Starch-based PHCH

Abstract

The invention relates to a process for preparing self-binding pigment particle suspensions, to a self-binding pigment particle suspension as well as to a paper product comprising self-binding pigment particles and to the use of the self-binding pigment particle suspension in paper applications, such as in paper coating or as filler material.

Claims

1. A self-binding pigment particle suspension obtained by a process comprising the following steps of: a) providing an aqueous pigment material suspension comprising pigment material, wherein the pigment material comprises calcium carbonate, b) providing a starch having a net negative charge and consisting of at least one anionic starch, c) mixing the starch of step b) with the aqueous pigment material suspension of step a), wherein the starch is added to the aqueous pigment material suspension in an amount from 0.5 to 20 wt.-%, based on the total dry weight of the pigment material in the suspension, and d) grinding the aqueous pigment material and starch of step c) during and/or after step c) at a temperature from 20 C. to 40 C., wherein grinding step d) is carried out to reduce the particle size of the pigment material of step a) and to obtain a fraction of self-binding pigment particles in which greater than 20 wt.-%, based on the total weight of the pigment particles have a particle size of less than 2 m, as measured with a Mastersizer 2000, thereby obtaining the self-binding pigment particle suspension, wherein the self-binding pigment particle suspension comprises self-binding pigment particles at least partially coated with the starch and the amount of free starch in the self-binding pigment particle suspension is less than 50 wt.-% based on the total amount of starch added in step c) and the pigment material in the self-binding pigment particle suspension has a surface charge density after step d) in the range of +2.5 Eq/g and 10 Eq/g.

2. The self-binding pigment particle suspension according to claim 1, wherein the pigment material of step a) comprises calcium carbonate and one or more of-dolomite, a calcium associated with magnesium, clay, kaolin, titanium dioxide, talc, aluminium hydroxide, mica, synthetic fibers, or natural fiber.

3. The self-binding pigment particle suspension according to claim 1, wherein the pigment material is a ground natural calcium carbonate, a precipitated calcium carbonate, a modified calcium carbonate, or any mixture thereof.

4. The self-binding pigment particle suspension according to claim 1, wherein the pigment material is a ground natural calcium carbonate.

5. The self-binding pigment particle suspension according to claim 1, wherein the at least one-anionic starch of step b) is an anionic starch comprising anionic groups selected from the group consisting of carboxyl groups, carboxymethyl groups, carboxymethyl hydroxypropyl groups, carboxymethyl hydroxyethyl groups, phosphate groups, sulfonate groups, and any mixture thereof.

6. The self-binding pigment particle suspension according to claim 1, wherein the at least one-anionic starch of step b) is an anionic starch having a degree of carboxylation in the range of 0.001 to 0.08.

7. The self-binding pigment particle suspension according to claim 1, wherein in step c) the starch is added to the aqueous pigment material suspension in an amount from 1 to 20 wt.-%, based on the total weight of the dry pigment material in the aqueous pigment material suspension.

8. The self-binding pigment particle suspension according to claim 1, wherein the solids content in step c) is adjusted such that it is at least 1 wt.-%, based on the total weight of the aqueous pigment material suspension.

9. The self-binding pigment particle suspension according to claim 1, wherein grinding step d) is carried out during step c).

10. The self-binding pigment particle suspension according to claim 1, wherein grinding step d) is carried out until the fraction of self-binding pigment particles having a particle size of less than 1 m is greater than 10 wt.-%, and/or until the fraction of self-binding pigment particles having a particle size of less than 2 m is greater than 20 wt.-%, based on the total weight of the pigment particles.

11. The self-binding pigment particle suspension according to claim 1, wherein grinding step d) is carried out until the fraction of self-binding pigment particles having a particle size of less than 1 m is greater than 70 wt.-%, and/or until the fraction of self-binding pigment particles having a particle size of less than 2 m is greater than 80 wt.-%, based on the total weight of the pigment particles.

12. The self-binding pigment particle suspension according to claim 1, wherein the pigment material in the obtained self-binding pigment particle suspension has a surface charge density in the range of +2 Eq/g and 8 Eq/g.

13. The self-binding pigment particle suspension according to claim 1, wherein the pigment material in the obtained self-binding pigment particle suspension has a surface charge density in the range of +0.5 Eq/g and 6 Eq/g.

14. The self-binding pigment particle suspension according to claim 1, wherein the obtained self-binding pigment particle suspension has a Brookfield viscosity in the range of 1 to 3500 mPas.

15. The self-binding pigment particle suspension according to claim 1, wherein grinding step d) is carried out such that the amount of free starch in the obtained self-binding pigment particle suspension is less than 45 wt.-%, based on the total amount of starch added in step c).

16. The self-binding pigment particle suspension according to claim 1 further comprising performing a concentration step e) before step d), such that the solids content in the self-binding pigment particle suspension obtained after step d) is at least 45 wt.-% based on the total weight of the self-binding pigment particle suspension, and the self-binding pigment particle suspension comprises a fraction of self-binding pigment particles in which greater than 20 wt.-% based on the total weight of the pigment particles have a particle size of less than 2 m as measured with a Mastersizer 2000, and self-binding pigment particles at least partially coated with the starch, and wherein the amount of free starch in the self-binding pigment particle suspension is less than 50 wt.-% based on the total amount of starch added in step c) and the pigment material in the self-binding pigment particle suspension has a surface charge density in the range of +2.5 Eq/g and 10 Eq/g.

17. The self-binding pigment particle suspension according to claim 1 further comprising performing a concentration step e) after step d), such that the solids content is the self-binding pigment particle suspension after step e) is at least 45 wt.-% based on the total weight of the self-binding pigment particle suspension, and the self-binding pigment particle suspension comprises a fraction of self-binding pigment particles in which greater than 20 wt.-% based on the total weight of the pigment particles have a particle size of less than 2 m as measured with a Mastersizer 2000, and self-biding pigment particles at least partially coated with the starch, and wherein the amount of free starch in the self-binding pigment particle suspension is less than 50 wt.-% based on the total amount of starch added in step c) and the pigment material in the self-binding pigment particle suspension has a surface charge density in the range of +2.5 Eq/g and 10 Eq/g.

18. The self-binding pigment particle suspension according to claim 1, wherein before or during or after step c) and/or step d) a dispersing agent is added.

19. The self-binding pigment particle suspension according to claim 1, wherein the starch of step b) is in a form of a starch solution or starch suspension having a starch concentration from 1 wt.-% to 50 wt.-%, based on the total weight of the starch solution or starch suspension, and having a temperature of <40 C.

20. The self-binding pigment particle suspension according to claim 19, wherein the starch of step b) is in form of a starch solution or starch suspension having a starch concentration from 15 wt.-% to 45 wt.-%, based on the total weight of the starch solution or starch suspension.

Description

EXAMPLES

(1) A. Methods and Materials

(2) In the following, materials and measurement methods implemented in the examples are described.

(3) BET Specific Surface Area of a Material

(4) The BET specific surface area was measured via the BET method according to ISO 9277 using nitrogen, following conditioning of the sample by heating at 250 C. for a period of 30 minutes. Prior to such measurements, the sample was filtered, rinsed and dried at 110 C. in an oven for at least 12 hours.

(5) Particle Size Distribution (Mass % Particles with a Diameter<X) and Weight Median Diameter (d.sub.50) of a Particulate Material

(6) Weight median grain diameter and grain diameter mass distribution of a particulate material were determined via the sedimentation method, i.e. an analysis of sedimentation behavior in a gravitational field. The measurement was made with a Sedigraph 5120.

(7) The method and the instrument are known to the skilled person and are commonly used to determine grain sizes of fillers and pigments. The measurement was carried out in an aqueous solution of 0.1 wt.-% Na.sub.4P.sub.2O.sub.7. The samples were dispersed using a high speed stirrer and ultrasonic.

(8) Molecular Weight (M.sub.w)

(9) The average molecular weight (Mw) is measured as 100 mol-% sodium salt at pH 8 according to an aqueous Gel Permeation Chromatography (GPC) method calibrated with a series of five sodium polyacrylate standards supplied by Polymer Standard Service with references PSS-PAA 18 K, PSS-PAA 8K, PSS-PAA 5K, PSS-PAA 4K and PSS-PAA 3K.

(10) pH of an Aqueous Suspension

(11) The pH of the aqueous suspension was measured using a standard pH-meter at approximately 22 C.

(12) Solids Content of an Aqueous Suspension

(13) The suspension solids content (also known as dry weight) was determined using a Moisture Analyser HB-S from the company Mettler-Toledo, Switzerland, with the following settings: temperature of 120 C., standard drying, 2.6 to 3.5 g of suspension.

(14) Tablet Crushing Test

(15) This test is a measure for the self-binding power of a pigment. It is a measure for the force needed to crush tablets that were formed from the self-binding pigment slurries.

(16) To demonstrate the suitability for the self-binding character of the pigmentary particles thus obtained, tablets were formulated using a membrane filtration process. In this regard, an apparatus of the high-pressure filter press type was used, manufactured from a hollow steel tube. The said tube is closed at the top by a lid and contains the filtration membrane at the bottom.

(17) Tablets were formed by applying a constant pressure (15 bar) to 80 ml of the starch PHCH suspension measured for 10 to 30 min such that water is released by filtration through a fine 0.025 m filter membrane resulting in a compacted tablet. This method produces tablets of about 4 cm diameter with a thickness of 1.5 to 2.0 cm. The obtained tablets were dried in an oven at 60 C. for 24 hours.

(18) The device and method used are described in detail in the document entitled Modified calcium carbonate coatings with rapid absorption and extensive liquid uptake capacity (Colloids and Surfaces A, 236 (1-3), 2003, pp. 91-102).

(19) Subsequently, the tablets were fashioned by grinding into disc-shaped samples of 2.0-2.1 cm diameter with a thickness of 0.6-0.7 cm for the strength test analysis by using a disk mill (Jean Wirtz, Phoenix 4000). This procedure is described in the document entitled Fluid transport into porous coating structures: some novel findings (Tappi Journal, 83 (5), 2000, pp. 77-78). These smaller tablet discs were crushed under pressure to test their strength property by using the penetration apparatus Zwick/Roell Alround Z020 from the company Zwick GmbH & Co. KG, Ulm, Germany. The piston is brought down into contact with the sample at a deformation speed of 3 mm per minute, the test stops at 95% deformation or 20 kN. At the first local maximum in the measurement a crack in the sample occurred. The values given herein are the average of three, alternatively two to five, measurements of independently prepared tablets and the error bars are the standard deviation of these three measurements.

(20) Polyelectrolyte Titration by Means of SCD

(21) The polyelectrolyte titration was performed on the particle charge detector (Streaming current detector) Mtek PCD-03-pH of BTG Instruments GmbH, Herrsching, Germany by using the Mettler T90 titrator of Mettler-Toledo GmbH, Giessen, Germany.

(22) The following ready-made solutions were used for the polyelectrolyte titration:

(23) Cationic reagent: 0.0025 N Poly DADMAC (Poly(diallyldimethyl-ammonium-chloride) for anionic samples available from Sigma-Aldrich GmbH, Buchs, Switzerland.

(24) Anionic reagent: 0.0025 N K-Polyvinyl-Sulfate (KPVS) for cationic samples available from WAKO Chemicals GmbH, Neuss, Germany.

(25) Procedure

(26) A solution was prepared in the detector by the addition of 0.5 ml KPVS (for cationic samples) to 10 ml distilled water. Then, the titration with Poly DADMAC was carried out until it is back to shortly after the equivalence point.

(27) Experience shows that between 0.5 and 2.0 ml of 0.0025 molar reagent should be used up during the titration to obtain reproducible values. This means that in the case of KPVS (for cationic samples) with 0.0025 mol/1 the consumption is between 1 and 4 ml.

(28) Depending on the charge to be expected, the following weight-in quantities have to be chosen:

(29) TABLE-US-00001 Charge Weight-in [Eq/g] [g] 0.1 30.0 1.0 3.0 10.0 0.30 100.0 0.03

(30) Small quantities were weighed into the detector by means of a tared single-use syringe. In case of slurries tending to rapid sedimentation the sample was drawn under stirring, by means of a tared syringe. The content of the syringe was then rinsed into the sample vessel by means of distilled water.

(31) Subsequently, the detector was filled with distilled water up to the lower edge and the piston inserted carefully.

(32) If a large volume has already been obtained due to a large weight-in quantity, it is filled up to a volume which is not exceeded in the subsequent comparison measurements. This end volume then applies for the subsequent measurements.

(33) Then, the oppositely charged titration solution is added into the titrator and the top of the burette is fixed at the detector ensuring that it does not come into contact with the detector or the liquid.

(34) The titrator is started according to the apparatus configuration. In particular, the titration is equilibrium controlled, i.e. the titrator adds, if necessary in several cycles, between 0.02 and 0.1 ml (in each cycle) of the respective cationic or anionic titration solution to the solution to be measured until a total signal change of about 8 mV is obtained. If the signal does not change by more than 2 mV per 2 seconds and a subsequent period of 5 to 60 seconds within each cycle, the titrator again adds between 0.02 to 0.1 ml of the respective cationic or anionic titration solution to the solution to be measured. The equivalence point is reached for each measurement at about 0 mV.

(35) In case of computer-controlled titrators, the calculation of the charge is made automatically.

(36) After each titration, the development of the titration was verified with the aid of the titration curve.

(37) All values are based on the triple determination of the electrochemical charge.

(38) The electrochemical charge has been determined by using the following equations:

(39) $\mathrm{Charge}\left[\mathrm{.Math.}\mathrm{Eq}\text{/}g\right]=\frac{V.Math.c.Math.z.Math.t}{E.Math.F}.Math.K\left[\mathrm{Coulomb}\text{/}g\right]=\left[\mathrm{.Math.}\mathrm{Eq}\text{/}g\right].Math.0.096485\mathrm{Conversion}\mathrm{by}\mathrm{the}\mathrm{Faraday}\mathrm{constant}$$\mathrm{wherein}\text{:}$$\mathrm{anionic}\text{:}K=-1000$$\mathrm{cationic}\text{:}K=+1000\begin{array}{cc}V\text{:}\mathrm{Consumption}\mathrm{KPVS}/\mathrm{PolyDADMAC}& \left[\mathrm{ml}\right]\\ c\text{:}\mathrm{Conventration}\mathrm{KPVS}/\mathrm{PolyDADMAC}& \left[\mathrm{mol}\text{/}l\right]\\ t\text{:}\mathrm{Titer}/\mathrm{factor}\mathrm{KPVS}/\mathrm{PolyDADMAC}& \\ E\text{:}\mathrm{Weight}\text{-}\mathrm{in}\mathrm{quantity}& \left[g\right]\\ F\text{:}\mathrm{Mass}\mathrm{fraction}\mathrm{solids},i.e.50\%\mathrm{solids}.Math.0.50& \left[g\text{/}g\right]\\ z\text{:}\mathrm{Valence}\left(\mathrm{equivalence}\mathrm{number}\right).Math.\mathrm{mostly}1& \end{array}$

(40) It should be noted that the unit Eq is equivalent to 1 proton, the charge of the proton being +1 e=1.60210.sup.19 As=1.60210.sup.19 C.

(41) Adhesion Test

(42) The adhesion test was carried out by determining the force necessary to separate a coating layer from a support. The ground suspensions were coated on a plastic support (PP foils) at a range of different coat weights using a laboratory coater Typ Model 624 from the company Erichsen, Germany. Polypropylene foils (YUPO Synteap foils) used in the adhesion test were obtained from the company Fischer Papier AG, Switzerland. The thickness of the white semi-matt foils was 80 m. The adhesion was measured as follows:

(43) 20 mm of an adhesive-tape-strip (length around 30 mm, width 19 mm, Scotch magic 3M 810 produced by 3M) was stuck to the coated foil. The protruding end was attached to a spring balance (precision balance, type 20100 by Pesola, measurement range 0 to 100 g). After gluing the coated foil to the ground/base table, the spring balance was pulled vertically (angle of 90) to the ground at a speed of around 30 cm/min wherein the deviation, i.e. the extension of the spring was measured. Adhesion of the coating to the PP-foil was determined by the weight required to induce a removal/de-bonding of the coating from the PP-foil. Values of greater than 100 g indicate that the coating did not de-bond during the measurement.

(44) Brookfield Viscosity

(45) The Brookfield viscosity of the self-binding pigment particles suspension and coating color were measured after one hour of production and after one minute of stirring at room temperature at 100 rpm by the use of a Brookfield viscometer type RVDVII+equipped with an appropriate spindle.

(46) Intrinsic Viscosity

(47) The intrinsic viscosity was determined by a Schott AVS 370 system. The samples were dissolved in a 0.2 M NaCl solution, and subsequently, the pH was adjusted to 10 with NaOH. Measurements were performed at 25 C. with a capillary type 0a and corrected using the Hagenbach correction.

(48) Dry Pick Resistance

(49) Dry pick resistance was determined by a Multipurpose printability tester (Prfbau Instruments) at 23 C. and a contact pressure of 150 N/cm. This test was carried out with increasing printing speed between 0 and 3 m/s. If no differentiation is obtained the printing is further carried out at a constant printing speed (starting at 3 m/s) with 0.5 m/s intervals until a printing speed of 6 m/s is reached. Low tack, normal tack and high tack ink (Michael Huber, Germany) were used as colour in an amount of 200 mm.sup.3.

(50) Brightness (R457)

(51) Brightness was measured by using a spectrophotometer (Elrepho No. 1686, Datacolor) in accordance with DIN 53146. The term brightness as used in the context of the present invention is a measurement of the percentage of diffuse light reflected from a paper's surface. A brighter sheet reflects more light. As used herein, brightness of the paper may be measured at a mean wavelength of light of 457 nm and is specified in percent.

(52) Opacity

(53) Opacity was measured by using a spectrophotometer (Elrepho No. 1686, Datacolor) in accordance with DIN 53146. The term opacity as used in the context of the present invention is a measurement of the optical coverage of a paper. A more translucent paper is more see-through. The measurement is based on the relation between the reflections of a single paper sheet in front of a black background to a non-translucent stack of paper. The opacity of the paper is specified in percent. Values close to 100% correspond to a high opacity.

(54) Light Scattering Coefficient S and Light Absorption Coefficient K

(55) The light scattering coefficient S and the light absorption coefficient K were measured on sheets of synthetic paper (Yuko, Synteape, Fischer Papier AG, Switzerland). These paper sheets each having A4 paper size were subjected to a light radiation of wavelength 457 nm on a black plate using an Elrepho 450X, serial no 1686 spectrophotometer from Datacolor (Switzerland) to determine the degree of brightness (R457) of the coated papers on a black background (black trap) and on a stack of 15 non-coated sheets of paper.

(56) A paper coating color was prepared by mixing 4 parts (on dry basis) of Acronal S 360 D, BASF, a paper coating styrene acrylic latex binder (8 parts of starch PHCH) and 100 parts (on dry basis) of the calcium carbonate suspension (which is a HCB95 slurry at s.c. 78%). Alternatively, the starch PHCH was used directly as a paper coating color. The coating color is then applied on the pre-weighed paper sheets in different coating weights ranging from 4 g/m.sup.2 and 56 g/m.sup.2 by using the rod bench top coater, Rakelauftragsgert K-Control-Coater K202, Model 624 from Erichsen, Hemer, Germany.

(57) Subsequently, the coated paper sheets were dried until a constant weight was reached, e.g. by drying the paper sheets at 150 C. on a belt dryer at a speed of 7.0 m/min.

(58) The coated paper sheets with different coating weights of between 4 g/m.sup.2 and 56 g/m.sup.2 and samples of uncoated paper were then subjected to light radiation of wavelength 457 nm using an Elrepho 450X, serial n 1686 spectrophotometer from Datacolor (Switzerland) on a black plate to determine the degree of whiteness (R457) of the paper on a black background (black trap) and on a pile of 15 non-coated sheets of paper. Subsequently, the coated paper sheets were cut into sheets each having dimensions of 16 cm*18 cm and weighed. The light scattering coefficient S and the light absorption coefficient K were then calculated in accordance with the Kubelka-Munk theory, which is well-known to experts, and described in the publications of Kubelka and Munk (Zeitschrift fr Technische Physik 12, 539, (1931)), and of Kubelka (J. Optical Soc. Am. 38(5), 448, (1948) and J. Optical Soc. Am. 44(4), 330, (1954)). The light scattering coefficient S and the light absorption coefficient K are quoted as the value interpolated at the coat weight 20 g/m.sup.2.

(59) Glossiness (75 Tappi (ISO 8254-1)

(60) The 75 glossiness of the sheet of paper previously coated was determined by the TAPPI method in accordance with ISO 8254-1 by using a Lehmann laboratory glossmeter (Lehmann LGDL-05.3) before as well as after calendering. As used herein, glossiness of the paper is specified in percent.

(61) Chemical Oxygen Demand

(62) Chemical oxygen demand (COD) was measured according to the Lange Method (ISO 15705), as described in the document issued by HACH LANGE LTD, entitled DOC042.52.20023.Nov08. Approximately, 100 ml of the liquid phase were added in a Lange CSB LCK 014 cuvette, covering a range between 1 000 and 10.000 mg/l and heated in the closed cuvette for two hours at 148 C. in a dry thermostat. This suspension was then analyzed according to the Lange Method.

(63) Thermo Gravimetric Analysis

(64) Thermo gravimetric analysis (TGA) was performed on the Mettler Toledo TGA/STDA 851.sup.e at 570 C. for 1 h in air (PPH Methode Q60B Hybrid, 570 C./1 h air).

(65) Degree of Carboxylation

(66) Degree of carboxylation was measured by a conductometric titration. The starch was added portion wise under stirring into water and stirred with a magnetic bar until a clear solution was obtained. The solution had a starch concentration of 3 wt.-%, based on the total weight of the solution. The solutions were shaked before use. The pH of the solution was adjusted to 3 by using aqueous HCl at 6% concentration. The solution was then titrated with 0.1 M aqueous NaOH and the pH and conductivity were measured.

(67) At the beginning of titration, the conductivity decreased until it reached a minimum. The slope was negative and corresponds to the titration of excess HCl. Then the conductivity increased again with a weak slope which corresponds to the deprotonation of the anionic groups of the starch. At the end, the slope of conductivity increased more which corresponds to the excess of NaOH.

(68) The measurement was repeated three times for each sample.

(69) d/d

(70) The term d/d refers to the dry amount based on the dry amount of pigment material.

(71) B. Preparation and Testing of Self-Binding Pigment Particle Suspensions and Corresponding Coatings

Example 1 (Comparative Example

(72) a) Preparation and Testing of the Self-Binding Pigment Particle Suspension

(73) A self-binding pigment particle suspension was prepared by using undispersed calcium carbonate ground with cationic starch.

(74) A starch solution having a starch concentration of 20 wt.-%, based on the total weight of the solution, was prepared by stirring 13 wt.-% (d/d which corresponds to 15 pph starch on 100 pph calcium carbonate), based on the total weight of the dry pigment material in the calcium carbonate slurry and starch, of a commercially available cationic starch (C*film 05978, from Cargill) in water at a temperature of about 95 C.

(75) 10 kg of undispersed calcium carbonate slurry was prepared having a solids content of about 20 wt.-%, based on the total weight of the slurry. The particulate material of the slurry has a weight median particle diameter d.sub.50 value of 0.7 m (measured according to the sedimentation method). Furthermore, the particulate material (calcium carbonate) of the slurry had a specific surface area of 9.5 m.sup.2/g (measured using nitrogen and the BET method).

(76) Subsequently, the calcium carbonate slurry was run through a Dynomill Multilab filled with 1 070 g (with 80% filler level) zirconium oxide/zirconium silicate grinding beads (0.6-1.0 mm) at about room temperature. The grinding chamber had a total volume of 600 cm.sup.3. The mill speed was set to 2 500 rpm and the flow was set to 500 cm.sup.3/min.

(77) Within 9 min, starting at grinding start, the starch solution was blended through a peristaltic pump over a three way valve directly into the inlet of the Dynomill Multilab mill to 100 pph (d/d), based on the total weight of dry calcium carbonate in the slurry, of the calcium carbonate slurry at room temperature.

(78) The calcium carbonate slurry was ground together with the starch solution to a target particle size of 98 wt.-% less than 2 m and 80 wt.-% less than 1 m, measured on a Sedigraph 5120. At the end of the grinding process, 4.99 ml (750 ppm based on the amount of water in the slurry) of a commercially available preserving agent (OmyAK, Rohm and Haas, Frankfurt, Germany) was added to the self-binding pigment particle suspension (starch PHCH-1 suspension) in circulation and stirred for 5 min. The obtained starch PHCH-1 suspension had a solids content of 20.9 wt.-%, based on the total weight of the suspension.

(79) The polyelectrolyte titration of the starch PHCH-1 suspension gave a charge density of +4.5 Eq/g.

(80) The details regarding the starch solution, calcium carbonate slurry and starch PHCH-1 suspension before up concentration as well as the trial conditions are summarized in Table 1.

(81) TABLE-US-00002 TABLE 1 Self-binding pigment Starch solution CaCO.sub.3 slurry particle suspension (cationic) (undispersed) (Starch PHCH-1) pph s.c. T pph s.c. T s.c. Target PSD of (d/d) [wt.-%] [ C.] (d/d) [wt.-%] [ C.] [wt.-%] grinding 15 20 95 100 20 RT 20.9 98 wt.-% < 2 m s.c. = solids content; RT = room temperature

(82) Subsequently, the starch PHCH-1 suspension was concentrated by centrifugation (Centrifuge Rotina 420, Hettich Laborapparate) at 3 000 rpm for about 15 min. The obtained filter cake had solids content of 58.5 wt.-%, based on the total weight of the filter cake, and was rediluted to final solids content of about 44.2 wt.-%, based on the total weight of the filter cake.

(83) The starch PHCH suspension as well as the filter cake comprising the self-binding pigment particles (starch PHCH-1) was, after drying, analyzed by thermogravimetric analysis (TGA). The TGA analysis for the starch PHCH suspension provided an amount of starch of 12.87 wt.-%, based on the total weight of the suspension. The TGA analysis for the filter cake provided an amount of starch of 4.84 wt.-%, based on the total weight of the filter cake.

(84) From the measured details, it can be gathered that the amount of cationic starch found in the starch PHCH suspension (12.87 wt.-%) corresponds widely to the amount of cationic starch blended into the calcium carbonate slurry during grinding (13 wt.-%). However, from the amount of starch found in the filter cake (4.84 wt.-%) it can be further concluded that approximately 8 wt.-% of the cationic starch blended into the calcium carbonate slurry during grinding must have gone into the water phase. Thus, it has to be assumed that the preparation of the starch PHCH suspension by grinding of calcium carbonate slurry with cationic starch results in a suspension in which about 62 wt.-%, based on the total weight of starch, is present in the form of free starch.

(85) b) Preparation and Testing of Coating Colors Prepared from the Self-Binding Pigment Particle Suspension

(86) Two coating colors were prepared by using the starch PHCH-1 suspension (cationic) in the form of a filter cake having a solids content of 44.2 wt.-%, based on the total weight of the filter cake.

(87) Coating Color-1 (Cationic)

(88) 100 pph of the starch PHCH-1 suspension (cationic) in the form of a filter cake having solids content of 44.2 wt.-% was used as pure coating color. Coating color-1 provided a Brookfield viscosity of 207 mPas.

(89) The S-coefficient of coating color-1 was determined as being 210 m.sup.2/kg, while the K-coefficient was determined as being 0.271 m.sup.2/kg.

(90) Coating color-1 was applied on two different base papers, Synteape, commercially available from Fischer Papier AG, Switzerland as well as SAPPI, commercially available from Sappi Magnostar GmbH, Austria. The base paper from Sappi Magnostar corresponds to an uncoated raw paper. Furthermore, each base paper was provided as calendered and uncalendered samples. The coatings have been applied with a rod bench top coater, Rakelauftragsgert K-Control-Coater K202, Model 624 (Erichsen)/Fabr. No. 57097-4/Rods 1-5 for the control of the liquid flow/Belt dryer 7.0 mmin.sup.1, 150 C.

(91) Mechanical properties of the uncalendered samples were characterized by the dry pick resistance test which was carried out with coating weights between 5 g/m.sup.2 and 31 g/m.sup.2. The dry pick resistance test provided a pick velocity of below 0.5 m/s across all coat weights of both of the uncalendered paper samples.

(92) The optical properties of the uncalendered paper samples were characterized by brightness, opacity and paper gloss for coating weights between 5 g/m.sup.2 and 30 g/m.sup.2. In addition thereto, the calendered paper samples were characterized by the paper gloss for coating weights between 5 g/m.sup.2 and 30 g/m.sup.2.

(93) The results for the mechanical and optical properties of the tested papers can be gathered from Tables 2 to 4.

(94) TABLE-US-00003 TABLE 2 Dry pick resistance Synteape Coat Pick Sappi base paper Coating weight velocity Coat weight Pick velocity color [gm.sup.2] [ms.sup.1] [gm.sup.2] [ms.sup.1] 1 5.2 <0.5 13.1 <0.5 15.2 <0.5 20.1 <0.5 30.2 <0.5

(95) Mechanical properties, like dry pick resistance, and the coat weights correspond to rods 1, 3 and 5

(96) TABLE-US-00004 TABLE 3 Optical properties Synteape Coat Brightness Paper gloss 75 Coating weight R-457 Opacity Tappi [%] color [gm.sup.2] [%] [%] uncalendered calendered 1 5.2 91.1 93.7 26.6 69.1 8.8 91.1 94.3 26.6 69.4 15.2 91.5 95.7 27.2 69.6 23.8 91.7 96.9 26.7 68.7 30.2 91.9 97.5 25.9 68.4

(97) The coat weights correspond to rods 1, 3, 4, 5

(98) TABLE-US-00005 TABLE 4 Optical properties Sappi base paper Coat Brightness Paper gloss 75 Coating weight R-457 Opacity Tappi [%] color [gm.sup.2] [%] [%] uncalendered calendered 1 13.1 86.7 93.6 10.7 60.4 15.1 87.0 94.4 12.2 60.6 20.1 88.1 96.0 15.1 64.4

(99) The coat weights correspond to rods 1, 2, 3, 4, 5

(100) Coating Color-2 (Cationic)

(101) Coating color-2 having a solids content of 60.1 wt.-%, based on the total weight of the coating color, was prepared by adding 8 pph (d/d) of the starch PHCH-1 suspension (cationic) in form of a filter cake having a solids content of 44.2 wt.-% to 100 pph (d/d) of a calcium carbonate slurry having solids content of 78 wt.-%, based on the total weight of the slurry. The particulate material of the calcium carbonate slurry has been wet ground in the presence of a sodium polyacrylate and has a weight median particle diameter d.sub.50 value of 0.65 m and a d.sub.95 of less than 2 m (all measured according to the sedimentation method) and a specific surface area of 14.8 m.sup.2/g (measured using nitrogen and the BET method). Furthermore, 4 pph (d/d) of commercially available styrene/acrylate basic latex as e.g. sold by the BASF Company under the name ACRONAL S 360 D was added. Coating color-2 provided a Brookfield viscosity of 96 mPas.

(102) The S-coefficient of coating color-2 was determined as being 99 m.sup.2/kg while the K-coefficient was determined as being 0.09 m.sup.2/kg.

(103) Coating color-2 was also applied on two different base papers, namely Synteape, commercially available from Fischer Papier AG, Switzerland as well as SAPPI, commercially available from Sappi Magnostar GmbH, Austria. The base paper from Sappi Magnostar corresponds to an uncoated raw paper. Furthermore, each base paper was provided as calendered and uncalendered sample. The coatings have been applied with a rod bench top coater, Rakelauftragsgert K-Control-Coater K202, Model 624 (Erichsen)/Fabr. No. 57097-4/Rods 1-5 for the control of the liquid flow/Belt dryer 7.0 m/min, 150 C.

(104) Mechanical properties of the uncalendered samples were characterized by the dry pick resistance test which was carried out with coating weights between 8 g/m.sup.2 and 56 g/m.sup.2. The dry pick resistance test provided a pick velocity of below 1 m/s across all coat weights of both of the uncalendered paper samples. In particular, on Synteape a pick velocity of 1.0 m/s was determined for a 8.1 g/m.sup.2 coating weight, while at 22.7 g/m.sup.2 coating weight the pick velocity was at 0.5 m/s and at 47.6 g/m.sup.2 coating weight the pick velocity was below 0.5 m/s. In contrast thereto, on SAPPI, a pick velocity of below 0.5 m/s was determined for all coatings weights beginning at a coating weight of 16.3 g/m.sup.2.

(105) The optical properties of the uncalendered paper samples were characterized by brightness, opacity and paper gloss for coating weights between about 8 g/m.sup.2 and 56 g/m.sup.2. In addition thereto, the calendered paper samples were characterized by the paper gloss for coating weights between about 8 g/m.sup.2 and 56 g/m.sup.2.

(106) The results for the mechanical and optical properties of the tested papers can be gathered from Table 5 to 7.

(107) TABLE-US-00006 TABLE 5 Dry pick resistance Synteape Coat Pick Sappi base paper Coating weight velocity Coat weight Pick velocity color [gm.sup.2] [ms.sup.1] [gm.sup.2] [ms.sup.1] 2 8.1 1.0 16.3 <0.5 22.7 0.5 29.1 <0.5 47.6 <0.5 55.8 <0.5

(108) Mechanical properties, like dry pick resistance, and the coat weights correspond to rods 1, 3 and 5

(109) TABLE-US-00007 TABLE 6 Optical properties Synteape Coat Brightness Paper gloss 75 Coating weight R-457 Opacity Tappi [%] color [gm.sup.2] [%] [%] uncalendered calendered 2 8.1 90.9 93.2 60.3 79.2 13.1 90.9 93.6 64.0 79.9 22.7 91.0 94.3 66.7 80.1 36.3 91.2 96.1 68.9 80.5 47.6 91.2 96.7 70.7 80.7

(110) The coat weights correspond to rods 1, 3, 4, 5

(111) TABLE-US-00008 TABLE 7 Optical properties Sappi base paper Coat Brightness Paper gloss 75 Coating weight R-457 Opacity Tappi [%] color [gm.sup.2] [%] [%] uncalendered calendered 2 16.3 86.2 92.2 21.3 66.8 20.1 86.6 93.0 24.2 72.3 29.7 87.4 94.8 29.3 74.9 42.7 88.7 95.5 34.8 76.3 55.8 88.7 97.0 34.7 76.3

(112) The coat weights correspond to rods 1, 2, 3, 4, 5

Example 2 (Inventive Example

(113) a) Preparation and Testing of the Self-Binding Pigment Particle Suspension

(114) A self-binding pigment particle suspension was prepared by using undispersed calcium carbonate ground with a thermally modified starch in an amount of about 0.99 wt.-% (corresponds to 1 pph starch on 100 pph calcium carbonate) and about 4.76 wt.-% (corresponds to 5 pph starch on 100 pph calcium carbonate), respectively.

(115) A starch suspension having a starch concentration of 40 wt.-%, based on the total weight of the suspension, was prepared by stirring 0.99 wt.-% (d/d which corresponds to 1 pph starch on 100 pph calcium carbonate), based on the total weight of the dry pigment material in the calcium carbonate slurry and starch, of a commercially available thermally modified starch (C*film 07311, from Cargill) in water at room temperature.

(116) Furthermore, a starch suspension having a starch concentration of 40 wt.-%, based on the total weight of the suspension, was prepared by stirring 4.76 wt.-% (d/d; corresponds to 5 pph starch on 100 pph calcium carbonate), based on the total weight of the dry pigment material in the calcium carbonate slurry and starch, of a commercially available thermally modified starch (C*film 07311, from Cargill) in water at room temperature.

(117) 10 kg of undispersed calcium carbonate slurry was prepared having solids content of about 20 wt.-%, based on the total weight of the slurry. The particulate material of the slurry has a weight median particle diameter d.sub.50 value of 0.74 m (measured according to the sedimentation method).

(118) Furthermore, the particulate material of the slurry had a specific surface area of 9.46 m.sup.2/g (measured using nitrogen and the BET method).

(119) Subsequently, the calcium carbonate slurry was run through a Dynomill Multilab filled with 1 070 g of (with 80% filler level) zirconium oxide/zirconium silicate grinding beads (0.6-1.0 mm) at about room temperature. The grinding chamber had a total volume of 600 cm.sup.3. The mill speed was set to 2 500 rpm and the flow was set to 500 cm.sup.3/min.

(120) Within 5 and 10 min, respectively, starting at grinding start, each of the starch suspensions were blended through a peristaltic pump over a three way valve directly into the inlet of the Dynomill Multilab mill to 100 pph (d/d) of calcium carbonate slurry, based on the dry weight of the calcium carbonate in the slurry.

(121) The obtained calcium carbonate slurries were ground together with the respective starch suspension to a target particle size of 98 wt.-% less than 2 m and approx. 80 wt.-% of less than 1 m, measured on a Sedigraph 5120. At the end of the grinding process, 5.3 ml (750 ppm based on the total amount of water amount) of a commercially available preserving agent (OmyAK, Rohm and Haas) was added to each of the self-binding pigment particle suspensions (starch PHCH suspensions) in circulation and stirred for 5 min. The obtained starch PHCH suspension prepared by adding about 0.99 wt.-% of the thermally modified starch had a solid content of 40 wt.-%, based on the total weight of the suspension, (starch PHCH-2) comprising particles having a charge density of +1.63 Eq/g while the obtained starch PHCH suspension prepared by adding about 4.76 wt.-% of the thermally modified starch had a solid content of 40 wt.-%, based on the total weight of the suspension, (starch PHCH-3) comprising particles having a charge density of 0.87 Eq/g.

(122) The details regarding starch suspensions, calcium carbonate slurries and starch PHCH suspensions as well as the trial conditions are summarized in Table 8.

(123) TABLE-US-00009 TABLE 8 Self-binding pigment Starch suspension CaCO.sub.3 slurry particle suspension (anionic) (undispersed) (Starch PHCH) pph s.c. T pph s.c. T Target PSD Trial (d/d) [wt.-%] [ C.] (d/d) [wt.-%] [ C.] of grinding Starch 1 40 RT 100 20 RT 98 wt.-% < 2 PHCH-2 m Starch 5 40 RT 100 20 RT 98 wt.-% < 2 PHCH-3 m s.c. = solids content; RT = room temperature

(124) Subsequently, both starch PHCH (starch PHCH-2 and starch PHCH-3) suspensions were concentrated by centrifugation (Centrifuge Rotina 420, Hettich Laborapparate) at 3 000 rpm for about 15 min. The filter cake obtained from the starch PHCH-2 suspension had solids content of 59.3 wt.-%, based on the total weight of the filter cake, and was rediluted to final solids content of about 43 wt.-%, based on the total weight of the filter cake (starch PHCH-2). The filter cake obtained from the starch PHCH-3 suspension had solids content of 58 wt.-%, based on the total weight of the filter cake, and was diluted to final solids content of about 41.8 wt.-%, based on the total weight of the filter cake (starch PHCH-3). Furthermore, the supernatant of the starch PHCH-2 suspension had a pH of 8.17, while the supernatant of the starch PHCH-3 suspension had a pH of 7.95.

(125) b) Preparation of Coating Colors Prepared from the Self-Binding Pigment Particle Suspension and Adhesion Tests

(126) The filter cakes starch PHCH-2 (coating color-3) and starch PHCH-3 (coating color-4) were used directly as coating colors without adding further additives. As reference a coating color having solids content of 33.2 wt.-%, based on the total weight of the coating color, was used. The reference coating color was prepared by diluting a calcium carbonate slurry having solids content of 67 wt.-%, based on the total weight of the slurry. The particulate material of this slurry had a weight median particle diameter d.sub.50 value of 0.74 m (measured according to the sedimentation method). Furthermore, the particulate material of the slurry had a specific surface area of 9.46 m.sup.2/g (measured using nitrogen and the BET method).

(127) The coating weights for the reference and the inventive starch PHCH samples used for the adhesion test as well as the test results are summarized in Table 9.

(128) TABLE-US-00010 TABLE 9 Coating weight [g/m.sup.2] Adhesion g (n = 5) Trial rod 1 rod 3 rod 5 rod 1 rod 3 rod 5 Reference 3.5 10.7 22.1 0 0 0 Coating color-3 4.7 14.8 31.5 10.8 11.4 7.8 Coating color-4 4.8 14.2 30.0 76.0 69.0 39.0 n = number of repeat experiments/measurements

(129) As can be gathered from the measured details, the coatings did not release or rip off the foil (de-bond). In particular, it can be gathered that a coating color prepared by using a calcium carbonate without an anionic and/or amphotheric starch shows no adhesion at all resulting thus in no binding power.

(130) In contrast thereto, the coating color-3 comprising the inventive composition starch PHCH-2 (about 0.99 wt.-% or 1 pph starch) shows some binding power. Furthermore, the coating color-4 comprising the inventive composition starch PHCH-3 (about 4.76 wt.-% or 5 pph starch) shows a clear increase in binding power. This test is the result of the average of five measurements.

Example 3 (Inventive Example

(131) Self-binding pigment particle suspensions were prepared by using undispersed calcium carbonate ground with a thermally modified starch at different temperatures.

(132) A starch suspension having a starch concentration of 40 wt.-%, based on the total weight of the suspension, was prepared by stirring 13 wt.-% (d/d which corresponds to 15 pph starch on 100 pph calcium carbonate), based on the total weight of the dry pigment material in the calcium carbonate slurry and starch, of a commercially available thermally modified starch (C*film 07311, from Cargill) in water at room temperature.

(133) 10 kg of undispersed calcium carbonate slurry was prepared having solids content of about 20 wt.-%, based on the total weight of the calcium carbonate slurry, at about 20 C. The particulate material of the slurry had a weight median particle diameter d.sub.50 value of 0.74 m (measured according to the sedimentation method). Furthermore, the particulate material of the slurry had a specific surface area of 9.46 m.sup.2/g (measured using nitrogen and the BET method).

(134) Subsequently, the calcium carbonate slurry was run through a Dynomill Multilab filled with 1 070 g (with 80% filler level) zirconium oxide/zirconium silicate grinding beads (0.6-1.0 mm) at about room temperature.

(135) The grinding chamber had a total volume of 600 cm.sup.3. The mill speed was set to 2 500 rpm and the flow was set to 500 cm.sup.3/min.

(136) Within 10 min, starting at grinding start, the starch suspension was blended through a peristaltic pump over a three way valve directly into the inlet of the Dynomill Multilab mill to 100 pph (d/d) of the calcium carbonate slurry at a temperature of 20 C.

(137) The calcium carbonate slurry was ground with the starch suspension to a target particle size of 98 wt.-% less than 2 m and 80 wt.-% less than 1 m, measured on a Sedigraph 5120. At the end of the grinding process, 750 ppm based on the amount of water (4.99 ml) of a commercially available preserving agent (OmyAK, Rohm and Haas) was added to the self-binding pigment particle suspension (starch PHCH suspension) in circulation and stirred for 5 min. The starch PHCH suspension obtained at 20 C. had solids content of 21.7 wt.-%, based on the total weight of the suspension (starch PHCH-4).

(138) The details regarding the starch suspension, calcium carbonate slurry and starch PHCH suspension as well as the trial conditions are summarized in Table 10.

(139) TABLE-US-00011 TABLE 10 Self-binding pigment Starch suspension CaCO.sub.3 slurry particle suspension (anionic) (undispersed) (Starch PHCH) pph s.c. T pph s.c. T Target PSD Trial (d/d) [wt.-%] [ C.] (d/d) [wt.-%] [ C.] of grinding Starch 15 40 RT 100 20 20 98 wt.-% < 2 PHCH-4 m s.c. = solids content; RT = room temperature

(140) Subsequently, the starch PHCH suspension was concentrated by centrifugation (Centrifuge Rotina 420, Hettich Laborapparate) at 3 000 rpm for about 15 min to solids content of 58.2 wt.-% (at 20 C.), based on the total weight of the filter cake. The filter cake obtained was diluted to final solids content of about 39 wt.-%, based on the total weight of the filter cake.

(141) The obtained filter cake comprising the self-binding pigment particle (starch PHCH) was, after drying, analyzed by TGA and BET. The obtained supernatant was analyzed by COD and starch content.

(142) Table 11 summarizes the measured details of the respective supernatant as well as the filter cake.

(143) TABLE-US-00012 TABLE 11 Supernatant Filter cake (dried) Starch content TGA* BET Trial [mg/l] [wt.-%] [m.sup.2/g] Starch PHCH-4 5.559 8.2611 6.4 *The results are given for thermogravimetric analysis (TGA) 0-570 C. In this regard, it should be noted that the moisture in these results is included. According to the TGA, the following data are obtained: Starch PHCH-4 0-180 C. 0.6416% (which is considered moisture) 180-570 C. 7.6226% (which is considered starch, organics)

(144) The amount of 7.6226 wt.-% starch in the filtercake corresponds to an amount of 58.6 wt.-% of the total amount of starch in the filtercake, based on the total amount of starch in the starch PHCH suspension, and therefore 41.4 wt.-% of starch is present as free starch (through loss during concentration as well as through microbial starch degradation).

(145) Tablets were prepared from the self-binding pigment particle suspension and measured in the tablet crushing test with respect to the maximum force, F.sub.max, required to make the first crack into a tablet. In particular, tablets were prepared from starch PHCH-4 obtained in this example. In particular, the tablets were formed by applying a constant pressure of 15 bar to the suspension for 30 min.

(146) The effects of the self-binding pigment particle suspension on the maximum force, F.sub.max, required to make the first crack into a tablet as measured in the tablet crushing test are outlined in Table 12.

(147) TABLE-US-00013 TABLE 12 F.sub.max Trial [N] Starch PHCH-4 507.4

(148) The result corresponds to an average of 5 measurements.

(149) From Table 12 it can be concluded that tablets prepared from a suspension made in accordance with the inventive process require a maximum force of about 507 N to make the first crack.

Example 4 (Inventive Example

(150) Self-binding pigment particle suspensions were prepared by using undispersed calcium carbonate ground with a thermally modified starch or an anionic starch having a degree of carboxylation of about 0.0082 at different temperatures.

(151) A starch suspension-1 having a starch concentration of 40 wt.-%, based on the total weight of the suspension, was prepared by stirring 13 wt.-% (d/d which corresponds to 15 pph starch on 100 pph calcium carbonate), based on the total weight of the dry pigment material in the calcium carbonate slurry and starch, of a commercially available thermally modified starch (C*film 07311, from Cargill) in water at room temperature.

(152) A starch solution-2 having a starch concentration of 10 wt.-%, based on the total weight of the solution, was prepared by stirring 13 wt.-% (d/d which corresponds to 15 pph starch on 100 pph calcium carbonate), based on the total weight of the dry pigment material in the calcium carbonate slurry and starch, of a commercially available anionic starch having a degree of carboxylation of about 0.0082 (C*iCoat 07525, from Cargill) in water at room temperature. C*iCoat 07525 is a cold water soluble starch and thus dissolves at room temperature.

(153) 10 kg of undispersed calcium carbonate slurry was prepared having a solids content of about 20 wt.-%, based on the total weight of the slurry. The particulate material of the slurries had a weight median particle diameter d.sub.50 value of 0.74 m (measured according to the sedimentation method). Furthermore, the particulate material of the slurries had a specific surface area of 9.46 m.sup.2/g (measured using nitrogen and the BET method).

(154) Subsequently, the calcium carbonate slurry was run through a Dynomill Multilab filled with 1 070 g (with 80% filler level) zirconium oxide/zirconium silicate grinding beads (0.6-1.0 mm) at about room temperature. The grinding chamber had a total volume of 600 cm.sup.3. The mill speed was set to 2 500 rpm and the flow was set to 500 cm.sup.3/min.

(155) Within 10 to 15 min (15 minutes for suspension-1, 10 minutes for solution-2), starting at grinding start, the respective starch suspension/solution was blended through a peristaltic pump over a three way valve directly into the inlet of the Dynomill Multilab mill to 100 pph (d/d), based on the total weight of dry calcium carbonate in the slurry, of the calcium carbonate slurry at room temperature.

(156) The respective calcium carbonate slurries were ground with the respective starch suspensions/solution to a target particle size of 98 wt.-% less than 2 m and 80 wt.-% less than 1 m, measured on a Sedigraph 5120. At the end of the grinding process, 750 ppm based on the amount of water in the starch PHCH suspension (4.8 ml for suspension-1, 5.3 ml for solution-2) of a commercially available preserving agent (OmyAK, Rohm and Haas) was added to each self-binding pigment particle suspension in circulation and stirred for 5 min.

(157) The obtained starch PHCH suspension prepared by using starch suspension-1 had a solids content of 20.9 wt.-%, based on the total weight of the suspension, (starch PHCH-5) while the obtained starch PHCH suspension prepared by using starch solution-2 had a solids content of 21.2 wt.-%, based on the total weight of the suspension, (starch PHCH-6).

(158) The details regarding starch suspension/solutions, calcium carbonate slurries and starch PHCH suspensions as well as the trial conditions are summarized in Table 13.

(159) TABLE-US-00014 TABLE 13 Self-binding Starch pigment suspension/solution CaCO.sub.3 slurry particle suspension (anionic) (undispersed) (Starch PHCH) pph s.c. T pph s.c. T Target PSD Trial (d/d) [wt.-%] [ C.] (d/d) [wt.-%] [ C.] of grinding Starch 15 40 RT 100 20 RT 98 wt.-% < 2 PHCH-5 m Starch 15 10 RT 100 20 RT 98 wt.-% < 2 PHCH-6 m s.c. = solids content; RT = room temperature

(160) Subsequently, all slurries were centrifuged (Centrifuge Rotina 420, Hettich Laborapparate) at 3 000 rpm for about 15 min. The obtained filter cakes were rediluted to final solids content of about 39.6 wt.-% (starch PHCH-5), based on the total weight of the filter cake and 44.5 wt.-% (starch PHCH-6), respectively.

(161) The obtained filter cakes comprising the self-binding pigment particles (starch PHCH) were, after drying, analyzed by TGA at 0 to 570 C. (not stepwise). The filter cake of starch PHCH-5 comprises an amount of 7.82 wt.-% (including moisture) starch, corresponding to an amount of 60.15 wt.-% of the total amount of starch in the filtercake, i.e. an amount of free starch of 39.85 wt.-%.

(162) b) Preparation and Testing of Coating Colors Prepared from the Self-Binding Pigment Particle Suspensions Coating colors were prepared by using the starch PHCH suspensions of this Example in the form of the respective filter cake.

(163) Coating Color-5

(164) 100 pph of the starch PHCH-5 suspension in the form of a filter cake having solids content of about 39.6 wt.-% was used as pure coating color. The S-coefficient of coating color-5 was determined as being 209 m.sup.2/kg, while the K-coefficient was determined as being 0.235 m.sup.2/kg.

(165) Coating Color-6

(166) 100 pph of the starch PHCH-6 suspension in the form of a filter cake having solids content of about 44.5 wt.-% was used as pure coating color. Coating color-6 provided a Brookfield viscosity of 90 mPas. The S-coefficient of coating color-6 was determined as being 205 m.sup.2/kg, while the K-coefficient was determined as being 0.406 m.sup.2/kg.

(167) Coating colors-5 and 6 were applied on two different base papers, Synteape, commercially available from Fischer Papier AG, Switzerland as well as SAPPI, commercially available from Sappi Magnostar GmbH, Austria. The base paper from Sappi Magnostar corresponds to an uncoated raw paper. Furthermore, each base paper was provided as calendered and uncalendered sample. The coatings have been applied with a rod bench top coater, Rakelauftragsgert K-Control-Coater K202, Model 624 (Erichsen)/Fabr. No. 57097-4/Rods 1-5 for the control of the liquid flow/Belt dryer 7.0 m/min, 150 C.

(168) Mechanical properties of the uncalendered samples were characterized by the dry pick resistance test which was carried out with coating weights between 4 g/m.sup.2 and 30.48 g/m.sup.2. The results for the dry pick resistance test of the tested papers can be gathered from Table 14.

(169) The optical properties of the uncalendered paper samples were characterized by brightness, opacity and paper gloss for coating weights between about 4 g/m.sup.2 and 30.5 g/m.sup.2. In addition thereto, the calendered paper samples were characterized by the paper gloss for coating weights between about 4 g/m.sup.2 and 30.5 g/m.sup.2. The results for the optical properties of the tested papers can be gathered from Tables 15 to 17.

(170) TABLE-US-00015 TABLE 15 Dry pick resistance Synteape Coat Pick Sappi base paper Coating weight velocity Coat weight Pick velocity color [gm.sup.2] [ms.sup.1] [gm.sup.2] [ms.sup.1] 5 4.0 <0.5 12.3 <0.5 12.7 <0.5 26.3 <0.5 6 5.1 0.9 11.7 <0.5 15.1 <0.5 15.7 <0.5 29.1 <0.5

(171) Mechanical properties, like dry pick resistance, and the coat weights correspond to rods 1, 3 and 5

(172) TABLE-US-00016 TABLE 16 Optical properties Synteape Coat Brightness Paper gloss 75 Coating weight R-457 Opacity Tappi [%] color [gm.sup.2] [%] [%] uncalendered calendered 5 4.0 90.9 93.4 10.6 81.3 7.5 91.1 94.2 11.8 85.8 12.7 91.5 95.3 10.8 84.2 21.2 91.8 96.3 7.0 71.7 26.3 91.9 97.1 7.0 75.1 6 5.1 90.7 93.8 33.0 81.4 7.5 90.8 94.4 22.8 78.9 15.1 90.8 95.6 12.2 72.9 23.1 90.9 97.0 16.6 78.8 29.1 90.9 97.8 19.4 75.7

(173) The coat weights correspond to rods 1, 2, 3, 4, 5

(174) TABLE-US-00017 TABLE 17 Optical properties Sappi base paper Coat Brightness Paper gloss 75 Coating weight R-457 Opacity Tappi [%] color [gm.sup.2] [%] [%] uncalendered calendered 5 12.3 87.2 92.7 6.3 67.9 13.1 87.8 93.4 6.2 68.4 6 11.7 86.9 93.3 47.9 62.1 15.7 87.2 94.0 42.8 65.4 20.5 87.2 96.3 33.5 67.2

(175) The coat weights correspond to rods 1, 2, 3, 4, 5

(176) Coating Color-7

(177) Coating color-7 having a solids content of 59.7 wt.-%, based on the total weight of the coating color, was prepared by adding 8 pph (d/d) of the starch PHCH-5 suspension in form of a filter cake having a solids content of 39.6 wt.-% to 100 pph (d/d) of a calcium carbonate slurry having solids content of 78 wt.-%, based on the total weight of the slurry. The particulate material of the calcium carbonate slurry has been wet ground in the presence of a sodium polyacrylate and has a weight median particle diameter d.sub.50 value of 0.65 m and a d.sub.95 of less than 2 m (all measured according to the sedimentation method) and a specific surface area of 14.8 m.sup.2/g (measured using nitrogen and the BET method). Furthermore, 4 pph (d/d) of commercially available styrene/acrylate basic latex as e.g. sold by the BASF Company under the name ACRONAL S 360 D was added.

(178) The S-coefficient of coating color-8 was determined as being 113 m.sup.2/kg while the K-coefficient was determined as being 0.064 m.sup.2/kg.

(179) Coating Color-8

(180) Coating color-8 having a solids content of 59.5 wt.-%, based on the total weight of the coating color, was prepared as described for coating color 7, except that the starch PHCH-6 suspension in form of a filter cake having a solids content of 44.5 wt.-% was used. Coating color-8 provided a Brookfield viscosity of 59 mPas. The S-coefficient of coating color-8 was determined as being 106 m.sup.2/kg while the K-coefficient was determined as being 0.345 m.sup.2/kg.

(181) Coating colors-7 and 8 were also applied on two different base papers, namely Synteape, commercially available from Fischer Papier AG, Switzerland as well as SAPPI, commercially available from Sappi Magnostar GmbH, Austria. The base paper from Sappi Magnostar corresponds to an uncoated raw paper. Furthermore, each base paper was provided as calendered and uncalendered sample. The coatings have been applied with a rod bench top coater, Rakelauftragsgert K-Control-Coater K202, Model 624 (Erichsen)/Fabr. No. 57097-4/Rods 1-5 for the control of the liquid flow/Belt dryer 7.0 mmin.sup.1, 150 C.

(182) Mechanical properties of the uncalendered samples were characterized by the dry pick resistance test which was carried out with coating weights between 7.2 g/m.sup.2 and 55.97 g/m.sup.2. The dry pick resistance test provided a pick velocity of above 0.5 m/s across all coat weights for both of the uncalendered paper samples. The results for the dry pick resistance test of the tested papers can be gathered from Table 18.

(183) The optical properties of the uncalendered paper samples were characterized by brightness, opacity and paper gloss for coating weights between 7.2 g/m.sup.2 and 55.97 g/m.sup.2. In addition thereto, the calendered paper samples were characterized by the paper gloss for coating weights between 7.2 g/m.sup.2 and 55.97 g/m.sup.2. The results for the optical properties of the tested papers can be gathered from Tables 19 and 20.

(184) TABLE-US-00018 TABLE 18 Dry pick resistance Synteape Coat Pick Sappi base paper Coating weight velocity Coat weight Pick velocity color [gm.sup.2] [ms.sup.1] [gm.sup.2] [ms.sup.1] 7 7.2 >3 15.6 1.2 21.6 1.8 29.2 0.8 46.4 0.6 56.0 0.8 8 7.4 >3 17.0 1.0 21.8 >3 29.0 0.6 46.6 0.7 55.5 <0.5

(185) Mechanical properties, like dry pick resistance, and the coat weights correspond to rods 1, 3 and 5

(186) TABLE-US-00019 TABLE 19 Optical properties Synteape Coat Brightness Paper gloss 75 Coating weight R-457 Opacity Tappi [%] color [gm.sup.2] [%] [%] uncalendered calendered 7 7.2 90.8 93.0 76.4 98.3 12.3 90.9 93.7 77.9 98.3 21.6 90.9 94.8 64.5 92.7 35.2 91.0 95.9 82.0 98.9 46.4 91.0 96.5 81.8 96.4 8 7.4 90.8 93.3 72.0 87.6 12.5 90.8 93.7 72.0 93.2 21.8 90.9 94.6 78.9 92.6 34.3 90.9 94.8 67.6 91.3 46.6 91.0 96.5 68.6 91.2

(187) The coat weights correspond to rods 1, 2, 3, 4, 5

(188) TABLE-US-00020 TABLE 20 Optical properties Sappi base paper Coat Brightness Paper gloss 75 Coating weight R-457 Opacity Tappi [%] color [gm.sup.2] [%] [%] uncalendered calendered 7 15.6 86.5 91.4 19.2 78.1 21.1 87.0 92.5 21.4 71.6 29.2 87.6 93.8 22.2 76.1 42.6 88.3 95.6 25.4 80.9 56.0 88.7 96.5 24.9 75.1 8 17.0 86.9 91.5 18.7 76.4 20.4 87.1 92.5 18.9 77.2 29.0 87.7 94.0 20.4 80.5 41.9 88.3 95.6 23.1 82.9 55.5 88.8 96.5 24.6 83.5