CA2611555A1

CA2611555A1 - Paper pigment, process for producing a paper product and paper product

Info

Publication number: CA2611555A1
Application number: CA002611555A
Authority: CA
Inventors: Vesa Myllymaki; Reijo Aksela; Hanna-Mari Kangaslahti; Petri Silenius
Original assignee: Individual
Current assignee: Kemira Oyj; Metsa Board Oyj
Priority date: 2005-06-15
Filing date: 2006-06-14
Publication date: 2006-12-21
Also published as: RU2007145079A; CN101218396A; BRPI0612820A2; JP2008544096A; WO2006134211A1; EP1891270A1; FI20050638A0; FI20050638A

Abstract

The object of the invention are organic paper pigments, which are ester derivatives of disaccharides, essentially insoluble in water. The invention also relates to a manufacturing process of a paper product, in which ester derivatives of disaccharides according to the invention are used as paper pigments. Another object of the invention are paper products, in which these organic ester derivatives of disaccharides have been used as paper pigments.

Description

Paper pigment, process for producing a paper product and paper product Field of invention This invention relates to new organic paper pigments, a process for manufacturing a paper product, the use of the paper pigments according to the invention in the manufacture of a paper product, and to new paper products.

Prior art technology Fillers and pigments in paper manufacture Paper pigments can be divided into filler pigments or fillers and precoating and surface coating pigments. Except for some special surface coating pigments, paper pigments are inorganic mineral particles in structure. The pigments used for surface finishing are generally more finely divided than filler pigments, but the particle size of both is such that they contribute notably to the increase of the reflection surface. Paper pigments are light-scattering materials.

One of the most important characteristics strived for with pigments is thus improvement of optical properties, such as opacity and gloss and even porosity, of the final product, i.e. paper or board. Through better surface properties, the printing properties improve, the distribution of printing ink becomes more uniform, and the gloss can be further fine-adjusted by means of calendering. In addition to better characteristics, the use of paper pigments also influences the price of the final product. Replacing 1% of expensive fiber with a filler the price of the final product reduces 2.5 US$/ton, Baker, C. and Nazir, B., Practical ways for achieving higher filler content papers, Use of Minerals in Papermaking, Pira International, Surrey, U.K., (1988), pp. 83-92.

The availability of wood fiber has certain limits, and hence the use of paper pigments also has significance in the environmental protection. Increased use of paper pigments has thus opened possibilities for increasing the manufacture of paper products without a need to increase the use of wood.

The use of paper pigments of course has also its limits. When certain limits are exceeded, the tensile properties of paper decrease dramatically and the need for using expensive additional chemicals, for example, increases. In addition, mineral pigments are hard materials in structure, causing easily wear in paper machines, finishing machines and printing machines. An excessive amount of mineral particles also generates linting during printing.

Paper pigments are typically used in relatively great amounts in fine papers and magazine printing papers, but their use is increasing also in normal newsprint as well as in packing papers. Special products, such as laminated papers, bible paper, tobacco paper, etc. easily contain 40% of paper pigments. In newsprint the amount of paper pigments is today between 0-10% (kaolin, talc, special pigments), 20-30% (kaolin, talc) in uncoated magazines (SC), 0-25% in fine papers (kaolin, talc, chalk, TiO2), and 0-10% in packing papers (kaolin, talc, chalk, TiO2).

Some of the properties required of the present paper pigments are:
= they must be chemically inert and insoluble in water = high retention in paper machine = high refractive index to achieve good opacity = high light-scattering coefficient = low density = soft structure = low price An optimum particle size for a paper pigment would be 0.2-0.3 pm, i.e.
approximately half of the average light wavelength, which thus produces maximum opacity. For keeping the refining costs at an economically reasonable level, a typical particle size of a paper pigment in the filler use, for example, is approximately 0.4-5 pm.

The present mineral-based paper pigments can be classified as natural and synthetic materials. The former are of course less expensive, the latter often possess some of the above mentioned desired properties. Typical mineral-based paper pigments include titanium dioxide, kaolin, calcined kaolin, talc, gypsum, chalk, ground calcium carbonate (GCC), precipitated calcium carbonate (PCC), barium sulphate, Na Al silicate (Zeolex), Ca Al silicate, aluminium oxide, kieseiguhr, zinc oxide, etc. In addition, a more advanced calcium oxalate based paper pigment has been introduced to the market, which reduces somewhat the ash content of the final product and has lower density.

Calcium carbonate is an alkaline paper pigment and hence it dissolves completely in water even at pH 6.5. Therefore its use is restricted to neutral and alkaline conditions only. For this reason the use of carbonates is strongly emphasized in the manufacture of wood-free papers.

Although the properties of inorganic paper pigments, such as the crystal structure, have been developed to allow decreasing the density, for example, they are still relatively heavy as "stone materials". In addition, inorganic paper pigments notably reduce the calorific value of paper products and prevent or significantly reduce their utilization possibilities after use for example as a source of energy by burning.
Despite of deinking, it is estimated that 24 millions of tons of paper products are taken to the dump areas every year in Europe only. The energy content of such an amount of paper products is approximately 8 Mtoe (Million tons oil equivalent).

Disaccharides Disaccharides can be defined as any sugars that are composed of two monosaccharide units. They are crystalline carbohydrates, dissolving extremely well in water due to their hydroxyl functions, of which a part is natural and a part is synthetic. The most common disaccharides are natural saccharose (cane sugar and beet root sugar) and lactose (milk sugar) as well as maltose (a hydrolysis product of starch) and cellobiose (a hydrolysis product of cellulose). The greatest production amounts are found with saccharose, which is produced approximately 134.1 millions of tons per year (in 2002). Due to its great production amounts, particularly saccharose but also lactose, which is generated in the waste flow of the milk processing industry, are inexpensive products that are available worldwide and all year round.

Disaccharides are optically active compounds, i.e. they contain chiral carbon atoms. For example, saccharose consists of two optically active monosaccharides, namely D-glucose and D-fructose. Lactose, in turn, is composed of D-galactose and D-glucose. These two monosaccharides are joined together via a glucose link.
This link may have further an a- or (3-configuration and the disaccharide may be a mixture of a disaccharide comprising these two different link configurations.
Maltose and cellobiose differ from each other in structure only with respect to this glucose link; both have two glucose units, which are combined with an a-glucoside link in maltose and with a(3-glucoside link in cellobiose.

Among disaccharides, saccharose is used as such as a food product and as an ingredient of food products. It is also used, like lactose, for example as additive components for pharmaceutical products due to its good preservability and harmlessness.

These have also been used as starting materials in pharmaceutical synthetics, in which case it has been possible to protect the hydroxyl groups of disaccharides for a later selective disassembly for example as esters, typically as acetates due to their preferredness. The chemical and physical properties of such products are greatly influenced by the type of the disaccharide and its stereochemistry.
For example, the melting points of saccharose, lactose, maltose and cellobiose octaacetates change owing to minor structural differences in the following way: a-saccharose octaacetate: about 82-83 C, P-lactose octaacetate: about 136-137 C, P-maltose octaacetate: about 159-160 C, and a-cellobiose octaacetate about 225 C. Since the acetate esters of disaccharides, for example, are inert molecules as such, no other noteworthy use has been found for them. Therefore, the production of disaccharide derivatives comprising longer alkyl or alkyl aryl ester chains has been insignificant.

Summary of invention An objective of this invention is an organic paper pigment, poorly soluble in water, consisting of ester derivatives of disaccharide, the particle size of which is 0.15-50 pm.

Further, an objective of this invention is a process for producing a paper product, in which process an ester derivative of disaccharide, essentially insoluble in water, is used as a paper pigment.

Another objective of the invention is the use of an essentially insoluble disaccharide as a paper pigment in the manufacture of a paper product.

Further, an objective of this invention is a paper product, for which paper product an ester derivative of disaccharide, poorly soluble in water, with a particle size of 0.15-50 pm, has been used as a paper pigment.

The invention now discovered is based on the surprising observation that particles composed of ester derivatives of disaccharides can be used as paper pigments.
This type of paper pigment is poorly soluble in water and has a high calorific value being an organic material. In addition, it is very lightweight and has good 5 brightness and a sufficiently high melting point to be used as a paper pigment. Its properties can be adjusted by the selection of the disaccharide and the esterification substrate, for example, as well as by the selection of the esterification degree. In addition, the stereochemical structure of the paper pigment and thus the properties can be adjusted by the selection of the esterification catalyst.

The paper pigments according to the invention can surprisingly be used as fillers, precoating pigments and coating pigments. The paper pigment can be refined to a suitable size for each purpose.

The paper product, in which the paper pigments according to the invention have been used, surprisingly showed excellent optical properties. Using the paper pigment according to the invention, better opacity and light-scattering coefficient were achieved than for example with a high-opacity mineral pigment developed for a corresponding purpose. In addition, the tensile properties of the paper product were surprisingly at the same level.

As the paper pigment according to the invention is organic, the calorific value of the paper products to be manufactured is notably higher than in corresponding paper products containing mineral-based paper pigments. This opens a possibility for a later use of the paper product or the slurry separated from it through deinking as bioenergy in combustion plants, for example.

The paper products manufactured according to the invention are also lightweight.
Grammages can be reduced without impairing the working characteristics of the final product. This reduces notably the transport costs, for example.

As the paper pigments according to the invention are also soft, they do not cause wear in the paper, board, finishing and printing machines in the same way as the currently used hard mineral pigments.

Figures Figure 1 is a SEM image of refined lactose octaacetate (LOA), used in sheet tests, having an average particle size of less than 2 pm, Figure 2 is a SEM image of a high-opacity PCC filler (Albacar HO) used as the reference filler, having an average particle size of less than 2 pm, Figure 3 shows the tensile index (Nm/g) as a function of the filler content (%) for test sheets, in which lactose octaacetate (LOA) or PCC has been used as filler, Figure 4 shows opacity (%) as a function of the filler content (%) for test sheets, in which lactose octaacetate (LOA) or PCC has been used as filler, Figure 5 shows gloss (%) as a function of the filler content (%) for test sheets, in which lactose octaacetate (LOA) or PCC has been used as filler, Figure 6 shows the light-scattering coefficient (m2/kg) as a function of the filler content (%) for test sheets, in which lactose octaacetate (LOA) or PCC has been used as filler.

Detailed description of invention The invention relates to a paper pigment, which is an ester derivative of a disaccharide, essentially insoluble in water, having a particle size of 0.15-50 pm.
Preferably the particle size of the paper pigment according to the invention is 0.15-8 pm, and more preferably between 0.5-2 pm.

The ester derivative of the disaccharide can be regarded here as essentially insoluble in water, of which a maximum of 2.5% by weight dissolves in water at the room temperature, preferably less than 1.5% by weight; and more preferably less than 1 % by weight.

As the carboxylate chain of the ester derivative of the disaccharide according to the invention is short (C2 i.e. acetate), a high, preferably a quantitative degree of convertion to esters of hydroxyl functions of the disaccharides is required to achieve poor solubility in water for the paper pigment according to the invention.
Preferred C2 carboxylate derivatives of disaccharides include lactose, saccharose, maltose and cellobiose octaacetates, for example.

When the number of carbon atoms in the carboxylate chain increases, it may not be necessary any more to convert all hydroxyl functions of the disaccharides to esters for achieving the poor solubility in water according to the invention.
The paper pigment according to the invention may be C2-C18 carboxylate of disaccharide, preferably it is C2-C8 carboxylate and more preferably C2-C6 carboxylate, with either a quantitative or a partial esterification degree of the hydroxyl functions of the disaccharides. According to the invention the carbon atoms of C2-C18 carboxylate can form straight or branched alkyl chains and saturated or unsaturated ring structures. Further, the ester functions of the disaccharide can be C2-C1$ carboxylates that are either similar with each other or alternatively different from each other.

The melting point of the paper pigment according to the invention should be over 75 C. Preferably it is over 85 C and more preferably the melting point of this ester derivative of the disaccharide is over 100 C.

The disaccharide of the ester derivative of the disaccharide according to the invention can be for example any stereoform of lactose, saccharose, maltose or cellobiose, or a mixture of these stereoforms. The ester derivative of the disaccharide according to the invention can also be a mixture of the above mentioned disaccharides and further of their various stereoforms. Neither does the invention exclude the use of other disaccharides and their various stereoforms as the disaccharide of the ester derivative.

The esterification of disaccharides can be performed, for example, by using natural carboxyl acids or their derivatives, such as anhydrides or acid chlorides.
Especially preferred substrates are anhydrides, such as acetic anhydride. The stereochemistry of the product created can be adjusted by the selection of the catalyst, for example. It is also possible to use synthetic esterification substrates.

A specially preferred paper pigment according to the invention is lactose octaacetate. Another preferred paper pigment according to the invention is saccharose octaacetate.

The objective of the invention is also a process for producing a paper product, in which process an ester derivative of a disaccharide, essentially insoluble in water, is used as a paper pigment. The paper pigment according to the invention is defined as above.

In one embodiment of the process according to the invention, the paper pigment particle formed by the ester derivative of the disaccharide essentially insoluble in water can be a filler, the particle size of which is 0.15 pm - 50 pm, preferably 0.5 pm - 8 pm; and most preferably 1pm - 2 pm.

In another preferred embodiment of the process according to the invention, the paper pigment particle formed by the ester derivative of the disaccharide essentially insoluble in water can be a precoating pigment, the particle size of which is 0.15 pm - 2 pm, preferably 0.5 pm - 1.5 pm.

Further, in another preferred embodiment of the invention, the paper pigment particle formed by the ester derivative of disaccharide essentially insoluble in water can be a surface coating pigment, the particle size of which is 0.15 pm -2 pm, preferably 0.5 pm -1.0 pm.

The invention also relates to the use of an ester derivative of a disaccharide essentially insoluble in water in the manufacture of a paper product, in which this ester derivative of the disaccharide is used as a paper pigment, the particle size of which is 0.15 pm - 50 pm. The paper pigment according to the invention is defined as above.

The 'paper product' is used here to refer to paper or board of any type or of any weight, white or colored.

The paper pigment according to the invention can be used as a filler in the manufacture of the paper product. In this case the particle size of ester derivatives of the disaccharide essentially insoluble in water is 0.15 pm - 50 pm, preferably 0.5 pm - 8 pm; and most preferably 1 pm - 2 pm.

Further, the paper pigment according to the invention can be used as a precoating pigment in the manufacture of a paper product. In this case the particle size of ester derivatives of the disaccharide essentially insoluble in water is 0.15 pm - 2 pm, preferably 0.5 pm - 1.5 pm.

In yet another preferred embodiment of the invention, the paper pigment according to the invention can be used as a surface coating pigment in the manufacture of the paper product. In this case the particle size of ester derivatives of the disaccharide essentially insoluble in water is 0.15 pm - 2 pm, preferably 0.5 pm -1.0 pm.

Preferably the paper pigment according to the invention has good brightness;
however, pigments with lower brightness can also be used to provide opacity in paper products for which brightness is not an important criterium.

The invention also relates to a paper product, in which an ester derivative of a disaccharide, poorly soluble in water, the particle size of which is 0.15 pm -pm, has been used as a paper pigment. The paper pigment according to the invention and the particle sizes providing various preferred properties to the paper product are defined as above.

In the paper product according to the invention, the portion of the ester derivative of the disaccharide, poorly soluble in water, from the total mass of the final product can vary between 1-55 % by weight, preferably 3-40 % by weight and most preferably 5-35 % by weight.

The main benefits of the invention now discovered include the following facts and characteristics:

= organic paper pigments, which have o very low density o excellent optical properties o very poor water solubility o high brightness o high calorific value o soft structure and easy workability to a suitable particle size o resistance in even acid paper production processes = production of paper pigments using disaccharides o disaccharides are a feedstock available worldwide and all year round o especially saccharose and lactose commodities o esterification reagents are typically natural carboxyl acids or their derivatives o inexpensive feedstock and production processes o the properties of the paper pigment are adjustable by changing the feedstock saccharide and esterification function = due to their softness the paper pigments cause less abrasion in paper machines, finishing machines and printing machines = new environmental-friendly paper products, which o have a high calorific value and can thus be used as bioenergy o are high-quality products with excellent optical properties ~ opacity ~ light-scaftering coefficient ~ gloss, etc.
o are lightweight ~ reduce transport costs ~ are user-friendly o have good strength properties.

Examples The paper pigment according to the invention and its use for manufacturing a paper product as well as the thus manufactured paper product are described 10 below without restricting the invention, however, to the examples set forth.
Example 1 Lactose octaacetate Lactose octaacetate (P-lactose octaacetate) to be used as a paper pigment was produced in several batches with a standard procedure by esterification of a-D-lactose (A.C.S reagent, Sigma-Aldrich) with an equimolar amount (8 equivalents) of acetic anhydride using sodium acetate as catalyst, diagram 1(stereochemical structures not considered). The progress of the reaction was monitored with HPLC
and the conversions of the reaction were practically quantitative. After carrying out the reaction, the product was separated from the reaction mixture by precipitating with water. After this the product was flushed with water and dried in a heating chamber (105-115 C). The extremely high purity degree of the products was still verified with HPLC before using them in sheet tests.

OH OH OAc OAc O O Ac20 O O
HO OH ' Ac0 OAc NaOAc HO OH HO OH AcO OAc OAc Diagram 1.

The water solubility of the produced P-lactose octaacetate was determined (DI-water, pH 5.45) at the room temperature, and the water solubility was defined to be about 45 ppm. Thus the product prepared is extremely poorly soluble in water.
The melting point of the prepared P-lactose octaacetate was measured and the result was 135.5-137 C.

Before using the P-lactose octaacetate as a paper pigment, the product was refined using a Dyno laboratory mill. The particle size distribution was verified with SEM and with a measuring device for the particle size distribution (Malvern).

Example 2 Several sheets with a grammage of 80 g/m2 were produced in the sheet tests using the Ernst Haage sheet forming unit. In the sheet tests, a stock mixture was used, which included 70% of bleached softwood pulp and 30% of bleached birchwood pulp (M-Real). The initial consistencies of the stocks were 3.9% for hardwood pulp and 4.0% for birchwood pulp. The freeness degrees CSF
(Canadian Standard Freeness) of stock were about 500 for hardwood pulp and about 450 for birchwood pulp. The retention aid used was Fennopol K3400R
(Kemira).

The previously prepared lactose octaacetate was used as filler in consistencies of about 5 and 9 percent. The reference filler used was a commercially available high-opacity PCC filler (Albacar HO) in corresponding consistencies. The technical characteristics of the fillers are described in Table 1. LOA and PCC used in the sheet tests were scanned with SEM (Scanning Electron Microscopy), Figures 1 and 2. The average particle size of the fillers used is below 2 pm. It should be noted in the table that the density of lactose octaacetate is only 47% of the density of PCC used as the reference pigment.

Table 1 Particle size R457* Solubility Density Refractive d50, index pm % ppm g/ml LOA <2 92 45 1.27 PCC <2 96 - 2.7 1.6 *R457 refers to ISO brightness. The ISO brightness or the diffuse blue reflectance factor is a reflectance factor, which is determined with a device whose maximum receptor sensitivity coincides with a wavelength of 457 nm.

When using lactose octaacetate as filler, water-based deforming agent was used due to the low density and hydrophobicity of the filler (Aerotech 1630V, Kemira; 2 ml/sheet mould).

Results of the sheet tests are shown in Table 2 and in Figures 3-6. Figure 3 shows the tensile index (Nm/g) as a function of the filler content (%), Figure shows opacity (%), Figure 5 shows gloss (%) and Figure 6 shows the light-scattering coefficient (m2/kg) as a function of the filler content (%).

Table 2 Test No. 1 2 5 6 Filler type Ref Ref LOA LOA
PCC PCC

Filler content [%] 5.3 9.5 9 5.2 Grammage, g/mz 79.4 80.1 78.8 80.7 Total thickness, pm 164.7 170.7 167.6 167.2 Total density, kg/m3 4818 469.4 469.9 482.4 Tensile strength, kN/m 3.1 2.7 2.5 2.9 Tensile index, Nm/g 39.3 34.1 31.1 36.1 Opacity*, % 85.5 87.9 90.6 88.6 Gloss, % 86.1 86.9 83.9 84.6 Light-scattering coefficient**, 46.7 55.6 55.9 49.9 m2/kg L' 96.3 96.6 94.8 95.2 a' -0.4 -0.3 -0.3 -0.4 b' 3.8 3.6 2.8 3.0 * opacity is a measure of untransparency of a paper product. The opacity of a completely untransparent material is 100% and that of a completely transparent material is 0%.

** the light-scattering coefficient is a measure indicating how well an indefinitely thin material layer scatters light.

As shown in Table 2 and Figures 3-6, lactose octaacetate (LOA) used as paper pigment surprisingly provides the currently prepared paper sheets both a higher light-scattering coefficient and opacity than a corresponding amount of PCC
used as reference. These excellent optical properties were achieved without notable impairing of the tensile index or tensile strength. The results are surprising, because LOA is an organic pigment, while PCC used as the reference pigment is specifically of the high opacity quality. In this way it was possible to increase the amount of a low-density organic material in the paper product not only by maintaining but also by simultaneously improving the optical properties of the final product without impairing notably the strengths of the final products.

Example 3 In the sheet tests, commercially available saccharose octaacetate (Aldrich) with a particle size of 13 pm was used as paper pigment. In the reference tests, precipitated calcium carbonate (PCC) with a particle size of 0.7 pm was used as filler. The test arrangements were as in Example 2. Results of the sheet tests are shown in Table 3.

Table 3 Test No. 1 2 3 4 5 Filler type - PCC PCC SOA SOA
Filler content (% 0 10 20 10 20 Gramma e/m2 85.6 84.9 86.1 84.7 81.4 Total thickness, pm 124 124 120 142 137 Total density k/m 693 687 717 595 593 Tensile strength kN/m 6.58 4.51 3.17 2.96 3.67 Tensile index Nm/ 76.9 53.1 36.8 34.9 45.1 Opacity (%) 78.8 87.3 90.8 86.2 82.0 When using saccharose octaacetate as filler, it was observed that the total density of the sheets decreased clearly compared to the sheet, in which a pigment was not used. The decrease of the total density is even more clearly visible when comparing the results to the results obtained with an inorganic pigment.
Regardless of the total density decrease of the sheets, which is an preferred aspect when producing paper, the tensile strength of the sheets treated with SOA
did not deviate notably compared to the sheet treated with an inorganic pigment.
Similarly, differences were not found in opacity compared to the sheets treated with an inorganic pigment, especially in the filler content of 10% (tests 4 and 2). It should be noted that the particle size of the filler used is unusually large compared to the particle size of fillers that are normally used. The particle size of calcium carbonate used as the reference material, in turn, was optimum for filler applications.

Regardless of the dispreferred particle size, the optical properties achieved in the sheet tests 4 and 5 are comparable to the results obtained when using an 5 inorganic filler.

It is to be assumed that when a saccharose octaacetate with a smaller particle size is used as filler, the properties of the obtained paper improve essentially compared to those gained in this test.

Claims

1. A paper pigment, characterized in that it is an ester derivative of a disaccharide, essentially insoluble in water, the particle size of which is 0.15-50 µm.

2. A paper pigment according to claim 1, characterized in that its particle size is 0.15-8 µm.

3. A paper pigment according to claim 1 or 2, characterized in that its particle size is 0.5-2 µm.

4. A paper pigment according to any of claims 1-3, characterized in that its melting point is over 75°C, preferably over 85°C and most preferably over 100°C.

5. A paper pigment according to any of claims 1-4, characterized in that the disaccharide of the ester derivative is any stereoform of lactose, saccharose, maltose or cellobiose or a mixture of these disaccharides and/or their stereoforms.

6. A paper pigment according to any of claims 1-5, characterized in that it is C2-C18 carboxylate, preferably a C2-C8 carboxylate and most preferably a C2-C6 carboxylate of the disaccharide.

7. A paper pigment according to any of claims 1-6, characterized in that it is lactose octaacetate or saccharose octaacetate.

8. A process for producing a paper product, characterized in that an ester derivative of a disaccharide essentially insoluble in water is used as a paper pigment.

9. A process according to claim 8, characterized in that the melting point of the ester derivative of a disaccharide is over 75°C, preferably over 85°C and most preferably over 100°C.

10. A process according to claim 8 or 9, characterized in that the disaccharide of the ester derivative is any stereoform of lactose, saccharose, maltose or cellobiose or a mixture of these disaccharides and/or their stereoforms.

11. A process according to any of claims 8-10, characterized in that the ester derivative is a C2-C7 carboxylate, preferably a C2-C4 carboxylate and most preferably C2-C3-carboxylate of the disaccharide or saccharose octaacetate.

12. A process according to claims 8-11, characterized in that the paper pigment is lactose octaacetate or saccharose octaacetate.

13. A process according to any of claims 8-12, characterized in that the paper pigment is a filler, the particle size of which is 0.15 µm - 50 µm, preferably 0.5 µm - 8 µm, and most preferably 1 µm - 2 µm.

14. A process according to any of claims 8-12, characterized in that the paper pigment is a precoating pigment, the particle size of which is 0.15 µm - 2 µm, preferably 0.5 µm - 1.5 µm.

15. The process according to any of claims 8-12, characterized in that the paper pigment is a surface coating pigment, the particle size of which is 0.15 µm -2 µm, preferably 0.5 µm - 1.0 µm.

16. The use of an ester derivative of a disaccharide essentially insoluble in water in the manufacture of a paper product, characterized in that it is used as a paper pigment, the particle size of which is 0.15-50 µm.

17. The use according to claim 16, characterized in that the melting point of the ester derivative of the disaccharide is over 75°C, preferably over 85°C and most preferably over 100°C.

18. The use according to claim 16 or 17, characterized in that the disaccharide of the ester derivative is any stereoform of lactose, saccharose, maltose or cellobiose or a mixture of these disaccharides and/or their stereoforms.

19. The use according to any of claims 16-18, characterized in that the ester derivative is a C2-C7 carboxylate, preferably a C2-C4 carboxylate and most preferably a C2-C3-carboxylate of the disaccharide.

20. The use according to any of claims 16-19, characterized in that the ester derivative of the disaccharide is lactose octaacetate or saccharose octaacetate.

21. The use according to any of claims 16-20, characterized in that the ester derivative of the disaccharide is a filler, the particle size of which is 0.15 µm - 50 µm, preferably 0.5 µm - 8 µm, and most preferably 1 µm - 2 µm.

22. The use according to any of claims 16-20, characterized in that the ester derivative of the disaccharide is a precoating pigment, the particle size of which is 0.15 µm - 2 µm, preferably 0.5 µm - 1.5 µm.

23. The use according to any of claims 16-20, characterized in that the ester derivative of the disaccharide is a surface coating pigment, the particle size of which is 0.15 µm - 2 µm, preferably 0.5 µm -1.0 µm.

24. A paper product, characterized in that an ester derivative of a disaccharide poorly soluble in water, the particle size of which is 0.15 µm - 50 µm, has been used as a paper pigment of the paper product.

25. A paper product according to claim 24, characterized in that the melting point of the ester derivative of the disaccharide is over 75°C, preferably over 85°C
and most preferably over 100°C.

26. A paper product according to claim 24 or 25, characterized in that the disaccharide of the ester derivative is any stereoform of lactose, saccharose, maltose or cellobiose or a mixture of these disaccharides and/or their stereoforms.

27. A paper product according to any of claims 24-26, characterized in that the ester derivative is a C2-C7carboxylate, preferably a C2-C4 carboxylate and most preferably a C2-C3 carboxylate of the disaccharide.

28. A paper product according to any of claims 24-27, characterized in that the ester derivative of the disaccharide is lactose octaacetate or saccharose octaacetate.

29. A paper product according to any of claims 24-28, characterized in that the ester derivative of the disaccharide is a filler, the particle size of which is 0.15 µm 50 µm, preferably 0.5 µm - 8 µm, and most preferably 1 µm - 2 µm.

30. A paper product according to any of claims 24-28, characterized in that the ester derivative of the disaccharide is a precoating pigment, the particle size of which is 0.15 µm - 2 µm, preferably 0.5 µm - 1.5 µm.

31. A paper product according to any of claims 24-28, characterized in that the ester derivative of the disaccharide is a surface coating pigment, the particle size of which is 0.15 µm - 2 µm, preferably 0.5 µm -1.0 µm.