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1. (WO2017137879) METHODS FOR MAKING PAPER OR BOARD, A BOARD TRAY AND PULP PARTICLES COATED WITH FOAMABLE POLYMER FOR USE IN THE SAME
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Claims

1 . A method of manufacturing paper or board, comprising the steps of

(i) coating pulp fibres and a foaming agent with polymer, to produce polymer-coated foamable particles,

(ii) incorporating an amount of said particles into a fibrous stock for pa- permaking,

(iii) forming a web from said fibrous stock on a forming fabric of a paper or board machine,

(iv) pressing and drying said web to a paper or board layer, and

(v) heating said paper or board layer to have the foaming agent contained in the particles to produce vapour or gas, which foams said polymer.

2. The method of claim 1 , characterized in that the foaming agent is moisture, which evaporates and foams the polymer.

3. The method of Claim 1 or 2, characterized in that the melt flow rate of the foamable polymer is at least about 15 g/10 min at 190°C.

4. The method of any one of the preceding claims, characterized in that the foamable polymer comprises low density polyethylene (LDPE).

5. The method of any one of the preceding claims, characterized in that

at step (i) said particles are provided with a double-layer coating, the melt viscosity of the foamable polymer of the inner layer being higher than the melt viscosity of the polymer of the outer layer, and

at step (v) the polymer of the inner layer is foamed by means of the enclosed foaming agent while the polymer of the outer layer remains substantially unfoamed.

6. The method of any one of the preceding claims, characterized in that the fibres in said particles have a length of 1 to 50 mm.

7. The method of any one of the preceding claims, characterized in that the share of polymer in said particles is 5 to 65 wt-%.

8. The method of any one of the preceding claims, characterized in that said particles are added to the fibrous stock at a headbox of the paper or board machine, preferably by mixing the particles with liquid circulated in the process, to form 5 to 25 % of the dry weight of the stock supplied onto the forming fabric.

9. The method of any one of the preceding claims, characterized in that said particles are incorporated in a middle layer of a multilayer board.

10. The method of any one of the preceding claims, characterized in that the temperature at step (v) to foam the polymer is about 1 10 to 150°C, preferably about 1 15 to 125°C.

1 1 . The method of any one of the preceding claims, characterized in that the paper or board is provided with a polymer coating layer on both sides thereof before the heating, which induces foaming in the particles incorporated in the stock.

12. The method of Claim 1 1 , characterized in that the polymer used for coating the paper or board has a lower melt viscosity than the foamable polymer of the particles incorporated in the stock.

13. The method of Claim 1 1 or 12, characterized in that foaming of the polymer is carried out before the newly produced paper or board is reeled.

14. Paper or board obtainable by use of the method of any one of the preceding claims, characterized in that at least one fibrous layer thereof contains foamed polymer enclosing wood pulp fibres.

15. A method of manufacturing a board article, such as a tray or a plate, from board produced in accordance to step (i) to (iv) in claim 1 , comprising the steps of

(i) placing the board produced in step (iv) in claim 1 over a mould, which has a recess shaped to accord with the article being produced,

(ii) drawing the board against the mould by means of vacuum,

(iii) during step (ii), heating the board to induce foaming in the polymer- coated particles incorporated in the board, and

(iv) cooling the newly moulded article to solidify the foamed polymer within the board.

16. A method of producing polymer coated particles for use in the method of claim 5, comprising the steps of

(i) suspending fibrous cellulosic particles of a length of 1 to 50 mm in a solution containing a foamable first thermoplastic polymer and a first solvent,

(ii) precipitating said first thermoplastic polymer onto said fibrous particles by means of added water and phase inversion, to obtain fibrous particles with enclosed humidity and a first polymer coating layer,

(iii) suspending the polymer-coated particles obtained at step (ii) in a solution containing a second thermoplastic polymer and a second solvent, said second thermoplastic polymer having a melt viscosity lower than the melt viscosity of said first thermoplastic polymer, and

(iv) precipitating said second thermoplastic polymer onto said fibrous particles by means of added water and phase inversion, to obtain fibrous particles with a double-layer polymer coating, in which the inner first polymer coating layer is foamable while an outer second polymer coating layer remains unfoamed.