Hydrophobically sized fibrous web and a method for the preparation of a sized web layer

Abstract

The invention relates to a hydrophobically sized fibrous web layer, methods for the preparation of a fibrous web or a fibre-based coating, a multilayer board product having at least a middle layer formed of said fibrous web, as well as use of a heat-sensitive surfactant for said methods and products. According to the method microfibrillated cellulose (MFC) and hydrophobic size are brought to a foam with water and the heat- sensitive surfactant, the foam is supplied to a forming fabric of a paper or board machine, dewatered by suction of air through the forming fabric, and dried to a web product. Alternatively the foam may be supplied onto a premade fibrous web and dried to form a coating layer. To prevent gradual degradation of the hydrophobic sizing the hydrophilic functionality of the surfactant contained in the web is finally destroyed by heating. The method uses e.g. AKD-based surfactants with a hydrophilic moiety which is decomposed by heat. If pulp of a greater fibre length, such as CTMP, is also included, a high bulk in combination with a high Scott bond value is achieved, to provide improved wet and dry tensile strength for the paper and board products.

Description

[0001] The present invention relates to a method for producing a hydrophobically sized layer of a fibrous web, a hydrophobically sized fibrous web obtainable by said method, and a multilayer paperboard comprising such a web as at least one layer. As a particular aspect, foaming techniques are used in the present invention to prepare the fibrous web. Background of the invention [0002] In the paper industry, foam technology has been used both in the web forming process and in the web coating process, where the foam is used as the carrier phase of the material. This technique is described, for example, in the following publications: Radvan, B., Gatward, A.P.J., The formation of wet-laid webs by a foaming process, Tappi, Vol. 55 (1972) p. 748; Wiggins Teape Research and Development Ltd. report, New process uses foam in papermaking instead of avoiding it, Paper Trade Journal, 29 November 1971; and Smith, M.K., Punton, V.W., Rixson, A.G., The structure and properties of paper for...

AI Technical Summary

Problems solved by technology

[0017] However, the disadvantages that accompany MFC are densification and high drying shrinkage of the paper, and the tendency of MFC to absorb and retain large amounts of water, which increases the energy required for drying and reduces paper machine speed and productivity

For these reasons, MFC has not gained widespread use in the paper industry so far.