : 200 to 1 : 5.

Again, and similar to the distribution of the thermoplastic particles in the binder, best results are obtained when the metal-bearing substrate has a small particle size. Consequently, in one aspect of the present invention the metal-bearing powder has a particle size below 2000 micrometer; in particular at least and about 40% wt of the metal-bearing powder has a particle size below 500 micrometer; more in particular at least and about 20% wt of the metal-bearing powder has a particle size below 100 micrometer.

As will be evident from the examples hereinafter, any one of the aforementioned compositions may further contains additives such as fillers, dyes, crosslinkers, pigments, UV-stabilizers, waxes.

In a third aspect the present invention provides substrates (composite materials) made using the binder as described herein, i.e. using any one of the aforementioned compositions. In the manufacture of said substrates, the aforementioned compositions comprising the metal-bearing substrate and binder are brought in a recipient and cured under high temperature and pressure. The curing temperature will be above the melting point or glass transition temperature of the thermoplastic material, alternatively even above 100°C to remove the present water. A pressure of at least 2 bar is used during the curing process. The curing time will be dependent on the curing temperature and someone skilled in the art will be able to determine the necessary curing time in relation to the curing temperature.

In the particular embodiment of the invention, wherein the binders are a combination of a water glass and an ester containing thermoplastic material. While the curing reaction takes place some hydrolysis of the ester containing thermoplastic material will take place, leading to the formation of the sodium salt of the carboxylic acid. As a result the ratio Si0 ₂ to Na ₂ 0 of the water glass will increase. Therefore the water resistance of the cured material will become higher. The water resistance of the substrate can be further increased by adding hydrophobizing agents such as e.g. oil or waxes.

This invention will be better understood by reference to the Experimental Details that follow, but those skilled in the art will readily appreciate that these are only illustrative of the invention as described more fully in the claims that follow thereafter. Particular embodiments and examples are not in any way intended to limit the scope of the invention as claimed. Additionally, throughout this application, various publications are cited. The disclosure of these publications is hereby incorporated by reference into this application to describe more fully the state of the art to which this invention pertains.

EXAMPLES Example

Waste iron powder is classified according its particle size. A composition of iron powder is made consisting of 150g of iron powder with a particle size between 500 and 2000 μηη, 50g of iron powder with a particle size between 3 and 500μηη and 50g of iron powder with a particle size between 1 and 100 μηη. After the powders are well mixed with each other during 30 seconds, 2.5g of a recycled powder paint is added and the mixture is mixed for another 30 seconds. The powder paint has a particle size distribution of which 90 % lies between 1 and 100 micrometer. The chemical composition of the powder paint is for about 50% polyester with a glass transition temperature of 55°C. Other main components in the powder paint are Ti0 ₂ , pigments and fillers. After that 2.5 g water glass (from Silmaco Belgium) is added. The water glass has a Si0 ₂ to Na ₂ 0 ratio of 3.2. The resulting mixture is well stirred during 30 seconds. A round steel mould with an inside diameter of 40 mm, an outside diameter of 70 mm and a height of 70 mm is pre-heated on a plate of 200°C and then filled with the mixture described above. A pestle with a diameter of 39 mm and a length of 100mm is introduced into the inner circle of the mould and a pressure is executed on the pestle of 20 tons, while the mould is still present on a plate of 200°C.

After 3 minutes the pressure is released and the mould removed from the heated plate. After cooling down the compressed iron piece is removed from the mould. The pressed material has a very homogeneous structure and resembles a piece of iron that has been made through pouring molten iron into the mould.

The pressed iron material has a density of 4800 kg\m ³ .

Furthermore the pressed iron material can be heated to a temperature up till 900°C without affecting the structure of the molded piece. In case only organic binders are used the pressed iron material will disintegrate at temperatures above 500°C.