Paper Sheet and Method of Making It

1 . A paper sheet comprising cellulose fibers and hydrophobic fibers, wherein the cellulose fibers represent 10% to 90% by weight of the dry matter of the paper sheet, the hydrophobic fibers represent 10% to 90% by weight of the dry matter of the paper sheet and the cellulose fibers and the hydrophobic fibers represent at least 50% by weight of the dry matter of the paper sheet.

2 . The paper sheet according to claim 1 , wherein

the hydrophobic fibers represent at least 30% by weight of the dry matter of the paper sheet and the cellulose fibers and the hydrophobic fibers represent at least 70% by weight of the dry matter of the paper sheet.

3 . The paper sheet according to claim 1 , wherein the weight ratio of hydrophobic fibers to cellulose fibers is 2:3 to 3:2.

4 . The paper sheet according to claim 1 , wherein the hydrophobic fibers are hydrophobic viscose fibers.

5 . The paper sheet according to claim 4 , wherein

the hydrophobic viscose fiber is a resulting mixture of a viscose fiber and a hydrophobic substance selected from the group consisting of alkyl ketene dimers, alkenyl ketene dimers, alkyl succinic anhydrides, alkenyl succinic anhydrides, alkyl glutaric acid anhydrides, alkenyl glutaric acid anhydrides, alkyl isocyanates, alkenyl isocyanates, fatty acid anhydrides, and mixtures thereof, and the content of the hydrophobic substance in the hydrophobic viscose fiber is 0.1% by weight to 13% by weight based on viscose fiber.

6 . The paper sheet according to claim 1 , wherein the cellulose fibers are refined and have a Shopper-Riegler degree (SR degree) of 9° SR to 90° SR.

7 . The paper sheet according to claim 1 , further comprising a binding agent.

8 . The paper sheet according to claim 7 wherein the binding agent has a shape of fiber and, preferably is chosen from polyvinyl alcohol fibers, polyvinyl acetate fibers, polyethylene fibers, polypropylene fibers, polyester fibers, cellulose acetate fibers, nylon, cellulose ester fiber and mixture thereof.

9 . The paper sheet according to claim 1 , having a water contact angle higher than 70°.

10 . The paper sheet according to claim 1 , having a capillary rise according to ISO 8787:1986 below 10 mm/10 min.

11 . The paper sheet according to claim 1 , having a basis weight of 15 g·m −2 to 60 g·m −2 .

12 . The paper sheet according to further comprising an additive.

13 . Forming the paper sheet as defined in claim 1 into a filter element.

14 . A filter material comprising the paper sheet as defined in claim 1 .

15 . A papermaking process for manufacturing a paper sheet as defined in claim 1 comprising the following steps:

a) mixing the cellulose fibers, hydrophobic fibers and water to obtain an aqueous slurry;

b) forming the aqueous slurry into a wet paper on an inclined wire paper machine or flat wire paper machine, and

c) drying the wet paper to obtain the paper sheet.

16 . The papermaking process of claim 15 for manufacturing a paper sheet wherein, before step a), the cellulose fibers are refined so as to have a SR degree of 9° SR to 90° SR.

17 . The papermaking process of claim 15 for manufacturing a paper sheet wherein the binding agent is added to the aqueous slurry during or after step a), is applied to one surface or to both surfaces of the wet paper after step b) or to the paper sheet after step c).

18 . The papermaking process of claim 15 , wherein, during step c), the wet paper is dried at a temperature of 60° C. to 175° C.

19 . The papermaking process of claim 15 , wherein, after the step c), the paper sheet is also shaped by being:

gathered;

crimped;

embossed and gathered;

crimped, embossed and gathered;

crimped, corrugated and gathered; or

embossed, corrugated, and gathered.