EP4771217A1

EP4771217A1 - Alkaline paper product containing calcium silicate mixtures

Info

Publication number: EP4771217A1
Application number: EP24786819.3A
Authority: EP
Inventors: Luis FERRAZ; Johannes Kritzinger; Michael Pohl
Original assignee: Omya International AG
Current assignee: Omya International AG
Priority date: 2023-10-13
Filing date: 2024-10-09
Publication date: 2026-07-08
Also published as: TW202536274A; KR20260089575A; MX2026004105A; CN121969804A; WO2025078438A1

Abstract

The invention relates to a paper filler comprising a mixture of three calcium silicate minerals being akermanite, gehlenite and larnite, a paper product comprising the paper filler as well as the use of the paper filler as alkaline paper filler in a paper product.

Description

Alkaline paper product containing calcium silicate mixtures

Technological Background

The production of paper products consumes millions of tons of wood fiber raw materials each year. However, there is a rapidly growing sensitivity for protecting forest resources, for preventing global warming and for reducing energy consumption. Thus, there is a growing market for the recycling and reuse of paper-based waste, which is produced in large amounts. In general, the recycling of wastepaper involves the separation of pulp fibers from other components of the paper, especially mineral fillers, printing inks etc, through a series of different steps depending on the recycling process used. Thus, the recycling produces pulp fibers that can be used as a recycled raw material in the production of paper and a material comprising a mixture of components that is removed as part of the deinking process, which is typically called de-inked sludge. However, such de-inked sludges are typically incinerated and then landfilled in form of fly ash.

Furthermore, it is well known that the pH of pulp suspensions derived from a recycling process will typically drop over time. During the repulping process, the starch (added as an additive for improved paper properties) hydrolyses to glucose and provides an abundant nutritional basis for bacteria. Bacteria metabolism generates fatty acids such as acetic acid, which lead to the acidification ofthe process water (pH drop), originating calcium ions (Ca²⁺) and also increases the water hardness. These cations interact with anionic surface charges of fibers and lead to charge neutralization and the accumulation of tacky deposits. These reduce the effectiveness of cationic wet-end additives such as internal sizing agents and retention aids. As a consequence, product specifications may not be reached, greater quantities of additives may be needed, and machine downtime may be increased. In view of this, pH drop in paper production is typically controlled by the addition of sodium hydroxide, the addition of biocides and/or the addition of CaO/Ca(OH)2 based concepts. However, due to the safety hazards involved by using these additives and additional materials to be used in the preparation of recycled materials, it is desired to provide a safe and economically viable pH control concept.

Due to its high alkalinity, calcium silicates may possess antimicrobial activities and may be used as paper filler, possessing a highly porous surface structure and large specific surface area which may result in paper products with higher opacity and brightness. Such calcium silicates may be present in fly ash of incinerated de-inked sludge in varying composition. Therefore, maximizing the use of resources and the reuse of wastes is a key for process efficiency and circularity in paper production.

In the art, several approaches of using calcium silicate or fly ash have been suggested and include the use of calcium silicate or fly ash in the production of paper products. For example, WO9628517A1 refers to a paper comprising cellulose fibers and a composite particulate material comprising an inner portion of an ash of an inorganic mineral material, and an outer portion of calcium carbonate. The inorganic mineral material may comprise an ash obtained from the incineration of wastepaper deink residue. JP2008025088A refers to a neutral paper that is bulky paper. The neutral paper comprises 0.3 to 20% by weight of particles containing calcium silicate having an aggregated form of petal flakes as a filler, and a mercury porosimeter method in the neutral paper. US5660900A relates to an article of manufacture comprising a starch-bound cellular matrix of starch and inorganic aggregate, the starch-bound cellular matrix comprising: a starch-based binder that has been substantially gelatinized by water and then hardened through the removal of a substantial quantity of the water by evaporation; and an inorganic aggregate dispersed throughout the starch-bound cellular matrix in a concentration in a range from about 20% to about 90% by weight of total solids within the starch-bound cellular matrix, wherein the starch-bound cellular matrix has a thickness less than about 1 cm and degrades after prolonged exposure to water. CN102433795A refers to a paper-making filler, characterized in that the filler is activated calcium silicate. The activated calcium silicate may be made of fly ash as a raw material and is prepared by a pre-treatment method comprising adding the activated calcium silicate to hot water with a water temperature of 50 to 100°C, fully stirring and dissolving into an emulsion. US6139960A relates to a mineral filler comprising: dry processed fly ash comprising from about 5-60% by weight aluminum oxide, from about 0.5-60% by weight calcium oxide, from about 5- 30% by weight silicon oxide, from about 0.5-15% by weight magnesium oxide and from about 0.1-10% by weight titanium dioxide. KR20130017453A refers to a method for enhancing the optical properties of waste paper by simultaneously synthesizing PCC and waste paper by an in-situ method of high-charge PCC synthesis using paper sludge ash.

In view of the foregoing, there is still a need in the art for an effective and efficient paper filler which can be used in the production of paper products, in particular, recycled paper products. More precisely, there is a need for a paper filler obtained from the incineration of de-inked sludge that provides alkaline properties for a paper product, especially a recycled paper product, prepared therefrom and thus provides a sufficient pH control.

Accordingly, it is an objective of the present invention to provide a paper filler for use in a paper product. It is a further objective of the present invention to provide a paper filler for use in a paper product providing alkaline properties. Preferably, the paper filler is obtained from the incineration of de-inked sludge and thus is derived from a paper recycling process. It is a further object of the present invention that the paper filler is preferably used in combination with recycled pulp fibers and thus is derived from a paper recycling process.

These and other objectives of the present invention can be solved by the inventive paper filler, the paper product comprising the paper filler as well as the use of the paper filler as alkaline paper filler in a paper product.

Summary of the Invention

According to one aspect of the present invention, a paper filler is provided. The paper filler comprises a mixture of three calcium silicate minerals being akermanite, gehlenite and larnite, wherein the paper filler comprises gehlenite in an amount of from 0.1 to 15 wt.-%, based on the total weight of the filler, and larnite in an amount of from 0.1 to 50 wt.-%, based on the total weight of the filler, and akermanite in an amount of from 0.1 to 15 wt.-%, based on the total weight of the filler.

A second aspect of the present invention relates to a paper product prepared from the paper filler defined herein and paper making furnish comprising pulp, preferably virgin pulp and/or recycled pulp obtained from paper and/or paperboard recycling. A third aspect of the present invention relates to the use of the paper filler as defined herein as alkaline paper filler in a paper product, preferably a recycled paper product, more preferably a carton board such as coated or uncoated carton board, or a container board such as liners, flutings and dual papers.

The inventors surprisingly found out that the paper filler provides alkaline properties to a paper product prepared therefrom. Furthermore, the use of additives for controlling a pH drop in paper production such as sodium hydroxide, biocides and/or CaO/Ca(OH)2 based concepts can be reduced or avoided. Furthermore, the paper filler can be obtained from fly ash of incinerated de-inked sludge and moreover can be used in combination with recycled pulp obtained from paper and/or paperboard recycling. Thus, the inventive paper filler and/or paper product maximize(s) the use of resources and therefore increase(s) process efficiency and circularity in paper production.

Advantageous embodiments of the present invention can be found in the corresponding dependent claims.

In one embodiment of any one of the aspects of the present invention, the paper filler comprises the mixture of three calcium silicate minerals, as determined by X-Ray Diffraction, in a total amount of > 0.3 wt.-%, preferably from 0.3 to 60 wt.-%, based on the total weight of the filler.

In another embodiment of any one of the aspects of the present invention, the mixture of three calcium silicate minerals comprises, as determined by X-Ray Diffraction, i) larnite and gehlenite in a weight ratio [larnite/gehlenite] ranging from 30:1 to 1 :2, preferably from 20:1 to 1 .2, and/or ii) larnite and akermanite in a weight ratio [larnite/akermanite] ranging from 10:1 to 2:1 , preferably from 8:1 to 2:1 , and/or iii) gehlenite and akermanite in a weight ratio [gehlenite/akermanite] ranging from 5:1 to 1 :5, preferably from 3:1 to 1 :3.

In yet another embodiment of any one of the aspects of the present invention, the paper filler has a Ca content, determined as CaO in X-Ray Fluorescence measurement, of > 50 wt.-%, preferably from 20 to 70 wt.-%, based on the total weight of the filler.

In one embodiment of any one of the aspects of the present invention, the paper filler has a volume median particle size cfeo in the range from 0.8 to 6.0 pm, preferably from 1 .0 to 3.0 pm, measured by using a laser diffraction system.

In another embodiment of any one of the aspects of the present invention, the paper filler further comprises one or more components selected from the group comprising calcite, portlandite, lime, quartz, mayenite, tricalcium aluminate, feldspar, anhydrous calcium sulfate, serpentine, crystobalite, clay, spinel, and mixtures thereof.

In yet another embodiment of any one of the aspects of the present invention, the paper filler comprises lime, as determined by X-Ray Diffraction, in an amount of > 3 to 30 wt.-%, preferably from 4 to 30 wt.-%, based on the total weight of the filler.

In one embodiment of any one of the aspects of the present invention, the paper filler is obtained from an incineration of de-inked sludge of white recycled paper, preferably from tissue, supercalendered paper or newsprint, at temperatures of at least 800°C, preferably at least 850°C. In another embodiment of any one of the aspects of the present invention, the paper filler is an alkaline paper filler.

In one embodiment of the paper product of the present invention, the paper filler is present in an amount ranging from 0.3 to 10 wt.-%, based on the total weight of the paper product.

In another embodiment of the paper product of the present invention, the paper product comprises lime, as determined by X-Ray Diffraction, in an amount of < 10 wt.-%, preferably < 5 wt.-%, based on the total weight of the paper product.

In yet another embodiment of the paper product of the present invention, the paper product i) has a surface pH of 7.9 or more, preferably a pH of 8.0 or more, and most preferably a surface pH of 8.1 or more, and/or ii) when slushed in water, resulting in a water pH of 9.4 or more, and preferably a water pH of 9.5 or more.

In one embodiment of the paper product of the present invention, the paper product is a recycled paper product, preferably a carton board such as coated or uncoated carton board, or a container board such as liners, flutings and dual papers.

In another embodiment of the paper product of the present invention, the paper product, when incinerated at 850°C ± 10°C, using a microwave muffle furnace, has a lime content, as determined by X-Ray Diffraction, ranging from > 3 to 40 wt.-%, preferably from 4 to 40 wt.-%, based on the total weight of the paper product.

For the purposes of the present invention, the term “recycled pulp” is understood to refer to pulp originating from paper and/or paperboard recycling, i.e., from paper and/or paperboard waste that has been subjected to a recycling method. Thus, the recycled pulp is preferably obtained from “postconsumer paper and/or paperboard waste” generated by consumers. Alternatively, the recycled pulp may be obtained from “post-industrial paper and/or paperboard waste” generated in industry or during the manufacture of paper products. Recycled pulp may be a mixture of fibers but it may also include only one kind of fibers. Furthermore, recycled pulp may contain further additives, such as mineral fillers, printing inks and the like.

For the purposes of the present invention, the term “virgin pulp” is understood to refer to pulp originating from renewable resources, i.e., the pulp is not obtained from a recycling method.

Where an indefinite or definite article is used when referring to a singular noun, e.g., “a”, “an” or “the”, this includes a plural of that noun unless anything else is specifically stated.

Where the term “comprising” is used in the present description and claims, it does not exclude other elements. For the purposes of the present invention, the term “consisting of’ is considered to be a preferred embodiment of the term “comprising”. If hereinafter a group is defined to comprise at least a certain number of embodiments, this is also to be understood to disclose a group, which preferably consists only of these embodiments.

Whenever the terms “including” or “having” are used, these terms are meant to be equivalent to “comprising” as defined hereinabove.

Terms like “obtainable” or “definable” and “obtained” or “defined” are used interchangeably. This, for example, means that, unless the context clearly dictates otherwise, the term “obtained” does not mean to indicate that, for example, an embodiment must be obtained by, for example, the sequence of steps following the term “obtained” though such a limited understanding is always included by the terms “obtained” or “defined” as a preferred embodiment.

When in the following reference is made to embodiments or technical details of the inventive paper filler, it is to be understood that these embodiments or technical details also refer to the inventive paper product and the inventive use.

The paper filler

The inventive paper filler comprises a mixture of three calcium silicate minerals. It is specifically required that the three calcium silicate minerals include akermanite, gehlenite and larnite in order to obtain a paper product therefrom having alkaline properties.

In the meaning of the present invention, akermanite is considered to be a calcium silicate mineral, in particular a calcium magnesium silicate mineral, having the formula Ca₂Mg[Si₂O₇].

In the meaning of the present invention, gehlenite is considered to be a calcium silicate mineral, in particular a calcium aluminium silicate mineral, having the formula Ca2AI[AISiC>7].

In the meaning of the present invention, larnite is considered to be a calcium silicate mineral, in particular a dicalcium silicate mineral, having the formula p-Ca2[SiC>4].

It is further required that the paper filler comprises gehlenite in an amount of from 0.1 to 15 wt.-%, based on the total weight of the filler, larnite in an amount of from 0.1 to 50 wt.-%, based on the total weight of the filler, and akermanite in an amount of from 0.1 to 15 wt.-%, based on the total weight of the filler. In one embodiment, the paper filler comprises gehlenite in an amount of from 1 to 15 wt.-%, based on the total weight of the filler, larnite in an amount of from 1 to 50 wt.-%, based on the total weight of the filler, and akermanite in an amount of from 1 to 15 wt.-%, based on the total weight of the filler or the paper filler comprises gehlenite in an amount of from 2 to 15 wt.-%, based on the total weight of the filler, larnite in an amount of from 5 to 50 wt.-%, based on the total weight of the filler, and akermanite in an amount of from 1 .5 to 15 wt.-%, based on the total weight of the filler.

In a preferred embodiment, the paper filler comprises gehlenite in an amount of from 3 to 15 wt.-%, based on the total weight of the filler, larnite in an amount of from 12 to 50 wt.-%, based on the total weight of the filler, and akermanite in an amount of from 2 to 15 wt.-%, based on the total weight of the filler.

It is to be noted that, if not otherwise indicated, the amount and composition of minerals in the paper filler, and in the incinerated paper product is determined by X-Ray Diffraction throughout the present invention. The method is further described in the example section herein.

For example, the paper filler comprises gehlenite in an amount of from 3 to 12 wt.-%, preferably from 3 to 10 wt.-% and most preferably from 3 to 8 wt.-%, based on the total weight of the filler.

Additionally, or alternatively, the paper filler comprises larnite in an amount of from 12 to 45 wt.-%, preferably from 14 to 40 wt.-% and most preferably from 15 to 38 wt.-%, based on the total weight of the filler.

Additionally, or alternatively, the paper filler comprises akermanite in an amount of from 2 to 12 wt.-%, preferably from 2 to 10 wt.-% and most preferably from 2 to 8 wt.-%, based on the total weight of the filler.

In one embodiment, the paper filler thus comprises i) gehlenite in an amount of from 3 to 12 wt.-%, preferably from 3 to 10 wt.-% and most preferably from 3 to 8 wt.-%, based on the total weight of the filler, ii) larnite in an amount of from 12 to 50 wt.-%, based on the total weight of the filler, and iii) akermanite in an amount of from 2 to 15 wt.-%, based on the total weight of the filler.

Alternatively, the paper filler thus comprises i) gehlenite in an amount of from 3 to 15 wt.-%, based on the total weight of the filler, ii) larnite in an amount of from 12 to 45 wt.-%, preferably from 14 to 40 wt.-% and most preferably from 15 to 38 wt.-%, based on the total weight of the filler, and iii) akermanite in an amount of from 2 to 15 wt.-%, based on the total weight of the filler.

Alternatively, the paper filler thus comprises i) gehlenite in an amount of from 3 to 15 wt.-%, based on the total weight of the filler, ii) larnite in an amount of from 12 to 50 wt.-%, based on the total weight of the filler, and iii) akermanite in an amount of from 2 to 12 wt.-%, preferably from 2 to 10 wt.-% and most preferably from 2 to 8 wt.-%, based on the total weight of the filler.

In another embodiment, the paper filler comprises i) gehlenite in an amount of from 3 to 12 wt.-%, preferably from 3 to 10 wt.-% and most preferably from 3 to 8 wt.-%, based on the total weight of the filler, ii) larnite in an amount of from 12 to 45 wt.-%, preferably from 14 to 40 wt.-% and most preferably from 15 to 38 wt.-%, based on the total weight of the filler, and iii) akermanite in an amount of from 2 to 15 wt.-%, based on the total weight of the filler.

Alternatively, the paper filler comprises i) gehlenite in an amount of from 3 to 12 wt.-%, preferably from 3 to 10 wt.-% and most preferably from 3 to 8 wt.-%, based on the total weight of the filler, ii) larnite in an amount of from 12 to 50 wt.-%, based on the total weight of the filler, and iii) akermanite in an amount of from 2 to 12 wt.-%, preferably from 2 to 10 wt.-% and most preferably from 2 to 8 wt.-%, based on the total weight of the filler.

Alternatively, the paper filler comprises i) gehlenite in an amount of from 3 to 15 wt.-%, based on the total weight of the filler, ii) larnite in an amount of from 12 to 45 wt.-%, preferably from 14 to 40 wt.-% and most preferably from 15 to 38 wt.-%, based on the total weight of the filler, and iii) akermanite in an amount of from 2 to 12 wt.-%, preferably from 2 to 10 wt.-% and most preferably from 2 to 8 wt.-%, based on the total weight of the filler.

In a preferred embodiment, the paper filler thus comprises i) gehlenite in an amount of from 3 to 12 wt.-%, preferably from 3 to 10 wt.-% and most preferably from 3 to 8 wt.-%, based on the total weight of the filler, and ii) larnite in an amount of from 12 to 45 wt.-%, preferably from 14 to 40 wt.-% and most preferably from 15 to 38 wt.-%, based on the total weight of the filler, and iii) akermanite in an amount of from 2 to 12 wt.-%, preferably from 2 to 10 wt.-% and most preferably from 2 to 8 wt.-%, based on the total weight of the filler.

As regards the mixture of three calcium silicate minerals, it is appreciated that the silicate minerals are preferably present in specific weight ratios. For example, the mixture of three calcium silicate minerals preferably comprises larnite and gehlenite in a weight ratio [larnite/gehlenite] ranging from 30:1 to 1 :2, preferably from 20:1 to 1 .2.

Additionally, or alternatively, the mixture of three calcium silicate minerals preferably comprises larnite and akermanite in a weight ratio [larnite/akermanite] ranging from 10:1 to 2:1 , preferably from 8:1 to 2:1.

Additionally, or alternatively, the mixture of three calcium silicate minerals preferably comprises gehlenite and akermanite in a weight ratio [gehlenite/akermanite] ranging from 5:1 to 1 :5, preferably from 3:1 to 1 :3,

In a preferred embodiment, the mixture of three calcium silicate minerals thus comprises i) larnite and gehlenite in a weight ratio [larnite/gehlenite] ranging from 30:1 to 1 :2, preferably from 20:1 to 1 .2, and ii) larnite and akermanite in a weight ratio [larnite/akermanite] ranging from 10:1 to 2:1 , preferably from 8:1 to 2:1 .

In another embodiment, the mixture of three calcium silicate minerals thus comprises i) larnite and gehlenite in a weight ratio [larnite/gehlenite] ranging from 30:1 to 1 :2, preferably from 20:1 to 1 .2, and ii) gehlenite and akermanite in a weight ratio [gehlenite/akermanite] ranging from from 5:1 to 1 :5, preferably from 3:1 to 1 :3.

It is preferred that the mixture of three calcium silicate minerals thus comprises i) larnite and gehlenite in a weight ratio [larnite/gehlenite] ranging from 30:1 to 1 :2, preferably from 20:1 to 1 .2, and ii) larnite and akermanite in a weight ratio [larnite/akermanite] ranging from 10:1 to 2:1 , preferably from 8:1 to 2:1 , and iii) gehlenite and akermanite in a weight ratio [gehlenite/akermanite] ranging from from 5:1 to 1 :5, preferably from 3:1 to 1 :3.

In one embodiment, the mixture of three calcium silicate minerals preferably comprises larnite and gehlenite in a weight ratio [larnite/gehlenite] ranging from 10:1 to 1 :1 , preferably from 8:1 to 2:1 .

Additionally, or alternatively, the mixture of three calcium silicate minerals preferably comprises larnite and akermanite in a weight ratio [larnite/akermanite] ranging from 10:1 to 2:1 , preferably from 8:1 to 4:1 .

Additionally, or alternatively, the mixture of three calcium silicate minerals preferably comprises gehlenite and akermanite in a weight ratio [gehlenite/akermanite] ranging from 5:1 to 1 :2, preferably from 3:1 to 1 :1.

In a preferred embodiment, the mixture of three calcium silicate minerals thus comprises i) larnite and gehlenite in a weight ratio [larnite/gehlenite] ranging from 10:1 to 1 :1 , preferably from 8:1 to 2:1 , and ii) larnite and akermanite in a weight ratio [larnite/akermanite] ranging from 10:1 to 2:1 , preferably from 8:1 to 4:1 .

In another embodiment, the mixture of three calcium silicate minerals thus comprises i) larnite and gehlenite in a weight ratio [larnite/gehlenite] ranging from 10:1 to 1 :1 , preferably from 8:1 to 2:1 , and ii) gehlenite and akermanite in a weight ratio [gehlenite/akermanite] ranging from 5:1 to 1 :2, preferably from 3:1 to 1 :1.

It is preferred that the mixture of three calcium silicate minerals thus comprises i) larnite and gehlenite in a weight ratio [larnite/gehlenite] ranging from 10:1 to 1 :1 , preferably from 8:1 to 2:1 , and ii) larnite and akermanite in a weight ratio [larnite/akermanite] ranging from 10:1 to 2:1 , preferably from 8:1 to 4:1 , and iii) gehlenite and akermanite in a weight ratio [gehlenite/akermanite] ranging from 5:1 to 1 :2, preferably from 3:1 to 1 :1.

Very generally, the paper filler comprises the mixture of three calcium silicate minerals in a specific range. More precisely, the paper filler preferably comprises the mixture of three calcium silicate minerals in a total amount of > 0.3 wt.-%, based on the total weight of the filler. In particular, the paper filler comprises the mixture of three calcium silicate minerals in a total amount of from 0.3 to 60 wt.-%, more preferably from 0.3 to 55 wt.-% and most preferably from 0.3 to 50 wt.-%, based on the total weight of the filler.

In one embodiment, the paper filler preferably comprises the mixture of three calcium silicate minerals in a total amount of > 1 wt.-%, based on the total weight of the filler, e.g. from 1 to 60 wt.-%, more preferably from 5 to 55 wt.-% and most preferably from 10 to 50 wt.-%, based on the total weight of the filler.

For example, the paper filler preferably comprises the mixture of three calcium silicate minerals in a total amount of > 20 wt.-%, based on the total weight of the filler. In particular, the paper filler comprises the mixture of three calcium silicate minerals in a total amount of from 20 to 60 wt.-%, more preferably from 24 to 55 wt.-% and most preferably from 25 to 50 wt.-%, based on the total weight of the filler.

As the paper filler comprises a mixture of three calcium silicate minerals, it is appreciated that the paper filler has a Ca content, determined as CaO in X-Ray Fluorescence measurement, in a certain range. It is especially preferred that the paper filler has a Ca content, determined as CaO in X-Ray Fluorescence measurement, of > 50 wt.-%, based on the total weight of the filler. In one embodiment, the paper filler has a Ca content, determined as CaO in X-Ray Fluorescence measurement, of from 20 to 70 wt.-%, based on the total weight of the filler.

Furthermore, it is appreciated that the paper filler has a rather low volume median particle size (doo) value supporting the alkaline properties of the paper product. Thus, the paper filler preferably has a volume median particle size cfeo in the range from 0.8 to 6.0 pm, measured by using a laser diffraction system. It is to be noted that the alkaline properties of the paper product are even further increased if the volume median particle size (doo) value of the paper filler is in the lower range of the volume median particle size cfeo range. Thus, the paper filler preferably has a weight median particle size cfeo in the range from 1 .0 to 3.0 pm, measured by using a laser diffraction system.

The paper filler of the present invention comprises the mixture of three calcium silicate minerals being akermanite, gehlenite and larnite.

In one embodiment, the paper filler of the present invention consists of the mixture of three calcium silicate minerals being akermanite, gehlenite and larnite. However, it is appreciated that the paper filler is preferably obtained from a recycling process and especially is obtained from an incineration of de-inked sludge. In view of this, the paper filler of the present invention preferably comprises further components typically included in such sludges.

For example, the paper filler further comprises one or more components selected from the group comprising calcite, portlandite, lime, quartz, mayenite, tricalcium aluminate, feldspar, anhydrous calcium sulfate, serpentine, crystobalite, clay, spinel, and mixtures thereof.

The wording “one or more” components indicates that the further components may comprise one further component or a mixture of two or more components. Preferably, the further components comprise a mixture of two or more components.

For example, the further components are a mixture comprising calcite, portlandite, lime, quartz, mayenite, tricalcium aluminate, feldspar, anhydrous calcium sulfate, serpentine, crystobalite, clay and spinel. In this embodiment, it is appreciated that the paper filler may comprise further components that are present in low amounts, e.g. in amounts of below 1 wt.-%, based on the total weight of the filler, differing from calcite, portlandite, lime, quartz, mayenite, tricalcium aluminate, feldspar, anhydrous calcium sulfate, serpentine, crystobalite, clay and spinel.

Alternatively, the further components are a mixture consisting of calcite, portlandite, lime, quartz, mayenite, tricalcium aluminate, feldspar, anhydrous calcium sulfate, serpentine, crystobalite, clay and spinel.

In one embodiment, the paper filler thus comprises a) a mixture of three calcium silicate minerals being akermanite, gehlenite and larnite, wherein the paper filler comprises gehlenite in an amount of from 0.1 to 15 wt.-%, based on the total weight of the filler, and larnite in an amount of from 0.1 to 50 wt.-%, based on the total weight of the filler, and akermanite in an amount of from 0.1 to 15 wt.-%, based on the total weight of the filler, and b) one or more components selected from the group comprising calcite, portlandite, lime, quartz, mayenite, tricalcium aluminate, feldspar, anhydrous calcium sulfate, serpentine, crystobalite, clay, spinel, and mixtures thereof.

For example, the paper filler comprises a) a mixture of three calcium silicate minerals being akermanite, gehlenite and larnite, wherein the paper filler comprises gehlenite in an amount of from 0.1 to 15 wt.-%, based on the total weight of the filler, and larnite in an amount of from 0.1 to 50 wt.-%, based on the total weight of the filler, and akermanite in an amount of from 0.1 to 15 wt.-%, based on the total weight of the filler, and b) components being a mixture comprising calcite, portlandite, lime, quartz, mayenite, tricalcium aluminate, feldspar, anhydrous calcium sulfate, serpentine, crystobalite, clay and spinel.

In a preferred embodiment, the paper filler consists of a) a mixture of three calcium silicate minerals being akermanite, gehlenite and larnite, wherein the paper filler comprises gehlenite in an amount of from 0.1 to 15 wt.-%, based on the total weight of the filler, and larnite in an amount of from 0.1 to 50 wt.-%, based on the total weight of the filler, and akermanite in an amount of from 0.1 to 15 wt.-%, based on the total weight of the filler, and b) one or more components selected from the group comprising calcite, portlandite, lime, quartz, mayenite, tricalcium aluminate, feldspar, anhydrous calcium sulfate, serpentine, crystobalite, clay, spinel, and mixtures thereof. Preferably, the paper filler consists of a) a mixture of three calcium silicate minerals being akermanite, gehlenite and larnite, wherein the paper filler comprises gehlenite in an amount of from 0.1 to 15 wt.-%, based on the total weight of the filler, and larnite in an amount of from 0.1 to 50 wt.-%, based on the total weight of the filler, and akermanite in an amount of from 0.1 to 15 wt.-%, based on the total weight of the filler, and b) components being a mixture comprising calcite, portlandite, lime, quartz, mayenite, tricalcium aluminate, feldspar, anhydrous calcium sulfate, serpentine, crystobalite, clay and spinel.

For example, the paper filler consists of a) a mixture of three calcium silicate minerals being akermanite, gehlenite and larnite, wherein the paper filler comprises gehlenite in an amount of from 0.1 to 15 wt.-%, based on the total weight of the filler, and larnite in an amount of from 0.1 to 50 wt.-%, based on the total weight of the filler, and akermanite in an amount of from 0.1 to 15 wt.-%, based on the total weight of the filler, and b) components being a mixture consisting of calcite, portlandite, lime, quartz, mayenite, tricalcium aluminate, feldspar, anhydrous calcium sulfate, serpentine, crystobalite, clay and spinel.

In another embodiment, the paper filler thus comprises a) a mixture of three calcium silicate minerals being akermanite, gehlenite and larnite, wherein the paper filler comprises gehlenite in an amount of from 3 to 15 wt.-%, based on the total weight of the filler, and larnite in an amount of from 12 to 50 wt.-%, based on the total weight of the filler, and akermanite in an amount of from 2 to 15 wt.-%, based on the total weight of the filler, and b) one or more components selected from the group comprising calcite, portlandite, lime, quartz, mayenite, tricalcium aluminate, feldspar, anhydrous calcium sulfate, serpentine, crystobalite, clay, spinel, and mixtures thereof.

For example, the paper filler comprises a) a mixture of three calcium silicate minerals being akermanite, gehlenite and larnite, wherein the paper filler comprises gehlenite in an amount of from 3 to 15 wt.-%, based on the total weight of the filler, and larnite in an amount of from 12 to 50 wt.-%, based on the total weight of the filler, and akermanite in an amount of from 2 to 15 wt.-%, based on the total weight of the filler, and b) components being a mixture comprising calcite, portlandite, lime, quartz, mayenite, tricalcium aluminate, feldspar, anhydrous calcium sulfate, serpentine, crystobalite, clay and spinel.

In a preferred embodiment, the paper filler consists of a) a mixture of three calcium silicate minerals being akermanite, gehlenite and larnite, wherein the paper filler comprises gehlenite in an amount of from 3 to 15 wt.-%, based on the total weight of the filler, and larnite in an amount of from 12 to 50 wt.-%, based on the total weight of the filler, and akermanite in an amount of from 2 to 15 wt.-%, based on the total weight of the filler, and b) one or more components selected from the group comprising calcite, portlandite, lime, quartz, mayenite, tricalcium aluminate, feldspar, anhydrous calcium sulfate, serpentine, crystobalite, clay, spinel, and mixtures thereof.

Preferably, the paper filler consists of a) a mixture of three calcium silicate minerals being akermanite, gehlenite and larnite, wherein the paper filler comprises gehlenite in an amount of from 3 to 15 wt.-%, based on the total weight of the filler, and larnite in an amount of from 12 to 50 wt.-%, based on the total weight of the filler, and akermanite in an amount of from 2 to 15 wt.-%, based on the total weight of the filler, and b) components being a mixture comprising calcite, portlandite, lime, quartz, mayenite, tricalcium aluminate, feldspar, anhydrous calcium sulfate, serpentine, crystobalite, clay and spinel.

For example, the paper filler consists of a) a mixture of three calcium silicate minerals being akermanite, gehlenite and larnite, wherein the paper filler comprises gehlenite in an amount of from 3 to 15 wt.-%, based on the total weight of the filler, and larnite in an amount of from 12 to 50 wt.-%, based on the total weight of the filler, and akermanite in an amount of from 2 to 15 wt.-%, based on the total weight of the filler, and b) components being a mixture consisting of calcite, portlandite, lime, quartz, mayenite, tricalcium aluminate, feldspar, anhydrous calcium sulfate, serpentine, crystobalite, clay and spinel.

It is thus appreciated that the sum of the mixture of three calcium silicate minerals being akermanite, gehlenite and larnite and the one or more components selected from the group comprising calcite, portlandite, lime, quartz, mayenite, tricalcium aluminate, feldspar, anhydrous calcium sulfate, serpentine, crystobalite, clay, spinel, and mixtures thereof in the paper filler is 100 wt.-%.

It is preferred that the paper filler comprises lime. In order to obtain the alkaline properties of the paper product, it is preferred that the paper filler comprises lime in an amount of > 3 to 30 wt.-%, based on the total weight of the filler. Preferably, the paper filler comprises lime in an amount of from 4 to 30 wt.-%, based on the total weight of the filler.

In one embodiment, the paper filler comprises lime in an amount of > 3 to 20 wt.-%, based on the total weight of the filler. Preferably, the paper filler comprises lime in an amount of from 4 to 20 wt.- %, based on the total weight of the filler.

As already mentioned above, the paper filler is preferably obtained from a paper recycling process. In particular, the paper filler is obtained from an incineration of de-inked sludge, especially of white recycled paper. It is appreciated that the de-inked sludge of white recycled paper is preferably obtained from tissue, supercalendered paper and/or newsprint. In one embodiment, the de-inked sludge is obtained from one paper source to be recycled only. Thus, the de-inked sludge of white recycled paper may be preferably obtained from tissue, supercalendered paper or newsprint. Alternatively, the de-inked sludge is obtained from a mixture of paper source to be recycled. Thus, the de-inked sludge of white recycled paper may be preferably obtained from tissue, supercalendered paper and newsprint.

For obtaining the paper filler of the present invention, it is required that the paper filler is obtained from an incineration of de-inked sludge of white recycled paper at temperatures of at least 800°C, preferably at least 850°C. For example, the paper filler is obtained from an incineration of de-inked sludge of white recycled paper at temperatures ranging from 800 to 1000°C, preferably from 850 to 900°C.

In view of the above, the paper filler of the present invention is preferably an alkaline paper filler.

The paper product

In a second aspect of the present invention, a paper product is provided. The paper product is prepared from the paper filler as defined herein and paper making furnish comprising pulp. It is to be noted that the paper product can be obtained by any method and device known in the art for preparing paper products. Such methods and devices are well known and do not need to be described in more detail herein.

The paper making furnish comprises pulp. The pulp used for preparing the paper product may be any pulp known to the skilled person that is suitable to be prepared into a paper product.

The pulp may thus be a virgin pulp and/or recycled pulp obtained from paper and/or paperboard recycling. Preferably, the pulp is a recycled pulp obtained from paper and/or paperboard recycling. In one embodiment, it may be favorable to change the composition of recycled pulp by adding virgin pulp. Thus, the pulp can be a mixture of recycled pulp obtained from paper and/or paperboard recycling and virgin pulp.

The pulp, either virgin pulp or recycled pulp, is preferably in form of an aqueous suspension comprising fibres.

It is appreciated that the amount of fibres in the aqueous suspension of the pulp may vary in a broad range. However, it is preferred that the amount of fibres in the aqueous suspension is such that the fibres can be easily deposited on a paper making device. Furthermore, it is preferred that the amount of solvent in the aqueous suspension is such that the water consumption and the energy required for removing moisture is as low as possible.

In general, the aqueous suspension thus comprises the fibres in an amount ranging from 0.1 to 30 wt.-%, based on the total weight of the aqueous suspension. Preferably, the aqueous suspension thus comprises the fibres in an amount ranging from 0.2 to 20 wt.-%, more preferably from 0.4 to 10 wt.-% and most preferably from 0.5 to 5 wt.-%, based on the total weight of the aqueous suspension. For example, the aqueous suspension comprises the fibres in an amount ranging from 0.5 to 10 wt.-%, based on the total weight of the aqueous suspension.

The fibres in the aqueous suspension are not restricted to a specific type of fibres. In general, any kind of fibre that is suitable for preparing paper products can be used for the present invention. More precisely, any fibre that is suitable for the desired paper product and its corresponding use can be used in the aqueous suspension.

Preferably, the fibres in the aqueous suspension comprise cellulose.

It is preferred that the fibres contained in pulp, either virgin pulp or recycled pulp, are selected from the group comprising eucalyptus pulp, spruce pulp, pine pulp, beech pulp, hemp pulp, cotton pulp, including cotton linters, wheat pulp, oat pulp, rye pulp, barley pulp, rice pulp, bamboo pulp, bagasse pulp, miscanthus pulp, sisal pulp, jute pulp, acacia pulp, birch pulp, fir pulp, lyocell pulp and mixtures thereof. In one embodiment, the fibres are contained in recycled or virgin eucalyptus pulp or in recycled or virgin cotton pulp.

In one embodiment, the pulp, either virgin pulp or recycled pulp, is a mixture of pulps comprising two or more pulps selected from the group comprising eucalyptus pulp, spruce pulp, pine pulp, beech pulp, hemp pulp, cotton pulp, wheat pulp, oat pulp, rye pulp, barley pulp, rice pulp, bamboo pulp, bagasse pulp, miscanthus pulp, sisal pulp, jute pulp, acacia pulp, birch pulp, fir pulp and lyocell pulp.

In view of this, the fibres in the aqueous suspension of the pulp, either virgin pulp or recycled pulp, are selected from the group comprising eucalyptus fibres, spruce fibres, pine fibres, beech fibres, hemp fibres, cotton fibres, cotton linters, wheat fibres, oat fibres, rye fibres, barley fibres, rice fibres, bamboo fibres, bagasse fibres, miscanthus fibres, sisal fibres, jute fibres, acacia fibres, birch fibres, fir fibres, lyocell fibres, viscose fibres and mixtures thereof. In one embodiment, the fibres in the aqueous suspension of the pulp are eucalyptus fibres or cotton fibres or cotton linters.

In one embodiment, the fibres in the aqueous suspension of the pulp, either virgin pulp or recycled pulp, are a mixture of fibres comprising two or more fibres, preferably the biocompatible fibres, selected from the group comprising eucalyptus fibres, spruce fibres, pine fibres, beech fibres, hemp fibres, cotton fibres, cotton linters, wheat fibres, oat fibres, rye fibres, barley fibres, rice fibres, bamboo fibres, bagasse fibres, miscanthus fibres, sisal fibres, jute fibres, acacia fibres, birch fibres, fir fibres, viscose fibres and lyocell fibres.

It is appreciated that the fibres have dimensions that are typically observed for the paper products to be prepared.

Thus, the fibres in the aqueous suspension of the pulp preferably have an average diameter ranging from 1 to 35 pm, preferably from 2 to 30 pm and most preferably from 3 to 25 pm.

Additionally, or alternatively, the fibres in the aqueous suspension of the virgin pulp preferably have an average length ranging from 0.7 to 250 mm, preferably from 0.8 to 230 mm and most preferably from 0.9 to 200 mm.

Additionally, or alternatively, the fibres in the aqueous suspension of the recycled pulp preferably have an average length ranging from 0.5 to 200 mm, preferably from 0.6 to 150 mm and most preferably from 0.7 to 100 mm.

For example, the fibres in the aqueous suspension of the virgin pulp have an average diameter ranging from 1 to 35 pm, preferably from 2 to 30 pm and most preferably from 3 to 25 pm or an average length ranging from 0.7 to 250 mm, preferably from 0.8 to 230 mm and most preferably from 0.9 to 200 mm. In another embodiment, the fibres in the aqueous suspension of the virgin pulp have an average diameter ranging from 1 to 35 pm, preferably from 2 to 30 pm and most preferably from 3 to 25 pm and an average length ranging from 0.7 to 250 mm, preferably from 0.8 to 230 mm and most preferably from 0.9 to 200 mm.

In case of recycled pulp, the fibres in the aqueous suspension of the recycled pulp have an average diameter ranging from 1 to 35 pm, preferably from 2 to 30 pm and most preferably from 3 to 25 pm or an average length ranging from 0.5 to 200 mm, preferably from 0.6 to 150 mm and most preferably from 0.7 to 100 mm. In another embodiment, the fibres in the aqueous suspension of the recycled pulp have an average diameter ranging from 1 to 35 pm, preferably from 2 to 30 pm and most preferably from 3 to 25 pm and an average length ranging from 0.5 to 200 mm, preferably from 0.6 to 150 mm and most preferably from 0.7 to 100 mm.

The solvent of the aqueous suspension comprises water, optionally in admixture with an organic solvent such as methanol, ethanol, n-butanol, isopropanol, n-propanol, acetone, dimethylsulphoxide, dimethylformamide, tetrahydrofurane, and mixtures thereof. Preferably, the solvent is water, methanol, ethanol and/or acetone. More preferably, the solvent comprises, most preferably consists of, water.

It is to be noted that the paper making furnish may further comprise typical additives used in the paper making process. For example, the paper making furnish may further comprise retention aids, filler such as calcium carbonate, clay, pitch control agents such as talc, antifoaming aids, sizing aids, starch, and the like as additive.

Preferably, the paper product comprises the paper filler in amounts typically used in the products to be prepared. Thus, the paper filler is preferably present in an amount ranging from 0.3 to 10 wt.-%, based on the total weight of the paper product. For example, the paper filler is present in an amount ranging from 0.4 to 7 wt.-%, most preferably from 0.5 to 5 wt.-%, based on the total weight of the paper product.

It is appreciated that the paper product comprises low amounts of lime. Preferably, the paper product comprises lime in an amount of < 40 wt.-%, preferably < 30 wt.-% and most preferably < 20 wt.-%, based on the total weight of the paper product. For example, the paper product comprises lime in an amount of < 10 wt.-%, preferably < 5 wt.-%, based on the total weight of the paper product.

Due to the presence of the inventive paper filler, it is appreciated that the paper product has alkaline properties. In particular, the paper product has a surface pH of 7.9 or more. For example, the paper product has a surface pH of 8.0 or more, and most preferably a surface pH of 8.1 or more. Preferably, the paper product has a surface pH ranging from 7.9 to 9.0, preferably a pH ranging from 8.0 to 8.8, and most preferably a surface pH ranging from 8.1 to 8.6.

Additionally, or alternatively, the paper product, when slushed in water, results in a water pH of 9.4 or more, and preferably a water pH of 9.5 or more. For example, the paper product, when slushed in water, results in a water pH ranging from 9.4 to 10.0, and preferably a water pH ranging from 9.5 to 9.9.

In a preferred embodiment, the paper product i) has a surface pH of 7.9 or more, preferably a pH of 8.0 or more, and most preferably a surface pH of 8.1 or more, and ii) when slushed in water, results in a water pH of 9.4 or more, and preferably a water pH of 9.5 or more.

It is appreciated that the lime content increases if the paper product is incinerated at 850°C ± 10°C. For example, the paper product, when incinerated at 850°C ± 10°C, using a microwave muffle furnace, has a lime content ranging from > 3 to 40 wt.-%, based on the total weight of the paper product. Preferably, the paper product, when incinerated at 850°C ± 10°C, using a microwave muffle furnace, has a lime content ranging from 4 to 40 wt.-%, based on the total weight of the paper product. For example, the paper product, when incinerated at 850°C ± 10°C, using a microwave muffle furnace, has a lime content ranging from > 3 to 30 wt.-%, preferably from > 3 to 20 wt.-% and most preferably from > 3 to 10 wt.-% based on the total weight of the paper product. Alternatively, the paper product, when incinerated at 850°C ± 10°C, using a microwave muffle furnace, has a lime content ranging from 4 to 30 wt.-%, preferably from 4 to 20 wt.-% and most preferably from 4 to 10 wt.-%, based on the total weight of the paper product.

As already mentioned above, the paper product is preferably a recycled paper product. In a preferred embodiment, the paper product is a carton board such as coated or uncoated carton board, or a container board such as liners, flutings and dual papers.

It is appreciated that examples of (recycled) coated carton board include coated recycled board (CRB), Greyback duplex (GBD), white-lined chipboard (WLC), whiteback duplex (WBD) and the like. Examples of (un recycled) coated carton board include cartonboard, coreboard, duplex, gypsum backing, gypsum facing, uncoated recycled board and the like. Examples of liners include brown testliner, brown high performance recycled liner, brown kraft top liner, whitetop testliner, mottled testliner and the like. Examples of fluting include recycled fluting (medium), light weight recycled fluting (medium) and the like. Examples of dual papers include recycled dual papers.

In view of the very good results achieved for the present paper filler, the present invention refers in another aspect to the use of the paper filler defined herein as alkaline paper filler in a paper product, preferably a recycled paper product, more preferably a carton board such as coated or uncoated carton board, or a container board such as liners, flutings and dual papers. With regard to the definition of the paper product, use of the paper filler and preferred embodiments thereof, reference is made to the statements provided above when discussing the technical details of the paper filler and paper product.

Brief description of the Figure

Fig. 1 relates to the effect of filler 1 particle size on pulp pH overtime.

The scope and interest of the invention will be better understood based on the following examples which are intended to illustrate certain embodiments of the present invention and are non- limitative.

Examples

Material

X-Ray Diffraction (XRD) measurements of filler

XRD is a versatile, nondestructive analytical technique that’s sensitive to the atomic structure of matter. XRD enables phase identification and quantification. Filler samples were split using a rifle splitter to reduce the samples to a suitable quantity for the analysis. The samples were then dried at 105 °C, overnight. Afterwards, the samples were ground using a Retsch RS200 mill at a speed of 1100 rpm for 90 seconds. 5 drops of isopropanol were used as grinding aid. The samples were homogenized in a glass bottle.

All samples were analyzed with a Bruker D8 Advance powder diffractometer obeying Bragg’s law. This diffractometer consists of a 1 kW X-ray tube, a sample holder, a 9-9 goniometer, and a LYNXEYE XE-T detector. The profiles were collected using a scan speed of 0.02° per second in 29. The resulting powder diffraction pattern is qualitatively analyzed using the DIFFRACsuite software packages EVA, based on reference patterns of the International Centre for Diffraction Data (ICDD) database.

Quantitative analysis of the diffraction data refers to the determination of amounts of different phases (minerals) in a multi-phase sample and was performed using the DIFFRAC suite software package TOPAS. In detail, quantitative analysis allows to determine structural characteristics and phase (mineral) proportions with quantifiable numerical precision from the experimental data itself. This involves modelling the full diffraction pattern (Rietveld approach) such that the calculated pattern(s) duplicates the experimental one. The Rietveld method requires knowledge of the approximate crystal structure of all phases (minerals) of interest in the pattern.

Table 1 : X-Ray Diffraction analysis of different fillers.

The total amount of the calcium silicate minerals akermanite, gehlenite and larnite is much higher in fillers 1 and 2 (28 and 44 %, respectively) as well as fillers 6, 7 and 8 (15, 20 and 27 %), originated from de-inked sludge incineration than in filler 3, originated from oil shale incineration (12%). In particular, fillers 1 and 2 incineration have a higher concentration of gehlenite and larnite in comparison to filler 3, while filler 6 incineration has a higher concentration of gehlenite in comparison to filler 3 and fillers 7 and 8 incineration have a higher concentration of larnite in comparison to filler 3. The amount of lime (wt.-%) is much higher in fillers 1 and 2 as well as fillers 6, 7 and 8 than in filler 3.

X-Ray Fluorescence (XRF) measurements of filler

XRF is a non destructive analytical technique used to determine the elemental composition of materials. Filler samples were prepared as fused beads with a loss on ignition (LOI)-free ratio flux: sample of 9:0.9 (g of fluxed material/g of sample). Lithium Tetraborate (66:34%) : Lithium Metaborate (99.98%) + 0.20% Lithium bromide was used as fluxed material. LOI was obtained via annealing the samples at 700 °C in the oven. The prepared fused beads were measured by XRF using the Perform’X sequential X-Ray florescence Spectrometer device from Thermo Fisher Scientific. The result represents the average of two measurements. The individual measurement is valid if its relative standard deviation is not higher than 10%.

Table 2: X-Ray Fluorescence analysis of different fillers.

The filler obtained from the incineration of de-inked sludge incineration, filler 1 , has a much higher Ca content, determined as CaO, in comparison to a filler obtained from industrial waste incineration, filler 4 (see Table 2).

Particle size distribution measurements

The "particle size" of a particulate material is described herein by the distribution d_x of its particle sizes, where the value d_x represents the diameter relative to which x % by volume of the particles have a diameter smaller than d_x. This means, for example, that the d2o value refers to a particle size in which 20% by volume of all particles are smaller than this particle size. The dso value is thus the volume median particle size, ie 50% by volume of all particles are smaller than this particle size. Particle size distribution of the employed filler materials was measured using a Malvern Mastersizer 3000 Laser Diffraction System with a dry dispersion unit (Malvern Instruments Pic., Great Britain). The method and instrument are known to the skilled person are commonly used to determine particle sizes of fillers and other particulate materials. The following parameters in Table 3 were used:

Table 3: Particle size distribution measurement parameters

Filler grinding

Filler samples grinding was done using a jet mill from Hosokawa Alpine. Grinding conditions are presented in Table 4. Filler 1 samples with a cfeo of 2.45 pm were obtained (see Table 5).

Table 4: Filler grinding conditions.

Table 5: Filler 1 particle size distribution before and after jet mill grinding.

Preparation of handsheets 100 g (dry) pulp of old corrugated carton in 10 dm³ tap water (20 °C), and then the filler to be tested was added in an amount so as to obtain the overall filler content based on the final paper weight. The suspension was stirred for 30 minutes. Subsequently, 0.06 % (based on dry weight) of a poly(amide) (Percol 1540) was added as a retention aid and sheets of 80 g/m² were formed using the Rapid-Kbthen hand sheet former. Each sheet was dried using the Rapid-Kbthen drier. The composition of the handsheets is given in Table 6 below.

Paper Surface pH

Measurement of the pH value on paper surfaces, was achieved after moistening of the sample surface with water. pH was measured for 60 seconds.

Table 6: Composition of handsheets created.

Table 7: pH measurements of surface pH of different paper handsheets.

The addition of fillers 1 and 2 having a total amount of the calcium silicate minerals akermanite, gehlenite and larnite of > 20 wt.-%, based on the total weight of the filler, resulted in an increase of surface pH of the paper sheets. Differently, fillers having a total amount of the calcium silicate minerals (akermanite, gehlenite and larnite) of < 20 wt.-%, based on the total weight of the filler such as, a filler from oil shale incineration (filler 3) did not result in increased surface pH levels. The addition of filler 5, a standard filler (natural ground calcium carbonate), or filler 4, from industrial waste incineration, did also not result in increased pH values.

Analysis of filler resulting from paper sheets incineration at 850 °C

Paper handsheets created were incinerated at 850 °C ± 10 °C, using a microwave muffle furnace. The resulting ash samples were analyzed via X-Ray Diffraction method (see Table 8)..

Table 8: Calcium silicate minerals and lime % identified by X-Ray Diffraction analysis of ash originated from handsheets incineration.

The addition of a standard filler, such as filler 5 (natural ground calcium carbonate), resulted in lower levels of calcium silicate minerals in comparison to the addition of filler obtained from de-inked sludge incineration (filler 1 and filler 2, S1 and S2, respectively) and to be absence of filler (SO). The addition of filler 1 and 2 (obtained from de-inked sludge incineration) (S1 and S2) resulted in higher levels of lime in comparison to the absence of filler. The addition of filler 3 did not affect the lime content.

T60 reactivity test

The method assesses the reactivity of filler. Ash samples were calcined at 950 °C for 1 hour to ensure that only CaO was present in the material. The necessary amount of sample was added to the selected amount of water at 20 °C. The mixture was stirred with a mechanical stirred at 300 rpm and the temperature rise was monitored with an ordinary thermometer and stopwatch. RDIN values were then calculated as prescribed by the European Norm².

Filler effect on pulp pH

0.8 liters of old corrugated carton board pulp (4% solids content) were added to a 1 liter bottle. Then, 1.8% of filler 1 with different particle size distribution (2.45 pm and 4.83 pm) was added to the bottles. A bottle containing only pulp was also added as a control. The pH of the mixtures was recorded over time. Results are presented in Fig. 1.

Claims

1 . Paper filler comprising a mixture of three calcium silicate minerals being akermanite, gehlenite and larnite, wherein the paper filler comprises gehlenite in an amount, as determined by X- Ray Diffraction, of from 0.1 to 15 wt.-%, based on the total weight of the filler, and larnite in an amount of from 0.1 to 50 wt.-%, based on the total weight of the filler, and akermanite in an amount of from 0.1 to 15 wt.-%, based on the total weight of the filler.

2. The paper filler of claim 1 , wherein the paper filler comprises the mixture of three calcium silicate minerals in a total amount, as determined by X-Ray Diffraction, of > 0.3 wt.-%, preferably from 0.3 to 60 wt.-%, based on the total weight of the filler.

3. The paper filler according to claim 1 or 2, wherein the mixture of three calcium silicate minerals comprises, as determined by X-Ray Diffraction, i) larnite and gehlenite in a weight ratio [larnite/gehlenite] ranging from 30:1 to 1 :2, preferably from 20:1 to 1 .2, and/or ii) larnite and akermanite in a weight ratio [larnite/akermanite] ranging from 10:1 to 2:1 , preferably from 8:1 to 2:1 , and/or iii) gehlenite and akermanite in a weight ratio [gehlenite/akermanite] ranging from 5:1 to 1 :5, preferably from 3:1 to 1 :3.

4. The paper filler according to any one of claims 1 to 3, wherein the paper filler has a Ca content, determined as CaO in X-Ray Fluorescence measurement, of > 50 wt.-%, preferably from 20 to 70 wt.-%, based on the total weight of the filler.

5. The paper filler according to any one of claims 1 to 4, wherein the paper filler has a volume median particle size cfeo in the range from 0.8 to 6 pm, preferably from 1 .0 to 3.0 pm, measured by using a laser diffraction system.

6. The paper filler according to any one of claims 1 to 5, wherein the paper filler further comprises one or more components selected from the group comprising calcite, portlandite, lime, quartz, mayenite, tricalcium aluminate, feldspar, anhydrous calcium sulfate, serpentine, crystobalite, clay, spinel, and mixtures thereof.

7. The paper filler according to any one of claims 1 to 6, wherein the paper filler comprises lime as determined by X-Ray Diffraction, in an amount of > 3 to 30 wt.-%, preferably from 4 to 30 wt.-%, based on the total weight of the filler.

8. The paper filler according to any one of claims 1 to 7, wherein the paper filler is obtained from an incineration of de-inked sludge of white recycled paper, preferably from tissue, supercalendered paper or newsprint, at temperatures of at least 800°C, preferably at least 850°C.

9. The paper filler according to any one of claims 1 to 8, wherein the paper filler is an alkaline paper filler.

10. Paper product prepared from the paper filler according to any one of claims 1 to 9 and paper making furnish comprising pulp, preferably virgin pulp and/or recycled pulp obtained from paper and/or paperboard recycling.

11 . The paper product according to claim 10, wherein the paper filler is present in an amount ranging from 0.3 to 10 wt.-%, based on the total weight of the paper product.

12. The paper product according to any one of claims 10 or 11 , wherein the paper product i) has a surface pH of 7.9 or more, preferably a pH of 8.0 or more, and most preferably a surface pH of 8.1 or more, and/or ii) when slushed in water, resulting in a water pH of 9.4 or more, and preferably a water pH of 9.5 or more.

13. The paper product according to any one of claims 10 to 12, wherein the paper product is a recycled paper product, preferably a carton board such as coated or uncoated carton board, or a container board such as liners, flutings and dual papers.

14. The paper product according to any one of claims 10 to 13, wherein the paper product, when incinerated at 850°C ± 10°C, using a microwave muffle furnace, has a lime content, as determined by X-Ray Diffraction, ranging from > 3 to 40 wt.-%, preferably from 4 to 40 wt.-%, based on the total weight of the paper product.

15. Use of the paper filler according to any one of claims 1 to 9 as alkaline paper filler in a paper product, preferably a recycled paper product, more preferably a carton board such as coated or uncoated carton board, or a container board such as liners, flutings and dual papers.