A PROCESS FOR THE PREPARATION OF FLOCCULATED FILLER PARTICLES

Abstract

The present invention concerns a process for the preparation of flocculated filler particles, wherein at least two aqueous suspensions of at least one filler material and at least one flocculating additive are combined.

Claims

1. A process for the preparation of flocculated filler particles comprising the steps of a) providing at least two aqueous suspensions each comprising at least one filler material, characterized in that i) a first aqueous suspension S1 comprises at least one flocculating additive A, and ii) a second aqueous suspension S2 comprises at least one flocculating additive B which is different from flocculating additive A, and iii) the at least one filler material in the first aqueous suspension S1 and the second aqueous suspension S2 is different, and b) combining the at least two aqueous suspensions provided in step a) by bringing them together to form an aqueous suspension SM of flocculated filler particles, wherein the mass ratio of the at least one filler material in the first aqueous suspension and the second aqueous suspension S1:S2 is from 1:100 to 100:1.

2. A process according to claim 1, characterized in that step b) is carried out by bringing the first aqueous suspension S1 and the second aqueous suspension S2 simultaneously together.

3. A process according to claim 1, characterized in that the Brookfield viscosity of the first aqueous suspension S1 and/or the second aqueous suspension S2 and/or the aqueous suspension SM is less than 5 000 mPa.Math.s at 25° C., preferably less than 1 000 mPa.Math.s at 25° C., and more preferably between 10 and 200 mPa.Math.s at 25° C.

4. A process according to claim 1, characterized in that the at least one flocculating additive A is a cationic polymer selected from the group consisting of cationic starch, polyamines, polyethyleneimines, polyacrylamides, cationic amine amide, epichlorohydrin resins, polydiallyldimethylammonium chloride, cationic guar and/or mixtures thereof, preferably the at least one flocculating additive A is cationic starch.

5. A process according to claim 1, characterized in that the at least one flocculating additive B is an anionic polymer selected from the group consisting of carboxymethyl cellulose, anionic starch, anionic guar, anionic xanthan gum and/or mixtures thereof, preferably the at least one flocculating additive B is anionic carboxymethyl cellulose.

6. A process according to claim 1, characterized in that the aqueous suspension SM is sheared during and/or after process step b), preferably in at least two steps at different shear rates, and more preferably in at least two steps at different shear rates, wherein the first shear rate is lower than the second shear rate.

7. A process according to claim 1, characterized in that the at least one filler material is selected from the group consisting of a calcium carbonate-comprising material like ground calcium carbonate, precipitated calcium carbonate, modified calcium carbonate, talc, clay, dolomite, marble, titanium dioxide, kaolin, silica, alumina, mica, aluminium trihydrate, magnesium hydroxide, plastic pigments, a hybrid material comprising an organic filler and an inorganic chemical composition and mixtures thereof, preferably the at least one filler material is precipitated calcium carbonate.

8. A process according to claim 1, characterized in that the at least one filler material in the first aqueous suspension S1 and the at least one filler material in the second aqueous suspension S2 is different and the at least one filler material is selected from the group consisting of a calcium carbonate-comprising material like ground calcium carbonate, precipitated calcium carbonate, modified calcium carbonate, talc, clay, dolomite, marble, titanium dioxide, kaolin, silica, alumina, mica, aluminium trihydrate, magnesium hydroxide, plastic pigments, and mixtures thereof, preferably the filler material in the first suspension S1 is ground calcium carbonate and the filler material in the second suspension S2 is selected from precipitated calcium carbonate and/or clay.

9. A process according to claim 1, characterized in that the content of the at least one flocculating additive A in the first aqueous suspension S1 is from 0.001 to 20 wt.-%, more preferably from 0.5 to 10 wt.-%, and most preferably from 3 to 5 wt.-%, based on the total weight of the first aqueous suspension S1, and/or the content of the at least one flocculating additive B in the second aqueous suspension S2 is from 0.001 to 20 wt.-%, more preferably from 0.1 to 10 wt.-%, and most preferably from 0.2 to 0.8 wt.-%, based on the total weight of the second aqueous suspension S2.

10. A process according to claim 1, characterized in that the content of the at least one filler material in the first aqueous suspension S1 is from 1 to 85 wt.-%, preferably from 15 to 65 wt.-%, and most preferably from 10 to 40 wt.-%, based on the total weight of the first aqueous suspension S1, and the content of the at least one filler material in the second aqueous suspension S2 is from 1 to 85 wt.-%, preferably from 15 to 65 wt.-%, and most preferably from 10 to 40 wt.-%, based on the total weight of the second aqueous suspension S2.

11. A process according to claim 1, characterized in that the mass ratio of the at least one filler material in the first aqueous suspension and the second aqueous suspension S1:S2 is between 99:1 and 1:99, preferably between 95:15, and 5:85 most preferably between 70:30 and 30:70.

12. A process according to claim 1, characterized in that the solids content of the aqueous suspension SM obtained after process step b) is from 1 to 75 wt.-%, preferably from 2 to 60 wt.-%, and most preferably from 5 to 35 wt.-%, based on the total weight of the aqueous suspension SM.

13. A process for the preparation of a fleece comprising steps a) and b) of the process according to claim 1, characterized in that the aqueous suspension SM of flocculated filler particles obtained after process step b) is combined in a further step c) with synthetic and/or natural fibres, and the resulting suspension SMF is subjected to a dewatering step d) to obtain a fleece.

14. A process according to claim 13, characterized in that the dewatering step d) is carried out on a screen, preferably via a head box of a paper machine.

15. Flocculated filler particle suspension obtained by a process according to claim 1, characterized in that the filler particles have a mono-modal particle size distribution and/or a volume defined particle size polydispersity expressed as full width at half maximum height (FWHM) of less than 45 μm and/or a volume determined median particle size (d.sub.50) in the range from 5 to 50 μm.

16. Flocculated filler particle suspension, characterized in that the filler particles have a mono-modal particle size distribution and/or a volume defined particle size polydispersity expressed as full width at half maximum height (FWHM) of less than 45 μm and/or a volume determined median particle size (d.sub.50) in the range from 5 to 50 μm.

17. Fleece, preferably a sheet of paper, obtained by a process according to claim 13.

18. A paper or paper coating comprising the flocculated filler particle suspension according to claim 15 in paper coating and/or paper wet end applications, preferably in high filler load paper wet end applications, or for cigarette paper.

Description

DESCRIPTION OF THE FIGURES

[0220] FIG. 1 shows an example of a batch process of the present invention.

[0221] FIG. 2 shows the particle size distribution of filler particles according to example 2 (sample 6).

[0222] FIG. 3 illustrates floc desaggregation under shear using a static mixer.

[0223] FIG. 4 illustrates the tensile energy of Handsheet Samples 1 to 12.

[0224] FIG. 5 shows the breaking length of Handsheet Samples 7 to 12.

[0225] FIG. 6 illustrates the internal bond of Handsheet Samples 1 to 6.

EXPERIMENTS

1. Measuring Methods

[0226] In the following the measurement methods implemented in the examples are described.

Particle Size Distribution (PSD) of the Employed Filler Materials Before Step a)

[0227] The particle size distribution of the products was measured using a Malvern Mastersizer 2000 Laser Diffraction System (Malvern Instruments Plc., Great Britain) using the Fraunhofer light scattering approximation. The method and instrument are known to the skilled person are commonly used to determine particle sizes of fillers and other particulate materials.

[0228] The measurement was carried out in an aqueous solution comprising 0.1 wt.-% Na.sub.4P.sub.2O.sub.7. The samples were dispersed using a high speed stirrer and in the presence of supersonics.

Particle Size Distribution (PSD) of the Filler Particles in Suspension S1, S2 and SM

[0229] The particle size distribution of the products was measured using a Malvern Mastersizer 2000 Laser Diffraction System (Malvern Instruments Plc., Great Britain) using the Fraunhofer light scattering approximation. The method and instrument are known to the skilled person are commonly used to determine particle sizes of fillers and other particulate materials.

[0230] The measurement was carried out in an aqueous solution comprising 0.1 wt.-% Na.sub.4P.sub.2O.sub.7. The samples were dispersed using a high speed stirrer and in the absence of supersonics.

Full Width at Half Maximum Height (FWHM)

[0231] The particle size distribution data were displayed in an xy scatter diagram and the data were arranged accordingly in x and y columns whereas the size data were put in the x-column and the frequency data was arranged in the y column. The maximum height (y.sub.m) was determined by sorting the particle size distribution curve by the frequency data points. The respective x-value was then defined as the peak position at the maximum height (x.sub.m). By dividing the maximum peak height by 2, the half maximal height was obtained (y.sub.m0.5).

[0232] The four data points that have the closest y-value compared to the half maximum height value were defined, whereas, compared to the data point of the half maximal height at the position of the maximal height P.sub.HM2 (x.sub.m/y.sub.m0.5):

[0233] P.sub.IL was the data point having the nearest lower x- and the nearest lower y-value (x.sub.1L/y.sub.1L). P.sub.1H was the data point having the nearest lower x- and the nearest higher y-value (x.sub.1H/y.sub.1H). P.sub.2L was the data point having the nearest higher x- and the nearest lower y-value (x.sub.2L/y.sub.2L). P.sub.2H was the data point having the nearest higher x- and the nearest higher y-value (x.sub.2H/y.sub.2H).

[0234] The linearly interpolated x-positions (x.sub.1I and x.sub.2I) of the data points having the y-value of the half of maximal height value (y.sub.m2) were linearly interpolated as follows:

[00003]$x_{1.Math.I}=x_{1.Math..Math.L}+\left(\frac{y_{m.Math.0.Math.\mathrm{.5}}-y_{1.Math..Math.L}}{y_{1.Math.H}-y_{1.Math.L}}\right).Math.\left(x_{1.Math.H}-x_{1.Math..Math.L}\right)$$x_{2.Math.I}=x_{2.Math..Math.H}+\left(\frac{y_{2.Math..Math.H}-y_{m.Math..Math.0.5}}{y_{2.Math.L}-y_{2.Math..Math.H}}\right).Math.\left(x_{2.Math..Math.L}-x_{2.Math..Math.H}\right).Math..Math.\mathrm{and}$$\mathrm{FHMW}=x_{2.Math..Math.I}-x_{1.Math..Math.I}.$

Filler Content

[0235] 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.

Mechanical Strength Properties

[0236] Breaking length and tensile energy have been determined according to EN ISO 1924-2 and the internal bond has been determined according to DIN 54516.

2. Materials

[0237] Filler material 1 (P1): undispersed, scalenohedral precipitated calcium carbonate (d.sub.50=4.3 μm, measured with Malvern Mastersizer 2000), commercially available from Omya AG, Switzerland.

[0238] Filler material 2 (P2): Undispersed, aragonitic precipitated calcium carbonate (d.sub.50=4 μm, measured with Malvern Mastersizer 2000), commercially available from Omya AG, Switzerland.

[0239] Filler material 3 (P3): Selected, natural ground calcium carbonate (marble), dispersed product (Hydrocarb 60 ME), commercially available from Omya AG, Switzerland. P3 is microcrystalline, has a rhombohedral particle shape of high fineness, and was used as pre-dispersed slurry having a solids content of 78 wt.-%.

[0240] Filler material 4 (P4): Clay (Intramax 50, d.sub.50=7 μm, measured by Mastersizer 2000), powder form, commercially available from Imerys International Ltd, UK.

[0241] Flocculating additive 1 (FA1): Carboxymethyl cellulose (Finnfix 10, M.sub.W=60000 g/mol, degree of substitution=0.8), commercially available from CP Kelko, USA.

[0242] Flocculating additive 2 (FA2): Starch powder (C*Bond HR 35845), commercially available from Cargill, USA.

3. Examples

Example 1—Preparation of Stock Solutions of Flocculating Additives

[0243] A stock solution of FA1 was prepared by adding FA1 into tap water at a temperature of 23° C. under stirring. Stirring was continued for 60 minutes until FA1 had completely dissolved. FA1 was added in such an amount that a solution with a FA1 content of 4 wt.-%, based on the total weight of the FA1 solution, was obtained.

[0244] A stock solution of FA2 was prepared by adding FA2 into deionized water and heating the mixture for 30 minutes at 100° C. FA2 was added in such an amount that a solution with a FA2 content of 1 wt.-%, based on the total weight of the FA2 solution, was obtained. The FA2 solution was cooled down to room temperature using a water bath and the amount of water lost by evaporation was added to readjust the solution to a FA2 content of 1 wt.-%, based on the total weight of the FA2 solution.

Example 2—Preparation of Flocculated Filler Particles (Inventive Example)

[0245] A first aqueous suspension S1 was prepared by adding the amount of the FA1 stock solution indicated in Table 1 below to a solution of a first filler material under stirring at room temperature. The amount of FA1 was chosen to obtain an overall FA1 content of 0.5 pph (parts per hundred on dry pigment) in the final aqueous suspension SM of flocculated filler particles.

[0246] A second aqueous suspension S2 was prepared by adding the amount of the FA2 stock solution indicated in Table 1 below to a solution of a second filler material under stirring at room temperature. The amount of FA2 was chosen to obtain an overall FA2 content of 4.0 pph (parts per hundred on dry pigment) in the final aqueous suspension SM of flocculated filler particles. During the addition of the FA2 solution flocculated filler particles formed.

[0247] The first aqueous suspension S1 and the second aqueous suspension S2 were combined at room temperature in a separate vessel by pouring both suspensions simultaneously into the vessel under stirring, whereby flocculated filler particles formed in the suspension. After complete addition the resulting mixture was stirred for additional 5 minutes at a shear rate of 50 s.sup.−1. Then the slurry was subjected for 15 minutes to a Megatron treatment for disaggregation of the flocs at a shear rate of 40 000 s.sup.−1 (Megatron MT 5000 with MTO 5000 Q working chamber, Kinematica AG, Luzern CH, circulation mode, 14 000 rpm).

[0248] The employed amounts and types of filler materials and the amounts of the employed flocculating additives are compiled in Table 1 below.

TABLE-US-00001 TABLE 1 Composition of prepared aqueous flocculated filler particle suspensions. Ratio first filler First material/second Amount of Amount of filler Second filler filler material FA1 in S1 FA2 in S2 Sample material material dry/dry [wt.-%] [pph.sup.a] [pph.sup.a] 1 P3 P1 90/10 0.56 40 2 P3 P1 10/90 5 4.4 3 P3 P1 50/50 1 8 4 P1 P3 50/50 1 8 5 P4 P3 50/50 1 8 6 P4 P1 50/50 1 8 7 P2 P1 10/90 5 4.4 8 P4 P3 70/30 0.7 13.3 .sup.aParts per hundred based on dry filler material.

[0249] For every sample, the volume determined median particle size (d.sub.50) of the flocculated filler particles, the particle size distribution thereof as well as the position of the main peak of the particle size distribution, main peak share i.e. the content of the area under the main peak in relation to the content of the sum of the area of all existing peaks, the main peak height, the main peak half height, and the FWHM values were measured. The results are given in Table 2 below.

TABLE-US-00002 TABLE 2 Properties of flocculated filler particles. Main peak Main d.sub.50 position Main peak Main peak peak half FWHM Sample [μm] [μm] share [%] height [%] height [%] [μm] 1 21.8 22.9 96.4 8.0 4.0 40.7 2 8.3 10.0 91.7 10.0 5.0 12.8 3 13.5 15.1 93.9 9.2 4.6 22.9 4 11.9 13.2 93.6 9.7 4.8 19.4 5 14.7 17.4 100.0 8.1 4.1 28.6 6 11.2 13.2 100.0 8.7 4.3 19.8 7 7.8 8.7 90.5 9.8 4.9 12.2 8 10.2 11.2 100 10.4 5.2 15.3

[0250] FIG. 2 shows the particle size distributions of a first aqueous suspension S1 including the filler material P1 and a second aqueous suspension S2 including the filler material P5 (see sample 6, Table 1). It can be gathered from said figure that the flocculation that occurred in the second aqueous suspension S2 during the addition of flocculating additive FA2 resulted in an increased size of the filler particles. The particle size of P5 in the first aqueous suspension S1 did not change at all after addition of the flocculating additive FA1. After combining the first and second aqueous suspensions the flocculated filler particle suspension obtained according to Example 2 (sample 6) had a FWMH of <20 μm, which means that a very homogenous particle size distribution of the first and second filler material is obtained. Thus, Example 2 (sample 6) confirms that the process of the present invention allows to manufacture flocculated fillers having a homogenous and mono-modal particle size distribution in the meaning of the present invention.

Example 3—Preparation of Flocculated Filler Particles (Comparative Example)

[0251] A first filler material and a second filler material indicated in Table 3 below were mixed by adding the first filler material to the second filler material under stirring at room temperature. The resulting mixture FM was stirred for additional 5 minutes at a shear rate of 50 s.sup.−1. Then, the amount of FA1 stock solution indicated in Table 3 below was added to this mixture under stirring at room temperature. The resulting mixture FM1 was stirred for additional 5 minutes at a shear rate of 50 s.sup.−1. Then, the amount of FA2 stock solution indicated in Table 3 below was added to this mixture under stirring at room temperature, whereby flocculated filler particles formed in suspension. After complete addition, the resulting mixture was stirred for additional 5 minutes at a shear rate of 50 s.sup.−1. Then the slurry was subjected for 15 minutes to a Megatron treatment for disaggregation of the flocs at a shear rate of 40 000 s.sup.−1 (Megatron MT 5000 with MTO 5000 Q working chamber, Kinematica AG, Luzern CH, circulation mode, 14 000 rpm).

TABLE-US-00003 TABLE 3 Composition of prepared aqueous flocculated filler particle suspensions. Amount Ratio first filler of First material/second FA1 in Amount of filler Second filler filler material FM FA2 in FM Sample material material dry/dry [wt.-%] [pph.sup.a] [pph.sup.a] 9 P3 P1 10/90 0.5 4 10 P4 P3 70/30 0.5 4 .sup.aParts per hundred based on dry filler material.

Example 4—Preparation and Testing of Handsheets

[0252] 60 g (dry) pulp were diluted in 10 dm.sup.3 tap water, and then the filler to be tested was added in an amount so as to obtain the overall filler content based on the final paper weight. The suspension was stirred for 30 minutes. Subsequently, 0.06% (based on dry weight) of a polyacrylamide (Polymin 1530, commercially available from BASF, Germany) was added as a retention aid and sheets of 80 g/m.sup.2 were formed using the Rapid-Köthen hand sheet former. Each sheet was dried using the Rapid-Köthen drier. The composition of the handsheets is given in Table 4 below.

TABLE-US-00004 TABLE 4 Composition of handsheets. Flocculated FM of Flocculated filler of Flocculated Flocculated FM of Example filler of Example filler of filler of Example 3- Example 3- Example Example Hand- 3- Sample 3- Sample 2- 2- sheet Pulp Sample 9 10 Sample 9 10 Sample 2 Sample 8 Sample [wt.-%] [wt.-%] [wt.-%] [wt.-%] [wt.-%] [wt.-%] [wt.-%] 1 (c) 80 — 20 — — — — 2 (c) 75 — 25 — — — — 3 (c) 80 — — — 20 — — 4 (c) 75 — — — 25 — — 5 (i) 80 — — — — — 20 6 (i) 75 — — — — — 25 7 (c) 80 20 — — — — — 8 (c) 75 25 — — — — — 9 (c) 80 — — 20 — — — 10 (c)  75 — — 25 — — — 11 (i)  80 — — — — 20 — 12 (i)  75 — — — — 25 — (i) = inventive; (c) = comparative.

[0253] The mechanical properties of the prepared Handsheet Samples 1 to 12 were tested, in particular the tensile energy, the breaking length and the internal bond have been determined. The results are shown in FIGS. 4, 5 and 6.

[0254] As can be gathered from FIG. 4, the flocculation of the filler particle mixture (Example 3) leads to an increased tensile energy in hand sheets (compare Handsheet Sample 3 to 1, 4 to 2, 9 to 7 and 10 to 8). However, if the flocculation is done according to the present invention (Example 2), the tensile energy increases even further (compare Handsheet Sample 5 to 3, 6 to 4, 11 to 9 and 12 to 10).

[0255] FIG. 5 reveals also that the breaking length of hand sheets containing flocculated filler mixtures (Handsheet Sample 9 and 10) is increased compared to the filler mixture alone (compare Handsheet Sample 9 to 7 and 10 to 8). An even higher increase in breaking length can be seen for flocculated filler containing hand sheets where the filler mixture was flocculated according to the present invention (compare Handsheet Sample 11 to 9 and 12 to 10).

[0256] The flocculation of particle filler mixtures also increases the internal bond of hand sheets containing such fillers, compared to hand sheets containing the filler mixtures alone as can be seen in FIG. 6 (compare Handsheet Sample 3 to 1 and 4 to 2). When the filler is flocculated according to the present invention, the internal bond of hand sheets containing such flocculated filler is increased even more (compare Handsheet Sample 5 to 3 and 6 to 4).