Packaging board, its use and products made thereof

Abstract

The invention relates to a packaging board comprising a fibrous base and one or more polymer coating layers on one or both sides of the fibrous base. According to the invention the fibrous base contains the combination of an alkyl ketene dimer size, stearic acid anhydride, a wet-strength size and an aluminium compound, which give the board resistance to aggressive liquids as well as thermal treatment, particularly an improved resistance to raw edge penetration in such circumstances. The invention further relates to containers and packages made of the board, for instance disposable drinking cups, dairy product cartons and auto-clave packages, as well as use of the board for such purposes.

Claims

1. A board drinking cup made with packaging board, said packaging board comprising a fibrous base and one or more polymer coating layers on one or both sides of the fibrous base, said cup being configured such that at least the inside of the cup is polymer-coated, wherein said fibrous base contains the combination of stearic acid anhydride (SA), present in an amount of less than 0.9 kg/t, an alkyl ketene dimer (AKD) size, present in an amount greater than the amount of SA which is present in the fibrous base, polyamido amine epichlorohydrin resin (PAAE) as a wet-strength size, and alum, said board having resistance to strong alcohol.

2. The drinking cup of claim 1, wherein the AKD size has a carbon chain length of C.sub.18-C.sub.22.

3. The drinking cup of claim 1 or 2, wherein the fibrous base also contains anhydride of a fatty acid having a chain longer than that of stearic acid.

4. The drinking cup of claim 1, wherein the fibrous board base contains 0.2 to 3.0 kg/t of AKD, 0.5 to 4.0 kg/t of SA, 0.5 to 2.0 kg/t of PAAE, and 0.5 to 10 kg/t of alum.

5. The drinking cup of claim 1, wherein the fibrous board base further contains 0.5 to 2.0 kg/t of rosin size.

6. The drinking cup of claim 1, wherein one or more of said one or more polymer coating layers comprises polyethylene, polypropene, or polyester.

7. The drinking cup of claim 6, wherein the total weight of one or more polymer coating layers on one side of the fibrous base is at least 14 g/m.sup.2.

8. The drinking cup of claim 1, wherein the density of the fibrous board base is at least 600 kg/m.sup.3.

9. The board drinking cup of claim 1, which is a disposable drinking cup, capable of withstanding strong alcoholic drinks containing at least 30 vol-% of ethanol.

10. The drinking cup of claim 1, wherein the fibrous base also contains palmitic acid anhydride.

11. The drinking cup of claim 1, wherein the fibrous board base contains less than 0.75 kg/t of SA.

Description

DESCRIPTION OF THE INVENTION

(1) The problem the present invention is aimed to solve is finding an all-purpose sized packaging board that could be used for product packages sterilized during filling, for product packages autoclaved after filling, for product packages repellent to and withstanding the packaged moist or liquid product, and for containers such as drinking cups withstanding different drinks that they are used for. The aim is in particular to find sizing that could be performed reliably, cost-effectively and without complicated pH adjustments and control during board manufacturing.

(2) The solution according to the present invention is sizing the fibrous base of the packaging board with a combination of an alkyl ketene dimer (AKD) size, stearic acid anhydride (SA), a wet-strength size and an aluminium compound, which are giving the board resistance to dissolving liquids as well as thermal treatment.

(3) The invention as defined above has been found to be applicable to a wide variety of desired purposes, while the manufacture of the board avoids the problems experienced in the prior art, in particular the difficult pH control as discussed above. The major benefits include use of the same board grade for several different end uses, this wide applicability bringing increased demand and larger-scale manufacturing with lesser changes of board grade at the machine, thus increasing efficiency and reducing unit manufacturing costs. The manufacturing process copes without changes of pH, brings greater purity of the product, and avoids the previous running problems at the machine.

(4) In the pilot paper machine trials it has been found that by use of a mixture of

(5) AKD and stearic acid anhydride together with an aluminium compound it is possible to make retortable/autoclave board and cup stock board that is resistant against detergents, strong alcohol, H.sub.2O.sub.2, black coffee, cream coffee, milk, oat milk etc. liquid foods, autoclaving at 135 C. for 40 min, followed by cold water cooling, and aseptic packaging.

(6) The findings above mean that several different board grades/qualities as produced previously, such as detergent resistant cupboard or retortable board, may be replaced by a single product made according to the invention, by use of a single recipe.

(7) The weight of the board base may vary from about 130 g/m.sup.2 upwards, covering the paperboard and cardboard weights usual in connection with drinking cups and liquid carton packages.

(8) The AKD size used in the invention preferably has a fatty acid carbon chain length of C.sub.18-C.sub.22. The AKD size can be traditional low melting point AKD or higher melting point AKD.

(9) In addition to stearic acid anhydride the fibrous base may even contain anhydrides of shorter or longer-chained fatty acids, for instance palmitic acid anhydride. The stearic acid anhydride (SA-size) can thus be pure SA or a mixture of SA and one or more fatty acid anhydrides of a higher chain length. Too long carbon chains are disadvantageous, however, due to their slow settling on the fibre surface.

(10) Preferably the wet-strength size is polyamido amine epichlorohydrin resin (PAAE). It has been found that there is major improvement if a relatively large amount of a wet strength agent is used, preferably at least 0.5 kg/t, more preferably at least 1 kg/t and most preferably at least 1.5 kg/t. The presence of the wet-strength size allows limitation of the amount of SA-size, which if excessively used would undesirably reduce friction on the board surface. Except for PAAE even other wet strength chemicals may be used.

(11) The preferable aluminium compound being used is alum, particularly KAI(SO.sub.4).sub.2 .12(H.sub.2O). As alternative Al compounds polyaluminium chloride (PAC) and silicate (PAS) may be mentioned. The aluminium compound is believed to contribute to binding the AKD and SA carbon chains at the board surfaces.

(12) Preferably the AKD:SA weight ratio is in the range of 4:1 to 0.25:1, more preferably in the range of 2:1 to 0.5:1. An advantageous recipe for sizing the fibrous board base is 0.2 to 3.0 kg/t of AKD, 0.5 to 4.0 kg/t of SA, 0.5 to 2.0 kg/t of a wet strength size such as PAAE, and 0.5 to 10 kg/t of an aluminium compound.

(13) As SA has a tendency to reduce the static friction of a board surface, which may cause difficulties in processing of the board base, it may be advantageous to keep the amount of SA in the sizing composition relatively low, SA thus constituting a minor component as compared to AKD. The fibrous board base could thus contain less than 0.9 kg/t of SA, preferably about 0.75 kg/t of SA.

(14) In order to increase friction the fibrous board base may even contain 0.5 to 2.0 kg/t of rosin size, which is known to lend a high static friction to a board surface and better adhesion of a polymer coating layer.

(15) The one or more polymer coating layers may comprise polyethylene, polypropene or polyester. The preferred choice for autoclave use is polypropene of polyester. Preferably the minimum weight of the polymer coating is 14 g/m.sup.2, which avoids harmful air bubbles remaining between the board base and the polymer layers.

(16) To achieve maximal resistance against aggressive chemicals such as strong alcohols or detergents, or harsh conditions such as autoclaving, hot filling etc., it is even beneficial to modify the physical properties of the board, mainly in regard of board porosity/density and the wet strength and swelling properties.

(17) For instance, it has been found that the density of the fibrous board base preferably should be at least 600 kg/m.sup.3, preferably at least 650 kg/m.sup.3 and most preferably at least 700 kg/m.sup.3.

(18) The invention further relates to board packages, which are made of the packaging board according the invention as claimed and discussed above. Such packages include autoclaved product packages, dairy product packages as well as detergent packages. Furthermore, the invention comprises open containers, e.g. a board drinking cup made of the packaging board of the invention as claimed.

(19) The invention further relates to the use of the packaging board according to the invention for packages autoclaved at a temperature of at least 130 C., as well as to the use of the packaging board according to the invention for disposable drinking cups withstanding strong alcoholic drinks containing at least 30 vol-% of ethanol. Preferably the cup withstands drinks containing about 40 vol-% of ethanol.

EXAMPLE 1 (COMPARATIVE)

(20) A fibrous board base having a density of 750 kg/m.sup.3 and a weight of 150 g/m.sup.2 was made in a pilot paper machine at a machine speed of 45 m/min. The pulp stock was 100% birch refined to SR22-25. For sizing, 4 kg/t of rosin size and 10 kg/t of alum were added to the thick pulp, calculated per ton of the finished board base. The AKD grade used had a carbon chain length of C.sub.18. Before the headbox the pulp stock was diluted with circulated white water having a pH of 6.5-6.8.

(21) At first static friction was measured from the surface of the board base. To let raw edge penetration (REP) testing be performed before the final polymer coating step required in the invention, the board surfaces on both sides were masked with a plastic film, and the REP was measured in different liquids and conditions. The results were as follows:

(22) TABLE-US-00001 Lactic acid (1%) REP (24 h, 23 C.) 14.0 kg/m.sup.2 REP H.sub.2O.sub.2 (10 min, 70 C.) 0.6 kg/m.sup.2 REP coffee (10 min, 80 C.) 2.4 kg/m.sup.2 REP 40 vol-% ethanol (1 h, 23 C.) 7.0 kg/m.sup.2 autoclave REP (1 h, 125 C.) 13.0 kg/m.sup.2 static friction 0.5

EXAMPLE 2 (COMPARATIVE)

(23) A fibrous board base was made in accordance with example 1, except for use of 1.5 kg/t of a 1:1 mixture of AKD and SA and 5 kg/t of alum for sizing. The finished board base was tested for static friction and REP as in example 1. The results were as follows:

(24) TABLE-US-00002 Lactic acid (1%) REP (24 h, 23 C.) 2.3 kg/m.sup.2 REP H.sub.2O.sub.2 (10 min, 70 C.) 0.3 kg/m.sup.2 REP coffee (10 min, 80 C.) 3.7 kg/m.sup.2 REP 40 vol-% ethanol (1 h, 23 C.) 7.0 kg/m.sup.2 autoclave REP (1 h, 125 C.) 2.4 kg/m.sup.2 static friction 0.27

EXAMPLE 3 (INVENTION)

(25) A fibrous board base was made in accordance with example 1, except for use of 1.5 kg/t of a 1:1 mixture of AKD and SA, 1 kg/t of PAAE and 5 kg/t of alum for sizing. The finished board base was tested for static friction and REP as in example 1. The results were as follows:

(26) TABLE-US-00003 Lactic acid (1%) REP (24 h, 23 C.) 1.7 kg/m.sup.2 REP H.sub.2O.sub.2 (10 min, 70 C.) 0.3 kg/m.sup.2 REP coffee (10 min, 80 C.) 3.3 kg/m.sup.2 REP 40 vol-% ethanol (1 h, 23 C.) 5.5 kg/m.sup.2 autoclave REP (1 h, 125 C.) 2.3 kg/m.sup.2 static friction 0.26

EXAMPLE 4 (COMPARATIVE)

(27) A fibrous board base was made in accordance with example 1, except for use of 2.5 kg/t of a 1:1 mixture of AKD and SA and 5 kg/t of alum for sizing. The finished board base was tested for static friction and REP as in example 1. The results were as follows:

(28) TABLE-US-00004 Lactic acid (1%) REP (24 h, 23 C.) 1.8 kg/m.sup.2 REP H.sub.2O.sub.2 (10 min, 70 C.) 0.3 kg/m.sup.2 REP coffee (10 min, 80 C.) 3.0 kg/m.sup.2 REP 40 vol-% ethanol (1 h, 23 C.) 3.8 kg/m.sup.2 autoclave REP (1 h, 125 C.) 2.3 kg/m.sup.2 static friction 0.23

EXAMPLE 5 (COMPARATIVE)

(29) A fibrous board base was made in accordance with example 1 and coated with 14 g/m.sup.2 of polyethylene on one side and with 17 g/m.sup.2 of polyethylene on the opposite side, for obtaining a cupboard suitable for the manufacture of disposable drinking cups. The coated cupboard was tested for the raw edge penetration (REP) by use of coloured liquids. The results were as follows:

(30) TABLE-US-00005 REP colored hot water (10 min, 93 C.) <3 mm REP cream coffee (10 min, 93 C.) <3 mm REP black coffee (10 min, 93 C.) <11 mm

EXAMPLE 6 (COMPARATIVE)

(31) A fibrous board base was made in accordance with example 2 and coated with 14 g/m.sup.2 of polyethylene on one side and with 17 g/m.sup.2 of polyethylene on the opposite side, for obtaining a cupboard suitable for the manufacture of disposable drinking cups. The coated cupboard was tested for the raw edge penetration (REP) by use of coloured liquids. The results were as follows:

(32) TABLE-US-00006 REP colored hot water (10 min, 93 C.) <4 mm REP cream coffee (10 min, 93 C.) <2 mm REP black coffee (10 min, 93 C.) <11 mm

EXAMPLE 7 (INVENTION)

(33) A fibrous board base was made in accordance with example 3 and coated with 14 g/m.sup.2 of polyethylene on one side and with 17 g/m.sup.2 of polyethylene on the opposite side, for obtaining a cupboard suitable for the manufacture of disposable drinking cups. The coated cupboard was tested for the raw edge penetration (REP) by use of coloured liquids. The results were as follows:

(34) TABLE-US-00007 REP colored hot water (10 min, 93 C.) <1 mm REP cream coffee (10 min, 93 C.) <1 mm REP black coffee (10 min, 93 C.) <3 mm

EXAMPLE 8 (COMPARATIVE)

(35) A fibrous board base was made in accordance with example 4 and coated with 14 g/m.sup.2 of polyethylene on one side and with 17 g/m.sup.2 of polyethylene on the opposite side, for obtaining a cupboard suitable for the manufacture of disposable drinking cups. The coated cupboard was tested for the raw edge penetration (REP) by use of coloured liquids. The results were as follows:

(36) TABLE-US-00008 REP colored hot water (10 min, 93 C.) <1 mm REP cream coffee (10 min, 93 C.) <1 mm REP black coffee (10 min, 93 C.) <2 mm

(37) The above examples 1-8 show that conventional rosin sizing performs quite badly in lactic acid and autoclave REP tests. Sizing with AKD and SA is a considerable improvement in both respects, but with hot black coffee marked colouring along the raw edges remains to be a problem. Increasing the amount of the AKD and SA sizes solves the problem with coffee, but an increased static friction is a significant disadvantage. Adding a corresponding amount of wet strength size instead, as taught by the present inventors, gives a similar improvement for coffee, while avoiding the static friction handicap. For overall performance the board according to the invention is found to be an improvement over the tested comparisons.