Paper making and fiber liberation – Processes and products – Non-fiber additive
Reexamination Certificate
2001-08-16
2003-07-01
Fortuna, Jose A. (Department: 1731)
Paper making and fiber liberation
Processes and products
Non-fiber additive
76, 76, 76
Reexamination Certificate
active
06585859
ABSTRACT:
TECHNICAL FIELD
The invention relates to a new composition, which is applicable as a so-called size composition in connection with the production of paper, paper board and similar products. The invention also relates to a method for manufacturing sized paper or sized paper board. Finally, the invention relates to sized paper or sized paper board, which paper or paper board comprises a size composition according to the invention.
More specifically, the invention relates to a composition in the form of a water-based emulsion or dispersion comprising at least some hydrophobic, cellulose-reactive sizing agent and a cross-linked, anionic, cationic and/or amphoteric starch.
BACKGROUND TO THE INVENTION
Water-based emulsions or dispersions of hydrophobic sizing agents are used to reduce the rate of liquid penetration into the structure of a paper or paper board. Examples of paper and paper board grades of this kind are photocopying paper, writing and printing paper, paper for so-called inkjet printers and paper board for juice, milk and other liquid packagings. These grades thus need for their application to have certain liquid-repellent properties. This effect can be achieved in various ways. The most common method is to add an emulsion or dispersion of a hydrophobic material and a cationic starch during the paper production process. Many different hydrophobic materials can be used. Among the most effective and most used are so-called hydrophobic, cellulose-reactive sizing agents. When using this type of agent, it is believed that the hydrophobic effect is obtained by means of a reaction between the hydrophobic material and the hydroxyl groups in the cellulose.
In neutral or weakly alkaline conditions during paper or paper board manufacture, hydrophobic, cellulose-reactive material of the alkylketene dimer (termed AKD below) or alkenyl succinic anhydride (termed ASA below) type is often used. The above-named hydrophobic materials are thus cellulose-reactive and bind directly to the carboxyl groups in the cellulose.
For the aforementioned hydrophobic material to be attracted, often termed retained, to the anionic cellulose fibre material, a polymer is added in the emulsifying or dispersion process. This polymer, which in most cases consists of starch, will give each particle of the sizing agent (e.g. AKD and/or ASA) a charge, so that it is attracted (retained) to the cellulose fibre. The starches occurring most commonly in size compositions are normally of a cationic character. However, anionic and amphoteric starch types also occur.
The starch also acts like a protective colloid, lying like a thin “shell” around each particle of the sizing agent and producing a stabilizing effect on the size composition's dispersion or emulsion. The aim is that particles of the sizing agent should be prevented from reacting with substances other than cellulose fibres. Above all, the sizing agent is to be prevented from hydrolysis due to reacting with water.
Emulsions and dispersions in which the hydrophobic material consists of ASA are produced according to a so-called in-situ process, i.e. in close proximity to the composition's application, i.e. in practice adjacent to the machine or machines which manufacture the paper or paper board. This is due to the fact that ASA has a tendency to hydrolysis, i.e. it reacts with the water present in the emulsion or dispersion. The finished composition cannot therefore be stored, especially not under unfavourable conditions such as high temperature, which is a problem particularly in hotter countries.
AKD emulsions or dispersions, however, are more stable and can be stored for a long time without losing the sizing effect. In spite of this fact, it can be advantageous to produce these emulsions or dispersions also according to the so-called in-situ process.
Emulsions or dispersions can also consist of a mixture of AKD and ASA. These emulsions or dispersions are also best manufactured according to the so-called in-situ process.
Known size compositions exhibit problems such as a slowly developed hydrophobicity, poor adhesion of toner and deposition of hydrolysis products when photocopying and reduced effectiveness during paper manufacture due to interruptions as a result of poor hydrophobicity and the occurrence of hydrolysis products. Another problem is poor resistance to hydrogen peroxide in connection with the filling of liquids in packagings of liquid paper board. When using highly substituted starches, i.e. starches with high cation activity, problems of stability can also occur for the emulsion/size composition. With high dry contents in particular, i.e. dry contents of more than 20%, of the size composition, problems often occur with its stability. This is also temperature-dependent, it most often being necessary in hot countries to have dry contents which are even lower, in order to achieve stability.
Patent literature describes the use of cross-linked starch in connection with paper manufacture, the cross-linked starch not however being used in size compositions. Such patents include e.g. U.S. Pat. No. 4,810,785, U.S. Pat. No. 5,122,231, U.S. Pat. No. 5,368,690, U.S. Pat. No. 5,523,339.
DESCRIPTION OF THE INVENTION
The object of the invention is to provide a size composition by means of which the aforementioned problems are eliminated or restricted. This can be achieved in that the starch used on production of the size composition principally comprises anionic, cationic and/or amphoteric starch, which is cross-linked.
The cross-linked starch which is used in this invention can include starch which is treated with one or more of the compounds described in “Starch Derivates; Production and Uses” by M. Rutenberg and D. Solarek and “Starch; Chemistry and Technology”, Chapter X, pp. 324-332, 1984 or in the patents referred to above. Cross-linking compounds of this kind are selected preferably from the group which consists of methylamine compounds, polyvalent (multivalent) acids, polyvalent acid esters, polyvalent acid halogenides, polyvalent acid anhydrides, polyaldehydes, polyepoxides, polyisocyanates, divinyl compounds, phosphoryl chloride, polyamine polyepoxide resin, 1,4 butanediol diglycidylether, epichlorohydrin, trimethaphosphates, a mixture of anhydrides of acetic acid and two- or three-proton acids, sodium hypochlorite. However, other types of cross-linking compounds can also be used.
The starch, which is cross-linked and used in the size composition according to the invention, is selected preferably from the group which consists of potato starch, maize starch, wheat starch, waxy maize starch and tapioca. Other types of starch can also be used, however, or a mixture of different starches. Starch from potatoes which has been genetically modified in order to suppress formation of starch of the amylose type, in favour of starch of the amylopectin type, can also be used in the invention, see SE-A0-9704857-3. The weight ratio between starch and hydrophobic sizing agent (e.g. AKD and/or ASA) in the size composition is suitably 1:1 to 3:1, preferably 1.5:1 to 2.5:1, and most preferredly around 2:1.
The starch is substituted by chemical modification with cationic and/or anionic groups. When producing cationic starches, ammonium compounds are used in most cases which are preferably quaternary, but can also be primary or tertiary. A starch cationizing process of this kind is well known and described inter alia in U.S. Pat. No. 4,088,600, U.S. Pat. Nos. 2,876,217 and 4,840,705. In the production of anionic starches, the starch is substituted with anionic groups, which in most cases consist of carboxyl, carboxylate, sulphone, sulphonate, phosphonate or phosphate groups. This procedure is well described in literature, inter alia in the abovementioned publications of Morton W. Rutenberg and D. Solarek or STARCH: Chemistry and Technology by Roy L. Whistler, James N. Bemiller and Eugene F. Paschall. When manufacturing amphoteric starches, the starch is substituted with both cationic and anionic groups. This is also well known in literature.
The chemical co
Fortuna Jos'e A.
Nixon & Vanderhye
Stora Kopparbergs Bergslags Aktiebolag (publ)
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