Process for colouring building materials

A process is disclosed for coloring building materials with inorganic pigments in the form of microgranulates. The granulates comprise one or more pigments and one or more compounds selected from boron, aluminum, silicon, titanium, zinc and tin.

This invention relates to a process for coloring building materials with
 inorganic pigments in the form of microgranulates.
 If building materials bound with cement and lime, such as plaster,
 calcareous sandstone, cement fibreboards or concrete slabs and especially
 roof tiles and paving stones and slabs are required to be colored, color
 is generally imparted by means of inorganic pigments. It is customary in
 the building industry to use iron oxides or iron hydroxides as red, black,
 brown or yellow pigments, manganese oxides as blackish brown pigments,
 chromium oxides as green pigments and titanium dioxides as white pigments.
 Further, carbon blacks may be used as black pigments, nickel and chromium
 rutiles may be used as yellow pigments, spinels containing cobalt may be
 used as blue and green pigments, spinels containing copper may be used as
 black pigments and the mixed crystals of barium sulphate and barium
 manganate may be used as blue pigments.
 For coloring concrete materials, the pigments are normally used in a
 pulverulent form. As milled pigments they have the advantage of being
 easily dispersible. Completely homogenous distribution of such pigment
 powders in concrete mixtures can be completed within a short time of up to
 a few minutes. The disadvantage of these fine powders, however, is that
 they do not pour well but frequently cake together and agglomerate as
 lumps when kept in storage. Accurate dosing of the powders is then
 difficult. Another disadvantage of some powders is that they tend to throw
 up dust.
 It is known that these disadvantages can be avoided when pigmenting
 concrete parts by using aqueous pigment suspensions instead of dry pigment
 powders. The use of such pastes or slurries containing 30 to 70% by weight
 of pigment has, however, only slowly become established since the
 additional water content may considerably increase the cost of transport,
 depending on the distance between the site of manufacture and the building
 site. Moreover, the large quantity of water present in the paste or slurry
 cannot be absorbed in all concrete mixtures.
 The building industry has therefore mainly kept to the use of dry pigment
 powder. Pigments in the form of microgranulates such as are used in the
 plastics and lacquer industry have not hitherto been used because it was
 believed that such granulates with diameters from 25 to 600 .mu.m would be
 difficult to disperse in concrete mixtures. Pigment agglomerates which are
 difficult to disperse require much longer mixing times. In the short
 mixing times conventionally used in the building industry, specks, streaks
 and nests of color occur on the surface of the concrete due to imperfect
 distribution of the pigment. The full intensity of color of the pigment
 then cannot develop and larger quantities of pigment are therefore
 required for obtaining a given intensity of color in the concrete
 workpiece.
 Pigment granulates consisting substantially of pigment and one or more
 binder(s) for promoting dispersion of the pigment in concrete are
 described in DE-C 36 19363 for coloring concrete ware. The following are
 the binders mentioned in the said document for facilitating dispersion in
 concrete: Alkyl benzene sulphonate, alkyl naphthalene sulphonate, lignin
 sulphonate, sulphated polyglycol ether, melamine formaldehyde condensates,
 naphthalene formaldehyde condensates, gluconic acid, salts of low
 molecular weight, partially esterified styrene/maleic acid anhydride
 copolymers and copolymers of vinyl acetate and crotonic acid. The
 proportion in the pigment should preferably be from 2 to 6% by weight.
 The above-mentioned dispersing agents act as liquefiers in the concrete
 mixtures. They influence the ratio of water to cement and affect the
 consistency of the concrete.
 In the inorganic pigment itself, the binders added are organic substances
 which constitute foreign bodies.
 It is an object of the present invention to provide free-flowing,
 non-dusting inorganic pigment microgranulates which are free from the
 above-described disadvantages of the state of the art for coloring
 building materials.
 This problem has been solved by a process for coloring building materials
 with inorganic pigments in the form of microgranulates consisting of one
 or more pigments and of compounds of boron, aluminum, silicon, titanium,
 zinc and/or tin. The microgranulate inorganic pigments according to this
 invention can be mixed with building materials such as plaster, calcerous
 sandstone, cement or concrete, or other settable materials prior to
 curing. A completely homogeneous distribution of the pigment results when
 the microgranulates are mixed with the building materials in standard
 mixing units. The pigment disperses within the building materials in a
 short time, comparable to or better than that for pigment powders and
 slurries. This process is the subject matter of the present invention.
 It has surprisingly been shown that these pigment microgranulates
 containing purely inorganic additives are comparable in their properties
 of dispersion in concrete preparations to pigment granulates containing
 substances which act as liquefiers in concrete preparation although they
 contain no organic substances.
 Pigment microgranulates or bead granulates are granulates which are
 obtainable from pigment suspensions by spray drying. They may be produced
 in the spray drier by means of slowly rotating centrifugal atomizers or by
 pressure nozzles (one-material nozzles) or two-material nozzles having a
 low air/liquid ratio.
 Whereas two-material nozzles give rise to particles with diameters of up to
 200 .mu.m, the atomizer disc can be used for the production of larger
 particles with diameters of up to 300 .mu.m. The coarsest individual
 particles, measuring up to 600 .mu.m and having a relatively narrow grain
 size distribution, are obtained when pressure nozzles are used. Secondary
 agglomerates with diameters larger than those mentioned above may be
 obtained by using spray driers with an integrated fluidized bed.
 The compounds added according to the invention are preferably in the form
 of oxides and/or hydroxides but may consist of borates, aluminates,
 silicates, titanates, zincates and/or stannates which are added to the
 pigments either in the form stated or as substances which give rise to
 these compounds. Thus, for example, compounds which decompose in the
 manufacturing process to form oxides may be used, such as titanic acid
 esters or silicic acid esters.
 In one particular embodiment of the process according to the invention, the
 compounds added are silica sol or waterglass. These are substances which
 are in any case present as components of concrete.
 The quantity of compound added according to the invention may amount to
 0.05 to 5.0% by weight, preferably from 0.1 to 1% by weight, calculated as
 oxide and based on the quantity of pigment. Smaller quantities are
 ineffective while larger quantities may give rise to difficulties in
 dispersion. The compounds may be used in the form of their solutions, as
 colloids, or as suspensions during the whole process of manufacture of the
 granulates or they may have already been added at the stage of pigment
 formation as such.
 It has been found that the granulates according to the invention should not
 exceed a particular particle size, which depends on the pigment used. This
 particle size depends mainly on the bulk weight of the granulate, which in
 turn is a measure of the porosity of the particles. The porosity is in
 turn dependent on the solids content of the pumpable starting suspension
 before it is dried. This solids content of the suspension may vary
 according to the particle size and particle form of the pigment. The
 compacted bulk density or compacted bulk weight defined in DIN 53 194 of
 August 1957 is used as a measure of the bulk density. The pigment
 granulates according to the invention are distinguished by the fact that
 they do not decompose when the compacted bulk density is determined. The
 granulates according to the invention preferably have a compacted bulk
 density of from 0.5 to 2.5 g/ml, most preferably from 0.8 to 1.5 g/ml.
 The particle size should not be too low since the fine particles measuring
 about 50 .mu.m or less, depending on the properties of the pigment, are
 responsible for producing the dust of a dry powder. Moreover, the free
 flowing property of a powder is impaired by the presence of such small
 particles.
 The granulates claimed according to this invention have an average particle
 size of from 50 to 500 .mu.m, preferably from 100 to 300 .mu.m.
 Pigment microgranulates composed of particles of this size form
 free-flowing powders which are stable to handling and form no dust and are
 eminently suitable for coloring building materials when combined with the
 additives according to the invention. In contrast to what has hitherto
 been thought (DE-C 36 19363), the shearing forces acting on the granulates
 in concrete mixtures are sufficient for complete dispersion of the pigment
 during a mixing cycle.
 The inorganic pigments present in the granulates according to the invention
 are preferably oxides of iron, chromium or manganese and/or titanium
 oxides.
 Particularly good results are obtained with iron oxide pigments.
 The compacted bulk density of the granulates may vary according to the
 pigment, the type and quantity of additive and the water content of the
 suspension. If the compacted densities are low, the granulates obtained
 are unstable while high compacted densities result in poor dispersibility.
 The iron oxide black granulates according to the invention preferably have
 compacted bulk densities of from 0.8 to 1.0 g/ml and iron oxide red
 pigment granulates preferably have compacted bulk densities of 1.2 to 1.4
 g/ml.
 The granulates according to the invention normally contain about 1% by
 weight of water. The water content may be higher, depending on the
 fineness of the pigment particles and their form, without the free-flowing
 quality of the granulates being thereby deleteriously affected. Thus iron
 oxide red pigment granulates containing 0.15% by weight of SiO.sub.2 in
 the form of sodium silicate may contain 6% by weight of water without
 suffering any disadvantages, but the water content should not exceed 10%
 by weight.
 The process according to the invention will now be described in more detail
 with the aid of the following Examples which, however, should not be
 regarded as limiting the scope of the invention.
 In the examples given, the pourability was determined by applying the
 measurement of the outflow time from a DIN-4 cup (DIN 53211 of April 1974)
 analogously to the granulates to be tested.
 The dispersibility in concrete was tested by measuring the color intensity
 of prisms produced with white cement according to the following data:
 Ratio of cement to quartz sand 1:4, water:cement value 0.35, pigmentation
 level 1.2%, based on the cement; mixer used: Model 1551 of RK Toni
 Technik, Berlin, with 5 l mixing bowl, speed of rotation: 140 revs/min
 (mixture made up with 500 g of cement). Four sample mixtures (300 g) were
 removed after 30, 40, 50, 60, 70 and 80 seconds and used to produce sample
 bodies (5.times.10.times.2.5 cm) under a pressure of 32.5 N/mm.sup.2. The
 sample bodies were hardened for 24 hours at 30.degree. C. and 95% relative
 humidity followed by drying at 50.degree. C. for 24 hours. Color data
 measurement using a Hunterlab apparatus: 3 measuring points on the upper
 side and on the under side, 24 measuring points per pigment mixture. The
 average values obtained are based on the sample which was mixed for 80
 seconds (final color intensity=100%).
 For further testing of the dispersibility, mixtures were prepared in a
 larger "Zyklos" mixer having a capacity of 80 kg. For this purpose, sand
 and cement were first mixed dry (30 seconds) and the pigment granulate was
 added only after the addition of water and further mixing (again 30
 seconds). The results obtained, determined on concrete roof tiles, agree
 with the dispersibility obtained when a small laboratory mixer is used.

EXAMPLE 1
 40 kg per hour of an aqueous suspension of iron oxide black obtained as
 intermediate product of the production of black iron oxide Bayferrox 330
 (Trade Product of Bayer AG) were introduced into a spray drier. 1% by
 weight, based on the iron oxide, of sodium silicate solution containing
 360 g/l of SiO.sub.2 was added to the paste containing about 50% by weight
 of iron oxide in the form of finely divided magnetite.
 This suspension reached the hollow cone nozzle (spray angle 30.degree.,
 bore 1.1 mm) installed in the drier at a pressure of 4 bar. The combustion
 gases entered the spray drier from the natural gas surface burner at a
 temperature of 480.degree. C. The discharge temperature of the gases was
 140.degree. C.
 20 kg per hour of iron oxide black pigment in the form of a mechanically
 stable granulate having an average particle size of 200 .mu.m and a
 residual moisture content of about 1% by weight were obtained. The
 compacted density of the granulates was 0.93 g/ml. The pourability
 measured as the outflow time from a 4 mm DIN cup was satisfactory, being
 64 seconds. The test for dispersibility in concrete prisms by measuring
 the development of color intensity with increasing mixing time up to 80
 seconds showed that over 85% of the color intensity was developed after
 only 30 seconds mixing time and the final color intensity was obtained
 after 40 seconds, showing no change from then up to the complete 80
 seconds.
 For comparison, conventional pigment powder (iron oxide black Bayferrox
 330) was also tested in the same test series. The color intensity of the
 powder in this case reached its maximum after 60 seconds and underwent no
 further change during the remainder of the mixing period of 80 seconds.
 Only 80% of the final color intensity was obtained after a mixing time of
 40 seconds.
 EXAMPLE 2
 The procedure was the same as in Example 1 but with alterations of the
 additive introduced into the iron oxide black suspension. Instead of
 sodium silicate, 1% by weight, based on the pigment, of silica sol
 containing 30% by weight of SiO.sub.2 was added.
 The stable granulates obtained were composed of particles measuring from
 150 to 250 .mu.m which had a residual moisture content of 1.5% by weight,
 a compacted bulk density of 0.92 g/ml and an outflow time from a DIN-4 cup
 of 65 seconds. The final intensity of color in concrete was obtained after
 a mixing time of 40 seconds.
 EXAMPLE 3
 Sodium aluminate containing 2% by weight of Al.sub.2 O.sub.3, based on the
 iron oxide black pigment, was added to the iron oxide black suspension
 from Example 1. The procedure was otherwise the same as in Example 1.
 The granulates obtained, which were stable when handled, had particle
 diameters in the region of 200 .mu.m, a residual moisture content of 1.9%,
 a compacted bulk density of 0.90 g/ml and an outflow time of 70 seconds.
 In the test for dispersibility, the final color intensity was obtained
 after a mixing time of 50 seconds.
 EXAMPLE 4
 1% by weight of silicic acid tetraethyl ester, based on the quantity of
 pigment, was added to the iron oxide black suspension. The procedure was
 otherwise the same as in Example 1. The solid granulates obtained in this
 case had a particle size of 200 .mu.m, a moisture content of 1.5% by
 weight, a compacted bulk density of 0.94 g/ml and an outflow time from a
 DIN cup of 57 seconds. The final color intensity was obtained after mixing
 time of 50 seconds.
 EXAMPLE 5
 1% by weight of tetraethyl orthotitanate, based on the quantity of iron
 oxide, was added instead of the silicic acid ester used in Example 4.
 The stable granulates had particle sizes in the region of 200 .mu.m, a
 residual moisture content of 1.3% by weight and a compacted bulk density
 of 0.90 g/ml. The outflow time from the DIN cup was found to be 63 seconds
 and the final color intensity was obtained after a mixing time of 40
 seconds.
 EXAMPLE 6
 The suspension to be dried consisted of 100 kg of iron oxide red Bayferrox
 130 (Trade Product of Bayer AG) in 65 ml of water to which 0.5 kg of
 sodium silicate containing 360 g/l of SiO.sub.2 had been added. The other
 process conditions were the same as in Example 1 except that the quantity
 of suspension introduced was 70 kg per hour.
 The stable iron oxide red granulates obtained had an average particle size
 of 200 .mu.m and a residual moisture content of 6% by weight. The
 compacted bulk density was 1.30 g/ml and the pourability was found to be
 excellent, amounting to 58 seconds when measured as the outflow time from
 a DIN cup. In the dispersibility test, the final color intensity in
 concrete prisms was obtained after a mixing time of 50 seconds.
 COMISON EXAMPLE
 4% by weight, based on the iron oxide black pigment, of ammonium lignin
 sulphonate were added instead of the sodium silicate used in Example 1.
 Stable granulates having particle sizes of from 150 to 250 .mu.m were
 obtained. The residual moisture content was 1.5% by weight, the compacted
 bulk density was 0.97 g/ml and the outflow time from a DIN cup was 60
 seconds. The final color intensity was obtained after a mixing time of 40
 seconds.
 No improvement in results was therefore obtained in this case when
 dispersing aids were added to the concrete mixtures.