Light Packaging Paper for Food Having Improved Resistance to Fats

Abstract

Packaging paper for food, with a basis weight from 20 g/m.sup.2 to 50 g/m.sup.2, comprising cellulose fibers and one or more filler materials, wherein the total amount of filler materials is between 5% by weight and 20% by weight with respect to the weight of the packaging paper, wherein the packaging paper comprises a sizing agent that is contained in such an amount that a relative water absorption of 0.4 to 0.7 is obtained on both sides, wherein the relative water absorption is defined as the quotient of the Cobb.sub.60 value, determined in accordance with ISO 535:2014, and the basis weight, has a coating on at least one side that comprises nanoparticles of a starch, wherein the coating contains between 1 g/m.sup.2 and 6 g/m.sup.2 of said nanoparticles, does not contain any compounds with the structure CF.sub.3(CF.sub.2).sub.n(CH.sub.2).sub.mX, wherein n=5 or n=7 and m=0, 1 or 2 and X is a hydroxyl group (X=OH) or a carboxyl group (X=COOH), or the proportion of such compounds in the total mass of the packaging paper is less than 0.1, and has a resistance against greases and oils of 6 to 12, described by the KIT level in accordance with TAPPI T559 cm12, wherein in the test in accordance with TAPPI T559 cm12, the at least one side coated with said nanoparticles is exposed to the test liquids.

Claims

1. Packaging paper for food, with a basis weight from 20 g/m.sup.2 to 50 g/m.sup.2, comprising cellulose fibers and one or more filler materials, wherein the total amount of filler materials is between 5% by weight and 20% by weight with respect to the weight of the packaging paper, wherein the packaging paper comprises a sizing agent that is contained in such an amount that a relative water absorption of 0.4 to 0.7 is obtained on both sides, wherein the relative water absorption is defined as the quotient of the Cobb.sub.60 value, determined in accordance with ISO 535:2014, and the basis weight, has a coating on at least one side that comprises nanoparticles of a starch, wherein the coating contains between 1 g/m.sup.2 and 6 g/m.sup.2 of said nanoparticles, does not contain any compounds with the structure CF.sub.3(CF.sub.2).sub.n(CH.sub.2).sub.mX, wherein n=5 or n=7 and m=0, 1 or 2 and X is a hydroxyl group (X=OH) or a carboxyl group (X=COOH), or the proportion of such compounds in the total mass of the packaging paper is less than 0.1, and has a resistance against greases and oils of 6 to 12, described by the KIT level in accordance with TAPPI T559 cm12, wherein in the test in accordance with TAPPI T559 cm12, the at least one side coated with said nanoparticles is exposed to the test liquids.

2. Packaging paper according to claim 1, with a basis weight of between 25 g/m.sup.2 and 40 g/m.sup.2.

3. Packaging paper according to claim 1, wherein the pulp fibers are sulfate pulp fibers and comprise 25% by weight to 75% by weight long fibers and 25% by weight to 75% by weight short fibers, with respect to the mass of the pulp fibers.

4. Packaging paper according to claim 3, wherein the long fiber pulp is sourced from one or more of the plants spruce, pine, flax, hemp, sisal, aback ramie, jute and kenaf and/or the short fiber pulp is sourced from one or more of the tree species birch, beech and/or eucalyptus.

5. Packaging paper according to claim 1, wherein the pulp is bleached, or wherein the pulp is unbleached.

6. Packaging paper according to claim 1, wherein said pulp fibers are at least to 95% by weight with respect to the pulp mass, formed by fresh fibers.

7. Packaging paper according to claim 1, wherein the total amount of filler materials is between 5% by weight and 15% by weight with respect to the weight of the packaging paper.

8. Packaging paper according to claim 1, wherein the one or more filler materials are selected from the group consisting of precipitated or geologically sourced calcium carbonate, magnesium carbonate, titanium dioxide, magnesium oxide, magnesium hydroxide, aluminum hydroxide, kaolin or talc.

9. Packaging paper according to claim 1, wherein the filler materials comprise a combination of titanium dioxide and an extender which, in combination with titanium dioxide, enhances its effect, wherein the extender is formed by calcinated kaolin, aluminum hydroxide (Al(OH).sub.3), a precipitated, amorphous silicate or a combination thereof.

10. Packaging paper according to claim 1, wherein the amount of nanoparticles of a starch in the packaging paper is between 1.5 g/m.sup.2 and 5 g/m.sup.2.

11. Packaging paper according to claim 1, wherein the nanoparticles are sourced from one or more of the following starches: potato starch, corn starch, wheat starch, rice starch or tapioca starch.

12. Packaging paper according to claim 1, wherein the mean size of the nanoparticles is between 1 nm and 500 nm.

13. Packaging paper according to claim 1, wherein the sizing agent is formed by an alkyl ketene dimer (AKD), an alkenyl succinic anhydride (ASA) or a resin size.

14. Packaging paper according to claim 1, which further contains one or more of the following components: a wet strength agent, which is suitable for increasing the strength of the packaging paper in the wet state, starch, which is not present in the form of nanoparticles, wherein, in the case in which the packaging paper is coated with the nanoparticles of a starch on only one side, the starch is applied to the other side of the packaging paper, pigments or colorants, or gold foil.

15. Packaging paper according to claim 1, which is coated with the nanoparticles of a starch on only one side, and which is printed on the other side.

16. Packaging paper according to claim 1, wherein the relative water absorption of both sides is between 0.4 and 0.6.

17. Packaging paper according to claim 1, which has a resistance against greases and oils of 6 to 10, described by the KIT level in accordance with TAPPI T559 cm12, wherein in the test in accordance with TAPPI T559 cm12, the at least one side coated with said nanoparticles is exposed to the test liquids.

18. Packaging paper according to claim 1, with an air permeability according to Gurley of between 1000 s and 10000 s.

19. Packaging paper according to claim 1, with a thickness of between 20 m and 60 m.

20. Packaging paper according to claim 1 with a tensile strength in the machine direction of between 1 kN/m and 5 kN/m, and/or with a tensile strength in the cross direction of between 0.5 kN/m and 4 kN/m.

21. Packaging paper according to claim 1 with an elongation at break in the machine direction of between 1% and 3% and in the cross direction of between 2% and 6%.

22. Process for the manufacture of a packaging paper according to claim 1, wherein the nanoparticles of a starch are applied as component of a coating composition during manufacture of the packaging paper in a paper machine, or in an application device separated from the paper machine to form a preliminary paper, wherein the coating composition contains at least water and said nanoparticles, and wherein the coating composition contains between 10% by weight and 40% by weight of said nanoparticles, each with respect to the weight of coating composition.

23. Process according to claim 22, wherein the coating composition further contains talcum and/or kaolin, of which the total mass corresponds to 30% to 65% by weight of the mass of said nanoparticles.

24. Process according to claim 22, wherein the coating composition is applied to one side of the packaging paper in the form of a pattern, and wherein on the other side, the coating composition is applied in an at least approximately complementary pattern, so that every region of the packaging paper is coated with the nanoparticles of a starch on at least one side of the packaging paper.

25. Packaging paper according to claim 12, wherein the mean size of the nanoparticles is between 40 nm and 200 nm.

26. Packaging paper according to claim 14, wherein the pigments or colorants are yellow, red, brown or black iron oxides or carbon particles.

27. Process according to claim 22, wherein the nanoparticles of a starch are applied as a component of a coating composition during manufacture of the packaging paper in a film press or size press of said paper machine.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0070] FIG. 1 shows a table 1, in which properties of packaging papers according to the invention and comparative examples not according to the invention are summarized.

[0071] FIG. 2 shows a table 2, in which further properties of the packaging papers of FIG. 1 are summarized.

DESCRIPTION OF THE SOME EMBODIMENTS, IN ACCORDANCE WITH AND NOT IN ACCORDANCE WITH THE INVENTION

[0072] Several papers were produced from mixtures of long-fiber and short-fiber pulp (Table 1, columns Long Fiber and Short Fiber and various filler materials (Table 1, column Filler) which are designated in Tables 1 and 2 of FIG. 1 or 2, respectively, by A-L, wherein in Tables 1 and 2 the same letters in the column Paper indicate the same paper. The papers A, K and L are papers not according to the invention, which serve as comparative examples, while the papers B-J are packaging papers according to the invention.

[0073] The percentages regarding long-fiber pulp and short-fiber pulp are with respect to the weight of the fiber composition; the percentages regarding the filler materials are with respect to the basis weight of the packaging paper.

[0074] The papers were each sized in bulk with alkyl ketene dimer (AKD) according to the requirements on the Cobb.sub.60 value. An aqueous composition with 33% by weight nanoparticles of a corn starch was applied to the felt side of papers B-E, G, H, K and L in the film press of the paper machine. For paper A, no composition was applied, for paper F, it was applied to both sides and for paper J, to the wire side. The amount of nanoparticles of a starch is given in Table 1, column Nanoparticles. Table 1, column Coating indicates which side or which sides of the paper are coated; therein, FS designates the felt side and WS the wire side.

[0075] For all papers coated on one side, that is, B-E and G-L, ordinary starch was additionally applied to the uncoated side in a small amount of 0.1 g/m.sup.2 to 0.5 g/m.sup.2 to prevent curling of the packaging paper. After application of the coating composition, the papers were dried, conditioned in accordance with ISO 187 at 23 C. and 50% relative humidity and then measurements were carried out.

[0076] The basis weight of each packaging paper was measured in accordance with ISO 536:2012 and is given in Table 1, column Basis Weight. The basis weights are between 25.4 g/m.sup.2 and 46.3 g/m.sup.2.

[0077] The Cobb.sub.60 values, Table 2, column Cobb.sub.60 of the wire side (WS) and the felt side (FS) were measured in accordance with ISO 535:2014 for the papers B-L and with the basis weight from Table 1 the quotient of the Cobb.sub.60 value and the basis weight was calculated for each side of the paper. It is given in Table 2, column Relative Water Absorption.

[0078] The air permeability according to Gurley was determined in accordance with ISO 5636-5:2013, where the air was always flowing from the felt side to the wire side. The measurement results are given in Table 2, column Air Permeability (Gurley).

[0079] The resistance against greases and oils was measured several times in accordance with TAPPI T559 cm12 for the coated side or the coated sides for each of the papers B-L. The result is given in Table 2, column KIT level. For comparison, a measurement was carried out on both sides of the uncoated paper A.

[0080] Furthermore, the tensile strength and the elongation at break were determined in the machine direction and in the cross direction in accordance with ISO 1924-2:2008. The results are not given individually, but for the tensile strength in the machine direction they were always between 1.3 kN/m and 4.6 kN/m, while in the cross direction, they were between 0.9 kN/m and 2.4 kN/m. This tensile strength in any case is sufficient for trouble-free further processing.

[0081] The elongation at break in the machine direction was between 1.3% and 2.6% and in the cross direction between 2.9% and 5.8%. These values are also sufficient for trouble-free further processing.

[0082] From the uncoated paper A not according to the invention with a KIT level between 0 and 2 on each side, it can be seen that a coating of the paper with the nanoparticles of a starch is indeed necessary in order to obtain considerable resistance against greases and oils.

[0083] The papers according to the invention for the embodiments B to E show, for different basis weights from 25.4 g/m.sup.2 to 45.9 g/m.sup.2, that with a relative water absorption from 0.44 to 0.63 and an amount of nanoparticles of a starch from 1.7 g/m.sup.2 to 5.1 g/m.sup.2, a sufficient resistance against oils and greases, expressed by the KIT level, of 6-8 can be obtained.

[0084] The paper according to the invention of embodiment F exhibits a very high-quality packaging paper with a basis weight of 46.3 g/m.sup.2 and titanium dioxide in the mixture of filler materials. In this manner, the paper produces a high opacity and whiteness. Paper F is coated on both sides with nanoparticles of a starch and thus has a very high resistance against oils and greases, expressed by the KIT level, of 9 to 11.

[0085] A comparison of the papers D and G according to the invention shows that both papers are very similar having regard to their basis weight, with 38.8 g/m.sup.2 and 38.5 g/m.sup.2. They do not differ in other essential parameters except for the air permeability, which for paper D is 6685 s according to Gurley and for paper G is 8320 s according to Gurley. Thus, paper D has higher air permeability and a resistance against oils and greases, expressed by the KIT level, of 6-7, while paper G achieves a KIT level of 7-8. This shows that a low air permeability and thus a high value in seconds according to Gurley can be of advantage for the resistance against oils and greases independently of other properties.

[0086] The paper of embodiment H according to the invention tests the limits of the invention and shows, for a high relative water absorption of 0.62 (FS) and 0.67 (WS) and a high air permeability of 1224 s according to Gurley, a resistance against greases and oils, expressed by the KIT level, of only 5-6. Therefore, this packaging paper is still sufficiently suitable for applications as a packaging paper for food.

[0087] The paper according to the invention of embodiment J demonstrates the invention for an alternative fiber mixture, consisting of 70% by weight long-fiber pulp and 30% by weight short-fiber pulp, each with respect to the mass of the fiber mixture, as well as a low filler content of 5% by weight with respect to the mass of the packaging paper. In addition, in contrast to all other embodiments, the coating is applied to the wire side. Despite all these modifications, the packaging paper produces a resistance against greases and oils of 6-7, expressed as the KIT level. In combination with the other embodiments, this shows that the relative water absorption and the air permeability separately, but also in combination, are particularly important in obtaining a high resistance against oils and greases.

[0088] Papers K and L, which are not according to the invention, are constituted by a paper (K) with a very small amount of size, with a relative water absorption of 0.82 to 0.90, which is too high to carry out the invention, and a paper (L) with a very large amount of size, with a relative water absorption of 0.20 to 0.25, which is too low to carry out the invention. Both papers produce a KIT level of at most 5, despite the application of well over 4 g/m.sup.2 of the nanoparticles. In addition, these two exemplary embodiments not according to the invention demonstrate the particular importance of the relative water absorption for the resistance against greases and oils.