Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2000-08-01
2004-04-06
Yoon, Tae H. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S504000, C523S205000, C527S201000
Reexamination Certificate
active
06716903
ABSTRACT:
DESCRIPTION
Coating composition for the manufacture of printable coated paper and board, component of the coating composition and process for the manufacture of paper and board.
The present application deals with a coating formulation for the manufacture of coated paper and board, and a selected polymeric component for the production of coating colours, including a manufacturing process for paper and board.
Paper and board are composed of individual fibers, which cause a surface roughness related to the dimensions of the fiber components. Surface roughness adversely effects printability of paper and boards. In order to reduce this surface roughness, paper and board are coated with coating colours containing pigments like coating clay, fine and ultrafine ground limestone, dispersants, converted starch polymeric binder emulsions and other additives. The coating colour can be applied in several process stages, for instance as pre and topcoat.
Ideally application of the coating mix results in complete and homogeneous coverage of the raw stock surface and with no penetration into raw stock pores. The coating colour can be applied to a web running at speeds up to 1800 m/min with a roll applicator the surplus of applied colour is metered off with a blade. Drying of the coated web is effected with available and known technologies.
The process can be integrated into the paper production process or can be carried out as a separate production stage. The viscosity and runnability of coating colours depend largely on the solids level of the mix. A high solids level can reduce drying energy consumption, however high viscosities can cause problems, like high hydraulic flow resistance in pipes, poor colour distribution in the applicator pond and excessively high blade pressure. These problems can lead to reduced production speed.
A low solids level of the coating colour results in excessive wettening of the raw stock and hence a dramatic reduction of raw stock strength and an increased number of web breaks. Also drying energy consumption increases significantly. The coating colour should also exhibit viscosity stability over extended time periods.
High solids content in conjunction with suitable and stable viscosities are sought to be achieved with dispersants and other additives. Also dispersants derived from natural raw materials are used widely. An especially effective natural dispersant is carboxymethylcellulose.
For coating formulations containing UFGL (ultrafine ground limestone) as the major pigment, the use of gelatine for this application has been described for instance in patent DE-C-195 29 661. Also dispersants on a fully synthetic basis, such as polyvinylpyrrolidone are described in the same patent.
The present invention provides a coating formulation, which allows to obtain a coated product with improved quality parameters like brightness and gloss and a further improvement of runnability, e.g. avoidance of bleeding and streaking at the blade and loss wetting of the raw stock web. The coating mix of this invention is particulary suitable for the application of UFGL, which because of its high brightness and wide spread availability gains steadily more importance compared to kaolin. However, the high percentage of fines in UFGL can cause runnability problems.
For make up of a coating composition pigments or pigment mixtures, soluble and/or dispersed binder polymers are thoroughly mixed. Soluble polymers can cause volume exclusion or depletion flocculation of dispersion and emulsion particles. As a result wet packing characteristics of the coating colour can deteriorate. Also blending of pigment slurries with different optimal dispersant requirement can cause formation of pigment aglomerates due to over or underdispersion of a specific pigment fraction. As a result water release from such coating formulations into the web during the application stage is much higher.
It was now found, that in contrast to the generally used electrostatic stabilization, steric stabilization provides high viscosity stability, both over extended time periods at constant solids and in relation to solids variations occurring as a result of the coating process.
Steric stabilization functions by formation of a polymer layer around the particle. According to Huggins and Flory, the polymer should show a high interaction potential with the solvent. The attached polymer layer prevents formation of pigment agglomerates even at a very high solids level.
The coating mix of the present invention allows rapid structure formation in the wet film and prevents penetration of pigment and binder fines into raw stock pores. Thickness variance of the metered coating film is reduced accompanied by reduced micro gloss variation and improved calenderability.
Conventional coating formulations show much more penetration of fines into the raw stock pores, which over time leads to a coarsening of the pigment particle size distribution in the application system and gradually deteriorating gloss and smoothness parameters of the coated product. Because of increased coating thickness variance, micro gloss variations of the coated surface become very objectionable.
The present inventions relates to an aqueous formulation with a solids level range from 50 to 80% by weight, comprising pigments and binders, whose viscosity at 10 sec
−1
is higher than 10
−
3 mPa.s, preferably above 10
4
mPa.s and especially preferred 10
5
to 10
8
mPa.sec. At a shear rate of 10
5
sec
−1
viscosity of the coating composition of this invention drops to values ranging from 30 to 100 mPa.sec.
Viscosities were measured with a Stress Tec Viscometer manufactured by Reo Logica, Lund, Sweden, a Brookfield viscometer, manufactured by Brookfield Engeneering Laboratories, 240 Cushing St. Stroughton, Mass. 02072 USA and a HACAV II capillary viscometer.
The viscosity values determined according to the method of Brookfield are dependent upon spindle type and rotation velocity. The viscosity values indicated in this patent application have been determined by using spindle No. 4 and rotation velocities of 10/min or 100/min, respectively. The viscosity values were determined at temperatures of 20° C.
Preferred are coating formulations containing kaolin and especially preferred are formulations containing UFGL. Especially preferred is UFGL with a particle size distribution of 90-99% by weight below 2 &mgr;m diameter. Such pigments are used for production of high gloss printing paper grades.
The invention relates to pigment particles, which are encapsulated by a polymer shell, which prevents formation of pigment agglomerates. A preferred embodiment of the present invention contains pigment particles with a polymer shell consisting of graft polymers derived from proteins grafted with ethylenically unsaturated monomers with functional amide or amino groups.
Such polymers are strong polymeric Lewis bases (electron donors) and show a high adsorption affinity to the pigment surface. The adsorbed polymer layer stabilizes the pigment particles especially the ultra fine pigment fraction.
Examples of polymers, which can be used within the scope of this invention, are proteins like soy proteins, casein and as the preferred embodiment gelatine, which is polymer grafted with acrylamides, methacrylamides, aminoalkylacrylates, aminoalkylmethacrylates or blends of these monomers.
The polymers applied according to this invention can contain primary, secondary or tertiary amino groups. Other examples of polymers, which can be used according to this invention are proteins like soy proteins and preferably gelatin, which is grafted with lactames comprising ethylenically unsaturated groups, such as N-vinyllactames, like N-vinylcaprolactam or N-vinylpyrrolidon or with a blend of said monomers.
Especially, preferred components for the preparation of coating formulations, according to this invention are gelatines grafted with amide or amino group containing ethylenically unsaturated monomers. The weight ratio between ethylenically unsaturated monomers and gelatine can reach to
Connolly Bove & Lodge & Hutz LLP
CTP Papierhilfsmittel GmbH & Co.
Yoon Tae H.
LandOfFree
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