METHOD OF PRODUCING A FILLER

Abstract

The invention discloses a method of producing a filler composition to be used in paper or board production, said method comprising providing a suspension comprising calcium hydroxide and performing carbonation of the calcium hydroxide to form precipitated calcium carbonate (PCC). The invention is characterized in that starch and/or carboxy methyl cellulose (CMC) is added to the suspension during said carbonation of calcium hydroxide. The method of the invention enables an increased filler content in paper or paperboard without substantially increasing the dusting tendency or decreasing the strength of the paper or board.

Claims

1. A method of producing a filler to be used in paper or board production, said method comprising the steps of; providing a suspension comprising calcium hydroxide, performing carbonation of said calcium hydroxide to form precipitated calcium carbonate (PCC), wherein starch and/or carboxy methyl cellulose (CMC) is added to said suspension during said carbonation of calcium hydroxide.

2. A method of producing a filler according to claim 1, wherein the carbonation of said calcium hydroxide is performed by the addition of carbon dioxide to the suspension.

3. A method of producing a filler according to claim 2, wherein starch and/or CMC is added to the suspension at a time when between 50% and 95% of the calcium hydroxide has been reacted with carbon dioxide carbonated to form calcium carbonate.

4. A method of producing a filler according to any one of claims 2-3, wherein said starch and/or CMC is added to the suspension at a time when between 75-95% of the calcium hydroxide has been reacted with carbon dioxide to form calcium carbonate.

5. A method according to claim 1, wherein the starch is uncooked.

6. A method according to claim 1, wherein the starch is swollen starch.

7. A method according to claim 1, wherein the reaction temperature during the carbonation is between 50-100° C.

8. Filler to be used in paper or paperboard production, which filler is produced by the method according to claim 1.

9. A method of producing paper or paperboard comprising the steps of; providing a fiber-containing furnish; adding the filler produced according to claim 1 to said furnish; forming and dewatering the fiber containing furnish.

10. A method of producing paper or paperboard comprising the steps of; providing a fiber-containing furnish; forming and dewatering the fiber containing furnish to form a web, adding the filler produced according to claim 1 to the surface of said web.

11. Paper or paperboard comprising the filler produced by the method of claim 1.

12. The paper according to claim 11, wherein the paper is fine paper and the total filler content of the paper is from 25-35% by weight, based on dry paper.

13. The paper according to claim 11, wherein the paper is newsprint paper and the total filler content of the paper is from 10-15% by weight, based on dry paper.

14. The paper according to claim 11, wherein the paper is supercalendered (SC) paper and the total filler content of the paper is at least 39% by weight, preferably between 39-45% by weight, based on dry paper.

Description

DESCRIPTION OF THE FIGURES

[0102] FIG. 1 shows the SEM image of PCC particles (PCC 1) obtained according to Example 1 (comparative example), where 1 wt.-% of starch has been added to the milk of lime before carbonation.

[0103] FIG. 2 shows the SEM image of PCC particles (PCC 2) obtained according to Example 1 (comparative example), where 5 wt.-% of starch has been added to the milk of lime before carbonation.

[0104] FIG. 3 shows the SEM image of PCC particles (PCC 3) obtained according to Example 2 (comparative example), where no starch has been added to the milk of lime.

[0105] FIG. 4 shows the SEM image of PCC particles (PCC 8) obtained according to Example 3 (inventive example), where 2 wt.-% of starch were added to the milk of lime after 75% of the carbonation time.

[0106] FIG. 5 shows the conductivity, pH and temperature logging of PCC 8 obtained according to Example 3 (inventive example).

[0107] FIG. 6 shows different parameters of the hand sheets prepared in the hand sheet study.

EXAMPLES

1. Measurement Methods

[0108] In the following, measurement methods implemented in the examples are described.

Particle Size Distribution of Precipitated Calcium Carbonate (PCC)

[0109] The particle size distribution of the prepared PCC particles was measured using a Malvern Mastersizer 3000, from the company Malvern. The method and the instrument are known to the skilled person and are commonly used to determine grain size of fillers and pigments.

Solids Content of an Aqueous Suspension

[0110] The suspension solids content (also known as “dry weight”) was determined using a Moisture Analyser MJ33 from the company Mettler-Toledo, Switzerland, with the following settings: drying temperature of 160° C., automatic switch off if the mass does not change more than 1 mg over a period of 30 sec, standard drying of 5 to 20 g of suspension.

Specific Surface Area (SSA)

[0111] The 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 is filtered within a Buchner funnel, rinsed with deionised water and dried overnight at 90 to 100° C. in an oven. Subsequently the dry cake is ground thoroughly in a mortar and the resulting powder placed in a moisture balance at 130° C. until a constant weight is reached.

X-Ray Diffraction

[0112] The purity of the PCC samples was analysed with a D8 Advance powder diffractometer (Bruker Corporation, USA) obeying Bragg's law. This diffractometer consisted of a 2.2 kW X-ray tube (Cu), a sample holder, a θ-θ goniometer, and a VÅNTEC-1 detector. Nickel-filtered Cu K.sub.α radiation was employed in all experiments (λK.sub.α-Cu=1.5406 Å). The profiles were chart recorded automatically using a scan speed of 0.7° per minute in (XRD GV_7600). The measurement was carried out at angles from 5 to 70°.

[0113] The resulting powder diffraction pattern was classified by mineral content using the DIFFRAC.sup.suite software packages EVA and SEARCH, based on reference patterns of the ICDD PDF 2 database (XRD LTM_7603). Quantitative analysis of the diffraction data, i.e. the determination of amounts of different phases in a multi-phase sample, has been performed using the DIFFRAC.sup.suite software package TOPAS (XRD LTM_7604). This involved modelling the full diffraction pattern (Rietveld approach) such that the calculated pattern(s) duplicated the experimental one.

Pigment Brightness and Paper Opacity

[0114] Pigment brightness and paper opacity were measured using an ELREPHO 3000 from the company Datacolor according to ISO 2469:1994 (DIN 53145-2:2000 and DIN 53146:2000).

Whiteness (R457) Index Measurement

[0115] Whiteness index was determined according to norm TAPPI T452/ISO 247. Glossiness was determined according to DIN 54 502/TAPPI 75.

Light Scattering

[0116] Light scattering was measure according to ISO 9416:2009.

Filler Content

[0117] 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 Properties of Handsheets

[0118] The mechanical strength properties of the produced paper samples were characterised after drying of the paper samples by

the tensile strength according to ISO 1924-2,
the tensile energy absorption according to ISO 1924-2
the tensile energy absorption index according to ISO 1924-2,
the tensile index according to ISO 1924-2.

2. Materials

[0119] Calcium oxide, CaO, Réty Lhoist

Starch

[0120] Cationic: potato starch (Degree of substitution: 0.045), Roquette Actim, France

Fibers: Eucalyptus 30° SR

[0121] Retention aid: Nalco 74628 (in all sheets 0.06%)
Tap water

Slaking of Calcium Oxide

[0122] milk of lime preparation (suspension of calcium hydroxide) via standard lab slaking of CaO Réty [0123] standard slaking with 5 liter tap water (40° C.) and 1000 g CaO [0124] Slaking for 25 min. [0125] Then addition of 4 liter tab water. Total slaking time 30 min. [0126] Sieving over a 100 microns sieve, to obtain the milk of lime (or suspension of calcium hydroxide) that was used in the following examples.

Carbonation

[0127] standard lab carbonation: 60° C. starting temp. 15 l/min 20% CO.sub.2, 750 rpm [0128] pH, conductivity and temperature logging

PCC Laboratory Reactor

[0129] A stainless steel reactor with a total volume of 10 liter, filled with an amount of 8 liter calcium hydroxide in tap water was used. The solids content of the aqueous calcium hydroxide slurry was about 14% by weight. The initial temperature of the aqueous calcium hydroxide slurry was about 61° C. The content of the reaction vessel was stirred at a 750 rpm. Gas containing carbon dioxide (20 vol.-%) at a rate of 15 l/min and air at a rate of 60 l/min was injected into the reaction vessel until a pH of approximately 7 was reached. Conductivity, pH and temperature were continuously logged (FIG. 5). The resultant precipitated calcium carbonate was a scalenohedral precipitated calcium carbonate (S-PCC).

Suspension Conductivity Measurement

[0130] The conductivity of the suspension was measured directly in the reaction vessel during the reaction using an Endress+Hauser logging software, Memobase Plus, and an Indumax CLS50D conductivity probe.

Suspension pH Measurement

[0131] The pH of the suspension was measured directly in the reaction vessel during the reaction using an Endress+Hauser logging software, Memobase Plus, and a CPS96D pH electrode.

Weight Solids (% by Weight) of a Material in Suspension

[0132] The weight solids (also called solids content of a material) was determined by dividing the weight of the solid material by the total weight of the aqueous suspension.

Example 1 (Comparative)

[0133] Cationic starch was added as a pre-addition to the milk of lime (Ca(OH).sub.2), before the carbonation was started.

[0134] PCC 1. 1 wt-% (calculated on the estimated dry mass of the PCC when the reaction is done, i.e. 17% solids content) cationic starch was added as powder to the milk of lime (Ca(OH).sub.2). The total carbonation time was 110 minutes. The gas feed was 15 l/min CO.sub.2 mixed with 60 l/min air, and the reactor volume 10 liter, filled with 8 liter Ca(OH).sub.2 slurry at a solids content of 14%. The reactor temperature was about 65° C. FIG. 1, SEM image

[0135] PCC 2. 5 wt-% (calculated on the estimated dry mass of the PCC when the reaction is done, i.e. 17% solids content) cationic starch was added as powder to the milk of lime (Ca(OH).sub.2). The total carbonation time was 110 minutes. The gas feed was 15 l/min CO.sub.2 mixed with 60 l/min air, and the reactor volume 10 liter, filled with 8 liter Ca(OH).sub.2 slurry at a solids content of 14%. The reactor temperature was about 65° C. FIG. 2, SEM image.

[0136] As can be seen in FIGS. 1 and 2, the resulted PCC shows low brightness, changed particle shape and sieving problems due to high viscosity. (Compare SEM, FIGS. 1 and 2 to the reference sample without any starch addition in FIG. 3.)

Example 2 (Comparative)

[0137] 2 wt-% cationic starch was added as a post addition to the readymade PCC.

[0138] The total carbonation time was 110 minutes. The gas feed was 15 l/min CO.sub.2 mixed with 60 l/min air, and the reactor volume 10 liter, filled with 8 liter CaOH slurry at a solids content of 14%. The reactor temperature was about 65° C. FIG. 3, SEM image. The resulting PCC was a S-PCC with solids content of 17%.

[0139] PCC 3. PCC without addition of any starch. (This PCC has been used in hand sheet trials Nos. 1 and 2).

[0140] PCC 4. 2 wt-% (calculated on the dry mass of the PCC, 17% solids content) cationic starch was added in powder form and stirred with the 65° C. warm PCC for 30 minutes. (This PCC has been used in hand sheet trials Nos. 7 and 8).

[0141] PCC 5. 2 wt-% (calculated on the dry mass of the PCC, 17% solids content) cationic starch was added as preheated in water to 65° C. (2-wt % solution) and stirred with the 65° C. warm PCC for 30 minutes. (This PCC has been used in hand sheet trials Nos. 9 and 10).

[0142] PCC 6. 2 wt-% (calculated on the dry mass of the PCC, 17% solids content) cationic starch was added as cooked in water (open boiling) (2-wt % solution) and stirred with the 65° C. warm PCC for 30 minutes. (This PCC has been used in hand sheet trial No. 11).

Example 3 (Inventive)

[0143] Cationic starch was added into the PCC reactor during carbonation in powder form. The total carbonation time was 110 minutes. The gas feed was 15 l/min CO.sub.2 mixed with 60 l/min air, and the reactor volume 10 liter, filled with 8 liter Ca(OH).sub.2 slurry at a solids content of 14%. The reactor temperature was about 65° C.

[0144] PCC 7. 2 wt-% (calculated on the estimated dry mass of the PCC when the reaction is done, i.e. 17% solids content) cationic starch was added into the PCC reactor during carbonation in powder form, at 50% of the reaction time, i.e. after 55 minutes. (This PCC has been used in hand sheet trials Nos. 3 and 4).

[0145] PCC 8. 2 wt-% (calculated on the estimated dry mass of the PCC when the reaction is done, i.e. 17% solids content) cationic starch was added into the PCC reactor during carbonation in powder form, at 75% of the reaction time, i.e. after 82 minutes. (This PCC has been used in hand sheet trials Nos. 5 and 6). FIG. 4, SEM image. FIG. 5 shows the pH, conductivity and temperature logging for the manufacturing.

[0146] PCC 9. 3 wt-% (calculated on the estimated dry mass of the PCC when the reaction is done, i.e. 17% solids content) cationic starch was added into the PCC reactor during carbonation in powder form, at 75% of the reaction time, i.e. after 82 minutes.

Hand Sheet Study

[0147] Grammage: 80 g/m.sup.2
Total amount cationic starch in all trial sheets: 10 kg/ton, time and form of addition varied
Target filler (PCC) load (ash content): 25% and 30%. Exact achieved filler load (ash content) measured from each analyzed sheet and listed in FIG. 6.

Fibers: Eucalyptus 30° SR

[0148] Retention aid: Nalco 74628 (in all sheets 0.06%)
Tap water

Comparative Samples (Trials Nos. 1 and 2)

[0149] No addition of starch added in the production of the PCC. 10 kg/ton starch was added in the mixing chest.

1. Eucalyptus fibers, target 25 wt-% PCC 3 load+10 kg/ton cationic starch+0.06% retention aid
2. Eucalyptus fibers, target 30 wt-% PCC 3 load+10 kg/ton cationic starch+0.06% retention aid

Inventive Samples (Trials Nos. 3 to 9)

[0150] 5 kg/ton starch addition as included in the PCC (equals 2 wt-% calculated dry/dry on the PCC). Starch added during carbonation to the PCC. 5 kg/ton starch addition in the mixing chest.

3. Eucalyptus fibers, target 25 wt-% PCC 7 load+5 kg/ton cationic starch+0.06% retention aid
4. Eucalyptus fibers, target 30 wt-% PCC 7 load+5 kg/ton cationic starch+0.06% retention aid
5. Eucalyptus fibers, target 25 wt-% PCC 8 load+5 kg/ton cationic starch+0.06% retention aid
6. Eucalyptus fibers, target 30 wt-% PCC 8 load+5 kg/ton cationic starch+0.06% retention aid

Comparative Samples (Trials Nos. 7 to 11)

[0151] 5 kg/ton starch addition as included in the PCC (equals 2 wt-% calculated dry/dry on the PCC). Starch added as post addition to the PCC. 5 kg/ton starch addition in the mixing chest.

7. Eucalyptus fibers, target 25 wt-% PCC 4 load+5 kg/ton cationic starch+0.06% retention aid
8. Eucalyptus fibers, target 30 wt-% PCC 4 load+5 kg/ton cationic starch+0.06% retention aid
9. Eucalyptus fibers, target 25 wt-% PCC 5 load+5 kg/ton cationic starch+0.06% retention aid
10. Eucalyptus fibers, target 30 wt-% PCC 5 load+5 kg/ton cationic starch+0.06% retention aid
11. Eucalyptus fibers, target 30 wt-% PCC 6 load+5 kg/ton cationic starch+0.06% retention aid

[0152] As can be seen from FIG. 6, the inventive samples (Trial No. 3-6) shows higher tensile strengths compared to the comparative samples at similar filler loads. The tensile strength and the opacity of a sheet with a filler load of about 30% according to the invention are comparable with the strength and opacity of a sheet with a filler load of about 25% according to the prior art (cf. e.g. Trial No. 6 and Trial No. 1). Thus, the results show that the inventive concept makes it possible to use higher filler loads and still achieve acceptable strength and opacity levels.