Surface treatment composition

Abstract

A surface treatment composition for paper, board or other fibrous webs. The composition of the invention comprises particles which comprise an active material and a supporting material. The active material comprises a salt of a multivalent metal, such as a divalent or trivalent metal. In accordance with the invention, the supporting material is adapted to release the active material from the particles when subjected to heat and/or pressure and/or a change in pH. Consequently, the active material's adverse effects on the rheology of the composition are avoided while its desired effects on the surface characteristics are retained or enhanced.

Claims

1. A process for the manufacture of a surface-treated and printed paper, board or other fibrous web comprising the following steps: a) forming a fibrous web from pulp, b) coating or surface sizing the fibrous web with at least one layer, wherein the fibrous web is coated or surface sized with a surface treatment composition, which composition comprises particles which comprise an active material comprising a salt of a multivalent metal, an acid, and a supporting material, c) melting or dissolving the supporting material thereby or releasing the active material and the acid from the particles on the surface of the fibrous web by the application of heat, or a change pH, or a change in heat and pressure, or a combination thereof, and d) printing the resulting coated or surface sized paper, board or fibrous web by use of inkjet and/or flexographic printing techniques.

2. The process according to claim 1, wherein the step c) of releasing the active material from the particles is accomplished in drying of the fibrous web.

3. The process according to claim 1, wherein the step c) of releasing the active material from the particles is accomplished in calendering of the fibrous web.

4. The process according to claim 1, wherein the active material comprises calcium salt.

5. The process according to claim 1, wherein the supporting material is selected from the group consisting of waxes, polyethylene waxes, polypropylene waxes, triglycendes, metal soaps, and co-polymers or a combination of any of these.

6. The process according to claim 1, wherein the supporting material is sensitive to heat and has a melting point or a glass transition point of between 60-180° C.

7. The process according to claim 1, wherein the supporting material further comprises dispersed finely divided particles of either citric acid, per acetic acid, hydrochloric acid, phosphoric acid, or combinations thereof.

8. The process according to claim 1, wherein the acid of the active material comprises at least one citric acid, per acetic acid, hydrochloric acid and phosphoric acid.

Description

DETAILED DESCRIPTION OF THE INVENTION

(1) The surface-treatment composition of the present invention comprises particles that comprise high concentrations of active materials, which active materials are released from the particles in a controlled manner after the composition has been applied on the surface of a web. Use of such particles in the composition decreases rheology and viscosity problems that are connected with prior art compositions comprising as high concentrations of the active materials as the inventive composition. Consequently, higher concentrations of the active materials may be used without causing rheology or viscosity problems.

(2) By the expression “release . . . from the particles” as used herein means that the active material is transformed from a state wherein it is held within or in another way being a part of a particle to a state wherein the active material is not a part of a particle form, but in contact with the surface of the web. Thus, the active material might be released from the particle as a separate material, or it might be released from the particle in a bonded form, e.g. bonded or in another way attached to the supporting or binding material.

(3) The invention is especially advantageous when dosing salt of multivalent ions to sizing composition, especially to anionically charged sizing composition, in order to enhance the inkjet printability of a paper or board. Said salts may e.g. be calcium chloride, aluminum chloride, magnesium chloride, magnesium bromide, calcium bromide, barium chloride, calcium nitrate, magnesium nitrate, barium nitrate, calcium acetate, magnesium acetate or barium acetate. Said anionic sizing composition may e.g. comprise anionic rosin soap sizing agents, anionic polymeric styrene maleic anhydride sizing agents or polyaluminium chloride.

(4) The particles of the invention can be of a shell/core construction, with the active material being encapsulated as a core within a shell of a supporting material. Such particles can be manufactured using e.g. an emulsion polymerization method.

(5) Alternatively, the particles may be of a composite construction, comprising a mixture of the active material and the supporting material. For example, instead of forming as shell/core structure, the particles may be a composite of a calcium stearate and calcium chloride. Such a particle may comprise calcium to an amount of 50 weight % or more. A calcium stearate/calcium chloride particle may be formed by mixing calcium stearate with calcium chloride, in a batch process. The formed particles are thereafter stabilized by use of e.g. starch and surfactants.

(6) The particles may also be formed by e.g. dry blending calcium stearate and calcium chloride whereupon the mixture is milled and finally fractionated. The particles can then be stabilized in solution by using the said stabilizing system.

(7) The composite materials can also be created using a spinning method, such as wet spinning, electrospinning or electrospraying. In such a method, a water soluble wax is, e.g., blended with calcium chloride and then spun. The temperature of the solution should preferably be above the melting point of the supporting or binding material, e.g. wax, in order to ensure solubility and blendability with the added components. The materials can be spun or sprayed (particulates) directly onto a substrate or indirect onto another collector plate, or alternatively, into a solution.