Surface treatment composition

Abstract

The invention relates to 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 or 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 surface treatment composition for paper, board or other fibrous webs, which composition comprises: particles which comprise a core comprising an active material comprising a salt of a multivalent metal, and a supporting material comprising a shell, wherein the core is encapsulated within the shell, wherein the core, the shell, or both further comprise an acid selected from the group consisting of hydrochloric acid, peracetic acid, and phosphoric acid, wherein the supporting material is adapted to release the active material and the acid from the particles when subjected to heat and/or a change in pH or when subjected to heat and pressure, and wherein the core further comprises a binding material selected from the group consisting of waxes, polyethylene waxes, triglycerides, metal soaps, or co-polymers and combinations thereof, and wherein the particles further comprise at least one stabilizer.

2. The composition according to claim 1, wherein the active material comprises calcium salt.

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

4. The composition 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.

5. The composition according to claim 1, wherein the particles comprises the active material to an amount of at least 50 weight %.

6. The composition according to claim 1, wherein the supporting material is adapted to release the active material during calendering of a paper, board or fibrous web that has been surface treated with the composition.

7. The composition according to claim 1, wherein the supporting material is adapted to release the active material during drying of a paper, board or fibrous web that has been surface treated with the composition.

8. The composition according to claim 1, wherein the composition is anionically, amphoterically, or nonionically charged.

9. The composition according to claim 1, wherein the composition further comprises at least one sizing or coating agent.

10. The composition according to claim 1, wherein the particles' spherical diameter is between 100-0.01 m.

11. The composition according to claim 1, wherein the core comprises the acid.

12. The composition according to claim 1, wherein the shell comprises the 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.