WO2009106684A1

WO2009106684A1 - A process for making paper and board and a formed product

Info

Publication number: WO2009106684A1
Application number: PCT/FI2009/050152
Authority: WO
Inventors: Tarja Sinkko; Teppo Sahlberg
Original assignee: Upm-Kymmene Oyj
Priority date: 2008-02-25
Filing date: 2009-02-25
Publication date: 2009-09-03
Also published as: EP2255036A1; EP2255036A4

Abstract

The invention relates to a process for making paper and board, wherein a product is formed from a fibrous starting material and a filler. According to the invention the properties of the product that is being formed are controlled by the employed filler containing at least one filler component which is formed from particles having a substantially tabular particle shape and which is formed substantially synthetically by a process selected from the group of precipitation, agglomeration, chemical modification and combinations thereof, the mean particle size in the filler component being less than 20μm, and the degree of brightness in the filler component, determined according to ISO standard, being at least 86. In addition, the invention relates to a corresponding product.

Description

A PROCESS FOR MAKING PAPER AND BOARD AND A FORMED PRODUCT

FIELD OF THE INVENTION The invention relates to a process as defined in the preamble of claim 1 for making paper, i.e. paper and board, and to a product as defined in the preamble of claim 13, using a filler that contains tabular particles.

BACKGROUND OF THE INVENTION

In making papers and boards it is known to use fillers with the intention of reducing the production costs of the product and improving the printing and other functional qualities of the fibrous web. In making papers, the long used fillers of a tabular particle shape include kaolin and talc, the use of which has provided papers with many desired properties. As the brightness of papers has increased, it has become imperative to seek brighter fillers, such as carbonates and calcinated kaolins, for making papers. These bright pigments are traditionally of a cubic or a tubular particle shape. The chances of the paper manufacturer to control the properties of the paper by the traditional fillers are often very limited and therefore a need exists to look for new control models wherein the properties of the filler could be better optimized to be suitable for the purpose.

The properties of the traditional fillers are mostly determined by the properties of the employed mineral and the processing conditions of the mineral.

The role of the filler in making paper and board has become more important than ever as the filler contents are continuously increasing. By se- lecting the right filler for each paper and board it is possible to considerably improve the properties of the product that is being made.

In addition to mineral pigments used as fillers, various synthetic pigments have been developed. The synthetic pigments were previously expensive specialty products, the use of which was not possible in bulk products, such as papers and boards. The new ways of making pigment by precipitation and/or chemical modification have provided quite a variety of pigments with controllable properties on the market with a reasonable price.

Known from publication US 4,801,355 is a tabular gypsum filler.

OBJECTIVE OF THE INVENTION

The objective of the invention is to disclose a new type of manner to control the properties of paper and board products by using a filler of a specific particle shape and properties as the filler. Another objective of the invention is to disclose a new type of paper wherein a filler of a specific particle shape and properties is used as the filler.

SUMMARY OF THE INVENTION The process and the product according to the invention are characterized by what has been presented in the claims.

The invention is based on a process for making paper and board, which product is formed at least from a fibrous starting material and a filler. According to the invention, the properties of the product that is being formed are controlled by means of the employed filler that contains at least one filler component, which filler component is formed from parti- cles having a substantially tabular particle shape and is formed substantially synthetically by a process se- lected from the group of precipitation, agglomeration, chemical modification and combinations thereof. The mean particle size in the filler component is less than 20μm and the degree of brightness in the filler component, determined according to ISO standard, is at least 86.

The invention is specifically based on the use of tabular filler particles having a degree of brightness of at least 86 and a mean size of less than 20μm as a filler in making paper and board. According to the invention it is possible to control the properties of the product, such as a paper or a board product, by the properties of at least one filler component comprised in the filler. In this context paper refers to any, mainly fiber-based, paper product or the like. The paper may have been made from mechanical pulp, chemimechanical pulp, chemical pulp, recycled pulp, fiber pulp or a mixture thereof or the like. The paper may be in the form of a wet web, dried web or sheet, or in other form which is suitable for the purpose. The paper may contain suitable fillers, pigments, binders and additives. Any agents known in the art may be used as the fillers, pigments, binders and additives. In this con- text board refers to a thickish inflexible paper that may be made in single or multiple layers.

In the process and the products according to the invention it is possible to use one filler, or a mixture of fillers containing a number of fillers in different percentages. The filler contains one or more filler components with tabular particles. The filler and/or the filler components may also contain particles of other particle shape. Moreover, the filler may contain other filler components as well. In one embodiment the product comprises filler in an amount of 2% to 80% by weight, more preferably 10% to 50% by weight.

In one embodiment of the invention the filler contains particles of a tabular particle shape in an amount of 20% to 100% by weight of the amount of filler.

In one embodiment the filler or the filler component containing the tabular particle shape parti- cles may have been arranged in the entire paper that is being formed or in a portion or a layer thereof.

In one embodiment of the invention precipitated filler is used as at least one filler component.

In one embodiment of the invention chemically modified filler is used as at least one filler component .

In one embodiment of the invention a filler that has been formed by agglomeration is used as at least one filler component, wherein the agglomeration has been provided by means of an auxiliary agent or without the auxiliary agent.

In one embodiment the precipitation, agglomeration and/or chemical modification of the filler or the filler component is performed in conjunction with the paper production process or as a separate process or as a combination thereof.

The synthetically produced fillers also allow one to apply a new approach to the use of fillers, because the properties of the fillers can now be varied to a greater extent than before and thereby the properties of the product that is being made may be controlled better than before.

In making fillers synthetically the shape, size, size distribution and surface chemistry of the filler particles can be controlled over a larger area than before and thereby it is possible to select the fillers or combinations thereof which best suit each purpose .

In one embodiment at least the filler component used for controlling the properties of the prod- uct that is being formed is precipitated in such a manner that one or more of the components that are being precipitated are present in an amount of more or less than the stoichiometric ratio, so that functional groups characterized in that they contain charged at- oms or polar groups concentrate on the surface of the filler. In one embodiment partially charged atoms having a valency of II or higher have concentrated in the crystal lattice of the filler surface.

In one embodiment at least the filler compo- nent used for controlling the properties of the product that is being formed is precipitated in such a manner that one or more of the components are present in an amount of more or less than the stoichiometric ratio, so that the stoichiometric ratio is varied back and forth during precipitation whereby functional groups characterized in that they contain charged atoms or polar groups concentrate on the surface of the filler. In one embodiment partially charged atoms having a valency of II or higher have concentrated in the crystal lattice of the filler surface.

In one embodiment at least the filler component used for controlling the properties of the product that is being formed is formed, e.g. precipitated, in the presence of an ionic or polar surface-active agent or polymer in such a manner that ionic or polar functional groups form on the surface of the filler.

In one embodiment at least one functional group containing element or compound is arranged by precipitation or chemical or mechanical bonding on the surface of at least the filler component used for controlling the properties of the product that is being formed, wherein the functional group contains a polar or an ionic component. In one embodiment the valency of the polar or the ionic component is II or higher. In one embodiment at least one ionic or polar functional group containing surface-active agent or polymer or a mixture thereof is chemically or mechanically bonded on the surface of the filler. In one embodiment the surface-active agent or the polymer or the mixtures thereof are contacted with the surface of the filler in high shear rate field. In one embodiment the surface- active agent or the polymer or the mixtures thereof are contacted with the surface of the filler when raising the solids content of the filler by means of mechanical or chemical drainage, such as by a filter belt press, vacuum filter, drum filter, ceramic filter or pressure filter.

The surface-active agent or the polymer contains a functional group or groups characterized by forming chemical and mechanical bonds with the other components of the paper. The bonds that have been formed are provided by ionic bonds, covalent bonds, hydrogen bonds or van der Waals forces. The bonds that have been formed increase the tensile strength of the paper web that has been formed in the machine direction or in a direction that is perpendicular to the machine direction or in a number of plane directions. The bonds that have been formed enable one to increase the level of the filler without degrading the strength properties of the paper. In addition, the bonds that have been formed allow the use of a shorter-fibered fiber fraction without degrading the strength properties of the paper.

In one embodiment the surface modification of the filler component particles may be performed by a process known per se. In one embodiment of the invention the filler component is selected from the group of gypsum and carbonates. In one embodiment the filler or a component thereof may have been selected from the group of cal- cium sulphates, calcium carbonates, kaolins, talc, satin white, aluminum trihydrates, metallic oxalate salts, silicates and mixtures thereof.

In one embodiment of the invention the degree of brightness of the filler component, determined ac- cording to ISO standard, is at least 88. In one embodiment the degree of brightness of the filler component, determined according to ISO standard, is at least 92.

In one embodiment the shape factor of a sin- gle tabular filler particle is in the range of 1:1 to 50:1, determined by the perimeter diameter process. In one embodiment the shape factor of the tabular filler component particle is at least 5:1. In one embodiment the shape factor of the tabular filler component parti- cle is at least 10:1. In one embodiment the shape factor of the tabular filler component particle is at least 15:1. In this context the shape factor is expressed as the ratio of the particle width to the particle thickness. The shape factor may be determined in a manner completely known per se.

In one embodiment the particle size in the filler component is determined based on laser diffraction. In one embodiment the mean particle size in the filler component is less than lOμm and in one embodi- ment less than 5μm.

In one embodiment the filler according to the invention is applicable over the pH range of 6 to 7, more preferably over the range of 5 to 8 and most preferably over the range of 4 to 9 without breaking its structure. In one embodiment the printability, structural properties, optical properties and processabil- ity of the product that is being formed are controlled. In one embodiment the printing properties of the paper or the board, such as ink absorption, ink settling, print through, porosity and evenness of the print, are controlled. In one embodiment the processing properties in making paper or board, such as retention, drainage and acidity, are controlled. In one embodiment the paper' s surface strength, dusting, piling property, i.e. sensitivity of piling up during printing, and strength properties in the plane direction are controlled. In one embodiment the structure, such as bulk and density, and/or optical properties of the paper are controlled.

In one embodiment of the invention the paper or the board product is mainly formed from mechanical pulp. In one embodiment the paper product that is being formed is selected for example from the group of SC, WFU, LWC, MWC, MFC and WFC and suchlike products. In one embodiment the paper product that is being formed is a high brightness SC paper. Said paper grades may be made in a manner completely known per se in the art, yet using a tabular filler component of a specific particle size and brightness as at least one filler component according to the invention.

The invention is further based on a paper or a board product formed at least from a fibrous starting material and a filler. According to the invention the filler contains at least one filler component which is formed from particles of a substantially tabular particle shape and which is formed substantially synthetically by a process selected from the group of precipitation, agglomeration, chemical modification and combinations thereof, the mean particle size in the filler component being less than 20μm, and the degree of brightness in the filler component, determined according to ISO standard, being at least 86.

The paper and the board may be made and processed further in manners known per se in the art. The process and the product according to the invention provide considerable advantages compared to the prior art.

By the process according to the invention it is possible to make paper and board products of better properties than before for the desired purposes. The filler according to the invention provides the product with improved properties, such as better gloss and opacity, and improved printing properties, such as lower print through and ink drop bleeding. The invention provides a simple and cost- effective manner of making quality paper and board suitable for printing. The invention provides an industrially applicable, easy, simple and affordable way of making paper and board. Thanks to the paper according to the invention, a quality printed product is provided.

DETAILED DESCRIPTION OF THE INVENTION

In the following section, the invention will be described with the aid of detailed examples of its embodiments .

Example 1

In this test conventional SC offset papers were made in a manner completely known per se in the art using fillers with different particle shapes and particle sizes. The amount of filler in the paper was 30%. The fillers were: A) tabular, mean particle size 1.92μm; B) columnar, mean particle size 1.2μm; and C) columnar agglomerate, mean particle size 1.7μm.

Based on the results obtained from the test run the tabular filler A was considerably superior to the two other fillers in terms of the printing properties of the paper. In HSWO printing the dusting and piling tendency of paper A was decidedly superior to the others . Filler C had the weakest piling tendency and the reason for the poor printability of that paper was the quick settling of ink. The quick ink settling on paper B resulted from the increase in the microporos- ity of the paper, which in turn resulted from the properties of the filler.

Based on the test run results the tabular pigment is the most suitable filler for an SC WO paper.

Example 2

In this test conventional SC papers were made in a manner completely known per se in the art using fillers with different particle sizes and particle shapes: A) tabular, size 2.6μm; B) tabular, size 0.7μm; and C) columnar, size 1.2μm. The amount of filler in the paper was 30%.

Based on the test run results filler A provided the paper with the best dusting and piling ten- dency. The poorest result was clearly met with filler C. Also filler B provided poorer printability than filler A, resulting from the negative effect of the filler on the pore structure of the paper.

Example 3 Conventional wood-free fine paper was made in laboratory scale in a manner completely known per se in the art using fillers with different particle sizes and shapes: A) cubic, particle size 2μm; B) cube- agglomerate, particle size 3.9μm; and C) cubic, particle size 4.2μm. The amount of fillers in the paper was in the range of 20% to 30%.

In comparing the effect of different fillers it was found that in using filler C, the bond strength (tensile and internal bond strength) of the paper is maintained substantially superior (+ 15%) to fillers A and B. Filler C was instead inferior to fillers A and B in terms of the opacity of the paper, and the opacity it provided remained 3.5% lower than with the other fillers.

Example 4

Conventional SC papers with a filler content of 28% were made in laboratory scale in a manner completely known per se in the art. A mixture of tabular (41%) and tubular fillers (59%) was used as the filler in paper A, and in paper B the tabular filler was replaced with a cubic filler. In printing the papers in the laboratory it was found that the need of printing ink at the standard density was 10% higher in paper B and the print through was at a poorer level (20% difference in strike-though) .

Example 5

In this test the use of a tabular filler in conventional SC paper made in a manner completely known per se in the art and the properties and advan- tages provided by the tabular filler in the paper and in printing were examined. The tendency of dusting that is present in offset printing of SC paper could be controlled by the particle shape and size in the precipitated filler used in the pore structure of the paper. By using a tabular filler it was possible to slow down the settling of printing ink and thereby to have a positive effect on the strain applied to the surface of the paper during printing.

The settling rate of the printing ink has also an important role in terms of the piling tendency of paper in WO printing. Use of the tabular filler proved to be advantageous also in terms of piling.

The piling tendency of SC paper could be improved be selecting a filler of a sufficiently large particle size. The larger particle size filler allowed one to eliminate the small pore structures from the paper structure that speed up the settling of the ink, and thereby to eliminate the piling behavior.

With the precipitated tabular filler it was possible to control the absorption and settling of the gravure ink in SC paper and thereby to improve the printability and print through of the paper.

Example 6

In this test a significantly better drainage was provided in a paper machine by selecting a structured precipitated pigment as the filler in a conventional paper. If the corresponding single crystalline product was used as the filler, the readily concentrating single crystals formed a drainage-slowing structure in the paper.

Based on the conducted studies and tests it could be found that a filler of a tabular particle shape allows one to improve the properties, such as printability, of the paper product that is being formed.

In the examples presented above, making and further processing of the paper were conducted in man- ners known per se which are not described in any more detail in this context.

The process according to the invention is suitable in different embodiments for use in making the most different kinds of paper and board products requiring certain desired properties of the product e.g. in terms of printing.

The invention is not limited merely to the examples referred to above; instead, many variations are possible within the scope of the inventive idea defined by the claims.

Claims

1. A process for making paper and board wherein a product is formed from a fibrous starting mate- rial and a filler, c h a r a c t e r i z e d in that the properties of the product that is being formed are controlled by the employed filler containing at least one filler component which is formed from particles having a substantially tabular particle shape and which is formed substantially synthetically by a process selected from the group of precipitation, agglomeration, chemical modification and combinations thereof, the mean particle size in the filler component being less than 20μm, and the degree of brightness, determined according to ISO standard, being at least 86.

2. The process according to claim 1, c h a r a c t e r i z e d in that precipitated filler is used as the filler component.

3. The process according to claim 1 or 2, c h a r a c t e r i z e d in that chemically modified filler is used as the filler component.

4. The process according to any one of claims 1 to 3, c h a r a c t e r i z e d in that a filler formed by agglomeration is used as the filler component, wherein the agglomeration has been performed by using an auxiliary agent.

5. The process according to any one of claims 1 to 4, c h a r a c t e r i z e d in that the filler contains particles of a tabular particle shape in an amount of 20% to 100% of the amount of filler.

6. The process according to any one of claims 1 to 5, c h a r a c t e r i z e d in that the degree of brightness in the filler component, determined according to ISO standard, is at least 88.

7. The process according to any one of claims

1 to 6, c h a r a c t e r i z e d in that the degree of brightness in the filler component, determined according to ISO standard, is at least 92.

8. The process according to any one of claims 1 to 7, c h a r a c t e r i z e d in that the filler component is selected from the group of gypsum and carbonates .

9. The process according to any one of claims 1 to 8, c h a r a c t e r i z e d in that the shape factor of the tabular particle in the filler component is at least 5:1 (determined by the perimeter diameter process) .

10. The process according to any one of claims 1 to 9, c h a r a c t e r i z e d in that the shape factor of the tabular particle in the filler component is at least 10:1 (determined by the perimeter diameter process) .

11. The process according to any one of claims. 1 to 10, c h a r a c t e r i z e d in that the shape factor of the tabular particle in the filler component is at least 15:1 (determined by the perimeter diameter process) .

12. The process according to any one of claims 1 to 11, c h a r a c t e r i z e d in that the paper or board that is being formed is mainly formed from me- chanical pulp.

13. A product, such as a paper or a board product, formed from a fibrous starting material and a filler, c h a r a c t e r i z e d in that the filler contains at least one filler component which is formed from particles having a substantially tabular particle shape and which is formed substantially synthetically by a process selected from the group of precipitation, agglomeration, chemical modification and combinations thereof, the mean particle size in the filler compo- nent being less than 20μm, and the degree of bright- ness, determined according to ISO standard, being at least 86.

14. The product according to claim 13, c h a r a c t e r i z e d in that the degree of brightness in the filler component, determined according to ISO standard, is at least 88.

15. The product according to claim 13 or 14, c h a r a c t e r i z e d in that the degree of brightness in the filler component, determined according to ISO standard, is at least 92.

16. The product according to any one of claims 13 to 15, c h a r a c t e r i z e d in that the filler contains particles of a tabular particle shape in an amount of 20% to 100% of the amount of filler.

17. The product according to any one of claims

13 to 16, c h a r a c t e r i z e d in that the shape factor of the tabular particle in the filler component is at least 5:1 (determined by the perimeter diameter process) .

18. The product according to any one of claims

13 to 17, c h a r a c t e r i z e d in that the paper product is selected from the group of SC, WFU, LWC, MWC, MFC, WFC and suchlike products.