Process for Producing a Paper or Board and a Paper or Board Produced According to the Process

Abstract

The present invention concerns a process for producing a paper or board product, which process comprises providing a furnish comprising fibers; subjecting a first portion (1) of the furnish to polymer treatment, in which polymers are added to the furnish in at least two steps; blending said polymer treated first portion with an untreated second portion (2) of the furnish; and dewatering the furnish on a wire to form a fiber web. By treating only a portion of the furnish, the strength of the resulting paper or board product is significantly improved whereas the bulk remains substantially unaffected. The invention also concerns a paper or board product produced according to the process.

Description

[0001] The present invention relates to a process for producing a paper or board product wherein the furnish used is partially treated with polymers in steps. BACKGROUND OF THE INVENTION [0002] In paper making processes there is a desire in obtaining strong paper and board products having high bulk (low density). Paper and board products having high bulk require a smaller amount of fibers, which is desirable especially for economical reasons. Bulky board products with low fiber content have better bending stiffness. Paper and board products are typically produced by dewatering furnish on a wire. The furnish often contains a mixture of different pulps, including both chemical pulps and mechanical pulps. In order to produce a bulkier sheet with higher structural stiffness the interest in using mechanical pulps with high freeness has increased. To obtain the best result the mechanical pulp should contain long, intact fibers and as little fine material as possible. However, pulps that a...

AI Technical Summary

Benefits of technology

[0007] The object of the invention is to provide a method of producing paper or board, which has an improved strength, without adversely affecting the bulk.

[0009] The present invention concerns a process for producing a paper or board product, which process comprises providing a furnish comprising fibers; subjecting a first portion (1) of the furnish to polymer treatment, in which polymers are added to the furnish in at least two steps; blending said polymer treated first portion with an untreated second portion (2) of the furnish; and dewatering the furnish on a wire to form a fiber web. By treating only a portion of the furnish, the strength of the resulting paper or board product is significantly improved whereas the bulk remains substantially unaffected.

Problems solved by technology

However, pulps that are rich in stiff, long fibers unfortunately show poor ability to produce sufficient fiber bonding of the paper or board.

It is however difficult to adsorb large amounts of starch to the fibers, especially when the fines amount is small.

However, there are two major problems with cationically modified starches as additives to paper-making pulp slurries.

The first is that the cationic starch molecules can overwhelm the anionic charge on the cellulose fibers, thus setting a limit on the amount of cationic starch which can be added to the slurry.

A second problems is that fibers which have been made cationic by excessive cationic starch addition, will not be able to adsorb other cationic additives which are commonly added the to the pulp slurry, such as sizing agents.

However, the polymer treatment according to this method has been found to have a negative effect on the bulk of the paper, i.e. the density of the paper becomes undesirably high.

The polymer treatment is also rather polymer consuming.

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