It is well known in the paper industry to prepare various kinds of sized paper by application of chemical compositions mainly consisting of aqueous binder dispersions or emulsions containing various additives depending on the result which one wants to obtain. For example it is usual to put dyes or pigments into the size press solution in order to obtain colored paper. It was difficult, however, to give the colored paper a pearlescent finish because the specific type of pigment which is used for obtaining such an effect, could not equally be distributed over the surface of the paper by the usual size press or on-line coater applications. In addition there would be several problems associated with producing this type of paper and further problems would occur in the subsequent processing of this paper.

It has been found that colored paper with a variety of excellent pearlescent finishes can be obtained, when the composition of the binder dispersion or emulsion is adequately chosen and when certain process parameters are carefully monitored.

It is, therefore, the object of the invention to provide a new process for the preparation of paper with a pearlescent finish. This process is characterized by the use of a special composition and by the application of this composition a) in a size press under humidity conditions of at least 90% moisture content and using drying rollers with a coating of fluorinated hydrocarbon resin; and/or b) in an on-line coater application A further object of the invention is the size press composition used in this process having a viscosity of 1800 cPs 50 cPs and comprising a polymeric binder, additives with dispersant, antistatic and lubricant effects, antifoaming agent, a synthetic thickener and a pearlescent pigment.

The pearlescent pigment can be any pigment known to give such an effect which is normally provoked by a mica component. As an example, pigments sold by the company Merck in Darmstadt, Germany under the name IRIODIN or by the company Maerl International in Haarlem, Holland under the name MAGNAPEARO are very suitable.

The synthetic thickener can be any thickener used in size process compositions.

Examples are the products Printofix Thickener NCN from Cariant or LYOPRINR TCF of Ciba Specialty Chemicals.

The antifoaming agent and the additives having a dispersant, antistatic and lubricant effect are well known chemical products normally used in binder dispersions or emulsions. To improve the runability of the paper sheet in the size-press, it is advantageous to use a dispersant of the quaternary ammonium type like Elfugin V of Cariant International Ltd.

The polymeric binder is of the type having a film forming temperature at around 7 degrees C. An example is the product APPRETAN° DM2 of the company Perstorp- Cariant which is a copolymer of vinylacetate and dibutylmaleate, stabilized with polyvinylalcohol.

The person skilled in the art of paper sizing will know how to make the choice of these components and how to combine these chemicals in order to obtain the prescribed viscosity of the paste which avoids the sedimentation of the pigment. If the viscosity is too high, the paper will slip at application of the composition, if the viscosity is too low, the binder will enter into the paper mass and the pigment will stay on the surface with the result that the paper has not the required finish.

The composition as above defined can be used in the common size press of a paper machine and/or in a common on-fine coating machine as i. e. a blade, air knife or rod coating.

For the application of the composition in a size press of a paper machine according to the invention, the rollers have to be kept as clean as possible in order to get a good runability and it was observed that the drying rollers after the size press should be coated with a fluorinated hydrocarbon resin (TEFLON@) in order to avoid adhesion.

An important feature of the process according to the invention is the observation of humidity conditions during application of the size press paste and it is advantageous to use a water mist distributor that gives a very fine water mist over the size press rollers.

The moisture content in the size-press should be preferably around 100%.

For the application of the composition in a on-line coating machine according to the invention, it can be said that the composition can be applied to the paper on one or both sides. If the composition is applied on both side the coatweight need not be the same on both sides. A preferred coatweight for the application of the composition according to the invention is 35-40 gm~2.

When applying a size press composition according to the invention and observing the process conditions in accordance with the above described features, paper with an excellent pearlescent finish is obtained.

The pearlescent effect can be varied and many different decorative effects can be produced, for example: -The size of the pearlescent particles can be changed to give a course or fine appearance.

-The color of the pearlescent material can be, for example, silver, gold, blue, red or green -The effect becomes more distinct on a colored paper, the color of the base paper can be varied along with the color of the pearlescence to produce an interesting and decorative range of papers, for example a silver pearlescence on a black paper or board, or a red pearlescence on a blue paper. The combinations are almost without limit.

-Pearlescent pigments can be mixed together to give two, three or more colors of pearlescence mixed together on the surface of the paper, for example, silver and red, or silver, red, green and blue.

The following examples illustrate the invention.

EXAMPLE 1 Composition Antifoaming Agent 15-30 parts Dispersant 15-30 parts Lubricant 10-25 parts Pigment 20-200 parts Binder 60-600 parts Thickener 5-20 parts Water To make up to 1000 Parts Total EXAMPLE 2 Application Of The Composition in the Size-press The paste obtained in example 1 is applied on a freshly produced paper using size press rollers of the usual type which are kept clean by the application of a very fine water mist provided by a water mist distributor (the moisture content is 100%) at a speed of 200-230 m/min and Nip pressure of 40 kp. After the size press rollers, the paper sheet covered by the size paste is lead over drying rollers with a coating of fluorinated hydrocarbon resin at a temperature of 70-75°C. Paper with good pearlescent effect is obtained.

EXAMPLE 3 Application Of The Composition in an on-line coating machine The paste obtained in example 1 is applied on a freshly produced paper using an on- line coating machine (blade coater). The paste is applied to the surface with a coatweight of 35-40 g/m-2. A paper with excellent pearlescent effect is obtained.