GB2259873A

GB2259873A - Coated particulate igneous material

Info

Publication number: GB2259873A
Application number: GB9219780A
Authority: GB
Inventors: William John Ferguson; Derek Grosvenor
Original assignee: Tioxide Group Services Ltd
Current assignee: Tioxide Group Services Ltd
Priority date: 1991-09-28
Filing date: 1992-09-18
Publication date: 1993-03-31
Anticipated expiration: 2012-09-18
Also published as: GB9120674D0; GB2259873B; GB9219780D0

Abstract

A coated material comprises particulate igneous material bearing a coating of a colouring agent or a precursor thereof. Suitable igneous material is perlite, especially expanded perlite, a preferred colouring agent is titanium dioxide and a preferred colouring agent precursor is ferrous sulphate. The coated material is useful for treating the surface of clay articles such as bricks and tiles before firing and pleasing aesthetic effects are produced after firing. A method of treating clay articles is also claimed.

Description

COATED MATERIAL ITS MANUFACTURE AND USE This invention relates to coated material, particularly coated igneous material, its manufacture and use.

According to the present invention a composition comprises particulate igneous material having a coating on the particles thereof of a colouring agent or a precursor thereof.

It is to be understood that in the context of this specification a colouring agent includes a white pigment.

According to the present invention also a method of coating comprises mixing a particulate igneous material with a colouring agent or a precursor thereof and causing said agent or a precursor thereof to form a coating on said particulate igneous material.

According to the invention also a method of manufacturing a shaped article from clay comprises forming a shaped green clay body with a surface treated with a composition according to the invention and firing the green body.

The present invention provides a composition which can be used to treat shaped green clay bodies which upon firing acquire interesting and novel surface effects including colour effects arising from the presence of the colouring agent or a precursor thereof in the compositions of the invention.

The compositions of the invention comprise a coated igneous particulate material and usually such material is a siliceous igneous material in particulate form and particularly is that igneous particulate material known as perlite. Perlite is a general name given to a glassy volcanic rock and usually such rocks are siliceous lavas. The most preferred particulate igneous rock material used in the compositions of the present invention are the expanded materials, such as expanded perlite, which are light weight products obtained by heating rapidly certain igneous rocks.

Expanded perlite can have a wide range of bulk densities ranging, say, from 0.03 to 0.7 gm/cm3.

Any colouring agent or a precursor thereof can be carried as a coating by the particulate igneous material but usually the agent will be an inorganic colouring agent or precursor thereof since usually it is desired that the colouring agent either retains its colouring effect after being heated or changes to a desired colour on heating and cooling.

Organic colouring agents can be destroyed by heating to high temperatures.

Any inorganic pigment can be carried as a coating on the particulate igneous material and typical pigments are aluminium pigments, barium pigments, calcium pigments, chromium pigments, iron pigments, lead pigments, magnesium pigments, zinc pigments and zirconium pigments. White pigments can be used such as titanium dioxide or magnesium oxide.

One particular preferred precursor of a colouring agent is ferrous sulphate of which a readily available form is copperas which is ferrous sulphate heptahydrate. Ferrous sulphate forms iron oxide as the colouring agent after heating. Copperas is widely available as a byproduct of the steel industry and the titanium dioxide pigment industry employing the so-called sulphate process. If desired, coatings including two or more colouring agents or precursors can be present on the igneous material to produce modified and blended colour effects.

Mixtures of copperas and titanium dioxide are particularly effective.

Typically the coating on the igneous material will include the colouring agent or precursor thereof in an amount within the range of 0.5% to 25% by weight of agent based on the weight of the particulate igneous material, preferably the amount is in the range 0.5% to 12.5% by weight of igneous material.

The coating of the colouring agent or precursor thereof on the particulate igneous material can be formed in any suitable manner such as by dry mixing the igneous material and the required amount of powdered colouring agent or precursor in, e.g., a tumbler mixer or by mixing dry igneous particulate material with an aqueous, or other liquid, paste of colouring agent or precursor. A paste can be prepared by mixing a solution of a colouring agent or precursor, or a dispersion thereof, in water with a small amount of particulate igneous material and then mixing this paste with the remainder of the particulate igneous material.

The compositions of the present invention can be applied to a surface of a shaped green body prior to firing to produce on firing interesting and novel colouring effects. The shaped green body need not necessarily have been subjected to the final shaping operation but at least some initial shaping will have taken place.

The surface of the green body can be treated with the coated particulate igneous material in an amount of up to 40 per cent by weight of the green body but usually smaller amounts of up to 20 per cent, preferably up to 10 per cent by weight of the body are used.

Preferably the green body is also treated with a salt of an alkali metal such as a halide, carbonate, or bicarbonate of sodium or potassium but usually sodium chloride is employed. The salt acts as a bonding agent during firing to fix surface pigmentation or otherwise improve the surface texture of the green body.

Although the salt of an alkali metal can be applied to the surface of the green body independently of the coated igneous material it is preferred to incorporate the salt in the coated material during manufacture. For instance the salt can be dissolved in a paste of the colouring agent or precursor or can be mixed dry in a dry coating process. Preferably equal weights of the colouring agent or precursor and the salt are used to treat the surface of the green body.

The surface of the shaped green body can also be treated with oxidising agent or reducing agents to modify the surface on firing.

Compositions of the present invention are of particular use in the treatment of bricks and tiles.

Treatment of a surface of a shaped green body can be carried out in any convenient way. After application the green body is fired at an appropriate temperature to produce the final product. Typical temperature of firing is up to 1200"C. When the composition contains copperas, iron oxide is formed during firing to provide the colour.

If desired, a glaze can be applied to the fired shaped article which improves the shedding of dirt from the treated surfaces.

The invention is illustrated in the following Examples.

In the Examples 1 to 14 coated expanded perlites were prepared by the general method: Copperas was prepared as a 25% w/w copperas solution in water. Sodium chloride was also prepared in the form of a 25% w/w aqueous solution.

A paste of copperas was prepared by adding a known amount of the solution of copperas to a small known quantity of expanded perlite and mixed.

A paste of sodium chloride was prepared by mixing a known amount of the solution of sodium chloride with a small known quantity of expanded perlite.

Various coated expanded perlite products were prepared by adding to a bag formed of polyethylene a known amount of paste and of expanded perlite and tumbling the bag until a well distributed product was obtained.

When the product also contained sodium chloride the appropriate quantity of the appropriate paste was also mixed with the perlite in the bag.

Coated products having the following compositions were prepared.

Product Copperas NaCI wt % on perlite A 1 B 5 C 10 D 1 1 E 5 5 F 10 10 The products had the following appearances.

Product A 2-5 mm granules Very pale yellowish grey B < 1-5 rnm granules Pale grey C 2-5 mm granules Non-uniform pale grey D 2-5 mm granules Very pale yellow E 2-5 mm granules Bright yellow F 1-10 mm granules Strong golden yellow EXAMPLES 1 to 7 Red Devon Shale clay was ground in an end-runner mill to produce a coarse powder having a maximum size of about 800 microns.

70g aliquots of the ground clay were mixed with water in a pestle and mortar to produce wet crumbs. Each aliquot was divided into two parts to provide two samples. A sample was placed in a press-mould having a diameter of 6.3 cm, levelled and compressed by hand. The ram was withdrawn and the exposed surface of the moulded clay was treated with the chosen expanded perlite by sprinkling the dry powder onto the surface. The ram was reinserted and a pressure of about 28 kilogrammes per square centimeter was applied. Duplicate samples were prepared for each coated expanded perlite.

The treated sample was removed from the press-mould and dried for 16 hours at 60"C.

The samples were then placed in a firing oven and raised to a temperature of 1000"C for 3 hours. The samples were held at 1000"C for 2 hours prior to cooling to room temperature over 16 hours.

Two control samples were treated in a similar manner with uncoated perlite and also fired under similar conditions.

The fired shaped articles were examined visually and the results are given below in Table I.

TABLE I

PRODUCT EXAMPLE USED FOR VISUAL APPRAISAL TREATMENT 1 A Pitted surface. Purple red specks in brick red background. Perlite granules loose, many having dropped out of pits. Slight white efflorescence on treated surface.

2 B As Example 1 except that remaining granules are deeper in colour and white efflorescence is more pronounced.

3 C Remaining granules deeper in colour than Example 1 or 2. Otherwise similar to Example 1.

4 D Pitted surface. Purple red specks in brick red background. Granules loose, many having dropped out. Those remaining have a slight gloss, white efflorescence.

5 E Very deep purple-red, glossy granular specks in brick-red background. Pitted surface, granules more strongly adherent, fewer having dropped out. No efflorescence apparent.

6 F Very deep purple-red, glossy granules. The deeper red colour has spread into the clay background. Good granule adhesion. No efflorescence apparent.

7 1 NONE Smooth, typical brick red colour. EXAMPLES 8 to 14 Examples 1 to 7 were repeated except that the shaped articles were fired at 1080"C for 2 hours after being raised to this temperature over a period of 3l/2 hours. The fired articles were cooled to room temperature over a period of 16 hours.

The fired articles were examined visually and the results are given below in Table II.

TABLE II

PRODUCT EXAMPLE USED FOR VISUAL APPRAISAL TREATMENT i 8 A Pitted. Deeper colour than zero addition. Granule adhesion quite strong. Adhering granules are purple red and glossy. No efflorescence.

9 B As Example 8 but gloss of perlite granules more pronounced.

10 C As Example 8 but gloss of perlite granules more pronounced.

11 D Pitted. Similar colour to Example 8.

Granules adhere strongly and have glossy appearance. No efflorescence.

i2 E Pitted. Darker overall than Example 11. Strong granule adherence.

Granules glossier than Example 11.

No efflorescence.

13 F Badly pitted. Similar colour to Example 12 but adhering granules are glossier. Adhesion very strong. No efflorescence.

14 NONE Quite deep, almost chocolate-brown.

Smooth.

From the above Examples it could be seen that treatment with the coated products produced a pitted finish which increases with increasing amounts of coating. Adhesion of the perlite to the surface increases with an increase in the firing temperature. The treated perlite fires to a purple-red colour of differing effects and can produce a glossy sheen at the higher firing temperatures. Antique weathered surface appearance can be obtained.

In Examples 15 to 26 a further series of treated perlite samples, all of which were treated with anatase titanium dioxide [TIOXIDE A HR ("TIOXIDE" is a Trade Mark)] using the treatment method described for Examples 1 to 14. The titanium dioxide was added as a dry powder.

Coated perlite products having the following compositions were prepared.

Product Copperas TiO2 NaCI wt % on perlite G 2 H 5 I - 2 5 J - 5 5 K 5 2 5 L 5 5 5 EXAMPLES 15 to 20 Samples of Red Devon Shale Clay were shaped and treated with perlite samples G to L as described under Examples 1 to 7. The treated samples were dried and fired using the same schedule as used for Examples 1 to 7.

The fired shaped articles were examined visually and the results are given below in Table III.

TABLE III

PRODUCT EXAMPLE USED FOR VISUAL APPRAISAL TREATMENT 15 G Rough surface. Buff-cream specks in a brick red background. A few of the cream coloured granules are loose, readily dropping out of the surface.

16 H Rough surface. Buff-gold specks in a brick red background. Granules seem to be more tightly bound that Example 15.

17 I Surface pitting quite pronounced. Pale buff and some white specks in deep brick red background. White specs seem to be more vitrified than the buff ones. Good adhesion to the clay.

18 J As Example 18 except that the white specks seem to be more numerous. Good adhesion to the clay.

19 K Severely pitted surface. Deep, red-purple specks in brick red background. Good adhesion to clay.

20 L As Example 19 except that the granules are glossier and more vitrified. Good adhesion to clay.

EXAMPLES 21 to 26 Examples 15 to 20 were repeated except that the firing schedule given under Examples 8 to 14 was used.

The fired shaped articles were examined visually and the results are given below in Table IV.

TABLE IV

PRODUCT EXAMPLE USED FOR VISUAL APPRAISAL TREATMENT 2f G Rough surface. Buff-white specks in brown background. Some 'rounding' and glossing of granules indicating vitrification. Good adhesion to clay.

22 H Rough surface. Buff specks in brown background, less evidence of vitrification than Example 21. Good adhesion to clay.

23 I Pitted surface. Cream white specks in deep brown-purple background. Some specks are rounded and glossy, indicating vitrification. Good adhesion to clay.

24 J Pitted surface. Buff specks in deep brown purple background. Less evidence for vitrification than with Example 23. Good adhesion to clay.

25 K Severely pitted surface. Purple-black specks in deep brown purple background.

Little colour contrast. Specks are glossy and rounded, indicating vitrification. Good adhesion to clay.

26 L Severely pitted surface. Similar to Example 25 except for a small, irregular golden bronze patch. Vitrification is extensive.

Good adhesion to clay.

Claims

1. A composition comprising particulate igneous material having a coating on the particles thereof of a colouring agent or a precursor thereof.

2. A composition according to claim 1 in which the igneous material is a siliceous igneous material.

3. A composition according to claim 2 in which the igneous material is perlite.

4. A composition according to claim 3 in which the igneous material is expanded perlite.

5. A composition according to claim 4 in which the expanded perlite has a bulk density in the range 0.03 to 0.7 gm/cm3.

6. A composition according to any one of the preceding claims in which the colouring agent or precursor of a colouring agent is an inorganic colouring agent or is a precursor thereof.

7. A composition according to claim 6 in which the colouring agent is an aluminium pigment, a barium pigment, a calcium pigment, a chromium pigment, an iron pigment, a lead pigment, a magnesium pigment, a zinc pigment or a zirconium pigment.

8. A composition according to claim 6 in which the colouring agent is titanium dioxide or magnesium oxide.

9. A composition according to claim 6 in which the precursor of a colouring agent is ferrous sulphate.

10. A composition according to claim 9 in which the ferrous sulphate is copperas.

11. A composition according to any one of the preceding claims in which a mixture of colouring agents or precursors is present.

12. A composition according to claim 11 in which the mixture comprises copperas and titanium dioxide.

13. A composition according to any of the preceding claims in which the colouring agent or precursor thereof is present in an amount within the range 0.5% to 25% by weight based on weight of particulate igneous material.

14. A composition according to claim 13 in which the amount is within the range 0.5% to 12.5% by weight with respect to weight of igneous material.

15. A composition according to any one of the preceding claims additionally comprising an alkali metal salt.

16. A composition according to claim 15 in which the alkali metal salt is present in an amount equal to the weight of the colouring agent or precursor.

17. A method of coating comprising mixing a particulate igneous material with a colouring agent or a precursor thereof and causing said agent or a precursor thereof to form a coating on said particulate igneous material.

18. A method according to claim 17 in which the particulate igneous material and a powdered colouring agent or precursor thereof are dry mixed in a tumbler mixer.

19. A method according to claim 17 in which dry igneous material is mixed with a paste of colouring agent or precursor thereof.

20. A method according to claim 17 or 19 in which a solution or a dispersion of a colouring agent or a precursor thereof in water is mixed with a small amount of igneous material to form a paste and this paste is then mixed with more igneous material.

21. A method according to claim 19 or 20 in which a salt of an alkali metal is dissolved in a paste of the colouring agent or precursor thereof.

22. A method of manufacturing a shaped article from clay comprising forming a shaped green clay body with a surface treated with a composition comprising particulate igneous material having a coating on the particles thereof of a colouring agent or a precursor thereof and firing the green body.

23. A method according to claim 22 in which the surface of the shaped green body is treated with an amount of the composition of up to 40 per cent by weight of the green body.

24. A method according to claim 23 in which the amount of composition is up to 20 per cent by weight of the green body.

25. A method according to claim 24 in which the amount of composition is up to 10 per cent by weight of the green body.

26. A method according to any one of claims 22 to 25 in which the green body is also treated with a salt of an alkali metal.

27. A method according to claim 26 in which the salt is a halide, carbonate or bicarbonate of sodium or potassium.

28. A method according to claim 26 in which the salt is sodium chloride.

29. A method according to any one of claims 26 to 28 in which the salt is applied to the surface of the green body independently of the coated igneous material.

30. A method according to any one of claims 22 to 29 in which the surface of the shaped green body is also treated with an oxidising agent or a reducing agent.

31. A method according to any one of claims 22 to 30 in which the green body is fired at a temperature of up to 12000C.

32. A method according to any one of claims 22 to 31 in which a glaze is applied to the fired shaped article.

33. A method according to any one of claims 22 to 32 in which the shaped article is a brick or a tile.

34. A method of coating as hereinbefore described with reference to the examples.

35. A method of manufacturing a shaped article from clay as hereinbefore described with reference to the examples.

36. A shaped fired article manufactured by a method according to any one of claims 22 to 33.