FIELD OF THE INVENTION

The present invention relates to fillers for paper, board, cardboard and tissue manufacture, said fillers comprising calcium silicate hydrate coated particles. The invention also relates to the use of said fillers for improving strength properties of paper, board, cardboard or tissue, to the use of said fillers in the manufacture of paper, board, cardboard and tissue, as well as to a method for the manufacture of paper, board, cardboard or tissue.

BACKGROUND

In the manufacture of paper, board, cardboard and tissue products raw materials typically form a major portion of costs. Thus it is particularly desirable to decrease the amount of more valuable raw materials such as pulp, and to increase the amounts of less expensive raw materials, such as fillers, and other additives etc. However, it is well known that the strength properties of the product, such as paper are impaired when the amount of filler is increased in the product.

Several attempts have been made in the field for improving the bonding properties of filler materials, for example by adding starch, cellulosic fibrillated fines or other cellulose material on the filler particles, or by chemical modification of filler particles by polymers, in order to increase the amount of fillers in final products.

WO 2011/048000 Al discloses a method for producing paper, paperboard and cardboard having high dry strength, where an aqueous composition comprising nanocellulose, anionic polymers and water-soluble cationic polymers is added to the fibre stock solution.

There exists constantly a need to provide improved fillers for paper, board, cardboard and tissue manufacture, for increasing the efficiency of the process, decreasing the costs of manufacture, and at the same time for yielding products with improved properties.

Early-age hydration of ordinary Portland cement was studied with semi-adiabatic calorimeter in the presence of limestone and calcium-silicate-hydrate (CSH) coated limestone in publication Vehmas, T., Kronlof, A: A Study of Early-age Ordinary Portland Cement Hydration According to Autocatalytic Reaction Model, The Nordic Concrete Federation, Proceedings of XXI Nordic Concrete Research Symposium, Finland, 2011 ; (The Nordic Concrete Federation Publication No. 43 1/2011, 269 - 272)

SUMMARY

An object of the invention was to provide improved fillers for paper, board, cardboard and tissue manufacture. Another object of the invention was to provide a new method for the manufacture of paper or board or cardboard or tissue.

The present invention relates to fillers for paper, board, cardboard and tissue manufacture, said fillers comprising calcium silicate hydrate coated particles.

The invention also relates to the use of fillers comprising calcium silicate hydrate coated particles for improving strength properties of paper, board, cardboard and tissue. The invention also relates to the use of fillers comprising calcium silicate hydrate coated particles, in the manufacture of paper, board, cardboard or tissue.

The invention further relates to a method for the manufacture of paper, board, cardboard or tissue where fillers comprising calcium silicate hydrate coated particles are used .

The invention further relates to paper, board, cardboard or tissue obtainable by said method. The characteristic features of the invention are presented in the appended claims. DEFINITIONS

Unless otherwise specified, the terms, which are used in the specification and claims, have the meanings commonly used in the field of paper, board, cardboard and tissue industry and in inorganic chemistry, particularly in the field of paper and pulp chemistry and industry. Specifically, the following terms have the meanings indicated below. The term "filler", also called "filler pigment" or "pigment", refers to particulate material used typically in the paper and board manufacture, for replacing fiber, decreasing costs, improving opacity, smoothness and improving printing quality, as well as machine runnability, etc. Talc and carbonates (GCC and PCC) are examples of major filler pigments used in the industry.

The expression "calcium silicate hydrate coated particles" refers here to solid particles and/or agglomerates coated with calcium silicate hydrate. The term "Portland Cement" includes, but is not limited to, Ordinary Portland Cement, Off-white Portland Cement, White Portland Cement (WPC), White Ordinary Portland Cement (WOPC) and blended cement. Portland Cement includes calcium silicate based cements typically used in construction applications, including OPCs, sulfate tolerant OPCs, fast OPCs, off-white Portland Cement, and blended cement.

The term "PCC" refers to scalenohedral or rhombohedral or aragonite crystal form of precipitated calcium carbonate.

The term "GCC" refers to ground calcium carbonate.

The expression "SC-paper" refers here to supercalendered paper grade, typically used in magazines.

The expression "nanofibrillated cellulose" (NFC) refers here to cellulose refined under applied energy whereby it becomes fi bri Mated as the cell walls are broken into fibrils. Nanofibrillated cellulose means that individual fibrils are in nanosize (thickness). Nanofibrillated cellulose can be also called nanocellulose, nanofibrillar cellulose, cellulose nanofibers, microfibrillated cellulose (MFC), microfibrillar cellulose, cellulose nanofibers (CNF), bacterial cellulose, microbial cellulose (MC), biocellulose and biofibrillar cellulose.

Unless otherwise noted, all percentages are by weight. DESCRIPTION OF THE DRAWINGS

Figure 1 illustrates scanning electron microscope images of uncoated calcite (1A) and CSH coated calcite surface (IB) .

Figure 2 illustrates the tensile strength of calendered SC handsheets as a function of pigment treatment intensity.

Figure 3 shows the modulus of elasticity of calendered SC handsheets as a function of pigment treatment intensity.

Figure 4 illustrates strain at break as a function of pigment treatment intensity.

Figure 5 shows air permeance of calendered sheets as a function of pigment treatment intensity.

Figure 6 illustrates light scattering coefficient of calendered sheets.

Figure 7 illustrates the opacity of calendered sheets as a function of pigment treatment intensity.

Figure 8 shows the tensile strength of calendered SC handsheets as a function of pigment treatment intensity.

Figure 9 shows the modulus of elasticity of calendered SC handsheets as a function of pigment treatment intensity.

Figure 10 shows the strain at break of calendered SC handsheets as a function of pigment treatment intensity.

Figure 11 shows the air permeance of calendered sheets as a function of pigment treatment intensity.

Figure 12 shows the light scattering coefficient of calendered sheets with cement CSH coating together with nanofibrillated cellulose.

Figure 13 shows the opacity of calendered sheets as a function of pigment treatment intensity. DETAILED DESCRIPTION OF THE INVENTION

The present invention is based on studies relating to coating of particles with a thin layer of calcium silicate hydrate (CSH) and to the use of said coated particles in the paper, board, cardboard and tissue manufacture. Surprisingly fillers with improved bonding properties were obtained, whereby the filler content in paper, board, cardboard or tissue can be increased significantly without impairing the properties of said products or their manufacturing conditions. Especially the strength and printing properties may be improved or at least maintained at acceptable level and the amount of fibrous starting materials, such as pulp can be reduced significantly and thus also manufacturing costs can be decreased.

Filler

The filler of the invention comprises particles and/or agglomerates, having a coating on their surface, of calcium silicate hydrate (CSH), i.e. calcium silicate hydrate coated particles. The surface of said particles comprises typically nanoscale and microscale "hairs" which particularly improve the bonding of cellulose and fines to the filler.

The particles, here also referred to as substrate particles, coated in the method of the invention, are suitably selected from precipitated calcium carbonate (PCC), ground calcium carbonate (GCC), limestone, clay, talc, fly ash, cement, gypsum, titanium dioxide, silicates, organic pigments, slag, ground granulated blast furnace slag, slags from metal manufacturing processes, silica dust, metakaolin, natural pozzolans and calcined oil shale. Preferably PCC is used.

Optionally the coating may additionally comprise nanofibrillated or microfibrillated cellulose.

The filler product of the invention (such as calcium silicate hydrate coated PCC particles) may be in the form of a dry product or an aqueous product. Said aqueous product may be in the form of slurries, suspensions, pastes, etc.

The filler product may optionally comprise additives known in the art and generally used in the manufacture of paper, board, cardboard or tissue, such as retention aids, viscosity enhancer polymers, as well as formulation components typically used in the field of paper or board chemicals, such as defoamers, air entrainers, dispersants, etc. Typically said filler has a mean particle size from 0.5 μιη to 15 μιη, preferably from 1.0 - 6 μιη.

Thus the invention also provides an aqueous filler compositions for paper, board, cardboard or tissue manufacture, comprising at least one filler comprising calcium silicate hydrate coated particles and at least one additive, suitably selected from retention aids, viscosity enhancer polymers, defoamers, air entrainers, and dispersants.

Method for manufacture of the filler

The filler comprising calcium silicate hydrate (CSH) coated particles may suitably be manufactured using the method described below. The method with carefully selected parameters provides filler particles and/or agglomerates with desired morphology and an average coating layer thickness suitable for acting in an efficient and cost effective way in the designed filler use.

The method for producing filler comprising calcium silicate hydrate coated particles, comprises the steps where

in the first step the specific surface area of substrate particles is measured,

in the second step an aqueous mixture is formed of water, substrate and at least one Si-compound to obtain molar amount of Si from O. lxlO ^"4 to lOxlO ^"4 mol/m ² of the substrate, followed by agitation, and

in the third step at least one Ca-compound is added to the mixture obtained in the second step, in an molar amount of 0.5 - 5 x Si molar amount of the first step, followed by agitation to yield an aqueous suspension comprising the filler comprising calcium silicate hydrate coated particles.

The substrate particles are coated with calcium silicate hydrate (CSH) in the method.

The substrate particles are suitably selected from precipitated calcium carbonate (PCC), ground calcium carbonate (GCC), limestone, clay, talc, fly ash, cement, gypsum, titanium dioxide, silicates, organic pigments, slag, ground granulated blast furnace slag, slags from metal manufacturing processes, silica dust, metakaolin, natural pozzolans and calcined oil shale. Preferably PCC is used. The substrate is suitably finely divided particulate material. The specific surface area of the substrate (substrate particles) is suitably measured using methods and equipment typically used for particle size distribution measurements, such as methods based on laser diffraction, microscopy, SEM, Coulter counter etc.

In the present application particle size distributions were measured with a Beckman Coulter LS particle size analyzer. The specific surface area (SSA) was calculated from the particle size distributions. This method ignores the smallest surface structure details accessible for example to nitrogen molecules in the BET method (method based on gas absorption on solid surface) and it results in smaller SSA values. Because the CSH layer is much thicker than the layers of nitrogen molecules, the CSH layer ignores small details of the molecule size as well. Other methods ignoring small details below the size of approximately 10 nm can also be used. Examples of such methods include methods for the determination of particle size distribution (X-ray sedimentation etc.) as well as methods for the determination of specific surface area, based on air permeability through a bed of particles. In said method the air permeability specific surface of a powder material is a single-parameter measurement of the fineness of the powder. The specific surface is derived from the resistance to flow of air (or some other gas) through a porous bed of the powder.

So-called Blaine method based on air permeability, commonly used in cement industry is also a suitable method as long as the fineness of the material tested lays within the fineness range of cement.

The Si-compound is a water-soluble compound selected from sodium silicate, potassium silicate, silicic acid, sodium metasilicate, potassium metasilicate and any combinations thereof. Suitably Na ₂ (Si0 ₂ )3,3 is used.

The water-soluble Si-compound is suitably present in the aqueous solution as sodium metasilicate, potassium metasilicate and/or waterglass. These compounds are readily soluble in water.

Preferably the molar amount of Si is from 0.8xl0 ^"4 to 1.5xl0 ^"4 mol/m ² of the substrate, particularly preferably from l .OxlO ^"4 to 1.3xl0 ^"4 mol/m ² of substrate. The specific surface area of the substrate is used for the determination of the needed amount of Si.

The Si concentration is from 100 to 10000 μΜ, suitably 400 - 1000 μΜ, particularly suitably 600 - 800 μΜ in the second step.

In the second step an aqueous mixture is formed of water, substrate and at least one Si-compound, and the components may be mixed in any order or simultaneously. Suitably the Si-compound is mixed with water and the substrate is added to the obtained mixture.

In the second step the agitation is carried out for a sufficient period of time to ensure wetting and even distribution of the particles, for more than one second, preferably from 0.5 to 5 min, particularly preferably from 0.5 to 1.5 min. Suitably vigorous agitation is used for ensuring sufficient mixing of the components.

In the third step the agitation is carried out for more than one second, preferably from 0.5 to 20 min, particularly preferably from 2 to 8 min. In this step the reaction of the Ca-compound and the Si-compound occurs in order to precipitate a layer of calcium silicate hydrate on the substrate particles.

Preferably the molar amount of the Ca-compound is 1.5 - 1.9 x Si molar amount, particularly preferably 1.6 - 1.8 x Si molar amount. The Ca-compound may be selected from sparingly soluble and readily soluble Ca- salts. Preferably the sparingly soluble solid Ca-compounds are used whereby the desired heterogenic reaction (heterogenic nucleation) occurs readily. In the case readily soluble Ca-compounds are used the addition of the Ca-compound is carried out gradually, step by step.

The Ca-compound is selected from calcium chloride, calcium nitrate, calcium formate, calcium acetate, calcium bicarbonate, calcium bromide, calcium citrate, calcium chlorate, calcium fluoride, calcium hydroxide, calcium hypochloride, calcium iodate, calcium iodide, calcium lactate, calcium nitrite, calcium oxalate, calcium sulphate, calcium sulphate hemihydrate, calcium sulphate dihydrate, calcium sulphide, tricalciumsilicate, Portland Cement and any combinations thereof, or impure forms thereof. Preferably Ca(OH) ₂ is used. The reactivity and particle size distribution of the Ca-compound, such as Ca(OH) ₂ effects the needed reaction time, and thus the time may be adjusted according the used calcium source. The temperature in the method may range from 5 to 100°C, suitably from 5 to 70°C, preferably from 15 to 25°C.

Suitably normal atmospheric pressure is used in the method. Optionally nanofibrillated cellulose or microfibrillated cellulose (NFC) is added in the second step of the method to obtain a filler comprising particles having a coating of NFC and calcium silicate hydrate. The amount of NFC is suitably in the range from 0.5 to 50% w/w, preferably from 3 to 20% w/w, calculated from the dry weight of the filler.

If desired, in order to increase the coating thickness, the method may be repeated one or more times with coated filler particles as the substrate. In the repeated treatment it is not necessary to use supersaturated Si-solution. Alternatively, for increasing coating thickness any materials comprising soluble Ca and Si may be added to the suspension after the earlier described primary calcium silicate hydrate coating. The amount of the added material can be from 0.01 to 10% of the substrate weight, preferably from 0.1 to 1% of the substrate weight, and the addition can be repeated multiple times. Suitably Portland Cement, and preferably White Portland Cement (WPC) or White Ordinary Portland Cement (WOPC) may be used.

Suitably any mixing tank or reactor may be used for the method, equipped with means to provide efficient/vigorous agitation.

The method may be carried out as a batch method, semi-batch method or continuous method.

If desired, the product may also be subjected to drying using methods known as such in the art. A powdery product can be obtained from the aqueous product by for example spray drying or drying in a fluid bed dryer. Filler comprising calcium silicate hydrate coated particles, for paper, board, cardboard, or tissue manufacture is obtained.

Scanning electron microscope images of uncoated calcium carbonate (calcite) (1A) and CSH coated calcite surface (IB) are illustrated in Fig. 1.

Use

The filler comprising calcium silicate hydrate coated particles may suitably be used in the manufacture of paper, board, cardboard or tissue, particularly for replacing traditional fillers partly or completely. The filler according to the invention may be used for example as a blend together with at least one traditional filler. Suitably at least 25 or at least 50% of the total filler amount may comprise the filler according to the invention. The filler according to the invention is used in amount from 1 to 80% w/w, preferably from 3 to 60% w/w, particularly preferably from 5 to 50% w/w calculated by the dry weight of fibers in the furnish.

Optionally the filler comprising calcium silicate hydrate coated particles may be used together with nanofibrillated cellulose or microfibrillated cellulose in the manufacture of paper, board, cardboard or tissue, for replacing traditional fillers partly or completely. Nanofibrillated cellulose or microfibrillated cellulose may be added to in any stage of papermaking process, suitably to the pulp, fibre stock solution or filler in an amount of 0.5 - 30% w/w, preferably 0.5 - 10%, more preferably 1.0 - 7% of the total weight of filler.

By the use of said filler strength properties of the final product are improved. This can be seen particularly in the manufacture of SC-papers, even after calendering. The use of the filler improves the tensile strength of paper, particularly of calendered printing paper, typically 7 - 15 % and modulus of elasticity typically 18 - 25%. The use makes it possible to increase the amount of filler, whereby less of the expensive fiber material is needed, significant amounts of energy can be saved and production costs can be decreased. When the filler is used together with nanofibrillated or microfibrillated cellulose in the paper or board manufacture, an 25% improvement in the modulus of elasticity can be achieved even after calendaring when compared for example to the use of conventional PCC as filler. Without calendaring the strength effect is even more significant. The filler according to the invention is particularly suitable for use in the manufacture of calendered SC-paper where the filler content can be increased, the total amount of fillers being preferably from 30 to 50 % by weight in calendered SC-papers. However, said filler may as well be used in other paper types, board, cardboard, tissue and the like, and also with higher filler contents from 30 up to 70 % by weight, in all paper and board manufacturing processes based on traditional formation or foam formation, and generally for providing improved strength properties, mechanical properties and printing properties.

Manufacturing method for paper or board

The method for the manufacture of paper, board, cardboard or tissue comprises the steps where starting material comprising paper/board furnish and at least one filler comprising calcium silicate hydrate coated particles is fed into a forming section of a paper/board/cardboard or tissue machine, and to a forming wire, where water is removed from the furnish by draining in the forming section and then by pressing in pressing section to obtain a paper/board/tissue web, which is dried in drying section and finished to paper or board or cardboard or tissue product. Optionally other fillers and additives may also be used. Nanofibrillated cellulose or microfibrillated cellulose may be added, suitably to furnish, pulp, filler or fibers stock solution.

The invention further relates to paper or board obtainable by said method. The invention has several advantages.

For providing the desired average layer thickness of 1-100 nm, preferably 2-20 nm, particularly preferably 5-9 nm of the calcium silicate hydrate coating on the filler particle, it is necessary to use a supersaturated Si solution having saturation around 10-fold. Higher saturation results in a coating with inferior morphology where the coating is not evenly divided on the filler. Because the specific surface area of the filler is high, the amount of the precipitating or crystallizing material needed for the coating is high, and very large liquid volumes for providing around 10-fold supersaturation are required. This would make the method practically impossible.

However, when the average thickness of the coating layer was predetermined (for example as 8.4 nm) and the necessary amount of the coating material was calculated therefrom as the molar amount of Si mol/m ² of substrate, as well as the corresponding amounts of the reagents needed and by following the described procedure, particles with desired coating could be obtained even though the amounts of reactants present correspond to the supersaturation of several hundred folds (100 - 10 000, preferably 600 fold) without the need to use large liquid volumes. Thus practically no waste is formed with the method .

In the repeated coating steps where the coating thickness is increased, supersaturation is not necessary.

The coating is directed to surface of the filler particles, and it was surprising that with such high concentrations and high supersaturation (even 600-fold) a coating with desired morphology was obtained rapidly and easily with heterogeneous precipitation and heterogeneous nucleation. Particularly, in a preferable embodiment where only the Si-compound was dissolved in the second step and the Ca-compound was added as solid material (powder) in the fourth step, the solution in the beginning of the reaction was not saturated, but the saturation increased with the dissolving of the Ca-compound (Ca(OH) ₂ ) and at the same time precipitation took place heterogeneously on the surfaces of the substrate, readily available because of vigorous agitation. The product (calcium silicate hydrate coated particles) was precipitated or crystallized simultaneously with the dissolving of the Ca-compound, resulting in that the solution never reached the situation of too high supersaturation which would affect negatively on the morphology of the product.

For example particles having average particle size of less than 10 μιη may be obtained, with a "hairy" coating, the average layer thickness of the coating being typically from 1 to 100 nm, suitably from 2 to 20 nm. The strength properties of products manufactured using the filler comprising calcium silicate hydrate coated particles are improved, and the bonding of fibres to the filler is better. Particularly, in calendered SC-papers the tensile strength and modulus of elasticity can be increased to a significant extent using said filler alone, or together with nanocellulose. Thus substantial savings can be achieved in the manufacturing costs, particularly as the amount of more valuable starting materials can be decreased and in energy consumption. In a typical paper machine 1% increase in filler content may result in very substantial yearly savings. The following examples are illustrative of embodiments of the present invention, as described above, and they are not meant to limit the invention in any way.

EXAMPLES

EXAMPLE 1

Manufacture of SC-paper using filler comprising calcium silicate hydrate (CSH) coated calcium carbonate particles The materials used in this example were the following :

Fibres

Commercial bleached thermomechanical pulp (TMP) was used as furnish mix 83% and commercial bleached Enorein lightly refined chemical spruce/pine pulp 17%. Canadian standard freeness for TMP pulp was about 35 ml and for Enorain pulp approximately 450 ml. Deletion of latency was made for TMP pulp. Wet disintegration was done for both fibres in 2 I of water at consistency of 1.5% (30g/2l) in mixing speed 10 000 rpm according to standard SCAN-C 18 : 65. PCC filler

The PCC filler was undispersed scalenohedral precipitated calcium carbonate (PCC) having average particle size of 1.9 μιη. The dry matter content was 32.7%. The added amount of PCC in the sheets was adjusted to 30%, depending on filler retention.

Cement

The used cement in this example was CEM I 52, 5R, White Ordinary Portland Cement. Chemicals

The chemicals used in this example were calcium hydroxide from Fluka Analytical and sodium silicate Na ₂ (Si0 ₂ )3,3 from Huber Engineered Materials.

Water used in this example was deionized water.

During the preparation, TMP pulp and chemical Enorein pulp were mixed together in a vessel. The furnish mix and filler were mixed in 35 I container at dry content of 0.933g/l for at least 15 minutes. After that filler-fiber furnish mix was mixed at 600 rpm in 1 I container in same consistency. Calculated added amount of PCC filler was 13.98 g but it was adjusted so that total filler content in sheets was 30 ± 1%.

For the preparation of the different test points (presented in Table 1 with details of trial points) five different compositions of pulp slurry were used :

(1) one reference with fibres and untreated reference PCC filler (30%)

(2) one with fibres and chemically treated pigment coated filler (30%)

(3) one with fibres and chemically and cement treated pigment coated filler (30%) with coating treatment intensity of 1.25

(4) one with fibres and chemically and cement treated pigment coated filler (30%) with coating treatment intensity of 1.5

(5) one with fibres and chemically and cement treated pigment coated filler (30%) with coating treatment intensity of 2.0

Table 1. Details of trial points

According to these test points, three different intensities of cement pigment treatment were used : 3, 6 and 13 following treatments with cement meaning corresponding intensities of 1.25, 1.5 and 2. Treatment intensity refers here particularly to the relative amount of coating/surface area unit, in repeated coating. The calcium silicate hydrate (CSH) chemical treatment of pigment in recipe of reference (1) was following : Specific surface area of PCC dispersion was 10.8 m ² /g. PCC filler amount of 53.69g at 8.4 pH was added with additional water (amount of 1449. lg) to reactor. Water was added up to total volume of 37 litres. These were mixed at 10 000 rpm with two DESOI AKM-70D mixers at 90 I container. Amount of 2.25g of sodium silicate was added. Amount of 1.27g of CaOH was added and mixed at 5 minutes. Treated pigment suspension was settled down at least 1 hour. Additional bright water was decanted away. On calcium silicate hydrate (CSH) cement treated pigments, after Ca(OH) ₂ addition the cement was added (dosage 12.31g) and mixed with two mixers. Cement addition was repeated either 3, 6 or 13 times. Detailed mixing times are presented in Table 2, with detailed times and phases of coating treatment.

Table 2. Phases of coating process

On cement coated samples. Phases 7 ja 8 were repeated 3, 6 or 13

Vigorous mixing increased suspension temperatures and in Table 3 temperatures measured in different phases of coating process are presented.

Table 3. Measured temperatures in different trial points Laboratory handsheets were made with a standard sheet moulder (Lorentzen & Wettre AB, Sweden according to standard SCAN-C 26: 76) with a 100 mesh wire and using circulated water. The sheets were wet-pressed by 3.5 bar at first 5 minutes and after that 2 minutes. The grammage of sheets were adjusted to be 52 g/m ² . Pressed sheets were dried in laboratory upper side against gloss plate in following conditions: Temperature 23 °C and relative humidity of 50 % ± 2 %). Sheets were tightened against fabric frame and dried at least 16 hours. The samples were conditioned at temperature 23 ± 1°C and RH = 50 ± 2 % at least 4 hours before analyzing them. The sheets were calendered with soft nip by DT Laboratory Calender laboratory from DT Paper Science before measurements. Before calendaring SC paper sheets were moisturized at relative humidity 90% at least 24 hours. Speed of calendaring was 15-20 m/s and calendaring pressure was 42bar meaning approximately 113 kN/m line pressures for sheets. The temperature of heated lower roll was about 50 - 55°C. Number of calendaring times was 3 / each paper sheet side meaning 6 calendering nip numbers for each sheet. The smoothness of sheets measured by Lorentze-Wettre device PPS IMPa was from 0.87 - 1.11 μιη. The sheet properties were analyzed according to SCAN standards and the basis weight according to SCAN-P 6: 75. The thickness and the density (SCAN-P 7: 75) were determined with Lorentzen & Wettre micrometer. The tensile strength and the strain at break according to SCAN-P 38: 80 and calculation of elasticity of modulus according to SCAN-P 67 :93 with Lloyd measurement device. The optical properties were determined with Minolta CM-3610d spectrophotometer, ISO-brightness R457 according to SCAN-P 3 :93 and opacity and light scattering coefficient according to SCAN-P 8:93. The ash content of sheets was measured according to the SCAN-P 5 : 63 standard using calculations the coefficient 1.78 for calcium carbonate. The air permeability was measured by Lorentzen & Wettre SE 166 device based on standard SCAN P-26: 78.

The main objective of this example was to evaluate the effect of the pigment CSH coating treatment on filler surface, to strength and basic technical properties of calendered SC paper grade. It was demonstrated that the strength of SC-paper sheets can be increased with high filler content.

Figure 2 shows the tensile strength of calendered SC handsheets as a function of pigment treatment intensity. With cement CSH treatment approximately 15% improvement was observed compared to reference not treated trial point (-). The improvement does not depend on pigment treatment intensity. With chemical CSH treatment no improvement was achieved on tensile strength properties.

Figure 3 shows the modulus of elasticity of calendered SC handsheets as a function of pigment treatment intensity. With cement CSH treatment about 25% improvement obtained with highest treatment intensity of 2 compared to reference not treated trial point (-). Linear growing behaviour as a function of pigment treatment intensity observed. The strain at break decreased linearly as a function of pigment treatment intensity as can be seen in Figure 4. Figure 5 shows the air permeance of calendered sheets as a function of pigment treatment intensity. With chemical CSH treatment of pigment no effect on air permeance observed compared to reference untreated trial point (-). With cement CHS treatment of pigment about 40% decreased air permeance obtained. Optical properties of calendered sheets were measured. Figure 6 shows the light scattering coefficient of calendered sheets. The light scattering coefficient decreased both with chemical and cement CSH treatment. The pigment treatment intensity has some decreasing effect on light scattering coefficient. In Figure 7 the opacity of calendered sheets as a function of pigment treatment intensity is presented. The opacity increased as a function of pigment treatment intensity in cement CSH treated pigment sheets after calendaring.

Calcium silicate hydrate (CSH) treatment (chemical or cement) can be used to make nanostructured surface on filler particles. Within this invention these treated particles were used to enhance paper properties. Improved strength properties, modulus of elasticity and tensile index were obtained and also increased opacity of calendered SC sheets. EXAMPLE 2

Manufacture of paper using NFC and a filler comprising calcium silicate hydrate (CSH) coated calcium carbonate particles

The materials used in this example are described below:

Fibres

Commercial bleached thermomechanical pulp (TMP) was used as furnish mix 83% and commercial bleached Enorein lightly refined chemical spruce/pine pulp 17%. Canadian standard freeness for TMP pulp was about 35 ml and for Enorain pulp approximately 450 ml. Deletion of latency was made for TMP pulp. Wet disintegration was done for both fibres in 2 I of water at concistency 1.5% (30g/2l) in mixing speed 10 000 rpm according to standard SCAN-C 18: 65. PCC filler

The PCC filler was undispersed scalenohedral precipitated calcium carbonate (PCC), having average particle size of 1.9 μιη. The dry matter content was 32.7%. The added amount of PCC in the sheets was adjusted to be 30% depending on filler retention.

Nanofibrillated cellulose

Once dried bleached birch kraft pulp (BHKP) from Finland was used as raw material. The fibre slurry was first soaked at 3% dry solid content for one day and dispersed using a high shear Diaf dissolver for 10 minutes at 700rpm. Suspension was then fed into Masuko Sangyo ^' s Supermasscolloider (Masuko Sangyo Co., Kawaguchi- city, Japan) type MKZA10-15J. During grinding fibre slurry was fed into hopper and forced through a gap between rotary and stator grinding stones. Grinding stone type was a modified stone type MKGA10-80 made of aluminium oxide and resins. Stone diameter was 10". The stone type was non-porous and allows contact grinding to produce ultra-fine particle size. The stone geometry causes intensive dispersing effect and defibrillation of fibres by applying cyclic shear forces.

The fibril cellulose was obtained after eight passes through the grinder by using decreasing gap width and increasing operating power. Rotation speed was fixed to 1500rpm. The quality of fibril cellulose was controlled by moving the lower stone to set the clearance between the grinding stones. Fibre suspension was subjected to compression and shear forces between the stones, which determined the particle size of the output material. The operating power of the grinder motor was monitored through a frequency converter, which was connected to the grinder. Grinding conditions were recorded during trials and the operating power was used as the primary control parameter. Because of thermal expansion of grinding stones the zero point of clearance altered and the gap between the stones was not used to control the quality of output material.

Cement

The used cement in experiments was CEM I 52, 5R, White Ordinary Portland Cement. Chemicals

The chemicals were calcium hydroxide from Fluka Analytical, and sodium silicate Na ₂ (Si0 ₂ )3,3 from Huber Engineered Materials. Water was deionized water.

During the preparation, TMP pulp and chemical Enorein pulp were mixed together in a vessel.

The furnish mix and filler were mixed in 35 I container at dry content of 0.933g/l at least 15 minutes. After that filler-fiber furnish mix was mixed eat 600 rpm in 1 I container in same consistency. Calculated added amount of PCC filler was 13.98 g but it was adjusted so that total filler content in sheets was 30 ± 1%.

For the preparation of the different test points (presented in Table 4) different compositions of pulp slurry were used :

(1) one reference with fibres and untreated reference PCC filler (30%)

(2) one with fibres and chemically and cement CSH coated filler (30%) with coating treatment intensity of 1.25

(3) one with fibres and chemically and cement CSH together with nanofibrillated cellulose coated filler (30%) with coating treatment intensity of 1.25 Table 4. Details of trial points

The calcium silicate hydrate (CSH) coated pigment treatment was done similar way than described in Example 1. The pigment treatment intensity was 1.25 in both trial points 2 and 3. The nanofibrillated cellulose was added to the suspension in coating process in phase 4 as described in Table 5. The dry solid content of nanofibrillated cellulose was 3% and the added amount was PCC: NFC 90 : 10. Table 5. Phases of coating process

** On cement coated samples. Phases 7 ja 8 were repeated 3 times (trial points 2 and 3).

Laboratory handsheets and calendaring were made using same conditions and equipment's as described in Example 1. The sheet properties were measured using the same methods as presented in Example 1.

The main objective of this example was to evaluate the effect of nanofibrillated cellulose in the pigment CSH coating treatment on filler surface to strength and basic technical properties of calendered SC paper grade. Figure 8 shows the tensile strength of calendered SC handsheets as a function of pigment treatment intensity. With cement CSH treatment together with nanofibrillated cellulose approximately 12% improvement observed in lower treatment intensity 1.25 compared to reference not treated trial point (-). The improvement with dosage ratio of 90: 10 nanofibrillated cellulose: PCC in sheets was slightly better (about 2%) than with only cement CSH coating alone.

Figure 9 shows the modulus of elasticity of calendered SC handsheets as a function of pigment treatment intensity. With cement CSH treatment together with nanofibrillated cellulose approximately 19% improvement observed in lower treatment intensity 1.25 compared to reference not treated trial point (-). The improvement with nanofibrillated cellulose in coating cement CSH process was slightly better (about 7 %) than with only cement CSH coating alone. The effect of nanofibrillated cellulose was larger to modulus of elasticity than tensile index. Figure 10 shows the strain at break of calendered SC handsheets as a function of pigment treatment intensity. With cement CSH treatment together with nanofibrillated cellulose slightly decreased on strain at break observed in lower treatment intensity 1.25 compared to reference not treated trial point (-). No significant difference observed by adding nanofibrillated cellulose during coating process. Figure 11 shows the air permeance of calendered sheets as a function of pigment treatment intensity. With cement CSH treatment together with nanofibrillated cellulose air permeance decreased approximately 39% in lower treatment intensity 1.25 compared to reference not treated trial point (-). The decrease on air permeance with nanofibrillated cellulose in coating cement CSH process was slightly better (about 7 %) than with only cement CSH coating alone.

The optical properties of calendered sheets were measured. Figure 12 shows the light scattering coefficient of calendered sheets with cement CSH coating together with nanofibrillated cellulose. The light scattering coefficient decreased for both trial points (2&3) on low pigment treatment intensity 1.25 compared to untreated reference. The decrease was slightly lower when nanofibrillated cellulose was used in coating process.

Figure 13 shows the opacity of calendered sheets as a function of pigment treatment intensity. The opacity increased as a function of pigment treatment intensity in cement CSH coating together with nanofibrillated cellulose. As conclusion can be said that no significant effect of nanofibrillated cellulose to the measured optical properties on these treatment intensities and amount of cellulose. As a summary can be concluded that nanofibrilllated cellulose can be used together with calcium silicate hydrate (CSH) treatment (by chemicals or cement) in pigment coating process. Using nanofibrillated cellulose the strength properties, especially modulus of elasticity, can be enhanced. The air permeance decreased when nanofibrillated was used in CSH coating process.