KRAFT PAPER AND PAPER SACK MANUFACTURED THEREFROM

Abstract

A kraft paper having a pulp according to ISO 536 of between 60 g/m.sup.2 and 120 g/m.sup.2, a density of between 680 kg/m.sup.3 and 720 kg/m.sup.3, and a tensile strength index in the machine direction according to ISO 1924-3 of between 79 kNm/kg and 98 kNm/kg, the kraft paper optionally having a coating and/or an auxiliary element on at least one side. The kraft paper is made of a pulp having an average pulp fibre length of 2.2 mm to 2.7 mm with a minimum pulp content of at least 96% wt. %; a pore volume of the uncoated kraft paper is between 200 l/g and 220 ml/g; in the thickness direction of the paper, there are regions of different porosities; and at least one region has pores with a pore diameter of less than or equal to 0.3 m. The invention also relates to a paper sack.

Claims

1. A Kraft paper having a pulp according to ISO 536 in the range from 60 g/m.sup.2 to 120 g/m.sup.2, a density in the range from 680 kg/m.sup.3 to 720 kg/m.sup.3 and a tensile strength index in the machine direction according to ISO 1924-3 between 79 kNm/kg and 98 kNm/kg, which kraft paper has a coating and/or an auxiliary element on at least one side, wherein the kraft paper is made from a pulp with an average fibre length of the pulp of from 2.2 mm to 2.7 mm with a minimum content of pulp in the kraft paper of at least 96 wt. %, and a pore volume of the uncoated kraft paper measured by mercury porosimetry according to ISO 15901-1 is from 200 l/g to 220 ml/g, in the thickness direction of the paper, there are formed regions of different porosity from one another measured by mercury porosimetry according to ISO 15901-1, and at least one region has pores with a pore diameter less than or equal to 0.3 m.

2. The kraft paper according to claim 1, wherein the at least one coating and/or the at least one auxiliary element applied to at least one side is/are selected from optical markings or UV marking, an indicator dye, a a sensor ink, chemically or physically processed viewing windows.

3. The kraft paper according to claim 1, wherein the regions of different porosity in the thickness direction of the paper, measured by mercury porosimetry according to ISO 15901-1, are layers which merge into one another.

4. The kraft paper according to claim 1, wherein at least one formed region of different porosity has pores with a pore diameter smaller than or equal to 0.01 m to smaller than 0.3 m, and in that an average value of the pore volumes of this formed region or these formed regions is smaller than or equal to 5.5 l/g measured by mercury porosimetry according to ISO 15901-1.

5. The kraft paper according to claim 1, wherein a mean fibre length of the pulp is from 2.3 to 2.6 mm.

6. The kraft paper according to claim 1, wherein the kraft paper its air resistance (Gurley) is greater than 20 sec and less than 40 sec.

7. The kraft paper according to claim 1, wherein the kraft paper it is made water-repellent by sizing and has a water absorption value Cobb.sub.60 according to ISO 535 of between 14 g/m.sup.2 and 21 g/m.sup.2.

8. (canceled)

9. The kraft paper according to claim 2, wherein the viewing window, is provided as an auxiliary element.

10. A paper sack made of the kraft paper according to claim 1, wherein the paper sack is formed with a closure element at its upper free edge region, and in that the closure element consists of a closure band or a closure region provided with an adhesive.

11. The paper sack made of the kraft paper according to claim 10, wherein the paper sack is formed with an upper edge region provided at least partially with an adhesive on one side or is formed with a flap provided at least partially with an adhesive.

12. The paper sack according to claim 10, wherein the paper sack the adhesive is biodegradable and is selected from the group of natural glues, dextrin and water-based biodegradable adhesives.

13. The paper sack according to claim 2, wherein the paper sack has applied to an outwardly directed surface, the auxiliary element selected from the optical markings, UV markings, an indicator dye, a sensor ink, chemically or physically processed viewing windows.

14. The paper sack according to claim 13, wherein the auxiliary element is a UV marking on at least 20%, of the surface of the sack.

15. The paper sack according to claim 13, wherein the auxiliary marking is formed from a fluorescent ink with a pigment concentration of greater than 0.3%.

Description

EXAMPLE OF THE INVENTION

[0031] The invention is explained in more detail below with reference to an example for producing a refuse sack according to the invention.

[0032] For this purpose, a Clupak paper is produced in the conventional manner, in which a spraying device is additionally provided in the Clupak system and applies a pattern consisting of bars and lines, which lines substantially have a width of several centimetres, to the wire side of the paper. The lines are selected here in such a way that they are not covered by the paper flap, which is folded over the opening and glued during the course of closing the sack.

[0033] Such a paper is used to make a single-layer refuse sack with a stand-up bottom of about 10 cm in width and a capacity of 140 l. The paper has a pulp of 90 g/m.sup.2, a density of 700 kg/m.sup.3, a tensile strength index in the machine direction of 85 kNm/kg, an air resistance according to Gurley of 25 s and a pore volume of the base paper of 210 ml/g. The sack is formed with a flap which has a dextrin adhesive layer applied to one side, which only becomes adhesive by wetting and is subsequently firmly bonded to the underlying paper after the flap has been folded over, in order to prevent any unintentional leakage of objects contained therein.

[0034] In the lower region directed towards the stand-up bottom, a marking visible in UV light in the form of a grid is applied over the circumference of the paper sack, wherein the marking has a bar width of about 4 cm. The indicator colour was applied here in a concentration of 0.40% pigment concentration and a diamond or bar pattern fluorescing yellow in UV light was formed.

[0035] After producing such refuse sacks, one such refuse sack was filled with green waste for test purposes, one refuse sack was filled with household waste, wherein organic waste and non-organic waste, and lastly, in a third case, it was filled with differently biodegradable or decomposable household waste.

[0036] All sacks were sealed by moistening the adhesive layer and gluing the flap.

[0037] During a test in a waste sorting plant, all bags produced in this way were detected by the UV reader of the sorting plant and subsequently sorted out of the system. All three sacks were in tact after being sorted out. The correct sacks were sorted out of the waste stream and subsequently deposited at a composting plant to be able to observe the composting of the contents and the sack.

[0038] After three months in the composting plant with a permanent supply of moisture and the use of a rapid composting agent, it was found that the sacks, which were 100% in tact after sorting, were now completely rotted and residues of the paper could no longer be found in the compost.