Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Including a second component containing structurally defined...
Reexamination Certificate
2003-02-05
2004-08-31
Killiman, Leszek (Department: 1773)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Including a second component containing structurally defined...
C428S534000, C524S413000, C524S497000, C427S361000, C427S365000, C427S395000, C427S396000, C427S391000, C427S392000, C523S200000, C523S205000, C523S206000
Reexamination Certificate
active
06783846
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the use of a nonionic alkylhydroxyalkyl cellulose to improve gloss and printability of a surface, for instance paper or cardboard, which is coated with a coating composition containing calcium carbonate and a latex. Advantageously, the non-ionic alkylhydroxyalkyl cellulose can be combined with a carboxymethyl cellulose.
BACKGROUND OF THE INVENTION
When coating, such as smearing or surface sizing of cellulose-based surface-shaped products, for instance paper or cardboard, with a composition the primary aim is to change the properties of the paper product, such as improved strength, improved appearance, improved properties of printability, improved impermeability or improved properties of adhesion. Thus, it is common to surface size paper or cardboard with an aqueous binder-containing composition in order to improve, inter alia, wet strength or to coat paper or cardboard with a composition that contains pigment pastes in order to improve the printing properties and the appearance of the surface. The coating compositions may, apart from binders and pigment, also contain secondary binders (co-binders), protective colloids, thickening agents and dispersing agents. It is common to add water-soluble or water-swellable polymers as thickening agent, protective colloid or secondary binders, on the basis of polyvinyl alcohol, modified celluloses, starch, casein, alginate or high molecular carboxyl-group-containing polymerizate.
EP 15 517 discloses the use of cellulose ethers in coating mixtures, where carboxymethyl cellulose is added as a secondary binder. It is already known from EP 307 795 to use, inter alia, methyl cellulose as a protective colloid. EP 425 997 discloses that hydrophobically modified alkyl cellulose, alkylhydroxyalkyl cellulose or hydroxyalkyl cellulose can be used as a thickening agent in aqueous paper coating compositions. The hydrophobic groups are preferably C
12-16
alkyl groups or alkyl aryl groups. When used in coating compositions these cellulose ethers, when compared with carboxymethyl cellulose ethers, give an improved viscosity at high shear rates.
From EP 496 269 it is also known to prepare a polysaccharide-containing suspension for paper coating, the suspension containing a low-molecular polysaccharide which is dissolved in aqueous phases and may be a carboxymethyl cellulose or a hydroxyethyl cellulose. Moreover, the coating composition contains one or more dispersed, i.e. not dissolved, cellulose polymers, such as hydroxypropyl cellulose, methyl cellulose, methylhydroxypropyl cellulose and hydrophobically modified hydroxyethyl cellulose.
WO 97/46757 discloses the use of a water-soluble non-ionic alkylhydroxyalkyl cellulose which contains alkyl groups having 1-3 carbon atoms and hydroxyalkyl groups having 2-3 carbon atoms but which is free from hydrophobically modified hydrocarbon groups having at least 4 carbon atoms, the cellulose ether having a turbidity point in the range 35-80° C., as a thickening agent in aqueous compositions for coating cellulose-based surface-shaped products. By using the cellulose ethers as a thickening agent, process engineering advantages are obtained when applying the coating compositions to surface-shaped cellulose products.
SUMMARY OF THE INVENTION
The present invention generally relates to the use of a non-ionic alkylhydroxyalkyl cellulose, which has alkyl groups having 1-3 carbon atoms and hydroxyalkyl groups having 2-3 carbon atoms, is free from hydrophobically modifying hydrocarbon groups having at least 4 carbon atoms and has a turbidity point of 50-95° C., or a combination of the alkylhydroxyalkyl cellulose with a carboxymethyl cellulose, where the amount of the carboxymethyl cellulose is 1200 percent by weight at the most of the amount of the alkylhydroxyalkyl cellulose in an aqueous coating composition containing a calcium carbonate and a latex in order to improve the gloss and the printability of the surface which is obtained when paper or cardboard is coated with the coating composition.
DETAILED DESCRIPTION OF THE INVENTION
According to the present invention, it has now been found that the use of a non-ionic alkylhydroxyalkyl cellulose, which has alkyl groups having 1-3 carbon atoms and hydroxyalkyl groups having 2-3 carbon atoms, is free from hydrophobically modifying hydrocarbon groups having at least 4 carbon atoms and has a turbidity point of 50-95° C., or a combination of the alkylhydroxyalkyl cellulose with a carboxymethyl cellulose, where the amount of the carboxymethyl cellulose is 1200 percent by weight at the most of the amount of the alkylhydroxyalkyl cellulose, in an aqueous coating composition containing a calcium carbonate, and a latex considerably improves the gloss and the printability of the surface that is obtained when paper or cardboard are coated with the coating composition.
Extensive studies have shown that the use of the alkylhydroxyalkyl cellulose in a latex coating composition which is pigmented with calcium carbonate gives an improved gloss and changes in the surface of the coating layer, such as higher hydrophilicity, higher surface energies and a higher relative polarity. These changes of the surface lead to improved printing properties. For example, the gloss, set-off and smoothness of the surface are improved. It has also been found that the carboxymethyl cellulose in combination with the alkylhydroxyalkyl cellulose gives a surprisingly good result, although the use of the carboxymethyl cellulose only gives a considerably lower hydrophilicity, surface energies, relative polarity, gloss and printability than the alkylhydroxyalkyl cellulose. Since the carboxymethyl cellulose in relation to the alkylhydroxyalkyl cellulose is easier to prepare and, moreover, is produced on a large scale, using a combination of carboxymethyl cellulose and alkylhydroxymethyl cellulose means a commercially attractive embodiment of the invention. It has also turned out that the coating composition which contains both an alkylhydroxyalkyl cellulose and a carboxymethyl cellulose according to the invention exhibit excellent rheology properties compared to a coating composition which contains carboxymethyl cellulose only. For instance, the viscosity of a coating composition containing the combination is less dependent on the shear rate than may be expected. If a combination of alkylhydroxyalkyl cellulose and carboxymethyl cellulose is used, the amount of carboxymethyl cellulose usually constitutes 20-1200 percent by weight, preferably 50-600 percent by weight, of the amount of the alkylhydroxyalkyl cellulose.
The viscosity of the alkylhydroxyalkyl cellulose may vary considerably and should in a conventional manner be adapted to the composition of the coating mixture. Usually it is in the range 5-100,000 mPa·s, preferably in the range 10-10,000 mPa·s, measured in a Brookfield viscosimeter of the type LV in a 2% solution at 20° C. Examples of suitable alkylhydroxyalkyl celluloses are ethylhydroxyethyl cellulose, methylethylhydroxyethyl cellulose, methylethylhydroxy-ethylhydroxypropyl cellulose, methylhydroxyethyl cellulose and methylhydroxypropyl cellulose. Usually the hydroxyethyl groups constitute at least 30% of the total number of hydroxyalkyl groups and the number of ethyl substituents usually constitute at least 10% of the total number of alkyl substituents. Examples of such cellulose ethers are ethylhydroxyethyl cellulose with DS
ethyl
=0.8-1.3 and MS
hydroxyethyl
=1.9-2.9 and methylethylhydroxyethyl cellulose with DS
methyl
=1.0-2.5; DS
ethyl
=0.1-0.6 and MS
hydroxyethyl
=0.1-0.8. The amount of alkylhydroxyalkyl cellulose is usually from 0.05 to 3, preferably from 0.2 to 1.5 percent by weight of the composition.
The carboxymethyl cellulose usually has a degree of substitution of carboxymethyl of 0.6−1.5. It can exist in acid form, but preferably the salt form with a preferably monovalent cation, such as sodium, is used. The carboxymethyl cellulose usually has a somewhat lower viscosity than the alkylhydroxyalky
Hermansson Erland
Larsson Kerstin
Akzo Nobel N.V.
Killiman Leszek
Mancini Ralph J.
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