FI116573B - Filler for making thin base paper and method for making base paper - Google Patents

Description

116573 Filler for making thin base papers and process for making base paper

Fyllnadsämne för framställning av baspapper och forfarande för framställning av baspapper 5

The present invention relates to the use of precipitated calcium carbonates (PCC) as fillers for the production of base paper in combination with mechanical hardwood pulp and softwood pulp, and to a method for producing base paper comprising pulp from softwoods, particularly Populus genus and softwood.

BACKGROUND OF THE INVENTION Kaolin and ground calcium carbonate (GCC) are used as fillers in base papers, particularly thin base papers. Thin base papers are traditionally made under acidic conditions, whereby calcium carbonates but other compounds cannot be used, so PCC and GCC are used mainly in fine papers.

In coated base papers, the paper must be dense so that the coating paste remains a well-covering layer on the surface of the paper and does not penetrate the base paper during the coating process. and the gloss of the printed paper should be high with no disturbing variation, and the paper's tensile strength, if necessary measured as ScottBond, should be high enough to prevent the paper from cracking during printing.

v 30 Paper is typically printed on a heatset offset printing press to produce a finished overlay. , · The surface of blotted paper may bubbles if the strength of the base paper in the z direction is not sufficient 2 1 1 6573. This phenomenon is particularly critical in the case of dual-coated paper when the paper surface is dense and the vapor generated by the paper's own moisture cannot escape through the paper surfaces in the drying section of the heatset offset printing press. In addition, the filler should have a high opacity 5 (light scattering) and brightness in terms of the quality of the base paper, but at the same time it is also very important that the filler does not reduce the peel strength of the paper or increase the porosity of the base paper.

In sheet offset printing, the z-directional strength is also critical even though the ink-10 is not dried in a separate dryer. In sheet offset, the strength requirement comes from the fact that the inks are highly viscous and that there is a tendency to split the paper at the exit of the press nip.

Alloyed Calcium Carbonates (PCCs) are known to be good fillers, especially in uncoated fine papers. They achieve high brightness and opacity and also have a higher bulk compared to other mineral fillers. The advantages to be obtained are essentially based on the fact that the shape and size of the particles in the PCC manufacturing process can be controlled by a process control variable. The high brightness is based on the fact that, because the process is synthetic: ·: 20 fine raw materials can be used to achieve a powdery: | better than SiC. PCC is also manufactured in large plants: "· * economically competitive with other fillers.

The shape and size of the filler particles are adjustable within a fairly wide range of paper manufacture. This has led to e.g. to the fact that PCC pigments have also become competitive as coating pigments.

*., · Calcium carbonate pigments can generally only be used in papermaking processes with a neutral or alkaline pH. Under acidic conditions the carbonates dissolve. This limitation has also been overcome by the development of PCC pigments which can be used in mildly acidic conditions.

116573 3 PCC pigments have achieved a strong position as a filler for uncoated fine papers, whereby the particles are typically complex in shape and quite large, and also in fine paper coatings, where the par-5 particles are typically simpler and smaller in size.

Traditionally, PCC fillers are used in uncoated office papers in proportions of more than 15% by weight, with the aim of increasing the brightness and opacity and reducing the cost. The particle morphology of the PCC is designed in such a way as to preserve the bulk as well as possible. As a result, the PCC particles have a "sea urchin" morphology, which in turn is very poor in web tightness and splitting strength. Synthetic precipitated PCC is either aragonite or calcite depending on the manufacturing conditions. Typically, aragonite is a needle-like morphology suitable for paper coating. Calcite sa-15 is purchased in the form of paper-swelling, scalenoedral, i.e., predominantly granular, or light-transmitting rhombohedral, or cuboidal, prismatic, spherical, or spherical particles, which are often bulky in size and compact in size. The attached Figure 1 illustrates particle size · · 20 by means of SEM images. Particles · 'used in fine paper coatings are of a simpler type and smaller in size.

However, PCC pigments have not achieved much success as fillers for thin base papers. The quality of the filler is desired in these products. 25 lightness and opacity, i.e. light scattering, but at the same time it is very important that the fillers do not reduce the paper's pile strength nor on the other hand increase the porosity of the base paper. Paper development generally aims to reduce the basis weight of the paper, thereby reducing the opacity, which in turn must be compensated by increasing the light scattering coefficient. In addition, the density naturally - ::; 30 decreases as the basis weight decreases. The ever-increasing travel speeds of paper machines and overhead *, * ·: machines further emphasize the criticality of 116573 4. The problem with known PCC fillers is that they do not meet all the requirements for producing thin base paper at the same time. Typically, the brightness and opacity of the base paper can be high, but at the same time, the peel strength of the base paper is alarmingly reduced and the density is reduced so that the coating paste penetrates into the base paper.

FI100 729 describes a filler used in papermaking, mainly consisting of calcium carbonate, and a process for making it. In the method, calcium carbonate is precipitated on the surface of fine pulp fibrils made from cellulose fiber and / or mechanical pulp fiber. The fine fibrils on which the calcium carbonate particles are deposited on the surface form pearl-like strands, and the calcium carbonate aggregates thus produced resemble mainly pearl strands. Based on pulp or mechanical pulp fiber and calcium carbonate, this filler-15 gives the paper good optical properties and good strength.

A process for producing base paper suitable for the production of coated fine paper by combining hardwood pulp and softwood pulp is disclosed in Patent Application No. 103,417. The method utilizes a combination of mechanical pulp of aspen or aspen wood and softwood pulp to provide high strength. suitable • * · '·' · pulp. The advantages of aspen pulp are high brightness and lightness retention compared to spruce pulp. This is due, in particular, to the low lignin content and low carbonyl group content of aspen ground or similar mechanical pulp. In this way, high-brightness fine paper can be produced with a * * lower basis weight.

* · • * ·

From the foregoing, it can be seen that there is an obvious need for a PCC-type filler which is particularly suited for the manufacture of fine base paper in combination with mechanical hardwood pulp and softwood pulp, and which simultaneously satisfies all requirements for a base paper filler. a method for producing base paper using mechanical pulp based on hardwoods, such as aspen or aspen-like wood, and softwood pulp together with a PCC filler.

5 Objective of the Invention

It is an object of the invention to provide a method of producing base paper, in particular a thin base paper, which provides a base paper having a low basis weight, good internal strength and density, and improved light scattering and opacity.

It is also an object of the invention to use precipitated calcium carbonate (PCC) as a filler in the manufacture of base paper in combination with mechanical hardwood pulp and softwood, which in particular meets the requirements for base filler 15 above.

It is also an object of the invention to provide a method for making base paper which utilizes mechanical pulp based on hardwoods, such as aspen or aspen-like trees and softwood pulp, in combination with PCC filler, to achieve all desired properties of the base paper at the same time.

Characteristics of the Invention The use of a PCC filler according to the invention in the manufacture of base paper in combination with mechanical hardwood pulp and softwood pulp, as well as in the base of the process; Characteristic features for making paper are set forth in the claims.

• »1 I t 116573 6

Description of the Invention

It has been found that by using mechanical hardwood pulp and softwood pulp together with PCC filler in the manufacture of base paper, it is surprisingly possible to achieve at the same time all the properties required of the base paper. Preferably, in the process of the invention, mechanical hardwood made from wound or aspen species, i.e., Populus species, in particular Pressure Ground Wood (PGW) or Chemimechanical Pulp (CTMP), is combined with softwood pulp with a particle size of 90% PCC. <9 µm, 50% <5 µm, and 20% <1.5 µm, which are morphologically granular, granular or spherical.

Mechanical hardwood pulp, preferably derived from wound or aspenous hardwoods, i.e., Populus species, more preferably selected from the group consisting of P. tremula, P. tremuloides, P. balsamea, P. balsamifera, P. trichocarpa and P may be used for the base paper. .mix of mechanical pulps made from heterophylic or various strain wounds such as hybrid aspen and genetically engineered or poplar, or from the above species. Particularly preferred wood species are the pine aspen P.

• | 20 tremula, Canadian aspen P. tremuloides, poplar and hybrid aspen. Mechanical • · ·; : Hardwood may optionally contain up to 70% by weight of spruce or pine.

Other hardwoods such as birch, eucalyptus or acacia may be used instead of wounds. Such mechanical hardwood pulps can be made of mixtures of e.g. two hardwoods and then softwood, for example spruce. The proportion of spruce can be up to 70%, preferably up to 50% and particularly preferably below 30%.

'·' 'Mechanical hardwood pulps are shorter fiber than birch pulp or mechanical' * pulps. Therefore, the same basis weight of mechanical hardwood pulp is more than: 30: 15 than that of birch pulp or mechanical spruce pulp. This results in better light scattering, »116573 7, good formability, i.e. small basis weight variation on a small scale, low surface roughness, and good bulk.

Mechanical hardwood pulp made from aspen or other species of the Populus genus, and in particular chemimechanical pulp (CTMP) and pressure pulp (PGW), contain a large amount of short fibers that give the pulp a sweat and light scatter. By combining a mechanical pulp of wound or aspen species with chemical pulp of coniferous wood using PCC filler, a base paper with excellent light scattering and high opacity, high brightness and good strength and density can be produced.

Mechanical hardwood pulp, preferably aspen-CTMP or aspen-PGW or a combination thereof, is used in an amount of 20-70% by weight and bleached softwood pulp 80-30% by weight of the stock dry matter, and at least 20% of the mechanical hardwood pulp fibers are included. the fraction <200 mesh and preferably 10-40 wt% is contained in the 28/48 mesh fiber size fraction. Preferably, at least 30 wt.%, And particularly preferably at least 50 wt.% Of the hardwood pulp fibers are derived from a wound, hybrid wound and / or poplar.

• · 20 The hardwood raw material is chipped, and then chipped into mechanical pulp, pulp (TMP) or chemimechanical pulp (CTMP) in a manner known per se. When using the grinding method (GW or PGW), the raw material is fed into the process as bobbins. The pulp is formed from the mechanical pulp together with the chemical pulp, i.e. pulp, and the filler used is a PCC filler having a particle size distribution of 90% <9 µm, 50% <5 µm and 20% <1.5 µm. In addition, the stock * · ... may contain additives such as various starches, starch derivatives and retention agents. The dry matter content of the stock is 0.1-5% by weight. The aqueous phase of the stock can be, for example, circulating water from a paper machine. Preferably, bleached softwood pulp is used as pulp. The amount of mechanical pulp is then 20-80 wt%, it is preferably 30-70 wt% and the amount of bleached softwood pulp is 80-20 wt%, preferably • · t 1 t 1 70-30 wt% based on the dry weight of the stock -aineesta.

116573 8

The pulp of mechanical hardwood pulp and pulp is formed into a paper web according to the prior art using, for example, guitar material.

In laboratory tests, it has been found that when using mechanical hardwood pulp, preferably aspen-based pulp with low freeness, CFS <-150 ml and high brightness> 75, preferably> 77, and softwood pulp with a PCC filler of 90% <9 μηι , 50% <5 μπα and 20% <1.5 μm, preferably 90% <6.3 μm, 50% <2.7 μηι and 20% <0.8 10 μιη and very preferably 90% <4.3 μηι , 50% <1.8 μηι and 20% <0.5 μηι, which have a morphological, granular, rag-like or spherical shape, it is possible to produce a thin base paper meeting the quality requirements of the base paper and having the following characteristics: g / m2, preferably 25-80 g / m2, 15 · light scattering coefficient> 45, preferably> 50 and very preferably> 55 m2 / kg, • peel strength> 200, preferably> 250 and very preferably> 300 J / m, • porosity of paper <500 ml / min, preferred <300 ml / min and very preferably <250 ml / min (50 g / m 2) ·. I · Paper bulk 1.2-1.8 cm / g. ' 20 · brightness> 75%.

• · • ♦ · • »

The fibrous composition of the base paper according to the invention contains 20-70% by weight of mechanical hardwood pulp, preferably aspen-based pulp, more preferably aspen pulp. or aspen CTMP pulp, and very preferably aspen CTMP pulp, and 80-30. | 25 wt% softwood pulp, suitably bleached pine pulp.

The base paper may be coated by any suitable prior art method, wherein a coating layer having a basis weight of 5 to 50 g / m 3, preferably 5 to 30 g / m 2, is formed on at least one surface of the paper web, preferably both.

116573 9

From the base paper according to the invention, high-quality fine paper is obtained by coating it with a suitable pigment-containing coating composition. The coating composition may be applied to the material web in a manner known per se. The paper coating can be carried out on-line or off-line by conventional coating apparatus 5, i.e., by blade coating, or by film coating or surface spraying.

The base paper produced by the process of the invention and the coated paper further prepared therefrom may be calendered by any of the prior art calendering methods. Preferably, the calendering is carried out as an on-line 10 soft calendering to provide smooth and glossy or matte products with the bulk, opacity and stiffness required.

EXAMPLES The invention is illustrated by the following examples. However, it will be obvious to one skilled in the art that the invention is not intended to be limited to the embodiments of the examples.

9 Ψ ·

Example 1 • \\ 20 '. /. Laboratory tests with different fillers. The test series consisted of laboratory sheets with Formette Dynamique sheet mold. Fiber pulps, wreckage and various fillers as described below were used in the test points.

....: 25 In addition, a constant amount of retention agents and starch was used.

• ·

The following pulps were used for the tests: iit>. - Nordic bleached softwood pulp which was ground to SR number 24 Escher

Wyss Laboratory Refiner Bleached CTMP containing 30-85% aspen and 15% moon, milled to CSF * with 48ml Voith Sulzer Laboratory Refiner (4.2% consistency, specific gravity 116573 ¾ο load, 0.3 J / m, specific energy consumption) 90 kWh / t). The fiber distribution of the pulp and the most important paper technical values measured from the laboratory sheet were: length-weighted fiber length: 0.69 mm 5 - McNett classification +28 mesh: 3.3%

McNett classification 28/48 mesh: 39.4%

McNett Grade 48/100 Mesh: 22.4% - McNett Grade 100/200 Mesh: 11.0% - McNett Grade -200 Mesh: 23.9% 10 - Tensile Index 37.8 Nm / g Tear Index 3.4 mNm / g - bulk 1.79 cm3 / g ScottBond 152 J / m2 scattering factor 47.4 m2 / kg 15 - brightness 80.9

All test points contained a total of 12% filler. In a coated paper mill, under practical conditions, the base paper filler consists of both; *, ns. from fresh filler and filler from coated paper wreck • · · 20 (contains mineral pigments in the coating layer). This is why I can take the test *. *. of you, the filler was dispensed as a paper mill coated sheath with the main mineral component being the powdered carbonate contained in the coating. In these points • ·. ···. in you, 6% of the filler was fresh filler and 6% of the filler from the wreck.

The fillers used are described in Table 1 below and Figure 2 below. are shown graphically for particle size). Values are measured by Malvem Master. Size.

i * k 11

Table 1 116573 Filler Particle Size Surface D50, μιη m2 / g GCC1, Powdered Calcium Carbonate 1.67 6.64 GCC2, Powdered Calcium Carbonate 1.1 7.77 PCCl, Scalenoedric 2.6 4.98 PCC2, Rhombohedral 1.4 7.58 PCC3, mixture scalenoedric / prismatic 3.6 3.77

Sheet properties are described in Table 2 below. Tensile and tear-5 indexes are geometric averages of machine and transverse results.

Table 2

Feature Filler GCC1 GCC1 GCC2 PCCl PCCl PCC2 PCC2 PCC3 PCC3 Wreck No / Yes No No No Yes No No

Square weight, g / m2 52.2 50.4 51.9 50.9 50.3 51.7 50.8 51.5 50.6

Density, kg / mJ 567 56Ö 552 53Ö 541 544 546 5Ϊ5 550

Porosity, bendt ~ 2 \ Ö 170 240 32Ö 3ÖÖ 28Ö 230 480 24Ö * * · *. 1 ml ISO / min 823 8Ϊ3 823 833 8Ϊ3 843 823 833 822

Scattering factor, 473 44.8 522 542 483 623 5Ϊ2 582 523 .... 1 m2 / kg

ScottBond, J / m2 287 3Ö6 28Ϊ 234 3Ö8 266 35Ö 24Ö 286

Tensile index, Nm / g δt 6T3 572 58.0 57.6 532 573 552 573

Tear Index, 7.0 7.2 7.7 8.0 7.8 7.9 7.6 8.3 7.5 ···. '. mNm2 / g * * «10 As expected, the results show that the brightness and scattering coefficient are increased with PCC compared to calcium carbonate. Surprisingly, however, it is seen that PCCl, and PCC2 in particular, can, in addition to improved optical properties, even | improves strength properties. This has been the case with the wreckage points at Scott's 1 1 6573 12

Bond peel strength and tear resistance. The porosity of the papers has also remained low enough and here too attention is drawn to the surprisingly good results of PCC2.

Example 2

Manufacture of base paper with pilot paper machine, coating and calendering

The following pulps were used in the tests: - milled Nordic bleached softwood pulp with 10-85% aspen and 15% spruce bleached CTMP, which was a post-refiner on a pilot-sized refiner with a low specific gravity load of 140 kWh / h. The CSF of the pulp before refining was 115 ml. After post-milling, the main properties of the pulp and laboratory sheets were: 15 - CSF 59 ml - Length Weighted Fiber Length 0.73 mm McNett Grading +16 Mesh: 0.0%

McNett Classification 16/30 Mesh: 5.4% '· [- McNett Classification 30/50 Mesh: 31.3% 20 - McNett Classification 50/200 Mesh: 34.1% - McNett Classification-200 Mesh: 29.1%! - brightness: 78.6 - tensile index 46.7 Nm / g • t-y - tear index 3.9 mNm / g 25 - density 570 kg / m3 (bulk 1.75 cm 3 / g). · · ·. - ScottBond 329 J / m2 *, - scattering factor 51.5 m2 / kg.

Comparing these results in the laboratory of Example 1 with the properties of the post-ground pulp, it can be seen that the pilot-scale refiner produced significantly more • '· 200 mesh fractions, compared with 30/50 mesh (equivalent to 28/48 mesh in the example). 116573 13 1) is clearly less in the pilot. The result is typical and in practice it has been found that the refiner used in the pilot test corresponds very well to the conditions of the paper mill. The mill has the same structure as a factory refiner, but with a smaller pilot refiner size.

5

The pulps were made into base paper on a pilot-sized paper machine. The paper machine had a guitar recorder. The same fillers as in Example 1 were added to the papers as follows: - PCC1, scalenoedric - PCC2, rhombohedral.

10

Comparison with ground calcium carbonates was no longer made and the top 2 PCCs were included in the experiment.

At all test points, standard amounts of starch and the same reten-15 thiols were added to the stock.

The base papers were made into rolls which were dried and then analyzed. Follow-. . Table 3 shows the average of four roll measurements. Veto- • · ·; '. and the tear index are the geometric mean of the machine and transverse directions.

20 * «« 1 »* · · · · · * 1» 14 116573

Table 3

Feature Filler PCC1 PCC2

Gross weight, g / m2 51.2 52.3 Filler content,% 14.7 13.4

Density, kg / mJ _ 756,751

Porosity, Bendtsen, ml / min 264,283

Vaaleus 77 ^ 2 78 ^ 8

Scattering coefficient, m2 / kg 49.6 51.6

ScottBond, J / m2 479,377

Tensile index, Nm / g 37.7 35.9

Tear Index, mNm2 / g 7.5 7.5 5 Table 3 shows that the properties of the base papers were quite close to each other. The comparison is complicated by the higher concentration of PCCl. As the laboratory-.Y; PCC2 also achieved better optical properties, e.g. brightness and · scattering factor.

»· · * T Y * · 10 Subsequently, the base papers were coated with the same pastes and supercalendered.

The coating target was 18 g / m2 on both sides of the paper. Calendering: line pressure was 280 kN / m.

'' · The main characteristics of the finished paper are given in the following Table 4 15 (the properties are the average of the sides of the paper).

»* · * I ·

Table 4 15 116573

Feature Filler PCC1 PCC2

Gross weight, g / m2 88.4 89.7 Coating quantity, g / m2 36.4 36.6

Bulk, cm Vg 0.75 0.75

Whale 923 93 ^ 4

Opacity 93.4 93.4

Smoothness 0.60 0.59

Kiilto 793 783 5 According to Table 4, the only clear difference after coating is the brightness, which is better with PCC2. However, the usual expectation is that if the brightness is as high as 1.3 units in the finished paper, the opacity of the higher brightness paper is expected to be significantly lower than that of the lower brightness paper. Therefore, the optical properties of PCC2-containing paper should be considered to be superior to · · 10 PCCl paper. There is no practical difference in the surface properties of the paper (smoothness, gloss) ».

• ·> * * 4 * · • · '* * * * »»

Claims (14)

Use of precipitated calcium carbonate (PCC) for the production of thin base papers together with mechanical hardwood pulp and chemical softwood pulp, characterized in that> 20% by weight of the fiber of the mechanical hardwood pulp is included in the fiber size fraction <200 mesh and 10 -40% by weight is included in the fiber size fraction 28/48 mesh, the brightness of the mechanical hardwood pulp is> 75, the particle size distribution of the precipitated calcium carbonate is 90% <9 μιη, 50% <5 μιη and 20% <1.5 μιη and the basis weight of the base paper is 25-150 g / m2. 10 Use according to claim 1, characterized in that the brightness of the mechanical hardwood pulp is> 77, the particle size distribution of the precipitated calcium carbonate is 90% <6.3 μνη., 50% <2.7 μιη and 20% <0.8 μm. and the basis weight of the base paper is 25-80 g / m2. 15 Use according to claim 1 or 2, characterized in that the mechanical hardwood pulp is made of aspen and / or tree species related to aspen. Use according to any one of claims 1-3, characterized in that the mechanical hardwood pulp contains CTMP pulp or compression sanding pulp (PGW) or a combination thereof, and the hardwood pulp is made from tree species from, the Populus genus, which are selected from the following species: P. tremula, P. tremuloides, P. balsamea, P. balsamifera, P. trichocarpa, P. heterophylla, of various tribal species, asparagus crossed, such as hybrid species, genetically produced species and poplar. Use according to any one of claims 1-4, characterized in that at least 30% of the fibers of the mechanical hardwood pulp originate from aspen; > · And / or tree species related to aspen. 30 1 1 6573 Use according to any of claims 1-5, characterized in that the mechanical hardwood pulp contains at least 50% fiber derived from aspen and / or tree species related to aspen. Use according to any one of claims 1-6, characterized in that the mechanical hardwood pulp contains 70-100% fibers derived from aspen and / or trees related to aspen and 0-30% fibers derived from conifers and / or other deciduous trees. 10 8. A process for making base paper, in which a paper web is formed from a fibrous raw material in a papermaking machine, characterized in that the fibrous raw material is formed by the association of precipitated calcium carbonate (PCC) with mechanical hardwood pulp and chemical softwood pulp, and> 20% by weight of the fibers of the mechanical hardwood pulp contains in the fiber size fraction <200 mesh and 10-40 weight percent in the 28/48 mesh fiber size, the brightness of the mechanical hardwood pulp is> 75, the particle size distribution of the dropped calcium carbonate is 90% <9 µm , 50% <5 µιη and 20% <1.5 µm and the basis weight of the base paper is 25-150 g / m2. 20 9. Process according to claim 8, characterized in that the brightness of the mechanical hardwood pulp is> 77, the particle size distribution of the precipitated calcium carbonate is 90% <6.3 µm, 50% <2.7 µm and 20% <0. 8 µm and the basis weight of the base paper is 25-80 g / m2. 25 Method according to claim 8 or 9, characterized in that the mechanical hardwood pulp has been made of aspen and / or tree species related to aspen. Method according to any of claims 8-10, characterized in that the mechanical hardwood pulp contains CTMP pulp or pulp sanding pulp (PGW) or a combination thereof, and the hardwood pulp is made from tree species from> II * 116573 Populus genus , which have been selected from the following species: P. tremula, P. tremuloides, P. balsamea, P. balsamifera, P. trichocarpa, P. heterophylla, of asparagus species cross-bred asparagus, such as hybridasparts, genetically produced species and poplar. 5 Method according to any of claims 8-11, characterized in that at least 30% of the fibers of the mechanical hardwood pulp are derived from aspen and / or tree species related to aspen. 13. A process according to any of claims 8-12, characterized in that the mechanical hardwood pulp contains at least 50% of fibers derived from aspen and / or tree species related to aspen. Method according to any of claims 8-13, characterized in that the mechanical hardwood pulp contains 70-100% fibers derived from aspen and / or trees related to aspen and 0-30% fibers derived from coniferous trees and / or other deciduous trees.