Method for manufacturing a packaging material and a packaging material made by the method

Abstract

The invention refers to a method to produce a packaging material comprising the steps of; treating at least one surface of a paperboard substrate with a binder and with a metal salt, printing at least a part of said treated surface with ink, and applying at least one polymer layer on said printed surface. The packaging material produced in accordance with the invention shows good printability and simultaneously good adhesion of the applied polymer layer.

Claims

1. A method of manufacturing a packaging material comprising the steps of: providing a paperboard substrate, comprising cellulosic fibres, treating at least one surface of said substrate with a binder and with a metal salt or combination of metal salts, wherein a total amount of metal salts applied to the surface is in the range of 0.01 g/m.sup.2 to 1 g/m.sup.2, wherein the metal salt is selected from the group consisting of calcium chloride, aluminium chloride, magnesium chloride, magnesium bromide, calcium bromide, calcium nitrate, magnesium nitrate, magnesium acetate, barium acetate, or combinations thereof, wherein the binder comprises polydiallyldimethylammonium chloride (polyDADMAC) in combination with at least one co-binder selected from microfibrillated cellulose (MFC), or starch, printing at least a part of said treated surface with ink, and applying at least one polymer layer on said printed surface, wherein adhesion of the treated surface to the at least one polymer layer is greater than adhesion of the treated surface to the at least one polymer layer when the binder is polydiallyldimethylammonium chloride (polyDADMAC) alone.

2. A method according to claim 1, wherein the binder comprises MFC which is applied to the surface in an amount of at least 0.1 g/m.sup.2.

3. A method according to claim 1, wherein the binder comprises starch which is applied to the surface in an amount of at least 0.1 g/m.sup.2.

4. A method according to claim 1, wherein the polydiallyldimethylammonium chloride (polyDADMAC) is applied to the surface in an amount of at least 0.05 g/m.sup.2.

5. A method according to claim 1, wherein the binder is applied in a separate step, prior to the treatment of the surface with the metal salt.

6. A method according to claim 1, wherein the treatment with the binder and the metal salt is done by addition of a composition comprising a binder and a metal salt to the surface of the paperboard substrate.

7. A method according to claim 1, wherein the polymer layer comprises polyethylene (PE), polyethylene terephthalate (PET), polypropylene (PP), polylactic acid (PLA), or combinations thereof, or biobased materials of any of these.

8. A method as in claim 1, wherein the total amount of metal salts applied to the surface is in the range of 0.1 g/m.sup.2 to 1 g/m.sup.2.

9. A method according to claim 1 wherein the metal salt is selected from the group consisting of aluminium chloride, magnesium bromide, calcium bromide, calcium nitrate, magnesium nitrate, magnesium acetate, barium acetate, or combinations thereof.

10. A method according to claim 1 wherein the metal salt is selected from the group consisting of calcium chloride, aluminium chloride, magnesium chloride, magnesium bromide, calcium bromide, calcium nitrate, magnesium nitrate, magnesium acetate, barium acetate, or combinations thereof.

11. A method of manufacturing a packaging material comprising the steps of: providing a paperboard substrate, comprising cellulosic fibres, treating at least one surface of said substrate with a binder and with a metal salt or combination of metal salts, wherein the metal salt or combination of metal salts is selected from the group consisting of calcium chloride, aluminium chloride, magnesium chloride, magnesium bromide, calcium bromide, calcium nitrate, magnesium nitrate, magnesium acetate, barium acetate, or combinations thereof, wherein the binder comprises polydiallyldimethylammonium chloride (polyDADMAC) in combination with at least one co-binder selected from microfibrillated cellulose (MFC), or starch, and wherein a total amount of metal salts applied to the surface is in the range of 0.01 g/m.sup.2 to 1 g/m.sup.2, printing at least a part of said treated surface with ink, and applying at least one polymer layer on said printed surface, wherein adhesion of the treated surface to the at least one polymer layer is greater than adhesion of the treated surface to the at least one polymer layer when the binder is polydiallyldimethylammonium chloride (polyDADMAC) alone.

12. A method according to claim 11, wherein the total amount of metal salts applied to the surface is in the range of 0.1 g/m.sup.2 to 1 g/m.sup.2.

13. A method according to claim 11, wherein the co-binder is applied to the surface in an amount of at least 0.1 g/m.sup.2.

14. A method according to claim 11, wherein the binder is applied in a separate step, prior to the treatment of the surface with the metal salt.

15. A method according to claim 11, wherein the treatment with the binder and the metal salt is done by addition of a composition comprising a binder and a metal salt to the surface of the paperboard substrate.

16. A method according to claim 11, wherein the polymer layer comprises polyethylene (PE), polyethylene terephthalate (PET), polypropylene (PP), polylactic acid (PLA), or combinations thereof, or biobased materials of any of these.

Description

(1) FIG. 1 is a schematic figure of a packaging material according to the invention

(2) FIG. 2 is a schematic figure of a second packaging material according to the invention.

(3) The packaging material shown in FIG. 1 comprises a paperboard substrate, an innermost layer (2) in direct contact with the paperboard substrate, which innermost layer comprises a binder and a multivalent metal salt. The innermost layer is printed with ink (3) and a polymer layer (4) is applied on said printed surface.

(4) The packaging material shown in FIG. 2 comprises a paperboard substrate (1), a first, innermost, layer (2) comprising a binder, a second layer (3), applied on said first layer, which second layer comprises a metal salt, ink (4) printed on at least a part of said second layer (3) and a polymer layer (5) applied on said printed second layer.

(5) In the context of this application, the term “innermost” means that the layer is applied directly on the paperboard substrate.

(6) The ink used in the invention comprises pigments, or pigments and dyes, and may be aqueous or solvent based, or a mixture of aqueous and (co-)solvent thus forming a suitable carrier medium for the ink particles. Preferably, the ink comprises anionic nanoparticles (as colorants). Preferably, the ink is printed by use of inkjet printing, thus most preferably high speed inkjet either reel to reel or sheet fed, but other printing techniques are also applicable, such as flexographic, offset, liquid toner electrophotography printing and/or hybrid printing meaning for example a combination of flexography and inkjet. The substrate may be provided with an additional primer layer before being printed with the ink comprising pigments. Such a primer layer may comprise salt or ink without pigments and can be applied with either normal flexography, rotogravure methods which are obvious for a person skilled in the art. Thus, an additional primer layer can also be applied with the high speed inkjet prior to deposition of the inkjet inks.

(7) The packaging material of the invention may be provided with further barrier layers. The back ply may e.g. be provided with polymer barriers in one or several layers.

Example

(8) In order to evaluate the paperboard materials of the invention, a test series was performed in which the print quality and the polymer adhesion of paperboards treated in accordance with the invention was compared with a conventional, untreated, paperboard. All paperboards in the test were of a three-ply construction, having top and back plies and a middle ply. The top ply comprised bleached sulphate pulp, the middle ply comprised CTMP and unbleached sulphate pulp and the back ply comprised unbleached sulphate pulp. The basis weight of the paperboards was approximately 255 gsm. The inventive samples (2-5) were blade coated (blade coater equipped with applicator roll) in an amount of approximately 3 g/m.sup.2 with multivalent metal salt (CaCl2) and binder in accordance with table 1.

(9) Comparative tests were performed on the reference paperboard (sample 1) and the paperboards of the invention (sample 2-5). All samples were printed with a Kodak desktop printer ESP 5 with colour ink cartridge 10, CAT394 7066 and black ink cartridge 10, CAT 394 7058 (The said ink is comprises nanoparticle colorants). The print quality was evaluated by measuring Optical (Print) Density (OD), print mottle and horizontal bleeding. “Optical Density” was measured by color filter according to DIN 16536, by use of Greta Macbeth D19C 47B/P. SUM YCM means the sum of yellow, cyan and magenta, 100% tone areas, and is an indicative of the colour density. “Print Mottle” was measured in accordance with ISO 13660 by use of Scanner IAS. “Horizontal bleeding black” means that the bleed of a black line printed on yellow printed background is measured in accordance to ISO 13660, by use of Scanner IAS.

(10) TABLE-US-00001 TABLE 1 Sample 1 Sam- Sam- Sam- (ref) Sample 2 ple 3 ple 4 ple 5 Cationic starch 70 50 60 (15%), [pph] MFC (2%), [pph] 60 CaCl2 (30%) 30 20 20 20 [pph] PolyDADMAC 20 20 [pph] CMC [pph] 30 Optical Density, 1.7 2.6 2.8 2.6 2.8 K100 [ ] Optical Density 2.4 3.4 3.5 3.4 3.7 SUM YCM100 [ ] Print mottle, 2.3 1.2 1.0 0.6 0.7 magenta (100% area). [ ]-comment other same trend Horizontal 1680 1350 1340 1330 1320 Bleeding black, line width [μm]

(11) The print quality measurements are also summarized in table 1. The comparison shows that the print quality was remarkable better for the samples treated in accordance with the invention compared to the reference paperboard. The highest optical density, lowest mottle and lowest bleeding were observed for the sample treated with polyDADMAC, starch and salt.

(12) All paperboards were thereafter coated in a blade coater with polyethylene in an amount of approximately 14 g/m.sup.2. The polymer adhesion to the reference paperboard (sample 1), to the paperboard treated with MFC, polyDADMAC and salt and to the paperboard treated with polyDADMAC, starch and salt was measured. The polymer adhesion measurements are summarized in table 2.

(13) TABLE-US-00002 TABLE 2 Sample 1 (ref) Sample 4 Sample 5 PE adhesion, 70.9 67.4 PE was too [N/m] tight to release.

(14) As can be seen in table 2, the paperboard treated with MFC, polyDADMAC and metal salt showed comparable polymer adhesion as the reference board, while the paperboard treated with polyDADMAC, cationic starch and metal salt showed much stronger polymer adhesion. Thus, the results show that the treatment according to the invention gives rise to paperboard with much higher print quality and comparable or enhanced polymer adhesion.