FIELD OF THE INVENTION

The present invention relates to a method of preparing an aqueous suspension comprising microfibrillated cellulose and inorganic particulate material suitable for use in a method of making paper or coating paper, and to filled and coated papers made from said aqueous suspension.

BACKGROUND OF THE INVENTION

Inorganic particulate materials, for example an alkaline earth metal carbonate (e.g. calcium carbonate) or kaolin, are used widely in a number of applications. These include the production of mineral containing compositions which may be used in paper manufacture or paper coating. In paper products such fillers are typically added to replace a portion of other more expensive components of the paper product. Fillers may also be added with an aim of modifying the physical, mechanical, and/or optical requirements of paper products. Clearly, the greater the amount of filler that can be included, the greater potential for cost savings. However, the amount of filler added and the associated cost saving must be balanced against the physical, mechanical and optical requirements of the final paper product. Thus, there is a continuing need for the development of fillers for paper which can be used at a high loading level without adversely effecting the physical, mechanical and/or optical requirements of paper products. There is also a need for the development of methods for preparing such fillers economically.

The present invention seeks to provide alternative and/or improved fillers for paper products which may be incorporated in the paper product at relatively high loading levels whilst maintaining or even improving the physical, mechanical and/or optical properties of the paper product. The present invention also seeks to provide an economical method for preparing such fillers. As such, the present inventors have surprisingly found that a filler comprising microfibrillated cellulose and an inorganic particulate material can be prepared by economical methods and can be loaded in paper products at relatively high levels whilst maintaining or even improving the physical, mechanical and/or optical properties of the final paper product.

Further, the present invention seeks to address the problem of preparing microfibrillated cellulose economically on an industrial scale. Current methods of microfibrillating cellulosic material require relatively high amounts of energy owing in part to the relatively high viscosity of the starting material and the microfibrillated product, and a commercially viable process for preparing microfibrillated cellulose on an industrial scale has hitherto before proved elusive.

SUMMARY OF THE INVENTION

According to a first aspect, the present invention is directed to a method for preparing an aqueous suspension comprising microfibrillated cellulose and inorganic particulate material, the method comprising a step of microfibrillating a fibrous substrate comprising cellulose in an aqueous environment in the presence of an inorganic particulate material.

According to a second aspect, the present invention is directed to an aqueous suspension suitable for use as filler in paper or a paper coating obtained by a method according to the first aspect.

According to a third aspect, the present invention is directed to an aqueous suspension suitable for use as filler in paper or a paper coating comprising microfibrillated cellulose and inorganic particulate material.

According to a fourth aspect, the present invention is directed to a papermaking composition comprising the aqueous suspension of the second and third aspects.

According to a fifth aspect, the present invention is directed to a paper product prepared from the papermaking composition of the fourth aspect.

According to a sixth aspect, the present invention is directed to a paper coating composition comprising the aqueous suspension of the second and third aspects and other optional additives.

According to a seventh aspect, the present invention is directed to a paper product, for example paper board, coated with the paper coating composition of the sixth aspect.

According to an eighth aspect, the present invention is directed to a process for making a paper product comprising: (i) obtaining or preparing a fibrous substrate comprising cellulose in the form of a pulp suitable for making a paper product; (ii) preparing a papermaking composition from the pulp in step (i), the aqueous suspension according to the second or third aspects of the invention, and other optional additives; and (iii) forming a paper product from said papermaking composition.

According to a ninth aspect, the present invention is directed to an integrated process for making a paper product comprising: (i) obtaining or preparing a fibrous substrate comprising cellulose in the form of a pulp suitable for making a paper product; (ii) microfibrillating a portion of said fibrous substrate comprising cellulose in accordance with the method of the first aspect of the invention to prepare an aqueous suspension comprising microfibrillated and inorganic particulate material; (iii) preparing a papermaking composition from the pulp in step (i), the aqueous suspension prepared in step (ii), and other optional additives; and (iv) forming a paper product from said papermaking composition.

According to a tenth aspect, the present invention is directed to the use of an aqueous suspension according to the second and third aspects of the invention as a filler in a papermaking composition.

According to an eleventh aspect, the present invention is directed to the use of an aqueous suspension according to the second and third aspects of the invention in a paper coating composition.

