COATED PAPER

Abstract

What is described is a coated paper comprising a base paper and at least three coatings applied thereto, wherein the at least three coatings, proceeding from the base paper, in this sequence, comprise a first barrier layer comprising at least one hydrophobic polymer, a second barrier layer comprising at least one hydrophilic polymer, and a third barrier layer comprising at least one hydrophobic polymer, a method for producing such a coated paper, and the use of the coated paper as packaging material.

Claims

1. A coated paper comprising a base paper and at least three coatings applied thereto, wherein the at least three coatings, proceeding from the base paper, in this sequence, comprise a first barrier layer comprising at least one hydrophobic polymer, a second barrier layer comprising at least one hydrophilic polymer, and a third barrier layer comprising at least one hydrophobic polymer.

2. The coated paper according to claim 1, characterised in that the first barrier layer contains or consists of substances which are selected from the group of lipophilic substances, paraffins, in particular hard paraffins, waxes, in particular microcrystalline waxes, waxes based on plant oils or fats, waxes based on animal oils or fats, plant waxes, animal waxes, low-molecular polyolefins, polyterpenes, and mixtures thereof.

3. The coated paper according to claim 1 or 2, characterised in that the transfer of substances, in particular of hydrophobic substances, is reduced or prevented by the second barrier layer.

4. The coated paper according to one of the preceding claims, characterised in that the transfer of substances, in particular of hydrophobic substances, from the first barrier layer or through the first barrier layer, into the third barrier layer or therebeyond is reduced or prevented.

5. The coated paper according to one of the preceding claims, characterised in that the transfer of substances, in particular of hydrophobic substances, from the third barrier layer or through the third barrier layer, into the first barrier layer is prevented.

6. The coated paper according to one of the preceding claims, characterised in that the transfer of substances which are selected from the group of lipophilic substances, paraffins, in particular hard paraffins, waxes, in particular microcrystalline waxes, waxes based on plant oils or fats, waxes based on animal oils or fats, plant waxes, animal waxes, low-molecular polyolefins, polyterpenes, and mixtures thereof, is reduced or prevented.

7. The coated paper according to any one of the preceding claims, characterised in that the third barrier layer, apart from unavoidable or admissible impurities, is free from substances which are not permitted for direct contact with foods, in particular substances which are selected from the group of lipophilic substances, paraffins, in particular hard paraffins, waxes, in particular microcrystalline waxes, waxes based on plant oils or fats, waxes based on animal oils or fats, plant waxes, animal waxes, low-molecular polyolefins, polyterpenes, and mixtures thereof.

8. The coated paper according to any one of the preceding claims, characterised in that a pre-coat comprising at least one inorganic pigment and a polymer binder is provided between the base paper and the first barrier layer.

9. The coated paper according to any one of the preceding claims, characterised in that a sealing layer comprising at least one thermoplastic polymer is provided on the third barrier layer.

10. The coated paper according to any one of the preceding claims, characterised in that the base paper has an area density of from 20 to 120 g/m.sup.2, preferably of from 40 to 100 g/m.sup.2.

11. The coated paper according to any one of the preceding claims, characterised in that the first barrier layer comprises at least one hydrophobic polymer based on a polyacrylate and/or a polyolefin.

12. The coated paper according to any one of the preceding claims, characterised in that the second barrier layer comprises at least one hydrophilic polymer based on a polyvinyl alcohol.

13. The coated paper according to any one of the preceding claims, characterised in that the third barrier layer comprises at least one hydrophobic polymer based on a polyacrylate, a styrene/butadiene copolymer and/or a polyolefin.

14. The coated paper according to any one of claims 2 to 7, characterised in that the inorganic pigment comprises a silicate, preferably a phyllosilicate, and very particularly preferably a kaolin, and/or in that the polymer binder comprises a polymer binder based on a polyacrylate.

15. The coated paper according to any one of claims 3 to 8, characterised in that the sealing layer comprises a thermoplastic polymer based on a polyacrylate, a styrene/butadiene copolymer and/or a polyolefin.

16. The coated paper according to any one of the preceding claims, characterised in that no adhesion promoter is used between the individual barrier layers.

17. The coated paper according to any one of the preceding claims, characterised in that the coated paper is free from halogen-containing compounds.

18. The coated paper according to any one of the preceding claims, characterised in that the coated paper does not comprise an aluminium, Al.sub.2O.sub.3 and/or SiO.sub.2 layer.

19. The coated paper according to any one of the preceding claims, characterised in that the base paper has a long-fibre content of from 10 to 80% and a short-fibre content of from 20 to 90 wt. %, a long fibre being a fibre with a fibre length of from 2.6 to 4.4 mm and a short fibre being a fibre with a fibre length of from 0.7 to 2.2 mm.

20. A method for producing a coated paper according to any one of the preceding claims, characterised in that aqueous suspensions comprising the starting materials of the first, second and third barrier layer are applied successively to the base paper, the aqueous application suspensions having a solids content of from 10 to 60 wt. %, preferably from 30 to 50 wt. %, and being applied by means of the curtain coating process at an operating speed of the coating plant of at least 200 m/min.

21. The method according to claim 20, characterised in that the first and second or the second and third barrier layer are applied immediately successively wet-on-wet by means of a double curtain coating process.

22. Use of a coated paper according to any one of claims 1 to 19 or of a coated paper obtainable by the method according to any one of claim 20 or 21 as packaging material or as a constituent of packaging material, in particular of packaging material based on cardboard or paperboard, in particular as packaging material for foods, preferably for food fats or oil- and/or fat-containing foods.

Description

EXAMPLES

[0135] The following coatings were applied to a 60 g/m.sup.2 base paper with 40% long fibre and 60% short fibre content.

Precoat/Primer:

[0136] The precoat contains 75.9% pigment (Capim NP), 22.8% latex (Ligos K4079) and 1.3% rheology modifiers (0.2% Acroflex VX559, 1.1% Auerzirc PZCS20).

Barrier Layer 1:

[0137] V1+V2: The first barrier layer comprises 99.05% styrene/butadiene copolymer (CHT Coat 230) and 0.95% rheology modifiers (0.1% Sterocoll DF3; 0.15% Acroflex VX559; 0.7% Aerosol OT 70 PG).

[0138] V3+V4+V5: The first barrier layer comprises 99.3% polymer (BimBA 8510) and 0.7% rheology modifiers (0.7% Aerosol OT 70 PG)

Barrier Layer 2:

[0139] The second barrier layer comprises 99.5% polyvinyl alcohol which was mixed with glyoxal (V1+2: MFB 1000; V3: MFB 1001). The remaining 0.5% comprise rheology modifiers (0.1% Sterocoll DF3; 0.4% Aerosol OT 70 PG).

Barrier Layer 3:

[0140] V1+V2+V3: The third barrier layer comprises 98.74% styrene/butadiene copolymer (Ultraseal W-952) and 1.26% rheology modifiers (0.08% Sterocoll DF3; 0.69% Acroflex VX559; 0.49% Aerosol OT 70 PG).

[0141] V4+V5: The third barrier layer comprises 97.74% ethylene/acrylic acid copolymer (W?koseal 630) and 2.26% rheology modifiers (0.18% Sterocoll DF3, 0.08% Acroflex VX559, 0.25% Aerosol OT 70 PG, 1.66% Metolat 368, 0.10% Genapol PF10).

[0142] For this purpose, the precoat was applied using a blade. The first and second barrier layer were applied in a double curtain process. The third barrier layer was applied as a single curtain.

TABLE-US-00002 Application Structure method Unit V1 V2 V3 V4 V5 Base paper Paper machine g/m.sup.2 60 60 60 60 60 Precoat/primer Coating machine - blade g/m.sup.2 4 4 4 4 4 Barrier layer 1 Coating machine - double curtain g/m.sup.2 10 10 10 10 10 Barrier layer 2 Coating machine - double curtain g/m.sup.2 5 5 5 5 5 Barrier layer 3 Coating machine - curtain g/m.sup.2 5 10 5 10 5 WVTR 38? C., 90% r.h. g/m.sup.2/d 41.6 17.8 27.1 37.2 45.6 23? C., 85% r.h. g/m.sup.2/d 12.3 9.3 5.1 12.8 15.6 23? C., 50% r.h. g/m.sup.2/d 2.2 1.7 n.d. n.d. n.d. OTR 0% rel. humidity cm.sup.3/m.sup.2/d <2 <2 <2 <2 <2 80% r.h., 23? C. cm.sup.3/m.sup.2/d 17 4 n.d. n.d. n.d. HVTR g/m.sup.2/d <10 <10 <10 <10 <10 Palm kernel oil test Test condition II Display paper d < 1 mm 0 0 n.d. 0 0 Display paper d > 1 mm 0 0 n.d. 0 0 Test paper d < 1 mm 0 0 n.d. 0 0 Test paper d > 1 mm 0 0 n.d. 0 0 Sealed-seam strength optim. sealing force - transverse N/15 mm 5.2 7.1 4.8 5.4 3.5 optim. sealing temperature - transverse ? C. 140 150 150 100 100 WVTR: Water vapour transmission rate, determined according to ISO 15106-2. OTR: Oxygen transmission rate, determined according to DIN 53380-2 (0% rel. humidity, 23? C.), ISO 15105-2 (80% r.h., 23? C.). HVTR: Hexane vapour transmission rate. Here, hexane is filled into a beaker (solvent-resistant), tightly sealed with the test sample, and the decrease in weight is monitored over time. Palm kernel oil test: Analogous to DIN 53116. Display paper: Evaluation of the display paper mentioned in DIN 53116. Here, grease penetration points with a diameter (d) >/<1 mm are counted. Test paper: Evaluation of the rear side of the test sample from DIN 53116. Here, grease penetration points with a diameter (d) >/<1 mm are counted. Sealed-seam strength: The samples are sealed at 3.3 bar for 0.3 seconds in the temperature range of from 100? C. to 200? C., transverse to the running direction of the paper, and the sealed-seam strength is determined according to DIN 55529 (2012). n.d. not determined

[0143] The coated papers according to the invention were compared with commercially obtainable papers (see tables below).

TABLE-US-00003 Algro Algro Algro Finess/ Guard Finess/ PET Seal Paper V1 V2 V3 V4 V5 OHG PET met Silk Manufacturer Sappi Sappi Sappi Sappi Area density g/m.sup.2 84 89 84 89 84 93 71 70 70 Observations Without wax in the contains metallised third barrier layer PVDC WVTR 38? C., 90% r.h. g/m.sup.2/d 41.6 17.8 27.1 27.1 37.2 1.7 22.3 1.1 >500 23? C., 85% r.h. g/m.sup.2/d 12.3 9.3 5.1 5.1 12.8 n.d. n.d. n.d. n.d. 23? C., 50% r.h. g/m.sup.2/d 2.2 1.7 n.d. n.d. n.d. 0.12 n.d. 0.37 17.1 OTR 0% rel. humidity cm.sup.3/m.sup.2/d <2 <2 <2 <2 <2 <2 >20000 2.5 >20000 80% r.h., 23? C. cm.sup.3/m.sup.2/d 17 4 n.d. n.d. n.d. n.d. n.d. n.d. n.d. HVTR g/m.sup.2/d <10 <10 <10 <10 <10 <10 938 <10 655 Palm kernel oil test Test condition II Display paper d < 1 mm 0 0 n.d. 0 0 n.d. n.d. n.d. n.d. Display paper d > 1 mm 0 0 n.d. 0 0 n.d. n.d. n.d. n.d. Test paper d < 1 mm 0 0 n.d. 0 0 n.d. n.d. n.d. n.d. Test paper d > 1 mm 0 0 n.d. 0 0 n.d. n.d. n.d. n.d. Sealed-seam strength optim. sealing force - transverse N/15 mm 5.2 7.1 4.8 5.4 3.5 4.9 6.4 n.d. 3.9 optim. sealing temperature - transverse ? C. 140 150 150 100 100 140 120 n.d. 130

TABLE-US-00004 Barricote ShieldPlus ShieldPlus ShieldPlus ShieldPlus BAG WG 1 2 3 4 Manufacturer Mitsubishi Nippon Nippon Nippon Nippon Paper Paper Paper Paper Area density g/m.sup.2 83 n.d. 136 66 66 Observations PE-coated white white brown WVTR 38? C., 90% r.h. g/m.sup.2/d 72.2 24.4 33.3 43.0 33.1 23? C., 85% r.h. g/m.sup.2/d n.d. n.d. n.d. n.d. n.d. 23? C., 50% r.h. g/m.sup.2/d 8.1 n.d. n.d. n.d. n.d. OTR 0% rel. humidity cm.sup.3/m.sup.2/d n.d. >20000 2000 >20000 13900 80% r.h., 23? C. cm.sup.3/m.sup.2/d n.d. n.d. n.d. n.d. n.d. HVTR g/m.sup.2/d n.d. n.d. <10 <10 <10 Palm kernel oil test Test condition II Display paper d < 1 mm n.d. n.d. n.d. n.d. n.d. Display paper d > 1 mm n.d. n.d. n.d. n.d. n.d. Test paper d < 1 mm n.d. n.d. n.d. n.d. n.d. Test paper d > 1 mm n.d. n.d. n.d. n.d. n.d. Sealed-seam strength optim. sealing force - transverse N/15 mm 3.5 3.5 n.d.* n.d.* n.d.* optim. sealing temperature - transverse ? C. 140 140 n.d.* n.d.* n.d.* *not sealable according to the manufacturer

Examples V4 and V5

V4:

[0144] V3+that the third barrier layer, apart from unavoidable or admissible impurities, is free from substances which are not permitted for direct contact with foods, in particular substances which are selected from the group of paraffins, in particular hard paraffins, waxes, in particular microcrystalline waxes, low-molecular polyolefins, polyterpenes, and mixtures thereof, and waxes obtained from plants or animals or waxes produced from plant oils/fats or animal oils/fats.

V5:

[0145] Analogously to V4, but half the application weight of the third barrier layer. [0146] Algro Guard OHG: The material has a precoat based on aluminium silicate and, applied thereto, a PVDC coating 8 ?m thick. The permeabilities to oxygen and hexane are similar to examples V1 to V3 according to the invention; the permeability to water vapour is even slightly better. The obtained sealing force lies in the range of the examples according to the invention. However, it is considered to be a large disadvantage that the material contains PVDC as barrier medium. This is unjustifiable from ecological viewpoints. [0147] Algro Finess/PET: This is a paper that has been coated with 20 ?m PE/PET. An acrylate-co-acrylonitrile was used as adhesion promoter or precoat. [0148] The water vapour permeability and sealing force are comparable to the examples according to the invention, however, the hexane and oxygen permeability are very high. [0149] Algro Finess/PETmet: The material is a paper coated with metallised PE or PET. This naturally has very good barriers on account of the metallisation. The main difference from the examples according to the invention is the metallisation considered to be highly disadvantageous from an economic and ecological viewpoint. [0150] Barricote BAG WG: The material initially has a clay-containing precoat and then a functional coating with poly(ethylene-co-acrylic acid). The water vapour permeability lies between 1.7 and 4 times examples V1 to V3; the sealing force is also at the same level as Shieldplus 1 and thus 27-50% lower than in the examples according to the invention. [0151] SealSilk: The SealSilk is constructed similarly to the Barricote BAG WG. Here, a coat of GCC with styrene/butadiene latex was initially applied, to which a poly(ethylene-co-acrylic acid) dispersion was then applied. The sealing force of this material was still about 1 N/15 mm below that of examples V1 to V3 according to the invention. All transmission rates (WVTR, OTR, HVTR) are far below those of the examples according to the invention. [0152] ShieldPlus 1: The material ShieldPlus 1 has a simple PE coating. At 3.5 N/15 mm, this seals 27 to 50% less strongly than the examples according to the invention. Furthermore, the oxygen permeability of the material is very high. The hexane permeability of the material was not examined, but is not expected to be particularly high. The water vapour barrier is good, which is clearly attributable to the PE. [0153] ShieldPlus 2-4 The ShieldPlus 2-4 consist of a styrene/butadiene coat and a PVOH coat; in addition, one or both coats contains clay. The water vapour and hexane permeability of these materials is in the range of the examples according to the invention (WVTR between V3 and V1), however, the oxygen permeability is very high and the materials are thus unsuitable for sensitive foods. Furthermore, the materials are not heat-sealable.