Paper making and fiber liberation – Processes and products – With coating after drying
Reexamination Certificate
2002-03-11
2004-08-10
Chin, Peter (Department: 1731)
Paper making and fiber liberation
Processes and products
With coating after drying
C162S135000, C162S136000, C162S162000, C427S157000, C427S158000, C524S522000, C524S523000
Reexamination Certificate
active
06773549
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a coated, optically brightened printing paper and to a process for its production.
2. Description of the Related Arts
Coated, optically brightened printing papers are known per se and find manifold use in higher-quality printed products, such as illustrated books, brochures and company reports. Optical brighteners are likewise known. In addition to their main field of use in the detergent industry, they have also already been used for decades in the paper industry in order to increase the brightness of the paper produced. Viewed chemically, optical brighteners are derivatives of diaminostilbene disulfonic acid. Their effect is based on the absorption of UV light in a wavelength range from 300-400 nm and emission in a blue range of visible light in the range from 400-450 nm. This leads to a shift in the yellow cast of fibers and fillers into the blue-white range and ultimately to an increase in the spectral reflectance.
The use of optical brighteners during paper making can be carried out in various ways. During the production of coated printing papers, it can be added into the fibers stock suspension upstream of the flow box of the paper machine. If the paper machine has a size press, as it is known, for the surface treatment of the paper, the optical brightener can for example be metered into the starch solution used there. A third possibility is to meter the optical brightener into a coating color which is applied to the coating base paper inside or outside the paper machine or is possibly applied to an already pre-coated coating base paper.
In Wochenblatt für Papierfabrikation No. 15, pp. 529-534 (1983), a report is given on the size-press application of optical brighteners together with a starch suspension. It has also already been proposed to divide the amount of optical brightener to base paper, size press and coating, see PTS-Vortragsband 02/91, pp. 172-175, 15
th
Coating Symposium 1991.
A device for applying size suspensions, in addition to the known size press, is disclosed by DE-A-34 17 487, which corresponds to U.S. Pat. No. 4,848,268, where a paper web guided around a roll is treated on the front side with coating color and on the rear side with liquid media.
EP-A-0 373 276 describes a process and an apparatus for the continuous spraying of additives onto a moving paper web.
Coated, optically brightened papers produced in accordance with the prior art exhibit certain disadvantages. If the optical brightener is added to the fibers stock suspension upstream of the flow box or is applied to the surface of the coating base paper by means of a size press, then attenuation of the UV light and of the reflected blue light occurs as a result of the coating layer subsequently applied, so that the action of the optical brightener occurs only to an inadequate extent. Increasing the amount of additive is ruled out for cost reasons. Adding the optical brightener into the coating color to be applied is certainly possible in principle, but requires the addition of carrier substances, as they arm known, since the optical brightener itself does not adhere to the pigments of the coating color and therefore, to some extent, is absorbed into the base paper together with the water from the coating color. This problem was solved by the addition of carrier substances, as they are known. These are, for example, starches CMC and polyvinyl alcohol. Because of their anionic charge, they are capable of holding the cationically charged optical brighteners in the applied layer of coating color and bringing them into action under the influence of light.
However, the drawback with using carrier substances is their relatively high inherent viscosity in aqueous solution, which is added to the already relatively high viscosity of the coating color used.
This leads to viscosity problems when processing at high operating speeds in blade coating machines, said problems either limiting the operating speed, leading to non-uniform coating application or making it necessary to dilute the coating color, which in turn entails problems with the drying capacity of the drying equipment arranged downstream.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a coated, optically brightened printing paper and a process for its production which overcomes the problems listed above.
In order to solve the problem, an optically brightened printing paper coated on one or both sides and coated once or many times is proposed, which comprises a coating base paper and a coating layer applied thereto and comprising pigment, binder and coating color aids, which is characterized in that the optical brightener is arranged on the outer side of a coating layer.
Printing paper coated on one side is understood to mean those papas which are provided only for single-sided printing. These include, for example, label papers for bottles and can wrappers. In the same sense, printing pap coated on both sides are printed on both sides. These include, for example, magazine papers, as they are known, for illustrated magazines or catalogues, but also art papers. High-value printed products require the highest surface quality of the side to be printed. This can no longer be achieved with a single coat, as it is known. For this reason, the coating base paper is firstly coated with one or two pre-coats, as they are known, and the top coat, as it is known, is arranged on them.
The pigments considered for the coating layer are all familiar coating pigments, such kaolin, calcium carbonate, talc, titanium dioxide, gypsum, etc.
The binders considered for the coating layer are likewise all familiar coating color binders, such as starch, protein, casein, synthetic lattices etc. Likewise, the coating layer contains conventional coating color aids, such as defoamer, deaerator, lubricant and viscosity regulator. Pigments, binders and coating color aids are familiar to those skilled in the art and active in this field.
The arrangement of the optical brightener on the outer side of the coating layer states that said it is arranged both on the outer side of the coating layer and in the outer layer under the outer side. The porosity of the coating layer, which is always present, if appropriate even after a preceding calendering operation brings about this arrangement with the advantageous effect that the UV proportion of the light strikes the optical brightener without or only with slight attenuation and is emitted as visible blue light in the range from 400-450 nm without or with only slight attenuation as result of which the yellow cast of the fibers and pigments is shifted into the blue-white range. This ultimately leads to an increase in the spectral reflectance and to an improvement in the paper quality. With this arrangement of the optical brightener, a reduction in the amount of brightener is also possible, because of the improved efficiency, so that a reduction in costs is possible.
In a preferred embodiment of the optically brightened printing paper, the optical brightener is arranged on the outer side of the top coat of a coating layer consisting of one or more pre-coats and a top coat. This embodiment has the advantage that no excessively high demands have to be made on the brightness quality of the pre-coat pigments, since the lower brightness of these pigments is compensated for by the whitening effect on the outer layer of the top coat. A reduction in costs is therefore possible.
In a further embodiment of the optically brightened printing paper, the optical brightener is arranged on the outer side of a first coating layer and a further coating layer without an optical brightener is arranged over that. It is known that optical brighteners are destroyed by the continuous action of UV light, and the paper grays. On the other hand, however, in specific applications of the optically brightened printing paper it is not possible to avoid said paper being continually exposed to light. This occurs, for example, in the case of illuminated advertising pl
Chin Peter
Cohen & Pontani, Lieberman & Pavane
Halpern Mark
Stora Enso Publication Paper GmbH & Co., KG
LandOfFree
Method for producing an enameled, optically brightened... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for producing an enameled, optically brightened..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for producing an enameled, optically brightened... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3310279