The invention deals with a method for inline application of nano-hybrid particles during a papermaking process.
Application of this composition on porous substrates such as paper is not very effective, because the nano-particles tend to disappear in the pores of the substrate during application, especially when applied with a blade or roll.
It is desirable to further improve the surface characteristic of porous substrates such as paper, by using all beneficial properties of a coating solution and to simplify the method of producing said paper.
It is an object of the invention to provide a method for producing a paper especially a printing paper with improved surface properties, especially enhanced optical appearance and improved print quality.
Object of the invention is therefore a method of making a paper with improved surface properties, characterized in that that nano-hybrid particles consisting of organic nano particles and inorganic particles, the organic nano-particles being adhered to the surface of the inorganic particles wherein the nanohybrid particles contain 1-99% organic nano particles of polystyrene or a styrene copolymer having a size of 2 - 100 nm and 99-1% inorganic particles having a size of 50 nm - 20 µm are applied in the wet end of the paper making process by addition to the fiber suspension or applied onto the wet or dried paper fiber web.
The nano-hybrid particles consist of an organic and an inorganic part. Preferably the organic part is nano sized having a particle size of about 2-100 nm. The organic part preferably is of spherical shape.
The organic nano-particles are adhered to the surface of the inorganic particles, thus when applied in an aqueous solution on the surface of a porous substrate the nano-particles cannot disappear in the pores but are kept close to the surface.
Organic part of the nano-hybrid particles may be a polymer or a copolymer preferably polystyrene or styrene copolymers. Especially preferred are styrene maleimid copolymers or other styrene containing copolymers e.g. with butadiene, acrylic acid and the like. The styrene part may also have functional groups such as sulfonic acid groups, carboxylic groups or pyridine groups.
The nano-hybrid particles may be prepared for example by dissolving the polymer or a copolymer of maleic anhydride with a vinyl monomer in water, adding a RNH2 compound, R being H, alkyl with 1 - 18 carbon atoms or aryl and heating the resultant mixture in the presence of larger particles to make the imides. The polymeric particles will settle down on the larger particles.
Inorganic part can be CaCO3 (ground or precipitated), TiO2, clay, aluminium oxide, aluminium hydroxide, talkum, zincoxide, zeolithe and the like.
The hybrid particles contain 1-99 wt% organic and 99-1 wt% inorganic material. Preferably the hybrid particles contain 3-45% of organic material and 97-55 wt% of inorganic material.
The nano-hybrid particles are preferably applied dry or preferably in an aqueous suspension with a solid content of 1-99%, preferably 10 - 80wt%, more preferably 35 - 70 wt% .
For application at the wet end the composition preferably contains 1- 20% of organic material and 99 - 80 wt% of inorganic material, for application on the dry or wet fiber web, the composition preferably contains 3 - 45 wt% of organic material and 97 - 55 wt% of inorganic material.
The nano-hybrid particles can be applied in the wet end by addition to the fiber suspension or applied onto the wet or dried fiber web.
For application in the wet end of the paper making process up to 20 - 35 wt% of the nano hybrids may be added.
Usually the fiber content of the paper fiber suspension will be 0,6 to 1,5 wt%.
In the second case (application to the dry or wet fiber web) the nano-hybrid particles suspension may be applied pure or mixed with different types of binders, eg. starch and starch derivates, PVOH, branched polymers, styrene acrylate latex, styrene butadiene latex, casein and/or several additives for brightness, shading and adjustment of the dielectrical properties, as NaCl, KCI, CaCl2, and the like.
Starch and starch derivatives may be added in an amount up to 10 wt%, preferably 1 - 2 wt%, PVOH may be added up to 10 wt%, preferably 0- 5 wt%, branched polymers up to 20 wt%, preferably 2-10 wt%, styrene acrylate latex, and styrene butadiene latex up to 20 wt%, preferably 5- 12 wt%. Additives for brightness may be present in an amount of 0 - 5 wt%, preferably 1- 2 wt%, shading additives may be present in an amount of 0 - 2 wt% preferably 0 - 1 wt%, additives for the adjustment of dielectric properties may be added 0 - 7 wt %, preferably 0 - 2 wt %.
The nano particles may be applied inline or offline on the fiberweb.
Inline application of the dry nano-hybrid particles or the suspension of the nano-hybrid particles may be carried out by conventional surface coating methods e.g. size press, film press, blade, roller bar, curtain coating, spray coating and the like.
Offline application may be carried out by conventional surface coating methods e.g. size press, film press, blade, roller bar, curtain coating, spray coating and the like or by conventional printing techniques such as intaglio or gravure printing or flexographic printing or the like.
Further, if applied in the wet end of the paper making process addition of the aqueous solution of nano-hybrid particles results in improved process parameters, such as improved de-watering performance. Thus the process or method for preparing the paper becomes more economical and thus cheaper.
The paper produced shows improved surface appearance, as well as improved printing quality, especially in laser and digital printing processes.
Product will be an uncoated, pigmented or coated office and communication paper. Depending on process parameters the resulting paper may be glossy ot have a matt glaze.
Production of a multipurpose grade:
Production of a pigmented laser or digital printing grade paper
pH=7-10
Application on film press with rod no.4 or different rod.
Application of 15 g/m2 per side
Machine calendering or offline calendering for enhanced smoothness
This list of references cited by the applicant is for the reader's convenience only. It does not form part of the European patent document. Even though great care has been taken in compiling the references, errors or omissions cannot be excluded and the EPO disclaims all liability in this regard.