Paper Sheet and Method of Making It

Abstract

The present invention relates to a biodegradable paper sheet for filter element comprising refined cellulose fibers and hydrophobic fibers.

Claims

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.Math.m.sup.−2 to 60 g.Math.m.sup.−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.

Description

EXAMPLES

Example 1Manufacture of Paper Sheet of the Present Invention

Example 1-1: Paper Sheet Comprising 50% of Refined Bleached Softwood Fibers and 50% of Hydrophobic Viscose Fibers Having a Dry Basis Weight of 36 g.Math.m.SUP.−2

[0101] The hydrophobic viscose fibers are the DANUFIL OLEA® viscose fibers manufactured by Kelheim Fibres GmbH. These fibers have a titer of 1.7 dtex and a length of 5 mm.

[0102] Bleached softwood fibers are refined using a conventional disk refiner. The SR degree of the refined softwood fibers is 15° SR.

[0103] The refined softwood fiber and the hydrophobic viscose fibers are mixed with water to obtain an aqueous slurry. The aqueous slurry is then deposited onto a porous forming surface of an inclined wire paper machine to form a wet paper. The wet paper is then dried between 80° C. and 100° C. to obtain the paper sheet of Example 1-1.

Example 1-2: Paper sheet comprising 40% of refined bleached softwood fibers and 60% of hydrophobic viscose fibers having a dry basis weight of 37 g.Math.m.SUP.−2

[0104] The hydrophobic viscose fibers are the DANUFIL OLEA® viscose fibers manufactured by Kelheim Fibres GmbH. These fibers have a titer of 3.3 dtex and a length of 5 mm.

[0105] Bleached softwood fibers are refined using a conventional disk refiner. The SR degree of the refined cellulose fibers is 15° SR.

[0106] The process is the same as described in Example 1-1.

Example 1-3: Paper Sheet Comprising 50% of Refined Unbleached Softwood Fibers and 50% of Hydrophobic Viscose Fibers Having a Dry Basis Weight of 37 g.Math.m.SUP.−2

[0107] The hydrophobic viscose fibers are the DANUFIL OLEA® viscose fibers manufactured by Kelheim Fibres GmbH. These fibers have a titer of 1.7 dtex and a length of 5 mm.

[0108] Unbleached softwood fibers are refined using a conventional disk refiner. The SR degree of the refined cellulose fibers is 15° SR.

[0109] The process is the same as described in Example 1-1.

Example 1-4: Paper Sheet Comprising 50% of Refined Bleached Softwood Fibers and 50% of Hydrophobic Viscose Fibers Having a Dry Basis Weight of 26 g.Math.m.SUP.−2

[0110] The hydrophobic viscose fibers are the DANUFIL OLEA® viscose fibers manufactured by Kelheim Fibres GmbH. These fibers have a titer of 1.7 dtex and a length of 5 mm.

[0111] The bleached softwood fibers are refined using a conventional disk refiner. The SR degree of the refined cellulose fibers is 15° SR.

[0112] The process is the same as described in Example 1-1, but slightly adapted to obtain the paper sheet having a basis weight of 26 g.Math.m.sup.−2.

Example 1-5: Paper Sheet Comprising 49.925% of Refined Cellulose Fibers, 49.925% of Hydrophobic Viscose Fibers and 0.15% of an Additive and Having a Dry Basis Weight of 26 g.Math.m.SUP.−2

[0113] The bleached cellulose fibers are refined using a conventional disk refiner. The SR degree of the refined cellulose fibers is 15° SR.

[0114] The hydrophobic viscose fibers are the DANUFIL OLEA® viscose fibers manufactured by Kelheim Fibres GmbH. These fibers have a titer of 1.7 dtex and a length of 5 mm.

[0115] The same process as described in Example 1-1 is used, except that the additive (sizing agent being alkyl ketene dimer), is added by size press to the wet paper while forming the paper sheet.

Example 1-6: Laboratory Scale Paper Sheet Comprising 50% of Cellulose Fibers and 50% of Hydrophobic Viscose Fibers and Having a Dry Basis Weight of 35 g.Math.m.SUP.−2

[0116] The paper sheet of Example 1-6 has been produced at a laboratory scale using laboratory equipment.

[0117] The paper sheet is made with unrefined cellulose fibers and the DANUFIL OLEA® viscose fibers manufactured by Kelheim Fibres GmbH of Example 1.

Example 1-7: Laboratory Scale Paper Sheet Comprising 40% of Cellulose Fibers, 40% of Hydrophobic Viscose Fibers and 20% of PVA Fibers and Having a Dry Basis Weight of 35 g.Math.m.SUP.−2

[0118] The paper sheet of Example 1-7 has been produced at a laboratory scale using laboratory equipment.

[0119] The paper sheet is made with unrefined cellulose fibers, the DANUFIL OLEA® viscose fibers manufactured by Kelheim Fibres GmbH of Example 1 and PVA fibers having a titer of 1.1 dtex and a length of 4 mm.

Example 1-8: Paper Sheet Comprising 50% of Refined Unbleached Softwood Fibers and 50% of Hydrophobic Viscose Fibers Having a Dry Basis Weight of 30 g.Math.m.SUP.−2

[0120] Kelheim Fibres GmbH. These fibers have a titer of 1.7 dtex and a length of 5 mm.

[0121] The bleached softwood fibers are refined using a conventional disk refiner. The SR degree of the refined cellulose fibers is 15° SR.

[0122] The process is the same as described in Example 1-1, but slightly adapted to obtain the paper sheet having a basis weight of 30 g.Math.m.sup.−2.

Example 2—Characterisation of the Paper Sheets of Example 1

[0123] The characteristics of the paper sheets of Examples 1-1 to 1-5 are presented in Table 1 below.

[0124] All five paper sheets can be easily used to manufacture a filter element since: [0125] the tensile strength MD of all five papers is above 2500 cN/30 mm, and [0126] the tensile strength CD of all five papers is above 950 cN/30 mm.

[0127] Moreover, the physical properties of these five paper sheets are such that these paper sheets may be used as a filter media in a filter element.

[0128] The characteristics of the laboratory scale paper sheets of Examples 1-6 to 1-7 are presented in Table 2 below.

TABLE-US-00001 TABLE 1 Example 1-1 Example 1-2 Example 1-3 Example 1-4 Example 1-5 Basis weight 36 37 37 26 26 (g/m.sup.2) Porosity 18700 21500 11000 24600 16900 (Coresta) Tensile strength MD 3110 2690 3200 2500 2830 (cN/30 mm) Tensile strength CD 1600 1075 1200 990 1120 (cN/30 mm)

TABLE-US-00002 TABLE 2 Example 1-6 Example 1-7 Basis weight (g/m.sup.2) 35.4 35.5 Thickness (μm) 156 145 Porosity (Coresta) 30500 14000

[0129] The characteristics of the paper sheet of example 1-8 are:

[0130] Basis weight: 31 g/m.sup.2; porosity: 15900 Coresta, Tensile strength MD: 2150 cN/30mm; Tensile strength CD: 900 cN/30mm; Thickness:91 μm

Example 3—Characterisation of the Hydrophobic Properties of the Paper Sheets of Example 1 and of Comparative Paper Sheets

Comparative Examples 3-1 to 3-4

[0131] Comparative Example 3-1: paper sheet comprising 100% unrefined softwood fibers; basis weight: 36 g/m.sup.2 [0132] Comparative Example 3-2: paper sheet comprising 50% refined softwood fibers having a SR degree of 15° SR and 50% viscose fibers; basis weight: 36 g/m.sup.2 [0133] Comparative Example 3-3: paper sheet comprising 50% of refined softwood fibers having a SR degree of 15° SR and 50% cellulose acetate fibers; basis weight: 36 g/m.sup.2 [0134] Comparative Example 3-4: non woven cellulose acetate fibers sheet; basis weight: 25 g/m.sup.2

Characterization of the Hydrophobic Properties

[0135] The hydrophobic properties of the paper sheets of Example 1-1 to 1-5 and 1-8 and Comparative Examples 3-1 to 3-4 are presented in Table 3 below.

TABLE-US-00003 TABLE 3 Capillarity Rise Water Drop Water contact angle (mm/10 min) (s) (°) Examples 1-1 0 >180 94 1-2 0 >180 116 1-3 0 >180 103 1-4 0 >180 84 1-5 0 >180 not measured 1-8 0 >180 110 comparative examples 3-1 96 <2 <15 3-2 129 <1 <15 3-3 81 <2 <15 3-4 0 >180 89

[0136] The Capillary Rise of the paper sheet is measured by ISO 8787:1986.

[0137] Water drop corresponds to the time necessary for a drop of water to be absorbed by the paper sheet as measured by TAPPI T432 of 1964.

[0138] The water contact angle is determined as described above.

[0139] The paper sheets of Comparative Examples 3-1 to 3-3 are hydrophilic.

[0140] In the contrary the paper sheets of Examples 1-1 to 1-5 and 1-8 have a water contact angle higher than 80. These paper sheets are hydrophobic.

[0141] As presented in Table 3, the introduction of the hydrophobic viscose fibers in the paper sheet makes the paper sheet hydrophobic such as Comparative Example 3-4 (100% cellulose acetate fibers).

[0142] By comparing the Comparative Examples 3-1 to 3-3, it can be seen that the introduction of cellulose acetate or of viscose fibers does not make the paper sheet hydrophobic.

Example 4—Filter element made of the paper sheet of Example 1-1

[0143] A filter element made of the paper sheet of Example 1-1 is manufactured. This filter element is combined to a tobacco rod to form a cigarette.

[0144] A filter element made of the paper sheet of Comparative Example 3-1 is manufactured. This filter element is combined to a tobacco rod to form a cigarette.

[0145] The two cigarettes are tested by sensory experts.

[0146] The filter element made of the paper sheet of Example 1-1 has excellent filtration properties and produces a smoke having a superior sensory appreciation comparing to the filter element made of the paper sheet of Comparative Example 3-1. In particular the smoke produced by the filter element made of the paper sheet of Example 1-1 has less harsh and dry taste.