A COMPOSITION COMPRISING A FINE POWDER

Abstract: The present invention relates to a composition comprising a fine powder and more particularly, though not exlusively, to a composition in which the fine powder is a colorant. Such compositions have particular use in the construction industry for colouring building materials, particularly cementitious products, mortar, asphalt and tarmac. The composition comprises a fine powder and a particulate material, the fine powder being releasably bound to the particulate material with a coating agent. The invention also discloses a method of making the composition and a method of making an end product with the composition.

Description: DESCRIPTION A COMPOSITION COMPRISING A FINE POWDER The present invention relates to a composition comprising a fine powder and more particularly, though not exclusively, to a composition in which the fine powder is a colorant. Such compositions have particular use in the construction industry for colouring building materials, particularly cementitious products, mortar, asphalt and tarmac. It will, however, be appreciated that the invention disclosed, whilst exemplified with reference to colorants as the fine powders, could be applied to other situations where the handling of a fine power is subject to the problems outlined below with reference to colorants. GB2291600 discloses a mix comprising a colourant powder and a particulate material, for example, sand, which mix has improved flowability and is less likely to block, for example pneumatic and mechanical conveying lines than a colourant powder per se. Whilst the mix is a considerable improvement over the use of a colourant powder it is not ideal as the fine powder in the mixture can still cause blockage and can become airborne. Pigment loadings are also restricted. Airborne powder can give rise to health problems, losses and cause cross contamination thereby affecting the quality of coloured products. Because of these problems, the industry has tried using liquid colourants. These are considerably more expensive than powders and suffer a number of drawbacks including settlement. They are also prone to freeze in winter, are messy if spilt and can't be used with wet aggregates in concrete block pavings. Granular versions of pigments have also been produced and are typically made by a process involving pre-dispersion followed by spray drying. This process is very expensive and is suitable only for long runs and large batches of single colours. The granules are often not of a particularly resilient nature and tend to break down easily on handling, conveying and metering. This has the effect of re-creating the dust and handling problems associated with 'powders' . It is an aim of the present invention to provide a composition which overcomes one or more of the problems associated with fine powder products of the art. According to one aspect of the present invention there is provided a composition comprising a fine powder and a particulate material characterised in that the fine powder is releasably bound to the particulate material with a coating agent. Preferably the coating agent is a liquid, more preferably a wetting-agent and more preferably still a non-drying wetting agent. The coating agent functions by displacing the air from about the particle, maximising the amount of fine powder that can be bound thereto. Since the preferred coating agents comprise hydrophilic groups the fine powder can be easily displaced from the particle by the addition of water. The fine powder will typically have a particle size (diameter) of from O.Olμ to 10μ. The fine powder is preferably a colourant and may comprise one or more pigments such as, for example, red iron oxide, yellow iron oxide, black iron oxide, carbon and phthalocyanine blues-greens etc. The particulate material will typically have a particle size (diameter) of greater than 20μ. More preferably it will have a particle size (diameter) ranging from 20μ - 500μ with a mean particle size (diameter) of about lOOμ. The particulate material is preferably an ingredient of the end product to be produced. Preferred particulate materials for use in a composition for use in the building industry include sand and limestone, although other particulate materials, such as microsphere, which have little or no effect on the properties of the end product can be used. In this regard the end products to be produced for use in the building industry include, for example, paving blocks, roof tiles or bricks, and will typically contain 0.5 to 5 % by weight of a colorant. It is preferred to maximise the amount of fine powder relative to the particulate material to reduce transport costs ie. attain greater than 1: 1 by weight loadings of fine powder: particulate. To achieve this aim, the coating agent is added in an amount of 0.1 to 15 % by weight based on the weight of the composition. The coating agent allows the particulate material to be wholly or partially coated by the fine powder, alleviating many of the problems associated with the use of fine powders. Because of the nature of the colourants used in producing cementicious products and their manufacturing processes it has been found that a coating agent which enables the fine powder to be releasably bound to the particulate material such that the fine powder can be released in an aqueous environment is preferred. The preferred coating agents are wetting agents, more particularly non- drying wetting agents and more particularly still surfactants. Preferred coating agents are carboxylated surfactants, sorbitan esters, alcohol ethoxylates, alkylphenol ethoxylates and sulphonates. Of these ethoxylated sorbitan esters with a high degree of ethoxylation i.e. those with an ethylene oxide content of 10-20 have been found to be particularly good. According to a further aspect of the present invention there is provided a method of preparing a composition of the invention comprising wetting the particulate material with a coating agent and releasably binding the fine powder to the coated particulate material. The fine powder is coated to the particulate material using a coating agent in an amount of 0.1 to 15% by weight based on the weight of the composition. Preferably the coating agent is an ethoxylated surfactant. According to a further aspect of the present invention there is provided a method of producing a product, for use in the building industry, comprising from 1-5 % by weight of a fine powder and one or more other ingredients characterised in that the fine powder is added to the other ingredients as a composition of the invention. The invention will be further described, by way of example only, with reference to the following methods of manufacture, compositions and test data. Method of Production The particulate material (sand) was placed in a low intensity mixing chamber, the coating agent (ethoxylated surfactant) added, mixed and the fine powder (colourant) gradually added. The components were subjected to further mixing and then packaged. Mixing was by way of a tumbling action and at a circumferential speed of between 0.2 - 1.2 metres per second, more preferably at 0.7 m sec "1 . Composition 1 % by weight Fine Powder red iron oxide 45 natural ion oxide 5 Particulate sand 49 Coating agent Sorbitan ester 1 Composition 2 % by weight Red Iron Oxide 85 Sand 7.5 Sorbitan Ester 7.5 Composition 3 % by weight Yellow Iron Oxide 66 Sand 28 Sorbitan Ester 6 Composition 4 % by weight Phthalocyanine Green 9.1 Sand 86.9 Sorbitan Ester 4.0 Composition 5 % by weight Chrome Green 48 Sand 48 Sorbitan Ester 4 Composition 6 % by weight Red Iron Oxide 80 Sand 17 Alcohol Ethoxylate 8 Composition 7 % by weight Black Iron Oxide 80 Sand 11 Alcohol Ethoxylate 9 Comparative Example 1 % by weight Red Iron Oxide 40 Sand 60 Comparative Example 2 % by weight Red Iron Oxide 50 Sand 50 Comparative Example 3 % by weight Red Iron Oxide 60 Sand 40 Test Samples of each composition were placed in a clear plastic vial, shaken and the degree of "dusting" determined visually. The samples were characterised on a scale of 1 to 5. 1 was used if the vial wall remained clear on shaking, indicating a lack of dusting (good coating of fine powder (colorant) to particulate (sand)) and 5 was used if a dense layer of fine powder formed on the vial wall on shaking (poor coating of fine powder (colorant) to particulate (sand)). The bulk density was also determined and is given as the amount in Kgs occupied by 1 litre volume. The results are shown in the table below. Composition No Dust Factor Bulk : 1 1 1.4 2 2 1.2 3 2 1.2 4 1 1.3 5 1 1.2 6 1 1.3 7 2 1.4 Comparative 1 3/4 1.2 Comparative 2 4/5 1.2 Comparative 3 5 + 1.2 Of course it will be apparent to the man skilled in the art that a single coating agent could be replaced by a number of components so long as the fine powder is releasably bound to the particulate material such that the fine powder can be readily dissolved or dispensed in water.

Claims: CLAIMS 1. A composition comprising a fine powder and a particulate material characterised in that the fine powder is releasably bound to the particulate material with a coating agent. 2. A composition as claimed in claim 1 wherein the coating agent is a liquid. 3. A composition as claimed in claim 1 or 2 wherein the coating agent is a wetting agent. 4. A composition as claimed in claim 3 wherein the wetting agent is non-drying. 5. A composition as claimed in any of the preceding claims wherein the coating agent is a surfactant. 6. A composition as claimed in any of the preceding claims wherein the coating agent is an ethoxylated sorbitan ester. 7. A composition as claimed in claim 6 wherein the ethoxylated sorbitan ester has an ethylene oxide content of 10 - 20. 8. A composition as claimed in any of the preceding claims in which the particulate material is partially coated with the fine powder. 9. A composition as claimed in any of claims 1 to 7 wherein the particulate material is wholly coated with the fine powder. 10. A composition as claimed in any of the preceding claims wherein the fine powder is a colourant. 11. A composition as claimed in claim 10 wherein the colourant comprises one or more pigments selected from the group consisting of: red iron oxide, yellow iron oxide, black iron oxide, carbon and phthalocyanine blue-green. 12. A composition as claimed in any of the preceding claims wherein the fine powder has an average diameter of from O.Olμ to 10μ. 13. A composition as claimed in any of the preceding claims wherein the particulate material has an average diameter greater than 20μ. 14. A composition as claimed in any of the preceding claims wherein the particulate material has an average diameter of from 20μ to 500μ. 15. A composition as claimed in any of the preceding claims wherein the particulate material has an average diameter of about lOOμ. 16. A composition as claimed in any of the preceding claims wherein the particulate material is selected from the group consisting of sand, limestone and microspheres. 17. A composition as claimed in any of the preceding claims wherein the ratio (weight: weight) of fine powder to particulate material is greater than 1 part fine powder to 1 part particulate material. 18. A composition as claimed in any of the preceding claims wherein the coating agent is present in an amount of from 0.1 to 15 % by weight based on the total weight of the composition. 19. A method of preparing a composition as claimed in any of claims 1 to 18 comprising wetting the particulate material with a coating agent and releasably binding the fine powder to the coated particulate material. 20. A method as claimed in claim 19 comprising sequentially adding, with mixing, to the particulate material first the coating agent and then the fine powder. 21. A method as claimed in claim 19 or 20 wherein the mixing step is conducted in a slow speed mixer at a circumferential speed of from 0.2 to 1.2 m sec "1 . 22. A method of producing a product, for use in the building industry, comprising from 0.5 - 5 % by weight of a fine powder and one or more other ingredients characterised in that the fine powder is added to the other ingredients as a composition as claimed in any of claims 1 to 18. 23. A method as claimed in claim 22 wherein the product is a concrete product, mortar, asphalt or tarmac. 24. A method as claimed in claim 23 wherein the concrete product is a paving block, roof tile or brick.

Inventors: SWAISLAND BRENT, TANTON RICHARD, SWAISLAND, BRENT, TANTON, RICHARD
Applicants: SAITRON LIMITED, SWAISLAND BRENT, TANTON RICHARD, SWAISLAND, BRENT, TANTON, RICHARD
Application year: 1998
Main classification: B01F3
IPC codes: C04B20, C04B40