SAASTAMOINEN SIRPA (FI)
| WO2013062783A1 | 2013-05-02 | |||
| WO2009109705A1 | 2009-09-11 | |||
| WO2015007954A1 | 2015-01-22 |
| US2805955A | 1957-09-10 | |||
| US20160264786A1 | 2016-09-15 | |||
| US3510335A | 1970-05-05 | |||
| US3945965A | 1976-03-23 |
| Claims 1. A pigment composition comprising at least one precipitated porous pigment, which is selected from aluminium silicates, calcium silicates, magnesium silicates, aluminium magnesium silicates, aluminium calcium silicates, aluminium calcium magnesium silicates, zinc silicates, aluminium zinc silicates, calcium zinc silicates, calcium magnesium silicates, aluminium calcium zinc silicates, aluminium calcium magnesium zinc silicates, aluminium magnesium zinc silicates, a combination/mix- ture of any other aluminium, magnesium, calcium and/or zinc silicate, silicas or any mixture thereof, wherein the average particle size of the pigment composition is at most 10 pm, determined by a laser diffraction technique. 2. The pigment composition of claim 1 , wherein the pigment composition comprises at least one precipitated porous pigment, which is selected from aluminium silicates, magnesium silicates, aluminium magnesium silicates and/or silicas. 3. The pigment composition of claim 1 , wherein the pigment composition comprises at least one precipitated porous pigment, which is selected from aluminium silicates, calcium silicates and/or aluminium calcium silicates. 4. The pigment composition of any one of claims 1 to 3, which comprises Na-, K-, L-, S04-, SO3-, P04-, BO3-, B-, PO3-, NO2-, NO3-, F-, carbonic acid-, carboxylic acid-, zinc-, manganese-, iron-, zirkonium-, nickel-, cobolt-, chrome-, barium-, sul- phur-, strontium-, carbon- and/or Cl- residues. 5. The pigment composition of any one of claims 1 to 4, wherein the average particle size of the pigment composition is below 10 pm, below 5 pm, below 2 pm or below 1 pm, determined by a laser diffraction technique. 6. The pigment composition of any one of claims 1 to 5, wherein the average particle size of the pigment composition is at most 5 pm, at most 2 pm or at most 1 pm, determined by a laser diffraction technique. 7. The pigment composition of any one of claims 1 to 5, which has an average par- ticle size in the range of 0.1-10 pm, in the range of 0.1-5 pm, in the range of 0.1-2 pm, in the range of 0.1-1 pm or in the range of 0.1-0.6 pm, determined by a laser diffraction technique. 8. The pigment composition of any one of claims 1 to 7, wherein the pores inside the composition contain air. 9. Use of the pigment composition of any one of claims 1 to 8 as a pigment in fillers of paper, carton, plastic, rubber, laminate and printing inks or as a filler in any ma- terial wherein high light scattering is needed. 10. Use of the pigment composition of any one of claims 1 to 8 as a pigment in coating compositions which are used for coating paper, carton, plastic, rubber, lam- inate, concrete, meta, composite and wood or as a raw material for a material where high light scattering is needed. 11. Use of the pigment composition of any one of claims 1 to 8 as a pigment in a paint. 12. Use of the pigment composition of any one of claims 1 to 8 as a substitute for titanium dioxide as a pigment in fillers of paper, carton, plastic, rubber, laminate and printing inks, in a coating composition which is used as a coating in paper, carton, plastic, rubber, concrete, metal, composite or wood, or in a paint. 13. The use of claim 12, wherein the pigment composition replaces 25 -100% by weight, 50 -100% by weight 75 -100% by weight, about 100% by weight of titanium dioxide. 14. Use of the pigment composition of any one of claims 1 to 8 in reducing the basis weight of paper and/or carton or in thinning the coating layers, or paint or laminate without imparing the optical properties of the material. 15. A method for producing the pigment composition of any one of claims 1 to 8, wherein the method comprises: a) optionally providing and/or adding at least one compound containing mag- nesium and/or compound containing calcium and/or compound containing zinc in a liquid form, or optionally bringing at least one compound containing magnesium and/or compound containing calcium and/or compound containing zinc into a liquid form, b) optionally providing and/or adding at least one compound containing alu- minium, acid such as sulphur acid or carbon dioxide, a base or any mixture thereof, c) providing and/or adding at least one compound containing silicon, d) mixing with a peripheral speed of at least 1 m/s, preferably 1 - 500 m/s, more preferably 1 -250 m/s., e) filtrating the obtained composition, f) optionally dispersing the filter cake, g) optionally grinding the dispersion, h) optionally drying the dispersion. 16. The method of claim 15, wherein, the steps a), b), c) and/or d) can be per- formed in any order. 17. The method of claim 15 or claim 16, wherein the compounds used in the method steps a), b) and/or c) can be provided and/or added at once or in several portions during the precipitation. 18. The method of any one of claims 15-17, wherein the mixing is performed with rotor-rotor-mixing and/or rotor-stator-mixing. 19. The method of any one of claims 15-18, wherein there is no grinding step g). |
FIELD OF THE INVENTION
The present invention relates to a pigment composition, which comprises at least one precipitated porous pigment. The invention also relates to the use of such a pigment composition as a pigment providing opacity and/or brightness. Fur- ther, the invention relates to the use of the pigment composition according to the invention as a titanium dioxide substitute without impairment of the optical proper- ties. The invention also relates to a method for preparing the pigment composition of the invention. BACKGROUND OF THE INVENTION
Titanium dioxide (T1O2) is commonly used as a white pigment in paints, fillers of paper, carton, plastic, rubber, laminate and printing inks as well as in different kinds of coatings. The most important properties achived by the use of titanium di- oxide are opacity, coverage, brightness, tintability and L-value. T1O2 is the most ef- fective and very expensive pigment providing optical properties. White titanium di- oxide is commercially available as anatase crystals and rutile crystals. Both anatase and rutile crystals are non-amorphous and widely commercially available. There are also amorphous forms of T1O2 but these are not commercially widely available.
Because T1O2 is expensive and hard to recycle, so-called extenders are typi- cally added to titanium dioxide to substitute part of the required amount of titanium dioxide. Extenders are pigments or fillers, which are substantially cheaper than tita nium dioxide and which can be used to separate physically the crystals of titanium dioxide from each other and have the distances of the crystals more fitted for the light scattering.
The amount of extenders should, however, be kept low, since the high refrac- tive index of T1O2 (about 2.49 - 2.61 ) gives finally the highest light scattering effi- ciency and bigger amounts of extenders diminish the light scattering efficiency. Typ- ically, at most 25% by weight of titanium dioxide can be replaced in different appli- cations without losing the optical properties achieved with titanium dioxide, espe- dally opacity. In addition, the producers of titanium dioxide commonly coat titanium dioxide with different organic and/or inorganic precipitation or polymer products of chemicals by an amount of 1 -20% based on the weight of the pigment.
Patent publication WO 2009/109705 (FP-Pigments Oy) discloses replacing ti- tanium dioxide partly with calsium carbonate. Patent publication WO 2015/007954 (FP-Pigments Oy) discloses compositions comprising titanium dioxide and addi- tives, which can be used for substitution of at least part of the titanium dioxide in said composition. The first additive comprises a composite pigment, which corn- prises a shell-forming component and an optical pigment, and a second additive comprises a reactive polymer. The shell-forming component is preferably an inor- ganic compound having a low water solubility, such as precipitated calcium car- bonate, calcium sulphate, barium sulphate, magnesium carbonate, magnesium sili- cate, aluminium hydroxide or aluminium silicate.
BRIEF DESCRIPTION OF THE INVENTION
An object of the present invention is to provide a pigment composition which is suited to be used in fillers of paper, carton, plastic, rubber and printing inks, in coating compositions for coating paper, carton, plastic, rubber, laminate, concrete, metal, composites and wood as well as in paints. An object of the present inven- tion is to provide a pigment composition for use as a pigment providing opacity and/or brightness. Further, an object of the present invention is to use the pigment composition of the invention as a titanium dioxide substitute without impairment of the optical properties. An object of the present invention is also to provide a method for preparing the pigment composition.
The objects of the invention are achieved by the product, the use and the method characterized by what is stated in the independent claims. The preferred embodiments of the invention are disclosed in the dependent claims.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 shows the SEM images of the sample of the present invention and a control sample as disclosed in Example 6.
DETAILED DESCRIPTION OF THE INVENTION
The invention is directed to a pigment composition, which is suitable to be used in fillers of paper, carton, plastic, rubber and printing inks, in coatings of pa- per, carton, plastic, rubber, laminate, concrete, metal, composites and wood, as well as in paints.
The invention is directed to a use of the pigment compostion as a pigment providing opacity and/or brightness. Further, the present invention is directed to the use of the pigment composition of the invention as a titanium dioxide substitute without impairment of the optical properties. Titanium dioxide can be replaced with the pigment composition of the invention partly or totally without impairment of the optical properties. The invention is also directed to a method for producing the pig ment composition of the invention.
The following facts affect the optical efficiency or the light scattering in a ma- terial when light attempts to traverse the material in coated or uncoated materials:
- air-solid -interfaces (the refractive index of air is about 1 whereas usually the refractive indexes of other substances, such as plastics, fibers, rubbers and the most of pigments and fillers, are in the range of 1.4 -1.8),
- the distance between the pigments,
- the empty air pores of the pigments,
- the refractive indexes of substances,
- the small average particle size of the pigments - optimum half of the wave- lenght of the light (visible light is in the range of 400-780 nm).
Critical Pigment Volume Concentration (CPVC) is, especially in coatings, an important measure describing the ratio of the binder and the pigment in the coat- ing, wherein the pigments are totally coated with the binder and the pores of the pigment are filled with the binders. With values smaller than CPVC, the portion of the binder is higher than that of pigments in the coating, and the other way around, when the value is higher than CPVC. In coatings of papers and in primers, there is usually considerably more pigment than binder. In gloss paints, on the other hand, there is considerably more binder than pigment.
It was suprisingly found that titanium dioxide can be replaced partly (about 1 % by weight, 1 -5% by weight, 5-15% by weight, 10-25% by weight, at least 25% by weight, 25-50% by weight, 50-75% by weight, 75-100% by weight) or totally (100% by weight) with the pigment composition of the invention as a pigment providing optical properties (opacity and/or brightness) without imparing the optical properties provided to the produced material.
It was suprisingly found that pigments and fillers cheaper than titanium diox- ide can be replaced with the pigment composition of the invention having a better cost/light-scattering ability, which offers a possibility to modify the ratios of the ma- terials in order to have overall savings.
Thus, the raw material expenses of coated and uncoated materials can be reduced because of the excellent light-scattering ability and low cost of the pig- ment composition of the invention, or the materials can be thinned down without impairing the optical properties. The invention works best when the average particle size of the pigment corn- position is about half of the wavelenght of light. It is advantageous to the invention that the pores of the pigment are full of air after drying.
The pigment composition according to the invention comprises at least one precipitated porous pigment selected from aluminium silicates, calcium silicates, magnesium silicates, aluminium magnesium silicates, aluminium calcium silicates, aluminium calcium magnesium silicates, zinc silicates, aluminium zinc silicates, calcium zinc silicates, calcium magnesium silicates, aluminium calcium zinc sili- cates, aluminium calcium magnesium zinc silicates, aluminium magnesium zinc silicates, a combination/mixture of any other aluminium, magnesium, calcium and/or zinc silicate, silicas or any mixture thereof.
In one embodiment, the pigment composition according to the invention corn- prises at least one precipitated porous pigment selected from the group consisiting of aluminium silicates, calcium silicates, magnesium silicates, aluminium magne- sium silicates, aluminium calcium silicates, aluminium calcium magnesium sili cates, zinc silicates, aluminium zinc silicates, calcium zinc silicates, calcium mag- nesium silicates, aluminium calcium zinc silicates, aluminium calcium magnesium zinc silicates, aluminium magnesium zinc silicates, a combination/mixture of any other aluminium, magnesium, calcium and/or zinc silicate, silicas or any mixture thereof.
In one embodiment of the invention, the pigment composition consists of at least one precipitated porous pigment selected from aluminium silicates, calcium silicates, magnesium silicates, aluminium magnesium silicates, aluminium calcium silicates, aluminium calcium magnesium silicates, zinc silicates, aluminium zinc sil- icates, calcium zinc silicates, calcium magnesium silicates, aluminium calcium zinc silicates, aluminium calcium magnesium zinc silicates, aluminium magnesium zinc silicates, a combination/mixture of any other aluminium, magnesium, calcium and/or zinc silicate, silicas or any mixture thereof, optionally Na-, K-, L-, S0 4 -,
SO3-, P0 4 -, BO3-, B-, PO3-, NO2-, NO3-, F-, carbonic acid-, carboxylic acid-, zinc-, manganese-, iron-, zirkonium-, nickel-, cobolt-, chrome-, barium-, sulphur-, stron- tium-, carbon-, Cl- residues and/or residues of other elements as well as optionally stabilizing agents, dispersing agents, surfactants and/or other conventional addi- tives.
In one embodiment of the invention, the pigment composition comprises at least one precipitated porous pigment selected from aluminium silicates, calcium silicates, magnesium silicates, zinc silicates, aluminium magnesium silicates, alu- minium calcium silicates, aluminium zinc silicates, silicas, or any mixture thereof.
In one embodiment of the invention, the pigment composition comprises at least one precipitated porous pigment selected from aluminium silicates, calcium sili- cates, magnesium silicates, aluminium magnesium silicates, aluminium calcium silicates, aluminium calcium magnesium silicates, silicas, or any mixture thereof. In one embodiment of the invention, the pigment composition comprises at least one precipitated porous pigment selected from aluminium silicates, magnesium sili cates and/or aluminium magnesium silicates. In one embodiment of the invention, the pigment composition comprises at least one precipitated porous pigment se- lected from calcium silicates, aluminium silicates and/or aluminium calcium sili- cates. In one embodiment of the invention, the pigment composition comprises at least one precipitated porous pigment selected from aluminium silicates, zinc sili- cates and/or aluminium zinc silicates.
In addition, the precipitated porous pigments of the invention may contain
Na-, K-, L-, S0 4 -, SO3-, P0 4 -, BO3-, B-, PO3-, NO2-, NO3-, F-, carbon acid-, carbox- ylic acid-, zinc-, manganese-, iron-, zirkonium-, nicel-, cobolt-, chrome-, barium-, sulphur-, strontium-, carbon-, Cl-residues and/or residues of other elements.The type of these residues and/or elements depends on the starting materials and/or other compounds used in the manufacture of the pigment composition.
The precipitated porous pigments of the invention do not substantially contain titanium dioxide. In one embodiment, the precipitated porous pigments of the inven- tion do not contain titanium oxide, i.e., the precipitated porous pigments of the in- vention are Ti0 2 -free.
The pigment composition of the invention may also contain additives, such as stabilizing agents, dispersing agents, biocides and/or surfactants. The type of the additive depends on the purpose of use of the pigment composition.
The particles of the pigment composition of the invention are aggregates, which have a cluster-type formation made up of primary/ultimate particles. Aggre- gates have a definite pattern of molecules formed of primary (elemental) particles by an irreversible process and they cannot be broken by mechanical forces. As a result of the process, the specific surface area of an aggregate is smaller than the sum of its primary particles. Agglomerates consist of primary particles and/or ag- gregates which are joined loosely together e.g. at the corners or edges and can be broken by mechanical forces.Thus agglomerates can change their size and shape. The average particle size of the pigment composition of the invention is at most 10 pm (0-10 pm), determined by laser measurement. In one embodiment, the average particle size of the pigment composition of the invention is below 10 pm, determined by laser measurement. In one embodiment of the invention, the average particle size of the pigment composition is in the range of 0.1-10 pm or in the range of 0.2-10 pm, determined by laser measurement. In one embodiment of the invention, the average particle size of the pigment composition is in the range of 1-10 pm, determined by laser measurement. In one embodiment, the average particle size of the pigment composition of the invention is at most 5 pm (0-5 pm), determined by laser measurement. In one embodiment, the average particle size of the pigment composition of the invention is below 5 pm, determined by laser measurement. In one embodiment of the invention, the average particle size of the pigment composition is in the range of 0.1-5 pm or in the range of 0.2-5 pm, de- termined by laser measurement. In one embodiment of the invention, the average particle size of the pigment composition is in the range of 1-5 pm, determined by laser measurement. In one embodiment, the average particle size of the pigment composition of the invention is at most 2 pm (0-2 pm), determined by laser meas- urement. In one embodiment, the average particle size of the pigment composition of the invention is below 2 pm, determined by laser measurement. In one embodi- ment of the invention, the average particle size of the pigment composition is in the range of 0.1-2 pm or in the range of 0.2-2 pm, determined by laser measure- ment. In one embodiment of the invention, the average particle size of the pigment composition is in the range of 1-2 pm, determined by laser measurement. In one embodiment, the average particle size of the pigment composition of the invention is at most 1 pm (0-1 pm), determined by laser measurement. In one embodiment, the average particle size of the pigment composition of the invention is below 1 pm, determined by laser measurement. In one embodiment of the invention, the average particle size of the pigment composition is in the range of 0.1-1 pm or in the range of 0.2-1 pm determined by laser measurement. In one embodiment of the invention, the average particle size of the pigment composition is 0.1-0.6 pm or 0.2-0.6 pm, determined by laser measurement.
In one embodiment, the average particle size of the pigment composition of the invention after the precipitation step and before any grinding step is at most 10 pm (0-10 pm), determined by laser measurement. In one embodiment, the aver- age particle size of the pigment composition of the invention after the precipitation step and before any grinding step is below 10 pm, determined by laser measure- ment. In one embodiment of the invention, the average particle size of the pigment composition after the precipitation and before grinding is in the range of 0.1-10 pm, 0.2-10 pm or 1-10 pm, determined by laser measurement. In one embodi- ment, the average particle size of the pigment composition of the invention after the precipitation and before grinding is at most 5 pm (0-5 pm), determined by la- ser measurement. In one embodiment, the average particle size of the pigment composition of the invention after the precipitation and before grinding is below 5 pm, determined by laser measurement. In one embodiment of the invention, the average particle size of the pigment composition after the precipitation and before grinding is in the range of 0.1-5 pm, 0.2- 5 pm or 1-5 pm, determined by laser measurement. In one embodiment, the average particle size of the pigment corn- position after the precipitation and before grinding is at most 2 pm (0-2 pm), deter- mined by laser measurement. In one embodiment, the average particle size of the pigment composition after the precipitation and before grinding is below 2 pm, de- termined by laser measurement. In one embodiment of the invention, the average particle size of the pigment composition after the precipitation and before grinding is in the range of 0.1-2 pm, 0.2-2 pm or 1-2 pm, determined by laser measure- ment. In one embodiment, the average particle size of the pigment composition af- ter the precipitation and before grinding is at most 1 pm (0-1 pm), determined by laser measurement. In one embodiment, the average particle size of the pigment composition after the precipitation and before grinding is below 1 pm, determined by laser measurement. In one embodiment of the invention, the average particle size of the pigment composition after the precipitation and before grinding is in the range of 0.1-1 pm or 0.2-1 pm, determined by laser measurement. In one em- bodiment of the invention, the average particle size of the pigment composition af- ter the precipitation and before grinding is in the range of 0.1-0.6 pm or 0.2-0.6 pm, determined by laser measurement.
In one embodiment of the invention, the average particle size and/or the par- tide size distribution of the pigment composition is determined by laser diffraction technique. In one embodiment of the invention, the average particle size and/or the particle size distribution of the pigment composition is determined by laser dif fraction technique using equipment which is able to determine particle sizes in the range of 0.02-2000 pm. In one embodiment of the invention, the average particle size and/or the particle size distribution of the pigment composition is determined with Malvern 2000-analyzer. The pore volume of the pigment composition of the invention is typically in the range of 0.20-0.30 cm 3 /g.
In one embodiment, the pigment composition of the invention is not subjected to a grinding step after the precipitation. Grinding the precipitated pigment compo- sition after the precipitation may break the structure of the pigment and thus affect harmfully to the light scattering ability of the pigment. In addition, energy is saved when the grinding step can be omitted in the preparation of the pigment composi- tion.
In one embodiment, the pigment composition of the invention is prepared us- ing a wet method of production.
In one embodiment of the invention, the air pores of the precipitated pig ments are kept empty after the drying, wherein the difference between the refrac- tive index of the air in the pores (about 1 ) and the refractive index of the pigment (1.4-1.8) can be utilized as light scattering, which is shown as better opacity and brightness.
The pigment composition of the invention is suited to be used as a pigment in fillers of paper, carton, plastic, rubber and printing inks. In addition to the pigment, filler compositions of this kind also contain conventional manufacturing agents and additives of fillers.
In addition, the pigment composition of the invention is suited to be used as a pigment in coating compositions, which are used for coating paper, carton, plastic, rubber, laminate, concrete, metal, composites and wood. In addition to the pig- ment, coating compositions of this kind also contain conventional manufacturing agents and additives of coating compositions.
The pigment composition of the invention is suited to be used as a filler in any material wherein high light scattering is needed. Further, the pigment compo- sition of the invention is suited to be used as a pigment in paints. In addition to the pigment, paints of this kind also contain conventional manufacturing agents and additives of paints. Titanium dioxide, other pigments, binders, rheological modifi- ers, adhesives and other necessary additives depending on the application can be used with the pigment composition of the invention.
In one embodiment of the invention, the pigment composition is suited to be used as a pigment providing opacity and/or brightness. In one embodiment of the invention, the pigment composition is suited to be used to replace titanium dioxide without impairing the optical characteristics. The pigment composition of the inven- tion is suited to be used as a substitute for titanium dioxide in fillers of paper, car- ton, plastic, rubber, laminate and printing inks. In addition, the pigment composi- tion of the invention is suited to be used as a substitute for titanium dioxide in coat- ing compositions which are used as coatings in paper, carton, plastic, rubber, con- Crete, metal, composites and wood, and as a pigment in paints. About 1 -100% by weight of titanium dioxide can be replaced with the pigment composition of the in- vention without any detectable impairment in the optical characteristics.
In one embodiment of the invention, 5-100% by weight, 10-100% by weight, 15-100% by weight of titanium dioxide can be replaced with the pigment composi- tion of the invention without any detectable impairment in the optical characteris- tics. In one embodiment of the invention, 25-100% by weight of titanium dioxide can be replaced with the pigment composition of the invention without any detecta- ble impairment in the optical characteristics. In one embodiment of the invention, 50-100% by weight of titanium dioxide can be replaced with the pigment composi- tion of the invention without any detectable impairment in the optical characteris- tics. In one embodiment of the invention, 75-100% by weight of titanium dioxide can be replaced with the pigment composition of the invention without any detecta- ble impairment in the optical characteristics. In one embodiment of the invention, about 25% by weight, about 50% by weight, about 75% by weight, about 85% by weight, about 95% by weight or about 100% by weight of titanium dioxide can be replaced with the pigment composition of the invention without any detectable im- pairment in the optical characteristics. In one embodiment of the invention, about 100% by weight of titanium dioxide can be replaced with the pigment composition of the invention without any detectable impairment in the optical characteristics.
Since titanium dioxide can be replaced partially or totally with the pigment composition of the invention, remarkable savings in raw material costs can be achieved. With the pigment composition of the invention an equivalent light-scat tering ability is achieved more advantageously than with titanium dioxide. With the pigment composition of the invention the materials to be produced can be thinned and/or lightened without weakening the attainable light-scattering ability (bright ness and opacity) compared to the use of titanium dioxide. Thus, lowering the ba- sis weight of paper or carton is enabled, the number of coating layers can be re- duced, coating layers from multilayer structures can be removed as unnecessary, or the coating layers, paint or laminate can be thinned without weakening the spreading capacity and/or brightness and opacity. Each of these actions leads to the reduction of material costs, increase in productivity and environmental sustain- ability.
The present invention also relates to a method for producing the described pigment composition, which method comprises the following steps:
a) optionally providing and/or adding at least one compound containing mag- nesium and/or at least one compound containing calcium and/or at least one corn- pound containing zinc in a liquid form, or optionally bringing at least one corn- pound containing magnesium and/or at least one compound containing calcium and/or at least one compound containing zinc into a liquid form,
b) optionally providing and/or adding at least one compound containing alu- minium, acid such as sulphur acid or carbon dioxide, a base or any mixture thereof,
c) providing and/or adding at least one compound containing silicon, d) mixing with a peripheral speed of at least 1 m/s,
e) filtrating the obtained composition,
f) optionally dispersing the filter cake,
g) optionally grinding the dispersion,
h) optionally drying the dispersion.
In the method of the invention, the method steps a), b), c) and/or d) can be per- formed in any order. Selection of the order of performing the method steps belongs to the knowledge of a skilled person and depends, among other things, on the corn- pounds and reaction conditions to be used. In one embodiment of the invention, the method for producing the pigment composition does not contain a step of grinding the precipitated pigment (step g).
The compounds used in the method of the invention can be added simultane- ously or separately. The compounds used in the method steps a), b) and/or c) can be provided and/or added at once or in several portions during the precipitation. In the method of the invention, several compounds can be used. Typically, the reac- tions of the method take place in a solution. The“at least one compound contain- ing magnesium” can be any compound that is suitable for the method, such as magnesium hydroxide, magnesium carbonate, magnesium sulphate and/or mag- nesium chloride. The“at least one compound containing calcium" can be any corn- pound that is suitable for the method, such as, calcium hydroxide, calcium car- bonate, calcium sulphate and/or calcium chloride. The“at least one compound containing zinc” can be any compound that is suitable for the method, such as zinc sulphate, zinc chlorate, zinc chloride, zinc nitrate and/or zinc oxide. The“at least one compound containing aluminium”can be any compound that is suitable for the method, such as aluminium sulphate, polyaluminium chloride and/or sodiumalumi- nate. The“at least one compound containing silicon" can be any compound that is suitable for the method, such as Na-, K- and/or L-silicate.
The pigment composition of the invention can be produced with an industri ally applicable method, wherein mixing having peripheral speed of at least 1 m/s is utilized at least once in at least one method step. In a method according to one embodiment of the invention, the peripheral speed is 1-500 m/s. In a method ac- cording to one embodiment of the invention, the peripheral speed is 1-250 m/s. The mixing is performed preferably with mixers operating with rotor-rotor and/or ro- tor-stator techniques. In the mixing, a shock mixer, rotors rotating into opposite di- rections, rotors rotating into the same direction with big relative speed difference, dropping, a pin mill, strikes and/or counter-strikes can be exploited. In rotors and stators, the mixing elements are pins, wings, plates with holes, furrows or other corresponding bodies of different forms. The speed difference between the circles of rotors rotating to opposite directions or to the same direction or the circles of the adjacent rotors and stators is typically in the range of 5-400 m/s, preferably in the range of 5-200 m/s. Consequently, the material is subjected to very strong turbu- lence, shear and impact forces during processing (disintegration and atomization).
The following examples are given to illustrate the invention without, however, restricting the invention thereto.
Example 1
The preparation of the pigment sample was started with adding solutions of magnesium hydroxide and aluminium sulphate into the medium of the reactor. A temperature above the freezing point of water and uniform mixing were used in the preparation. Dilute aluminium sulphate and sodium silicate were added into this so- lution so that the target pH was kept constant. Sodium siliacte was used at least in an amount which is required for the stoichiometric reaction of magnesium and alu- minium. Rotor-rotor-mixing with peripheral speed of at least 1 m/s is was utilized along during the preparation. Finally before dispersing the filter cake into an aque- ous slurry, the pigment sample was filtrated and washed with water. The pigment sample thus obtained is called OPA1.
Example 2
The preparation of the pigment sample was started with adding a solution of calcium hydroxide into the medium of the reactor. A temperature above the freezing point of water and uniform mixing were used in the preparation. Dilute aluminium sulphate and sodium silicate were added into this solution so that the target pH was kept constant. Sodium silicate was used at least in an amount, which is required for the stoichiometric reaction of calcium and aluminium. Rotor-rotor-mixing with pe- ripheral speed of at least 1 m/s was utilized along during the preparation. Finally, before dispersing the filter cake into an aqueous slurry, the pigment sample was filtrated and washed with water. The average particle size of this pigment sample was 0.42 pm (Malvern 2000, version 5.60). Example 3
The preparation of the pigment sample was started with adding a solution of zinc sulphate into the medium of the reactor. A temperature above the freezing point of water and uniform mixing were used in the preparation. Dilute aluminium sulphate and sodium silicate were added into this solution so that the target pH was kept constant. Sodium siliacte was used at least in an amount which is required for the stoichiometric reaction of zinc and aluminium. Rotor-rotor-mixing with peripheral speed of at least 1 m/s was utilized along during the preparation. Finally, before dispersing the filter cake into an aqueous slurry, the pigment sample was filtrated and washed with water. The average particle size of this pigment sample was 1.91 pm (Malvern 2000, version 5.60).
Example 4
A paint paste was prepared from the pigment dispersion prepared in Example 1. The paste contained 5% dried pigment and 5% latex (Acronal S728, BASF) based on the amount of dry pigment. The pH of this aquoeus slurry was kept above pH- value 8.3 with the additions of lye while adding a thickener (Sterocoll FS, BASF) until the viscosity of the dispersion of 800 - 850 cp (Brookfield, 100 rpm, Spindle LV-4) was achieved.
The opacity and tone of the coatings of both 2.5 g/m 2 and 5 g/m 2 were meas- ured with an opacimeter (Rhopoint Novoshade Duo+). The coating was spread with standard rods nos. 4 and 7 (K Bar) of the rod coating method (RK101 Control Coater) onto a plastic film (Leneta 1 mm, clear polyester sheets). The pigments used were OPA1 , Ti02A (SR5, Venator) and Ti02B (Ti-pure R102, Dupont). The results are shown in Table 1. Table 1.
Example 5
The pigments 0PA1 and Ti02A (SR5, Venator) were also tested in an un- coated fine paper. Tha pulp contained bleached pine and bleached eucalyptus (40:60) refined to the value SR30. Medium-cationic starch (0.5% based on dry pulp) and size (AKD, 0.2% based on dry pulp) were added to the thick pulp. The tests were done in a dynamic sheet former so that the targets for basis weight and ash were 30 g/m 2 and 10 %. These target values were achieved by adjusting the amount of furnish and the retention aid (PAM) in the dynamic sheet former. The papers pro- duced were machine calandered and dried in a drying drum before the conditioning of paper and testing. The results are shown in Table 2.
Table 2.
Example 6
The aim in this example was to reduce the basis weight of a standard un- coated copying paper from a value of 80 g/m 2 to a value of 50 g/m 2 without impair- ment of the optical properties. In the reference test of 80 g/m 2 , aragonite-contain- ing PCC (PCC-A) is used as a pigment when it was compared to the funtion of OPA1 in 50 g/m 2 paper. The pulp contained bleached pine and bleached eucalyp- tus (40:60) refined to the value SR30. Medium-cationic starch (0.5% based on dry pulp) and size (AKD, 0.2% based on dry pulp) were added to the thick pulp. The tests were done in dynamic sheet mould. The papers produced were machine cal- andered and dried in a drying drum before the conditioning of paper and testing. The results are shown in Table 3.
Table 3.
Example 7
The pigment OPA1 prepared in Example 1 is used in this example. In addi- tion, a control sample is prepared according to Example 1 , wherein no rotor-rotor mixing is used. Figure 1 shows SEM-images of both samples. The average parti- cle size of OPA1 was 0.7 pm and the average particle size of the control sample was 8.7 pm, respectively. In the plastic film coating of Example 3, the opacity of OPA1 was 73.3 % and the opcity of the control sample was 57.8 %. It can be con- cluded from Figure 1 , that the product according to the invention (OPA1 ) has smaller primary particle size than the control sample. Example 8
The pore sizes and the pore size distributions of pigment samples OPA1 , Ti02A and Ti02C were determined based on the measurements of isothermal ad- soption-desorption points in a temperature of liquid nitrogen and the computational handling of thus received adsoption-desorption isoterms. The pigment samples were analysed with is -sorption at -196 C (TriStar 3000, Micromeritics).
The porocity of the pigments was estimated based on the amount of N2 in a proportional pressure of p/pO = 0.97. Barrett-Joyner-Halenda (BJH) theory was used herein.
The porocity of the pigments of the pigment samples OPA1 , Ti02A and Ti02C
(Kronos 2971 ) is shown in table 4. Sample Ti02A contained 6.5% inorganic finish ing . Sample Ti02C contains no finishing.
Table 4.
Only the pore volume of the sample OPA1 was significant. The pore volumens of the samples Ti02A and Ti02C were so low, that they could be due to agglomer- ation of the particles.
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