Paper making and fiber liberation – Processes and products – Non-fiber additive
Reexamination Certificate
2001-08-06
2004-11-16
Chin, Peter (Department: 1731)
Paper making and fiber liberation
Processes and products
Non-fiber additive
C162S164100, C162S164600, C162S168100, C162S168200, C162S168300, C162S175000, C162S178000, C162S183000
Reexamination Certificate
active
06818100
ABSTRACT:
The present invention relates to a process for sizing paper which comprises adding to a suspension containing cellulosic fibres, and optical fillers, a sizing dispersion comprising a sizing agent and a polymer having one or more aromatic groups, and a sizing promoter comprising a polymer having one or more aromatic groups, forming and draining the obtained suspension, wherein the sizing dispersion and the sizing promoter are added separately to the aqueous suspension.
BACKGROUND
Dispersions or emulsions of sizing agents are used in papermaking in order to give paper and paper board improved resistance to wetting and penetration by various liquids. The sizing dispersions are usually added to an aqueous suspension containing cellulosic fibres, optional fillers and various additives. The aqueous suspension is fed into a headbox ejecting the suspension onto a wire where a wet web of paper is formed. To the suspension is further commonly added compounds such as starches and microparticulate materials which facilitate the dewatering of the suspension on the wire. The water drained from the wire, referred to as white water, is usually partly recirculated in the papermaking process. The cellulosic suspension contains a certain amount of non-fibrous material, for example fillers, charged polymers, sizing agents and various charged contaminants, i.e. anionic trash, electrolytes, colloidal substances, etc. Part of the non-fibrous material has an influence on the sizing efficiency and will likely impair the sizing efficiency. High amounts of charged compounds such as high contents of salts in the suspension renders a suspension which is increasingly difficult to size, i.e. to obtain a paper with satisfactory sizing properties. Other compounds contained in the suspension which deteriorates sizing are various lipophilic wood extractives which may come from recycled fibres and high yield pulps, i.e. mechanical pulps. An increased amount of added sizing agent often improve sizing, however, leading to higher costs as well an increased accumulation of sizing agents in the white water. The accumulation of non-fibrous material as well as any other component present in the suspension will be even more pronounced in mills where white water is extensively recirculated with the introduction of only low amounts of fresh water into the papermaking process. Thus, it is an objective of the present invention to further improve sizing. Another objective of the present invention is to improve sizing when applying sizes on cellulosic suspensions having high conductivity and/or high amounts of lipophilic wood extractives. Yet further objectives will appear hereinafter.
WO 99/55964 refers to a process for production of paper, where a drainage and retention aid is added to a suspension comprising a cationic or amphoteric polysaccharide having a hydrophobic group. The polysaccharide may be used in conjunction with anionic microparticulate materials and sizing agents.
WO 99/55965 relates to a process for production of paper, where a drainage and retention aid is added to a suspension comprising a cationic organic polymer having an aromatic group. The cationic organic polymer is suitably used together with anionic microparticulate materials.
U.S. Pat. No. 6001166 refers to aqueous alkyl diketen dispersions containing cationic starch and anionic dispersants such as lignin sulphonic acids, condensates of naphthalenesulphonic acid and formaldehyde.
WO 9833979 discloses aqueous dispersions of cellulose-reactive sizing agents comprising cationic organic compounds and anionic stabilisers.
Invention
It has been found that the invention according to the claims surprisingly improves sizing in general and specifically improves sizing of aqueous suspensions containing cellulosic fibres having high conductivities. More specifically, the invention refers to a process for sizing paper which comprises adding to a suspension containing cellulosic fibres, and optional fillers, a sizing dispersion comprising a sizing agent and a polymer having one or more aromatic groups, and a sizing promoter comprising a polymer having one or more aromatic groups, forming and draining the obtained suspension, wherein the sizing dispersion and the sizing promoter are added separately to the aqueous suspension.
The sizing agent comprised in the dispersion of the present process added to the suspension is suitably any sizing agent known, such as non-cellulose-reactive agents including rosins, e.g. fortified and/or esterified rosins, waxes, fatty acids and resin acid derivatives, e.g. fatty amides and fatty esters, e.g. glycerol triesters of natural fatty acids, and/or cellulose-reactive agents. Preferably, the sizing dispersion contains cellulose-reactive sizing agents. The cellulose-reactive sizing agents comprised in the sizing dispersion can be selected from any cellulose-reactive agents known in the art. Suitably, the sizing agent is selected from hydrophobic ketene dimers, ketene multimers, acid anhydrides, organic isocyanates, carbamoyl chlorides and mixtures thereof, preferably ketene dimers and acid anhydrides, most preferably ketene dimers. Suitable ketene dimers have the general formula (I) below, wherein R
1
and R
2
represent saturated or unsaturated hydrocarbon groups, usually saturated hydrocarbons, the hydrocarbon groups suitably having from 8 to 36 carbon atoms, usually being straight or branched chain alkyl groups having 12 to 20 carbon atoms, such as hexadecyl and octadecyl groups. The ketene dimers may be liquid at ambient temperature, i.e. at 25° C., suitably at 20° C. Commonly, acid anhydrides can be characterized by the general formula (II) below, wherein R
3
and R
4
can be identical or different and represent saturated or unsaturated hydrocarbon groups suitably containing from 8 to 30 carbon atoms, or R
3
and R
4
together with the —C—O—C— moiety can form a 5 to 6 membered ring, optionally being further substituted with hydrocarbon groups containing up to 30 carbon atoms. Examples of acid anhydrides which are used commercially include alkyl and alkenyl succinic anhydrides and particularly isooctadecenyl succinic anhydride.
Suitable ketene dimers, acid anhydrides and organic isocyanates include the compounds disclosed in U.S. Pat. No. 4,522,686, which is hereby incorporated herein by reference. Examples of suitable carbamoyl chlorides include those disclosed in U.S. Pat. No. 3,887,427 which is also incorporated herein by reference.
The sizing dispersion added to the suspension can have a sizing agent content from 0.1 to 50% by weight based on total dispersion/emulsion, suitably over 20% by weight. Dispersions comprising ketene dimer sizing agents may have ketene dimer contents from 5 up to 50% by weight based on total dispersion, preferably from 10 up to 35% by weight. Dispersions, or emulsions, comprising acid anhydride sizing agents may have acid anhydride contents from 0.1 up to 30% by weight based on total dispersion/emulsion, suitably from 1 up to 20% by weight. Dispersions containing non-cellulose reactive sizing agents suitably have sizing agent contents from 5 up to 50% by weight, preferably from 10 up to 35% by weight. The polymer having one or more aromatic groups, i.e. both anionic and cationic polymer having one or more aromatic groups, comprised in the sizing dispersion is suitably present in an amount of from about 0.1% by weight up to about 15% by weight based on sizing agent.
The amount of sizing agent added to the aqueous suspension containing cellulosic fibres can be from 0.01 to 5% by weight, suitably from 0.05 to 1.0% by weight, based on dry weight of cellulosic fibres and optional fillers, where the dosage is dependent on the quality of the pulp or paper to be sized, the sizing agent and the level of sizing.
The sizing dispersion comprising a polymer containing at least one aromatic group can be anionic or cationic, i.e. the dispersing and/or stabilising agents present in the dispersion which can be referred to as the dispersing system have an overall anionic or cationic charge, respectively. The disp
Frölich Sten
Lindgren Erik
Magnusson Barbro
Persson Michael
Akzo Nobel N.V.
Burke Michelle J.
Chin Peter
Fennelly Richard P.
Parker Lainie E.
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