Fibrous sheet disintegrating in water, process for manufacturing said fibrous sheet, use of said fibrous sheet for the manufacture of a core

1. A pressed or calendered fibrous sheet having a basis weight of between 20 and 1000 g/m 2 , comprising 10 to 70% starch and at least 30% of papermaking fibres on the basis of a total weight of the pressed or calendered fibrous sheet when dry and manufactured according to a wet papermaking process, wherein the pressed or calendered fibrous sheet has a disintegration time in water of less than 50 seconds, wherein the disintegration time in water is measured in accordance with standard NF Q34-020 applied to a specimen of the fibrous sheet of 9×8 cm 2 , and wherein the starch added during the wet papermaking process is water-insoluble starch at the temperature at which it is incorporated.

2. The pressed or calendered fibrous sheet according to claim 1 , wherein the pressed or calendered fibrous sheet comprises 15 to 40% starch on the basis of the total weight of the dry pressed or calendered fibrous sheet.

3. The pressed or calendered fibrous sheet according to claim 1 , wherein the basis weight is between 100 and 600 g/m 2 .

4. The pressed or calendered fibrous sheet according to claim 1 , wherein a ratio of the pressed or calendered fibrous sheet's lateral compressive strength values between a wet state and a dry state is less than 1%.

5. The pressed or calendered fibrous sheet according to claim 1 , wherein a loss of strength measured according to a defined table test corresponds to a loss of strength of a specimen of said pressed or calendered fibrous sheet forming an angle of at least 85°, and wherein the defined table test comprises the steps of

i) preparing a rectangular specimen of the pressed or calendered fibrous sheet having a size of 2.54 cm in width by 13 cm in length;

ii) laying the specimen on a table having a horizontal plane surface, a vertical plane, and a straight edge at the intersection between the horizontal plane surface and the vertical plane, wherein 10 cm of the specimen extends beyond the table, and wherein the specimen make an angle of 0° with the table's horizontal plane;

iii) depositing 3 ml of water in 6 seconds at the center of the specimen above the straight edge to wet the specimen and allow the specimen to bend around the straight edge to have a bend angle between the specimen and the horizontal plane;

iv) measuring the bend angle 6 seconds after depositing the water.

6. A pressed or calendered fibrous sheet having a basis weight of between 20 and 1000 g/m 2 , comprising 10 to 70% starch and at least 30% of papermaking fibres on the basis of a total weight of the pressed or calendered fibrous sheet when dry and manufactured according to a wet papermaking process, wherein the pressed or calendered fibrous sheet has a disintegration time in water of less than 50 seconds, wherein the disintegration time in water is measured in accordance with standard NF Q34-020 applied to a specimen of the fibrous sheet of 9×8 cm 2 , and wherein the starch is substantially uniformly distributed through a thickness of the pressed or calendered fibrous sheet.

7. The pressed or calendered fibrous sheet according to claim 6 , wherein the pressed or calendered fibrous sheet comprises 15 to 40% starch on the basis of the total weight of the dry pressed or calendered fibrous sheet.

8. The pressed or calendered fibrous sheet according to claim 6 , wherein the basis weight is between 100 and 600 g/m 2 .

9. The pressed or calendered fibrous sheet according to claim 6 , wherein a ratio of the pressed or calendered fibrous sheet's lateral compressive strength values between a wet state and a dry state is less than 1%.

10. The pressed or calendered fibrous sheet according to claim 6 , wherein a loss of strength measured according to a defined table test corresponds to a loss of strength of a specimen of said pressed or calendered fibrous sheet forming an angle of at least 85°, and wherein the defined table test comprises the steps of

i) preparing a rectangular specimen of the pressed or calendered fibrous sheet having a size of 2.54 cm in width by 13 cm in length;

ii) laying the specimen on a table having a horizontal plane surface, a vertical plane, and a straight edge at the intersection between the horizontal plane surface and the vertical plane, wherein 10 cm of the specimen extends beyond the table, and wherein the specimen make an angle of 0° with the table's horizontal plane;

iii) depositing 3 ml of water in 6 seconds at the center of the specimen above the straight edge to wet the specimen and allow the specimen to bend around the straight edge to have a bend angle between the specimen and the horizontal plane;

iv) measuring the bend angle 6 seconds after depositing the water.

11. A pressed or calendered fibrous sheet having a basis weight of between 20 and 1000 g/m 2 , comprising 10 to 70% starch and at least 30% of papermaking fibres on the basis of a total weight of the pressed or calendered fibrous sheet when dry and manufactured according to a wet papermaking process, wherein the pressed or calendered fibrous sheet has a disintegration time in water of less than 50 seconds, wherein the disintegration time in water is measured in accordance with standard NF Q34-020 applied to a specimen of the fibrous sheet of 9×8 cm 2 , and wherein the pressed or calendered fibrous sheet in a wet state has a residual strength less than 1% of its dry state.

12. The pressed or calendered fibrous sheet according to claim 11 , wherein the pressed or calendered fibrous sheet comprises 15 to 40% starch on the basis of the total weight of the dry pressed or calendered fibrous sheet.

13. The pressed or calendered fibrous sheet according to claim 11 , wherein the basis weight is between 100 and 600 g/m 2 .

14. The pressed or calendered fibrous sheet according to claim 11 , wherein a ratio of the pressed or calendered fibrous sheet's lateral compressive strength values between a wet state and a dry state is less than 1%.

15. The pressed or calendered fibrous sheet according to claim 11 , wherein a loss of strength measured according to a defined table test corresponds to a loss of strength of a specimen of said pressed or calendered fibrous sheet forming an angle of at least 85°, and wherein the defined table test comprises the steps of

i) preparing a rectangular specimen of the pressed or calendered fibrous sheet having a size of 2.54 cm in width by 13 cm in length;

ii) laying the specimen on a table having a horizontal plane surface, a vertical plane, and a straight edge at the intersection between the horizontal plane surface and the vertical plane, wherein 10 cm of the specimen extends beyond the table, and wherein the specimen make an angle of 0° with the table's horizontal plane;

iii) depositing 3 ml of water in 6 seconds at the center of the specimen above the straight edge to wet the specimen and allow the specimen to bend around the straight edge to have a bend angle between the specimen and the horizontal plane;

iv) measuring the bend angle 6 seconds after depositing the water.