PROCESS FOR PREPARING SELF-BINDING PIGMENT PARTICLE SUSPENSIONS

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 as filler material.

Claims

1. Paper, plastic, paint, concrete or an agriculture product comprising self-binding pigment particles prepared by the process comprising the following steps: a) providing an aqueous pigment material suspension, wherein the pigment of the pigment material suspension comprises calcium carbonate; b) providing a polymeric binder, wherein the binder consists of at least one polysaccharide comprising galactose and/or mannose units; c) mixing 0.1 wt.-% to 10 wt.-% of the binder of step b), based on the total weight of the aqueous pigment material suspension, with the aqueous pigment material suspension of step a), to obtain a mixture of the binder and the aqueous pigment material suspension; and d) grinding the mixture of the binder and the aqueous pigment material suspension obtained in step c) to obtain a suspension of self-binding pigment particles, wherein the weight median diameter (d.sub.50) of the self-binding pigment particles is less than the weight median diameter (d.sub.50) of the pigment from step a).

2. The paper, plastic, paint, concrete or an agriculture product according to claim 1, wherein the pigment material of the pigment material suspension of step a) comprises calcium carbonate and one or more of-dolomite, magnesium, clay, talc, kaolin, aluminium hydroxide, mica, titanium dioxide, synthetic fibers or natural fibers.

3. The paper, plastic, paint, concrete or an agriculture product according to claim 1, wherein the pigment material of the pigment material suspension of step a) is a ground natural calcium carbonate, a precipitated calcium carbonate, a modified calcium carbonate, or any mixture thereof.

4. The paper, plastic, paint, concrete or an agriculture product according to claim 1, wherein the pigment material of the pigment material suspension of step a) is a ground natural calcium carbonate.

5. The paper, plastic, paint, concrete or an agriculture product according to claim 1, wherein the binder of step b) is at least one polysaccharide comprising galactose and mannose units.

6. The paper, plastic, paint, concrete or an agriculture product according to claim 1, wherein the binder of step b) is at least one polysaccharide comprising a linear chain of 1,4-linked -D-mannopyranosyl units or a linear chain of 1,4-linked -D-mannopyranosyl units with 1,6-linked -D-galactopyranosyl units.

7. The paper, plastic, paint, concrete or an agriculture product according to claim 1, wherein the binder of step b) is at least one polysaccharide having a ratio of mannose units to galactose units from 6:1 to 1:1.

8. The paper, plastic, paint, concrete or an agriculture product according to claim 1, wherein the binder of step b) is at least one polysaccharide having a ratio of mannose units to galactose units from 5:1 to 1:1.

9. The paper, plastic, paint, concrete or an agriculture product according to claim 1, wherein the binder of step b) is at least one polysaccharide having a ratio of mannose units to galactose units from 4:1 to 1:1.

10. The paper, plastic, paint, concrete or an agriculture product according to claim 1, wherein the binder of step b) is at least one polysaccharide having a ratio of mannose units to galactose units from 3:1 to 1:1.

11. The paper, plastic, paint, concrete or an agriculture product according to claim 1, wherein the binder of step b) is in a form of a hydrocolloidal solution or a dry material.

12. The paper, plastic, paint, concrete or an agriculture product according to claim 1, wherein the binder of step b) is in a form of a hydrocolloidal solution having a binder concentration from 0.05 wt.-% to 10 wt.-%, based on the total weight of the solution.

13. The paper, plastic, paint, concrete or an agriculture product according to claim 1, wherein the binder of step b) is in a form of a hydrocolloidal solution having a binder concentration from 0.1 wt.-% to 5 wt.-%, based on the total weight of the solution.

14. The paper, plastic, paint, concrete or an agriculture product according to claim 1, wherein in step c) 0.05 wt.-% to 5.0 wt.-% of the binder of step b), based on the total weight of the aqueous pigment material suspension, is mixed with the aqueous pigment material suspension of step a).

15. The paper, plastic, paint, concrete or an agriculture product according to claim 1, wherein in step c) 0.1 wt.-% to 2 wt.-% of the binder of step b), based on the total weight of the aqueous pigment material suspension, is mixed with the aqueous pigment material suspension of step a).

16. The paper, plastic, paint, concrete or an agriculture product according to claim 1, wherein in step c), the pigment material suspension has a solids content of 5 wt.-% to 80 wt.-%, based on the total weight of the pigment material suspension.

17. The paper, plastic, paint, concrete or an agriculture product according to claim 16, wherein in step c), the pigment material suspension has a solids content of 10 wt.-% to 60 wt.-%, based on the total weight of the pigment material suspension.

18. The paper, plastic, paint, concrete or an agriculture product according to claim 1, wherein grinding step d) is carried out at a temperature from 10 C. to 110 C.

19. The process according to claim 26, 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 20 wt.-%, based on the total weight of the pigment particles.

20. The paper, plastic, paint, concrete or an agriculture product 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 50 wt.-%, based on the total weight of the pigment particles.

21. The paper, plastic, paint, concrete or an agriculture product according to claim 1, wherein the suspension of self-binding pigment particles obtained in step d) is concentrated such that the solids content in the suspension is from 45 wt.-% to 80 wt.-%, based on the total weight of the pigment material suspension.

22. The paper, plastic, paint, concrete or an agriculture product according to claim 1, wherein before or during or after step c) and/or step d) a dispersing agent is added.

23. The paper, plastic, paint, concrete or an agriculture product according to claim 1, which is paper.

24. The paper, plastic, paint, concrete or an agriculture product according to claim 1, which is plastic.

25. The paper, plastic, paint, concrete or an agriculture product according to claim 1, which is paint.

26. The paper, plastic, paint, concrete or an agriculture product according to claim 1, which is concrete.

27. The paper, plastic, paint, concrete or an agriculture product according to claim 1, which is an agricultural product.

Description

DESCRIPTION OF THE FIGURES

[0129] FIG. 1: illustrates the effect of the self-binding pigment particle suspensions on the tensile index for handsheets prepared from such suspensions.

[0130] FIG. 2: illustrates the effect of the self-binding pigment particle suspensions on the internal bond (in z-Direction) for handsheets prepared from such suspensions.

[0131] FIG. 3: illustrates the maximum force, F.sub.max, required to make the first crack into a tablet.

EXAMPLES

Methods and Materials

[0132] In the following, materials and measurement methods implemented in the examples are described.

BET Specific Surface Area of a Material

[0133] 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.

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

[0134] 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.

[0135] 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.

pH of an Aqueous Suspension

[0136] The pH of the aqueous suspension was measured using a standard pH-meter at approximately 22 C.

Solids Content of an Aqueous Suspension

[0137] The suspension solids content (also known as dry weight) was determined using a Moisture Analyser HR73 from the company Mettler-Toledo, Switzerland, with the following settings: temperature of 120 C., automatic switch off 3, standard drying, 5 to 20 g of suspension.

Handsheet Study

[0138] The handsheet study and the consequent testing of the mechanical strength properties of the paper is a measure for the binding ability of the self-binding pigment to other surfaces like cellulosic fibres.

[0139] Eucalyptus pulp (Jarilyptus) refined to 30 SR was used for this study. 60 g (dry) pulp blend were diluted in 10 dm.sup.3 tap water, and then the filler was added. The suspension was stirred for 30 minutes. Subsequently 0.06% (based on dry weight) of a polyacrylamide (Polymin 1530, commercially available from BASF, Ludwigshafen, Germany) was added as a retention aid and sheets of 78 g/m.sup.2 were formed using the Rapid-Kothen hand sheet former. Each sheet was dried using the Rapid-Kothen drier. The filler content in the handsheets was determined by burning a quarter of a dry handsheet in a muffle furnace heated to 570 C. After the burning was completed, the residue was transferred in a desiccator and allowed to cool down. When room temperature was reached, the weight of the residue was measured and the mass was related to the initially measured weight of the dry quarter hand sheet. The filler content in the examples was 20-30%.

[0140] The mechanical strength properties of the handsheets were characterized by the tensile index and internal bond according to ISO 1924-2 and SCAN-P80:98/TAPPI T541, respectively, after drying of the handsheets.

Tablet Crushing Test

[0141] 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.

[0142] 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.

[0143] Tablets were formed by applying a constant pressure (15 bar) to 80 ml of the aqueous pigment material suspension measured for 2 to 48 hours such that water is released by filitration 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 48 hours.

[0144] 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).

[0145] Subsequently, the tablets were ground 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 measurements of independently prepared tablets and the error bars are the standard deviation of these three measurements.

Polyelectrolyte Titration (PET)

[0146] The polyelectrolyte content in the aqueous suspension is determined using a Memotitrator Mettler DL 55 equipped with a Phototrode DP 660 commercialised by Mettler-Toledo, Switzerland. The measurements of the poylelectrolyte content was carried out by weighing a sample of the calcium carbonate suspension into a titration vessel and diluting said sample with deionized water up to a volume of approximately 40 ml. Subsequently, 10 ml of 0.01 M cationic poly(N,N-dimethyl-3,5-dimethylene-piperidinium chloride) (PDDPC; obtained from ACROS Organics, Belgium) are slowly added under stirring into the titration vessel within 5 min. and than the content of the vessel is stirred for another 20 min. Afterwards the suspension is filtered trough a 0.2 m mix-ester membrane filter (47 mm) and washed with 5 ml of deionized water. The thus obtained filtrate is diluted with 5 ml of phosphate buffer pH 7 (Riedel-de Han, Germany) and than 0.01 M of a potassium polyvinylsulfate (KPVS; obtained from SERVA Feinbiochemica, Heidelberg) solution is added slowly to the filtrate to titrate the excess of cationic reagent. The endpoint of titration is detected by a Phototrode DP660, which is adjusted to 1200 to 1400 mV in deionized water, prior to such measurement. The charge calculation is carried out according to the following evaluation:

[00001]$Q_{\mathrm{atro}}=\frac{\left(\left(V_{\mathrm{PDDPC}}*t_{\mathrm{PDA}}\right)-V_{\mathrm{KPVS}}\right)*\left(-1000\right)}{E_P*\mathrm{Fk}}.Math.\left[\mathrm{.Math.}.Math.\mathrm{Val}.Math.\text{/}.Math.g\right]$$w_{\mathrm{atro}}=-\frac{Q_{\mathrm{atro}}}{K_{\mathrm{DM}}*100}.Math.\left[\%\right]$

Calculation of the Optimal Sample Weight:

[0147] [00002]$E_P=\frac{60}{w_{\mathrm{DM}}*K_{\mathrm{DM}}*\mathrm{Fk}}$

[0148] Calculation of Adapted Sample Weight for 4 ml Consumption:

[00003]$E_{4.Math..Math.\mathrm{ml}}=\frac{E_1*6}{\left(10-V_{\mathrm{KPVS},1}\right)}$

Abbreviations

[0149] E.sub.P=sample weight [g]
w.sub.DM=Dispersing agent content in [%]
K.sub.DM=Dispersing agent constant [Val/0.1 mg dispersing agent]
Fk=Solids content [%]
V.sub.PDDPC Volume PDDPC [ml]
V.sub.KPVS=Volume KPVS [ml]
t.sub.PDDPC=Titer PDDPC
E.sub.DM=Dispersing agent weight [mg]

Q=Charge [Val/g]

[0150] w.sub.atro=Dispersing agent content atro [%]
E.sub.1=Sample weight of experiment to be optimised [g]
V.sub.KPVS,1=experimental consumption KPVS [ml] of experiment to be optimised

Loss on Ignition (LOI) Method

[0151] For the measurement of the loss on ignition, samples of the self-binding pigment material suspensions were dried in a microwave at approximately 200 W for about 75 min such that the samples have maximum moisture of about 0.5 wt.-%, based on the total weight of the particulate material. Subsequently, the dried samples were de-agglomerated by using a RETSCH ultra-centrifugal mill (type ZM) with 200 m screen and rotor having 24 teeth. 3 to 4 g of the obtained sample was weighed into a porcelain crucible and heated in a muffle oven at about 570 C. until constant mass. After cooling in a desiccator, the porcelain crucible was weighed with the obtained residue. The values given herein are the average of two measurements of independently prepared samples.

[0152] The loss on ignition is an absolute measurement displayed in percent and calculated according to the following formula:

[00004]$\frac{100*\left(m_1-m_2\right)}{m_1}$

with
m.sub.1: mass of initial weight [g]
m.sub.2: mass after heating to about 570 C. in a muffle oven [g]

Example 1 (Inventive Example)

[0153] The particulate material used for the preparation of the slurry was a marble of Norwegian origin.

[0154] The pigment slurry had a solids content of about 20 wt.-%, based on the total weight of the suspension. The particulate material has a weight median particle diameter d.sub.50 value of 0.8 m, a d.sub.90 of less than 2 m and a d.sub.60 of less than 1 m (all measured according to the sedimentation method). Furthermore, the particulate material of the slurry had a specific surface area of 7 m.sup.2/g (measured using nitrogen and the BET method).

[0155] A powder of guar in an amount of 0.4% by weight (commercialised by Sigma Aldrich under G4129), based on the total weight of the suspension, was blended before grinding into the suspension of the particulate material and stirred with a dissolver stirrer for 30 minutes.

[0156] The low solid suspension at 20 wt.-% was run through a Dynomill Multilab filled with 460 cm.sup.3 Verac grinding beads (0.6-1.0 mm) for 90 minutes. 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. Grinding was carried out at room temperature.

[0157] No significant increase in temperature was observed.

[0158] The product obtained was analysed by Sedigraph, solids content, PET, pH and LOI. Table 1 summarizes the measured details of the final product.

TABLE-US-00001 TABLE 1 Inventive Example 1 <2 m/% 97.7 <1 m/% 83.0 D.sub.50/m 0.56 solids content/wt.-% 20.2 PET/Eq/g 14.8 pH 6.28 LOI/% 2.6

[0159] In addition thereto, the effect of the self-binding pigment particle suspensions on the tensile index for handsheets prepared from the suspension obtained in Example 1 is outlined in FIG. 1.

[0160] Furthermore, the effect of the self-binding pigment particle suspensions on the internal bond (in z-Direction) for handsheets prepared from the suspension obtained in Example 1 is outlined in FIG. 2.

[0161] For comparative reasons, also the tensile index and the effect on the internal bond (in z-Direction) for handsheets prepared from a suspension comprising a commercially available product have been measured. The pigment particles used therefore are commercially available as Hydrocarb HO-ME from Omya International AG, Oftringen, Switzerland. The product is in the form of a suspension of a natural CaCO.sub.3 and has a solids content of 66 wt.-%, based on the total weight of the suspension. The particulate material in the suspension, measured on a Sedigraph 5120, has a weight median particle diameter d.sub.50 value of 0.8 m, a d.sub.90 of less than 2 m and a d.sub.60 of less than 1 m. Furthermore, the particulate material of the Hydrocarb HO-ME has a specific surface area of 7 m.sup.2/g (measured using nitrogen and the BET method).

[0162] From FIGS. 1 and 2, it can be concluded that handsheets prepared from a suspension made in accordance with the inventive process achieve a tensile index of about 22 Nm/g and internal bond (in z-Direction) of at least 475 kPa. In contrast thereto, the measured tensile index of the handsheets prepared from the suspension comprising the commercially available pigment particles was 20 Nm/g, while the internal bond (in z-Direction) of below 400 kPa. Thus, it has to be assumed that the suspensions of self-binding pigments particles obtained by the inventive process impart positive effects on the mechanical strength properties of end products prepared from said suspensions.

Example 2 (Comparative Example)

[0163] The particulate material used for the preparation of the slurry was a marble of Norwegian origin.

[0164] The pigment slurry had a solids content of about 20 wt.-%, based on the total weight of the suspension. The particulate material has a weight median particle diameter d.sub.50 value of 0.8 m, a d.sub.90 of less than 2 m and a d.sub.60 of less than 1 m (all measured according to the sedimentation method). Furthermore, the particulate material of the slurry had a specific surface area of 7 m.sup.2/g (measured using nitrogen and the BET method).

[0165] The low solid suspension at 20 wt.-% was run through a Dynomill Multilab filled with 460 cm.sup.3 Verac grinding beads (0.6-1.0 mm) for 90 minutes. 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.

[0166] No significant increase in temperature was observed.

[0167] A powder of guar in an amount of 2% by weight (commercialised by Sigma Aldrich under G4129), based on the total weight of the suspension, was blended after grinding into the suspension and stirred for a short period of time. PET measurements of the guar showed an anionic charge of <150 Eq/g.

[0168] The final product was analysed by Sedigraph, solids content, PET, pH and LOI. Table 2 summarizes the measured details before the addition of guar and after the addition of guar.

TABLE-US-00002 TABLE 2 Comparative Example 2 Before addition of guar After addition of guar <2 m/% 96.7 97.0 <1 m/% 77.9 68.8 D.sub.50/m 0.61 0.77 solids content/wt.-% 19.4 PET/Eq/g 16.8 pH 6.41 LOI/% 2.7

[0169] From the measured details, it can be concluded that the addition of guar after grinding the aqueous pigment material suspension results in an increased weight median particle diameter d.sub.50 value of the particulate material. Furthermore, it can be concluded that the amount of particulate material in the suspension having a weight median particle diameter value of less than 1 m is decreased. Thus, it has to be assumed that the comparative example results in an undesired agglomeration of particulate material in the suspensions.

Example 3 (Inventive Example)

[0170] The particulate material used for the preparation of the slurry was a marble of Norwegian origin.

[0171] The pigment slurry had a solids content of about 20 wt.-%, based on the total weight of the suspension. The particulate material has a weight median particle diameter d.sub.50 value of 0.8 m, a d.sub.90 of less than 2 m and a d.sub.60 of less than 1 m (all measured according to the sedimentation method). Furthermore, the particulate material of the slurry had a specific surface area of 7 m.sup.2/g (measured using nitrogen and the BET method).

[0172] A powder of guar in an amount of 0.4% by weight (commercialised by Sigma Aldrich under G4129), based on the total weight of the suspension, was blended before grinding into the suspension of the particulate material and stirred with a dissolver stirrer for 60 minutes.

[0173] The low solid suspension at 20 wt.-% was run through a Dynomill Multilab filled with 460 cm.sup.3 Verac grinding beads (0.6-1.0 mm) for 90 minutes. 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. Grinding was carried out at room temperature.

[0174] No significant increase in temperature was observed.

[0175] Tablets were prepared 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 the suspension obtained in this Example and tablets prepared from suspensions comprising the commercially available products Covercarb 75-ME having a weight median particle diameter d.sub.50 value of 0.6 m, Hydrocarb 90-ME having a weight median particle diameter d.sub.50 value of 0.7 m or Omyacarb 1-AV having a weight median particle diameter d.sub.50 value of 1.7 m (all available from Omya AG, Oftringen, Switzerland) but without using a binder.

[0176] The effect of the self-binding pigment particle suspensions on the maximum force, F.sub.max, required to make the first crack into a tablet as measured in the tablet crushing test is outlined in FIG. 3.

[0177] From FIG. 3 it can be concluded that tablets prepared from a suspension made in accordance with the inventive process require a maximum force of about 1 400 N to make the first crack compared to a required maximum force of less than 350 N for tablets prepared without binder. Thus, it has to be assumed that the suspensions of self-binding pigments particles obtained by the inventive process impart positive effects on the mechanical strength properties of end products prepared from said suspensions.