Shaped tray or plate of fibrous material and a method of manufacturing the same

Abstract

The invention relates to a method of manufacturing a shaped tray or plate of fibrous material. The method comprises the steps of (i) providing a fibrous pulp, in which the fibres substantially consist of at least 85 wt-% of softwood fibres having an average fibre length of at least 2.0 mm and at most 15 wt-% of broke having a fibre length of about 0.05 mm to 1.0 mm, (ii) turning the pulp into a foamed suspension, (iii) supplying the foamed suspension from a headbox to a forming fabric of a board machine to form a fibrous web, (iv) drying the web to obtain a dried web having a compressibility in the thickness direction of at least 20%, and (v) including the web as a layer in a board, which is turned to said tray or plate by thermopressing or deep-drawing. The invention even covers shaped trays and plates produced by use of the method.

Claims

1. A method of manufacturing a shaped tray or plate of fibrous material, comprising the steps of: foam forming a web consisting of the steps of providing a fibrous pulp, in which the fibres consist of at least 85 wt-% of softwood fibres having an average fibre length of at least 2.0 mm and at most 15 wt-% of broke having a fibre length of about 0.05 mm to 1.0 mm, adding a surface active agent to the pulp and turning the pulp into a foamed suspension, supplying the foamed suspension from a headbox to a forming fabric of a board machine to form a fibrous web, and dewatering and/or drying the web to obtain a dried web having a compressibility in the thickness direction of at least 20%, and, including the web, consiting of the dried web formed by the dewatering and/or drying step, as a layer in a board, which is turned to said tray or plate by thermopressing or deep-drawing.

2. The method of claim 1, wherein 90 to 100 wt-% of the fibres of the fibrous pulp are said softwood fibres, the share of said broke being 0 to 10 wt-%.

3. The method of claim 1, wherein the softwood fibres are fractionated so as to reduce a share of the softwood fibers having a length of less than 2.0 mm.

4. The method of claim 1, wherein the softwood fibres consist of fibres selected from the group of pine (Pinus), spruce (Picea) or Douglas fir.

5. The method of claim 1, wherein said broke comprises hardwood fibres.

6. The method of any one of claim 1, wherein the foamed suspension supplied to the forming fabric has a fibre consistency in a range of 0.65% to 2.5%.

7. The method of claim 1, wherein said web made by foam forming is positioned as a middle layer of a multilayer board, while outer surface layers on both sides of said middle layer are produced from unfoamed fibrous pulp.

8. The method of claim 7, wherein said broke used for the middle layer comprises rejects from the production of said outer surface layers.

9. The method of claim 7, wherein the softwood pulp used for the middle layer is CTMP and the pulp for the outer surface layers is chemical pulp or CTMP of hardwood.

10. A method of manufacturing a shaped tray or plate of fibrous material, comprising the steps of: foam forming a web consisting of the steps of providing a fibrous pulp, in which at least 85 wt-% of the fibers are softwood fibres having an average fibre length of at least 2.0 mm and from 5 to 15 wt-% of broke having a fibre length of about 0.05 mm to 1.0 mm, turning the pulp into a foamed suspension, supplying the foamed suspension from a headbox to a forming fabric of a board machine to form a fibrous web, drying the web to obtain a dried web having a compressibility in the thickness direction of at least 20%, including the web, consisting of the dried web from the drying step, as a middle layer of a multilayer board, while outer surface layers on both sides of said middle layer are produced from unfoamed fibrous pulp, and thermopressing or deep-drawing the multilayer board to form said tray or plate.

11. A shaped tray or plate of fibrous material manufactured by the method comprising the steps of: foam forming a web consisting of the steps of providing a fibrous pulp, in which the fibres consist of at least 85 wt-% of softwood fibres having an average fibre length of at least 2.0 mm and at most 15 wt-% of broke having a fibre length of about 0.05 mm to 1.0 mm, turning the pulp into a foamed suspension, supplying the foamed suspension from a headbox to a forming fabric of a board machine to form a fibrous web, dewatering and/or drying the web to obtain a dried web having a compressibility in the thickness direction of at least 20%, and including the web, consisting of the dried web from the dewatering and/or drying step, as a layer in a board, which is turned to said tray or plate by thermopressing or deep-drawing.

12. The shaped tray or plate of claim 11, wherein it has folds, in which the layer has been compressed at least 20% in the thickness direction.

Description

EXAMPLE

(1) For the production of trays a triple-layer board was produced, comprising a middle layer of a weight of 180 g/m.sup.2 sandwiched between two outer layers of a weight of 60 g/m.sup.2, the board thus having a total weight of 300 g/m.sup.2. The fibrous material for the outer layers was a virgin chemical pulp blend of 60 wt-% of birch (hardwood) and 40 wt-% of pine (softwood). The fibrous material for the middle layer was a blend of 90 wt-% of virgin pine (softwood) CTMP and 10 wt-% of broke derived from the preparation of the fibrous material blends for each one of the three layers. The broke thus had a share of about 25 wt-% of hardwood. The pine CTMP for the middle layer had an average fibre length above 2.0 mm, while the fibre length of the broke was generally less than 1.0 mm.

(2) For the middle layer a furnish was made by mixing (i) 90 wt-% of pine CTMP and (ii) 10 wt-% of broke, which comprised the rejects from the preparation of said pine CTMP as well as rejects from preparation of chemical pulps of birch (60%) and pine (40%) for making the two outer layers. Water was added to achieve a fibre consistency of about 2% (not including eventual fillers). Sodium dodecyl sulphate (SDS) as a surface active agent was added to the furnish to turn it into a foam having an air content of 60-70% and content of SDS about 50 ppm. The foam was immediately supplied from a headbox to a forming fabric of a board machine. A foam formed web was thus produced, dewatered by suction through the forming fabric, and dried in known manner. The resulting dried web had a bulk of about 5 cm.sup.3/g and a weight of 180 g/m.sup.2.

(3) For the outer layers webs were formed by mixing 60 wt-% of birch cellulose and 40 wt-% of pine cellulose (kraft pulp), turning this mixture to an aqueous furnish, and making the webs by use of standard wet-forming technique in a board machine. The high-bulk webs thus obtained had a weight of of 60 g/m.sup.2. The three webs were combined in the board machine to form the finished triple-layer board product.

(4) To produce a tray a rectangular piece of the board was provided by score lines pressed to its four corners to determine the location of the folds, and then thermoformed to a rectangular tray of a depth of 2.5 cm at a temperature of about 80 C. and moisture content of about 13%. The finished tray had folds in the corners, which had formed without cracks or other damage.