WO2017207635A1

WO2017207635A1 - Paper containing scalenohedral precipitated calcium carbonate (s-pcc)

Info

Publication number: WO2017207635A1
Application number: PCT/EP2017/063168
Authority: WO
Inventors: Heinrich Follmann; Michael Boschert; René BAUCH; Anja HOFMANN
Original assignee: Hf Biotec Berlin Gmbh
Priority date: 2016-05-31
Filing date: 2017-05-31
Publication date: 2017-12-07
Also published as: EP3252229A1; CN109477307A; SI3252229T1; EP3464719A1; EP3252229B1; US20190093289A1; KR20190029537A

Abstract

The invention relates to paper containing scalenohedral precipitated calcium carbonate (s-pcc) with a determined specification. The invention also relates to the use of a s-PCC with a given specification as a filler for paper.

Description

Skalemoedrise it precipitated calcium carbonate (s-PCC) skinning paper

The invention relates to paper containing scalenohedral precipitated calcium carbonate (s-PCC) of a particular specification. Furthermore, the invention relates to the use of a s-PCC with a specific specification as a filler for paper.

Technological background

Paper is a sheet material that consists essentially of fibers of plant origin and is formed by dewatering a fiber suspension on a wire. The resulting nonwoven fabric is compacted and dried.

A major component of paper is cellulose fibers ranging in length from a few millimeters to a few centimeters. The cellulose is initially largely uncovered, so separated from hemicelluloses, resins and other plant components. The pulp thus obtained is mixed with water and defibered. The aqueous suspension is placed as a thin layer on a fine sieve and mechanically compacted during dripping by movement of the sieve. When the paper has dried, the surface is impregnated (so-called sizing).

The starting materials necessary for the paper can be divided into four groups.

a) Fibers (groundwood, semi-pulp, pulp, waste paper, other fibers)

b) sizing and impregnation (animal glues, resins, paraffins, waxes)

c) Fillers (kaolin, talc, gypsum, barium sulfate, chalk, titanium white, etc.)

d) auxiliaries (dyes, defoamers, dispersants, retention aids, flocculants, wetting agents)

The present invention relates to the use of PCC as a filler. PCC is a synthetic industrial mineral made from quicklime or its raw material, limestone. Unlike other industrial materials, PCC is a synthetic product that can be shaped and modified to give different properties to the paper being made. The physical form of the PCC can change significantly in the reactor. Variable factors include the reaction temperature, the rate at which carbon dioxide gas is added, and the rate of movement. These variables affect PCC grain size and grain shape, surface area and surface chemistry, and grain size distribution. Though As a result of the PCC's ability to control the properties of the paper (greater brightness, opacity, and thickness than GCC ground calcium carbonate), many advantages, however, conventional PCC can only be used to a limited extent as a filler because it reduces fiber strength.

In practice, conventionally produced s-PCC with a mean particle size D4.3 of 1, 5 μηι to about 5 μηι used inter alia as a filler in copy paper, but only up to a degree of filling of about 30%, otherwise the tear strength is low. It would thus be desirable to be able to increase the degree of s-PCC filling without deteriorating the paper properties.

Summary of the invention

With the provision of the paper according to the invention, the described disadvantages can be overcome. The paper contains modified skaleonehyde precipitated calcium carbonate (s-PCC). The s-PCC has a particle size distribution in which times 100> 59, preferably> 60, particularly preferably> 62, very particularly preferably>

65 and the average grain size D4.3 of the s-PCC in the range of 1, 5 to 5, 0 μηι, particularly preferably 2.0 to 4.0 μηι, in particular 2.9 to 3.1 μηι.

The invention is based on the knowledge gained experimentally that with increasing D4,3 value of the s-PCC and the width of the particle size distribution increases, which adversely affects some paper properties, such as the tensile strength. It could be shown that a narrow particle size distribution is advantageous.

The paper according to the invention is preferably a graphic paper. Graphic papers are papers for printing, writing and copying. With the growing demand for graphic papers, process technology designed specifically for these grades is of particular importance.

The paper preferably has a basis weight of 20 to 90 g / m ² , more preferably 40 to 80 g / m ² , in particular of 50 to 60 g / m ² . The paper may therefore in particular be tissue paper (about 20 to 30 g / m ² ), thin paper (about 40 g / m ² ), newsprint or LWC paper (about 50 g / m ² ), stationery or rippling paper (approx 60 g / m ² ), typewriter paper (about 70 g / m ² ) or copy paper (about 80 g / m ² ). It is also possible, so-called heavy paper, eg cardboard papers with a basis weight of 200 to 500 g / m ² , to be filled advantageously with this invention s-PCC.

The degree of filling of s-PCC of the specified specification in the paper can be increased and the proportion of substantially more expensive pulp can be correspondingly reduced, without the essential paper properties deteriorating. On the contrary, it has been shown that the addition of the s-PCC used according to the invention improves important paper properties such as opacity, tensile strength and specific volume.

Preferably, the degree of filling of s-PCC in the paper is in the range of 10% to 30% ash. In this case, the total amount of inorganic material contained in a sample is called "ash." When organic matter is burned, essentially only C0 ₂ and water vapor, possibly S0 ₂ or NH _{3, are formed and} these gases escape, leaving no residue the inorganic constituents salts or oxides, which generally do not even melt at normal flame temperatures, so that the incineration residues, the ashes, contain all inorganic constituents of the sample Incineration means controlled burning by heating to 575 ± 25 ° C for as long as possible The burning must be draft-free and must not be too violent so that fine fly ash can not be carried away The "ash" of uncoated papers consists mainly of filler, with coated papers can still be found in it The amount of ash is expressed as a percentage of the total Paper pulp (dried) indicated.

A further aspect of the invention is therefore the use of skaleonedrische precipitated calcium carbonate (s-PCC) with a particle size distribution, in which for

D 90 times 100 ratio applies: D 90 times 100> 59, and with a mean grain size D 4,> 3 im

Range from 1, 5 to 5.0 um as a filler for paper. The ^ - ^ times 100 ratio (D4.3 / D90 x 100) is preferably> 60, particularly preferably> 62, very particularly preferably> 65. The mean grain size D4.3 of the s-PCC is preferably in the range of 2, 0 to 4.0 μηι, in particular 2.9 to 3, 1 μηι.

There was therefore a need for s-PCC having an average particle size of D4,3 ranging from 1, 5 to 5.0 URM at a £> 90 times ratio of 100 g ^a g ^a horses or facilitated 59th However, there has been no industry process that provides such material. However, this problem has also been solved according to the invention. According to the prior art, a large number of processes are known in which the PCC is formed in aqueous suspension of Ca (OH) ₂ (the so-called lime milk) with entry of C0 ₂ . The C0 ₂ can be entered as a gas in the milk of lime in liquid form or via a suitable ventilation system. With the aid of additives or seed crystals and with appropriate process control, the desired PCC morphologies can be generated. On a large scale it is usual to work in batch mode.

Modifications of the PCC are well described in the literature. The term "modification" as used herein refers to the family of industrially produced crystals of defined morphology, of which particularly important are aragonites and calcites, and much less of the vaterites and icites, and special transitional forms such as basic calcium carbonates or amorphous carbonates which are also isolable The person skilled in the industry generally knows the sometimes quite complex boundary conditions of his PCC plant, which can influence the modification, from numerous experiments and failed attempts.Firstly controlling parameters, such as the starting temperature at the beginning of a typical batch cycle in connection with the concentration of the milk of lime submitted and the C0 ₂ concentration are determined in advance. influences from the raw material be eliminated in long series and optionally made controllable by additives of various sorts. succeeds Also, the degree of agglomeration of the PCC crystals by adjusting the reaction conditions.

However, so far there is no systematic approach to the production of PCC with a defined grain size and defined (narrow) particle size distribution. This may be due to the complex interaction of a large number of parameters. These include, for example, fumigation parameters in conjunction with the C0 ₂ concentration, the geodetic effective height of a reactor and the dissipative energy input. Furthermore, in a typical batch reaction, which is industrially dominant, at each moment of the reaction, important process parameters change in each case in a different characteristic, such as the pH of the suspension to be fumigated, the conductivity, the temperature, the ratio of free Caicium Ions to bicarbonate ions, the density of the suspension and the viscosity of the suspension. In addition, the dynamics of these changes are not consistently steady, but some of the parameters change only towards the end of the batch cycle, but then dramatically, such as pH and conductivity; however, other parameters show a quasi linear change characteristic, such as the temperature increase, the change in density and viscosity. In addition, the fact that apparently two main phases occur during the carboxylation, a phase of preferential nucleation right at the beginning of the reaction followed by a phase of the preferentially preferred germ growth. As described in the recent literature, the nucleation is not straightforward, but over a whole series of intermediates of different morphology.

For these reasons, the knowledge about which of the numerous phenomena for the characteristic expression of the mean grain size (D4,3 value) as well as the width of the grain size distribution are decisive, influenceable and adjustable, at most very limited. Accordingly, there are hardly any indications as to which measures the specialist has to take on an existing PCC system in order to arrive at a product with a defined particle size as well as a defined particle size distribution. So far, the goal could at best be reached erratic.

US Pat. No. 6,251,356 B1 proposes influencing the mean grain size in a pressure reactor via the height of the established working pressure. The particle size ratio should be narrower compared to conventional process control. The process itself is technically very complicated.

EP 1 222 146 B1 relates to a two-stage continuous process. In the first stage, a certain concentration of germs is generated. For this purpose, the volume flow rate of the lime milk is changed at a constant gas throughput. In addition, influence on the desired grain size is assumed by the presentation of a fine milk of lime whose reactivity is increased.

According to Gernot Krammer et al. (Part. Part. Syst. Charact. 19 (2002) 348-353), an increasing C0 ₂ concentration leads to a reduction in the average particle size. An opposite influence of the C0 ₂ concentration on the mean grain size is described by Bo Feng et al., Materials Science and Engineering A 445-446 (2007) 170-179. Effect of various factors on the particle size of calcium carbonate formed in a precipitation process ".

The concentration of milk of lime is another parameter that influences the mean grain size (Kralj et Brecivic from Croatica Chimica Acta, 80 (3-4) 467-484 (2007) "On Calcium Carbonates from fundamental research to application") The lime milk usually lead to coarser particles, lower solids content should lead to finer particles. It is also known that, with continuous operation of a PCC plant, aragonitic crystals gradually become larger.

Pust (from the dissertation "The production of precipitated calcium carbonate - PCC" RWTH Aachen, 1992) describes the influence of the quenching parameters in the production of quicklime on the size of the crystals later formed during the carboxylation.

EP 1 712 597 A1 describes the influence of the addition of various additives, such as Zn salts, Mg salts, and cationic and anionic dispersants on the particle size distribution.

Thus, there has been a continuing need for systematic approaches that allow the precipitation of precipitated calcium carbonate of a defined grain size and grain size distribution with a given PCC plant. The described limitations of the prior art could be remedied by introducing a newly developed process for the production of s-PCC by introducing carbon dioxide into milk of lime in a PCC plant. The method comprises the following steps:

a) Detecting all parameters of the PCC system, which provide a significant contribution to the specific molar energy input during operation of the PCC system, wherein the specific molar energy input corresponds to the energy input of the entire system, which is required to one mole C0 ₂ from the beginning of the Enter reaction to a degree of conversion of 90% of the batchwise carboxylation reaction;

b) determining the mean grain size D4.3 as a function of the specific molar energy input; c) 's of ^a Setting a time

D 90 100 ratio depending on at least one of the following parameters: C0 ₂ concentration during the reaction, temperature of the milk of lime, level in the reactor of the PCC plant, and speed of a gassing stirrer of the PCC plant; and

d) introducing carbon dioxide into the milk of lime according to the specifications specified in steps b) and c).

There are different ways to describe the width or narrowness of the grain size distribution. In the present case, the characterization is carried out by the ratio of D 90 times 100, which is frequently used in the range of particle goods, such as PCC. D90 means that 90% of the Particle volume weighted are less than the assigned value.

The average particle size D4.3 is the arithmetic mean of a distribution over all particles. A very narrow particle size distribution is given, for example, when the D4.3 at

3, 1 and the associated D90 at 5.0 μηι lies. For the times 100 ratio results then the numerical value 62. The information applies to the formation of the so-called primary particles of the PCC process. Agglomerations at a later date are not taken into account.

The sizing can be done with a laser diffraction particle size meter. All values refer to a dispersed product in order to exclude agglomeration as far as possible. In the present case, all measurements were carried out either with a particle size analyzer from Malvern (device designation Malvern 3000) or from Quantachrome (device designation Cilas 1064 L). Both measuring instruments are very common in the paper industry and always delivered very similar values.

Among other things, the newly developed method is based on the insight that the specific molar energy input is the decisive controlling parameter for the grain size. This value describes the sum of the total system specific energy input required to introduce one mole of CO ₂ in the major part of the reaction, from about zero to 90% of the batchwise carboxylation reaction. The energy input is independent of the source from which it originates. In a conventional PCC system in particular contributions from the applied C0 ₂ - concentration of the gas, the volumetric specific gas flow rate, the level of the reactor, the number of revolutions of the frequency-controlled gas turbine or the stirrer, the power output of an upstream blower, if one is present the determination of the specific energy input.

In step a) of the method, the individual influencing variables of a PCC system are therefore recorded, which provide a significant contribution to the specific molar energy input. It has been shown that the cumulative contribution of all these factors to the specific molar energy input is directly related to the particle size to be achieved.

In step b), therefore, this relationship for the relevant PCC plant determined. Basically, it was found that the grain size decreases with increasing specific molar energy input. Preferably, in step b), a linear relationship between the mean grain size D4.3 and the specific molar energy input of the overall system is determined. For concrete determination of the relationship between the specific molar energy input and the particle size at a PCC system, in practice, for example, a number of test settings are run with a given specific molar energy input and then the particle sizes are determined. Both values are plotted against each other and a corresponding linear function is determined by a graphical evaluation method. For a desired particle size, the necessary energy input can now be determined with the help of the function. Subsequently, the influencing variables are adjusted accordingly in order to represent this energy input.

It was therefore surprisingly found that only the specific energy input of the substance introduction system is the decisive parameter for the grain size of the resulting crystals. It can be set from any combination of the gassing parameters with the applied C0 ₂ concentration so that the target value for the desired grain size is formed. It is thus possible for the first time to use the basic knowledge of the characteristic values of the gassing device to make targeted specifications for the particle size of the PCC crystals. The ratio times 100 is conventionally produced particle sizes in the range

D 90

of about 2.8 μηι and greater than 55 and is usually numerically usually much smaller. This is due to spinodal demixing processes during carboxylation, which result in constantly smaller zones with higher or lower supersaturation than average. As a result, on the one hand, new smaller germs form, on the other hand, already existing crystals grow on to larger crystals.

It was only in the context of the present invention that it was experimentally determined which influencing factors from the wealth of almost infinite possibilities for the particle size distribution are actually significant and must be taken into account when determining the respective desired value for the times 100 ratio. Determines ^a D 90 ^a

were the following parameters: C0 ₂ concentration during the reaction, temperature of the milk of lime, level in the reactor of the PCC plant, and speed of a gassing stirrer PCC plant (step c) of the process). The four measures can be applied individually or in any combination and cause a reduction in the particle size distribution, if obvious consideration.

In particular, it is preferred if in step c) at the beginning of the reaction, the C0 ₂ concentration corresponds to 0.5 to 0.8-fold, in particular 0.6 to 0.7-fold, the C0 ₂ concentration at the end of the reaction, and the C0 ₂ concentration is increased continuously or stepwise. So if, as almost always the case, a fixed value for the C0 ₂ concentration of the source is known (eg at power plants between 10 to 1 1%, in kilns for the production of quick lime about 22 to 26%, in biogas plants between about 35 and 55%, or about 98% in the case of synthetic gases), the starting concentration is reduced to a value which is smaller by 20 to 50%, in particular 30 to 40%, than the C0 ₂ concentration of the source and continuously or stepwise until raised to the maximum possible concentration at the end of the reaction. This can be done in the simplest way by dilution with air. It was surprisingly found that the measure increases the ratio of the value for D 90 times 100,> in particular to 59 or more.

It is further preferred if, in step c), a temperature is predetermined at the beginning of the reaction in which the PCC is obtained in the particular desired morphology, and this temperature is kept constant over the reaction or until the end of the reaction continuously or stepwise up to 15 ° C, in particular 10 ° C is lowered. Accordingly, the starting temperature is the temperature at which the desired morphology can be decisively determined. In the case of s-PCC, the starting temperature is in the range of 25 to 45 ° C. Conventionally, although a certain starting temperature is also given, but the temperature is not controlled below and due to the exothermic reaction of the temperature rise is the result. In contrast, according to the invention, the temperature is kept constant or lowered gradually or continuously by up to 15 ° C.

It has surprisingly been found that this measure increases the value for times 100 a D 90, in particular to 59 or more.

Furthermore, it is preferred if in step c) at the beginning of the reaction, a level of lime is 50% to 80%, in particular 50% to 70% of the working volume of the reactor and after a nucleation phase continuously or stepwise lime milk is supplied to the end of the reaction. The reactor is therefore filled at the beginning of the reaction only to 50% to 80% of its working volume with lime of the required strength. At the earliest after the end of the so-called nucleation phase, in practice for all morphologies, this is the case after about 20 minutes, lime milk is added gradually or continuously and distributed as evenly as possible over the entire T90 running time until the reactor has reached its nominal working volume. After the T90 time, ie the relevant reaction time, in which 90% of the total sales are completed, is no longer refilled. It was surprisingly found that the measure increases the value for D 90 times 100, in particular to 59 or more.

Finally, it is preferred if in step c) at the beginning of the reaction, the speed of the gassing stirrer corresponds to 0.5 to 0.9 times, in particular 0.8 to 0.9 times the speed at the end of the reaction and the speed continuously or stepwise to the final value is increased when more than 90% conversion of the reaction is achieved. The reactor is thus started with the predicted speed, which was chosen so that even an increase potential of about 10 to 50% is possible. After the end of the nucleation phase, but at the latest after the expiry of the T 90 time, the speed of the gassing stirrer is continuously or incrementally increased by the missing 10 to 50% until the end of the reaction. It was surprisingly found that the measure increases the value for D 90 times 100, in particular to 59 or more. The s-PCC obtainable by the process has a particular combination of particle size D4.3 and the ratio of 100 times. The properties can be compared with previously known PCC

D 90 ^a

Do not reach procedure.

Further preferred embodiments of the invention can be taken from the claims and the following description.

Brief description of the figures

The invention will be explained in more detail with reference to embodiments and associated drawings. The figures show:

Fig. 1 is a schematic representation of a PCC system; Figure 2 shows the results of batch carboxylations in the pilot reactor for s-PCC, with D4.3 plotted as a function of specific energy input; Figure 3 shows the results of batch carboxylations in the pilot plant reactor for s-PCC, with D4.3 plotted as a function of specific energy input;

4 shows the particle size distribution of an s-PCC sample according to the invention and two comparative samples; and

Figures 5-10 show comparative results for paper samples having different degrees of filling of s-PCC and conventional s-PCC and GCC, respectively, for specific volume, stiffness, opacity, whiteness, tear length and thickness of the paper samples.

Detailed description of the invention

1 illustrates - highly schematically - the basic structure of a PCC plant 10, which can be used for carrying out a PCC process: The process provides S-PCC with a Korng ^a rößenverteilung ^a, 'when the value times

D 90 100 a numerical value of> 59 results in a mean particle size D4,3 in the range of 1, 5 to 5.0 μηι. The PCC plant 10 comprises a batch reactor 20 in which an aqueous suspension of Ca (OH) ₂ (so-called lime milk) is initially introduced and in which C- _{2 is} subsequently added to form s-PCC. The milk of lime is supplied via a template 30. The C0 ₂ is introduced here as a gas into the lime milk via a suitable ventilation system 40, which in this example comprises a gassing stirrer 42. Another agitator 50 may be provided. The reactor 20 is tempered. The PCC system 10 includes here not shown sensory means for monitoring the level of the reactor 20 and detecting the temperature of the milk of lime. Furthermore, sensory means may be provided, which can be concluded directly or indirectly to a C0 ₂ concentration in the milk of lime.

Among other things, the method is based on the knowledge that the specific molar energy input is the decisive controlling parameter for the grain size. Accordingly, all the parameters of the PCC system 10, which provide a significant contribution to the specific molar energy input during operation thereof, are to be recorded. The specific molar energy input corresponds to the energy input of the total system, which is required to enter one mole of C0 ₂ from the beginning of the reaction to a degree of conversion of 90% of the batchwise carboxylation reaction. As is well known, the formation of calcium carbonate from calcium hydroxide and C0 ₂ in the main part of the reaction is approximately linear. From a value of about 90 to 95% of the total reaction, the pH value and the conductivity value drop sharply and the C0 ₂ yield also decreases sharply. The relevant reaction time is therefore the average value of C0 ₂ yield in the first 90% of the total reaction time.

Common for the calculation of the specific aeration rate is the so-called vvm value which means the following: Volume unit of gas per unit volume of reactor contents per unit time. In industrial practice and with a typical reactor volume of 10 m ³ , for example, gassing rates of about 0.25 vvm to 5 vm are common, which means that the reactor with possible gassing rates of 150 Nm ³ per h up to about 3000 Nm ³ per h is fumigated. Smaller values are considered uneconomical, larger values are technically not possible because of the increasing risk of the gas in the reactor being blown through. Breakthrough means that the gas bubbles coalesce abruptly when the permissible gassing rate is exceeded and thus no significant mass transfer is possible.

In most cases, PCC systems have complex arrangements for the gassing of the reactor, which allow the most uniform possible C0 ₂ entry over the height and the cross section of the reactor with the lowest possible energy consumption. From the sum of the energy consumption of the reactor located in the reactor, operated by means of motor power stirrers or gassing turbines and possibly supplying the form pressure blower station essentially balances the hourly energy consumption of the entire system. Typical are energy consumption figures based on the mass of produced PCC in the range of about 60 kWh to 250 kWh per ton of PCC produced, depending on the characteristics of the gassing device and the given C0 ₂ concentration. The plant operator generally knows this energy consumption very precisely. For simplification, it can be assumed that the total energy consumed is proportional to the actual energy input.

The following example illustrates the calculation of the specific molar energy input. calculation example

The following record of a carboxylation is given, the goal being the recovery of s-PCC:

Preparation of a reactive lime milk with 1 1% dry weight fraction of calcium hydroxide and with the density 1,065 kg per m ³ , thus containing 15.8 kmol calcium hydroxide in 10 m ³ The viscosity of the lime milk is about 50 mps.

The reactor is filled with 10 m ^{3 of} this milk of lime.

The constant aeration rate is 2,000 Nm ³ / h, which corresponds to a value of 3.33.

The C0 ₂ concentration is 26%.

The average utilization rate of C0 ₂ is 90%. The significant 90% time of carboxylation (T90 time) is 46 min.

The measured power requirement of a turbine is 130 kW.

The power consumption of an upstream blower contributes 40 kW.

The gas inlet temperature is adjusted by cooling to 40 ° C.

The starting temperature in the reactor (lime milk) is 38 ° C. After 90% of the carboxylation, the temperature in the reactor is 72 ° C.

Accordingly, in the 41 minutes of the reaction, 90% of the lime milk submitted was converted to s-PCC. This corresponds to a formation of 14.3 kmol or 1430 kg s-PCC. For the remaining 10% of unreacted milk of lime, a longer reaction time is required because the specific conversion rate is known to decrease at the end of the batch cycle.

The total energy consumption for the T90 time is 1 17 kWh.

14.3 kmol C0 ₂ were registered during this period. The specific energy input (ε) per mole of C0 ₂ is ^{117 kwh} = 8.2 Wh / mole C0 ₂

^ ^a 14.3 moles CO 2

The influence of the individual quantities on the specific molar energy input is basically known or can be determined in a simple manner by the person skilled in the art on a given PCC system. For example, for a system, the level of the reactor can be plotted against the total power input (sum of blower, gassing unit, stirrer, etc.). Similarly, the dependence of the gas utilization of the applied C0 ₂ concentration, the speed of the Gassing stirrer, the relative gas input, etc. record and evaluate.

Figures 2 and 3 show the results of series of experiments that were carried out with a pilot reactor or technical reactor. In each case, the characteristic mean particle size D4.3 is plotted against the specific energy input per mole of registered C0 ₂ in the relevant part of the batch reaction 0 to 90%. The characteristic particle size D4.3 was determined in each case with a Laser Diffraction Particle Sizer Mastersizer from Malvern.

Scalenohedral crystals (s-PCC) with a particle size D4.3 in the range from about 1.1 μm to 3.0 μm in the pilot reactor (FIG. 2) and the technical reactor (FIG. 3) were produced in one experimental range. In order to adapt the energy input, the C0 ₂ concentration, the level, the amount of gas and the speed and the admission pressure of the gassing turbine were varied individually or in combination in the individual tests.

By way of example, a data set for the pilot reactor is given below.

Example 1 - Preparation of s-PCC in the pilot reactor

The following data set was used as the basis:

Lime milk 1 1, 3 weight percent

Level of reactor: 9 l

Speed of the gas turbine: 35 Hz

vvm: 0.5 (0.27 Nm ³ / h)

C0 ₂ concentration: 30%

Reaction time T 90: 281 min

Gas efficiency: 81%

C0 ₂ entry in time T 90: 12.8 mol

Total energy input in time T 90: 536 Wh

Specific energy input per mol C0 ₂ : 42 Wh per mol C0 ₂

It was generated s-PCC with a D4.3 of 2.83 μηι.

It can be seen that there is a direct dependence between the molar energy input per mole of registered C0 ₂ and the resulting characteristic grain size D4.3. The larger the amount of energy applied to one mole of C0 ₂ , the smaller the crystals become and vice versa. Surprisingly, even at lower CO ₂ concentrations, by combining appropriate parameters - for example the fumigation, the fill level and the speed of the fumigation device - smaller particles can be produced if only corresponding parameters are combined in such a way that the associated specific energy input can be represented ,

The two examples 2 and 3 below show by way of example s-PCC batches with a very large value for times 100, which was achieved by targeted variation of the experimental conditions.

Example 2 - Preparation of s-PCC

The following data set was used as the basis:

Lime milk 1 1, 3 weight percent

Level reactor: at the beginning of the carboxylation: 220 l, after 20 min 280 l, after 40 min 240 l until the end of the reaction

Speed of the fumigation turbine: 38 Hz at the beginning of the carboxylation, 40 Hz after 20 min, 45 Hz after 40 min until the end of the reaction

Temperature: 45 ° C, constant (heat dissipation via internal cooler)

C0 ₂ concentration: 45% (biogas), constant

vvm: 1, 5 per min, constant

Specific energy input per mole of C0 ₂ immediately at the beginning of the reaction: 7 Wh per mole of C0 ₂

It was generated s-PCC with a characteristic D4.3 of 3.0 μηι and a value for times 100 of greater than 62.

D 90 ^a

Example 3 - Preparation of s-PCC

The following data set was used as the basis:

Lime milk 1 1, 3 weight percent Level reactor: at the beginning of the carboxylation: 220 l, after 20 min 280 l, after 40 min 240 l until the end of the reaction

Temperature: at the beginning of the carboxylation 45 ° C, after 20 min 43 ° C, after 40 min 41 ° C until the end of the reaction (heat removal via internal cooler)

C0 ₂ concentration: at the beginning of the carboxylation 35%, after 40 min 45%

vvm: 1, 5 per min, constant

Specific energy input per mole of C0 ₂ immediately at the beginning of the reaction: 8 Wh per mole of C0 ₂

It was generated s-PCC with a characteristic D4.3 of 2.9 μηι and with a value for times 100 of greater than 61.

D 90 ^a

Example 4 - Preparation of paper samples

In general, papermaking fillers are evaluated for their quantitative use according to a number of criteria. These include processing characteristics such as sizing, retention, abrasiveness, strength, rigidity, and further performance characteristics such as printability, porosity, roughness, surface energy, and finally optical properties such as opacity, whiteness, light scattering. As a rule, a basic assessment takes place according to four criteria: thickness in μηι, specific volume in g / m ² , opacity and rigidity. If these basic criteria for the respective paper are met, the other properties can usually be corrected in a corrective manner. A filler is particularly suitable if it meets the basic criteria even at high filling level.

Standard stock paper samples were prepared with various fillers and fill levels of 15%, 20% and 24% ash, respectively. These papers were then uniformly referred to as "100% ash". In addition, these papers were replenished with additional PCC until values for the ash content of 135% ash and 175% ash resulted.

Samples A-1 to A-3: indicate s-PCC obtained by the above method (= invented PCC) with a value for D ₉₀ times 100 of 59.3 and a mean particle size D4,> 3 of 2,> 9 μm.

Samples B-1 to B-3: refer to commercially available s-PCC (PCC = H) with a value fo _r D__ ₉ _ ₀ _! _ma i loo of 55.75 and a mean grain size D4,> 3 of 2,> 8 u rm.

Samples C-1 to C-3: denote ground carbonates (GCC) (= HW GCC) with a value for times 100 of 53 and an average grain size of 1.8 μm. GCC with larger values

D 90 ^ara

for the D4.3 as about 1, 8 μηι paper technology are not used because of the undesirable high abrasiveness.

The particle size distribution of the samples was determined as indicated above and can be taken from FIG. On the x-axis, the size distribution in μηι is plotted logarithmically and the y-axis shows the distribution in percent. As can be seen, the s-PCC according to the invention exhibits a very narrow particle size distribution (PCC solid line) compared to GCC (HW GCC, dotted line) and commercial PCC (HW PCC, dashed line), respectively.

The paper samples were prepared on a conventional industry standard sheet former, the experimental experimental conditions were made according to a standard data set.

Subsequently, for paper samples having different degrees of filling of inventive s-PCC and commercial s-PCC and GCC (fill levels 100% ash, 135% ash and 170% ash), the specific volume (FIG. 5), the stiffness (FIG. 6), the opacity (Figure 7), the whiteness (Figure 8), the tear length (Figure 9) and the thickness (Figure 10). The results of the investigations are shown in FIGS. 5 to 10.

As can be seen, the specific volume, opacity, tear length, whiteness and stiffness could be increased. As expected, the thickness of the paper increases at the same basis weight.

In general, it should be noted in all measurements that humidity and temperature have a significant influence on the measured values. Therefore, the measurements always take place in climatic rooms with a standard climate (23 ° C, 50% humidity) defined according to ISO standards. The paper sample was stored in the room for 24 hours prior to measurement to acclimatise it.

The degree of opacity of the paper (opacity) refers to its ability to Light does not shine through. Paper is opaque when the incident light is scattered back or absorbed in the paper. The higher the scattering of the light, the more opaque the paper is. Opacity is a desirable quality that minimizes the bleed through of the print. A sheet with 100% opacity leaves no light at all and therefore not the print, unless the ink penetrates. In general, the lower the basis weight of the paper, the lower the opacity of the paper. The whiteness and brightness of the filler, its grain structure and size, its refractive index and filler content are factors that determine the opacity of the paper. All the important paper-technical properties could be obtained or increased with the use of the PCC according to the invention despite an almost 50% higher degree of filling. The results could be confirmed on a paper machine.

Claims

Patent claims

Paper containing scaleonedral precipitated calcium carbonate (s-PCC) with a grain ^a size distribution ^a in which ^ D^ 90 times 100 > 59 and the average grain size D 4.3 in the range from 1.5 to 5.0 μηι lies.

Paper according to claim 1, in which the paper has a basis weight of 20 to 90 g/m ² .

3. Paper according to claim 1, in which the paper has a basis weight of 200 to 500 g / m ² .

D 4.3

4. Paper according to claim 1, in which times 100 is > 60.

D90

5. Paper according to claim 1, in which the s-PPC has an average grain size D 4.3 in the range from 2.0 to 4.0 μηι.

6. Paper according to claim 1, in which a filling level of s-PCC in the paper is in the range of 10% to 30% ash.

7. Use of scaleonedral precipitated calcium carbonate (s-PCC) with a

D 4.3

Grain size distribution where times 100 > 59 and with an average grain size

D90

D 4.3 in the range from 1.5 to 5.0 μηι as a filler for paper.