Composition of precipitated calcium carbonate, method of producing the same and the uses thereof

Abstract

Composition of precipitated calcium carbonate and method of producing the same and the uses of the composition. The composition comprises a plurality of essentially spherical granules having an average diameter of 1-50 um formed from primary precipitated calcium carbonate particles having an average diameter of 30 to 60 nm, capable of liberating at least a part of the primary particles by deagglomeration in aqueous suspension. The present compositions can be used for modifying binders of paints, printing inks, plastics, adhesives, sealants and surface sizes and pulp sizes. The invention further concerns a method for storing of precipitated calcium carbonate particles having an average diameter in the nanometer range.

Claims

1. A composition of precipitated calcium carbonate, consisting of a plurality of essentially spherical granules having an average diameter of 1-50 um formed from only primary precipitated calcium carbonate particles having an average diameter of 30 to 60 nm, the granules being capable of liberating the primary particles by deagglomeration in aqueous suspension.

2. The composition according to claim 1, wherein the granules have an average size of about 2 to 40 um.

3. The composition according to claim 1, wherein the granules are capable of liberating the primary particles when subjected to shear forces in aqueous suspension.

4. The composition according to claim 1, wherein the composition comprises an essentially dry powder of granules of precipitated calcium carbonate.

5. The composition according to claim 1, obtained by spray drying of an aqueous slurry of primary particles of precipitated calcium carbonate, said slurry having a solids content of 10 to 50%, and recovering the granules thus obtained.

6. The composition according to claim 5, wherein spray drying is carried out by conducting the aqueous slurry through a spraying nozzle or an atomizer disc in a spray dryer.

7. The composition according to claim 1, wherein the granules are binder-free.

8. A method of producing a composition consisting of a plurality of precipitated calcium carbonate granules having an average diameter of 1-50 um formed from only primary precipitated calcium carbonate particles, said method comprising the steps of providing an aqueous slurry of particles of precipitated calcium carbonate having an average diameter of 30 to 60 nm, said slurry being essentially free from binders, drying said slurry preferably in a spray dryer using a spraying nozzle or an atomizer disc, and recovering the granules in dry state.

9. The method according to claim 8, comprising spray drying an aqueous slurry having a solids content of 10 to 50%.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a scanning micrograph of a granule according to one embodiment.

(2) FIG. 2 is a scanning electron microscope image showing nano-sized primary particles of PCC obtained by deagglomerating of PCC granules in a pin mill.

DETAILED DESCRIPTION

(3) In the present context, the abbreviation “PCC” is used to designate precipitated calcium carbonate.

(4) Further, the abbreviation “nPCC” is used to designate particles of precipitated calcium carbonate having an average particle size in the nanometer range, in particular the average particle size of the “nPCC” particles are, in the present context, about 30 to 60 nm.

(5) As was discussed above, the present technology comprises in a first embodiment compositions of precipitated calcium carbonate, which are formed by a plurality of essentially spherical granules having an average diameter of 1-50 um formed from primary PCC particles having an average diameter of 30 to 60 nm. In a preferred embodiment the granules have an average size (diameter) of about 2 to 40 um, in particular about 2.5 to 30 um, preferably about 4 to 15 um, such as 5 to 10 um.

(6) By “essentially spherical” is meant that the ovality (deviation from spherical shape) is 20% or less.

(7) The compositions according to the first embodiment can be composed of (i.e. consist) of the granules only. It is also possible to provide compositions wherein the present granules make up 50% of the weight of the composition, the remainder being formed by other particles, such as other kinds particles of precipitated calcium carbonate or other pigments, such as silicates, bariums sulphate, Kaolin clay, Bentonite, Magnesium carbonate, dolomite, talc, mica, aluminium silicates, silica, aluminium hydroxide, titanium dioxide and organic polymers, or combinations thereof.

(8) It is also possible to provide compositions of PCC particles having the indicated average diameter of 30 to 60 nm, only a part of which are present as granules. Typically, in the first embodiment of the invention, discussed in the present context, at least 20% by total weight of the particles is formed into granules.

(9) The primary particles are characterized as having a “diameter” of 30 to 60 nm. This is not to be taken as a positive indication that all of the particles are spherical although it is believed that at least a considerable part of them roughly meets the above given definition for spherical particles. Broadly, the term “diameter” designates that the particles have an average size in the indicated range. Typically, the smallest diameter is 20 nm.

(10) The primary particles can be produced for example by a method typically comprising the steps of continuously feeding calcium hydroxide as fine drops and/or particles into gas which contains carbon dioxide and which is inside a precipitation reactor, in order to carbonate the calcium hydroxide, i.e. in order to produce precipitated calcium carbonate in the precipitation reactor.

(11) Calcium hydroxide or other suitable Ca.sup.++ ion sources can be used as a reactive mineral substance, from which calcium carbonate is formed using carbon dioxide. Typically, calcium hydroxide is fed into the precipitation reactor as a calcium hydroxide sludge, i.e. as calcium hydroxide dispersed in water, such as lime milk, but it can also be fed in as a calcium hydroxide solution. The material is advantageously fed into the reactor through a disintegration and spraying apparatus located in the reactor or in association with it.

(12) In the method, a disintegration and spraying apparatus of the so-called impact mixer type can be employed. In that kind of mixer, very fine drops and/or particles are formed from the calcium hydroxide sludge or solution.

(13) In addition to the calcium hydroxide sludge, a gas containing carbon dioxide which effects precipitation and which may be pure or nearly pure carbon dioxide, or combustion gas, or other suitable gas containing CO.sub.2, is continuously fed into the precipitation reactor.

(14) In order to produce the small particles desired it is advantageous to arrange for precipitation to take place in a lowered reaction temperature, below 65° C., typically at 10-65° C., more typically at 30-65° C., most typically at a temperature below 40° C.

(15) Although the granules can be supplied in the form of an aqueous slurry, one particularly preferred embodiment comprises a composition which is formed by an essentially dry powder of granules of precipitated calcium carbonate. To that purpose, the drying is carried out such that the primary particles, the nano-sized PPC particles, agglomerate to form the granules upon drying.

(16) Spray drying will produce in a repeatable fashion spherical granules formed from a great plurality of primary particles.

(17) Typically, the granules are binder-free.

(18) The granules are capable of liberating the primary particles when subjected to shear forces in aqueous suspension.

(19) Thus, in a preferred embodiment, the particles of precipitated calcium carbonate are liberated from granules, in particular binder-free granules, of precipitated calcium carbonate—said granules having a size of about 2 to 40 um, in particular about 2.5 to 30 um, preferably about 4 to 15 um, by subjecting the granules to shear forces in an aqueous suspension formed by water and said binder. In one embodiment, the granules are subjected to a shear rate in the range of 1 to 10000 s.sup.−1, typically between 10 and 1000 s.sup.−1. The present technology also provides for the production of the novel particles.

(20) “Binder-free” or “free from binders” shall be interpreted so that no binder or other additive that could affect the ability of the primary PCC particles to connect to each other is added.

(21) Thus, in a particular embodiment, a composition comprising a plurality of precipitated calcium carbonate granules having an average diameter of 1-50 um, in particular 2 to 40 um, are produced by a method comprising the steps of providing an aqueous slurry of particles of precipitated calcium carbonate having an average diameter of 30 to 60 nm, said slurry being essentially free from binders, drying said slurry preferably in a spray dryer using a spraying nozzle or an atomizer disc, and recovering the granules in dry state.

(22) It is particularly preferred to subject to spray drying an aqueous slurry having a solids content of 10 to 50%, in particular 20 to 40%, for example about 30±5%. Operating at high solids content is advantageous from capacity point of view.

(23) Another embodiment comprises a composition of precipitated calcium carbonate in aqueous slurry further containing a binder. The composition contains normally 1 to 35%, advantageously about 5 to 20%, calculated from the weight of the binder, of precipitated calcium carbonate particles having an average diameter of 30 to 60 nm.

(24) In this context, it should be noted that the compositions according to the second alternative may contain other particles and pigments just as disclosed for the first embodiment above.

(25) The binder of the composition is preferably selected from the group of natural and modified polysaccharides, such as starch and modified starch, and synthetic latexes. Naturally, there may be other binders present as well, but generally the natural or modified polysaccharides, such as starch or derivatives thereof, preferably make up at least 20%, in particular at least 30%, advantageously at least 50% of the binders present, said percentage being calculated from the solids content of the binder.

(26) The aqueous slurry disclosed before can be produced by a method typically comprising the steps of providing a composition of dry granules of precipitated calcium carbonate having an average diameter of 1 to 50 um, about 2 to 40 um, in particular about 2.5 to 30 um, preferably about 4 to 15 um; mixing the granules into a water phase to provide an aqueous slurry; and subjecting the granules to shear forces so as to deagglomerate the granules to yield particles of precipitated calcium carbonate particles, having an average diameter of 30 to 60 nm.

(27) The dry granules are typically binder-free, but in order to produce an aqueous slurry suitable for surface treatment it is preferred to mix into the water phase a binder. In particular, so much binder is added that the aqueous slurry exhibits, based on the weight of the binders, a pigment content of 1 to 35%, advantageously about 5 to 20%.

(28) Just as discussed above, for the granules of the first embodiment, to break up the granules, shear forces are applied on the granules when they are slurried in an aqueous medium. In one preferred embodiment, the granules are subjected to shear rates in the range 1 to 10000 s.sup.−1, typically between 10 and 1000 s.sup.−1. As a result, the primary particles are released into the aqueous medium.

(29) The composition described above—i.e. the aqueous slurry with pigments and binder—can be used for example in a process of coating of fibrous webs and products. One possible mode of application is as a coating colour. Thus the composition can be formulated into the coating colour by adding brighteners and conventional auxiliary agents, if so desired, which regulate viscosity and pH of the coating colour. Other pigments can be added also, optionally along with further binders.

(30) A particularly interesting application of an aqueous slurry of the indicated kind is for treating fibrous webs which can be used for producing paper and cardboard products with improved stiffness.

EXAMPLES

Example 1

Surface Starch

(31) The table below shows the surface starch behavior when structured PCC particle is introduced with cooked surface starch with ‘gentle’ or ‘high energy efficient’ mixing.

(32) The following components were used: HiCat which is a cationic starch derivative supplied by Roquette Corporation, Blankophor a whitener supplied by Blankophor GmbH & Co. KG, EX-135 an Engineered Nano Granulate supplied by FP-Pigments Oy and produced as expained above using the impact mixer technology. The particles have an average particles size of 30 to 60 nm. Dispermat was used as a stirring device.

(33) TABLE-US-00001 TABLE 1 Trial 1. Mixing study. Control Trial 1 Trial 2 Trial 3 Trial 4 HiCat SP0052 100 100 100 100 100 Blankophor P 01 0.5 0.5 0.5 0.5 0.5 EX-135, gentle mixing 10 30 EX-135, efficient mixing 10 30 Viscosity 100 rpm, cP 150 90 154 384 5580 Viscosity 50 rpm, cP 160 80 160 362 8380 Solids, % 15.8 16 15.1 15.1 15.4 Temperature, ° C. 66 64 64 64 64

(34) As apparent, the viscosity increase (Trial 3 vs. Trial 4) is a clear indication of the phenomena, the structured PCC particles de-agglomerates and number of ultrafine pigment particles is substantially increased.

Example 2

Paper Stiffness

(35) Table 2 below shows the paper stiffness when even low level of structured PCC is used correctly with surface starch. The de-agglomeration of structured PCC material was ensured with ‘efficient mixing’, viscosity increase and the impact on paper stiffness is +10%.

(36) TABLE-US-00002 TABLE 2 Trial 2. Coating study. Control Trial 1 Trial 2 HiCat SP0052 100 100 100 Blankophor P 01 0.5 0.5 0.5 EX-135, gentle mixing 10 EX-135, efficient mixing 10 Bending stiffness, mNm 105.2 103.2 114.6 Brightness, % (R457 D65) 89.68 89.93 88.6 Fluoresence (R457 Fluor D65) 7.17 7.5 6.19 Opacity, % (D65) 86.95 86.74 87.45 Scattering coefficient, m.sup.2/g 32.41 32.76 32.97 Absorption coefficient, m.sup.2/g 0.74 0.74 0.75 Grammage, g/m2 87 85.4 87.8 Coat weight, g/m2 7.1 7.4 7.5

Example 3

(37) Another study was conducted to compare blocky GCC and blocky PCC against nPCC. In the table below, the GCC is commonly used ground calcium carbonate with particle size 60% below 2.0 microns. PCC1 is nPCC and PCC2 is blocky pigment with average particle size 1.0 microns.

(38) TABLE-US-00003 TABLE 3 Binder (100 pph) Starch Starch Starch Starch Pigment (30 pph) — GCC PCC1 PCC2 Basis weight, g/m.sup.2 62.5 62.2 62.2 62.7 Total coatweight, g/m.sup.2 3 3 3 3 Coatweight/side, g/m.sup.2 1.45 1.45 1.45 1.45 Bending resistance MD 44.6 42.1 48.7 44.7 Bending resistance CD 23.5 23.7 27.6 20.7 Stiffness change, % −3.4 12.0 −4.0 Optics (D65): L* 92.56 92.52 92.57 92.53 a* 0.76 0.67 0.69 0.68 b* −4.52 −4.22 −4.15 −4.14 CIE Whiteness, % 102.86 101.4 101.19 101.03 Fluoresence 12.96 11.54 11.45 11.35 Brightness, % 88.3 87.7 87.7 87.6 Opacity, % 81.7 82.9 83.5 83.8 Scattering coefficient, m.sup.2/g 35.8 37.8 39.0 39.2 Absorption coefficient, m.sup.2/g 0.77 0.81 0.82 0.84

(39) Table 3 shows the common issue when pigment is used with surface starch, paper stiffness is often lowered. This happens with both blocky pigments.

(40) nPCC improves paper stiffness by 12% and shows clear potential in terms of paper stiffness enhancer.

Example 4

Deagglomeration of PCC Granules into PCC Primary Particles

(41) The PCC granules shown in FIG. 1, exhibiting an average diameter in the range of about 1 to 50 um, were subjected to shear forces in an Alpine Z100 pin mill. FIG. 2 shows that the granules were deagglomerated to yield the constituent primary particles in the nanometer range.

(42) The present compositions can be used for modifying binders of paints, printing inks, plastics, adhesives, sealants and surface sizes and pulp sizes.

(43) The compositions can be formulated into coating colours for fibrous products, such as paper and cardboard products, webs and sheets.

(44) In particular, the composition can be used for producing fibrous webs having ability to improve paper stiffness. For this purpose, the compositions can be used for example as surface sizes.

(45) It should be pointed out that the present technology provides for the use of compositions of nanosized PCC (as defined above) for the purpose of modifying paints, printing inks, plastics, adhesives, sealants, and surface and pulp sizes irrespective of whether the nanosized PCCs are obtained directly from carbonation or from deagglomeration of granules.

(46) While the present disclosure has been illustrated and described with respect to a particular embodiment thereof, it should be appreciated by those of ordinary skill in the art that various modifications to this disclosure may be made without departing from the spirit and scope of the present disclosure.