FI123287B - paper Product - Google Patents

Description

FIELD OF THE INVENTION

The invention relates to a supercalendered paper product containing a gypsum-fiber composite product as a coating pigment or filler pigment. The present invention also relates to a process for producing a supercalendered paper product and the use of a gypsum fiber composite product as a coating pigment or filler pigment in the manufacture of a supercalendered paper product.

Background of the Invention

The papermaking process begins with the production of a stock in which cellulose fibers are mixed with water and an inorganic filler (usually clay or calcium carbonate or also gypsum). The resulting slurry is applied via a headbox to a wet wire or press felt or wire to form a fibrous web of cellulosic fibers in the wire section of the papermaking machine. The water is then removed in the dewatering section and the formed web is led to a press section having a series of roll presses where the excess water is removed. The web is then led to a dryer section of a papermaking machine, where most of the remaining water is typically evaporated by means of steam-heated dry drums. Post-drying operations include calendering, in which the dry paper product travels between the rollers under pressure, whereby the smoothness and gloss of the surface is improved and the wing / thickness profile becomes more uniform. There are various calendars, such as machine calendars, in which the rolls are generally steel rolls and include a heated roll (heat roll), and super calendars which alternate between hard and soft heated rolls.

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™ The Super Calender is a calender with alternating hard and soft rolls through which the paper passes, increasing its density, smoothness and gloss.

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Gypsum, i.e., calcium sulfate dihydrate CaSO 4 2H 2 O, is a suitable material both as a coating pigment and as a filler, especially in paper products. Particularly good

Lo coating pigment and filler are obtained if the gypsum in question has good brightness, io gloss and opacity. Gloss is good when the particles are sufficiently small, flat and wide (tile-like). Opacity is good when a little

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the cartridges are refractive, small and of the same size (narrow particle size distribution).

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The morphology of gypsum product particles can be determined by scanning electron micrographs. Useful micrographs are obtained, for example, with a Philips FEI XL 30 FEG-type scanning electron microscope.

The particle size of the gypsum product is expressed as the weight-average diameter D50 of the particles it contains. More specifically, the D50 is the diameter of a particle assumed to be circular, smaller than 50% of the total weight of the particles. The D50 can be measured by suitable means such as microscopy.

The flatness of the crystal means that it is thin. The shape of the flat crystals is suitably expressed by the aspect ratio SR (shape ratio). SR is the ratio of crystal length (longest dimension) to crystal thickness (shortest transverse dimension). The SR of a gypsum product is the average SR of its individual crystals.

The crystalline plateau means that it is wide. The aspect ratio is suitably expressed as aspect ratio AR. AR is the ratio of crystal length (longest dimension) to crystal width (longest transverse dimension). The AR of a gypsum product is the average AR of individual crystals.

The SR and AR of the gypsum product can be evaluated by examining its scanning electron micrographs. A suitable scanning electron microscope is the aforementioned Philips FEI XL 30 FEG.

The same crystal particle size means that the crystal particle size distribution is narrow. The width is expressed as the gravimetric weight distribution WPSD and is expressed as (D75-D25) / D50, where D75, D25 and D50 are the diameters of the assumed circular particles, the smaller particles representing 75%, 25% and 50% of the total weight, respectively. The particle size distribution is obtained with a suitable particle size-5 lyser such as the Sedigraph 5100 of the type mentioned above.

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o Gypsum occurs as a natural mineral or is formed as a by-product of chemical processes, eg phospho-gypsum or flue gas gypsum. In order to further refine the gypsum by crystallizing it into a coating pigment or filler, it must first be calcined into calcium sulfate hemihydrate (CaSO 4 FbO), followed by

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can be hydrated back by dissolving the hemihydrate in water and precipitating to obtain pure gypsum. Calcium sulfate can also be present in an anhydrite form lacking crystalline water (CaSCU).

Depending on the calcining conditions of the gypsum raw material, calcium sulfate hemihydrate can exist in two forms: α and β hemihydrate. The β-form is obtained by heat treatment of the gypsum crude material at atmospheric pressure, while the α-form is obtained by treating the gypsum crude material at a vapor pressure higher than atmospheric pressure, or by chemical wet calcination of saline or acid solutions, e.g., at about 45 ° C.

WO 88/05423 describes a process for the preparation of gypsum by hydrating calcium sulfate hemihydrate in an aqueous slurry thereof having a dry matter content of 20-25% by weight. Gypsum with a maximum dimension of 100-400 µm and a second largest dimension of 10-40 µm is obtained.

AU 620857 (EP 0334292 A1) describes a method of making gypsum from a slurry containing up to 33.33% by weight of powdered hemihydrate to obtain needle-type crystals having an average size of 2 to 200 µm and an aspect ratio of 5 to 50 µm. See page 15, lines 5-11, and examples in this publication.

US 2004/0241082 describes a process for the preparation of small needle-type gypsum crystals (length 5-35 µm, width 1-5 µm) from an aqueous slurry of hemihydrate having a dry matter content of 5-25% by weight. The idea in this US publication is to reduce the water solubility of gypsum with an additive in order to prevent crystals from dissolving during papermaking.

DE 32 23 178 C1 describes a process for producing organic fibers coated with one or more inorganic materials. In one embodiment, cellulosic fibers, gypsum and water are mixed. The mixture is compressed to give a plastic mass, which is then dried and finely pulverized to give fine particles. The resulting product can be used as an additive or filler, e.g. in bitumen pulps or crystals.

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5 WO 2008/092990 describes a gypsum product consisting of intact crystals of size

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^ 0.1 - 2.0 pm. The aspect ratio SR of the crystals is at least 2.0, preferably 2.0 to 50, and the aspect ratio AR is 1.0 to 10, preferably 1.0 to less than 5.0, m

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x WO 2008/092991 describes a method for preparing a gypsum product, wherein calcium sulfate hemihydrate and / or calcium sulfate anhydrite and water are contacted

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such that the calcium sulfate hemihydrate and / or calcium sulfate anhydrite and water g react with each other to form a crystalline gypsum product. The resulting reaction mixture has a solids content of 34-84% by weight.

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Description of the Invention

It is an object of the invention to provide a supercalendered paper product having improved properties such as good brightness, good brightness, low yellowness, good light scattering, good opacity, low roughness, good gloss and high density.

According to the present invention, it has been found that a particular gypsum-fiber composite product having gypsum crystallized on the fiber surface and adhering to the fiber quite strongly can be used as a filler pigment or coating pigment in the manufacture of a supercalendered paper product, resulting in unexpected good whiteness, slight yellowing, good light scattering, good opacity, low roughness, good gloss and high density. In the manufacture of supercalendered paper, improved filler pigment retention and homogeneous filler distribution can also be achieved. A higher amount of filler can also be achieved.

Thus, according to a first aspect of the invention, there is provided a supercalendered paper product containing first cellulosic fibers and a gypsum fiber composite product as a filler pigment or a coating pigment, wherein the gypsum fiber gypsum composite product gypsum is or calcium sulphate anhydrite and an aqueous second fiber suspension.

The gypsum-fiber composite product may be similar to that described in Finnish Patent Application Fl 20085767, filed August 11, 2008.

The gypsum adheres to the fiber and as a result most gypsum-fiber composites are shown as a single piece. The shape and size of the gypsum can be roughly estimated by microscopic images. With fiber-attached gypsum

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™ you may have the forms described in WO 2008/092990 and WO 2008/092991 and | sizes. However, the gypsum crystallized according to the invention may also be of the needle type.

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The size of the gypsum crystals formed on the fiber surface is preferably 0.1 to 5.0 µm, g more preferably 0.1 to 4.0 µm, and most preferably 0.2 to 4.0 µm. However, in a finished paper, a percalendered paper product may have a larger size of gypsum crystals.

Preferably, the first cellulosic fibers are conventional papermaking pulp fibers, which are chemical, mechanical, chemimechanical, or deinked pulp fibers. The chemical pulps are sulphate pulp and sulphite pulp. The mechanical pulps include rock grit (SGW), cold pulp (RMP), pressure grit (PGW), hot pulp (TMP), and chemically treated high yield pulps such as Kemi-thermomechanical pulp (CTMP). The deinking compound can be produced using mixed office waste (MOW), newsprint (ONP), magazines (OMG), etc. Mixtures of different pulps can also be used.

Preferably, the second fiber of the gypsum-fiber composite product contains a second cellulosic fiber, such as a chemical, mechanical, chemimechanical or deinked pulp fiber or a synthetic fiber such as a polyolefin, e.g. polypropylene. The chemical pulps are sulphate pulp and sulphite pulp. Mechanical pulps include rock pulp (SGW), cold pulp (RMP), pressure pulp (PGW), heat pulp (TMP), and chemically treated high-yield pulps such as Kemi-thermomechanical pulp (CTMP). The deinking compound can be produced using mixed office waste (MOW), newsprint (ONP), magazines (OMG), etc. Mixtures of different pulps can also be used.

Said first cellulose fiber and said second cellulose fiber may be the same or different, preferably the same.

Preferably, the weight ratio of gypsum to fiber, calculated as dry matter, in the gypsum-fiber composite product is 95: 5-50:50, preferably 75:25-50:50.

According to the invention, the supercalendered paper product may further comprise one or more of the following: a natural or synthetic polymeric binder, an optical brightener, a rheology modifier, and an adhesive. These materials or some of these materials may be incorporated into a gypsum-fiber composite product. The adhesive may be a resin adhesive or a reactive adhesive such as an alkyl ketene dimer (AKD) or an alkylene mimetic acid anhydride (ASA), δ

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The amount of Gypsum Fiber Composite Product in the supercalendered paper product is preferably 10 to 60% by weight, more preferably 20 to 50% by weight,

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™ by dry weight. Correspondingly, the amount of the first cellulosic fibers in the | the product preferably contains 40-90% by weight, more preferably 50-80% by weight, determined on a dry weight basis.

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g When used as a coating pigment, the gypsum-fiber composite product contains gypsum crystals having a size of preferably 0.1 to 1.0 µm, more preferably 0.5 to 1.0 µm. When used as a filler, the gypsum-fiber composite product contains gypsum crystals having a size of preferably 1.0 to 5.0 µm, more preferably 1.0 µm to 0.0 µm. As discussed above, the size of the gypsum crystals in the finished supercalendered paper product may be larger.

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Preferably, in the crystallization, the weight ratio of calcium sulfate hemihydrate and / or calcium sulfate anhydrite to water is 0.03-0.6: 1, more preferably 0.05-0.5: 1.

Preferably, the dry fiber content in the crystallization is from 3 to 30% by weight.

Preferably, the content of calcium sulfate hemihydrate and / or calcium sulfate anhydrite in the crystallization is 10-57% by weight.

Further, the resulting gypsum-fiber composite product can be homogenized to form a homogenized product, or dried and ground to form a gypsum-fiber composite product in the form of dry particles.

The other fiber can be finely ground before crystallizing the gypsum. However, it is preferable to finely grind the gypsum-fiber composite product.

The gypsum-fiber composite product can be manufactured at a pulp mill or on site at a paper mill. In the latter case, the gypsum-fiber composite product preferably requires a retention time of at least 15 minutes.

The fastener can be included for crystallization.

The fastener may be selected from the group consisting of polyaluminium chloride, polydiallyldi-methylammonium chloride (poly-DADMAC), anionic or cationic polyacrylates.

The crystallization can be carried out without the crystallization mode modifier.

Crystallization may also be carried out in the presence of a crystallization mode modifier.

The crystallization mode modifier may be added to water or aqueous fiber suspension prior to the addition of calcium sulfate hemihydrate and / or calcium sulfate anhydrite.

The temperature of the water in the reaction mixture may be anything from 0 to 100'em.

9 Preferably the temperature is 0-80 ° C, more preferably 0-50 ° C, more preferably 0- ™ 40 ° C, most preferably 0-25 ° O.

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The crystallization mode modifier may be an inorganic acid, an oxide, a base or a salt.

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Examples of useful inorganic oxides, bases and salts g are AIF 3, Al 2 (SO 4) 3, CaCl 2, Ca (OH) 2, H 3 BO 4, NaCl, Na 2 SO 4, NaOH, NH 4 OH, g (NH 4) 2 SO 4, MgCl 2, MgSO 4 and MgO.

The crystallization mode modifier may also be an organic compound which is an alcohol, acid or salt. Suitable alcohols include methanol, ethanol, 1-butanol, 2-butanol, 7-hexanol, 2-octanol, glycerol, i-propanol, and C 5 -C 10 fatty alcohols based on alkylpolyglycoside.

The crystallization mode modifier is preferably a compound having one or more carboxylic or sulfonic acid groups in the molecule, or a salt of such a compound. Among the organic acids, mention may be made of carboxylic acids such as acetic acid, propionic acid, succinic acid, tartaric acid, ethylenediamine-succinic acid (EDDS), iminodimeric acid (ISA), ethylenediamine tetraacetic acid (EDA), bis (2- (1,2-dicarboxyethoxy) ethyl aspartic acid (AES), and sulfonic acids such as amino-1-naphthol-3,6-disulfonic acid, 8-amino-1-naphthol-3,6-disulfonic acid, po, 2-aminophenol-4-sulfonic acid, anthraquinone-2,6-disulfonic acid, 2-mercaptoethanesulfonic acid, poly (styrene sulfonic acid), poly (vinyl sulfonic acid), and di-, tetra- and hexanaminostilbenzenesulfonic acids.

Among the organic salts, there may be mentioned salts of carboxylic acids such as Mg formate, Na and NH4 acetate, Na2 maleate, NH4 citrate, Na2 succinate, K-oleate, K-stearate, Na2-ethylenediaminetetraacetic acid (Na2-EDTA), Na6 -as -paragic acid ethoxysuccinate (Na6-AES) and Na6-aminotriethoxysuccinate (Na6-TCA).

Salts of sulfonic acids are also useful, such as Na-n- (C 10 -C 13) alkylbenzenesulfonate, C 10 -C 16 alkylbenzene sulfonate, Na-1 octyl sulfonate, Na-1 dodecane sulfonate, Na-1 hexadecane sulfonate, K-fatty acid , Na-Cu-C16-olefin sulfonate, Na-alkyl naphthalene sulfonates with anionic or non-ionic surfactants, di-K-oleic acid sulfonates, and salts of di-, tetra- and hexa-aminostilbenzenesulfonic acids. Among the sulfur-containing organic acids, mention should also be made of sulphates such as C-12-Cu fatty alcohol ethanol ™ terisulphates, Nα-2-ethyl xylsulphate, Na-n-dodecyl sulphate and Na-lauryl o oate, and sulfosuccinates such as Na-sulfosuccinate monoalkylpolyglycol ether,

Na-dioctylsulfosuccinate and Na-dialkylsulfosuccinate.

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Phosphates such as Na-nonylphenyl and Na-dinonylphenyl ethoxylated esters, K-aryl ether phosphates, and tri-ethanolamine salts of polyaryl polyether phosphate can also be used.

Cationic surfactants such as octylamine, triethanolamine, di (hydrogenated animal fatty alkyl) dimethylammonium chloride, and nonionic surfactants such as various modified fatty alcohol ethoxylates can be used as modifiers of the crystallization. Useful polymeric acids, salts, amides and alcohols include, but are not limited to, polyacrylic acids and polyacrylates, acrylate-maleate copolymers, polyacrylamide, poly (2-ethyl-2-oxazoline), polyvinylphosphonic acid, acrylic acid (allyl), , poly-α-hydroxyacrylic acid (PHAS), polyvinyl alcohol and poly (methyl vinyl ether - alpha-maleic acid).

Particularly preferred crystallization modifiers are ethylenediamine succinic acid (EDDS), iminodimeric succinic acid (ISA), ethylenediamine tetraacetic acid (EDTA), diethylenetriaminepentaacetic acid (DTPA), nitrileotriacetic acid (NDTA), - tetra- and hexa-aminostilbenzenesulfonic acids and their salts, such as Na-aminotriethoxysuccinate (Na6-TCA), and alkylbenzenesulfonates.

The crystallization mode modifier may be used in an amount of 0.01-5.0%, most preferably 0.02-1.78%, based on the weight of calcium sulfate hemihydrate and / or calcium sulfate anhydrite.

Crystallization typically uses β-calcium sulfate hemihydrate. It can be prepared by heating the gypsum raw material to a temperature of 140-300 Ό, preferably 150-200 Ό. At lower I temperatures, the gypsum crude material is not sufficiently dehydrated and at higher temperatures it is overhydrated to anhydrite. The calcined calcium sulfate hemihydrate generally contains impurities in the form of small amounts of calcium sulfate dihydrate and / or calcium sulfate anhydrite. It is preferred to use the β-calcium sulfate hemihydrate obtained by flash calcination, e.g. fluidized bed calcination, whereby the gypsum crude material is heated to the required temperature as quickly as possible. However, it has been possible to use α-calcium sulfate hemihydrate for crystallization, o

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ώ It is also possible to use calcium sulphate anhydrite as a start. Anhydrite «is obtained by calcination of gypsum crude material. There are three forms of anhydrite

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TOA; the first, so-called anhydrite I, cannot form gypsum by reaction with water, such as insoluble anhydrites II-u and II-E. Other forms, so-called anhydrite III, also known as soluble anhydrite and having S in three forms: β-anhydrite III, β-anhydrite ΙΙΓ and α-anhydrite III, and anhydrite II-10 form pure gypsum in contact with water.

After contacting the calcium sulfate hemihydrate and / or calcium sulfate anhydrite, the aqueous fiber suspension, and possibly the crystallization mode modifier, all of them are reacted to calcium sulfate dihydrate, i.e. gypsum. The reaction is effected, for example, by stirring, preferably vigorously stirring, the said substances together for a sufficient time, which can easily be determined experimentally. At high solids contents, vigorous mixing is necessary because the slurry is thick and the reagents do not easily contact each other. Preferably, the hemihydrate and / or anhydrite, the aqueous fiber suspension and, optionally, the crystallization mode modifier are mixed at the temperature given above for the water. The initial pH is typically acidic, preferably 3-7, more preferably 3-6. If necessary, the pH is adjusted with aqueous NaOH and / or H2SO4, typically with 10% NaOH and / or H2SO4.

Because gypsum has a lower solubility in water than hemihydrate and soluble anhydrite, gypsum formed by reaction of hemihydrate and / or anhydrite with water tends to crystallize immediately from the aqueous medium onto another fiber. This crystallization can be controlled by the above crystallization modifier to provide a useful gypsum-fiber composite product.

The gypsum-fiber composite product may also be treated with other additives. A typical additive is a biocide that inhibits the activity of microorganisms during storage and use.

According to another aspect of the invention there is provided a process for producing a supercalendered paper product as defined above, comprising providing a pulp in which the first cellulosic fibers are mixed with water and a gypsum fiber composite product, the resulting slurry is discharged into a , where the excess water is removed, the web is then led to a drying section where most of the remaining water is evaporated, and finally the paper is recalendered to improve the smoothness and gloss of the paper surface.

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The gypsum-fiber composite product can be incorporated into the mixture in the form of an aqueous product or in a dried form, optionally finely ground to a particulate form.

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Supercalendering of paper can be performed in an on-line calender or in a separate calender. In the latter case, the calender is separate from the actual paper machine. The rollers of the super calendars may be heated heat rollers.

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The invention further relates to the use of a gypsum-fiber composite product in which gypsum appears as crystals on the surface of the fiber and wherein the gypsum crystals are obtained by contacting calcium sulphate hemihydrate and / or calcium sulphate anhydrite with an aqueous

Preferably, the amount of gypsum-fiber composite product in the supercalendered paper product is 10 to 60% by weight, more preferably 20 to 50% by weight, determined on a dry weight basis. Correspondingly, the amount of said cellulose fibers in the paper product is preferably 40-90% by weight, more preferably 50-80% by weight, determined on a dry weight basis.

Brief description of the drawings

Figures 1-8 show electron microscope micrographs of the calcium sulfate dihydrate-fiber-composite products of Examples 1-8, and Figures 9-17 show different properties of supercalendered (SC) paper samples in which the filler is calcium sulfate dihydrate-fiber-composite product, or kaolin clay.

Figure 1a shows a calcium sulfate dihydrate / TMP composite at 18% hemihydrate solids (HH / (HH + water)) on an SEM micrograph, Figure 1b shows a SEM micrograph for the same composite as washed in saturated calcium sulfate solution / SEM micrograph with 42% hemihydrate solids (HH / (HH + water)),

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Fig. 2b shows a SEM micrograph of the same composite as Fig. 2a washed with cd in a saturated calcium sulfate solution, Fig. 3 shows a calcium sulfate dihydrate / eucalyptus sulfate mass composite | SEM micrograph with a hemihydrate solids content of 6.25% m (HH / (HH + water)),

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g Figure 4 shows a SEM micrograph of fibers derived from a calcium sulphate dihydrate / eucalyptus sulphate composite with a hemihydrate solids content of 7.5% (HH / (HH + water)); and washing the composite with a saturated calcium sulfate solution, Figure 5b shows a SEM micrograph for the same composite as Figure 5a and mixing with a Heidolph laboratory mixer at 350 rpm for a few minutes, Figure 6a showing calcium sulfate dihydrate / pine washed with a saturated calcium sulfate solution, Figure 6b for the same composite of the SEM micrograph as in Figure 6a, and mixed with a Heidolph laboratory mixer at 350 rpm for a few minutes, Figure 7 shows the calcium sulfate Fig. 8 shows a SEM micrograph of a hydrate / birch sulphate mass composite, wherein the composite is washed with a saturated calcium sulphate solution, Fig. 8 shows a SEM micrograph of a calcium sulphate dihydrate / plastic fiber composite; Figure 11 shows the scattering of the SC paper samples, Figure 12 shows the light scattering of the SC paper samples,

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Figure 13 shows opacity of SC paper samples, i

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Figure 14 shows the PPS roughness of SC paper samples, m c x x Figure 15 shows the gloss of SC paper samples,

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£ 3 Figure 16 shows the gloss of SC paper samples vs. the pulp of the pulp and

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Figure 17 shows the air permeability (Bendtsen porosity) of SC paper samples.

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eXAMPLES

The invention will now be described in more detail by way of examples. The examples are not intended to limit the scope of the claims. Percentages in this specification refer to weight percent unless otherwise specified.

First, general information on synthesis and product analysis is provided. The information for each example is then presented.

Synthesis

First, general information. Method optimization for paper pigments was performed. The parameters were: HH (original hemihydrate, wt%) 5-57

Fiber content (% by weight) 3-30

Additive content (% by weight of DH (dihydrate)) 0.100-1

The reaction was carried out at the pH of the system. The amount of the conventional modifying chemical is calculated as a percentage of the precipitated calcium sulfate dihydrate (% w / w DH).

Experiments were performed on the following apparatus.

The reactor is Hobart, type N50CE. The hemihydrate and chemicals are batch-added to the aqueous fiber suspension phase to give a hemihydrate slurry having an initial solids content of 5-57% by weight. The agitation speed is about 250-500 rpm. The reaction is carried out at the pH of the system.

Analysis

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° The morphology of calcium sulfate dihydrate was examined using a FEI XL 30 FEG toweling electron microscope. The conversion of the hemihydrate to the dihydrate was analyzed using a Mettler Toledo TGA / SDTA85 1/1100 thermogravimetry analyzer (TG).

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The crystal structure was determined with a Philips X'pert X-ray powder diffractometer (XRD).

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lq Example 1

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g 1. 800 g of water is placed in a Hobart N50 CE Laboratory Mixer. Add a few drops of biocide (Fennosan IT 21).

2. 200 g of TMP (thermomechanical pulp) with a solids content of 36% are added to the reactor.

3. Fluidized bed calcined β-calcium sulphate hemihydrate is steadily added to the reactor, setting the agitator speed to position 1. The total amount of added hemihydrate is 200 g (giving an HH / (HH + water) value of 18% by weight). After the addition, the mixer speed is increased to position 2. The composite is mixed for five minutes.

4. Allow the formation of calcium sulfate dihydrate for one hour.

The resulting pigment-fiber composite is shown in Figure 1a, after washing with saturated calcium sulfate water in Figure 1b.

Example 2 1. 430 g of water is placed in a Hobart N50 CE laboratory mixer. Add a few drops of biocide (Fennosan IT 21).

2. 570 g of TMP (thermomechanical mass) with a solids content of 36% is added to the reactor.

3. Fluidized bed calcined β-calcium sulphate hemihydrate is steadily added to the reactor, setting the agitator speed to position 1. The total amount of added hemihydrate is 570 g (giving 42% HH / (HH + water)). After the addition, the mixer speed is increased to position 2. The composite is mixed for five minutes.

4. Allow the formation of calcium sulfate dihydrate for one hour.

The resulting pigment-fiber composite is shown in Fig. 2a, after washing with saturated calcium sulfate water in Fig. 2b.

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™ Example 3 i

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cp lq 1. 456.5 g of eucalyptus sulfate pulp with a solids content of 17.7%

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n Hobart N50 CE laboratory mixer.

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lq 2. Fluidized bed calcined β-calcium sulphate hemihydrate is uniformly added to the reaction mixture.

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By setting the mixer to speed 1, the total amount of hemihydrate added is 25 g (giving a HH / (HH + water) value of 6.25% by weight). After adjusting the Li-™, the agitator speed is increased to position 2. The composite is agitated for five minutes.

3. Wait for 1 hour for calcium sulfate dihydrate to form.

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The resulting pigment-fiber composite after washing with saturated calcium sulfate water is shown in Figure 3.

Example 4 1. 47 g of water is placed in a Hobart N50 CE laboratory mixer. Add a few drops of biocide (Fennosan IT 21).

2. 295.5 g of eucalyptus sulfate pulp with a solids content of 17.7% are added to the reactor.

3. Fluidized bed calcined β-calcium sulphate hemihydrate is steadily added to the reactor, setting the agitator speed to position 1. The total amount of added hemihydrate is 25 g (giving an HH / (HH + water) value of 7.5% by weight). After the addition, the mixer speed is increased to position 2. The composite is mixed for five minutes.

4. Allow the formation of calcium sulfate dihydrate for one hour.

The resulting fiber product is shown in Figure 4.

Example 5 1. 44.8 g of water are placed in a Hobart N50 CE laboratory mixer. Add 1.6 g of polyaluminium chloride and a few drops of biocide (Fennosan IT 21).

2. 640 g of pine sulfate pulp with a solids content of 7% is added to the reactor.

cm 3. Fluidized bed calcined β-calcium sulfate hemihydrate is steadily added to the reactor with the mixer operating speed set to 1. The size of the added hemihydrate is 160 g (giving 20% by weight of HH / (HH + water)). After adjusting Li-lq, the operating speed of the mixer is raised to position 2. Composite c \ j,. .....

stir for five minutes.

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lq 4. Wait for 1 hour for calcium sulphate dihydrate to form.

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g The resulting pigment-fiber composite after washing with saturated calcium sulfate water is shown in Figure 5.

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Example 6 1. 15.8 g of water is placed in a Hobart N50 CE laboratory mixer. Add 0.6 g of poly-DADMAC and a few drops of biocide (Fennosan IT 21).

2. 226 g of pine sulfate pulp with a solids content of 7% are added to the reactor.

3. Fluidized bed calcined β-calcium sulphate hemihydrate is uniformly added to the reactor, setting the agitator speed to position 1. The total amount of added hemihydrate is 300 g (giving a HH / (HH + water) value of 57% by weight). After the addition, the mixer speed is increased to position 2. The composite is mixed for five minutes.

4. Allow the formation of calcium sulfate dihydrate for one hour.

The resulting pigment-fiber composite after washing with saturated calcium sulfate water is shown in Figure 6.

Example 7 1. 116g of water is placed in a Hobart N50 CE Laboratory Mixer. Add a few drops of biocide (Fennosan IT 21).

2. 800 g of pine sulfate pulp (14.5% solids content) is added to the reactor.

3. Fluidized bed calcined β-calcium sulphate hemihydrate is steadily added to the reactor, setting the agitator speed to position 1. The total amount of added hemihydrate is 200 g (giving an HH / (HH + water) value of 20% by weight). After addition, the agitator speed is raised to position 2. The composite w is stirred for five minutes.

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cp ^ 4. Formation of calcium sulfate dihydrate is expected for one hour.

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| The resulting pigment-fiber composite after washing with saturated calcium sulfate water is shown in Figure 7.

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o Example 8 o o

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1. 600 g of water is placed in a Hobart N50 CE Laboratory Mixer. Add a few drops of biocide (Fennosan IT 21).

2. 10 g of synthetic polypropylene fiber are added to the reactor.

3. Fluidized bed calcined β-calcium sulphate hemihydrate is steadily added to the reactor, setting the agitator speed to position 1. The total amount of added hemihydrate is 300 g (giving 34% HH / (HH + water)). After the addition, the mixer speed is increased to position 2. The composite is mixed for five minutes.

4. Allow the formation of calcium sulfate dihydrate for one hour.

The resulting pigment-fiber composite after washing with saturated calcium sulfate water is shown in Figure 8.

Example 9

A pigment-filler composite was prepared as described in Example 1 using a thermomechanical pulp (TMP) at a fiber solids content of 8%. The rebated β-calcium sulfate hemihydrates were added in an amount giving an HH / (HH + water) value of 20%.

The application test for uncoated supercalendered paper was performed as follows.

Composite samples were disintegrated using a Hollander mill. In sheet making, the composite was blended with the crude fiber fraction and compared with conventional kaolin and PCS fillers (precipitated calcium sulfate). The filler level used was 30% and the target basis weight was 60 ± 2 g / m2. The filler level was controlled by changing the ratio of composite to untreated fiber. Samples were calendered using 2 + 2 nips with in-line weights of 100, 175, and 250 kN / m. The roll temperature was 80 °, the relative humidity 85%, and the calendering speed 30 m / min.

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° The ISO brightness of the paper samples was measured in Rye. The results are shown in Figure 9.

The results show that the effect of PCS and the composite of the present invention on pairwise brightness was similar, whereas kaolin clay gave 4 percentage points / l worse in brightness than PCS and the composite.

CVJ

g The ClE whiteness of the paper samples was measured. The results are shown in Figure 10. The results show that the filler-fiber composite gave significantly better brightness to the paper than PCS and kaolin clay.

17

The yellowing of the paper samples (ClE yellow color coordinate 0 * ^ / 2 *) was measured. The results are shown in Figure 11. The results show that the filler-fiber composite gave significantly lower yellows than PCS and kaolin clay.

The light scattering of the paper samples was measured. The results are shown in Figure 12. The results show that the filler-fiber composite improved light scattering by about 5 to 10 units compared to PCS and kaolin clay.

The opacity of the paper samples was measured. The results are shown in Figure 13. From the results, it can be concluded that the improvement in light scattering also had a positive effect on the opacity values. At lower line loads, the filler-fiber composite showed about one unit higher opacity than kaolin and about 2 units higher than PCS. The differences increased with higher line loads and were, respectively, 2 and 3 units higher than kaolin and PCS.

The PPS roughness of the paper samples was measured. The results are shown in Figure 14. The results show that kaolin and filler-fiber composite had similar roughness whereas PCS had a roughness of about 0.1 µm. The filler-fiber composite had a smaller difference between the coarseness of the top side (TS) and wireside (WS) route.

The gloss of the paper samples at 75 ° was measured. The results are shown in Figure 15. The results indicate that the filler-fiber composite had a calendered luster about 4 units higher than PCS and one unit higher than kaolin.

In Figure 16, the calendered luster is shown against the fluffiness of the paper pulp. From the results, it can be seen that the filler-fiber composite had a bulk density of about 0.1 units higher than kaolin with the same gloss value.

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The porosity of the paper samples was measured by the Bendtsen method. This method o measures the speed at which air passes through a sheet of paper at various pressures. The high porosity indicates that the paper allows air to pass through fairly easily. The results are shown in Fig. 17. The results show that the filler-fiber composite had a lower porosity, i.e., a higher density than PCS. Kaolin samples had the highest density.

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Claims (14)

A supercalendered paper product containing first cellulose fibers and a gypsum-fiber composite product as a filler pigment, wherein the gypsum of the gypsum-fiber composite product is displayed as crystals on the fiber surface and wherein the gypsum crystals are contacted with calcium sulfate and / or dihydrate The supercalendered paper product of claim 1, wherein the first cellulosic fibers are chemical, mechanical, chemimechanical, or deinked pulp fibers. The supercalendered paper product of claim 1 or 2, wherein the second fiber of the gypsum fiber composite product comprises a second cellulosic fiber, such as a chemical, mechanical, chemimechanical, or deinked pulp or synthetic fiber. The supercalendered paper product according to any one of claims 1 to 3, wherein the weight ratio of gypsum to fiber in the gypsum fiber composite product, calculated as dry matter, is 95: 5-50: 50, preferably 75: 25-50: 50. The supercalendered paper product of any one of claims 1 to 4, further comprising one or more of the following: a natural or synthetic polymeric binder, an optical brightener, a rheology modifier, and an adhesive. The supercalendered paper product of any one of claims 1 to 5, wherein the gypsum fiber composite product is present in an amount of 10 to 60% by weight, preferably 20 to 50% by weight, determined on a dry weight basis. C \ J The supercalendered paper product of any one of claims 1 to 6, wherein the calcium sulfate hemihydrate used for crystallization is α-calcium sulfate-1 hemihydrate or β-calcium sulfate hemihydrate. CVJ The supercalendered paper product according to any one of claims 1 to 7, wherein the weight ratio of calcium sulfate hemihydrate and / or calcium sulfate anhydrite CVJ J to water is 0.03-0.6: 1, preferably 0.05-0.5: 1. CD o The supercalendered paper product of any one of claims 1-8, wherein the second fiber has a crystallization content of from 3 to 30% by weight. The supercalendered paper product according to any one of claims 1 to 9, wherein the content of calcium sulfate hemihydrate and / or calcium sulfate anhydrite in the crystallization is 5-57% by weight. A process for producing a supercalendered paper product as defined in any one of claims 1 to 10, comprising providing a stock in which the first cellulosic fibers are mixed with water and a gypsum fiber composite product, the resulting slurry being led into a wire section of a papermaking machine the web is led to a press section where excess water is removed, then the web is led to a dryer section where most of the remaining water is evaporated, and finally the paper is supercalendered to improve the smoothness and gloss of the paper surface. The method of claim 11, wherein the gypsum-fiber composite product is introduced into the mixture in the form of an aqueous product or in a dried form, optionally ground into a particulate form. Use of a gypsum-fiber composite product in which gypsum appears as crystals on the surface of the fiber and wherein the gypsum crystals are obtained by contacting calcium sulfate hemihydrate and / or calcium sulphate anhydrite with an aqueous fiber suspension in a filler pigmented supercalendered paper. The use according to claim 13, wherein the gypsum fiber composite product is present in an amount of 10-60% by weight, preferably 20-50% by weight, based on dry weight of the supercalendered Paper Product. C \ J δ c \ j i CD O m c \ j X cc CL m c \ j LO O) O o C \ l