Patent Application
20190093289
The invention relates to paper which contains scalenohedral precipitated calcium carbonate (s-PCC) having a certain specification. The invention relates further to the user of a s-PCC having a certain specification as filler material for paper.
Paper is a two-dimensional material which consists substantially of fibres of plant origin and is formed by removing the moisture from a fibre suspension on a sieve-like screen. The fibre fleece formed thereby is compressed and dried.
One of the main components of paper are cellulose fibres, which have a length in the range from a few millimetres to a few centimetres. The cellulose is first largely exposed, that is to say separated from the hemicelluloses, resins and other vegetable components. The pulp obtained thereby is mixed with water and defibred. The aqueous suspension is deposited in a thin layer on fine-meshed screen and thickened mechanically by moving the screen as it drips through.
When the paper has dried, its surface is impregnated (this process is called sizing).
The essential starter materials for paper can be divided into four groups.
The present invention relates to the use of PCC as filler material. PCC is a synthetic industrial mineral which is manufactured from burned lime its raw material, limestone. Unlike other industrial materials, PCC is a synthetic product which can be shaped and modified to lend various properties to the paper that is to be produced. The physical form of the PCC can change considerably in the reactor. Variable factors include the reaction temperature, the speed with which the carbon dioxide gas is added, and the speed of movement. These variables influence the granularity and the shape of the PCC grain, its surface area and surface chemistry, and the grain size distribution. While many advantages may be gained from the ability to control the paper's properties with the aid of the PCC (greater brightness, impermeability to light and thickness than with ground calcium carbonate GCC), until now the possible use of conventional PCC as filler material has been limited because it renders the fibres less stable.
In practice, conventionally manufactured s-PCC with an average grain size D4.3 from 1.5 μm to about 5 μm is used as filler material in photocopier paper among other things, although only up to a filler percentage of about 30%, because otherwise the tear resistance is too low. It would therefore be desirable if it were possible to increase the degree to which s-PCC can be used as filler without detracting from the properties of the paper.
The disadvantages described above can be overcome with the preparation of the paper according to the invention. For this purpose, the paper contains modified scalenohedral precipitated calcium carbonate (s-PCC). The s-PCC has a grain size distribution in which
preferably ≥60, particularly preferably ≥62 most particularly preferably ≥65, and the average grain size D4.3 of the s-PCC is in the range from 1.5 to 5.0 μm, particularly preferably 2.0 to 4.0 μm, particularly 2.9 to 3.1 μm.
The invention is prompted by the realisation made experimentally that as the D4.3 value of the s-PCC increases, the width of the grain size distribution increases as well, which has a detrimental effect on some paper properties, such as tear resistance. It was demonstrated that a narrow grain size distribution is helpful in counteracting this.
The paper according to the invention is preferably a graphic paper. Graphic papers are papers that are used for printing, writing and copying. As the need for graphic papers grows, a process technology designed specifically for these types of paper also become more important.
The paper preferably has a grammage from 20 to 90 g/m2, particularly preferably 40 to 80 g/m2, in particular from 50 to 60 g/m2. Thus, the paper may particularly be tissue paper (approx. 20 to 30 g/m2), Bible paper (approx. 40 g/m2), newsprint paper or LWC paper (approx. 50 g/m2), notepaper or stationery paper (approx. 60 g/m2), typewriter paper (approx. 70 g/m2) or photocopier paper (approx. 80 g/m2). However, it is also possible to fill “heavy” papers such as cartonboard with a grammage from 200 to 500 g/m2 with this s-PCC according to the invention to good effect.
The degree to which the paper is filled with s-PCC of the stated specification may be increased the percentage of the significantly more expensive pulp may be reduced correspondingly without impairing the essential paper properties. On the contrary, it has been found that adding the s-PCC that is used according to the invention improves important paper properties such as opacity, tensile strength and specific volume.
The proportion of s-PCC as filler in the paper is in the range from 10% to 30% ash. The total quantity of the inorganic material contained in a sample is called “ash”. When organic material is burned, substantially only CO2 and water vapour is generated, possibly also SO2 or NHa. These gases dissipate, no residue remains. In contrast, the inorganic components form salts or oxides, which typically do not even melt at normal flame temperatures. The combustion residues, the ash, thus contain all inorganic components of the sample. Incineration is understood to mean controlled combustion by heating to 575±25° C. until no further weight loss is observed. Combustion must be carried out without atmospheric circulation and must not take place too intensely to prevent any fine fly ash from being transported away. The “ash” of uncoated papers consists mostly of filler material, that of coated papers still contains the inorganic coating pigments. The quantity of ash is expressed as a percentage of the total weight of the (dried) paper mass.
Accordingly, a further aspect of the invention relates to the use of scalenohedral precipitated calcium carbonate (s-PCC) with a grain size distribution for which the ratio
is resolved to:
and with an average grain size D 4.3 in the range from 1.5 to 5.0 μm as filler material for paper. The ratio
is preferably ≥60, particularly preferably ≥62, most particularly preferably ≥65. The average grain size D4.3 of the s-PCC is preferably in the range from 2.0 to 4.0 μm, particularly 2.9 to 3.1 μm.
Thus, there was a need for s-PCC that has an average grain size D4.3 in the range from 1.5 to 5.0 μm with a
ratio greater than or equal to 59. But until now an industrial process which can deliver such a material has not existed. However, this problem was also solved according to the invention.
Many processes are known according to the related art in which PCC is formed in aqueous suspension from Ca(OH)2 (“lime milk”) by the addition of CO2. The CO2 may be in liquid form or it may be introduced into the lime milk as a gas via a suitable ventilation system. The desired PCC morphologies can be generated with the aid of additives or seed crystals and with correspondingly adapted process management. In large-scale production, a batch manufacturing mode is usually adopted.
Modifications to the PCC are described sufficiently in the literature. In the present context, the term “modification” is understood to refer to the family of industrially manufactured crystals with defined morphology, of which aragonite and calcite are particularly important representatives, and vaterite and ikaite are much less relevant. There are also special transition forms such as basic calcium carbonates or amorphous carbonates which can also be isolated. The person skilled in the art in this industry will typically familiar with the limit conditions of the PCC system—some of which are highly complex—that may influence the modification, from many successful and unsuccessful experiments. The fundamental control parameters, such as the start temperature at the beginning of a typical batch cycle in conjunction with the concentration of the supplied lime milk and the CO2 concentration are specified in advance. Influences from the raw material are eliminated in extensive test series, and if necessary rendered manageable with various types of additives. It is also possible to modify the degree of agglomeration of the PCC crystals by adjusting the reaction conditions.
However, until now there has been no systematic approach to the production of PCC with a defined grain size and a defined (narrow) grain size distribution. The reason for this may lie in the complex interplay of a multitude of parameters. These include for example gassing parameters in conjunction with the CO2 concentration, the geodetically effective height of a reactor and the dissipative energy input. Furthermore, in a typical batch reaction, which is by far the most frequently used in industry, at any moment of the reaction important process parameters can change in respect of a different characteristic in each case, for example the pH value of the suspension that is to be gassed, the conductivity, the temperature, the ratio between free calcium ions and bicarbonate ions, the density of the suspension and the viscosity of the suspension. The dynamics of all these changes are also not consistent at all times, some of the parameters, for example the pH value and conductivity do not change noticeably until close to the end of the batch cycle, but then they do so dramatically; meanwhile, other parameters like the temperature rise, the change in density and the change in viscosity manifest a practically linear change characteristic. This is further complicated by the fact that two main phases evidently take place during carboxylation, a preferred nucleation phase right at the start of the reaction, followed by a particle growth phase which tends to be preferred. As described in the recent literature, not even the particle growth takes place in linear manner, but instead via a whole series of intermediate states of immensely differing morphology.
For these reasons, information about which of the many phenomena are decisive, controllable and adjustable for the characteristic variation of the average grain size (D4.3 value) and the width of the grain size distribution is at best very limited. Consequently, there are hardly any indicators as what steps the person skilled in the art has to take with an existing PCC system in order to arrive at a product that has a defined grain size and also a defined grain size distribution. Therefore, until now it has not been possible to attain this objective consistently.
U.S. Pat. No. 6,251,356 B1 suggests regulating the average grain size in a pressure reactor by controlling the order of the working pressure. It is contented that the grain size ratio is narrower than with 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 particles is generated. For this, the volume flow rate of the lime milk can be changed with constant gas flow rate. In addition, influence can be exercised on the desired grain size by supplying a fine lime milk with increased reactivity.
According to Gernot Krammer et al. (Part. Part. Syst. Charact. 19 (2002) 348-353), an increase in CO2 concentration results in a reduction of the average grain size. An adverse influence of the CO2 concentration on the average 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 the lime milk is another parameter that affects the average grain size (Kralj et Brecivic from Croatica Chimica Acta, 80 (3-4) 467-484 (2007) “On Calcium Carbonates from fundamental research to application”). Higher solids contents in the lime milk usually lead to coarser particles, lower solids contents should lead to finer particles.
It is also known that aragonitic crystals gradually become larger in continuous operation of a PCC plant.
Pust (in a thesis entitled “Die Herstellung von gefälltëm Calciumcarbonat—PCC” [The production of precipitated calcium carbonate—PCC] RVVTH Aachen, 1992) describes the influence of the quenching parameters in the production of quicklime on the size of the crystals which are formed subsequently during carboxylation.
EP 1 712 597 A1 describes the effect of adding various additives such as Zn-salts, Mg salts, and cationic and anionic dispersing agents on the grain size distribution.
There was thus a continuing need for systematic solution approaches to enable the production of precipitated calcium carbonate of a defined grain size and defined grain size distribution with a given PCC plant. The limitations of the prior art as described in the preceding text could be solved with a recently developed method for producing s-PCC by introducing carbon dioxide into lime milk in a PCC plant. The method comprises the following steps:
ratio depending on at least one of the following parameters: CO2 concentration during the reaction, temperature of the lime milk, fill level in the reactor of the PCC plant, and rotating speed of the gassing stirrer of the PCC plant; and
There are various ways to describe the width or narrowness of the grain size distribution. In the present context, it is characterized using the ratio
which is often used in the field of particulates such as PCC. Here, D90 means that 90% of the particles are smaller than the assigned value with volume weighting.
The average grain size D4.3 is the arithmetic mean of a distribution across all of the particles. A very narrow grain size distribution is obtained for example if the D4.3 is 3.1 and the associated D90 is 5.0 μm. Then the
ratio yields the numeric value 62. The figures apply for the formation of the “primary particles” of the PCC process. Subsequent agglomerations are ignored.
The size determination can be made with a laser diffraction particle size analyser. All values are based on a dispersed product to prevent agglomeration to the extent possible. In the present case, all measurements were taken using a particle size analyser either from the company Malvern (instrument name Malvern 3000) or Quantachrome (instrument name Cilas 1064 L). Both devices are very common in the paper industry and consistently returned very similar values.
The newly developed method is based among other things on the finding that the specific molar energy input is the decisive parameter for controlling the grain size. This value describes the sum of the specific energy input of the overall system, which is required to input one mole of CO2 in the decisive part of the reaction from about zero to 90% when the carboxylation reaction is proceeding in batch mode. The energy input is to be measured without regard for its source. In a conventional PCC plant, particularly inputs from the ambient CO2 concentration of the gas, the volumetric specific gas flow rate, the fill level of the reactor, the rotating speed of the frequency-controlled gassing turbine and/or the stirrer, the power output of an upstream fan will have to be taken into account.
Accordingly, in step a) of the method the individual influencing factors of a PCC plant which deliver a significant contribution to the specific molar energy input are captured. It has been found that the cumulative contribution of all these influencing factors to the specific molar energy input is in direct correlation with the target grain size.
Therefore, in step b) this correlation is calculated for the PCC plant in question. In general, it was found that the grain size decreases as the specific molar energy input increases. For this purpose, preferably in step b) a linear correlation is calculated between the average grain size D4.3 and the specific molar energy input of the total system. For the determination of the correlation between the specific molar energy input and the grain size at a specific PCC plant, in practice for example a number of test settings are run with predefined specific molar energy input and then the grain sizes are determined. The two values are plotted against each other and an associated linear function is determined by means of a graphical evaluation process. Now the required energy input can be determined for a desired grain size with the aid of the function. Then, the influencing factors are adapted appropriately to represent this energy input.
Surprisingly, it was then found that only the specific energy input of the substance delivery system represents the decisive parameter for the grain size of the resulting crystals. It may be adjusted by any combinations of the gassing parameters with the ambient CO2 concentration such that the target value for the desired grain size is formed. Thus, for the first time it is possible to set requirements selectively for the grain size of the PCC crystals using the basic information about the characteristic values of the gassing apparatus.
In conventionally produced particle sizes, the ratio
lies in the range from about 2.8 μm and larger up to a maximum of 55 and is typically much smaller numerically. This is attributable to spinodal separation processes during the carboxylation, which lead to the formation of continuously smaller zones with higher or lower oversaturation compared with the average value. As a consequence, not only are new, smaller grains formed, but already existing crystals also continue growing into larger crystals.
It was only during the course of the research for the present invention that it was demonstrated experimentally which influencing factors from the plethora of practically infinite possibilities are actually significant for grain size distribution and are to be taken into account when defining the respective desired value for the
ratio. The following parameters were identified: CO2 concentration during the reaction, temperature of the lime milk, fill level of the reactor of the PCC plant, and rotating speed of the gassing stirrer of the PCC plant (step c) of the method). The four measures can be applied singly or in any combination and when observed coherently have the effect of reducing the grain size distribution.
In particular it is preferable that in step c) the CO2 concentration at the start of the reaction corresponds to 0.5 to 0.8, particularly 0.6 to 0.7 of the CO2 concentration at the end of the reaction, and the CO2 concentration is increased progressively or incrementally. Thus, if a fixed value for the CO2 concentration of the source is known, as is almost always the case (e.g., in power stations between 10 and 11%, in kilns for producing burnt lime about 22 to 26%, in biogas plants between about 35 and 55%, or in synthetic gases about 98%), the starting concentration is reduced to a value which is about 20 to 50%, particularly 30 to 40% smaller than the CO2 concentration of the source and increased progressively or incrementally to the maximum possible concentration until the end of the reaction. This may be achieved most simply by diluting with air. Surprisingly, it was discovered that this action increased the ratio of the value for
particularly to 59 or more.
It is further preferable that in step c) a temperature is fixed at the start of the reaction at which the PCC is precipitated in the respectively desired morphology, and that this temperature is kept constant for the duration of the reaction or is lowered progressively or incrementally to 15° C., particularly 10° C. until the end of the reaction. Accordingly, the starting temperature is specified as the temperature at which the desired morphology can form definitively. In the case of s-PCC, the starting temperature lies in the range from 25 to 45° C. A starting temperature is also specified conventionally, but the temperature is not controlled subsequently, and as a consequence the temperature rises due to the exothermal nature of the reaction. In contrast, according to the invention the temperature is kept constant or reduced incrementally or progressively to as low as 15° C. Surprisingly, it was found that this measure increases the value for
particularly to 59 or more.
It is further preferable that in step c) a fill level of the lime milk is equal to 50% to 80%, particularly 50% to 70% of the work volume of the reactor at the start of the reaction, and after a grain formation phase lime milk is added progressively or incrementally until the end of the reaction. Thus, at the start of the reaction the work volume of the reactor is only 50% to 80% filled with lime milk of the required strength. Not before the end of the “grain formation phase”, in practical operation for all morphologies this is the case after about 20 minutes, more lime milk is added in measured quantities incrementally or progressively, spread as evenly as possible over the entire T90 runtime until the reactor has reached its nominal work volume. At the end of the T90 time, that is to say the significant reaction time in which 90% of the total conversion is complete, no more lime milk is added. Surprisingly, it was found that this measure increases the value for
particularly to 59 or more.
Finally, it is preferable in step c) that the rotating speed of the gassing stirrer is equal to 0.5 to 0.9, particularly 0.8 to 0.9 as fast at the start of the reaction as the speed at the end of the reaction, and the speed is increased progressively or incrementally to the final speed when 90% of the conversion reaction is reached. Accordingly, the reactor is started at the pre-calculated rotating speed, which was selected such that a potential for increase of about 10 to 50% is still possible. After the grain formation phase is completed, but not later than the end of the T90 time, the rotating speed of the gassing stirrer is increased progressively or incrementally by the remaining 10 to 50% until the end of the reaction. Surprisingly, it was found that this measure increases the value for
particularly to 59 or more. The s-PCC that may be obtained according to the method has a particular combination of the grain size D4.3 and the ratios
The properties cannot be obtained with previously known PCC methods.
Further preferred variations of the invention will be evident from the claims and from the following description.
In the following text, the invention will be explained in greater detail with reference to exemplary embodiments and associated drawings. The figures show:
with an average grain size D4.3 in the range from 1.5 to 5.0 μm. The PCC plant 10 comprises a batch reactor 20, into which an aqueous suspension of Ca(OH)2 (also called “lime milk”) is introduced, and s-PCC is then formed by the input of CO2. The lime milk is fed in via a supply system 30. Here, the CO2 is mixed with the lime milk as a gas by means of a suitable ventilation system 40, which in this example comprises a gassing stirrer 42. A further agitation mechanism 50 may be provided. The temperature in the reactor 20 is controllable. In this case, the PCC plant 10 contains sensor means—not shown in more detail—for monitoring the fill level of the reactor 20 and capturing the temperature of the lime milk. Further sensor means may also be provided to enable a direct or indirect assessment to be made of a CO2 concentration in the lime milk.
One of the bases for the invention is that the specific molar energy input is the decisive parameter for controlling the grain size. Accordingly, all parameters of the PCC plant 10 which are of significance for the specific molar energy input during operation, must be captured. In this context, the specific molar energy input corresponds to the energy input for the entire system that is needed to introduce a mole of CO2 to the carboxylation reaction in batch production mode from the start of the reaction until a 90% degree of conversion is reached.
As is generally known, the process of calcium carbonate formation from calcium hydroxide and CO2 is approximately linear in the main part of the reaction. After a value of about 90 to 95% of the total reaction, the pH and conductivity values fall sharply, and the CO2 yield also decreases rapidly. Therefore, the average value for the yield of CO2 in the first 90% of the total reaction time is taken as the defining reaction time.
In order to measure the specific gassing rate, it is common to use the value “vvm”, which means: unit volume of gas per unit volume of reactor contents per unit of time. In industrial practice and in typical reactor contents of 10 m3, gassing rates of about 0.25 vvm to 5 vvm for example are customary, which after conversion mean that the reactor is gassed with possible gassing rates from 150 Nm3 per hour up to about 3000 Nm3 per hour. Smaller values are considered uneconomical, while larger values are technically not possible because of the increasing risk that the gassing air in the reactor will merge. Merging means that when the permissible gassing rate is exceeded the gas bubbles coalesce all at once, and material transfer is no longer possible on a significant scale.
PCC plants are usually equipped with complex arrangements for supplying gas to the reactor, which allow the CO2 to be introduced as evenly as possible over the full height and cross-section of the reactor with the lowest possible energy consumption. The energy consumption per hour of the overall system is derived substantially from the sum of the energy consumption by the agitator elements and gassing turbines located in the reactor, which are motor-driven, together with any ventilator station delivering admission pressure. Indicators for energy consumption relative to the mass of PCC produced are typically in the range from about 60 kWh to 250 kWh per ton of PCC depending upon the characteristics of the gassing apparatus and the predetermined CO2 concentration. The plant operator generally has a very accurate idea of this energy consumption. For the sake of simplicity the total energy consumed may be assumed to be the energy amount which behaves proportionally for the energy actually input. In the following section, the calculation of the specific molar energy input will be illustrated with reference to an example.
Example Calculation
The following dataset is provided for carboxylation, wherein the objective is to recover s-PCC:
Production of a reactive lime milk having 11% dry weight content of calcium hydroxide and with a density of 1,065 kg per m3, thus containing 15.8 kmol calcium hydroxide in 10 m3. The viscosity of the lime milk is approximately 50 mps.
The reactor is filled with 10 m3 of this lime milk.
Gassing is carried out at constant rate of 2,000 Nm3/h, corresponding to a vvm value of 3.33.
The CO2 concentration is 26%.
The average utilisation factor of the CO2 is 90%. The decisive time for completion of 90% carboxylation (T90 time) is 46 min.
The measured power requirement for a turbine is 130 kW.
The power consumption of an upstream fan is 40 kW.
The gas inlet temperature is adjusted to 40° C. by cooler.
The starting temperature in the reactor (lime milk) is 38° C. After the carboxylation is 90% complete, the temperature in the reactor is 72° C.
Accordingly, in the 41 min of the reaction, 90% of the supplied lime milk was converted into s-PCC. This is equivalent to the formation of 14.3 kmol or 1,430 kg s-PCC. A longer reaction time is needed for the remaining 10% of unconverted lime milk, because the specific conversion rate is known to decline at the end of the batch cycle.
The total energy consumption for the T90 time is 117 kWh.
During this period, 14.3 kmol CO2 are input. The specific energy input (ε) per mole CO2 is
The influence of the individual parameters on the specific molar energy input is generally known, or can be determined easily by the person skilled in the art at a given PCC plant. Thus, for example the fill level of the reactor may be plotted against the total power input (total from fan, gassing unit, stirrer, etc.). The dependency of the gas utilisation on the ambient CO2 concentration, the rotating speed of the gassing stirrer, the relative gas input, etc. can also be captured and evaluated.
In one test series, scalenohedral crystals (s-PCC) with a grain size D4.3 in the range from approx. 1.1 μm to 3.0 μm are produced in the pilot reactor (
The following represents an exemplary dataset for the pilot reactor.
The following dataset was applied:
Lime milk 11.3 weight percent
Reactor fill level: 9 l
Speed of gassing turbine: 35 Hz
CO2 concentration: 30%
Reaction time T 90: 281 min
Gas utilisation rate: 81%
CO2 input in time T 90: 12.8 moles
Total energy input in the period T 90: 536 Wh s
Specific energy input per mole CO2: 42 Wh per mol CO2
s-PCC was produced with a D4.3 of 2.38 μm.
It is evident that there is a direct relationship between the molar energy input per mol input CO2 and the resulting characteristic grain size D4.3. The larger the amount of input energy applied to a mole of CO2, the smaller the crystals become, and vice versa. Surprisingly, it is therefore also possible to produce smaller particles with lower concentrations of CO2 by combining corresponding parameters—for example those of gassing, the fill level and the rotating speed of the gassing devices—provided that corresponding parameters are combined in such manner that the associated resulting specific energy input can be represented.
The two following examples 2 and 3 show examples of s-PCC batches with a very large value for
which was achieved by selective variation of the test conditions.
The following dataset was applied:
Lime milk 11.3 weight percent
Reactor fill level: at the start of carboxylation: 220 l, after 20 min 280 l, after 40 min 240 l until the end of the reaction
Speed of gassing turbine: at the start of carboxylation: 38 Hz, after 20 min 40 Hz, after 40 min 45 Hz until the end of the reaction
Temperature: 45° C., constant (heat dissipation via internal cooler)
CO2 concentration: 45% (biogas), constant
vvm: 1.5 per min, constant
Specific energy input per mole CO2 immediately at the beginning of the reaction: 7 Wh per mol CO2
s-PCC was produced with a characteristic D4.3 of 3.0 μm and a value for
greater than 62.
The following dataset was applied:
Lime milk 11.3 weight percent
Reactor fill level: at the start of carboxylation: 220 l, after 20 min 280 l, after 40 min 240 l until the end of the reaction
Speed of gassing turbine: at the start of carboxylation: 38 Hz, after 20 min 40 Hz, after 40 min 45 Hz until the end of the reaction
Temperature: at the start of carboxylation 45° C., after 20 min 43° C., after 40 min 41° C. until the end of the reaction (heat dissipation via internal cooler)
CO2 concentration: at the start of carboxylation 35%, after 40 min 45%
vvm: 1.5 per min, constant
Specific energy input per mole CO2 immediately at the beginning of the reaction: 8 Wh per mol CO2
s-PCC was produced with a characteristic D4.3 of 2.9 μm and a value for
greater than 61.
In general, filler materials for paper manufacturing are assessed according to a number of different criteria with regard to their quantitative use. These criteria include processing-related features such as sizing, retention, abrasiveness, mechanical strength, stiffness, and application-related features such as compressibility, porosity, roughness, surface energy, and finally optical properties such as opacity, whiteness, light scattering. Typically, a basic assessment is carried out according to four criteria: thickness in μm, specific volume in g/m2, opacity and stiffness. If these basic criteria for the respective paper are satisfied, most often the other properties can be corrected by readjustment. A filler material is particularly suitable if it satisfies the basic criteria even when the filler content is high.
Paper samples with various filler materials and filler contents of 15%, 20% and 24% ash in each case were produced as standard starter material. These papers were then referred to uniformly as “100% ash”. These papers were also filled with further PCC until values of 135% ash and 175% ash for the ash content resulted.
Samples A-1 to A-3: denote s-PCC obtained according to the method described above (=Inv. PCC) with a value for
of 59.3 and an average grain size D4.3 of 2.9 μm.
Samples B-1 to B-3: denote commercially available s-PCC (=HW PCC) with a value for
of 55.75 and an average grain size D4.3 of 2.8 μm.
Samples C-1 to C-3: denote ground carbonates (GCC) (=HW GCC) with a value for
of 53 and an average grain size of 1.8 μm. GCCs with D4.3 values larger than about 1.8 μm are not used in paper production because of their unacceptably high abrasiveness.
The particle size distribution in the samples was determined as described earlier in this document, and is represented in
The paper samples were produced in conventional sheet formers usual in the industry, the experimental test conditions were prepared according to a standard dataset.
Then, the specific volume (
As may be seen, it was possible to increase the specific volume, the opacity, the tearing length, the whiteness and the stiffness. As expected, the thickness of the paper increased with no change in grammage.
In general, it should be noted with respect to all measurements that atmospheric humidity and temperature have a significant impact on the measured values. For this reason, the measurements are always taken in air-conditioned rooms with a standard climate (23° C., 50% atmospheric humidity) fixed in accordance with ISO standards. The paper sample was stored in the room for 24 hours before the measurement to enable it to acclimatise.
The degree of light impermeability of the paper (opacity) refers to its ability to block the passage of light. Paper is impermeable to light when the incident light is scattered back or absorbed in the paper. The greater the scattering of the light, the more impermeable to light the paper is. Light impermeability is a desirable quality which minimises the extent to which printed material can be seen through the back of the sheet. A sheet with 100% light impermeability prevents any light at all from passing through, and therewith also the printing on the sheet unless the printing ink penetrates the paper. In general, the light impermeability of paper decreases as the grammage gets lower. The degree of whiteness and brightness of the filler material, its grain structure and size, its refractive index and the content of filler material are factors which determine the light impermeability of paper. All important properties relating to paper-technology were maintained or improved by using the PCC according to the invention despite an increase of almost 50% in the degree of filling. The results were confirmed on a papermaking machine.
| Number | Date | Country | Kind |
|---|---|---|---|
| 16172231.9 | May 2016 | EP | regional |
This application is a continuation of PCT/EP2017/063168 file May 31, 2017, which claims priority to EP 16172231.9 filed May 31, 2016, both of which are incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/EP2017/063168 | May 2017 | US |
| Child | 16204776 | US |
